Physiologic Tooth Form and Periodontium

Physiologic Tooth Form

• The tooth is supported by protective tissue called periodontium, which consists of alveolar bone, cementum, periodontal ligament, and gingiva.

Indirect Form

• The tooth form is divided into indirect and direct forms.
• Indirect form includes:
  • Crown form
  • Root form
  • Angulation of root and crown
  • Self-cleaning ability of the tooth
  • Occlusal anatomy
  • Continuity of marginal ridge
  • Continuity of central groove

Crown Form

• The shape of the crown is typically triangular, trapezoidal, or rhomboid buccally, labially, and occlusally.
• The crown form creates:
  • Interproximal spaces to accommodate interproximal gingiva
  • Space between roots for bone and supporting structures
  • Contact area between adjacent teeth to protect interproximal gingiva
• Proximal maximal contour:
  • Crest of curvature is the maximum height point on the tooth surface
  • Anterior: incisal third, Posterior: middle third
  • Significant for developing interproximal space and embrasure
• Facial and lingual contour:
  • Anterior: labial contour mostly cervical third (cervical ridge), lingual contour also cervical third (cingulum)
  • Posterior: buccal contour cervical third, lingual contour middle third
  • Significant for normal food passage and gentle massage on the gingiva

Root Form

• Number and length of the root: function
• Distribution of root: decreases bone resorption
• Root outline:
  • Facially more bone support the tooth
  • Mesiodistally root broad, which compensates for strength

Angulation of Crown and Root

• Lingual angulation of lower teeth for normal occlusion
• Distal inclination of crown and root due to progressive tilt to the occlusal surface for preserving contact mesially

Self-Cleaning Ability of the Tooth

• Proper form (rounded surface)
• Proper alignment of the teeth
• Normal gingival attachment
• Brushing activity
• Saliva

Direct Form

• Proximal contact relation:
  • Formation
  • Observation
  • Location
  • Significance
  • Sequence of abnormal proximal contact
  • Affecting factors
• Interproximal space:
  • Triangle shape with base to the alveolar bone and apex to the contact area
  • Significance: provides space for alveolar bone, preserves internal gingival tissue, and provides good oral hygiene
• Embrasure:
  • Also called spillway
  • Position: incisal, occlusal, buccal, and lingual embrasures
  • Size: depends on position
  • Significance: esthetic, spillway, and decreases masticatory force
• Cervical line:
  • Junction of enamel with cementum
  • Curvature depends on contact area and diameter of the crown facio-lingually

Learn about the physiologic tooth form and its protecting tissue, the periodontium, which consists of alveolar bone, cementum, periodontal ligament, and gingiva. Understand the direct and indirect forms of tooth structure.