A new modified laser pretreatment for porcelain zirconia bonding

Objectives: The aim of this study was to compare the effects of three different surface treatments in enhancing porcelain zirconia bonding. Methods: Totally, 160 densely sintered zirconia specimens were prepared and randomly divided into four study groups: control (no treatment, Group C), sandblasting (Group S), sandblasting followed by regeneration firing (Group SH), and laser irradiation (pulse mode) on a CO2laser system (Group L). After surface treatment, porcelain powders were veneered on zirconia surface. Half of the specimens in each group were evaluated without aging (initial shear bond strength - initial SBS), and the other half was tested after being stored in water for one month (aging SBS). X-ray diffractometry (XRD) was used to observe any crystallographic transformation at zirconia surface. Results were statistically analyzed using analysis of variance (ANOVA) and Turkey test (=0.05). Results The initial average SBS values of Group S, Group SH, and Group L were 31.3 ± 5.7 MPa, 29.2 ± 7.0 MPa and 32.1 ± 7.5 MPa, respectively. The differences among these three groups were not significant. The control group had significantly lower value, 24.8 ± 6.7 MPa, than those of Group S and Group L. Furthermore, there was no significant difference between initial and aging values in each group. XRD analysis showed that sandblasting caused tetragonal to monoclinic phase transformation. Regeneration firing reversed such a transformation. However, crystallographic transformation could not be detected in laser treated specimens. Significance: Both sandblasting and laser irradiation increased porcelain zirconia bond strength. The presented new modified laser pre-treatment might be an alternative way to sandblasting for improving zirconia/porcelain integration.