Journal of Dental School
Year:2012 | Volume:29 | Issue:4 (90)|Papers Count:11

Background & Aim: Ni-Ti alloys are widely used in orthodontics. The aim of this study was to evaluate & compare the load- deflection properties of Ni-Ti wires. Materials & Methods: In this experimental study, 65 Ni-Ti round wire (0.014 inch) from 13 different brands were subjected to a 3-bracket bending test at 37oC using an upper central bracket attached to rod in a manner the distance between the midpoint of brackets was 15.5mm. For each wire, the average force was determined at 1, 1.5, 2 & 2.5 deflections in unloading area. Then, SEM equipped with EDX system was used to asses element composition of each brand of wire.Results: The drawing graphs had the overall shape of superelastic graphs; however, the amount of force applied by different wires at different deflections were significantly different, so 13 wires was divided to 4 categories according to their force delivery: high force (orthoforce), moderate force (Proflex, ORG, Ortho technology, IMD, GAC & Force I), Low force (Smart, Nitanium, Nitinol SE, SE NITI, Rematitan Lite) & very low force (Imagination). Additionally it was revealed that wires belong to one manufactory doesn’t act similarly. The maximum & minimum Coefficient of Vriation belonged to Ortho Force & ORG, respectively. In element analysis, the ratio of Ni/Ti was not similar in different wire brands. It seemed likely that wires with higher Ti atomic percentage show lower load- deflection rate.Conclusion: It is revealed by this study that although studied wires almost showed superelastic graphs, the slope of the graph showed significant difference among the wires. So in this regard, the manufacturers’ propagations are not reliable completely. The general recommendation is application of caution & precision in wire selection and attention to study results, element analysis & amount of crowding.

Background and Aim: Non- Steroidal Anti Inflammatory (NSAIDs) medications used for treatment of pain related to orthodontic treatment could slow down tooth movements. Selective cyclooxigenase- 2 inhibitors are alternatives to conventional non steroidal drugs. The aim of this study was to compare three different doses of Celecoxib on orthodontic tooth movement and root resorption in Rats.Materials & Methods: Forty male Rats randomly divided in to the following groups; D (the application of orthodontic appliance with taking medications); E (without any intervention) and experimental groups included A (received 25 mg/kg), B (received 50 mg/kg) and C (received 100 mg/kg) dose of Celecoxib. NiTi coil spring was ligated between the right side maxillary incisor and 1st molar. The animals were sacrificed after two weeks and distance between 2 teeth was measured with Caliper. After preparation of histological sections, amount of root resorption, numbers and maximum depth of resorption lacunae in mesial root surfaces of molar was measured. Data were analyzed with ANOVA, LSD and Tukey HSD.Results: The maximum tooth movement was found in group A (0.8537 mm), D, C, B and E respectively. Statistical analysis did not show any significant difference between the different doses of Celecoxib drug in tooth movement. The usage of Celecoxib (particularly in higher doses; 100 mg/kg) decreased the number of resorption lacaunae in mesial root of first maxillary molar (P<0.05).Conclusion: 100 mg/kg dose of celecoxib was found to be optimum for the lowest effect on tooth movement and the most protection against root resorption.

Background and Aim: Over the last few years, concept of platform switching has gained popularity for reducing degree of crestal bone resorption. Many researchers believe that, this theory can be used for improving stress distribution in implant-bone interface. The purpose of this three dimensional Finite Element Analysis (FEA) was to study and compare stress distribution in implant-bone interface and implant-abutment interface of 3i implants (Biomet 3i, USA) in mandibular molar area.Materials & Methods: For this FEA, computed tomography (CT) images of an adult human mandible was used to make the three-dimensional model of posterior edentulous mandible. The implant systems which used was the 3i system consisted of 3i fixtures: 4 and 5 mm in diameter and 11.5 mm in length, and 3i Certain abutment 4.1 and 5mm (Biomet 3i, USA). This implant systems were assembled on the mandible model in 3 different designs: a platform-switched configuration; MODEL 4: 4-mm 3i fixture, 4.1-mm abutment; MODEL 5: 5-mm 3i fixture, 5-mm abutment; MODEL 6: 5-mm 3i fixture, 4.1-mm abutment, a platform-switched configuration. A linear static analysis was performed on the prepared 3D solid models with two different oblique load of 100 and 250 N in the lingobuccal direction with 15 degrees of inclination on the center of the abutment.Results: Regardless of the implant system used, maximum Von Mises stresses in cortical bone around implants were lower in platform switched models compared to matching diameter implant-abutment. This effect was not related to the usage of larger implant diameters in these models. However, Von Mises stresses in implant-abutment interface were the lowest in models with larger implant diameter. Conclusion: The platform switching technique reduces the stress concentration in the area of crestal bone-implant interface and shifted it to the area of implant-abutment interface. In the present study, this stress reduction was not.

Background and Aim: Intrapulpal posts are used as retention for reconstructing of missed crown. Today fiber posts eliminated most of disadvantages of metal posts. The purpose of this study is a comparison of stress distribution in these types of posts (casting and Quartz fiber post) on root canals of teeth with photo elastic method.Materials & Methods: In this experimental study Quartz fiber and casting posts with length of 15 mm and diameter of 0.9 mm were used. Four epoxy resin models (10×20×40 mm) were made that two of them include casting posts and two other include Quartz fiber posts. Then, cores were prepared for each model. Vertical force of 100N and oblique force with 30' and 150 N were applied on cores and isochromatic fringe patterns around post were recorded in the field of Polariscope. Results: In the vertical loads the minimum cervical stress was observed in casting post that was 1.22 (in Quartz fiber post it was 2.65) But in apical region maximum stress was recorded in casting post that was 1.63 (in Quartz fiber post it was 1.38). In the oblique load, casting post showed 1.39 stress in cervical that was the minimum (in Quartz fiber post it was 2.35) and in the apical region, casting post showed the maximum stress that was 1.68 (in Quarts fiber post it was 1) display more critical stress pattern (1.63).Conclusion: In the vertical and oblique loads casting posts shows the maximum stress in the apical region that makes the worse fracture in tooth that couldn’t be prepared but in Quartz fiber post maximum stress was in cervical region so it is more repairable.

Background and Aim: CPP-ACP is one of the numerous materials which is used in dental hypersensitivity and works through changing Cagradient in tooth surface, besides glass ionomer is a selective material in restoring non -carious cervical lesions because of chemical bonding. In this study we evaluate the effect of CPP-ACO on shear bond strength of glass ionomer to dentine. Materials & Methods: In this experimental study, 40 third molar teeth were sectioned to obtaine dentine with tubule orientation perpendicular to the surface. The specimens were divided into 4 groups (A to D). Groups A and B were treated with CPP-ACP paste for 60 min × 5 days. Groups A and C were treated with polyacrylic acid 10% for 20 min before glass ionomer adhesion. All specimens were bonded with glass ionomer. After 24±1 hours water storage, the bonded specimens were sectioned with universal testing machine.Results: There was no significant effect in shear bond strength to dentine in groups except groups B. There was no significant effect in failure pattern. Most of the failure patterns were adhesive mode.Conclusion: CPP-ACP application in dentine surface reduces the shear bond strength of glass ionomer except the preconditioning of dentine with polyacrylic acid 10%. Preconditioning in dentine surface nontreated with CPP-ACP paste, does not affect the shear bond strength of glass ionomer.

Background and Aim: Extensive caries restoration has always been considered as one of dental issues. To resolve this problem different methods have been suggested such as dentinal pins. Previous clinical studies revealed that the use of retentive pins, faces numerous risks (pulp exposure, dentin cracks, root perforations, etc). Introducing of bonding and composite systems, resulted in minimized mechanical retention for cavity preparation. Advantages of amalgam restorations such as simplicity of use, better mechanical properties, suitable clinical longevity and being less costly sustained its use in practice. On the other hand, caries removal usually results in a cavity form with small undercuts. So if we fill these small undercuts with “Bonding & Composite”, then insertion of pins in this base could be considered as a safe way for obtaining retention. The purpose of this study was comparing the retention of creative pin placement (using composite) to the retention of traditional method.Materials & Methods: In this experimental study thirty sound human mandibular molar teeth free from decay and restoration were selected. The occlusal surface of samples was removed up to 3 mm above CEJ. Teeth were divided in 2 groups: Group A: (N=15) T.M.S. Minim pin inserted in dentin at 2 mm depth.Group B: (N=15) One layer of composite (1 mm) bond to flat occlusal surface of teeth and then the pin was inserted in it at 2 mm depth so only 1mm of pin placed into dentin.Group C: (N=15) cylinders of composite were prepared (height=5 mm, dimension=8 mm) and pin was inserted in them at 2 mm depth. The retention of pins was determined under tensile force with Zwick universal testing machine and data was charted by Test Xpert. 10-11 program.Results: Data were analyzed by variance analysis (ANOVA) and L.S.D. test. The ANOVA showed: a statistically significant difference between all groups. (P£0.05) The L.S.D. test showed:- No significant difference between A and B. (p>0.05) - Significant difference between A, B and C (p<0.05).Conclusion: The highest tensile strength belonged to group A. there was no significant difference between group A & B. So by using this technique 1mm depth of pin in dentin can result as same retention as 2 mm depth. The lowest tensile strength belonged to group C.

Background & Aim: Tooth brushing along with a toothpaste is the most frequent and important method in managing a healthy oral hygiene. However, using such products also has its side-effects and shortcomings. Considering the large range of toothpastes available and the insufficiency of proper researches in this area in Iran, this study was designed to evaluate the abrasiveness of toothpaste for sensitive teeth and a whitening one with two similar Iranian brands.Materials & Methods: This was an invitro experimental study. Four groups of enamel samples consisting of each 6 specimens were prepared and embedded in acrylic blocks. The initial surface profile for each specimen was calculated using a profilometer. The samples undertook the wear phase in a V8 Cross Brushing machine using toothbrushes and a toothpaste solution. The samples were then dried and the surface profile was again calculated. The variation of the first and second profilometer calculations demonstrate the amount of wear for each specimen. Data was analyzed using the SPSS program by means of one way ANOVA and Repeated Measure ANOVA tests.Results: The amount of wear recorded for the 4 experimental groups was significantly different (p=0.039). However, the two by two comparison tests showed that the Iranian brands did not appear to have a significant difference with their foreign counterparts (p>0.05). The only difference was apparent between the two Iranian brand groups.Conclusion: According to the present study, it seems that there is no significant difference in the abrasive properties of the Iranian and foreign made toothpastes. However, similar researches considering different effects of toothpastes and especially in more clinical conditions and by utilizing different measurement methods appears to be necessary in Iran.

Background and Aim: One important function of leptin is the regulation of immune or inflammatory responses. Moreover, in a recent study no correlation between leptin and periodontal diseases was found. Therefore the aim of this study is to determine the correlation between leptin concentration and chronic periodontitis.Materials & Methods: In this analytical study, 20 healthy gingival tissue samples (control group) and 20 gingival tissues with advanced and moderate chronic periodontitis (case group) and 20 blood samples were taken from 20 patients. Patients were consisted of 55% females and 45% males with average age of 42. 25 yrs. Tissue samples were cultured for 72 hours. In the case of blood samples, the serum was immediately collected. Then ELISA was used for detecting of leptin and IL-6 in supernatant fluids of explant cultures and leptin in serum samples. Statistical analysis was made by Paired T-test and Wilcoxon signed Ranks test.Results: There was no leptin in gingival samples of both cases and control groups. The mean concentration of IL-6 in control and case groups was 81.08±36.72 and 90.35±29.71 pg/ml, respectively. Statistical analysis has shown no difference between case and control groups regarding IL-6 concentration.Conclusion: It is concluded that leptin does not have any role as an inflammatory protein in chronic periodontitis and regarding the absence of leptin in all of gingival samples, we could not consider gingiva as a possible source of leptin.

Background and Aim: Simulated patients are highly effective in the medical education and are potentially useful to present tobacco cessation counseling. Although, some studies have reported the advantages of this method in TCC, different aspects of it did not clarified yet. The present study assessed the effects of training by the standardized patients on the confidence and skills of dental students in Shahid Beheshti Medical Sciences University to provide TCC on 2010-2011. Materials & Methods: In this controlled non randomized trial, 28 students of semester 11 (controls) and 39 students of semester 12 (cases) were selected and their confidence and skills in providing TCC were determined using a questionnaire. Case students received training by means of standardized patients and TCC was presented according to WHO guidelines of 5A’s & 5R’s. Finally, confidence and TCC skills of the students were assessed using the same measures. The changes occurred in the confidence and TCC skills of both groups were statistically analyzed using student t and ANCOVA tests.Results: The mean skills scores of the case participants were 5.10 and 13.05 before and after training while the values were 5.14 and 5.25 for the controls. Furthermore, the mean confidence scores were 43.19 and 47.13 for the cases with the means of 43.75 and 43.32 for the control participants before and after the training. Significant differences were noted between two groups regarding the increased confidence (p<0.001) and skills scores (p<0.001) while ANCOVA test showed training via standardized patients significantly affected the final confidence and skills of the participants after adjustment for age, gender, marriage status and the primary confidence and skills (both: p<0.001).Conclusion: According to the results, TCC training via standardized patients improved the dental students’ confidence and skills as compared to the control participants.