TEETH DEVELOPMENT AND ERUPTION. TYPES OF OCCLUSION
Teeth are located in the sockets of the alveolar bone and intended for biting and chewing food. Teeth are the derivatives of oral mucosa from embryo's oral portion. Development of teeth is a complex process. Enamel develops from mucosal epithelium; dentin, cementum, pulp and periodontium develop from the mesenchyme. In the development of temporary and permanent teeth there are three periods: formation of tooth buds, differentiation and histogenesis of hard tissues. Formation begins at 6-8 weeks gestation. Differentiation of tooth buds occurs at 12-14 weeks of embryogenesis; histogenesis begins at the end of the 4th month. In the process of histogenesis dentin is the first to appear followed by the enamel. Mineralization of dental tissues starts at the end of the 5th month of gestation. Development of permanent and temporary teeth follows the same mechanism. Development of the roots of temporary and permanent teeth begins shortly before the eruption of the tooth. Complete formation of the root apex is complete two years after eruption. In clinical practice the terms of root formation in permanent and temporary teeth and root resorption in deciduous teeth are very important. These data determine the choice of treatment, indications for extraction, etc.
Eruption of teeth is regulated by the nervous and endocrine systems. Differentiation of the tooth structure is accompanied by an increasing of volume and creating pressure inside the tooth bud. Rebuilding of bone tissue in front of and behind the bud in conjunction with an increasing pressure inside the bud provides eruption of the tooth. The timescale for teeth eruption is presented in table 11.1.