dental disorders
Dental Anatomy and Development
Teeth
The teeth are categorized as incisors, canines, premolars, and molars and conventionally are numbered beginning with the maxillary right 3rd molar (see figure Identifying the teeth ). The numbering system shown is the one most commonly used in the US. Each tooth has a crown and a root. The canines have the largest and strongest roots. An inner pulp contains blood vessels, lymphatics, and nerves, surrounded by the hard but porous dentin, which is sensitive to touch and to temperature changes. A very hard enamel coating covers the crown. The bonelike cementum is over the root, which, when healthy, is covered by gingiva (see figure Cross section of a canine tooth ). Twenty deciduous teeth normally begin appearing at close to age 6 months and should all be in place by age 30 months (see table Tooth Eruption Times ). These teeth are followed by 32 permanent teeth that begin to appear by about age 6 years. The period from age 6 to 11 is called the mixed dentition stage, in which both deciduous and permanent teeth are present. Timing of tooth eruption is one indicator of skeletal age and may identify growth retardation or establish age for forensic purposes. (See also Introduction to the Approach to the Dental Patient .) 