Evaluation of Different Thickness, Die Color, and Resin Cement Shade for Veneers of Multilayered CAD/CAM Blocks.

PURPOSE: To investigate the effect of resin cement color on the post-cementation shade of thin laminate veneers milled from multilayered glass ceramic blocks for each layer. MATERIALS AND METHODS: Thin slices (N = 180) with two thicknesses (A: 8 × 8×0.55 mm and B: 8×8×0.8 mm; n = 90/group) were obtained from multilayered glass ceramic blocks using a diamond saw. Resin die specimens were prepared (8 × 8 × 4 mm) (n = 180) and divided into two resin cement colors (D: -3. L: +3) and one control group (C: translucent). Each slice was luted to the composite specimens using a dual-curing resin cement under a constant load of 250 g and light-polymerized for 120 seconds. Specimens were placed on a white background and CIELab values for each layer of the blank slices (incisal [In], body [Bo], and cervical [Ce]) were recorded using a dental contact spectrophotometer. The values were calculated as ΔE, and the data were statistically analyzed (one-way ANOVA, Shapiro-Wilk). RESULTS: Mean ΔE values for A and B were significant (p < 0.05) for In (A: 6.2 ± 1.1; B: 6.6 ± 1.2), Bo (A: 5.1 ± 2.6; B: 3.9 ± 1), and Ce (A: 5.3 ± 2.7; B: 3.8 ± 1.2). Mean ΔE values for In for D and L for A and B groups were significantly higher (6.3 ± 1.2; 6.6 ± 1.2) than Bo and Ce for D (4.4 ± 2.4; 4.6 ± 2.6) and L (4.6 ± 1.4; 4.5 ± 1.7) groups (p < 0.05), respectively. Mean differences between Bo and Ce for A and B groups were insignificant (p ≥ 0.05), while for In the differences were significant. Mean differences between Bo and Ce for A (5.1 ± 2.6; 5.3 ± 2.7) and for B (3.9 ± 1; 3.5 ± 1.2) groups were insignificant (p ≥ 0.05), while for In the differences were significant (6.2 ± 1.1 for A and 6.6 ± 1.2 for B). CONCLUSION: The color changes for body and cervical regions of multilayered ceramic veneers were not affected by resin color or ceramic thickness, but the incisal area was affected. The translucency of each layer in ceramic veneer fabricated with multilayered blanks should be considered for clinical situations.

Effect of Veneering Methods on Zirconia Framework-Veneer Ceramic Adhesion and Fracture Resistance of Single Crowns.

PURPOSE: The aim of this study was to evaluate the fracture resistance (FR) and shear bond strength (SBS) via finite element analysis (FEA) of zirconia framework veneered with different methods. MATERIALS AND METHODS: Zirconia frameworks were prepared as crowns for FR and cubic blocks for SBS (N = 60, n = 10). The specimens were veneered with one of the following veneering methods: (a) overcemented file-splitting (OCF), (b) layering (L), or (c) overpressing (P). For crowns, stainless steel dies (N = 30; chamfer: 1 mm) were scanned using a contrast spray. Bilayered design for OCF and reduced design (1 mm) for both L and P were performed by computer-aided design and manufacturing. For the SBS test, zirconia blocks were sectioned (4 × 4 × 4 mm(3)) under water cooling and sintered. Frameworks were veneered with compatible ceramics for each veneering method and subjected to mechanical tests. The milled suprastructures were bonded to zirconia frameworks using a resin composite in Group OCF and photopolymerized. Crowns were cemented to the metal dies with resin modified glass-ionomer cement. All specimens were stored at 37°C, 100% humidity for 48 hours prior to mechanical tests. Data were statistically analyzed (ANOVA, Bonferroni tests, α = 0.05). Fractured specimens were examined under scanning electron microscopy (SEM), and FEA modeling of the crowns was performed. RESULTS: Mean FR values (N) were significantly higher with L (6102 ± 1519) and P (4117 ± 1083) than with of OCF (1900 ± 254) (p = 0.01). The mean SBS (MPa) in OCF (24 ± 4) was significantly lower (p < 0.002) than L (35 ± 6) and P (32 ± 6) (p > 0.05). For crown restorations, while only adhesive failures were found in OCF, cohesive failures within veneering ceramic were more frequent in P and L. FEA verified these findings. CONCLUSION: Veneering methods based on layering or pressing may reduce ceramic chipping but the overcemented file-splitting method does not seem to prevent this failure. CLINICAL SIGNIFICANCE: Layering and overpressing veneering methods on zirconia frameworks with reduced design might decrease chipping compared to overcemented file-splitting, where in the latter, zirconia framework and feldspathic suprastructure are combined using a resin cement.

Effect of various veneering techniques on mechanical strength of computer-controlled zirconia framework designs.

PURPOSE: The objectives of this study were to evaluate the fracture resistance (FR), flexural strength (FS), and shear bond strength (SBS) of zirconia framework material veneered with different methods and to assess the stress distributions using finite element analysis (FEA). MATERIALS AND METHODS: Zirconia frameworks fabricated in the forms of crowns for FR, bars for FS, and disks for SBS (N = 90, n = 10) were veneered with either (a) file splitting (CAD-on) (CD), (b) layering (L), or (c) overpressing (P) methods. For crown specimens, stainless steel dies (N = 30; 1 mm chamfer) were scanned using the labside contrast spray. A bilayered design was produced for CD, whereas a reduced design (1 mm) was used for L and P to support the veneer by computer-aided design and manufacturing. For bar (1.5 × 5 × 25 mm(3) ) and disk (2.5 mm diameter, 2.5 mm height) specimens, zirconia blocks were sectioned under water cooling with a low-speed diamond saw and sintered. To prepare the suprastructures in the appropriate shapes for the three mechanical tests, nano-fluorapatite ceramic was layered and fired for L, fluorapatite-ceramic was pressed for P, and the milled lithium-disilicate ceramics were fused with zirconia by a thixotropic glass ceramic for CD and then sintered for crystallization of veneering ceramic. Crowns were then cemented to the metal dies. All specimens were stored at 37°C, 100% humidity for 48 hours. Mechanical tests were performed, and data were statistically analyzed (ANOVA, Tukey's, α = 0.05). Stereomicroscopy and scanning electron microscopy (SEM) were used to evaluate the failure modes and surface structure. FEA modeling of the crowns was obtained. RESULTS: Mean FR values (N ± SD) of CD (4408 ± 608) and L (4323 ± 462) were higher than P (2507 ± 594) (p < 0.05). Mean FS values (MPa ± SD) of CD (583 ± 63) and P (566 ± 54) were higher than L (428 ± 41) (p < 0.05). Mean SBS values (MPa ± SD) of CD (49 ± 6) (p < 0.05) were higher than L (28 ± 5) and P (30 ± 8). For crown restorations, while cohesive failures within ceramic and zirconia were seen in CD, cohesive failures within ceramic were found in both L and P. Results were verified by FEA. CONCLUSION: The file splitting technique showed higher bonding values in all mechanical tests, whereas a layering technique increased the FR when an anatomical core design was employed. CLINICAL SIGNIFICANCE: File splitting (CAD-on) or layering veneering ceramic on zirconia with a reduced framework design may reduce ceramic chipping.

Detection of artificial demineralization bordering different types of laminate veneers using visual inspection and storage phosphor radiography.

OBJECTIVE: The objective of this study is to compare the diagnostic accuracy of visual inspection (VI) and storage phosphor plate (SPP) radiography for the detection of artificial demineralization bordering different laminate veneers. MATERIALS AND METHODS: Twenty human maxillary canine teeth were prepared. All-ceramic (A) and hybrid ceramic (H) laminate veneers were fabricated and luted. Veneered teeth were covered except for a circular window on the proximal surface bordering restorations. Teeth were kept in acetic acid buffer to create demineralization and imaged with a SPP system. Ten observers evaluated all teeth first visually then with SPP images for the presence/absence of demineralization. Teeth were examined using scanning electron microscopy (SEM) as well. The accuracy was expressed as the area under the ROC curves (A(z)). Pair-wise comparisons were performed using two-way ANOVA and post hoc t test (p = 0.05). Fleiss kappa (κ) was used for agreement. RESULTS: SPP radiography was better than the VI for both veneers (p = 0.004). The A(z)s of two veneers were different for both VI (p < 0.005) and SPP (p < 0.005). SEM evaluation revealed lesions confined to enamel. κ was fair for H, and fair to moderate for A. Agreement was higher for the radiographic evaluation for both veneers. CONCLUSION: Enamel demineralizations bordering hybrid and ceramic laminate veneers can be detected better with SPP radiography than VI and detectability was better for all-ceramic veneers than the hybrid ceramic ones. CLINICAL RELEVANCE: Early detection of enamel demineralizations bordering laminate veneers would result in time-saving and less-invasive treatment methods; therefore, SPP radiography may be recommended in clinically suspicious cases since it provides better diagnostic accuracy.