Occlusal Schemes MCQ

Three classical occlusal schemes organize tooth contact. Mutually protected occlusion is the modern default for dentate adults: canine guidance in lateral movement, with posterior centric stops in MIP. Group function distributes lateral guidance across multiple posterior teeth and is used when canines cannot guide alone (worn dentition). Balanced occlusion uses bilateral simultaneous contact in all positions to stabilize complete dentures. Underneath these schemes sit the centric stops, supporting vs non-supporting cusps, marginal ridges, and Hanau's quint of articulator inputs that determine posterior morphology.

Mutually Protected Occlusion

• Mutually PROTECTED occlusion means the anterior teeth and posterior teeth protect each other: in MIP the POSTERIOR teeth bear the load (canines lightly contact); in LATERAL movement, the canine on the working side DISOCCLUDES the posterior teeth on both sides, protecting them from lateral force.
• In PROTRUSIVE movement, the anterior teeth (the maxillary palatal surfaces of the incisors and canines contacting the mandibular incisal edges) disocclude the posterior teeth.
• The CANINE is favored as the working guide because of its long root (better resistance to lateral force), its single cusp, and its proprioceptive richness; canine-protected occlusion is a common synonym in older texts.
• Mutually protected occlusion is the MODERN DEFAULT for dentate adults; non-working contacts in this scheme are interferences, and adjustments aim to restore canine guidance with posterior disocclusion.

Group Function

• GROUP FUNCTION distributes lateral guidance across MULTIPLE working-side posterior teeth simultaneously; the load is shared, not concentrated on the canine.
• Group function is the appropriate scheme when the CANINE CANNOT GUIDE alone: severely worn or missing canines, periodontally compromised canines, or canines positioned out of guide (e.g., severe Class II Div 1).
• Group function distributes lateral force across multiple periodontal ligaments and may be more protective in worn or compromised dentitions; however, the broader contact pattern requires more careful equilibration.
• Selecting group function is a clinical judgment that depends on the existing condition of the canine, the wear pattern of the posterior teeth, and the patient's parafunction; modern restorative work often restores canine guidance when feasible.

Balanced Occlusion (Complete Dentures)

• BALANCED OCCLUSION is bilateral SIMULTANEOUS contact in centric AND in all eccentric positions (lateral and protrusive); both working AND non-working sides contact, and the anterior and posterior teeth contact in protrusion.
• Balanced occlusion is used in COMPLETE DENTURES to stabilize the dentures during function; without balancing contacts, the denture tilts and loses retention during chewing or swallowing.
• Balanced occlusion is INAPPROPRIATE in a dentate adult: bilateral non-working contacts that stabilize a denture are damaging interferences on natural teeth.
• Lingualized occlusion (a variant) places maxillary palatal cusps in contact with mandibular central fossae across the arch; it simplifies setup and is widely used in modern complete denture fabrication.

Centric Stops, Cusps, and Marginal Ridges

• CENTRIC STOPS are the tooth-to-tooth contact points in MIP that stabilize the bite; for posterior teeth, TRIPOD CONTACTS (three contacts per centric stop, distributed around the contact point) are the ideal target, distributing load across the supporting cusp tip and surrounding inclines.
• SUPPORTING (also called STAMP, FUNCTIONAL, HOLDING, or CENTRIC) cusps are the cusps that bear the load in MIP: the maxillary PALATAL cusps and the mandibular BUCCAL cusps; they fit into the central fossae and marginal ridges of the opposing arch.
• NON-SUPPORTING (also called GUIDE, SHEARING, NON-CENTRIC) cusps are the cusps that shape lateral movement without bearing centric load: the maxillary BUCCAL cusps and the mandibular LINGUAL cusps.
• MARGINAL RIDGES of adjacent teeth meet to form an occlusal table; cusp tips of the opposing arch contact the marginal-ridge area (specifically the embrasure and the central fossa) to distribute load.

Hanau's Quint and the Determinants of Posterior Morphology

• HANAU'S QUINT (or Hanau's formula) summarizes five factors that determine posterior tooth morphology in articulator setup: condylar guidance, anterior guidance, plane of occlusion, curve of Spee, and cusp height.
• Condylar guidance is joint-determined and fixed; anterior guidance is tooth-determined and modifiable in restorative work; plane of occlusion, curve of Spee, and cusp height are restorative variables the dentist controls.
• These five factors together determine how steeply the posterior cusps must rise and fall to clear the opposing teeth during lateral and protrusive movement without producing non-working interferences.
• When restoring a full arch or rehabilitating a worn dentition, the dentist designs the posterior morphology around the patient's specific Hanau-quint inputs (recorded through facebow + CR + protrusive/lateral records on a semi-adjustable articulator).

Non-Working Interferences and Adjustments

• A NON-WORKING (balancing) interference is a contact on the non-working side during a lateral movement; in mutually protected occlusion (and group function), the non-working side should disocclude during lateral movement.
• Non-working interferences risk fracturing supporting cusps, loosening restorations, and producing TMD-like symptoms; they also expose teeth to torque in directions the periodontium is poorly designed to absorb.
• Identification: articulating paper records contacts; the patient moves laterally while light marks are made; non-working-side marks during lateral excursion indicate interferences.
• Adjustment: SELECTIVE GRINDING of the non-working cusp inclines (typically the lingual incline of the maxillary buccal cusps and the buccal incline of the mandibular lingual cusps - the BULL rule: buccal-upper, lingual-lower) reduces interferences while preserving centric stops.