Journal of Dental School
Volume:29 Issue: 1, 2011

Metal-ceramic crowns have been considered an acceptable treatment plan for the rehabilitation of edentulous patients in implant dentistry. Furthermore, porcelain fractures associated with an implant-supported metal-ceramic crown occur more than tooth-supported restorations; then, assessment of the associated factors in this regard needs more studies. The present study evaluated porcelain fractures in the implant-supported crowns compared to the tooth-supported metal-ceramic crowns in the patients referred to the Specialist Ward of Fixed Prosthodontics, Shahid Beheshti University of Medical Sciences, Dental School during 2001-2010. In this retrospective descriptive study, 42 patients (24 males, 18 females) having received implant or tooth-supported metal-ceramic crowns were underwent follow-up examinations by two operators. There were 185 tooth-supported and 158 implant-supported units in total. Porcelain fractures were assessed regarding California Dental Association criteria (severe, small, no fracture). The presence of parafunctional habits, opposing dentition, treatment location, type of prostheses, implant system, type of occlusion, number of prostheses units and the applied cements were determined in the prostheses. The results were reported by descriptive statistics and the data statistically compared by Chi-square and Exact Fisher tests as well as odd's ratio calculation. Porcelain fracture occurred in 5.4% tooth-supported (1.6% severe and 3.8% small ratings) and 10.2% implant-supported (5.1% severe and 5.1% small ratings) crowns without significant differences. Porcelain fractures had approximately 2 times higher odds (odd's ratio=2.1) in patients with bruxism habits, with higher rates in mandibular regions than maxillary, in posterior regions than anteriorly located prostheses and in multiple-unit prostheses than single units. However, overbite, overjet, opposing type and angle classification showed no significant effect on the porcelain fractures. Implant-supported crowns showed 2 times more porcelain fractures than tooth-supported prostheses and the frequency of post-treatment complications was statistically higher in implant- compared to tooth-supported metal-ceramics. However, the difference of two systems was not statistically significant regarding porcelain fractures

Apical leakage of tissue fluids around root canal space was cited as the most common cause of root canal treatment failures, for which, fillings of root canal with root filling materials was suggested to achieve adequate apical seal and to prevent leakage. Due to the importance of adequate apical seal, different root canal filling materials were developed and used for this purpose. The purpose of this study was to compare bacterial apical leakage through root canal filling materials of Resilon, GuttaFlow and Gutta-Percha with AH26 sealer. In this in vitro experimental study, 55 single-rooted teeth with healthy roots meeting the study inclusion criteria were selected and randomly divided in 3 experimental groups each containing 15 specimens and 2 positive and negative control groups each with 5 samples. The teeth crown were sectioned near the CEJ, the teeth canals were instrumented with step- back technique while group 1 was obturated with Gutta-Percha, and group 2 with Resilon using a cold condensation technique. Group 3 was obturated with GuttaFlow as recommended by manufacturer. Two-chamber bacterial methods were used to assess bacterial apical leakage by means of Enterococcus Faecalis bacterium during a 60 days time interval. The data were analyzed by Kaplan-Meier test. In root canals filled with Resilon, the median of the day in which leakage was occurred was 17, in Gutta-Percha specimens it was 18 and in canals filled with GuttaFlow the median was 19. 93.3% of the roots filled with each Resilon or Gutta-Percha showed apical bacterial leakage during 60 days while in canals filled with GuttaFlow, the leakage was observed in 80%. Kaplan-Meier test showed no significant differences comparing the day in which the leakage was occurred or the overall incidence of leakage in three materials. Under the conditions of the present study, three root canal filling materials showed similar rates of apical bacterial leakage as no significant statistical differences were noted among them.

The aim of this study was to compare the effect of Mtwo rotary system and step back hand system in reduction of enterococcus faecalis bacteria from the root canals of human extracted teeth.

In this study, 62 human extracted teeth were divided into two equal experimental groups with 23 teeth each and one control group two extra control groups with 5 teeth each as negative and positive were chosen for confirmation of the canal reinfection too. All of the samples were prepared by K Flie No 20 and Gates Glidden No 2 & 3 before sterilization. Then the teeth were autoclaved and reinfected with enterococcus faecalis. The experimental groups were instrumented either with Mtwo system or step back system. Bacteriological samples were taken after instrumentation to determine the amount of remaining bacteria.

In the group 1, fourteen samples and in the group 2, twelve samples represented complete reduction of bacteria. There was not statistically significant difference between two techniques (p>0.05)

Both Mtwo and step back systems are the same on reduction of the bacteria from root canal system, up to the same apical size.

Periodontal diseases consist of chronic inflammation in periodontal tissues that induced by periodontophathic bacteria and develop by host immune responses. Several studies reported that IL-17 and RANKL are important in autoimmune diseases, inflammation and bone resorption. Since the exact role of them remains unknown, so the aim of this study was to evaluate the relationship between IL-17A or RANKL concentrations and periodontal diseases. In this analytical and case control study; GCF samples were collected from forty patients with gingivitis and moderate to advanced chronic periodontitis referred to the periodontics clinic of Shahid Beheshti University of medical sciences. IL-17A and RANKL were assayed by enzyme-linked immunosorbent assay. The differences of IL-17 and RANKL concentration analyzed between gingivitis and periodontitis, by Mann-Whitney U-test. The protein level of IL-17A was significantly higher in periodontitis group, while there was not any significant difference regarding RANKL concentration. The elevated level of IL-17A in periodontitis suggests that IL-17A might be an important cytokine in pathogenesis of periodontal disease, which presumably exerts its effect independent of RANKL. Correlations between concentration IL-17A with PD and CAL amplify the role of IL-17A in periodontal tissue destruction.

In recent years, stem cells are of great interest in order to regenerating disturbed tissue and organs. These cells are commonly isolated from bone marrow, but other tissues are interested in recent years. In this study, we decided to evaluate possibility of isolation of stem cells from oral connective tissue and assess their characteristics. This is an experimental study. Sampling from bone marrow and oral connective tissue of beagle dog was done under general anesthesia. Isolation of bone marrow stem cells was done according to the established protocols. For isolating connective tissue stem cells, this protocol was changed a little. Then characteristics of the cells were compared to evaluate if the cells from connective tissue are stem cells. Morphology of the cells from bone marrow and connective tissue were the same. The result of colony-forming-unit assay was relatively similar; however, the percentage of connective tissue colonies was more. Population doubling time was similar too. In addition, both of groups of cells differentiated to osteoblasts in osteogenic media. The cells isolated from oral connective tissue have the characteristics of stem cells, including: fibroblastoid morphology, self renewal properties, high proliferation rate, and differentiation potential.

Nowadays, there is great emphasis on the commitment of dentists as health care workforce, thus, awareness of their motivations and expectations is important in order to promote general and oral health. The aim of the present study was to evaluate dental post graduate student’s motivations and career choice plans in relation to sex, marital status and parent’s education in Shahid Beheshti University of Medical Sciences, Tehran, Iran in 2009-2010. A total of 116 dental post graduate students have been participated in this survey and a valid and reliable questionnaire was designed in three sections based on previous studies consisting of motivations and career choice plans and was distributed among them. Data were entered in to SPSS (16) and were analyzed with Mann Whitney test. Social/occupational prestige was the most important motivation (%92). On the other hand, there was significant association between motivations and career choice plans with marital status and parent’s job as dentist/physician. Influence of family had significantly more impact among residents who had dentist/physician parents compared to those with parents in other occupations (p=0.011) (%65). The most important career choice plan was to work in private sector (94/84%). The married people were inclined to constitute a professional dental clinic with colleagues (p=0.0037) (%86). Single students had more interest in research in the field of dentistry (p=0.047) (%60). The most important motivations were social/ occupational prestige, income, independence and personal interest in dentistry respectively. The most important career choice plans were working in private sector, recruitment in university as dental faculty and constitution a professional dental clinic with colleagues.

Polymerization shrinkage is one of the disadvantages of Polymethyl Methacrylate, resulting in distortion of resin denture bases. One of the methods, designed to reduce this distortion, is mechanical anchoring to the cast. This study aimed to evaluate the effect of numbers and locations of retentive holes on reducing polymerization distortion. This was an experimental study, including 48 similar master casts in 4 groups, fabricated during the study. A power analysis using a power factor of 0.8 and a significance level of 0.01 determined the sample size of 12 casts per each test group. Groups were assigned as: A (control); B (one anchoring hole in midline along the posterior border); C (additionally, two extra anchoring holes in lateral palate, between midline extending to ridge crest); D (two more anchoring holes along the midline, within 15 mm and 20 mm from the posterior border(. An Olympus-SZX9 measuring microscope was used for the gap measurement across the denture base and cast interface. Variables were the gap distance between the denture base and the cast in midline, in PPSA and the mean gap in right and left lateral palate in PPSA. The data were analyzed with one-way ANOVA followed by the Post-Hoc test. Variables were significantly different in four studied groups (p=0.000) and the gap distance between the denture base and the cast in mid-palate was less affected than lateral palate in anchorage technique. In general, anchoring significantly reduced mean gap distances (p=0.000). Generally, anchoring during processing, improved adaptation of the denture base to the master cast. Mechanical anchorage between denture base and cast significantly reduced the gap distances in lateral and mid-palate; and this decrease was significantly affected by numbers and locations of anchoring holes.

Diagnosis of periapical pathology is of paramount importance in enabling the clinician to provide immediate and appropriate dental treatment. Both intraoral digital radiography and film radiography are used to detect periapical pathology. The purpose of this study was to compare the accuracy of digital radiographic imaging with conventional radiography in detecting chemically created lesions. For conducting this experimental study one cow cadaver mandibular Jaw was used. After building four 1×1cm2 pools at first molar areas, 35% Hydrochloric acid solution used to create chemically lesions. The designed time for chemically lesions was 4, 12, 24 and 36 hrs following acid exposure. Then, 1 digital and 1 conventional image with E-Speed film was taken from each half-jaw and images evaluated by five examiners. Wilcoxon signed Ranks test used for statistical analysis. The results of this study showed that diagnosis were more precise in detecting lesions with RVG than conventional radiography. This difference was statistically significant (p<0.05). Regarding the acceptable quality of digital radiographs comparing to conventional radiographs we suggest using this method for detecting bone lesions.