15. Dynamics and development of primary dentition. Development periods and stages. Factors influencing tooth eruption. Mechanism, signs and sequence of eruption. Resorption organ. Pathology of tooth eruption.

DYNAMICS OF TOOTH DEVELOPMENT- PERIODS AND STAGES OF TOOTH ERUPTION

• Dynamics of tooth development is the studying of the chronological stages of primary and permanent teeth development, characterized by quantitative and qualitative differences.
• It is the period from birth to 14 years of age of the child
• Tooth formation is a continuous process, characterized by a series of easily distinguishable stages

Stages of Tooth Development

(1) Initiation of Tooth Development- Bud Stage

• Initiation is the formation of the dental germ, which starts with initiation and continues with proliferation
• Tooth formation starts with the development of dental lamina over which 20 buds for the 20 primary teeth will develop
• Process involved in these stages are proliferation and Histodifferentiation
• Elements of the tooth germ are:
• Enamel organ
• Forms tooth enamel. Stimulates the dental papilla and sac
• Dental papilla
• Forms dentin and pulp
• Dental follicle
• Forms cementum, periodontium and alveolar bone
• At the bud stage starts the prevention of dental diseases through the means of nutritional prevention, providing function of ectoderm and mesoderm
• Absence of tooth bud means missing tooth. Fewer than 6 teeth missing is hypodontia. More than 6 teeth missing is oligodontia. Absence of all teeth is anodontia

(2) Start of Mineralization

• Start of mineralization represents the starting point of apposition and calcification through the first deposition and mineralization of dentin matrix
• Immediately after this, first layer of enamel is deposited
• The enamel organ is built with the differentiation of ameloblasts and odontoblasts is completed
• At this stage, deposition of an organic matrix and mineralization are performed in parallel
• Mineralization starts from the tip of the cusps. Deposition of matrix and mineralization continue to complete construction of the enamel and enamel organ is consumed
• At this point, enamel hypoplasia or other disturbances in mineralization can occur

(3) Crown Formation

• Enamel is completely formed as the enamel organ has exhausted its function, only remaining as reduced enamel epithelium
• Enamel mineralization is at 50%
• Maturation of enamel is performed with help of reduced enamel epithelium
• Cervical loop passes into Hertwig’s epithelial root sheath, setting the beginning of root development
• When the crown is ready, this starts the eruption of the tooth through several movements and displacements
• It begins bone resorption in front of the crown and apposition after the crown
• At this stage, Hypomineralization and Hypomaturation can occur

(4) Eruption

• 1st clinically detectable stage of tooth development