Journal of Mashhad Dental School
Year:2019 | Volume:43 | Issue:2 |Papers Count:12

Introduction: Short implants are used in the posterior mandible where the bone is insufficient. In these cases, the clinical crown is often made to match the level of the occlusal. As a result, the length of the lever arm and the stress of the implant complex, as well as the surrounding bone, are increased leading to the biomechanical problems. The purpose of this study was to evaluate dynamically the effect of increasing crown height space on the maximum stress induced in the abutment screw and the surrounding bone of the short dental implants in the posterior mandible using finite element analysis. Materials and Methods: Mandibular bone resorption in the posterior region, second premolar with three-crown lengths of 8. 8, 11. 2, and 13. 6, two implants of 4 and 8 mm, two abutments, and two abutment screws were modeled using Solidworks software in this laboratory experimental study. In addition, Abacus software was used to the dynamic reconstruction of screw tightening and external load at an angle of 75. 8 degrees with the occlusal plane. The stress values were calculated for the screw, abutment, fixture, and bone. Results: In both 4-and 8-mm implants, the increased vertical height of the crown decreased the stress on the abutment screw and increased the stress on the abutment and fixture. For a 4-mm implant, the stress to the abutment screw at all three heights was less than 8 mm. At all heights, the stress values to the abutment and the fixture were more than 8mm for the 4-mm implant. The increased vertical height of the crown resulted in an increase in compressive and tensile stress in the surrounding bone for both 4-mm and 8-mm implants. The magnitude of these stresses in the 4-mm implant was more than 8 mm. Conclusions: Increased vertical height of the crown and crown-to-implant ratio reduced the stress on abutment screws as the weakest member of the implant. However, it probably increased the failure due to fatigue in the abutment and fixture as well as bone resorption.

Introduction: The present study aimed to evaluate the micro-shear bonding strength and failure patterns of two types of Universal Bonding agents to superficial dentin using self-etch and etch-and-rinse. Materials and methods: In this study, 35 intact extracted premolar teeth were selected and superficial dentin were exposed by disk. In the next step, two blocks were obtained from each tooth and they were subsequently divided into 5 equal groups (n=14). Scotchbond Universal (3M/USA) was used in group 1 with a self-etch method. The same bond was utilized in group 2 with total-etch technique. In group 3, All-bond universal (BISCO/USA) was used with self-etch method and it was used in group 4 by etch-and-rinse technique. Finally, Single bond 2 was used in group 5 as a control group. The Z250 XT (3M/USA) resin composite was bonded on the surfaces of samples and were cured. Micro shear bonding strength was calculated by microtensile testing machine and failure modes were determined by stereomicroscope. The data were analyzed using one-way ANOVA and Tukey test. Results: The mean± SD values of scotch bond self, scotch bond total, All-bond self, All-bond total, and Single bond total were 35. 74± 6. 21, 29. 50± 3. 89, 24. 60± 3. 53, 31. 47± 4. 73, 18. 09± 3. 87, respectively. The self-etch technique for Scotchbond Universal and the etch-and-rinse technique for All-bond Universal has higher microshear bonding strength. Adper single bond 2 showed significantly the lowest bond strength (P<0. 05). Conclusion: According to the obtained results, the microshear bonding strength of universal adhesives was material-dependent although universal adhesives showed higher bond strength.

Introduction: The aim of this study was to evaluate the effect of time elapsed after extraction on the buccolingual angulation of alveolar bone in the posterior mandibular region using cone beam computed tomography (CBCT) images. Materials & Methods: The CBCT images of 56 patients who referred to the Radiology Department of Hamadan Dental School, Hamadan, Iran, were evaluated in this study. The scans were performed using the New Tom 3G scanner. The patients were divided into three groups regarding the time elapsed after extraction, namely: 6 month-2 years, 2-5years and >5 years. Buccolingual angulation of ridge in the second premolar, first molar, and second molar areas on both sides (with and without tooth) were measured in cross-section views (slice thickness: 1mm, interval: 2mm) using NNT viewer software. The data were analyzed in SPSS software (Version. 22) through paired t-test and regression. Results: The changing of buccolingual angulation in the second molar area in each group was not statistically significant (P<0. 05). In the first molar area, buccolingual angulation increased in the time elapsed after 6 months-2years and over 5 years and it was statistically significant (P<0. 05). However, regarding the time elapsed between 2-5 years, the difference was close to the margin of statistical significance. In the second premolar area, changes were not statistically significant in time elapsed from 6 months to 2 years and 2-5 years; however, it was significant regarding the time elapsed after extraction of over 5 years (P<0. 05). Conclusion: The elapsed time did not have any significant effect on the buccolingual angulation in the toothless area of the second molar. Regarding the first molar area, tooth extraction increased the buccolingual angulation. In addition, an increase was observed in the buccolingual angulation after 5 years of the tooth extraction at the area of the second molar.

Introduction: Bone injuries are among the challenges of medical science that each year has high costs for treatment in the world. Fluorhydroxyapatite plays an important role in promoting the integration of bones and dental implants, increasing bone density and calcium levels, and accelerating the recovery of bone fractures. Materials and Methods: In this study, fluorhydroxyapatite powder and composite scaffolds with different weight percentages (40, 50, and 60) of fluorhydroxyapatite were fabricated through co-precipitation and freeze drying mechanisms, respectively. In order to investigate the microscopic properties of composite scaffolds, scanning electron microscopy was used. Also, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy tests were used to evaluate the purity of the manufactured specimens. In addition, in order to evaluate the biological properties of composite scaffolds, MTT and alkaline phosphatase (ALP) tests were used, and finally, the strength of scaffolds and the rate of water absorption were studied. Data analysis was performed using one-way analysis of variance. Results: Microscopic investigations indicated a porous microstructure with pore diameters within the range of 100-350 μ m, which is acceptable for osteoblastic cells to grow and proliferate. Also, the results of FTIR and XRD confirmed the absence of impurities in the samples. In addition, the non-toxicity of the produced specimens and the proper functioning of the bone cells were confirmed through MTT assay (after 3 and 7 days) and ALP activity (after 3, 7, and 14 days), respectively. Accordingly, the scaffold with 60 wt% of fluorhydroxyapatite showed more biocompatibility and ALP activity than the other two scaffolds. Also, the average of Young's modulus and yield strength for the samples were 40 and 7 MPa, which are acceptable for use in bone tissue engineering. Conclusion: The results showed that the application of fluorhydroxyapatite with gelatin not only improves biological properties but also improves the mechanical properties of the scaffold. Additionally, the obtained results emphasized the potential use of prepared scaffolds to repair bone tissue.

Introduction: This study aimed to identify the level of knowledge of dental authors regarding the use of MeSH indexing tools in research by comparing the keywords of the articles published in Iranian dental journals indexed in PubMed. Materials and Methods: In this descriptive and applied study, a total of 1, 091 keywords in 239 research articles published in 20 issues of 5 Iranian dental Latin journals indexed in PubMed in 2016 were matched with MeSH descriptors. The keywords were classified according to the degree of compliance in three groups of exact compliance, relative compliance, and noncompliance. Results: According to the results, 483 (44. 3%), 153 (14%), and 455 (41. 7%) keywords had exact compliance, relative compliance, and non-compliance with MeSH descriptors, respectively. The three keywords, namely Cone-Beam Computed Tomography, Scanning Electron Microscopy, and Mineral Trioxide Aggregate, were among the top most frequent keywords with exact compliance, relative compliance, and noncompliance with MeSH descriptors, respectively. Conclusion: The articles in all the reviewed journals, with the exception of the Journal of Dentistry of Tehran University of Medical Sciences, were prone to the risk of nonretrieval and anonymity due to the inefficiency of researchers in using MeSH for keyword selection.

Introduction: Dental amalgam is considered as the most tolerable restorative dental material due to its proper physical and mechanical properties, cost-effectiveness, and long term clinical performance. In this study, the physical and mechanical properties of nine relevant amalgams in Iranian dental material market were investigated based on ISO 24234: 2015. Moreover, the morphological characterization of dental amalgam alloy was evaluated using field emission scanning electron microscopy (FE-SEM). Materials and Methods: An amalgamator was utilized to mix the amalgam alloy powder with mercury. In addition, the investigation of the microstructure of dental amalgam was conducted using FE-SEM equipped with an Energy Dispersive Spectroscopy system to analyze the composition of the elements. The required samples for the evaluation of compressive strength, creep, and dimensional changes during hardening were prepared using the recommended standard template based on the suggested program. The data were analyzed using one-way ANOVA and Tukey's test. P-value less than 0. 05 was considered statistically significant. Results: The evaluation of morphological characteristics of amalgams showed that amalgams, namely “ GK-110” and “ 110 Plus” were prepared from lath cut particles. In addition, amalgams, such as “ Cinasilver” , “ Solaloy” , and “ World Work” were composed of spheroid-like particles. However, alloys, including ANA 2000, Contour, SDI GS-80, and Cinalux showed mixed morphologies of spherical (or spheroid-like) and lath cut particles. Regarding the mixed alloys, “ Contour Regular Kerr” and “ SDI GS-80 Regular Set” contained more spherical particles. However, higher levels of lath cut particles were observed in “ ANA 2000” and “ Cinalux” . The homogenous and fine-grained microstructures were observed in spherical and spheroid-like particles. All studied dental amalgams comply with the requirements for creep according to the standard ISO 24234: 2015. The results of one-way ANOVA revealed that one-hour compressive strength of Cinasilver amalgam was significantly higher than that of the other amalgams (P<0. 05). According to Tukey Post Hoc analysis, there was no significant difference regarding one-hour compressive strength in Contour, Cinalux, and Cinasilver (P>0. 05). Out of all studied amalgams, SDI gs-80 showed the lowest coefficient of variation regarding compressive strength. In terms of the number of specimens with higher strength more than the minimum strength requirement of the standard, Cinasilver amalgam completely met the standard requirements for one hour and one day. Except for 110 Plus amalgam, the other amalgams met the requirement regarding the dimensional changes during the hardening within the specified standard range. Conclusion: The results indicated that amalgam “ Cinasilver” met the standard requirements of ISO 24234: 2015 regarding creep, dimensional changes, and compressive strength in one hour and a day. However, amalgams, namely Cinalux, Contour, and SDI gs-80 may be considered as appropriate amalgams.

Introduction: Dental implants are one of the most interesting therapeutic approaches that have been brought about a great revolution in dental procedures. The cantilever-based implant is also an appreciable treatment method. Previous researches point to increased pressure on bone in this prosthesis, while some other studies emphasize on its clinical success. The present study aimed to evaluate the bone loss around cantilever-based implants and compare it with single-tooth implants. Materials and Methods: In this study, 26 samples with the cantilever-based implant and 26 samples with single-tooth implant treatment plans were examined in this historical cohort study. Patients recovering less than 6 months following the treatment were excluded. Alveolar crestal bone loss around both implant techniques was evaluated by a periodontist on radiographic images. Statistical analysis of the data was performed using the Kolmogorov-Smirnov's normality assessment test, as well as the non-parametric tests, including the Mann-Whitney U test, Wilcoxon signed-rank test, Spearman’ s rank correlation coefficient test, Kaplan-Meier estimator, and Kruskal-Wallis test. The significance level was considered 0. 05. Results: No significant relationship was observed between the presence or absence of cantilever, gender, age, type of bone, and implant length with bone loss. The rate of bone resorption was related to the time factor, and it increased over time. In addition, the rate of bone loss in implant systems of NeoBiotech and Ritter was proven significantly higher than other systems. Conclusion: If the technical principles in surgery and prosthesis implantation are applied, the use of cantilever-based implant can be considered as a valid method of treatment. However, further research is required in this field of study.

Introduction: Sensory processing problems can affect social, cognitive, sensorimotor development, and emotional level leading to behavioral difficulties in children. The purpose of this study was to investigate the relationship between sensory processing abilities and anxiety with the cooperation of preschool children in dentistry. Materials and Methods: In this cross-sectional study, 101 patients within the age range of 4-6 years (52 females and 49 males) were selected using convenience sampling. Sensory profile questionnaire was used to evaluate sensory processing problems. Moreover, children’ s anxiety and cooperation during injection and drilling procedures evaluated by Venham Clinical Anxiety Scale and Venham Clinical Cooperation Scale, respectively. The data were analyzed in SPSS Software (Version. 18) through the Kruskal-Wallis test, Mann-Whitney U test, and Spearman's rank correlation coefficient. Results: According to the results, a significant relationship was observed between auditory processing and children’ s anxiety with cooperation during injection and drilling procedures (P<0. 05). In addition, the results showed that higher levels of oral processing were correlated with non-cooperation during drilling (P=0. 008). There was also a significant relationship between children’ s sensory processing related to tolerance/endurance and anxiety with cooperation during injection (P<0. 05). Conclusion: The evaluation of oral, endurance, and auditory sensory processing abilities using the sensory profile questionnaire can be helpful in the prediction of dental anxiety and level of cooperation in children.

Introduction: Nowadays, in the healthcare professions, evaluation of the soft skills is taken into account during student admission process. However, in the Iranian academic society, student admission is only based on scientific criteria and soft skills are not considered in accepting the students. Considering the significance of soft skills in the quality of dental care performance, this study was conducted to clarify viewpoints of the faculty members and students regarding evaluation of the soft skills in dental students admission. Materials and Methods: The statistical population of this qualitative descriptive study consisted of the faculty members and dental students of Isfahan and Mazandaran Universities of Medical Sciences. The participants were selected through the purposive sampling method. The Data of the study were collected through semi-structured interviews and data analysis was performed using conventional content analysis method. Results: Analysis of the recorded interviews of the participants in this study resulted in two main categories, namely the theoretical context of soft skills evaluation in admission of dental students and the practical context of soft skills evaluation in admission of dental students. In the theoretical context, most faculty members and dental students had favorable views of the need for soft skills evaluation in admission of dental students. Moreover, regarding the practical context, the individuals pointed out several cultural-social challenges, such as the reduced justice and increased favoritism in admitting the students. In addition, they mentioned some executive challenges, including the difficulty of evaluating the soft skills, lack of soft skills training in pre-university education, and competence of the evaluators. Conclusion: According to the results of this study, the participants expressed favorable views concerning evaluation of the soft skills during submission of dentistry students. Therefore, we recommend that the dental education planners provide appropriate practical context in coordination with the training measurement organization to evaluate the soft skills in admitting dental students by designing and implementing comprehensive research.

Introduction: Sialolith known as salivary calculi or salivary stone is a calcified organic mass that obstructs salivary duct and may occur in main or accessory glands or ducts. Most of sialoliths (80-90%) happen in submandibular gland and size of the sialoliths is usually 5-10 mm. The sialolith is considered as an unusual size in case it is larger than 10-15 mm. The ones with the size of >15 mm in any dimension are regarded as giants and are rare. The aim of this study was to report a giant sialolith presenting with some clinical symptoms. Case report: A 30-year old male patient presented to the oral and maxillofacial diseases department of outpatient clinic, Mashhad Faculty of dentistry with a history of submandibular swelling and pain in the left. In clinical examination, an exophytic lesion (nodular-like) was observed in the lingual area of lower incisors. The lesion measured 34×18 mm and extended from distal left lower incisor to the midbuccal of left lower second premolar. The lesion texture was hard with a smooth mucosal surface. Cone beam computed tomography revealed a large radiopaque mass in the floor of mouth. The sialolith was surgically removed. Conclusion: Infection of the submandibular salivary gland might be due to stasis of salivary flow associated with stone formation in saliva gland or duct. In order to rule out the diagnosis of sialolith, the dentist should use bimanual palpation from the posterior area of salivary duct to the anterior part. Proper diagnosis and evaluation result in suitable treatment.