Background and Aims: Disc displacement is the most common temporomandibular joint disorder and magnetic resonance imaging (MRI) is the gold standard in its diagnosis. This disorder can lead to changes in signal intensity of magnetic resonance (MR). The purpose of this study was evaluation of correlation between relative signal intensity of MR images of retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle with type of anterior disk displacement and condylar head flattening in patients with temporomandibular disorder (TMD).Materials and Methods: In this retrospective study, 31 MR images of patients who had anterior disc displacement were evaluated. After relative signal intensity measurement for retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle, the correlation between relative signal intensity and type of anterior disc displacement was evaluated with repeated measure ANOVA test. In each of these 3 areas, t-test was used to compare the groups with and without condylar head flattening.Results: The correlation between relative signal intensity of MR images and type of anterior disc displacement in retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle was not significant. There was also no statistically significant correlation between relative signal intensity of MR images and flattening of condylar head in retrodiscal tissue, superior and inferior head of lateral ptrygoid muscle (P>0.05).Conclusion: According to findings of this study, relative signal intensity of MR images in retrodiscal tissue, superior and inferior head of ptrygoid muscle is not a good predictor for type of anterior disc displacement and flattening of condylar head. It seems that this cannot be used as a diagnostic marker for TMD progression.

Introduction: Usually osseointegration takes between three to six months after implant placement but patients are interested to have early loading. There are no definitive criteria for measuring bone mineral density (BMD), insertion torque (IT) (final torque force) and resonance frequency analysis (RFA) (primary implant stability) to determine exact loading time based on the relationship between the above-mentioned parameters. The aim of this study was to determine the relationship between IT, RFA and BMD in screw-type implants.Materials and Methods: This clinical trial was conducted on 18 patients who were candidates for ITI implant placement. Written consent was taken and jaw bone density was determined via a digital radiography technique before surgery. After implant placement, RFA and IT were measured. Fifty-five ITI implants of the total 62 implants placed were evaluated; the implants were 12 mm long with a diameter of 4.1 mm. Data was analyzed with Pearson’s test using SPSS.15 software (a=0.05).Results: There was a significant relationship between IT, RFA and BMD. Pearson’s test showed a correlation coefficient of 0.872 to 0.789 between the three parameters, indicating a strong relationship between them. The mean bone density was 1.468±0.042 g/cm2; the mean RFA was 66.01±2.2 ISQ and the mean IT was 34.62±3.33 N/cm2.Conclusion: Based on the results of the present study there is a significant relationship between, IT, RFA and BMD (p value=0.001).

The equations of nonlinear motion of clamped-hinged beam with an open crack were extracted and through solving them, the internal resonance in the cracked beam was studied. To this end, the crack was modeled as a torsional spring and the cracked beam was considered as two beam segments connected by a torsional spring. The equations of motion of the cracked beam were extracted considering the geometrical nonlinearity. Then, using the Galerkin’ s method, these equations were changed to a set of nonlinear differential equations for vibration modes which were solved by the perturbation method. Since the mechanical energy of the beam in each mode depends on the instantaneous amplitude of vibration of the beam at the corresponding mode, so to analyze the influence of the crack on the energy exchange between the modes, the instantaneous amplitudes of the vibration modes were obtained. The results show that in the cracked beam the magnitude of the energy exchanged between the modes is less and the frequency is more than that in the intact beam. Also, by increasing the crack depth the frequency of energy exchange between the modes increases. The Vibration response obtained for the cracked beam with various amounts of the damping ratios shows that the frequency and the amplitude of energy exchange between the modes are independent of the system damping. To validate the results by the perturbation method, the equations of motions are also solved by a numerical method and the obtained results are in agreement with the results of the analytical method.

Sound is one of the forms of mechanical energy and the two main characteristics of sound are intensity or power and frequency or wavelength of sound.their performance against the incoming sound wave, industrial silencers can be divided into two general groups of resonating and absorption silencers, the main difference between these silencers is the release of sound energy from the channeling system, which is one of the common examples of the use of resonating type silencers, their use in It is the internal combustion engines that distinguish absorption silencers from the resonator type based on the fact that the main and visible part of the act of muting the sound is achieved by changing sound energy to heat energy.The goal of this article is to design a muffler based on the breaking of sound frequencies resulting from the movement of fluid in the exhaust output of vehicles, which leads to a reduction of at least 50 db of sound and gives the operator enough peace and concentration. In this article, after examining three types of mufflers, absorbent mufflers that use the properties of porous absorbent material to absorb passing sound and are the simplest form of mufflers, have been selected, analyzed and reviewed and are suitable for the OM457 engine of Idem Industrial Company. It designed for maximum inlet exhaust temperature is 520 and for the maximum kW power is 315 with the maximum discharge relative pressure of 185 mbar for homogenization with the standard atmosphere.

Background: Temporomandibular joint disorders (TMDs) are the most common cause of non-odontogenic pain in the maxillofacial region. internal derangement (ID) is one of the most prevalent causes of TMDs, and disc displacement is recognized as the most common ID. The masticatory muscles are among anatomical structures involved in TMDs that may be aff, ected by ID. Objectives: This study aimed to evaluate the correlation between the masticatory muscle dimensions and ID of temporomandibular joints using magnetic resonance imaging (MRI). Patients and Methods: This cross-sectional study was conducted on the MRI images of 145 patients, retrieved from the archives of the MRI diagnostic and research center during 2020-2021. The patients were categorized into three main groups of normal disc position (NP) (n = 42), disc displacement with reduction (DDR) (n = 54), and disc displacement without reduction (DDWR) (n = 49). The maximum width and height of the masseter and medial pterygoid muscles and the maximum height and length of the superior and inferior heads of the lateral pterygoid muscle were measured on MRI images for each of the groups. Data were analyzed using t-test, Pearson’, s correlation test, ANOVA test, and Tukey’, s test (alpha < 0. 05). Results: Signifi, cant diff, erences were observed between the NP, DDR, and DDWR groups regarding the height (P < 0. 001) and length (P < 0. 001) of the superior head of the lateral pterygoid muscle,both parameters were signifi, cantly higher in the NP group, followed by the DDR and DDWR groups (P < 0. 05). The dimensions of masticatory muscles were signifi, cantly greater in males than females (P < 0. 05), except for the width of the medial pterygoid muscle (P = 0. 064). The height of the masseter muscle (r = 0. 190, P = 0. 022) and the medial pterygoid muscle (r = 0. 166, P = 0. 046) was signifi, cantly correlated with age. Conclusion: Signifi, cant correlations were found between the height and length of the superior head of the lateral pterygoid muscle and ID of TMJ,the corresponding values were lower in the DDWR group compared to the DDR and NP groups, respectively.

Since resonant micro/nanoresonators are very delicate devices with very small dimensions, therefore, any defects and faults caused by the process of manufacturing and laboratory implementation can lead to fundamental changes in their vibration behaviors. Therefore, the effects of the mentioned disadvantages should be considered as much as possible to obtain more accurate sensors with higher efficiency. In this study, a general model of a doubly clamped microbeam (nanotube) with an asymmetric cross-section with external excitation is considered. Then, linear and non-linear behaviors of an ideal nanotube with a circular cross-section are investigated. The results of the simulations indicate a good agreement with the experimental references available in the literature. Then, taking into account the asymmetry in the resonator cross-section, the system is moved away from an ideal model to a more real model, and the possible effects of the asymmetric cross-section in adjustment, reduction, and vanish of internal resonance are investigated and studied. Finally, the advantages and disadvantages caused by asymmetries and the optimal use of such an opportunity to obtain more innovative and complete models with higher efficiency are explained.

Background and Aims: internal derangement of the Temporomandibular joint (TMJ) is the most common form of Temporomandibular disorders, which represents an abnormal internal strucural and functional change of the disk, as well as an abnormal relationship of the disk to the condyle, glenoid fossa and articular eminence when the teeth are in the closed- mouth position. The aim of this study was to evaluate the correlation between eminence steepness and condyle disk movements in TMJs affected by internal derangements using magnetic resonance imaging (MRI).Materials and Methods: In this cross-sectional study, digital MRI files of 90 joints belong to 45 patients in open and closed-mouth positions were evaluated. Patients were subdivided into two groups: 64 individuals with anterior disk displacement with reduction and 26 individuals with anterior disk displacement without reduction. Appropriate oblique sagittal sections were selected and printed. Outlines of the fossa, eminence, condyle and disk were traced on matte acetate sheets and evaluated by an oral and maxillofacial radiologist and a postgraduate student of oral and maxillofacial radiology. Disk rotation, condyle rotation, condyle translation and eminence steepness were measured. The data were analyzed using T-test.Results: In this study, no significant difference was found in measurements between the two groups, (for steepness P=0.64, for Disc rotation P=0.77, for condyle rotation P=0.28 and for condyle translation P=0.12). Disk rotation showed statistically significant correlation with eminence steepness in the anterior disk displacement with reduction group (P=0.034).Although this correlation was weak (r=0.27) (P>0.05). No statistically significant correlations were found between other variables and eminence steepness in this group (for condyle rotation P=0.3 and for condyle translation P=0.98). Disk rotation and condyle translation had statistically significant relationship in the anterior disk displacement without reduction group (P=0.011, r=-0.49). In addition, a significant difference was found between disk rotation and condyle rotation in this group (P=0.004, r=0.54). The relationship between other variables and eminence steepness were not statistically significant (for disc rotation P=0.06, for condyle rotation P=0.72 and for condyle translation P=0.73) (P>0.05).Conclusion: According to the results of the present study, there is no obvious relationship between eminence steepness and movements of the condyle- disk assembly in patients with TMJ internal derangements. Therefore, the hypothesis that a steep articular eminence of the TMJ is a predisposing factor for disk displacement without reduction could not be verified. Performing prophylactic Eminectomy as a part of patient treatment plan is doubtful and need further evaluations.

Background and Aims: The most frequent cause of TMJ dysfunction is internal derangement which that largely involves the function of the articular disc. Anterior disc displacement (ADD) is one of the major findings in TMJ internal derangement. Since the importance of knowledge of its etiology and also the role of all structural indicators association with TMD was not evaluated, in this research was investigated Correlation between TMJ structure and disc displacement. Materials and Methods: This study was done based on case-control method. 31 Joints with TMJ internal derangements and 57 normal joint Were examined. The two groups of clients were matched in age, sex, Economic and social situation. MRI finding was Disk position in Open and closed mouth and condyle morphology coronal and axial view. MRI findings were Disk position in Open and closed mouth and condyle morphology coronal and axial view. The data were analyzed using Chi-square test and Fisher's test. Results: Patients with TMJ internal derangement (ID), In all three groups inchiding disk displacement with reduction(DDWR), disk displacement without reduction(DDWOR), anterior disc displacement(ADD), was encountered more frequently in Anterior, Anterior-inferior disk position in closed mouth, A statistically significant correlation was found( P <0. 001 ). Also no significant difference was found in measurements between the three groups, for condyle morphology in coronal and axial view. ( P > 0. 4) Conclusion: It seems, Anterior disc displacement (ADD) is correlated Anterior, Anterior-inferior disk position in closed mouth But There is no correlation between Anterior disc displacement (ADD) And condyle morphology in coronal and axial view.