The effect of full-contour Y-TZP ceramic surface roughness on the wear of bovine enamel and synthetic hydroxyapatite : an in-vitro study

Abstract

THE EFFECT OF FULL-CONTOUR Y-TZP CERAMIC SURFACE ROUGHNESS ON THE WEAR OF BOVINE ENAMEL AND SYNTHETIC HYDROXYAPATITE: AN IN-VITRO STUDY by Alaa Hussein Aref Sabrah Indiana University School of Dentistry Indianapolis, Indiana Full-contour yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) restorations have been advocated recently in clinical situations where occlusal/palatal space is limited, or to withstand parafunctional activities. The objectives of this in-vitro study were to investigate the effects of different polishing techniques on the surface roughness of Y-TZP (Ardent Dental, Inc.) and to investigate the effects of different polishing techniques on the wear behavior of synthetic hydroxyapatite (HA) and bovine enamel. An in-vitro study was conducted by fabrication of 48 Y-TZP sliders (diameter = 2 mm × 1.5 mm in height) using CAD/CAM technique; then the samples were embedded in acrylic resin using brass holders. Samples were then randomly allocated into four groups according to the finishing/polishing procedure: G1-as-machined (n = 8), G2- glazed (n = 16), G3-diamond bur-finishing (Brasseler, USA) (n = 8) and G4- G3+OptraFine polishing kit (Ivoclar-Vivadent) (n = 16). Thirty-two sintered HA disks (diameter = 11 mm × 2.9 mm in height) and 16 bovine enamel samples with a minimum surface area of 64 mm2 were mounted in brass holders. Baseline surface roughness (Ra and Rq, in μm) were recorded using a non-contact profilometer (Proscan 2000) for all the samples. A two-body pin-on-disk wear test was performed for 25,000 cycles at 1.2 Hz in which the four zirconia groups were tested against HA, and only G2-glazed and G4- G3+OptraFine polishing kit (Ivoclar-Vivadent) were tested against bovine enamel. Vertical substance loss (μm) and volume loss (mm3) of HA were measured (Proscan). Zirconia height loss was measured using a digital micrometer. One-way ANOVA was used for statistical analysis. The results indicated that surface roughness measurements showed significant differences among the surface treatments with G1 (Ra = 0.84, Rq = 1.13 μm) and G3 (Ra = 0.89, Rq = 1.2 μm) being the roughest, and G2 (Ra = 0.42, Rq = 0.63 μm) the smoothest. The glazed group showed the highest vertical loss (35.39 μm) suggesting wear of the glaze layer, while the polished group showed the least vertical loss (6.61 μm). HA antagonist volume loss and vertical height loss for groups (G1, G2 and G3) were similar, while polished group (1.3 mm3, 14.7 μm) showed significant lower (p = 0.0001) values. Antagonist height loss and antagonist volume loss were significantly higher for bovine antagonist than for HA antagonist (197.6 μm/116.2 μm, and 28.5 mm3/17.7 mm3 for bovine against glazed/polished zirconia sliders, respectively) (p < 0.0001). From the results it can be concluded that glazed zirconia provided an initially smooth surface, but a significant increased antagonist wear compared with the polished surface was seen. Bovine enamel showed higher wear compared with HA, which suggested that more studies should be performed to validate the use of bovine enamel as a substitute for human enamel in wear studies.