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Muscle relaxant and rest position—A cephalometric study
Muscle relaxant and rest position-A study Jayashree V. Dikshit,
B.D.S., M.D.S.,*
cephakmetric
and Firoze D. Mirza, L. D.Sc., M. S. D. * *
Nair Hospital Dental College, Bombay, Maharashtra
State, India
T
1n
spite of the several advances in prosthodontics, basic procedures such as recording the vertical dimensions of occlusion and rest are a matter of judgement by the clinician. No definite scientific criteria have been devised to record the vertical dimension at rest. In edentulous patients the range of closure is greater than in dentulous patients, and overclosure of the mandible induces hyperactivity in its elevator muscles. Emotional disturbances may also cause the hyperactivity of the motor system through the pyramidal cells of the cortex, which in turn would cause irregular muscle contraction. This hyperactivity persists even when the mandible appears to be at rest. A state of tremor is introduced in the postural muscles of the mandible. It is impossible to record a true rest position consistently when such a state of tremor exists in the postural muscles of the mandible. When the same muscles are stretched to their physiologic resting lengths these tremors disappear. There are two ways of eliminating these tremors: (1) by the use of exercises suggested by BOOS’ and (2) by use of muscle relaxant drugs such as Valium.? The possibility still remains that tissue elasticity and gravitational forces determine the basic rest position of the mandible and that muscle activity exerts only a small influence on jaw position.’ Atwood” has established that in edentulous patients it is difficult to obtain identical measurements during a given sitting and those which are identical in consecutive sittings on different days. In clinical work the constancy of rest vertical dimension
*Lecturer, Department of Prosthodontics and Crown and Bridge. **Professor and Head, Department of Prosthodontics and Crown and Bridge. tTrade name of Diazepam, Roche Products Ltd., Bombay, India.
0022-3913/79/110579
+ 05$00.50/0~
1979 The C. V. Mosbv Co
is important because the vertical dimension of occlusion is dependent on it. The purpose of this study was first to study the effect of a muscle relaxant drug on rest position of the mandible and second to find a suitable dose of Valium which would help in finding a consistent rest position.
METHOD Fifteen edentulous subjects were chosen at random from the Prosthetic Department of the Nair Hospital Dental College. The only criteria were those of general health and body weight. No consideration was given to the period of edentulousness. Valium was administered in two dosages of 10 and 20 mg. The patient was asked to wet the lips, swallow, and relax. As soon as the patient eame to rest position, three cephalograms were made before taking Valium, three after administration of 10 mg Valium, and three after administration of 20 mg Valium. The three cephalograms were made at intervals of 2 minutes, and all were taken 1 hour after the administration of the drug. On the lirst day, three cephalograms were made before administration of Valium and three after giving 10 mg of Valium. The same patient was called on the alternate day and sedated with 20 mg Valium. Again three cephalograms were made for the same patient (Figs. 1 and 2). The series of lateral cephalograma were made ultraspeed ancl Siemens dentograph* using 6% X 8% inch films at a target distance 5 feet from the x-ray tube, with 85 kVp, 15 mA, and an exposure of 2.5 seconds. The cassettes were used with intensifying screens. It was thought that perhaps by administering a “Siemens Aktiengesellschaft Wernerwerk nik, Erlangen. West Germany.
THE JOURNAL
Fur nlrdizinischr
OF PROSTHETIC
DENTISTRY
Terh-
579
DIKSHIT AND MIRZA
35
,,, j3 12 -1
Fig. 1. Patient in cephalostat, front view.
Fig. 3. Graph showing the number of subjects achieving constancy (decrease in variance in 53% of subjects) for variable ND, after giving 10 mg Valium.
Librium and a series of six cephalograms were made for each patient. For all patients in this study the following points were traced on each cephalogram: (1) point N-the anterior-most point on the frontonasal suture in the midsagittal plane, (2) point D--the midpoint of the menton bone as described by Steiner,’ and (3) point S-the midpoint of the sella turcica. The first cephalogram was traced by marking the above-mentioned points. .This tracing paper was superimposed on the subsequent films to locate points D and S. Thus all three points N, D, and S were fairly constant on different cephalograms. Lines ND and DS were measured. Angle SND was also measured.
Fig. t. Patient in cephalostat, profile view. tranquilizer such as Librium,* which does not have a muscle relaxant property, one might show different readings. Therefore, five patients were given 10 mg of Librium and six cephalograms were made as described. A dose response for Librium was also tried. A different set of six patients were given 20 mg *Trade name of Bombay, India.
580
Chloridazepoxide,
Roche
Products
Variable ND Change in Variance Mter IOhij Valium
Ltd.,
RESULTS On the average, the mean values of ND and SD increased when 10 mg of Valium was given. These values further increased for ND and SD when the dose of Valium was increased to 20 mg. The mean values for angle SND decreased on giving 10 mg of Valium and further decreased on giving 20 mg of Valium. On administration of 10 mg of Librium the
NOVEMBER 1979
VOLUME 42
NUMBER 5
MUSCLE
RELAXANT
AND
REST POSITION
Vuriabb Change Mter
SD in Variance
10mg Valium
0
‘I
Perear
Fig. 4. Graph showing the number of subjects achieving constancy (decrease in variance in 48% of subjects) for variable SD, after giving 10 mg Valium.
Fig. 5. Graph showing the number of subjects achieving constancy (decrease in variance in 73% of subjects) for variable angle SND, after giving 10 mg Valium.
mean values of ail variables decreased. On giving 20 mg of Librium the mean values of variable ND increased and the mean values of variables SD and angle SND decreased. Increase or decrease in the mean values of the several variables in different patients while under drug influence indicated a certain pattern of behavior of variables. These were not found statistically significant at the 95% level of confidence (Table I). On the average the variances of all the three variables decreased on giving 10 mg Valium. A decrease in the variance may be interpreted as achieving constancy. A definite constancy was achieved in the observations of all the variables when 10 mg of Valium was given. However, on increasing the dose of Valium to 20 mg the constancy was lost. Thus administration of 10 mg of Valium did help to achieve constancy in the various variables (Table
change in different variables was due to the drug only. It was further shown that the genera1 trend was toward the increase in the means of different variables (viz, ND and SD) on an average on giving 10 mg of Valium and that constancy was achieved. On giving 20 mg of Valium there was further increase in means of different variables (viz, ND and SD), but the constancy was lost. On giving 10 mg of Librium there was a decrease in the means of different variables and the constancy was-lost. On administration of 20 mg of Librium there was an increase in the mean of variable ND on an average, but there was a decrease in the mean of variable SD on an average and the constancy was lost (Table I).
1). Subjects achieving constancy of results (decrease in variance) for the various variables (ND, SD, and angle SND) with 10 mg of Valium and 20 mg of Librium are shown in Figs. 3 to 8. The chi-square test was applied and definitely indicated that the
THE JOURNAL
OF PROSTHETIC
DENTISTRY
DISCUSSION The edentulous state of a person conveys not only the absence of teeth but a difference in the state of the musculature supporting the mandible. The mandibular posture is mainly governed by the proprioceptors in the periodontal membrane. With’the loss of teeth the patient loses the contribution which the proprioceptive mechanism of the periodontal structures of the teeth afford. For exam-
581
DIKSHIT
Vwiable Change After
ND in Variance 20mg Librium
Variable Change After
AND
MIRZA
L SND in Variance
209
Librium
3
Fig. 6. Graph showing the number of subjects achieving constancy (decrease in variance in 17% of subjects) for variable ND, after giving 20 mg Librium.
Variable Change After
SD in Variance 20 mg Librium
” -3
7-
Ji
6-
Fig. 7. Graph showing the number of subjects achieving constancy (decrease in variance in 50% of subjects) for variable SD, after giving 20 mg Librium. ple, the masticating muscles no longer receive messages which dictate the path of closure of the mandible and the patient finds it difficult to position the mandible. The mandibular posture is then governed by the more primitive proprioceptors from the musculature and the temporomandibular joint. Since the occlusal stops are lost, there is a tendency for overclosure of the jaws, which causes the contraction of the fibers of the temporal muscles. The imbalance that occurs due to abnormal motor impulses from postural muscles of the mandible 582
Fig. 8. Graph showing the number of subjects achieving constancy (decrease in variance in 33% of subjects) for variable angle SND, after giving 20 mg Librium. eventually is reflected in the abnormal resting state. Muscle tension may be differentiated from muscle length, for they are not synonymous and may change independently of one another. Ideal tension is developed at physiologic resting length. The tone of skeletal muscle is maintained basically through the stretch reflex. Skeletal muscle relaxation, i.e., reduction of muscle tone, without loss of consciousness can be achieved by (1) drugs acting on higher centers, e.g., Diazepam, (2) drugs acting on (3) drugs acting spinal cord, e.g., mephenesin, peripherally at the neuromuscular junction such as competitive blockade-d-tubocurarine, or depolarization, e.g., succinylcholine and decamethonium. Boos’ is of the opinion that conditioning muscles will aid in placing the mandible and the condyles in a more central position. He conditioned the muscles with exercises. These exercises in no way develop muscle power. The procedure is to learn relaxation and relieve tension. The idea of exercise is to fatigue the muscles so that they come to their resting length. At the time the dental treatment is indicated the patient should be put on relaxation exercises. BOOS’ states “A complete exercise is to have the patient hold the head in an upright position and go through a series of movements of the mandible. First the patient opens wide for about half a minute, then relaxes and lets the mandible come to rest position. Do not attempt to position the jaw. The teeth should never come together, so that there will not be any guidance by the existing occlusion. Next, the patient NOVEMBER
1979
VOLUME
42
NUMBER
5
MUSCLE
RELAXANT
AND
REST POSITION
Table I. Changes in measurements after drug administration Valium
Librium
10 mg
Measurement
Mean
m (mm) SD (mm) < SND (degree)
GO.87 +0.40 -0.20
20 mg
Average Variance -0.38 -0.24 -0.31
Mean
+ 0.37
-0.27
-0.15
CONCLUSIONS 1. Since 53% of patients achieved constancy in the vertical dimension of rest after taking 10 mg of Valium 1 hour prior to recordings, it can be concluded that they tend to achieve true rest position. 2. The constancy of the resting vertical dimension was lost with 20 mg of Valium. Thus, 10 mg of Valium is considered as an ideal dose. 3. Librium in a dosage of 10 mg neither causes an increase in the vertical dimension of rest nor helps to attain constancy.
OF PROSTHETIC
DENTISTRY
Average Variance
+ 1.27 + 0.53
moves the jaw to the right, as far as possible, in a slow continuous stretch and then lets it drop back to rest position. Then he moves the jaw to the left and drops it back; then forward, back to rest, retruded as far as possible, and then to rest, and then open and back to rest. The forward position and dropping back to rest, as well as opening wide and coming to rest, will often help in bringing about a normal unstrained mandibular position. This exercise may be used as B prescription by requiring the patient to follow the prescribed movements for two or three minutes four times a day.” It appears that the exercises are tedious and time consuming. There is also a great deal of dependence on the patients to perform them effectively. The administration of muscle relaxant is more convenient, less time consuming, and a more reliable procedure to achieve similar results. The purpose of giving a muscle relaxant and prescribing exercises is the same-to eliminate hyperactivity so that the muscles can return to their normal resting length. When a muscle relaxant is given, the muscle tone is reduced and the action of gravity on the mandible is more pronounced, causing a drop of the mandible and thereby stretching the shortened muscles to their normal resting length.
THE JOURNAL
10 mg
-0.07
20
Mean
Average Variance
-1.20 -0.20 -0.60
+ 1.27 + 0.20 + 1.80
Mean
mg Average Variance
+ 0.67
+0.72
-0.67 -0.33
+ 0.56
+0.11
4. Librium in a dosage of 20 mg causes an insignificant increase in the vertical dimension of rest but does not help to attain constancy. Thus the muscle relaxant property of 10 mg of Valium given orally has some bearing on achieving constancy of the vertical dimension of rest. 5. The vertical dimension of rest recorded on a retruded mandibular position on giving 10 mg of Valium is further retruded on giving 20 mg of Valium. However, the magnitude of retrusion is not statistically significant. Hence a muscle relaxant is of limited value in retruding the mandible at the vertical dimension of rest. 6. The rest position is dependent on the tonicity of muscles. Although the passive tissue elasticity of the muscles, ligaments, and fascial sheets may be primarily responsible for the mandibular posture, the motor unit activity (tone) acts as a fine adjustment for maintaining the mandibular posture in a living individual. Valium and Librium tablets were supplied courtesy of Roche Products Ltd., Bombay. India.
REFERENCES Boos, R. H.: Physiologic denture technique. J PRO~THET DENT 6:726, 1956. Yemm, R.. and Nordstrom, S. H.: Forces developed by tissue elasticity as a determinant of mandibular resting posture in the rat. Arch Oral Biology 19:347, 1974. Atwood, D. A.: A cephalometric study of the clinical rest position of the mandible. Part 1. The variability of the clinical rest position following the removal of occlusai contact. J PROSTHET DENT 6:504, 1956. Steiner, C. S.: Steiner’s analysis. J Am Dent Assoc. 46:721, 1960. Reprmt requestJ to: DR. J. V. DIKSHIT NAIR HOSPITAL DENTAL COLLEGE DR. A. L. NAIR Roan BOMBAY 8 INDIA
B.D.S., M.D.S.,*
cephakmetric
and Firoze D. Mirza, L. D.Sc., M. S. D. * *
Nair Hospital Dental College, Bombay, Maharashtra
State, India
T
1n
spite of the several advances in prosthodontics, basic procedures such as recording the vertical dimensions of occlusion and rest are a matter of judgement by the clinician. No definite scientific criteria have been devised to record the vertical dimension at rest. In edentulous patients the range of closure is greater than in dentulous patients, and overclosure of the mandible induces hyperactivity in its elevator muscles. Emotional disturbances may also cause the hyperactivity of the motor system through the pyramidal cells of the cortex, which in turn would cause irregular muscle contraction. This hyperactivity persists even when the mandible appears to be at rest. A state of tremor is introduced in the postural muscles of the mandible. It is impossible to record a true rest position consistently when such a state of tremor exists in the postural muscles of the mandible. When the same muscles are stretched to their physiologic resting lengths these tremors disappear. There are two ways of eliminating these tremors: (1) by the use of exercises suggested by BOOS’ and (2) by use of muscle relaxant drugs such as Valium.? The possibility still remains that tissue elasticity and gravitational forces determine the basic rest position of the mandible and that muscle activity exerts only a small influence on jaw position.’ Atwood” has established that in edentulous patients it is difficult to obtain identical measurements during a given sitting and those which are identical in consecutive sittings on different days. In clinical work the constancy of rest vertical dimension
*Lecturer, Department of Prosthodontics and Crown and Bridge. **Professor and Head, Department of Prosthodontics and Crown and Bridge. tTrade name of Diazepam, Roche Products Ltd., Bombay, India.
0022-3913/79/110579
+ 05$00.50/0~
1979 The C. V. Mosbv Co
is important because the vertical dimension of occlusion is dependent on it. The purpose of this study was first to study the effect of a muscle relaxant drug on rest position of the mandible and second to find a suitable dose of Valium which would help in finding a consistent rest position.
METHOD Fifteen edentulous subjects were chosen at random from the Prosthetic Department of the Nair Hospital Dental College. The only criteria were those of general health and body weight. No consideration was given to the period of edentulousness. Valium was administered in two dosages of 10 and 20 mg. The patient was asked to wet the lips, swallow, and relax. As soon as the patient eame to rest position, three cephalograms were made before taking Valium, three after administration of 10 mg Valium, and three after administration of 20 mg Valium. The three cephalograms were made at intervals of 2 minutes, and all were taken 1 hour after the administration of the drug. On the lirst day, three cephalograms were made before administration of Valium and three after giving 10 mg of Valium. The same patient was called on the alternate day and sedated with 20 mg Valium. Again three cephalograms were made for the same patient (Figs. 1 and 2). The series of lateral cephalograma were made ultraspeed ancl Siemens dentograph* using 6% X 8% inch films at a target distance 5 feet from the x-ray tube, with 85 kVp, 15 mA, and an exposure of 2.5 seconds. The cassettes were used with intensifying screens. It was thought that perhaps by administering a “Siemens Aktiengesellschaft Wernerwerk nik, Erlangen. West Germany.
THE JOURNAL
Fur nlrdizinischr
OF PROSTHETIC
DENTISTRY
Terh-
579
DIKSHIT AND MIRZA
35
,,, j3 12 -1
Fig. 1. Patient in cephalostat, front view.
Fig. 3. Graph showing the number of subjects achieving constancy (decrease in variance in 53% of subjects) for variable ND, after giving 10 mg Valium.
Librium and a series of six cephalograms were made for each patient. For all patients in this study the following points were traced on each cephalogram: (1) point N-the anterior-most point on the frontonasal suture in the midsagittal plane, (2) point D--the midpoint of the menton bone as described by Steiner,’ and (3) point S-the midpoint of the sella turcica. The first cephalogram was traced by marking the above-mentioned points. .This tracing paper was superimposed on the subsequent films to locate points D and S. Thus all three points N, D, and S were fairly constant on different cephalograms. Lines ND and DS were measured. Angle SND was also measured.
Fig. t. Patient in cephalostat, profile view. tranquilizer such as Librium,* which does not have a muscle relaxant property, one might show different readings. Therefore, five patients were given 10 mg of Librium and six cephalograms were made as described. A dose response for Librium was also tried. A different set of six patients were given 20 mg *Trade name of Bombay, India.
580
Chloridazepoxide,
Roche
Products
Variable ND Change in Variance Mter IOhij Valium
Ltd.,
RESULTS On the average, the mean values of ND and SD increased when 10 mg of Valium was given. These values further increased for ND and SD when the dose of Valium was increased to 20 mg. The mean values for angle SND decreased on giving 10 mg of Valium and further decreased on giving 20 mg of Valium. On administration of 10 mg of Librium the
NOVEMBER 1979
VOLUME 42
NUMBER 5
MUSCLE
RELAXANT
AND
REST POSITION
Vuriabb Change Mter
SD in Variance
10mg Valium
0
‘I
Perear
Fig. 4. Graph showing the number of subjects achieving constancy (decrease in variance in 48% of subjects) for variable SD, after giving 10 mg Valium.
Fig. 5. Graph showing the number of subjects achieving constancy (decrease in variance in 73% of subjects) for variable angle SND, after giving 10 mg Valium.
mean values of ail variables decreased. On giving 20 mg of Librium the mean values of variable ND increased and the mean values of variables SD and angle SND decreased. Increase or decrease in the mean values of the several variables in different patients while under drug influence indicated a certain pattern of behavior of variables. These were not found statistically significant at the 95% level of confidence (Table I). On the average the variances of all the three variables decreased on giving 10 mg Valium. A decrease in the variance may be interpreted as achieving constancy. A definite constancy was achieved in the observations of all the variables when 10 mg of Valium was given. However, on increasing the dose of Valium to 20 mg the constancy was lost. Thus administration of 10 mg of Valium did help to achieve constancy in the various variables (Table
change in different variables was due to the drug only. It was further shown that the genera1 trend was toward the increase in the means of different variables (viz, ND and SD) on an average on giving 10 mg of Valium and that constancy was achieved. On giving 20 mg of Valium there was further increase in means of different variables (viz, ND and SD), but the constancy was lost. On giving 10 mg of Librium there was a decrease in the means of different variables and the constancy was-lost. On administration of 20 mg of Librium there was an increase in the mean of variable ND on an average, but there was a decrease in the mean of variable SD on an average and the constancy was lost (Table I).
1). Subjects achieving constancy of results (decrease in variance) for the various variables (ND, SD, and angle SND) with 10 mg of Valium and 20 mg of Librium are shown in Figs. 3 to 8. The chi-square test was applied and definitely indicated that the
THE JOURNAL
OF PROSTHETIC
DENTISTRY
DISCUSSION The edentulous state of a person conveys not only the absence of teeth but a difference in the state of the musculature supporting the mandible. The mandibular posture is mainly governed by the proprioceptors in the periodontal membrane. With’the loss of teeth the patient loses the contribution which the proprioceptive mechanism of the periodontal structures of the teeth afford. For exam-
581
DIKSHIT
Vwiable Change After
ND in Variance 20mg Librium
Variable Change After
AND
MIRZA
L SND in Variance
209
Librium
3
Fig. 6. Graph showing the number of subjects achieving constancy (decrease in variance in 17% of subjects) for variable ND, after giving 20 mg Librium.
Variable Change After
SD in Variance 20 mg Librium
” -3
7-
Ji
6-
Fig. 7. Graph showing the number of subjects achieving constancy (decrease in variance in 50% of subjects) for variable SD, after giving 20 mg Librium. ple, the masticating muscles no longer receive messages which dictate the path of closure of the mandible and the patient finds it difficult to position the mandible. The mandibular posture is then governed by the more primitive proprioceptors from the musculature and the temporomandibular joint. Since the occlusal stops are lost, there is a tendency for overclosure of the jaws, which causes the contraction of the fibers of the temporal muscles. The imbalance that occurs due to abnormal motor impulses from postural muscles of the mandible 582
Fig. 8. Graph showing the number of subjects achieving constancy (decrease in variance in 33% of subjects) for variable angle SND, after giving 20 mg Librium. eventually is reflected in the abnormal resting state. Muscle tension may be differentiated from muscle length, for they are not synonymous and may change independently of one another. Ideal tension is developed at physiologic resting length. The tone of skeletal muscle is maintained basically through the stretch reflex. Skeletal muscle relaxation, i.e., reduction of muscle tone, without loss of consciousness can be achieved by (1) drugs acting on higher centers, e.g., Diazepam, (2) drugs acting on (3) drugs acting spinal cord, e.g., mephenesin, peripherally at the neuromuscular junction such as competitive blockade-d-tubocurarine, or depolarization, e.g., succinylcholine and decamethonium. Boos’ is of the opinion that conditioning muscles will aid in placing the mandible and the condyles in a more central position. He conditioned the muscles with exercises. These exercises in no way develop muscle power. The procedure is to learn relaxation and relieve tension. The idea of exercise is to fatigue the muscles so that they come to their resting length. At the time the dental treatment is indicated the patient should be put on relaxation exercises. BOOS’ states “A complete exercise is to have the patient hold the head in an upright position and go through a series of movements of the mandible. First the patient opens wide for about half a minute, then relaxes and lets the mandible come to rest position. Do not attempt to position the jaw. The teeth should never come together, so that there will not be any guidance by the existing occlusion. Next, the patient NOVEMBER
1979
VOLUME
42
NUMBER
5
MUSCLE
RELAXANT
AND
REST POSITION
Table I. Changes in measurements after drug administration Valium
Librium
10 mg
Measurement
Mean
m (mm) SD (mm) < SND (degree)
GO.87 +0.40 -0.20
20 mg
Average Variance -0.38 -0.24 -0.31
Mean
+ 0.37
-0.27
-0.15
CONCLUSIONS 1. Since 53% of patients achieved constancy in the vertical dimension of rest after taking 10 mg of Valium 1 hour prior to recordings, it can be concluded that they tend to achieve true rest position. 2. The constancy of the resting vertical dimension was lost with 20 mg of Valium. Thus, 10 mg of Valium is considered as an ideal dose. 3. Librium in a dosage of 10 mg neither causes an increase in the vertical dimension of rest nor helps to attain constancy.
OF PROSTHETIC
DENTISTRY
Average Variance
+ 1.27 + 0.53
moves the jaw to the right, as far as possible, in a slow continuous stretch and then lets it drop back to rest position. Then he moves the jaw to the left and drops it back; then forward, back to rest, retruded as far as possible, and then to rest, and then open and back to rest. The forward position and dropping back to rest, as well as opening wide and coming to rest, will often help in bringing about a normal unstrained mandibular position. This exercise may be used as B prescription by requiring the patient to follow the prescribed movements for two or three minutes four times a day.” It appears that the exercises are tedious and time consuming. There is also a great deal of dependence on the patients to perform them effectively. The administration of muscle relaxant is more convenient, less time consuming, and a more reliable procedure to achieve similar results. The purpose of giving a muscle relaxant and prescribing exercises is the same-to eliminate hyperactivity so that the muscles can return to their normal resting length. When a muscle relaxant is given, the muscle tone is reduced and the action of gravity on the mandible is more pronounced, causing a drop of the mandible and thereby stretching the shortened muscles to their normal resting length.
THE JOURNAL
10 mg
-0.07
20
Mean
Average Variance
-1.20 -0.20 -0.60
+ 1.27 + 0.20 + 1.80
Mean
mg Average Variance
+ 0.67
+0.72
-0.67 -0.33
+ 0.56
+0.11
4. Librium in a dosage of 20 mg causes an insignificant increase in the vertical dimension of rest but does not help to attain constancy. Thus the muscle relaxant property of 10 mg of Valium given orally has some bearing on achieving constancy of the vertical dimension of rest. 5. The vertical dimension of rest recorded on a retruded mandibular position on giving 10 mg of Valium is further retruded on giving 20 mg of Valium. However, the magnitude of retrusion is not statistically significant. Hence a muscle relaxant is of limited value in retruding the mandible at the vertical dimension of rest. 6. The rest position is dependent on the tonicity of muscles. Although the passive tissue elasticity of the muscles, ligaments, and fascial sheets may be primarily responsible for the mandibular posture, the motor unit activity (tone) acts as a fine adjustment for maintaining the mandibular posture in a living individual. Valium and Librium tablets were supplied courtesy of Roche Products Ltd., Bombay. India.
REFERENCES Boos, R. H.: Physiologic denture technique. J PRO~THET DENT 6:726, 1956. Yemm, R.. and Nordstrom, S. H.: Forces developed by tissue elasticity as a determinant of mandibular resting posture in the rat. Arch Oral Biology 19:347, 1974. Atwood, D. A.: A cephalometric study of the clinical rest position of the mandible. Part 1. The variability of the clinical rest position following the removal of occlusai contact. J PROSTHET DENT 6:504, 1956. Steiner, C. S.: Steiner’s analysis. J Am Dent Assoc. 46:721, 1960. Reprmt requestJ to: DR. J. V. DIKSHIT NAIR HOSPITAL DENTAL COLLEGE DR. A. L. NAIR Roan BOMBAY 8 INDIA