Development of Teeth

Development of Teeth

• Dr. Archana Rani
• Associate Professor
• Department of Anatomy
• KGMU UP, Lucknow

• 15.6.2015

Introduction

• Teeth are formed in relation to the alveolar process.
• Epithelial thickening: Dental lamina
• Enamel organs: Series of 10 local thickenings on dental lamina in each alveolar process.
• Each thickening forms one milk tooth.

Formation of enamel organs

Stages in the formation of enamel organ

• Bud stage :
• Characterized by formation of a tooth bud.
• The epithelial cells begin to proliferate into the ectomesenchyme of the jaw.

Cap stage :

• Cap stage :
• Formation of dental papilla.
• The enamel organ & dental papilla forms the tooth germ.
• Formation of ameloblasts.
• Formation of odontoblasts.

Bell stage :

• Bell stage :
• The cells on the periphery of the enamel organ separate into three important layers:
• Cuboidal cells on the periphery of the dental organ form the outer enamel epithelium.
• The cells of the enamel organ adjacent to the dental papilla form the inner enamel epithelium.
• The cells between the inner enamel epithelium and the stellate reticulum form a layer known as the stratum intermedium.
• The dental lamina begin to disintegrates, leaving the developing teeth completely separated from the epithelium of the oral cavity.

Crown stage :

• Crown stage :
• Mineralization of hard tissues occur.
• The inner enamel epithelial cells change in shape from cuboidal to columnar. The nuclei of these cells move closer to the stratum intermedium and away from the dental papilla.
• The adjacent layer of cells in the dental papilla suddenly increases in size and differentiates into odontoblasts, which form dentin.
• The inner enamel epithelium and the formation of odontoblasts continue from the tips of the cusps.

Crown stage (contd….):

• Crown stage (contd….):
• 5. The odontoblasts secrete an organic matrix into their immediate surrounding and form the dentin.
• 6. After dentin formation begins, the cells of the inner enamel epithelium secrete an organic matrix against the dentin. This matrix immediately mineralizes and becomes the tooth's enamel.
• 7. Outside the dentin are ameloblasts, which are cells that continue the process of enamel formation; therefore, enamel formation moves outwards, adding new material to the outer surface of the developing tooth.

Enamel: is a hard outer layer consisting primarily of calcium and phosphate in the form of hydroxyapatite.

• Enamel: is a hard outer layer consisting primarily of calcium and phosphate in the form of hydroxyapatite.
• Dentin: is the inner layer, the bulk of the tooth.
• Pulp: is the core, containing nerves and blood vessels.
• Cementum: is the thin layer around the root; a bone-like material which connects the teeth to the jaw.

• Structural components of teeth

Types of teeth according to their attachments

• Acrodont: On the alveolar surface of the jaw. each tooth resides on the occlusional surface of the jaws in a very shallow socket. Replacement teeth arise adjacent to the active teeth (e.g. in snakes).
• Thecodont : Teeth may be attached in sockets (replace within the same socket reptiles). with sockets (e.g. in mammals, crocodiles, dinosaurs).
• 3. Pleurodont: Attachment on the inner side of the jaws (e.g. in lizards). Teeth is continuously replaced.

Stages in the formation of a tooth germ

• Parts of a developing tooth

• An erupting temporary tooth

Origin of germs of permanent teeth

Anomalies of Teeth

• Anodentia
• Supernumerary teeth
• Gemination
• Malocclusion
• Precocious eruption of teeth
• Delayed eruption of teeth
• Improper formation of enamel or dentine
• Abnormal location of teeth e.g. in ovary or in hypophysis cerebri

REFERENCES

• 1. Langman’s Medical Embryology, 11th Edition.
• 3. I.B. Singh. Human Embryology, 10th Edition.

MCQs

• The cells of the enamel organ that line the papilla are called:
• a) Ameloblasts
• b) Odontoblasts
• c) Cementoblasts
• d) Dental cuticle

MCQs

• 2. Mesenchymal cells which cover dentine are called:
• a) Ameloblasts
• b) Odontoblasts
• c) Cementoblasts
• d) Dental cuticle

MCQs

• 3. Temporary canines erupt at:
• a) 6-9 months
• b) 8-10 months
• c) 16-20 months
• d) 24-36 months

MCQs

• 4. The epithelium overlying the alveolar process become thickened to form:
• a) Dental lamina
• b) Dental papilla
• c) Dental cuticle
• d) Periodontal ligament

MCQs

• 5. Absence of ameloblasts is a feature of:
• a) Crown
• b) Enamel
• c) Dentine
• d) Root