Biomedical subjects

T Sohmura

Publications and source records attributed to T Sohmura.

At least 19 recordsLinked to original sources

PubMed2004

Prototype of simulation of orthognathic surgery using a virtual reality haptic device.

A maxillofacial simulator can support education and training. In the present study, cutting, separation, and quantitative rearrangement of bone during orthognathic surgery were simulated by means of a haptic device with virtual tactile perception. Computed tomographic (CT) images of two patients with severe jaw deformity, one women and one man, were input into the device. In the woman, Le Fort I osteotomy of the maxilla and sagittal splitting ramus osteotomy of the mandible were initially simulated. During surgery with the haptic device, separation and rearrangement of the maxilla and the ramus of the mandible were initially processed. However, there was discrepancy and overlapping of the ramus with the mandible. Intraoral vertical osteotomy of the right ramus was then performed, with satisfactory results and less discrepancy and interference. The simulation was referred to at surgery, and satisfactory surgical assistance was postoperatively confirmed on CT images. The male patient had severe jaw deformity due to unequal growth between the ramuses, resulting in anterior crossbite. Sagittal splitting ramus osteotomy with rotation of the mandible was successfully simulated. Because of its versatility and functions, the present device was found to be useful for simulating various procedures for orthognathic surgery and thereby three-dimensionally determine surgical movements.

Adult↗

PubMed2004

Training in tooth preparation utilizing a support system.

Tooth preparation is an essential technique for dental treatment, but it is a skill not easily learned by a dental student. To facilitate this leaning process, a new tooth preparation support system with a parallel link mechanism was developed. This study reports the educational efficiency of this system for dental students. Dental students with no experience in clinical practice were selected and divided into two groups; one trained with this support system; and the other, with freehand preparation. They prepared axial walls in right maxillary second premolars and molars mounted in a phantom manikin with an air-turbine handpiece. Convergence angles of the axial walls and parallelisms between axes of prepared teeth were evaluated. Training with the support system led to significantly smaller convergence angles and parallelisms as compared with freehand preparation training. With the freehand preparation after training, the convergence angles and parallelisms became smaller in the group trained with the support system than those trained with freehand. The above findings suggest that training in tooth preparation utilizing the newly developed support system can be one of practical programs that are useful for dental students to achieve greater competency in tooth preparation.

Bicuspid↗

PubMed2004

Computer-assisted morphological analysis of dental casts with maxillary prognathism and reversed occlusion.

The morphologic characteristics of the dentition with maxillary prognathism and reversed occlusion were examined by a computer-assisted dental cast analysing system. Dental casts with normal occlusion, maxillary prognathism and reversed occlusion were selected and measured by a 3D shape measuring system. The dental arches and anteroposterior occlusal curves were approximated numerically by the polynomial expression with a fourth order and second order coefficients, respectively. The coefficients were analysed statistically. Maxillary dental arches with mandibular prognathism showed a more acuminate shape (V-shape) with a significant larger second order coefficient, while arches with reversed occlusion showed more angulate shapes (U-shape) with significantly smaller second order coefficients compared with arches with normal occlusions. However, a notable difference in the shape of the mandibular dental arches was not observed. The mandibular dental arches with maxillary prognathism were positioned backward relative to maxillary dental arches, while the arches with reversed occlusion were positioned forward. The anteroposterior occlusal curves with maxillary prognathism showed larger curvatures in maxilla and mandible, while the curves with reversed occlusion showed smaller curvatures in mandible comparing with the curves with normal occlusion. These results suggest that the present method could offer a useful and objective examination technique for the diagnosis of malocclusion.

Adolescent↗

PubMed2003

A preliminary report on a computer-assisted dental cast analysis system used for the prosthodontic treatment.

To accomplish computerized 3D morphological analyses of maxillary and mandibular casts with malocclusions on the same co-ordinate system, a new reference co-ordinate located on soft tissue has been proposed consisting of the top of maxillary bilateral tubercles and incisive papilla on the maxillary cast. To test the validity of this co-ordinate system, the angles of the occlusal plane in this system were examined on 10 subjects with normal occlusion. In addition, to analyse maxillary and mandibular casts on the same co-ordinate system, a bite block was made under the intercuspal position. The maxillary cast was measured by 3D measuring system, then, the bite block was placed on maxillary casts, and measured similarly. To examine the position reproducibility of this method, 3D co-ordinates of the apex of the buccal cusp of the mandibular pre-molar in five bite blocks were determined. The angles formed of the occlusal plane were 1.3 +/- 1.3 degrees and 0.2 +/- 1.1 degrees on the sagittal and frontal base plane, respectively. This co-ordinate system had enough stability to replace the occlusal plane. By the measurement of bite blocks, the co-ordinates of the mandibular cusp tips were determined within the deviation of 0.2 mm.

Dental Casting Technique↗

PubMed2001

Calcium-phosphate surface coating by casting to improve bioactivity of titanium.

In order to improve the bioactivity of titanium, an original surface treatment was attempted with the use of a casting technique was attempted. Pure titanium was cast into a special graphite mold in which the cavity wall was coated with hydroxyapatite (HA) powder. According to analyses of X-ray diffraction and EDX, the existence of HA and CaO and uptake of Ca and P on the surface of the titanium castings were identified. By immersing the specimen in Hank's solution, the concentrations of Ca and P on the surface increased with immersion time, and the formation of a thin layer with characteristics of spherical HA precipitates was observed after 1 week. The concentrations of Ca and P elements and the Ca/P ratio on the HA layer increased with immersion time. The formation of the HA layer on the titanium cast by this treatment was significantly accelerated compared with pure titanium. The present surface treatment of Ti is expected to improve early bone fixation of Ti implants.

Biocompatible Materials↗

PubMed2001

Complete 3-D reconstruction of dental cast shape using perceptual grouping.

To achieve the complete three-dimensional (3-D) data retrieval of the shape of dentition, dental casts were measured from four directions; occlusal, right, left, and labial sides using a line laser scanner. Reconstruction of the entire shape, including undercuts and tooth crowding area, was attempted by applying a perceptual grouping algorithm, which is one of pattern-recognition theories. In the data measured from occlusal, right and left sides, the rows of measurements were parallel to the frontal plane, and three-directionally combined data (3-DC data) was accomplished by affine transformation. While, in the labial side, transformation to the frontal plane was done since rows of the measured data were parallel to the sagittal plane. To combine the labial data with the 3-DC data and reconstruct the complete image, rearrangement of the order of the data in the file was attempted by applying the perceptual grouping. That is, the minimum total length of data combining was examined by considering the factor of proximity and continuity between the data. The most appropriate order of data combining and recognition of islands were accomplished. Using a computer graphic (CG) with a wire-frame model, complicated regions such as anterior segments showing tooth crowding and undercut area were found to be successfully reconstructed without any data defects. The accuracy of reconstruction was ascertained by comparing the characteristic distances between apexes of molars in the reconstructed model with the real cast. The difference was within 0.3 mm, and present method for dental cast reconstruction is considered to be satisfactory for the present purpose such as orthodontics.

Dental Casting Technique↗

PubMed2000

Use of an ultrahigh-speed laser scanner for constructing three-dimensional shapes of dentition and occlusion.

STATEMENT OF PROBLEM: Acquisition of the 3-dimensional shape of dental casts is useful for quantitative evaluation of the diagnosis and treatment of occlusion. PURPOSE: This study demonstrated the acquisition of data through the use of an ultrahigh-speed laser scanner and an originally developed goniometer, the use of these tools to measure the entire 3-dimensional shape of the dental cast from multiple directions, and the connection of the data measurements to reconstruct the cast's occlusion with the use of a computer. MATERIAL AND METHODS: A commercially available apparatus that emits a line laser and completes 1 scan in only 0.6 seconds was used. To compensate for the unmeasured region, the cast was measured from 4 directions on the original goniometer, and the connection of data to obtain the entire image was carried out. Further, the reconstruction of the occlusion between the upper and lower casts was attempted by transferring the upper cast data to the lower cast. RESULTS: By the data connection, the entire shape of the upper and lower casts was constructed, and the characteristic structure was reproduced. The data connections were satisfactory for the flat surfaces but less accurate for the inclined surfaces. Reconstruction of the occlusion between the upper and lower casts was accomplished. It was then possible to visualize the occlusion from arbitrary directions and sections with computer graphics. CONCLUSION: The construction of the entire 3-dimensional shape of a dental cast and the reconstruction of the occlusion were accomplished using an ultrahigh-speed measurement system and original goniometer. These results will be useful for clinical applications such as computerized diagnoses and treatment of occlusion, and for the replacement of the stone casts in the dental office by computerized data.

Calibration↗

PubMed1999

Development of a new high-speed measuring system to analyze the dental cast form.

A new non-contact measurement system employing of a line laser and CCD camera was developed to rapidly measure maloccluded dental casts with large depth and high accuracy. In this system, the measuring interval along the line laser and the model scanning direction perpendicular to the line laser were both 0.2 mm. By averaging the raw data through repetitious input and smoothing by local filtering, the noise was effectively decreased. Sub-pixel processing, which calculates the pixel position with the largest brightness within one pixel, improved the accuracy in the measurement to 22 microns compared with 65 microns before sub-pixel processing. Dental casts with malocclusion were measured with this system. The time and the depth for the measurement were about 10 minutes and 60 mm, respectively. This was a vast improvement compared with our previous system employing a point laser. In the CG of the measured dental casts, smooth and detailed surface morphology were sufficiently reproduced, and recognition of the characteristic points in the cast could be accomplished with the accuracy of 30 microns. This measurement system will be helpful to analyze the dental cast form with malocclusion in progress.

Humans↗

PubMed1997

CAD/CAM system to fabricate dental prostheses--CAD for bridge restoration.

An original CAD process for bridge restoration was developed, and CAD for a maxillary left three unit bridge was attempted. The measured shape data of the standard crown of a second premolar and molar were deformed, and were applied on the dies. The measured pontic data were inserted between two molars. Here, bite data of the opposing teeth were introduced, and the occlusal relationship with the applied molars was adjusted. The bite data were then replaced by the FGP data, and the occlusal surface interference with FGP data was eliminated. Connection processes were then carried out. The clearances between the pontic and molars were filled with interpolation, and the ends of the applied second molar and premolar were connected with the margin of each die. Finally, the data above the margin of each die were extracted, and used as the inner crown data for the bridge. The whole bridge was designed using a newly developed computer program.

Bicuspid↗

PubMed1997

Development of the computerized dental cast form analyzing system--three dimensional diagnosis of dental arch form and the investigation of measuring condition.

To analyze the functional and morphological harmonies of the tooth and dental arch, a computerized system to measure a dental cast and to detect the apex of dental cusps and angle points of incisors was developed. Detailed morphology in the measured dental cast could be displayed distinctively by computer graphics (CG) with a surface model. Accuracy in determining the position of the apex of the dental cusp was examined by increasing the measuring pitch from 50 microns to 400 microns, the error increased gradually with increased measuring pitch. Taking the measuring error, the time for measurement and the memory size for analysis into account, a measuring pitch of 200 microns was determined to be reasonable. Three-dimensional data measurements from the apex of the dental cusp in molar, and the mesial and distal angles in canine and incisor were fitted to a polynomial formula. In the present measured model, the 4th order polynomial formula was used for the dental arch, and the 2nd order polynomial formula was used for the anteroposterior and lateral occlusal curves. These formulae could be simultaneously superimposed on the surface model of the dental cast, and displayed using CG.

Computer Graphics↗

PubMed1993

Improvement of CAD to produce crown by considering occlusion.

Improvement of the CAD process to design the shape of crown restorations of a 6 die was carried out by including the bite data of the antagonistic tooth in addition to the data measured in the previous paper. Initially, the position adjustment of the crown data with the bite data in the centric occlusion was attempted. After fixation of the crown data to a suitable position, modulation of the occlusal surface by the functionally generated path (FGP) data was carried out. To connect between the end of the crown data and the margin, a parabolic function was used instead of the B-Spline function used in the previous paper. As a result, the data points were connected more smoothly. Thus, CAD data which were composed of the die data, the crown data, and the connecting data were accomplished. They will be used as the basic data to CAM.

Computer-Aided Design↗

PubMed1993

A development of computerized laminate veneer restoration system.

The fabrication of laminate veneer requires many complicated procedures and skills to obtain good accuracy and shape. Thus, the use of CAD/CAM is subjected to in laminate veneer fabrication in order to reduce complication and time consuming. In this study, CAD/CAM system of laminate veneer fabrication was developed. The system consisted of laser displacement meter, computer-controlled scanning machine and personal computer. This system is able to measure tooth shape with three dimension, design and manufacture laminate veneer shells of ABS resin with satisfied accuracy and shape.

Computer-Aided Design↗

PubMed1992

Three dimensional shape measurement of teeth (2). CAD to produce crown considering occlusion.

Use of a CAD program to design the shape of a crown, restoration of 6 molar was studied. Stone models of 5 to 7 molars with 6 prepared die for crown and a complete 6 crown which was applied for restoration were measured. The 6 crown data were adapted on the 6 die, and adjusted with 5 and 7 proximal teeth. The coordinates of the data of 6 were then transferred to that of the 6 die. The ends of the adapted crown data were linked with the margin of 6 die. Further the occlusal condition with antagonistic tooth was adjusted by applying the FGP (functionally generated path) technique. FGP was recorded on bite wax and measured. Comparing FGP record and adapted crown, modulation of the occlusal surface was accomplished.

Computer-Aided Design↗

PubMed1990

Three dimensional shape measurement of teeth. (3) The measurement by the newly developed laser displacement meter with double sensors.

A laser displacement meter which equips two sensors was developed in order to measure the shape of teeth with higher efficiency and accuracy. By this displacement meter the rotational measurement to compensate the data at the shaded points became needless. The measurement of the 6 molar was carried out, and the regions such as cusps and fissures of the occlusal plane were measured precisely without errors. The time required for the measurement was about 10 min. and reduced to one third that of the previous system. While, by the measurement from one direction, the undercut portion such as toothneck is less accurate. Then, 7 molar model was tilted on the gonio stage with +/- 20 degrees and measured divisionally, and two groups of data were connected. By this method, the whole shape of tooth including the undercut portion became to be measurable. In the case of a crown abutment tooth with steeply inclined axial wall and margin, tilting method was also applied to measure more accurately. 7 abutment was tilted with +/- 30 degrees and measured and connected. The gingival and marginal line which are the characteristic spots for designing the crown were recognized. These data thus obtained will be able to give the inner and outer shape of crown for processing the prostheses by CAD/CAM technique.

Crowns↗

PubMed1990

[Three-dimensional shape measurement of teeth. (6) Measurement of tooth model by tilting method by means of the double sensor laser displacement meter, and the simulation of occlusion].

To measure the three-dimensional shape of the undercut portion of a molar model tooth, the tilting method was used. The measuring system was composed of a laser displacement meter with double sensor and a computer controlled tooth model scanning machine (CAMM-3). A model tooth was tilted on the gonio stage with +/- 20 degrees and measured divisionally, and a couple of data were connected by the TILCOMPO program. The undercut portions from the survey line to the tooth neck were measured and drawn by CG. By this tilting method, the whole shape of tooth including the undercut portion could be measured, and these data will be available for the production of the data base for CAD of prosthesis. The marginal line on the crown abutment measured previously was searched. Initially, the difference in the inclination dz/dx between the data before and behind was calculated, and the gingival line was extracted by limiting its value. Then, also by limiting the difference value, the margin located above the gingival line was determined. Thus the marginal line in contact with the inner and outer crown and a significantly important point for the production of crown by the CAD/CAM technique could be determined around the crown abutment. Another elementary attempt to simulate the occlusion by using the data of teeth models measured on the articulator was carried out. The maxillary and mandibular teeth were set on the articulator and the maxillary teeth turned over. The shapes of the 5-7 upper and lower molar were measured. The two data were connected and occluded by the "OCCLUS" program.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Simulation↗

PubMed1990

[Three dimensional shape measurement of teeth. (5) On the measurement by the newly developed double sensor laser displacement meter].

A laser displacement meter equipped with two PSD (Position Sensitive Device) sensors located 45 symmetrical to the incident beam was developed to measure the three dimensional shape of a tooth with a higher efficiency and accuracy. This displacement meter enabled compensation of the data at the shaded points without the rotational measurement which could not be done by the former single sensor displacement meter. The output voltages on the declined plane measured by the two sensors were different on the complicatedly declined plane. in such a case, the output measured by the sensor which made a larger angle with the declined plane was adopted since it was affected less by the secondary scattering. All regions of the 6 molar were measured without errors, and the cusps and fissures of the occlusal plane were measured as precisely as by the single sensor displacement meter. The time required for the measurement was about 10 min, which was one third that required for the former single sensor displacement meter. For measurement of a crown abutment tooth with steeply inclined slope and margin, by the single sensor displacement meter, the tooth area had to divided into four parts by tilting and rotation on the gonio stage, and required about one and half hours. However, with the present displacement meter, only the measurements with tilting were required and the time was reduced to about 40 min. Besides, the data connection for CG was accomplished in about 5 min, and the complete data without errors and overlap could be saved. This data will be able to give the inner shape of a crown for machining by CAM technique. As mentioned, the newly developed double sensor laser displacement meter greatly simplified the procedure to measure the shape of a tooth and enabled measurements with high precision.

Crowns↗

PubMed1990

[Three dimensional shape measurement of teeth. (7) CAD of crown prosthesis by using the data measured].

A preliminary CAD system to design the inner and outer shape of crown prosthesis was developed using the data of 7 abutment and molar measured in the previous paper. The gingival and marginal line in the abutment tooth could be recognized more certainly by the "GIN-MAGN" program, and the three dimensional data of tooth crown above the gingival line could be output and saved. To prepare the data base of the occlusal surface of tooth crown, the data of tooth crown above the gingival line of 7 molar were also output by the "GIN-M" program. The data around the toothneck were excluded with an arbitrary height above the gingival line in order to connect smoothly with the margin line of the abutment tooth. The tooth crown data were set up on the abutment data by means of the program "AB-CR-E". In the present system, even though the occlusal condition with the antagonistic tooth could not be taken into account, the CAD procedure to set up a tooth crown with an arbitrary size on the arbitrary position of abutment tooth could be accomplished, and the toothneck data of crown were connected with the margin of abutment tooth.

Crowns↗

PubMed1989

[Three dimensional shape measurement of teeth (4). On the measurement by the laser displacement meter which is able to move on Z-direction].

A three dimensional shape measurement using a wide area teeth model was constructed using a high precision laser displacement meter, teeth model scanning machine and personal computer. The system employed a Z-directional movement of a laser displacement meter which tracked wide and complicated changes of shape, allowing for the accurate measurement of not only the crown and alveolar crista of the molar, but also maxillary root, the height difference between which extends about 25mm. As for the labialis of the incisors, teeth model was stood on a gonio stage and measured. In the present study, arrange arc and rugged array of incisors were measured. Improvements in the accuracy of measurement were also expected. Higher resolutions were obtained by the measurement at the center of the measurable range of the displacement meter where the laser beam is most focused. Since the lineality of the measured value varies with the sensitivity coefficient, if the coefficient drifted, values measured in the outer measurable ranges yielded large errors than those in the central positions. The present Z-directional movement enables measurement at the center of the measurable range, yielding smaller errors. The data obtained with the present method of Z-directional movement of a laser displacement meter enables not only the precise measurement of the shape and position of teeth for CAD prosthesis design but also provides basic data for simulation of occlusion by adding the relative positions of the maxilla and mandible to computer models.

Computer Graphics↗