Woo-Jin Lee

Interferences between mandibular proximal and distal segments in orthognathic surgery for patients with asymmetric mandibular prognathism depending on different osteotomy techniques

OBJECTIVEnThe aim of this study was to evaluate, using computer simulation, the amount of interference between the proximal and distal segments of the mandible incurred by 3 different osteotomy methods.nnnSTUDY DESIGNnWith the 3-dimensional facial computerized tomography data of 20 patients showing mandibular prognathism with asymmetry, simulation surgeries of conventional sagittal split ramus osteotomy (SSRO), intraoral vertical ramus osteotomy (IVRO), or short lingual osteotomy (SLO) was performed. The distal segments were moved backward (3, 6, or 9 mm) and rotated (2 degrees, 4 degrees, or 6 degrees). The amounts of interference between the proximal and distal segments of the mandible were measured and statistically analyzed.nnnRESULTSnConventional SSRO demonstrated the greatest interference between the proximal and distal segments of the mandibles (P < .01), followed by IVRO and SLO. SLO showed less interference than IVRO in mild asymmetry cases (P < .05), but no difference was noted in severe prognathism and asymmetry cases.nnnCONCLUSIONnSLO is the most favorable osteotomy method for reducing displacement of the proximal segment in mandibular prognathism with asymmetry.

Towards a Formal Framework for Product Line Test Development

Product line test development is more complicated than the conventional test development for a single application. There were numerous research works in the past that address various issues and aspects that arise in product line testing and test development. However, we still lack a coherent framework that can guide product line test development and link various product line development concepts to relevant product line testing concepts. In this paper we provide a basis for a formal framework for product line test development by linking product line development concepts such as feature, variability, product line architecture, component and use case scenario to product line test concepts such as test architecture, variability for test and test scenario and by providing a systematic way for deriving product line tests, adapting product line tests to a specific product and deriving product specific tests.

Comparison of dental implant stabilities by impact response and resonance frequencies using artificial bone

PURPOSEnWe compared implant stability as determined by the peak frequency from the impact response with the implant stability quotient (ISQ) by resonance frequency analysis (RFA) in various artificial bone conditions. The clinical bone conditions were simulated using an artificial bone material with different cortical thicknesses and trabecular densities.nnnMATERIALS AND METHODSnThe artificial bone material was solid, rigid polyurethane. The polyurethane foam of 0.8g/cm(3) density was used for the cortical bone layer, and that of 0.08, 0.16, 0.24, 0.32, and 0.48g/cm(3) densities for the trabecular bone layer. The cortical bone material of 4 different thicknesses (1.4, 1.6, 1.8, and 2.0mm) was attached to the trabecular bone with varying density. Two types of dental implants (10 and 13mm lengths of 4.0mm diameter) were placed into the artificial bone blocks. An inductive sensor was used to measure the vibration caused by tapping the adapter-implant assembly. The peak frequency of the power spectrum of the impact response was used as the criterion for implant stability. The ISQ value was also measured for the same conditions.nnnRESULTSnThe stability, as measured by peak frequency (SPF) and ISQ value, increased as the trabecular density and the cortical density increased in linear regression analysis. The SPF and ISQ values were highly correlated with each other when the trabecular bone density and cortical bone thickness changed (Pearson correlation=0.90, p<0.01). The linear regression of the SPF with the cortical bone thickness showed higher goodness of fit (R(2) measure) than the ISQ value with the cortical bone thickness. The SPF could differentiate implantation conditions as many as the ISQ value when the trabecular bone density and the cortical density changed. However, the ISQ value was not consistent with the general stability tendency in some conditions.nnnCONCLUSIONnThe SPF showed better consistency and differentiability with implant stability than the ISQ value by resonance frequency analysis in the various implantation conditions.

Material depth reconstruction method of multi-energy X-ray images using neural network

With the advent of technology, multi-energy X-ray imaging is promising technique that can reduce the patients dose and provide functional imaging. Two-dimensional photon-counting detector to provide multi-energy imaging is under development. In this work, we present a material decomposition method using multi-energy images. To acquire multi-energy images, Monte Carlo simulation was performed. The X-ray spectrum was modeled and ripple effect was considered. Using the dissimilar characteristics in energy-dependent X-ray attenuation of each material, multiple energy X-ray images were decomposed into material depth images. Feedforward neural network was used to fit multi-energy images to material depth images. In order to use the neural network, step wedge phantom images were used for training neuron. Finally, neural network decomposed multi-energy X-ray images into material depth image. To demonstrate the concept of this method, we applied it to simulated images of a 3D head phantom. The results show that neural network method performed effectively material depth reconstruction.

A new method for the evaluation of dental implant stability using an inductive sensor.

We developed a new method for the measurement of dental implant stability by analyzing the impulse response of the implant. The movement of the implant was measured by an inductive sensor with a dedicated adaptor. The large inductance of the adapter amplified the small displacement signal of the implant. The Periotest (Siemens, Bensheim, Germany) was used as a source of excitation force to acquire the impact response of the implant. Power spectrum analysis was applied to the impact response of the implant. The peak frequency of the spectrum was used as a measure of the implant stability. The performance of the system was tested and verified through simulation of the implant-bone interface in an in vitro model. Various implant-bone interfacial conditions were assessed. Holes of varying depth and diameter were drilled into a dental implantation model. Two types of impression materials (EXAMIXFINE, Regisil Rigid) with different degrees of hardness were used to fix the implant into the hole. The implant stability was also measured using the ISQ (implant stability quotient) by resonance frequency analysis on the Osstell Mentor (Integration Diagnostics AB, Goteborgsvagen, Sweden) for comparison. Linear regression analysis of the peak frequency as a stability parameter showed a linear relationship with both the depth and the diameter of the hole (p<0.05). When EXAMIXFINE was used, the peak frequency was linearly associated with the depth (R(2)=0.443) and diameter (R(2)=0.396) of the hole. When Regisil Rigid was used, the peak frequency also showed a linear relationship with the depth (R(2)=0.555) and diameter (R(2)=0.350) of the hole. The peak frequency also increased as the hardness of the impression material increased. Differentiability of the system was evaluated by an ANOVA test. A statistically significant difference (p<0.01) was found between all implantation conditions, except in one case using the Regisil Rigid material. In contrast, the ISQ value did not consistently differentiate under several implantation conditions. The developed method could differentiate the stability changes in simulated implantation conditions with a wider dynamic range and with higher resolution than the ISQ value.

Product Line Approach to Role-Based Middleware Development for Ubiquitous Sensor Network

Currently sensor network middlewares are developed so that they include all functionalities for various nodes. Since sensor network nodes usually operate with limited resources, it is desirable for them to have middlewares that have only the functionalities necessary to perform their roles. This paper proposes a systematic method for developing sensor network middleware using the product line approach In this method, functionalities of the sensor network middleware common to all nodes and functionalities specific to the different roles of nodes are carefully separated and grouped so that nodes with different roles have different middlewares that are specialized to their roles but minimally consumes the resources.

An advanced navigational surgery system for dental implants completed in a single visit: An in vitro study

In this study, we have developed an advanced navigational implant surgery system to overcome some disadvantages of the conventional method and have evaluated the accuracy of the system under in vitro environment. The patient splint for registration and tracking was improvised using a bite splint without laboratory work and the offset of an exchanged drill was calibrated directly without pivoting during surgery. The mean target registration errors (TRE) were 0.35 ± 0.11 mm using the registration body, 0.34 ± 0.18 mm for the registration method with prerecorded fiducials, and 0.35 ± 0.16 mm for the direct calibration of a drill offset. The mean positional deviations between the planned and placed implants in 110 implant surgeries were 0.41 ± 0.12 mm at the center point of the platform and 0.56 ± 0.14 mm at the center point of the apex. The mean angular deviation was 2.64°± 1.31 for the long axis of the implant. In conclusion, the developed system exhibited high accuracy, and the improved tools and simplified procedures increased the convenience and availability. With this advanced approach, it will be possible to complete dental implant surgery during a single visit at local clinics using a navigational guidance involving cone-beam computed tomographic images.

Volumetric quantification of bone-implant contact using micro-computed tomography analysis based on region-based segmentation

Purpose We have developed a new method of segmenting the areas of absorbable implants and bone using region-based segmentation of micro-computed tomography (micro-CT) images, which allowed us to quantify volumetric bone-implant contact (VBIC) and volumetric absorption (VA). Materials and Methods The simple threshold technique generally used in micro-CT analysis cannot be used to segment the areas of absorbable implants and bone. Instead, a region-based segmentation method, a region-labeling method, and subsequent morphological operations were successively applied to micro-CT images. The three-dimensional VBIC and VA of the absorbable implant were then calculated over the entire volume of the implant. Two-dimensional (2D) bone-implant contact (BIC) and bone area (BA) were also measured based on the conventional histomorphometric method. Results VA and VBIC increased significantly with as the healing period increased (p<0.05). VBIC values were significantly correlated with VA values (p<0.05) and with 2D BIC values (p<0.05). Conclusion It is possible to quantify VBIC and VA for absorbable implants using micro-CT analysis using a region-based segmentation method.

Development of a robot-assisted orthognathic surgery system integrated with image-guided navigation

Summary form only given. The aim of this study was to develop a robot-assisted system for orthognathic surgery and to evaluate robot movement. The registration procedure was performed in coordinates among a robot, an optical tracking system (OTS) and a CT image with fiducials. According to the surgical plan in the CT coordinate, the robot arm moved to the corresponding robot position. The results were below 0.15mm in translational movement and below 0.41mm in rotational movement.

Three-dimensional assessment of condylar surface changes and remodeling after orthognathic surgery

Purpose This study was performed to evaluate condylar surface changes and remodeling after orthognathic surgery using three-dimensional computed tomography (3D CT) imaging, including comparisons between the right and left sides and between the sexes. Materials and Methods Forty patients (20 males and 20 females) who underwent multi-detector CT examinations before and after surgery were selected. Three-dimensional images comprising thousands of points on the condylar surface were obtained before and after surgery. For the quantitative assessment of condylar surface changes, point-to-point (preoperative-to-postoperative) distances were calculated using D processing software. These point-to-point distances were converted to a color map. In order to evaluate the types of condylar remodeling, the condylar head was divided into six areas (anteromedial, anteromiddle, anterolateral, posteromedial, posteromiddle, and posterolateral areas) and each area was classified into three types of condylar remodeling (bone formation, no change, and bone resorption) based on the color map. Additionally, comparative analyses were performed between the right and left sides and according to sex. Results The mean of the average point-to-point distances on condylar surface was 0.11±0.03 mm. Bone resorption occurred more frequently than other types of condylar remodeling, especially in the lateral areas. However, bone formation in the anteromedial area was particularly prominent. No significant difference was found between the right and left condyles, but condylar surface changes in males were significantly larger than in females. Conclusion This study revealed that condylar remodeling exhibited a tendency towards bone resorption, especially in the lateral areas. Condylar surface changes occurred, but were small.