Journal of Dental School, Shahid Beheshti University of Medical Sciences

Objective: The aim of this study was to evaluate and compare the effect of dental surface treatment with Er:YAG , Nd:YAG ,CO2 lasers and sodium ascorbate to recently laser bleached enamel by scanning electron microscope (SEM).

Methods: 15caries-free extracted human third molars were selected for this study. The samples were bleached by Heydent JW power activated by diode laser 810 nm. After 7 day, the bleaching procedure was repeated as same as first time. Then, the samples were divided to five groups randomly as follow: Group 1: treated using Nd:YAG laser with output power of 1 W, Group 2: treated using Er:YAG laser with output power of 0.5 W, Group 3: treated using CO2 laser with output power of 0.5 W, Group 4: sodium ascorbate 10%, Group 5: no surface treatment. After treatments, the surfaces were evaluated using Scanning Electron Microscope (SEM) analysis.

Results: The surfaces treated by Nd:YAG laser showed some melting area but the surface treated by Er:YAG laser showed irregular and micro porous surface. CO2 laser treatment of surfaces resulted in melting of superficial layer of dental substrate and micro cracks. Sodium ascorbate did not change the surface except changes raised from bleaching.

Conclusion: Laser conditioning of laser-bleached teeth can be beneficial for enhancing bond  strength of resin material to recently bleached enamel.

Objective: Recently, a wide variation has been reported in delivery of the target torque by spring- style mechanical torque limiting devices (MTLDs) but the effect of aging on their accuracy has not been independently evaluated. The purpose of this study was to determine the effect of aging on the accuracy of spring-style MTLDs.

Methods: In this in-vitro experimental study, 15 new spring-style MTLDs were selected of three different manufacturers. To measure their accuracy, the peak torque was measured in 10 sequences by a Tohnichi torque gauge before and after 1000 times of use. In each sequence, 10 repetitions of peak torque values were registered. The intra-class correlation coefficient (ICC) was calculated and Repeated Measures ANOVA and two-way ANOVA were applied to calculate and compare the absolute error values between the three understudy groups.

Results: The absolute error value was in the range of -3.5(-3) Ncm for 3i group, -2.5 (1) Ncm for ITI and -4-+2 Ncm for Nobel Biocare group. The latter value showed a significant difference with the two former values (p<0.05). All samples in the ITI group had error values within 10% of the clinically acceptable range. About 5% of measurements (maximum of 11.4%) in Nobel Biocare and 9% of measurements (maximum of 14.53%) in the 3i group showed error values greater than the 10% range.

Conclusion: Aging decreased the accuracy of spring-style MTLDs. The magnitude and trend of reduction in accuracy were variable among different groups.

Objective: Extraction of premolars is believed to affect the eruption of third molars. This comparative study aimed to assess the change in angulation of third molars following first/second premolar extraction versus non-extraction orthodontic treatments.

Methods: This historical cohort study was conducted on patients assigned to three treatment groups: extraction of mandibular first premolars (group A), extraction of mandibular second premolars (group B) and non-extraction orthodontic treatment (group C). Each group included 30 third molars. Patients were in the age range of 11-19 years and the third molars were in Nolla’s6-8 stage of tooth development. Pre- and post-treatment panoramic radiographs were analyzed.

Results: The angle between the long axis of the mandibular third molar and mandibular plane increased by 7 (2.2°) in group A and 5.2° in group B and the increase in both groups was statistically significant (p<0.05). Angular changes in group C were not statistically significant (p>0.05). The angle between the long axes of mandibular first and third molars decreased by 6.83 (0.3°) in group A. This reduction was statistically significant (p<0.05).

Conclusion: In extraction orthodontic treatments (versus non-extraction treatments), mandibular third molars tend to straighten up and become upright so the risk of their impaction may be decreased.

Objective: A clinical challenge of using zirconia frameworks is to achieve adequate bond with different substrates. This study aimed to evaluate the effect of bioglass and silica coating of zirconia substrates on microshear bond strength of resin cement to tetragonal zirconia.

Methods: This laboratory experimental study was conducted on zirconia discs. A total of 120 YTZP zirconia (Zirkonzahn) discs were fabricated and based on surface treatments were categorized into 8 groups of 15 including 1. Control, 2.Sandblast, 3. Etch + bioglass powder coating, 4. Silane + etch + bioglass powder coating, 5. Etch + bioglass slurry coating, 6. Silane + etch+ bioglass slurry  coating.

7. Silane + colloidal silica coating, and 8. Silane + etch + colloidal silica coating. Samples were subjected to microshear bond strength testing. In coated groups, thickness of the coating was measured as well. Kruskal Wallis test and ANOVA were applied for intragroup statistical analysis and Dunnett’s test and Mann Whitney U test were used for pairwise comparisons.

Results: The mean bond strength of silica-coated samples was significantly lower than the sandblasted specimens (p<0.001). No significant difference was detected in the mean bond strength between specimens with different glass coatings and sandblasted samples. In other words, bond strength of sandblasted and different glass-coated samples was not significantly different. The thickness of coating in the slurry group was significantly less than in other groups.

Conclusion: Bioglass coating could effectively increase the bond strength of resin cement to  zirconia in short-term.

Objective: E-cadherin is a classic cadherin that plays a key role in epithelial cell adhesion. This protein is being referred to as the suppressor of proliferation and invasion. Limited studies have investigated E-cadherin expression in salivary gland neoplasms. This study sought to assess the expression of E-cadherin and its possible role in progression and invasion of salivary gland neoplasms.

Methods: In this retrospective cross-sectional study, 15 samples of pleomorphic adenoma (PA)   and

9 samples of mucoepidermoid carcinoma (MEC) were immunohistochemically stained for  evaluation of E-cadherin expression. Degree of staining was calculated as the percentage of positively stained cell membranes out of a minimum of 1000 neoplastic cells.

Results: In normal salivary gland specimens, intense membrane staining was observed around the acinar mucous and serous cells as well as the ductal cells. Myoepithelial cells were negative. In PA, intense staining was noted along the membrane of attached cells forming the ducts, islands, cellular cords and cellular sheets but the stromal myoepithelial cells were negative. In MEC, epidermoid and intermediate cells showed intense membrane staining. Mucous cells also showed membrane staining. After statistical analysis, the percentage of positive cells was found to be 82.56±11.66 and 67.4±7.24 in MEC and PA, respectively. This difference was not statistically significant (P>0.05).

Conclusion: E-cadherin expression was not a suitable marker for differentiation of PA from MEC. It was only correlated with cell phenotype.

Objective: Administration of amoxicillin and metronidazole along with scaling and root planning (SRP) is an effective adjunctive therapy for chronic periodontitis. Studies have shown that administration of azithromycin is also effective for treatment of chronic periodontitis. This study aimed to compare the effect of short-term and long-term azithromycin regimen with amoxicillin and metronidazole for treatment of moderate chronic periodontitis in adults.

Methods: This experimental study was carried out on 75 patients with moderate chronic  periodontitis aged 35-50 yrs. with at least one pocket with a probing depth of 4-6 mm and  attachment loss of 3-4 mm in each quadrant. Loe and Silness Gingival Index (GI),  Modified Papillary Bleeding Index (MPBI) of Barnett, Loe and Silness Plaque Index (PLI), Probing Pocket Depth (PPD) and Attachment Loss (AL) were calculated at 0, 2 and 4 days, 6 weeks and 2 and 3 months after therapy. The patients underwent SRP and assigned to three groups. Group one received 250 mg metronidazole plus 250 mg amoxicillin 3 times a day for 7 days. Group 2 received 500 mg azithromycin twice daily for 7 days and group 3 received 250 mg azithromycin once a day for one month. Data were analyzed using ANOVA and Repeated Measures ANOVA.

Results: PLI, MPBI, GI, PPD and AL parameters showed a significant reduction in all groups at all understudy time points (p<0.05). The reduction in BI, GI and PLI parameters was greater in group 3 compared to groups 1 and 2 (p <0.05); but, no significant difference was observed between groups 1 and 2 in this respect. A greater reduction in PPD was noted in groups 2 and 3 compared to group 1 (p<0.05). AL showed a significant reduction in group 3 compared to groups 1 and 2 only in the final follow-up session (p =0.042).

Objective: Active and passive smoking lead to the production of a number of oxidants and antioxidants with various adverse health effects compromising the immune system. Tobacco use increases the production of free radicals as well. The purpose of this study was to determine the effects of passive smoking on total antioxidant capacity (TAC) of serum and saliva in rats.

Methods: This experimental study was conducted on 18 rats with an age range of 7-11 weeks weighing 160-200 g; 9 of them were exposed to cigarette smoke 3 times daily for 8 minutes. The 9 controls were not exposed to cigarette smoke. After injection of 0.2 mg/kg midazolam and 0.5  mg/kg pilocarpine, serum and saliva samples were taken from subjects in the exposure and control groups at 0, 15 and 30 days. Serum cotinine was measured using ELISA kit. TAC of saliva and serum was measured using ferric reducing antioxidant power (FRAP) assay. TAC values at different time points were statistically analyzed in each group using Repeated Measures ANOVA and compared between the two groups using t-test.

Results: At baseline, no significant difference existed between the two groups in terms of serum cotinine concentration but at days 15 and 30, cotinine serum concentration significantly increased in the exposure group. At baseline and 30 days, no significant difference existed between the two groups of passive smoker and non-smoker in terms of serum TAC values but at day 15, serum TAC values were significantly higher in the exposure group. Also, TAC of salivawas significantly higher in the passive smoker group at baseline and at day 15 but at day 30, the difference in this respect between the two groups was not statistically significant.

Conclusion: Based on the obtained results, changes in TAC of serum and saliva in rats due to exposure to cigarette smoke were compensated by their immune system activity. However, further investigations are still required in this respect.

Objective: An immediate complete denture is fabricated before the extraction of all teeth. It has several advantages such as preservation of esthetics, muscular tone, normal speech and reduction of post-operative pain. This report describes a method of using patient’s current fixed partial denture (FPD) for single-appointment construction of interim immediate denture.

Case: We used patient’s existing maxillary FPD for single-appointment fabrication of an interim immediate denture; which was delivered to the patient after the extraction of his remaining maxillary teeth.

Conclusion: Within a short time, an interim immediate denture can be fabricated for patients to preserve occlusion, vertical facial height and facial appearance until the fabrication of final prosthesis.