This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Ferrule is a feature of: 
Select and explain. 
A. Retention form, B. Resistance form, C. Conservation of tooth structure, D. Antirotational design
C: Conservation of tooth structure
Answer: C: Conservation of tooth structure 
Explanation: Although there is evidence that preserving as much coronal tooth structure as possible will enhance prognosis, it is less clear whether the prognosis will improve by creating a ferrule in an extensively damaged tooth by surgical crown-lengthening. In this latter circumstance, although the crown-lengthening allows a ferrule, it also leads to a much less favorable crown to root ratio and therefore increased leverage on the root during function.