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Purpose: To compare effects of free-hand and mechanically applied uniform irradiation on tensile bond strength of 4- META/MMA-TBB resin to Er:YAG laser-irradiated dentin using an X-Y moving stage. Materials and Methods: Three different laser conditions were evaluated: 1.0 W, 100 mJ/pulse, 10 pps; 1.0 W, 50 mJ/pulse, 20 pps; 1.0 W, 33 mJ/pulse, 30 pps. Samples of bovine dentin were set on a moving stage and mechanically irradiated with an Er:YAG laser at a scanning speed of 1.0 mm/s or subjected to free-hand irradiation. The lased dentin surfaces were acid conditioned with 10% citric acid/3% ferric chloride for 15 s, rinsed, and dried. The surfaces were bonded to PMMA rods with 4-META/MMA-TBB resin, and mini-dumbbell-shaped bonded specimens were prepared. Tensile bond strength was measured and compared with the results for free-hand irradiated samples obtained under the same conditions in an earlier study. SEM observations of fractured surfaces after tensile bond testing were also performed. Results: A significant difference was found in tensile bond strength among the 3 laser settings in both free-hand and mechanically uniform irradiations. A comparison of free-hand laser irradiation and mechanically performed uniform laser irradiation revealed no significant difference under either laser condition (p > 0.05). SEM observation of the fractured surfaces showed no difference between the two irradiation methods under all laser conditions. Conclusion: No significant difference was found in tensile bond strength between free-hand and mechanically irradiated dentin. Significant differences were found, however, with changes in laser setting in both groups. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to measure the flexural strength and the elastic modulus of composite resin with and without reinforcing fibers and to evaluate the reinforcing effect of various fibers. Materials and Methods: A polyethylene fiber (Ribbond), a polyaramid fiber (Fibreflex), and three glass fibers (FibreKor, GlasSpan, Vectris) were used to reinforce composite resins. The flexural strength and elastic modulus of specimens in the three-point bending mode were measured using a universal testing machine at a cross-head speed of 1 mm/min after storage in water at 37°C for 24 hours. All tests were carried out in a water bath at 37°C. The data were analyzed using analysis of variance and the Sheffé test at P = 0.05. After testing, the fractured surface was evaluated using a scanning electron microscope at 50, 500, and 3,000 magnifications. Results: Yield flexural strengths of nonreinforced resins were 48 to 56 MPa, and those of reinforced resins were 56 to 134 MPa. Ultimate flexural strengths of nonreinforced specimens were 96 to 119 MPa, and those of reinforced ones were 203 to 386 MPa. Elastic modulus of nonreinforced resin was 6 to 9 GPa, and fiber reinforcing increased the value to 9 to 15 GPa, while it had no effect in Ribbond. Conclusion: Most of the fibers used in this study increased both yield and ultimate flexural strengths of composite resins, with the exception of the yield strength of Vectris. GlasSpan, Fibreflex, and FibreKor were effective in reinforcing elastic modulus, while Ribbond had no effect on it. Unidirectional glass fibers and polyaramid fiber were effective in reinforcing both flexural strength and elastic modulus of composite resin. [ABSTRACT FROM AUTHOR]

Purpose: This study evaluated the effect of acid conditioners on resin bonding to dentin following irradiation with an Er:YAG laser and investigated the characteristics of resin bonding to the laser-treated dentin. Materials and Methods: Extracted bovine teeth were cervically sectioned to expose a dentin surface. After polishing, the dentin was irradiated with an Er:YAG laser. Aqueous solutions of 10% citric acid (10-0) or 10% citric acid/3% ferric chloride (10-3) were then applied to the laser-treated surface as acid conditioners. After the acid treatment, a PMMA rod was bonded to the irradiated dentin using 4-META/MMA-TBB resin, and miniaturized dumbbell-shaped bonded specimens were prepared. These specimens were subjected to tensile testing, and fractured surfaces were observed with field-emission scanning electron microscopy (FE-SEM) to determine the mode of fracture. Additionally, the resin-dentin interfaces were observed under FE-SEM. Results: The tensile bond strength of acid-conditioned bonded specimens was lower than that of specimens not subjected to acid treatment (11.1 MPa) in the laser-irradiated group. No significant difference was observed between 10-0 and 10-3 treatments. 10-3 treatment yielded the highest bond strength (24.6 MPa) in the nonirradiated group, as opposed to only 7.7 MPa in the laser-treated group. Cohesive failure in the dentin was observed in almost all specimens in the irradiated group. Furthermore, a 10- to 30-µm-thick resin-penetrated layer was observed at the interface between the dentin and the resin. Conclusion: These results suggest that the effect of acid conditioners on resin bonding to dentin differs according to whether the dentin has been laser irradiated or not. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the effects of fatigue on the strength of materials used in all-ceramic crowns, the biaxial flexural strength of air-ceramic restorative materials was measured with precracked and laminated specimens after cyclic loading. Materials and Methods: Two types of all-ceramic systems were used to prepare specimens: a glass-infiltrated alumina core system (In-Ceram) and a leucite-reinforced feldspathic porcelain system IPS-Empress). Monolayer and laminated disks with a diameter of about 11.75 mm and a thickness of 1.20 ± 0.05 mm were prepared. The biaxial flexural strength of the specimens that were polished and/or created with a precrack was measured. Their strength was also measured following cyclic loading. A cyclic load that was 60% of the mean breaking load of the specimens (before cyclic loading) was applied to specimens for 105 cycles in 37°C water. Results: Although 20% to 30% of the polished specimen samples fractured during cyclic loading, the biaxial flexural strength of specimens that survived the cyclic loading was nearly the same as that of specimens not subjected to the cyclic loading. The strength of the alumina system decreased with the introduction of precracks, and nearly all specimens fractured during cyclic loading. The strength of the leucite system, however, did not decrease with the presence of precracks, and no fractures were observed on these specimens during cyclic loading. Conclusion: These results suggest that although the alumina system has high flexural strength, it is more sensitive to flaws and susceptible to fatigue fracture. The effect of fatigue on the leucite system appears to be low. [ABSTRACT FROM AUTHOR]