مجله دندانپزشکی دانشگاه علوم پزشکی تهران
سال شانزدهم شماره 4 (پیاپی 37، زمستان 1382)

Statement of Problem: Composite reins have recently become popular for posterior teeth restorations. Gap formation and subsequent microleakage are of the complications resulting from such restorations. One of the techniques to overcome polymerization shrinkage of composite resins is sandwich technique (application of glass ionomer as a base beneath the composite resin). Since polymerization patterns in two types of composite resins (light cure and self cure) differ from each other, various effects on the bond strength between glass ionomer and dentin are expected. The aim of this in vitro study was to evaluate the effects of self- cure and light- cure composite resins in sandwich technique on the bond strength of light cure glass ionomer and dentin. 40 extracted human premolars were selected and divided into four groups:Group 1: Light cure glass ionomer of 1mm thickness was placed on dentin.Group 2: 1mm thickness of light cure glass ionomer plus a mass of self cure composite resin of 2mm thickness were placed.Group 3: 1mm thickness of light cure glass ionomer plus light cure composite resin as two separate 1mm layer were placed.Group 4: 1mm thickness of light cure glass ionomer with 37% phosphoric acid etching followed by two separate layers of light cure composite resin of 1 mm thickness were placed.SEM was used to determine gap size ai Gl- dentin and Gi- composite interlaces. The findings were analyzed by ANOVA and t-student tests. Groups 1 and 2 showed no gap at Gl-dentm interface and also cracks were not observed in all these specimens. In group 3, there was gap between light cure GI and light cure composite resin and cracks were seen in GI, too. Group 4 showed gap at both interfaces and more cracks were seen in GI. Groups I and 2 showed the least gap formation and group 4 showed the most. Statistically significant difference was found between groups 3, 4 and group 1 (control), 2. Base on this study, the application of self-cure composite resin on light cure GI showed no gap and crack formation on Gl-dentin and Gl-composite interfaces and GI itself. However, light cure composite resins and glass ionomer etching aggregated crack and gap formation.

Statement of Problem: Color matching and accurate shade selection are the challenging problems common to restorative dentistry. In ceramometal restorations, the type of substructure alloy affects the final color of bonded porcelain. Nickel- chromium alloy is the most commonly used one that its Iranian product, namely Minalux, is similar to Verabond2. The aim of this study was to assess and compare various color dimensions resulting from Minalux and Verabond2 alloys. Nine disks, approximately 16 mm in diameter and 0.5 mm thickness, were cast from each alloy. Then, porcelain Vita VMK68 A2 was baked onto the entire test disks, following the manufacturer's instruction. Color samples, at the same time and under the same conditions, was measured by Data color spectrophotometer in CIE Lab System and Munsel system under four light sources (A, C, D65 and TL81). Then MATLAB TOOL BOX Statistic 5.2 was used to determine mean and bilateral variance analysis. It was indicated that the F value on hue, value and chroma was less than of the table value stated with 99% coefficient confidence, confirming Ho theory. In other words, there were not any significant differences between ceramometal disks made of Minalux and Verabond2 in the three dimensions of color. Having desirable physical, mechanical and biological properties, Verabond2 can be replaced by Minalux alloy.

Statement of Problem:The choung osteotomy (Intraoral Vertico- Sagittal Ramus Osteotomy) has developed since 1992 in the treatment of mandibular prognathism. In IVSRO, osteotomy plane is theoretically parallel to the original sagittal plane and thereby attempting to decrease the incidence of condylar dispacement. This osteotomy designed additionally to decrease neurosensory disturbances. The aim of this study was to evaluate the incidence of neurosensory deficit and condylar displacement with IVSRO and Sagittal Split Ramus Osteotomy (SSRO). In this study, mandibular set back surgery was accomplished upon 7 patients by choung osteotomy. In addition to choung osteotomy, in 2 patients Lefort 1 osteomy was performed for maxillary protrusion and for 2 other patients, chain surgery was performed. Variables such as the neurosensory disturbances of inferior alveolar nerve and condylar displacement following choung osteotomy were investigated. All the patients were followed up one year after osteotomy. OPG, Lateral Cephalogram and Submentovertex radiographies were take pre and postoperatively for all patients. No statistically significant differences were found in condylar displacement (P>0.5). However, Mc Nemar analysis showed significant difference of neurosensory deficit between IVSRO and SSRO (P=0.001). It is suggested that choung osteotomy is a safe procedure for mandibular surgery.

Statement of Problem: The determination of the dental midline is necessary in most dental procedures.One of the methods to fulfill this goal is to determine the facial midline based on the midpoints of the forehead, nose, upper lip and chin. However, for various reasons, this method has not always been proved successful. In such cases, different techniques, based on the investigations in the edentulous patients, have been suggested. The aim of this study was to investigate the conformity of some landmarks such as labial frenum, incisive papilla and mid palatal suture with dental and facial midlines among people with natural dentition in order to obtain accurate anatomic landmarks for denture replacement. In this descriptive study, 96 dental students, having all their permanent teeth and without any orthognathic problem, were chosen. For each subject, Alginate impressions and dental casts were prepared. Then, centric occlusion was recorded with a biting wax and the facial mid line was determined on the anterior part of it. The distances from the facial midline to the upper teeth midline,incisive papilla, labial frenum and mid palatal suture were determined with a special tool and were measured by a VERNIEH two times. In order to analyze the results, Chi- Square and t-student tests were used. The average of facial midline distance to the upper teeth midline, the labial frenum, the incisive papilla and the mid palatal suture were 0.83±0.60, 0.67±G.54, 0.83±00.63 and 0.81±0.62 mm,respectively. There was no significant difference between males and females. Labial frenum showed the minimum distance to the facial midline, while the incisive papilla had the maximum. There was no significant difference between these anatomic landmarks, in conformity or unconformity with the facial midline Considering the low percentage of the subjects with complete conformity and the lack of significant differences between these three landmarks, it is suggested that there is no superiority among these landmarks for the determination of facial midline. The similar distances from the facial midline to the incisive papilla and upper teeth midline indicate that using incisive papilla to determine the upper teeth midline in edentulous patients lead to normal face.

Statement of Problem:Recurrent aphthous stomatitis (RAS) is a common oral disorder that despite extensive researches, the etiology of this phenomenon is still unknown. Because this phenomenon has been observed more often in families than in individual cases, genetic influence has been investigated in most researches. The aim of the present study was to evaluate the association between Human Leukocyte Antigen (HLA) and aphthous stomatitis more precisely. in this study, 60 patients with RAS were examined for HLA-A and HLA- B types and 37 of them were examined for HLA- DR and HLA-DQ types. The results were compared through Fisher test with those of 25 healthy control subjects, aged more than 30 years. A significant decrease in the frequency of some antigens such as HLA-DQW 3 and HLA-A 26 in subjects with RAS was observed. Therefore, according to the results of this study, these antigens were considered as resistant antigens to recurrent aphthous stomatitis. In contrast, there was no significant increase in the frequency of any HLA antigens in the test group, compared to the control group. This finding is in contrast with the multiple reports about Behcet's disease. (Because a high frequency of HLA-B 51 has been found in Behcet's syndrome.) According to the findings of this study, it is suggested that the pathogenicity of aphthous ulcerations in Behcet's disease and recurrent aphthous stomatitis is not the same. However, further studies are necessary to prove this theory.

Statement of Problem:The surface topography of denture base material is an important factor for the adhesion of Candida albicans and other microorganisms. The aim of this study was to evaluate the adherence of Candida albicans to four types of denture base materials (Acropars acrylic resin, Meliodent acrylic resin, rough and smooth surfaces of Molloplast B). Seven blocks of two types of acrylic resins and ten blocks of silicone with one rough and one smooth surface were made and incubated in a suspension of Candida albicans. After washing,the blocks were stained with acridine orange and examined under fluorescent microscope. For statistical analysis ANOVA and Duncan tests were used. It was observed that Candida adhesion to rough surfaces of acrylic resins and silicone was significantly more than polished surfaces of acrylic resins and smooth silicone (PO.0001). However, no statistical significant difference was found between polished acrylic resins surfaces and smooth silicone. Significant differences in the adherence of Candida to the surfaces of different denture base materials are due to differences in surface topography, chemical, physical and hydrophobic properties so it is recommended to minimize the roughness and irregularities of denture base.

Statement of Problem: Pain control is of high importance in dentistry. Prescribing sedatives such a Diazepam, as an anti-depressant and pain threshold elevator drug is able to influence the patient's reaction to pain and reduce it. The aim of the current study was to evaluate the effect of Diazepam in pain reduction following mandibular impacted third molar surgery. In this study, which was conducted in the department of Oral and Maxillofacial surgery Faculty of Dentistry, Tehran University of Medical sciences. The patients were divided into two equal groups (n=30). For controls, antibiotics and analgesics were prescribed after surgery. However, except the aforementioned drugs, Diazepam (5mg), three times per day, was prescribed for the experimental group. The amount of mouth opening was also measured as an auxiliary sign after one week. The data were compared byX2 test after one week. 60% of the experimental group and 13.8% of the control group felt a weak pain. Statistically significant differences were observed regarding pain feeling between two groups (P<0.001). Severe pain feeling was 34.5% and 10%, for control and experimental groups, respectively. It is suggested that Diazepam is an effective pain reduction drug following third molar surgery.This drug has also a relative effect on temporary trismus resulting probably from muscle trauma or pain.

Statement of Problem:Iranian product, Acropars autopolymerizing acrylic resin is nowadays widely used in dental prostheses. Dimensional change is a common problem among Iranian made acrylic resins in making custom trays and record bases, seems to be more than the similar foreign products. In order to achieve a technique for making a record base with minimum dimensional changes, more research is necessary. The aim of the present study was to determine a curing technique for Iranian autopolymerizing acrylic resins leading to the least polymerization shrinkage and the most adaptation between record bases and stone casts. In this experimental study, 40 stone casts were divided into four 10- member group. For each group, polymerization shrinkage was determined at three points with one of the following techniques: Bench curing, Curing under a coat of petroleum jelly, Curing in a monomer saturated atmosphere, Curing in boiled water. Adaptation between bases and stone casts were measured at three points (the right and left crests of the ridge and the midpalatal region) with a light-measuring microscope. To analyze the data, Variance analysis was used. The monomer atmosphere technique showed the minimum dimensional changes and the samples in boiled water group had the maximum dimensional changes. No statistical differences were observed between other groups. More adaptation between record bases and stone casts was observed in monomer atmosphere polymerization technique. The differences between bench curing and curing under a coat of petroleum jelly techniques with this method were not statistically significant. Therefore, it is suggested for making base records with maximum adaptation.

Statement of Problem:Various methods have already been suggested to measure the working length in root canal therapy among which the use of paper point, tactile sense, radiography and electronic apex finder instruments can be named. Investigations on EAL (Electronic Apex Locator) indicate that these instruments can reduce the number of required radiography to a great extent. Moreover, in special cases such as patients with high risk reflex, pregnant women, the mental disabled and handicapped and also in cases with special anatomical structures these instruments are proper substitutes for radiography. The aim of this study was to compare the accuracy of an Iranian made apex finder instrument with Neosono Ultima EZ and radiography. This study was conducted on 51 mandibular molars, devoid of calcification, internal and external resorption, severe root curve or fracture, which were extracted due to periodontal disease or severe caries. All the specimens were washed in 2.5% hypochlorite sodium and washing with water, kept in 10% formalin solution, under room temperature. The accuracy of the Iranian instrument was measured (81.8%) similar to that of radiography (81.2%). But the accuracy of Neosono Wtima EZ was (92.9%) which was higher than the two other methods. No statistically significant difference was found between Neosono Ultima EZ instrument and two other groups, using SPSS 10 statistical soft ware.

Statement of Problem: Dental practices such as oral, periodontal and endodontic surgeries cause damages to the intraoral tissues, so having knowledge of the dental procedures that necessiciate endocarditis prophylaxis is of high importance. The aim of the present study was to determine the knowledge level of dental senior students in Tehran dental faculties about endocarditis In this cross- sectional descriptive- analytic study, 253 senior students of four dentistry faculties in Tehran took part as follows: Tehran University: 71 students (M:42, F:29), Shahid Beheshti University: 74 students (M:40, F:34), Shahed University: 35 students (M:35, F:38), Azad University:73 students (M:35, F:38). The questionnaire used in this research consisted of three parts as follows: part one:information on cardiac diseases, part two: dental procedures requiring endocarditis prophylaxis, part three:antibiotic diet in endocarditis prophylaxis. Sex and place of education of the students were also studied in detail. For statistical analysis, Chi-square test was used. On the basis of the sex, the correct answers of the female respondents of different universities wereranked as: Azad University: 72.5%, Tehran University: 71.1%, Shahid Beheshti: 57%, ShahedUniversity:55.7%. In the same way, the male respondents were reported as: Tehran Universitys: 71.6%, Azad University:66.2%, Shahed University: 57.3%, Shahid Behesti University: 52.1%, On the basis of the place of education,the following results were reported: Tehran University students managed to answer 71.3%, Azad University,Shahed University and Shahid Beheshti University students could answer 69.5%, 56.5% and 54.6%,respectively. All these differences were statistically significant, indicating that first ranked students have more information than the students of other schools. It is recommended to develop more practical training programme in dental schools on cardiac diseases, dental procedures requiring endocarditis prophylaxis and antibiotic diets.

Statement of Problem: Panoramic radiography seems necessary at examination, diagnosis and treatment plan phases of removable prostheses treatment since most of the patients who request removable prostheses treatment have retained root fragments, impacted teeth, cycts and tumors that might not otherwise be detected. The aim of the present study was to investigate the incidence rate of retained roots, impacted teeth and suspected pathologic conditions in panoramic radiographics of patients referred to removable prosthodontics departments of four dental schools and five public centers. In this case series study, 1232 panoramic radiographs were analyzed to detect retained root fragments, impacted teeth and pathologic conditions. From among 850 panoramic radiographs of patients seeking complete denture, the incidence rates of impacted teeth, retained roots and pathologic lesions were 1.3%, 9.5% and 4.0% respectively.Also from 382 panoramic radiographs of removable partial denture patients the corresponding measures were 2.9%, 11% amd 0.1%. Due to the significant and evident problems in residual ridge, as well as pathologic conditions of the remaining teeth structures and their supporting tissues as partial prosthesis base, the necessity for panoramic radiographics in edentolous and semi- edentulous patients is reemphasized.

The use of root canal models in endodontics education is of high importance. So, in this article a new method is presented that the students can produce these models with simple and low cost instruments.These plastic models are made of polyester which is low cost, available and has the approximate cutting properties of dentin. The best molds were disposable syringes due to their low cost, availability and producing smooth surfaces on polyester models. A spreader with desired curve and tapering is used for producing canals. Rockwell A hardness coefficient of polyester is "33", which is near dentin "31" and foreign made models "35.5". Since these polyester models can tolerate up to 280°C and have acceptable resistance to chloroform, all root canal therapy techniques such as vertical condensation and retreatments are practicable. Their transparency encourage the students to work on them. As a result, the use of these models is recommended for endodontics training.