Occlusal Curves and Cusp Roles

Overview

Lecture covers dental occlusion concepts: static vs dynamic occlusion, cusp types, and occlusal curves (Spee, Wilson, Monson), with clinical relevance.

Types of Occlusion

• Static occlusion: form of teeth, alignment, articulation between arches, and relation to supporting structures.
• Dynamic occlusion: function of stomatognathic system including teeth, gingiva, periodontal ligament, alveolar bone, TMJ, nerves, muscles, and nutrition.
• Normal and malocclusion terms mainly refer to static, form-related aspects.

Posterior Tooth Cusps

• Two cusp types: centric holding (supporting) and non-supporting (shearing/guiding).
• Centric holding cusps: maxillary palatal cusps and mandibular facial cusps.
• These occlude in opposing teeth’s central fossae and marginal ridges.
• Non-supporting cusps: maxillary buccal cusps and mandibular lingual cusps.
• Functions: guide mandible in lateral excursions and shear food during mastication.

Occlusal Curves: Spee, Wilson, Monson

• Curve of Spee: sagittal plane; anteroposterior curve starting at lower canine, through premolars to molars.
• Benefits: guides arrangement of teeth in denture construction.
• Maxilla shows convex curve; mandible shows concave curve due to tooth angulation.
• Extended Curve of Spee forms a 4-inch (101.6 mm) radius circle centered at the glabella.
• Basis for Curve of Monson when extended across all posterior teeth.
• Formation: progressive mesial tilting of lower teeth aligns with arcs of closure around condylar axis.

Curve of Wilson

• Coronal plane curve formed by posterior occlusal surfaces in a curved plane.
• Contacts buccal and lingual cusp tips of mandibular posterior teeth.
• Results from inward inclination of lower posterior teeth.
• Extension bilaterally across posterior teeth contributes to Monson sphere.

Curve of Monson

• Spherical concept from combined extensions of Curves of Spee and Wilson.
• Radius defined by angulation at contact points of upper and lower posterior teeth.
• Orientation lines meet at the center of the Monson sphere.

Clinical Significance

• Identification and assessment of occlusal curves are essential in orthodontic treatment planning.
• Correction of occlusal curve is a primary initial step in orthodontics.
• Occlusal curves guide artificial teeth arrangement for complete dentures.

Variations in Curve of Spee

• Physiological: deciduous dentition shows flat to mild curve; adults show more pronounced curve.
• Pathological: exaggerated in deep overbite, brachycephalic patterns, and short mandibular bodies.

Management of Exaggerated Curve of Spee

• Two approaches: posterior teeth extrusion or incisor intrusion.
• Posterior extrusion: for short facial height with moderate to minor incisor display.
• Incisor intrusion: for adolescents and adults when posterior extrusion is not feasible.

Key Terms & Definitions

• Static occlusion: tooth form, alignment, articulation, and relation to supports.
• Dynamic occlusion: functional interactions of teeth, TMJ, muscles, nerves, and nutrition.
• Centric holding cusps: supporting cusps that contact fossae and marginal ridges.
• Non-supporting cusps: guiding/shearing cusps for lateral guidance and mastication.
• Curve of Spee: sagittal anteroposterior occlusal curvature from lower canine posteriorly.
• Curve of Wilson: coronal transverse occlusal curvature across posterior teeth.
• Curve of Monson: theoretical sphere from combined Spee and Wilson curvatures.

Structured Summary

Action Items / Next Steps

• Assess each patient’s occlusal curves before orthodontic planning.
• For deep Curve of Spee, select either posterior extrusion or incisor intrusion based on facial height and display.
• Follow occlusal curves when arranging complete denture teeth.