- Email: [email protected]
Evaluation of a digitizer and computer system designed to analyze articulator-generated occlusal tracings
RESEARCH AND EDUCATION SECTION
EDITOR
LOUIS J. BOUC.KER
Evaluation of a digitizer and computer system designed to analyze articulator-generated occlusal tracings Josef N. Kolling, D.D.S., M.S.,* Richard B. Price, B.D.S., L.D.S., M.S.,** Richard L. Miller, B.S., M.S.,*** and Joseph A. Clayton, D.D.S., M.S.**** University of Michigan, School of Dentistry, Ann Arbor, Mich., and Dalhousie University, School of Dentistry, Halifax, Nova Sostia
C
omputers have been used to collect, store, and analyze experimental data in dentistry for over a decade. In 1970, Miller et al.’ introduced a system to provide computer acquisition, storage, and recall of cephalometric tracing data. With this system, complete tracings could be computer displayed, superimposed, scaled, and moved for analysis. Advances in computer graphics have improved the speed and accuracy of this system.2 This study determines the validity of this system for research of mandibular movement. MATERIAL
AND
METHODS
To control patient variables, occlusal tracings obtained from a Denar SE (Denar Corp., Anaheim, Calif.) articulator were used in this study. The articulator settings were obtained from previous patient data. The apparatus generating these occlusal tracings was similar to that of Jaarda et a1.3 (Fig. 1). A table and stylus were attached to a Denar SE articulator. The table and stylus can be oriented in the horizontal, frontal, and sagittai planes while maintaining a constant center point. This point was oriented to monitor the movement of th.e maxillary first molar. In addition to this center point, a fixed reference line was needed to accurately digitize the occlusal tracing data. A vernier height gauge was used to scribe the reference line (Figs. 2 and 3). The tracings produced by the scribing device represented the movement of the mesiolingual cusp of the maxillary first molar. The first 3 mm of each line from the centric point was used to compare the tracings.
From a thesis in partial fulfillment of the requirements for the Master of Science degree, University of Michigan, Ann Arbor, Mich. *Assistant Professor, Department of Crown and Bridge, University of Michigan, Schoo.l of Dentistry. **Assistant Profesr:or, Operative Dentistry, Dalhousie University, School of Dentistry. ***Senior Programmer Analyst, Center for Human Growth and Development, University of Michigan. ****Professor, Department of Crown and Bridge, University of Michigan, Schoo:. of Dentistry. THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 1. Tracing
apparatus mounted on Denar articula-
tor. Differences between tracings greater than 0.1 mm were considered clinically significant. To improve the accuracy of detecting minute differences, the tracings were photographed and projected. A Canon Fl camera with a 100 mm Macro lens (Canon USA Inc., Lake Success, N.Y.) was mounted in a jig to ensure that the film was parallel to the tracings and that the photographs were made at identical magnification. To provide a scale, the tracings were photographed through a transparent overlay that had a square grid larger than the tracings with a 2 mm reference scale drawn on the four sides (Fig. 4). The slides were projected by using a Kodak 750H projector with an F/3.5 zoom lens (Eastman Kodak Co., Rochester, N.Y.) onto the digitizing pad (ID-3 Digitizer, Summagraphics Corp., Fairfield, Conn.). Projecting the slides produced an image approximately 10 times the original size of the tracing. The digitizing program corrected errors in magnification by referencing the data with the 2 mm scale from the photographed grid. To eliminate distortion errors produced during slide projection, a square grid was drawn on the digitizing pad. The angulation of the pad and the projector was positioned so 499
KOLLING
ET AL
TOP
Fig. 4. Example slide of tracing with reference grid.
Fig. 2. Vernier height gauge.
Fig. 5. Projected tracing on digitizer with cursor.
Fig. 3. Scribing of reference line with gauge. that the square on the slide, when projected, was superimposed on the square on the digitizer. The images were verified with this method for projection accuracy before the tracings were digitized. The digitizer, a 14 inch X 14 inch pad and cursor, collects x and y coordinates of points on the tracing. The 500
cursor had a transparent sight with cross hairs on the bottom to control the effects of parallax. Thus, the slide image was projected through the sight onto the digitizing pad. The cursor was positioned to center the cross hairs in the middle of tracing lines and reference points (Fig. 5). By using a button on the cursor, a series of points along the tracings were recorded. A digitizing program called ACQUIRE received these points and stored them on a Michigan Terminal System (MTS) file. The ACQUIRE program also provided user definition of the data structure. The ACQUIRE menu control provided case identification, missing point data codes, error correction, coordinate system registration, and area determination. This procedure was performed at the digitizing station at the University of Michigan Center for Human Growth and Development. APRIL
1988
VOLUME
59
NUMBER
4
EVALUATION
OF A. DIGITIZER
AND
COMPUTER
SYSTEM
Fig. 6. Computer plot of tracing.
Fig. 7. Tracing plotted in Fig. 6.
SLICE, a program written for this project, was used to analyze each tracing in relation to the scribed line (xJ and 2 mm reference scale. For an x value, the corresponding y value on the tracing was interpolated from the series of points previously collected. In addition, the area between the tracing line and the hori~ntal reference line was determined. The program was written so that increments between given x values could be chosen. For this study, x increments of 0.2 mm were used for the analyses. For each x value in a tracing, the program calculated the corresponding y value, incremental area, and total area. These data were then analyzed by the Michigan Interactive Data Analysis System (MIDAS) to determine differences between the tracings. In addition, the collected data for a tracing could be plotted on a CalComp plotter (California Computer Products, Inc., Anaheim, Calif.) (Fig. 6). Where significant differences were identified by MIDAS, these plots were superimposed and visually compared. This provided a final check of accuracy to determine whether there was an actual difference or an error (Fig. 7). To assess the error of ~~tizing, a single occlusal tracing was projected and digitized five times. The error was determined by obtaining the range of y values at each 0.2 mm x interval extending to 3 from the centric position. The error of the scribing device’was determined by obtaining five sets of occlusal tracings using a constant stylus position and articulator settingk This procedure was performed for all three planes. Analysis of the occlusal tracings determined the experimental error for this step. These tracings were then digitized and analyzed to determine the range (~imum error} at each 0.2 mm increment. THE JOURNAL
OF PROSTHETIC
DENTISTRY
Table I, Tracing and digitizing interval
in horizontal
for each
plane
Working
Balancing
X
A
B
c
D
0.0 0.2 0.4 0.6 0.8 1.0 x.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
0.021 0.036 0.058 0.087 0.100 0.071 0.096 0.110 0.101 0.098 0.100 0.088 0.076 0.077 0.080 0.083
-0.043 -0.028 -0.006 0.023 0.036 0.007 0.032 0.046 0.037 0.034 0.036 0.024 0.012 0.013 0.016 0.019
0.023 0.038 0.052 0.066 0.103 0.107 0.117 0.160 0.209 0.210 0.192 0.173 0.166 0.163 0.160 0.161
-0.041 -0.026 -0.012 0.002 0.039 0.043 0.053 0.096 0.145 0.146 0.128 0.109 0.102 0.099 0.096 0.097
X = 0.2 mm; A and C = tracing and digitizing error (in mm); B and D = tracing error, A or C minus the digitizing error of 0.064 mm.
RESULTS A slight variation was found in digitizing between intervals, but the error was constant. The average maximum error of digitizing at any given interval was 0.064 mm with a standard deviation of 0.02 mm. When this digitizing error was subtracted from the error of occlusal tracing and digitizing, the tracing error was determined (Tables I through III, columns B and D). The scribing apparatus was designed to be stable. However, this could not be tested without considering flexing of the articulator that may have occurred during the movements. In this study, the effects of the tracing 501
KOLLING
Table II. Tracing and digitizing interval
in frontal
for each
interval
Working A
B
C
0.0
0.032 0.035 0.034 0.045 0.057 0.083 0.088 0.087 0.087 0.085 0.084 0.084 0.083 0.083 0.082 0.081
-0.032 -0.029 -0.030 -0.019 -0.007 0.019 0.024 0.023 0.023 0.021 0.020 0.020 0.019 0.019 0.018 0.017
0.011 0.020 0.025 0.035 0.058 0.056 0.055 0.054 0.053 0.053 0.052 0.051 0.050 0.050 0.049 0.049
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
for each
in sagittal plane
Balancing
X 0.2 0.4 0.6 0.8
Table III. Tracing and digitizing
plane
Working D
-0.053 -0.044 -0.039 -0.029 -0.006 -0.008 -0.009 -0.010 -0.011 -0.011 -0.012 -0.013 -0.014 -0.014 -0.015 -0.015
ET AL
Balancing
X
A
B
C
D
0.0
0.024 0.053 0.049 0.058 0.067 0.75 0.076 0.087 0.081 0.076 0.069 0.076 0.082 0.087 0.092 0.093
-0.040 -0.011 -0.015 -0.006 0.003 0.011 0.012 0.023 0.017 0.012 0.005 0.012 0.018 0.023 0.028 0.029
0.018 0.052 0.073 0.078 0.080 0.081 0.080 0.086 0.092 0.094 0.095 0.097 0.099 0.101 0.103 0.105
-0.046 -0.012 0.009 0.014 0.016 0.017 0.016 0.022 0.028 0.030 0.031 0.033 0.035 0.037 0.039 0.041
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
X = 0.2 mm; A and C = tracing and digitizing error (in mm); B and D = tracing error, A or C minus digitizing error of 0.064 mm.
X = 0.2 mm; A and C = tracing and digitizing error (in mm); B and D = tracing error, A or C minus digitizing error of 0.064 mm.
apparatus, articulator flexure, and operator variability in generating the occlusal tracings were reported as a single error. It was observed that this error increased slightly as tracings moved from the centric starting point (X = 0.0). The data indicated that there was no detectable tracing error for the first 0.6 mm of movement in any excursion and/or plane. Beyond X = 0.6 mm, maximum tracing errors from 0.01 mm to 0.15 mm were detected. The tracing errors below 1.4 mm in the horizontal plane and those in the sagittal and frontal planes were less than 0.053 mm. For excursions in the frontal plane and the working excursion in the sagittal plane, the tracing errors were minimal (0.01 to 0.02 mm). The largest errors were revealed in the horizontal plane beyond X = 1.2 mm. Columns A and C in the Tables list the values for the total experimental error at each interval.
by the stylus design and movement in each plane. In the horizontal plane the stylus assembly moved up and laterally from the centric point, while the stylus maintained contact with the table and moved only laterally. Although the stylus fit well in the sleeve, as the excursion proceeded, the length of the stylus became progressively more unsupported. The decreased support allowed a greater chance for errors. This explanation is supported by the finding that the next greatest errors (after the horizontal plane) were in the balancing excursion in the sagittal plane.‘ In this excursion a similar but less dramatic stylus-to-sleeve relationship existed. For excursions in the frontal plane and the working excursion in the sagittal plane, the length of unsupported stylus decreased during the excursions. The tracing errors in these excursions were minimal (0.01 to 0.02 mm). Future studies with this stylus and sleeve assembly should investigate reduction of the length of unsupported stylus by orienting the sleeve close to the table in the horizontal and sagittal planes. With the exception of the values in the horizontal plane (beyond 0.6 mm on the x axis), the data confirmed that the experimental method was accurate in detecting differences exceeding 0.1 mm between occlusal tracings. Analysis of the occlusal tracings was done after computerization of the data by using a digitizer to transform a series of coordinates into a machinereadable form. The sensitivity of the digitizer was directly related to the area of the digitizing pad used to record an image. Therefore, the ability to record small images was limited. Accuracy was increased by magnifying the occlusal tracings through projection onto the digitizing pad. The effect of magnification was
DISCUSSION Although the articulator and scribing apparatus were considered stable, some flexing did occur during the movement of the articulator. The magnitude of this error increased slightly as the tracings departed from the centric starting point. This finding was expected because the centric starting point was mechanically the most stable point of a tracing. Flexure in the apparatus or operator variability in performing successive tracings was anticipated to produce increasing error away from the centric point. There was no tracing error for the first 0.6 mm of movement. Beyond 0.6 mm, errors ranging from 0.01 mm to 0.15 mm were discovered. The largest values were revealed in the horizontal plane. This variation in the error between planes can be explained 502
APRIL
1988
VOLUME
59
NUMBER
4
EVALUATION
OF A DIGITIZER
AND
COMPUTER
SYSTEM
accounted for in the computer program, which based all calculations on the original millimeter scale.
SUMMARY Occlusal tracings generated on a Denar fully adjustable articulator were photographed, projected, digitized, and stored in a computer data file. These steps were accomplished with sufficient accuracy for clinical analysis. This study demonstrated that appropriately referenced tracing data can be transferred accurately into a machine-readable form. Studies of pantographic tracings for mandibular movements are facilitated by this convenient and accurate method of handling data.
CONCLUSIONS 1. The average maximum error in digitizing occlusal tracings into machine-readable form was 0.064 mm in this investigation. 2. Dependent on the plane and excursion, the experimental error of tracing plus digitizing at any interval ranged from 0.01 to 0.21 mm. Tracing problems in the
horizontal plane were responsible for the greater values. 3. The use of a computer to analyze and compare occlusal tracings was an effective method of detecting differences between tracings that exceeded 0.1 mm. REFERENCES Miller RL, Hunter WS, Moyers RE. Computer storage and retrieval system for two-dimensional outlines. J Dent Res 1970;49:1176. Miller RL, Dijkman DJ, Riolo ML, Moyers RE. Graphic computerization of cephalometric data. J Dent Res 1971; 50:1363. Jaarda MJ, Clayton JA, Myers GE. Measurement of cusp height and ridge and groove direction using an electrical transducer. Part I: instrumentation. J PROSTHET DENT 1978;39:67881. Reprint
requeststo:
DR. JOSEF N. KOLLINC UNIVERSITY OF MICHIGAN SCHOOL OF DENTISTRY ANN ARBOR, MI 48109-1056
Corrdsion of dental burs in sterilizing disinfec,ting solutions
and
M. S. Bapna, Ph.D.,* and H. J. Mueller, Ph.D.** University of Illinois, College of Dentistry, and American Dental Association, Chicago, 111.
.,!.he chemical and electrochemical aggressiveness of disinfecting and sterilizing solutions must not affect the performance of the instruments. The corrosive effects from irrigating solutions on endodontic instruments have been reportedlm4as well as the improvement in corrosion resistance when inhibitors were used.5-7However, the effects from commercial disinfecting and sterilizing solutions on dental instruments (burs) have not been reported. Corrosion at the microscopic level is important because the attack of the microstructural phases is directly related to dulling of the cutting edges. Corrosion at the macroscopic level, as seen in mixed metal coupling between bur shank and carbide by a solder, is likely to contribute in reducing the instrument’s neck strength
*Professor, Dental Materials, Department of Prosthodontics, University of Illinois, College of Dentistry. **Research Associate, American Dental Association, Council on Dental Materials, Instruments and Equipment. THE JOURNAL
OF PROSTHETIC
DENTISTRY
1
I
IA -.
iOMN1 ‘\
l.2-
n
I/
..’ ,,t ,i ,.(
II
::'/ -
f IO-
-.4 - .6 ~--r---v“.. . . . .. . *. . . . . . . mm . . . . . .. . . . .. .. -. 81
1
1
7
6
5 -LOG
1 4
I 3
I (AMPS/CM2)
Fig. 1. Polarization curves of stainless steel bum in different sterilizing and disinfecting solutions. 503
EDITOR
LOUIS J. BOUC.KER
Evaluation of a digitizer and computer system designed to analyze articulator-generated occlusal tracings Josef N. Kolling, D.D.S., M.S.,* Richard B. Price, B.D.S., L.D.S., M.S.,** Richard L. Miller, B.S., M.S.,*** and Joseph A. Clayton, D.D.S., M.S.**** University of Michigan, School of Dentistry, Ann Arbor, Mich., and Dalhousie University, School of Dentistry, Halifax, Nova Sostia
C
omputers have been used to collect, store, and analyze experimental data in dentistry for over a decade. In 1970, Miller et al.’ introduced a system to provide computer acquisition, storage, and recall of cephalometric tracing data. With this system, complete tracings could be computer displayed, superimposed, scaled, and moved for analysis. Advances in computer graphics have improved the speed and accuracy of this system.2 This study determines the validity of this system for research of mandibular movement. MATERIAL
AND
METHODS
To control patient variables, occlusal tracings obtained from a Denar SE (Denar Corp., Anaheim, Calif.) articulator were used in this study. The articulator settings were obtained from previous patient data. The apparatus generating these occlusal tracings was similar to that of Jaarda et a1.3 (Fig. 1). A table and stylus were attached to a Denar SE articulator. The table and stylus can be oriented in the horizontal, frontal, and sagittai planes while maintaining a constant center point. This point was oriented to monitor the movement of th.e maxillary first molar. In addition to this center point, a fixed reference line was needed to accurately digitize the occlusal tracing data. A vernier height gauge was used to scribe the reference line (Figs. 2 and 3). The tracings produced by the scribing device represented the movement of the mesiolingual cusp of the maxillary first molar. The first 3 mm of each line from the centric point was used to compare the tracings.
From a thesis in partial fulfillment of the requirements for the Master of Science degree, University of Michigan, Ann Arbor, Mich. *Assistant Professor, Department of Crown and Bridge, University of Michigan, Schoo.l of Dentistry. **Assistant Profesr:or, Operative Dentistry, Dalhousie University, School of Dentistry. ***Senior Programmer Analyst, Center for Human Growth and Development, University of Michigan. ****Professor, Department of Crown and Bridge, University of Michigan, Schoo:. of Dentistry. THE JOURNAL
OF PROSTHETIC
DENTISTRY
Fig. 1. Tracing
apparatus mounted on Denar articula-
tor. Differences between tracings greater than 0.1 mm were considered clinically significant. To improve the accuracy of detecting minute differences, the tracings were photographed and projected. A Canon Fl camera with a 100 mm Macro lens (Canon USA Inc., Lake Success, N.Y.) was mounted in a jig to ensure that the film was parallel to the tracings and that the photographs were made at identical magnification. To provide a scale, the tracings were photographed through a transparent overlay that had a square grid larger than the tracings with a 2 mm reference scale drawn on the four sides (Fig. 4). The slides were projected by using a Kodak 750H projector with an F/3.5 zoom lens (Eastman Kodak Co., Rochester, N.Y.) onto the digitizing pad (ID-3 Digitizer, Summagraphics Corp., Fairfield, Conn.). Projecting the slides produced an image approximately 10 times the original size of the tracing. The digitizing program corrected errors in magnification by referencing the data with the 2 mm scale from the photographed grid. To eliminate distortion errors produced during slide projection, a square grid was drawn on the digitizing pad. The angulation of the pad and the projector was positioned so 499
KOLLING
ET AL
TOP
Fig. 4. Example slide of tracing with reference grid.
Fig. 2. Vernier height gauge.
Fig. 5. Projected tracing on digitizer with cursor.
Fig. 3. Scribing of reference line with gauge. that the square on the slide, when projected, was superimposed on the square on the digitizer. The images were verified with this method for projection accuracy before the tracings were digitized. The digitizer, a 14 inch X 14 inch pad and cursor, collects x and y coordinates of points on the tracing. The 500
cursor had a transparent sight with cross hairs on the bottom to control the effects of parallax. Thus, the slide image was projected through the sight onto the digitizing pad. The cursor was positioned to center the cross hairs in the middle of tracing lines and reference points (Fig. 5). By using a button on the cursor, a series of points along the tracings were recorded. A digitizing program called ACQUIRE received these points and stored them on a Michigan Terminal System (MTS) file. The ACQUIRE program also provided user definition of the data structure. The ACQUIRE menu control provided case identification, missing point data codes, error correction, coordinate system registration, and area determination. This procedure was performed at the digitizing station at the University of Michigan Center for Human Growth and Development. APRIL
1988
VOLUME
59
NUMBER
4
EVALUATION
OF A. DIGITIZER
AND
COMPUTER
SYSTEM
Fig. 6. Computer plot of tracing.
Fig. 7. Tracing plotted in Fig. 6.
SLICE, a program written for this project, was used to analyze each tracing in relation to the scribed line (xJ and 2 mm reference scale. For an x value, the corresponding y value on the tracing was interpolated from the series of points previously collected. In addition, the area between the tracing line and the hori~ntal reference line was determined. The program was written so that increments between given x values could be chosen. For this study, x increments of 0.2 mm were used for the analyses. For each x value in a tracing, the program calculated the corresponding y value, incremental area, and total area. These data were then analyzed by the Michigan Interactive Data Analysis System (MIDAS) to determine differences between the tracings. In addition, the collected data for a tracing could be plotted on a CalComp plotter (California Computer Products, Inc., Anaheim, Calif.) (Fig. 6). Where significant differences were identified by MIDAS, these plots were superimposed and visually compared. This provided a final check of accuracy to determine whether there was an actual difference or an error (Fig. 7). To assess the error of ~~tizing, a single occlusal tracing was projected and digitized five times. The error was determined by obtaining the range of y values at each 0.2 mm x interval extending to 3 from the centric position. The error of the scribing device’was determined by obtaining five sets of occlusal tracings using a constant stylus position and articulator settingk This procedure was performed for all three planes. Analysis of the occlusal tracings determined the experimental error for this step. These tracings were then digitized and analyzed to determine the range (~imum error} at each 0.2 mm increment. THE JOURNAL
OF PROSTHETIC
DENTISTRY
Table I, Tracing and digitizing interval
in horizontal
for each
plane
Working
Balancing
X
A
B
c
D
0.0 0.2 0.4 0.6 0.8 1.0 x.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
0.021 0.036 0.058 0.087 0.100 0.071 0.096 0.110 0.101 0.098 0.100 0.088 0.076 0.077 0.080 0.083
-0.043 -0.028 -0.006 0.023 0.036 0.007 0.032 0.046 0.037 0.034 0.036 0.024 0.012 0.013 0.016 0.019
0.023 0.038 0.052 0.066 0.103 0.107 0.117 0.160 0.209 0.210 0.192 0.173 0.166 0.163 0.160 0.161
-0.041 -0.026 -0.012 0.002 0.039 0.043 0.053 0.096 0.145 0.146 0.128 0.109 0.102 0.099 0.096 0.097
X = 0.2 mm; A and C = tracing and digitizing error (in mm); B and D = tracing error, A or C minus the digitizing error of 0.064 mm.
RESULTS A slight variation was found in digitizing between intervals, but the error was constant. The average maximum error of digitizing at any given interval was 0.064 mm with a standard deviation of 0.02 mm. When this digitizing error was subtracted from the error of occlusal tracing and digitizing, the tracing error was determined (Tables I through III, columns B and D). The scribing apparatus was designed to be stable. However, this could not be tested without considering flexing of the articulator that may have occurred during the movements. In this study, the effects of the tracing 501
KOLLING
Table II. Tracing and digitizing interval
in frontal
for each
interval
Working A
B
C
0.0
0.032 0.035 0.034 0.045 0.057 0.083 0.088 0.087 0.087 0.085 0.084 0.084 0.083 0.083 0.082 0.081
-0.032 -0.029 -0.030 -0.019 -0.007 0.019 0.024 0.023 0.023 0.021 0.020 0.020 0.019 0.019 0.018 0.017
0.011 0.020 0.025 0.035 0.058 0.056 0.055 0.054 0.053 0.053 0.052 0.051 0.050 0.050 0.049 0.049
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
for each
in sagittal plane
Balancing
X 0.2 0.4 0.6 0.8
Table III. Tracing and digitizing
plane
Working D
-0.053 -0.044 -0.039 -0.029 -0.006 -0.008 -0.009 -0.010 -0.011 -0.011 -0.012 -0.013 -0.014 -0.014 -0.015 -0.015
ET AL
Balancing
X
A
B
C
D
0.0
0.024 0.053 0.049 0.058 0.067 0.75 0.076 0.087 0.081 0.076 0.069 0.076 0.082 0.087 0.092 0.093
-0.040 -0.011 -0.015 -0.006 0.003 0.011 0.012 0.023 0.017 0.012 0.005 0.012 0.018 0.023 0.028 0.029
0.018 0.052 0.073 0.078 0.080 0.081 0.080 0.086 0.092 0.094 0.095 0.097 0.099 0.101 0.103 0.105
-0.046 -0.012 0.009 0.014 0.016 0.017 0.016 0.022 0.028 0.030 0.031 0.033 0.035 0.037 0.039 0.041
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
X = 0.2 mm; A and C = tracing and digitizing error (in mm); B and D = tracing error, A or C minus digitizing error of 0.064 mm.
X = 0.2 mm; A and C = tracing and digitizing error (in mm); B and D = tracing error, A or C minus digitizing error of 0.064 mm.
apparatus, articulator flexure, and operator variability in generating the occlusal tracings were reported as a single error. It was observed that this error increased slightly as tracings moved from the centric starting point (X = 0.0). The data indicated that there was no detectable tracing error for the first 0.6 mm of movement in any excursion and/or plane. Beyond X = 0.6 mm, maximum tracing errors from 0.01 mm to 0.15 mm were detected. The tracing errors below 1.4 mm in the horizontal plane and those in the sagittal and frontal planes were less than 0.053 mm. For excursions in the frontal plane and the working excursion in the sagittal plane, the tracing errors were minimal (0.01 to 0.02 mm). The largest errors were revealed in the horizontal plane beyond X = 1.2 mm. Columns A and C in the Tables list the values for the total experimental error at each interval.
by the stylus design and movement in each plane. In the horizontal plane the stylus assembly moved up and laterally from the centric point, while the stylus maintained contact with the table and moved only laterally. Although the stylus fit well in the sleeve, as the excursion proceeded, the length of the stylus became progressively more unsupported. The decreased support allowed a greater chance for errors. This explanation is supported by the finding that the next greatest errors (after the horizontal plane) were in the balancing excursion in the sagittal plane.‘ In this excursion a similar but less dramatic stylus-to-sleeve relationship existed. For excursions in the frontal plane and the working excursion in the sagittal plane, the length of unsupported stylus decreased during the excursions. The tracing errors in these excursions were minimal (0.01 to 0.02 mm). Future studies with this stylus and sleeve assembly should investigate reduction of the length of unsupported stylus by orienting the sleeve close to the table in the horizontal and sagittal planes. With the exception of the values in the horizontal plane (beyond 0.6 mm on the x axis), the data confirmed that the experimental method was accurate in detecting differences exceeding 0.1 mm between occlusal tracings. Analysis of the occlusal tracings was done after computerization of the data by using a digitizer to transform a series of coordinates into a machinereadable form. The sensitivity of the digitizer was directly related to the area of the digitizing pad used to record an image. Therefore, the ability to record small images was limited. Accuracy was increased by magnifying the occlusal tracings through projection onto the digitizing pad. The effect of magnification was
DISCUSSION Although the articulator and scribing apparatus were considered stable, some flexing did occur during the movement of the articulator. The magnitude of this error increased slightly as the tracings departed from the centric starting point. This finding was expected because the centric starting point was mechanically the most stable point of a tracing. Flexure in the apparatus or operator variability in performing successive tracings was anticipated to produce increasing error away from the centric point. There was no tracing error for the first 0.6 mm of movement. Beyond 0.6 mm, errors ranging from 0.01 mm to 0.15 mm were discovered. The largest values were revealed in the horizontal plane. This variation in the error between planes can be explained 502
APRIL
1988
VOLUME
59
NUMBER
4
EVALUATION
OF A DIGITIZER
AND
COMPUTER
SYSTEM
accounted for in the computer program, which based all calculations on the original millimeter scale.
SUMMARY Occlusal tracings generated on a Denar fully adjustable articulator were photographed, projected, digitized, and stored in a computer data file. These steps were accomplished with sufficient accuracy for clinical analysis. This study demonstrated that appropriately referenced tracing data can be transferred accurately into a machine-readable form. Studies of pantographic tracings for mandibular movements are facilitated by this convenient and accurate method of handling data.
CONCLUSIONS 1. The average maximum error in digitizing occlusal tracings into machine-readable form was 0.064 mm in this investigation. 2. Dependent on the plane and excursion, the experimental error of tracing plus digitizing at any interval ranged from 0.01 to 0.21 mm. Tracing problems in the
horizontal plane were responsible for the greater values. 3. The use of a computer to analyze and compare occlusal tracings was an effective method of detecting differences between tracings that exceeded 0.1 mm. REFERENCES Miller RL, Hunter WS, Moyers RE. Computer storage and retrieval system for two-dimensional outlines. J Dent Res 1970;49:1176. Miller RL, Dijkman DJ, Riolo ML, Moyers RE. Graphic computerization of cephalometric data. J Dent Res 1971; 50:1363. Jaarda MJ, Clayton JA, Myers GE. Measurement of cusp height and ridge and groove direction using an electrical transducer. Part I: instrumentation. J PROSTHET DENT 1978;39:67881. Reprint
requeststo:
DR. JOSEF N. KOLLINC UNIVERSITY OF MICHIGAN SCHOOL OF DENTISTRY ANN ARBOR, MI 48109-1056
Corrdsion of dental burs in sterilizing disinfec,ting solutions
and
M. S. Bapna, Ph.D.,* and H. J. Mueller, Ph.D.** University of Illinois, College of Dentistry, and American Dental Association, Chicago, 111.
.,!.he chemical and electrochemical aggressiveness of disinfecting and sterilizing solutions must not affect the performance of the instruments. The corrosive effects from irrigating solutions on endodontic instruments have been reportedlm4as well as the improvement in corrosion resistance when inhibitors were used.5-7However, the effects from commercial disinfecting and sterilizing solutions on dental instruments (burs) have not been reported. Corrosion at the microscopic level is important because the attack of the microstructural phases is directly related to dulling of the cutting edges. Corrosion at the macroscopic level, as seen in mixed metal coupling between bur shank and carbide by a solder, is likely to contribute in reducing the instrument’s neck strength
*Professor, Dental Materials, Department of Prosthodontics, University of Illinois, College of Dentistry. **Research Associate, American Dental Association, Council on Dental Materials, Instruments and Equipment. THE JOURNAL
OF PROSTHETIC
DENTISTRY
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Fig. 1. Polarization curves of stainless steel bum in different sterilizing and disinfecting solutions. 503