Dental Occlusion and Cusp Types

Study Notes

Occlusion

Occlusion refers to the way the upper and lower teeth come together.
Centric Occlusion: Also known as maximum intercuspation, it's the position where teeth make the most contact. It's determined by the teeth.
Centric Relation: This is the reproducible position of the mandible (lower jaw) with or without teeth. The articular disc is in place and muscles are relaxed, determined by the joint.
Convex surfaces touching each other. Points of contact are limited to specific areas.
Normal Intercuspation: Ideal tooth contacts and relationships contribute to stability. Occlusal forces are directed along the tooth's long axis during intercuspation. Cusp arrangements allow lateral jaw movement without interference.
Exception: The mandibular central incisor and maxillary third molar are exceptions to the general pattern.
Arch Shape: The maxillary arch is generally larger than the mandibular arch (contained).

Cusp Types

Stamp cusp: Occludes into the fossa of the opposing tooth or marginal ridge. Maxillary = palatal cusp; Mandibular = buccal cusp.
Shear cusp: Deflects tongue/cheek from occlusal table. Occludes in embrasures or grooves. Maxillary = buccal cusp; Mandibular = lingual cusp.

Normal Characteristics

Overjet and Overbite: Normal ranges are 2-3mm.
Cusp-Fossa Relationship: Mesiolingual cusp of upper molars to central fossa of lower molars.
Cusp-Marginal Ridge Relationship: Cusp of 15 to the marginal ridge of 45 and 46.
Cusp-Embrasure/Groove Relationship: Cusp tips of 14 to the embrasure between 44 and 45.

Tooth Contacts

Tooth Contacts: Prevent buccal-lingual and mesiodistal drifting of teeth.

Alignment of Dentition

Plane of Occlusion:
Curve of Spee: Curved line from anterior to posterior touching the tips of all mandibular teeth (lateral view).
Curve of Wilson: Curved line from right to left.
Sphere of Monson: 3D representation of the curve of occlusion (combined Spee and Wilson). This variation is because of varying tooth inclinations.

Inter-Arch Tooth Alignment

Mesial/Distal Inclines: Maxillary mesial inclined planes and mandibular distal inclined planes.
Buccal Cusp Position: Buccal cusps of max teeth are lateral to buccal cusps on mandible. This prevents tongue or cheek biting. It also guides jaw during lateral movements.

Malocclusions (Classes)

Class I (Neutroocclusion):
First Molar Relationship: Mesiobuccal cusp of upper 6 to mesiobuccal groove of lower 6.
Canine Relationships: Mesial inclined plane of the upper 3 occluding to the distal inclined plane of the lower 3.
Class II:
Canine Relationship: More complex.

Muscles of Mastication

Muscles responsible for elevation, depression, protrusive and retrusive movements of the mandible.

Lateral Movements

Working Side: Side towards which the mandible is moving.
Non-Working Side: Opposite side.
Muscles Involved: Masseter, temporalis, medial pterygoid, lateral pterygoid.

Muscle Descriptions

(Note: Specific origins and insertions are included in your original text, and are repeated here for detail)*
Masseter:
- Anterior fibers: elevate mandible
- Posterior fibers: protrude mandible
- Unilateral (one-sided) contraction: pulls mandible laterally toward working side.
Temporalis:
- Origin: temporal fossa
- Insertion: coronoid process of mandible
Medial Pterygoid: Elevates and protrudes mandible
Lateral Pterygoid: Pulls mandible forward during opening. Controls return of condyle to fossa during closing.
- Origin: lateral surface of lateral pterygoid plate of sphenoid bone.
- Insertion: condyle of mandible.

Description

Explore the fundamentals of dental occlusion, including the concepts of centric occlusion, centric relation, and arch shape. This quiz covers the ideal tooth relationships and occlusal forces essential for stability. Understand various cusp types and their significance in dental anatomy.