Effect of surface treatments on resin-zirconia bonding

Abstract

Zirconia offers a favorable choice for esthetic indirect dental restorations with excellent mechanical properties and biocompatibility. In the hostile oral environment, the longevity of dental restorations relies heavily on whether a strong and stable bond between the restoration and underlying supporting tooth structures can be achieved. However, unlike conventional ceramics, zirconia is a chemically inert material which makes it notoriously difficult to bond with any dental composite resin cement. This thesis aimed at developing and evaluating different zirconia surface pretreatments for improving the resin-zirconia bonding.

The first laboratory experiment evaluated the effect of Er,Cr:YSGG laser treatment on topographic changes of zirconia surface. Laser parameters including power, irradiation time and water spray at different levels were tested and the treated zirconia surfaces were assessed by scanning electron microscope (SEM) and atomic force microscope (AFM). Results showed that all three tested laser parameters could affect the topographic changes of zirconia surface. Significant topographic changes were found when the power was set at 3.0 W with 50% water spray for 120 s or the power was set at 4.0 W with 75% water spray for 60 s.

The second experiment evaluated the effects of grit-blasting (sandblasting), selective infiltration etching (SIE), 3.0 W and 4.0 W laser zirconia surface treatments on the resin-zirconia bonding. Resin composite was bonded to the treated zirconia which was then sectioned into resin-zirconia micro-beams of a standard size. Microtensile bond strength (MTBS) tests were performed for adhesion strength testing. In dry storage conditions, SIE, grit-blasting and 3.0 W laser groups showed significantly higher MTBSs than the control group while no difference in MTBSs was found between the 4.0 W laser group and the control group. After water storage, SIE treatment showed significant higher MTBSs than the remaining groups. MTBSs of water storage specimens were significantly less than the dry specimens except the ones in 4.0 W groups. Zirconia surface treatments could enhance the resin-zirconia bonding in dry storage conditions. The SIE treatment appeared to provide the strongest resin-zirconia adhesion despite hydrolytic degradation.

The third experiment evaluated the fatigue performance of resin-zirconia bonding with different surface treatments. Resin-zirconia beams were prepared and loaded at 36 N with 1.5 Hz frequency for 104 cycles at room temperature, before sectioned for MTBS tests. In dry storage conditions, SIE and grit-blasting groups showed significantly higher MTBSs than the control group while no differences in MTBSs were found among the 3.0 W, 4.0 W and control groups. After fatigue loading, only the SIE and 3.0 W groups showed significantly lower MTBSs while the other groups did not. After water storage, MTBSs of water storage specimens were significantly less than the dry specimens except the ones in SIE and 4.0 W groups. No significant differences in MTBSs were found in all groups after fatigue loading. The SIE group showed significantly higher MTBSs than the other study groups after water storage and fatigue loading. In general, it could be concluded that water and cyclic fatigue environment could affect the resin-zirconia bonding.