مهدی عابد کهنموئی

Despite acceptable bond strength of self-etch adhesive resins to dentin, some concerns remain regarding their bonding effectiveness to enamel. The purpose of this study was to evaluate the effect of doubling application time of all-in-one adhesive resins on shear bond strength of composite resin to bovine enamel. Subsequent to removing the roots and mounting 176 intact bovine incisors in acrylic resin, the facial enamel surface was abraded with silicon carbide papers. The samples were randomly divided into 8 groups of 22. In groups 1-4, four types of all-in-one adhesive resins, including Clearfil S3 Bond, G Bond, Absolute 2 and Opti Bond All-In-One were respectively used according to the suggested time by the manufacturer. In groups 5-8, the same adhesive resins were used for twice as much time recommended by the manufacturer. Then the composite of each adhesive was placed in the plastic mold and cured. Subsequent to thermocycling, the shear bond strength test was carried out and the data were analyzed. The highest bond strength value was related to Opti Bond All-In-One and the lowest value was related to Absolute 2. The adhesive resin type and time showed a statistically significant influence on bond strength (P<0.0005). Moreover, there were statistically significant differences among different adhesive resins (P<0.0005). Furthermore, the interaction between the adhesive resin type and time was statistically significant (P<0.0005). Doubling the application time resulted in a significant increase in bond strength only in two adhesive resins, Clearfil S3 Bond and G Bond (P<0.0005). The adhesive resin type was effective in bond strength to enamel and doubling the application time of Clearfil S3 Bond and G Bond adhesive resins resulted in a considerable increase in bond strength to enamel.

Today application of cavity disinfectants such as chlorhexidine after cavity preparation and before placement of restorative material has gained wide acceptance. However، some researchers believe that these materials interfere with function of adhesive resins. The aim of the present study was to evaluate the effect of chlorhexidine on microleakage of gingival margin of composite class V cavities restored with one-step self-etch (seventh-generation) adhesive resin in bovine tooth in vitro. In buccal surfaces of 60 sound bovine permanent incisors، class V cavities were prepared with occlusal margins at the enamel and gingival margins in dentin. The teeth were randomly divided into two groups of 30. In group 1، the samples were restored without chlorhexidine while group 2 specimens were restored using chlorhexidine. In order to restore the teeth، in both groups one-step self-etch adhesive resin (Clearfil tri S Bond) and Z100 composite (using incremental technique) were used. After finishing and polishing، the samples were subjected to thermocycling. Thereafter، they were immersed in 2% basic Fushin solution for 24 hours. Following sectioning، the microleakage of gingival margin of the samples was evaluated under stereomicroscope. There was no statistically significant difference in microleakage between the two groups (P=0. 91). The use of chlorhexidine as a cavity disinfectant had no effect on microleakage of gingival margin in composite class V cavities restored with one-step self-etch adhesive resin.

Incomplete polymerization of resin cement leads to a decrease in its physical properties increases its water sorption, solubility and pulpal irritation. Measurement of surface hardness is one of the methods for assessment the degree of polymerization. The aim in this study was to evaluate the effect of two photo-curing units with two curing times on the microhardness of two resin cements. In this labrotory study total numbers of 80 porcelain disks were made. After etching with HF (hydrofluoric acid) and using silane and bonding agent, samples were divided randomly into 8 groups (n=10). Dual-cured and light-cured cements were used in groups 1-4 and 5-8, respectively. In prepared samples from each type of cement, 20 samples were irradiated using QTH (Quartz Tungsten Halogen), (10 samples were cured for 30 seconds; groups 1 and 5 and 10 samples were cured for 60 seconds; groups 2 and 6). The remaining 20 samples were cured using LED (light-emitting diode) in the same manner (groups 3 and 7) and (groups 4 and 8), respectively. Microhardness of the cements was measured. In order to compare the microhardness in study groups, three-factor ANOVA was used. There were statistically significant differences in microhardness mean values depending on the time, the type of cement and the curing unit (P<0.0005). Microhardness of the cements increased with an increase in curing time with two light-curing units. The use of LED resulted in an increased microhardness in two cements. Regardless of the time and the type of the light-curing unit, microhardness of the dual-cured cement was higher than that of the light-cured cement.

Statement of Problem: There is a probability of interaction between impression materials especially Polyether with the external surface of the adhesive layer of the immediately sealed dentin in the presence of oxygen inhibited layer. The aim of the present study was to evaluate the effect of three different surface cleaning methods on the shear bond strength of porcelain to the immediately sealed dentin.Methods and Material: In this in-vitro study, the facial surfaces of 60 extracted premolars were immediately sealed, using single-bond adhesive. Then, the immediately sealed dentin surfaces were buried in the polyether impression material while setting. After the impression materials were removed, the samples were randomly divided into 4 groups. In group 1, porcelain samples were bonded to the teeth surfaces using resin cement without any surface cleaning. In groups 2, 3 and 4, surface cleaning using acid etche, air abrasion and pumice with rubber cup prophylaxis were applied respectively for each group before bonding the porcelain samples. Shear bond strength test was performed at the strain rate of 0.5 mm/min. The data were analyzed using One-way ANOVA and Tukey post-hoc tests. There were significant differences between the shear bond strength of the control group and the three surface cleaning method groups (p <0.001). The mean of the shear bond strength in the acid etch group was greater than that of the two other experimental groups; however, there were no significant differences between the three surface cleaning methods (p = 0.5). Surface cleaning of immediately sealed dentin using acid etche, air abrasion and prophylaxis, after impression with polyether, significantly improves the strength of the bond.

One of the disadvantages of dental composites is polymerization shrinkage and subsequent microleakage. Since the use of a thin layer of flowable composite under composite restorations is one of the methods in improving marginal seal and microleakage reduction, the aim of the present study was to evaluate the effect of flowable composite liner on the microleakage of gingival margin of class V cavities restored with a seventh-generation (all-in-one) adhesive resin. In buccal surfaces of 30 sound human premolars (with closed apex and extracted for orthodontic reason) class V cavities were prepared and their gingival margins were located 1 mm below CEJ. The teeth were randomly divided into two groups. In group 1, the samples were restored without flowable composite liner while group 2 specimens were restored using flowable composite liner. In order to restore the teeth, in both groups all-in-one adhesive resin and Z100 composite (using incremental technique) were used. Following finishing and polishing, the samples were subjected to thermocycling. Then they were immersed in 2% basic Fushin solution for 24 hours. Following sectionings the microleakage of gingival margin of the samples was evaluated under stereomicroscope. Non-parametric Mann-Whitney U test was used to compare the gingival microleakage of two groups. There were statistically significant differences in microleakage scores between two groups (P<0.0005). The use of flowable composite liner in composite class V cavities restored with an all-in-one adhesive resin significantly reduced the microleakage of gingival margin.

Carbon fiber posts are widely used in dentistry. The most problem is their low bond strength with composite resin utilized as core. The aim of this study was to evaluate the effect of different surface treatments on the tensile bond strength of composite resin core to carbon fiber posts. Methods & Materials: Thirty six posts free of defects, were selected and randomly divided into 4 groups and treated as follows: Group1: No treatment (control). Group2: Surface treatment with Single Bond Group3: Surface treatment with Sandblast + Single Bond Group4: Surface treatment with Sandblast + Silane + Single Bond. A cylindrical composite resin core (5×5×5 mm) was built around each post using Z100. Post-core assemblies were tested for tensile failure by Instron testing machine at a cross-head speed of 10 mm/min. The bond strength was assessed by Newton (N). The tensile bond strength were respectively, Group 1: 262.33± 23.37N, Group 2: 522.77± 37.33N, Group 3: 613.50± 39.93N, Group 4: 641.00± 43.35N. ANOVA and Scheffe test showed that group 1was the least retentive group of all (p<0.05), and group 3 and group 4 were significantly more retentive than group 2 (p<0.05).There was no significant difference between group 3 and group 4. The surface treatment of carbon fiber posts significantly improved their retention to composite resin.