Tooth Development

Introduction

Gaboon Viper - Copyright RVC

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 their 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

Tooth Development Histology - Copyright RVC 2008

Tooth development occurs in the following stages;

1. Focal thickening of oral epithelium on the medial aspect of the labiogingival groove forms the dental lamina.

2. The mesenchyme under each laminae condenses.

3. The dental lamina invaginates to form the dental bud.

4. The dental bud expands and branches to become the enamel organ.

5. The enamel organ surrounds the neural crest cell derived, dental papilla.

6. The combination of the 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. The inner cell layer of enamel organ (from oral epithelium) differentiates into ameloblasts.

9. Neighbouring cells in the dental papillae (from neural crest cells) differentiate into odontoblasts.

10. Dentine surrounds pulp to produce the root of the tooth.

11. Epithelial cells near the distal tooth form cementoblasts, secreting cementum around the tooth root.

There is a reciprocal inductive interaction between the oral epithelium and mesenchyme precursors. The mesenchyme forms the tooth, it has labile differentiative properties but stable morphogenic properties. Tooth formation starts at the crown and progresses towards the root. The tooth does not acquire full length until the crown has emerged. Tooth growth is appositional.

Eruption

Deciduous Tooth

Eruption occurs after the crown has fully formed (prior to complete root formation). It provides the space required for root completion. The epithelial covering is continuous with gums after eruption. Erosion (wear) removes the epithelium. The 'toothless' gene stops eruption.

Tooth Radiograph - Copyright Nottingham 2008

Permanent Tooth

The tooth migrates into the socket of the deciduous tooth on the lingual side. It increases the pressure on the deciduous tooth by increased growth. Resorption of the deciduous tooth root leads to its loosening. The deciduous tooth then sheds and the permanent tooth replaces it. Premature loss of the deciduous tooth leads to disorganised (non-occluding) permanent teeth.

Tooth Development Learning Resources
Flashcards Test your knowledge using flashcard type questions	Teeth and Gingiva Flashcards
PowerPoint Selection of relevant PowerPoint tutorials	Histology of the oral cavity, see part 2 for developing teeth

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