- Email: [email protected]
Effects of intense chewing on some parameters of masticatory function
Effects of intense chewing masticatory function
on some
Mihail G. Tzakis, DDS, OdontDr,a Stig Karlsson, Gunnar E. Carlsson, LDS, OdontDrC
parameters
of
LDS, OdontDr,b
University of Gateborg, Faculty of Odontology, Giiteborg, Sweden This study recorded the influence of 30 minutes of intense chewing on the masticatory function in 17 healthy subjects. Functional recordings of mandibular movements and velocity, measurements of masticatory efficiency, maximal occlusal force, and occlusal force endurance time were performed before and after functional stimulation and finally in a 2- to 5-day follow-up registration. After intense chewing, a substantially decreased masticatory cycle and occlusal level phase duration were recorded. No major mandibular displacements or changes in velocity were recorded. Masticatory efficiency and maximal occlusal force in the incisal region diminished after 30 minutes of intense chewing. Occlusal force endurance time was also lowered after intense chewing. The measurements were close to their original values at the follow-up. Intense chewing had various short-term effects on masticatory function, including a significant reduction of masticatory efficiency, maximal occlusal force, occlusal force endurance, and masticatory cycle duration. (J PROSTHET DENT 1992;67:405-9.)
M
asticatory function is generated by rhythmic contraction of the masticatory muscles.However, several other parameters are important such as the number of teeth, number and quality of occlusal contacts, and the health of the masticatory system.This function is difficult to examine objectively with one method becauseit is also subject to individual variations. Chewing is an alternating rhythm of isotonic and isometric contractions governed by a central pattern generator in the brain stem.l, 2 Masticatory muscleshave the capacity to contract during daily use of the stomatognathic system and maintain muscletone in the mandibular rest position. Oral function normally does not demandexcessiveenergy or causeadversesymptomsin a healthy stomatognathic system.3However, pain appears in healthy subjectsafter hyperactivity of the masticatory muscles (expressed as experimental teeth clenching at maximal occlusal force) probably becauseof fatigue, as suggested by Christensen.4-6 Although the etiology of fatigue is unclear, one explanation may be impaired blood Supported by grants from the Kungl. och Hvitfeldtska Stipendieinriittningen, Goteborg, and the Faculty of Odontology, University of Gateborg. aLecturer, Department of Prosthodontics, University of Athens, Faculty of Dentistry. bAssociate Professor, Department of Prosthetic Dentistry, University of Gateborg, Faculty of Odontology. CProfessor and Chairman, Department of Prosthetic Dentistry, University of Giiteborg, Faculty of Odontology. 10/l/32996
THE JOURNAL
OF PROSTHETIC
DENTISTRY
circulation within the muscle7becauseit effects an aerobic to anaerobic metabolic change. This alteration is characterized by lower efficiency and elevated metabolites for a specific mechanical pr0cedure.s However, Christensen’s results were not basedon a method representative of normal function. The stomatognathic system may react differently in normal chewing,causingfatigue of the masticatory musclesand concomitantly stimulating the structures active during mastication. How does the stomatognathic system react to a functional stimulation suchaschewing training or chewing exercises?It has been suggestedthat intense chewing has variable effects on the function of the stomatognathic system and, when extended for 30 minutes, increasesthe interocclusal rest space9and diminishesmasticatory efficiency.l” It has alsobeen suggestedthat changesin the threshold of occlusalperception occur after intense chewing for 30 minutes.l’ It is suspect that stimulation generated by sensory input from proprioceptors in the periodontium musclesand joints of the oral cavity may have an influence on mastication, so it would be interesting to examine the effects on governed mandibular movements. This study reports the effects of intense chewing on mandibular movements with respect to the duration of a masticatory cycle, mandibular velocity, displacement in three dimensions(including the angleof opening and closing strokes),masticatory efficiency, maximal occlusalforce, and the endurance time on a submaximal occlusal force level.
405
TZAKIS,
MATERIAL
AND
METHODS
The test subjects were randomly selected from men and women who were dental students or members of the staff at the Department of Prosthetic Dentistry, University of Giiteborg, Sweden. They were thoroughly informed of the experiments and participated voluntarily. The participants were in good health and had a complete natural dentition without mandibular dysfunction. The chewing gum selected for this experiment, because of its hardness, was the resin from the bark of the mastiche tree grown on the Greek island of Chiosg Registration
methods
A clinical examination of the masticatory system was performed for the test subjects by the same investigator. This examination included palpation of the muscles and the TM joints, recording of joint sounds for clicking/crepitation, locking, pain on movement of the mandible, deviation on opening and closing movements (including protrusion), and measurement of the mandibular movements.12 The interobserver variability has been considered acceptable by several authors.13s l4 Subjects presenting signs of dysfunction were excluded from the experiments. Seventeen participants were selected after this examination, nine men and eight women with a mean age of 28 years, SD 6.9, in the age range of 21 to 45 years. An optoelectronic device, intended for three-dimensional recording, was used for monitoring the mandibular movements (Selspot Company, Partille, Sweden) as detailed previously.15 The system consisted of three basic units, light-emitting diodes (LED) with driver electronics, a position-sensitive detector in a camera, and a computer with a camera interface. During recording of mandibular movements, the LEDs were attached to the test subject in a specific manner controlled by the computer, and a recorded masticatory sequence then displayed in three planes-frontal, horizontal, and sagittal. Head movements were compensated for by a three-LED coordinate system attached to the spectacle frames of the test subject. Duplicate recordings of a masticatory sequence were made from start to swallowing during chewing of an almond with the test person seated upright in a dental chair. A single masticatory cycle was divided for analysis into three separate phases: mandibular opening (OP), mandibular closing (CP), and the occlusal level phase (OLP). OLP is defined as any position in which the mandible is located, from maximal intercupation to a level 0.5 mm inferior, and the OP and CP phases started and ended at this position. A quantitative analysis of the following variables was performed: (1) the cycle duration (TCD), including subdivisions-0P, CP, and OLP; (2) the velocities in the OP and CP phases; (3) the three-dimensional mandibular spatial displacement in the OP and CP phases; and (4) the angle
406
KARLSSON.
AND
CARLSSON
to the sagittal plane when the mandible approaches the intercuspal position. Masticatory efficiency was tested with a methodgr I6 that used almonds and a sieve combined with coffee filters. Each almond was dried under the same conditions in an oven. The mean weight of the almonds was 1 gm. The coffee filter and the almonds were weighed to the nearest 0.001 gm. The sieve had meshes of 0.7 mm and was made to fit securely on the surface of the filter holder. Each test subject was instructed to chew an almond for ten seconds and expectorate into the sieve. A glass of water was then given to the subject to rinse the mouth and expectorate again into the sieve. This procedure was repeated twice. The sieve was then rinsed under water to collect the particles that did not pass through the sieve meshes. These particles were collected into the coffee filter by turning the sieve upside down into the filter holder and using repeated rinses of water. The filter was dried for 24 hours at room temperature (24’ C) and then weighed so the weight of the retained pieces of almond could be calculated. The masticatory efficiency (ME) was calculated from the weight of the almond before (A) and the weight of the collected pieces after the test (B) with the formula: ME = 100 (A - B)/A
ME equalsthe percentageof the food reducedto passthe sieve. The occlusalforce enduranceand maximal occlusalforce were estimated by use of a bite fork with strain guage transducerscoatedwith soft rubber (Dentoforce 2, ITL AB, Sollentuna, Sweden) and attached to metal beams, On loading of the bite fork, the occlusalforce wasregisteredon a digital display (Multimeter 4055, ITL AB). The digital display wasprovided with various options that could continuously display in newton’s (N) the force exerted on the bite fork and the minimal and the maximal occlusalforce during a measurement.The device wasprovided with filters to increasethe quality of the output signal and measure forces of up to 1000N. Calibration of the apparatus was performed automatically before each measurement, and adjustmentswere made if necessary.The test was accomplishedwith the bite fork in the region of the central incisors.This resulted in an 11mm increaseof the interocclusaldistance. The test subjectswere askedto occludeas hard as possible for estimation of the maximal occlusal force. To measurethe occlusal force endurance time, the subjectswere askedto occlude on the opposingcentral incisors,at the 150 N level, and the time in secondswas recorded in a manner similar to a previous study.17 Experimental
procedure
A recording sessionincluded the following registration: (1) masticatory efficiency measurement(ME), (2) mandibular displacement and velocity registration, (3) occlusal
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1992
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MASTICATORY
Table
I.
FCNCTION
Masticatory
cycle duration (ms) before (l), after 30 min of intense chewing (2), and at follow-up
registration
(3)
Before
(1) SD
Mean
Opening Closing
phase phase
Occlusal level Total duration Means
and standard
deviations
After
(2)
Follow-up
(3)
Mean
SD
Mean
SD
P NS
163
45
165
38
165
35
232
78
203
48
211
55
191
50
150
36
171
50
587
101
518
66
548
82
of significance
at differences
(SD)
for 17 test persons;
p denotes
level
between
NS 1> 1 > 2 (0.004), three
2 (0.001) 3 > 2 (0.02)
registrations.
II. Mandibular displacement (mm) and opening and closing angles (1) before (l), after 30 min of intense chewing (2) and at follow-up registration (3)
Table
Before
(1)
Mean
Opening distance Closing distance Max lateral Max vertical Opening angle Closing angle Means
and
standard
deviations
(SD)
After SD
PROSTHETIC
SD
P
4.0
13.8
3.4
13.5
4.2
3.9
13.2
3.2
12.9
3.9
NS
5.8
1.3
5.7
1.6
5.6
1.4
NS
NS
12.6
3.7
12.5
2.9
12.2
3.1
NS
67.2
9.6
68.6
10.9
68.6
10.2
NS
55.1
12.7
55.1
10.5
54.4
13.3
NS
for 17 test persons;
p denotes
level
The total duration of the masticatory cycle diminished substantially after 30 minutes of intense chewing (Table I). This decrease was due to a significant reduction of the duration for the occlusal level phase (p < 0.001) and the closing phase, but the opening phase was stable. Mandibular displacement and velocity did not change significantly. The means of all measurements of mandibular displacement and the angle in relation to the sagittal plain were similar at all three registrations (Table II). After the intense chewing period, mandibular velocity recorded higher means compared with sessions 1 and 3. However,
OF
Mean
(3)
13.7 13.1
RESULTS
JOURNAL
SD
Mean
force endurance test (ET), and (4) maximal occlusal force performance (BF). Each participant was examined according to the following schedule: After the first recording session (l), 1 g m of Chios chewing gum was given to the test subjects and they were instructed to chew intensely for 30 minutes. Immediately after the intense chewing, the registrations were repeated (2). Finally, 2 to 5 days later, a third, follow-up registration was performed (3). The means, the standard deviations of the means, and the standard error were computed to evaluate the results. A paired Student t-test was calculated to determine differences between the three recording sessions, before and after the 30 minutes of intense chewing and at the follow-up.
THE
Follow-up
(2)
DENTISTRY
of significance
of differences
between
three
registrations.
none of the differences between the registrations was statistically significant (Table III). ME decreased significantly (p < 0.0001) after the intense chewing. The mean ME was 77 % before and 71% after the intense chewing. At the follow-up, ME was 79 % , which was a significant recovery in comparison with ME2 (p < 0.0001). The difference betweenME3 and ME1 wasalsosignificant (p < 0.05), (ME3 > ME1 > ME2 < ME3) (Fig. 1, A). Maximal occlusalforce (BF) decreasedsignificantly after intense chewing (Fig. 1, B). The mean BF was 392 N before (1) and 345 N after (2) intense chewing (p < 0.05). The meanvalue at the follow-up registration (3) was412N, which differed significantly from the secondregistration (p < 0.05), (BF3 = BFl > BF2 < BF3). The endurancetime (ET) averaged60secondsbefore the intensechewingand decreasedsignificantly (p < 0.0001)to 33 secondsafter the intensechewing (Fig. 1, C). At the follow-up registration (3), the ET elevated significantly (p < 0.0001) to the baseline value of 59 seconds (ET 3 = ET1 > ET2 < ET3).
DISCUSSION Various clinical methods have been proposedto study masticatory function from different view points. The main problem has been in achieving objective clinical methods for monitoring function of the stomatognathic system. Mastication is a complex motor activity influenced by pe-
407
TZAKIS,
MASTICATORY
% 100
KARLSSON,
AND
CARLSSON
EFFICIENCY
901
before
A MAXIMAL
N
(1)
after
(2)
set
BITE FORCE
-
follow-up
BITE FORCE ENDURANCE ON THE LEVEL OF 150 N
80
400
70
350
60
(3)
300
; z
2.50
50 4o
200
30
150
24l
loo
10
so
0
0
before
(1)
after
follow-up
(2)
(3)
before
(1)
after
follow-up
(2)
C
B
(3)
Fig. 1. Mean and standard error of mean measurements before and after chewing intensely for 30 minutes on 1 gm of Chios chewing-gum at follow-up registration. A, Percentage distribution of masticatoryefficiency (ME) that decreased significantly (p < 0.0001) after 30 minutes of intense chewing (ME 3 > ME 1 > ME 2 < ME 3). B, Maximal occlusal force at incisal area (BF) decreased significantly after intense chewing (p < 0.05), (BF 3 = BF 1 > BF 2 < BF 3). C, Endurance time in seconds on 150 N occlusal force level (ET) decreased significantly after intense chewing (p < O.OOOl), (ET 3 = ET 1 > ET 2 < ET 3). Table
intense
III. Mandibular velocity (mm/set) at incisor point in opening chewing (2), and at follow-up registration (3) Before
(1)
Mean
Maximal opening Maximal closing Mean opening Mean closing Means and standard
deviations
153.9 142.1 89.3 82.4 (SD)
for 17 test persons;
After
(2)
Follow-up
(3)
SD
Mean
SD
Mean
SD
P
33.2 38.2 20.5 21.6
161.8 151.8 95.3 91.2
40.5 37.9 24.8 23.4
156.5 148.3 90.9 88.6
42.0 37.0 27.5 23.2
NS
p denotes
level
ripheral and central inputs. The many parameters that influence oral function and the multidimensional character of mastication might explain the lack of objective methods for evaluating mastication. The methods in this study are considered acceptable for evaluation if compared with previous results.lO, 15, l7 Previous studies indicated that masticatory mandibular displacement and velocity is affected by different experimental foods.15 Thirty minutes of intense chewing that might have caused fatigue to the masticatory muscles did
408
and closing phases before (l), after 30 min of
of significance
of differences
between
three
NS NS NS
registrations.
not influence these parameters, which were stable with the same test food. Masticatory mandibular displacement was not affected, but the duration of the masticatory cycle and the occlusal phase of the cycle diminished significantly after the intense chewing. The difference in the masticatory cycle duration was consistent with a previous study in which the frequency of the masticatory cycles increased after the same training intervaLg The stability of the opening movement can be attributed to a ballistic character, governed by central commands, in contrast to the closing
MARCH
1992
VOLUME
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NUMBER
3
MASTICATORY
FUNCTION
movement that is influenced by feedback. However, it is difficult to explain the difference in both masticatory cycle duration and the occlusal phase of the cycle between the first and third registration. This difference could be the effect of learning or the different times of the day for the recordings. This experimental schedule included the measurement of masticatory efficiency before the registration of the mandibular displacement and velocity, and incorporated at least a 2-minute delay between the completion of the intense chewing and the registration of the mandibular displacement and velocity. The proprioceptive mechanism influenced by intense chewingll, la recovers rather easily.lg Recovery of the receptors and a modified sensory feedback also affects the rhythmic output from the central pattern generator similar to the preexisting condition, resulting in a consistent chewing pattern. Masticatory efficiency was strongly influenced by the intense chewing exercises and corroborated a previous study.8 The masticatory efficiency in this study (77 % ) was higher than in the previous study (70 % ), although they were both performed on healthy dentate subjects. Individual biologic variations may partly explain this difference, but the two studies comprised different age groups and this is critical because the natural wear of the dentition may be responsible for improving masticatory efficiency with age.20 The test subjects in this study had a mean age of 28 years compared with 23 years, or 15% higher than in the previous study. Endurance tests should be performed on a submaximal occlusal force level and preferably on a level close to half of the maximal voluntary occlusal force.17 The 150 N occlusal force level for the endurance time test was close to that in this study. The results were in agreement with previous studies showing that the endurance times were stable on the 50% level of maximal voluntary occlusal force (Fig. 1, C). Maximal occlusal force and occlusal force endurance diminished substantially after intense chewing, probably because of muscle fatigue, a complex phenomenon. Kroon21 reported that the condition of the muscles can be described by the EMG signal that is different in a fatigued muscle. He also reported that total recovery from fatigue was incomplete 24 hours after the fatigue stimulation.21 The third follow-up registration in this study was performed at least two days after the stimulation to the masticatory system, and no differences were observed related to maximal occlusal force and occlusal force endurance between the first and the third follow-up registrations (Fig. 1, B and C). CONCLUSIONS Functional stimulation of the stomatognathic system with 30 minutes of intense chewing created a short-term effect on masticatory function. This stimulation signifi-
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
cantly reduced the occlusal level phase and the duration of the masticatory cycle, masticatory efficiency, maximal occlusal force, and occlusal force endurance. REFERENCES central mechanisms and reAex 1. Grillner S. Locomotion in vertebrates; interaction. Physiol Rev 1971;55:247-304. Y, Kubo Y, Nozaki S, Tagasi M. Cortically induced masti2. Nakamura catory rhythm and its modification by tonic peripheral inputs in immobilized cats. Bull Tokyo Med Dent Univ 1976;23:101-7. In: Mohl NO, Zarb GA, Carlsson GE, 3. Rugh DJ, Smith RB. Mastication. Rugh J, eds. A textbook of occlusion. Chicago: Quintessence Publ, 1988,143-52. 4. Christensen LV. Facial pain and internal pressure of masseter muscle in experimental bruxism in man. Archs Oral Biol1971;16:1021-31. LV. Jaw muscle fatigue and pains induced by experimen5. Christensen tal tooth clenching: a review. J Oral Rahabil 1981;8:27-36. 6. Christensen LV. Experimental teeth clenching in man [Thesis]. Swed Dent J 1989,(Suppl 60):29-48. 7. Strijm D. Masseter muscle performance. Signilicance of structure and metabolism [Thesis]. Swed Dent J 199O$Suppl67):51-2. a. Silvestri RA, Cohen NS, Connoly JR. Muscle physiology during functional activities and parafunctional habits. J PROSTHET DENT 1960;44:64-7. 9. Tzakis MG,
10. 11.
12.
13.
14.
15.
16.
17.
18. 19.
20.
21.
Carlsson GE, Kiliaridis S. Effect of chewing training on mandibular postural position. J Oral Rehabil 1989;6:503-8. Tzakis MG, Kiliaridis S, Carlsson GE. Effect of chewing training on masticatory efficiency. Acta Odontol Stand 1989;47:355-60. Kiliaridis S, Tzakis MG, Carlsson GE. Short-term and long-term effects of chewing training on the occlusal perception of thickness. Stand J Dent Res 1990;98:159-66. Carlsson GE, Helkiio M. Funktionell undersokning av tuggapparaten. In: Holst J J et al, eds. Nordisk Klinisk Odontologi. Copenhagen: A/S Forlaget for faglitteratur, 1972:8-l;l-21. Carlsson GE, Egermark-Eriksson I, Magnusson T. Intra- and interobserver variation in functional examination of the masticatory system. Swed Dent J 1980;4:187-94. Kopp S, Wenneberg B. Intra- and interobserver variability in the assessment of signs of disorder in the stomatognathic system. Swed Dent J 1983;7:239-46. Karlsson S, Carlsson GE. Recording of masticatory mandibular movements and velocity by an optoelectronic method. Int J Prosthodont 1989;2:490-6. Tzakis MG, Linden B, Jemt T: Oral function in patients treated with bridges on Branemark osseointegrated implants in the partially edentulous jaw. A pilot study. Int J Oral Maxillofac Implants 1990;5:107-II. Dahlstriim L, Tzakis MG, Haraldson T. Endurance tests of the masticatory system on different bite force levels. Stand J Dent Res 1988;96:137-42. Gwall B, MGller E. Oral tactile sensibility during chewing and biting. Odont Rev 1974;25:327-46. De Laat A. Masseteric reflexes and their relationship towards occlusion and temporomandibular joint dysfunction [Thesis]. Leuven: Catholic University of Leuven, 1985. Carlsson GE. Bite force and chewing efficiency. In: Kawamura Y, ed. Front oral physiol: physiology of mastication. Baael: Karger, 1974; vol 1, 265-92. Kroon GW. Muscle fatigue. An experimental and clinical electromyographic study with emphasis on the masticatory system [Thesis]. Amsterdam: ACTA University of Amsterdam, 1990.
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to:
DR. MIHAIL G. TZAKIS FACULTY OF DENTISTRY UNIVEFWTV OF ATHENS 2 THIVON STR., GOUDI 11527 ATHENS GREECE
409
on some
Mihail G. Tzakis, DDS, OdontDr,a Stig Karlsson, Gunnar E. Carlsson, LDS, OdontDrC
parameters
of
LDS, OdontDr,b
University of Gateborg, Faculty of Odontology, Giiteborg, Sweden This study recorded the influence of 30 minutes of intense chewing on the masticatory function in 17 healthy subjects. Functional recordings of mandibular movements and velocity, measurements of masticatory efficiency, maximal occlusal force, and occlusal force endurance time were performed before and after functional stimulation and finally in a 2- to 5-day follow-up registration. After intense chewing, a substantially decreased masticatory cycle and occlusal level phase duration were recorded. No major mandibular displacements or changes in velocity were recorded. Masticatory efficiency and maximal occlusal force in the incisal region diminished after 30 minutes of intense chewing. Occlusal force endurance time was also lowered after intense chewing. The measurements were close to their original values at the follow-up. Intense chewing had various short-term effects on masticatory function, including a significant reduction of masticatory efficiency, maximal occlusal force, occlusal force endurance, and masticatory cycle duration. (J PROSTHET DENT 1992;67:405-9.)
M
asticatory function is generated by rhythmic contraction of the masticatory muscles.However, several other parameters are important such as the number of teeth, number and quality of occlusal contacts, and the health of the masticatory system.This function is difficult to examine objectively with one method becauseit is also subject to individual variations. Chewing is an alternating rhythm of isotonic and isometric contractions governed by a central pattern generator in the brain stem.l, 2 Masticatory muscleshave the capacity to contract during daily use of the stomatognathic system and maintain muscletone in the mandibular rest position. Oral function normally does not demandexcessiveenergy or causeadversesymptomsin a healthy stomatognathic system.3However, pain appears in healthy subjectsafter hyperactivity of the masticatory muscles (expressed as experimental teeth clenching at maximal occlusal force) probably becauseof fatigue, as suggested by Christensen.4-6 Although the etiology of fatigue is unclear, one explanation may be impaired blood Supported by grants from the Kungl. och Hvitfeldtska Stipendieinriittningen, Goteborg, and the Faculty of Odontology, University of Gateborg. aLecturer, Department of Prosthodontics, University of Athens, Faculty of Dentistry. bAssociate Professor, Department of Prosthetic Dentistry, University of Gateborg, Faculty of Odontology. CProfessor and Chairman, Department of Prosthetic Dentistry, University of Giiteborg, Faculty of Odontology. 10/l/32996
THE JOURNAL
OF PROSTHETIC
DENTISTRY
circulation within the muscle7becauseit effects an aerobic to anaerobic metabolic change. This alteration is characterized by lower efficiency and elevated metabolites for a specific mechanical pr0cedure.s However, Christensen’s results were not basedon a method representative of normal function. The stomatognathic system may react differently in normal chewing,causingfatigue of the masticatory musclesand concomitantly stimulating the structures active during mastication. How does the stomatognathic system react to a functional stimulation suchaschewing training or chewing exercises?It has been suggestedthat intense chewing has variable effects on the function of the stomatognathic system and, when extended for 30 minutes, increasesthe interocclusal rest space9and diminishesmasticatory efficiency.l” It has alsobeen suggestedthat changesin the threshold of occlusalperception occur after intense chewing for 30 minutes.l’ It is suspect that stimulation generated by sensory input from proprioceptors in the periodontium musclesand joints of the oral cavity may have an influence on mastication, so it would be interesting to examine the effects on governed mandibular movements. This study reports the effects of intense chewing on mandibular movements with respect to the duration of a masticatory cycle, mandibular velocity, displacement in three dimensions(including the angleof opening and closing strokes),masticatory efficiency, maximal occlusalforce, and the endurance time on a submaximal occlusal force level.
405
TZAKIS,
MATERIAL
AND
METHODS
The test subjects were randomly selected from men and women who were dental students or members of the staff at the Department of Prosthetic Dentistry, University of Giiteborg, Sweden. They were thoroughly informed of the experiments and participated voluntarily. The participants were in good health and had a complete natural dentition without mandibular dysfunction. The chewing gum selected for this experiment, because of its hardness, was the resin from the bark of the mastiche tree grown on the Greek island of Chiosg Registration
methods
A clinical examination of the masticatory system was performed for the test subjects by the same investigator. This examination included palpation of the muscles and the TM joints, recording of joint sounds for clicking/crepitation, locking, pain on movement of the mandible, deviation on opening and closing movements (including protrusion), and measurement of the mandibular movements.12 The interobserver variability has been considered acceptable by several authors.13s l4 Subjects presenting signs of dysfunction were excluded from the experiments. Seventeen participants were selected after this examination, nine men and eight women with a mean age of 28 years, SD 6.9, in the age range of 21 to 45 years. An optoelectronic device, intended for three-dimensional recording, was used for monitoring the mandibular movements (Selspot Company, Partille, Sweden) as detailed previously.15 The system consisted of three basic units, light-emitting diodes (LED) with driver electronics, a position-sensitive detector in a camera, and a computer with a camera interface. During recording of mandibular movements, the LEDs were attached to the test subject in a specific manner controlled by the computer, and a recorded masticatory sequence then displayed in three planes-frontal, horizontal, and sagittal. Head movements were compensated for by a three-LED coordinate system attached to the spectacle frames of the test subject. Duplicate recordings of a masticatory sequence were made from start to swallowing during chewing of an almond with the test person seated upright in a dental chair. A single masticatory cycle was divided for analysis into three separate phases: mandibular opening (OP), mandibular closing (CP), and the occlusal level phase (OLP). OLP is defined as any position in which the mandible is located, from maximal intercupation to a level 0.5 mm inferior, and the OP and CP phases started and ended at this position. A quantitative analysis of the following variables was performed: (1) the cycle duration (TCD), including subdivisions-0P, CP, and OLP; (2) the velocities in the OP and CP phases; (3) the three-dimensional mandibular spatial displacement in the OP and CP phases; and (4) the angle
406
KARLSSON.
AND
CARLSSON
to the sagittal plane when the mandible approaches the intercuspal position. Masticatory efficiency was tested with a methodgr I6 that used almonds and a sieve combined with coffee filters. Each almond was dried under the same conditions in an oven. The mean weight of the almonds was 1 gm. The coffee filter and the almonds were weighed to the nearest 0.001 gm. The sieve had meshes of 0.7 mm and was made to fit securely on the surface of the filter holder. Each test subject was instructed to chew an almond for ten seconds and expectorate into the sieve. A glass of water was then given to the subject to rinse the mouth and expectorate again into the sieve. This procedure was repeated twice. The sieve was then rinsed under water to collect the particles that did not pass through the sieve meshes. These particles were collected into the coffee filter by turning the sieve upside down into the filter holder and using repeated rinses of water. The filter was dried for 24 hours at room temperature (24’ C) and then weighed so the weight of the retained pieces of almond could be calculated. The masticatory efficiency (ME) was calculated from the weight of the almond before (A) and the weight of the collected pieces after the test (B) with the formula: ME = 100 (A - B)/A
ME equalsthe percentageof the food reducedto passthe sieve. The occlusalforce enduranceand maximal occlusalforce were estimated by use of a bite fork with strain guage transducerscoatedwith soft rubber (Dentoforce 2, ITL AB, Sollentuna, Sweden) and attached to metal beams, On loading of the bite fork, the occlusalforce wasregisteredon a digital display (Multimeter 4055, ITL AB). The digital display wasprovided with various options that could continuously display in newton’s (N) the force exerted on the bite fork and the minimal and the maximal occlusalforce during a measurement.The device wasprovided with filters to increasethe quality of the output signal and measure forces of up to 1000N. Calibration of the apparatus was performed automatically before each measurement, and adjustmentswere made if necessary.The test was accomplishedwith the bite fork in the region of the central incisors.This resulted in an 11mm increaseof the interocclusaldistance. The test subjectswere askedto occludeas hard as possible for estimation of the maximal occlusal force. To measurethe occlusal force endurance time, the subjectswere askedto occlude on the opposingcentral incisors,at the 150 N level, and the time in secondswas recorded in a manner similar to a previous study.17 Experimental
procedure
A recording sessionincluded the following registration: (1) masticatory efficiency measurement(ME), (2) mandibular displacement and velocity registration, (3) occlusal
MARCH
1992
VOLUME
67
NUMBER
3
MASTICATORY
Table
I.
FCNCTION
Masticatory
cycle duration (ms) before (l), after 30 min of intense chewing (2), and at follow-up
registration
(3)
Before
(1) SD
Mean
Opening Closing
phase phase
Occlusal level Total duration Means
and standard
deviations
After
(2)
Follow-up
(3)
Mean
SD
Mean
SD
P NS
163
45
165
38
165
35
232
78
203
48
211
55
191
50
150
36
171
50
587
101
518
66
548
82
of significance
at differences
(SD)
for 17 test persons;
p denotes
level
between
NS 1> 1 > 2 (0.004), three
2 (0.001) 3 > 2 (0.02)
registrations.
II. Mandibular displacement (mm) and opening and closing angles (1) before (l), after 30 min of intense chewing (2) and at follow-up registration (3)
Table
Before
(1)
Mean
Opening distance Closing distance Max lateral Max vertical Opening angle Closing angle Means
and
standard
deviations
(SD)
After SD
PROSTHETIC
SD
P
4.0
13.8
3.4
13.5
4.2
3.9
13.2
3.2
12.9
3.9
NS
5.8
1.3
5.7
1.6
5.6
1.4
NS
NS
12.6
3.7
12.5
2.9
12.2
3.1
NS
67.2
9.6
68.6
10.9
68.6
10.2
NS
55.1
12.7
55.1
10.5
54.4
13.3
NS
for 17 test persons;
p denotes
level
The total duration of the masticatory cycle diminished substantially after 30 minutes of intense chewing (Table I). This decrease was due to a significant reduction of the duration for the occlusal level phase (p < 0.001) and the closing phase, but the opening phase was stable. Mandibular displacement and velocity did not change significantly. The means of all measurements of mandibular displacement and the angle in relation to the sagittal plain were similar at all three registrations (Table II). After the intense chewing period, mandibular velocity recorded higher means compared with sessions 1 and 3. However,
OF
Mean
(3)
13.7 13.1
RESULTS
JOURNAL
SD
Mean
force endurance test (ET), and (4) maximal occlusal force performance (BF). Each participant was examined according to the following schedule: After the first recording session (l), 1 g m of Chios chewing gum was given to the test subjects and they were instructed to chew intensely for 30 minutes. Immediately after the intense chewing, the registrations were repeated (2). Finally, 2 to 5 days later, a third, follow-up registration was performed (3). The means, the standard deviations of the means, and the standard error were computed to evaluate the results. A paired Student t-test was calculated to determine differences between the three recording sessions, before and after the 30 minutes of intense chewing and at the follow-up.
THE
Follow-up
(2)
DENTISTRY
of significance
of differences
between
three
registrations.
none of the differences between the registrations was statistically significant (Table III). ME decreased significantly (p < 0.0001) after the intense chewing. The mean ME was 77 % before and 71% after the intense chewing. At the follow-up, ME was 79 % , which was a significant recovery in comparison with ME2 (p < 0.0001). The difference betweenME3 and ME1 wasalsosignificant (p < 0.05), (ME3 > ME1 > ME2 < ME3) (Fig. 1, A). Maximal occlusalforce (BF) decreasedsignificantly after intense chewing (Fig. 1, B). The mean BF was 392 N before (1) and 345 N after (2) intense chewing (p < 0.05). The meanvalue at the follow-up registration (3) was412N, which differed significantly from the secondregistration (p < 0.05), (BF3 = BFl > BF2 < BF3). The endurancetime (ET) averaged60secondsbefore the intensechewingand decreasedsignificantly (p < 0.0001)to 33 secondsafter the intensechewing (Fig. 1, C). At the follow-up registration (3), the ET elevated significantly (p < 0.0001) to the baseline value of 59 seconds (ET 3 = ET1 > ET2 < ET3).
DISCUSSION Various clinical methods have been proposedto study masticatory function from different view points. The main problem has been in achieving objective clinical methods for monitoring function of the stomatognathic system. Mastication is a complex motor activity influenced by pe-
407
TZAKIS,
MASTICATORY
% 100
KARLSSON,
AND
CARLSSON
EFFICIENCY
901
before
A MAXIMAL
N
(1)
after
(2)
set
BITE FORCE
-
follow-up
BITE FORCE ENDURANCE ON THE LEVEL OF 150 N
80
400
70
350
60
(3)
300
; z
2.50
50 4o
200
30
150
24l
loo
10
so
0
0
before
(1)
after
follow-up
(2)
(3)
before
(1)
after
follow-up
(2)
C
B
(3)
Fig. 1. Mean and standard error of mean measurements before and after chewing intensely for 30 minutes on 1 gm of Chios chewing-gum at follow-up registration. A, Percentage distribution of masticatoryefficiency (ME) that decreased significantly (p < 0.0001) after 30 minutes of intense chewing (ME 3 > ME 1 > ME 2 < ME 3). B, Maximal occlusal force at incisal area (BF) decreased significantly after intense chewing (p < 0.05), (BF 3 = BF 1 > BF 2 < BF 3). C, Endurance time in seconds on 150 N occlusal force level (ET) decreased significantly after intense chewing (p < O.OOOl), (ET 3 = ET 1 > ET 2 < ET 3). Table
intense
III. Mandibular velocity (mm/set) at incisor point in opening chewing (2), and at follow-up registration (3) Before
(1)
Mean
Maximal opening Maximal closing Mean opening Mean closing Means and standard
deviations
153.9 142.1 89.3 82.4 (SD)
for 17 test persons;
After
(2)
Follow-up
(3)
SD
Mean
SD
Mean
SD
P
33.2 38.2 20.5 21.6
161.8 151.8 95.3 91.2
40.5 37.9 24.8 23.4
156.5 148.3 90.9 88.6
42.0 37.0 27.5 23.2
NS
p denotes
level
ripheral and central inputs. The many parameters that influence oral function and the multidimensional character of mastication might explain the lack of objective methods for evaluating mastication. The methods in this study are considered acceptable for evaluation if compared with previous results.lO, 15, l7 Previous studies indicated that masticatory mandibular displacement and velocity is affected by different experimental foods.15 Thirty minutes of intense chewing that might have caused fatigue to the masticatory muscles did
408
and closing phases before (l), after 30 min of
of significance
of differences
between
three
NS NS NS
registrations.
not influence these parameters, which were stable with the same test food. Masticatory mandibular displacement was not affected, but the duration of the masticatory cycle and the occlusal phase of the cycle diminished significantly after the intense chewing. The difference in the masticatory cycle duration was consistent with a previous study in which the frequency of the masticatory cycles increased after the same training intervaLg The stability of the opening movement can be attributed to a ballistic character, governed by central commands, in contrast to the closing
MARCH
1992
VOLUME
67
NUMBER
3
MASTICATORY
FUNCTION
movement that is influenced by feedback. However, it is difficult to explain the difference in both masticatory cycle duration and the occlusal phase of the cycle between the first and third registration. This difference could be the effect of learning or the different times of the day for the recordings. This experimental schedule included the measurement of masticatory efficiency before the registration of the mandibular displacement and velocity, and incorporated at least a 2-minute delay between the completion of the intense chewing and the registration of the mandibular displacement and velocity. The proprioceptive mechanism influenced by intense chewingll, la recovers rather easily.lg Recovery of the receptors and a modified sensory feedback also affects the rhythmic output from the central pattern generator similar to the preexisting condition, resulting in a consistent chewing pattern. Masticatory efficiency was strongly influenced by the intense chewing exercises and corroborated a previous study.8 The masticatory efficiency in this study (77 % ) was higher than in the previous study (70 % ), although they were both performed on healthy dentate subjects. Individual biologic variations may partly explain this difference, but the two studies comprised different age groups and this is critical because the natural wear of the dentition may be responsible for improving masticatory efficiency with age.20 The test subjects in this study had a mean age of 28 years compared with 23 years, or 15% higher than in the previous study. Endurance tests should be performed on a submaximal occlusal force level and preferably on a level close to half of the maximal voluntary occlusal force.17 The 150 N occlusal force level for the endurance time test was close to that in this study. The results were in agreement with previous studies showing that the endurance times were stable on the 50% level of maximal voluntary occlusal force (Fig. 1, C). Maximal occlusal force and occlusal force endurance diminished substantially after intense chewing, probably because of muscle fatigue, a complex phenomenon. Kroon21 reported that the condition of the muscles can be described by the EMG signal that is different in a fatigued muscle. He also reported that total recovery from fatigue was incomplete 24 hours after the fatigue stimulation.21 The third follow-up registration in this study was performed at least two days after the stimulation to the masticatory system, and no differences were observed related to maximal occlusal force and occlusal force endurance between the first and the third follow-up registrations (Fig. 1, B and C). CONCLUSIONS Functional stimulation of the stomatognathic system with 30 minutes of intense chewing created a short-term effect on masticatory function. This stimulation signifi-
THE
JOURNAL
OF PROSTHETIC
DENTISTRY
cantly reduced the occlusal level phase and the duration of the masticatory cycle, masticatory efficiency, maximal occlusal force, and occlusal force endurance. REFERENCES central mechanisms and reAex 1. Grillner S. Locomotion in vertebrates; interaction. Physiol Rev 1971;55:247-304. Y, Kubo Y, Nozaki S, Tagasi M. Cortically induced masti2. Nakamura catory rhythm and its modification by tonic peripheral inputs in immobilized cats. Bull Tokyo Med Dent Univ 1976;23:101-7. In: Mohl NO, Zarb GA, Carlsson GE, 3. Rugh DJ, Smith RB. Mastication. Rugh J, eds. A textbook of occlusion. Chicago: Quintessence Publ, 1988,143-52. 4. Christensen LV. Facial pain and internal pressure of masseter muscle in experimental bruxism in man. Archs Oral Biol1971;16:1021-31. LV. Jaw muscle fatigue and pains induced by experimen5. Christensen tal tooth clenching: a review. J Oral Rahabil 1981;8:27-36. 6. Christensen LV. Experimental teeth clenching in man [Thesis]. Swed Dent J 1989,(Suppl 60):29-48. 7. Strijm D. Masseter muscle performance. Signilicance of structure and metabolism [Thesis]. Swed Dent J 199O$Suppl67):51-2. a. Silvestri RA, Cohen NS, Connoly JR. Muscle physiology during functional activities and parafunctional habits. J PROSTHET DENT 1960;44:64-7. 9. Tzakis MG,
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Carlsson GE, Kiliaridis S. Effect of chewing training on mandibular postural position. J Oral Rehabil 1989;6:503-8. Tzakis MG, Kiliaridis S, Carlsson GE. Effect of chewing training on masticatory efficiency. Acta Odontol Stand 1989;47:355-60. Kiliaridis S, Tzakis MG, Carlsson GE. Short-term and long-term effects of chewing training on the occlusal perception of thickness. Stand J Dent Res 1990;98:159-66. Carlsson GE, Helkiio M. Funktionell undersokning av tuggapparaten. In: Holst J J et al, eds. Nordisk Klinisk Odontologi. Copenhagen: A/S Forlaget for faglitteratur, 1972:8-l;l-21. Carlsson GE, Egermark-Eriksson I, Magnusson T. Intra- and interobserver variation in functional examination of the masticatory system. Swed Dent J 1980;4:187-94. Kopp S, Wenneberg B. Intra- and interobserver variability in the assessment of signs of disorder in the stomatognathic system. Swed Dent J 1983;7:239-46. Karlsson S, Carlsson GE. Recording of masticatory mandibular movements and velocity by an optoelectronic method. Int J Prosthodont 1989;2:490-6. Tzakis MG, Linden B, Jemt T: Oral function in patients treated with bridges on Branemark osseointegrated implants in the partially edentulous jaw. A pilot study. Int J Oral Maxillofac Implants 1990;5:107-II. Dahlstriim L, Tzakis MG, Haraldson T. Endurance tests of the masticatory system on different bite force levels. Stand J Dent Res 1988;96:137-42. Gwall B, MGller E. Oral tactile sensibility during chewing and biting. Odont Rev 1974;25:327-46. De Laat A. Masseteric reflexes and their relationship towards occlusion and temporomandibular joint dysfunction [Thesis]. Leuven: Catholic University of Leuven, 1985. Carlsson GE. Bite force and chewing efficiency. In: Kawamura Y, ed. Front oral physiol: physiology of mastication. Baael: Karger, 1974; vol 1, 265-92. Kroon GW. Muscle fatigue. An experimental and clinical electromyographic study with emphasis on the masticatory system [Thesis]. Amsterdam: ACTA University of Amsterdam, 1990.
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409