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Movement of maxillary complete dentures—a Kinesiographic study
Journal of Dentistry,
11, No. 3,
Movement dentures-a
pp. 257-263
Printed in Great Britain
of maxillary complete Kinesiographic study
Chong Lin Chew, BDS, MDS, MSD Department Singapore
of Prosthetic
Dentistry,
Faculty
of Dentistry,
National
University
of
ABSTRACT A clinical study on the movement of maxillary complete dentures was carried out on ten patients using the Kinesiograph. The results indicated a significant difference in the amount of movement between well-fitting and ill-fitting dentures. A comparison of this method with other methods used as well as the precautions to be taken when using the Kinesiograph are discussed.
INTRODUCTION Dentures move in the mouth during function. The amount of movement depends on the retention and stability of the dentures as well as the patient’s ability to control the dentures in the mouth. Many studies have been conducted to measure the retention of dentures (Hamrick, 1962; Wain, 1963; Boucher et al., 1968; Gesser and Castaldi, 1971). However, there are only a few studies where movements of dentures during function have been looked into. Winkler (1967) studied the effectiveness of magnets as aids in retention of dentures using cineradiography where denture movements could be observed by means of cineradiographic films. Culver and Watt (1973) investigated by cinefluorography the movement of dentures during incising, the part played by the tongue in their control, and the timing of the incising-swallowing sequence. Their results showed that there is a tendency for the majority of dentures to tilt, sometimes by as much as 20 mm measured at the back edge on biting into a bun (apple or chocolate). The purpose of this study was to measure the amount of movement of the maxillary complete denture during function by means of the Kinesiograph.
METHODS
AND MATERIALS
Ten patients with maxillary complete dentures were included as subjects in the study. Their ages ranged from 47 to 65 years. For each patient, a duplicate maxillary complete denture was made. If the patient’s denture was ill-fitting, an improvement was made to the duplicate denture to make it well-fitting (i.e. a reline) or improvement was made to the borders of the denture. However, for those dentures which were originally well-fitting, the duplicate was made ill-fitting by trimming the borders. The clinical fit of the denture and the condition of the denture-bearing tissues were evaluated by two dentists using Kapur’s (1967) criteria. Of the ten patients, nine of them had mandibular complete dentures and one had a removable partial denture. The movement of the mandibular dentures would not affect the measurements made of the maxillary complete dentures.
258
Journal of Dentistry Vol. 1 l/No.
3
Fig. 7. The Kinesiograph.
The Kinesiograph The Kinesiograph instrumentation (Fig. 1) was introduced by Jankelson and his associates in 1974 to track mandibular movements in three dimensions, namely, anteroposterior, lateral and vertical. The Kinesiograph used in this investigation is a research model (Kinesiography, Myo-tronics Research Inc., Seattle, Washington, USA). The system senses the spatial location of a magnet that is mounted on the mandibular incisors with a dental plastic. However, to measure movements of the maxillary complete denture, an additional feature known as the ‘Dual Magnet System’ was incorporated into the Kinesiograph. The positions of the magnets are detected by an array of sensing elements which are responsive to the strength of the field emanating from the magnets. As the denture moves, each sensor responds to the changes in field strengths which result as the distance from the magnets varies. The circuitry of the Kinesiograph converts the outputs of the sensors to a readily usable representation in three dimensions. The outputs are suitable for recording or display on a cathode ray tube screen. The data may also be stored in an FM magnetic tape system. System output includes separate data channels for the vertical, lateral and anteroposterior components. However, in this study, only the vertical components were used. The magnetic field sensors are specially constructed flux gate magnetometers encapsulated (Fig. 2). The sensors are mounted on a in plastic with rigid dimensional specifications superstructure of thin-walled aluminium tubing with careful attention given to the orientation of the sensitive axis of each magnetometer. The entire sensory array is fully adjustable to permit accommodation to a wide variety of facial contours. It also permits operator adjustments to ensure that the sensor does not come into contact with the patient’s mandible during its movements. An additional unit incorporated into the Kinesiograph was the Sweep Mechanism. This enabled the study of segmental movements of the denture with time.
Chong Lin Chew: Movement
of maxillary
complete
Fig. 2. Dual sensor array. A, B and C are magnetometers that detect movements of the magnets in the vertical, antero-posterior and lateral directions respectively.
Measurement
of denture
dentures
259
Fig. 3. The magnet attached to the buccal surface of the maxillary complete denture at the premolarmolar region with the north pole facing anteriorly.
dislodgement
The dimensions of each magnet were 13 X 6 X 3 mm. On each of the buccal surfaces of the test maxillary complete denture, at the premolar-molar region, one magnet was attached with Myo-print, a synthetic resin, and the north pole ofthe magnet was made to face anteriorly (Fig. 3). The lower borders of the magnets were about 2mm above the occlusal plane and the magnets were adjusted to be at the same level in a vertical plane. The positions of the magnets were noted so that they could be re-positioned at the same place for each test. The well-fitting denture was used first, then the ill-fitting denture. The patient’s mandibular complete denture was stabilized with an adhesive 30 minutes before the initial measurements were made, to allow for hydration of the adhesive. One patient had a mandibular removable partial denture and no adhesive was applied. The adhesive was used to stabilize the mandibular complete denture throughout the study. The sun-glasses to hold the sensor array were strapped firmly on the patient. The sensor array was fitted on and centralized to the patient’s face (Fig. 4). The two lower magnetometers were positioned so that they would not come in contact with the patient’s chin during chewing movements of the mandible. The beams were turned on. Final adjustments of the sensor array were made so that the beams on the screen were at the centre + 1.0 cm in a horizontal plane. The patient chewed on a food substitute. It was a disc 1.2 cm in diameter and 0.5 cm in thickness prepared from Kerr FITT, a tissue conditioner, using a powder-liquid ratio of 2.5 (Fig. 5). The discs were stored in tapwater for 48 hours before use. The material had a soft
260
Fig. 4. The dual sensor patient’s face.
Journal of Dentistry
array strapped
to the
Fig. 5. Food substitute
Vol. 1 l/No.
3
made from Kerr FIlT.
rubber consistency that was maintained throughout the chewing cycle. The patient was unable to chew through the material. The disc was placed in the patient’s mouth on top of the tongue until the chewing test was begun. The sweep control was turned to the 1-O div./s position. There were three horizontal beams moving across the screen and 20-s were required for the beams to travel from one end of the screen to the other. One beam represented the vertical components of Channel A, the second the vertical component of Channel B; and the third the lateral component of both channels. They were set in this sequence with one above the other, at about 2-3 cm apart. The lateral component was not considered in this study. Before the start of each chewing cycle, the patient was asked to relax his mandible without any tooth contact. The beams were allowed to travel across the screen once, thereby giving three horizontal lines which served as the baselines (rest position of the maxillary denture) for measurements of dislodgements during chewing. When the beams reached the other end of the screen, the patient was asked to chew on the disc on his right side. There was a lapse of about three seconds before the beams appeared on the screen a second time. The patient was asked to stop chewing the moment the beams fully traversed the screen. The beams were then turned off. While these tracings were obtained, the patient was asked to keep his heady steady by placing the back of his head against a head rest. The grid was then added to the screen. Denture movements were shown on the screen as peaks on either side of the baselines (Figs. 6 and 7). Peaks above the baselines of the vertical components represented compression of the denture against the tissues while those below were due to dislodgements. Dislodgements that occurred through the middle ten chewing strokes were measured and
Chong Lin Chew: Movement
of maxillary complete
261
dentures
Fig. 6. Tracings of movements of well-fitting denture with patient chewing on right side. L. left side of denture; R, right side of denture.
L
R
Fig. 7. Tracings of movements of ill-fitting denture with patient chewing right side. L, left side of denture: R, right side of denture.
on
recorded. Only 10 chewing strokes were considered although some patients had more than this number per 20-s chewing cycle. Measurements were made to the nearest 0.1 cm on the screen. Compression and lateral movements were not considered in this study. The tracings on the screen were then erased and a second set obtained with the patient chewing on his left side. The sun-glasses on the sensor array were removed, after the measurements were made. Adhesive on the mandibular denture was cleaned off and the patient discharged. The patient was asked to return for more appointments to repeat the measurements. Three sets of measurements were made for each of the well-fitting and ill-fitting dentures.
RESULTS The ten patients selected for this study had good denture-bearing tissues (score 8). Each patient had a well-fitting and an ill-fitting denture. The ill-fitting dentures had a minimum retention score of + 1. Kapur’s (1967) criteria were used for all these evaluations.
262
Journal of Dentistry Vol. 1 l/No.
Tab/e /. Average dislodgement of denture on left side
Patient
3
Table I. Average dislodgement of denture on right side
Patient chewing on right side
Patient chewing on left side
Well-fitting denture M-fitting denture (mm) lmml
Well-fitting denture Ill-fitting denture fmml lmml
f 4 : 7 6 9 10
0.3 1.4 0.4 0.1 0.9 0.6 A:;
2.0 1.9 0.2 0.5 3.4 0.7 0.3 1.3
0 0.5
1.2 1.5
Patient 1 z
1.6 0.4
4
0.1
: 7 :
0.6 01
10
0.1 ;:3”
2.4 0.5 0.5 0.5 0.8 1.6 1.8 0.9
0.1
Samples of tracings of the denture movements obtained from the Kinesiograph are shown in Figs. 6 and 7. The tracings were those obtained when the patients were chewing on the right sides. The data shown in Tables Iand IIrepresent denture dislodgement on the side opposite that of the chewing side. For example, if the patient was chewing on the right side, the amount of dislodgement on the left side was recorded. Dislodgement of the denture on the chewing side did occur, but only on rare occasions when compared to that on the non-chewing side. Therefore, they were not considered significant. Tables I and II show the average amount of dislodgement of both the well-fitting and illfitting dentures. Statistical analysis of the results using the Student t test (paired observation) showed that a greater amount of movement or dislodgement occurred with ill-fitting than with well-fitting dentures. It was significant at IYO.05. This was true no matter which side the patient was chewing on.
DISCUSSION The results obtained from this study showed that a well-fitting denture is more retentive and stable than an ill-fitting denture. Previous studies on retention were based on determining the forces required to dislodge the denture. Gesser and Castaldi (197 1) used the pully system while Boucher et al. (1968) as well as Battersby and co-workers (1968) used the lever system to measure denture retention. Boone (1962) measured the anterior biting force that would dislodge the maxillary denture with the aid of the gnathodynamometer. ln all these studies, the dentures were static and not in function. Retention and stability play an important role in the denture function, for example, in speech and mastication. The poorer the retention and stability, the greater will be the amount of denture dislodgement during function. Therefore, more meaningful results might be attained if measurements of retention and stability were made under such conditions. The Kinesiograph enables such measurements to be made. Movements of the magnets attached to the dentures represent movements of the dentures. Since these measurements can be recorded on the screen, actual denture movements are seen and may be measured.
Chong Lin Chew: Movement of maxillary complete dentures
263
The Kinesiograph had been used by Jankelson et al. (1974) to study the movements of the mandibular. However, with modifications made to it, movements of the maxillary complete denture may be measured. It has been used by Barco et al. (1979) to investigate the stability of heat-cured maxillary dentures before and after relining. Jankelson (1980) in his study of the accuracy of the Kinesiograph with the aid of a computer has shown that the data are displayed to an accuracy within 1.5 per cent of the exact value. Certain precautions must be taken when using the Kinesiograph. Patient selection is important. The patient’s face should neither be too broad nor so long as to come into contact with the magnetometers during the normal range of movement of the jaw. The clinical fit of the denture should have a minimum retention score of one, so that a repeatable rest position of the denture may be obtained. If the denture is so loose as to be out of contact with the supporting tissues, it would be very difficult to ensure that the same starting point is obtained for subsequent tests. In this study, only the vertical movements of the denture were measured. The Kinesiograph also enables anteroposterior as well as lateral movements to be studied. The results from such experiments may provide better insight into denture function. Further, it can also be used to study the effects of denture adhesives on, or the role of the tongue in, denture retention and stability. At the present moment, only the maxillary denture movements may be studied. It is hoped that a method would be developed in the near future where retention and stability of mandibular dentures may be measured as well. REFERENCES Barco M. T. jun., Moore B. K., Swartz M. L. et al. (1979) The effect of relining on the accuracy and stability of maxillary complete dentures-an in vitro and in vivo study. J. Prosthet. Dent.
42, 17. Battersby B. J., Gehl D. H. and O’Brien W. J. (1968) Effect of an elastic lining on the retention of dentures. J. Prosthet. Dent. 20, 498. Boone M. E. (1962) The Effect of a Denture Reline and a Denture Stabilizer upon the Biting Force of Complete Denture Wearers. Master Thesis, Indiana University. Boucher L. J., Ellinger C., Lutes M. et al. (1968) The effects of microlayer of silica on the retention of mandibular complete dentures. J. Prosthet. Dent. 19, 581. Culver P. A. J. and Watt I. (1973) Denture movements and control. Br. Dent. J. 135, 111. Gesser H. D. and Castaldi C. R. (197 1) The preparation and evaluation of wetting dentures for adhesion and retention. J. Prosthet. Dent. 25, 236. Hamrick J. E. (1962) A comparison of the retention of various denture-base materials. J. Prosthet. Dent. 12, 666. Jankelson B. (1980) Measurement accuracy of the mandibular Kinesiograph-a computerised study. J. Prosthet. Dent. 44, 656. Jankelson B., Swain C. W., Crane P. F. et al. (1974) Kinesiometric instrumentation: a new technology. J. Am. Dent. Assoc. 90, 834. Kapur K. K. (1967) A clinical evaluation of denture adhesives. J. Prosthet. Dent. 18, 550. Wain E. A. (1963) A method of measuring retention. Dent. Pratt. 13, 251. Winkler S. (1967) The effectiveness of embedded magnets in complete dentures during speech and mastication: a cineradiographic study. Dent. Digest 73, 118.
11, No. 3,
Movement dentures-a
pp. 257-263
Printed in Great Britain
of maxillary complete Kinesiographic study
Chong Lin Chew, BDS, MDS, MSD Department Singapore
of Prosthetic
Dentistry,
Faculty
of Dentistry,
National
University
of
ABSTRACT A clinical study on the movement of maxillary complete dentures was carried out on ten patients using the Kinesiograph. The results indicated a significant difference in the amount of movement between well-fitting and ill-fitting dentures. A comparison of this method with other methods used as well as the precautions to be taken when using the Kinesiograph are discussed.
INTRODUCTION Dentures move in the mouth during function. The amount of movement depends on the retention and stability of the dentures as well as the patient’s ability to control the dentures in the mouth. Many studies have been conducted to measure the retention of dentures (Hamrick, 1962; Wain, 1963; Boucher et al., 1968; Gesser and Castaldi, 1971). However, there are only a few studies where movements of dentures during function have been looked into. Winkler (1967) studied the effectiveness of magnets as aids in retention of dentures using cineradiography where denture movements could be observed by means of cineradiographic films. Culver and Watt (1973) investigated by cinefluorography the movement of dentures during incising, the part played by the tongue in their control, and the timing of the incising-swallowing sequence. Their results showed that there is a tendency for the majority of dentures to tilt, sometimes by as much as 20 mm measured at the back edge on biting into a bun (apple or chocolate). The purpose of this study was to measure the amount of movement of the maxillary complete denture during function by means of the Kinesiograph.
METHODS
AND MATERIALS
Ten patients with maxillary complete dentures were included as subjects in the study. Their ages ranged from 47 to 65 years. For each patient, a duplicate maxillary complete denture was made. If the patient’s denture was ill-fitting, an improvement was made to the duplicate denture to make it well-fitting (i.e. a reline) or improvement was made to the borders of the denture. However, for those dentures which were originally well-fitting, the duplicate was made ill-fitting by trimming the borders. The clinical fit of the denture and the condition of the denture-bearing tissues were evaluated by two dentists using Kapur’s (1967) criteria. Of the ten patients, nine of them had mandibular complete dentures and one had a removable partial denture. The movement of the mandibular dentures would not affect the measurements made of the maxillary complete dentures.
258
Journal of Dentistry Vol. 1 l/No.
3
Fig. 7. The Kinesiograph.
The Kinesiograph The Kinesiograph instrumentation (Fig. 1) was introduced by Jankelson and his associates in 1974 to track mandibular movements in three dimensions, namely, anteroposterior, lateral and vertical. The Kinesiograph used in this investigation is a research model (Kinesiography, Myo-tronics Research Inc., Seattle, Washington, USA). The system senses the spatial location of a magnet that is mounted on the mandibular incisors with a dental plastic. However, to measure movements of the maxillary complete denture, an additional feature known as the ‘Dual Magnet System’ was incorporated into the Kinesiograph. The positions of the magnets are detected by an array of sensing elements which are responsive to the strength of the field emanating from the magnets. As the denture moves, each sensor responds to the changes in field strengths which result as the distance from the magnets varies. The circuitry of the Kinesiograph converts the outputs of the sensors to a readily usable representation in three dimensions. The outputs are suitable for recording or display on a cathode ray tube screen. The data may also be stored in an FM magnetic tape system. System output includes separate data channels for the vertical, lateral and anteroposterior components. However, in this study, only the vertical components were used. The magnetic field sensors are specially constructed flux gate magnetometers encapsulated (Fig. 2). The sensors are mounted on a in plastic with rigid dimensional specifications superstructure of thin-walled aluminium tubing with careful attention given to the orientation of the sensitive axis of each magnetometer. The entire sensory array is fully adjustable to permit accommodation to a wide variety of facial contours. It also permits operator adjustments to ensure that the sensor does not come into contact with the patient’s mandible during its movements. An additional unit incorporated into the Kinesiograph was the Sweep Mechanism. This enabled the study of segmental movements of the denture with time.
Chong Lin Chew: Movement
of maxillary
complete
Fig. 2. Dual sensor array. A, B and C are magnetometers that detect movements of the magnets in the vertical, antero-posterior and lateral directions respectively.
Measurement
of denture
dentures
259
Fig. 3. The magnet attached to the buccal surface of the maxillary complete denture at the premolarmolar region with the north pole facing anteriorly.
dislodgement
The dimensions of each magnet were 13 X 6 X 3 mm. On each of the buccal surfaces of the test maxillary complete denture, at the premolar-molar region, one magnet was attached with Myo-print, a synthetic resin, and the north pole ofthe magnet was made to face anteriorly (Fig. 3). The lower borders of the magnets were about 2mm above the occlusal plane and the magnets were adjusted to be at the same level in a vertical plane. The positions of the magnets were noted so that they could be re-positioned at the same place for each test. The well-fitting denture was used first, then the ill-fitting denture. The patient’s mandibular complete denture was stabilized with an adhesive 30 minutes before the initial measurements were made, to allow for hydration of the adhesive. One patient had a mandibular removable partial denture and no adhesive was applied. The adhesive was used to stabilize the mandibular complete denture throughout the study. The sun-glasses to hold the sensor array were strapped firmly on the patient. The sensor array was fitted on and centralized to the patient’s face (Fig. 4). The two lower magnetometers were positioned so that they would not come in contact with the patient’s chin during chewing movements of the mandible. The beams were turned on. Final adjustments of the sensor array were made so that the beams on the screen were at the centre + 1.0 cm in a horizontal plane. The patient chewed on a food substitute. It was a disc 1.2 cm in diameter and 0.5 cm in thickness prepared from Kerr FITT, a tissue conditioner, using a powder-liquid ratio of 2.5 (Fig. 5). The discs were stored in tapwater for 48 hours before use. The material had a soft
260
Fig. 4. The dual sensor patient’s face.
Journal of Dentistry
array strapped
to the
Fig. 5. Food substitute
Vol. 1 l/No.
3
made from Kerr FIlT.
rubber consistency that was maintained throughout the chewing cycle. The patient was unable to chew through the material. The disc was placed in the patient’s mouth on top of the tongue until the chewing test was begun. The sweep control was turned to the 1-O div./s position. There were three horizontal beams moving across the screen and 20-s were required for the beams to travel from one end of the screen to the other. One beam represented the vertical components of Channel A, the second the vertical component of Channel B; and the third the lateral component of both channels. They were set in this sequence with one above the other, at about 2-3 cm apart. The lateral component was not considered in this study. Before the start of each chewing cycle, the patient was asked to relax his mandible without any tooth contact. The beams were allowed to travel across the screen once, thereby giving three horizontal lines which served as the baselines (rest position of the maxillary denture) for measurements of dislodgements during chewing. When the beams reached the other end of the screen, the patient was asked to chew on the disc on his right side. There was a lapse of about three seconds before the beams appeared on the screen a second time. The patient was asked to stop chewing the moment the beams fully traversed the screen. The beams were then turned off. While these tracings were obtained, the patient was asked to keep his heady steady by placing the back of his head against a head rest. The grid was then added to the screen. Denture movements were shown on the screen as peaks on either side of the baselines (Figs. 6 and 7). Peaks above the baselines of the vertical components represented compression of the denture against the tissues while those below were due to dislodgements. Dislodgements that occurred through the middle ten chewing strokes were measured and
Chong Lin Chew: Movement
of maxillary complete
261
dentures
Fig. 6. Tracings of movements of well-fitting denture with patient chewing on right side. L. left side of denture; R, right side of denture.
L
R
Fig. 7. Tracings of movements of ill-fitting denture with patient chewing right side. L, left side of denture: R, right side of denture.
on
recorded. Only 10 chewing strokes were considered although some patients had more than this number per 20-s chewing cycle. Measurements were made to the nearest 0.1 cm on the screen. Compression and lateral movements were not considered in this study. The tracings on the screen were then erased and a second set obtained with the patient chewing on his left side. The sun-glasses on the sensor array were removed, after the measurements were made. Adhesive on the mandibular denture was cleaned off and the patient discharged. The patient was asked to return for more appointments to repeat the measurements. Three sets of measurements were made for each of the well-fitting and ill-fitting dentures.
RESULTS The ten patients selected for this study had good denture-bearing tissues (score 8). Each patient had a well-fitting and an ill-fitting denture. The ill-fitting dentures had a minimum retention score of + 1. Kapur’s (1967) criteria were used for all these evaluations.
262
Journal of Dentistry Vol. 1 l/No.
Tab/e /. Average dislodgement of denture on left side
Patient
3
Table I. Average dislodgement of denture on right side
Patient chewing on right side
Patient chewing on left side
Well-fitting denture M-fitting denture (mm) lmml
Well-fitting denture Ill-fitting denture fmml lmml
f 4 : 7 6 9 10
0.3 1.4 0.4 0.1 0.9 0.6 A:;
2.0 1.9 0.2 0.5 3.4 0.7 0.3 1.3
0 0.5
1.2 1.5
Patient 1 z
1.6 0.4
4
0.1
: 7 :
0.6 01
10
0.1 ;:3”
2.4 0.5 0.5 0.5 0.8 1.6 1.8 0.9
0.1
Samples of tracings of the denture movements obtained from the Kinesiograph are shown in Figs. 6 and 7. The tracings were those obtained when the patients were chewing on the right sides. The data shown in Tables Iand IIrepresent denture dislodgement on the side opposite that of the chewing side. For example, if the patient was chewing on the right side, the amount of dislodgement on the left side was recorded. Dislodgement of the denture on the chewing side did occur, but only on rare occasions when compared to that on the non-chewing side. Therefore, they were not considered significant. Tables I and II show the average amount of dislodgement of both the well-fitting and illfitting dentures. Statistical analysis of the results using the Student t test (paired observation) showed that a greater amount of movement or dislodgement occurred with ill-fitting than with well-fitting dentures. It was significant at IYO.05. This was true no matter which side the patient was chewing on.
DISCUSSION The results obtained from this study showed that a well-fitting denture is more retentive and stable than an ill-fitting denture. Previous studies on retention were based on determining the forces required to dislodge the denture. Gesser and Castaldi (197 1) used the pully system while Boucher et al. (1968) as well as Battersby and co-workers (1968) used the lever system to measure denture retention. Boone (1962) measured the anterior biting force that would dislodge the maxillary denture with the aid of the gnathodynamometer. ln all these studies, the dentures were static and not in function. Retention and stability play an important role in the denture function, for example, in speech and mastication. The poorer the retention and stability, the greater will be the amount of denture dislodgement during function. Therefore, more meaningful results might be attained if measurements of retention and stability were made under such conditions. The Kinesiograph enables such measurements to be made. Movements of the magnets attached to the dentures represent movements of the dentures. Since these measurements can be recorded on the screen, actual denture movements are seen and may be measured.
Chong Lin Chew: Movement of maxillary complete dentures
263
The Kinesiograph had been used by Jankelson et al. (1974) to study the movements of the mandibular. However, with modifications made to it, movements of the maxillary complete denture may be measured. It has been used by Barco et al. (1979) to investigate the stability of heat-cured maxillary dentures before and after relining. Jankelson (1980) in his study of the accuracy of the Kinesiograph with the aid of a computer has shown that the data are displayed to an accuracy within 1.5 per cent of the exact value. Certain precautions must be taken when using the Kinesiograph. Patient selection is important. The patient’s face should neither be too broad nor so long as to come into contact with the magnetometers during the normal range of movement of the jaw. The clinical fit of the denture should have a minimum retention score of one, so that a repeatable rest position of the denture may be obtained. If the denture is so loose as to be out of contact with the supporting tissues, it would be very difficult to ensure that the same starting point is obtained for subsequent tests. In this study, only the vertical movements of the denture were measured. The Kinesiograph also enables anteroposterior as well as lateral movements to be studied. The results from such experiments may provide better insight into denture function. Further, it can also be used to study the effects of denture adhesives on, or the role of the tongue in, denture retention and stability. At the present moment, only the maxillary denture movements may be studied. It is hoped that a method would be developed in the near future where retention and stability of mandibular dentures may be measured as well. REFERENCES Barco M. T. jun., Moore B. K., Swartz M. L. et al. (1979) The effect of relining on the accuracy and stability of maxillary complete dentures-an in vitro and in vivo study. J. Prosthet. Dent.
42, 17. Battersby B. J., Gehl D. H. and O’Brien W. J. (1968) Effect of an elastic lining on the retention of dentures. J. Prosthet. Dent. 20, 498. Boone M. E. (1962) The Effect of a Denture Reline and a Denture Stabilizer upon the Biting Force of Complete Denture Wearers. Master Thesis, Indiana University. Boucher L. J., Ellinger C., Lutes M. et al. (1968) The effects of microlayer of silica on the retention of mandibular complete dentures. J. Prosthet. Dent. 19, 581. Culver P. A. J. and Watt I. (1973) Denture movements and control. Br. Dent. J. 135, 111. Gesser H. D. and Castaldi C. R. (197 1) The preparation and evaluation of wetting dentures for adhesion and retention. J. Prosthet. Dent. 25, 236. Hamrick J. E. (1962) A comparison of the retention of various denture-base materials. J. Prosthet. Dent. 12, 666. Jankelson B. (1980) Measurement accuracy of the mandibular Kinesiograph-a computerised study. J. Prosthet. Dent. 44, 656. Jankelson B., Swain C. W., Crane P. F. et al. (1974) Kinesiometric instrumentation: a new technology. J. Am. Dent. Assoc. 90, 834. Kapur K. K. (1967) A clinical evaluation of denture adhesives. J. Prosthet. Dent. 18, 550. Wain E. A. (1963) A method of measuring retention. Dent. Pratt. 13, 251. Winkler S. (1967) The effectiveness of embedded magnets in complete dentures during speech and mastication: a cineradiographic study. Dent. Digest 73, 118.