氧化锆和纳米金刚石比例对核树脂挠曲强度的影响

目的 探讨二氧化锆、纳米金刚石比例对核树脂挠曲强度的影响.方法 采用双酚A-甲基丙烯酸缩水甘油酯(Bis-GMA)和二甲基丙烯酸三甘醇酯(TEGDMA)为树脂基质, 钡玻璃粉(BG)为主填料, 选择不同比例的微米或纳米级二氧化锆,纳米金刚石作为功能填料, 采用原位聚合法生成光固化牙科核树脂,万能材料试验机测定其挠曲强度.结果 含60wt%钡玻璃粉、0.2wt%纳米金刚石的树脂中,加入纳米级或微米级的二氧化锆含量分别为2wt%、3.5wt%、5wt%,3.5wt%相应核树脂挠曲强度最高;含70wt%钡玻璃粉、0.1wt%纳米金刚石的树脂中,加入40 nm的二氧化锆含量为0wt%、2wt%、3.5wt%、5wt%,2wt%质量百分比相应核树脂挠曲强度最高.结论 适当比例填料的核树脂挠曲强度能达到相应的国家标准及ISO标准的规定,能满足临床需要.     

丙酮及甲基丙烯酸甲酯表面处理对基托树脂与软衬材料粘接效果的影响

目的 研究丙酮及甲基丙烯酸甲酯表面处理对基托树脂与软衬材料间微渗漏、粘接强度及基托树脂抗弯强度的影响.方法 制备30 mm×30 mm×2 mm树脂块36块,根据随机数字表随机均分为3组,每组12块,丙酮组:树脂块粘接面浸泡于丙酮溶液中30 s;甲基丙烯酸甲酯组:树脂块粘接面浸泡于甲基丙烯酸甲酯溶液中180 s;对照组:不进行表面处理.两树脂块间衬以2 mm软衬材料后粘接,冷热循环5000次,浸泡于131Ⅰ溶液中24h后计数γ射线,即微渗漏数.制备36块30 mm×10 mm ×7.5 mm树脂块,分组及表面处理同上.两树脂块间衬以3 mm软衬材料后粘接,冷热循环5000次后,测试拉伸强度,即粘接强度.制备18块65 mm× 10 mm×3.3 mm树脂块,分组及表面处理同上,涂布软衬材料粘接剂后测试抗弯强度.结果 丙酮组和甲基丙烯酸甲酯组的微渗漏数(520.0±562.2和493.5±447.9)均小于对照组(1369.5±590.2,P＜0.05);丙酮组和甲基丙烯酸甲酯组粘接强度[(1.5±0.4)和(1.4±0.5) MPa]均大于对照组[(0.9±0.2) MPa,P＜0.05];两实验组间微渗漏数和粘接强度差异均无统计学意义(P＞0.05);3组抗弯强度差异均无统计学意义(P＞0.05).结论 丙酮及甲基丙烯酸甲酯表面处理可减少软衬材料与基托树脂间微渗漏,增加两者间粘接强度,未导致基托树脂抗弯强度下降.     

Effect of 3-year water storage on the performance of one-step self-etch adhesives applied actively on dentine

Objectives

To evaluate the effect of the application method on the immediate and 3-year resin-dentine bond strength (μTBS) and nanoleakage (NL) for 3 one-step self-etch adhesives (Adper Prompt L-Pop; Clearfil S³ Bond and Xeno III).

Methods

The occlusal enamel of 42 human molars were removed to expose a flat dentine surface. The adhesives were applied under inactive or active application. After light-curing (600 mW/cm² for 10 s), composite buildups were constructed incrementally and sectioned to obtain bonded sticks (0.8 mm²) to be tested in tension immediately or after 3 years of water storage of water storage. For NL, 2 bonded sticks from each tooth at each time were coated with nail varnish, placed in silver nitrate and polished down with SiC paper. The μTBS data was submitted to a two-way repetead mesures ANOVA and Tukey's test for each adhesive (α = 0.05).

Results

The active application showed higher immediate and 3-year μTBS than the inactive application (p < 0.05). An increase in the silver nitrate deposition was seen for all conditions after 3 years; however this was more pronounced for all materials under inactive application (p < 0.05).

Conclusions

The active application improves the immediate bonding performance of the adhesive systems. Reductions of the bond strength were observed for all materials after 3 years, however reduced degradation rate was observed when the materials are applied actively in dentine.     

Effect of different light curing methods on mechanical and physical properties of resin-cements polymerized through ceramic discs

Objective

The aim of this study was to compare the polimerization ability of three different light-curing units (quartz tungsten halogen, light-emitting diodes and plasma arc) and their exposure modes (high-intensity and soft-start) by determination of microhardness, water sorption and solubility, and diametral tensile strength of 5 dual-curing resin cements.

Material and methods

A total of 720 disc-shaped samples (1 mm height and 5 mm diameter) were prepared from different dual-curing resin cements (Duolink, Nexus, Bifix-QM, Panavia F and RelyX Unicem). Photoactivation was performed by using quartz tungsten halogen (high-power and soft-up modes), light-emitting diode (standard and exponential modes) and plasma arc (normal and ramp-curing modes) curing units through ceramic discs. Then the samples (n=8/per group) were stored dry in the dark at 37ºC for 24 h. The Vickers hardness test was performed on the resin cement layer with a microhardness tester (Shimadzu HMV). For sorption and solubility tests; the samples were stored in a desiccator at 37ºC and weighed to a constant mass. The samples were weighed both before and after being immersed in deionized water for different periods of time (24 h and 7 days) and being desiccated. The diametral tensile strength of the samples was tested in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed statistically by nonparametric Kruskal Wallis and Mann-Whitney U tests at 5% significance level.

Results

Resin cement and light-curing unit had significant effects (p<0.05) on microhardness, diametral tensile strength, water solubility and sorption. However, no significant differences (p>0.05) were obtained with different modes of LCUs.

Conclusion

The study indicates that polymerization of resin cements with different light-curing units may result in various polymer structures, and consequently different mechanical and physical properties.     

The effect of thermal cycling on the bovine dentine shear bond strength of current adhesive systems

The aim of this study was to evaluate the effect of thermal cycling on shear bond strength to bovine dentine of four current adhesive systems. Forty bovine incisors were ground flat with #600-grit silicon carbide paper to obtain superficial coronal dentine surfaces. Three one-bottle (etch and rinse) adhesive systems (Single Bond, Bond 1, One Step), and one self-etching primer adhesive system (Clearfil Liner Bond 2V) were evaluated. Dentine was conditioned and bonded with the adhesive systems tested according to the manufacturers' instructions. A cylindrical teflon mould (3 x 4 mm) was placed over the bonded area (to eliminate the bonded surface) and filled with composite resin. For each adhesive system the filling composite used was from the same manufacturer. Ten specimens were prepared for each material and all specimens were conditioned at 37 degrees C for 24 h. Five specimens of each material (half of the specimens) were thermocycled at 5000 cycles (at 5, 37, 55 and 37 degrees C) with a dwell time of 15 s and bonds were stressed in shear at a rate of 0.5 mm min(-1) until failure. Data were analysed by one-way anova and Student-Newman-Keuls rank test (alpha=0.05). Statistical analysis revealed that thermal cycling significantly (P < 0.05) reduced the bond strengths of all adhesive systems. Bond strengths prior to thermocycling were not significantly different (P > 0.05), except for One Step which revealed the lowest bond strength, and varied from 22.5 +/- 3.34 to 10.98 +/-0.87 MPa. After thermal cycling, the bond strengths ranged from 9.35 +/- 1.13 to 6.06 +/- 1.77 MPa. Failures after testing and prior to thermal cycle were most commonly adhesive failures between the bonding resin and dentine associated with partial cohesive failures in the adhesive resin (type 2). Adhesive failures between bonding resin and dentin (type 1) after thermocycling were most commonly seen.     

The effect of disinfectants on the properties of dental gypsum: 1. Mechanical properties

PURPOSE: This study was conducted to evaluate the effect of selected disinfectants incorporated in the liquid of dental stones on material strength properties with the aim of developing a material with acceptable mechanical properties. MATERIALS AND METHODS: Two types of dental stone (types III and V) were mixed with aqueous solutions of 0.525% sodium hypochlorite, 0.1% and 10% povidone-iodine, and 2% glutaraldehyde, and with water as a control. The liquid/powder ratios recommended by the manufacturer were used. These materials were subjected to further modification by adding a mixture of 1.0% gum arabic and 0.132% calcium hydroxide to the hemihydrate powders before mixing with the disinfectant solutions at 2 different liquid/powder ratios for each. Both the regular and the modified materials were tested for compressive and diametral tensile strength after 1 hour and 1 week from the start of the mix. The structure of set materials was determined by scanning electron microscopy examination of fracture surfaces. RESULTS: The disinfectants often reduced the strength of both types of dental stone. However, using either 0.1% povidone-iodine or 0.525% sodium hypochlorite resulted in strength values comparable with that of the control. The addition of gum arabic and calcium hydroxide helped reduce the mixing liquid/powder ratios, improving the strength properties of the disinfected materials. CONCLUSIONS: Chemical disinfectants reduce the strength of dental gypsum when used as mixing water substitutes. Gum arabic and calcium hydroxide additives permit a lower liquid/powder ratio and can help offset this weakening.     

Bond strength of a new universal self-adhesive resin luting cement to dentin and enamel

The objective of this study was to assess the bonding performance of a new universal self-adhesive cement RelyX Unicem (RXU) to dentin and enamel compared to four currently used luting systems, using a shear bond strength test with and without thermocycling. Median bond strengths were determined after 24 h storage, and after thermocycling (6,000 cycles, 5–55°C) for RXU and compared to Syntac/Variolink II (SynC/V) as a standard for luting conventional ceramics, ED-Primer II/Panavia F2.0 (EDII/PF2), Prime&Bond NT/Dyract Cem Plus (PBNT/DyCP), and a glass ionomer cement, Ketac Cem (KetC), as a standard for luting high-strength ceramic and metal-based restorations. Data (n=10 per group) were statistically analyzed using the Mann–Whitney–Wilcoxon test at the 0.05 level of significance. The bond strength (MPa) of RXU to dentin (10.8) was not statistically different from those of SynC/V (15.1), EDII/PF2 (10.5) or PBNT/DyCP (10.1), and statistically higher than KetC (4.1). The bond strength of RXU to enamel (14.5) was significantly lower than those of SynC/V (32.8), EDII/PF2 (23.6), and PBNT/DyCP (17.8), but higher than KetC (6.1). After thermocycling, the bond strength of RXU to enamel significantly decreased, but was still significantly higher than that of KetC. RelyX Unicem may be considered an alternative to Ketac Cem for high-strength ceramic or metal-based restorations, and may be used for luting conventional ceramic crowns with little or no enamel left.     

SHEAR BOND STRENGTH OF ORTHODONTIC BRACKETS TO ENAMEL UNDER DIFFERENT SURFACE TREATMENT CONDITIONS

The purpose of the present study was to evaluate the shear bond strength to enamel and the adhesive remnant index (ARI) of both metallic and polycarbonate brackets bonded under different conditions. Ninety bovine permanent mandibular incisors were embedded in acrylic resin using PVC rings as molds and assigned to 6 groups (n=15). In Groups 1 (control) and 3, metallic and polycarbonate orthodontic brackets were, respectively, bonded to the enamel surfaces using Transbond XT composite according to the manufacturer''s recommendations. In Groups 2 and 4, both types of brackets were bonded to enamel with Transbond XT composite, but XT primer was replaced by the OrthoPrimer agent. In Groups 5 and 6, the polycarbonate bracket bases were sandblasted with 50-μm aluminum-oxide particle stream and bonded to the enamel surfaces prepared under the same conditions described in Groups 3 and 4, respectively. After bonding, the specimens were stored in distilled water at 37°C for 24 hours and then submitted to shear bond strength test at a crosshead speed of 0.5 mm/min. The results (MPa) showed no statistically significant difference between Groups 4 and 6 (p>0.05). Likewise, no statistically significant differences (p>0.05) were found among Groups 1, 2, and 5, although their results were significantly lower than those of Groups 4 and 6 (p<0.05). Group 3 had statistically significant lower bond strength than Groups 2, 4, and 6, but no statistically significant differences were found on comparison to Groups 1 and 5. A larger number of fractures at the bracket/composite interface were evidenced by the ARI scores. OrthoPrimer bonding agent yielded higher bond strength in the groups using either conventional or sandblasted polycarbonate brackets, which was not observed in the groups using metallic brackets.     

An In Vitro Investigation of a Comparison of Bond Strengths of Composite to Etched and Air-Abraded Human Enamel Surfaces

PURPOSE: The purposes of the study were to measure the tensile bond strength of composite resin to human enamel specimens that had been either etched or air-abraded, and to compare the quality of the marginal seal, through the assessment of microleakage, of composite resin to human enamel specimens that had been either etched or air-abraded. MATERIALS AND METHODS: Thirty mandibular molar teeth were decoronated and sectioned mesio-distally to produce six groups, each containing ten specimens that were embedded in acrylic resin using a jig. In each of the four treatment groups, the specimen surfaces were treated by either abrasion with 27 or 50 microm alumina at 4 mm or 20 mm distance, and a composite resin was bonded to the treated surfaces in a standardized manner. In the two control groups the specimens were treated with 15 seconds exposure to 36% phosphoric acid gel and then similarly treated before being stored in sterile water for 1 week. All specimens were then subjected to tensile bond strength testing at either 1 or 5 mm/min crosshead speed. For the microleakage study, the degree of dye penetration was measured 32 times for each treatment group, using a neutral methylene blue dye at the interface between composite and either 27 or 50 microm air-abraded tooth structure or etched enamel surfaces. RESULTS: The mean bond strength values recorded for Group 1 (phosphoric acid etch, 5 mm/min crosshead speed) was 25.4 MPa; Group 2 (phosphoric acid etch, 1 mm/min), 22.2 MPa; Group 3 (27 microm alumina at 4 mm distance), 16.8 MPa; Group 4 (50 microm alumina at 4 mm distance), 16.9 MPa; Group 5 (27 microm alumina at 20 mm distance), 4.2 MPa; and for Group 6 (50 microm alumina at 20 mm distance) 3.4 MPa. An analysis of variance (ANOVA) demonstrated significant differences among the groups, and a multiple comparison test (Tukey) demonstrated that conventionally etched specimens had a greater bond strength than air-abraded specimen groups. No significant difference in dye penetration could be demonstrated among the groups (p= 0.58). CONCLUSIONS: Composite resin applied to enamel surfaces prepared using an acid etch procedure exhibited higher bond strengths than those prepared with air abrasion technology. The abrasion particle size did not affect the bond strength produced, but the latter was adversely affected by the distance of the air abrasion nozzle from the enamel surface. The crosshead speed of the bond testing apparatus had no effect on the bond strengths recorded. The marginal seal of composite to prepared enamel was unaffected by the method of enamel preparation.     

Tensile bond strength of light-cured resin-reinforced glass ionomer cement with delayed light exposure

In the clinical situations, the time intervals between material mixing and light exposure during bracket bonding, using light-cured resin-reinforced glass ionomer cement (LCGIC), may vary for each individual bracket. This study determined the tensile bond strengths of LCGIC subjected to various time intervals, and evaluated the durability with thermocycling. Comparisons were made between LCGIC and light-cured composite resin (LCR). Two hundred and forty bovine teeth were chosen as specimens. Light exposure was performed 5, 10, 20, and 40 min after the commencement of powder/liquid mixing. The durability was evaluated by thermocycling for 2000 times at temperatures between 5°C and 55°C, with a 30-s dwell time. Tensile bond strengths of LCGIC and LCR after 5 min, representing the general condition in clinical use, equaled 5.7 ± 1.5 MPa and 5.1 ± 2.6 MPa, respectively. For the LCGIC groups, no significant differences were seen between bond strengths with and without thermocycling. Also, no significant differences were noted among any time intervals. For the LCR groups, there were also no significant differences with and without thermocycling. The tensile bond strength of LCR showed highly significant differences within groups across time. Compared with LCR, the failure sites for brackets bonded with LCGIC appeared to be predominantly at the bracket/adhesive interface. The standard deviations of LCR were high when compared with those of LCGIC. The bond strength of LCGIC with or without thermocycling surpassed the clinically required minimum. LCGIC may be an advantageous alternative to LCR for orthodontic bracket bonding. Received: October 3, 2000 / Accepted: June 19, 2001