**Core Concept**
Relining of a complete denture is a procedure to improve fit and stability by adding a new layer of acrylic resin to the denture base. It is most effective when the underlying alveolar ridge remains stable and the vertical dimension (VD) is within acceptable limits. When the VD is significantly altered, relining cannot restore proper occlusal relationships or facial height.

**Why the Correct Answer is Right**
When the vertical dimension is excessively reduced and requires adjustment, relining becomes inadequate. The vertical dimension is critical for facial aesthetics, mastication, and proper occlusal contact. Relining only adds material to the denture base and cannot reestablish lost vertical dimension. A change in VD necessitates a complete reprocessing of the denture, including recontouring and repositioning of teeth, making relining inappropriate.

**Why Each Wrong Option is Incorrect**
Option A: Broken teeth can be repaired with dental restorations or repositioning; relining is still feasible after tooth repair.
Option B: Excessive ridge resorption may require relining to improve retention, though it is not ideal, relining can still be performed to enhance fit.
Option D: Centric relation and centric occlusion mismatch is a functional issue that can be addressed by repositioning teeth or adjusting the denture, not by relining.

**Clinical Pearl / High-Yield Fact**
Always assess vertical dimension before relining—reducing VD significantly is a contraindication. If VD must be changed, a new denture is required. Relining is a salvage procedure, not a solution for fundamental structural or dimensional changes.

✓ Correct Answer: C. Vertical dimension is excessively reduced and has to be changed