MDS AIPGDEE preparations B-IDS | A crown margin can be extended subgingivally when required

A crown margin can be extended subgingivally when required
1. for esthetics.
2. to increase retention.
3. to reach sound tooth structure.
4. for caries prevention.
A. (1) (2) (3)
B. (1) and (3)
C. (2) and (4)
D. (4) only
E. All of the above.

Ans A(1) (2) (3) 

Indications for subgingival margin: -                              

•   dental caries,cervical erosion extend subgingivally

• crown lengthening procedure not indicated                                 

•   proximal contact area extends to gingival crest

•  additional retention /resistance needed