Güngör Ma

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.

Preliminary evaluation of titanium tetrafluoride as an alternative ceramic etchant to hydrofluoric acid.

PURPOSE The etching of dental ceramics with a glassy matrix by means of hydrofluoric acid (HF) is highly effective and after the application of a silane coupling agent, a strong link between the adhesive and the ceramic is achieved. The purpose of this study was to investigate whether aqueous titanium tetrafluoride (TiF4) solution could be used as an alternative ceramic etchant or not. MATERIALS AND METHODS Seventy lithia-based all-ceramic specimens (IPS Empress 2, Ivoclar Vivadent) (diameter: 4 mm, height: 4 mm) were prepared and ultrasonically cleaned for 15 min in ethanol and deionized water, then divided into 1 control and 4 experimental groups (n = 14/group). The control group was acid etched with 4.9% HF for 20 s as described by the manufacturer. The experimental groups were treated with 2.5% TiF4 solution for 60 s, 2.5% TiF4 solution for 120 s and 5% TiF4 solution for 60 s, as well as 5% TiF4 solution for 120 s. Seven of the ceramic specimens in each group were luted to the other seven by a dual-curing cement (Variolink II, Ivoclar Vivadent,) with silane application (Monobond-S). After storage of luted specimens in deionized water at 37 degrees C for 24 h, the specimens were embedded in plastic holders with cyanoacrylate, and the shear-bond strength (SBS) tests were performed with a Shimadzu universal testing machine at a crosshead speed of 0.5 mm/min. A one-way ANOVA and Bonferroni correction, followed by the Tukey test, were applied for statistical analysis. Scanning electron microscopic examination was performed to evaluate the pattern of debonding. RESULTS Significantly higher SBS values (p <or= 0.05) were obtained for the control group (28.71 +/- 9.74). The SBS for 2.5%-60 s (25.25 +/- 5.13) and 2.5%-120 s TiF4 (22.65 +/- 5.68) were significantly higher than 5%-60 s (16.77 +/- 3.92) and 5%-120 s TiF4 (18.54 +/- 3.52) groups (p <or= 0.05). Differences between 60- and 120-s groups irrespective of TiF4 concentrations were insignificant (p > 0.05). CONCLUSION Aqueous TiF4 solution exhibited similar shear bond strength values in comparison to commonly used HF and can be considered as an alternative ceramic etchant within the limitations of this preliminary report.

Comparison of the mechanical properties of nitrogen ion implantation and micro-pulsed plasma nitriding techniques of Cr-Ni alloy

Abstract Cr–Ni alloys are frequently used in dentistry for economical reasons. While they gain popularity, an increase in systemic and local concerns of these dental metals is observed. With the progressions in surface technology, the surface characteristics of the metals can be changed. In this study, nitrogen ion (N ion) implantation and plasma nitriding techniques were used to change the properties of Cr–Ni alloy (Wirollay). Nitrogen implantation at dose 1×10 17 ion/cm 2 and micro-pulsed plasma nitriding techniques were applied to Cr–Ni alloy samples. After the process, the friction coefficient was decreased in ion implantation, but this ratio was increased in the plasma nitriding technique with respect to the substrate. The roughness did not change after N ion implantation but it increased after the plasma nitriding procedure. Wear volume of the implanted and plasma nitriding samples were lower than the substrate. Hardness values were increased four times for N ion implantation and eight times for the plasma nitriding technique.

Microshear Bond Strength and Finite Element Analysis of Resin Composite Adhesion to Press-on-Metal Ceramic for Repair Actions after Various Conditioning Methods

PURPOSE This study evaluated the repair bond strength of differently surface-conditioned press-on-metal ceramic to repair composites and determined the location of the accumulated stresses by finite element analysis. MATERIALS AND METHODS Press-on-metal ceramic disks (IPS InLine PoM, Ivoclar Vivadent) (N = 45, diameter: 3 mm, height: 2 mm) were randomly divided into 3 groups (n = 15 per group) and conditioned with one of the following methods: 9.5% hydrofluoric acid (HF) (Porcelain etch), tribochemical silica coating (TS) (CoJet), and an unconditioned group acted as the control (C). Each group was divided into three subgroups depending on the repair composite resins: a) Arabesk Top (V, a microhybrid; VOCO), b) Filtek Z250 (F, a hybrid;3M ESPE); c) Tetric EvoCeram (T, a nanohybrid; Ivoclar Vivadent) (n = 5 per subgroup). Repair composites disks (diameter: 1 mm, height: 1 mm) were photopolymerized on each ceramic block. Microshear bond strength (MSB) tests were performed (1 mm/min) and the obtained data were statistically analyzed using 2-way ANOVA and Tukeys post-hoc test (α = 0.05). Failure types were analyzed under SEM. Vickers indentation hardness, Youngs modulus, and finite element analysis (FEA) were performed complementary to MSB tests to determine stress accumulation areas. RESULTS MSB results were significantly affected by the surface conditioning methods (p = 0.0001), whereas the repair composite types did not show a significant effect (p = 0.108). The interaction terms between the repair composite and surface conditioning method were also statistically significant (p = 0.0001). The lowest MSB values (MPa ± SD) were obtained in the control group (V = 4 ± 0.8; F = 3.9 ± 0.7; T = 4.1 ± 0.7) (p < 0.05). While the group treated with T composite resulted in significantly lower MSB values for the HF group (T= 4.1 ± 0.8) compared to those of other composites (V = 8.1 ± 2.6; F = 7.6 ± 2.2) (p < 0.05), there were no significant differences when TS was used as a conditioning method (V = 5 ± 1.7; F = 4.7 ± 1; T = 6.2 ± 0.8) (p > 0.05). The control group presented exclusively adhesive failures. Cohesive failures in composite followed by mixed failure types were more common in HF and TS conditioned groups. Elasticity modulus of the composites were 22.9, 12.09, and 10.41 GPa for F, T, and V, respectively. Vickers hardness of the composites were 223, 232, and 375 HV for V, T, and F, respectively. Von Mises stresses in the FEA analysis for the V and T composites spread over a large area due to the low elastic modulus of the composite, whereas the F composite material accumulated more stresses at the bonded interface. CONCLUSION Press-on-metal ceramic could best be repaired using tribochemical silica coating followed by silanization, regardless of the repair composite type in combination with their corresponding adhesive resins, providing that no cohesive ceramic failure was observed.

Stress Analysis of Fiber-reinforced Maxillary Dentures Under Different Loadings

The aim of this study was to compare maxillary dentures having different reinforcing materials in terms of stress distribution under concentrated forces applied to anterior and posterior regions. For this purpose, stress analyses of finite element models of 3 mm thick maxillary denture-bone systems were performed by using ANSYS software. First, concentrated forces making various angles, such as 0°, 15°, 30°, 45°, 60°, 75°, and 90°, with horizontal axis were applied to the anterior incisor and the posterior molar tooth regions of a maxillary denture without reinforcement material. The results show that the highest stress in critical zones occur at 75° and 45° angles, under loadings of 150 N to molar and 75 N to incisor region, respectively. Secondly, four different reinforcing materials including unidirectional and woven glass fibers, unidirectional carbon fibers, and alloyed chrome—cobalt fibers were placed in the denture in two different positions. Under vertical loadings, the σx stress distributions occurring in critical zones were investigated. It is concluded from the stress analyses that use of Cr—Co as a reinforcing material at the center of the maxillary denture gives the best results in terms of stress distribution and strength.

Comparison of Stress Distributions of Dental Woven and Unidirectional Fiber-Reinforced Composite Crowns Under Different Loadings

The aim of this numerical study was to investigate and compare the stresses occurring in dental woven and unidirectional experimental fiber-reinforced composite (FRC) crowns under different thermal and singular force loading conditions. For this reason, finite element models of FRC crown and tooth systems were performed by using the ANSYS program. Stress analyses of the models were carried out under thermal loading conditions heated from 37 to 55°C, cooled from 37 to 5°C, and 450 N singular force loading conditions at different angles. The results indicated that high stresses occurred in both woven and unidirectional FRC crowns under horizontal loadings because of bending moment. Thermal stresses exhibited small values that did not cause any damage. It can also be concluded that since the stress component of σ z in the woven type FRC was smaller than that of unidirectional type FRC, use of the woven FRC might be beneficial in comparison with the unidirectional composite.