16. Dynamics and development of permanent dentition. Development periods and stages. Development and formation of the roots. Factors influencing tooth eruption. Mechanism and sequence of eruption. 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