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Kinesiograph studies of jaw movement using the commodore pet microcomputer for data storage and analysis
Journal of Dentistry, 12, No. I, 1984,
pp. 53-61
Printed in Great Britain
Kinesiograph studies of jaw movement using the Commodore Pet microcomputer for data storage and analysis* D. J. Neill, DFC, MDS, FDS P. G. T. Howell, BSc, BDS United
Medical
and
Dental
Schools
of
Guy’s
and
St
Thomas’s
Hospitals,
London
ABSTRACT The use of the mandibular kinesiograph to study jaw movements eliminates some of the constraints imposed by previous systems, but there were errors in the instrument, and the manual plotting of each chewing cycle was laborious and restricted the volume of data which could be collected. By feeding the output of the four kinesiograph channels to a microcomputer by way of an A to D converter, the sampling frequency was increased and the data was stored for subsequent computer analysis. Two BASIC programs were written which allowed the recorded data to be corrected to establish linearity, perform the off-line analysis and provide a print-out ofthe results and their associated statistical values.
dates from 1889 when Lute used still photography to attached to the mandible, it has only recently been possible to study jaw movement without any limitation upon the subject’s ability to function normally. Among the constraints facing earlier workers were: (a) the need to attach cumbersome equipment to the teeth to affix extra-oral markers, and (b) the need for the subject’s head to be fixed throughout the duration of the experiment. The advent of the mandibular kinesiograph or the sirognathograph has made it possible for masticatory movements to be monitored without interfering with normal function. Both of these devices monitor the movement of a small magnet attached to the labial aspect of the lower central incisors (Fig. I). This is accomplished by three pairs of magnetometers attached to the patient’s head by means of a light spectacle frame (Fig. 2). In the kinesiograph the magnetometers are responsive to changes in the field strength as the magnet moves, and the output of the sensors is fed into the electronic equipment which converts the data to a visual display on an oscilloscope with storage facilities (Fig. 3). The full range of the instrument has been described elsewhere (Neill, 1981), so we will confine ourselves to those parameters used in analysing jaw movements. By selecting the sag&al display and requiring the subject to carry out the necessary border movements, Posselt’s envelope of motion can be traced. The functional pathways taken during chewing can then be viewed against this background (Fig. 4). It will be noted that in chewing all the strokes fall within the boundaries of the envelope and end at or near C.O. Using the frontal trace alone, the occlusal guidance in right and left translations can be traced, and the cycle of Although
record
the study of jaw movement
the movements
of external
markers
*Paper presented at the Annual Conference of the British Society of the Study of Prosthetic Dentistry, Royal Holloway College, March 1983.
54
Journal of Dentistry, Vol. 1 ~/NO.
1
Fig 1. Bar magnet attached to lower incisor teeth.
Fig 2 Framework supporting attac:hed to spectacle frames.
magnetomete !rs
Fig 3 The kinesiograph.
jaw movements associated with chewing of different foods can be observed (Fig. 5). This shows the degree of penetration at each chewing stroke, as well as the varying degrees of vertical and lateral movement occurring with the different phases of the masticator-y cycle. Whereas the shape of the chewing envelope may be observed directly on the oscilloscope and a composite pattern retained using the storage facility, in our earlier experiments analysis of successive individual cycles was achieved by focussing a television camera on the screen (Fig. 6) and recording the movement of the strobe on videotape at 25 frames per second. By playing the picture back and plotting the strobes at every other frame (at 80 msec intervals)
Neil1 and Howell: Kinesiograph studies of jaw movement
Fig 4 Sagittal trace of Posselt’s envelope showing chewing strokes within its boundaries.
55
Fig 5 Frontal trace of multiple chewing strokes and with tooth guidance angle.
Fig 6 Television camera focussed on oscilloscope screen to record movement of the strobe on videotape.
(Fig. 7), a very accurate magnified trace of the jaw movement was obtained together with an indication of the speed of movement. Whereas sag&al and frontal traces can be recorded simultaneously in order to achieve the highest magnification without overlapping traces, separate recordings of jaw movements in each plane were obtained. Initial experiments were carried out using apple, biscuit and chewing gum as the test foods which enabled us to classify chewing strokes into 16 different categories (Fig. 8). This showed that all subjects followed a clockwise chewing pattern on the right and movement was in the opposite direction when chewing on the left. When instructed to chew freely each subject exhibited a trend in favour of one side rather than the other, which can easily be determined by analysis of the MKG trace. Whereas deviation of the chewing stroke towards the chewing side was found to be the normal, this was varied when the malalignment of teeth interfered with movement into and out of occlusion on one side. As the test foods had necessarily been selected and were not representative of the subject’s normal diet, a group of three subjects was observed eating lunch, comprising a meat course and
56
Journal of Dentistry, Vol. 1 Z/No.
1
MOVEMENT PATTERNSOFTHE MANDIBLE DURING MASTICATION -FRONTALTRACES
Fig Z Individual traces of chewing strokes obtained by plotting the position of the strobe at 80-ms intervals.
Fig 61 Classification of chewing strokes observed in the frontal plane.
two vegetables (Fig. 9). As each fork-load of food was placed in the mouth, the nature of the food about to be chewed was recorded so that the pattern ofjaw movements could be analysed. At the beginning of each sequence, the subjects were asked to slide their teeth from the centric position into left and right lateral excursion so that the tooth guidance pathway could be determined. This ensured that the relationship of the opening and the closing trajectory could be related to the guidance angle, and the length of any tooth contact glide could be measured. It was found that the tooth-contact glide was related to the nature of the food being consumed. With food which merely needed to be crushed, movement into and out of centric occlusion occurred in a more vertical direction and with little or no tooth-contact slide (Fig. 10). On the other hand, when a tougher fibrous food was being chewed, initial contact is made some distance lateral to centric occlusion and this was followed by a tooth-contact glide into centric occlusion (Fig. I I). Alter a pause in centric occlusion this may be followed by a further toothcontact glide in the opposing direction. This finding was at variance with that of Atkinson and Shepherd (1967) who concluded that during the mastication of a refmed type of diet, gross sliding of the occlusal surfaces of the lower teeth over the upper could not be detected and therefore stated that the grinding and crushing of food is accomplished in the intercuspal zones. By selecting the appropriate mode, the velocity of movement can be monitored. The strobe moves to the right indicating the opening velocity and to the left when the jaws are closing (Fig. 12). This illustration showing the velocity trace on the left and the frontal trace on the right relates to the subject opening the jaw and snapping her teeth together. During chewing, we have
Neil1 and Howell: Kinesiograph studies of jaw movement
Fig 9 Subject eating lunch with the recording equipment in position.
Fig 10. Frontal trace of subject chewing soft food (note the absence of any tooth contact slide).
Fig 17. Frontal trace of subject chewing resistant food.
Fig 72 Trace showing velocity of movement (on the left) and frontal trace of subject opening and closing the jaws.
more
found that the mean velocity of opening is always greater than the mean velocity of closing and the maximum velocity is also recorded during opening. This is in agreement with the findings of Atkinson and Sheppard. There appears to be evidence which suggests that the velocity of jaw movements increases with the toughness of the food being chewed, and that the teeth are separated a little more which may result in a more powerful closing stroke. The dimensions of the chewing envelope show that both the height and the width tend to be increased when chewing more resistant types of food (Fig. 13). Up until this point our results had been obtained from manual analysis of over 2000 chewing strokes observed in the frontal plane. Progress was limited because of the time required for each
58
Journal of Dentistry, Vol. 1 ~/NO.
1
subject 1. M. txldllng
metm
Beef Wet
93% br 150min
Beef fillet
75% br 100 min
Beef fillet
WC for 50 min
Pork
Canteen meal
Vegetables Canteen meal
wlahefennbp
IwmmJy
BE,
01234561 Beef fillet
WC for 154 min
Beef fillet
75°C for
Beef fillet
60°C for M min
012315bl
I
I-L
im min
Pork
Cantean meal
V0Whr
Canteen meal I..
.
.
.
.
.
.
.
.
01234567891011~~~~ Haiphtdmmlq9mml
.
..-
’
Fig 13 Histogram showing the increase in the dimension of the chewing envelope with more resistant foods.
experiment. Subsequently we have developed a technique for feeding the output of all four channels of the kinesiograph through an A-D convertor to a microcomputer. Due to errors in the instrument, the kinesiograph had to be calibrated and corrections had been applied to the recorded data to establish linearity. These corrections were incorporated in our computer program and over the past nine months we have been developing the necessary software to allow for the storage and analysis of data by the computer. The primary limitation of the early analysis described above was the considerable operator time required to replay the video recordings and manually trace and measure the paths of the jaw movement during mastication. Furthermore, correction for any non-linearity exhibited by the kinesiograph was not possible. The introduction of a microcomputer into the recording procedure was considered a possible approach which would permit real-time data logging and automatic otTline analysis with non-linearity correction. The signals derived from the kinesiograph sensors provide the three positional (X, Y, Z) coordinates plus a fourth velocity reading. After suitable amplification these are displayed on an oscilliscope and are available for simultaneous recording via four BNC sockets at the rear of the oscilloscope. The outputs are passed via an 8-channel 1Zbit analogue to digital converter (manufactured by 3D Digital Design and Development, Grafton Mews, London WCl) to a Commodore Pet Model 3032 microcomputer. The arrangement is shown schematically in Fig. 14. The A-D converter’s 12-bit resolution implies that it can allocate one of 2l* (or 4096) levels to the incoming analogue signal and output this digital value to the microcomputer. Calibration of the kinesiograph and A-D converter combination was carried out by placing the magnet on a mechanical stage translatable in three mutually orthogonal directions (Fig. 15). Points were selected for measurement such that they lay in and around the normal volume enclosed by a subject during mastication. Seventy-six such points were recorded for the three commonly used kinesiograph amplification settings. Twenty individual measurements were made for each point and the mean and standard deviation recorded. The data values were then
Neil1 and Howell: Kinesiograph studies of jaw movement
59
STOP.& SWICH
Fig
14 Schematic arrangement of kinesiograph and microcomputer.
Fig 15 Arrangement for controlling movement of the magnet when calibrating the equipment to eliminate errors of linearity.
used by a least-squares of the form:
analysis program to determine the coefficients of a calibration
F(XY,Z) This gave a regression
coefficient
=f(a, of
equation
x, Y, z, XY, xz, YZ, x2, y2, 2’)
R2 = 0.99.
A short machine-code computer program was provided with the A-D converter to permit rapid data acquisition at a user defined rate over a wide range of frequencies, 10-1000 Hz (i.e. sampling lOO-ms to 1-ms intervals). A compromise has to be made between the desire for the fastest possible rate of data acquisition and hence the greatest time resolution, and the rate at which this would cause the limited memory capacity of the microcomputer to become used up. With the control progams loaded, 24 K bytes of memory remained available for data storage so with the 12-bit data, stored as two &bit bytes, 2560 discrete data points on the 4 channels can
60
Fig
Journal of Dentistry, Vol. 1 ~/NO.
16. ‘Playing back’ the stored data on the
1
oscilloscope to classify each chewing stroke.
be recorded. A frequency of 100 Hz (i.e. sampling the kinesiograph output every 10 ms) was chosen as a suitable compromise and represents a total recording time of 25.6 s. This was usually found to be sufficient time for the subject to chew and swallow one mouthful of food. The initial program sets the rate for data capture and the number of data points required from the four channels. The 12-bit data is temporarily stored in RAM (Random Access Memory). until the preset number of data points is achieved. A short machine-code subroutine then transfers the raw data to the single-sided single-density 5-in floppy disc in the Commodore 3040 disc drive. The microcomputer is then free for another chewing sequence. Subsequent analysis of the recorded data was performed off-line from the kinesiograph by two separate BASIC programs. The first program reads the data block from disc back into RAM and converts it to its real three-dimensional (X,Y,Z,) coordinate values for use by the main body of the program. A search is then made for the primary chewing cycles involved in mastication-the traverse of the teeth and jaws away from tooth contact back to, or close to, tooth contact again. These periods are of approximately one-second duration and have between them a brief pause when the teeth are held close together, or in contact (the dwell time). The start of each cycle is found by a movement away from ‘centric’, and the end of the cycle is recognized by the return to this position together with the brief period in which no movement occurs. The program also searches for the maximum and minimum excursions of the teeth and jaws during each cycle in the anteroposterior, lateral and vertical directions. The data concerning each cycle is then saved on disc for statistical analysis. The real 3-D coordinates may also be displayed on the screen of the Commodore Pet at an 80 X 50 point resolution to provide an indication of the jaw movements to facilitate the cycle type to be identified (Fig. 16).
61
Neil1 and Howell: Kinesiograph studies of jaw movement
The second program inputs the data stored about each chewing cycle, determines the mean, standard deviation, maximum and minimum, and range values for each of the following parameters: Total cycle time Dwell time in centric Mean distance travelled during cycle Mean cycle velocity Mean velocity in the opening phase of the cycle Mean velocity in the closing phase of the cycle Maximum and minimum values of lateral excursion anteroposterior excursion vertical movement velocity and their associated (X,Y,Z) coordinates, velocity and time during the cycle. This enables a correlation for each of these parameters to be made with the mastication of an individual subject with differing foods or occlusal pattern, or for the same food type between a large group of subjects. REFERENCES Atkinson H. T. and Shepherd R. W. (1967) Masticator-y movement and tooth form. Ausf. Dent. J. 12,49.
Neil1 D. J., Mandibular Kinesiography.
Proc.
E.P.A.,
pp. 40-50.
Book Review DENTAL MATERIALS. PROPERTIES AND MANIPULATION, 3rd ed. By R. Craig, W. O’Brien and J. Powers. 238 X 164mm. Pp. 328. 1983. London, C. V. Mosby. Softback, 512.75. This is an introductory text which deliberately places greater emphasis on the use and manipulation of materials in the clinic than on those in the dental laboratory. In producing a new edition the authors have taken the opportunity to update some information but the extent of this revision is limited. or certainlv more limited than is implied in the Preface. This edition does. however. contain in addition to review questions at the end of each chapter a number of multiple-choice or short-answer questions previously published separately as a Workbook for Dental Materials. As only 17 of the 328 pages are devoted to the properties ofmaterials and, in general, the relationship between structure and properties is largely ignored, many teachers will doubtless feel that this text will need to be supplemented. Nevertheless this book has many merits. The subject matter is well covered, well put together and, last but not least, it is readable. There are a number of good illustrations to counterbalance the few of poor quality. A useful feature is the incorporation ofinformation on the main constituents of a number of commercial materials many of which are available in this country. To conclude, perhaps not a text which one would want students to use as their sole source of reference but certainly one which they would profit from reading. N. Waters
pp. 53-61
Printed in Great Britain
Kinesiograph studies of jaw movement using the Commodore Pet microcomputer for data storage and analysis* D. J. Neill, DFC, MDS, FDS P. G. T. Howell, BSc, BDS United
Medical
and
Dental
Schools
of
Guy’s
and
St
Thomas’s
Hospitals,
London
ABSTRACT The use of the mandibular kinesiograph to study jaw movements eliminates some of the constraints imposed by previous systems, but there were errors in the instrument, and the manual plotting of each chewing cycle was laborious and restricted the volume of data which could be collected. By feeding the output of the four kinesiograph channels to a microcomputer by way of an A to D converter, the sampling frequency was increased and the data was stored for subsequent computer analysis. Two BASIC programs were written which allowed the recorded data to be corrected to establish linearity, perform the off-line analysis and provide a print-out ofthe results and their associated statistical values.
dates from 1889 when Lute used still photography to attached to the mandible, it has only recently been possible to study jaw movement without any limitation upon the subject’s ability to function normally. Among the constraints facing earlier workers were: (a) the need to attach cumbersome equipment to the teeth to affix extra-oral markers, and (b) the need for the subject’s head to be fixed throughout the duration of the experiment. The advent of the mandibular kinesiograph or the sirognathograph has made it possible for masticatory movements to be monitored without interfering with normal function. Both of these devices monitor the movement of a small magnet attached to the labial aspect of the lower central incisors (Fig. I). This is accomplished by three pairs of magnetometers attached to the patient’s head by means of a light spectacle frame (Fig. 2). In the kinesiograph the magnetometers are responsive to changes in the field strength as the magnet moves, and the output of the sensors is fed into the electronic equipment which converts the data to a visual display on an oscilloscope with storage facilities (Fig. 3). The full range of the instrument has been described elsewhere (Neill, 1981), so we will confine ourselves to those parameters used in analysing jaw movements. By selecting the sag&al display and requiring the subject to carry out the necessary border movements, Posselt’s envelope of motion can be traced. The functional pathways taken during chewing can then be viewed against this background (Fig. 4). It will be noted that in chewing all the strokes fall within the boundaries of the envelope and end at or near C.O. Using the frontal trace alone, the occlusal guidance in right and left translations can be traced, and the cycle of Although
record
the study of jaw movement
the movements
of external
markers
*Paper presented at the Annual Conference of the British Society of the Study of Prosthetic Dentistry, Royal Holloway College, March 1983.
54
Journal of Dentistry, Vol. 1 ~/NO.
1
Fig 1. Bar magnet attached to lower incisor teeth.
Fig 2 Framework supporting attac:hed to spectacle frames.
magnetomete !rs
Fig 3 The kinesiograph.
jaw movements associated with chewing of different foods can be observed (Fig. 5). This shows the degree of penetration at each chewing stroke, as well as the varying degrees of vertical and lateral movement occurring with the different phases of the masticator-y cycle. Whereas the shape of the chewing envelope may be observed directly on the oscilloscope and a composite pattern retained using the storage facility, in our earlier experiments analysis of successive individual cycles was achieved by focussing a television camera on the screen (Fig. 6) and recording the movement of the strobe on videotape at 25 frames per second. By playing the picture back and plotting the strobes at every other frame (at 80 msec intervals)
Neil1 and Howell: Kinesiograph studies of jaw movement
Fig 4 Sagittal trace of Posselt’s envelope showing chewing strokes within its boundaries.
55
Fig 5 Frontal trace of multiple chewing strokes and with tooth guidance angle.
Fig 6 Television camera focussed on oscilloscope screen to record movement of the strobe on videotape.
(Fig. 7), a very accurate magnified trace of the jaw movement was obtained together with an indication of the speed of movement. Whereas sag&al and frontal traces can be recorded simultaneously in order to achieve the highest magnification without overlapping traces, separate recordings of jaw movements in each plane were obtained. Initial experiments were carried out using apple, biscuit and chewing gum as the test foods which enabled us to classify chewing strokes into 16 different categories (Fig. 8). This showed that all subjects followed a clockwise chewing pattern on the right and movement was in the opposite direction when chewing on the left. When instructed to chew freely each subject exhibited a trend in favour of one side rather than the other, which can easily be determined by analysis of the MKG trace. Whereas deviation of the chewing stroke towards the chewing side was found to be the normal, this was varied when the malalignment of teeth interfered with movement into and out of occlusion on one side. As the test foods had necessarily been selected and were not representative of the subject’s normal diet, a group of three subjects was observed eating lunch, comprising a meat course and
56
Journal of Dentistry, Vol. 1 Z/No.
1
MOVEMENT PATTERNSOFTHE MANDIBLE DURING MASTICATION -FRONTALTRACES
Fig Z Individual traces of chewing strokes obtained by plotting the position of the strobe at 80-ms intervals.
Fig 61 Classification of chewing strokes observed in the frontal plane.
two vegetables (Fig. 9). As each fork-load of food was placed in the mouth, the nature of the food about to be chewed was recorded so that the pattern ofjaw movements could be analysed. At the beginning of each sequence, the subjects were asked to slide their teeth from the centric position into left and right lateral excursion so that the tooth guidance pathway could be determined. This ensured that the relationship of the opening and the closing trajectory could be related to the guidance angle, and the length of any tooth contact glide could be measured. It was found that the tooth-contact glide was related to the nature of the food being consumed. With food which merely needed to be crushed, movement into and out of centric occlusion occurred in a more vertical direction and with little or no tooth-contact slide (Fig. 10). On the other hand, when a tougher fibrous food was being chewed, initial contact is made some distance lateral to centric occlusion and this was followed by a tooth-contact glide into centric occlusion (Fig. I I). Alter a pause in centric occlusion this may be followed by a further toothcontact glide in the opposing direction. This finding was at variance with that of Atkinson and Shepherd (1967) who concluded that during the mastication of a refmed type of diet, gross sliding of the occlusal surfaces of the lower teeth over the upper could not be detected and therefore stated that the grinding and crushing of food is accomplished in the intercuspal zones. By selecting the appropriate mode, the velocity of movement can be monitored. The strobe moves to the right indicating the opening velocity and to the left when the jaws are closing (Fig. 12). This illustration showing the velocity trace on the left and the frontal trace on the right relates to the subject opening the jaw and snapping her teeth together. During chewing, we have
Neil1 and Howell: Kinesiograph studies of jaw movement
Fig 9 Subject eating lunch with the recording equipment in position.
Fig 10. Frontal trace of subject chewing soft food (note the absence of any tooth contact slide).
Fig 17. Frontal trace of subject chewing resistant food.
Fig 72 Trace showing velocity of movement (on the left) and frontal trace of subject opening and closing the jaws.
more
found that the mean velocity of opening is always greater than the mean velocity of closing and the maximum velocity is also recorded during opening. This is in agreement with the findings of Atkinson and Sheppard. There appears to be evidence which suggests that the velocity of jaw movements increases with the toughness of the food being chewed, and that the teeth are separated a little more which may result in a more powerful closing stroke. The dimensions of the chewing envelope show that both the height and the width tend to be increased when chewing more resistant types of food (Fig. 13). Up until this point our results had been obtained from manual analysis of over 2000 chewing strokes observed in the frontal plane. Progress was limited because of the time required for each
58
Journal of Dentistry, Vol. 1 ~/NO.
1
subject 1. M. txldllng
metm
Beef Wet
93% br 150min
Beef fillet
75% br 100 min
Beef fillet
WC for 50 min
Pork
Canteen meal
Vegetables Canteen meal
wlahefennbp
IwmmJy
BE,
01234561 Beef fillet
WC for 154 min
Beef fillet
75°C for
Beef fillet
60°C for M min
012315bl
I
I-L
im min
Pork
Cantean meal
V0Whr
Canteen meal I..
.
.
.
.
.
.
.
.
01234567891011~~~~ Haiphtdmmlq9mml
.
..-
’
Fig 13 Histogram showing the increase in the dimension of the chewing envelope with more resistant foods.
experiment. Subsequently we have developed a technique for feeding the output of all four channels of the kinesiograph through an A-D convertor to a microcomputer. Due to errors in the instrument, the kinesiograph had to be calibrated and corrections had been applied to the recorded data to establish linearity. These corrections were incorporated in our computer program and over the past nine months we have been developing the necessary software to allow for the storage and analysis of data by the computer. The primary limitation of the early analysis described above was the considerable operator time required to replay the video recordings and manually trace and measure the paths of the jaw movement during mastication. Furthermore, correction for any non-linearity exhibited by the kinesiograph was not possible. The introduction of a microcomputer into the recording procedure was considered a possible approach which would permit real-time data logging and automatic otTline analysis with non-linearity correction. The signals derived from the kinesiograph sensors provide the three positional (X, Y, Z) coordinates plus a fourth velocity reading. After suitable amplification these are displayed on an oscilliscope and are available for simultaneous recording via four BNC sockets at the rear of the oscilloscope. The outputs are passed via an 8-channel 1Zbit analogue to digital converter (manufactured by 3D Digital Design and Development, Grafton Mews, London WCl) to a Commodore Pet Model 3032 microcomputer. The arrangement is shown schematically in Fig. 14. The A-D converter’s 12-bit resolution implies that it can allocate one of 2l* (or 4096) levels to the incoming analogue signal and output this digital value to the microcomputer. Calibration of the kinesiograph and A-D converter combination was carried out by placing the magnet on a mechanical stage translatable in three mutually orthogonal directions (Fig. 15). Points were selected for measurement such that they lay in and around the normal volume enclosed by a subject during mastication. Seventy-six such points were recorded for the three commonly used kinesiograph amplification settings. Twenty individual measurements were made for each point and the mean and standard deviation recorded. The data values were then
Neil1 and Howell: Kinesiograph studies of jaw movement
59
STOP.& SWICH
Fig
14 Schematic arrangement of kinesiograph and microcomputer.
Fig 15 Arrangement for controlling movement of the magnet when calibrating the equipment to eliminate errors of linearity.
used by a least-squares of the form:
analysis program to determine the coefficients of a calibration
F(XY,Z) This gave a regression
coefficient
=f(a, of
equation
x, Y, z, XY, xz, YZ, x2, y2, 2’)
R2 = 0.99.
A short machine-code computer program was provided with the A-D converter to permit rapid data acquisition at a user defined rate over a wide range of frequencies, 10-1000 Hz (i.e. sampling lOO-ms to 1-ms intervals). A compromise has to be made between the desire for the fastest possible rate of data acquisition and hence the greatest time resolution, and the rate at which this would cause the limited memory capacity of the microcomputer to become used up. With the control progams loaded, 24 K bytes of memory remained available for data storage so with the 12-bit data, stored as two &bit bytes, 2560 discrete data points on the 4 channels can
60
Fig
Journal of Dentistry, Vol. 1 ~/NO.
16. ‘Playing back’ the stored data on the
1
oscilloscope to classify each chewing stroke.
be recorded. A frequency of 100 Hz (i.e. sampling the kinesiograph output every 10 ms) was chosen as a suitable compromise and represents a total recording time of 25.6 s. This was usually found to be sufficient time for the subject to chew and swallow one mouthful of food. The initial program sets the rate for data capture and the number of data points required from the four channels. The 12-bit data is temporarily stored in RAM (Random Access Memory). until the preset number of data points is achieved. A short machine-code subroutine then transfers the raw data to the single-sided single-density 5-in floppy disc in the Commodore 3040 disc drive. The microcomputer is then free for another chewing sequence. Subsequent analysis of the recorded data was performed off-line from the kinesiograph by two separate BASIC programs. The first program reads the data block from disc back into RAM and converts it to its real three-dimensional (X,Y,Z,) coordinate values for use by the main body of the program. A search is then made for the primary chewing cycles involved in mastication-the traverse of the teeth and jaws away from tooth contact back to, or close to, tooth contact again. These periods are of approximately one-second duration and have between them a brief pause when the teeth are held close together, or in contact (the dwell time). The start of each cycle is found by a movement away from ‘centric’, and the end of the cycle is recognized by the return to this position together with the brief period in which no movement occurs. The program also searches for the maximum and minimum excursions of the teeth and jaws during each cycle in the anteroposterior, lateral and vertical directions. The data concerning each cycle is then saved on disc for statistical analysis. The real 3-D coordinates may also be displayed on the screen of the Commodore Pet at an 80 X 50 point resolution to provide an indication of the jaw movements to facilitate the cycle type to be identified (Fig. 16).
61
Neil1 and Howell: Kinesiograph studies of jaw movement
The second program inputs the data stored about each chewing cycle, determines the mean, standard deviation, maximum and minimum, and range values for each of the following parameters: Total cycle time Dwell time in centric Mean distance travelled during cycle Mean cycle velocity Mean velocity in the opening phase of the cycle Mean velocity in the closing phase of the cycle Maximum and minimum values of lateral excursion anteroposterior excursion vertical movement velocity and their associated (X,Y,Z) coordinates, velocity and time during the cycle. This enables a correlation for each of these parameters to be made with the mastication of an individual subject with differing foods or occlusal pattern, or for the same food type between a large group of subjects. REFERENCES Atkinson H. T. and Shepherd R. W. (1967) Masticator-y movement and tooth form. Ausf. Dent. J. 12,49.
Neil1 D. J., Mandibular Kinesiography.
Proc.
E.P.A.,
pp. 40-50.
Book Review DENTAL MATERIALS. PROPERTIES AND MANIPULATION, 3rd ed. By R. Craig, W. O’Brien and J. Powers. 238 X 164mm. Pp. 328. 1983. London, C. V. Mosby. Softback, 512.75. This is an introductory text which deliberately places greater emphasis on the use and manipulation of materials in the clinic than on those in the dental laboratory. In producing a new edition the authors have taken the opportunity to update some information but the extent of this revision is limited. or certainlv more limited than is implied in the Preface. This edition does. however. contain in addition to review questions at the end of each chapter a number of multiple-choice or short-answer questions previously published separately as a Workbook for Dental Materials. As only 17 of the 328 pages are devoted to the properties ofmaterials and, in general, the relationship between structure and properties is largely ignored, many teachers will doubtless feel that this text will need to be supplemented. Nevertheless this book has many merits. The subject matter is well covered, well put together and, last but not least, it is readable. There are a number of good illustrations to counterbalance the few of poor quality. A useful feature is the incorporation ofinformation on the main constituents of a number of commercial materials many of which are available in this country. To conclude, perhaps not a text which one would want students to use as their sole source of reference but certainly one which they would profit from reading. N. Waters