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An electromyographic investigation of patients with a normal jaw relationship and a Class III jaw relationship
An electromyographic investigation of patients with a normal jaw relationship and a Class III jaw relationship J. P. Moss, Ph.D., B.D.S., F.D.S., D.Orth., C. P. Chalmers, B.Sc.**
R.C.S.,* and
London, Englan’d
E
lectromyographic studies on persons with normal occlusion have been carried out by various workers,7-*0, 30,32 and the muscle patterns associated with various jaw positions are well documented. Recordings made in the intercuspal position, referred to as the habitual bite, show a typical muscle pattern, but this alters as the mandible changes its position.“, an,22,28, 36 Alteration in muscle activity in the intercuspal position of patients with malocclusion has been shown by several investigators in small groups of cases.]’ 5, 8, 11,I43 16,21,ZJ Because of the diversity of recording techniques for different muscles and the small sample size, it is difficult to make a comparison of the various findings. The position of the jaw depends on the coordination of the masseter and temporal muscles, and electromyograms made with the jaw in the intercuspal position have been used to try and indicate the position of the mandible in relation to the maxilla in subjects with malocclusion.12, I39w 34 Various studies of the electromyograms associated with a malocclusion have been undertaken. One of the first studies was undertaken by Moyers,26 who studied patterns of activity in a group of Class II, Division 1 patients, and since that time various authors have attempted to identify patterns of activity associated with a malocclusion.12~ 13,33, 34 A survey of thirty-two patients with Class III malocclusion was undertaken by Moss and Greenfield,“s and their electromyographic patterns were compared with those of forty patients with normal occlusion. It was shown that different patterns of activity were associated with the two groups. During the treatment *University *“Department
538
College of
Hospital Statistics,
Dental Birkbeck
School. College.
Electromyographic
investigation
of patients
539
of twenty of the patients with Class III malocclusion; the patterns of activity showed some change. The purpose of this study was (1) to see whether it was possible to differentiate patients on the basis of electromyographic patterns of activity; (2) to see which of the three positions of the jaw (the retrudcd contact, the intercuspal position, and the protruded contact) were best for discrimination; and (3) to determine whether the patterns of a.ctivity changed during treatment, Method
For this study surface electrodes were used to record activity, as the amplitude of recordings show more consistent resultsls, lG and the electrodes are easy to apply, especially in children. We used a unipolar method of recording, in which one electrode is placed over the muscle and the reference electrode is placed some distance away where electrical activity is slight or absent. The main problem with the unipolar technique is that the remote reference electrode may pick up activity from beneath it and result in a source of error when the electromyograms are interpreted. 27 It is, however, a most useful method for the comparison of activity between groups of muscles, as there is the same source of error associated with each recording.“? The subject was placed in an grounded, screened room, and seated in a comfortable chair with the head unsupported. The electrodes used were of a suction type filled with electrode jelly. The common or reference electrode was placed in the midline of the neck opposite the sixth cervical vertebra. This position was selected because it gave the most satisfactory recording with little or no interference in any channel. The subject was asked to move the head, thus using the neck muscles, and no appreciable activity was seen in any of the channels unless the gain was increased considerably. At the levels of recording a 250 microvolt signal gave a 1 cm. deflection of the galvanometer unless the activity was too great, in which case the gain was adjusted so that 500 microvolts ga,ve a 1 cm. deflection of the galvanometer. The recordings were made with the electrodes positioned as described previously,= and each of the subjects was asked to close and bite in the normal intercuspal position several times. The intercuspal position was the intermaxillary relationship characterized by the interdigitation of the cusps and occluding sulci of the occlusal reliefs. The patients were also asked to bite in the protruded contact and retruded contact positions. The sequence of movements was standardized. The operator visually observed the patient to ensure that the teeth were in the correct position. In order to test the accuracy of the method, 120 habitual bites of one person were measured, using four of the muscles (right and left posterior temporal and anterior masseter). These were recordecl in intercuspal relationship. In this position the muscles would be active isometrically, and hence any increase in pressure should give a linear increase in all muscle activitiesI As a comparison was being made between the activities of the muscles, it was important also to assess the muscle activities in a relationship in which there was a different activity of the muscles under observation, and therefore protruded contact and retruded contact positions were also measured.
540
Am. J. Orthod. November 1974
Moss and Cblmers
Fig. 1. The position of the electrodes on representation of the method of recording measuring the raw electromyographic data.
one side of the muscle
the head activity.
and Note
a the
diagrammatic method
of
In order to test the accuracy of recording and the accuracy of electrode placement, four adults with normal occlusions who had not undergone orthodontic treatment mere examined. A sequence of 100 recordings of the bite were measured. Forty recordings of the bite mere made of persons with normal occlusion on the same day with different electrode placings, twenty were recorded a week or more later, and forty were of a patient producing consecutive bites. A method of measurement used by M@llerz3 and Ahlgrenl was used on the raw electromyographic data in order for a comparison of muscle activities to be made. A section of the recording was taken where the mu&e activity in all channels was steady, neither increasing nor decreasing, and a line aa’ bb’ was then drawn through the majority of the peaks above and below the line and the
Volume Nwnber
66 5
Fig. 2. Scatter diagram standard deviations.
Electromyographic
The
showing the mean muscle activities line y = 2x is drawn in.
iwvestigation
plotted
against
of patients
their
541
respective
distance A bet vveen the two lines was measured in millimeters at the same point in time for each of the eight muscles recorded (Fig. 1). The accuracy of measurement was assessed by measuring eighty records ten times on different occasions. The variation in measurement was a maximum of 2 per cent, and this was considered to be acceptable. Material
The material consisted of the records of twenty adult patients (over 16 years of age) with normal occlusion and twenty children (under 16 years of age) with normal occlusion. These were compared with fifteen patients with postural Class III malocclusion and fi Steen with skeletal Class III malocclusion. Nineteen Class III cases were record& when treatment had been completed, and eleven cases were recorded when they had been out of retention for one year. Results
As it has been shown that the anterior masseter and the posterior temporal activities give an indication of the position of the jaw whereas a.nterior temporal and posterior masseter give an indication of the strength of bite force,24 it was decided to investigate the anterior masseter and posterior temporal activities only in the four groups of patients. The means and standard deviations of each muscle for each bite in each group combination were obtained. These showed that there was a wide variation in the sample standard deviations, suggesting that the data were not normally distributed with errors independent of any linear model. The scatter diagram of
542
Moss ad
Table
I. Means
transformed
muscle
Am.
Chalmers and
standard activity
deviations for
each
of
muscle
activity
and
log-
combination activity
I,oll-tl.tr,a.sformct~
muscle
actizjity
1 ZAM
/ ET’T
/ EA;1Z
MCFLll S.D. Mean S.D. Mean S.D.
4.5 2.2 1.0 0.5 5.0 2.4
8.3 3.0 5.3 2.8 2.1 0.9
4.9 3.0 1.1 0.5 6.0 3.3
1.4 0.5 ~0.2 0.5 1.5 0.4
0.4 1.5 0.5 0.6 0.5
1.4 0.7 -0.1 0.5 1.7 0.5
2.0
2.6 5.1 2.2 1.9 0.9
Mean S.D. Mean S.D. Mean S.D.
4.2 2.4 1.2 0.5 5.0 2.5
4.9 2.5 4.8 2.2 1.9 0.9
4.0 cl,.<3 1.2 0.4 4.6 2.3
4.8 2.0 4.2 1.4 2.0 1.0
1.3 0.6 0.1 0.5 7.5 0.5
1.5 0.4 1.5 0.5 0.5 0.:
1.2 0.6 0.1 0.4 I.4 0.5
1.5 0.4 1.4 0.4 0.5 0.5
Mean S.D. Mean S.D. Mean S.D.
3.7 2.1 1.1 0.6 4.7 1.6
6.2 2.7 4.5 2.9 2.1 1.4
3.7
0.4 4.7 I .4
5.1 2.2 4.0 2.8 1.9 1.3
1.1 0.7 -0.0 0.6 1.5 0.3
0.5 1.3 0.6 0.5 0.6
1.1 0.7 -0.1 0.5 1.5 0.::
1.6 0.5 1.2 0.5 0.4 0.7
Mean S.D. Mean S.D. Mean SD.
4.9 2.0 1.2 0.6 5.7 3.0
4.9 3.0 5.5 2.7 2.6 1.1
4.5 1.4 1.2 0.5 5.3 2.3
5.6 3.4 6.1 2.7 2.7 1.5
1.5 0.4 0.0 0.6 I .ij 0.5
1.3 0.9 I.5 0.8 0.9 0.5
1.5 0.3 0.1 0.4 1.6 0.5
1.5 0.8 1.7 0.5 0.8 0.6
ZPT
/ LAN
1 &PT
/ BAM
adults
Hahit~unl Vrotrusive Ketrusive
7.6
2.1
0.4 1.6 0.4 0.5 0.6
children
Habitual Protrusive Retrusive Postural
III
Habitual Protrusive Rctrusivc Skeletal Habitual Protrusive Retrusive
muscle
1974
--__ T,Z’T
Bite
Normal
untransformed
group/bite/muscle
Cntmn~~fometl
Normal
J. Orthod.
November
2.G 1.0
III
their means against their respective standard deviations shows an approximate linear relationship which indicated that an appropriate transformation would be logarithmic (Fig. 2). The stability in the stantlartl tlcviation as a result of this transformation was striking, and yet tht: activity patterns within the hitcs had not been alteretl drastically (Table I). The muscle activities oi’ a single putic:nt with I ‘informal” occlusions ill the habitual bite position were: itivcstigatc~tl ; 120 bitts were analyzed, ailtl tlic: results arc seen in Table 111. Although the a~w~~g,rcadi\-itg \\-as slightly lower than that for the group of normal adults, it was recognizable as being of the same type. The pattern was distinct when compared with tlic adult protruded and rctruded contaet positions. The r&dual mean syua,rw (Table 111) were very similar to the l)ctwecn-patient mean squaws (Table II) al~tl tlenioiistratt~tl that the variability due to electrode placing on tliffercnt persons did not present a problem so far as the interpretation of the results was concerned. This conclusion was strengthened
vozunae 66 NWE be?- 5
Table
Electromyographic
HA. Multivariate
analysis
of
variance
of muscle
i?zvestigation activity
(log
8.S. t3ource
I
D.F.
I
LPI
Groups (G) Patients Bites (B) BxG Error
Table
IIB. Correlation
Source
1 LAM
/
M.S. RPT
1
LPT
/
LAN
1
RPT
1 RAM
0.7s
2.46
1.44
3.14
0.26
0.82
0.48
1.04
33.74
26.86
27.75
0.45
0.51
0.40
0.42
2
97.48
42.11
94.72
45.60
48.74
21.05
47.36
22.80
6 132
1.26
4.42
1.41
3.44
0.21
0.73
0.23
0.57
23.80
27.01
25.93
25.55
0.18
0.20
0.19
0.19
structure
1 LPT/LAM
1 LAiU/RPT
) LPT/RPT
1 LAN/RAM
-0.05
0.62
0.95
0.73
0.53
0.55
0.48
0.71
0.75
-0.50
0.99
0.99
-0.47
-0.18
0.90
0.91
-0.12
0.76
0.73
0.56 -0.48 0.12
0.15 0.09
Results
from
the
0.17
analysis
1. T,PT Mean S.D. MS
1 RPT/RAM
-0.50
0.22
of I
120
repeated
2. LAN
measurements I
1 LPT/RAX 0.50 0.52
0.27
on
3. RPT
one I
individual 4. RAN
0.80 0.60
1.80
0.80
1.90
0.80
0.60
0.80
0.44
0.64
0.40
0.71
Correhtion
pairs
RAM
29.86
BxG
Muscle
data)
3
Error
Ill.
543
66
Groups (G) Patients Bites (R)
Table
of patients
structwre
12
23
34
13
24
14
0.83
0.72
0.72
0.77
0.93
0.76
by the examination of the correlation structure, for although the single-patient residual correlation structure was, as one would expect, very much stronger, it is directly comparable to the within-patients correlation structure. By contrast, it bore little resemblance to the error structure. It was concluded that recordings of a group of patients with a similar occlusal relationship would look like recordings of the same individual made on separate occasions. Their pattern would be distinct, and the correlation and variance covariance structure would bc fixed and quite unlike that due to the errors in the method itself. A principal component analysis of the 120 bites of a single subject showed that, because the residual variances were so similar, the principal components with a large variance looked very much the same, whether they had been extracted from the variance-covariance matrix or the correlation matrix. These were :
Am J. Orthod. November 1974
M
AR.
-1
-2 Fig. 3. A diagram the masseter adult group. position.
of the activity muscle for a group P, Protruded contact
0 of the temporal muscles of adults with a normal position. R, Retruded
1 plotted occlusion contact
2
T
against the activity of (log data). A, Normal position. H, lntercuspal
1. A general strength component (0.5, 0.5, 0.5, 0.5) accounting for 86 per cent of the variability when obtained from the correlation matrix. 2. A temporal masseter contrast (0.2, -0.4, 0.7, -0.5) accounting for 8 per cent of the variability when extracted from the correlation matrix, suggesting a difference in a&i&y from left to right when the jaw was protruded or retruded. The other two components are discussed in the appendis. A multivariatc analysis of variance was undertaken on the transformed data of the groups of patients. The relevant partition and correlation structure for these data showed two main sources of variation, the differences between patients and the over-all error in measurement and other noise. It showed that in both cases there was approximately the same residual variation in each muscle activity, but the variation between patients within groups was roughly twice that of the noise level. Also, the correlation structure between patients was of a different nature than that in the over-all error (Table II). In the patients, variability affects all the muscles, with the greatest correlations between the corresponding masseter and temporal activities, whereas in the over-all error the only correlation present was between the corresponding temporal and masseter muscles (Table IlB) . There was also a high positive correlation in the between-bites component and
Electromyographic
0 Fig.
4. A diagram
of
the
the masseter muscle for C, Normal child group. Protruded contact position.
activity
1 of
the
all the groups P3, Postural R, Retruded
temporal
2 muscles
of patients
investigation
plotted
of patients (log data). A, Class III group. 53, Skeletal contact position. H, lntercuspal
545
T against
the
activity
of
Normal adult group. Class III group. P, position.
between equivalent muscle activities on the left and right, while nonequivalent muscles had a large negative correlation. This indicated the different functions of the muscle in the protruded contact, retruded contact, and intercuspal positions (Fig. 3). Consideration of the bites x groups interaction partition showed that there was an interaction present in the masseter muscles, but there was little difference between the groups. Although the amount of activity in the temporal muscles showed the greatest variability over bite, it varied equally over the four groups, whereas the masseter activity, although it did vary over bite and groups, had a different function within each group as the position varied from retruded contact, to intercuspal position, to protruded contact (Fig. 4). A component analysis of the data showed that investigation could be undertaken of the bites by considering the masseter/temporal comparison, with additional information being obtained from the total activity. This clearly showed the different nature of the three bites as far as the activity in the four muscles was concerned (Fig. 5). In terms of the untransformed data, it was equivalent to considering the ratio of masseter and temporal activity as has been already used in a previous study.2S When a similar analysis was undertaken for the bite x group interaction, it was clear that the four groups showed a completely different pattern of activity over the three bites when plotted in natural data space (Fig. 4). The adult activity was greater than that of the children or the two malocclusion groups, although the children resemble the postural Class III group. The skeletal Class III group stood out as having greater masseteric activity in the protruded contact position than in the intercuspal position. The derived variables were then plotted (Fig. 5)) using a weighted temporal/
Am. J. Orthod. November 1974
TA
T/M Fig.
5.
A
diagram
showing
the
plot
of
weighted total activity for all groups of child group. P3, Postural Class III group. contact position. R, Retruded contact position.
the
weighted
patients. A, 53, Skeletal H, lntercuspal
temporal/masseter
contrast
and
Normal adult group. C, Normal Class III group. P, Protruded position.
masseter contrast and weighted total activity. The children were distinguished from the other groups by their smaller temporal/masseter contrast activity in the retruded contact position. The postural Class III resembled a weak adult and the skeletal Class III showed no variation at all in the total activity direction in which marked changes were observed in all other groups. The habitual bite for this group closely resembled the retrusive bite, which was to be expected. In the intercuspal position there was a significant difference between the various groups. In the retruded contact position there was a significant difference between the skeletal Class III group and the normal and postural Class III groups. In the protruded contact position there was little difference. It is therefore suggested that the best discriminator of the groups would be the intercuspal or retruded contact positions. Data from a group of Class III patients who had been recorded at the completion of treatment and a group who had been recorded out of retention vvcrc evaluated. The figures are given in a comparable fashion in Tables VII and VIII. The plots of natural variables and dcrivcd variables are shown in Figs. 6 and 7, with normal adults shown for comparison. After treatment the activity remained low, resembling the postural Class III group. Out of retention, however, the activity increased and took on a normal pattern. Thus, the findings for the treated group were quite distinct from those before treatment. Discussion
The analysis of the muscle patterns of twenty children with normal occlusion in the study confirmed the results of MacDougall and Andrew,“’ Greenfield and
Electrom~yographic
i~wvestigatbn
of pa’tients
T
2 Fig.
6.
A diagram
of
the
activity
of
the
temporal
muscle
the masseter muscle for the normal adult group and end of treatment and a year or more out of retention. Ill patients at contact position.
the end of R, Retruded
treatment. contact
plotted
against
the
activity
a group of Class III patients A, Normal adult group.
0, Class III patients position. H, lntercuspal
out of position.
547
retention.
of
at the T, Class
P, Protruded
JV~yke,~and LatifzO that during the habitual bite there was a balance of muscle activity between the two sides. This was seen in the high correlations of muscle activity between the left and right posterior temporal and anterior masseter muscle activities. It also showed that the muscles on the left tended to be slightly more active than those on the right. This was tested statistically, and it was found that the two sides were different and should not be considered together. The protruded contact position of children did not show the same high degree of correlation between the anterior masscter and posterior temporal muscle activities on opposite sides. This was probably due to the deviation of the jaw in protrusion, resulting in an imbalance in the muscle activities.’ The retruded contact position of children was similar to that described by Latif”’ and showed a high correlation of muscle activity between all muscles. The high correlation of activity in retrusion was due to the inability of the children to deviate appreciably during this movement. The habitual, protruded contact and retruded contact positions of the adult patients with normal occlusion are typical of those described by various investigators,8, 22,30 The correlation matrices showed that the best correlations were found in the rctruded contact, and the worst were found during protruded contact. Once again, this was probably due to deviation of the jaw in the protruded contact position. In this study, patients with a skeletal Class III relationship and a postural Class III relationship were investigated and compared with patients with normal occlusion to see whether or not there was an alternation in muscle pattern with malocclusion. Baril and Moyers, * Findlay and Kilpatrick,F Krazer,lQ Witt,35 and Ahlgren’ maintain that there is no change, whereas Grossmann,l2’ 13 Timms,33’ 34
548
Am. J. Orthod. November 1974
Moss and Chalmers
I
2 Fig. 7. weighted the end
A
1
diagram showing the plot of the total activity for the normal adult of treatment and out of retention.
1 weighted temporal/masseter group and the treated
2 Class
TIM contrast III group
and at
and Perry”“, 31 and their co-authors found a difference in muscle activity in patients with malocclusion. The pattern of activity during habitual biting was significantly different in children and adults and showed a poor correlation between muscles except between the same muscle on each side. The protruded contact and retruded contact patterns were slightly different from those of the adults and children, and the correlation matrices showed a poor correlation between muscles except in the postural Class III group, which showed a significant correlation between all muscles in the protruded contact position. This was probably due to a learned path of closure,” and therefore the patient was better able to produce a protruded contact position. There was a definite alteration in pattern in the activities of the muscles of the Class III patients in the study during treatment. A similar alteration in muscle pattern had been noted by Moy~rs,~~ Ahlgren,’ Okun,*” and Grosfeldll in Class II, Division 1 cases. Haralabakisl’ also reported on a group of cross-bites which were treated, and he noted a change to the normal pattern of muscle activity. Grosfeldll also noted a change to a normal pattern of activity following functional treatment. In this study, at the end of treatment the correlation matrices revealed a poor correlation between the muscle activities in the habitual, protruded contact, and retruded contact positions. Out of retention there was a great improvement in the correlations between the muscle activities in the habitual bite but not in the protruded contact and retruded contact positions.
1~oZwne Nmnbw
Statistical
BG .5
Electromyographic
investigation
of patients
549
method
IllititrI 0 )Inl?jsis. As a preliminary study, the means and standard deviations of the activity of each muscle within a bite/group combination were obtained. These results arc shown in Table I. It appeared that there was a wide.variation in the sample standard deviations, which su ggested that the data were not normally tlistribntcd with errors independent of any linear model. A scatter diagram of the means against their respective standard deviations (Fig. 2) showed an approximate linear relationship which indicated that an appropriate transformation, both to normalize the data and to produce homoscedasticity, would be logarithmic. This agreed with observed behavior of muscle activity and with the practice of some investigators of clectromyographic techniques. Table I shows the results of applying such a tra.nsformation. The stability in the standard deviation was now quite striking, and yet the activity patterns within the bites had not been altered drastically. A~~ultivnrirtte nwlysis of vuritr~~c~~There are two main aims in any analysis of variance : (1) the partitioning of the total sum of squares into components attribntablc to the various components of the design and (2) the construction of relevant F tests so that hypotheses concerning various factors in the design may bc examined. It is arguable that the first aim was the> more important, enabling one as it tloes to produce estimates and confidcncc intervals for both the paramct.crs and components of variance in the model and also, when simple ANOVA tables only have been constructed, to test rather more informative u I)riori hypotheses. Multivariate analysis of varianc:e is a natural extension of this technique to a partition of the total sum of squares and products matrix. As a byproduct, one obtains the usual F statistics for csach component of the data but over-all tests arc available to examine the variation of the response \-cctor as a whole, taking into account the correlation between its various components. However, the comment on univariate analysis of variance still seems appropriate and the main applications of any MANOVA routine are likely to be in the examination of the residual error structure and its application in the testing of further hypotheses. The relevant partition and correlation structure for these data arc shown in Table II. There were two main sources of random variation in the data, the differences between the individual patients and then the over-all error in measurement and other noise. The tables made it clear that in both cases there was approximately the same residual \,ariation in each muscle activity but that the variation between patients within groups was roughly twice that of the noise level. However, the correlation structure between patients was of a different nature from that in the over-all error. The patients’ variability affected all the muscles, with the greatest correlation being between the corresponding regions of the temporal ant1 masseter muscles. In the over-all error t,his latter was practically the only correlation present. Thus: random fluctuations will tend to affect either the masseter or the temporal muscles equally on the left ant1 the right, whereas between patients the main cause of their variability provccl to be the strength of their bite, affecting all muscles equally, after which the random fluctuations affected the two muscles separately. Looking at the between-groups mean
550
Moss and Chalmers
Am. J. Orthod. November 1974
squares, it was clear that great difficulty would be experienced in distinguishing between members of different groups on the basis of an average bite unless we were to allow repeated bites, in which cast the masseter muscle could prove a discriminator. However, the type of bitt being made was very easily ascertained, for the bites/error F ratios were all of the order of 100 with 2/6 degrees of freedom. This difference was examined in greater detail later. There was a high positive correlatiorI in the between-bites component between equivalent muscle responses on the left, and right, while nonequivalent muscles had a large negative correlation. This indicated the different functions of the muscles in habitual, protrusive, and retrusive bite positions. This effect could also be examined in greater detail, using the error structure and the table of means, and this was done. Although both muscles sl~o~ed great variability between the three bite positions, the temporal muscle showed the greatest variation. Consideration of the bites x groups interaction partition showed that while little evidence was found to suggest over-all differences between the groups there was clearly evidence to suggest that an interaction was present in the masseter muscles. Thus, although the strength of action in the temporal muscles showed the greatest variability over bites, it varied equally over the four groups. The masseter muscle, on the other hantl, while its strength did vary generally over all bites and groups, had a different function within each group as the position varied from retrusive to habitual to protrusive. Results from repeated obseruatio~~s ON nlle patiellt. At this stage the results obtained by multivariate analysis of variance on this set of widely differing experimental material were compared with those obtained by repeated observations made on a single patient in his habitual bite position. There were available the data from 120 such bitts, ant1 the results comparable to those shown in Table I and Table II are given in Table 111. Again, log (activity) was used. Although the average response in all four muscles was somewhat lower than that for the group of normal adults, the pattern was immediately recognizable as being of the same type, having roughly twice the activity in masscter muscles when compared to temporal muscles but an appreciable amount in each. This pattern was distinct when compared with the activities in the adult retrudecl contact and protruded contact positions and all bites in the other groups. The residual mean squares (Table III) wcrc \-cry similar to the between-patients mean squares (Table II), with perhaps a slight increase in the rnassetcr variability. One can suggest that the explanation for this lies in the process of replication in that the patient varied his habitual bite from time to time, sometimes producing a slightly retrusive and sometimes a slightly protrusive bite. This would also explain the slight decrease in over-all muscle activity. Structure withk the 1,lILl~iz’aricrbles. I3ven in as few as four dimensions, it \vas not always immediately obvious what characterized the group properties of the data. In biologic data, often a principal component analysis of the variancecovariance matrix (or sometimes the correlation matrix) will bring out this structure more clearly. When such structure has been revealed, this may suggest a recasting of the data in various ways so as to emphasize particular propertics. Such further analyses are canonical analyses.
Volume Number
66 5
Electromyographic
investigatim
of patients
551
In these data we have both the single individual and the groups to consider Principal components on the reszllts from a single individual. Since the residual variances were so similar, it was found that the principal components with large variance looked very much the same, whether they had been extracted from the variance-covariance matrix or from the correlation matrix. They were: 1. A general strength component of 0.5, 0.5, 0.5, 0.5 when obtained from the correlation matrix, accounting for some 86 per cent of the variability. Recast in terms of the unstandardized data by using the variance-covariance matrix, we obtain 0.4, 0.6, 0.4, and 0.6, reflecting the greater variance in the masseter muscle, that is, some idea of relative bite strength can be obtained from 2 x total temporal activity + 3 x total masseter activity. 2. A temporal masseter contrast accounts for a further 8 per cent of the variability of the data, giving a component of 0.2, -0.4, 0.7, -0.5 when extracted from the correlation matrix and 0.4, -0.3, 0.7, -0.5 when extracted from the variance-covariance matrix. This component, which accounted for an appreciable amount of the variability of the data in this one individual, was precisely the phenomenon that was accepted earlier. Added to the variation in strength of bite, it increased the temporal and decreased the masseter or vice versa. This was exactly equivalent to what was seen in normal adults as the change is made from habitual to protrusive or retrusive bite, Table I. In this single person there was an asymmetry of the result, suggesting either an imbalance in electrode placing or a genuine difference in activity from left to right when the jaw was protruded or retruded. 3. The next component accounted for a further 5 per cent of the variability and emphasized this asymmetry. Taking only the variancecovariance matrix, we had -0.7, -0.2, 0.6, and 0.2, that is, a component which balanced the activity between the two sides though not balancing the activity in the two muscles. 4. The last component in the individual contributed only a negligible amount, and -0.2, +0.7, +O.l, -0.6 represented variation due to “shearing” in the jaw position. The fact that this component turned out to be relatively constant throughout the data for this one patient was reassuring, for the anatomy of the jaw would suggest that the progression from protrusive to habitual to retrusive is a natural one and should not contain any element of “shear.” This result, in turn, suggested a direct link between the measurement of activity by electromyography and the real activity of the muscle, and hence the patient’s potential for change. Component analysis from the MANOVA table. Within the MANOVA table there were two main sources of error: the between-patients and with within-patients errors. Taking principal components for each case and comparing the results obtained with those for the single patient
552 Table from
IV. A comparison the betweenSingle
Per cent Variation
of principal
and
/ CM
patient
86
84
8
9
5
6
1
1
vclll t4 +6 t4 +6 -4 +3 -7 +5 -7 -2 +6 +4 4 t7 t2 -6
components
within-patient
results Between
I
Per cent Variation
Loadhg
VCN
Both matrix
Am. J. Orthod. November1974
Moss a,nnd Chalmers
1
from
patient
(‘M
FCM
t5 t5 +5 +5 -2 +4 -7 t5 -8 -0 t5 t4 -2 t7 +l -6
70
70
17
17
7
7
6
6
+5 +5 +5 t5 -5 t5 -5 15 -6 +3 +6 -3 -3 -6 +3 t7
variance-covariance
with
those
Error
I Per cent Variation 1
obtained
table
Loading
VCMI
the
a single
patients
CM
principal components from are shown for comparison.
for
the MANOVA
CM
VCM
t5 t5 +5 +5 -5 t4 -5 +6 -7 t2 t7 -2 -2 -7 +2 +7 matrix
/
Loading CM
VCM
53
53
35
34
7
7
5
6
t5 +5 t5 t5 -5 +5 -5 +4 -2 -6 +1 +7 -7 t2 t7 -1
and
from
the
/
CM +5 t5 +5 +5 -4 +5 -5 +5 -3 -6 t2 t7 -7 +3 t7 -2
correlation
already outlined, we obtain the data presented in Table IV. From this table it was apparent that the structure of each matrix was basically the same in that the principal components were very similar but that their loadings (the amount they contributed to the total variability) differed in the three cases. Thus, between patients and for a single individual, between bites, the primary source of variability was the index representing strength of bite. However, this did not appear in quite such a strong fashion in the error where the second component, representing a masseter/ temporal comparison, played a much larger role. Conversely, this latter component also entered into the between-patients set but with a smaller loading. These results reflected the varied experimental material, for while each patient differed from the others in the strength of bite, the additional action necessary to produce a retrusire or protrusive bite also differed from individual to individual. This phenomenon was seen in the bites x groups interaction in the masseter muscles, but the multivariate analysis now shows that this effect caried over to the complete muscle activity. The single patient was more consistent in his bite pattern, as was evident from the per cent variation explained by the first principal component, strength of bite. However, as has already been noted briefly in the earlier description, while the pattern of the loadings was very much the same as for the patients and error, the weights were not the same and we had a certain asymmetry. This demonstrated the uniqueness of this patient, and this
Volume
Number
66 5
Table
V.
partition
Electromyographic First in the
two
principal
MANOVA
components
investigation
obtained
from
cent
Table
Bites
variation
Loadings
CM
VCM
79
75
21
25
+6 -3 +6 -3 +3 +6 +3 +6
VCM
1
VIA.
Individual
bite
(
Per CM +5 -5 +5 -5 +5 +5 +5 +5
activities
cent
vciv
Bite Habitual Protrusive Retrusive
x
groups
(weighted
x Groups Loadings vclll
CM
74
49
26
48
1
CM i-6 -1 +7 -3 +2 +7 +2 +6
0 +8 0 +7 +T +2 +7 -2
means]
LPT
LAM
RPT
RAM
1.31 -0.17 1.52
1.61 1.47 0.62
1.29 0.06 1.54
1.62 1.46 0.58
masseter
I 4
bites
Muscle
Habitual Protrusive Retrusive
VIB. Average
and
variation
1
I Bite
Table
bites
553
table
Bites Per
the
of patients
and
temporal
activities
and
canonical
variables
Component T
1
!
1.30 -0.05 1.53
M 1.62 0.97 0.60
I,
TOM 0.98 -1.08 0.92
/I
Acthit?/ 1.51 0.63 0.91
slight abnormality could be attributed either to bc a genuine effect or to the patient’s tendency to vary his habitual bite. The pooled between-patients structure was more reliable, since it averaged out any odd tendencies of this nature. It is also of some interest to examine principal components extracted from both the bites and bites x groups interaction partitions in the MANOVA table. The relevant results are given in Table V. The bites can clearly be investigated by considering the masscter/temporalis comparison, with additional information being obtained from the total activity. However, the interaction components were little more difficult to identify as obtained. If, however, one assumed that both components attempt to explain 50 per cent of the variability, then any linear combination of the two would play the same role. In this case, it was suggested that total masseter and total temporal activity may prove helpful indicators. In terms of the original untransformed data, this is equivalent to considering the ratio of masseter to temporal activity and has been sug-
554
Moss ma Cblmers
Table
VII. Data
AH
for
interaction
1.37
AP
Am. J. Orthod. November 1974
of bites
2.05
-0.16
x groups
1.41
1.55
1.39 -0.13
2.01
1.35
1.97
-0.09
0.77
1.55
1.80
-1.80
0.99
AR CH CP
1.51
0.60
1.65
0.51
1.58
0.56
2.60
0.90
1.27
1.49
1.21
1.49
1.24
1.49
0.99
1.41
0.09
1.45
O.Ofi
1.36
0.08
1.41
CR
1.49
0.50
1.41
1.47
0.83
1.10
1.54
1.06
1.45 1.08
0.53
PH PP PR
0.55 1.52
1.53
0.63
1.38
1.23
-0.05 1.51
1.29
0.84
0.49
-1.39 2.52
1.42
1.54
1.10 1.10
-0.02
SH
SP SR
Table Group TH TP TR OH OP OR
VIII. 1
1.35
-0.08
1.50
0.54
1.51
0.43
1.49 0.02
1.34 1.52
1.47 0.12
1.49 I.7L
1.48 0.07
1.62
1.60
0.85
1.58
0.82
1.59
0.84
Data
for
LPT
/
1.28
-0.13
“finish LAM 1.07
1.31
of 1
treatment RPT 1.23
-0.08
group
1 IZAX 1.05
1.19
)
(T)”
and
T
)
1.26
-0.11
“out M 1.06 1.25
-1.28
0.63
0.83
-1.45 2.34
of
retention /
TV4 1.45 -1.46
1.09
group 1
(0)” A 1.13
0.80
1.54
0.53
1.51
0.52
1.53
0.53
2.52
0.86
1.47
2.02
1.58
2.09
1.53
2.06
0.99
1.88
0.34
1.86
0.31
1.86
0.33
1.86
1.80
0.97
1.74
0.88
1.7;
0.93
-1.21 2.61
1.35 1.21
gested.already as a suitable discriminator in earlier studies.‘” In Tables VIA and VIB and Fig. 3, both the elementary variables, total masseter and temporal activity, and the derived variables, weighted temporal masseter contrast and weighted total activity, are examined. These showed clearly the different nature of the three bites as far as the activity in the four muscles was concerned. However, a more detailed analysis was necessary to see the improvement in separation gained by using the derived variables rather than the “natural” variables. In Table VII and VIII and Fig. 4, a similar exercise was undertaken for the bites x groups interaction. Again, while quite a clear picture was painted by this analysis, rather more detail was required to justify the gain in information. Summary
The method of analyzing the electromyographic data from patients has been described, and the results of the investigation of twenty adult patients with normal occlusion, twenty children with normal occlusion, fifteen patients with skeletal Class III malocclusion, and fifteen patients with postural Class III malocclusion have been presented. Each patient was recorded in the protruded contact, retruded contact and intercuspal positions. A group of Class III patients who had received orthodontic treatment were recorded after treatment and out of retention, and this group was also investigated. The results showed that the best jaw position for discrimination between the
Electronzyographic groups was the intcrcuspal the muscle activity returned
iwvestigation
of patients
position and that, following orthodontic to a more normal pattern of activity.
555
treatment,
REFERENCES
1. .\hlgrcn, .I. : An electromyographic analysis of the response to activator therapy. Odontol. Rev. 11: 125-151, 1960. 2. Ahlgren, J.: Mechanism of mastication: A quantitntivc cinematographic and clectromyographic study of masticatory movements in children, with special reference to occlusion of the teeth, Acta Odontol. &and. 24: Supp. 44, pp. l-109, 1966. 3. Ballard, C. F.: Consideration of the physiological background of mandibular posture and movement, Tr. Br. Sac. Study Orthod, pp. 117-127, 1955. 4. Baril, C., and Moyers, R. E.: An clcctron~yogmpl~ic analysis of the temporal muscles and certain facial muscles in thumband finger-sucking patients, J. Dent. Rcs. 39: 536-553, 1960. 5. Dominik, K,: Die clcktromyograpl~ischc Bcwertung verschiedener Rcizc, welchc kieferorthopadischc Funktionsapparntc aktivieren, ZahnBrztl. Welt. 69: 730-732, 1968. 6. Findlay, I. A., and Kilpatrick, 8. J.: Analysis of myographic records of swallowing in normal and almormal subjects, J. Dent. Res. 39: 629-637, 1960. 7. Greenfield, B. E., and Wyke, B. D.: Electromyographic observations on some of the muscles of mastication, J. Anat. 89: 578, 1955. 8. Greenfield, B. E., and Wyke, B. D.: Electromyographic studies of some of the muscles of mastication, Br. Dent. J. 100: 129-143, 1956. 9. Grosfcld, 0.: Die Rolle der Elektromyographischcn Analyst in der kieferorothopldischcn Diagnose, Dtsch. Stomntol. 11: 942-952, 1961. 10. Grosfeld, 0. : Badania Elektromigraficzne W Zahurzeniach Szchekowo-Zgryzowych l’whodzcnia Czwnnoscio\vcgo, Czas. Htumatol. 11-12: 965972, 1QfiZ. 11. Grosfcld, 0.: Changes in muscle activity patterns as a result of orthodontic treatment, Tr. Eur. Orthod. Sot. 41: 203-213, 1965. 12. Grossmann, IV., and Grcenficld, B. E.: An analysis of treated casts, Tr. Br. Sot. Study Orthod., pp. l-12, 1956 13. Grossmann W., Grccnfield, B. E., and Timms, D. J.: Electromyography as an aid in diagnosis and treatment analysis, Ant. J. ORTHOII. 47: 481-497, 1901. 14. Haralabakis, V.: Elcctromyographic analysis of a scrics of 50 treated posterior crossbites, Tr. Eur. Orthod. Sot. 40: 206-220, 1963. 15. Hodcs, R.: Electromyographic study of defects of ncuro-muscular transmission in human poliomyelitis, Arch. Neurol. Psychiat. 60: 457-473, 1948. 16. Hodcs, R., Larrabec, M. G., and German, W.: The human electromyogram in response to nerve stimulation and the conduction velocity of motor axons, Arch. Ncurol. Psychiat. 60: 340-365, 1948. 17. lnman, V. T., Ralston, II. J., Saunders, .J. B. de C. M., Fcinstcin, B., and Wright, E. W., Jr. : Relation of human clectromyogram to muscular tension, Elcctroencephalogr. Clin. Ncurophysiol. 4: 187-194, 1952. 18. Jarabak, J. R.: Elcctromyographic analysis of muscular and temporomandibular joint disturl):rnccs due to imbalances in occlusion, Angle Orthod. 26: 170-190, 1956. 19. Krazcr, K. : Untersuchungcn iiber die Bczichungcn zwischcn Eugnathien und Dysgnathien cincrscits und den Aktionsstromen dcs M. Masseter obliguus, M. Masscter verticalis, M. Temporalis anterior und der Mundboden muskulatur nnderseits, Medical Dissertation, Freilmrg University, 1960. 20. Latif, A.: Electromyographic study of the temporalis muscle in normal persons during selected positions and movements of the mnndible, AM. J. ORTHOD. 43: 577-591, 1957. 21. Liebman, F. M., and Cosenzn, F.: Evaluation of electromyography in the study of the etiology of malocclusion, J. Prosthet. .Dent. 10: 1065-1077, 1960. 22. MacDougall, J. D. B., and Andrew, B. L.: An electromyographic study of temporalis and masseter muscles, J. Anat. 87: 37-45, 1953.
556 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36.
Am. J. Orthod. November 1974
Moss and Chalmers
Meller, E. : Methodological investigations concerning electromyographic analysis of muscle co-ordination, Tr. Eur. Orthod. Sot., pp. 328-340, 1958. Moss, J. P.: An electromyographic investigation of certain muscle activities associated with malocclusion of the teeth, Ph.D. thesis, University of London, 1971. B. E.: An electromyographic investigation and survey of Moss, .J. I’., and Greenfield, Class 111, cases, Tr. Br. Sot. Study Orthod. pp. 147-156, 1965. Moycrs, R. E.: Temporomandibular muscle contraction patterns in Angle Class II, Division 1 malocclusions: An electromyographic analysis, AM. 5. ORTHOD. 35: 837-857, 1949. O’Connell, A. L., and Gardner, E. B.: The use of electromyography in kinesiological research, Xcs. Quart. 34: 16&184, 19(i3. Okun, .J. H.: Electromyographic study of Class II cases during orthodontic treatment, M.D.S. thesis, Northwestern University Dental School, June, 1960. Okun, J. H.: Electromyographic study of Class II cases during orthodontic treatment, AM. J. ORTHOD. 48: 474-475, 1962. Perry, II. T., and Harris, S. C.: Role of the neuromuscular system in functional activity of the mandible, J. Am. Dent. Assoc. 48: 665673, 1954. Perry, H. T.: Functional electromyography of the temporal and masseter muscles in Class II, Division 1 malocclusion and excellent occlusion, Angle Orthod. 25: 49-58, 1955. Pruzansky, S.: : Application of electromyography to dental research, J. Am. Dent. Assoc. 44: 49-68, 1952. Timms, D. J.: Analysis of treated cases, Tr. Eur. Orthod. Soe. pp. 368-377, 1960. Timms, I). J., and Greenficld, B. E.: Some clectromyographic observations on maxillomandibular relationships in orthodontics, Tr. Eur. Orthod. Sot., pp. 312-327, 1961. IVitt, E.: Kinnmuskulatur und Kinnformung, Fortschr. Kieferorthop. 25: 225-232, 1964. \\‘oelfcl, J. B., Jlickey, J. C., Stacy, R. W., and Rinear, L.: Elcctromyographic analysis of of jaw movements, J. Prosthet. Dent. 10: 688-697, 1960. U.C.Z.
Dental
School,
Hortimcr
Market
(WCIE
6JD)
R.C.S.,* and
London, Englan’d
E
lectromyographic studies on persons with normal occlusion have been carried out by various workers,7-*0, 30,32 and the muscle patterns associated with various jaw positions are well documented. Recordings made in the intercuspal position, referred to as the habitual bite, show a typical muscle pattern, but this alters as the mandible changes its position.“, an,22,28, 36 Alteration in muscle activity in the intercuspal position of patients with malocclusion has been shown by several investigators in small groups of cases.]’ 5, 8, 11,I43 16,21,ZJ Because of the diversity of recording techniques for different muscles and the small sample size, it is difficult to make a comparison of the various findings. The position of the jaw depends on the coordination of the masseter and temporal muscles, and electromyograms made with the jaw in the intercuspal position have been used to try and indicate the position of the mandible in relation to the maxilla in subjects with malocclusion.12, I39w 34 Various studies of the electromyograms associated with a malocclusion have been undertaken. One of the first studies was undertaken by Moyers,26 who studied patterns of activity in a group of Class II, Division 1 patients, and since that time various authors have attempted to identify patterns of activity associated with a malocclusion.12~ 13,33, 34 A survey of thirty-two patients with Class III malocclusion was undertaken by Moss and Greenfield,“s and their electromyographic patterns were compared with those of forty patients with normal occlusion. It was shown that different patterns of activity were associated with the two groups. During the treatment *University *“Department
538
College of
Hospital Statistics,
Dental Birkbeck
School. College.
Electromyographic
investigation
of patients
539
of twenty of the patients with Class III malocclusion; the patterns of activity showed some change. The purpose of this study was (1) to see whether it was possible to differentiate patients on the basis of electromyographic patterns of activity; (2) to see which of the three positions of the jaw (the retrudcd contact, the intercuspal position, and the protruded contact) were best for discrimination; and (3) to determine whether the patterns of a.ctivity changed during treatment, Method
For this study surface electrodes were used to record activity, as the amplitude of recordings show more consistent resultsls, lG and the electrodes are easy to apply, especially in children. We used a unipolar method of recording, in which one electrode is placed over the muscle and the reference electrode is placed some distance away where electrical activity is slight or absent. The main problem with the unipolar technique is that the remote reference electrode may pick up activity from beneath it and result in a source of error when the electromyograms are interpreted. 27 It is, however, a most useful method for the comparison of activity between groups of muscles, as there is the same source of error associated with each recording.“? The subject was placed in an grounded, screened room, and seated in a comfortable chair with the head unsupported. The electrodes used were of a suction type filled with electrode jelly. The common or reference electrode was placed in the midline of the neck opposite the sixth cervical vertebra. This position was selected because it gave the most satisfactory recording with little or no interference in any channel. The subject was asked to move the head, thus using the neck muscles, and no appreciable activity was seen in any of the channels unless the gain was increased considerably. At the levels of recording a 250 microvolt signal gave a 1 cm. deflection of the galvanometer unless the activity was too great, in which case the gain was adjusted so that 500 microvolts ga,ve a 1 cm. deflection of the galvanometer. The recordings were made with the electrodes positioned as described previously,= and each of the subjects was asked to close and bite in the normal intercuspal position several times. The intercuspal position was the intermaxillary relationship characterized by the interdigitation of the cusps and occluding sulci of the occlusal reliefs. The patients were also asked to bite in the protruded contact and retruded contact positions. The sequence of movements was standardized. The operator visually observed the patient to ensure that the teeth were in the correct position. In order to test the accuracy of the method, 120 habitual bites of one person were measured, using four of the muscles (right and left posterior temporal and anterior masseter). These were recordecl in intercuspal relationship. In this position the muscles would be active isometrically, and hence any increase in pressure should give a linear increase in all muscle activitiesI As a comparison was being made between the activities of the muscles, it was important also to assess the muscle activities in a relationship in which there was a different activity of the muscles under observation, and therefore protruded contact and retruded contact positions were also measured.
540
Am. J. Orthod. November 1974
Moss and Cblmers
Fig. 1. The position of the electrodes on representation of the method of recording measuring the raw electromyographic data.
one side of the muscle
the head activity.
and Note
a the
diagrammatic method
of
In order to test the accuracy of recording and the accuracy of electrode placement, four adults with normal occlusions who had not undergone orthodontic treatment mere examined. A sequence of 100 recordings of the bite were measured. Forty recordings of the bite mere made of persons with normal occlusion on the same day with different electrode placings, twenty were recorded a week or more later, and forty were of a patient producing consecutive bites. A method of measurement used by M@llerz3 and Ahlgrenl was used on the raw electromyographic data in order for a comparison of muscle activities to be made. A section of the recording was taken where the mu&e activity in all channels was steady, neither increasing nor decreasing, and a line aa’ bb’ was then drawn through the majority of the peaks above and below the line and the
Volume Nwnber
66 5
Fig. 2. Scatter diagram standard deviations.
Electromyographic
The
showing the mean muscle activities line y = 2x is drawn in.
iwvestigation
plotted
against
of patients
their
541
respective
distance A bet vveen the two lines was measured in millimeters at the same point in time for each of the eight muscles recorded (Fig. 1). The accuracy of measurement was assessed by measuring eighty records ten times on different occasions. The variation in measurement was a maximum of 2 per cent, and this was considered to be acceptable. Material
The material consisted of the records of twenty adult patients (over 16 years of age) with normal occlusion and twenty children (under 16 years of age) with normal occlusion. These were compared with fifteen patients with postural Class III malocclusion and fi Steen with skeletal Class III malocclusion. Nineteen Class III cases were record& when treatment had been completed, and eleven cases were recorded when they had been out of retention for one year. Results
As it has been shown that the anterior masseter and the posterior temporal activities give an indication of the position of the jaw whereas a.nterior temporal and posterior masseter give an indication of the strength of bite force,24 it was decided to investigate the anterior masseter and posterior temporal activities only in the four groups of patients. The means and standard deviations of each muscle for each bite in each group combination were obtained. These showed that there was a wide variation in the sample standard deviations, suggesting that the data were not normally distributed with errors independent of any linear model. The scatter diagram of
542
Moss ad
Table
I. Means
transformed
muscle
Am.
Chalmers and
standard activity
deviations for
each
of
muscle
activity
and
log-
combination activity
I,oll-tl.tr,a.sformct~
muscle
actizjity
1 ZAM
/ ET’T
/ EA;1Z
MCFLll S.D. Mean S.D. Mean S.D.
4.5 2.2 1.0 0.5 5.0 2.4
8.3 3.0 5.3 2.8 2.1 0.9
4.9 3.0 1.1 0.5 6.0 3.3
1.4 0.5 ~0.2 0.5 1.5 0.4
0.4 1.5 0.5 0.6 0.5
1.4 0.7 -0.1 0.5 1.7 0.5
2.0
2.6 5.1 2.2 1.9 0.9
Mean S.D. Mean S.D. Mean S.D.
4.2 2.4 1.2 0.5 5.0 2.5
4.9 2.5 4.8 2.2 1.9 0.9
4.0 cl,.<3 1.2 0.4 4.6 2.3
4.8 2.0 4.2 1.4 2.0 1.0
1.3 0.6 0.1 0.5 7.5 0.5
1.5 0.4 1.5 0.5 0.5 0.:
1.2 0.6 0.1 0.4 I.4 0.5
1.5 0.4 1.4 0.4 0.5 0.5
Mean S.D. Mean S.D. Mean S.D.
3.7 2.1 1.1 0.6 4.7 1.6
6.2 2.7 4.5 2.9 2.1 1.4
3.7
0.4 4.7 I .4
5.1 2.2 4.0 2.8 1.9 1.3
1.1 0.7 -0.0 0.6 1.5 0.3
0.5 1.3 0.6 0.5 0.6
1.1 0.7 -0.1 0.5 1.5 0.::
1.6 0.5 1.2 0.5 0.4 0.7
Mean S.D. Mean S.D. Mean SD.
4.9 2.0 1.2 0.6 5.7 3.0
4.9 3.0 5.5 2.7 2.6 1.1
4.5 1.4 1.2 0.5 5.3 2.3
5.6 3.4 6.1 2.7 2.7 1.5
1.5 0.4 0.0 0.6 I .ij 0.5
1.3 0.9 I.5 0.8 0.9 0.5
1.5 0.3 0.1 0.4 1.6 0.5
1.5 0.8 1.7 0.5 0.8 0.6
ZPT
/ LAN
1 &PT
/ BAM
adults
Hahit~unl Vrotrusive Ketrusive
7.6
2.1
0.4 1.6 0.4 0.5 0.6
children
Habitual Protrusive Retrusive Postural
III
Habitual Protrusive Rctrusivc Skeletal Habitual Protrusive Retrusive
muscle
1974
--__ T,Z’T
Bite
Normal
untransformed
group/bite/muscle
Cntmn~~fometl
Normal
J. Orthod.
November
2.G 1.0
III
their means against their respective standard deviations shows an approximate linear relationship which indicated that an appropriate transformation would be logarithmic (Fig. 2). The stability in the stantlartl tlcviation as a result of this transformation was striking, and yet tht: activity patterns within the hitcs had not been alteretl drastically (Table I). The muscle activities oi’ a single putic:nt with I ‘informal” occlusions ill the habitual bite position were: itivcstigatc~tl ; 120 bitts were analyzed, ailtl tlic: results arc seen in Table 111. Although the a~w~~g,rcadi\-itg \\-as slightly lower than that for the group of normal adults, it was recognizable as being of the same type. The pattern was distinct when compared with tlic adult protruded and rctruded contaet positions. The r&dual mean syua,rw (Table 111) were very similar to the l)ctwecn-patient mean squaws (Table II) al~tl tlenioiistratt~tl that the variability due to electrode placing on tliffercnt persons did not present a problem so far as the interpretation of the results was concerned. This conclusion was strengthened
vozunae 66 NWE be?- 5
Table
Electromyographic
HA. Multivariate
analysis
of
variance
of muscle
i?zvestigation activity
(log
8.S. t3ource
I
D.F.
I
LPI
Groups (G) Patients Bites (B) BxG Error
Table
IIB. Correlation
Source
1 LAM
/
M.S. RPT
1
LPT
/
LAN
1
RPT
1 RAM
0.7s
2.46
1.44
3.14
0.26
0.82
0.48
1.04
33.74
26.86
27.75
0.45
0.51
0.40
0.42
2
97.48
42.11
94.72
45.60
48.74
21.05
47.36
22.80
6 132
1.26
4.42
1.41
3.44
0.21
0.73
0.23
0.57
23.80
27.01
25.93
25.55
0.18
0.20
0.19
0.19
structure
1 LPT/LAM
1 LAiU/RPT
) LPT/RPT
1 LAN/RAM
-0.05
0.62
0.95
0.73
0.53
0.55
0.48
0.71
0.75
-0.50
0.99
0.99
-0.47
-0.18
0.90
0.91
-0.12
0.76
0.73
0.56 -0.48 0.12
0.15 0.09
Results
from
the
0.17
analysis
1. T,PT Mean S.D. MS
1 RPT/RAM
-0.50
0.22
of I
120
repeated
2. LAN
measurements I
1 LPT/RAX 0.50 0.52
0.27
on
3. RPT
one I
individual 4. RAN
0.80 0.60
1.80
0.80
1.90
0.80
0.60
0.80
0.44
0.64
0.40
0.71
Correhtion
pairs
RAM
29.86
BxG
Muscle
data)
3
Error
Ill.
543
66
Groups (G) Patients Bites (R)
Table
of patients
structwre
12
23
34
13
24
14
0.83
0.72
0.72
0.77
0.93
0.76
by the examination of the correlation structure, for although the single-patient residual correlation structure was, as one would expect, very much stronger, it is directly comparable to the within-patients correlation structure. By contrast, it bore little resemblance to the error structure. It was concluded that recordings of a group of patients with a similar occlusal relationship would look like recordings of the same individual made on separate occasions. Their pattern would be distinct, and the correlation and variance covariance structure would bc fixed and quite unlike that due to the errors in the method itself. A principal component analysis of the 120 bites of a single subject showed that, because the residual variances were so similar, the principal components with a large variance looked very much the same, whether they had been extracted from the variance-covariance matrix or the correlation matrix. These were :
Am J. Orthod. November 1974
M
AR.
-1
-2 Fig. 3. A diagram the masseter adult group. position.
of the activity muscle for a group P, Protruded contact
0 of the temporal muscles of adults with a normal position. R, Retruded
1 plotted occlusion contact
2
T
against the activity of (log data). A, Normal position. H, lntercuspal
1. A general strength component (0.5, 0.5, 0.5, 0.5) accounting for 86 per cent of the variability when obtained from the correlation matrix. 2. A temporal masseter contrast (0.2, -0.4, 0.7, -0.5) accounting for 8 per cent of the variability when extracted from the correlation matrix, suggesting a difference in a&i&y from left to right when the jaw was protruded or retruded. The other two components are discussed in the appendis. A multivariatc analysis of variance was undertaken on the transformed data of the groups of patients. The relevant partition and correlation structure for these data showed two main sources of variation, the differences between patients and the over-all error in measurement and other noise. It showed that in both cases there was approximately the same residual variation in each muscle activity, but the variation between patients within groups was roughly twice that of the noise level. Also, the correlation structure between patients was of a different nature than that in the over-all error (Table II). In the patients, variability affects all the muscles, with the greatest correlations between the corresponding masseter and temporal activities, whereas in the over-all error the only correlation present was between the corresponding temporal and masseter muscles (Table IlB) . There was also a high positive correlation in the between-bites component and
Electromyographic
0 Fig.
4. A diagram
of
the
the masseter muscle for C, Normal child group. Protruded contact position.
activity
1 of
the
all the groups P3, Postural R, Retruded
temporal
2 muscles
of patients
investigation
plotted
of patients (log data). A, Class III group. 53, Skeletal contact position. H, lntercuspal
545
T against
the
activity
of
Normal adult group. Class III group. P, position.
between equivalent muscle activities on the left and right, while nonequivalent muscles had a large negative correlation. This indicated the different functions of the muscle in the protruded contact, retruded contact, and intercuspal positions (Fig. 3). Consideration of the bites x groups interaction partition showed that there was an interaction present in the masseter muscles, but there was little difference between the groups. Although the amount of activity in the temporal muscles showed the greatest variability over bite, it varied equally over the four groups, whereas the masseter activity, although it did vary over bite and groups, had a different function within each group as the position varied from retruded contact, to intercuspal position, to protruded contact (Fig. 4). A component analysis of the data showed that investigation could be undertaken of the bites by considering the masseter/temporal comparison, with additional information being obtained from the total activity. This clearly showed the different nature of the three bites as far as the activity in the four muscles was concerned (Fig. 5). In terms of the untransformed data, it was equivalent to considering the ratio of masseter and temporal activity as has been already used in a previous study.2S When a similar analysis was undertaken for the bite x group interaction, it was clear that the four groups showed a completely different pattern of activity over the three bites when plotted in natural data space (Fig. 4). The adult activity was greater than that of the children or the two malocclusion groups, although the children resemble the postural Class III group. The skeletal Class III group stood out as having greater masseteric activity in the protruded contact position than in the intercuspal position. The derived variables were then plotted (Fig. 5)) using a weighted temporal/
Am. J. Orthod. November 1974
TA
T/M Fig.
5.
A
diagram
showing
the
plot
of
weighted total activity for all groups of child group. P3, Postural Class III group. contact position. R, Retruded contact position.
the
weighted
patients. A, 53, Skeletal H, lntercuspal
temporal/masseter
contrast
and
Normal adult group. C, Normal Class III group. P, Protruded position.
masseter contrast and weighted total activity. The children were distinguished from the other groups by their smaller temporal/masseter contrast activity in the retruded contact position. The postural Class III resembled a weak adult and the skeletal Class III showed no variation at all in the total activity direction in which marked changes were observed in all other groups. The habitual bite for this group closely resembled the retrusive bite, which was to be expected. In the intercuspal position there was a significant difference between the various groups. In the retruded contact position there was a significant difference between the skeletal Class III group and the normal and postural Class III groups. In the protruded contact position there was little difference. It is therefore suggested that the best discriminator of the groups would be the intercuspal or retruded contact positions. Data from a group of Class III patients who had been recorded at the completion of treatment and a group who had been recorded out of retention vvcrc evaluated. The figures are given in a comparable fashion in Tables VII and VIII. The plots of natural variables and dcrivcd variables are shown in Figs. 6 and 7, with normal adults shown for comparison. After treatment the activity remained low, resembling the postural Class III group. Out of retention, however, the activity increased and took on a normal pattern. Thus, the findings for the treated group were quite distinct from those before treatment. Discussion
The analysis of the muscle patterns of twenty children with normal occlusion in the study confirmed the results of MacDougall and Andrew,“’ Greenfield and
Electrom~yographic
i~wvestigatbn
of pa’tients
T
2 Fig.
6.
A diagram
of
the
activity
of
the
temporal
muscle
the masseter muscle for the normal adult group and end of treatment and a year or more out of retention. Ill patients at contact position.
the end of R, Retruded
treatment. contact
plotted
against
the
activity
a group of Class III patients A, Normal adult group.
0, Class III patients position. H, lntercuspal
out of position.
547
retention.
of
at the T, Class
P, Protruded
JV~yke,~and LatifzO that during the habitual bite there was a balance of muscle activity between the two sides. This was seen in the high correlations of muscle activity between the left and right posterior temporal and anterior masseter muscle activities. It also showed that the muscles on the left tended to be slightly more active than those on the right. This was tested statistically, and it was found that the two sides were different and should not be considered together. The protruded contact position of children did not show the same high degree of correlation between the anterior masscter and posterior temporal muscle activities on opposite sides. This was probably due to the deviation of the jaw in protrusion, resulting in an imbalance in the muscle activities.’ The retruded contact position of children was similar to that described by Latif”’ and showed a high correlation of muscle activity between all muscles. The high correlation of activity in retrusion was due to the inability of the children to deviate appreciably during this movement. The habitual, protruded contact and retruded contact positions of the adult patients with normal occlusion are typical of those described by various investigators,8, 22,30 The correlation matrices showed that the best correlations were found in the rctruded contact, and the worst were found during protruded contact. Once again, this was probably due to deviation of the jaw in the protruded contact position. In this study, patients with a skeletal Class III relationship and a postural Class III relationship were investigated and compared with patients with normal occlusion to see whether or not there was an alternation in muscle pattern with malocclusion. Baril and Moyers, * Findlay and Kilpatrick,F Krazer,lQ Witt,35 and Ahlgren’ maintain that there is no change, whereas Grossmann,l2’ 13 Timms,33’ 34
548
Am. J. Orthod. November 1974
Moss and Chalmers
I
2 Fig. 7. weighted the end
A
1
diagram showing the plot of the total activity for the normal adult of treatment and out of retention.
1 weighted temporal/masseter group and the treated
2 Class
TIM contrast III group
and at
and Perry”“, 31 and their co-authors found a difference in muscle activity in patients with malocclusion. The pattern of activity during habitual biting was significantly different in children and adults and showed a poor correlation between muscles except between the same muscle on each side. The protruded contact and retruded contact patterns were slightly different from those of the adults and children, and the correlation matrices showed a poor correlation between muscles except in the postural Class III group, which showed a significant correlation between all muscles in the protruded contact position. This was probably due to a learned path of closure,” and therefore the patient was better able to produce a protruded contact position. There was a definite alteration in pattern in the activities of the muscles of the Class III patients in the study during treatment. A similar alteration in muscle pattern had been noted by Moy~rs,~~ Ahlgren,’ Okun,*” and Grosfeldll in Class II, Division 1 cases. Haralabakisl’ also reported on a group of cross-bites which were treated, and he noted a change to the normal pattern of muscle activity. Grosfeldll also noted a change to a normal pattern of activity following functional treatment. In this study, at the end of treatment the correlation matrices revealed a poor correlation between the muscle activities in the habitual, protruded contact, and retruded contact positions. Out of retention there was a great improvement in the correlations between the muscle activities in the habitual bite but not in the protruded contact and retruded contact positions.
1~oZwne Nmnbw
Statistical
BG .5
Electromyographic
investigation
of patients
549
method
IllititrI 0 )Inl?jsis. As a preliminary study, the means and standard deviations of the activity of each muscle within a bite/group combination were obtained. These results arc shown in Table I. It appeared that there was a wide.variation in the sample standard deviations, which su ggested that the data were not normally tlistribntcd with errors independent of any linear model. A scatter diagram of the means against their respective standard deviations (Fig. 2) showed an approximate linear relationship which indicated that an appropriate transformation, both to normalize the data and to produce homoscedasticity, would be logarithmic. This agreed with observed behavior of muscle activity and with the practice of some investigators of clectromyographic techniques. Table I shows the results of applying such a tra.nsformation. The stability in the standard deviation was now quite striking, and yet the activity patterns within the bites had not been altered drastically. A~~ultivnrirtte nwlysis of vuritr~~c~~There are two main aims in any analysis of variance : (1) the partitioning of the total sum of squares into components attribntablc to the various components of the design and (2) the construction of relevant F tests so that hypotheses concerning various factors in the design may bc examined. It is arguable that the first aim was the> more important, enabling one as it tloes to produce estimates and confidcncc intervals for both the paramct.crs and components of variance in the model and also, when simple ANOVA tables only have been constructed, to test rather more informative u I)riori hypotheses. Multivariate analysis of varianc:e is a natural extension of this technique to a partition of the total sum of squares and products matrix. As a byproduct, one obtains the usual F statistics for csach component of the data but over-all tests arc available to examine the variation of the response \-cctor as a whole, taking into account the correlation between its various components. However, the comment on univariate analysis of variance still seems appropriate and the main applications of any MANOVA routine are likely to be in the examination of the residual error structure and its application in the testing of further hypotheses. The relevant partition and correlation structure for these data arc shown in Table II. There were two main sources of random variation in the data, the differences between the individual patients and then the over-all error in measurement and other noise. The tables made it clear that in both cases there was approximately the same residual \,ariation in each muscle activity but that the variation between patients within groups was roughly twice that of the noise level. However, the correlation structure between patients was of a different nature from that in the over-all error. The patients’ variability affected all the muscles, with the greatest correlation being between the corresponding regions of the temporal ant1 masseter muscles. In the over-all error t,his latter was practically the only correlation present. Thus: random fluctuations will tend to affect either the masseter or the temporal muscles equally on the left ant1 the right, whereas between patients the main cause of their variability provccl to be the strength of their bite, affecting all muscles equally, after which the random fluctuations affected the two muscles separately. Looking at the between-groups mean
550
Moss and Chalmers
Am. J. Orthod. November 1974
squares, it was clear that great difficulty would be experienced in distinguishing between members of different groups on the basis of an average bite unless we were to allow repeated bites, in which cast the masseter muscle could prove a discriminator. However, the type of bitt being made was very easily ascertained, for the bites/error F ratios were all of the order of 100 with 2/6 degrees of freedom. This difference was examined in greater detail later. There was a high positive correlatiorI in the between-bites component between equivalent muscle responses on the left, and right, while nonequivalent muscles had a large negative correlation. This indicated the different functions of the muscles in habitual, protrusive, and retrusive bite positions. This effect could also be examined in greater detail, using the error structure and the table of means, and this was done. Although both muscles sl~o~ed great variability between the three bite positions, the temporal muscle showed the greatest variation. Consideration of the bites x groups interaction partition showed that while little evidence was found to suggest over-all differences between the groups there was clearly evidence to suggest that an interaction was present in the masseter muscles. Thus, although the strength of action in the temporal muscles showed the greatest variability over bites, it varied equally over the four groups. The masseter muscle, on the other hantl, while its strength did vary generally over all bites and groups, had a different function within each group as the position varied from retrusive to habitual to protrusive. Results from repeated obseruatio~~s ON nlle patiellt. At this stage the results obtained by multivariate analysis of variance on this set of widely differing experimental material were compared with those obtained by repeated observations made on a single patient in his habitual bite position. There were available the data from 120 such bitts, ant1 the results comparable to those shown in Table I and Table II are given in Table 111. Again, log (activity) was used. Although the average response in all four muscles was somewhat lower than that for the group of normal adults, the pattern was immediately recognizable as being of the same type, having roughly twice the activity in masscter muscles when compared to temporal muscles but an appreciable amount in each. This pattern was distinct when compared with the activities in the adult retrudecl contact and protruded contact positions and all bites in the other groups. The residual mean squares (Table III) wcrc \-cry similar to the between-patients mean squares (Table II), with perhaps a slight increase in the rnassetcr variability. One can suggest that the explanation for this lies in the process of replication in that the patient varied his habitual bite from time to time, sometimes producing a slightly retrusive and sometimes a slightly protrusive bite. This would also explain the slight decrease in over-all muscle activity. Structure withk the 1,lILl~iz’aricrbles. I3ven in as few as four dimensions, it \vas not always immediately obvious what characterized the group properties of the data. In biologic data, often a principal component analysis of the variancecovariance matrix (or sometimes the correlation matrix) will bring out this structure more clearly. When such structure has been revealed, this may suggest a recasting of the data in various ways so as to emphasize particular propertics. Such further analyses are canonical analyses.
Volume Number
66 5
Electromyographic
investigatim
of patients
551
In these data we have both the single individual and the groups to consider Principal components on the reszllts from a single individual. Since the residual variances were so similar, it was found that the principal components with large variance looked very much the same, whether they had been extracted from the variance-covariance matrix or from the correlation matrix. They were: 1. A general strength component of 0.5, 0.5, 0.5, 0.5 when obtained from the correlation matrix, accounting for some 86 per cent of the variability. Recast in terms of the unstandardized data by using the variance-covariance matrix, we obtain 0.4, 0.6, 0.4, and 0.6, reflecting the greater variance in the masseter muscle, that is, some idea of relative bite strength can be obtained from 2 x total temporal activity + 3 x total masseter activity. 2. A temporal masseter contrast accounts for a further 8 per cent of the variability of the data, giving a component of 0.2, -0.4, 0.7, -0.5 when extracted from the correlation matrix and 0.4, -0.3, 0.7, -0.5 when extracted from the variance-covariance matrix. This component, which accounted for an appreciable amount of the variability of the data in this one individual, was precisely the phenomenon that was accepted earlier. Added to the variation in strength of bite, it increased the temporal and decreased the masseter or vice versa. This was exactly equivalent to what was seen in normal adults as the change is made from habitual to protrusive or retrusive bite, Table I. In this single person there was an asymmetry of the result, suggesting either an imbalance in electrode placing or a genuine difference in activity from left to right when the jaw was protruded or retruded. 3. The next component accounted for a further 5 per cent of the variability and emphasized this asymmetry. Taking only the variancecovariance matrix, we had -0.7, -0.2, 0.6, and 0.2, that is, a component which balanced the activity between the two sides though not balancing the activity in the two muscles. 4. The last component in the individual contributed only a negligible amount, and -0.2, +0.7, +O.l, -0.6 represented variation due to “shearing” in the jaw position. The fact that this component turned out to be relatively constant throughout the data for this one patient was reassuring, for the anatomy of the jaw would suggest that the progression from protrusive to habitual to retrusive is a natural one and should not contain any element of “shear.” This result, in turn, suggested a direct link between the measurement of activity by electromyography and the real activity of the muscle, and hence the patient’s potential for change. Component analysis from the MANOVA table. Within the MANOVA table there were two main sources of error: the between-patients and with within-patients errors. Taking principal components for each case and comparing the results obtained with those for the single patient
552 Table from
IV. A comparison the betweenSingle
Per cent Variation
of principal
and
/ CM
patient
86
84
8
9
5
6
1
1
vclll t4 +6 t4 +6 -4 +3 -7 +5 -7 -2 +6 +4 4 t7 t2 -6
components
within-patient
results Between
I
Per cent Variation
Loadhg
VCN
Both matrix
Am. J. Orthod. November1974
Moss a,nnd Chalmers
1
from
patient
(‘M
FCM
t5 t5 +5 +5 -2 +4 -7 t5 -8 -0 t5 t4 -2 t7 +l -6
70
70
17
17
7
7
6
6
+5 +5 +5 t5 -5 t5 -5 15 -6 +3 +6 -3 -3 -6 +3 t7
variance-covariance
with
those
Error
I Per cent Variation 1
obtained
table
Loading
VCMI
the
a single
patients
CM
principal components from are shown for comparison.
for
the MANOVA
CM
VCM
t5 t5 +5 +5 -5 t4 -5 +6 -7 t2 t7 -2 -2 -7 +2 +7 matrix
/
Loading CM
VCM
53
53
35
34
7
7
5
6
t5 +5 t5 t5 -5 +5 -5 +4 -2 -6 +1 +7 -7 t2 t7 -1
and
from
the
/
CM +5 t5 +5 +5 -4 +5 -5 +5 -3 -6 t2 t7 -7 +3 t7 -2
correlation
already outlined, we obtain the data presented in Table IV. From this table it was apparent that the structure of each matrix was basically the same in that the principal components were very similar but that their loadings (the amount they contributed to the total variability) differed in the three cases. Thus, between patients and for a single individual, between bites, the primary source of variability was the index representing strength of bite. However, this did not appear in quite such a strong fashion in the error where the second component, representing a masseter/ temporal comparison, played a much larger role. Conversely, this latter component also entered into the between-patients set but with a smaller loading. These results reflected the varied experimental material, for while each patient differed from the others in the strength of bite, the additional action necessary to produce a retrusire or protrusive bite also differed from individual to individual. This phenomenon was seen in the bites x groups interaction in the masseter muscles, but the multivariate analysis now shows that this effect caried over to the complete muscle activity. The single patient was more consistent in his bite pattern, as was evident from the per cent variation explained by the first principal component, strength of bite. However, as has already been noted briefly in the earlier description, while the pattern of the loadings was very much the same as for the patients and error, the weights were not the same and we had a certain asymmetry. This demonstrated the uniqueness of this patient, and this
Volume
Number
66 5
Table
V.
partition
Electromyographic First in the
two
principal
MANOVA
components
investigation
obtained
from
cent
Table
Bites
variation
Loadings
CM
VCM
79
75
21
25
+6 -3 +6 -3 +3 +6 +3 +6
VCM
1
VIA.
Individual
bite
(
Per CM +5 -5 +5 -5 +5 +5 +5 +5
activities
cent
vciv
Bite Habitual Protrusive Retrusive
x
groups
(weighted
x Groups Loadings vclll
CM
74
49
26
48
1
CM i-6 -1 +7 -3 +2 +7 +2 +6
0 +8 0 +7 +T +2 +7 -2
means]
LPT
LAM
RPT
RAM
1.31 -0.17 1.52
1.61 1.47 0.62
1.29 0.06 1.54
1.62 1.46 0.58
masseter
I 4
bites
Muscle
Habitual Protrusive Retrusive
VIB. Average
and
variation
1
I Bite
Table
bites
553
table
Bites Per
the
of patients
and
temporal
activities
and
canonical
variables
Component T
1
!
1.30 -0.05 1.53
M 1.62 0.97 0.60
I,
TOM 0.98 -1.08 0.92
/I
Acthit?/ 1.51 0.63 0.91
slight abnormality could be attributed either to bc a genuine effect or to the patient’s tendency to vary his habitual bite. The pooled between-patients structure was more reliable, since it averaged out any odd tendencies of this nature. It is also of some interest to examine principal components extracted from both the bites and bites x groups interaction partitions in the MANOVA table. The relevant results are given in Table V. The bites can clearly be investigated by considering the masscter/temporalis comparison, with additional information being obtained from the total activity. However, the interaction components were little more difficult to identify as obtained. If, however, one assumed that both components attempt to explain 50 per cent of the variability, then any linear combination of the two would play the same role. In this case, it was suggested that total masseter and total temporal activity may prove helpful indicators. In terms of the original untransformed data, this is equivalent to considering the ratio of masseter to temporal activity and has been sug-
554
Moss ma Cblmers
Table
VII. Data
AH
for
interaction
1.37
AP
Am. J. Orthod. November 1974
of bites
2.05
-0.16
x groups
1.41
1.55
1.39 -0.13
2.01
1.35
1.97
-0.09
0.77
1.55
1.80
-1.80
0.99
AR CH CP
1.51
0.60
1.65
0.51
1.58
0.56
2.60
0.90
1.27
1.49
1.21
1.49
1.24
1.49
0.99
1.41
0.09
1.45
O.Ofi
1.36
0.08
1.41
CR
1.49
0.50
1.41
1.47
0.83
1.10
1.54
1.06
1.45 1.08
0.53
PH PP PR
0.55 1.52
1.53
0.63
1.38
1.23
-0.05 1.51
1.29
0.84
0.49
-1.39 2.52
1.42
1.54
1.10 1.10
-0.02
SH
SP SR
Table Group TH TP TR OH OP OR
VIII. 1
1.35
-0.08
1.50
0.54
1.51
0.43
1.49 0.02
1.34 1.52
1.47 0.12
1.49 I.7L
1.48 0.07
1.62
1.60
0.85
1.58
0.82
1.59
0.84
Data
for
LPT
/
1.28
-0.13
“finish LAM 1.07
1.31
of 1
treatment RPT 1.23
-0.08
group
1 IZAX 1.05
1.19
)
(T)”
and
T
)
1.26
-0.11
“out M 1.06 1.25
-1.28
0.63
0.83
-1.45 2.34
of
retention /
TV4 1.45 -1.46
1.09
group 1
(0)” A 1.13
0.80
1.54
0.53
1.51
0.52
1.53
0.53
2.52
0.86
1.47
2.02
1.58
2.09
1.53
2.06
0.99
1.88
0.34
1.86
0.31
1.86
0.33
1.86
1.80
0.97
1.74
0.88
1.7;
0.93
-1.21 2.61
1.35 1.21
gested.already as a suitable discriminator in earlier studies.‘” In Tables VIA and VIB and Fig. 3, both the elementary variables, total masseter and temporal activity, and the derived variables, weighted temporal masseter contrast and weighted total activity, are examined. These showed clearly the different nature of the three bites as far as the activity in the four muscles was concerned. However, a more detailed analysis was necessary to see the improvement in separation gained by using the derived variables rather than the “natural” variables. In Table VII and VIII and Fig. 4, a similar exercise was undertaken for the bites x groups interaction. Again, while quite a clear picture was painted by this analysis, rather more detail was required to justify the gain in information. Summary
The method of analyzing the electromyographic data from patients has been described, and the results of the investigation of twenty adult patients with normal occlusion, twenty children with normal occlusion, fifteen patients with skeletal Class III malocclusion, and fifteen patients with postural Class III malocclusion have been presented. Each patient was recorded in the protruded contact, retruded contact and intercuspal positions. A group of Class III patients who had received orthodontic treatment were recorded after treatment and out of retention, and this group was also investigated. The results showed that the best jaw position for discrimination between the
Electronzyographic groups was the intcrcuspal the muscle activity returned
iwvestigation
of patients
position and that, following orthodontic to a more normal pattern of activity.
555
treatment,
REFERENCES
1. .\hlgrcn, .I. : An electromyographic analysis of the response to activator therapy. Odontol. Rev. 11: 125-151, 1960. 2. Ahlgren, J.: Mechanism of mastication: A quantitntivc cinematographic and clectromyographic study of masticatory movements in children, with special reference to occlusion of the teeth, Acta Odontol. &and. 24: Supp. 44, pp. l-109, 1966. 3. Ballard, C. F.: Consideration of the physiological background of mandibular posture and movement, Tr. Br. Sac. Study Orthod, pp. 117-127, 1955. 4. Baril, C., and Moyers, R. E.: An clcctron~yogmpl~ic analysis of the temporal muscles and certain facial muscles in thumband finger-sucking patients, J. Dent. Rcs. 39: 536-553, 1960. 5. Dominik, K,: Die clcktromyograpl~ischc Bcwertung verschiedener Rcizc, welchc kieferorthopadischc Funktionsapparntc aktivieren, ZahnBrztl. Welt. 69: 730-732, 1968. 6. Findlay, I. A., and Kilpatrick, 8. J.: Analysis of myographic records of swallowing in normal and almormal subjects, J. Dent. Res. 39: 629-637, 1960. 7. Greenfield, B. E., and Wyke, B. D.: Electromyographic observations on some of the muscles of mastication, J. Anat. 89: 578, 1955. 8. Greenfield, B. E., and Wyke, B. D.: Electromyographic studies of some of the muscles of mastication, Br. Dent. J. 100: 129-143, 1956. 9. Grosfcld, 0.: Die Rolle der Elektromyographischcn Analyst in der kieferorothopldischcn Diagnose, Dtsch. Stomntol. 11: 942-952, 1961. 10. Grosfeld, 0. : Badania Elektromigraficzne W Zahurzeniach Szchekowo-Zgryzowych l’whodzcnia Czwnnoscio\vcgo, Czas. Htumatol. 11-12: 965972, 1QfiZ. 11. Grosfcld, 0.: Changes in muscle activity patterns as a result of orthodontic treatment, Tr. Eur. Orthod. Sot. 41: 203-213, 1965. 12. Grossmann, IV., and Grcenficld, B. E.: An analysis of treated casts, Tr. Br. Sot. Study Orthod., pp. l-12, 1956 13. Grossmann W., Grccnfield, B. E., and Timms, D. J.: Electromyography as an aid in diagnosis and treatment analysis, Ant. J. ORTHOII. 47: 481-497, 1901. 14. Haralabakis, V.: Elcctromyographic analysis of a scrics of 50 treated posterior crossbites, Tr. Eur. Orthod. Sot. 40: 206-220, 1963. 15. Hodcs, R.: Electromyographic study of defects of ncuro-muscular transmission in human poliomyelitis, Arch. Neurol. Psychiat. 60: 457-473, 1948. 16. Hodcs, R., Larrabec, M. G., and German, W.: The human electromyogram in response to nerve stimulation and the conduction velocity of motor axons, Arch. Ncurol. Psychiat. 60: 340-365, 1948. 17. lnman, V. T., Ralston, II. J., Saunders, .J. B. de C. M., Fcinstcin, B., and Wright, E. W., Jr. : Relation of human clectromyogram to muscular tension, Elcctroencephalogr. Clin. Ncurophysiol. 4: 187-194, 1952. 18. Jarabak, J. R.: Elcctromyographic analysis of muscular and temporomandibular joint disturl):rnccs due to imbalances in occlusion, Angle Orthod. 26: 170-190, 1956. 19. Krazcr, K. : Untersuchungcn iiber die Bczichungcn zwischcn Eugnathien und Dysgnathien cincrscits und den Aktionsstromen dcs M. Masseter obliguus, M. Masscter verticalis, M. Temporalis anterior und der Mundboden muskulatur nnderseits, Medical Dissertation, Freilmrg University, 1960. 20. Latif, A.: Electromyographic study of the temporalis muscle in normal persons during selected positions and movements of the mnndible, AM. J. ORTHOD. 43: 577-591, 1957. 21. Liebman, F. M., and Cosenzn, F.: Evaluation of electromyography in the study of the etiology of malocclusion, J. Prosthet. .Dent. 10: 1065-1077, 1960. 22. MacDougall, J. D. B., and Andrew, B. L.: An electromyographic study of temporalis and masseter muscles, J. Anat. 87: 37-45, 1953.
556 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36.
Am. J. Orthod. November 1974
Moss and Chalmers
Meller, E. : Methodological investigations concerning electromyographic analysis of muscle co-ordination, Tr. Eur. Orthod. Sot., pp. 328-340, 1958. Moss, J. P.: An electromyographic investigation of certain muscle activities associated with malocclusion of the teeth, Ph.D. thesis, University of London, 1971. B. E.: An electromyographic investigation and survey of Moss, .J. I’., and Greenfield, Class 111, cases, Tr. Br. Sot. Study Orthod. pp. 147-156, 1965. Moycrs, R. E.: Temporomandibular muscle contraction patterns in Angle Class II, Division 1 malocclusions: An electromyographic analysis, AM. 5. ORTHOD. 35: 837-857, 1949. O’Connell, A. L., and Gardner, E. B.: The use of electromyography in kinesiological research, Xcs. Quart. 34: 16&184, 19(i3. Okun, .J. H.: Electromyographic study of Class II cases during orthodontic treatment, M.D.S. thesis, Northwestern University Dental School, June, 1960. Okun, J. H.: Electromyographic study of Class II cases during orthodontic treatment, AM. J. ORTHOD. 48: 474-475, 1962. Perry, II. T., and Harris, S. C.: Role of the neuromuscular system in functional activity of the mandible, J. Am. Dent. Assoc. 48: 665673, 1954. Perry, H. T.: Functional electromyography of the temporal and masseter muscles in Class II, Division 1 malocclusion and excellent occlusion, Angle Orthod. 25: 49-58, 1955. Pruzansky, S.: : Application of electromyography to dental research, J. Am. Dent. Assoc. 44: 49-68, 1952. Timms, D. J.: Analysis of treated cases, Tr. Eur. Orthod. Soe. pp. 368-377, 1960. Timms, I). J., and Greenficld, B. E.: Some clectromyographic observations on maxillomandibular relationships in orthodontics, Tr. Eur. Orthod. Sot., pp. 312-327, 1961. IVitt, E.: Kinnmuskulatur und Kinnformung, Fortschr. Kieferorthop. 25: 225-232, 1964. \\‘oelfcl, J. B., Jlickey, J. C., Stacy, R. W., and Rinear, L.: Elcctromyographic analysis of of jaw movements, J. Prosthet. Dent. 10: 688-697, 1960. U.C.Z.
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