Evaluating the effect of dentin surface pretreatment on the static contact angle of a drop of a bonding agent: an in vitro study

Introduction: The aim of this study was to investigate the effect of dentinal pretreatment on the static contact angle of a bonding agent as a measure of dentin surface wettability. Materials &Methods: Twenty mid-coronal dentin surfaces were prepared and randomly allocated to four groups (n=5) according to the priming solutions. All segments were etched with 35% phosphoric acid gel for 15 s, rinsed for 30 s and dried. Each group was rehydrated with 10 µL of distilled water, 0.2 % chlorhexidine, 70% ethanol and 5.25% Sodium Hypochlorite respectively and the excess solution was removed after 60 sec using an absorbent paper. Using a micro syringe, a droplet of the Adper Single Bond 2 was placed on each prepared surface. Then the profile and the static contact angle of the droplet were analyzed with a video-based optical contact angle measuring system. The statistical analysis was performed using One-way ANOVA and Dunnett’s t tests (p<0.05). Results: There was a statistically significant difference between the water and sodium hypochlorite groups which indicates the negative effect sodium hypochlorite may have on dentinal surface energy. (p=0.013). The differences between the water and ethanol groups (p=0.168) and between the water and chlorhexidine groups (p=0.665) were not significant. Conclusion: The use of 5.25% sodium hypochlorite as a priming solution in bonding procedure is not recommended. There is no improvement in dentinal surface wettability by using 70% ethanol or 0.2% chlorhexidine instead of water and the recommendation for use of any of the two should be based on other long-term or short-term effects they may have on the bonding procedure

The Effect of Different Polishing Methods and Composite Resin Thickness on Temperature Rise of Composite Restorative Materials

Background and Aim : Along with improvements in aesthetics and longevity of restorations, finishing and polishing, can produce potentially injurious temperature rise within the pulp chamber. The purpose of the current study was to find whether different polishing methods and thickness of composites have any effect on temperature rise of composite restorative materials .   Materials and Methods : Sixty composite resin specimens 9 mm in diameter were prepared and assigned to three experimental groups with three sample thicknesses (2, 3 and 4mm). Each group was divided into four subgroups randomly. Polishing in subgroups 1 and 2 (continuous and intermittent dry polishing) and subgroups 3 and 4 (continuous and intermittent wet polishing) was carried out with a slow speed contra-angle hand piece at a medium speed for 120 seconds in a roll on motion. Immediately after polishing, temperature was measured on the top and bottom surface of each sample using a laser thermometer. One and two way ANOVA, Duncan, and paired T-test was used to analyze the data .   Results: The mean temperature rise after polishing in different methods was significant continuous dry polishing produced the maximum temperature rise. In addition, increasing the thickness of composite resin up to 4mm did not significantly affect thermal transfer from the top surface to the base during polishing .   Conclusion : Copious use of water coolant during finishing and polishing procedures is considered a simple and effective method for pulpal protection. Increasing the thickness of composite resin does not have a significant role in compensating the heat generated during polishing procedure

Comparison of Stress Between Endodontists, Postgraduate and Undergraduate Students During Endodontic Therapy

Background and Aim : Endodontic therapy is considered as one of the most stressful dental treatments. This study was designed with the aim of comparing stress levels during different stages of endodontic treatment among endodontic professionals under- and post-graduate students .   Materials and Methods : In this ex-post facto investigation, three groups including professional endodontists (n=36), undergraduate (n=41) and postgraduate dental students (n=47) were involved by convenience sampling. A questionnaire including 48 items, with five-point scales (very few to very much), was prepared for this study based on interview. The questionnaire was filled out by participants in a self report method. Data were analyzed by multivariate analysis of variance and Scheffe’s post - hoc tests .   Results: The stress among undergraduate dental students in all fields were more than those of professionals and postgraduate dental students, except for the stress of local anesthetic injection with lidocaine. Stress levels of all three groups were significantly different in inferior alveolar block injections with lidocaine, with professionals having more stress than under- and post- graduate dental students. The most stressful aspect of endodontic treatment, among the three groups was canal obturation, followed by obturation of the molar canals, preparing molar access cavities in special conditions and taking the final radiographs. The suggested methods offered for occupational stress reduction, was experience and knowledge, adequate knowledge, concentration and self confidence, and trust to God, respectively .   Conclusion : The stress among under graduate dental students in all fields was more than professionals and post graduate dental students, except for the stress of local anesthetic injections with lidocaine

The Effect of Finishing and Polishing Time on Microleakage of Composite Restorations

Background and Aim : Composite resins require time to complete their polymerization. This process usually reaches its maximum rate after 24 hours. On the other hand, immediately after restoration, water sorption results in hygroscopic expansion of composite resins and the mentioned two factors usually reachequilibrium after a week. Considering the effect of mentioned processes on the microleakage of composite restorations, the purpose of the present study was to evaluate the effect of finishing and polishing time on the mean microleakage of composite restorations .   Materials and Methods : In this in-vitro experimental study, 60 sound human premolar teeth were selected. A standard Class V cavity was prepared measuring 1.5 mm in depth, 3 mm in width and 2 mm in length on the buccal surface of each tooth and incrementally restored with composite resin. Next, the teeth were randomly divided into 4 groups. The teeth in groups 1, 2, 3 and 4 were finished and polished immediately, 15 min, 24 h and one week after storage in distilled water at 37°C, respectively. Specimens in each group were subjected to 500 thermal cycles. The teeth were then coated with adhesive wax and nail varnish and immersed in 2% fuchsin solution for 24h. The specimens were washed and each sample was longitudinally sectioned in half by a diamond saw. Both halves were evaluated in terms of dye penetration under a stereomicroscope at 28X magnification. For each sample, the section with greater degree of microleakage was selected. Kruskal Wallis test and Mann Whitney U test were used for data analysis with a 99.1% confidence interval .   Results : The lowest mean microleakage was observed in the occlusal margin of group 3 teeth while the highest mean microleakage belonged to the occlusal and gingival margins of teeth in group 2. A significant difference was noted between the 4 groups in occlusal margin microleakage (P<0.009). However, no such difference was found in gingival margin .   Conclusion: This study showed that the finishing and polishing timewas effective on the mean microleakage in the enamel margin of composite restorations. The best time of finishing and polishing was 24h after the restoration. Time of finishing and polishing had no effect on microleakage in dentin margins of restorations