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

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.

Bone Tissue Engineering in Rat Calvarial Defects Using Induced Bone-like Tissue by rhBMPs from Immature Muscular Tissues In Vitro.

This study aimed to induce bone-like tissue from immature muscular tissue (IMT) in vitro using commercially available recombinant human bone morphogenetic protein (rhBMP)-2, rhBMP-4, and rhBMP-7, and then implanting this tissue into a calvarial defect in rats to assess healing. IMTs were extracted from 20-day-old Sprague-Dawley (SD) fetal rats, placed on expanded polytetrafluoroethylene (ePTFE) with 10 ng/µL each of rhBMP-2, BMP-4, and BMP-7, and cultured for two weeks. The specimens were implanted into calvarial defects in 3-week-old SD rats for up to three weeks. Relatively strong radiopacity was observed on micro-CT two weeks after culture, and bone-like tissue, comprising osteoblastic cells and osteoids, was partially observed by H&E staining. Calcium, phosphorus, and oxygen were detected in the extracellular matrix using an electron probe micro analyzer, and X-ray diffraction patterns and Fourier transform infrared spectroscopy spectra of the specimen were found to have typical apatite crystal peaks and spectra, respectively. Furthermore, partial strong radiopacity and ossification were confirmed one week after implantation, and a dominant novel bone was observed after two weeks in the defect site. Thus, rhBMP-2, BMP-4, and BMP-7 differentiated IMT into bone-like tissue in vitro, and this induced bone-like tissue has ossification potential and promotes the healing of calvarial defects. Our results suggest that IMT is an effective tissue source for bone tissue engineering.

Proliferation of mouse fibroblast-like and osteoblast-like cells on pure titanium films manufactured by electron beam melting.

The physical characteristics and biological compatibility of surfaces produced by electron beam melting (EBM) are not well known. In particular, there are not many reports on biocompatibility qualities. In this study, pure Ti films were manufactured using EBM. While it is reported that moderately hydrophilic biomaterial surfaces display improved cell growth and biocompatibility, contact angle measurements on the EBM-produced pure Ti films showed slight hydrophobicity. Nonetheless, we found the cell count of both fibroblast-like cells (L929) and osteoblast-like cells (MC3T3-E1) increased on pure Ti films, especially the MC3T3-E1, which increased more than that of the control. In addition, the morphology of L929 and MC3T3-E1 was polygonal and spindle-shaped and the cytoskeleton was well developed in the pure Ti surface groups. Upon staining with Alizarin red S, a slight calcium deposition was observed and this level gradually rose to a remarkable level. These results indicate that pure Ti films manufactured by EBM have good biocompatibility and could be widely applied as biomedical materials in the near future.

Bonding Characteristics of Silane Coupling Agent and MMA-Containing Primer to Various Composite CAD/CAM Blocks.

This study evaluated the bonding characteristics of a silane coupling agent (SCA) and a methyl methacrylate (MMA)-containing primer (MCP) for 11 types of commercial composite blocks (CBs) for sandblasted and non-sandblasted surfaces. The shear bond strength (SBS) was measured according to ISO 29022: Notched-edge shear bond strength test. The SBS results demonstrated statistically significant differences between the CBs under all identical conditions. For the non-sandblasted groups, the SBSs of MCP-treated specimens were significantly higher than those of SCA-treated specimens for all but two CBs. Comparing the two treatments in sandblasted groups, the SBS was significantly higher for seven out of 11 MCP-treated RCB specimens, in contrast with three cases for the SCA-treated group. Two-way ANOVA for SBS showed the interaction effect between sandblasting and primer type for specific CBs, indicating that the sandblasting treatment improved SBS more effectively for SCA-treated specimens. Moreover, the effect of the SCA treatment was more material-dependent compared to that of the MCP treatment, which did not achieve a strong bond in all CBs but proved more effective than the SCA treatment, especially for non-sandblasted surfaces.

Measurement of exothermic heat released during polymerization of a lightcuring composite resin: Comparison of light irradiation modes.

High-power light-curing units have emerged that reduce the time of procedures in dental clinical work. However, patients sometimes complain of pain during the polymerization of composite resin. In this experiment, we investigated how differences in light-curing mode affect the temperature rise during composite resin polymerization in vitro. Light-curing mode conditions were divided into four groups: 3 s in plasma mode (Plm3) and 5, 10, and 20 s in standard mode. The temperature curve under Plm3 exhibited a rapid increase during the first 3 s of light curing before reaching a maximum of around 55°C. In contrast, the temperature rose rapidly but less sharply for irradiation in each standard mode compared with Plm3. These results suggest that irradiation using a high-power mode increases the temperature at an excessively high rate, and this may raise concern about side effects on the pulp.

Shrinkage characteristics of a novel lower contractile acrylic pattern resin.

Forming models and brazing parts, both of which require high accuracy, are greatly affected the polymerization shrinkage of pattern resin. In 2018, a lower-shrinkage autopolymerizing pattern resin (PRK) was introduced. In this work, we compared the rate of polymerization shrinkage between PRK with that of three autopolymerizing resins -GC Pattern Resin (GPR), Pi-Ku Plast (PIK), and Fixpeed (FIX)- as controls. The shrinkage percentages at 10 min were 7.26±0.88 for PRK, 10.78±2.28 for GPR, 8.03±1.08% for PIK, and 7.46±1.25 for FIX. The shrinkage of PRK was significantly lower than that of GPR. The lower-shrinkage autopolymerizing resin contains some multifunctional monomer and indicated that the amount of monomer was accordingly reduced from the result of polymer size and abundance ratio. Our results suggested that the monomer component and the polymer particle size were factors that contribute to reducing contraction of the resins.

Leaching behaviors of computer-aided design/computer-aided manufacturing composite resin component elements immersed in water.

PURPOSE: Immersion tests in purified water were conducted to evaluate the leaching behaviors of filler elements contained in computer-aided design/computer-aided manufacturing (CAD/CAM) composite resin. METHODS: Four commercial CAD/CAM resin composite blanks were tested: Shofu block HC 2 layer, Cerasmart, Katana Avencia block, and KZR-CAD HR Block 2. The specimens in the size of 10.0×12.0×2.0mm were immersed in a 50-mL conical tube containing 40mL of purified water, and then placed in a constant-temperature oven set at a temperature of 37, 60, 70, or 80°C and stored statically for 30 days. After storage, the concentrations of leached elements in the immersion solution were measured with an inductively coupled plasma atomic emission spectrometer. To characterize the surface of the specimen after the immersion test, secondary electron images were obtained. RESULTS: The immersion test resulted in the leaching of Si, the main component, from all materials tested. Some materials were found to have leached high amount of Ba or Sr in addition to Si, and remarkable surface degradation was observed. The amount of leached elements increased with increased immersion temperatures. CONCLUSIONS: Filler elements in CAD/CAM composite resins used in this study leached into purified water. The leached elements and its quantities greatly differed among materials and depend on the types of the oxides composing the filler. The amounts of leached elements varied in a temperature-dependent manner.

Rheological approach for determining yield stresses in flowable resin composites prior to setting.

The purpose of this study is to develop a method for quantifying the fluidity of flowable resin composites using determinations of yield stress. Five commercially available composites (AliteFlo LV, Flow-it ALC, Venus flow, Tetric N-flow, Revolution Formula2) were investigated. Yield stress values were obtained by plotting shear stresses for a range of shear rates, followed by fitting of Casson fluid models to flow curve data and extrapolation to the stress axis. To confirm that yield stress reflected fluidity, apparent viscosity at the lower shear rate (0.2 s-1) was calculated from flow curves. Yield stresses ranged from 5.4 to 43.1 Pa, and were found to capture differences in the fluidity of composites that were not captured by viscosity measurement at the low shear rate. Yield stress is directly proportional to fluidity, and could serve as a simple and precise indicator for selecting flowable resin composites for use in various clinical applications.