Tooth Eruption and Shedding of Teeth

Tooth Eruption: Emergence of developing teeth through tissues to the oral cavity; involved in mastication.
Continuous process as teeth move from developmental positions to functional positions.

Pre-eruptive Phase: Tooth germs move from initiation to crown completion.
Eruptive Phase:Initiation of root formation; moves teeth into functional occlusion with intraosseous and extraosseous stages.
Post-eruptive Phase: Maintains erupted tooth position as jaws grow and wear occurs.

Onset of Eruption: Tooth movement toward the occlusal direction begins as root formation starts.
Intraoral Movement: Eruption continues until the crown contacts the opposing tooth.
Rhythmic Process: Eruption involves alternating periods of active movement and rest.
Phases: Includes intraosseous (slower, 1-10 µm/day) and extra-osseous (faster, 75 µm/day) phases.
Multifactorial: Influenced by genetic and environmental factors.

Bodily Movement: Tooth growth within a bony crypt creates pressure, triggering bone resorption on one side and bone formation on the opposite side, shifting the tooth's position.
Eccentric Growth: The root apex remains fixed, while the growing tooth germ exerts pressure in specific directions, causing movement during formation.
Preeruptive Phase: Tooth crowns shift within crypts to adapt to jaw growth and neighboring teeth, ensuring proper positioning.
Permanent Teeth Development: Permanent teeth develop lingual to primary teeth, positioning lingual to the apical third of primary roots as primary teeth erupt.
Permanent Premolars: These move within primary tooth roots, with upper premolars moving downward and lower premolars moving upward.

Eruption Process: Tooth movement toward the occlusal direction begins as root formation starts.
Intraoral Movement: Eruption continues until the crown contacts the opposing crown.
Rhythmic Process: Eruption involves alternating periods of active movement and rest (quiescence).
Phases:
- Intraosseous phase (slower, 1–10 µm/day).
- Extraosseous phase (faster, ~75 µm/day).
Multifactorial: Influenced by genetic and environmental factors.

Root Formation:
- Proliferation of Hertwig’s epithelial root sheath.
- Initiation of root dentin and pulp formation.
- Increase in fibrous tissue of the follicle.
Movement:
- Tooth moves incisally/occlusally to allow normal root formation.
- Reduced enamel epithelium fuses with oral epithelium.
Penetration:
- Crown tip penetrates fused epithelial layers, entering the oral cavity.
Occlusal Contact:
- Intraoral movement continues until the crown contacts the opposing crown.

Root Formation: Resistance beneath the root moves the tooth crown occlusal.
Bone Remodeling: Eruption driven by pressure and tension changes result into the bone being remodeled.
Vascular Pressure: Changes in blood pressure influencing tooth movement.
Ligament Traction: Dental follicle or Periodontal ligament traction pulls the tooth into the oral cavity

Connective Tissue Degeneration: Blood vessels and nerves degenerate over the erupting tooth.
Reduced Enamel Epithelium: Secretes enzymes (desmolytic phase) to lyse tissues, aiding tooth movement.
Periodontal Ligament (PDL): Undergoes drastic changes; has contractile properties.
Myofibroblasts: Accumulate on the eruptive pathway, aiding tooth movement through contractile properties.
Macrophages: Secrete hydrolytic enzymes to destroy cells and fibers.
Collagen Fibers: Rapid formation and turnover allow fibers to attach, release, and reattach as the tooth moves . Fibers organize and increase in density during eruption.
Eruption Pathway: Tissue overlying the tooth is altered to facilitate movement.
Gubernacular Cord: Connective tissue strand linking the successional tooth to the oral mucosa. The Gubernacular canal widens as the tooth erupts, enabling its movement.

Accommodating Jaw Growth:
- Occurs between 14–18 years.
- New bone forms at the alveolar crest and socket base to match jaw height increase.
Compensating Occlusal Wear:
- Cementum deposits around the apex (hypercementosis) to compensate for wear.
Mesial Drift:
- Lateral bodily movement of teeth to maintain proximal integrity after tooth loss or interproximal wear.
- Transeptal fibers between adjacent teeth aid this movement.

Shedding: Removal of deciduous teeth for permanent teeth adaption; involves osteoclast activity and resorption of soft tissues.

Hard tissue-resorbing cells, histologically similar to osteoclasts.
Multinucleated cells derived from monocytes, migrating from blood vessels.
TRAP-positive (tartrate-resistant acid phosphatase) and found in resorption bays, like osteoclasts.
Present on resorbing root surfaces and inside crown portions of molars.
Tooth shedding occurs with intact pulpal tissue.

Resorption Process:
- Bone Resorption: Triggered by hormones and cytokines.
- Tooth Resorption: Initiated by pressure from the erupting permanent successor, with odontoclasts identified at pressure sites.
Cementum Barrier:
- Cementoblasts on the root surface do not respond to bone-resorbing hormones.
- Cementum must be broken down for odontoclasts to reach dentin.
Cementoblast Damage:
- Caused by substances from reduced enamel epithelium or inflammation.
Odontoclast Activity:
- Attach to hard tissue through the clear zone for resorption.
- Resorption is intermittent, with rest periods where cementum may form on resorbing surfaces.
Ankylosis:
- Fusion of tooth roots to the bony socket or permanent tooth crown.
- Results in lack of eruption due to cementum fusing with alveolar bone.

Active eruption: to compensate incisal and occlusal wear.
Passive eruption: gradual recession of the gingiva and the underlying alveolar bone. Both active and passive eruption leads to lengthening of clinical crown.
Clinical crown: During eruption, the exposed crown extending from the cusp tip to the area of the gingival attachment.
Anatomic crown: Entire crown, extending from cusp tip to the cemento-enamel (CEJ) junction. Environmental factors affecting the final position of the tooth are muscular forces and habits such as Thumb-sucking.
Teething: is symptoms like fever, and irritability in gums felt during eruption of teeth.
Natal teeth: Tooth present at birth.
Neonatal tooth: primary tooth erupting within 30days after birth.
Delayed eruption: Generally eruption is genetically determined. Also some local and systemic factors influences the eruption.
Pericoronitis: Eruption of the third molars may be disturbed due to lack of space with local inflammation and infection called pericoronitis.
Remnants of deciduous tooth: root fragments may present as asymptomatic embedded structures.
Retained deciduous teeth: this may be due to the failure of eruption or absence of the permanent tooth.