ABSTRACT
Statement of Problem: Impacts and accidents are considered as the main factors in losing the teeth, so the analysis and design of the implants that they can be more resistant against impacts is very important. One of the important numerical methods having widespread application in various fields of engineering sciences is the finite element method. Among its wide applications, the study of distribution of power in complex structures can be noted
Objectives: The aim of this research was to assess the geometric effect and the type of implant thread on its performance; we also made an attempt to determine the created stress using finite element method
Materials and Methods: In this study, the three dimensional model of bone by using Cone Beam Computerized Tomography [CBCT] of the patient has been provided. The implants in this study are designed by Solid Works software. Loading is simulated in explicit dynamic, by struck of a rigid body with the speed of 1 mm/s to implant vertically and horizontally; and the maximum level of induced stress for the cortical and trabecular bone in the ANSYS Workbench software was calculated
Results: By considering the results of this study, it was identified that, among the designed samples, the maximum imposed stress in the cortical bone layer occurred in the first group [straight threads] and the maximum stress value in the trabecular bone layer and implant occurred in the second group [tapered threads]
Conclusions: Due to the limitations of this study, the implants with more depth thread, because of the increased contact surface of the implant with the bone, caused more stability; also, the implant with smaller thread and shorter pitch length caused more stress to the bone
Subject(s)
Humans , Bone and Bones , Printing, Three-Dimensional , Finite Element Analysis , Dental Stress Analysis , Stress, MechanicalABSTRACT
The effect of different mouthrinses on the surface characteristics of ceramic materials is not documented.The aim of this study was to determine the effect of three mouthrinses, containing either alcohol, hydrogen peroxide or fluoride, on microhardness of two dental ceramics, [Duceram love, IPS e.max Ceram].Eighty cylindrical disks were prepared and divided into eight experimental groups [n=10 for each group] according to the ceramic material and storage solutions. The microhardness of each sample in all groups was recorded prior to testing. For each ceramic, three groups were immersed in one of the three mouthrinses for a total of 24 and 96 hours. The fourth group was immersed in distilled water as the control. At the end the specimens were taken out, rinsed, dried and tested using microhardness tester.The results of the two-way ANOVA indicated that there was no interaction between media, time and materials [P>0.05]. Microhardness of the ceramics was not adversely affected by immersion in the studied mouthrinses.The patients with porcelain restorations should be assured that using mouthrinses containing hydrogen peroxide, alcohol or fluoride do not damage the surface hardness of the porcelain
ABSTRACT
A general process in implant design is to determine the reason of possible problems and to find the relevant solutions. The success of the implant depends on the control technique of implant biomechanical conditions. The goal of this study was to evaluate the influence of both abutment and framework materials on the stress of the bone around the implant by using three-dimensional finite element analysis.A three-dimensional model of a patient's premaxillary bone was fabricated using Cone Beam Computed Tomography [CBCT]. Then, three types of abutment from gold, nickel-chromium and zirconia and also three types of crown frame from silver-palladium, nickel-chromium and zirconia were designed. Finally, a 178 N force at angles of zero, 30 and 45 degrees was exerted on the implant axis and the maximum stress and strain in the trabecular, cortical bones and cement was calculated.With changes of the materials and mechanical properties of abutment and frame, little difference was observed in the level and distribution pattern of stress. The stress level was increased with the rise in the angle of pressure exertion. The highest stress concentration was related to the force at the angle of 45 degrees. The results of the cement analysis proved an inverse relationship between the rate of elastic modulus of the frame material and that of the maximum stress in the cement.The impact of the angle at which the force was applied was more significant in stress distribution than that of abutment and framework core materials
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Cannabinoids exert widespread effects on cognitive functions. An overlapped distribution of GABA receptors and cannabinoid receptors has been reported in some brain structures [e.g. dorsal hippocampus]. Thus, the present study was undertaken to examine the possible role of the dorsal hippocampus GABA[A] receptors on ACPA induced amnesia and ACPA state-dependent memory. This experimental study was conducted on 250 adult male NMRI mice. Muscimol and ACPA were used as agonists of GABA[A] and the cannabinoid CB1 receptors, respectively. Mice were anaesthetized and cannulae were implanted bilaterally into the CA1 regions of the dorsal hippocampus. Seven days after post-surgery recovery, the behavioral testing was performed using an inhibitory avoidance task and the step-down latency of the animals was used to assess memory retention. Post-training administration of ACPA [3ng/mouse] impaired the memory retrieval. The memory impairment induced by ACPA was fully reversed by pre-test administration of ACPA or muscimol. The results suggest that the GABA[A] receptors of the dorsal hippocampal may play an important role in ACPA-induced amnesia and ACPA state-dependent memory
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AIM: To study the frequency of amblyogenic factors in patients with congenital ptosis.congenital ptosis more than 1 year old were included. Amblyopia was defined as best-corrected visual acuity (BCVA) less than 10/10 or a difference between the two eyes of at least 2/10. In patients too young to be measured by the linear Snellen E test, fixation behavior was observed. Different types of amblyopia were assessed for each patient as: 1) anisometropic amblyopia: astigmatic anisometropia≥ 1dpt, hyperopic spherical anisometropia≥ 1dpt, myopic spherical anisometropia≥ -3dpt (with cycloplegia);2) strabismic amblyopia, and 3) stimulus deprivation amblyopia (SDA). Then the total incidence of amblyopia and each type of it were obtained. Patients with uni-and bi-lateral ptosis were also compared. Each specific cause was refractive amblyopia in 29.8%, SDA in 10.5%, strabismic amblyopia in 4.3%. Amblyopia was more frequent in severe ptosis, 76% in patients with covered optical axes (OA), compared to non-covered OA (22.5%). In unilateral ptosis with covered OA, astigmatic anisometropic amblyopia was more frequent, and in bilateral ptosis with at least one eye covered OA, spherical anisometropic amblyopia was more frequent. In both unilateral and bilateral ptosis, SDA was more common if the OA was covered. Paying attention to all causes of amblyopia may be important in preventing amblyopia in a child with a ptotic eye.
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AIM:TO evaluate chromosome 8 abnormalities in Duane's retraction syndrome(DRS)type 1.METHODS:We evaluated chromosome 8 abnormalities in 29 consecutive cases of DRS type Ⅰ.DNA was isolated from the peripheral leukocytes of patients using a genomic DNA extraction kit,then D8S553 and D8S1797 markers used for polymerase chain reaction(PCR).RESULTS:None of the cases were positive for the two markers D8S553 and D8S1797 on chromosome 8 which were tested in our study.CONCLUSION:The possible cause of this finding is that DRS in our patients is more commonly sporadic rather than familial.We recommend study with more cases,other markers,and different chromosomes.
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Purpose: to evaluate the prevalence of contat lens wear among highschool girls and their general knowledge about contact lenses and also to evaluate the specific knowledge of contact lens wearers about the lens
Methods: in a cross-sectional study, 1664 students of 22 randomly selected girl highschools were enrolled. A questionaire including questions about wearing contact lens, age of first use, cause of lens wear, type of lens, source of providing, way of wearing, and medical and hygienic care was filled out by the participants. Contact lens wearers were classified in two groups according to the main cause of lens wear: cosmetic and therapeutic
Results: the prevalence of contact lens wear was 16.5% including 81.8% for cosmetic purposes and 18.2% for therapeutic reasons. The age of starting lens wear was before 14 in 36%. About 50% of contact lens wearers had at least once worn the lens of another person. General knowledge was often weak or little and the knowledge about serious complications of contact lens wear was good only in 43% of the students. There was no significant differences between weares and nonwearers regarding these issues. The source of providing of lens among the therapeutic group was physicians in 90% and boutiques in 2% corresponding figures were 9.8% and 32% respectively in the cosmetic group. The most common type of lens was soft [98%] and colored [84.3%]. Lens handling was bad or inappropriate in 73.1 %; however appropriate handling was greater in the therapeutic group [42%] than the cosmetic group [23.6%]. Medical care was appropriate in 30.9% [68% in the therapeutic group and 22.7% in the cosmetic group]. Hygienic care of lens was appropriate in 53.8% [62% in the therapeutic group and 52% in the cosmetic group]. Hygienic care of lens container was appropriate in 16.4% [24% in the therapeutic group vs 4.7% in the cosmetic group]. Specific knowledge of lens wearers was appropriate in 46.6% [58% in the therapeutic group vs 44% in the cosmetic group]
Conclusion: the prevalence of contact lens wear among highschool girls in Tehran is considerable especially for cosmetic purposes. Furthermore, general and specific knowledge about contact lens use was inadequate in the majority of lens wearers