Does dental zinc phosphate cement really shrink in clinical applications?

Crowns are cemented onto abutments with adhesives; and zinc phosphate cement is a routine permanent luting agent, which is believed to secure crowns to abutments by non-adhesive micro-mechanical interlocking. Because it has been proven, and the public widely accepts, that zinc phosphate cement forms no chemical bonds with either the crown or the tooth tissue; it is impossible for the cement to attain adequate retention force if it contracts in volume. Assuming that the cement contracts in volume after setting, the prosthesis tends to loose and is doomed to be hampered by fretting damage when it functions during the masticatory cycle; thus the prognosis for the prosthesis is questionable. However, zinc phosphate is popular because of its brilliant clinical record. This paradox between theory and practice indicates that something might be wrong with the standing theory. The most possible problem with previous studies is that their samples' dimensions differ from those that are used clinically, which causes the studies' results, which claim that the cement shrinks, to deviate from clinical results. The real rationale must be that the zinc phosphate cement tends to expand in volume, and thus mechanically fasten the crown to the abutment.