Tooth Eruption and Exfoliation

Tooth Eruption and Exfoliation

• Tooth eruption is a continuous process throughout life, beginning in early embryological development.
• Eruption involves three phases: pre-eruptive, eruptive, and post-eruptive.
• The pre-eruptive phase includes tooth movement within the alveolar bone until crown formation is complete. The bony crypt remodels during the bell stage to make room for the developing tooth.
• The eruptive phase involves tooth movement through the alveolar bone (intraosseous) and soft tissue (supraosseous) to the oral cavity. This phase begins roughly at the same time as root formation and continues until the tooth reaches its occlusion.
• The post-eruptive phase is the continued movement of teeth, maintaining occlusion and compensating for wear and growth.
• Tooth eruption is a complex, multi-factorial process and is not fully understood. Multiple theories exist, including bone remodeling, dental follicle, periodontal ligament, and molecular determinants.
• The reduced enamel epithelium plays a protective role by creating a seal between the oral epithelium and the underlying ectomesenchyme to prevent haemorrhage.
• Exfoliation is the physiological resorption of primary teeth until they are lost. This is triggered by the development of the permanent successor tooth. Masticatory forces can also contribute to this process.

Learning Outcomes

• Students should be able to describe the phases of tooth eruption.
• Students should be able to describe the origin of the dentogingival junction.
• Students should outline theories of tooth eruption.
• Students should be able to link eruption to the development timeline.
• Students should be able to identify normal and abnormal tooth eruption/exfoliation.
• Students should be able to identify missing or supernumerary teeth.
• Students should be able to use knowledge of eruption to identify cases needing orthodontic referral.

Definitions

• Eruption: Physiological movement of teeth from their developmental position in the alveolar bone through soft tissues to their functional position in the oral cavity.
• Exfoliation: Physiological resorption of primary teeth until they are lost.

Embryological Links

• Eruption begins during the bell stage of tooth development.
• Ameloblasts, osteoclasts, and odontoclasts are involved.
• Knowledge of these embryological interactions helps explain different theories about eruption mechanisms.

Clinical Links

• Developmental timelines are essential for identifying missing or supernumerary teeth and evaluating crowding issues.
• The developmental timeline of teeth is crucial for diagnosing issues concerning tooth eruption or exfoliation.

Workbook Activity

• Complete the workbook sections 1 and 2 for a review of embryological knowledge, using clinical examples as appropriate.

Single Best Answer (Quiz Question Example)

• The eruption process starts during the bell stage of tooth development.

Active Eruption Phase

• The process involves the completion of crown formation, merging with the oral epithelium, and eruption into the oral cavity.

Role of Reduced Enamel Epithelium

• The reduced enamel epithelium forms a protective layer and eruption pathway and joins with the oral epithelium after the completion of amelogenesis.
• It forms a seal that prevents exposure of the underlying ectomesenchyme to prevent hemorrhage during eruption.
• It protects the developing tooth from osteoclasts and odontoclasts.

Eruption Pathway

• Bone is resorbed by osteoclasts, creating a pathway for tooth movement.
• The reduced enamel epithelium protects the tooth crown during this process, fusing with the oral epithelium.

Formation of Dentogingival Junction and Sulcus

• This critical location is formed as the tooth pushes through the gingiva during eruption, uniting the reduced enamel epithelium with the gingival epithelium.
• It functions to seal off the oral cavity from the rest of the body, playing a role in periodontal health (i.e., preventing disease).

Rate of Eruptive Movement

• Tooth movement through bone is slow (1-10 µm/day).
• Soft tissue movement is faster (75 µm/day).
• Muscular forces guide the tooth into place.

Root Formation Theory

• The elevated tooth crown is thought to be driven by root development.
• However, this theory has been refuted as eruption occurs throughout life, and root development doesn't consistently align with this.

Bone Remodeling

• Bone resorption and deposition may play a role in tooth eruption, but it is not the sole mechanism.
• Bone remodeling during tooth eruption is modulated by the dental follicle.

Dental Follicle Theory

• Signals between the dental follicle and reduced enamel epithelium are linked and influence bone remodeling.
• This theory explains why eruption consistency aligns with the ameloblast lifecycle.

Periodontal Ligament Theory

• Periodontal ligament formation and fibroblast activities have been suggested as contributing factors to tooth movement during eruption.
• However, this theory is not universally accepted.

Molecular Determinants

• Various molecules are involved in the complex process of tooth eruption, playing diverse roles.
• Additional factors such as bite forces and neuromuscular forces influence this process.

Summary

• Tooth eruption is a complex and multifactorial process.
• The process involves pre-eruptive, eruptive, and post-eruptive phases.
• The active phase involves a combination of embryological developments, bone remodeling, and molecular signaling.