The aim of this study was to investigate how changes in the thermal characteristics of veneer ceramics with almost identical chemical and mechanical properties but with different coefficients of thermal expansion (CTE) can modify their interfacial adhesion to zirconia. 48 bilayers made of one Y-TZP ceramic and four veneer ceramics were fabricated (n=12). Thermal residual stresses were calculated on the basis of the CTE and glass transition temperatures. After defined notching all specimens were loaded in a four-point bending test and the critical loads were recorded which induced stable crack extension at the adhesion interface. The strain energy release rate (G, J/m2) was calculated and was taken as a measure of interfacial adhesion. The CTE of the veneer ceramics were significantly correlated with their adhesion to Y-TZP (p<0.001). Interfacial adhesion in zirconia/veneer bilayers is predominantly affected by the thermal characteristics of the veneer ceramic.
This study investigated the contrast ratio and grain size depending on sintering parameters of twelve different zirconia materials and compared with glass-ceramic (N=156, n=12 per group). Contrast ratio of all ceramics was measured using a spectrophotometer according to ISO 2471: 2008. Grain sizes of zirconia were determined by SEM. Data was analyzed using one-way ANOVA followed by post-hoc Scheffé-test, Kruskal-Wallis-H-test and Spearman correlation (p<0.05). The area under the sintering curve up 25°C (AUC25) and 1200°C (AUC1200) of zirconia was calculated. Glass-ceramic showed significantly lowest contrast ratio compared to zirconia. Final sintering temperature and AUC1200 influenced contrast ratio. Grain size was affected by final sintering temperature, sintering duration and AUC. Contrast ratio and grain size showed an association.
This study aimed to investigate the surface roughness and gloss of composite resins after using two polishing systems and toothbrushing. Six composite resins (Durafill VS, Filtek Z250, Filtek Z350 XT, Kalore, Venus Diamond, and Venus Pearl) were evaluated after polishing with two polishing systems (Sof-Lex, Venus Supra) and after toothbrushing up to 40,000 cycles. Surface roughness (Ra) and gloss were determined for each composite resin group (n=6) after silicon carbide paper grinding, polishing, and toothbrushing. Two-way ANOVA indicated significant differences in both Ra and gloss between measuring stages for the composite resins tested, except Venus Pearl, which showed significant differences only in gloss. After polishing, the Filtek Z350 XT, Kalore, and Venus Diamond showed significant increases in Ra, while all composite resin groups except the Filtek Z350 XT and Durafill VS with Sof-Lex showed increases in gloss. After toothbrushing, all composite resin demonstrated increases in Ra and decreases in gloss.
This study evaluated fracture load of single-tooth, implant-supported, zirconia-based, porcelain- and indirect composite-layered restorations after artificial aging. Forty-four zirconia-based molar restorations were fabricated on implant abutments and divided into four groups, namely, zirconia-based all-ceramic restorations (ZAC group) and three types of zirconia-based composite-layered restorations (ZIC-P, ZIC-E, and ZIC groups). Before layering an indirect composite material, the zirconia copings in the ZIC-P and ZIC-E groups were primed with Clearfil Photo Bond and Estenia Opaque Primer, respectively. All restorations were cemented on the abutments with glass-ionomer cement and then subjected to thermal cycling and cyclic loading. All specimens survived thermal cycling and cyclic loading. The fracture load of the ZIC-P group (2.72 kN) was not significantly different from that of the ZAC group (3.05 kN). The fracture load of the zirconia-based composite-layered restoration primed with Clearfil Photo Bond (ZIC-P) was comparable to that of the zirconia-based all-ceramic restoration (ZAC) after artificial aging.
In this study, effects of the degree of dissociation of acids on the hydrolysis rate of methoxy group in γ-methacryloxypropyltrimethoxysilane (γ-MPS) and the adsorption characteristics of γ-MPS on ceramic surfaces were studied using acetic, phosphoric, and hydrochloric acids. Hydrolytic stability of γ-MPS adsorption layer at the resin-ceramic interface was thus examined. 29Si NMR observations of acidactivated γ-MPS and contact angle measurements following ceramic surface silanization were performed. Bond strengths of resin to the silanized ceramic surfaces were measured. Statistical analyses of shear bond strength and contact angle data were performed. Increase in the degree of dissociation of the acid used increased the hydrolysis rate of methoxy group in γ-MPS, but lowered the contact angle to the silanized ceramic surface. Decrease in the contact angle increased the hydrolytic stability of γ-MPS adsorption layer.
The purpose of the present study was to investigate the effect of the composition of experimental fluorinated soft lining materials on bond strength to denture base resin. Vinylidene fluoride/hexafluoro propylene copolymer (2-6F), tridecafluorooctyl methacrylate (13FMA), methoxy diethylene glycol methacrylate (MDGMA), and silica (as filler) were used for fabrication of the experimental soft lining materials. Nine experimental soft lining materials having various compositions of 2-6F, 13FMA, and MDGMA were prepared. Shear and tensile bond strength tests were performed before and after immersion in water. The water sorption for the materials was also measured. An increase in the content of acrylic monomer, MDGMA, in the experimental materials increased the bond strength before immersion in water but reduced the bond strength after immersion in water as compared to that before immersion in water. The inclusion of fluorinated monomer (13FMA) in the materials appeared to affect water sorption.
The purpose of this study was to evaluate mechanical properties, surface characteristics and castability of Zr-14Nb dental castings. The mean 0.2% proof and ultimate tensile strengths of Zr-14Nb were approximately 68% and 76% those of Ti-6Al-7Nb, respectively, while they were comparable to Co-29Cr-6Mo. Elongation of Zr-14Nb was the highest of all alloys tested. The hardened reaction layer was formed on the surfaces of the Zr-14Nb castings. The layer consisted of oxygen and aluminum originating form investment. The castability of Zr-14Nb was comparable to that of Ti-6Al-7Nb. Dental castings of Zr-14Nb reveal mechanical properties that were within the range of the other dental alloys. Further improvements in castability and minimization of the surface reaction layer are needed for applications in dental prostheses.
Titanium (Ti) is widely used for oral cavity biomedical devices. However, because it penetrates the mucosa and exists partially external to the tissue, it sometimes induces tissue inflammation, minor infection, or peri-implantitis due to oral bacteria after implantation and causes serious consequences. We have previously shown that poly(ethylene glycol) (PEG)- electrodeposited Ti inhibits bacterial adhesion and biofilm formation. However, the effect of the PEG coating in body fluid is still unclear. In this study, we investigated bacterial colony morphology and biofilm formation on PEG-electrodeposited Ti in comparison with untreated Ti in the presence of saliva. After 48 h incubation, Streptococcus mutans biofilms adhered on the untreated Ti were rigid and cohesive, while those on the PEG-electrodeposited were loose and were easily washed off. These results indicate electrodeposited-PEG layers inhibit the biofilm formation on Ti in the presence of saliva.
Effects of a fluoride-releasing varnish containing surface reaction-type prereacted glass ionomer (S-PRG) filler on dentin demineralization were examined using optical coherence tomography. Bovine incisors that were sliced and treated with undersaturated 0.1 M lactic acid buffer solution (DE group). A thin film of varnish-containing S-PRG filler was applied before demineralization (PRG group). Control was maintained in artificial saliva. Using optical coherence tomography of selected locations on the dentin surface, peak intensity (dB) and width (μm) at 1/e2 were obtained and integrated values calculated. Although alterations in integrated values were different in each group, there was a slight but not significant increase in those for the control group and a slight but significant increase for the De group. For the PRG group, integrated values were doubled seven days after experiment initiation, followed by a significant increase. Fluoride-releasing varnish containing S-PRG fillers prevented dentin demineralization as detected by optical coherence tomography.
This present study investigated the potential of adeno-associated virus serotype 2 (AAV2) mediated BMP-7 (AAV2-BMP-7) to induce odontoblastic differentiation of human dental pulp cells (DPCs) in vitro. AAV2-BMP-7 was constructed to overexpress BMP-7, and the biologic effects of BMP-7 on DPCs were investigated by the evaluation of the activity of alkaline phosphatase (ALPase), the detection of the expression of dentin sialophosphoprotein (DSPP) and osteocalcin (OCN) expression and the analysis of the proliferative ability of the cells. DPCs that were infected with AAV2-BMP-7 displayed significantly upregulated ALP activity and formed mineralized nodules. Moreover, AAV2-BMP-7 promoted the expression of mineralization-related genes, which included DSPP and OCN. In addition, there was no significant difference between the proliferative ability of AAV2-BMP-7 and the control group. In conclusion, AAV2-BMP-7 promoted the odontoblastic differentiation in DPCs, a clear indication of the therapeutic potential of AAV2-BMP-7 in dental tissue regeneration.
Salivary macromolecules infiltrate white and brown spot enamel lesions and adsorb onto hydroxyapatite. Calcium-binding salivary proteins such as statherin hinder remineralization of these lesions. We assessed whether bleaching agents can remove salivary components that have infiltrated and bound to experimental subsurface lesions in bovine enamel prepared by immersing specimens in acid and then human saliva. Transversal microradiography showed that such demineralized lesions mimicked incipient carious lesions. Bound proteins to the experimental and untreated control specimens were eluted in a stepwise manner with phosphatebuffered saline, 0.4 M phosphate buffer, and 1 M HCl. SDS-PAGE of dialyzed extracts showed that specific salivary proteins bound to the lesions, while virtually no protein bands were detected if the specimens were bleached. Western blotting showed that even statherin, which was more firmly bound than other proteins, was removed. In-office bleaching agent may be useful in treating enamel lesions for removing proteins bound to these lesions.
The finite element method has been considered to be excellent evaluative technique to study magnetic circuit optimization. The present study analyzed and quantitatively evaluated the different effects of magnetic circuit on attractive force and magnetic flux density using a three-dimensional finite element method for comparative evaluation. The diameter of a non-magnetic material in the shield disk of a magnetic assembly was variably increased by 0.1 mm to a maximum 2.0 mm in this study design. The analysis results demonstrate that attractive force increases until the diameter of the non-magnetic spacing material reaches a diameter of 0.5 mm where it peaks and then decreases as the overall diameter increases over 0.5 mm. The present analysis suggested that the attractive force for a magnetic attachment is optimized with an appropriate magnetic assembly shield disk diameter using a non-magnetic material to effectively change the magnetic circuit efficiency and resulting retention.
The purpose of this study was to evaluate a thin gelatin hydrogel membrane containing β-tricalcium phosphate (G-TCP) for use in guided bone regeneration, a technique that we developed. G-TCP membranes were fabricated from gelatin and β-TCP powder, freezedried, and cross-linked by heating. The resulting G-TCP membranes were as thin as collagen membranes, with high mechanical integrity. Proliferation and differentiation of rat bone marrow stromal cells (BMSCs) on G-TCP and collagen membranes were examined. On both membranes, BMSCs proliferated well and expressed alkaline phosphatase. However, more bone-like mineralized tissue formed on G-TCP membranes than on collagen membranes at 4 weeks. The effects of G-TCP and collagen membranes on bone regeneration in rat parietal bone defects were histologically examined. Bone bridges with mature uniform bone were observed under G-TCP membranes as early as 2 weeks. These results indicate that G-TCP is a GBR membrane that is comparable or superior to collagen membrane.
The current study evaluated the effect of primers on the shear bond strength of an indirect composite material joined to a silverpalladium-copper-gold (Ag-Pd-Cu-Au) alloy (Castwell). Disk specimens were cast from the alloy and were air-abraded with alumina. Eight metal primers were applied to the alloy surface. A light-polymerized indirect composite material (Solidex) was bonded to the alloy. Shear bond strength was determined both before and after the application of thermocycling. Two groups primed with Metaltite (thione) and M. L. Primer (sulfide) showed the greatest post-thermocycling bond strength (8.8 and 6.5 MPa). The results of the X-ray photoelectron spectroscopic (XPS) analysis suggested that the thione monomer (MTU-6) in the Metaltite primer was strongly adsorbed onto the Ag-Pd-Cu-Au alloy surface even after repeated cleaning with acetone. The application of either the thione (MTU-6) or sulfide primer is effective for enhancing the bonding between a composite material and Ag-Pd-Cu-Au alloy.
Three commercially available porcelains bonded to titanium were evaluated to determine the weakest zone of the titanium-porcelain bonding structures. Tensile bond tests were performed for these specimens (NO, DU, and VI) and for Ni-Cr alloy-porcelain bonding samples that served as controls. The maximum bond strengths between porcelain and titanium and the Ni-Cr alloy subjected to different metal surface treatments were compared. Sand blasting effectively increased bond strengths in titanium-porcelain bonding materials. No statistically significant differences in the maximum bond strengths were found between the NO sample and a control; however, sample NO exhibited greater maximum bond strength than DU and VI samples. The bond strengths increased with increasing area fractions of porcelain failure on fracture surfaces. The weakest zones were investigated based on the oxygen chemical states determined by electron spectroscopy for chemical analysis, which include bridging oxygen (Si-O-Si), nonbridging oxygen (Si-O− M+), and titanium oxide (O2−) states. We concluded that the titanium oxide layer is the weakest zone of titanium-porcelain bonding structures.
Initial attachment of human oral keratinocytes cultured on yttria-stabilized tetragonal zirconia polycrystal (TZP) surfaces that were subjected to UV or oxygen plasma (O2-plasma) treatment was investigated. The viability of the attached cells, mRNA expression of laminin γ2 and integrin β4, distribution of laminin γ2 and integrin β4, cell area, and cell morphology were assessed. The results showed that no differences in the viability of attached cells were recognized among the conditions. However, expression of laminin γ2 and integrin β4 as well as cell morphology were promoted only in O2-plasma specimens even though superhydrophilicity was obtained in both the UV and O2-plasma specimens compared with the untreated control specimen. The photocatalytic activity was believed to be closely involved in the above-mentioned differences. The results of this study suggest that TZP surface treated with oxygen plasma promotes the initial attachment capability of human oral keratinocytes with enhancing the extracellular matrix such as laminin γ2.
This study compared commercial composite resin blocks with one ceramic block for use in computer-aided design/computer aided manufacturing (CAD/CAM). Four composite resins, one composite ceramic, and one feldspar-ceramic block were investigated. Flexural strength (FS), flexural modulus (FM), and Vickers hardness (VH) were determined under three conditions: dry storage; immersion in water at 37°C for 7 days; and immersion in water at 37°C for 7 days followed by 10,000 thermocycles. After dry storage, FS ranged from 127 to 242 MPa, FM from 9.6 to 51.5 GPa, and VH from 64 to 455. Two-way ANOVA was performed for FS, FM and VH followed by Tukey’s multiple comparison (α<0.05). Results demonstrated that the materials degraded after water immersion and thermocycling, but their properties were within the acceptable range for fabrication of single restorations according to the ISO standard for ceramics (ISO 6872:2008).