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Home , Crown (dentistry), Occlusion (dentistry)

RESTORATIVERESTORATIVE DENTISTRY

Making 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 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 to restore occlusion with smooth uninterrupted in Table 1. the OVD, and ; 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 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 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 is case in unstable ICP relationships, a influenced by anterior guidance and

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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 No Yes erupted into an existing under- Mandibular dysfunction No Possibly contoured or scooped out restoration, producing a ‘plunger’ = Stable ICP = Unstable ICP ; 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

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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 . (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 . 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 . l What are the anterior tooth contacts? l What design of tooth preparation? ab l How even is the occlusal plane? l Occlusal vertical dimension – adequate or reduced? l What type of occlusal scheme is desirable – conformative or reorganized?

The objectives are: Figure 5. (a) Single-quadrant interocclusal record and (b) self-curing acrylic copings. The over- erupted first has been prepared and waxed-up to produce an even occlusal plane. l To leave stable occlusal contacts

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Reduced Vertical Dimension ab Associated with Short Clinical Crown Height Both the OVD and ICP may be altered in this situation (Figure 6). Such cases usually require restoration in RCP and the production of a stable and coincident ICP using the reorganized approach. Occasionally, the anterior tooth contact and condylar position are cd stable, allowing the existing ICP to be used. The details of recording the OVD were discussed in the previous article. On articulated study casts mounted in RCP at the correct OVD, occlusal adjustments are carried out to eliminate any discrepancy between RCP and ICP. These are then carried out on the patient’s teeth as an occlusal e Figure 6. (a) Occlusion in ICP at a reduced equilibration. On the casts, the teeth to vertical dimension. (b) Teeth in RCP showing be restored are next prepared and restored vertical dimension and creation of waxed up to full contour, bringing them space anteriorly. (c) Diagnostic wax-up in into occlusal contact with the opposing RCP. (d) Composite resin build-ups on anterior teeth in RCP at the new vertical arch. The new ICP and OVD are dimension. (e) Metal ceramic crowns maintained by developing the cusp duplicating the occlusal scheme developed height and fossa depth. Temporary using the composite restorations. restorations are constructed from this wax-up and cemented onto the prepared teeth; minor occlusal adjustments may be necessary to develop coincident ICP and RCP. the occlusal contacts on the teeth are unchanged the approach is The patient is reviewed over several the same as on the casts (Figure 4). The conformative. weeks to check his/her adaptation to thickness of the copings can also be The inter-occlusal record (Figure 5) is the new occlusal scheme. This is measured to see how much available taken following adjustment and tooth determined by a lack of symptoms from space has been created. preparation. This only needs a record the TMJs, a feeling of comfort and of the relationship on the prepared side, stability of the restorations. Definitive providing a full arch impression has restorations are then made duplicating Single Quadrant been taken and there are adequate the newly established occlusion. Following loss of posterior teeth in a occlusal contacts on the contralateral quadrant the antagonistic teeth may side to maintain stability. over-erupt or tilt, producing an uneven Multiple Units in One Arch occlusal plane. Unless the over- If most occlusal contacts will be lost in erupted teeth are recontoured by Opposing Quadrants the preparation of teeth, then a selective occlusal adjustment or In this situation the occlusal plane and reorganized approach should be used. restoration, any replacement of the curves of Spee and Monson can be A diagnostic wax-up on articulated missing teeth will have contact in ICP restored to produce the most casts in RCP will determine the new and an irregular occlusal form that is favourable occlusal contacts. The OVD position of ICP and temporary determined by the shape of the is maintained by tooth contact restorations will be constructed opposing teeth. By eliminating the anteriorly and on the contralateral side, maintaining the occlusal vertical irregularities, a harmonious occlusal posteriorly by the condylar position in dimension (Figure 7). contour will be created that ensures ICP using the conformative approach. stable ICP contacts and avoids lateral When the abutment teeth form interferences. The replacement has interferences and ICP is unstable it is Full Mouth Rehabilitation been developed to a modified advisable to reorganize the entire The restoration of all four quadrants occlusion, but as ICP remains occlusion. together requires that all the

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with articulating paper. Matt ab surfaces more easily show such marks and should be used at the try-in stage to verify occlusal contacts before polishing and cementation. Gold occlusals would be preferred where:

l there is a history of parafunctional activity; cd l clinical crown height is reduced; l optimal occlusal control is necessary in the reorganized approach.

RESTORATION OF ANTERIOR TEETH

Figure 7. The replacement of a maxillary denture and crowns. (a) The displaced maxillary Preoperative considerations: denture. (b) Palatal view of the restorations and edentulous space. (c) Complete arch diagnostic wax-up in RCP. (d) Temporary bridge replacing all the maxillary restorations. The missing teeth l stability of ICP; were replaced by single tooth implants and the remaining teeth crowned. l reproduction of correct palatal contours; l tooth preparation; determinants of occlusion be developed stable ICP contacts. The wear l metal coping design; in unison. It is advisable to provide characteristics of direct composite l protrusive and working guidance; long-term temporary restorations in resins are less favourable and more l relationship; such cases as the patient’s tolerance abrasive to the opposing : l phonetics and appearance. to changes in ICP, RCP, excursive this material should not be used when movements and possibly the OVD restoring large cavities where tooth Objectives (in addition to the must be monitored over a long time. contact is solely on the material. Small posterior objectives): The proposed changes can be Class II restorations can be restored gradually introduced on the temporary with composite, providing that the l even distribution of forces in restorations, which are easier to adjust occlusal contacts are primarily on the incisal guidance; or add to. Such restorations should tooth and not the material. l immediate posterior disclusion have a metal substructure overlaid with (except in Class III occlusions). acrylic or composite resin. The Porcelain versus Gold principles of a reconstruction are no Porcelain occlusal surfaces offer different from those already described. improved posterior aesthetics but the Anterior Guidance The treatment plan is divided into technique for developing them is more The anterior teeth are in a balanced four stages: difficult than in gold and the highly position determined by the , polished surface does not readily mark , occlusal relationship and 1. Occlusal splint therapy. 2. Occlusal equilibration so that ICP = RCP. 3. Restoration of the anterior teeth. a b 4. Restoration of the posterior teeth, either by opposing quadrants or all at one time.

Materials for Restoring Occlusal Surfaces

Amalgam is an excellent material for Figure 8. (a) A Class II division II incisor relationship with a complete . (b) Shortening the restoring posterior teeth as it has a lower and building out the palatal surfaces creates stable occlusal contacts. high resistance to wear, producing

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into protrusion and lateral excursions. ab Anterior guidance can be duplicated on an articulator with a customized incisal guidance table. Self-cure acrylic resin is shaped by moving the upper member of the articulator while maintaining contact with the incisors and on the study casts. The incisal pin carves out a path in the setting resin resembling a Gothic arch cd tracing (Figure 9). This technique is used when a new reorganized guidance to which a patient has adapted has been established on multiple temporary crowns or when the existing guidance must be copied. The canine tooth has a favourable crown/root ratio for absorbing occlusal forces as well as a root configuration e Figure 9. (a) Failing bridgework. (b) Short providing greater surface area, more clinical tapering crown preparations. (c) periodontal ligament and proprioception Immediate temporary bridge. Anterior than adjacent teeth.3 It is eminently guidance was established on the bridge in the suited to guide lateral excursive mouth, allowing the retention of the re- mandibular movements and produce prepared teeth to be checked as well as the stability of the occlusal contacts. (d) A immediate disclusion of the posterior customized incisal guidance was produced on teeth. Scaife and Holt4 reported an the articulator to copy the anterior guidance incidence of 57% bilateral canine developed in the mouth. (e) The definitive guidance in 1200 individuals. There is crowns and bridge restoring the upper arch little scientific evidence to assist in using a customized incisal guidance table, ensuring duplication of the palatal surfaces of identifying exactly what canine the temporary restorations. guidance should be. McHorris5 suggested that the disclusive angle (which governs the palatal contour of the working canine) should be 5o greater alveolar bone support. Changes to the In Class II division I incisor than the condylar guidance angle. shape of the teeth can produce relationships the overbite and There are several mechanical unwanted movement if these factors will be increased, leading to the advantages in providing canine are disrupted, leading to migration, mandibular incisors occluding to the guidance: rotation over-eruption or formation of palatal aspect of the cingulum close to . Restorations must be placed the dentogingival junction. If this l easier access in the front of the in this balanced envelope to achieve relationship is copied in maxillary mouth for adjustments; stability and longevity. Anterior restorations, ICP contacts may become l smooth mandibular movements can guidance should provide smooth even unstable, leading to an increase in be produced with immediate contact on as many anterior teeth as tooth mobility, migration and splaying. disclusion posteriorly; possible from ICP through the The incisal guidance can be altered by l recording and producing canine excursions discluding the posterior building out the palatal surfaces of the guidance is less complicated, both teeth immediately. It should be shallow, restorations to provide occlusal rests in clinically and technically. work harmoniously with condylar the area of contact of the lower teeth; it guidance and fit in with the skeletal and may also be necessary to shorten the incisor relationship, appearance and mandibular incisors. The edges are Occlusion on Pontics speech. If a single tooth is to be reduced horizontally to produce a flat Occlusal contacts on full-sized pontics restored the existing guidance can be rather than bevelled incisal edge, which should be in ICP. When the canine is readily duplicated. When all the would make it difficult to achieve stable replaced by a pontic on a fixed bridge anterior teeth are to be restored some contacts (Figure 8), especially in Class canine, guidance can be developed, changes to the guidance, crown II division II relationships. This will providing there are anterior and position and appearance can be made. create harmonious movements from ICP posterior retainers. If a cantilever bridge

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is made using the , group occlusion requires a high level of skill function should be developed. and knowledge from both technician ACKNOWLEDGEMENT The occlusal contacts on a simple and clinician to ensure a good result. The author thanks Mr Stephen Davies for his constructive comments on these two articles. cantilever bridge must be in ICP on A functional dynamic approach to both units but the pontic must be free occlusion based on theoretical of any lateral contacts. This reduces principles is a useful concept in the lateral forces on the pontic that restorative dentistry. Most patients REFERENCES would otherwise cause a lever effect, require little more than an acceptance of 1. Gray SJ, Davies SJ, Quayle AA. A Clinical Guide to Temporomandibular Disorders. London: BDJ Books, forcing the bridge to rotate outwards. their existing occlusions, ensuring that 1997; pp.39–42. restorations fit into their individual 2. Dawson PE. Occlusal adjustment In: Evaluation, schemes, providing they are harmonious Diagnosis and Treatment of Occlusal Problems. St Louis: CONCLUSION and stable. There are a number of C.V. Mosby, 1974; pp194–206. 3. Bonaguro JG, Dusza GR, Bowman DC. Ability of The basic principles in restoring approaches to extensively reorganizing human subjects to discriminate forces applied to anterior and posterior teeth have been the occlusion that will produce an certain teeth. J Dent Res 1969; 48: 236. discussed, highlighting the necessity acceptable result, providing the 4. Scaife PR, Holt JE. Natural occurrence of canine for careful preoperative planning. The underlying principles of each theory are guidance. J Prosth Dent 1969; 22: 225. 5. McHorris WH. Occlusion with particular emphasis conformative approach is applicable to fully understood and their individual on the functional and parafunctional role of most patients: reorganizing an practical application adhered to. anterior teeth. J Clin Orthod 1979; 13: 684.

illustrated at different stages of BOOK REVIEW treatment. Advantages and pitfalls of the treatment mechanics are Invisible Orthodontics: Current mentioned as the cases progress to Concepts and Solutions in Lingual completion. The precision involved in Orthodontics. By Giuseppe Scuzzo loop mechanics not only bears a and Kyoto Takemoto. Quintessence heavy resemblance to laborious wire Books, New Malden, 2002 (173 pp., bending in edgewise mechanics, but £65.00 h/b). ISBN 3-87652-181-5. seems more demanding when trying to fit these systems intra-orally. Lingual orthodontics has been part of Sliding mechanics also requires the orthodontic profession for some greater care because the force time, although apparently only about moment ratios are applied differently 10,000 orthodontic cases are treated from the lingual aspect and these using this technique in Europe, Japan then tend to tip teeth in unwanted and the USA. Considering the high directions. In the final chapter, the numbers of orthodontic cases treated authors describe the various ways in each year worldwide, the number of which the finished results are retained clinicians using lingual orthodontics with lingual retainers, clear must be very small. to four different laboratory positioning splints and transparent The authors have written this book techniques in the pre-clinical set-up retainers. largely on their own experiences and of lingual orthodontics. The book This book will be of interest to are well supported with excellent seems to emphasize the reliance upon postgraduate students and illustrations of case studies. The good technicians and laboratory orthodontic practitioners who want to book starts by introducing the topic facilities which may be a reason for develop a private ‘invisible of lingual orthodontics aimed at its limited use. orthodontics’ practice. It provides an specialist orthodontists. It skips over The well illustrated case reports excellent overview of the lingual the diagnostic and therapeutic indicate how the lingual appliance technique and has brought to light considerations in lingual technique can be utilized to a high the immense technical skills from both orthodontics and suggests useful standard. The laboratory and clinician in the hints for successful treatment. These presented certainly require some treatment of a single case. Although include the use of loop mechanics, lateral thinking and boldness in this book is not fully comprehensive, power arm auxiliaries and force execution, even for most well- it does provide a structured approach delivery systems and mechanics in seasoned orthodontists. Two to lingual orthodontics. lingual orthodontic extraction cases. contrasting biomechanics, closing C.H. Kau and S. Richmond Two chapters of the book are devoted loops and sliding mechanics, are Cardiff Dental School

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