Dental Anatomy: Understanding Occlusion

Dental Anatomy

Sheet number: 13
Written by: Lajneh Teejan
Edited by: Noor Hamadneh
Doctor: Siham Alarag
Date: 2024

Occlusion

Definition: Occlusion is the act of closure or being closed (focused on occlusal surfaces of teeth). It's a static, morphological relationship between teeth. It includes factors related to development and stability of the masticatory system, and how teeth are used in oral motor behavior. It encompasses the integrated functioning of teeth, jaws, joints, and muscles of the head and neck (including the TMJ).
Physiology & Occlusion: Physiology focuses on the alignment of individual teeth within each jaw (maxillary or mandibular). Occlusion describes the relationship between the two dental arches.
Concepts of Occlusion:
- 1-Balanced Occlusion (ideal): Bilateral contacts in all functional excursions (movements). Bilateral contact means equal distribution of masticatory forces on both sides of the jaw. A maximum number of teeth in contact is ideal (70% of people have normal occlusion). If no ideal occlusion = malocclusion.
- 2-Inter-cuspal Position: Each functional cusp contacts a specific fossa of the opposing tooth. Lingual cusps for posterior maxillary teeth, buccal cusps for lower posterior teeth. Non-functional cusps exist but are important (B.U.L.L. - buccal of upper, lingual of lower).
- 3-Centric Occlusion: A position of balanced, bilateral contact between the cusps of the maxillary and mandibular arches. Centric relation is the position of the mandible where the condyle is positioned as far posterior and superior as possible in its fossa/glenoid fossa.

Primary Molar Relationship

Terminal Plane Relationship: Predicts the secondary dentition occlusion based on the primary dentition.
Types:
- Flush (straight): 56% of permanent teeth demonstrate a Class I molar relationship.
- Distal step: Class II molar relationship (malocclusion).
- Mesial step: Higher probability for Class I molar relationship; lesser probability for Class III.

Factors Influencing Effect of Terminal Plane Relationship

Factors impacting the relationship include skeletal jaw changes, mandibular growth, sufficient leeway space for permanent molar movement, and combined dimensions of primary vs. permanent tooth sizes. Leeway space is the difference in mesiodistal dimension between primary and permanent molars.

Permanent Occlusion

Anteroposterior Relationship:
- Incisors: Class I, II, or III.
- Canines: Class I, II, or III.
- Molars: Angle's Class I, II, or III.
Faciolingual Relationship: Describes the anterior-posterior relationship between opposing teeth and the amount of overlap.

Incisal Relationship

Class I (Normal): Overjet (horizontal) and overbite (vertical) are typically 2-3mm.
Class II (Malocclusion): Overbite is greater than 2-3mm, with the upper central incisor covering more than one-third of the lower central incisor. Either overjet increase (type 1) or overbite increase with normal overjet (type 2).
Class III (Malocclusion): Overbite is less than 2-3mm, with the lower incisors positioned forward of the upper incisors.

Canine Relationship

Class I (Normal): The maxillary canine cusp tip occludes within the embrasure between the mandibular canine and first premolar.
Class II (Malocclusion): The maxillary canine is mesial/anterior to its mandibular counterpart position, with the mandible often positioned further back.
Class III (Malocclusion): The maxillary canine is distal to its mandibular counterpart, and the position of the mandible is often further advanced.

Angle's Class III

Mesiobuccal cusp tip: Position of the maxillary first molar in distal/posterior relationship to the mandibular first molar groove. Mandible moves anteriorly.

Arch Occlusal Relationship

Curves of Spee: Imaginary occlusal line observed from the lateral aspect of the posterior teeth.
Curves of Wilson: Observations of the mesiodistal relationship in the coronal or anatomical area of the teeth.

Inclination & Angulation of Roots

Mandibular arch: Wider than maxillary.
Posterior tooth position: Outward in the maxilla, inward in the mandible, to meet in centric or occlusal relationship.
Optimal tooth placement: Teeth position for maximum force resistance during function.

Antagonists

Antagonist: A tooth in one jaw that contacts or articulates during mastication or occlusion with a tooth in the opposite jaw.
Exceptions: Mandibular incisors and maxillary third molars each contact two opposing teeth.
Teeth Loss: Loss of one tooth often forces adjacent teeth to contact with the opposing antagonists.
Space Disturbances: Mesial or distal drifting causes disturbances in occlusal contact with opposing antagonists.

Centric Stops

Definition: Point where opposing teeth touch during centric occlusion.
Supporting Cusps: Lingual/palatal cusps in maxilla and buccal in mandible used to make or establish centric contacts.
Centric Stops: Areas of occlusal contact and the cusp tips themselves. Critical for restoring dentistry due to the large number of contact points (nearly 138 when all 32 teeth are involved).

Movements Away From Centric Occlusion

Working Side: Jaw moves laterally with contact; non-working side has no contact (in complete dentures).
Non-working Side: Jaw movement with no contact; complete dentures use this side as balancing side.

Movements in TMJ

Working Side: Condyle moves downward, forward, laterally
Non-Working Side: Condyle moves downward, forward, and medially.

Tooth and Canine Guidance

Guidance for mandible movements that is provided by teeth contact, or occlusion.
Types: Canine, Group and Incisal.

Protrusive and Retrusive Movements

Protrusive: Mandible moves forward, often determined by the guidance from the incisors.
Retrusive: Mandible moves backward, culminating in centric occlusion.

Group Functions, Canine Guidance, Incisal & Condylar Guidance

Different types of guidance for mandible movements during occlusal activity relating to group of teeth contact, or only one tooth contact (canine guidance), tooth-to-tooth contact during lateral/eccentric jaw movement (incisal guidance), and the guidance related to the condylar movement along the articular eminence during protrusive movement (condylar guidance).