Development of Teeth (Odontogenesis)

1. Initiation - Dental Lamina Formation (Week 6)

• Each dental lamina develops 10 centers of proliferation, giving rise to 10 tooth buds per jaw (20 total for the deciduous/primary dentition).
• Tooth development begins in the anterior mandibular (lower jaw) region first, then in the anterior maxillary region, and progresses posteriorly in both jaws.

2. Bud Stage (Week 6-8)

• These buds will develop into the 20 deciduous (baby) teeth.
• At approximately 10 weeks, tooth buds for permanent teeth (those with deciduous predecessors) begin forming as deep continuations of the dental lamina, positioned lingual (tongue-side) to the deciduous buds.
• Permanent molars have no deciduous predecessors - they develop from posterior extensions of the dental laminae.

3. Cap Stage (Week 8-10)

• Outer enamel epithelium - the outer cell layer of the cap
• Inner enamel epithelium - the inner cell layer lining the dental papilla

4. Bell Stage (Week 10+)

Dentin Formation (Dentinogenesis)

• Mesenchymal cells of the dental papilla, directly adjacent to the inner enamel epithelium, differentiate into odontoblasts (dentin-forming cells).
• Odontoblasts produce predentin, which then calcifies to become dentin - the second hardest tissue in the body.
• As dentin thickens, odontoblasts migrate inward toward the center of the dental papilla, but leave behind long cytoplasmic projections called odontoblastic processes, which remain embedded in the dentin (in microscopic channels called dentinal tubules).

Enamel Formation (Amelogenesis)

• The inner enamel epithelium cells, under the inductive influence of odontoblasts, differentiate into ameloblasts (enamel-forming cells).
• Ameloblasts produce enamel in the form of prisms (rods) deposited over the dentin surface.
• As enamel thickens, ameloblasts migrate outward toward the outer enamel epithelium.
• Enamel is the hardest tissue in the body. Its translucent color is influenced by the underlying dentin.
• Both enamel and dentin formation begin at the cusp (tip) of the tooth and progress toward the future root.

5. Root Formation

1. The inner and outer enamel epithelia meet at the neck of the tooth (cementoenamel junction) and fold downward, forming the epithelial root sheath (Hertwig's sheath).
2. This sheath grows into the mesenchyme and initiates root dentin formation by inducing adjacent odontoblasts.
3. As dentin increases, it narrows the dental pulp cavity to a thin root canal carrying vessels and nerves.
4. Inner cells of the dental sac differentiate into cementoblasts, which deposit cement (cementum) over the root dentin.
5. Outer cells of the dental sac participate in bone formation, surrounding the tooth in an alveolus (tooth socket).
6. The tooth is anchored by the periodontal ligament - fibers of which embed into both the cement of the root and the bony wall of the alveolus.

6. Tooth Eruption

• As deciduous teeth develop, they begin a slow, continuous movement toward the oral cavity.
• The mandibular teeth erupt before maxillary teeth; females erupt teeth slightly earlier than males.
• As the permanent tooth grows beneath it, the root of the corresponding deciduous tooth is resorbed by osteoclasts (odontoclasts), so when the tooth is shed, only the crown and upper root remain.

Eruption Timeline

Note: Delayed eruption of all teeth may indicate a systemic or nutritional disturbance such as hypopituitarism or hypothyroidism.

Summary of Tissue Origins