What is the PRIMARY cause of mobility and distal bone loss in tooth #21 related to the RPD with the precision attachment?

Correct answer: D. Torquing/lateral forces generated by the precision attachment on the abutment tooth

• A. Occlusal overload from opposing teeth would typically cause wear or sensitivity, not localized distal bone loss specifically related to the RPD design.
• B. Root fracture would show on radiograph as a fracture line and would not specifically cause distal bone loss.
• C. Periodontal disease would cause bone loss around multiple teeth and be associated with plaque/calculus. If only #21 is affected, RPD-related torque is more likely.
• D. CORRECT. Precision attachments transfer forces from the RPD to the abutment tooth. The lever arm created by the distal extension base generates TORQUING (rotational) forces on the abutment during function. These horizontal/tipping forces cause stress to the crestal bone distal to the abutment, leading to bone loss and tooth mobility — a recognized complication of precision-retained distal extension RPDs.