- Email: [email protected]
Three-dimensional dental cast analyzing system using laser scanning
Three-dimensional dental cast analyzing system using laser scanning Takayuki Kuroda, DDS, PhD," Nobuyoshi Motohashi, DDS, PhD,b Reiji Tominaga, DDS, PhD,° and Koji Iwata, DDS, PhDc
Tokyo, Japan The purpose of this article is to introduce the outline of our newly developed three-dimensional dental cast analyzing system with laser scanning, and its preliminary clinical applications. The system is composed of a measuring device with a slit-ray laser projector and two sets of coupled charged devised video cameras, an image processing unit, a 16-bit personal computer as a controllerl and an engineering workstation as a post processor. The dental cast is projected and scanned with a slit-ray laser beam. The raster coordinates of the target are determined with an image processor. Triangulation is applied to determine the location of each point. Generation of three-dimensional graphics of the dental cast takes approximately 40 minutes. About 90,000 sets of X,Y,Z coordinates are stored in the main memory of the microcomputer. The measurement error is less than 0.05 mm. Besides the conventional linear and angular measurements of the dental cast, we are also able to demonstrate the size of the palatal surface area and the volume of the oral cavity. The advantage of this system is that it facilitates the otherwise complicated and time-consuming mock surgery necessary for treatment planning in orthognathic surgery. (Am J Orthod Dentofac Orthop 1996;110:365-9.)
I n orthodontic treatment the information obtained from the dental cast is invaluable not only for the diagnosis, but also for treatment planning. However, it has b e e n difficult to obtain quantitative information regarding probable changes in the volume of the oral cavity after treatment. Furthermore, it is imperative to set the treatment goal before commencing active treatment (VTO). For this purpose, we have used h a n d m a d e set-up models to determine what the treatment goal would be. However, that is extremely time consuming and makes comparing multiple alternative treatment plans in an individual case a long and laborious process. Hence, the development of a computer-aided designing system for the orthodontic field has long b e e n an important goal. The purpose of this article is to introduce the outline of our newly developed three-dimensional analyzing system with laser scanning, together with From the 2nd Department of Orthodontics, Faculty of Dentistry, Tokyo Medical and Dental University. Supported by a grant-in-aid for Developmental Scientific Research from the Japanese Ministry of Education, Science and Culture (No. 065077004). aProfessor bLecturer CResearch associate Reprint requests to: Dr. Takayuki Kuroda, 2nd Department of Orthodontics, Faculty of Dentistry, Tokyo Medical and Dental University, 1-5-45 Yushima Bunkyo-ku, Tokyo, Japan 113. Copyright © 1996 by the American Association of Orthodontists. 0889-5406/96/$5.00 + 0 8/1/65232
some initial clinical results that indicate clinical feasibility.
MATERIAL AND METHOD The system is composed of a measuring unit (3DVMS250R UNISN, Inc., Osaka, Japan), a 16-bit personal computer (PC-9821Ap, NEC, Inc., Tokyo, Japan) as the controller, and an engineering work station (Titan Vistra 800X Kubota Computer, Inc., Tokyo, Japan) as the post processor. All units are linked on the network.
Data Acquisition The measuring device consists of a slit-ray laser projector, two CCD video cameras to capture reflected images, X-Y object tables, an R-table to measure the circumference of the object, an image processor, and a personal computer used as a data controller. The dental cast is projected and scanned with a slit-ray laser beam of a 670 mm wavelength at 3 mW output, through a revolving polygon mirror (Fig. 1). This slit beam is projected in the X-Y plane that crosses the x-axis at right angles, and the reflected laser beams are simultaneously received with two CCD video cameras. The drive mechanism of the measuring device is driven by a stepping motor with a measuring pitch of 0.01 mm x N (iV max = 500). The object to be measured is fixed on the rotary table, and the X-table is moved in the slit-ray plane. In the case of a large object, y-axis measurements are made by dividing the y-axis plane into two
365
366
Kuroda et al.
American Journal of Orthodontics and Dentofacial Orthopedics October
1996
CCD
camera
Revolving /~ polygon mirror ( . 1 1 /'~
CCD camera
'LASER EMITTER (SLIT RAY) DETECTOR CCD CAMERA
R table
/
~ La~\
/
I~.
X,Y
ON" O CAMER~ CENTERI
able
Fig. 1. Measuring device composed of slit-ray laser projector, two CCD video cameras to capture reflected images, X-Y object tables, and R-table to measure circumference of object.
parts. The R-table provides an automatic full circle sampling with a minimum blind sector by dividing 360° into six sectors. The z-axis measurements are calculated by using the principle of triangulation (Fig. 2). Triangulation requires only one CCD camera, but two cameras are used to ensure adequate sampling of recessed areas, which might not be sufficiently accessible with a single camera. The image processor converts raster coordinates and brightness data of analog video signals input from the CCD cameras into digital data, which is then sent to the personal computer on real time. The personal computer imports the data from the image processor and, after moving the target to the next measurement position, converts the picture coordinates to three-dimensional spatial coordinates. Approximately 90,000 sets of X,Y,Z coordinates are stored in the main memory of the personal computer. The measurement error is less than 0.05 mm.
Fig. 2. Principle of triangulation. In this figure, laser emitter is positioned so that its light axis crosses at angle of 0. As point P shifts from camera center O, image point P' of CCD camera changes accordingly. By reading position of P', deviation of Z from camera center can be calculated.
RESULTS OF C L I N I C A L A P P L I C A T I O N
To show the clinical use of our system, some experimental results are shown. Fig. 3 shows oral photographs of a patient in our orthodontic clinic with severe mandibular prognathism, and Fig. 4 shows a computed graphic of the corresponding dental cast. Three-Dimensional M e a s u r e m e n t Function
Fig. 5 shows the palatal surface area, and Fig. 6 the lateral view of the oral cavity. We can calculate automatically the size of the palatal surface a r e a and the volume of the oral cavity with a computer program. Three-Dimensional Computer Simulation
Generation of Three-Dimensional Graphics
The three-dimensional dot map data is relayed from the personal computer into the engineering workstation on the network, and the curved surface is automatically generated by root mean squaring the measurement data. Generation of a three-dimensional graphic of the dental cast takes approximately 40 minutes. A solid wax model can also be generated from the measurement data, with a numerical control milling machine (Comms PNC2400G Corp., Hamamatsu, Japan Roland Digital Group).
In the computer simulation of the set-up model, two u p p e r premolars and four third molars were removed. Lower anterior teeth were moved labially about 4 m m from their original position, and all teeth were aligned on the basal arch with the oval line as the guideline of the arch shape (Figs. 7 and 8). Consequently, the simulation (Fig. 9) suggested that the mandible should be surgically moved 8.5 m m backward and rotated 4.4 ° to achieve proper overjet (2 m m ) and overbite (2 ram).
American Journal of Orthodontics and Dentofacial Orthopedics Volume 110, No. 4
Fig. 3. Oral photographs of patient with severe mandibular prognatism.
Fig. 4. Computer graphication of dental cast.
Kuroda et al.
367
Fig. 5. Palatal surface area (3021.6 mm2).
Fig. 6. Lateral view of oral cavity (61153.S mma).
DISCUSSION
Since Simon I reported the analysis of the gnathostatic model in 1922, many research reports have been published regarding analysis of the dental cast, not only for evaluation of malocclusion but also for determining the treatment plan. Mooreees et al. 2'3 reported the averages of tooth size, and Howes 4"5 reported the relation of tooth size to the dental arch form. However, because conventional dental cast analysis was based on contact manual two-dimensional measurement, the problems regarding reproductive accuracy of the dental cast, measurement errors, and long data acquisition time were inherent in such an analysis. It was also difficult to obtain three-dimensional information,
such as the size of the palatal surface area and the volume of the oral cavity. Recently, coupled with the remarkable development of computer graphics, various noncontact three-dimensional analyzing systems that use Moire topography,6 stereophotogrammetry,7 and laser scanning techniques~ have been developed in the field of dentistry. The laser scanning technique, particularly, has been applied not only in the orthodontic field but also in the prosthodontic field, to obtain various kinds of three-dimensional information from the dental cast. 9 The features of our laser beam scanning system are as follows:
:368
Kuroda et al,
American Journal of Orthodontics and Dentofacial Orthopedics October 1996
4 4
!
Fig. 8. Computed lower teeth alignment.
Fig. 7. Computed upper teeth alignment.
1. High-speed measuring and processing. Unlike the spot laser measuring method, this system produces 254-point data with a single slit scanning ray, thus greatly reducing processing time. In addition, several tens of thousands of sampled data obtained by image scanning can be speedily and accurately converted into three-dimensional coordinates for a graphic display by using a look-up table, s° This table is created by calibrating 40 sections in the vertical plane at 25 points on a slit-ray axis of known coordinates. The table includes parameters of camera position and lens parallax. 2. High accuracy. Usually, the resolution of the slit-ray projection is dependent on the pixel alignment of the CCD camera. To enhance the resolution, a one-dimensional camera with a large pixel count may be used, but this
is time consuming because it involves spot measurement. This system uses a slit-ray projection for high-speed measurement, and the slit video image is then analog-to-digital converted with an 8-bit analog-to-digital converter in the image processor. The personal computer calculated the location of the brightest data in the pixel with its neighboring bright data of the slit image, thus improving the accuracy of the generated pictures. However, a disadvantage of the slit-ray projection is the impossibility of sampling beneath overhangs. It should also be noted that a parallax angle between the laser emitter and receiver causes a blind region around deep grooves, with an overhang. Accordingly, more study on the specifications and geometric alignment of the slit-ray emitter and the CCD cameras, with respect to the target, is necessary to minimize blind sectors. Trial clinical applications suggest that the use of this system is feasible not only for clinical evaluation of maloc-
Kuroda et al.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 110, No. 4
369
clusion and treatment results but also for saving time necessary for treatment planning and diagnosis through the use of computed simulation of tooth movement. We express our great appreciation to Mr. Muramoto and Mr. Fujisato of UNISN INC., for their kind assistance in designing clinical applications of this system. REFERENCES
Fig. 9. Computed surgery.
1. Simon PW. Grundzuge einer systematiehen diagnostic der gebissanomalien. Berlin: Herman Meusser, 1922. 2. Moorrees CFA, Reed RB. Biometrics of crowding and spacing of the teeth in the mandible. Am J Phys Anthropol 1954;12:77-88. 3. Moorrees CFA, Thomsan SO, Jensen E, Kai-Jen Yen P. Mesiodistal crown diameters of the deciduous and permanent teeth in individuals. J Dent Res 1957;36:39-47. 4. Howes AE. A polygon portrayal of coronal and basal arch dimensions in the horizontal plane. Am J Orthod 1954;40:811-31. 5. Howes AE. Arch width in the premolar region -- still the major problem in orthodontics. Am J Orthod 1957;43:5-31. 6. Kuroda T, Motohashi N, Kato Y. Prediction system of facial change. J Stomatol Soc Jpn 1960;57:441-5. 7. Chaya H, Ishikawa H, Imai T, Nakamura S. A three-dimensional analyzing system of face using stereophotogrammetsy and computer graphics. J 3pn Orthod Sue 1988;47:560-78. 8. Soma K, Hisano M, Kuroki T, Ishida T, Kuroda T. High accuracy measuring device for dental cast - using device with fiat laser beam. J Stomatot Sue Jpn 1992;59:259-64. 9. Maeda Y, Minoura M, Okada M, et al. A CAD/CAM system for removable dentures: part 1, a system for complete denture fabrication. J Jpn Prosthod Sue 1993;37:800-5. 10. Ishimatsu T, Taguchi N, Ochiai T, Oohata T. Fast 3-dimensional measuring technique using a look-up table (measurement of a human head). Trans Jpn Soc Mech Eng 1991;57:1969-73.
Tokyo, Japan The purpose of this article is to introduce the outline of our newly developed three-dimensional dental cast analyzing system with laser scanning, and its preliminary clinical applications. The system is composed of a measuring device with a slit-ray laser projector and two sets of coupled charged devised video cameras, an image processing unit, a 16-bit personal computer as a controllerl and an engineering workstation as a post processor. The dental cast is projected and scanned with a slit-ray laser beam. The raster coordinates of the target are determined with an image processor. Triangulation is applied to determine the location of each point. Generation of three-dimensional graphics of the dental cast takes approximately 40 minutes. About 90,000 sets of X,Y,Z coordinates are stored in the main memory of the microcomputer. The measurement error is less than 0.05 mm. Besides the conventional linear and angular measurements of the dental cast, we are also able to demonstrate the size of the palatal surface area and the volume of the oral cavity. The advantage of this system is that it facilitates the otherwise complicated and time-consuming mock surgery necessary for treatment planning in orthognathic surgery. (Am J Orthod Dentofac Orthop 1996;110:365-9.)
I n orthodontic treatment the information obtained from the dental cast is invaluable not only for the diagnosis, but also for treatment planning. However, it has b e e n difficult to obtain quantitative information regarding probable changes in the volume of the oral cavity after treatment. Furthermore, it is imperative to set the treatment goal before commencing active treatment (VTO). For this purpose, we have used h a n d m a d e set-up models to determine what the treatment goal would be. However, that is extremely time consuming and makes comparing multiple alternative treatment plans in an individual case a long and laborious process. Hence, the development of a computer-aided designing system for the orthodontic field has long b e e n an important goal. The purpose of this article is to introduce the outline of our newly developed three-dimensional analyzing system with laser scanning, together with From the 2nd Department of Orthodontics, Faculty of Dentistry, Tokyo Medical and Dental University. Supported by a grant-in-aid for Developmental Scientific Research from the Japanese Ministry of Education, Science and Culture (No. 065077004). aProfessor bLecturer CResearch associate Reprint requests to: Dr. Takayuki Kuroda, 2nd Department of Orthodontics, Faculty of Dentistry, Tokyo Medical and Dental University, 1-5-45 Yushima Bunkyo-ku, Tokyo, Japan 113. Copyright © 1996 by the American Association of Orthodontists. 0889-5406/96/$5.00 + 0 8/1/65232
some initial clinical results that indicate clinical feasibility.
MATERIAL AND METHOD The system is composed of a measuring unit (3DVMS250R UNISN, Inc., Osaka, Japan), a 16-bit personal computer (PC-9821Ap, NEC, Inc., Tokyo, Japan) as the controller, and an engineering work station (Titan Vistra 800X Kubota Computer, Inc., Tokyo, Japan) as the post processor. All units are linked on the network.
Data Acquisition The measuring device consists of a slit-ray laser projector, two CCD video cameras to capture reflected images, X-Y object tables, an R-table to measure the circumference of the object, an image processor, and a personal computer used as a data controller. The dental cast is projected and scanned with a slit-ray laser beam of a 670 mm wavelength at 3 mW output, through a revolving polygon mirror (Fig. 1). This slit beam is projected in the X-Y plane that crosses the x-axis at right angles, and the reflected laser beams are simultaneously received with two CCD video cameras. The drive mechanism of the measuring device is driven by a stepping motor with a measuring pitch of 0.01 mm x N (iV max = 500). The object to be measured is fixed on the rotary table, and the X-table is moved in the slit-ray plane. In the case of a large object, y-axis measurements are made by dividing the y-axis plane into two
365
366
Kuroda et al.
American Journal of Orthodontics and Dentofacial Orthopedics October
1996
CCD
camera
Revolving /~ polygon mirror ( . 1 1 /'~
CCD camera
'LASER EMITTER (SLIT RAY) DETECTOR CCD CAMERA
R table
/
~ La~\
/
I~.
X,Y
ON" O CAMER~ CENTERI
able
Fig. 1. Measuring device composed of slit-ray laser projector, two CCD video cameras to capture reflected images, X-Y object tables, and R-table to measure circumference of object.
parts. The R-table provides an automatic full circle sampling with a minimum blind sector by dividing 360° into six sectors. The z-axis measurements are calculated by using the principle of triangulation (Fig. 2). Triangulation requires only one CCD camera, but two cameras are used to ensure adequate sampling of recessed areas, which might not be sufficiently accessible with a single camera. The image processor converts raster coordinates and brightness data of analog video signals input from the CCD cameras into digital data, which is then sent to the personal computer on real time. The personal computer imports the data from the image processor and, after moving the target to the next measurement position, converts the picture coordinates to three-dimensional spatial coordinates. Approximately 90,000 sets of X,Y,Z coordinates are stored in the main memory of the personal computer. The measurement error is less than 0.05 mm.
Fig. 2. Principle of triangulation. In this figure, laser emitter is positioned so that its light axis crosses at angle of 0. As point P shifts from camera center O, image point P' of CCD camera changes accordingly. By reading position of P', deviation of Z from camera center can be calculated.
RESULTS OF C L I N I C A L A P P L I C A T I O N
To show the clinical use of our system, some experimental results are shown. Fig. 3 shows oral photographs of a patient in our orthodontic clinic with severe mandibular prognathism, and Fig. 4 shows a computed graphic of the corresponding dental cast. Three-Dimensional M e a s u r e m e n t Function
Fig. 5 shows the palatal surface area, and Fig. 6 the lateral view of the oral cavity. We can calculate automatically the size of the palatal surface a r e a and the volume of the oral cavity with a computer program. Three-Dimensional Computer Simulation
Generation of Three-Dimensional Graphics
The three-dimensional dot map data is relayed from the personal computer into the engineering workstation on the network, and the curved surface is automatically generated by root mean squaring the measurement data. Generation of a three-dimensional graphic of the dental cast takes approximately 40 minutes. A solid wax model can also be generated from the measurement data, with a numerical control milling machine (Comms PNC2400G Corp., Hamamatsu, Japan Roland Digital Group).
In the computer simulation of the set-up model, two u p p e r premolars and four third molars were removed. Lower anterior teeth were moved labially about 4 m m from their original position, and all teeth were aligned on the basal arch with the oval line as the guideline of the arch shape (Figs. 7 and 8). Consequently, the simulation (Fig. 9) suggested that the mandible should be surgically moved 8.5 m m backward and rotated 4.4 ° to achieve proper overjet (2 m m ) and overbite (2 ram).
American Journal of Orthodontics and Dentofacial Orthopedics Volume 110, No. 4
Fig. 3. Oral photographs of patient with severe mandibular prognatism.
Fig. 4. Computer graphication of dental cast.
Kuroda et al.
367
Fig. 5. Palatal surface area (3021.6 mm2).
Fig. 6. Lateral view of oral cavity (61153.S mma).
DISCUSSION
Since Simon I reported the analysis of the gnathostatic model in 1922, many research reports have been published regarding analysis of the dental cast, not only for evaluation of malocclusion but also for determining the treatment plan. Mooreees et al. 2'3 reported the averages of tooth size, and Howes 4"5 reported the relation of tooth size to the dental arch form. However, because conventional dental cast analysis was based on contact manual two-dimensional measurement, the problems regarding reproductive accuracy of the dental cast, measurement errors, and long data acquisition time were inherent in such an analysis. It was also difficult to obtain three-dimensional information,
such as the size of the palatal surface area and the volume of the oral cavity. Recently, coupled with the remarkable development of computer graphics, various noncontact three-dimensional analyzing systems that use Moire topography,6 stereophotogrammetry,7 and laser scanning techniques~ have been developed in the field of dentistry. The laser scanning technique, particularly, has been applied not only in the orthodontic field but also in the prosthodontic field, to obtain various kinds of three-dimensional information from the dental cast. 9 The features of our laser beam scanning system are as follows:
:368
Kuroda et al,
American Journal of Orthodontics and Dentofacial Orthopedics October 1996
4 4
!
Fig. 8. Computed lower teeth alignment.
Fig. 7. Computed upper teeth alignment.
1. High-speed measuring and processing. Unlike the spot laser measuring method, this system produces 254-point data with a single slit scanning ray, thus greatly reducing processing time. In addition, several tens of thousands of sampled data obtained by image scanning can be speedily and accurately converted into three-dimensional coordinates for a graphic display by using a look-up table, s° This table is created by calibrating 40 sections in the vertical plane at 25 points on a slit-ray axis of known coordinates. The table includes parameters of camera position and lens parallax. 2. High accuracy. Usually, the resolution of the slit-ray projection is dependent on the pixel alignment of the CCD camera. To enhance the resolution, a one-dimensional camera with a large pixel count may be used, but this
is time consuming because it involves spot measurement. This system uses a slit-ray projection for high-speed measurement, and the slit video image is then analog-to-digital converted with an 8-bit analog-to-digital converter in the image processor. The personal computer calculated the location of the brightest data in the pixel with its neighboring bright data of the slit image, thus improving the accuracy of the generated pictures. However, a disadvantage of the slit-ray projection is the impossibility of sampling beneath overhangs. It should also be noted that a parallax angle between the laser emitter and receiver causes a blind region around deep grooves, with an overhang. Accordingly, more study on the specifications and geometric alignment of the slit-ray emitter and the CCD cameras, with respect to the target, is necessary to minimize blind sectors. Trial clinical applications suggest that the use of this system is feasible not only for clinical evaluation of maloc-
Kuroda et al.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 110, No. 4
369
clusion and treatment results but also for saving time necessary for treatment planning and diagnosis through the use of computed simulation of tooth movement. We express our great appreciation to Mr. Muramoto and Mr. Fujisato of UNISN INC., for their kind assistance in designing clinical applications of this system. REFERENCES
Fig. 9. Computed surgery.
1. Simon PW. Grundzuge einer systematiehen diagnostic der gebissanomalien. Berlin: Herman Meusser, 1922. 2. Moorrees CFA, Reed RB. Biometrics of crowding and spacing of the teeth in the mandible. Am J Phys Anthropol 1954;12:77-88. 3. Moorrees CFA, Thomsan SO, Jensen E, Kai-Jen Yen P. Mesiodistal crown diameters of the deciduous and permanent teeth in individuals. J Dent Res 1957;36:39-47. 4. Howes AE. A polygon portrayal of coronal and basal arch dimensions in the horizontal plane. Am J Orthod 1954;40:811-31. 5. Howes AE. Arch width in the premolar region -- still the major problem in orthodontics. Am J Orthod 1957;43:5-31. 6. Kuroda T, Motohashi N, Kato Y. Prediction system of facial change. J Stomatol Soc Jpn 1960;57:441-5. 7. Chaya H, Ishikawa H, Imai T, Nakamura S. A three-dimensional analyzing system of face using stereophotogrammetsy and computer graphics. J 3pn Orthod Sue 1988;47:560-78. 8. Soma K, Hisano M, Kuroki T, Ishida T, Kuroda T. High accuracy measuring device for dental cast - using device with fiat laser beam. J Stomatot Sue Jpn 1992;59:259-64. 9. Maeda Y, Minoura M, Okada M, et al. A CAD/CAM system for removable dentures: part 1, a system for complete denture fabrication. J Jpn Prosthod Sue 1993;37:800-5. 10. Ishimatsu T, Taguchi N, Ochiai T, Oohata T. Fast 3-dimensional measuring technique using a look-up table (measurement of a human head). Trans Jpn Soc Mech Eng 1991;57:1969-73.