Effect of different irradiation patterns on shear bond strength of composite resin to enamel and dentin

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 micro leakage between the restoration and tooth, and will decrees 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: Group 1, HIP [High Intensity Program]. Group 2, LOP [Low Intensity Program]. Group 3, 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 ANOYA 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

[Evaluation of histopathologic changes in impacted third molar follicles in Mashhad dental school in 2005]

Since remaining impacted teeth may result in pathologic lesions, prophylactic extraction of third molar-which is the most frequent impaction-is among the most common surgical procedures. Our study was performed to evaluate the histopathoiogical changes of impacted molar teeth follicles. In this descriptive study, 54 impacted molar teeth follicles of 50 patients with age range of 15-38, and examined in the surgery ward of Mashhad dental school from June to November 2005, were extracted by a surgeon and pathologic evaluation were performed. In this study, the most commonly extracted teeth were mandibular molars [79%] and 74% of patients were under 25. The most frequent location of the extracted teeth was mesioangular [46%]. In microscopic evaluation of specimens, 61% were unchanged dental follicles, 12.9% were odontogenic cysts and 24% had inflammation. Considering the low incidence of pathologic changes in impacted third molar follicles, it is better not to extract them except in a clear indication. These teeth are better to be monitored by imaging with the 6-12 month intervals

[Evaluation and comparison of the effects of different irradiation patterns and new suggested light exposure pattern on microhardness of composite resin]

Overcoming the side effects of polymerization phenomenon has provoked many researches to find out the solution. Since a desirable polymerization of composite resin is effective in success rate of restorations with these materials, and as there is a direct relationship between light intensity and desirable polymerization or curing depth, therefore it is expected that a suitable exposure pattern to produce a desirable curing depth to could overcome the side effects of polymerization phenomenon. The aim of this study was to present a new light exposure pattern for composite curing and evaluation of its effect on microhardness and degree of polymerization of composite in respect to some other light exposure patterns. In an in vitro study, 4 groups of 5 brass cylinders were used and one bulky was filled with Tetric [registered]Ceram composite. Then samples in the first three groups were exposed 80 seconds to 3 types of Astralis 7[registered] light exposed patterns, including: HIP [High Intensity Program], LOP [Low Intensity Program] and PUL [Pulse Program]. The forth group was also exposed same time with SUP [Suggestive Progressive Polymerization] respectively. After sample preparation, they were analyzed with micro hardness tester in 6 different depths and dye penetration test was done for all samples and were evaluated by stereomicroscope. The data were analyzed statistically using One-way ANOVA and Duncan test through SPSS software. In absence of depth factor consideration, the mean micro hardness in all four groups of exposure patterns had no significant difference [p=0.362]. The HIP, LOP, PUL, SUP light exposure patterns produced significantly different micro hardness in 0-5 mm depth significantly [p=0.001]. In other words there was a significant difference in micro hardness in different depths in each testing group. In the same depths, there was no significant difference in composite microhardness between the 4 groups up to 4 mm depth, but at the depth of 5 mm in HIP group, micro hardness was significantly higher than the depth of 5 mm in the other group. The analyzes clarified that the suggestive light exposure pattern [sup] can control and guide the rate of polymerization along with having the same quality to the other light exposure patters in producing hardness up to the depth of 4 mm of composite restorations

Evaluation and comparison of effect of different irradiation patterns and new suggested light exposure pattern on microleakage of composite resin restorations

There is a significant relationship between polymerization rate and polymerization shrinkage stress in restoration. The more the polymerization rate is, the shorter viscoplastic phase of the composite would be, leaving no time for the composite to flow and consequently sudden hardening of the composite occurs. This leads into severe shrinkage stresses followed by composite detachment from cavity walls resulting in microleakage within restoration and tooth. The aim of this study was to suggest a new method of light exposure pattern for composite curing and evaluation of its effect on enamel and dentinal microleakage in respect to some other light exposure patterns. In this exprimental invitro study, flat tooth sections, 40 dentinal and 40 enamel samples were etched and Dentin Bonding Agent [DBA] [Excite] was applied according to the manufacturer's instruction. While placed on the samples, one bulk Tetric ceram A3 composite was inserted in to a 2x2 mm polyethylene cylindrical mould. Samples were divided into dentinal and enamel groups of ten and light cured with Astralis 7 light exposure patterns including HIP [High Intensity Program], LOP [Low Intensity Program], PUL [Pulse Program] and SUP [Suggested Progressive Program] for 80 seconds. After curing, thermocycling, dye penetration and medial sectioning, samples were observed under a scaled reflective microscope for microleakage measurement. The data were analysed statistically using One-Way and Two-Way ANOVA and Duncan test through SPSS software. There was a significant difference in microleakage between enamel samples. The microleakage rate was the highest in HIP group while no microleakage was detected in the other groups. The degree of microleakage in dentin samples was significantly less in SUP group than the others but there was no significant difference between the other groups. 1. The least dentinal microleakage occurred with application of suggested progressive program [SUP] compared to other testing groups. 2. Like LOP and PUL light exposure patterns, no enamel microleakage occurred with SUP application. 3. Enamel microleakage was detected in HIP group which had higher light intensity