Making Occlusion Work: 2

RESTORATIVERESTORATIVE DENTISTRY DENTISTRY Making Occlusion Work: 2. Practical Considerations A.J. MCCULLOCK stable maxillomandibular relationship Abstract: In the first of these two articles, occlusal terminology, techniques for should be developed to allow examining the occlusion, articulators and interocclusal records were discussed. Here reproducibility of the jaw registration and the authors consider some of the practical applications. stability of restorations and teeth. The Dent Update 2003; 30: 211–219 retruded position is the only relatively reproducible position of the mandible Clinical Relevance: A practical knowledge of occlusion is required for successful that is physiologically acceptable. placement of the smallest and largest restorations. When the reorganized approach is indicated, and this is in a small number of patients, the new ICP is established by: l occlusal splint therapy to achieve estorations must be planned and occlusal scheme is to be reorganized to muscle relaxation,1 allowing the R designed to fit harmoniously with create a new and stable position, the final condyles to move into the retruded the complexities of the neuromuscular restorations are made to the new ICP that position; control system, the temporomandibular coincides with RCP and may involve a l elimination of RCP–ICP discrepancy joints (TMJs) and supporting structures change to the occlusal vertical dimension using provisional restorations, of the teeth without introducing occlusal (see previous article for abbreviations). occlusal equilibration, additions to interferences. A stable posterior The factors to be considered are given existing partial dentures to restore occlusion with smooth uninterrupted in Table 1. the OVD, and orthodontics; protrusive and lateral movement of the A functional stable posterior occlusion l final restorations when mandible is necessary. Once the exists when enough teeth are in maxillomandibular relationships are occlusion has been assessed, which may simultaneous even contact to direct stable. require articulated study casts, the occlusal forces axially, stabilizing the decision must be made as to which type positions of both the teeth and the TMJs. In the previous article two theories were of occlusal scheme should be used for Appropriate posterior stability distributes mentioned describing idealized occlusions the restorations. occlusal forces over a wide area, – gnathology and Pankey-Mann-Schulyer. preventing damage to the individual A third concept, of a dynamic individual components of the masticatory system. occlusion, has developed, based on the TO CONFORM OR Loss of posterior stability may result fact that not all dentitions fit into a REORGANIZE? in: prescribed concept and so a more Before embarking on treatment the functional approach should be adopted. practitioner must decide whether to l increased toothwear; However, one fact is clear: that an provide restorations within the existing l mechanical failure of teeth or occlusion should be stable and thus occlusal scheme (the conformative restorations; ideally ICP and RCP should coincide when approach) or to change it deliberately l hypermobility, drifting, rotation and an occlusion is reorganized. (the reorganized approach). If the entire tilting; l mandibular dysfunction. STABLE TOOTH CONTACTS A.J. McCullock, BDS, MSc, FDS RCS, MRD, MRD RCS In the presence of mandibular The morphology of the occlusal (Edin.), Consultant in Restorative Dentistry, Lister dysfunction, which is not always the Hospital, Stevenage, Hertfordshire. surfaces of restored posterior teeth is case in unstable ICP relationships, a influenced by anterior guidance and Dental Update – May 2003 211 RESTORATIVE DENTISTRY Posterior occlusion Stable Unstable indicated before restoration when: No. of teeth for restoration Small (>6) Large Slide from RCP to ICP Large/small Large/small l the opposing tooth has over- Drifting of anterior teeth No Yes erupted into an existing under- Mandibular dysfunction No Possibly contoured or scooped out restoration, producing a ‘plunger’ = Stable ICP = Unstable ICP cusp; Conformative approach Reorganized approach l tilted or over-erupted teeth have Table 1. Factors to be considered when considering provision of restorations. produced an uneven occlusal plane; l the tooth to be restored has a the angulation of the condylar paths. the occlusion has been assessed and non-working side interference; Stable occlusal contacts in ICP are unwanted contacts identified, l the tooth to be restored creates an generated using a tripodized, cusp to adjustments can be made in the mouth, occlusal interference in the fossa or cusp to marginal ridge contact if uncomplicated, or through trial retruded path of closure. relationship according to preference, adjustments on articulated casts restoring the intercuspal relation of (Figure 2) to establish their effect. Contacts in RCP should be adjusted the posterior teeth in the retruded Such mock equilibrations allow an first, then the lateral and, finally, the position (Figure 1). In many natural accurate assessment of the effects of protrusive interferences. Before the dentitions supporting cusps contact tooth adjustment and correct planning teeth are touched with a bur the effect opposing marginal ridges in ICP, of the stages of the adjustment of each adjustment must be directing occlusal forces along the without damaging the teeth. anticipated. Adjustments to contacts long axis of the tooth. The cusp to Selective occlusal adjustment is on maxillary teeth will move the point fossa theory suggests that restored cusps should contact triangular fossae developed on the mesial or distal aspects of posterior teeth. This pattern is suited to producing restorations against an existing occlusion. A tripodized occlusion has each of the supporting cusps contacting the opposing teeth at three points, suspending the cusp tips B L above the opposing fossa and preventing them making contact. Protrusive guidance should immediately separate posterior teeth and in lateral movement the working guidance should immediately disclude teeth on the non-working side. The steepness of anterior guidance directly influences the angle of the cuspal inclines. To achieve immediate Figure 1. (a) Cusp tip to fossa contact. (b) Tripodized relationship: each cusp tip contacts the opposing tooth at three points. posterior disclusion in canine guidance, mandibular cusps must be able to glide between maxillary cusps ab without interference. When anterior guidance is steep cusps can be made steep and the fossae deeper. OCCLUSAL ADJUSTMENT Occlusal interferences occurring during mandibular movement may Figure 2. (a) Articulated casts covered in indicator varnish. (b) Trial adjustments to show the require adjustment before restorative effect of the procedure on the next point of contact. procedures are contemplated. Once 212 Dental Update – May 2003 RESTORATIVE DENTISTRY objectives for various clinical a b situations of increasing complexity is discussed in the following paragraphs. Small Number of Units to be Restored A single unit or a couple of units must fit into the existing occlusal scheme Figure 3. (a) Checking tooth contacts with Shimstock before cementing a bridge. (b) Same (conformative approach) and provide contacts verified after cementation. the correct supporting cusp contacts. Before tooth preparation the occlusal contacts must be checked with articulating paper and Shimstock, not of contact buccally and mesially; by ensuring: tooth-to-tooth only on the tooth to be prepared but those on mandibular teeth will be contact in ICP; no slide from RCP also on the adjacent teeth. The same moved lingually and distally. This will to ICP if reorganizing the contacts can be verified on the help in deciding which points to adjust occlusion; no occlusal articulated working casts. At the try-in when opposing teeth have been marked interferences; correct guidance in stage, ICP and lateral contacts should by articulating paper, remembering that lateral excursions. be checked with articulating paper on cusp tips are sacrosanct. If, for l There should be no mandibular the restoration and Shimstock on the example, the marked contact falls on the dysfunction. adjacent teeth (Figure 3). lingual facing incline of a maxillary l Thickness of restorative materials When the distal tooth in an arch is buccal cusp and the buccal facing must be adequate. prepared it is especially necessary to incline of the opposing mandibular l Occlusal contour of restorations ensure the occlusal record is accurate, cusp, the latter contact should be must be correct. as errors can readily be introduced adjusted as the contact will then move l Occlusal vertical dimension must with the vertical dimension if the casts towards the centre of the tooth. be correct. are tipped or rotated. One way to For more detailed information readers guarantee accuracy is to try-in self- are referred to expanded texts on the The practical application of these curing acrylic resin copings, ensuring mechanisms of occlusal adjustment.2 RESTORATION OF ab POSTERIOR TEETH The posterior teeth provide stable vertical and horizontal relationships between the mandible and maxilla. When planning any posterior restoration, the practitioner must consider the following questions: Figure 4. (a) Self-curing acrylic copings on distal abutments to verify occlusal contacts on the l Is ICP stable? cast. (b) Ensuring contact and assessing available space for correct thickness of material for crown. l What are the anterior tooth

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