Anatomy of the tooth and dentition

• The human dentition is heterodont (has different types of teeth) and diphyodont (has two different dentitions in a lifetime)
• In the primary dentition, there are 2 incisors, 1 canine, and 2 molars in one arch (212) → 20 teeth in total
• In the permanent dentition, there are 2 incisors, 1 canine, 2 premolars, and 3 molars in one arch (2123) → 32 teeth in total
• The deciduous teeth are more bulbous, have more divergent and shorter roots (need to provide space for the developing permanent tooth bud), and a larger pulp chamber comapred to permanent teeth
• The deciduous teeth are also whiter; the enamel of permanent teeth is more mineralised so it is less white
• The dentition is divided into maxillary/mandibular arches as well as left/right quadrants per arch (divided by the median line/midline)
• Permanent teeth that replace deciduous teeth are called succedaneous teeth; however, permanent molars are nonsuccedaneous as permanent premolars replace the deciduous molars
• Tooth naming: dentition-arch-quadrant-tooth (e.g. permanent maxillary left central incisor)
• Three main tooth numbering systems: universal numbering system, Palmer notation, FDI notation
• Universal system numbers from 1-32 for permanent teeth (starting from upper right to lower right), and A-T for primary teeth
• Palmer notation uses 1-8 for permanent teeth and A-E for primary teeth, but also has a prefix symbol that denotes the quadrant of the tooth
• The FDI notation uses a two digit number for each tooth, the first digit denoting quadrant and the second denoting tooth
• In FDI notation, 1-4 are used for quadrants in permanent teeth (upper right to lower right), 5-8 for primary teeth
• In FDI notation, 1-8 is used to name each tooth in permanent teeth, and 1-5 is used for primary teeth
• Clinical crown: portion of the tooth visible in the oral cavity
• Anatomical crown: portion of a tooth covered with enamel
• Clinical root: portion of tooth in the alveolus
• Anatomical root: portion of the tooth covered with cementum
• Cervical margin/cementoenamel junction: junction of the anatomical crown and root
• Anterior teeth (incisors and canines) have four surfaces and an incisal ridge
• Posterior teeth (molars and premolars) have five surfaces, including an occlusal surface
• Proximal surfaces of the teeth can be mesial (towards midline) or distal (away from midline); the mesial surfaces of the central incisors touch each other
• When two teeth in the same arch meet, their curvatures adjacent to the contact region forms embrasures/spillways, which prevents forces from coming in contact with the gingiva, facilitates self-cleaning of the tooth, and directs food away from the gingiva → must be preserved during restoration
• Cusp: a prominent elevation found on the occlusal surface of a posterior tooth
• Tubercle: a smaller elevation on the crown, usually a malformation of the tooth and the extra formation of enamel
• Cingulum: seen in anterior teeth, it is a bulbous convexity near the cervical region of a tooth on the lingual side
• Ridge: a linear elevation on the surface of the tooth
• Marginal ridge: ridge at the mesial/distal edges
• Triangular ridge: ridge descending from the tip of the cusp towards the central part of the occlusal surface, covers half the tooth
• Oblique ridge: ridge running in an oblique fashion across the occlusal surface, specifically found in maxillary molars
• Fossa: irregularly rounded depression or concavity on the surface of the tooth
• Sulcus: a broad and long (but not necessarily deeper) depression/valley on the surface of a tooth between the ridges and cusps
• Developmental grooves: more narrow and shallow depressions on the tooth, usually formed during the development of the teeth and demarcates margins between the main parts of the crown (cusps)
• Pits: small, pinpoint depressions located at the junction between or at the end of a developmental groove
• Fissures: usually located at the depth of a developmental groove, formed when the tooth fails to fuse enamel at the developmental groove; not found in all teeth and caries are often found
• Lobes were the primary growth centers of the tooth and give rise to cusps; as the lobes grow and coalesce, the lines formed by their fusion are the developmental grooves
• Usually all anterior teeth are formed by 4 lobes, 3 labial and 1 lingual (makes up the cingulum)
• Mamelons are usually seen on upper central incisors, and indicate the three labial developmental labial lobes
• Maxillary premolars have 3 facial and 1 large lingual lobe
• Mandibular first premolars also have 3 facial and 1 lingual lobe, but the lingual lobe is smaller