The effect of accelerated aging on crystalline structures and optical properties of different monolithic zirconia: A qualitative systematic review.

OBJECTIVE

This study aimed to systematically review the literature related to the impact of low temperature degradation (LTD) on the crystalline structures and optical properties of different types of dental monolithic zirconia materials.

METHODS

The systemic review was performed based on the PRISMA statement. In vitro studies investigating the effect of accelerated aging in autoclave (2 bar pressure 134°C - ISO standard 13356-2008) on the crystalline structure and/or optical properties of Yttria-partially stabilized zirconia (Y-PSZ) were included. Specific search terms were used for peer-reviewed articles published in PubMed, Ovid MEDLINE, and EMBASE databases.

RESULTS

From 286 eligible articles, 51 articles were selected for full-text analysis, 10 failed to meet the inclusion criteria, and 41 articles were included in this review. Autoclave aging (30 min - 300 h) results in an increase in monoclinic phase (m) content up to 80% for tetragonal zirconia and reaching saturation after 35 h of autoclave aging. All included articles reported less than 1% of monoclinic phase for cubic zirconia after autoclave aging. Translucency parameter was reported between 2.34 and 19.7 after autoclave aging (4-100 h). For same aging time, contrast ratio ranged between 0.48 and 0.95.

SIGNIFICANCE

An increase in monoclinic phase was reported for tetragonal zirconia, while cubic zirconia demonstrates resistance to LTD. The optical properties for all zirconia materials investigated seem more compromised with increasing aging time.