Interfacial aspects of dental zirconia

Abstract

Zirconia has now been popular in dentistry due to its excellent mechanical properties, satisfied aesthetics, and superior biocompatibility. Various studies have been conducted on the development of surface modification on zirconia for improving its bonding ability and biocompatibility. However, the application of dental restorations based on zirconia remains restricted by the limited knowledge of its interfacial aspects, including biological interface of bacteria adhesion to zirconia implant, cell attachment to zirconia implant, and bonding interface of resin to zirconia restoration. The aim of this project was to evaluate the interfacial aspects of some surface modification treatments on the biological performance of dental zirconia implant, as well as on the adhesion durability of zirconia restoration.

In the first study, different sterilization treatments were applied on zirconia. The effect of these sterilization treatments on surface characteristics and biofilm formation on zirconia was evaluated. It is evidently found that colour change on zirconia and different biofilm formation could be induced by these sterilization methods applied.

The second study aimed to explore the effect of hydrofluoric acid etching treatment on the zirconia surface characteristics and biofilm formation on zirconia. According to the outcomes of this study, hydrofluoric acid treatment on zirconia could increase surface roughness, moreover, the hydrophilicity of zirconia also increased. The study also indicated that mature biofilm formation did not increase on zirconia surface treated with hydrofluoric acid.

The third study examined the changes of surface characteristics of zirconia dental implants after dynamic UVA and UVC irradiation for different time, and analysed the respective changes of MC3T3-E1 osteoblast cell adhesion on zirconia by UVA or UVC light. This study indicated that UVC treatment could change the surface free energy and promote osteoblast proliferation and differentiation on zirconia, while the effect of UVA on these aspects was not significant.

In the fourth study, three different phosphoric acid ester primers under different pH were used to prime zirconia. Atomic level interactions between primers and zirconia surfaces were analysed by solid-state NMR. Tensile bond strength was used to evaluate the resin-zirconia adhesive strength. This study revealed that the hydrogen bond via hydroxyl group, electrostatic interaction, and coordinate bond between P–O- anions and positive Zr4+ groups were responsible for this chemical interaction. Such chemical interactions between phosphoric acid ester primers and zirconia, as well as phosphate functional monomer modified hydrophobicity on zirconia surface, can influence the resin-zirconia tensile bond strength.

Ultimately, the interfacial performance of zirconia could be changed significantly by different surface modifications, both in the biological interface of bacteria adhesion and cell attachment to zirconia, and bonding interface of resin to zirconia restoration. (429 words)