A 36 year old male patient has come for the cementation of a crown on his root canal treated tooth. Slight gap is noticed between the crown and the prepared tooth margins which is subsequently burnished. Which of the following statements is true regarding this procedure?
Burnishing of a cast metal margin is a process sometimes used to reduce the width of a gap between the crown margin and the tooth surface. For a metal with relatively high ductility and moderate yield strength, application of a high pressure against the margin will plastically deform the margin and reduce the gap width. However, because elastic deformation has also occurred, the margin will spring back as elastic strain decreases during the decrease in pressure. Thus, burnishing the margin will close the gap only to the extent of the plastic deformation (strain) that is induced during burnishing. After the force is removed, the margin springs back an amount equal to the total elastic strain. Only by removing the crown from a tooth or die can total closure be accomplished. Because we must provide at least 25 µm of clearance for the cement, total burnishing on the tooth or die is usually adequate since the amount of elastic strain recovery is relatively small.
Plastic deformation of the margin will reduce the gap width
The margin will spring back an amount equal to the total elastic strain
Only by removing the crown from a tooth or die can total closure be accomplished
All of the above