Journal of Dental School, Shahid Beheshti University of Medical Sciences

Objective: Secondary caries is a common problem in dental treatments and its occurrence is attributed to several factors. The present study aimed at assessing the prevalence of secondary caries in posterior teeth of patients presenting to the Department of Operative Dentistry, Shahid Beheshti Dental School.

Methods: This descriptive study was conducted on 350 patients with 1,339 posterior teeth restored with amalgam or composite resin. Restorations older than 3 years were evaluated. Data regarding presence or absence of secondary caries, age of restoration, location of receiving dental care, tooth brushing technique and use of dental floss and mouthwash were recorded in a questionnaire. Statistical analysis was done using chi-square test.

Results: The prevalence of secondary caries was 26% among the understudy patients. Mesio Ocluso Distal restorations (19.2%) had the highest prevalence of secondary caries. Composite restorations had higher prevalence of secondary caries compared to amalgam restorations (p=0.01). Teeth restored in private dental offices had a higher prevalence of secondary caries compared to those restored in university clinics (p=0.007). Patients who used mouthwash had a significantly lower prevalence of caries recurrence (p=0.05).

Conclusion: The prevalence of secondary caries in patients presenting to the Department of Operative Dentistry of Shahid Beheshti Dental School was higher in the MOD restorations, composite restorations and teeth restored in private dental offices finally it was less in the patients using mouthwash.

Objective: Despite the high strength of zirconia restorations, aging in the oral environment and masticatory loading may result in transformation of tetragonal to monoclinic phase and decrease their strength. Statements in this regard are controversial. This study sought to compare the flexural strength (FS) of Zirkonzahn (ZirkonZahn, Cercon, Ceramill) and Mamut (Dubai Medical Equipment LLC, Dubai, UAE) zirconia ceramics and assess the effect of thermal and mechanical aging on their FS.

Methods: In this in vitro experimental study, 40 bar-shaped specimens measuring 20×5×2 mm were cut from Zirkonzahn and Mamut zirconia blocks and polished. Specimens in the aging groups were subjected to thermocycling (12,000 cycles, 5-55°C, dwell time of 20 seconds). Next, they were subjected to mechanical stress in a chewing simulator (40,000 cycles, 200N force). The three-point flexural strength (TPFS) was determined in megapascal (MPa) using a Universal Testing Machine at a crosshead speed of 0.5 mm/min. Data was analyzed using two-way ANOVA.

Results: The mean and standard deviation (SD) of TPFS of Zirkonzahn and Mamut specimens in the no aging group was 809.57 (205.95) and 708.53 (158.72) MPa, respectively. These values were

810.53 (158.96) and 839.06 (217.49) MPa for the Zirkonzahn and Mamut specimens subjected to aging, respectively. Type of zirconia (Zirkonzahn or Mamut) and exposure to aging process (p=0.27) had no significant effect on TPFS of specimens.

Conclusion: Within the limitations of this study, the results showed that the process of aging did not decrease the TPFS of Zirkonzahn and Mamut specimens. Thus, these ceramics may be successfully used in the clinical setting.

Objective: Studies have demonstrates that physical properties of denture base affect patient satisfaction and acceptance. Thermal conductivity is among the most important properties of denture base influencing the sense of taste and gingival health. The conventionally used acrylic resin has a low coefficient of thermal conductivity. This study aimed to improve the thermal conductivity of acrylic resin by adding small concentrations of nanosilver.
Methods: In this laboratory experimental study, 0.2wt% and 2wt% silver nanoparticles measuring 10-100 nm were mixed with the conventional denture base acrylic powder. Cylindrical samples were fabricated and thermal conductivity was measured. One-way ANOVA and Scheffe’s post-hoc test were used to compare the mean thermal conductivity of different groups. Data were analyzed using SPSS 15 and p<0.05 was considered statistically significant.
Results: The thermal conductivity of resins reinforced with nanosilver was significantly higher than that of the conventional resin. By increasing the amount of nanoparticles in the acrylic powder, thermal conductivity further increased.
Conclusion: Addition of small amounts of nanosilver to denture base acrylic resin increases its thermal conductivity.

Objective: Different techniques have been suggested for the repair of bone defects at the injured sites. Use of biomembranes, or application of plasma rich in growth factor (PRGF) at the site of proliferation of osteoblasts are among the suggested techniques. The current study aimed to compare the biocompatibility of human periodontal ligament fibroblasts (hPLF) cultured on Hypro-Sorb F, Pericardium and Tutodent resorbable membranes coated with PRGF.

Methods: This experimental study was conducted on four resorbable membranes namely Hypro- Sorb F, Pericardium, Tutodent and Vicryl. Fibroblast cells isolated from the periodontal ligament of premolar tooth were passaged three times and 105 cells/ cm2 were cultured on  membranes coated with PRGF. After 72 hours, the cells were evaluated in terms of biocompatibility and alkaline phosphatase (ALP) activity. Statistical analysis was carried out using one-way ANOVA.

Results: PRGF increased cell adhesion and Tutodent membrane coated with PRGF showed the highest cell adhesion compared with Hypro-Sorb F and Pericardium membranes (p=0.005).

Conclusion: PRGF increases cell viability and ALP activity of cells on biomembranes. PRGF treatment increases the adhesion of fibroblast cells to these membranes.

Objective: Dental profession is associated with a high level of stress experienced by clinicians in private practice as well as students and instructors in dental school environment. The purpose of this study was to detect the main stressors in dental students of School of dentistry, Babol University of Medical Sciences in 2011-2012.

Methods: In this descriptive, analytical study, data were collected via Dental Environment Stress (DES) questionnaire. Understudy subjects were all dental students in Babol University (n=199) selected by census sampling. Data were analyzed using chi-square and t-tests.

Results: Six factors were found to be the main stressors in dental students: 1. More than one exam in the same day (2.76 (0.596)); 2.Insufficient time interval between exams (2.74 (0.581)); 3.Insufficient exam time (2.62 (0.693)); 4.Instructors humiliating students or showing their dissatisfaction of the procedure done by the students in front of patients (2.61 (0.618)); 5.Too many credits offered per semester (2.35 (0.849)) and 6. In appropriate behavior of the staff (2.33 (0.793)). Of all departments in Babol Dental School, departments of Prosthodontics, Radiology and Endodontics caused the highest level of stress and anxiety in students and had statistically significant differences in this regard with other departments.

Conclusion: The stressors had greater impacts on female students particularly the fourth year dental students. Attempts must be made to modify the curricula and exam schedules particularly in the most stressful departments to decrease the level of stress in dental students.

Objective: Numerous studies have emphasized on the importance of developing an ideal educational system for high-quality dental education. The present study sought to assess the perception of dental students on operative dentistry education in Department of Restorative Dentistry, Shahid Beheshti Dental School, Tehran, Iran.

Methods: In this descriptive cross-sectional study, 220 students were selected and given a questionnaire including demographic , grades in operative dentistry clinical and didactic courses, the efficacy of preclinical courses in preparing students for clinical practice, ways to improve competency and expertise of students for clinical setting, student’s opinion on relating the  assessment tests with the taught topics, required instructional resources for assessment of students’ proficiency in restorative dentistry and satisfaction rate of students with clinical courses offered in the current curriculum.  Data were analyzed using descriptive statistics (SPSS 18).

Results: The Clinical Operative Dentistry 3 and Preclinical Dental Anatomy received a mean satisfaction score of 3.31 and 2.74, respectively. Furthermore, 57.3% of students highly emphasized the necessity of studying textbooks of restorative dentistry. 50.5% of students believe that lectures  by instructors along with active participation of students were the best method for didactic operative dentistry courses. In addition, 60.5% were in favor of using a combination of textbooks, lectures, and class notes for the assessment of students’ learning.

Conclusion: The present study revealed that Department of Restorative Dentistry in Shahid Beheshti Dental School is successful in its teaching and achieving students’ satisfaction. However, some revisions need to be made in educational methods and contents and active participation of students in class discussions should be encouraged as well.

Objective: For the assessment of primary arch form, different methods have been used including qualitative classifications, inter-canine and inter-molar widths and quantitative and numerical methods using mathematical models. The purpose of this study was to compare the validity and reliability of Cast Analyzer X Iranian software with those of Curve Expert Professional version 1.1 for arch form construction based on mathematical models.

Methods: This diagnostic, in vitro study was performed on 18 sets of dental casts with normal Class I occlusion. The clinical buccal points (bracket attachment sites)(CBPs) were marked on each tooth and their spatial coordinates were digitized using a three-dimensional (3D) laser scanning system. These coordinates were entered in Cast Analyzer X and Curve Expert software programs. Arch forms were constructed by the software programs using Brown’s beta function, Noroozi’s beta function and fourth order polynomial equation. The root mean square (RMS) of the distance from a reference point to their corresponding points on the curve was calculated. The RMS values in the  two software programs were compared.

Results: The RMS values in Brown’s beta function, Noroozi’s beta function and fourth order polynomial equation were significantly different in the Cast Analyzer X software (p<0.001) and the fourth order polynomial equation had the lowest RMS. The difference in RMS values between the two software programs was not clinically considerable and was 0.45 and 0.68 mm for the fourth order polynomial equation and Brown’s beta function, respectively.

Conclusion: Considering the RMS values, the fourth order polynomial equation is the most suitable analysis for describing normal dental arch forms best fitted with the CBPs. Although the difference between the two software programs was statistically significant, this difference was not clinically noticeable. The RMS value was lower in Cast Analyzer X and consequently the fitting of curves  with the landmarks (CBP) was better in the Iranian software.

Objective: At present, growth factor-containing products such as enamel matrix derivatives, recombinant bone morphogenetic protein (rh-BMP), recombinant platelet derived growth factor and platelet rich plasma (PRP) have gained increasing attention. PRP is an autologous source of platelet growth factors used to enhance healing of soft and hard tissues. PRP has gained popularity due to its autologous nature, easy procurement and low cost.

Review of Literatures: This study focuses on procurement and clinical applications of PRP.

Conclusion: Controversy exists regarding the efficacy and applications of PRP and longitudinal studies are required to further elucidate this subject.