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Muscle activity in Class II, Division 1 malocclusions treated by bite jumping with the Herbst appliance
Muscle activity in Class II, Division 1 malocclusions treated by bite jumping with the Herbst appliance An electromyographic
Dr. Pancherz
study
H. Pancherz, D.D.S., Odont. Dr., and M. Anehus-Pancherz, D.D.S. Mulmii, Stteden The
e#cw
of contimrous
in ten growing upplicmce.
quantitutiveiy
chewing
of peanuts.
treatment
during
vulues. temporul clcti\itJ trppliunce
maximal
rrctivity
unteriorlv
biting removed
in all patients.
.seen in the 11’0s due
The
in the
was
EMG
in the
in EMG
nctivity
results
of this
investigation
Division
I cuses
Cluss
II,
to un ultereti
seen
sugittul
After
with
from
(3)
When
normul muscles
for
greater suggest during
bu.se
bite or dentrrl
treatment
the
,jumping
tbt’o muscles
the
Herbst Mlere
pretreatment
masseter the
contucts
the
relutions
exceeded
that
the mandible
no occlusal
occlusal
Before
temporal
either
nppliunce,
rrctivity
reduced.
the
during
EMG
two
was
jaw
muscles,
were
during (I)
,from
position The
markedly
uctivity
than
position.
the two
of treatment,
6 months
und
the following: less
of the Herbst
segments.
chebving
after
wus
the Herbst muscles
position
intercuspul
insertion
IVUS investigated with
masseter
revealed
muscle
edge-to-edge
urch
and
in intercuspul
between
(2) During
and
The
increase
muscle.
biting
MUS found
dental
wus
biting
musseter
to an incisor
muximul
The
the
activity treated
temporul
qf the investigation
from
or chewing.
mu.scle
I nmlocc~lusion the
mclximal
results
during
in the posterior
uppliance @nd
The
on musticutory Division
recordingsfrom
activity
in EMG
~t’as ,jumped present
II,
during
especiully
biting
Cluss
EMG
the EMG
no d$ference mtrximul
with
lntegruted
unuly:ed
muscle.
bite jumping
boys
than
increused with
the
for
the
muscle Herbst
relationship.
Key words: Integrated EMG, muscle activity, bite jumping, malocclusion, Herbst appliance
A
n abnormal electromyographic (EMG) pattern in the temporal and masseter muscles associated with Class II, Division 1 malocclusions has been ascertained in several investigations. 1-STreatment with functional appliances was found to normalize the muscle pattern in some studies.“, 4 When treating Class II, Division 1 malocclusion by bite jumping with the Herbst From the Departmentof 0002-9416/80/090321+09$00.90/0
0
Orthodontics,
School
of Dentistry
1980 The C. V. Mosby Co.
321
Am. J. Orrhod. Sr~rrmher 1980
Fig.
1. Plaster casts of a Class Ii, Division 1 malocclusion treated with the Herbst appliance for 6 months. A, Before treatment. B, Start of treatment. C, After treatment. Note the telescope mechanism (tube and plunger) which works as an artificial joint and keeps the mandible in a continuous anterior jumped position.
appliance, Pancherz” suggested that mandibular growth might be stimulated. Bitejumping experiments in growing monkeys have also shown that structural adaptations in the mandibular condyles occurred concomitantly with alterations in muscle function.‘. ’ The purpose of the present investigation was to analyze electromyographically the effect of bite jumping with the Herbst appliance on the activity of the temporal and masseter muscles. Material Ten consecutive patients with Class II, Division 1 malocclusion treated by continuous bite jumping with the Herbst appliance” were surveyed (Fig. 1). All subjects were growing boys with a skeletal Class II relationship. The mean pretreatment age was 12 years 1 month (S.D. = 11 months). Treatment with the Herbst appliance was performed during a fixed time period of 6 months (mean = 6 months 4 days, S.D. = 5 days). After treatment, normal dental arch relationships were established in all patients (Fig. 1). Methods A quantitative analysis of electromyographic (EMG) activity from the temporal and masseter muscles was made before treatment, at the start of treatment when the appliance was inserted, during treatment (after 3 months), and after 6 months of treatment when the appliance was removed. For the EMG recordings, bipolar hook electrodes” were placed bilaterally on the temporal and masseter muscles as shown in Fig. 2. Direct and integrated recordings were obtained from all muscles studied with the aid of a Mingograph 800 (Elema-Schonander, Stockholm). The integrating technique has been described in a previous study.” An amplification of 500 PV per centimeter was used for all recordings. The EMG activity was registered as follows: 1. During maximal biting in intercuspal position. The patients were instructed to close their jaws in centric occlusion as forcibly as possible. The maximal integrated activity during a biting cycle (the mean value of five consecutive cycles) was used for evaluation. For both the temporal and masseter muscles, the mean value of right- and left-side measurements was used. 2. During the chewing ofjve peanuts. No instructions were given to the patients other than to eat the peanuts. The maximal integrated activity during a chewing cycle (the mean
Volume 78 Number 3
Fig. 2. Diagram
Bite jumping
demonstrating
electrode
placement
on temporal
with
Herhst
and masseter
uppliumx,
323
muscles.
value of ten consecutive cycles) was used for evaluation. A chewing cycle was defined as the opening and closing phase of one masticatory movement of the mandible. For the temporal muscle, the mean value of right- and left-side measurements was used. For the masseter muscle, the mean value of right- and left-side measurements was used in cases with a bilateral chewing pattern. In cases with an unilateral chewing pattern, the EMG activity was recorded from the chewing side only. All measurements on the electromyograms were made to the nearest millimeter. An evaluation of occlusal contact conditions was performed at all times of EMG examination by counting the number of mandibular teeth in contact with each maxillary tooth.“) In a case with excellent occlusion, the maximal possible number of tooth contacts is twenty-eight (excluding third molars). Assessment was made on dental casts (before and after treatment) and clinically (during treatment). Statistical methods. Differences in measurements before and after treatment and between different muscles were tested by Student’s t test. The levels of significance used were p < 0.001, p < 0.01, and p < 0.05. Results
EMG uctivity during maximal biting in intercuspulposition (Fig. 3). Before treatment the EMG activity from the masseter muscle was significantly (p < 0.01) less than from the temporal muscle. After treatment, however, no statistically significant difference in EMG activity was found between the two muscles. When the Herbst appliance was inserted, the mandible was jumped anteriorly to an incisor edge-to-edge position. In this way, no occlusal contacts were present in the premolar and molar regions. The EMG activity from both the temporal and masseter muscles was markedly reduced. After 3 months of treatment antagonist contacts in the
Am. J. Orrhod.
324 Puncher; md Anehus-Parlcherz
Sqmmher
1980
UV ------
Temporal
-
Masseter
600
400
300
I
200
100 1
I
;
:
A
B
C
0
Fig. 3. Maximal integrated EMG activity in PV (mean and SD.) from temporal and masseter muscles during maximal biting in intercuspal position in ten boys with Class II, Division 1 malocclusion treated with the Herbst appliance. A, Before treatment. 6, At start of treatment when the appliance was inserted. C, After 3 months of treatment. D, After 6 months of treatment, when the appliance was removed.
posterior dental arch segments (mainly molar contacts) were found in seven cases, while in three cases contacts still existed between the incisors only. The EMG activity in the two muscles had increased to almost pretreatment values. When the Herbst appliance was removed after 6 months of treatment, normal occlusal relations were found in all patients. The EMG activity had increased significantly for the temporal (p < 0.05) and masseter (p < 0.001) muscles when after-treatment records were compared with those obtained before treatment. EMG activity during chewing (Fig. 4). During chewing, no significant difference in EMG activity between the temporal and masseter muscles was found before or after treatment with the Herbst appliance. When the appliance was inserted, the EMG activity in both muscles was reduced to an insignificant level and no distinct chewing cycle could be identified. After 3 months of treatment the EMG activity had increased markedly, and after 6 months it exceeded pretreatment values. This was especially true for the masseter muscle, for which the increase in EMG activity during the period before treatment-after treatment was statistically significant (p < 0.05). Comparison between EMG activity und occlusal contact conditions. In the ten subjects investigated, the average number of antagonist contacts was eleven before treatment and fourteen after treatment. When the number of teeth in occlusion was related to the EMG
Vdumr 78 Number 3
Bite jumping
------
Temporal
-
Masseter
with
Herhst
appliawc~
325
Fig. 4. Maximal
integrated EMG activity in PV (mean and SD.) from temporal and masseter muscles during chewing of peanuts in ten boys with Class Ii, Division 1 malocclusion treated with the Herbst appliance. A, Before treatment. B, At start of treatment when the appliance was inserted. C, After 3 months of treatment. D, After 6 months of treatment, when the appliance was removed.
activity from the temporal and masseter muscles, or after treatment with the Herbst appliance.
no connection
was found,
either before
Case presentation photographs and electromyograms of a typical Class II, Division 1 malocclusion the Herbst appliance are presented in Figs. 5 and 6. Before treatment, a cusp-to-cusp relationship was present in the premolar region. The number of intermaxillary tooth contacts was eleven. The EMG activity from the masseter muscle was reduced in relation to the temporal muscle, and the contraction pattern between the right and left muscles in each respective pair was unbalanced. When the appliance was inserted, intermaxillary tooth contacts were found between one pair of incisors only. The EMG activity during biting and chewing was markedly reduced in both muscles. After 3 months of treatment still no occlusal contacts were found in the posterior dental arch segments. The EMG activity from both muscles had increased to almost pretreatment values. After 6 months of treatment, when the appliance was removed, occlusal contacts were established bilaterally between the molars. The number of tooth contacts was thirteen. The EMG activity from the temporal and masseter muscles had increased beyond pretreatment values, and the contraction pattern was more balanced.
Intraoral treated with
Discussion An earlier study” has suggested that the EMG activity from the temporal and masseter muscles was reduced in Class II, Division 1 malocclusions when compared to normal occlusions. It was also suggested that in Class II cases the masseter muscle exhibited a
Am. J. Orrhod. Seprembrr 1980
Fig. 5. Intraoral photographs of an 1 l-year-old boy with Class II, Division 1 malocclusion treated with the Herbst appliance. A, Before treatment. B, At start of treatment, when the appliance was inserted. C, After 3 months of treatment. D, After 6 months of treatment, when the appliance was removed.
deficient activity in relation to the temporal muscle. In normal occlusion cases, on the other hand, the EMG activity in the two muscles was about the same. When the present Class II cases were treated by jumping the bite with the Herbst appliance. the EMG activity in the temporal and masseter muscles was increased and the contraction pattern in the two muscles was more like that seen in persons with normal occlusion. Similar results were found in patients treated with functional appliances.‘, 4 At the start of treatment, when the mandible was positioned anteriorly with the incisors in an edge-to-edge relationship, a marked reduction in EMG activity from especially the temporal muscle was found during biting and chewing. Similar changes in EMG activity were seen in children with normal occlusion when the mandible was protracted” or when biting with the incisors in an edge-to-edge position was performed. “l. I:( Biting on a Class I1 activator has also been shown to reduce temporal muscle activity.14. I5 After 3 months of Herbst appliance treatment the EMG activity in the two muscles investigated increased markedly, and after 6 months, when the appliance was removed, the muscle activity exceeded pretreatment values in most patients. A significant increase in EMG activity was found, especially for the masseter muscle. When after-treatment records were compared with before-treatment records, the average increase in EMG activity during
Volume 78 Number 3
Bite jumping
A -
C
B
/
--I
sac.
with
Herbst
/
--L.-
- -. LT LM
DIRECT EMG
RT
. ..-- ._-.
Fig. 6. Electromyograms and chewing of peanuts appliance was inserted. appliance was removed. masseter.
327
D
--w*y*H-
,NTEGRPNITD
uppliunce
-----~
._: --.----
--.
LT --
( 5oop ----_
~_ ..__..
-_--
_----._
-- .- __----
LM
from the case presented in Fig. 5. Maximal biting in intercuspal position (top) (bottom). A, Before treatment. B, At start of treatment, when the Herbst C, After 3 months of treatment. D, After 6 months of treatment, when the LT, Left temporalis. LM, Left masseter. FIT, Right temporalis. RM, Right
maximal biting in intercuspal position was 98 percent for the masseter and 41 percent for the temporal muscle. During peanut chewing the corresponding figures were 40 percent and 28 percent respectively. A relationship between EMG activity and facial morphology has been demonstrated by several workers.. ‘L ‘~3‘IL Ii Animal studies have also shown that form and function are interrelated. Experimental alterations in muscle function resulted in a change of skeletal morphology. lx. Is Before treatment all the present patients had Class II malocclusion with a large ANB angle (mean = 5.5 degrees). Treatment with the Herbst appliance resulted in normal occlusal relationships in all patients, and the ANB angle was reduced by an average of 2 degrees. Thus, these morphologic changes induced by treatment may affect muscle function and may possibly explain the increase in EMG activity found in the temporal and masseter muscles. The relationship between the number of teeth in occlusal contact and masticatory
328
Pamher,- cud Anehus-Puncher;
Am. .I. Orrhod Sqmmber 1980
muscle activity during biting and chewing has been the subject of several investigations.“, “. I”. I6 In the present cases, the number of intermaxillary tooth contacts in the posterior dental arch segments was the same before and after treatment. In the anterior segment, on the other hand, the number of tooth contacts increased during treatment as a result of a reduction in overjet and overbite. No relationship was found, however, between occlusal contact conditions in the posterior or anterior dental arch segment and EMG activity from the temporal and masseter muscles during maximal biting or chewing. These results were in agreement with those of other investigations.“, ifi In earlier investigations”, I0 a connection was found between an impaired EMG activity from the masticatory muscles and a cusp-to-cusp occlusion. In many of the present subjects such an occlusion in the posterior dental arch segments was found before treatment. Thus, one cannot rule out the possibility that this unstable occlusal condition was a cause of the reduced and imbalanced EMG activity seen in the children (Fig. 5). Imbalance in muscle activity may also be due to cuspal interferences.“’ Small occlusal interferences between the retruded contact position and intercuspal position were found in three of the present patients before treatment. These interferences were eliminated, however. by occlusal adjustment before EMG registrations were performed. Conclusion When the present Class II, Division 1 malocclusions were treated by continuous bite jumping with the Herbst appliance, the EMG activity from the temporal and masseter muscles was increased during treatment. The change in muscle activity seen was probably due to an altered sagittal jaw base or dental relationship. REFERENCES 1. Moyers, R. E.: Temporomandibular muscle contraction patterns in Angle Class 11, Division 1 malocclusions: An electromyographic analysis, AM. J. ORTHOD. 35: 837-857, 1949. 2. Grosfeld, 0.: Changes of muscle activity patterns as a result of orthodontic treatment, Tr. Eur. Orthod. Sot. 41: 203.214, 1965. 3. Ah&en, J.. Ingervall, B., and Thilander, B.: Muscle activity in normal and postnormal occlusion, AM. J. ORTHOD.
64: 445456,
1973.
4. Moss, .I. P.: Function-Facts or fiction? AM. J. ORTHOD. 67: 625.646, 1975. 5. Pancherz, H.: Activity in the temporal and masseter muscles in Class II, Division 1 malocclusions: An electromyographic investigation, AM. J. ORTHOD. 77: 679-688, 1980. 6. Pancherz. H.: Treatment of Class II malocclusions by jumping the bite with the Herbst appliance: A cephalometric investigation, AM. J. ORTHOD. 76: 423-441, 1979. 7. McNamara, J. A., Jr.: Neuromuscular and skeletal adaptations to altered function in the orofacial region, AM.
J. ORTHOD.
64: 578-606,
1973.
8. McNamara, J. A., Jr.: Functional adaptations in the temporomandibular joint, Dent. Clin. North Am. 19: 457-471, 1975. 9. Ahlgren, J.: An intracutaneous needle electrode for kinesiologic EMG studies, Acta Odontol. Stand. 25: 15-19, 1967. 10. Pancherz, H., and Anehus, M.: Masticatory function after activator treatment: An analysis of masticatory efficiency, occlusal contact conditions and EMG activity, Acta Odontol. Stand. 36: 309-316, 1978. 1 1. Latif, A.: An electromyographic study of the temporalis muscle in normal persons during selected positions and movements of the mandible, AM. J. ORTHOD. 43: 577-591, 1957. 12. Greenfield, B. E., and Wyke, B. D.: Electromyographic studies of some of the muscles of mastication, Br. Dent. J. 100: 129-143, 1956. 13. Ahlgren, J.: Mechanism of mastication, Acta Odontol. Stand. 24: Supp. 44, pp. I-109, 1966.
Voiume 78 NW&V- 3
Bite jumping
with
Herhst
applianw
329
14. Ahlgren, J.: The neurophysiologic principles of the Andresen method of functional jaw orthopedics: A critical analysis and new hypothesis, Swed. Dent. J. 63: 1-9, 1970. 15. Ahlgren, .I.: Early and late electromyographic response to treatment with activators, AM. J. ORTHOD. 74: 88-92, 1978. 16. Ingervall, B., and Thilander, B.: Relation between facial morphology and activity of the masticatory muscles, J. Oral Rehab. 1: 131-147, 1974. 17. Moller, E.: The chewing apparatus, Acta Physiol. Stand. 69: Supp. 280, pp. l-229, 1966. 18. Nanda. S. K., Merow, W. W., and Sassouni, V.: Repositioning of the masseter muscle and its effect on skeletal form and structure, Angle Orthod. 37: 304-308, 1967. 19. McFee, C. E., and Kronman, J. H.: Cephalometric study of craniofacial development in rabbits with impaired masticatory function, J. Dent. Res. 48: 1268-1273, 1969. 20. Randow, K., Carlsson, K., Edlund, J., and Oberg, T.: The effect of an occlusal interference on the masticatory system, Odontol. Revy 27: 245.256, 1976.
Dr. Pancherz
study
H. Pancherz, D.D.S., Odont. Dr., and M. Anehus-Pancherz, D.D.S. Mulmii, Stteden The
e#cw
of contimrous
in ten growing upplicmce.
quantitutiveiy
chewing
of peanuts.
treatment
during
vulues. temporul clcti\itJ trppliunce
maximal
rrctivity
unteriorlv
biting removed
in all patients.
.seen in the 11’0s due
The
in the
was
EMG
in the
in EMG
nctivity
results
of this
investigation
Division
I cuses
Cluss
II,
to un ultereti
seen
sugittul
After
with
from
(3)
When
normul muscles
for
greater suggest during
bu.se
bite or dentrrl
treatment
the
,jumping
tbt’o muscles
the
Herbst Mlere
pretreatment
masseter the
contucts
the
relutions
exceeded
that
the mandible
no occlusal
occlusal
Before
temporal
either
nppliunce,
rrctivity
reduced.
the
during
EMG
two
was
jaw
muscles,
were
during (I)
,from
position The
markedly
uctivity
than
position.
the two
of treatment,
6 months
und
the following: less
of the Herbst
segments.
chebving
after
wus
the Herbst muscles
position
intercuspul
insertion
IVUS investigated with
masseter
revealed
muscle
edge-to-edge
urch
and
in intercuspul
between
(2) During
and
The
increase
muscle.
biting
MUS found
dental
wus
biting
musseter
to an incisor
muximul
The
the
activity treated
temporul
qf the investigation
from
or chewing.
mu.scle
I nmlocc~lusion the
mclximal
results
during
in the posterior
uppliance @nd
The
on musticutory Division
recordingsfrom
activity
in EMG
~t’as ,jumped present
II,
during
especiully
biting
Cluss
EMG
the EMG
no d$ference mtrximul
with
lntegruted
unuly:ed
muscle.
bite jumping
boys
than
increused with
the
for
the
muscle Herbst
relationship.
Key words: Integrated EMG, muscle activity, bite jumping, malocclusion, Herbst appliance
A
n abnormal electromyographic (EMG) pattern in the temporal and masseter muscles associated with Class II, Division 1 malocclusions has been ascertained in several investigations. 1-STreatment with functional appliances was found to normalize the muscle pattern in some studies.“, 4 When treating Class II, Division 1 malocclusion by bite jumping with the Herbst From the Departmentof 0002-9416/80/090321+09$00.90/0
0
Orthodontics,
School
of Dentistry
1980 The C. V. Mosby Co.
321
Am. J. Orrhod. Sr~rrmher 1980
Fig.
1. Plaster casts of a Class Ii, Division 1 malocclusion treated with the Herbst appliance for 6 months. A, Before treatment. B, Start of treatment. C, After treatment. Note the telescope mechanism (tube and plunger) which works as an artificial joint and keeps the mandible in a continuous anterior jumped position.
appliance, Pancherz” suggested that mandibular growth might be stimulated. Bitejumping experiments in growing monkeys have also shown that structural adaptations in the mandibular condyles occurred concomitantly with alterations in muscle function.‘. ’ The purpose of the present investigation was to analyze electromyographically the effect of bite jumping with the Herbst appliance on the activity of the temporal and masseter muscles. Material Ten consecutive patients with Class II, Division 1 malocclusion treated by continuous bite jumping with the Herbst appliance” were surveyed (Fig. 1). All subjects were growing boys with a skeletal Class II relationship. The mean pretreatment age was 12 years 1 month (S.D. = 11 months). Treatment with the Herbst appliance was performed during a fixed time period of 6 months (mean = 6 months 4 days, S.D. = 5 days). After treatment, normal dental arch relationships were established in all patients (Fig. 1). Methods A quantitative analysis of electromyographic (EMG) activity from the temporal and masseter muscles was made before treatment, at the start of treatment when the appliance was inserted, during treatment (after 3 months), and after 6 months of treatment when the appliance was removed. For the EMG recordings, bipolar hook electrodes” were placed bilaterally on the temporal and masseter muscles as shown in Fig. 2. Direct and integrated recordings were obtained from all muscles studied with the aid of a Mingograph 800 (Elema-Schonander, Stockholm). The integrating technique has been described in a previous study.” An amplification of 500 PV per centimeter was used for all recordings. The EMG activity was registered as follows: 1. During maximal biting in intercuspal position. The patients were instructed to close their jaws in centric occlusion as forcibly as possible. The maximal integrated activity during a biting cycle (the mean value of five consecutive cycles) was used for evaluation. For both the temporal and masseter muscles, the mean value of right- and left-side measurements was used. 2. During the chewing ofjve peanuts. No instructions were given to the patients other than to eat the peanuts. The maximal integrated activity during a chewing cycle (the mean
Volume 78 Number 3
Fig. 2. Diagram
Bite jumping
demonstrating
electrode
placement
on temporal
with
Herhst
and masseter
uppliumx,
323
muscles.
value of ten consecutive cycles) was used for evaluation. A chewing cycle was defined as the opening and closing phase of one masticatory movement of the mandible. For the temporal muscle, the mean value of right- and left-side measurements was used. For the masseter muscle, the mean value of right- and left-side measurements was used in cases with a bilateral chewing pattern. In cases with an unilateral chewing pattern, the EMG activity was recorded from the chewing side only. All measurements on the electromyograms were made to the nearest millimeter. An evaluation of occlusal contact conditions was performed at all times of EMG examination by counting the number of mandibular teeth in contact with each maxillary tooth.“) In a case with excellent occlusion, the maximal possible number of tooth contacts is twenty-eight (excluding third molars). Assessment was made on dental casts (before and after treatment) and clinically (during treatment). Statistical methods. Differences in measurements before and after treatment and between different muscles were tested by Student’s t test. The levels of significance used were p < 0.001, p < 0.01, and p < 0.05. Results
EMG uctivity during maximal biting in intercuspulposition (Fig. 3). Before treatment the EMG activity from the masseter muscle was significantly (p < 0.01) less than from the temporal muscle. After treatment, however, no statistically significant difference in EMG activity was found between the two muscles. When the Herbst appliance was inserted, the mandible was jumped anteriorly to an incisor edge-to-edge position. In this way, no occlusal contacts were present in the premolar and molar regions. The EMG activity from both the temporal and masseter muscles was markedly reduced. After 3 months of treatment antagonist contacts in the
Am. J. Orrhod.
324 Puncher; md Anehus-Parlcherz
Sqmmher
1980
UV ------
Temporal
-
Masseter
600
400
300
I
200
100 1
I
;
:
A
B
C
0
Fig. 3. Maximal integrated EMG activity in PV (mean and SD.) from temporal and masseter muscles during maximal biting in intercuspal position in ten boys with Class II, Division 1 malocclusion treated with the Herbst appliance. A, Before treatment. 6, At start of treatment when the appliance was inserted. C, After 3 months of treatment. D, After 6 months of treatment, when the appliance was removed.
posterior dental arch segments (mainly molar contacts) were found in seven cases, while in three cases contacts still existed between the incisors only. The EMG activity in the two muscles had increased to almost pretreatment values. When the Herbst appliance was removed after 6 months of treatment, normal occlusal relations were found in all patients. The EMG activity had increased significantly for the temporal (p < 0.05) and masseter (p < 0.001) muscles when after-treatment records were compared with those obtained before treatment. EMG activity during chewing (Fig. 4). During chewing, no significant difference in EMG activity between the temporal and masseter muscles was found before or after treatment with the Herbst appliance. When the appliance was inserted, the EMG activity in both muscles was reduced to an insignificant level and no distinct chewing cycle could be identified. After 3 months of treatment the EMG activity had increased markedly, and after 6 months it exceeded pretreatment values. This was especially true for the masseter muscle, for which the increase in EMG activity during the period before treatment-after treatment was statistically significant (p < 0.05). Comparison between EMG activity und occlusal contact conditions. In the ten subjects investigated, the average number of antagonist contacts was eleven before treatment and fourteen after treatment. When the number of teeth in occlusion was related to the EMG
Vdumr 78 Number 3
Bite jumping
------
Temporal
-
Masseter
with
Herhst
appliawc~
325
Fig. 4. Maximal
integrated EMG activity in PV (mean and SD.) from temporal and masseter muscles during chewing of peanuts in ten boys with Class Ii, Division 1 malocclusion treated with the Herbst appliance. A, Before treatment. B, At start of treatment when the appliance was inserted. C, After 3 months of treatment. D, After 6 months of treatment, when the appliance was removed.
activity from the temporal and masseter muscles, or after treatment with the Herbst appliance.
no connection
was found,
either before
Case presentation photographs and electromyograms of a typical Class II, Division 1 malocclusion the Herbst appliance are presented in Figs. 5 and 6. Before treatment, a cusp-to-cusp relationship was present in the premolar region. The number of intermaxillary tooth contacts was eleven. The EMG activity from the masseter muscle was reduced in relation to the temporal muscle, and the contraction pattern between the right and left muscles in each respective pair was unbalanced. When the appliance was inserted, intermaxillary tooth contacts were found between one pair of incisors only. The EMG activity during biting and chewing was markedly reduced in both muscles. After 3 months of treatment still no occlusal contacts were found in the posterior dental arch segments. The EMG activity from both muscles had increased to almost pretreatment values. After 6 months of treatment, when the appliance was removed, occlusal contacts were established bilaterally between the molars. The number of tooth contacts was thirteen. The EMG activity from the temporal and masseter muscles had increased beyond pretreatment values, and the contraction pattern was more balanced.
Intraoral treated with
Discussion An earlier study” has suggested that the EMG activity from the temporal and masseter muscles was reduced in Class II, Division 1 malocclusions when compared to normal occlusions. It was also suggested that in Class II cases the masseter muscle exhibited a
Am. J. Orrhod. Seprembrr 1980
Fig. 5. Intraoral photographs of an 1 l-year-old boy with Class II, Division 1 malocclusion treated with the Herbst appliance. A, Before treatment. B, At start of treatment, when the appliance was inserted. C, After 3 months of treatment. D, After 6 months of treatment, when the appliance was removed.
deficient activity in relation to the temporal muscle. In normal occlusion cases, on the other hand, the EMG activity in the two muscles was about the same. When the present Class II cases were treated by jumping the bite with the Herbst appliance. the EMG activity in the temporal and masseter muscles was increased and the contraction pattern in the two muscles was more like that seen in persons with normal occlusion. Similar results were found in patients treated with functional appliances.‘, 4 At the start of treatment, when the mandible was positioned anteriorly with the incisors in an edge-to-edge relationship, a marked reduction in EMG activity from especially the temporal muscle was found during biting and chewing. Similar changes in EMG activity were seen in children with normal occlusion when the mandible was protracted” or when biting with the incisors in an edge-to-edge position was performed. “l. I:( Biting on a Class I1 activator has also been shown to reduce temporal muscle activity.14. I5 After 3 months of Herbst appliance treatment the EMG activity in the two muscles investigated increased markedly, and after 6 months, when the appliance was removed, the muscle activity exceeded pretreatment values in most patients. A significant increase in EMG activity was found, especially for the masseter muscle. When after-treatment records were compared with before-treatment records, the average increase in EMG activity during
Volume 78 Number 3
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A -
C
B
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Fig. 6. Electromyograms and chewing of peanuts appliance was inserted. appliance was removed. masseter.
327
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from the case presented in Fig. 5. Maximal biting in intercuspal position (top) (bottom). A, Before treatment. B, At start of treatment, when the Herbst C, After 3 months of treatment. D, After 6 months of treatment, when the LT, Left temporalis. LM, Left masseter. FIT, Right temporalis. RM, Right
maximal biting in intercuspal position was 98 percent for the masseter and 41 percent for the temporal muscle. During peanut chewing the corresponding figures were 40 percent and 28 percent respectively. A relationship between EMG activity and facial morphology has been demonstrated by several workers.. ‘L ‘~3‘IL Ii Animal studies have also shown that form and function are interrelated. Experimental alterations in muscle function resulted in a change of skeletal morphology. lx. Is Before treatment all the present patients had Class II malocclusion with a large ANB angle (mean = 5.5 degrees). Treatment with the Herbst appliance resulted in normal occlusal relationships in all patients, and the ANB angle was reduced by an average of 2 degrees. Thus, these morphologic changes induced by treatment may affect muscle function and may possibly explain the increase in EMG activity found in the temporal and masseter muscles. The relationship between the number of teeth in occlusal contact and masticatory
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Am. .I. Orrhod Sqmmber 1980
muscle activity during biting and chewing has been the subject of several investigations.“, “. I”. I6 In the present cases, the number of intermaxillary tooth contacts in the posterior dental arch segments was the same before and after treatment. In the anterior segment, on the other hand, the number of tooth contacts increased during treatment as a result of a reduction in overjet and overbite. No relationship was found, however, between occlusal contact conditions in the posterior or anterior dental arch segment and EMG activity from the temporal and masseter muscles during maximal biting or chewing. These results were in agreement with those of other investigations.“, ifi In earlier investigations”, I0 a connection was found between an impaired EMG activity from the masticatory muscles and a cusp-to-cusp occlusion. In many of the present subjects such an occlusion in the posterior dental arch segments was found before treatment. Thus, one cannot rule out the possibility that this unstable occlusal condition was a cause of the reduced and imbalanced EMG activity seen in the children (Fig. 5). Imbalance in muscle activity may also be due to cuspal interferences.“’ Small occlusal interferences between the retruded contact position and intercuspal position were found in three of the present patients before treatment. These interferences were eliminated, however. by occlusal adjustment before EMG registrations were performed. Conclusion When the present Class II, Division 1 malocclusions were treated by continuous bite jumping with the Herbst appliance, the EMG activity from the temporal and masseter muscles was increased during treatment. The change in muscle activity seen was probably due to an altered sagittal jaw base or dental relationship. REFERENCES 1. Moyers, R. E.: Temporomandibular muscle contraction patterns in Angle Class 11, Division 1 malocclusions: An electromyographic analysis, AM. J. ORTHOD. 35: 837-857, 1949. 2. Grosfeld, 0.: Changes of muscle activity patterns as a result of orthodontic treatment, Tr. Eur. Orthod. Sot. 41: 203.214, 1965. 3. Ah&en, J.. Ingervall, B., and Thilander, B.: Muscle activity in normal and postnormal occlusion, AM. J. ORTHOD.
64: 445456,
1973.
4. Moss, .I. P.: Function-Facts or fiction? AM. J. ORTHOD. 67: 625.646, 1975. 5. Pancherz, H.: Activity in the temporal and masseter muscles in Class II, Division 1 malocclusions: An electromyographic investigation, AM. J. ORTHOD. 77: 679-688, 1980. 6. Pancherz. H.: Treatment of Class II malocclusions by jumping the bite with the Herbst appliance: A cephalometric investigation, AM. J. ORTHOD. 76: 423-441, 1979. 7. McNamara, J. A., Jr.: Neuromuscular and skeletal adaptations to altered function in the orofacial region, AM.
J. ORTHOD.
64: 578-606,
1973.
8. McNamara, J. A., Jr.: Functional adaptations in the temporomandibular joint, Dent. Clin. North Am. 19: 457-471, 1975. 9. Ahlgren, J.: An intracutaneous needle electrode for kinesiologic EMG studies, Acta Odontol. Stand. 25: 15-19, 1967. 10. Pancherz, H., and Anehus, M.: Masticatory function after activator treatment: An analysis of masticatory efficiency, occlusal contact conditions and EMG activity, Acta Odontol. Stand. 36: 309-316, 1978. 1 1. Latif, A.: An electromyographic study of the temporalis muscle in normal persons during selected positions and movements of the mandible, AM. J. ORTHOD. 43: 577-591, 1957. 12. Greenfield, B. E., and Wyke, B. D.: Electromyographic studies of some of the muscles of mastication, Br. Dent. J. 100: 129-143, 1956. 13. Ahlgren, J.: Mechanism of mastication, Acta Odontol. Stand. 24: Supp. 44, pp. I-109, 1966.
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14. Ahlgren, J.: The neurophysiologic principles of the Andresen method of functional jaw orthopedics: A critical analysis and new hypothesis, Swed. Dent. J. 63: 1-9, 1970. 15. Ahlgren, .I.: Early and late electromyographic response to treatment with activators, AM. J. ORTHOD. 74: 88-92, 1978. 16. Ingervall, B., and Thilander, B.: Relation between facial morphology and activity of the masticatory muscles, J. Oral Rehab. 1: 131-147, 1974. 17. Moller, E.: The chewing apparatus, Acta Physiol. Stand. 69: Supp. 280, pp. l-229, 1966. 18. Nanda. S. K., Merow, W. W., and Sassouni, V.: Repositioning of the masseter muscle and its effect on skeletal form and structure, Angle Orthod. 37: 304-308, 1967. 19. McFee, C. E., and Kronman, J. H.: Cephalometric study of craniofacial development in rabbits with impaired masticatory function, J. Dent. Res. 48: 1268-1273, 1969. 20. Randow, K., Carlsson, K., Edlund, J., and Oberg, T.: The effect of an occlusal interference on the masticatory system, Odontol. Revy 27: 245.256, 1976.