In Vitro Evaluation of Bond Strength between Zirconia Core and CAD/CAM-Produced Veneers.

PURPOSE: To evaluate the shear bond strength between various CAD/CAM veneer materials and the zirconia ceramic core. MATERIALS AND METHODS: Ninety square prism zirconia specimens (10 specimens per each group, n = 10) in dimensions of 10 × 5 × 5 mm were prepared. Eighty square prism veneering specimens (40 feldspathic ceramic [Cerec Bloc] and 40 lithium disilicate [IPS e.max CAD]) in dimensions of 3 × 3 × 1 mm were connected to zirconia specimens. Conventional layering was applied to the remaining zirconia specimens as control group (n = 10). CAD/CAM-produced veneers were connected to the zirconia specimens using fusion porcelain or resin cement. One of following treatments were applied to the cemented specimens: no surface treatment, HF etching of the veneering material, or HF acid etching of the veneer in combination with the application of a glaze layer to the zirconia surface. Following the veneering procedures, a shear bond strength test was performed at a speed of 1 mm/min using a universal testing machine. Univariate ANOVA (α = 0.05) was performed for statistical analyses of the obtained data. RESULTS: Statistically significant differences were not found among the materials (F = 0.176, p = 0.656), while statistically significant differences were found amongst the veneering procedures (F = 57.921, p < 0.001). Statistical differences were observed between the groups (F = 13.766, p < 0.001). The highest shear bond strength values were observed in IPS e.max CAD specimens connected to zirconia with low fusion porcelain (27.11 ± 7.7 MPa), and the lowest values were observed in IPS e.max CAD specimens connected to zirconia with resin cement without surface treatment (9.82 ± 2.8 MPa). The application of fusion porcelain with IPS e.max CAD (p = 0.967) and Cerec Blocs (p = 1.00) showed statistically similar results to those with conventional layering. CONCLUSIONS: The application of fusion porcelain to bond zirconia and digitally produced veneering material can serve as an alternative veneering method to the conventional layering method by accelerating and facilitating clinical and laboratory stages.

Effect of selective infiltration etching on the bond strength between zirconia and resin luting agents.

OBJECTIVE: To evaluate the shear bond strength of resin cements to zirconia treated with the selective infiltration etching technique (SIE). MATERIALS AND METHODS: Forty-seven zirconia specimens were prepared with a sequence of silicon carbide abrasives, cleaned in an ultrasonic bath. Three samples were separated for atomic force microscope (AFM) analyses (one nontreated for control, one sandblasted, and one selective infiltration etched) and the remaining were randomly distributed in four groups, according to the combination of surface treatment and resin cement: group 1a (sandblasting + Variolink II), group 1b (sandblasting + Panavia SA Plus), group 2a (SIE + Variolink II), group 2b (SIE + Panavia SA Plus). A composite resin cylinder (3 mm × 3 mm) was cemented to the zirconia surface, as per each group's specific protocol. After storing 24 hours in distilled water at 37°C, the specimens were tested for shear bond strength and the results were subjected to statistical analysis. RESULTS: At 24 hours, the highest SBS values were observed in group 2b, where the SIE technique was used in conjunction with Panavia SA Plus. Lowest values were found in group 1a. Increased surface roughness was observed with SIE. CONCLUSIONS: SIE significantly enhanced the resin bond strength to zirconia. However, cement selection was also an important factor, for both surface treatments tested. CLINICAL SIGNIFICANCE: Use of SIE method combined with MDP monomer containing resin cement can provide clinically acceptable bond strength between zirconia and resin cement.

Cytotoxicity of long-term denture base materials.

INTRODUCTION: The aim of this study was to evaluate the cytotoxic effect of various denture base materials following four different aging periods. METHODS: In total, 48 disc-shaped specimens per each group were prepared: Group I: acrylic resin polymerized in cool water and heated up to 100°C over 45 min and boiled for 15 min; Group II: acrylic resin polymerized under pressure in 40°C-45°C water bath for 10 min; Group III: autopolymerized hard relining resin Cold Liner Rebase; Group IV: autopolymerized hard relining resin Truliner; Group V: soft relining resin DentuSil. Then the specimens were stored in water for 24 h or 15 days, or thermocycled 2500 times or 10,000 times. Cytotoxicity was evaluated with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using L929 cells after 72-h cell incubation. Cell viability percentages were counted and statistical analyses were performed. The results were also evaluated according to ISO standard 10993-5. RESULTS: All materials showed similar cell viability percentages following 24-h water storage and 2500 and 10,000 thermal cycles. Following 15-day water storage, a statistically significant difference was observed between the materials. Comparisons of the aging periods for each material showed statistically significant differences. Groups III and IV showed moderately cytotoxic effect following 15-day water storage. The remaining groups showed slightly cytotoxic or non-cytotoxic effect. DISCUSSION: Polymerizing acrylic resins under pressure can be an alternative to conventional polymerizing to ensure a faster denture repair while providing similar cell viability values. Heat-cured acrylic resins provide higher cell viability than hard chairside lining materials in a 15-day period.

Effects of Hot Chemical Etching and 10-Metacryloxydecyl Dihydrogen Phosphate (MDP) Monomer on the Bond Strength of Zirconia Ceramics to Resin-Based Cements.

PURPOSE: The purpose of this in vitro study was to evaluate the hot chemical etching method on the shear bond strength between zirconia and two resin cements. MATERIALS AND METHODS: Sixty zirconia specimens (13 × 7.5 × 2.5 mm3 ) were prepared and treated as follows: (1) airborne-particle abrasion with 50 µm Al2 O3 particles; (2) hot chemical etching for 10 minutes; (3) hot chemical etching for 30 minutes. Sixty composite cylinders of 3 mm diameter and height were prepared and bonded to zirconia specimens, which were divided into subgroups A and B. Group A: cemented with conventional resin cement (Variolink II); group B: cemented with 10-metacryloxydecyl dihydrogen phosphate (MDP) monomer containing resin cement (Panavia SA) after the application of surface treatments. Next, the specimens were stored in 37ºC distilled water for 24 hours. Following water storage, shear bond strength test was performed at a 1 mm/min crosshead speed in a universal testing machine. The statistical analyses were performed with one-way ANOVA and post hoc Tukey tests. p < 0.05 was considered statistically significant. RESULTS: The results from all of the tested groups exhibited lower shear bond strength values than group II-B and higher shear bond strength values than group I-A (p < 0.05). CONCLUSION: The use of the hot chemical etching method for 10 minutes increased the shear bond strength of zirconia ceramics to both conventional and resin cements and seems to be an effective method. The MDP monomer-containing resin cement, Panavia SA, improved the resin bonding of zirconia ceramics when combined with airborne-particle abrasion.