Before revision: The tooth has the apico-coronal distance from the marginal crest of bone to the contact point in order to increase from the much narrower mesial-distal dimension to the greater mesial-distal dimension, and this distance is partially subgingival (below the gum line) and partially supragingival (above the gun line).
After revision: The tooth has the apico-coronal distance from the marginal crest of bone to the contact point in order to increase from the much narrower mesial-distal dimension to the greater mesial-distal dimension, and this distance is subgingival (below the gum line).