[Investigation of Preferences in Working Environment of Students for Maintaining Uniform Geographical Distribution of Radiological Technologists].

PURPOSE: This study was designed to assess working environment preferences of students in the Department of Radiological Technology using conjoint analysis for establishing an efficient medical system. METHOD: We carried a questionnaire survey on working environment preferences for 196 students in the Department of Radiological Technology in Japan. We defined eight characteristics for virtual medical facilities as follows: presence of colleagues who can be consulted, employment status, number of night shift per month, academic meeting participation, number of hospital beds, possession of nuclear medicine imaging systems and radiation therapy systems, location of medical facilities, and change rate in annual income. A total of 18 virtual medical facilities were selected by an orthogonal array table using above-mentioned characteristics. The acquired data by the pairwise comparison method were analyzed by conjoint analysis. Marginal rates of substitution that represent students' preferences were also calculated. RESULT: The factors that influenced their preferences were the following: placement of medical facilities in great city, presence of colleagues who can be consulted, employment status is not non-regular employment, set up of nuclear medicine imaging systems and radiation therapy systems, the number of night shift is twice per month, and attendances at academic meetings. CONCLUSION: In summary, students in the Department of Radiological Technology tend to prefer the facilities with regular employment, great city, presence of colleagues who can be consulted, and possession of nuclear medicine imaging systems and/or radiation therapy systems.

Risk factors for abutment and implant fracture after loading.

PURPOSE: Implant component fractures are one of the most serious complications in implant treatment. With a better understanding of the risk factors for fracture in the preoperative, surgery, superstructure, and post-loading phases of implant treatment, low-risk treatment could reduce implant component fractures, leading to a better prognosis. The aim of this study was to clarify the risk factors for abutment and implant fractures that occur after loading, and to perform a retrospective, approximately 10-year follow-up study to explore the risk factors in each treatment phase. METHODS: Subjects were fitted with an implant prosthesis between January 2008 and December 2009. In total, 1,126 Ankylos implants in 430 patients were included for analysis. Binary logistic regression analysis was performed to extract factors related to non-fracture and fracture of the abutment or implant as a dependent variable. RESULTS: Gender (OR = 3.466, 95% CI 1.296-9.268, P = 0.013), gonial angle (OR = 3.420, 95% CI 1.308-8.945, P = 0.012), and splinting status of the superstructure (OR = 4.456, 95% CI 1.861-10.669, P = 0.001) were identified as significant risk factors. CONCLUSION: The risk of fracture is increased in males, especially those with a mandibular angle of less than 120° on panoramic radiographs, and those with a non-splinted superstructure.

Effects of material and coefficient of friction on taper joint dental implants.

PURPOSE: The aim of this study was: (1) to compare the coefficients of friction between commercially pure titanium (cpTi), titanium (Ti) alloy, and yttria-stabilized zirconia (YSZ) and: (2) to investigate the dynamic behavior of an implant system before, during, and after loading, by transient dynamic three-dimensional finite element analysis (FEA). METHODS: Coefficients of friction were measured by a ball-on-disk frictional wear testing device. The preload in the screw shaft was calculated from geometric parameters. Two abutment model designs were created, namely a Ti alloy abutment model with a porcelain-fused-to-metal super structure and a YSZ abutment model with a porcelain-fused-to-zirconia super structure. Transient dynamic three-dimensional FEA was performed on ANSYS Workbench Ver. 15.0. RESULTS: The coefficients of friction of YSZ/cpTi, YSZ/Ti alloy, Ti alloy/cpTi, and Ti alloy/Ti alloy were 0.4417, 0.3455, 0.3952, and 0.3489, respectively. The preload generated in the abutment screw of the FEA model was set to be 158 N. Significantly differences were not found in the maximum von Mises equivalent stress between the Ti alloy and YSZ abutment models before, during, and after loading. CONCLUSION: The findings indicate differences in the coefficients of friction of cpTi, Ti alloy, and YSZ before, during, and after loading. Fractures caused by stress did not depend on the use of different materials (Ti alloy and YSZ) at the abutment.

Investigation of Preferences in Working Environment of Radiological Technologists Using Conjoint Analysis.

The purpose of this study is to assess working environment preferences of radiological technologists using conjoint analysis. We carried a questionnaire survey on working environment preferences for 200 radiological technologists working in medical facilities in Japan. We defined eight characteristics for virtual medical facilities as follows: presence of colleagues who can be consulted, employment status, number of overtime work per month, academic meeting participation, number of hospital beds, presence of nuclear medicine imaging systems and radiation therapy systems, location of medical facilities, and change rate in annual income. A total of 18 virtual medical facilities were selected by an orthogonal array table using above-mentioned characteristics. The acquired data by the pairwise comparison method were analyzed by conjoint analysis. Marginal rates of substitution between income and non-pecuniary characteristics, which represent radiological technologists' preferences, were also calculated. The factors influenced on their preferences were the following: employment status is not part-time, medical facility is smaller in scale, nuclear medicine imaging systems and radiation therapy systems are set up, and the number of overtime work is less. It was suggested that radiological technologists have a tendency to avoid increase of workloads and select his/her working place with emphasis on own experiences.

Clinical management of implant prostheses in patients with bruxism.

There is general agreement that excessive stress to the bone-implant interface may result in implant overload and failure. Early failure of the implant due to excessive loading occurs shortly after uncovering the implant. Excess load on a final restoration after successful implant integration can result in physical failure of the implant structure. Many clinicians believe that overload of dental implants is a risk factor for vertical peri-implant bone loss and/or may be detrimental for the suprastructure in implant prostheses. It has been documented that occlusal parafunction, such as, bruxism (tooth grinding and clenching) affects the outcome of implant prostheses, but there is no evidence for a causal relation between the failures and overload of dental implants. In spite of this lack of evidence, often metal restorations are preferred instead of porcelain for patients in whom bruxism is presumed on the basis of tooth wear. The purpose of this paper is to discuss the importance of the occlusal scheme used in implant restorations for implant longevity and to suggest a clinical approach and occlusal materials for implant prostheses in order to prevent complications related to bruxism.

[Studies evaluating measurement accuracy of CMS-JAW, a jaw motion tracking device with six degrees of freedom using an ultrasonic recording system].

PURPOSE: For diagnoses of temporomandibular dysfunction, reports indicate the importance of analyzing jaw movements using a jaw motion tracking device with six degrees of freedom. However, such devices are not widely applied in clinical practice, due to difficulty of use. To determine whether CMS-JAW (a newly developed six degrees of freedom jaw motion tracking device that features easy analysis of jaw movements) offers the measurement accuracy required for clinical use, we evaluated the device by measuring condyle translation and rotation during jaw movement. METHODS: In this study, we evaluated measurement accuracy by comparing measurements of condyle movements obtained from the Win Jaw System, a comparable jaw motion tracking device with six degrees of freedom based on an ultrasonic recording system; the Gnathohexagraph II, a device based on a different measurement principle; and the CMS-JAW. In the experiment, we confirmed the condyle translations and rotations obtained by each device by measuring distances and angles, respectively, with a micro slider for three-dimensional measurements (to an accuracy of 0.01 mm and 0.02 mm) and a digital protractor (to an accuracy of 0.1 degrees). RESULTS: No significant distortions were observed in the space replicated based on the range of condyle translations obtained with CMS-JAW. Deviations from theoretical values were greatest along the z-axis, with a maximum error of 0.20 mm and root mean square (RMS) error of 0.10 mm. The maximum error for angles of condyle rotation was 0.50 degrees; RMS errors ranged from 0.05 to 0.30 degrees. CONCLUSION: Our analysis of condyle movement demonstrates that the CMS-JAW provides acceptable measurement accuracy for clinical applications.

Experimental and computational approach for evaluating the mechanical characteristics of dental composite resins with various filler sizes.

This study aimed to investigate the influence of particle size of fillers on flexural properties of dental composite resins by laboratory testing with computational analysis validation. Four kinds of silica fillers with mean particle sizes of 3.3, 4.3, 7.9, and 15.5 microm were used. Filler content was kept constant at 70 mass% (or 53.8 vol.%). The three-point bending test was performed with a constant loading speed of 1.0mm/min, and a span length of 20mm using an Instron machine, in order to measure flexural strength and modulus of composite resins with various particle sizes. Test specimens were 2-mm wide, 2-mm thick, and 25-mm long rectangular bars. Furthermore, a numerical simulation using three-dimensional finite element (FE) analysis was performed to investigate stress distribution in composite resins under loading. As a result, flexural strength decreased with increasing particle size of the filler of the composite resins (p<0.05). On the other hand, there was no significant difference in Young's modulus among composite resins with various filler sizes (p>0.05). Moreover, FE analysis indicated that stress concentration increased with increasing particle size in agreement with experimental results of flexural strength. In conclusion, within the limitations of this investigation, we confirmed that flexural strength of composite resins decreased with increasing filler particle size. In addition, FE analysis was effective for evaluating stress distributions of dental composite resins with various filler sizes.

Influence of implant/abutment joint designs on abutment screw loosening in a dental implant system.

The objective of this study was to investigate the influence of implant/abutment joint designs on abutment screw loosening in a dental implant system, using nonlinear dynamic analysis of the finite element method (FEM). This finite element simulation study used two dental implant systems: the Ankylos implant system (Degusa Dental, Hanau, German) with a taper joint (taper joint-type model), and the Bränemark implant system (Nobel Biocare, Gothenburg, Sweden) with an external hex joint (external hex joint-type model). The nonlinear dynamic analysis was performed using three-dimensional finite element analysis. In comparing the movement of the taper type-joint model and external hex type-joint model, it was found that the external hex type-joint model had greater movement than the taper type-joint model. The external hex joint-type model showed rotation movement, whereas the movement of the taper joint-type model showed no rotation. It was concluded that the nonlinear dynamic analysis used in this study clearly demonstrated the differences in rotation of components in dental implant systems with taper or external hex joints.

Influence of cortical bone quality on stress distribution in bone around dental implant.

Using finite element method (FEM), this study sought to investigate how the thickness and Young's modulus of cortical bone influenced stress distribution in bone surrounding a dental implant. The finite element implant-bone model consisted of a titanium abutment, a titanium fixture, a gold alloy retaining screw, cancellous bone, and cortical bone. The results showed that von Mises equivalent stress was at its maximum in the cortical bone surrounding dental implant. Upon investigation, it was found that maximum von Mises equivalent stress in bone decreased as cortical bone thickness increased. On the other hand, maximum von Mises equivalent stress in bone increased as Young's modulus of cortical bone increased. In conclusion, it was confirmed that von Mises equivalent stress was sensitive to the thickness and Young's modulus of cortical bone.