Journal of Dental Medicine

Background and Aims: A suitable restorative material must have acceptable mechanical properties. The aim of this study was to evaluate the effect of conventional acidic drinks on the micro-hardness of two dental resins.
Materials and Methods: 48 samples of each of P60 and G-aenial composites were prepared and randomly divided into six groups: Coca-Cola, Fanta, yoghurt drinks, soft beer, Sprites and control groups. The study was in 3 steps: after one day in distilled water and after one day and one week of immersion in beverages per day
(6 hours). The Vickers micro-hardness was then evaluated. Finally, data were analyzed by, t-tests, ANOVA and Tukey tests.
Resultes: Comparing the results between the two groups, a significant difference between the two composite was found. After one day in the water, the average micro-hardness for P60 was of 27.12 (kgf/mm²) and 16.51 (kgf/mm²) for G-aenial amount and these differences were found statistically significant (P=0.0001). For the
6-hour maintenance interval, the average micro-hardness between P60 and G-aenial was statistically significant (P=0.0001). For 42 hours, the average micro-hardness ranged between P60 and G-aenial that were statistically significant (P=0.0004). The stiffness of the P60 composite after 42 hours’ storage in soft beer significantly decreased compared with the control group (P=0.03). G-aenial composite hardness after 42 hours of soaking in the Coca-Cola was reduced significantly compared to yogurt drinks (P=0.02).
Conclusion: As a result, the hardness of P60 composite was higher than that of G-aenial. The hardness of both composites reduced in acidic drinks after one week.

Background and Aims: One of the most important challenges for dentists is providing a crown with appropriate marginal fit and gap. The 135-degree tooth preparation found to have some advantages such as technical ease and appropriate finish line record. Despite the advantages of 135-degree tooth preparation, scant research has been done in this area. Therefore, the aim of this study was to compare 135-degree and deep chamfer tooth preparation on the marginal fit and marginal gap of posterior metal-ceramic crowns.
Materials and Methods: Deep chamfer and 135-degree tooth preparation were performed on the two first mandibular molars with healthy coronal tissue and similar size. Impression was taken from each tooth and 30 crowns were made on each die. The sample plastered with fit checkers were pressed under the force of 40 N for 3 min in a universal testing machine. They were measured and recorded under a loop with 40x power in three points on each aspect. Data were analyzed by Wilcoxon and Kolmogorov-Smirnov tests using SPSS version 24.
Results: The mean marginal fit values in deep chamfer and 135-degree were 48.5417µm and 55.3333 µm, respectively with no statistically significant difference (P>0.05). While the mean marginal gap in deep chamfer (2.4833 µm) was significantly higher (P<0.05) than 135-degree (1.0083).
Conclusion: It can be concluded that the marginal gap by 135-degree’s tooth preparation was lower than that of deep chamfer in metal-ceramic crowns. However, no significant difference in the marginal fit between the deep chamfer and 135-degree tooth preparation was found.

Background and Aims: Despite significant advancements in rehabilitation of edentulism with implants, complications such as implant failure before and after prosthetic loading remain concerns. This study aimed to evaluate the frequency of dental implant failure before and after prosthetic loading in some of Yazd dental clinics between 2018 and 2023.
Materials and Methods: In this descriptive cross-sectional study, 1060 patients’ files from three public dental clinics were reviewed. These patients were treated by dental implants between April 2018 and June 2023. The collected data included patients’ age and gender, implant diameter, brand, and placement site, type of prosthesis, and fixture failure after surgical and prosthetic phases. Data were statistically analyzed by independent t-tests and chi-square tests.
Results: The mean age of patients was 55.25 ± 12.37 years and 56.3% were female. The frequency of overall implant failure was 3.4%. The implant failure rate after prosthetic loading was 2.8% in females and 2.3% in males (P=0.47). This rate was 2% and 1.9% for maxillary and mandibular implants, respectively (P=0.5). This amount was 2.4% in molar areas,1.7% and 1.8% in premolar and anterior regions, respectively  (P=0.8). Implant failure rate was 1.3% in overdentures, 5.9% in cement-retained, and 3.2% in screw-retained prosthesis (P<0.001). This amount for implants with a diameter less than 3.75 mm was 2.6% and for those with a diameter more than 4.5 mm was 3.7% (P<0.001). Implants with a diameter less than 3.75 mm had a 2.6% failure rate, whereas those with a diameter greater than 4.5 mm had a 3.7% failure rate (P<0.001). The implants failure rate was 1.6% for Dio brand and 2.5% for Dentis (P=0.5).
Conclusion: The overall implant failure rate in this study was 3.4%, of which 1.5% occurred before and 1.9% occurred after prosthetic loading. The frequency of implant failure after loading was significantly associated with the implant diameter and prosthesis type. This was not related to the patient's gender, implant site, or the implant brand.