Effect of zirconia surface conditioning before glazing on the wear of opposing enamel: an in vitro study

Abstract

Objectives: This in vitro study aimed to evaluate the wear of natural teeth opposing 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) with different surface conditions.

Materials and methods: Sixty 3Y-TZP specimens were randomly assigned to six groups (n = 10), differing in surface condition. In three groups, the samples underwent glazing-with the glaze applied to roughened (i.e., 106-µm-grit diamond-finished), as-sintered, and polished zirconia. The three remaining groups consisted of unglazed specimens: solely polished samples and diamond-finished samples (106-µm-grit and 46-µm-grit) without further conditioning. Two-body wear was evaluated at extracted, non-carious molars (n = 60), which served as antagonists in chewing simulation (10,000 masticatory cycles, 49N load). As a control, natural teeth with intact enamel surfaces were tested against natural molars (n = 10). All samples were 3D-scanned before and after the chewing simulation (7 Series, Straumann). Volume loss was calculated (Inspect Software, GOM), and statistically analyzed (SPSS Statistics 24, IBM).

Results: Volume loss of the natural antagonists decreased in the following order: 106-µm-grit diamond-finished zirconia (4.6 ± 2.5 mm³), glazed 106-µm-grit diamond-finished zirconia (3.8 ± 1.1 mm³), glazed as-sintered zirconia (3.5 ± 0.9 mm³), 46-µm-grit diamond-finished zirconia (1.7 ± 0.6 mm³), control (1.6 ± 0.7 mm³), glazed polished zirconia (1.4 ± 0.5 mm³), and solely polishing (0.4 ± 0.2 mm³). Even when polishing the surfaces before glazing, volume loss was not mitigated to the same extent as after polishing alone.

Conclusions: The zirconia surface condition beneath the glazing influences antagonist wear. Although polishing before glazing resulted in acceptable levels of antagonist wear, this approach did not yield as favorable results as polishing alone.

Clinical relevance: For operators favoring glazing, pre-polishing the zirconia surface could be advantageous to reduce wear.

Keywords: Enamel; Glaze; Surface treatment; Two-body wear; Zirconia.