Tooth Development
Introduction
Teeth develop differently in different regions of the mouth in most species, a process called heterodonty. In some animals teeth develop identically in different regions of the mouth, a process called homodonty. Different species will have varying numbers of teeth and different shapes depending largely on diet.
Not all species possess teeth and there is huge variation in dental formulae between the species that have teeth.
Teeth are mainly used for mastication - chewing and grinding food particles, but are also used for seizing prey and tearing.
The occlusion surface is where opposing teeth touch. The contact surface is where adjacent teeth touch.
Tooth Development
1. Focal thickening of oral epithelium on medial aspect of the labiogingival groove forms the dental lamina
2. Mesenchyme under each laminae condenses
3. Dental lamina invaginates to form the dental bud
4. Dental bud expands and branches to become the enamel organ
5. Enamel organ surrounds the neural crest cell derived dental papilla
6. Combination of enamel organ and dental papillae forms the deciduous tooth
7. Small mass of cells bud off the dental lamina forming the primordium of the permanent tooth which continues development
8. Inner cell layer of enamel organ (from oral epithelium) differentiates into ameloblasts
9. Neighbouring cells in dental papillae (from neural crest cells) differentiate into odontoblasts
10. Dentine surrounds pulp to produce root of tooth
11. Epithelial cells near the distal tooth form cementoblasts, secreting cementum around the tooth root
- Reciprocal inductive interaction between the oral epithelium and mesenchyme precursors
- Mesenchyme forms the tooth. It has labile differentiative properties but stabile morphogenic properties.
- Tooth does not aquire full length until the crown has emerged
- Tooth growth is appositional
Eruption
Deciduous Tooth
- Provides the space required for root completion
- Epithelial covering is continuous with gums after eruption
- Erosion (wear) removes epithelium
- 'Toothless' gene stops eruption
Permanent Tooth
- Migrates into socket of deciduous tooth on lingual side
- Increases pressure on deciduous tooth by increased growth
- Resorption of deciduous tooth root leads to loosening of deciduous tooth
- Shedding of deciduous tooth
- Permanent tooth replaces deciduous tooth
- Premature loss of deciduous tooth leads to disorganised (non-occluding) permanent teeth
