I appreciate Dr. Boland’s comments and observations.
Yes, zinc phosphate cemented restorations are successful. Further, it is interesting to me that, from an historical standpoint, cast gold restorations cemented with zinc phosphate cement are among the longest-lasting dental restorations.
However, judgment of that clinical concept, based on the popular technique of microleak-age, indicates that zinc phosphate leaks and should fail. Obviously, that is not true. Is microleakage really a negative factor? I doubt it. There are many unknowns in crown and fixed prosthesis cementation.
Die spacers placed over the coronal portion of dies and ending about 1 millimeter from the margins provide an escapeway for the cement hydraulic forces involved during cementation. The spacers range from 30 mm to 55 mm thick on a short tooth preparation; up to 100 mm thick on a long tooth preparation. The cement layer is also an insulator, reducing hot and cold transfer to the tooth preparation, and potential postoperative tooth sensitivity.
The newer cement category, hybrid ionomer, has almost completely eliminated postoperative tooth sensitivity while providing low solubility, high strength, increased retention, bond-to-tooth structure and fluoride release. Cements are getting better!
