In rats, what explains continuous growth of incisors?

• A. PDL remodeling
• B. Root elongation
• C. Cementum thickening
• D. Occlusal wear reduction

Answer: (A)

Continuous growth of rat incisors is driven by the tooth’s ongoing eruption to compensate for gnawing wear, and this eruption is enabled by remodeling of the periodontal ligament and surrounding alveolar bone. As the incisor wears on the labial edge, forces within the periodontal ligament promote resorption of bone on the pressure side and new bone formation on the opposite side, allowing the tooth to move bodily upward and outward. This PDL-mediated movement keeps the tooth exposed to a fresh surface while the root and pulp continue to support new eruption, independent of just extending the root or thickening cementum. Cementum thickening happens with aging but doesn’t drive the continuous eruption, and reducing occlusal wear would lessen the need for eruption without explaining how growth is maintained.