In Vitro Study of Zirconia Surface Modification for Dental Implants by Atomic Layer Deposition

Abstract

Zirconia is a promising material for dental implants; however, an appropriate surface modification procedure has not yet been identified. Atomic layer deposition (ALD) is a nanotechnology that deposits thin films of metal oxides or metals on materials. The aim of this study was to deposit thin films of titanium dioxide (TiO2), aluminum oxide (Al2O3), silicon dioxide (SiO2), and zinc oxide (ZnO) on zirconia disks (ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn, respectively) using ALD and evaluate the cell proliferation abilities of mouse fibroblasts (L929) and mouse osteoblastic cells (MC3T3-E1) on each sample. Zirconia disks (ZR; diameter 10 mm) were fabricated using a computer-aided design/computer-aided manufacturing system. Following the ALD of TiO2, Al2O3, SiO2, or ZnO thin film, the thin-film thickness, elemental distribution, contact angle, adhesion strength, and elemental elution were determined. The L929 and MC3T3-E1 cell proliferation and morphologies on each sample were observed on days 1, 3, and 5 (L929) and days 1, 4, and 7 (MC3T3-E1). The ZR-Ti, ZR-Al, ZR-Si, and ZR-Zn thin-film thicknesses were 41.97, 42.36, 62.50, and 61.11 nm, respectively, and their average adhesion strengths were 163.5, 140.9, 157.3, and 161.6 mN, respectively. The contact angle on ZR-Si was significantly lower than that on all the other specimens. The eluted Zr, Ti, and Al amounts were below the detection limits, whereas the total Si and Zn elution amounts over two weeks were 0.019 and 0.695 ppm, respectively. For both L929 and MC3T3-E1, the cell numbers increased over time on ZR, ZR-Ti, ZR-Al, and ZR-Si. Particularly, cell proliferation in ZR-Ti exceeded that in the other samples. These results suggest that ALD application to zirconia, particularly for TiO2 deposition, could be a new surface modification procedure for zirconia dental implants.

Atomic Layer Deposition of Zirconia on Titanium Implants Improves Osseointegration in Rabbit Bones

“… 12 Accordingly, various methods of coating zirconia particles on the surface of titanium implants have been studied, but appropriate standards have not yet been established. 15 Zirconia undergoes a phase transition into a monoclinic or tetragonal structure depending on temperature or stress, and this changes its strength or volume. 27 If zirconia is deposited by physical or chemical treatments at high temperatures and pressures using the conventional methods, its films may contain impurities or undergo unexpected phase transitions.…”

“… 14 It has been found that zirconia-coated implants have more reliable osseointegration than titanium implants, thereby being composed of histologically mature bone. 14 However, Hayashi et al 15 reported that while many studies have suggested various surface modification procedures of zirconia, appropriate standards have not yet been established.…”

“…Studies on depositing zirconia using ALD have shown excellent results in inhibiting bacterial adhesion and activating osteoblasts. 15 , 22 However, to date there has been no research that has reported the osseointegration effect of implants deposited with zirconia using ALD in vivo.…”

“…22 In contrast, since ALD can process zirconia precursors at a relatively low temperature compared with conventional methods and can uniformly deposit them on an atomic basis without impurities, 20 it is suggested as a suitable method for depositing them on screw-shaped implant surfaces. 15 However, to date no studies have reported the effect of implants deposited with zirconia using ALD on osseointegration in vivo. This study was conducted under the null hypothesis that zirconia deposited on titanium implants using ALD would not affect the BIC ratio.…”