مجله تحقیق در علوم دندانپزشکی
سال ششم شماره 4 (پیاپی 22، زمستان 1388)

Elastomeric ligatures are used to secure archwires into orthodontic brackets, but color changing and deformation and at last torn of them is the most current problem. Due to the lack of knowledge about effect of mouth rinse on the mechanical properties of ligatures, goal of this study was to compare the effect of Oral-B and Orthokin mouth rinse on Ultimate Tensile Strength (UTS) of elastomeric ligatures in 2009.

This experimental laboratory-based study was carried out on 100 transparent elastomeric ligatures of Dentaurom Company. After division of ligatures in three groups of Oral-B, Orthokin and artificial saliva, Ultimate Tensile Strength of 10 ligatures from each group were measured after 1, 7 and 28 days and also ten ligatures in as received condition using H & P Testing Machine with 5 mm/min cross head speed. Data were subjected to ANOVA and lSD test.

Results showed no significant difference in UTS between Three times in artificial saliva group. UTS in Oral-B and Orthokin group was the least after 28 days, also UTS in three groups after 1, 7, 28 days compared to as received condition has a significant decrease.

UTS of elastomeric ligatures decreased after using in different conditions and has a significant decrease in all groups. Thus there is no different between using Oral-B and Orthokin, and it is recommended that all ligatures should be replaced at each visit to reduce risk of tearing.

For each and every graduate student the process of composing a thesis is the center part of training and education in research methodology. The content of such material becomes important when the research study turns into a manuscript which is submitted for publication in a journal of medical sciences. Deficiencies and drawbacks in terms of research methodology in student theses still remains a controversial issue. Due to lack of sufficient information concerning the accuracy of research methodology in student theses, the purpose of this study was to evaluate the accuracy of research methodology in "materials and methods" part of student theses and associated factors. The research was conducted on student theses in Islamic Azad University, Dental Branch in 2007-2008.

All presented theses from 09/23/2007 to 09/21/2008 in Islamic Azad University, Dental Branch were evaluated in this descriptive study. The materials and methods aspect of the theses were assessed for accuracy based on 15 variables and classified into 3 categories (correct, relatively correct and incorrect). Information regarding associated factors including student specifications, related department and head researcher… were collected and entered into a data sheet. Each thesis was assessed for accuracy as follows: "correct: if more than 75% of variables were correct"; "relatively correct: if 50-75% of variables were correct"; "incorrect: if less than 50% of variables were correct". The role of associated factors was determined using chi-square statistical test.

137 student theses were evaluated. The rate of inaccuracy in research methodology of materials and methods was found to be 30.6%. Not reporting the reliability of the instrument measurement was seen in 79% of the cases. 71% of the authors failed to justify the sample size and 25% used incorrect statistical tests for data analysis.

This study indicated that there are significant deficiencies in methods and materials section of student written theses which requires proper steps to be taken to reduce the level of inaccuracies in research methodology. This will not only improve the validity of the research itself but will also prevent erroneous results from being presented to the public.

Using fiber reinforced composites in recent years is expanding and different methods in preparation and framework design have been developed. The aim of this literature is to study a special method for using prefabricated fiber reinforced posts, in designing posterior FRC-IFPDs’ frameworks. Also invitro fracture resistance of this framework is compared with two different traditional intercoronal inlay bridge designs, all of them have been directly fabricated. This study was done experimentally. 60 freshly extracted, intact human mandibular teeth were used to make three groups (ten each)of three-unit posterior inlay bridges, for mandibular second premolar replacement. Group A was prepared using FRC fibers and box-shaped preparation, group B with FRC fibers and tub-shaped preparation, and group C, which is newly designed, with prefabricated FRC posts and groove-preparation. After covering with artificial PDL, the abutment teeth were embedded in PMMA resin 7 mm apart, using a surveyor instrument, and the FRC bridges which replaced second premolars were directly fabricated. Then samples were loaded into initial failure at a crosshead speed of 1 mm/min in a Universal Testing Machine (Instron 1195),and forcing graphs and fracture sites were recorded. Mean fracture resistance in groups A,B and C, were reported as 512 ±101 (N), 548.2±155 (N) and 584±136 (N) respectively. Using Kruskal-Wallis and Bonferroni-Dunn’s multiple comparisons post hoc statistical tests, no significant difference among 3 groups were observed.(p>0.05)The failures were detected as cracks and fractures in veneer composite. Frameworks remained intact and undamaged in all the specimens. Fracture resistance were higher than occlusal forces in premolar region in all three groups. Although no significant difference in fracture resistance was observed among three groups, due to significant decrease in preparation curettage of abutment teeth in new framework design (group C), this method can be accepted as a satisfactory way for replacement of a small posterior tooth with minimal curettage of the adjacent teeth.

Considering the importance of the design of framework in the stress distribution and probability of creating initial cracks in connectors region, proper design of framework is considered as a requirement. For this purpose, in order to examine the stress distribution in two designs of straight and curved framework, comparison was made using FEM method. Research using a descriptive method of FEM was performed. A laboratory prototype was produced and was scanned in a digital form, using CMM equipment by the laboratory and a super spot from the geometry of the part was created. The super spot was transformed to a 3D solid model by utilizing Catia software. The above model was divided into a high number small elements, using Meshing method, by Abaqus software to analyze the finite elements. Afterwards, by Boundary Condition definition, the part was ready to be analyzed. The mechanical properties of Zirconia was entered into the software in the form of a table. Reviewing stress distribution in the bridge specially with the stress on connectors region was performed. Three vertical loading models for each part were applied in central and distal Fosa and analyzed separately. In this study, the findings were described in the form of Von mises stress in Mpa scale. The stress in the Curved model was more than the Straight model. As a result, the stress distribution is more desirable. According to the results of this study, the straight model showed a more desirable stress distribution compared with the curved model. However, it should be noted that these results were obtained in F.E. environment.

successful dental implant therapy is influenced by many factors such as volume density of the bone. The use of computer softwares for evaluating the bone density in Hounsfield Unit has been recommended. The aim of this study was to assess the bone density and related factors in patients requiring implant therapy, using efilm and Planmeca Romexis softwares. in this descriptive study, CT images of 42 maxillary and 41 mandibular implant sites were studied. Trabecular bone density was assessed by efilm and Planmeca Romexis softwares. Data analysis was performed by Paired T-test and Multiple linear regression test (Backward LR). strong correlation was found between two softwares(r=0.856). Mean bone density with both softwares was higher in anterior mandilble, followed by posterior mandible, anterior maxilla & posterior maxilla. The differences between the regions was highly significant (P<0.001).Among all the related factors there was only a statistically significant association between the Hounsfield values and the anatomical region. This study confirms the impotrtance of a site specific bone tissue evaluation prior to implant installation. A quantitive reliable scale could be helpful if it is taken together with all clinical relevant information for implant treatment planning.

Diametral tensile strength is a property of brittle restorative materials and cements like glass ionomers. Being an adequate and standard amount of this characteristic is necessary for obtaining clinically acceptable results in their use. According to the lack of reports about S.D.S glass ionomer cement that recently has been introduced to Iranian market, this study was conducted with the aim of comparing of the diametral tensile strength(D.T.S) of Fuji Type II and restorative S.D.S glass ionomer cements in different periods of time. This experimental study was performed on 20 disk shaped specimens of each cement; they were prepared according to ANSI / ADA 66 specification (9 mm diameter and 4/5 mm length).The ratios of powder to liquid meticulously followed manufacturers recommendations for use. All specimens were holded in an incubator at 37±1ºc and 95±5% relative humidity prior to testing. each group of cements were tested in two periods of time after the beginning of mixing (15minute and 24hours) in a universal testing machine (Zwick Roell- Germany Z020) at a crosshead speed of 0/5 mm/min. The test results were analyzed by One-Sample Kolmogorov- Smirnov Test and T Test. Mean values of diametral tensile strength of FT II in 15minute and 24hours, were 5/67 MPa and 6/98 MPa and for restorative S.D.S cement were 4/54 MPa and 6/61 MPa respectively. Statistical analysis revealed that there was no significant difference between diametral tensile strength of these two cements at 15 minute and 24 hours, but D.T.S had an increase during time which was statistically significant in both cements.

Cortisol is the most important glucocorticoid that increases in stressful situations. The goal of this study was to evaluate the effect of audiovisual distraction (cartoon watching) on salivary cortisol among 5-9 year – old children during dental treatment, in a dental clinic in Tehran. This matched cross over single blind clinical trial study was performed on fifteen 5-9 year – old children. Patients who had at least two identical counterpart teeth with same treatment plan participated in the study. The children were divided into two groups. In one group in first visit, the treatment was performed under normal dental set up without watching cartoon films and in second visit cartoon films was presented during the administration of local anesthetic and treatment, and vise versa. The children were asked to give a total of three Saliva samples in each visit: one prior to dental treatment, one after administration of local anesthetic and one after dental treatment completion. Samples were sent to laboratory and cortisol in saliva was measured using the ECLIA method. Intra group statistical analysis was performed using wilcoxon test and intergroup analysis was performed using Manu witheny. cortisol variation level in visit without audiovisual distraction after local anesthetic administration was 3/3  6/05 and after completion of treatment was 1/62/7, in visit with audiovisual distraction after injection was 2/59/5 and after treatment completion was 0/56/2. There was no statistical significant difference between two groups. Also sex, age, birth rank, the number of family members, the type of treatment have no influence on decreasing salivary cortisol. Audiovisual distraction (cartoon watching) has no significant effect on decreasing salivary cortisol during dental treatment.

In removable dentures, artificial teeth are a significant part of the overall esthetical outcome. In the maintenance of esthetical effects, the color stability of artificial tooth materials is one major factor. The purpose of this in vitro study was to evaluate the color stability of one resin composite teeth (Glamour)and one resin acrylic teeth (Ideal dent) in tea & coffee. This in vitro-experimental study was done on a sample with size of 36. all of the samples selected of the upper right santral; between them 18 teeth was the resin composite(Glamour) with size A13 and color A1 and 18 teeth was the re sin acrylic teeth (Ideal dent) with size I18and color A1. Sample were immersed in to two staining beverage as test groups (tea & coffee) and distilled water as control. Color measurements of teeth were performed by using spectrophotometer, before immersion, the initial color value of each tooth was recorded. Color change values were determined after 1 month. Color differences were characterized using the CIE lab color space.for evaluation color with clinical environment we use from NBS units. Statistically analyzes done with ANOVA test. In the Glamour mark, for all samples, there were statistically significant differences between the mean ∆ E values after 1 month but in Ideal dent mark there were not. Color differences with corresponding ∆E values than 3.3are acceptable and NBS values than 3 are acceptable in clinical dentistry in the current study the ∆E values of all groups did not exceed 3.3. In the Glamour mark, coffee was found the more chromomeric agent between solutions. but in Ideal dent mark we did not found any color changes.

Small amount of Fluoride is one of the most well-known factors being useful in controlling decay. Since high consumption of fluoride may cause fluorosis and osteoarthritis. Considering the high consumption of tea in Iran (as a national drink) and high degree content of fluoride in Iranian commonly-used teas, and considering non-awareness on the effect of brewing time on the degree of fluorine freed from tea, the present research aimed to determine the effect of brewing time on the amount of fluorine released from tea in academic year 2007-08 in Chemistry Laboratory of the Faculty of Pharmacology, Tehran University. This survey was done in experimental study. Out of 13 brands of tea in Iranian market two brands named Oghab and Doghazal which, in Iranian market in year 1386 (2007-08), were best seller brands of Iranian and foreign teas respectively were selected and three packs of each brand were purchased from three different places of Tehran City. From each type of the teas six samples were taken and brewed in different periods of time 3, 5, 15, 30, 60, and 120 minutes. In each brewing, one gram dry tea was added to 100 ml of boiling distilled water in a Teflon tea pot. For brewing tea, the tea pots were placed in a incubator at temperature of 80 degrees Celsius. When the pre-determined times passed, 10 ml tea extract was taken from each pot and filtered. Then TISAB II buffer at proportion of 1 to 1 was added to the filtered extract. The concentration of fluoride ion was measured in potentiometer method.The amount of the fluoride of tea for each brewing time and for each tea sample were studied with T-Test statistics in each section and between two teas in following up times through ANOVA Test. The average amount of fluoride in Doghazal tea was 0.77±0.04ppm and in Oghab tea was 2.6±0.11ppm. For all times, this difference was statistically meaningful (p‹0.001). The amount of fluoride freed from both brands (Oghab abd Doghazal) increased meaningfully along with increase in brewing time ((p‹0.001). As the brewing time increases, the amount of fluoride freed from tea increases. The best brewing time for tea is about 5 minutes. Furthermore, comparing Oghab tea with Doghazal tea indicates that fluorine content of Oghab tea is higher than other brand. The brewing time suggested by producing company of Doghazal tea (which has been printed on the packages) is 5 minutes which is suitable time. But the brewing time suggested for Oghab tea is 15 minutes which, as the results of this research indicates, leads to introducing of considerable amount of fluoride in the body and thus it does not seem to be advisable time for brewing tea.

Regarding the high rate of caries prevalence and the lack of enough treatment supplies in the society as well as the significant role played by the proper amount of fluoride in water supplies in dental health.The goal of this study was to detmine the amount of fluoride in the cities of zanjan province drinking water summer of 2009. This descriptive research was performed on water samples of all drinking water sources in the cities of Zanjan province The sampling process was conduct at nearest home surrounding each source. All samples were delivered to Tehran dental school IA university quality control laboratories. The amount of each samples fluoride was determined as less than normal, normal and more than normal using potentiometer method. This study was performed on 58 samples. The total volume of the cities of zanjan province water source was one hundred and eighty one thousand and fifty cubic meters and the total amount of fluoride in the cities of zanjan province drinking water was 0.06±0.09 ppm. The amount of fluoride in 100% of the total drinking water was less than standardized level. Unfortunately the amount of fluoride in the cities of zanjan province drinking water is significantly less than standardized level.