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The effect of anteroposterior inclination of the occlusal plane on biting force
The effect of anteroposterior plane on biting force
inclination
Hideaki Okane, D.D.S.,* Toru Yamashina, D.D.S.,** Hiromichi Tsuru, D. D. S., Ph.D. **** Hiroshima
University,
School of Dentistry,
Tooru Nagasawa, D.D.S.,
Ph.D.,***
and
Hiroshima, Japan
1 he orientation of the occlusal plane is an important clinical procedure in prosthodontic treatment for edentulous patients. Many dentists position the anterior end of the occlusal plane 1 to 3 mm below the resting upper lip and make the posterior end parallel to the ala-tragus line, According to surveys made by Levin and Sauer,’ Kawabe and associates,’ and Ukai and associates,” the concepts concerning the occlusal plane orientation differ considerably among dental schools in Japan. the United States, and Canada (Table I). Two important questions are whether the alatragus line is best and whether the inclination of the occlusal plane affects masticatory function. Sharry’ stated that the plane of orientation established on the ala-tragus line is not rigid, but can be altered for special reasons. Boucher and associates” pointed out that the ala-tragus plane is adequate for many patients and usually results in satisfactory dentures, but it certainly cannot be regarded as applicable to all patients. Kapur and Soman’ and Carey’ have shown that masticatory performance is influenced by the inclination of the occlusal plane. There have been no published reports regarding masticatory muscle activity and biting force with the occlusal plane placed at various inclinations. The purpose of the present study was to investigate the effect of anteroposterior inclination of the This investigation was supported in part by Scientific Research Grant No. A-977365 of the Japanese Ministry of Education. *Graduate Student, Department of Removable Prosthodontics. **Chief Staff Dentist, Department of Removable Prosthodontics.
***Associate Professor. Department of Removable tics. ****Professor, Department of Prosthodontics.
0022-3913/79/l
of the occlusal
Prosthodon-
10497 + 05$00.50/O 0 1979 The C. V. Mosby Co.
Table I. Methods of determining the occlusal plane: Results of surveys by Levin and Sauer’ and others’. 3 USA and Canada, 33 dental
schwls
Height of the
retromolar
Japan, 15
dental scbofs
12
pad
Ala-tragus line Esthetics Dividing the interarch space evenly
16
4 14 2 1
9 2
4
Uncertain Miscellaneous
1
occlusal plane on muscle activity during clenching and biting force and to estimate physiologically the applicability of the ala-tragus line. The integrated electromyographic activity and biting forces of patients were examined at three different anteroposterior inclinations of the occlusal plane at a constant vertical dimension of occlusion.
MATERIALS
AND METHODS
Four patients with complete dentures, three men and one woman, from 61 to 79 years of age, were selected. Three major criteria used in their selection were: (I) the patient must not have any physical disability which would interfere with the study; (2) the patient must have good denture-bearing tissues (Kapur’s’ scoring method was employed for this clinical screening examination); and (3) the patient must have a normal maxillomandibular relation. Autopolymerizing acrylic resin occlusion rims were made for each patient on dental stone casts made from silicone rubber impressions. The test bases were composed of resin baseplates and flat
THE JOURNAL
OF PROSTHETIC
DENTISTRY
497
ORANE
Fig. 1. Three different inclinations of the occlusal plane. y/k: Blocks used for the location of the occlusal plane were fixed on the occlusion rims.
resin occlusion rims (Fig. 1). The rims could be fixed on the baseplate and were used for locating the occlusal plane. The occlusal plane was changed in its anteroposterior inclination as follows. 1. The A occlusal plane was positioned about 2 mm below the resting upper lip anteriorly and made parallel to the ala-tragus line posteriorly. The alatragus line was drawn from the lowest point of the ala of the nose to the lower border of the external auditory meatus. 2. The B occlusal plane was inclined about 5 degrees anteriorly by raising it posteriorly. 3. The C occlusal plane was lowered about 5 degrees posteriorly. After the maxillomandibular relation was established, a chrome-cobalt plate, 2 mm in thickness, was attached on the occlusal plane of the maxillary occlusion rim with autopolymerizing acrylic resin.
ET AL
The plate was centered laterally and anteroposteriorly on the occlusal plane. A small depression was ground in the center of the inferior surface of the plate. Then the lower occlusion rim was eliminated to provide 4 mm clearance between the upper and lower occlusal planes. Another chrome-cobalt plate of the same thickness was attached on the mandibular base, and a central bearing point was set in the center of the plate. The tip of the point occluded in centric relation at the depression in the upper plate and constantly maintained the maxillomandibular relation, even when the inclination of the occlusal plane was changed (Fig. 2). The recordings were made under the following conditions: (1) maximum clenching with A, B, and C occlusal planes and (2) clenching at given forces (50%,30’S, and 10% of the magnitude of biting force in maximum clenching with A occlusal plane) with A, B, and C occlusal planes. During the recording each patient was seated in an upright position with his head against the head support and the Frankfort plane horizontal. In each of the conditions the subject was instructed to clench 10 times at an interval of 5 seconds at a signal from the instructor. The clenching had to be progressive and held for 2 seconds. After a series of 10 clenchings with one occlusal plane the subject was allowed to rest for 10 minutes, after which the other series was started with another occlusal plane. When asked to clench with prescribed force, the subject could check by watching the amount of force displayed on the monitor oscilloscope of the polygraph* (biophysical amplifier). The amount of muscle activity was expressed as integrated EMG activity. Nonpolarizing surface electrodes? were attached 30 mm apart on the skin over the bilateral masseter muscles and the anterior part of the temporal muscles. Electrical action potentials were amplified by the polygraph and recorded on data tapes. The recorded EMG signals were played back through an analog integrator* and recorded on oscillograph paper. The amount of integrated EMG activities for 1 second was measured on the holding stages of every 10 clenchings. The unit of measurement of the integrated EMG activity was expressed in microvolt-seconds. The biting force was obtained with a foil strain gauge which was placed in the center of the superior surface of the chrome-cobalt plate on the maxillary *Sanei Instrument Co., Tokyo, Japan. tNihon Kohden Kogyo Co., Tokyo, Japan.
NOVEMBER
19’79
VOLUME
42
NUMBER
5
ANTEROPOSTERIOR
INCLINATION
Table II. Biting clenching (kg)
OF OCCLUSAL
force during
500
15.8 2 27.9 f 20.1 2 33.0 * 24.2
1 2 3 4
Mean
B occhal plane
1.3 3.4 2.4 1.4
11.4 -c 25.2 + 18.7 _t 29.2 + 21.1
0.9 1.6 1.0 1.2
of muscle activity clenching (pV set)
Subject
449.4 rt 463.7 t 624.5 f 664.0 t 550.4
1 2 3 4
Mean
l
set/kg)*
Subject 1 2 3 4
Mean *Amount
B occlusal plane
14.3 7.1 8.8 17.2
Table IV. Efficiency (pV
10.8 k 23.9 f 14.3 t 23.8 I 18.2
0.8 1.3 1.4 1.5
340.6 IL 9.2 427.6 _C 6.3 596.0 + 5.0 632.9 -t 15.1 499.3
of biting -
l
C occlusal plane 433.4 + 413.7 i 570.8 i 619.1 + 509.3
17.6 4.2 6.3 5.5
force exertion -
IO x
30
BITING
FORCE
Fig. 3. The amount of total activity of four muscles per second during clenching at given forces.
muscle activity required to exert the biting force of 1 kg on the occlusal plane. The more this value decreased, the greater was the efficiency.); (4) the amount of total activity per second of four muscles during clenching at given forces with each occlusal plane.
RESULTS B
C
ucclusal plane
occlusal plane
28.6 16.6 31.1 20.1 24.1
29.9 17.0 31.9 21.7 25.1
40.1 17.3 39.9 26.0 30.8
force.
*San& Instrument Co., Tokyo, Japan. thstron Corp., Canton, Mass.
OF PROSTHETIC
*
50
occlusion rim and connected to a strain amplifier* and a polygraph. The biting force was recorded simultaneously with EMG recordings. The biting force calibration was made with Instron universal testing instruments.f The following measurements were made: (1) the maximum biting force on each occlusal plane; (2) the amount of total activity per second of four muscles during maximum clenching with each occlusal plane; (3) the efficiency of the biting force exertion (This suggested value was obtained by dividing (2) by (I), and showed the amount of
THE IOURNAL
plane
100
during
A occlusal plane
of muscle activity/biting
A-Ocelusal
g 200 9
l
A occlusal plane
O-O
I
C ocdusal plane
Table III. Amount maximum
pv.sec
maximum
A ocdusal plane
Subject
PLANE
DENTISTRY
Biting force during maximum clenching. In all subjects the highest magnitude of biting force was exerted upon the A occlusal plane, followed by the B occlusal plane and the C occlusa1 plane. The mean value of maximum biting force was 24.2 kg on the A plane, 21.1 kg on the B plane, and 18.2 kg on the C occlusal plane (Table II). The amount of muscle activity during clenching, The amount of total activity of four muscles per second was obtained by measuring the integrated EMG activity during maximum clenching. AI1 subjects showed almost the same amount of total activity for the three different occlusal planes (Table III). Efficiency of biting Force exertion. The amount of total activity was divided by the magnitude of biting force. The calculated value represented the efficiency of biting force exertion on the occlusal plane. Table IV shows that all subjects had the lowest scores with the A occlusal plane followed by the B occlusal plane and the C occlusal plane. This indicates that the biting force was exerted more efficiently on the A occlusal plane than on the 3 or C occlusal planes. Total activity. The amount of total activity was measured in clenching at various given forces (SO%,
OKANE ET AL
30%, and 10% of the magnitude of maximum biting force on the A occlusal plane). The amount of each activity at given forces is shown in Fig. 3. At any magnitude of biting force, the amount of muscle activity with the A occlusal plane was found to be the minimum, followed by those with the B occlusal plane and the C occlusal plane. This also showed that the biting force was exerted most efficiently on the A occlusal plane. DISCUSSION Many dentists have observed that the orientation of the occlusal plane may affect the denture function and that it is important to determine this orientation correctly in making comfortable dentures. Investigators”-‘;’ have suggested various concepts or methods for the orientation of the occlusal plane based on morphologic studies on natural and artificial dentitions and on clinical experiences. However, no one has shown an easy method for locating the occlusal plane correctly for every patient. This difficulty may be attributable to the ladk of physiologic knowledge of the occlusal plane orientation. Gehl”’ has suggested that the occlusal plane should be placed so that favorable leverage would be exerted. It is important to investigate the effect of the anteroposterior inclination of the occlusal plane on masticatory function. Therefore, biting force exertion, one of the important factors of masticatory function, was tested in this study. Biting force is a vector which is the sum of all jaw-closing muscle tensions. The direction of the vector is constant individually at a constant vertical dimension of occlusion. Under the same activity of jaw closing muscles, biting force is most efficient on the occlusal plane which intersects perpendicular to the direction of the vector of muscle action. Morphologic search for the direction of the vector is difficult. Therefore the efficiency of biting force exertion was measured in this study. The present results showed that in any magnitude of clenching, the biting force was exerted most efficiently on the occlusal plane which was made parallel to the ala-tragus line posteriorly. The conventional method with the ala-tragus line seems to be suitable for clinical use in patients who have good denture bearing tissues, normal maxillomandibular relation, and no functional disorders, In other patients further study is required, and the occlusal plane inclination may have to be altered for excellent denture function.
500
CONCLUSIONS With the experimental design of this study the following conclusions were reached. 1. Biting force during maximum clenching was the greatest when the occlusal plane was made parallel to the ala-tragus line. It decreased when the occlusal plane was inclined about 5 degrees anteriorly or about 5 degrees posteriorly. 2. The efficiency of biting force exertion during maximum clenching showed the best value when the occlusal plane was made parallel to the ala-tragus line. 3. Muscle activity during clenching at various given forces was least when the occlusal plane was made parallel to the ala-tragus line. The anteroposterior inclination of the occlusal plane tends to affect the biting force, and the method with the ala-tragus line seems to be the most reasonable for occlusal plane orientation. REFERENCES 1. L&n, B., and Sauer, J. L.: Results of a survey of complete denture procedures taught in American and Canadian dental schools. J PROSTHET DENT 22:171, 1969. 2. Kawabe, S., Aoki, H., and Reitz, P. V.: Examination into the questionnaire, “Results of a survey of complete denture procedures taught in American and Canadian dental schools.” Prac Prostbod 3:330, 1970. (Japanese) 3. Ukai, H., Yanagida, S., Katoh, Y., Nishiura, M., and Hayashi, T.: Examination into the questionnaire, “Results of a survey of complete denture procedures taught in Japanese dental schools,” Prac Prosthod 3:324, 1970. (Papanese) 4. Sharry, J. J.: Complete Denture Prosthodontics, ed 2. New York, 1968, McGraw-Hill Book Co., p 245. 5. Boucher, C. O., Hickey, J. C., and Zarb, G. A.: Prosthodontic Treatment for Edentulous Patients, ed 7. St. Louis, 1975, The C. V. Mosby Co., pp 218-220. 6. Kapur, K. K., and Soman, S.: The effect of denture factors on masticatory performance, Part III. The location of the food platforms. J PROSTHET DENT 15:451, 1965. 7. Carey, P. D.: Occlusal plane orientation and masticatory performance of complete dentures. J PROSTHET DENT 39:368, 1978. 8. Kapur, K. K.: A clinical evaluation of denture adhesives. J PROSTHET DENT l&550, 1967. 9. Augsburger, R. H.: Occlusal plane relation to facial type. J PROSTHET DENT 3:755, 1953. 10. Hartono, R.: The occlusal plane in relation to facial types. J PROSTHET DENT 17:549, 1967. 11. Ismail, Y. H., and Bowman, J. F.: Position of the occlusal plane in natural and artificial teeth. J PROSTHET DENT 20:407, 1968. 12. Aoki, H.: The various aspects of the imaginary occlusal plane and the plane determinant instruments. Pratt Prosthod 5:257, 1972. (in Japanese) 13. Uehara, J., Tsuta, A., Yoshioka, M., Kubota, Y., and Aoki,
NOVEMBER
1979
VOLUME
42
NUMBER
5
ANTEROPOSTERIOR
INCLINATION
OF OCCLUSAL
PLANE
H.: A study of Camper’s plane by lateral cephalometrics. J Kanagawa Odont Sot 5: 11, 1970. (Japanese) 14. Itoh, I., and Nozaka, Y.: Studies of the relation between occlusal plane and Frankfort plane. Jap J Oral Biol 18~84, 1976. (Japanese) 15. Tsuru, H., Hiranuma, K., Nishiura, M., and Matsumoto, N.: Complete denture technique, ed 1. Tokyo, 1974, Ishiyaku Shuppan Co., pp 39-41. (Japanese)
16. Gehl, D. H.: Vertical dimension, jaw relation records and occlusion. Dent Clin North Am July 1960, pp 321-332. Rqmts request to: DR. HIDEAKI OKANE HIROSHIMA
SCHOOL.OF DENTISTRY
UNIVERSITY
KASUMI l-2-3 HIROSHIMA, JAPAN
ARTICLES TO APPEAR IN FUTURE ISSUES Influence Hueyching
of tooth proprioception Ghi, B.D.S.,
on speech articulation
M.S., and Glen P. McGivney,
D.D.S.
Prerestorative therapy using a modified Hawley splint Lynne
Heckert,
D.D.S.
The fracture strength of amalgam overlying
base materials
Abbas A. Hormati,
D.D.S.,
D.D.S.,
M.S.,
and James L. Fuller,
M.S.
Surgical nasal prosthesis PhiIlip
E. Hutcheson,
D.D.S.,
M.S.D.,
and Ariyadasa
Udagama,
D.D.S.,
M.S.D.
Mandibular movements of young adults recorded by intraurally light-emitting diodes Torsten
Jemt,
D.D.S.,
Stig Karlsson,
A two-piece radiation J. L. Kabcenell,
D.D.S.,
D.D.S.,
and Bjorn
Hedegard,
A. Kaiser,
Prosthodontic glossectomy
D.D.S.,
therapy surface mold
M.S.D.,
and Harold
D.D.S.,
Thomas
Vergo,
wax
B. Wise, D.D.S.
and speech rehabilitation
Frank R. Lauciello, Zimmerman, Ph.D.
Dr.Odont.
M.S.D.
Fitting cast gofd restorations with the aid of disclosing David
D.D.S.,
placed
after partial and complete
D.D.S.,
Norman
G. Schaaf,
D.D.S.,
and Robert
EMG, bite force, and elongation of the masseter muscle under isometric voluntary contractions and variations of vertical dimension Arturo
THE JOURNAL
Manns,
OF PROSTHETIC
Rodolfo
Miralles,
DENTISTRY
and Carmen
Palazzi
501
inclination
Hideaki Okane, D.D.S.,* Toru Yamashina, D.D.S.,** Hiromichi Tsuru, D. D. S., Ph.D. **** Hiroshima
University,
School of Dentistry,
Tooru Nagasawa, D.D.S.,
Ph.D.,***
and
Hiroshima, Japan
1 he orientation of the occlusal plane is an important clinical procedure in prosthodontic treatment for edentulous patients. Many dentists position the anterior end of the occlusal plane 1 to 3 mm below the resting upper lip and make the posterior end parallel to the ala-tragus line, According to surveys made by Levin and Sauer,’ Kawabe and associates,’ and Ukai and associates,” the concepts concerning the occlusal plane orientation differ considerably among dental schools in Japan. the United States, and Canada (Table I). Two important questions are whether the alatragus line is best and whether the inclination of the occlusal plane affects masticatory function. Sharry’ stated that the plane of orientation established on the ala-tragus line is not rigid, but can be altered for special reasons. Boucher and associates” pointed out that the ala-tragus plane is adequate for many patients and usually results in satisfactory dentures, but it certainly cannot be regarded as applicable to all patients. Kapur and Soman’ and Carey’ have shown that masticatory performance is influenced by the inclination of the occlusal plane. There have been no published reports regarding masticatory muscle activity and biting force with the occlusal plane placed at various inclinations. The purpose of the present study was to investigate the effect of anteroposterior inclination of the This investigation was supported in part by Scientific Research Grant No. A-977365 of the Japanese Ministry of Education. *Graduate Student, Department of Removable Prosthodontics. **Chief Staff Dentist, Department of Removable Prosthodontics.
***Associate Professor. Department of Removable tics. ****Professor, Department of Prosthodontics.
0022-3913/79/l
of the occlusal
Prosthodon-
10497 + 05$00.50/O 0 1979 The C. V. Mosby Co.
Table I. Methods of determining the occlusal plane: Results of surveys by Levin and Sauer’ and others’. 3 USA and Canada, 33 dental
schwls
Height of the
retromolar
Japan, 15
dental scbofs
12
pad
Ala-tragus line Esthetics Dividing the interarch space evenly
16
4 14 2 1
9 2
4
Uncertain Miscellaneous
1
occlusal plane on muscle activity during clenching and biting force and to estimate physiologically the applicability of the ala-tragus line. The integrated electromyographic activity and biting forces of patients were examined at three different anteroposterior inclinations of the occlusal plane at a constant vertical dimension of occlusion.
MATERIALS
AND METHODS
Four patients with complete dentures, three men and one woman, from 61 to 79 years of age, were selected. Three major criteria used in their selection were: (I) the patient must not have any physical disability which would interfere with the study; (2) the patient must have good denture-bearing tissues (Kapur’s’ scoring method was employed for this clinical screening examination); and (3) the patient must have a normal maxillomandibular relation. Autopolymerizing acrylic resin occlusion rims were made for each patient on dental stone casts made from silicone rubber impressions. The test bases were composed of resin baseplates and flat
THE JOURNAL
OF PROSTHETIC
DENTISTRY
497
ORANE
Fig. 1. Three different inclinations of the occlusal plane. y/k: Blocks used for the location of the occlusal plane were fixed on the occlusion rims.
resin occlusion rims (Fig. 1). The rims could be fixed on the baseplate and were used for locating the occlusal plane. The occlusal plane was changed in its anteroposterior inclination as follows. 1. The A occlusal plane was positioned about 2 mm below the resting upper lip anteriorly and made parallel to the ala-tragus line posteriorly. The alatragus line was drawn from the lowest point of the ala of the nose to the lower border of the external auditory meatus. 2. The B occlusal plane was inclined about 5 degrees anteriorly by raising it posteriorly. 3. The C occlusal plane was lowered about 5 degrees posteriorly. After the maxillomandibular relation was established, a chrome-cobalt plate, 2 mm in thickness, was attached on the occlusal plane of the maxillary occlusion rim with autopolymerizing acrylic resin.
ET AL
The plate was centered laterally and anteroposteriorly on the occlusal plane. A small depression was ground in the center of the inferior surface of the plate. Then the lower occlusion rim was eliminated to provide 4 mm clearance between the upper and lower occlusal planes. Another chrome-cobalt plate of the same thickness was attached on the mandibular base, and a central bearing point was set in the center of the plate. The tip of the point occluded in centric relation at the depression in the upper plate and constantly maintained the maxillomandibular relation, even when the inclination of the occlusal plane was changed (Fig. 2). The recordings were made under the following conditions: (1) maximum clenching with A, B, and C occlusal planes and (2) clenching at given forces (50%,30’S, and 10% of the magnitude of biting force in maximum clenching with A occlusal plane) with A, B, and C occlusal planes. During the recording each patient was seated in an upright position with his head against the head support and the Frankfort plane horizontal. In each of the conditions the subject was instructed to clench 10 times at an interval of 5 seconds at a signal from the instructor. The clenching had to be progressive and held for 2 seconds. After a series of 10 clenchings with one occlusal plane the subject was allowed to rest for 10 minutes, after which the other series was started with another occlusal plane. When asked to clench with prescribed force, the subject could check by watching the amount of force displayed on the monitor oscilloscope of the polygraph* (biophysical amplifier). The amount of muscle activity was expressed as integrated EMG activity. Nonpolarizing surface electrodes? were attached 30 mm apart on the skin over the bilateral masseter muscles and the anterior part of the temporal muscles. Electrical action potentials were amplified by the polygraph and recorded on data tapes. The recorded EMG signals were played back through an analog integrator* and recorded on oscillograph paper. The amount of integrated EMG activities for 1 second was measured on the holding stages of every 10 clenchings. The unit of measurement of the integrated EMG activity was expressed in microvolt-seconds. The biting force was obtained with a foil strain gauge which was placed in the center of the superior surface of the chrome-cobalt plate on the maxillary *Sanei Instrument Co., Tokyo, Japan. tNihon Kohden Kogyo Co., Tokyo, Japan.
NOVEMBER
19’79
VOLUME
42
NUMBER
5
ANTEROPOSTERIOR
INCLINATION
Table II. Biting clenching (kg)
OF OCCLUSAL
force during
500
15.8 2 27.9 f 20.1 2 33.0 * 24.2
1 2 3 4
Mean
B occhal plane
1.3 3.4 2.4 1.4
11.4 -c 25.2 + 18.7 _t 29.2 + 21.1
0.9 1.6 1.0 1.2
of muscle activity clenching (pV set)
Subject
449.4 rt 463.7 t 624.5 f 664.0 t 550.4
1 2 3 4
Mean
l
set/kg)*
Subject 1 2 3 4
Mean *Amount
B occlusal plane
14.3 7.1 8.8 17.2
Table IV. Efficiency (pV
10.8 k 23.9 f 14.3 t 23.8 I 18.2
0.8 1.3 1.4 1.5
340.6 IL 9.2 427.6 _C 6.3 596.0 + 5.0 632.9 -t 15.1 499.3
of biting -
l
C occlusal plane 433.4 + 413.7 i 570.8 i 619.1 + 509.3
17.6 4.2 6.3 5.5
force exertion -
IO x
30
BITING
FORCE
Fig. 3. The amount of total activity of four muscles per second during clenching at given forces.
muscle activity required to exert the biting force of 1 kg on the occlusal plane. The more this value decreased, the greater was the efficiency.); (4) the amount of total activity per second of four muscles during clenching at given forces with each occlusal plane.
RESULTS B
C
ucclusal plane
occlusal plane
28.6 16.6 31.1 20.1 24.1
29.9 17.0 31.9 21.7 25.1
40.1 17.3 39.9 26.0 30.8
force.
*San& Instrument Co., Tokyo, Japan. thstron Corp., Canton, Mass.
OF PROSTHETIC
*
50
occlusion rim and connected to a strain amplifier* and a polygraph. The biting force was recorded simultaneously with EMG recordings. The biting force calibration was made with Instron universal testing instruments.f The following measurements were made: (1) the maximum biting force on each occlusal plane; (2) the amount of total activity per second of four muscles during maximum clenching with each occlusal plane; (3) the efficiency of the biting force exertion (This suggested value was obtained by dividing (2) by (I), and showed the amount of
THE IOURNAL
plane
100
during
A occlusal plane
of muscle activity/biting
A-Ocelusal
g 200 9
l
A occlusal plane
O-O
I
C ocdusal plane
Table III. Amount maximum
pv.sec
maximum
A ocdusal plane
Subject
PLANE
DENTISTRY
Biting force during maximum clenching. In all subjects the highest magnitude of biting force was exerted upon the A occlusal plane, followed by the B occlusal plane and the C occlusa1 plane. The mean value of maximum biting force was 24.2 kg on the A plane, 21.1 kg on the B plane, and 18.2 kg on the C occlusal plane (Table II). The amount of muscle activity during clenching, The amount of total activity of four muscles per second was obtained by measuring the integrated EMG activity during maximum clenching. AI1 subjects showed almost the same amount of total activity for the three different occlusal planes (Table III). Efficiency of biting Force exertion. The amount of total activity was divided by the magnitude of biting force. The calculated value represented the efficiency of biting force exertion on the occlusal plane. Table IV shows that all subjects had the lowest scores with the A occlusal plane followed by the B occlusal plane and the C occlusal plane. This indicates that the biting force was exerted more efficiently on the A occlusal plane than on the 3 or C occlusal planes. Total activity. The amount of total activity was measured in clenching at various given forces (SO%,
OKANE ET AL
30%, and 10% of the magnitude of maximum biting force on the A occlusal plane). The amount of each activity at given forces is shown in Fig. 3. At any magnitude of biting force, the amount of muscle activity with the A occlusal plane was found to be the minimum, followed by those with the B occlusal plane and the C occlusal plane. This also showed that the biting force was exerted most efficiently on the A occlusal plane. DISCUSSION Many dentists have observed that the orientation of the occlusal plane may affect the denture function and that it is important to determine this orientation correctly in making comfortable dentures. Investigators”-‘;’ have suggested various concepts or methods for the orientation of the occlusal plane based on morphologic studies on natural and artificial dentitions and on clinical experiences. However, no one has shown an easy method for locating the occlusal plane correctly for every patient. This difficulty may be attributable to the ladk of physiologic knowledge of the occlusal plane orientation. Gehl”’ has suggested that the occlusal plane should be placed so that favorable leverage would be exerted. It is important to investigate the effect of the anteroposterior inclination of the occlusal plane on masticatory function. Therefore, biting force exertion, one of the important factors of masticatory function, was tested in this study. Biting force is a vector which is the sum of all jaw-closing muscle tensions. The direction of the vector is constant individually at a constant vertical dimension of occlusion. Under the same activity of jaw closing muscles, biting force is most efficient on the occlusal plane which intersects perpendicular to the direction of the vector of muscle action. Morphologic search for the direction of the vector is difficult. Therefore the efficiency of biting force exertion was measured in this study. The present results showed that in any magnitude of clenching, the biting force was exerted most efficiently on the occlusal plane which was made parallel to the ala-tragus line posteriorly. The conventional method with the ala-tragus line seems to be suitable for clinical use in patients who have good denture bearing tissues, normal maxillomandibular relation, and no functional disorders, In other patients further study is required, and the occlusal plane inclination may have to be altered for excellent denture function.
500
CONCLUSIONS With the experimental design of this study the following conclusions were reached. 1. Biting force during maximum clenching was the greatest when the occlusal plane was made parallel to the ala-tragus line. It decreased when the occlusal plane was inclined about 5 degrees anteriorly or about 5 degrees posteriorly. 2. The efficiency of biting force exertion during maximum clenching showed the best value when the occlusal plane was made parallel to the ala-tragus line. 3. Muscle activity during clenching at various given forces was least when the occlusal plane was made parallel to the ala-tragus line. The anteroposterior inclination of the occlusal plane tends to affect the biting force, and the method with the ala-tragus line seems to be the most reasonable for occlusal plane orientation. REFERENCES 1. L&n, B., and Sauer, J. L.: Results of a survey of complete denture procedures taught in American and Canadian dental schools. J PROSTHET DENT 22:171, 1969. 2. Kawabe, S., Aoki, H., and Reitz, P. V.: Examination into the questionnaire, “Results of a survey of complete denture procedures taught in American and Canadian dental schools.” Prac Prostbod 3:330, 1970. (Japanese) 3. Ukai, H., Yanagida, S., Katoh, Y., Nishiura, M., and Hayashi, T.: Examination into the questionnaire, “Results of a survey of complete denture procedures taught in Japanese dental schools,” Prac Prosthod 3:324, 1970. (Papanese) 4. Sharry, J. J.: Complete Denture Prosthodontics, ed 2. New York, 1968, McGraw-Hill Book Co., p 245. 5. Boucher, C. O., Hickey, J. C., and Zarb, G. A.: Prosthodontic Treatment for Edentulous Patients, ed 7. St. Louis, 1975, The C. V. Mosby Co., pp 218-220. 6. Kapur, K. K., and Soman, S.: The effect of denture factors on masticatory performance, Part III. The location of the food platforms. J PROSTHET DENT 15:451, 1965. 7. Carey, P. D.: Occlusal plane orientation and masticatory performance of complete dentures. J PROSTHET DENT 39:368, 1978. 8. Kapur, K. K.: A clinical evaluation of denture adhesives. J PROSTHET DENT l&550, 1967. 9. Augsburger, R. H.: Occlusal plane relation to facial type. J PROSTHET DENT 3:755, 1953. 10. Hartono, R.: The occlusal plane in relation to facial types. J PROSTHET DENT 17:549, 1967. 11. Ismail, Y. H., and Bowman, J. F.: Position of the occlusal plane in natural and artificial teeth. J PROSTHET DENT 20:407, 1968. 12. Aoki, H.: The various aspects of the imaginary occlusal plane and the plane determinant instruments. Pratt Prosthod 5:257, 1972. (in Japanese) 13. Uehara, J., Tsuta, A., Yoshioka, M., Kubota, Y., and Aoki,
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1979
VOLUME
42
NUMBER
5
ANTEROPOSTERIOR
INCLINATION
OF OCCLUSAL
PLANE
H.: A study of Camper’s plane by lateral cephalometrics. J Kanagawa Odont Sot 5: 11, 1970. (Japanese) 14. Itoh, I., and Nozaka, Y.: Studies of the relation between occlusal plane and Frankfort plane. Jap J Oral Biol 18~84, 1976. (Japanese) 15. Tsuru, H., Hiranuma, K., Nishiura, M., and Matsumoto, N.: Complete denture technique, ed 1. Tokyo, 1974, Ishiyaku Shuppan Co., pp 39-41. (Japanese)
16. Gehl, D. H.: Vertical dimension, jaw relation records and occlusion. Dent Clin North Am July 1960, pp 321-332. Rqmts request to: DR. HIDEAKI OKANE HIROSHIMA
SCHOOL.OF DENTISTRY
UNIVERSITY
KASUMI l-2-3 HIROSHIMA, JAPAN
ARTICLES TO APPEAR IN FUTURE ISSUES Influence Hueyching
of tooth proprioception Ghi, B.D.S.,
on speech articulation
M.S., and Glen P. McGivney,
D.D.S.
Prerestorative therapy using a modified Hawley splint Lynne
Heckert,
D.D.S.
The fracture strength of amalgam overlying
base materials
Abbas A. Hormati,
D.D.S.,
D.D.S.,
M.S.,
and James L. Fuller,
M.S.
Surgical nasal prosthesis PhiIlip
E. Hutcheson,
D.D.S.,
M.S.D.,
and Ariyadasa
Udagama,
D.D.S.,
M.S.D.
Mandibular movements of young adults recorded by intraurally light-emitting diodes Torsten
Jemt,
D.D.S.,
Stig Karlsson,
A two-piece radiation J. L. Kabcenell,
D.D.S.,
D.D.S.,
and Bjorn
Hedegard,
A. Kaiser,
Prosthodontic glossectomy
D.D.S.,
therapy surface mold
M.S.D.,
and Harold
D.D.S.,
Thomas
Vergo,
wax
B. Wise, D.D.S.
and speech rehabilitation
Frank R. Lauciello, Zimmerman, Ph.D.
Dr.Odont.
M.S.D.
Fitting cast gofd restorations with the aid of disclosing David
D.D.S.,
placed
after partial and complete
D.D.S.,
Norman
G. Schaaf,
D.D.S.,
and Robert
EMG, bite force, and elongation of the masseter muscle under isometric voluntary contractions and variations of vertical dimension Arturo
THE JOURNAL
Manns,
OF PROSTHETIC
Rodolfo
Miralles,
DENTISTRY
and Carmen
Palazzi
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