8.3 Occlusion Concepts in Prosthodontics

8.3 Occlusion Concepts in Prosthodontics

Quick Answer: Prosthodontic occlusion is planned, not accidental. Mutually protected occlusion (canine/anterior guidance discluding posteriors in excursions; posteriors protect anteriors in MIP) is the common goal for natural teeth and many fixed restorations. Bilateral balanced occlusion is often preferred for complete dentures so bases stay stable in excursions. Group function (working-side posterior contacts in laterotrusion) is an alternative when canines are weak. Know CR vs MIP, determinants of mandibular movement, and Hanau’s factors for balanced setups.

Occlusion links anatomy (TMJ, muscles, teeth) to every crown, denture, and RPD. AFK stems may show wear patterns, fractured ceramics, or unstable dentures—answer with the governing occlusal principle.

Foundational Definitions

Slide from CR to MIP of 1–2 mm is common in natural dentitions. Large slides with fremitus, wear, or restoration failure warrant occlusal analysis before extensive prosthetics.

Determinants of Occlusion and Mandibular Movement

Rule of harmony: steeper condylar guidance → steeper cusps may be tolerated if anterior guidance separates teeth appropriately; shallow guidance + steep cusps → posterior interferences. When restoring anteriors, anterior guidance is a design decision: too steep may overload periodontium/TMJ in susceptible patients; too flat may allow posterior interferences.

Mutually Protected Occlusion (Natural Dentition Ideal)

In a mutually protected scheme:

1. In MIP / heavy closure, posterior teeth contact and support vertical load; anteriors contact lightly or slightly less heavily so posteriors “protect” anteriors from crushing loads.
2. In protrusive and lateral excursions, anterior teeth (especially canines) contact and disclude posterior teeth, protecting posteriors from lateral destructive forces and protecting cusps/restorations from non-axial load.

Clinical translation for crowns: check excursions with articulating film after cementation protocols allow; eliminate nonworking (balancing) interferences on natural teeth and fixed prostheses. A high crown that only “looks fine in MIP” can still destroy a ceramic opposing cusp in lateral movement.

Canine Guidance vs Group Function

Group function is not the same as bilateral balance. Group function allows working-side posterior contacts but still aims to avoid harmful nonworking contacts in natural teeth. Bilateral balance intentionally creates balancing-side contacts for denture stability.

Bilateral Balanced Occlusion (Complete Dentures)

Definition: simultaneous contacts of maxillary and mandibular teeth on both left and right sides (and ideally anterior–posterior) in centric and eccentric positions, so that the denture bases are not tipped by unilateral contacts.

Anatomic balanced occlusion uses cusped teeth with compensating curves and careful setup. Monoplane occlusion uses 0° teeth; balance may be achieved with balancing ramps or slight compensating curves; indicated for flat ridges, Class II/III discrepancies, or poor control.

Hanau’s Quint (five factors of balanced occlusion)

Classically interrelated factors (Hanau):

1. Condylar guidance (patient anatomy; facebow/protrusive records approximate)
2. Incisal guidance (set by dentist with overbite/overjet of anterior teeth)
3. Occlusal plane orientation
4. Cuspal inclination
5. Compensating curve (Spee/Wilson analogs in setup)

Thielemann’s formula (conceptual): balance relates condylar and incisal guidance to cusp height and compensating curve—if you steepen incisal guidance, you may need to adjust cusp heights or curves to maintain balance. AFK: know the five names and that changing one factor forces compensation in others.

Christensen’s phenomenon

In protrusion, the mandible’s downward translation creates a posterior space between opposing posterior teeth if the occlusal plane is flat—Christensen’s phenomenon. Compensating curves and cuspal inclines close that space for denture balance. Explains why monoplane setups behave differently from steep cusp setups.

Occlusion for Fixed Prosthodontics and Single Crowns

Goals for a single posterior crown in a mutually protected dentition:

• MIP contacts shared—not a single hypercontact
• No nonworking interference
• Working contacts consistent with existing scheme (canine guidance vs group function)—do not invent group function on one crown if the arch is canine-guided unless rebuilding comprehensively
• Embrace form allows floss; axial contours protect periodontium

FPD pontics should not create hyperocclusion; slightly lighter pontic contact is sometimes preferred to protect abutments—follow contemporary loading principles without leaving a supraeruption stimulus if opposing is natural and will supraerupt (judgment case by case).

Anterior crowns/veneers: establish protrusive and lateral guidance on restorations carefully; heavy posterior interferences after raising vertical dimension are common if only anteriors are lengthened without a full plan.

RPD Occlusion Notes

• Tooth-supported RPDs (Class III): occlusion can resemble fixed—stable MIP stops on natural teeth and prosthetic teeth coordinated
• Distal-extension RPDs: prosthetic teeth should not create premature contacts that tip the free-end or overload the terminal abutment; selective grinding and framework fit first
• Combination syndrome risk (classic teaching): complete upper vs distal-extension lower—anterior upper resorption, tuberosity hyperplasia, lower anterior overeruption—mitigate with balanced contacts, implant support when possible, and avoid excessive anterior function only

Vertical Dimension Changes

Increasing VDO with restorations is possible but not casual:

Articulators and Records (Exam-Level)

Semi-adjustable articulators suffice for much crown-and-bridge and denture work when records are accurate. Hand-articulating casts for multi-unit posterior reconstructions invites excursive errors.

Wear Patterns and Diagnosis

Attrition = tooth-to-tooth wear; abrasion = foreign object (brushing); erosion = chemical; abfraction debated (occlusal stress + cervical lesion narrative)—know definitions for AFK biomedical/clinical crossover.

Choosing a Scheme: Decision Table

Integration Scenarios (AFK Style)

1. Patient fractures PFM lingual cusp of upper molar on balancing side → look for nonworking interference; adjust scheme, not only “stronger ceramic.”
2. New complete dentures drop when patient chews on one side → check bilateral balance, flange extensions, and CR=CO.
3. Distal-extension RPD abutment hurts on biting sticky food → evaluate clasp design (RPI), indirect retention, and occlusion on free-end teeth.
4. Anterior veneers chip repeatedly → verify posterior disclusion in protrusion; may need occlusal equilibration or nightguard for parafunction.
5. “My bite feels high only when I slide sideways” → eccentric interference; mark laterotrusive pathways.

Rapid review list

• Mutual protection: posteriors hold MIP load; anteriors guide excursions and disclude posteriors
• Canine guidance vs group function (working side only)—≠ bilateral balance
• Complete dentures: bilateral balanced occlusion for base stability
• Hanau’s Quint: condylar guidance, incisal guidance, plane, cusps, compensating curve
• Christensen’s phenomenon: posterior open space in protrusion on flat planes
• Eliminate nonworking interferences in natural/fixed teeth
• CR records and facebow improve accuracy when changing VDO or rebuilding

Mastering occlusion schemes lets you predict why a restoration fails and which contact to change—core prosthodontic judgment for the AFK and for clinical practice.