The crownçroot ratio is
1. the comparison of the length of root retained in bone to the amount of tooth external to it.
2. an important factor in abutment tooth selection.
3. determined from radiographs.
4. determined during surveying of the diagnostic cast.

None of the above.

All of the above.

(1) (3) (4)

(1) (2) (4)

(1) (2) (3)