Impact of oral fluids on dental ceramics: what is the clinical relevance?

OBJECTIVES

In this brief and selective overview, basic factors contributing to aqueous induced dissolution, phase changes of zirconia and mechanical strength degradation of dental ceramics are considered.

METHODS

Dissolution is important for porcelain and glass-ceramic materials as they predominantly contain a silica glass structure with various other cations incorporated which disrupt the silica network. In glass-ceramic materials and porcelains containing crystalline components the situation is more complex as the difference in the dissolution rate may increase the surface roughness and contribute to abrasion of the opposing definition.

RESULTS

Factors contributing to the aqueous dissolution of silicate based dental ceramics and induced destabilization of Y-TZP zirconia or low temperature degradation (LTD) are considered. It is also noted that there have been a number of reports of spontaneous fracture of 3Y-TZP specimens because of LTD in the absence of external stress. A simple analysis of this situation is presented which indicates a strong specimen-size effect and also implicates the role of the remnant "pseudo-grain" structure resulting from the pressing of spray-dried powder agglomerates.

SIGNIFICANCE

The final section of this review addresses the consequences of various environments on crack growth and strength degradation. In some situations it is suggested that the aqueous environment may enhance the strength of restorative materials. In all instances discussed above the clinical consequences are pointed out.