Journal of Dental School
Year:2012 | Volume:30 | Issue:1 (91)|Papers Count:11

Objective: Implant-retained overdenture is the standard of treatment of edentulous patients. The aim of this study was to compare the effect of different implant location (ABDE, 6AE6, 6BD6) on the retention and stability of mandibular implant overdenture with ball attachment.Methods: An experimental study was designed. An acrylic resin model of edentulous mandible with six implant in the location of first molars, first premolar and between lateral incisor and canine on the left and right side was fabricated. A metallic overdenture was fabricated precisely adapted to the model and attached to a Zwick testing machine (crosshead speed of 51 mm/min). The ball attachments were screw in three patterns. The balls were first screwed in ABDE, then in 6AE6, and finally in 6BD6 position. Dislodging tensile forces were applied in three vertical, oblique, anterior-posterior directions for each sample. For each of these three situations, five tests were done. The maximum dislodging force was measured. Normal distributions of data were analyzed with Shapiro-Wilk test. Levene’s test analyzed the variances. A Three-way ANOVA test was employed followed by Tukey’s test.Results: The amount of vertical load was significantly higher than the oblique and Anterior-posterior load (P<0.001). The amount of ant-post load is significantly higher than the oblique load (P<0.001). The average of MDF is significantly higher in 6BD6 position (P<0.001). This average was also significantly lower in ABDE position (P<0.001). The amount of measured force was the lowest in ABDE and the highest in 6BD6 positions (ABDE=64.51 N and 6AE6=66.06 N). Vertical and oblique dislodging force are the minimum and maximum measured forces respectively (mean vertical= 87.95 N, mean Lateral= 48.1 N and mean Ant. Post= 63.5 N).Conclusion: Lateral and Ant-Post dislodgment forces are higher in 6BD6 and 6AE6 positions respectively. The greatest vertical dislodgment force was observed in 6BD6 position. Vertical retention was higher than lateral and Ant-Post retentions. The more posterior position the distal implant the more the retention and stability.

Objective: Nowadays, composite restorations have gained more popularity and are widely used due to their high esthetic properties, rapid application, ease of use and low costs. There are various composite resins of different brands available in the market and it is necessary to find the most favorable one in terms of reliability and long term prognosis. The present study aimed at evaluating and comparing the compressive strength of hybrid and nanocomposites.Methods: In this experimental in-vitro study 4 different types of composite resins were used as follows: Group 1- Filtek Z 250 (3M) (hybrid composite) Group 2- Filtek Supreme (3M) Group 3-Gradia Direct X(GC) Group 4-Herculite XRV Ultra (Kerr Hawe)composite resins (groups 2, 3 and 4 are nanocomposites). Twelve samples were made in stainless steel molds of 4mm diameter and 6mm height of each composite. Following photopolymerization of cylindrical samples using Radi plus light curing unit (SDI limited), the specimens were stored in distilled water at 37°C for 48 hours. The specimens were subjected to compressive stress test using Mechanical Testing Machine (Zwick/Roell) at cross head speed of 0.5 mm/min. One way ANOVA and Tukey’s Post-hoc tests were employed for statistical analyses and determining level of significance.Results: The obtained results were as follows: Group 1: 362.51 group 2: 266.70 group 3: 268.72 and group 4: 275.75 Newton. Compressive strength of group 1 (Filtek Z 250) was higher than other three groups and it was statistically significant (P<0.05). No statistically significant difference was detected among groups 2, 3 and 4.Conclusion: Hybrid composite showed more compressive strength than nano composites.

Objective: Extensive dental treatments for young healthy and medically compromised children are performed under general anesthesia in a daily basis. Considering the side effects of sedatives and anesthetic drugs and also the high risk of dental caries in this group of patients, it is especially important to decide the safest and the most cost beneficial treatments. This study aimed at clinical evaluation of the failure rate of various dental procedures performed under general anesthesia on children presenting to Mofid Pediatric Hospital in Tehran during 2010-2011.Methods: This descriptive cross sectional study was conducted on a total of 104 patients who received dental treatments under general anesthesia in Mofid Pediatric Hospital and a minimum of 6 months had been passed from their treatment. Dental examination was performed on a dental chair using dental mirror and a probe in the out-patient dental clinic of Mofid Pediatric Hospital. Recorded information included all types of treatment failures occurred in patients that were registered in especially prepared forms. Overall difference in failure rates was calculated using Chi square test while multiple logistic regression test was used to investigate the effect of different factors on the failure rate of treatment modalities.Results: Our study results indicated that stainless steel crown (SSC) was the most successful treatment with the lowest failure rate (1.5%). SSC had a significantly lower failure rate compared to amalgam (7.9%) and posterior composite restorations (9.9%) (P=0.003 and P<0.000, respectively). Composite buildup of the anterior teeth had the highest failure rate (22.4%) among all types of anterior restorations (11.6%) (P=0.009). The failure rates of both pulpectomy and pulpotomy procedures were found to be reasonably low rating at 0.8% and 1.1%, respectively.Conclusion: The highest failure rate belonged to anterior teeth build-ups. Teeth restored with SSC had the highest success rate indicating it as the treatment of choice for badly carious posterior teeth of children who require dental treatments under general anesthesia.

Objective: Propolis, a natural product of the honeybee, is currently used as an anti-inflammatory and antimicrobial agent. Using different antibacterial agents is an important step to reduce the number of microorganisms within the root canal and improve the endodontic treatment prognosis. The present in vitro study investigated the antibacterial efficacy of Propolis against Enterococcus faecalis compared to calcium hydroxide.Methods: In this experimental study, 42 single-rooted human teeth were selected and their smear layer was completely removed after access cavity and canal preparation. After infecting the prepared canals with Enterococcus faecalis species, negative control group was used during sterilization period and in two groups of 18 each, canals were filled with 30%propolis extract and calcium hydroxide, respectively. No material was added to the positive control group. The specimens were stored in CO2 incubator for 72 hours, 1 week and 1 month and afterwards, samples were taken from inside the canals and Enterococcus faecalis colonies were counted. Number of colonies at different time intervals was statistically analyzed using Kruskal-Wallis test. Mann-Whitney U test was used to compare the number of colonies after using the understudy medicaments.Results: Number of colonies was 55, 000±46, 368.09 and 43, 333.33±48, 027.077 after incubation for 72 hours and using 30% Propolis extract and calcium hydroxide, respectively. After 1 week incubation, number of colonies was 166.67±408.25 in the Propolis group and zero in the calcium hydroxide group. No colonies were observed after 1 month incubation in both groups. No significant differences were noted between two medicaments at different time intervals.Conclusion: In general, antimicrobial activity of Propolis against Enterococcus faecalis species was comparable with that of calcium hydroxide at different time intervals. Therefore, it can be used as an alternative natural material for disinfection of canals during endodontic treatment.

Objective: Contamination leads to decreased bond strength causing failure of restorative treatments. The present study evaluated micro-shear bond strength of composite-composite after saliva contamination and searched for the best method to maintain primary bond strength.Methods: In this in-vitro trial, specimens made by Z100 composite resin were divided into 7 groups each containing 15 samples and were prepared as follows: Group 1- Control (no contamination), Group 2: Saliva+air drying, Group 3- Saliva+rinsing+ air drying, Group 4- Saliva+ rinsing+ air drying+ etching, Group 5- Saliva+ rinsing+ air drying+ etching+ bonding, Group 6- Saliva+ alcohol, and Group 7- Saliva+ 0.5 mm removal of composite+ rinsing + air drying. Z100 composite was added through tiny tubes (0.7x1 mm) to the prepared surfaces and cured. The microshear bond strength was then determined. Data were analyzed using ANOVA and Tukey’s multiple comparison tests.Results: Mean and standard deviation of the microshear bond strength was 23.0±3.60 MPa in group 1, 11.71±2.49 MPa in group 2, 17.60±4.25 MPa in group 3, 21.84±6.34 MPa in group 4, 21.25±7.58 MPa in group 5, 21.65±5.53 MPa in group 6 and 17.34±5.95 MPa in group 7. Differences between groups 1 and 2 (P<0.0001), 2 and 4 (P<0.0001), 2 and 5 (P<0.001) and 2 and 6 (P<0.0001) were statistically significant.Conclusion: The results of this study showed that air drying of the surface after saliva contamination decreased microshear bond strength significantly. All cleansing methods increased bond strength of the specimens up to that of the control group.

Objective: This randomized clinical trial was aimed at comparing the outcomes of palatal connective tissue + Bio-Oss + PRGF versuscollagen membrane + Bio-Oss+ PRGFin the treatment of intrabny defects.Methods: Fifteen patients affected by chronic periodontitis were enrolled. Each patient had at least two intrabonydefect (³3 mm). They were randomly assigned into two groups: patients treated i) with collagen membrane + PRGF + Bio-oss (control group) and ii) with palatal connective tissue as membrane + PRGF + Bio-Oss (experimental group). Clinical and intrasurgical examinations included probing depth (PD), clinical attachment level (CAL), gingival recession (GR), defect fill (DF), alveolar crest level (AC) and defect resolution (DR) were measured at baseline and after 6 months with re-entry surgery. Statistical analysis was performed usingTwo-way Repeated Measure ANOVA and Wilcoxon.Results: After 6 months, all of the evaluated clinical parameters showed statistically significant changes from baseline within each group (p<0.05). The test group showed a significantly smaller amount of gingival recession as compared with control group (0.8 mm versus 1.7 mm respectively; P<0.05). But there were not any statistically differences in other clinical parameters between the test and control groups (P>0.05): pocket depth reduction (3.7 mm versus 3.5 mm), clinical attachment gain (1.8 mm versus 1.6 mm), alveolar crest loss (1.8 mm versus 1.7 mm), defect fill (2.3 mm versus 2.2 mm) and defect resolution (4.1 mm versus 3.9 mm).Conclusion: According to the results obtained from this study it can be suggested that clinical effects of application of palatal connective tissue as a membrane and collagen membrane, in combination with Bio-Oss and PRGF in treatment of vertical bone defects, did not have any statistical significant differences except for gingival recession that was statistically smaller in connective tissue group.

Objective: The aim of this study was to compare retention of implant-tissue supported overdentures with ball attachments in the most anterior and posterior implant positions at the symphysis region.Methods: An acrylic resin model of edentulous mandible with no undercuts was fabricated. Two pairs of implants, two by two, were placed symmetrically in the most anterior and posterior positions in the anterior mandible. Two were placed at 5 mm distance from the midline in anterior positions while the other two were inserted 5 mm mesial to mental foramina in posterior position.A metallic overdenture was made on the model precisely. Then an overdenture housing was prepared on the framework and joined to it. The ball abutments were screwed into the pair of implants in different positions and the complex of attachment housing and clinical insert was attached to the over denture housing. Five samples were tested for each position. Zwick testing machine applied and measured tensile forces in vertical direction for each sample. Maximum Dislodging Force (MDF) was recorded at the moment of complete dislodgement of over denture from the model.Independent sample T-test was used to analyze the data and results reported by confidence coefficient of 95%.Results: There was no statistically difference in retention of implant-tissue supported over dentures in the most anterior and posterior positions of implants at symphysis region (P>0.05).Conclusion: The amount of retention is the same in the most anterior and posterior positions of implans in anterior mandible.

Objective: The purpose of this study was to investigate the histologic interaction between two different allografts and first premolar root; following orthodontic tooth movement.Methods: This experimental study was conducted on 4 male dogs. In each animal, four defects were created at the mesial aspects of the maxillary and mandibular first premolars. The defects were filled with DFDBA or FDBA equally. NiTi closed coil with 150 gr force was used for mesial movement of the first premolar tooth. When the experimental teeth moved about halfway into the defects i.e. after nine weeks, the animals were sacrificed and the area of interest was harvested. The first premolar root and adjacent tissues were histologically evaluated. Tooth movements were analyzed using paired t-test.Results: Study findings demonstrated that it was possible to move a tooth into a defect, filled with DFDBA or FDBA with the same rate of tooth movement. Mean tooth movement in DFDBA and FDBA was 2.6±0.11 mm in DFDBA and 2.4±0.12 mm in FDBA. Apical root resorption occurred on the pressure sides in both groups.Conclusion: These findings indicate that FDBA and DFDBA could be used as a biocompatible bone substitute for bone defects subjected to orthodontic tooth movement.

Objective: The purpose of this study was to investigate the histologic interaction.Background and Aim: Theses are among the most important research sources of the universities and should be authored according to the international standards of scientific writing. The present study aimed at determining the accuracy of the methodology section of graduate and post-graduate theses conducted in Shahid Beheshti Medical University, School of Dentistry from March 2009 to October 2011.Methods: In this descriptive cross-sectional study all approved theses of the Shahid Beheshti Medical University, School of Dentistry from March 2009 to October 2011 were evaluated according to the international check lists. For data analysis, SPSS version 16.0 software, ANOVA and independent t-test were used.Results: A total of 101 theses with observational design and 72 with experimental design were evaluated. The mean conformity of observational theses with STROBE check list was 75%. The highest conformity was observed in the complete description of inclusion and exclusion criteria (95%) while the lowest conformity was observed in the bias control (48%). The mean conformity of the interventional theses with all the items of CONSORT checklist was 62%. The highest conformity was found in complete description of the type and process of intervention (90.3%) whereas the lowest conformity was found in allocation concealment mechanism (88%). No significant correlation was found between the presence of a consulting professor and academic ranking of the thesis instructor and the mean score of thesis. Conclusion: professor and academic ranking of the thesis instructor and the mean score of thesis.Conclusion: In observational theses, the lowest conformity was observed in the description of the bias control; whereas, in interventional theses the lowest conformity was detected to be in allocation concealment mechanism.