جستجوی مقالات مرتبط با کلیدواژه « استحکام پیوند برشی » در نشریات گروه « پزشکی »

In most shear bond strength (SBS) studies, different cross head speeds have been used.The effect of different speeds on the shear bond strength has been studied in very limited researches.The aim of this study was to evaluate the influence of changing cross head speed of testing machine on the shear bond strength and failure mode of orthodontic adhesive (Transbond XT) in bracket bonding. For this experimental study, 175 human premolars with intact enamels were divided into seven equal groups of 25. After surface preparation, brackets were bonded to teeth using transbond XT adhesive. For debonding process various cross head speeds of 0.5, 1, 2.5, 5, 7.5, 10, 25 mm/min were applied. Shear bond strength and Adhesive Remnant Index (ARI) were recorded for different groups. One way ANOVA and Tukey tests were used for bond strength comparison. Data on shear bond strength evaluations and modes of bond failure were analyzed using Kruskal- wallis and spearman tests.The means of shear bond strength for the applied 0.5, 1, 2.5, 5, 7.5, 10 and 25 mm/min cross- head speeds were 16.39, 14.37, 13.30, 14.12, 13.32, 16.58, and 13.83 respectively. Shear bond strengths in groups receiving 0.5, 10 mm/min cross head speeds, were significantly greater than other groups. No significant differences were obtained between these two speeds, as well as, between 1, 2.5, 5, 7.5, 25 mm/min speeds, but there were significant differences in the shear bond strengths between the two groups with the cross head speeds of 0.5, 10, and 1, 2.5, 5, 7.5, 25 mm/min. Considering the ARI, no differences were found between the groups. Also, there was no relation between ARI and bond strength in groups with different cross head speeds, except in 5mm/min. Cross head speed of Instron is an effective factor on the SBS of the adhesives, but it does not have significant effect on the failure mode of bonding materials.

With more polymerization rate there would be less time for the composite to flow and consequently sudden hardening occurs. This leads into composite detachment from cavity walls resulting in microleakage between the restoration and tooth, and will decreas the bond strength.The aim of this study was to investigate the shear bond strengths of the enamel and dentin-resin composite using Suggested Progressive program (SUP) and some other light exposure patterns.In this experimental in vitro study, the test groups were composed of 40 dentinal and 40 enamel samples prepared on facial surfaces of 80 human canine teeth. 2x2mm polyethylen cylandric molds were filled in bulk with Tetric Ceram composite and were placed on the prepared surfaces. Irradiation patterns for 4 groups of 10 dentinal and 10 enamel samples were as follows: Group1, HIP (High Intensity Program). Group 2, LOP (Low Intensity Program). Group3, PUL (Pulse Program) of Astralis 7 light curing unit exposure patterns, and Group 4, SUP (Suggested Progressive Program). After curing and 24 hours incubation in 37°c, the samples were thermocycled under 500 cycles (5-55°c), and mounted with acrylic resin. Shear bond strengths of all samples were obtained using the Instron testing machine with 0.5 mm/min crosshead speed. For statistical analysis, one way and two way ANOVA and Duncan testes were used by SPSS software. There was no significant difference between the shear bond strengths of four light exposure patterns in dentinal and enamel groups (p<0.001). It was also revealed that various light exposure patterns had no significant effect on shear bond strength of composite to enamel and dentin (p=0.388).SUP light exposure pattern has the same capability of producing appropriate bond strength with the tooth structures as other light exposure patterns.

Statement of problem: For reducing light exposure time of tooth-colored restorations, and chair time reduction, different experiments have been conducted. The purpose of this study was to determine the effect of different light exposure times to adhesive layers (Excite and Prompt L-pop) on the shear bond strength of dentin- composite interface. In this in-vitro study, 72 human intact premolar teeth were mounted in acrylic casts and enamel buccal surfaces were removed. The bonding surfaces were equalized using a surface index. Teeth were divided into six equal groups each of 12 (A, B, C, D, E, and F). According to the manufacturer instructions, Excite adhesive in groups A, B and C, and prompt L-pop in groups D, E and F was used. A and D groups were not exposed to light, but the exposure time in groups B, E and C, F was 20s, and 40s respectively. After one week of storage in 37°C water, synergy composite resin was applied and then was exposed to light. The specimens were loaded by shear force with 1 mm/min cross head speed. Data were analyzed by two-way analysis of variance (ANOVA). The means shear bond strength of groups A,B,C,D,E, and F were 3.9, 13.45, 18.1, 8.3, 24.81, 24.99 Mpa, respectively. The differences between shear bond strength of groups A, B and C and between groups B, D were statistically significant (p=0.0001). However, the differences between groups E, F were not statistically significant. In all exposure times, the bond strength of Prompt L-pop was significantly higher than that of Excite. According to the results of this study, increase in the light exposure led to the higher bond strengths in Excite groups. In Prompt L-pop groups, 20s exposure time was adequate and by increasing the light exposure time, shear bond strength was not affected. Without light exposure in both materials, the least bond strength for the composite resins was not attainable.