2. Serious deep overlap, crossing, excessive wear, etc. The occlusal relationship cannot be coordinated by grinding.

3. Long-term tooth loss and disordered relationship lead to limited mandibular movement.

4. The alveolar ridge defect in the edentulous area is too large, especially in the anterior tooth area.

5. Progressive gingivitis, alveolar bone absorption exceeds 1/3 of root length.

6. Free loss of posterior teeth.