ABSTRACT
Composite resins require time to complete their polymerization. This process usually reaches its maximum rate after 24 hours. On the other hand, immediately after restoration, water sorption results in hygroscopic expansion of composite resins and the mentioned two factors usually reachequilibrium after a week. Considering the effect of mentioned processes on the microleakage of composite restorations, the purpose of the present study was to evaluate the effect of finishing and polishing time on the mean microleakage of composite restorations. In this in-vitro experimental study, 60 sound human premolar teeth were selected. A standard Class V cavity was prepared measuring 1.5 mm in depth, 3 mm in width and 2 mm in length on the buccal surface of each tooth and incrementally restored with composite resin. Next, the teeth were randomly divided into 4 groups. The teeth in groups 1, 2, 3 and 4 were finished and polished immediately, 15 min, 24 h and one week after storage in distilled water at 37°C, respectively. Specimens in each group were subjected to 500 thermal cycles. The teeth were then coated with adhesive wax and nail varnish and immersed in 2% fuchsin solution for 24h. The specimens were washed and each sample was longitudinally sectioned in half by a diamond saw. Both halves were evaluated in terms of dye penetration under a stereomicroscope at 28X magnification. For each sample, the section with greater degree of microleakage was selected. Kruskal Wallis test and Mann Whitney U test were used for data analysis with a 99.1% confidence interval. The lowest mean microleakage was observed in the occlusal margin of group 3 teeth; while the highest mean microleakage belonged to the occlusal and gingival margins of teeth in group 2. A significant difference was noted between the 4 groups in occlusal margin microleakage [P<0.009]. However, no such difference was found in gingival margin. This study showed that the finishing and polishing timewas effective on the mean microleakage in the enamel margin of composite restorations. The best time of finishing and polishing was 24h after the restoration. Time of finishing and polishing had no effect on microleakage in dentin margins of restorations. Key words: Composite resins, polishing, microleakage
ABSTRACT
Posts are used as retention mechanism in repairing fractured or missing crowns of teeth. Nowadays composite fiber postes have eliminated most disadvantages of prefabricated metal and casting posts. the purpose of this study is to compare the amount of fracture resistance in three fiber posts [carbon fiber, quartz fiber, glass fiber] while shearing force [perpendicular to long axis] is applied. This invitro, experimental study was performed on 30 maxillary lncisors with the same size without fracture, dentin caries or any root problems they were in three groups randomly. [Carbon fiber, quartz fiber, glass fiber] After root canal treatment and post space preparation with specified drill, samples were carried under universal test machine [prinston] to evaluate the amount of fracture resistance Data was analyzed with Kruskall-wallis Test under spss13. There was significant difference in fracture resistance in all three groups. [P=0.001]. Also, the carbon fiber posts had the maximum and the glass fiber posts had the minimum amount of fracture resistance. since the carbon fiber posts have the maximum fracture resistance in comparison with other groups, their application in anterior teeth is preferred
ABSTRACT
Introduction: Since content of mediastinal cavity as tract. Great vessels and heart are of vital importance. Mediastinal tumours should be diagnosed and treated exact, accurate and on time
Materials and Methods: We have operated 75 patients with mediastinal tumour in Valiasr Hospital [Tehran University of Medical Science] and Ghaem Medical Center [Mashhad University of Medical Science], from 1996-2002
Results: They were 37 female and 38 male, in similar reports in literature both sexes are equal. Frequency of various histologic diagnosis of these patient are: 25 lymphomas [33.33%], 22 thymic tumours [29.33%] 13 neural tumours [17.33%], 6 substernal thyroid [8%], 2 germ cell tumours, 1 cavernous hemangioma, 1 cystic higroma, benign tratoma, 2 invasive condrosarcomas, 2 misclaneus tumours. Our operative approach and procedure have been, 24 left or right thoracotomies, 21 sterenotomies, 14 anterior mediastinotomies, 9 lymph node biopsies, 6 thyroidectomics with cervical incision, 1 higroma resection
Conclusion: Mediastinal tumours are uncommon, regarding to other reports in literature 8 to 10 patients with mediastinal tumours are operated annually in referral centers. And mean rates of our patients have been 11 cases per year [2,3]