Introduction
Occlusal morphology is the shape of the chewing surfaces and the way upper and lower surfaces fit together. Restoring it correctly decides whether a crown chews well, stays stable and spares the periodontium.
How the arches fit
In a normal (Angle Class I) intercuspation:
- The mesiobuccal cusp of the upper first molar sits in the buccal groove of the lower first molar: the key of occlusion.
- The upper arch is slightly larger and overlaps the lower one on the outside: upper buccal cusps lie buccal to the lower teeth, and upper incisors cover the lower incisal edges.
- Each tooth meets two opposing teeth, except the lower central incisors and the upper third molars.
- The upper canine fits in the embrasure between the lower canine and first premolar.
Supporting and guiding cusps
Forces in the intercuspal position should run along the long axes of the teeth. Supporting cusps must therefore be restored with stable contacts on flat areas, not on steep slopes.