Dimensional changes from the sintering process and fit of Y-TZP copings: Micro-CT analysis

- The sintering shrinkage of Y-TZP might depend on the specimen shape.
- Dimensional changes from sintering of Y-TZP do not occur uniformly in pre-molar shaped single copings.
- Dimensional changes from sintering process of Y-TZP can lead to non-uniform cement space in single copings.
- Manufacturing process of Y-TZP blanks may have an influence on sintering shrinkage pattern and, consequently, on the prostheses fit.

ObjectiveTo evaluate the dimensional changes from the sintering process of Y-TZP and relate them to the fit of zirconia copings.MethodsThe sintering shrinkage rate (SSR) was obtained from the measurement of geometric specimens (4 × 4 × 2 mm). Thirty-six zirconia copings made using CAD/CAM were equally divided into three groups (n = 12): ZMAX - IPS e.max ZirCAD (Ivoclar Vivadent, Liechtenstein); ZYZ - InCeram YZ (Vita Zahnfabrik, Germany); and ZK - Zirklein (Zirklein, Brazil). The copings were scanned in micro-CT before and after sintering so that SSR was obtained. The SSR of geometrical specimens and copings was compared to each other and those the manufacturers reported (ANOVA-2 and Tukey, p ≤ .05). The copings were settled on an abutment and taken to the micro-CT to evaluate their marginal and internal fit. The data enabled the statistical comparison (ANOVA-2 and Tukey, p ≤ .05) between groups and measurement sites and between the fit obtained with that stipulated by the CAD/CAM software (80 μm) (Dunnett test, p ≤ .05).ResultsAll groups showed statistical differences between the SSR the manufacturer reported and those obtained experimentally and between the SSR of the geometric specimens and copings. In general, the SSR of the copings showed no uniformity. There was no statistical difference among the groups for marginal fit, with differences only for internal fit and between the different regions measured. The fit obtained experimentally differed from the internal space determined in the CAD/CAM software.SignificanceThe lack of uniformity of sintering shrinkage might lead to a non-uniform internal fit of Y-TZP copings.