مجله دندانپزشکی دانشگاه علوم پزشکی تهران
سال هفدهم شماره 1 (پیاپی 38، بهار 1383)

Statement of Problem: One of the major goals¡ in most dental researches¡ is to measure bone destruction or deposition due to the progression or regression of disease. Failure of human eyes to detect minor radiographic density changes resulted in more accurate methods such as optical densitometry and direct or indirect digital densitometry.
The aim of this study was to determine the accuracy of a newly proposed method of indirect digital densitometry using modified Photoshop software.
Radiographs from 37 samples of urografin solution with three concentrations (12.5%¡ 25% and 37.5%) were taken on dental radiographic films no.2 and digitized by a scanner. A region with 800*800 pixels was cropped from each image and compressed with the Joint Photographic Experts Group (JPEG) compression algorithm and saved. These new images were then put into registration with new algorithm using MATLAB software version 6.1. This algorithm assigned each image and average pixel value (between 0 and 255). The association between concentration and calculated values for each image was tested with regression analysis and the meaning fullness of differences between calculated values was also analysis by ANOVA test. Tukey HSD and Alpha Krunbach were used whenever needs.
Regression analysis revealed significant correlation between concentration and calculated average pixel value (r=0.883). The differences between average of pixels value for different concentration was significant (P=0.0001). Pixel values showed a good intra- sample and intra-group repeatability (Alpha Krunbach: a=99.96%¡ a=99.68%).
This method due to its high accuracy¡ easy usage and densitometer independency can be considered as a suitable alternative for conventional densitometry methods.

Statement of Problem: Chronic periodontitis is one of the most prevalent periodontal diseases in the world which may be treated through surgical or non-surgical approaches. The aim of this study was to compare the efficacy of Doxycycline and placebo following SRP in non-surgical treatment of chronic periodontitis. This double blind interventional study was conducted on patients attended to the periodontology department of Tehran faculty of dentistry from 2002 to 2003. After SRP, 22 cases and 23 controls were received Doxycycline and placebo, 20 mg twice a day for 3 months, respectively. Bleeding on probing (BOP), pocket depth (PD)<6mm and PD>7mm, and also clinical attachment level (CAL)<6mm and CAL>7mm in cases and controls after 3 and 6 months were compared by student t-test. BOP after 3 and 6 months in Doxycycline recipients following SRP were significantly lower than in placebo recipients (P^0.007 and P=0.045 respectively). PD<6mm, PD>7mm, CAL<6mm and CAL>7mm in 3 and 6 months after SRP in cases were much lower than controls. This study showed that the administration of Doxycycline for 3 months after SRP resulted in improvement of clinical indices as compared with SRP alone. Therefore, Doxycycline administration is recommended for chronic periodontitis treatment after SRP.

Statement of Problem: One of the problems associated with the treatment of periodontal diseases is caused through the extension of disease toward furcation area. Several techniques in Conservative, Resective and Regenerative categories have been suggested for the treatment of furcation involvement. The aim of this study was to compare the results of the treatment of grade II furcation involvement in mandibular molars using an allograft material named 'Dynagraft' (a type of demineralized bone matrix) and the coronally positioned flap. In this randomized controlled clinical trial study, twelve patients (9 females and 3 males), aged 25 to 40, suffering from bilaterally grade II furcation involvement of mandibular molars who referred to dental faculty Tehran University of medical Sciences, were investigated. The molars of one side were treated by Dynagraft whereas those of the opposite side underwent the CPF method. Measurements of the probing pocket depth (PPD), clinical attachment level (CAL), keratinized gingiva (KG) and horizontal probing depth (HPD) were recorded at baseline, 3 and 6 months after surgery. In order to investigate the bone radiographic changes, radiovisiography at the mentioned periods in addition to clinical investigation, were performed. For statistical analysis, Paired West was used. The mean PPD reduction three months and six months after the operation were 1.75 mm and 2.25mm, respectively in the Dynagraft (test) group whereas 1.26mm and 1.27mm in the CPF (control) group (P<0.005). The mean attachment gain three months and six months after the operation were 1.1 mm and 1.5mm respectively in the test group, and 0.2mm and 0.3mm in the control group (P<0.005). The mean KG reduction three months and six months after the operation were 0.5mm and 0.6mm respectively in the test group and those of the control group were 1.1mm and 1.1mm. The mean HPD reduction three months and six months after the operation were 1.55mm and 2mm respectively in the test group (P<0.005) and 0.55mm and 0.55mm in the control group (PO.01). Radiovisiography of the mentioned areas three months and six months after the operation confirmed the changes obtained from clinical measurements, showing appreciable reconstructive results (Bone filling) in the test group as compared with the control group. Moreover, root resorption was not observed. Based on the results of this study, Dynagraft can be used as an appropriate material in the treatment of grade II furcation involvement in mandibular molars. However, for a through evaluation of such regenerative techniques in furcation involvement, further studies with larger population and long term follow up in addition to histologic studies are suggested.

Statement of Problem: Root canal cleaning and shaping are important steps in endodontic therapy. In order to develop better techniques, new instruments are constantly designed and delivered to the market. The aim of the present study was to compare the effectiveness of one manual with three rotary root canal instrumentations techniques. In this in-vitro study, 80 mesial roots of freshly extracted human mandibular molars were divided in to four groups equally and prepared by one of the following instrumentation methods profile NiTi rotary system, Protaper NiTi rotary system, Flex Master NiTi rotary system and hand NiTi K-file instrumentation. In each root one of the canals was instrumented and the other was used as control.After decalcification, cross sections at 3mm and 5mm of apical portion were prepared and examined for remaining debris, predentin and smooth walls under light microscope. The data were analyzed by Kxuskal-Wallis test. Significantly less debris was found at 3mm cross- section using protaper and Flex Master techniques (P<0.05). No significant differences were found at 5mm cross section. Also no significant differences were observed for remaining predentin at all regions. Significantly more smooth walls were found at both regions using protaper technique (P<0.05). The protaper technique employed in this study resulted in cleaner root cana! walls than the other techniques.

Statement of Problem: Radiography is the most common technique in working length determination, however, because of its limitations is not considered as an ideal technique. Its application, particularly for children due to radiation hazards, technical problems in young and unco-operative children and the superimposition of permanent teeth bud on primary teeth root, lead to numerous problems. The goal of this study was to evaluate the accuracy of an electronic apex locator (EAL) in working length determination of primary teeth. In this in-vitro study 96 canals of the extracted primary teeth, with at least 2/3 of the root length remained, were investigated. There were no obstructed canal, previous root canal therapy and perforation of pulp chamber floor. All working lengths were also measured by radiography. The results of Raypex 4 and radiography were compared with actual root canal lengths determined by direct observation. The applied EAL, in this study was called Raypex 4, a new device belonged to the fourth generation (Ratio Type). The results were analyzed by Chi-Square and Pearson correlation statistical tests. The accuracy of Raypex and radiography were 61.5% and 63.5%, respectively. The differences between Reypex 4 root canal length measurements and those of direct observation were not significant (P=0.08), but such difference between radiography and direct observation was statistically significant (P=0.01). The diameter of the apical foramen (the site of canal opening) did not affect on Raypex 4 accuray (P>0.05). Considering the acceptable safetyness, Painlessness, simple and rapid application and an accuracy comparable to that of radiography, the use of Raypex4 EAL for the measurement of primary teeth length is suggested.

Statement of Problem: Subtraction is a newly presented radiography technique to detect minor density changes that are not visible by conventional radiography. The aim of this In-vitro study was to evaluate the efficacy of photoshop subtraction software for detecting minor density changes between two dental images. In this research, five dried human mandibles were held in fixed position while thin aluminium sheets were superimposed on each mandible on the 1th and 2nd molar teeth regions.A reference image, without aluminium sheet placement, was obtained from each mandible subsequently series consist of 20 images with aluminium sheets, ranging from 50p. to "5Q0"x were recorded by radiovisiography (RVG) system. Initial images were subtracted from subsequent ones by Photoshop subtraction software. The difference in density between the two images at the 1st and 2nd molar sites was related to the aluminium sheets. The optical density of aluminium sheets was determined by densitometer. In the present study, 6.6% of the optical density changes of the minimum aluminium thickness as 300u. could be detected by photoshop software software. The findings of this study showed that the accuracy of photoshop subtraction software was equal to that of the conventional subtraction softwares. Additionally, the accuracy of this software was proved to be suitable for clinical investigations of small localized changes in alveolar bone.

Statement of Problem: Dental porcelain is one of the best materials ever used in dentistry. Excellent tissue compatibility, esthetics, very low solubility in oral fluids, high compressive strength, and the lowest bacterial plaque accumulation on the glazed porcelain are some of its advantages. Porcelain brittleness due to its low tensile strength, impact strength and the occlusal attrition of opposing teeth enamel are some of its disadvantages. The most important mechanical properties of dental porcelains are their flexural strength that is the ability of a porcelain to resist fracture when loaded from above. Different ways have been proposed to eliminate porcelain brittleness and develop its flexural strength, among which baking porcelain on a metal framework is more commonly used. Considering that restoration and replacement of teeth by porcelain fused to metal restorations is still the most commonly used technique, the aim of the present study was to measure the flexural strength of a porcelain bonded to metal powder, D4 Dentin, and to compare it with Vita Dentin powder. In this experimental study, a stainless steel box, 25x5x2mm was made according to ISO 6872: 1995 (E) Standard and filled with D4 Dentin powder and Vita Dentin (VMK 68N) and baked in Vita furnace. Then 10 blocks of D^ Dentin and 10 of Vita Dentin were made. Samples were placed on the three point bending test machine and force was applied the middle of each block. To analyze the data, t- student test and co-variance analysis were used. Mean flexural strength of D4 Dentin was 53.40±1.35 MPa and that of Vita Dentin was 53.86+7.38 MPa. The difference was not statistically significant. According to ISO 6872: 1995 (E) standard, the flexural strength of all D4 Dentin samples were greater than 50 Mpa.

Statement of Problem: Hepatitis C is a relatively common infection which can be transmitted through accidental inoculation consequently dentists are highly at the risk of exposure to this virus. The aim of this study was to determine prevalence of Hepatitis C among the dentists of Yazd and to evaluate their knowledge about the existing ways for the transmission and prevention of this infection. In this descriptive- analytic study which was performed periodically (2002), the sera of all dentists practicing in Yazd were tested (104 samples) in the laboratory of Yazd blood transfusion organization initially by 1st generation of Elisa for Anti HCV followed by Riba on positive samples to confirm the results. Meanwhile a questionnaire assessing their knowledge about hepatitis was completed the by the dentists. Data were analyzed by ANOVA and t test. None of the one hundred and four samples of sera were positive for Anti HCV. Mean score of their knowledge was 14.80 (of 20). The knowledge of 92.1% of them was at moderate to high level. No significant difference was observed between Yazd's dentists knowledge about hepatitis C in different age, gender and length of professional experience groups. According to this study, the absence of HCV among the dentists of Yazd is mainly attributed to the low prevalence of HCV infection among general population, though it can also be an indicative of the knowledge and excellent performance of the dentists to prevent the transmission of infection through blood and saliva.

Statement of Problem: Nowadays economical issues on high gold alloys have changed the practice of metal-ceramic restorations toward base-metal alloys. Minalux is one of the base-metal alloys produced in Iran. Marginal fitness is of high importance to be evaluated in dental alloys. The aim of the present study was to compare the marginal adaptation of two base-metal alloys, Minalux (Mavadkaran Co. Iran) and VeraBond2 (Aibadent Co. USA) during firing cycles of porcelain. In an experimental study 24 standard brass dies, with 135° chamfer finishing line were fabricated by Computer Numeric Controlled (CNC) milling machine. The samples were randomly divided in two groups, A and B, 12 in each. Following wax-up, the samples were equally cast with two mentioned alloys. In each group, there were 4 controlled samples, which proceeded to firing cycle without veneering porcelain. Scanning electron microscope (SEM) measurements of marginal gap from buccal and lingual aspects were performed after 4 stages of casting, degassing, porcelain application and glazing. The data were analyzed using Four-way ANOVA and multiple comparative test based on Tukey criteria. The findings of this study revealed that there was no significant difference in the marginal gap of Minalux (31.10±7.8u.m) and VeraBond2 (30.27±6.96u.m) with confidence level at 0.95 (P=0.43). For both alloys the greatest gap was observed after degassing stage (P<0.05). Porcelain and porcelain veneering proximity caused significant changes in the marginal gap of Minalux castings (P<0.05), however, such changes did not occur in VeraBond2 (PO.05). Based on the findings of this study, the marginal gaps of two base metal alloys, Minalux and VeraBond2, were proved to be identical and that of the Minalux alloy existed in the range of acceptable clinical application. It was also concluded that Minalux dental alloys could provide proper marginal adaptation.

Statement of Problem: Differentiation of dentigerous cyst from unicystic ameloblastoma, discovering any initial ameloblastic changes in lining epithelium of dentigerous cyst at early stage, and differentiation between hyperplastic odontogenic epithelium in fibrous capsule of dentigerous cyst from ameloblastic proliferation, need to an accurate and reliable technique. The aim of this study was to determine and compare Ki-67 immunoreactivity in various locations of the epithelium of Dentigerous cyst and Unicystic Ameloblastoma. In this historical Cohort study, 15 cases of dentigerous cyst and 9 cases of unicystic ameloblastoma were selected. Immunohistochemistry staining was performed by M1B-1 (murine monoclonal antibody against Ki-67). The stained nucleous were counted in basal and suprabasal layer of lining epithelium of both lesions in 3000 epithelial cells. Finally, the percentage of positive cells (presented as labeling index) was calculated, t- student test was used to analyze the related data. Ki-67 (LI) in basal layer of Dentigerous cyst (2.59±1.66) and Unicystic Ameloblastoma (3.76±79) had no significant differences, but Ki-67 (LI) in suprabasal layer of unicystic ameloblastoma (2.15±0.69) was significantly higher than dentigerous cyst (0.77±0.55) P=0.003).The difference between the average numbers of positive cells for Ki-67 (LI) in these two lesions was statistically significant (P<0.05) and it was higher in Unicystic Ameloblastoma than Dentigerous cyst. Based on the findings of this study, it is suggested that Ki-67 (LI) in suprabasal layer or throughout the epithelium can be considered as a useful marker for differential diagnosis between dentigerous cyst and unicystic ameloblastoma.

Statement of Problem: With due attention to the control of quality of dental materials and its role in improvement of quality and accuracy of treatment, in this research, Zoiiran made in Golchai company was evaluated according to international standards. The aim of this study was the evaluation of properties of Zinc-oxide-eugenoi reinforced cement with trade name "Zoiiran". According to ISO 3107, BS 7214, EN 23107 standards (1991), the number of samples were as follows: 2 for setting time, 5 for compressive strength, 4 for disintegration and 3 for film thickness testing. The experiments were followed standards instructions. Setting time was between 5.57-6.03 min. The compressive strength was between 21.29-25.79 MPa. Zoiiran had about 1.3-1.5 % disintegration. Finally, the film thickness was between 11-11.5 u. According to mentioned experiments, physical properties of Zoiiran as temporary cement of fixed-prosthodontic (Typel-class I) and base liner (Type IV-class I), were similar to stated standards.

Statement of Problem: Tooth extraction is always considered as the final treatment option in dentistry.Considering the numerous advances in dentistry, nowadays the preservation of the permanent teeth until old age is common. However, in most economically poor countries or those without security service insurance,the high rate of extraction, particularly among restorable teeth, is regrettable. The aim of the present study was to determine the reasons for tooth extraction among patients referred to the faculty of Dentistry, Tehran University of Medical Sciences in 2002. This descriptive and cross-sectional study was conducted on 320 patients. The information about patient's general knowledge, oral health status, tooth location and causes of extraction were collected and recorded in a questionnaire. The data were submitted to statistical Chi-Square test. No statistically significant difference was found between two genders in their mentioned causes for extraction. The most prevalent reasons were as follows: Caries (50%), Periodontal diseases (16.6%). Absence of an acceptable occlusion, prosthetic problems, patient's request, etc... make up the remaining 33.4% of the reasons. According to this study, it is suggested to investigate extraction etiology at the society level and if similar results are obtained, necessary steps should be taken to prevent caries and periodontal problems as the major mentioned causes for tooth extraction.