Factors influencing the survival of implant-supported ceramic-ceramic prostheses: A randomized, controlled clinical trial.

OBJECTIVE: The goals of this research are: (1) to determine the clinical survival of ceramic-ceramic 3-unit implant supported fixed dental prostheses (FDPs) compared with control metal-ceramic and; (2) to analyze the effects of design parameters such as connector height, radius of curvature of gingival embrasure, and occlusal veneer thickness. MATERIALS AND METHODS: This randomized, controlled clinical trial enrolled 96 participants with 129 3-unit implant-supported FDPs. Participants were randomized to receive different design combinations to include FDP material, thickness of occlusal veneer ceramic, radius of curvature of gingival embrasure and connector height. Participants were recalled for 6 months, 1year and yearly thereafter for the next 5 years. FDPs were examined for evidence of fracture and radiographs were made to assess viability of implants. Fractographic analyses and Kaplan Meier survival analysis was used to analyze the data. RESULTS: 27 FDPs, representing 21%, exhibited chipping fractures of the veneer during the 5-year observation period. There was no statistically significant effect of type of material, veneer thickness, radius of curvature of gingival embrasure and connector height on occurrence of fracture. Fractographic and occlusal analyses reveal that fractures originated from the occlusal surface and that occlusion was the most important factor in determining survival. Stresses calculated at failure demonstrated lower values compared with in vitro data. CONCLUSION: Implant-supported ceramic-ceramic prosthesis is a viable alternative to metal-ceramic. Survival analysis for both materials were comparable and design parameters employed in this study did not affect survival as long as zirconia was used as the core material.

Novel Testing for Corrosion of Glass-Ceramics for Dental Applications.

The effects of pH cycling immersion on the corrosion of glass-based ceramic materials were investigated by examining the silicon release level in the immersion solution and the surface morphology of the ceramic after immersion. The hypothesis that pH cycling causes more surface degradation than constant immersion was tested. An inductively coupled plasma atomic emission spectrometer was used for Si ion concentration determination and scanning electron microscopy for surface morphology analyses. Two pH cycling sequences (pH 2, 7, 10 and pH 10, 2, 7) were employed in this study. Glass-ceramic disks were immersed in each pH solution for 3 d, then cycled for 27 d. The silicon release levels during the pH cycling were significantly higher than those in the constant pH immersion. The silicon levels for both cycling sequences were around 47 and 2 times higher than that in constant pH conditions for 2 and 10, respectively. The morphology of the ceramic treated with cycling was also significantly degraded as compared with the ceramic immersed in the constant pH solution. Thus, the severity of glass-ceramic degradation depends not only on the pH of the immersed solution but also on the pH of the previous solution. Since the pH of the oral environment can vary depending on the diet and buffering capacity of saliva, materials testing in constant pH immersion might underestimate the in vivo corrosion. New mechanisms were proposed to account for the effect of pH cycling on glass-ceramic corrosion.

Randomized clinical study of wear of enamel antagonists against polished monolithic zirconia crowns.

OBJECTIVES: To test the hypothesis that there is no difference in the in vivo maximum wear of enamel opposing monolithic zirconia crowns, enamel opposing porcelain fused to metal crowns and enamel opposing enamel. METHODS: Thirty patients needing single crowns were randomized to receive either a monolithic zirconia or metal-ceramic crown. Two non-restored opposing teeth in the same quadrants were identified to serve as enamel controls. After cementation, quadrants were scanned for baseline data. Polyvinylsiloxane impressions were obtained and poured in white stone. Patients were recalled at six-months and one-year for re-impression. Stone models were scanned using a tabletop laserscanner to determine maximum wear. Statistical analysis was performed using Mann-Whitney U to determine any significant differences between the wear of enamel against zirconia and metal-ceramic crowns. RESULTS: Sixteen zirconia and 14 metal-ceramic crowns were delivered. There were no statistical differences in mean wear of crown types (p=0.165); enamel antagonists (p=0.235) and enamel controls (p=0.843) after one year. CONCLUSION: Monolithic zirconia exhibited comparable wear of enamel compared with metal-ceramic crowns and control enamel after one year. SIGNIFICANCE: This study is clinically significant because the use of polished monolithic zirconia demonstrated comparable wear of opposing enamel to metal-ceramic and enamel antagonists.

Surface degradation of dental ceramics as a function of environmental pH.

We tested the hypotheses that glass-ceramic veneers and overglazes degrade by ion exchange in an acidic environment, and that they degrade by breakdown of the silica network in a basic environment. Disk specimens of glass-ceramic veneer and glaze were fabricated and immersed in pH 2, 7, or 10 buffer solutions, for 1, 3, 5, 10, 15, and 30 days. Each specimen was placed in a shaker bath containing de-ionized distilled water at 80°C. Concentrations of Al(3+), Ca(2+), Zn(2+), Li(2+), and Si(4+) were analyzed by means of inductively coupled plasma atomic emission spectrometry (ICP/AES). Statistical analyses were performed by factorial ANOVA. Significant differences occurred among leached ion concentrations as a function of material type, solution pH, and exposure time. A substantial release of Si occurred at pH 10 over time, leading to a breakdown of the glass phase. At pH 2, dissolution was controlled by an ionic exchange mechanism. We conclude that ceramic veneers and glazes may be susceptible to considerable degradation in low- and high-pH buffer solutions.

Resistance to staining, flexural strength, and chemical solubility of core porcelains for all-ceramic crowns.

PURPOSE: The increased demand for tooth-colored restorations has prompted the use of ceramics in areas that are subject to masticatory stresses. To maximize the strength of these restorations, manufacturers and clinicians advocate placement of core materials in lieu of veneering materials in areas that are more susceptible to fracture. The objectives of this study were to determine the: resistance to staining of three core porcelains used for all-ceramic restorations, Procera, IPS Empress, and In-Ceram, through the use of colorimetry and visual observation; flexural strength of these porcelains under a three-point bend test; and chemical solubility in a controlled environment. MATERIALS AND METHODS: L*a*b* values were obtained for each specimen before and after immersion in a saturated solution of methylene blue in ethanol for 24 hours. Visual observation was also performed to ascertain color differences before and after staining. A three-point bend test was used to determine flexural strength. A reflux-condenser type, three-piece extraction apparatus was used with 4% acetic acid solution for 16 hours to determine solubility. Each sample was weighed before and after the reflux procedure to ascertain percentage weight loss. RESULTS: The mean delta E obtained for IPS Empress was 14.5; In-Ceram was 9.2, and Procera was 9.0. Flexural strength obtained for IPS Empress, In-Ceram, and Procera was 176.9 MPa, 323.4 MPa, and 464.3 MPa, respectively. Weight loss of IPS Empress, In-Ceram, and Procera was 0.056%, 0.734%, and 0.003%, respectively. CONCLUSION: IPS Empress showed the least resistance to staining. IPS Empress had the lowest flexural strength, while Procera had the highest. In-Ceram demonstrated the highest chemical solubility.

Fracture resistance of all-ceramic and metal-ceramic inlays.

PURPOSE: Metal-ceramic inlay designs were developed to determine if the esthetic qualities of all-ceramic inlays could be duplicated and at the same time improve their strength and stability. The objectives of this study were to: (1) compare the fracture resistance of metal-ceramic inlays with that of all-ceramic inlays; (2) determine the correlation between the degree of preparation taper and fracture resistance; and (3) determine the correlation between marginal gap width and fracture resistance. MATERIALS AND METHODS: Inlay preparations were made on 60 Dentoform teeth, with 30 teeth allocated for metal-ceramic inlays and 30 teeth for all-ceramic inlays. Each group was further subdivided into 5-, 10-, and 20-degree taper preparations. Metal-ceramic inlays were fabricated using Goldtech Bio 2000 metal and Ceramco porcelain extending to the margin, while all-ceramic inlays were made from Empress II ceramic. Marginal gap widths were measured at six critical areas after fabrication. The load at failure was measured using an Instron Universal Testing Machine. RESULTS: The mean fracture load for all-ceramic inlays and metal-ceramic inlays at 5, 10, and 20 degrees was 70+/-40 N, 48+/-37 N, 33+/-7 N, and 40+/-23 N, 29+/-22 N, and 14+/-4 N, respectively. The mean gap width was 105 microm and 126 microm for all-ceramic and metal-ceramic inlays, respectively. CONCLUSION: The mean fracture load for Empress inlays was significantly higher than that for metal-ceramic inlays. Inlays with a 5-degree taper were significantly more fracture resistant than those with a 20-degree taper. There was no relation between marginal gap width and fracture resistance.

Ceramic design concepts based on stress distribution analysis.

This article discusses general design concepts involved in fabricating ceramic and metal-ceramic restorations based on scientific stress distribution data. These include the effects of ceramic layer thickness, modulus of elasticity of supporting substrates, direction of applied loads, intraoral stress, and crown geometry on the susceptibility of certain restoration designs to fracture.