Anatomy of the teeth and periodontium

Chapter 4


Anatomy of the teeth and periodontium



Introduction


The dentition of dogs and cats resembles that of man. There are differences in tooth number and shape, but the basic anatomy is similar. The dentition of rodents and lagomorphs is covered in Chapter 14.


Each tooth has a crown (above the gum) and one or more roots (below the gum). The bulk of the mature tooth is composed of dentine, which is covered by enamel on the crown and by cementum on the roots. The centre of the tooth contains the pulp or endodontic system. Figure 4.1 depicts the basic structure of a tooth.



The crowns of dog and cat teeth have a more tapered shape with sharp cutting edges and fewer chewing surfaces than human teeth. Also, the teeth are spaced further apart and, where there is contact between teeth, the contact area is smaller and not as tight. Humans, dogs and cats are diphyodont, i.e. primary (deciduous) teeth are followed by a permanent dentition. Dental formulae describe the type and number of teeth in each quadrant of the oral cavity. ‘I’ represents incisor teeth, ‘C’ represents canine teeth, ‘P’ represents premolars and ‘M’ represents molars. The respective dental formulae of the primary and permanent dentitions of dog and cat are shown in Box 4.1.



Box 4.1   Dog and cat dental formulae




The formation of the crown of both primary and permanent teeth occurs within the alveolar bone. Enamel formation is completed before the tooth erupts into the oral cavity. Once the enamel has formed, the ameloblasts (the cells which produce the enamel matrix) are lost and further development of enamel does not occur. The only natural form of repair that can occur to enamel after eruption is surface mineralization, through deposition of minerals, mainly from saliva, into the superficial enamel layer.


Although enamel formation is completed by the time the tooth erupts, dentine production is just beginning. Moreover, root development, i.e. growth in length and formation of a root apex, is by no means complete at the time of eruption. Figure 4.2 depicts maturation of a permanent tooth following eruption.



The primary teeth start forming in utero and erupt between 3 and 12 weeks of age. The permanent crowns start forming at or shortly after birth and mineralization of the crowns is complete by around 11 weeks of age. Resorption and exfoliation of the primary teeth and replacement by the permanent dentition occurs between 3 and 7 months of age in the dog and between 3 and 5 months of age in the cat. Once the crowns of the permanent teeth have erupted, root development continues for several months. The approximate ages when teeth erupt in dogs and cats are shown in Table 4.1.




Anatomy of the teeth


As already mentioned, the teeth consist of enamel, dentine, cementum and pulp. The detailed structure of these tissues will be discussed below.


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Oct 9, 2016 | Posted by in GENERAL | Comments Off on Anatomy of the teeth and periodontium

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