Effect of implant‒abutment connections on abutment screw loosening: An in vitro study.

Background: The widespread use of dental implants as a predictable treatment choice has drawn attention to their complications as a major challenge despite their high clinical success rates. In this context, loosening of the abutment screw in posterior single crowns is the most common problem; the use of adequate preload and proper anti-rotational features at implant‒abutment interface appear to be two main solutions to such a problem. The present study evaluated the effect of implant‒abutment connections in four different implant systems before and after cyclic loading. Methods: Intra-Lock, Dentis, Xive, and Dio implant systems were used in this study. Each system underwent one million cycles of dynamic forces eight times with a magnitude of 110 N. For each specimen after tightening the screw with a torque of 32 Ncm, the detorque values were measured and recorded by a digital torquemeter after and before cyclic loading. Data were analyzed by Kolmogorov-Smirnov, Levene's, one-way ANOVA, and post hoc Tukey tests. Results: Initial detorque values between the study groups showed significant differences (P<0.0001). Pairwise comparisons showed significantly lower primary detorque values in the Dentis system compared to the three other systems (P<0.0001). After cyclic loading, significant differences were observed between the study groups (P<0.0001). Pairwise comparisons of the groups showed significant differences between all the systems after loading. Conclusion: The type of implant‒abutment connection is an essential factor influencing the amount of abutment screw loosening.

Compressive Strength of Temporary Crowns Made from Default design in Two Types of Software.

Statement of the Problem: Various default values in each software can eventually lead to different crown thicknesses and affect their compressive strength. Purpose: This study aimed to compare the compressive strength of temporary crowns made with the milling machine, designed in Exocad and 3Shape Dental System software. Materials and Method: In this in vitro study, 90 temporary crowns were made and evaluated based on each software settings. For this purpose, a sound premolar was first scanned as a pre-operative model by 3Shape laboratory scanner. The standard tooth preparation and scanning were performed, and then the temporary crown files (designed by each software) were transferred to the Imesicore 350i milling machine. A total of 90 temporary crowns (45 based on the file of each software) were made using poly methyl methacrylate (PMMA) vita cad-temp block. The value of compressive force displayed on the monitor was recorded at the first crack and the ultimate failure of the crown. Results: The first crack and the ultimate strength of crowns designed with the Exocad software was 903.5±96N and 1490±139.3N and for crowns designed with 3Shape Dental System software was 1060.4±160.2N and 1691.1±73.9N, respectively. The amount of compressive strength of temporary crowns made with 3Shape Dental System was significantly higher than those made with Exocad software and this difference was statistically significant(p= 0.000). Conclusion: The compressive strength of temporary dental crowns made by both softwares is in a clinically acceptable range, but considering that the average compressive strength in the 3Shape Dental System group was slightly higher than of the other group, it is preferable to design and fabricate with 3Shape Dental System software to increase the compressive strength of these crowns.

Evaluation of implant abutment screw head deformation in hexagonal and star designs after successive tightening and loosening.

Background: Tightening and loosening of the prosthetic components of the implant are carried out with various screw designs. This study compared the rate of deformation of the abutment screw in two hexagonal and star screw head designs after consecutive tightening and loosening. Methods: In this study, two fixtures were mounted vertically in die stone blocks using a surveyor. Then the corresponding abutment (with a diameter of 4.5 mm and a gingival height of 2 mm; Dio-SM and Dio-UF system) was mounted on each fixture. In each fixture, six abutment screws from each manufacturer were used (12 abutment screws in total). The abutment screw head of the Dio-UF system is hexagonal, and the abutment screw head of the Dio-SM system is star-shaped. The samples were examined under a stereomicroscope (Nikon C-DS) at a magnification of×50. The image of each abutment screw head (6 abutment screws in each group) was prepared before the procedural steps and after 5, 10, and 15 times of tightening and loosening with 25-Ncm torque using a stereomicroscope. Then the differences in the surface areas of consecutive specimens (0, 5, 10, and 15 consecutive tightening and loosening rounds) between hexagonal and star-shaped abutment screws were calculated. The study results were reported via descriptive statistical methods (mean±standard deviation). Statistical analysis was performed using SPSS 24, and the significance level was defined at P<0.05. Results: Increasing the number of tightening and loosening rounds increased the screw head surface area in both hexagonal and star shapes. At all stages, the changes in the star-shaped screw head were greater than in the hexagonal screw. These changes were statistically significant at all stages (P<0.05). In addition, there was a statistically significant difference between the area values and the number of tightening and loosening rounds separately in both screw types (P<0.001). Also, the surface areas of the head of both screws in all tightening and loosening rounds were significantly different (P<0.001). Conclusion: Increasing the number of tightening and loosening rounds increased the screw head surface area in both hexagonal and star-shaped geometrical forms. Also, the extent of area changes at all stages in star-shaped screw heads was greater than in hexagonal screws.

Effect of the posterior stop on temporomandibular disorders: A systematic review.

Background. Temporomandibular disorders have common signs and symptoms, including pain in the masticatory muscles, limitation or deviation in a mandibular range of motion, and other common patient complaints, such as headache and earache. The main focus of this study was to collect comprehensive and integrated data on the effect of the posterior stop on temporomandibular joint disorders, as well as prevention, treatment, and follow-up care for the patients. Methods. The authors conducted the search in PubMed, SCOPUS, Web of Science, Cochrane Library, CINHAL, Medline, ProQuest, Google Scholar, Magiran, IranDoc, SID, and Iranmedex databases for relevant articles. A list of selected study sources, related conferences, and grey literature were manually searched in addition to the databases mentioned above. A 21-year time limit was imposed (2000-2021). Results. Finally, 16 articles were selected to be reviewed in this systematic review. The designs of the included studies were heterogeneous, and due to the low number of studies covered, the authors could not carry out a meta-analysis. Conclusion. The causes of temporomandibular disorders are multifactorial and complex. Therefore, it is difficult to investigate the relationship between this disorder and predictors. The results of the present study indicate that to determine the effect of the posterior stop on temporomandibular joint disorders, more clinical trials and case-control studies should be conducted.

The Comparison of Color Stability of Aloe Vera Gel and Chlorhexidine Solution on Acrylic Teeth.

Background: There is insufficient knowledge about aloe vera color change property on acrylic teeth compared to other denture cleaners, especially chlorhexidine solution (CHX). Objective: The present study aimed to compare the color change property of the aloe vera and chlorhexidine solution on denture acrylic teeth. Methods: This study was experimental in vitro study design conducted in the dental laboratory of Tabriz University of Medical Sciences, Iran, 2021. The sample size in each group was 21 acrylic teeth which were randomly divided into aloe vera gel 100% and chlorhexidine solution 2% groups. Tooth colors were measured by a spectrophotometer (Spectro Shade Micro, MHT S.P.A., Milan, Italy). The immersion time in both groups was 36 hours. Data analyzed using an independent t-test was used at a 95% of confidence level. Results: The comparison of the total color differences (ΔE) between the two groups was not statistically significant after 36 hours of immersion (P=0.440). In the chlorhexidine group, the brightness of teeth was lower than that in the aloe vera group (P=0.002). Conclusions: Clinicians should be aware that aloe vera gel does not change the color of denture acrylic teeth after 36 hours of immersion similar to the chlorhexidine solution. For patients who cannot use chlorhexidine, aloe vera gel is a good cleaner for denture acrylic teeth without worrying about the color change of the denture. It can be considered an acceptable cleaner for denture acrylic teeth.

Comparison of reverse torque values of abutment screws with the application of oil-based and water-based antibacterial agents.

Background: Using antibacterial agents to remove the foul odor of the implant cavity and prevent peri-implantitis can affect the detorque values and lead to the loosening of the abutment screw. This study investigated the effects of tetracycline and chlorhexidine gel on detorque values. Methods: This in vitro study was carried out on three groups of five implants. Group G1 was the control group, and no material was applied to the implant cavity. In group G2, the implant cavity was first filled with artificial saliva and then with chlorhexidine gel. In group G3, the implant cavity was first filled with artificial saliva and then with tetracycline. The abutments were tightened with 25 N/cm2 and then loosened. Finally, the detorque values were calculated. Results: The highest detorque values were recorded in group G1. Group G3 showed the lowest detorque values. ANOVA showed significant differences in mean detorque values (P<0.05) between the three groups. Conclusion: According to this study, applying antibacterial agents decreased the detorque values and increased the risk of screw loosening. The reduction of detorque values was more pronounced with the oil-based antibacterial agent (tetracycline).

Evaluation of Interdental Spaces of the Mandibular Posterior Area for Orthodontic Mini-Implants with Cone-Beam Computed Tomography.

INTRODUCTION: The use of mini-implants has increased in recent years because of their role in absolute anchorage, but the placement sites may affect the success or failure of the procedure, so it is very important to determine the appropriate and safe location for orthodontic mini-implants. On the other hand, the Cone Beam Computed Tomography (CBCT), which offers clear 3-Dimentional (3D) images, has been widely used in orthodontics and implant dentistry for surgical guidance of mini-implant placement. AIM: The aim of this retrospective study was to evaluate inter-radicular spaces between mandibular canines to second molars using cone beam 3D images. MATERIALS AND METHODS: In this retrospective cross-sectional descriptive study, maxillofacial CBCT scan data were obtained from 40 adults. The 3D images were evaluated in five axial sections at 2, 4, 6, 8 and 10 mm from the cementoenamel Junction (CEJ). To determine inter-radicular spaces, tangent lines were drawn buccolingually to the roots in axial section and the minimum distance between these two lines was measured. The data was analysed using Friedman test with SPSS(ver.13). RESULTS: Interradicular spaces of canine to second molar increased from cervical to apical direction. The maximum distance was recorded at 4 mm from the CEJ between first and second molars. CONCLUSION: According to our findings there is a distinct pattern of inter-radicular space changes in mandible. Attention to this pattern during placement of mini-implants can ensure the safety of the procedure.

Evaluation of changes in anthropometric indexes due to intermaxillary fixation following facial fractures.

Background. One of the treatment modalities for facial fractures is closed reduction technique, but treatment with intermaxillary fixation (IMF) interferes with normal nutrition, and malnutrition can affect the patient's recovery. Anthropometric measurements such as skinfold thickness and body mass index (BMI) are universal indexes for diagnosing malnutrition. Therefore, in this study we explain how treatment with IMF changes the anthropometric indexes. Methods. In this study 60 patients were treated with 4 weeks of IMF. Skinfold thickness and BMI of these patients were measured and compared before and after the treatment. Results. Patients' weight, BMI and skinfold thickness decreased during the IMF period, and this decrease was statistically significant (P < 0.01). Conclusion. Although no severe and acute malnutrition was seen among our patients, IMF led to mild to moderate malnutrition in some cases, making it necessary to use nutritional supplements.