Home Dentistry Articles 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
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