November 17, 2020

What is lateral excursion?

The human skull can be grossly divided into a movable and an immovable part. The movable part is formed by the lower jaw called the mandible. The rest of the skull forms the immovable portion. These two parts of the skull are connected by a joint near the ear. This joint is the temporomandibular joint (TMJ).

The TMJ has three main parts. A temporal part, that is the part of the immovable portion of the skull. The temporal bone is a depression that receives the condyle. The condyle is a part of the mandible that makes the primary movements of the lower jaw. A disc located between the temporal bone and the condyle helps in the range of movements. The smooth movements of the articular disk are possible because of a fluid called the synovial fluid. This fluid acts as a lubricant, as a result of which our lower jaw can move freely during speech, chewing, etc.

The movements produced by the TMJ are protrusion (moving the lower jaw forward), retrusion (moving the lower jaw backward), elevation (mouth closure), depression (mouth opening), lateral excursion (side to side). In this article, we would be focusing on lateral excursion.

Simply put, lateral excursion is when the mandible moves to one side. But the mechanism behind this is not as simple as it sounds. The mandible is capable of two movements if we take the condyle as the hinge: rotation and translation. Imagine a vertical and horizontal axis passing through the condyles. The movement of the mandible with respect to the vertical axis is called rotation and with respect to the horizontal axis it is translation.

The forward movement of the mandible is a translatory motion. The sideways movement is a rotational motion. In lateral excursion, both these motions take place simultaneously. Let us understand this movement with an example. Imagine you want to move your lower jaw to the left side. This means that both the condyles would have to move towards the left. Since the jaw has to be moved to the left, the left condyle will rotate in the desired direction. In our case, the left side is the working side. The mandible is a single bone, if the left condyle moves, the right condyle will be also stretched towards the left. However, since there are many structures that limit this movement of the right condyle, it will simply move forward in translation. Hence, the right side in our example would be the non-working side.

The working and the non-working side function in conjunction to produce the desired movement. However, lateral excursion is not simply a movement attributed to the condyles. A key role is played by the muscles that are attached to the mandible. These are the muscles that find their origin in the immovable part of the skull are terminate their fibres in the moving mandible. The four muscles are lateral pterygoid, medial pterygoid, temporalis and masseter. Each of these muscles help the mandible to glide forwards, downwards and sideways to make the lateral excursion.

Lateral excursion is one of the key functional movements that helps in chewing. It ensures that we humans do not simply chop down the food by simply opening and closing the mouth but also grind it to make a proper bolus for effective digestion. Lateral excursion is the second key step when we chew our food. Once the mouth opens and the food enters the oral cavity, the jaw moves sideways and grinds the food, closes gradually and finally the teeth meet each other before the mouth comes back in a state of rest.

Lateral excursion might be hampered due to problems in the gnathic system. A locked jaw, tumour, traumatic injury, muscle pain, disk injuries, congenital disorders may contribute to improper or no lateral excursion movement. While some of these disturbances need surgical intervention or pharmacological cover, minor disturbances can be corrected with home techniques focusing on physiotherapy.

Prosthetic treatments that involve fabrication of complete dentures give notable emphasis on lateral excursion. During the fabrication of dentures, the upper and lower canines are made to touch each other as the sideway movement occurs. When they glide over each other, the back teeth are no longer in contact which ensures proper lateral excursion. This is also called canine guidance .

Thus, lateral excursion is one of the vital movements that the mandible can perform considering how the entire surrounding musculature comes into picture for normal functioning.

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Dynamic occlusion: lateral excursion

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  • Dynamic occlusion: lateral excursion

The dynamic occlusion is the contact that teeth make during movements of the mandible - when the jaw moves side to side, forward, backward or at an angle. In dynamic occlusion, the contacts of the teeth are not points as in static occlusion, but they are described with lines. 

  • Dental occlusion
  • Occlusal relationship
  • Temporomandibular joint (TMJ)
  • Joint capsule and ligaments of TMJ
  • Movements of TMJ
  • Static occlusion: centric occlusion
  • Occlusion concepts: centric relation
  • Angle's classification
  • Angle's classification: Class I
  • Angle’s classification: Class II, Division 1
  • Angle's classification: Class II, Division 2
  • Angle's classification: Class III
  • Dynamic occlusion: canine guidance
  • Dynamic occlussion: protrusion
  • Curve of Spee
  • Curve of Wilson
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Occlusion Static Occlusion, Dynamic Occlusion and Guidance

Previous pages have looked at mandibular movements in the sagittal (forward-back) plane. We will now examine the effects of the mandible moving in lateral excursions.

magnify

Static occlusion

Static occlusion is the study of contacts between the teeth when the jaw is not moving. The contacts are points (seen as dots when articulating paper is used). For example, close your teeth in your intercuspal position (i.e. where they meet best). Is your bite heaviest on your back teeth? Is it evenly spread over all the back teeth? Is there hardly any weight on the front teeth? Many dentists would describe that as the “ideal”. If you are providing a crown or filling for a patient like this, you would try not to disturb such an occlusion by leaving the restoration high (or low). Click the picture above to see the ink marks made with a static occlusion (intercuspal position in this case - the patient was asked to "tap together on the back teeth"). more… All these bite marks have been Photo-shopped onto the pictures. They are rarely this neat in real life! Top Tip: To get neater marks, smear the articulating paper with Vaseline first. This helps transfer the ink to the teeth.

magnify

(No) Freedom In Centric

Bite on your back teeth. Can you slide a tiny way forwards before you bump into your anteriors? If so, you have "Freedom In Centric Occlusion" (also known as "Long Centric"). Remember - Centric Occlusion is another word for Intercuspal Position (ICP). The picture above shows no freedom in centric - ICP causes marks to appear on the incisors. Compare it with the picture at the page top, which has freedom in centric. Dynamic occlusion Dynamic occlusion is the study of the contacts that teeth make when the mandible is moving – contacts when the jaw moves sideways, forwards, backwards, or at an angle. The contacts are not points, they are lines. If you get a patient to grind their teeth in every direction on piece of articulating paper, you will see the lines formed by dynamic occlusion Although the jaw is moved by muscles, the contact lines depend on both the teeth positions and shapes (obviously), and the shape of the TMJ. These shapes GUIDE the occlusion. You may have heard the phrases posterior guidance and anterior guidance used when the mandible moves about in protrusive and lateral excursions Can you say what the terms mean? Check answer Posterior guidance is provided by the TMJ. As the condyle slides down the glenoid fossa, the angle of the mandible is changed depending how far the condyle is down the fossa’s slope. Anterior guidance is provided by the teeth. Not all of them, just the ones in contact during the movement. my score: 0 / 2 running total: 0 / 0 Reset Did you think posterior meant back teeth and anterior meant front teeth? Not here it doesn’t! Put your teeth together and slide all the way forwards: probably you can feel only your incisors “guiding”. Now imagine you had no upper front teeth or upper premolars at all, only molars on the top. In this case when you protrude, the “anterior guidance” is provided by molars. Some dentists prefer to use the phrase Anterior Determinant for teeth, and Posterior Determinant for the TMJs. This helps reduce the confusion. my score: 0 / running total: 0 / 0 Reset Working side and non-working side. Can you define these terms? Check answer If the mandible moves to the right , the right is the working side (and left is non-working). If the mandible moves to the left , the left is the working side (and right is non-working). my score: 0 / 2 running total: 0 / 0 Reset Types of anterior guidance in lateral excursions. Click the pictures to see typical ink marks associated with each type of guidance. Note the dots formed by intercuspal position (static), and the lines caused by a lateral excursion to the right.

These interferences are providing anterior guidance, but as the name suggests, not in a way that dentists approve of ! They are considered the least desirable types of anterior guidance.

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What Is Occlusion?

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lateral excursion meaning in dentistry

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Davies, S. (2022). What Is Occlusion?. In: A Guide to Good Occlusal Practice. BDJ Clinician’s Guides. Springer, Cham. https://doi.org/10.1007/978-3-030-79225-1_1

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Occlusal Techniques

A detailed occlusal examination of patients presenting with problems such as unexplained pain, wear, fracture, drifting and mobility (see Chapter 2) is an integral, invaluable part of the dental examination. A detailed occlusal examination is essential when planning any major restorative work to determine, for example, whether this should be provided as a conformative or reorganised procedure and to consider whether any occlusal adjustments are needed before providing definitive restorations (see Chapter 3). The clinical technique for carrying out a full occlusal examination is shown on the DVD.

Do I Need to Do a Full Occlusal Examination?

The answer in most cases is no. The extent of the examination will vary from patient to patient. It is possible to identify isolated occlusal problems without systematically following the procedure shown in the video, but this requires intuition and experience. A systematic approach is usually needed to resolve more complex problems. It is worth practising all parts of the examination when the opportunity arises, particularly techniques such as identifying guidance teeth and finding the hinge axis, so that they become second nature.

Some find it helpful to use a structured record form, but, once you are familiar with carrying out an occlusal examination, the relevant findings can be recorded as shown in Table 8-1.

“Good” and “Bad” Contacts

In essence, the occlusal examination allows important tooth contacts to be identified. There are “good” contacts, which support the occlusion and guide jaw movement, and “bad” contacts, which deflect jaw movement during closure or interfere with excursions. It is also important to identify those contacts which would otherwise be good, but which occur on teeth that are heavily restored and poorly equipped to handle the loads that result from guidance or parafunction.

Although most people are not troubled by deflective contacts and interferences, in some patients they are associated with problems such as pain, fracture, mobility and wear. Furthermore, the inadvertent removal of contacts during tooth preparation can give rise to unwanted changes in jaw position and loss of occlusal space, as described in Chapter 3. It is sensible to know in advance of preparing a tooth whether it includes a holding or guidance contact which needs to be incorporated in the restoration. A deflective contact or interference, however, can be eliminated before preparing the tooth, and so avoid reproducing it in the restoration. Detecting such contacts can be quickly and easily achieved with a systematic examination.

Deflective contacts and interferences may occur developmentally, but are often the result of tooth movements caused by extractions, poorly contoured restorations, periodontal disease, periapical inflammation and tooth wear. More unusual causes of deflective contacts and interferences include jaw fracture and tooth movements occurring during pregnancy (Fig 8-1). Whatever the cause, the principles of examining and adjusting the occlusion are the same.

lateral excursion meaning in dentistry

Fig 8-1 The patient shown on the DVD reported a clear history of occlusal changes during pregnancy which, despite an excellent periodontal condition, had not resolved over a year later.

Screening for Parafunction

It is always worth knowing if the patient is a bruxist, as this will help in both the diagnosis of problems of excessive occlusal loading (see Chapter 3) and the prescription of suitably robust restorations. Parafunction is often episodic, and so the detection of faceting and vertical microfractures does not mean that bruxism is active at that time. Clinical indicators of active parafunction include fremitus, tooth tenderness and ridging of the sides of the tongue or cheeks at the level of the occlusal plane.

Screening for Temporomandibular Disorders

As discussed in Chapter 7, it is also good practice to check all patients for signs and symptoms of temporomandibular disorders (TMDs), particularly those patients requiring extensive restorations. Screening for a history of a painful or clicking jaw, muscle and/or temporomandibular joint (TMJ) tenderness on examination, significant joint sounds (bearing in mind that mild clicking is very common) and limitation of jaw movement is appropriate for all patients.

Reserve the full TMD examination (shown in DVD video J) for patients who have a significant problem requiring more detailed diagnosis. A screening check can be combined with a brief occlusal examination.

Performing the Examination

The following sections are intended to be used in conjunction with Table 8-1 and the relevant video clips on the DVD.

What Instruments Do I Need?

Set up an examination tray (Fig 8-2) with thin articulating foils (< 20 μm thick) and shim stock. The foils are much easier to use if held in Miller’s forceps to stop them crumpling. Use one colour, for example black, for ICP marks and another, for example red, for excursive marks. Shim stock is a 10 μm-thick Mylar film and is held in mosquito forceps. It is used as a feeler gauge between occluding teeth. The extent of posterior contact can be quantified as the number of pairs of posterior teeth holding the shim. Some way of measuring the vertical dimension, such as a Willis gauge, may also be useful.

lateral excursion meaning in dentistry

Fig 8-2 Examination tray for occlusal examination, with Miller’s forceps holding black and red articulating foil and mosquito forceps holding shim stock.

What Should ICP Occlusal Contacts Look Like?

Occlusal contacts do not always mark well with thin occlusal marking foils, particularly if the teeth are wet. Sometimes the situation can be improved by first marking the teeth with a thicker paper, which leaves a broad smudge of colour against which the contrasting colour of the finer foil can be seen. The best way of ensuring you can see contacts is by making the teeth dry.

In the young, ICP contacts should ideally be small and discrete, with multiple contacts on each tooth providing occlusal stability (Fig 8-3). ICP contacts that are broad and rubbing, as seen in the patient in the DVD (Fig 8-4), can signify occlusal instability when associated with functional disturbances. Bear in mind, however, that the area of contacts can also increase with normal levels of wear.

lateral excursion meaning in dentistry

Fig 8-3 ICP contacts are ideally small and discrete.

lateral excursion meaning in dentistry

8-4 ICP contacts that are broad and rubbing are sometimes associated with underlying occlusal problems.

Do ICP Tooth Relationships Potentially Affect Anterior Guidance?

Before looking at mandibular excursions, the ICP can tell you quite a lot about guidance. If there is little or no vertical overlap of incisors or canines, the capacity of these teeth to guide jaw movement, with the disclusion of the posterior teeth, will be limited or non-existent. Similarly, if the overbite is incomplete, there may be a considerable delay during excursions before the anterior teeth come into contact.

Rather more difficult to comprehend is the effect of the occlusal plane. On the one hand, a flat occlusal plane with a shallow angle to the horizontal plane – the patient’s Frankfort plane – will dispose to posterior disclusion. On the other hand, a curved occlusal plane, or one with a steep angle to the horizontal, will dispose to clashing of posterior teeth. Cross-bites and scissor bites – the upper teeth occluding buccal to the lower teeth – often cause interferences or deflective contacts.

How Do I Assess the RCP–ICP Slide?

This is one of the most important skills to learn for assessing the occlusion. It is not difficult, but it only comes with practice. Using bimanual manipulation, with the patient completely relaxed and preferably supine, guide the patient into RCP (Fig 8-5a,b).

lateral excursion meaning in dentistry

Fig 8-5a Bimanual manipulation is used to seat the condyles in centric relation to examine the retruded contact and the RCP–ICP slide.

lateral excursion meaning in dentistry

Fig 8-5b Manipulation should take place with the patient supine and teeth only slightly separated.

Ask the patient to point to the contacting teeth and feel how the mandible slides into ICP. Qualitatively, the slide will either be present or absent, smooth or rough, small or large. Quantitatively, estimate how far the mandible deviates forwards or laterally by looking at the relationship between the upper and lower incisors during the slide. Chapter 3 and the DVD illustrate how to do this, looking both from in front and from the side of the patient.

How Do I Detect Fremitus?

Look out for an anterior thrust associated with a deflective RCP–ICP slide. Often, anterior teeth affected by an anterior thrust will exhibit fremitus, as do some teeth involved in guidance. You can easily detect fremitus as palpable vibration by placing your index finger on each of the teeth in turn and asking the patient to tap together. With marked fremitus, the vibrations will be clearly visible. The anterior thrust may also be associated with specific problems with the upper anterior teeth, such as localised palatal wear, damage to restorations or incisor drifting.

What Do I Need To Look for with Excursive Movements?

The important thing is to identify which teeth guide movement and which teeth interfere with it. Excursive contacts, when marked with foil, should appear smooth and unbroken. An irregular, broken or dog-legged appearance suggests an interference, either on the tooth itself or on a tooth distant to it (Fig 8-6a,b).

lateral excursion meaning in dentistry

Fig 8-6a Markings for left lateral excursion showing poorly defined guidance on the canine. The difficulty the patient had in making this movement suggested the heavier red marks on the premolars were interferences.

lateral excursion meaning in dentistry

Fig 8-6b There were also non-working-side interferences (again marked in red) on the upper right first and second molars.

In simple terms, the jaws and TMJs comprise a lever system. Forces applied to the teeth by the masticatory muscles diminish as you move anteriorly. Hence, anterior teeth are better positioned than posterior teeth to accept the non-axial forces associated with excursive loading of the mandible. Nevertheless, posterior teeth are often involved in guiding jaw movements. Provided these contacts are in harmony, the system works well.

Sometimes, as shown in the DVD (animation I) and discussed in more detail in Chapter 3, posterior contacts can act as pivots or fulcrums. In making assessments about whether and how such pivots may need to be managed, mounted casts usefully supplement the clinical occlusal examination.

When Do I Need to Assess Vertical Dimension?

The simple answer is, when you might be thinking about changing it. In practice this will be for very few patients. These tend to be patients who appear to have lost occlusal vertical dimension (OVD), either with excessive wear or tooth loss, and where an increase in OVD, and therefore an occlusal reorganisation, is planned. Excessive tooth wear is often compensated for by dentoalveolar extrusion. Even where there is considerable wear, the freeway space may be “normal”, but that does not preclude a change (see Chapter 4).

The usual procedure is to measure the OVD and resting vertical dimension with a Willis gauge. Subtracting one from the other gives the freeway space. With the patient sitting upright, the normal range of freeway space is 2–4 mm. This is notoriously imprecise because of its inherent variability and measurement inaccuracies, arising largely from compressibility of the soft tissues.

Do I Need Mounted Casts?

The answer to this is no, not for routine examinations. They can, however, be invaluable for planning treatment, communicating with the laboratory and explaining treatment to the patient. If you intend to perform irreversible changes to the occlusion as part of a restorative treatment plan, mounted casts are indispensable, both as a baseline record and in the planning of occlusal alterations. Changes to the occlusion often involve trial adjustments and diagnostic waxing (see Sections 8-7 and 8-8). Two sets of casts are therefore recommended, so that one set can be kept unchanged.

8-2 A CCURATE A LGINATE I MPRESSIONS

Many dentists treat alginate as a humble and somewhat inaccurate material. But accuracy is paramount when articulating diagnostic casts and when preparing opposing casts for indirect restorations. The opposing impression is often the last procedure following successful completion of preparation, temporisation and the working impression, and so it can end up as a bit of an afterthought. The implications of an inaccurate opposing impression are far from trivial. Precious time can be lost adjusting the occlusal surface of a crown because the opposing alginate impression was distorted or carelessly recorded, making for unnecessary expense, and the clinical outcome can be compromised. Simple quality control at this stage can save a lot of subsequent grief.

A high degree of accuracy can be achieved by avoiding common pitfalls and by being prepared to spend a few seconds checking the impression before sending it to the laboratory. Clearly, disinfection, bagging up to avoid drying out and ensuring alginates are cast within a few hours are essential measures.

The DVD shows a number of tips, including:

the use of rim-lock trays (Fig 8-7)

drying the teeth and smearing material on the occlusal surfaces prior to seating the tray to avoid occlusal air blows (Fig 8-8)

pulling unset material over the heel of the tray with a mouth mirror to help keep the impression in the tray on removal from the mouth

trimming the impression to allow inspection and reduce distortions prior to pouring up (Fig 8-9)

careful inspection of the impression.

lateral excursion meaning in dentistry

Fig 8-7 Rim-lock trays are a good option for alginate impressions.

lateral excursion meaning in dentistry

Fig 8-8 Reduce air bubbles by smearing alginate onto the occlusal surfaces.

lateral excursion meaning in dentistry

Fig 8-9 Always trim the heel and check the impression has not pulled away.

Perforated stock trays often come in a limited range of sizes and often do not fit well, sometimes failing to cover the most posterior teeth. It is not a problem to extend a stock tray – unless you choose to use wax. Unfortunately, wax distorts easily, and so distorts the alginate it is supposed to be supporting. A better option is to use impression compound (greenstick), which is rigid. The softened material is applied to the upper and lower surfaces of the tray heels and then teased out in sufficient thickness to include all the teeth in the tray. Perforated stock trays can occasionally cause problems when the alginate partly pulls out of the perforations on removal from the mouth. If you do not use adhesive with a perforated tray or you give insufficient time for the adhesive solvent to evaporate, the risk of this distortion is greatly increased. The rule is: use an adhesive and let it dry before the impression is taken.

Rim-lock trays are a good alternative to perforated trays. They come in a good range of sizes and can retain an alginate impression without the use of an adhesive. The disadvantages of rim-lock trays include ensuring their return from the laboratory and difficulties in cleaning prior to decontamination and sterilisation.

Although the cost of material is much higher, it is worth considering a fast-setting addition silicone as an alternative to alginate, particularly when multiple casts are required. Unlike alginate, silicone impressions can be re-poured without significant loss of accuracy. When taking impressions for study models in complex cases, this may prove to be cost effective. The use of a perforated tray is recommended for silicones, as silicone adhesives are more effective than those used for alginates. The set material is also more rigid and, therefore, more difficult to remove from the mouth.

8-3 I NTERCUSPAL R EGISTRATION

Icp or centric relation registration.

In the previous section, consideration was given to the importance of accurate alginate impressions, both for diagnostic casts and for opposing casts when making indirect restorations. One of the greatest sources of confusion relates to what type of registration should be used to articulate sets of casts. Put very simply, ICP registration is used to construct restorations on working casts, while centric relation (CR) registration is for diagnosis and treatment planning. For any given case, you might start with casts mounted in CR and plan treatment on this basis. You would then decide to conform to what is there, in which case you use ICP records to make your restorations or to reorganise, creating a new ICP in CR.

This, of course, is not absolute. Casts mounted in ICP – even hand-held casts – might provide some useful diagnostic information, but remember they give no information on deflective contacts and, at best, limited information on guidance and excursive interferences. Furthermore, restorations may, on occasion, be made on casts mounted in CR.

Mounting Casts in ICP

The fundamental problem with any interocclusal record used to articulate casts is that there is a substantial risk of the record itself preventing the casts coming fully together. An intervening layer of registration material commonly creates the sort of occlusal error that one is trying to avoid. Often, the best occlusal record is no occlusal record at all. Where one is used, it should be as minimal as is required to locate the casts accurately.

Diagnostic casts are often held in ICP by hand. This is quick and often effective when the teeth locate in a stable position. This approach can, however, mislead diagnosis. Problems with hand-held casts occur when they cannot be easily and reliably located in a stable intercuspal relationship. The reasons may include:

distorted casts – undetected impression distortion can result in normal looking casts

blebs and faults on the occlusal surfaces

a limited number and arrangement of teeth

malocclusions, such as open bites (Fig 8-10) or cusp-to-cusp occlusion

incorrect assumptions regarding the orientation of the occlusal plane.

lateral excursion meaning in dentistry

Fig 8-10 Silicone ICP record used for a patient with an anterior open bite – a rare case in which a full-arch record is justified.

All these factors can make it impossible to locate and record a reproducible, let alone relevant, position. In the event of an error, it may be necessary to start again, modify the casts to remove blebs or imperfections, or to use a different approach to registration to allow the casts to be mounted in an articulator. Articulator choice is covered in Section 8-6.

Working casts for indirect restorations are generally mounted in some form of articulator. An interocclusal record is often necessary to achieve this, but not always. The general principle is to limit, where possible, the ICP record to the preparations and the opposing teeth. In this way the unprepared teeth are not prevented from coming into contact by the record. This principle applies whatever material is used.

A full-arch record is almost never needed, perhaps only where there is an anterior open bite and the casts rock; but even then, trimmed localised records may be possible. Less is often more with ICP records.

Materials for ICP Records

The choice of materials for ICP registration is generally between:

nothing at all

silicone mousse

wax sheet, horseshoe or section

acrylic copings and stents.

A combination of materials is sometimes required, as indicated below.

Silicone Mousse

The important thing to remember about this type of material is that it needs to be trimmed, whether it is being used as a sectional or full-arch registration (Fig 8-11a,b). Another important point is that a silicone mousse records surface detail very well, often better than the material used to record the impressions. In other words, the detail recorded by the mousse may prevent the two casts seating in the record. Without trimming, and sometimes even with trimming, the mounting will often feel springy when the registration is sandwiched between the casts. Simply squeezing the casts together with, for example, an elastic band is not the answer, as the material will deform under pressure, resulting in unpredictable occlusal changes. Usually, trimming the record with a scalpel will allow an accurate mounting. It is equally important that bubbles and blebs on the casts are removed.

lateral excursion meaning in dentistry

Fig 8-11a Superfluous detail in a record, including embrasures and gingival tissues, can prevent it seating on the casts.

lateral excursion meaning in dentistry

Fig 8-11b Following disinfection, the record should be trimmed with a scalpel to leave only areas essential for location.

Wax Sheet, Horseshoe or Section

A “wax bite” horseshoe or sheet is often used as an intercuspal record. Unlike silicone mousse materials, waxes are not dimensionally stable and are very easily deformed in transit to the laboratory. As with silicone mousse materials, pressing casts into a wax record will result in an incorrect articulation. Wax is occasionally used for sectional ICP records (Fig 8-12).

lateral excursion meaning in dentistry

Fig 8-12 A localised wax and registration paste record offers the advantage of keeping unprepared teeth in contact. Again, trim for proper seating on casts.

With this technique, distortion is minimised as there is no cross-arch recording and the record is small enough to minimise the risk of it not seating. The use of a full-arch wax bite is rarely indicated as an intercuspal record as the risk of introducing an error in articulation is considerable.

Waxes are available in various consistencies, ranging from the comparatively soft, through pink modelling wax to hard wax. There is little clinical evidence to support the use of any particular wax.

Although silicone mousse registrations are surprisingly versatile, large edentulous areas may make it difficult to obtain a stable mounting without using wax occlusal registration rims, as one would use for partial denture construction. Wax rims are, however, supported only by soft tissues, so when patients bite onto a wax rim the baseplate is displaced into the soft tissues. As dental stone is not compressible like mucosa, this results in an inaccurate registration when the rim is transferred onto the cast. To minimise this, trim away the occlusal indentations in the rim until there is firm contact on the teeth and only light contact on the rim, so that it is sitting passively on the mucosa. Then record ICP with a thin layer of registration paste or silicone mousse placed on top of the rim; being fluid, these materials do not displace the rim into the mucosa.

Bear in mind that a baseplate made on the cast from one impression cannot reliably be transferred to a cast poured from another – there are always differences between casts recorded by multiple impressions. If a wax occlusal rim is needed, it is best made on the working cast, not transferred from study models.

Increasing Vertical Dimension, Acrylic Copings and Stents

When a registration is used in the construction of definitive restorations at an increased vertical dimension, the mandibular position is best stabilised during the procedure by using one or more provisional restorations made at the desired dimension. Of course, in such cases the new ICP is also in CR.

Some operators prefer to use acrylic copings to record ICP when managing more extensive cases (Fig 8-13), particularly where opposing arches are being restored simultaneously. These techniques are more involved, but in extensive cases the accuracy they allow can be invaluable. Copings are made either on silver dies or duplicate stone dies to prevent damage to the originals. The advantage is that mounting accuracy can be checked on the articulator using shim stock between both opposing copings and unprepared teeth. Rather than linking opposing copings together, the upper copings are made with a rounded occlusal excrescence, which is coated in petroleum jelly. This excrescence indents into registration material placed on the occlusal surface of the lower coping. Traditionally, self-cured acrylic is used as the registration material, but registration paste can be used. This has the advantages of not setting as quickly or undergoing polymerisation shrinkage, as occurs with acrylic. The paste can be made to stick to the coping by first applying a coat of dental varnish.

lateral excursion meaning in dentistry

Fig 8-13a Acrylic copings used with registration paste for a posterior reconstruction.

lateral excursion meaning in dentistry

Fig 8-13b Casts with silver dies mounted.

As shown in Fig 8-14, some configurations of teeth can be difficult to register, particularly when teeth oppose on edentulous space. One solution is to construct an acrylic stent or bar; this acts as a rigid vehicle to carry registration material, thereby avoiding the less reliable wax occlusal rims. In situations where you are doubtful about the accuracy of a registration it is worth having a metal try-in, which can be used as a form of registration coping to check and, if necessary, remount before the porcelain is applied.

lateral excursion meaning in dentistry

Fig 8-14 “Battlement occlusion” causes difficulty in having no directly opposing teeth for registration. A rigid acrylic stent provides greater reliability than wax rims.

Checking the Registration

A written record of the existing intercuspal contacts can be helpful to the technician to ensure that casts are correctly mounted. Some operators draw a diagram of the pattern of occlusal contacts marked with articulating foil. A simpler alternative is to record pairs of teeth that resist the removal of shim stock.

8-4 C ENTRIC R ELATION R EGISTRATION

Why choose cr.

Mounting casts in ICP is common practice. As discussed in the previous section, this is the position used typically for the construction of restorations conforming to an existing occlusion. Casts mounted in ICP can be used for diagnosis, but for the reasons mentioned previously they are wholly inadequate in more extensive cases. In these situations it is necessary to consider occlusal contacts relative to CR. Concerning the planning and construction of restorations, there are two specific situations where you might choose to mount casts in CR:

Diagnostic casts where you plan either to adjust or to reorganise the occlusion, including any case where you are planning to change the vertical dimension.

Working casts where the occlusion is being reorganised using indirect restorations to establish a new ICP in CR. This may occur when adhesively retained restorations are used to increase vertical dimension, providing the basis of a new ICP at an early stage of reorganisation (see Chapter 4). The new ICP is sometimes termed “centric occlusion”, which is defined as the occlusion that occurs in CR.

In such circumstances, the casts must be mounted to provide an accurate simulation of mandibular movement around CR, particularly during opening and closing. This involves mounting the upper cast on an appropriate articulator (see Section 8-6) using a facebow (see Section 8-5) and then mounting the lower cast with a CR registration.

As with an ICP record, obtaining accuracy to within a few micrometres is necessary if you are to make the most of the technology you are using.

What Techniques Are Available?

Being able to find the hinge axis and then record it is an essential skill in restorative dentistry. This gets much easier with practise. If finding the hinge axis is something you find difficult, then you are not alone. It is something you can practise on any patient. Once you have mastered the technique, it becomes a matter of routine.

The simplest and most frequently used technique involves bimanual manipulation to locate the patient’s condyles in CR (Fig 8-15) and then taking a hard wax record, as shown in detail on the DVD. With practice, this approach works very well for most patients. It has the advantage that you can readily re-manipulate the jaw to assess whether the teeth re-engage cleanly into the indentations (Fig 8-16).

lateral excursion meaning in dentistry

Fig 8-15 The nurse holds the wax record while the dentist uses bimanual manipulation to seat the condyles fully in their fossae.

lateral excursion meaning in dentistry

Fig 8-16 Remove the record, chill under cold water, replace and check the teeth close cleanly into the indentations. This gives an indication of reproducibility.

However, this technique is useless in cases in which a patient has mobile teeth, which will displace on closing into the viscous wax. In such circumstance it is better to use a low-viscosity material, such as a silicone registration mousse, or a traditional zinc-oxide eugenol registration paste carried on a gauze frame. The DVD shows how a silicone mousse record can be made.

When using a fluid material, a stable anterior stop is imperative for the mandibular incisors to rest against (Fig 8-17a,b). Otherwise, it is impossible to hold the mandible steady while the material sets, and the patient invariably slips back into ICP. For this purpose, it is helpful to use a Lucia jig at the selected vertical dimension, as described below.

lateral excursion meaning in dentistry

Fig 8-17a Lucia jig showing the arrowhead tracing for a single lower incisor making lateral and protrusive excursions.

lateral excursion meaning in dentistry

Fig 8-17b Silicone mousse used for jaw registration while the Lucia jig stabilises the jaw in CR. If there is sufficient space, syringe the mousse from the buccal aspects. Alternatively, syringe the mousse onto the occlusal surfaces of the lower arch and manipulate the patient into CR.

What About Patients Who Are Difficult to Manipulate?

The ability to find the hinge axis depends as much on your own demeanour as on the cooperation of the patient. The patient needs to relax, and so does the dentist. Having the patient supine is helpful, as is a calm voice – which you must maintain no matter how frustrated you may have become trying to find CR.

Nevertheless, some patients are difficult to manipulate. You can help such patients relax their mandible during jaw registration by preventing their teeth from closing into ICP for a few minutes by placing either a cotton wool roll or a tongue spatula between the incisors. Alternatively, you can use a slightly more sophisticated approach by forming a simple, flat, anterior jig made of self-cured acrylic – a Lucia jig. The key to success with a Lucia jig is to ensure that the occluding portion lies flat against no more than two incisors. Any indentations in the surface of the jig will only serve to guide the patient repeatedly back to an incorrect position. In essence, the jig, cotton wool roll or tongue spatula encourages the neuromuscular system to “forget” the ICP, the memory of which is reinforced by proprioceptive feedback every time the patient swallows.

Usually, simple techniques for separating the teeth are sufficient to allow successful bimanual manipulation. Indeed, some patients will experience “neuromuscular release”, whereby the mandible, previously affected by muscle splinting, suddenly becomes easy to manipulate. Nevertheless, in a small minority of patients, the muscle splinting consistently returns the teeth to ICP and the mandible remains extremely difficult to manipulate. For such patients you may need to consider, as a last resort, making them an occlusal stabilisation splint to condition the masticatory system before recording CR (see Section 8-10). Paradoxically, a CR registration is normally used for the construction of stabilisation splints, which implies that a certain amount of splint adjustment may be needed after fitting.

Electrical stimulation may be used in an attempt to condition the masticatory muscles prior to recording CR, together with electromyographic instrumentation to determine lack of muscle splinting. At the present time there is no strong evidence base to support such an approach.

How Can You Check a CR Registration?

The easiest way to check a CR registration, as shown on the DVD, is to inspect the mounted casts to see if they simulate the retruded contact and then the RCP–ICP slide. Of course you will need to lift, or possibly remove, the pin in the articulator to do this. Identifying which teeth make retruded contact is easy on an articulator, but it takes practice to determine if the RCP–ICP slide is similar to that in the patient. If the casts cannot be fully interdigitated in ICP, this may reflect a registration inaccuracy or a limitation in the function of the articulator.

Some articulator manufacturers supply devices to check the reproducibility of multiple CR registrations, for example the Denar Vericheck. This resembles an articulator, but with its condylar and fossa elements replaced by styli and paper flags. It requires three separate jaw registrations. Each registration is placed in turn between the casts mounted on the instrument and four styli marks are made – two horizontal and two vertical – representing a notional terminal hinge axis. If the styli marks from all three registrations correspond, you can be confident about the registration. If the marks do not correspond, the registration with the most superior/posterior position of the hinge axis is taken as the best attempt – but bear in mind it may still be incorrect. These are useful teaching and research instruments, but they find limited application in clinical practice.

8-5 F ACEBOW R ECORD

As shown on the DVD, a facebow record takes only a few minutes to complete, but it can save you a lot of time when planning restorative cases and when fitting restorations.

What Does a Facebow Do?

All a facebow does is to transfer the spatial relationship of the maxillary teeth and TMJs from the patient to the articulator, enabling accurate mounting of the upper cast in relation to the joints. When the lower cast is mounted, the similarity in geometry between articulator and jaws helps to simulate the paths of jaw movement. Remember that the three main uses of articulated casts are to supplement occlusal examination, to help plan treatment through trial occlusal adjustment and diagnostic waxing and, in the laboratory, to help make restorations that will require minimal adjustment in the mouth. If you plan to undertake any of these procedures, we recommend you use a facebow.

What Are the Main Components?

Some facebows come as two main components – the bow and the bitefork – with a clamping mechanism to join the two together. This type of facebow is cumbersome to transport to the laboratory. Other facebows, such as the Denar Slidematic (Fig 8-18), have three components – the bow, the bitefork and a transfer jig. The advantage of the transfer jig is that the bow remains in the surgery for use on other patients, while the transfer jig/bitefork assembly goes to the laboratory. The DVD shows how to use this facebow clinically. The principles are the same whichever system you choose to use.

lateral excursion meaning in dentistry

Fig 8-18 A facebow simply transfers the relationship between the maxillary teeth and the TMJs.

What Reference Points Do Facebows Use?

Facebows come in a number of designs. All of them locate to three reference points on a patient. Two of these reference points are the condyles, specifically the hinge axis running through both condyles in CR. Most modern facebows are termed “earbows”, as they use the external auditory meati as stable reference points adjacent to the hinge axis. With some old designs of facebow, the bow locates over the lateral aspect of the condyles, making accurate records more difficult to obtain – the process has been likened to nailing a jellyfish to the ceiling!

The third reference point aligns the bow to the horizontal plane, with the patient sitting upright. Anatomically, this is the Frankfort plane, extending from the tragus of the ear to the infraorbital notch. Some facebows use a pointer specifically to align with the infraorbital notch. Others use different anatomical landmarks. The Whip Mix facebow uses the nasal bridge (nasion), while the third reference point for the Denar is a fixed distance, marked on the cheek with a pen, above the incisal edge of the right lateral incisor (Fig 8-19). There is no mystery to this third reference point, it ensures that the casts when mounted are centrally placed between the two members of the articulator, giving an indication of the relationship between the occlusal and the Frankfort planes.

lateral excursion meaning in dentistry

Fig 8-19 This mark, called the “third reference point”, aligns the facebow to the patient’s horizontal plane.

How Accurate Are Facebows?

Facebows need to be used with care, but they do not need to be as accurate in their recording as interocclusal registrations. In practice, facebows are accurate to millimetres while interocclusal records need to be accurate to micrometres. Nevertheless, clinically significant inaccuracies can arise with earbow registrations for the following reasons:

failures in recording technique

discrepancies between the patient’s hinge axis and the average values used for earbows

facial asymmetry

laboratory errors.

The Technique

Success with facebows is a matter of being vigilant. All the parts of the bow should be able to move freely before it is tightened. Sometimes, the clamp holding the bitefork becomes too tight because of contamination with molten wax, or an overtightened and distorted clamp makes it difficult to position the bow properly. In such cases, clean off the wax or ease the distorted clamp by loosening off the screw and levering it open. One of the most common problems is that the facebow clamps are not tightened sufficiently, so the bitefork moves before or during mounting. Finally, remember to show your nurse how to guide the earpieces into the ears properly. The bow needs to be pulled forwards as the earpieces are moved inwards. With practice the procedure becomes second nature.

Hinge Axis Discrepancies

There may be a few millimetres discrepancy between the patient’s real hinge axis and that determined by an earbow. This usually does not produce any significant problems, but the rule to follow is to record the interocclusal registration at, or very close to, the vertical dimension required, thereby minimising the impact of any hinge axis discrepancy. This applies both to diagnosis and in the construction of restorations and appliances. You could use a hinge axis locator to make an extremely accurate facebow registration; however, the extra time taken to locate the patient’s terminal hinge axis is of little benefit – unless you routinely use a fully adjustable articulator and fit difficult full-mouth reconstructions all at one time, but not many dentists do that.

Patients with a Facial Asymmetry

When restoring multiple anterior teeth, a facebow helps to define the occlusal plane and avoid having a “run” on the restorations. Should a patient have a significant facial asymmetry, defining the incisal level of the new restorations can be difficult. There are, however, various strategies that can be employed to take account of this.

Laboratory Errors

In the laboratory, the bitefork must be supported during mounting of the upper cast or it will sag. An elegant way of doing this is shown in Fig 8-20.

lateral excursion meaning in dentistry

Fig 8-20 The bitefork and black transfer jig are attached to an articulator. Beneath the cast is a supporting device to prevent sagging during mounting.

Do I Need to Buy a Facebow?

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Related posts:

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  • Angle Orthod
  • v.80(1); 2010 Jan

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Functional Occlusal Patterns and Their Relationship to Static Occlusion

Kazem s. al-nimri.

a Associate Professor, Department of Orthodontics, School of Dentistry, Jordan University of Science and Technology, Irbid-Jordan

Anwar B. Bataineh

b Professor, Department of Oral and Maxillo-Facial Surgery, School of Dentistry, Jordan University of Science and Technology, Irbid-Jordan

Sawsan Abo-Farha

c Postgraduate student, Department of Orthodontics, School of Dentistry, Jordan University of Science and Technology, Irbid-Jordan

Objectives:

To test the hypothesis that there is no relationship between static occlusion and dynamic occlusion.

Materials and Methods:

The relationship between static and dynamic occlusion was investigated in a sample of 94 dental students (39 males and 55 females) with an age range of 21–30 years. Static occlusion was determined by intraoral examination. Dynamic occlusion was determined in regulated lateral (0.5 mm and 3 mm lateral to the intercuspal position) and protrusive movements of the mandible by intraoral examination with the aid of shimstock.

At the 0.5 mm lateral excursion, 24.5% had bilateral group function and 12.7% had bilateral canine guidance. At the 3 mm positions, the guidance pattern changed to a predominantly canine guidance. Fifty percent of subjects had bilateral canine guidance, and only 8.8% had bilateral group function. In terms of the anterior guidance pattern, a predominant anterior contact with posterior disocclusion (77.5%) was noted. Examination of the relationship between static and dynamic occlusions revealed that at the 0.5 mm position, the pattern of dynamic occlusion was different in relation to various static occlusion features but without reaching a significant level. While at the 3 mm position, the pattern of dynamic occlusion was significantly affected by incisor relationship. The distribution of protrusive excursion patterns was significantly influenced by incisor, canine, and molar relationships.

Conclusions:

The hypothesis is rejected. An association exists between dynamic occlusion and different aspects of static occlusion.

INTRODUCTION

Dental treatment has the capacity to fundamentally change static and dynamic occlusal relationships, while aiming for achieving as near “ideal” occlusion as possible. Accepted criteria for the “ideal” static occlusion were established based on the work of Angle, 1 who is credited with making the profession most aware of occlusion by presenting standards whereby a malocclusion could be compared with normal occlusion, and the work of Andrews, 2 who presented six keys that gave a well-delineated prescription for an ideal intercuspation of teeth. Conversely, the features that constitute “ideal” dynamic occlusion continue to be subject to great debate and have not, to date, been conclusively established.

There are three main concepts regarding tooth contact during the lateral excursion of mandibular movement: (1) balanced occlusion, which was developed from the work of Bonwill, 3 (2) canine guidance, described by D'Amico, 4 and (3) group function, as discussed by Beyron. 5

The relationship between static and dynamic occlusion is one of the aspects of the study of functional occlusion that has received little attention. Few studies have explored the possibility of an association but conflicting results have been reported. Scaife and Holt 6 found canine protected occlusion to be associated with Class II then Class I, and least associated with Class III, malocclusion. The above mentioned findings were confirmed by Al-Hiyasat and Abu-Alhaija 7 in a study of 447 school children, aged 14–17 years. Other studies found that most Class I Angle occlusion cases were associated with balanced occlusion. 8 – 10 On the other hand, Tipton and Rinchuse 11 found no significant association between static and dynamic occlusion.

A number of limitations can be noted in the above mentioned studies: No reference was made to the location of the canine in terms of its relationship to the line of the arch nor to the degree of attrition of the canine, which is of particular importance in examining the assumption that attrition could lead from one type of contact during lateral movement to another. 12 Moreover, the position at which the occlusal contact pattern was recorded (cusp to cusp) is not representative of the functional range of the lateral excursion of mandibular movement.

Another fact for consideration is that changes occurring during occlusal development could influence the occlusal contact pattern; Heikinheimo et al 13 reported an increase in occlusal interferences between the ages of 12 and 15 years in 167 Finns; other studies found a decreasing prevalence with increasing age. 14 , 15 Although the results of these studies are contradictory, they suggest that changes occur during occlusal development that must not be overlooked in sample selection; samples that are beyond the adolescent years would be more representative of a population as it avoids the effects of age and occlusal development on the results of research.

Based on the above mentioned facts, we thought it warranted to further investigate whether a relationship exists between static occlusion and dynamic occlusion, and, if such a relationship exists, which type of dynamic occlusion is associated with which type of static occlusion.

MATERIALS AND METHODS

The population for this study consisted of 94 dental students at Jordan University of Science and Technology (39 males and 55 females). The age of subjects ranged from 21–30 years, with a mean age of 23.1 (±1.44) years. Subjects who met the following criteria were selected:

  • No previous or current orthodontic treatment.
  • The presence of fully permanent dentition except for the third molars
  • No previous occlusal adjustments
  • No large restorations involving the incisal edge or a cusp tip
  • No crowns or bridges
  • No apparent pathologic periodontal problems
  • Upper and lower canines in the line of the arch
  • No tooth showing attrition into the dentine

The static occlusion of each subject was assessed by intraoral examination on a dental chair under direct vision. The following static occlusal features were recorded:

  • Incisor relationship classified according to the British Standard Institute 16
  • Canine relationship classified according to Houston et al 16
  • Molar relationship classified according to Angle's criteria 1

Dynamic occlusion was determined with the aid of shimstock (Almore shimstock, 8 mm wide, 8 µm thick, Hanel, Langenau, Germany) to confirm tooth contact. The examination was carried out with subjects seated in an upright position in a dental chair with the Frankfort plane parallel to the floor. All recordings were made by the same operator in the same period of the day (morning hours) to avoid possible diurnal variation. 17

For the lateral excursion, occlusal contacts were recorded on the working and the nonworking side at ½ mm and at 3 mm lateral to the habitual centric occlusion. To regulate each lateral position, marks were made on the maxillary central incisor with a water-resistant pencil to mark the intercuspal position at 0.5 mm and 3 mm positions for both right and left sides. Subjects were asked to perform the movements with the aid of a handheld mirror. The shimstock was placed on the occlusal surfaces of teeth from the canine backward; the subject was then asked to close his/her mandible into maximum intercuspation. Gliding movement was performed to the right or the left while the examiner maintained a constant pulling force on the shimstock; on reaching the 0.5 mm position, the teeth holding the shimstock were recorded as working side contacts. The subject was asked to repeat the movement with the shimstock placed on the opposite side to record nonworking side contact. The same procedure was carried out to record occlusal contact at 3 mm lateral to the habitual centric occlusion.

Occlusal contacts at the protrusive excursion of mandibular movement were recorded at the edge-to-edge position. The shimstock was placed on the occlusal surfaces of the anterior teeth; the subject was asked to close into maximum intercuspation and then slide to the edge-to-edge protrusive position while the examiner maintained a constant pulling pressure. Once the teeth were at the edge-to-edge position, teeth holding the shimstock were considered to be in contact and were recorded. The shimstock was then placed on the occlusal surfaces of post teeth, and the subject was asked to repeat the same movement to check for the presence of posterior teeth contact.

In the lateral excursion, the guidance pattern was considered as one of the following:

  • Bilateral canine protected occlusion
  • Bilateral group function occlusion
  • Mixed canine protected and group function
  • Bilateral balanced occlusion
  • Mixed balanced and group function
  • Mixed group function and single tooth contact
  • Others (this category included bilateral mediotrusive interference, mixed laterotrusive and canine, bilateral laterotrusive interference, mixed mediotrusive and group, mixed canine guidance, and laterotrusive interference)

In the protrusive excursion, the guidance pattern was considered as one of the following:

  • Anterior contact with posterior disocclusion
  • Anterior contact with unilateral posterior contact
  • Anterior contact with bilateral posterior contact
  • No anterior contact with unilateral posterior contact
  • No anterior contact with bilateral posterior contact

Ten subjects were reexamined at 2 months following the initial clinical examination to determine intraexaminer reliability. The Kappa ranged from (0.8–1), indicating a reliable examination.

Statistical Analysis

Data were analyzed using the Statistical Package for the Social Sciences (SPSS), version 11 (SPSS Inc, Chicago, Ill). The Chi-square test was used to examine the relationship between the different variables included in this study. P values less than .05 were considered statistically significant.

Dynamic Occlusion

In the total sample at 0.5 mm lateral guidance, 24.5% of subjects had bilateral group function and 18.1% had mixed canine guidance and group function. While at the 3 mm positions, the guidance pattern changed to a predominantly canine guidance. Fifty percent of subjects had bilateral canine guidance, and only 8.5% had bilateral group function ( Table 1 ).

Distribution (%) of Dynamic Occlusion at 0.5 mm and 3 mm Lateral Excursion and Incisor Classification a

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In the protrusive guidance patterns, a predominant anterior contact with posterior disocclusion (77.5%) was followed by anterior contact with unilateral posterior contact (12.7%). Anterior contact with bilateral posterior contact was found in 4% of subjects. The remaining 5.8% had no anterior contact with unilateral or bilateral posterior contact.

Static Occlusion

The incisor relationship was Class I in 49 subjects, Class II/1 in 10 subjects, Class II/2 in 17 subjects, and Class III in 18 subjects. The molar and canine relationships are reported in Tables 2 and ​ and3 3 .

Distribution (%) of Dynamic Occlusion at 0.5 mm and 3 mm Lateral Excursion and Canine Classification a

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Distribution (%) of Dynamic Occlusion at 0.5 mm and 3 mm Lateral Excursion and Molar Classification a

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No statistically significant differences were found between males and females in the various aspects of static occlusion or in the guidance pattern in lateral or protrusive excursions. Therefore, male and female subjects were pooled together in the analysis.

Relationship Between Static and Dynamic Occlusion

The type of guidance at the 0.5 mm position was not significantly associated with the incisor ( Table 1 ), canine ( Table 2 ), or molar classification ( Table 3 ). However, it should be noted that at 0.5 mm lateral excursion, bilateral canine protected occlusion was observed only in subjects with Class I incisor, canine, or molar relationships

As can be seen in Table 1 , 70% of subjects with Class II div 1 and Class II div 2 incisor relationships have bilateral canine protected occlusion at 3 mm lateral guidance, compared with 53% in Class I and 11% in Class III. This difference was statistically significant ( P  =  .047). On the other hand, no significant association was noted between the type of lateral guidance at the 3 mm positions and the canine relationship ( Table 2 ) or the molar relationship ( Table 3 ).

The pattern of guidance in protrusive mandibular excursions was significantly associated with incisor classification ( P < .0001; Table 4 ), canine classification ( P < .0001; Table 5 ), and molar classification ( P  =  .031; Table 6 ), with less anterior contact with posterior disocclusion observed in Class III subjects.

Distribution (%) of the Pattern of Guidance in Protrusive Mandibular Excursion and Incisor Classification a

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Distribution (%) of the Pattern of Guidance in Protrusive Mandibular Excursion and Canine Classification a

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Distribution (%) of the Pattern of Guidance in Protrusive Mandibular Excursion and Molar Classification a

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The criteria set for selecting subjects for this study were chosen to ensure the presence of a natural dentition. The absence of apparent pathologic periodontal problems was used as a criterion because the neuromuscular control of occlusion stability and masticatory muscles is influenced by the periodontal afferent. 18 , 19 The fact that the sample was composed of subjects aged 21 to 30 years was chosen because the changes occurring during occlusal development could influence the occlusal contact pattern. Cases with marked attrition were excluded based on the assumption made by McAdam 20 and Woda et al 12 that canine guidance and group function appear to correspond to two successive states of the evolving dentition under the effect of attrition.

Static occlusion was assessed by intraoral examination by direct vision with the aid of a dental mirror, as was done in previous investigations. 7 , 11 Ovsenik et al 21 reported that intraexaminer and inter-examiner malocclusion assessment recorded and measured intraorally is reliable and therefore is proposed as the method of choice to be used not only in epidemiologic studies and screenings, but also in clinical orthodontic assessments.

Occlusal contacts for both lateral and protrusive excursions of the mandible were determined by intraoral examination with the aid of shimstock to confirm the contact between the teeth, as was done in previous investigations. 7 , 22 – 24 Shimstock has been shown to have greater interexaminer reliability than articulating film 25 and high intraexaminer reliability. 7 The chosen thickness of the shimstock was 8 µm, which is below the range of reported thresholds for dental proprioception. This method allows identification of contacting teeth without disturbing this delicate mechanism; a system of measurement that disrupts proprioception may alter mandibular position and consequently tooth contact. 26

For the lateral excursion of the mandible, occlusal contacts were recorded at two positions: ½ mm and 3 mm lateral to the habitual centric. These two positions were selected based on the findings of Ogawa and coworkers, 23 who conducted a study in which tooth contacts were recorded at 0.5, 1, 2, and 3 mm lateral to the maximum intercuspation. They concluded that the occlusal contact patterns during lateral movement varied greatly with mandibular position. The occlusal contact pattern in the 3 mm position predicted the presence or absence of the occlusal contact in the 1 and 2 mm positions (sensitivity >0.7) but not in the 0.5 mm position (sensitivity <0.6). Finally, they suggest that the 0.5 mm position could be used to evaluate occlusal contact in a position close to maximum intercuspation in the functional range, and that the 3 mm position could be used to assess occlusal contact in an edge-to-edge position in the parafunctional range. 24

The orthodontic picture of “ideal occlusion” places considerable emphasis on the static occlusal relationship in assessing the quality of completed orthodontic treatment, with less emphasis on the importance of the dynamic occlusion. In fact, none of the available orthodontic indices for the assessment of treatment outcome contains any functional components! One could argue that this is caused by the absence of consensus regarding what constitutes an “ideal” dynamic occlusion. This, nonetheless, should not lead to a practice of disregarding basic functional principles during orthodontic treatment. As Clark and Evans 27 argue, the gradual adaptation of muscles and joints that occurs during the slow development of a specific occlusion during growth may not occur following the much quicker change related to orthodontic treatment. Other possible consequences of occlusal interference, such as tooth wear and relapse of tooth position, may become apparent only some time after completion of orthodontic treatment, but nevertheless may be attributable to interferences introduced during appliance therapy.

Based on all of the above, we found it particularly interesting to explore the relationship between static and dynamic occlusion. At 0.5 mm lateral excursion, canine protected occlusion was more dominant in Class I incisor, canine, and molar relationships; at 3 mm lateral excursion, canine protected occlusion was dominant in Class II occlusion. Our findings at the 3 mm position compare favorably with those of Al-Hiyasat and Abu-Alhaija, 7 who reported that canine guidance was more dominant in Class II followed by Class I; and those of Scaife and Holt, 6 who found canine protected occlusion to be associated with Class II then Class I and least associated with Class III. However, these results do not agree with other studies, in which investigators found most of Class I Angle occlusion to be associated with balanced occlusion 8 – 10 ; neither do they agree with the findings of Tipton and Rinchuse, 11 who found no significant association between static and dynamic occlusion.

This lack of agreement may be attributed to the different registration materials utilized. Registration material has a significant influence on the number of contacts recorded; some materials tend to record “near contact” as actual contact resulting in differences in the occlusal contact pattern registered. 28 Diurnal difference in occlusal contacts, 17 differences in the criteria used for sample selection, and differences in the classification system are additional factors that contribute to the observed differences.

Anterior guidance with posterior distocclusion was associated with Class II div 2 incisors, followed by Class I and Class II div 1; Class II canines followed by Class I; and Class II molars followed by Class I. These associations explain the high prevalence of posterior contact in protrusion observed in Class III cases and the high prevalence of anterior contact with posterior distocclusion in Class II div 2 cases.

These observations are consistent with those of Al-Hiyasat and Abu-Alhaija, 7 who reported that anterior guidance with posterior distocclusion was associated with Class II div 2 incisors, then Class I and Class II div 1. The prevalence of posterior contact in protrusion was dominantly associated with Class III incisor and molar relationships (50% and 33%, respectively).

Although an association between static and dynamic occlusion was found, it is very difficult to establish a definitive association between them. Therefore, it is necessary to evaluate dynamic occlusion with the aspects of length and inclination of the occlusal guidance of each tooth used as functional indicators.

CONCLUSIONS

  • The distribution of lateral guidance is different at the 0.5 mm and 3 mm positions.
  • At 0.5 mm lateral excursion, bilateral canine protected occlusion was observed only in subjects with Class I incisor relationships or subjects with unilateral or bilateral Class I molar or canine relationships.
  • At 3 mm lateral excursion, bilateral canine protected occlusion was predominant in subjects with Class II incisor, canine, and molar relationships.
  • Anterior guidance with posterior disocclusion was observed most often in subjects with Class II div 2 occlusion and was least observed in subjects with Class III occlusion.

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  • Published: 08 September 2001

What is occlusion?

  • S Davies 1 , 2 &
  • R M J Gray 3  

British Dental Journal volume  191 ,  pages 235–245 ( 2001 ) Cite this article

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In this part, we will discuss:

What 'occlusion' is

Why occlusion is important

The significance of 'ideal occlusion'

The aim of this series of papers is to explore the role of occlusion in dental practice. The range of opinion in the dental profession as to the importance of occlusion is enormous. 1 It is very important that the profession in general and practising dentists in particular have a balanced view of occlusion. This is more important than every patient having a balanced occlusion. The fact that the study of occlusion is characterised by extremes makes it confusing and possibly difficult for individual dentists to find a philosophy which is in line with contemporary good practice supported by evidence from practice-based research.

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lateral excursion meaning in dentistry

What is occlusion? Part 1

lateral excursion meaning in dentistry

What is occlusion? Part 2

lateral excursion meaning in dentistry

Occlusion: is there a third way? A discussion paper

'Occlusion' There is no escape Dentists cannot:

without being involved in occlusion

lateral excursion meaning in dentistry

At one end of the spectrum are dentists who believe that they can go through their working lives with scant regard for their patients' occlusion. They seem to believe that essentially they can conduct their practice ignoring the occlusal consequences of the treatments that they perform daily. Whereas all dentists know of the importance of the good marginal adaptation of their restoration to the health of the adjoining dental and periodontal tissues, some dentists do not appreciate the potential consequences of poor occlusal contact to the opposing teeth and their supporting structures. This is bizarre given the fact that very few dental treatments do not involve the occlusal surfaces of teeth.

Conversely there is a body of opinion that considers occlusion to be such a central pillar in our working lives, and to be of such systemic import to the well being of our patients, that 'occlusion' takes on an almost mystic importance and attracts a cult like devotion ( Fig. 1 ). This can lead some dentists to advocate occlusion as being the key to resolving or preventing a range of disorders far removed from the masticatory system, for example prolapsed lumbar discs. Often such enthusiastic fervour is associated with a didactic prescription of 'occlusal rules' which must be adhered to in the treatment of every patient.

figure 1

It has been claimed without evidence that occlusion causes:

The danger is that both of these approaches leads to inappropriate levels of patient care; patients suffer through either over or under treatment.

It is not surprising that these two extreme views co-exist so easily within a thinking profession because the one appears to provide the justification for the other. The 'occlusion doesn't matter' group probably justify their reluctance to become 'involved in occlusion' on the grounds of what they perceive to be the exaggerated and unsubstantiated claims of the group who believe occlusion to be the central pillar of holistic care. This congregation of opinion in turn may be so frustrated by the apparent disregard of the study of occlusion that they are led to 'gild the lily' by overstating the importance of occlusion and then in the absence of what they perceive to be an inability 'to see the obvious' they go on to lay down rules.

It is the objective of this series of papers to explore the role of occlusion in dental practice in a manner based on reason. There is good and bad practice in occlusion as in other aspects of clinical dentistry: we wish, therefore, to establish the concept of Good Occlusal Practice, which is applicable to all disciplines in dentistry.

Guidelines of good occlusal practice

These should be guidelines not rules.

All patients are different, reacting to similar stimuli in different ways. So the detail of a patient's individual needs can and should be left to the individual clinician. These Guidelines of Good Occlusal Practice should appear to be common sense and, upon reflextion, we hope that the reader will agree that they are obvious. We argue that any fog that has descended over this subject must be cleared, because no practising dentist can care well for their patients without having regard for good occlusal practice.

The importance of occlusion in dental practice

'Occlusion' = Contacts between teeth

Occlusion can be defined very simply: it means the contacts between teeth.

Before describing the significance of the different ways in which occlusal contacts are made occlusion needs to be put into context.

The masticatory (or stomatognathic) system ( Fig. 2 ) is generally considered to be made up of three parts: the Teeth, the Periodontal Tissues, and the Articulatory System.

figure 2

The masticatory system

It is a common criticism of dentists that our dental schools ignore the third part of the masticatory system, the articulatory system, in their teaching. It appears that dentists feel that their time at university did not prepare them adequately in this area; and this view seems to be the case worldwide. The undergraduate dental education must, however, by necessity concentrate initially on the first two parts of this triumvirate, because the dental schools must produce newly qualified dentists who are able to treat patients. Only once the dental undergraduate has an understanding of the diseases that affect the dental and periodontal tissues (parts 1 and 2 of the masticatory system) can the schools start to allow the student to treat patients. So there is justification for the study of the articulatory system being considered to be the third area of study from a chronological point of view. But because of the inescapable fact that almost all dental treatment has an occlusal consequence, it is wrong to consider the study of the articulatory system to be less important than the first two parts of the masticatory system. Given the increasing quantity of knowledge to be amassed in the modern undergraduate course, it may be that those responsible for setting the dental undergraduate curriculum will not be able to cover the articulatory system as they would wish. Now that there is a universal acceptance of the need for continuing education, it may be more realistic to consider a comprehensive study of the articulatory system as the first mandatory element of a post graduate dental education. But the articulatory system is the biomechanical environment in which dentists provide treatment. Although it maybe, by necessity, the last to be learnt it is not less important than the other parts of the masticatory system.

Is the articulatory system a true system?

( Fig. 3a , b )

figure 3

The articulatory system

A system is defined as: 'An assemblage that is connected or interdependent, so as to form a complex unity.'[OED] The articulatory system meets these criteria, so the answer to this question is: Yes.

In this system one can imagine the temporomandibular joints as the hinges, the masticatory muscles as the motors and the dental occlusion as the contacts ( Fig. 3b ).

When viewed in mechanical terms ( Fig. 3b ) it is clear that the elements of the articulatory system are inescapably connected. Furthermore, it can be argued that they are obviously interdependent because a change in any part will clearly affect the other two parts ( Fig. 4a ), but this effect will not necessarily be adverse.

figure 4

(a) Interconnections of the articulatory system (b) Interconnections of the masticatory system

The same sort of analysis of the interconnection within the masticatory system can be made ( Fig. 4 b ).

The importance of 'occlusion' in dental practice is based primarily upon the relationships that it has within these interconnected biomechanical systems. When one considers how almost all forms of dental treatment have a potential for causing occlusal change, the need to establish what constitutes good occlusal practice is overwhelming and obvious.

Analysis of occlusion

Having stated that occlusion simply means the contact between teeth, the concept can be further refined by defining those contacts between the teeth when the mandible is closed and stationary as the static occlusion, and those contacts between teeth when the mandible is moving relative to the maxilla as the dynamic occlusion.

Static occlusion

The first essential question when considering a patient's static occlusion is: 'Does centric occlusion occur in centric relation?'

This question will be clarified after defining terminology, which has been a 'red herring' and has been the cause of enormous and sometimes acrimonious debate. We, also, have preferred terms, but do not feel that they are important.

Centric Occlusion (CO) can be described as the occlusion the patient makes when they fit their teeth together in maximum intercuspation. Common synonyms for this are Intercuspation Position (ICP), Bite of Convenience or Habitual Bite. It is the occlusion that the patient nearly always makes when asked to close their teeth together, it is the 'bite' that is most easily recorded. It is how unarticulated models fit together. Finally, it should be remembered that it is the occlusion to which the patient is accustomed ie the habitual bite.

The word 'Centric' is an adjective. It should only be used to qualify a noun. Centric what?

Centric Relation (CR) is not an occlusion at all. CR has nothing to do with teeth because it is the only 'centric' that is reproducible with or without teeth present. Centric Relation is a jaw relationship: it describes a conceptual relationship between the maxilla and mandible. All attempts to lay down rigid definitions of centric relation are plagued by the fundamental difficulty that there is no sure or easy way of proving that the locating criteria have been achieved.

Centric Relation has been described in three different ways: anatomically, conceptionally, 2 and geometrically.

Centric Relation can be described as the position of the mandible to the maxilla, with the intra-articular disc in place, when the head of the condyle is against the most superior part of the distal facing incline of the glenoid fossa. This can be paraphrased as uppermost and foremost ( Fig. 5 ).

figure 5

Functional anatomy of the temporomandibular joint

This is subject to debate. Some clinicians prefer the idea that centric relation occurs in an 'uppermost and midmost' position within the glenoid fossa; whereas very few people now support the idea that it is in an 'uppermost and rearmost' position. There is support for the uppermost and foremost hypothesis from a study of anatomy: the bone and fibrous articulatory surfaces are thickest in the anterior aspect of the head of the condyle and the most superior aspect of the articular eminence of the glenoid fossa. This is, however, of only academic interest and not of clinical significance as there is no reliable simple means of determining the exact position of the head of the condyle within the glenoid fossa.

Centric relation can be described as that position of the mandible relative to the maxilla, with the articular disc in place, when the muscles that support the mandible are at their most relaxed and least strained position. This description is pertinent to an understanding of 'ideal occlusion'. This definition supports the concept of a 'qualitative' relationship between a jaw position and another element of the articulatory system.

Geometrical

Centric Relation can be described 'as the position of the mandible relative to the maxilla, with the intra-articular disc in place, when the head of the condyle is in terminal hinge axis'.

In order to understand what this frequently used definition means it is easier, initially, to think about one side of the mandible only. The mandible opens by firstly a rotation of the condyle and then a translation which is downwards and forwards. Therefore, when the mandible closes the the terminal closure is purely rotational. At this phase of closure the mandible is describing a simple arc, because the centre of its rotation is stationary. This provides the 'terminal hinge point' (of rotation) of one side of the mandible; but because the mandible is one bone with two connected sides these two terminal hinge points are connected by an imaginary line: the terminal hinge axis. This axis is, therefore, envisaged by imagining the stationary, centres of rotation of each condyle whilst the mandible is moving only in the rotational phase of movement. It is the fact that the mandible is describing this simple arc, when the heads of condyle are in the terminal hinge axis which is of the most clinical significance. This will be discussed later, when the techniques for finding centric relation are presented.

Significance of Centric Relation

There may be arguments about the exact position of centric relation and on how that position is clinically best found. There is, however, a broad agreement between dentists who have studied this subject that there exists a reproducible position of the mandible relative to the maxilla, and that this position is reproducible irrespective of the guidance that the occlusal surfaces of the teeth may provide. Patients with no teeth still have a centric relation. Furthermore there is inter- and intra-operator reliability in finding it.

'Freedom in centric'

'Does Centric Occlusion Occur in Centric Relation?' This is an essential question.

Another aspect of the static occlusion is the presence or absence of 'freedom in centric', this is also known as 'long centric'.

As previously stated the word centric is an adjective and so strictly it should never be used without a defining noun. So this long established term would better read: Freedom in centric occlusion or long centric occlusion. Freedom in centric occlusion occurs when the mandible is able to move anteriorly for a short distance in the same horizontal and sagittal plane while maintaining tooth contact ( Fig. 6b ). Alternatively there will be no freedom in centric occlusion if either the front teeth or the posterior occlusion do not allow this horizontal movement ( Fig. 6a ).

figure 6

(a) No freedom in centric occlusion (b) Freedom in centric occlusion

An easier way of imagining Freedom in Centric Occlusion is to state that if the front teeth hit together as hard or harder than the back teeth, then there is no freedom in that centric occlusion. Two common examples of occlusions that may not have this freedom are firstly those which have an Angles Cl II div (ii) incisor relationship and secondly when anterior crowns have been provided with palatal surfaces which are too thick.

In Figure 6a , there is no freedom in centric occlusion as the occlusal contacts 'lock in' the mandible to the maxilla. Whereas in Figure 6b the mandbible can move anteriorly, for a short distance, in the same sagital and horizontal plane.

Other aspects of the static occlusion that can be described are the extent of the posterior support, the Angle's classification of the incisor relationship together with measurement of the overbite and overjet, and the existence of any cross bites.

The answer to the question: 'Does Centric Occlusion occur in Centric Relation?' is therefore essential, because it describes the relationship of the mandible to the maxilla when the teeth fit together.

Dynamic occlusion

Ideal Occlusion Q. Who or what is it ideal for? Posterior Interference Q. Who or what is it interfering with?

The dynamic occlusion refers to the occlusal contacts that are made whilst the mandible is moving relative to the maxilla. The mandible is moved by the muscles of mastication and the pathways along which it moves are determined not only by these muscles but also by two guidance systems.

The posterior guidance system of the mandible is provided by the temporomandibular joints. As the head of the condyle moves downwards and forwards the mandible is moving along a guidance pathway which is determined by the intra-articular disc and the articulatory surfaces of the glenoid fossa, all of which is enclosed in the joint capsule.

If teeth are touching during a protrusive or lateral movement of the mandible then those (touching) teeth are also providing guidance to mandibular movement. This is the anterior guidance and this is provided by whichever teeth touch during excentric movements of the mandible.

No matter how far back these teeth are they are anterior to the temporomandibular joints and so a patient with a severe anterior open bite would still always have anterior guidance of their mandible, it could, for instance be on the second molars. Therefore, despite the ambiguity of the word 'anterior' in the term anterior guidance, it does not mean that the anterior guidance of the mandible is always on the front teeth. This definition differs from that given in some restorative textbooks, when the term anterior guidance is used to describe only those anterior guidances which involve front teeth.

Anterior guidance may be further classified. 'Canine guidance' refers to a dynamic occlusion that occurs on the canines during a lateral excursion of the mandible. A canine protected occlusion refers to the fact that the canine guidance is the only dynamic occlusal contact during this excursive movement.

Group function. In this type of anterior guidance the contacts are shared between several teeth on the working side during a lateral excursion. To qualify for the term 'group function', the contacts would be towards the front of the mouth and the most anterior of the group would be the earliest and hardest contacts. This would contrast with a 'working side interference', which infers a heavy or early occlusal contact towards the back of the mouth during an excursive movement. A 'non working side interference' is an anterior guidance on the back teeth on the non working side during lateral excursion. The working side is the side of the mandible towards which the mandible is moving during a lateral excursion. The non working side is the side of the mandible away from which the mandible is moving. These terms can be confusing when considering the temporomandibular joints, because it is the TMJ on the non working side which is moving the most.

One reason why restorative textbooks define anterior guidance as being solely the dynamic occlusal contacts between the front teeth is that it is generally considered to be more ideal if the anterior guidance is on those front teeth. Furthermore, the fact that the word 'interference' is used to describe an occlusal contact between back teeth infers that this anterior guidance is less ideal than others. This introduces the concept of 'ideal occlusion' and this raises two important considerations:

If some occlusions are ideal, for what or for whom are they ideal?

If occlusal contact between back teeth is deemed a posterior interference with what is it interfering?

Ideal occlusion

Let us examine this concept and question whether it has any useful function in routine clinical dentistry.

If two molars on the side from which the mandible is moving during an excursive movement can be deemed to provide a non working side interference, then what are they interfering with?

The posterior guidance of the mandible is provided by the temporomandibular joints. As the head of the condyle translates down the articular eminence of the joint on the non working side (which, paradoxically is the side that is moving the furthest) the mandible is being guided by this joint. If, as this is happening, a posterior maxillary and mandibular tooth hit against each other and because these two posterior teeth are close to the joint, then there is potential for the contact between these two teeth to influence or 'interfere' with the movement of the condyle within that joint. Contrast this with the situation, where the anterior guidance is provided not by posterior teeth which are close to the joint, but by front teeth which are further away; then the likelihood of 'interference' of condylar movement within the non-working side temporomandibular joint is less.

Anterior guidance, therefore, on back teeth, whilst still providing anterior guidance to the mandible, is described as a posterior interference because it may interfere with the posterior guidance system of the mandible, namely the temporomandibular joints. Posterior interferences are, therefore, considered to be a less ideal type of dynamic occlusion; and the term ideal relates to whether or not it is ideal for another part of the articulatory system: the temporomandibular joints ( Fig. 7a ). The anterior guidance provided by front teeth is potentially more ideal for the temporomandibular joints for the simple reason that it is further away from the temporomandibular joints. Consequently it can be argued that one aspect of the occlusion (anterior guidance) may or may not be ideal for another part of the articulatory system.

figure 7

Occlusion is ideal for another part of the articulatory system

It is, also, potentially more ideal if the teeth fit together (centric occlusion), in a position of the mandible relative to the maxilla, with the disc in place, where the muscles supporting the mandible are at their most relaxed and least strained (conceptual description of centric relation). This establishes another criterion of the occlusion that can be considered ideal or not ideal for the other part of the articulatory system, namely the muscles of mastication ( Fig. 7b ).

Definition of ideal occlusion

There is no such thing as an intrinsically bad occlusal contact, only an intolerable number of times for that patient at that time in their life to function or parafunction on it

This is given in established texts as: 3

The coincidence of Centric Occlusion in Centric Relation (CO = CR), when there is freedom for the mandible to move slightly forwards from that occlusion in the same sagittal and horizontal plane (Freedom in Centric Occlusion).

When the mandible moves there is immediate and lasting posterior disclusion (anterior guidance on front teeth)

It is presented in this section only after having considered for what or whom this type of occlusion is ideal, and the justification of why a particular type of occlusion could be considered as being potentially ideal for other parts of the articulatory system.

It is of paramount importance to appreciate that the term 'ideal occlusion' means something quite different from the term 'correct occlusion'. To state that an occlusion is correct or wrong betrays a mechanistic approach to the subject. Patients are not machines and an occlusion can only be judged on the reaction that it produces in the tissues of the system in which it inter-reacts. That reaction will be infinitely variable between individuals and will in some contexts (ie TMD pain) vary within an individual with time.

Guidelines of Good Occlusal Practice should be established because they offer the most prudent way in which to provide dental treatment to one part of the system whilst avoiding a potentially adverse reaction in another.

The importance of ideal occlusion as a concept

1. pretreatment examination and records.

The first and most important reason for defining ideal occlusion is that it gives a benchmark against which patients' occlusion can be measured. This needs to be done before, during and after dental treatment; especially in this increasingly litigious environment.

It is of paramount importance that dentists examine and record the pre-existing occlusion before providing treatment which involves changes to that occlusion. Study models would be a good way of doing this as long as they are mounted on an articulator in centric relation. At least the condylar guidance angles would also need to be correctly set so that the dynamic occlusion was recorded. This is not practicable for the vast majority of dentists. Alternatively and infinitely more easily notes can be made, which describe the patient's occlusion. These notes use criteria of ideal occlusion as a benchmark. To record an occlusion using only the criteria of Angle's classification is of very limited value, whereas to use the benchmark of ideal occlusion is considerable more informative (see Fig. 8 ).

figure 8

Example of a record of a patient's occlusion, using ideal occlusion as the benchmark

2. Treatment of Pain Dysfunction Syndrome (PDS)

Force > Resistance

Reduces tissue resistance

Causes failure

Promotes pain/dysfunction

The second reason why ideal occlusion is an important concept is found in the long held view that the most important factor in the development of Pain Dysfunction Syndrome (PDS) is 'the individual patient's lack of adaptation to a less than ideal occlusion'. 4 This is not describing a causal relationship between a less than ideal occlusion and PDS, as different patients will have different thresholds of tolerances to occlusion, in fact the same patients have a different tolerance to their occlusions at different times. It is, however, the case that some patients, at some times, do react adversely to their less than ideal occlusions; and this can lead to pain and dysfunction.

For these patients the provision of an ideal occlusion is, therefore, one but by no means the only way of treating the condition. When an ideal occlusion is provided this should always be initially in a temporary and reversible way: that is a stabilisation splint. The indications for the provision of an ideal occlusion in the patient's natural dentition, for the treatment of PDS are very rare.

3. Conformative versus reorganised approach

In providing treatment with an occlusal element, one of the first questions to be decided in the treatment planning stage is whether the aim is to maintain the same occlusion during treatment. If the pretreatment occlusion is to be preserved, then the is described as 'conformative approach'. 5

Some dental treatment, such as most major restorative and all orthodontic treatment, will however, inevitably change the patient's occlusion: this is known as the 'reorganised approach'. It is, therefore, prudent to design an occlusion that is more ideal and so potentially better tolerated by the patient's articulatory system.

Factors determining a patient's reaction to an occlusion

As stated an occlusion can only be judged as being good or bad in relation to the reaction it produces in the patient's tissues. In the same way that the danger of a substance can only be judged in relation to the concentration in which it occurs, a particular occlusal contact should be assessed in relation to the frequency at which it is made.

This is why bruxism is an important consideration in dentistry.

The 'occlusion' means the contacts between the teeth. The application of force from the muscles, through those occlusal contacts, results in load. Whether that load produces damage to tissues will depend on several factors:

The resistance of the tissues and/or restoration.

The magnitude of the force being applied.

The frequency of the force being applied.

The direction of the force being applied.

The number of contacts transmitting that force.

Risk management

The purpose of guidelines of good occlusal practice is to reduce the risk of damage occurring to the interrelated tissues of the masticatory system, and so increase the chances of a healthy function. This will reduce the chances of disease, mechanical failure and dysfunction or pain. Dentists can positively influence these factors as part of their care.

lateral excursion meaning in dentistry

The next section of this work will present the criteria for, and the technique of, a quick and simple occlusal examination. Thereafter, in subsequent sections, we will present the concepts of good occlusal practice in different disciplines of clinical practice. At the conclusion of each section further points will be added to create the cumulative Guidelines of Good Occlusal Practice.

Smith B G N . Occlusion: 1. General Considerations. Dent Update 1991; 18 : 141–145.

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Gray R M J, Davies S J, Quayle A A . Temporomandibular disorders: a clinical approach . pp20 BDJ publications, 1995, 1997.

Ash M M, Ramfjord S P . Occlusion 4th ed.: pp84–85. Philadelphia: Saunders, 1995.

Ramfjord S P, Ash M M . Occlusion 2nd ed.: p178. Philadelphia: Saunders, 1971.

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Davies, S., Gray, R. What is occlusion?. Br Dent J 191 , 235–245 (2001). https://doi.org/10.1038/sj.bdj.4801151

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Published : 08 September 2001

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Western researchers’ breakthrough paves way for ALS cure

Fueled by a $10-million gift from the temerty foundation, a possible new als treatment could move to clinical trials within five years.

Dr. Michael Strong

By Prabhjot Sohal

In a groundbreaking Canadian discovery powered by philanthropy, a team of Western University researchers led by Dr. Michael Strong has uncovered a potential path toward a cure for amyotrophic lateral sclerosis (ALS). 

The breakthrough, which illustrates how protein interactions can preserve or prevent the nerve cell death that is a hallmark of ALS, is the culmination of decades of Western research backed by the Temerty Foundation.

“As a doctor, it’s been so important for me to be able to sit down with a patient or their family and say to them, ‘we're trying to stop this disease,’” said Strong, a clinician-scientist who has devoted his career to finding a cure for ALS. “It's been 30 years of work to get here; 30 years of looking after families and patients and their loved ones, when all we had was hope. This gives us reason to believe we've discovered a path to treatment.”

ALS, also known as Lou Gehrig’s disease, is a debilitating neurodegenerative condition that progressively impairs nerve cells responsible for muscle control, leading to muscle wastage, paralysis and, ultimately, death. The average life expectancy of an ALS patient post-diagnosis is a mere two to five years.

In a study recently published in the journal Brain , Strong’s team found that targeting an interaction between two proteins present in ALS-impacted nerve cells can halt or reverse the disease’s progression. The team also identified a mechanism to make this possible.

“ This gives us reason to believe we've discovered a path to treatment.” —Dr. Michael Strong

“Importantly, this interaction could be key to unlocking a treatment not just for ALS but also for other related neurological conditions, like frontotemporal dementia,” said Strong, who holds the Arthur J. Hudson Chair in ALS Research at Western’s Schulich School of Medicine & Dentistry. “It is a gamechanger.”

In virtually all ALS patients, a protein called TDP-43 is responsible for forming abnormal clumps within cells, which causes cell death. In recent years, Strong’s team discovered a second protein, called RGNEF, with functions that are opposite to TDP-43.

The team’s latest breakthrough identifies a specific fragment of that RGNEF protein, named NF242, that can mitigate the toxic effects of the ALS-causing protein. The researchers discovered that when the two proteins interact with each other, the toxicity of the ALS-causing protein is removed, significantly reducing damage to the nerve cell and preventing its death.

In fruit flies, the approach notably extended lifespan, improved motor functions and protected nerve cells from degeneration. Similarly, in mouse models, the approach led to enhanced lifespan and mobility, along with a reduction in neuroinflammation markers.

“The investment – and foresight – of the Temerty Foundation has accelerated progress in finding an effective treatment for ALS.” —Western President Alan Shepard

The team’s path to discovery was paved by the Temerty family’s long-standing investment in ALS research at Western – support Strong calls “truly transformational.” Now Strong and his team have set a goal to bring their potential treatment to human clinical trials in five years, a mission that is fueled by a new gift from the Temerty Foundation.

The foundation, established by James Temerty, founder of Northland Power Inc., and Louise Arcand Temerty, is investing $10 million over five years to power the next steps to bring this treatment to ALS patients.

“Finding an effective treatment for ALS would mean so much to people living with this terrible disease and to their loved ones,” said James Temerty. “Western is pushing the frontiers of ALS knowledge, and we are excited for the opportunity to contribute to the next phase of this groundbreaking research.”

The new gift by the Temerty Foundation brings the family’s total investment in neurodegenerative disease research at Western to $18 million.

“Dr. Strong's relentless dedication to his field is matched only by the Temerty family’s deep desire to make a difference for the thousands of people around the world diagnosed with this devastating disease,” said Western President Alan Shepard.  “The investment – and foresight – of the Temerty Foundation has accelerated progress in finding an effective treatment for ALS. We are grateful for the Temerty family’s commitment to life-changing research.”

“This is a pivotal moment in ALS research that could truly transform patient lives,” said Dr. John Yoo, dean at Schulich Medicine & Dentistry. “With Dr. Strong’s leadership, our continued investment in the best tools and technology and the visionary support of the Temerty Foundation, we are thrilled to be heralding in a new era of hope for patients with ALS.”

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Land use changes in the environs of Moscow

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COMMENTS

  1. What is lateral excursion?

    Lateral excursion is the second key step when we chew our food. Once the mouth opens and the food enters the oral cavity, the jaw moves sideways and grinds the food, closes gradually and finally the teeth meet each other before the mouth comes back in a state of rest. Lateral excursion might be hampered due to problems in the gnathic system.

  2. Dental Occlusion

    Lateral excursion. Lateral excursions are a form of dynamic occlusion which occurs when the mandible moves left or right with teeth in contact. They can be described as: Canine guidance: canine protected articulation. The canines on the working side are the only occluding teeth whilst all other teeth become discluded when carrying out lateral ...

  3. Dynamic occlusion: lateral excursion

    Dynamic occlusion: lateral excursion The dynamic occlusion is the contact that teeth make during movements of the mandible - when the jaw moves side to side, forward, backward or at an angle. In dynamic occlusion, the contacts of the teeth are not points as in static occlusion, but they are described with lines.

  4. Range of Motion: Temporomandibular (TMJ) Lateral Excursion

    Learn the proper technique to measure lateral excursion range of motion for the temporomandibular (TMJ) joint using a ruler.

  5. Occlusal Adjustment

    A demonstration of the lateral excursion and an explanation of when and why lateral excursion adjustment is necessary. Orig. air date: AUG 14 74This is part...

  6. Occlusion Static Occlusion, Dynamic Occlusion and Guidance

    Dynamic occlusion is the study of the contacts that teeth make when the mandible is moving - contacts when the jaw moves sideways, forwards, backwards, or at an angle. The contacts are not points, they are lines. Although the jaw is moved by muscles, the contact lines depend on both the teeth positions and shapes (obviously), and the shape of ...

  7. (PDF) Fundamentals of occlusion and restorative dentistry. Part I

    Occlusion is the static relationship between the incising or masticating surfaces. of the maxillary or mandibular teeth or tooth. 5 It is a static position, as the. mandible is not moving. On the ...

  8. Student guide to occlusion

    Occlusion is determined by a patient's articulatory system. Like traditional systems, it relies on motors, hinges and contacts - or muscles, the TMJ and tooth-to-tooth contact. 2. 1. Tooth ...

  9. PDF STUDENT GUIDE TO OCCLUSION

    and Restorative Dentistry ... lateral excursions. 2. TMJ - this is the hinge that allows ... 'ideal occlusion', this does not mean that any variation in these features mean that the patient

  10. What Is Occlusion?

    'Canine Guidance' refers to a dynamic occlusion that occurs between the canines during a lateral excursion of the mandible. A canine-protected occlusion refers to the fact that the canine guidance is the only dynamic occlusal contact during this excursive movement. ... It is the definition of broken that has changed in the field of dental ...

  11. The examination and recording of the occlusion: why and how

    During a lateral excursion of the mandible, the principle movement within the TMJs is on the non-working side (NWS). The head of the condyle on the non-working side moves: forwards, downwards and ...

  12. Introduction to Occlusion

    Canine guidance - this means during lateral excursion of the mandible the canines are the teeth which guide the mandibles movement and the last to disclude ; Group function - this means during lateral excursion of the mandible, the tooth contact which guides the movement is shared between multiple teeth on the working side.

  13. 16: Occlusal Aspects in Restorative Dentistry

    During lateral excursion we can distinguish a working side, which is the side toward which the mandible moves, and a balancing side, or the side away from which the mandible moves. This movement is affected by canine guidance, meaning that the palatal surface of the upper canines is what actually guides movement, as we will explain ahead.

  14. Occlusal Techniques

    Right lateral excursion (RLE) ... Parafunction is often episodic, and so the detection of faceting and vertical microfractures does not mean that bruxism is active at that time. Clinical indicators of active parafunction include fremitus, tooth tenderness and ridging of the sides of the tongue or cheeks at the level of the occlusal plane ...

  15. Occlusion (dentistry)

    Occlusion, in a dental context, means simply the contact between teeth.More technically, it is the relationship between the maxillary (upper) and mandibular (lower) teeth when they approach each other, as occurs during chewing or at rest.. Static occlusion refers to contact between teeth when the jaw is closed and stationary, while dynamic occlusion refers to occlusal contacts made when the ...

  16. Functional Occlusal Patterns and Their Relationship to Static Occlusion

    There are three main concepts regarding tooth contact during the lateral excursion of mandibular movement: (1) balanced occlusion, which was developed from the work of Bonwill, 3 (2) canine guidance, described by D'Amico, 4 and (3) group function, as discussed by Beyron. 5. The relationship between static and dynamic occlusion is one of the ...

  17. Effect of Lateral Excursive Movements on the Progression of Abfraction

    There was canine guidance in lateral excursion. There was more than 3 mm of pocketing. The teeth were mobile. There was poor oral hygiene. Other restorative treatment was required of the teeth included in the current study. The subject had poor general health

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    Main page; Contents; Current events; Random article; About Wikipedia; Contact us; Donate; Pages for logged out editors learn more

  19. What is occlusion?

    A 'non working side interference' is an anterior guidance on the back teeth on the non working side during lateral excursion. The working side is the side of the mandible towards which the ...

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  21. Western researchers' breakthrough paves way for ALS cure

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  22. PDF Fundamentals of occlusion and restorative dentistry. Part I ...

    The vertical axis passes through the working condyle during lateral excursion of the mandible. The sagittal axis is an anteroposterior axis, which passes through the working condyle during the lateral excursion of the mandible. In this case the non-working condyle is seen rotating downwards and medially. Working and non-working side

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    Odintsovo Museum of History and Local Lore. 26. History Museums. Recreational Sports Park in the name of Larisa Lazutina. 8. Sports Complexes. Temple of the Grebnevskaya Icon of Mother of God. 37.

  24. Land use changes in the environs of Moscow

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