6.3 Occlusion Principles & Angle Classification

Quick Answer: Angle Class I = MB cusp of 16/26 in buccal groove of 46/36; Class II = mandible distal (molar); Class III = mandible mesial. Overjet = horizontal; overbite = vertical. CR is condylar; CO/MIP is dental. Know Curves of Spee and Wilson.

Occlusion links dental anatomy to orthodontics, prosthodontics, and TMD screening. AFK expects definitions and classification more than full articulator programming, but concepts of CR, MIP, and guidance appear across domains.

Ideal Occlusion — Working Framework

No single “perfect” occlusion exists in every patient, but teaching norms include:

• Static intercuspation with stable posterior contacts and lighter anterior contacts in MIP.
• Anterior guidance in protrusion that discludes posteriors.
• In lateral excursion, either canine guidance (canines disclude posteriors) or group function (shared working-side posterior contacts without nonworking interferences).
• Absence of nonworking (balancing) interferences that can load the joint or fracture restorations.
• Midlines roughly coincident; arches coordinated in transverse width.

Mutually protected occlusion concept: posteriors protect anteriors in MIP (vertical stops); anteriors protect posteriors in excursions (disclusion). This is a design ideal for many fixed reconstructions—not a claim that all natural dentitions show pure canine guidance.

Angle Classification (Sagittal Molar Relation)

Edward Angle’s system classifies malocclusion by first permanent molar relationship (canine relation is a parallel descriptor).

Half-cusp and subdivision language: Class II subdivision means Class II on one side and Class I on the other. AFK may describe relations in words without naming “Angle” if the molar landmark is clear.

Canine classification (often paired):

• Class I canine: maxillary canine cusp tip between mandibular canine and first premolar (distal to 33/43).
• Class II canine: maxillary canine mesial to that embrasure (sits over mandibular canine more).
• Class III canine: maxillary canine distal, toward the mandibular premolar embrasure more.

Important: Angle Class I molar does not equal “ideal occlusion.” Crowding, open bite, crossbite, and CR–MIP slides can all exist in Class I.

Overjet, Overbite, Open Bite, Crossbite

Functional shift: a premature contact (often a primary canine or molar interference) forces the mandible to slide into a crossbite appearance—treatment may be occlusal, not only orthopedic. AFK may contrast true skeletal asymmetry with a shift.

Centric Relation vs Centric Occlusion / MIP

In many dentate patients, MIP ≠ CR. A CR–MIP discrepancy (slide from first CR contact into MIP) is common. Large slides, especially with lateral components, matter for diagnosis of occlusal disease, prosthetic design, and TMD evaluation. Recording CR (e.g., bimanual manipulation, leaf gauge concepts at a high level) is more prosthodontic detail; AFK cares that CR is condylar and MIP is dental.

Retruded contact position (RCP) is often used synonymously with first tooth contact in CR in older literature—recognize the vocabulary cluster: CR / RCP vs ICP / MIP / CO.

Curves of Spee and Wilson; Compensating Curve

Curve of Spee (anteroposterior): From the cusp tip of the mandibular canine along buccal cusps of premolars and molars, the occlusal line forms a curve that is concave superiorly in the mandible (convex for the maxillary arch alignment). A deep Curve of Spee is associated with deep bite tendencies and may be leveled in orthodontics. Prosthodontic setups use a controlled curve for balanced or lingualized schemes.

Curve of Wilson (mediolateral): The mediolateral curvature of the occlusal plane across left and right posterior teeth. Mandibular posterior crowns incline lingually somewhat; maxillary posteriors have a compensating buccal inclination so lingual cusps can function. On frontal view, the mandibular curve is concave superiorly.

Compensating curve (complete dentures): Artificial curve incorporating Spee/Wilson concepts so that balanced occlusion can be developed on an articulator—high-yield when prosthodontics overlaps this chapter.

Bonwill triangle and Monson sphere are historical geometric models of mandibular arch form and spherical occlusal surfaces—occasionally mentioned; know they relate to idealized 4-inch sphere concepts rather than clinical measurement tools.

Guidance and Excursive Movements

• Protrusive movement: mandible moves forward; ideally incisal guidance (central/lateral incisors) separates posteriors.
• Laterotrusive (working) side: side toward which mandible moves; contacts may be canine only or group function.
• Mediotrusive (nonworking/balancing) side: opposite side; contacts here in natural dentition are often considered interferences for fixed restorative goals (though complete dentures may use balancing contacts for stability).
• Bennett movement: immediate/progressive mandibular side-shift of the working condyle—advanced articulator concept; recognition-level for AFK.

Clinical Integration

• Restoring a single crown: match existing MIP contacts; avoid introducing nonworking interferences.
• Raising vertical dimension: prosthodontic decision involving CR records and phonetics/esthetics—beyond pure classification but linked to CR vs MIP.
• Pediatric anterior crossbite or posterior crossbite: early interceptive thinking; distinguish dental crossbite of one tooth from skeletal transverse deficiency.
• Class II division 2: retroclined maxillary centrals with deep overbite—different from division 1 proclination/large overjet.

AFK Exam Traps

1. Overjet ≠ overbite—horizontal vs vertical; reverse them and you lose easy points.
2. Class II means the mandible is distal (or maxilla relatively mesial)—describe the mandibular molar’s position relative to the maxillary molar.
3. Class I molars can still be malocclusion (crowding, open bite).
4. CR is not MIP—CR is joint-based; MIP is maximum tooth fit.
5. Curve of Spee is sagittal (front-to-back); Curve of Wilson is frontal/mediolateral—do not swap names.

If you can assign Angle class from a molar description, define overjet/overbite/crossbite, and separate CR from MIP, you will clear the majority of AFK occlusion stems in this chapter.