What is the MOST common complication of internal (non-vital) bleaching?

Correct answer: D. External cervical root resorption

• A. Ankylosis follows trauma and PDL damage, not bleaching.
• B. Internal resorption is a pulpal phenomenon in a VITAL tooth with inflamed pulp — the internally bleached tooth has no pulp.
• C. Pulp canal obliteration is a response to trauma in a vital tooth.
• D. CORRECT. EXTERNAL CERVICAL ROOT RESORPTION is the recognized complication, and it is more likely with high-concentration hydrogen peroxide, heat activation, and in teeth traumatized before bleaching. The mechanism: bleaching agent diffuses through dentinal tubules and any gap at the CEJ, reaching the periodontal ligament where it denatures cementum and triggers an inflammatory resorptive response. Prevention is a well-sealed cervical barrier (2 mm of glass ionomer or RMGI placed 1–2 mm apical to the CEJ / apical to the epithelial attachment).

Note: Barrier placement is the single most important preventive step. Avoid the heat-activated 'thermocatalytic' technique.