Finite element stress analysis of composite resin veneers for diastema closure.

The fracture of restorations used for diastema closure is a clinical concern. The objective of this study was to perform a finite element-based comparative analysis of functional stress patterns in composite resin veneer restorations used for diastema closure to determine the influence of factors such as the preparation design, proximal extension, loading level, and vector of stress (loading angle). Three-dimensional finite element stress analysis was performed on a maxillary central incisor model to examine the stress distribution resulting from a nanofilled composite veneer restoration with 4 different extensions of unsupported composite (0.5, 1.0, 1.5, or 2.0 mm) and 2 different preparation designs (partial or full) under 3 loads (50, 150, or 250 N) and 3 loading angles (60°, 90°, or 125°). The maximum stress was found to be concentrated on the full-preparation design with a 0.5-mm mesial extension under a 250-N load and 60° loading angle. The minimum stress was found with the partial-preparation design with a 0.5-mm mesial extension under a 50-N load and 90° loading angle. Based on the results of the present study, a partial-preparation design is preferred when nanofilled composite resins are used for diastema closure.

Natural Resistance Associated Macrophage Protein 1 Gene Polymorphism is Associated with Chronic Periodontitis Not Peri-Implantitis in an Iranian Population: A Cross Sectional Study.

In inflammatory diseases such as peri-implantitis (PI) and chronic periodontitis (CP) both adaptive and innate immunity play a part. Natural resistance associated macrophage protein 1 (NRAMP1) has considerable effects on macrophage function (phagocytosis) and host innate immune response against infections. The present study was to investigate the relationship of NRAMP1 gene polymorphisms with PI and CP in an Iranian population. In this cross sectional study 79 patients with CP, 38 patients with PI and 84 healthy controls presenting to the Periodontology Department of Shahid Beheshti University of Medical Sciences were enrolled. DNA was extracted from fresh blood samples of arm vein of participants and transferred to KBiosience institute (United Kingdom) for genotyping. X2 and Fisher's exact tests were used by SPSS software v.19 for statistical analyzes. Significant differences were detected in the distribution of genotypes between control and CP groups both for rs17235409 and rs2276631 polymorphisms (P:0.044 and P:0.028 respectively). Distribution of genotypes differed insignificantly in comparison of PI and control groups for rs2276631 (P:0.623) and either rs17235409 (P:1) polymorphisms. Based on our results, we conclude that presence of G allele in both rs2276631 and rs17235409 location may be a protective factor against CP. More studies with a larger sample size in different populations are required for confirming NRAMP1 as a genetic determinant in periodontal disorders.

MiR146a and MiR499 gene polymorphisms in Iranian periodontitis and peri-implantitis patients.

AIM: MicroRNAs (MiRs) are small noncoding RNAs that are involved in protein translation, osteoclastogenesis, and immunoregulation. Peri-implantitis and chronic periodontitis are multifactorial diseases. They are the consequence of complex interactions among host response, genetics, and environment. In the present study, we aimed to investigate the possible association between MiR146a/MiR499 gene polymorphisms and periodontitis/peri-implantitis as a first report in oral implantology. METHODS: From 197 individuals referred to Periodontology Department of Shahid Beheshti Dental School, three groups were enrolled in the assessment: 75 patients in the chronic periodontitis (CP) group, 38 patients in the peri-implantitis (PI) group, and 84 healthy subjects. DNA was extracted from fresh blood samples from the arm veins of participants and transferred to KBiosience Institute (Hoddesdon, United Kingdom) for genotyping. Chi-squared and Kruskal-Wallis tests were performed using SPSS software v.19 for statistical analyses. P-value < 0.05 was considered significant. RESULTS: The genotype frequencies in MiR 146a and MiR 499 were significantly different among the three groups. CONCLUSIONS: MiR146a (rs2910146) and MiR499 (rs3746444) gene polymorphisms may be genetic determinants for increased risk of chronic periodontitis and peri-implantitis in Iranians. More studies with larger sample sizes in different populations are necessary for determining the effect of these SNPs.

The effect of amount of lost tooth structure and restorative technique on fracture resistance of endodontically treated premolars.

AIM: Endodontic treatment generally reduces the fracture resistance of teeth. The purpose of this study was to evaluate the fracture resistance and the mode of fracture of endodontically treated human premolars with different amounts of remaining tooth structure. MATERIALS AND METHODS: Seventy non-carious human premolars were randomly assigned into 7 groups. Group 1 (ST) did not receive any preparation. The teeth in groups 2-7 received root canal treatment and different preparations. Group 2 (MO-NF): Mesio-occlusal preparation without filling; Group 3 (MOD-NF): Mesio-occluso-distal preparation without filling; Group 4 (MO-F): Mesio-occlusal preparation with direct composite restoration (Z250); Group 5 (MOD-F): Mesio-occluso-distal preparation with direct composite restoration (Z250); Group 6 (CC-D): Mesio-occluso-distal preparation with cusp reduction and direct composite restoration (Z250); Group 7 (CC-InD): Mesio-occluso-distal preparation with cusp reduction and indirect composite restoration (Gradia GC). The fracture resistance (N) was assessed under compressive load in a universal testing machine (Zwick) perpendicular to the occlusal surface at a cross-head speed of 1 mm/min, and the mode of fracture was assessed under stereomicroscope. STATISTICAL ANALYSIS: Data was analyzed by Kruskal - Wallis and Mann - Whitney tests and the mode of fracture was analyzed by Chi-square test (P < 0.05). RESULTS: Statistical analysis showed that MO and MOD cavity preparations significantly reduced the fracture resistance of sound teeth. Direct composite restorations can improve the fracture resistance, and Groups 7 and 6 presented the highest fracture resistance values. CONCLUSIONS: Teeth with adhesive restorations showed significantly higher fracture resistance values as compared with the non-restored ones.

Radiographic evaluation of marginal bone levels around dental implants with different designs after 1 year.

OBJECTIVE: The aim of this study was to use intra-oral radiographs to evaluate changes in marginal bone levels around three different implant designs after 1 year. MATERIALS AND METHODS: Three implant designs; two with a straight and one with a conical design, were placed adjacent to each other in the partially edentulous areas of 25 patients. The patients received 46 implants with a straight design (All fit SSO and SPI-element) and 29 implants with a conical design (SPI-contact). Two-way repeated analysis of variance (ANOVA) was used to evaluate the marginal bone changes in each group at 12 months follow-up (p < 0.05). RESULTS: None of the implants had failed by the end of this study. After 12 months, significant differences were noted in the amount of alveolar bone loss recorded between the All fit SSO and SPI implants (p < 0.05). Mean crestal bone loss was 0.88 ± 0.43 mm for the All fit, 0.61 ± 0.34 mm for the SPI contact and 0.54 ± 0.27 mm for the SPI element implants. CONCLUSIONS: The results of this study demonstrate that straight (cylindrical) implants with shorter high polish surface displayed less bone resorption.

Dental implantation: an opportunity to stop smoking.

Cigarette smoking and tobacco consumption are serious hazards threatening the health of human beings. Several strategies have been proposed for smoking cessation in patients presenting to medical centers to seek treatment. Some believe that the dental profession plays a key role in quit smoking programs due to its extensive and long-term relationship with patients. Use of known strategies to create motivation for quitting smoking among patients has yielded relatively optimal results. However, it seems that patients' attitudes toward smoking can be changed if we enhance their knowledge about the hazards of tobacco consumption and its adverse effects on dental and oral health and especially the health of dental implants' surrounding structures. This study reports smoking cessation in two patients requiring dental implant treatment. Twenty-eight months after loading of implants, treatment success was confirmed by use of clinical and radiographic indices. No sign of peri-implant disease was detected and the patients were eagerly following the smoking cessation program. It seems that contemporary dental treatments, especially dental implant therapy, can provide a good opportunity to create the motivation required for lifestyle changes in patients.

Histologic effects of demineralized bone matrix on regeneration of alveolar socket in diabetic rats.

INTRODUCTION: The aim of this in vivo study was to determine the effect of demineralized bone matrix (DBM) on alveolar bone repair in type I diabetic rats. MATERIALS AND METHODS: This study was carried out on 40 adult (8 weeks-old) albino rats with an average weight of 200-250 grams. The animals were divided into four groups (n=10) as follows: group 1 nondiabetic rats, group 2, 3 and 4 were diabetic rats, group 4 rats took one unit of insulin daily. Diabetes was induced by Alloxan Monohydrate through the tail veins of the rats in groups 2-4. Only group 4 received insulin NPH 1 unit daily. After 10 days, the upper right incisors of all samples were extracted and the socket was filled with DBM in groups 3 and 4. The animals were sacrificed at the end of week 1 and 2. The specimens were prepared and stained with H&E. RESULTS: Histological results of group 4 displayed osteoblastic activity and bone formation with collagen fibers at the end of the first week and thick bone trabeculae formation in vicinity of DBM at the end of second week. In group 3, DBM showed some osteoinductivity at the end of the first week, but in some regions DBM particles were degraded by osteoclastic activity. Bone trabeculae formed with a dispersed and separate pattern at the end of second week. In group 2 hematoma and inflammation were dominant histological features at the end of first and second weeks; poor bone formation was detected in these two groups (2 and 3). In group 1, the results were as expected. CONCLUSION: It seems demineralized bone matrix simulate osteoblastic activity.