Journal of Islamic Dental Association of IRAN
Volume:25 Issue: 1, 2013

Bachground and Nowadays, with regard to the quantitative and qualitative development of dental esthetic services and qualitative advances made in tooth-colored restorations, there is a great rise of demands for use of composite resins. The aim of this study was to assess the efficiency of diamond and carbide burs on bond strength of a self-etch adhesive to dentin. In this in vitro experimental study sixty sound extracted human third molars were mounted in self cure acrylic resin. The teeth were randomly assigned to two groups (n=30 each). In the first group, the teeth were ground with high-speed medium grit diamond bur and in the second group the teeth were ground with high-speed carbide burs. A composite cylinder with a 3 mm diameter was bonded to each specimen with a self-etch adhesive system and the shear bond test was performed using a universal testing machine. The results were expressed in MPas and were subjected to and Tukey's test. The mean shear bond strength in diamond and carbide burs were 17.67 MPa (SD= ±4.41) and 14.51 MPa (SD= ±5.18), respectively. There was a significant difference in dentin bond strength between two groups. (P< 0.05). The use of different burs affect the shear bond strength of the self-etch adhesives to dentin. This adhesive performed significantly better when a diamond bur was used to prepared dentin surface.

Radioisotopes adhere to any surface in which they come in contact. Covering the sample surface with a suitable material prior to submersion and isolation of the material before counting make it possible to evaluate the penetrating radioisotopes within the interfacial area. The aim of this study was to determine a suitable material to cover implant and abutment in evaluation of microleakage in implant-abutment interface using radiotracers and gamma counter.

In this in vitro study, 46 samples were selected and divided into two groups. The first group consisted of implant samples covered with putty, nail polish and putty-super glue with 1mm distance from the interface. The second group included non-implant samples covered with putty, autopolymerizing acrylic resin, and nail polish. This group was used for evaluation of adherence levels of the radioisotopes. Microleakage test was performed with thallium-201 and gamma counting in three phases: 1) after removing samples from thallium solution, 2) after washout of samples, and 3) after removing covering materials. In order to compare penetration of radioisotopes within the samples analysis of co-variance was carried out.

There were statistically significant differences between three phases of gamma counting and between samples in different implant groups. Microleakage of implant-putty-glue was significantly less than that of implant-putty (217343.40± 86007.926). Similarly, implant-putty showed a significantly less microleakage than implant- nail polish. (313247.20±67933.031).

The best material among the ones considered in this study turned to be putty sealed by super glue. Contrarily, nail polish was not considered suitable due to increased microleakage.

Intraoral repair of fractured porcelain is an acceptable method to avoid replacement and therefore saving time and cost. The purpose of this study was to determine the in-vitro shear bond strengths of composite resin to feldspathic porcelain after different durations of sandblasting and to compare the effect of sandblasting with that of hydrofluoric acid (HF). In this in-vitro study, 40 porcelain disks were fabricated and randomly divided into 4 groups (n=10). Porcelain surface in group 1 was etched with 9.5% HF for 2 minutes. Groups 2, 3 and 4 were sandblasted with 50µm alumina particles for 5, 10 and 15 seconds, respectively. All specimens received the same silane agent, bonding agent and composite resin. The samples were subjected to 5000 thermal cycles and then underwent shear bond strength testing. The mean bond strength was analyzed with one-way ANOVA. The mode of failure was determined using stereomicroscope and scanning electron microscope. An additional porcelain sample was fabricated and prepared according to the aforementioned protocols in each group and its surface topography was observed by SEM. The mean bond strength was 15/28 (±3/64), 13/82(±4/03), 15/77(±3/94) and 16/54(±3/73) MPa in the 4 groups, respectively. There were no statistically significant differences among groups. The most common mode of failure was cohesive in porcelain. No statistically significant difference was found in SEM results of different durations of sandblasting. The shear bond strength was not significantly different after various durations of sandblasting treatment. The bond strength after sandblasting was similar to that of HF. SEM showed that HF acid etching and sandblasting patterns were different.

Erosion is a multi-factorial process that occurs during life and it happens by many external or internal factors. The current study aimed to evaluate the relation of swimming time and dental erosion among swimmers. In this descriptive-analytical study, 84women individuals were selected. The case group included 42 swimmers who swam more than 6 hours per week and the control group comprised of 42 swimmers who swam less than 6 hours. The information regarding dental erosions and other data was collected by questionnaires. The dental erosion evaluation was performed using Smith-Knight index. X2 was utilized for statistical comparisons. The P-value of less than 0.05 was considered statistically significant. Findings revealed that the dental erosion proportions was similar among two groups and there was no relation between swimming time and dental erosion among swimmers (p-value= 0/6, X2 = 0.26). There was no relation between swimming time and dental erosion among swimmers. Therefore, the role of swimming time on dental erosion was not proved. Corresponding Author: Dr. Bahramian A. , Assistant

During fixed orthodontic treatments the absolute number and percentage of salivary Streptococcus mutans increase. This will cause increase of enamel demineralization and dental caries. The purpose of present study is to evaluate the effect of fluoride-releasing elastomeric chains in the streptococcus mutans levels in saliva and bacterial plaque. In this randomized clinical trial sixty patients, who were under fixed-orthodontic appliance treatments were selected and randomly divided into two groups of 30 each. Conventional elastomeric chains were used in group 1. As for the second group fluoride-releasing elastomeric chains were utilized. Four samples of saliva collected on days 0, 7, 14 and 28, and two plaque samples were collected on the beginning and finishing days in both groups. The fluoride-releasing and conventional elastomeric chains were removed on day 28. All samples were then used for microbial culture to count the Streptococcus mutans colonies. The results were analyzed statistically with the repeated measures Analysis of Variance (ANOVA) and Student t-tests. The result of Streptococcus mutans (CFU) in saliva at each time point in the study showed no statistically significant difference between the two groups (p≥0.301). Comparison of the effect of elastomeric chains on the Streptococcus mutans colonization in dental plaque and elastomeric chains surface, also did not show any statistically significant difference between the two groups (p= 0.317and 0.803 respectively). There was no clinical evidence that fluoride-releasing elastomeric chains were effective in reducing the formation and colonization of Streptococcus mutans in saliva and dental plaque.

There is some evidence suggesting that dentists suffer a high level of occupational stress that can lead to burnout syndrome. The aim of this study was to evaluate the prevalence of burnout syndrome and its three dimensions in dental faculty members of Azad Dental University in 2008.

In this descriptive cross – sectional study, 99 dental faculty members of Azad Dental University in Tehran were evaluated using a questionnaire consisting of 10 questions regarding demographic characteristics and 22 questions adapted from Maslach Burnout Inventory (MBI). Burnout was assessed with MBI in three dimensions of emotional exhaustion, depersonalization and personal accomplishment. The final scores were categorized as high, moderate and low based on standard test scores. Data were analyzed using linear regression test with Enter method.

The prevalence of reduced personal accomplishment, depersonalization and emotional exhaustion was 19.1%, 7% and 4% among subjects, respectively. Work experience and weekly work hours did not have a significant association with occupational burnout (P>0.05).

The mean overall score gained by dental faculty members of Tehran Azad Dental University showed a low prevalence of occupational burnout in comparison to national statistics.

Severe mandibular deficiency may result in reduced oropharyngeal airway (OAW) dimensions and predispose patients to respiratory dysfunctions such as obstructive sleep apnea and snoring. The aim of this study was to assess the effects of functional treatment on anteroposterior and vertical dimensions of airway in skeletal class III patients with mandibular deficiency. This interventional study was done on lateral cephalogerams of 25 mandibular deficient patients with average 9.9 years of age who were treated with modified activator appliance. Digitized cephalograms were traced and analyzed by ViewBox version 3,1,1,3 cephalometric software. Paired t-test was performed to evaluate pre- and post-treatment data. Skeletal sagittal discrepancy was improved with decreasing ANB angle from 6.68 º to 4.48º and increasing SNB angle from 74.48 º to 76.78 º (p<0.001). Anterior–posterior dimensions of nasopharynx were increased from 19.64 to 21.52 mm (P=0/021), Anterior–posterior dimensions of oropharynx increased in AW2 and AW4 (p<0/05) but in AW3 increasing from11.26 to12.27 mm was not statistical significant(p=0.091). Anterior–posterior dimensions of hypopharynx increased from 16.54 to 19.22 mm (p<0/001). Vertical dimension of airway increased from 60.73 to 64.79 mm (p<0/05). Treatment of mandibular deficient patients with functional appliances improved mandibular position as well as airway dimensions.

In many studies reduction in bond strength of bleached enamel has been pointed out. The decrease in bond strength raised concern in cosmetic dentistry. However, there is little information about the effects of bleaching, on reduction of enamel bond strength in new bonding systems. This study aimed to investigate the effects of three dental bonding agents on shear bond strength of a composite to bleached enamel. In this in vitro study, sixty intact bovine mandibular incisors were collected and randomly divided into six groups (n=10). In group A, the facial enamel was etched with 35% phosphoric acid gel, then a single layer of bonding agent (SingleBond, 3M, ESPE) was applied and light-cured for 40 seconds by a light-curing device (ColtoluxII colten) with 400 mw/cm²light intensity according to the manufacturer’s instructions. In group B: after etching of enamel surfaces, Clearfil SE-Bond (Kuraray Medical Inc.) was used. In group C: after etching of enamel surface, Clearfil S3 Bond (Kuraray, Medical Inc.) was used. In groups D, E, and F 35% carbamide peroxide (Opalescence, Ultradent Products Inc.) was applied on the enamel surfaces for 5 hours according to the manufacturer’s recommendations. Afterwards the specimens were rinsed thoroughly with distilled water for 60 seconds and dried with compressed air. Immediately after bleaching, bonding regimes similar to groups A, B, and C were carried out in groups D, E, and F, respectively. Then, cylinders of hybrid composite were bonded to the facial enamel surface of all specimens, using 3 dental bonding agents. After 24 hours, the specimens were ther mo cycled (5–55°C, 1000cycles), and then subjected to shear bond testing by a universal machine Zwick (Zo20, Germany). The data were analyzed by one- and two-way ANOVA and post hoc tests. All statistical tests were performed with SPSS version 11. The mean shear bond strength of SingleBond to bleached and unbleached enamel was 8.36 ± 3.30 and 20.17 ± 6.52 MPa, respectively. For Clearfil SE bond, bleached enamel exhibited bond strengths of 12.25 ± 6.61Mpa and unbleached enamel exhibited a bond strength value of 17.66 ± 5.82 Mpa. The bond strength for Clearfil S3 bond was 6.66 ± 2.57 Mpa to bleached and10.40 ± 3.65Mpa to unbleached enamel. Shear bond strength of hybrid composite to bleached enamel in three experimental groups decreased but this reduction was not statistically significant for Clearfil SE bond.

some recent research have reported increased stability in mechanisms of adhesion to dentin in remove of collagen fiber of the dentin surface.The aim of this study was to evaluate the effect of sodium hypochlorite in microleakage of three step total etch dental adhesives with different solvents. this experimental study on 80 intact bovine incisor teeth, were prepared class V cavities on buccal surface of teeth, box shap and all walls on enamel. Then the specimens were randomly divided into eight groups (n=10). NaOCl+etching+ SBMP (waterbase), NaOCl+etching+ All Bond2 (Acetonebase), etching+ NaOCl+ SBMP, etching+ NaOCl+ All Bond2,, NaOCl+ SBMP, NaOCl+ All Bond2, etching+ SBMP, etching+ All Bond2. Then the cavities were restored using Z250 (3M) composite and Coltolux 75 light curing unit (350 mw/cm2). The specimens were thermo cycled for 1000 times on water baths of 5and 55oC. After thermocycling, the specimens were immersed in a 2 % aqueous solutions of basic fuchsin for 24 hours, then longitudinal section of each restoration was obtained and examined with a stereomicroscope for evaluation of micro leakage. The data were analyzed using kruskal-walis test and the mean of micro leakage of samples were compared by two- way ANOVA test. The findings showed that the higher rate of micro leakage was detected in hypo+Acid and lower rate of micro leakage was detected in Acid+hypo in different treatment method. The finding was different in hypo+Acid procedure, the higher rate of micro leakage was in SBMP. In hypo groups, the microleakage with ALL Bond 2 was higher than SBMP. In control groups, the microleakage with SBMP was higher than ALL Bond2. Application of Naocl before dentin etching for removal organic materials increase the rate of microleakage of All Bond2, SBMP to that of control group.

Dental stone type IV and V are predominantly used for construction of cast and die in fixed prosthodontics and must have some special properties. The aim of this study was to compare the three physical properties of an Iranian a German dental stone type IV. In this experimental study, setting time, setting expansion and compressive strength properties were evaluated according to ADA specification No.25for Iranian Tara and German Gildand type IV dental stone. For setting time, setting expansion and compressive strength tests, Vicat apparatus, extensometer and universal testing machine were used, respectively. Data were compared to ADA specification No.25 for dental stone type IV and statistically analyzed using t-test with a 0.05 level of significance. Mean of setting expansion for Iranian and German dental stone were 0.024±0.011 and 0.0245±0.009, respectively and were within the limits of ADA specification and there was no statistically significant difference between them (P=0.966). Mean of setting time for Iranian and German dental stone were 44.5±0.70 and 17.29±0.41 and mean of compressive strength for Iranian and German dental stone were 16.17±0.97 and 20.15±1.96 and both specifications were not within the limits of ADA specification, but statistically significant differences were found between groups (P<0.001). Iranian dental stone type IV could not fulfill 2 out of 3 tested ADA specification and modification of this stone is necessary for use in fixed prosthodontics laboratory processes

Use of glass fiber posts is of widespread acceptance in restoring root canal treated teeth, but studies concerning the most proper length of the post to provide the utmost fracture resistance are inadequate. The aim of this study was to evaluate the effect of glass fiber post length on fracture resistance of root canal treated central incisors. This experimental study was carried out on 40 maxillary central incisors in 4 groups of 10 each. RDT posts and cement was used in this experimental study with the lengths of 6, 8, 10, and 12 mm in the study groups. The samples were debrided and decoronated at the CEJ levels and endodontically treated using step-back technique. RDT drills were used for post space preparation. Then, the root canal walls were etched and the posts cemented in place. The composite cores were then prepared at the height of 5 mm and samples mounted 2mm down to their CEJ levels within acrylic blocks. An impression material (Impregum, 3M, ESPE) with a thickness of 0.2mm was used to simulate PDL around the samples. The samples were subjected to compressive forces at a 135-degree angle to their long axes using a Universal Testing Machine. Data pertaining to the fracture of the samples were analyzed using ANOVA and Tukey statistical tests. The maximum resistance to fracture was recorded in 8-and 10-mm-long posts and the minimum was observed in the lengths of 6 and 12 mm. Statistical tests showed a significant difference between 8- and 10-mm-long posts with those having lengths of 6 and 12 mm in terms of fracture resistance. There was no significant difference between 8- and 10-mm-long posts as well as 6- and 12-mm-long ones. It can be concluded that the length of post is influential in the fracture resistance of the root so that the maximal resistance can be obtained in 8 to 10 mm of length and such lengths can be recommended for non-metal posts.

External root resorption is not detectable clinically and radiography plays a key role in its diagnosis.The present study aimed at comparing the diagnostic efficacy of conventional anddigital radiography in detection of simulated root resorption cavities (In-vitro). This experimental observational study evaluated 39 extracted teeth. All roots, except for the palatal root of upper molars,were hypotheticallydividedinto apical and coronal sections.Half these sites were considered as the control group. Buccal cavities were randomly made in the remaining sectionsusing # 1/2,2 and 4 round burrs.Each tooth was imaged using a CCD-based digital system and E-speed film. Radiographs were taken at 0 and 20˚ mesial angulation. Six image groups were interpreted by two experienced oral and maxillofacial radiologists and one endodontist.Conventional and enhanced digital radiographs were also takenat 0 and 20˚ mesial angulation. Conventional radiographs were viewedat 2X magnification by a magnifying glass. Sensitivity, specificity,false positive and false negative percentages and accuracyof each method were compared with the gold standard. The degree of agreement among these techniques was measuredbykappa coefficient. Conventional radiography at 2X magnification had the highest sensitivity and specificity. No significant difference was found in sensitivity of digital radiography and enhanced digital radiography. Enhanced digital radiography ranked second in terms of specificity. Conventional radiography at 2X magnification followed by enhanced digital radiography had the highest diagnostic accuracy. Mesial angulation of the cone increasedsensitivity and decreased specificity in all three techniques and thus, it only improved the diagnostic accuracy of digital radiography with no significant effect on the other two techniques.The degree of agreement between the two digital techniques was higher (k=0.68). Diagnostic efficacy of conventional radiography at 2X magnification is more than digital radiographs for detection of external root resorption.