dr. mohammad amin tavakkoli

Statement of Problem: Recent clinical results for Zirconia all-ceramic restorations have revealed that the fracture rate 6-15% of the Zirconia framework is so low and the core of Zirconia has high stability. However, chipping-off fractures of porcelain are the most common reason for failures of Zirconia in the fixed partial dentures.
The purpose of this study was to compare the shear bond strength (SBS) of porcelain in the porcelain fused to metal and all-ceramic crowns with Zirconia core.
Two groups were selected: porcelain fused to metal (PFM) and porcelain fused to Zirconia (PFZ) (n = 30).In the PFM group, a wax model (10 × 10 × 10mm)was used to cast metal base (Ni_Cr alloy). In the PFZ group, an acrylic cubic model (10 × 10 × 10mm) was made as Zirconia model for scanning.15 cubic Zirconia samples were milled by CAD-CAM. The procedure of porcelain veneering was conducted by the conventional layering technique up to 2 mm thickness (2.5 × 2.5 × 2 mm). All specimens were stored in water for 48 hrs. Thermal cycling was conducted for 20000 cycles between 55°C and 5ºC alternatively for 30s.All samples were mounted in acrylic resin and the SBS test was performed, using a universal testing machine. The analysis of data was performed at a significance level of 0.05 using Kolmogorov-Smirnov and Mann-Whitney U-test.
Mean of SBS in PFM and PFZ was 24.57 and 20.88, respectively. The results of Mann-Whitney test showed that there was no statistically significant difference between the two groups of porcelain fused to metal and Zirconia in item shear bond strength (p = 0.455).
There was no significant difference between the two groups of PFM and PFZ in the item SBS.

An accurate imaging technique has an important role in implantology. Presence of sinus in the posterior maxilla is a limiting factor for implant insertion in this area. Therefore it is necessary to evaluate the relationship between alveolar ridge and sinus. The aim of the present in vitro study was to compare the accuracy of Cranex Tome Spiral and ProMax linear tomography to assess bone quality for the preoperative planning of implants in the posterior maxilla. Tomographs were taken from 3 dry human skulls using both units. Three sites were selected in each side of posterior maxilla and marked with orthodontic wires meaning a total of 24 sites (12 sites for each unit). Bone height and width were measured first on the tomography and then on the skulls after sectioning. In order to compare the measurement values between both units and to compare them with the values obtained from gold the Intraclass Correlation Coefficient of reliability (ICC) was used. The minimum Intraclass correlation coefficient of reliability was 0.569 in two times measurements of width for ProMax, and the maximum of this coefficient was 0.950 in two times measurements of height for Spiral. The mean difference between the real measurements and the height measurements of both units were less than 0.3 mm and for the width measurements were less than 0.5 mm of the real measurements. This study showed in both units, the height measurements were more accurate than the width measurements and all the measurements by Spiral were more valid then those of ProMax. Generally quantitative accuracy of Spiral unit was found to be higher than ProMax unit. Both units proved to be sufficient for quantity measurements. Adjustment an individual imaging plane for each site of tomography increases the accuracy. The most distal sites of Spiral unit may need separate adjustment other than manufacturer demands.

Traumatic injuries to the teeth are among the most serious dental accidents، with the anterior teeth being mostly affected. Some consequences of dental trauma include misshaping، speech defects، psychological and social effects. The knowledge of the field can reduce the suffering، cost، and the time for patients، parents، and health care providers. The aim of this study was to investigate the treatment prognosis of anterior traumatized teeth in patients referred to Endodontics and pediatrics Departments of Shahid Behesthi and Tehran Dental Schools during 1996-2001. Fifty patients participated in this descriptive study. All affected by trauma to the teeth and completing the proposed treatment. Retrospective data، based on trauma forms as well as the clinical notes a questionnaire prepared for the study and analyzed in terms of age، gender، the type of trauma and etiology. Eighty four percent of the studied traumatized teeth were maxillary centrals. Falling-outs are most frequent cause of the traumas (56. 5%)، followed by sport and play events (30. 4%). Enamel- dentin fractures with and without pulpal involvement were the most prevalent trauma types. Most of the selected treatment procedures were involved with pulp and periapical areas. Based on the finding of the study، the prognosis of traumatized anterior teeth in patients referred to the studied centers was estimated to be good.

Determining chronological age of individuals is an investigation key in legal medicine, to recognize the age of those without the date of birth or of those who have problems in birth registration and also the age of criminals under or above 18. The aim of this study was to compare between two developmental staging methods of third molars (Demirjian vs. Engstrom) and their correlation with chronological age of population. Methods & Materials: This cross-sectional and diagnostic study was accomplished in department of radiology, faculty of dentistry, university of Shaheed Beheshti in Tehran (1383–1384). Samples were composed of 350 young adults, 15–25 year–old, attending department of radiology. The radiographs were studied by a legal medicine resident and an oral and maxillofacial radiologist in order to determine developmental stages of third molars according to two methods of Demirjian and Engstrom. Statistical calculations were carried out by Levene, T, Wilcoxon’s signed rank, Mann–whitney, Friedman tests and Kendal correlation coefficients (tau-b). The frequency of different developmental stages of Demirjian and Engstrom methods was increased by development of third molars. In Demirjian method there is only a significant statistical difference between males and females in case of the left mandibular third molar, in a way that males were in a higher developmental rank. In Engstrom method, in case of the right and left mandibular third molars, the males were in a higher developmental rank, and in maxillary third molars there were no difference between males and females. According to Calton system about correlational coefficients, the relation between Demirjian method and age was average in maxillary third molars, and was strong in mandibular third molars. These results were similar to the results of Engstrom method but correlational coefficients in case of each tooth, were lower in Engstrom method in comparison to Demirjian. In order to determine the chronological age, Demirjian method was better than Engstrom.

The cephalometric analysis should be done for patients seeking orthognathic surgical treatments to diagnose dentoalveolar relationships properly. Finding a landmark for the analysis must be time consuming and depends on individual experience or errors and further needs more training. The aim of this study was to develop and evaluate a software for automatically locating of the cephalometric landmarks. Methods & Materials: A software was designed and developed by programmers group using 140 cephalometric radiographs as databases. Further to cephalograms were grabbed by a digital camera (Sony cybershot 1000X1200) in JPEG format and displayed on LCD monitor (Toshiba, 1600X1200 UXGA) for three expert orthodontists and asked them to locate 10 landmarks. The statistic analysis was based on Paired t test. The results showed 51% of the assigned points by software locating were within 1mm accuracy, 63% within 2 mm and 92% within 4mm accuracy. The mean distance from reference (the mean distance of three observers’ points) of seven out of ten points was less than maximum difference between observers. For B point the mean distance difference in computer locating (0.4mm) was less than mean distance observers’ points (3.1mm). For S point the mean distance difference from reference point was 3.4mm in computer locating which was greater than the mean distance difference between observers (0.6mm). The study showed that landmark locating errors by computer were not greater than errors of individuals so, perhaps, computer could be a proper substitute for individuals for locating and analysis of cephalometric landmarks.

Bifid uvula is the mildest form of cleft palate. The size of the cleft may vary from minimal to complete separation of the uvula into two lobes. The prevalence is %0.3-2.2 and is greater in males than in females (M/F:2.5/1). The disturbance appears to be autosomal dominant. This developmental defect may occur in syndromes such as Marfan, Crouzon, Apert and Pierre Robin. Case Report: In this report, the patient was a 29 years old man whoever referred for dental restoration and scaling. He had Bifid uvula, dome – shaped palate, malocclusion and limited movement of mandibule. He didn’t have any systemic problems and syndrome.

The aim of this research is assessment off radiation protection in Shahid Beheshti dental offices. Method & Material: This descriptive study was performed in 200 dental offices in 7 parts of Tehran under supervision of Shahid Beheshti University which were selected randomly in 2002. From these offices, 94% didn’t use Lead shielded wall, 75.5% didn’t use Lead partition, and in all of them distance between practitioner and x-ray unit was acceptable, in 1% rectangular collimator was used. The knowledge of dentists about radiation protection rules and methods were very poor and it is essential to emphasize on the radiation effects and x - ray risk and radiation protection guidelines in continuing education lectures.

This investigation was designed to evaluate upper airway spaces in patients with skeletal anteroposterior and vertical malocclusions. Methods and Materials: Ninty lateral cephalograms of patients were traced with Cl I, Cl II and Cl III malocclusions having normal bite, openbite and deepbite were traced. Hypopharyngeal, nasopharyngeal and oropharyngeal depths were measured considering a magnification of 1.1. Chisquare and ANOVA tests were used to analyse the data. Hypopharyngeal depth was found to be at 17.3±3.7mm in Cl I, 16.0±3 in Cl II and 16.7±4 in Cl III 17.4±0.1 in normal bite, 16.4±3.2 in openbite and 17.1±3.5 in deepbite. The mean oropharyngeal depth was 10.4±2.4 in ClI, 9.8±2.4 in ClII, 11.3±3.3mm in ClIII 10.9±3.1 in normal bite, 9.7±2 in openbite and 11±3.1mm in deepbite cases. Nasopharyngeal depth was found to be at 23.8±3.3 in ClI, 22:7±3.3 in Cl II: 21±4 mm in Cl III: 23±4.7 in normal bite, 22.1±3.5 in openbite and 22.4±3.1 in deepbite cases. No significant difference was found between hypopharyngeal and oropharyngeal depths of three vertical and sagittal malocclusions. However, nasopharyngeal depth showed a significant difference between Cl II and Cl III malocclusions and also between Cl I and Cl III malocclusions (P<0.05). No significant difference was found between different groups in vertical malocclusions too.