This is a case of an asymptomatic #14 in need of a full coverage crown. In the process of preparing the tooth a significant fracture is detected running mesial-distal.

The fracture was such that it involved the mesial margin and did not allow for margination in that area as the margin kept falling off the tooth as it tried to cross the chasm. The solution was to use the rarely utilized replace tool to edit the model and virtually create a solid surface on which to marginate and design the crown. The replace tool is selected and the defect is encircled in the same way we would use the cut tool. Hit apply and the software will fill in the void. 

Marginate, design and move forward as usual. 

Altering the model, particularly the preparation, can be a risky proposition that could affect the fit. In this case the risk was worth the reward as the mesial margin ended up nicely sealed.

The long term prognosis of the tooth is clearly guarded.