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Tooth development

The process of tooth development is highly complex. Enamel, dentin, cementum, and the periodontium must all develop at appropriate times in order to result in a healthy oral environment for teeth.

Enamel forms, a process known as amelogenesis, after dentin's initial formation, known as dentinogenesis. The requirement of dentin's presence is termed "reciprocal induction."

Seen microscopically in hisologic slides, the early formation of a tooth is seen in the distinction between the vestibular lamina and the dental lamina. The dental lamina will connect the developing tooth bud, which is the aggregation of cells eventually forming a tooth, to the epithelial layer of the mouth for a significant time.

Tooth development continues in the following stages: the bud stage, the cap stage, the bell stage, and finally maturation. It should be kept in mind that all the stages continue through a gradual change, and frequently it is difficult to distinguish absolutely in what stage is a developing tooth. The matter is further complicated that histologic in different planes of the same developing tooth can appear as different stages.

The bud stage is charaterized by the appearance of a tooth bud without any clear arrangement of cells. The tooth bud itself is the group of cells at the end of the dental lamina.

The cap stage has the first signs of an arrangement of cells in the tooth bud. A small group of ectomesenchymal cells discontinue producing extracellular substances, resulting in their aggregation with each other. This group of cells is named the dental papilla. At this point, the tooth bud seems to grow around the ectomesenchymal aggregation, taking on the appearance of a cap, and becomes known as the enamel (or dental) organ. Limiting the dental papilla and surrounding the enamel organ, a condensation of ectomesenchymal cells is given the name, the dental follicle. Eventually, the enamel organ will give rise to a tooth's enamel, the dental papilla will give rise to a tooth's dentin and pulp, and the dental follicle will give rise to all the supporting structures of a tooth.

The bell stage is known for the histodifferentiation and morphodifferentiaion which takes place. In appearance, the dental organ is compared to the shape of a bell, and the majority of its cells are termed stellate reticulum because of their star-shaped appearance. In the enamel organ, the cells on its periphery segregate into three important layers. Cuboidal cells on the periphery of the dental organ are known as outer enamel epithelium. The cells of the enamel organ adjacent to the dental papilla are known as inner enamel epithelium. The cells between the inner enamel epithelium and the stellate reticulum form a layer known as the stratum intermedium. The rim of the dental organ where the outer and inner enamel epithelium join is called the cervical loop.

Concurrently in the bell stage, other events occur. The dental lamina disintegrates, leaving the developing teeth completely separated from the epithelium of the oral cavity; the two will not come into contact again until the final eruption of the tooth into the mouth. Other structures that may appear in a developing tooth are enamel knots, enamel cords, and enamel niche.