Dental Anatomy and Occlusion: Morphology, Numbering, and Function
Numbering systems
Master three systems. Universal numbers permanent teeth 1–32, starting with the maxillary right third molar; primary teeth use letters A–T. FDI uses two digits, with the first digit as the quadrant (1 maxillary right, 2 maxillary left, 3 mandibular left, 4 mandibular right) and the second as the tooth position from the midline. Palmer uses a quadrant bracket with numbers 1–8.
Morphology
Know cusp and root counts: the maxillary first molar typically has three roots and four or five cusps including the cusp of Carabelli; the mandibular first molar has two roots and five cusps. Incisors have incisal edges and marginal ridges; canines have a single cusp; premolars typically have two cusps, with the mandibular first premolar having a small lingual cusp. Contact points, embrasures, and marginal ridges protect the interproximal periodontium.
Occlusion and movement
Centric occlusion is maximum intercuspation; centric relation is a jaw-to-skull relationship. Mutually protected occlusion means posterior teeth protect anterior teeth in maximum intercuspation, while anterior teeth disclude posteriors in excursive movements. Canine guidance occurs on the working side during lateral excursion; the nonworking (balancing) side should have no contact. The curve of Spee is anteroposterior; the curve of Wilson is mediolateral. Angle’s classification uses the first molar relationship: Class I normal, Class II distal, Class III mesial.
Traps
FDI quadrant reversal (3 versus 4) and working versus balancing side naming are the most frequent errors. Questions also confuse maximum intercuspation with centric relation and mislabel the nonfunctional cusp.
Rule of thumb
For FDI, read the number as “quadrant, then position”: 36 is the mandibular left first molar.