Relapse after activator treatment A biometric, cephalometric, and electromgographic studg of subjects with and without relapse of overjet Hans
elapse of overjet and overbite is a common finding after treatment of Class II, Division 1 malocclusion. Relapse has been reported especially after fixed appliance treatment.l-g After activator treatment relapse was found by Pancherzl” and Dass,*’ while Ahlgren I2 found no relapse in his material. Improper treatment methods, insufficient retention, and unfavorable growth changes after treatment are certainly factors of importance but they could not totally explain the occurrence of relapses. Goldstein’ proposed an inherent morphogenetie pattern which limited the extent of treatment. If tooth movement was more extensive than the pattern could sustain, relapse would follow. Horowitz and Hixon13 pointed out that the dentition changed constantly throughout life and that orthodontic treatment could interfere with this normal developmental process. Relapse after treatment might thus be considered a physiological recovery toward the patient’s original condition. Herzberg4 found that. an unfavorable growth of the mandible after treatment, especially when combined with tonguethrust swallowing, was the main reason for Class II relapse. Pancherz’O measured the electromyographic (EMG) activity from the mentalis muscle in nine patients with and in ten patients without relapse of overjet after activator treatment. The results revealed a greater EMG activity in patients with relapse. Pancherz’O also found that the frequency of clinical registered tongue thrust was higher in the patients with relapse than in the patients without relapse. The aim of the present investigation was to examine patients with and withFrom the Department 214 21 MalmG, Sweden.
Am. J. Orthod. November 1977
out relapse of overjet after activator treatment and to discuss morphologic and functional differences. The investigation attempted to answer the following : 1. Do patients with relapse of overjet have a different anterior dental arch structure and vertical incisor relationship than patients without relapse ? 2. Do patients with relapse of overjet have a different skeletal pattern than patients without relapse? 3. What causes the relapse of overjet in the patients investigated? Is it a result of an atypical muscle function and/or of an adverse growth pattern ? Material
From follow-up datalo of 112 patients treated with activator appliances 10 to 20 years previously, nineteen patients were selected with respect to relapse or stability of overjet after the completion of activator treatment. Relapse group. The overjet had increased during the period after treatmentfollow-up examination. The group consisted of nine patients (one male and eight females). Stable group. The overjet was unchanged or reduced during the period after treatment-follow-up examination. The group consisted of ten patients (three males and seven females). The average changes in overjet for the two groups during the period before treatment-after treatment-follow-up were as follows: Relapse group 7.9 mm. - 4.8 mm. - 6.4 mm. Stable group 8.3 mm. - 4.7 mm. - 4.0 mm. All nineteen subjects had, before treatment, a Class II or Class I malocclusion with a labial inclination of the maxillary incisors. The mean age for the two groups before treatment, after treatment, and at follow-up examination was as follows : Relapse group 11.0 - 13.7 - 28.9 years Stable group 11.1 - 13.2 - 28.7 years Fig. 1 shows the type of activator used in this study. Fig. 2 schematically demonstrates activator treatment of a Class II, Division 1 malocclusion. Methods
Biometric investigation. A biometric analysis was carried out on dental casts before treatment, after treatment, and at the follow-up examination, according to the methods used by Pancherz. lo The following variables have been investigated : 1. Overjet and overbite (Fig. 3). The overbite was also classified according to Fig. 4. 2. Arch width between the canines in the maxillary and mandibular arches. The crown tips were used as measuring points.14 3. Available space in the maxillary and mandibular incisor segments measured between the most mesial surface of the canines.14
Relapse after activator
Fig. 1. Different
of an for
Cephdometric investigation. Measurements on profile roentgenograms were made before treatment and at follow-up examination according to the methods employed by Pancherz. lo The points and reference planes used are shown in Fig. 5. Electromyographic investigation. A quantitative evaluation of EMG activity from the mentalis muscle was made at the follow-up examination. Bipolar hook electrodes were used as described by Bhlgren. I5 The interelectrode distance was 20 mm. The electrodes were placed over the most prominent part of the chin (soft-tissue pogonion), symmetrically in relation to the midline (Fig. 6). The EMG activity was recorded in the following positions and movements of the mandible : 1. Postural position. Calibration, 100 pV/cm. 2. Swallowing on command. Calibration, 100 pV/cm. 3. Strong biting in intercuspal position. Calibration, 500 pV/cm. 4. Chewing five peanuts and swallowing. Measurements were made during
Am. J. Orthod. November 1977
Fig. 2. Diagram demonstrating activator treatment of an Angle Class clusion. a, Before treatment. b, Working position of the activator, trimmed to permit desired distal tooth movement. c, After treatment.
II, Division with the
both the opening and closing phases of chewing. Calibration, 100 ti pV/cm. The EMG recordings were made with a Mingographe 800 (Elema-Schiinander, Stockholm). Paper speed was 50 mm. per second. The mentalis activity was quantitated by measuring the height of the average EMG potential (peak-to-peak) according to a six-grade scale (Table I and Fig. 7). Results
Biometric investigation. The measurements made on the dental casts revealed the following results of interest. * Overbite reduction during the treatment period was, on the average, greater for the relapse group than for the stable group (0.9 mm. and 0.2 mm., respectively). During the period after treatment-follow-up, a further reduction of the overbite occurred in the stable group, averaging 0.6 mm. (N.S.) In the relapse group, on the other hand, the overbite increased an average of 0.2 mm. (N.S.). Overbite classification, according to Fig. 4, is seen in Fig. 8. Before treatment two patients (22 per cent) from the relapse group and four patients (40 per cent) from the stable group had an open-bite. During treatment three more patients (34 per cent) in the relapse group developed an *Tabular available
material from the
the results by request.
I I I 1 6 ‘A’
Fig. 6. Diagram mentalis muscle.
in the of
Am J. Orthod. Novenzber 1977
Grade43 l’bak-to-peak activl between lox)- 72.5mm
Fig. 7. Diagram tion,
classification Grade 1 2 3 4 5 6
from mentalis Activity
o- 25 2s 50 50-100 loo-125 125-150 >I50
open-bite. In the stable group, on the other hand, two open-bite patients (20 per cent) were treated to a “normal vertical relationship.” During the period after treatment-follow-up the frequency of patients with open-bite remained constant in the stable group (20 per cent), but increased further in the relapse group to a total of 67 per cent. All patients diagnosed as having open-bite had a vertical overbite (Fig. 4) at all three times of examination. The arch width between the maxillary canines was significantly greater (p < 0.05) for the stable group than for the relapse group both after treatment and at follow-up examination. The arch width increase during treatment was greater for the stable group than for the relapse group (2.2 mm. and 1.3 mm., respectively). The subsequent decrease in arch width after treatment was greater for the relapse group (1.1 mm., p < 0.05) than for the stable group (0.4 mm., N.S.). No differences between the relapse and stable groups were found for mandibular intercanine arch width. There was an average excess of available space in the mandibular incisor segment for the relapse group, before treatment, after treatment, and at the followup examination. For the stable group, however, an average lack of available space in the mandibular incisor segment existed at all three times of examination. The differences between the groups were statistically significant (p < 0.05) at the time of follow-up examination. The reduction of available space during the period after treatment-follow-up was significant (p < 0.01) for the stable group. For the relapse group, on the other hand, the available space was almost unchanged during this period. No differences between the relapse and stable groups were found for available space in the maxillary incisor segment.
Fig. 8. Classification and
of occlusion overjet.
Cephalometric investigation. The measurements made on the roentgenograms revealed the following results of interest. The angle describing sagittal jaw relationship (ss-n-sm) was, on the average, greater for the relapse group than for the stable group, both before treatment and at follow-up examination. .The difference between the groups was not statistically significant, however. During the period before treatment-follow-up the following differences developed between the relapse and stable groups. The maxillary incisors retroclined (IL,/NL) much more in the stable group (8.4 degrees, p < 0.05) than in the relapse group (1.5 degrees N.S.). The incisal edges of the maxillary incisors (is&~), however, became anteriorly placed in the relapse group (2.1 mm., p < 0.05) and posteriorly placed in the stable group (1.4 mm., N.S.). The mandible rotated (NSL/ML) somewhat posteriorly in the relapse group (0.3 degree, N.S.) and anteriorly in the stable group (2.0 degrees, N.S.). The angle describing vertical jaw relationship (NL/ML) increased somewhat in the relapse group (0.9 degree, N.S.) and decreased somewhat in the stable group (0.9 degree, N.S.) . No differences between the groups were found for the ratio between upper and lower anterior facial height - n-sp’ . ( sp’-gn > EZectromyographic investigation. The quantitative evaluation of the EMG activity from the mentalis muscle is shown in Table II. The activity was, on the average, greater in the relapse group than in the stable group for all mandibular positions and movements investigated. Statistically significant differences (p
Am. J. Orthod. November 1977
6, * from with
Relapse (n = 9)
Posturalposition Swallowing Biting Closing Chewing Opening *For definition, tT test between
see Table difference
I and of
Stable (n = 10)
2.8 5.1 3.7 2.9
2.2 1.5 2.9 2.2
1.2 4.5 3.4 1.3
0.6 1.6 1.5 0.5
<0.05 N.S. N.S. <0.05
Fig. 6. means in
< 0.05) between the groups were found closing phase of chewing. Case
Two boys with Class II, Division 1 malocclusion are presented. Treatment was performed with activators as the sole orthodontic appliance. Case 1 (Figs. 9 and 10) exhibited a stable long-term treatment result, while Case 2 (Figs. 11 and 12) relapsed. Discussion
The results of the biometric investigation revealed a high frequency of openbite in the patients with relapse of overjet. This may be explained by the fact that, at the follow-up examination, seven patients (78 per cent) from the relapse group showed clinically observable tongue thrust while only three patients (30 per cent) from the stable group showed such a habit. These results were in agreement with those from several other investigations16-19 where a connection between tongue thrust and open-bite was found. Linder-AronsonnZo* *I proposed that a low rest position of the tongue in connection with mouth breathing could lead to a narrower upper dental arch. When the present patients were examined clinically, it was found that six patients (67 per cent) from the relapse group and two patients (20 per cent) from the stable group were mouth breathers. This finding could explain the differences found between the groups for intercanine arch width in the maxilla. The difference between the relapse and stable groups for available space in the mandibular incisor segment might be due to the different occlusal incisor relationship found in the groups. In the relapse group the overjet and frequency of open-bite were larger than in the stable group. Consequently, the restraining effect of the upper incisors upon the lower was thought to be less in the patients with relapse of overjet than in the patients without relapse. On the other hand,
Relapse after activator
Fig. 9. Case 1. Plaster ination. Stable long-term
casts before result after
after treatment, treatment.
it could be expected that the lower lip would produce a lingually directed pressure on the lower incisors in connection with tongue thrust and thus influence the available space negatively. However, as Windersz2 and MarxZ3 have point,ed out, the tongue probably plays the dominant role in shaping the dental arch, while the lip activity is of minor importance to incisor position. The results of the cephalometric investigation revealed a greater ANB angle in the relapse group than in the stable group. This was not in agreement with the findings of Pancherz’O and Ahlgren and Laurinz4 Pancherzl” found no difference in the ANB angle when investigating a relapse group and a stable group. Ahlgren and Laurin,2* on the other hand, found a smaller ANB angle in patients treated unsuccessfully with activators than in patients treated successfully. In the present investigation a different growth rotation of the mandible was found in the relapse and stable groups. This observation could be a contributing fa&or,25 in addition to atypical tongue function, in explaining the large fre-
Am. J. Orthod. November 1977
-----___ -I-.-.fig. 10. activator
Case 1. Superimposed therapy contributed
cephalometric to the stable
105 b&m treatment 140 after ttaatmt 28“ follow- up tracings. A favorable treatment result.
quency of open-bite found in the patients with relapse of overjet. It was also possible that the different growth patterns found in the groups were the cause of the relapse of overjet.4l 26 The changes of the position of the mandibular incisors (ILi/ML and ii/nsm) during the period before treatment-follow-up were small and could be ascribed to compensatory mechanisms in connection with mandibular growth rotation.1op 27 However, the possibility that the activators had a proclining effect on the mandibular incisors cannot be excluded. This is in agreement with several other investigations.lO, 24, 28-31 The position of the maxillary incisors in the relapse and stable groups was altered significantly during the period before treatment-follow-up. In the relapse group the maxillary incisors, as a whole, more often were displaced anteriorly in the alveolar bone. (The angle IL,/NL was almost unchanged while the incisal edges, is/nss, had shifted more anteriorly.) This agreed with the findings of Pancherz.10 Ahlgren and Laurin 24 found, however, a lingual inclination of the maxillary incisors in patients treated unsuccessfully with activators. In the stable group, the maxillary incisors tipped lingually. This result was in accordance with those found by Pancherz’O and Ahlgren and Laurin2” It thus seemed conceivable that the changes in the position of the maxillary incisors in the relapse group could be the result of tongue pressure or tongue thrust against the palatal portion of the alveolar process. The results of the electromyographic investigation revealed that the EMG activity from the mentalis muscle was greater in patients with relapse of overjet after completion of activator treatment than in patients without relapse. This could be explained by the fact that normal lip closure was more difficult to attain in patients with large overjets (relapse group) than in patients with small overjets (stable group). Further, the ANB angle was greater in the relapse group
Relapse after activator
Fig. 11. Case 2. Plaster casts before treatment, ination. Relapse of the Class II malocclusion after
after treatment, and activator treatment.
than in the stable group, and this could also contribute to make lip closure more difficult and account for the differences in EMG activity from the mentalis muscle found in both groupsz3$ 32 From the clinical examination, it was seen that the patients with great mentalis muscle activity had a higher frequency of tongue thrust than the patients with low mentalis muscle activity. This was also reflected in the EMG investigation where marked mentalis activity during swallowing was noted. An increased mentalis muscle activity in connection with tongue thrust during swallowing (atypical swallowing) has been found in many other investigations as we11.16,18,19, 23 Incompetent lips may be a factor of interest in the etiology of relapse. Gustafsson and AhlgreP found a direct relation between incompetent lips and EMG activity from the mentalis muscle. This connection, however, was not seen in the present investigation when the patients were examined clinically. Only two patients in the relapse group and one patient in the stable group had incompetent
Am. J. Orthod. November 1977
-.-.-.Fig. 12. Case 2. Superimposed mainly from an unfavorable growth
7s b&()[email protected]
)t 133 after treatment 173 fdb-up
cephalometric pattern after
The Class treatment.
lips. Gustafsson and Ahlgren32 pointed out, however, that electromyographically incompetent lips were not always possible to diagnose clinically. As a consequence of the results found in this investigation, it might be of clinical value in treatment planning to analyze the mentalis muscle activity electromyographically. Summary
In order to clarify the nature of overjet relapse after orthodontic treatment, nineteen patients (nine with relapse and ten without relapse of overjet) were selected from follow-up data on 112 patients treated with activators 10 to 20 years previously. The patients were analyzed by means of dental casts, cephalometric roentgenograms, and electromyographic registrations of mentalis muscle activity. The results of the investigation revealed the following : 1. The frequency of open-bite after treatment and at follow-up examination was much greater in patients with relapse of overjet than in patients without relapse. 2. The increase in intercanine arch width in the maxilla during treatment was greater and the subsequent reduction after treatment was less for the stable group than for the relapse group. 3. The available space in the mandibular incisor segment was almost unchanged after activator treatment for the relapse group, while it was significantly reduced for the stable group, 4. The ANB angle was greater in patients with relapse of overjet than in patients without relapse, both before treatment and at follow-up examination. 5. There was a posterior growth rotation of the mandible in the relapse group and an anterior growth rotation of the mandible in the stable group. 6. The maxillary incisors tipped lingually in the stable group and became
more anteriorly placed, as a whole, in the rela,pse group during the period before treatment-follow-up. 7. The EMG activity from the mentalis muscle was greater in the relapse group than in the stable group. The activity from the mentalis muscle seemed to be related to an atypical tongue function. 8. The cause of relapse of overjet after activator treatment seemed to be connected with an adverse growth pattern and an atypical tongue function. 9. In planning Class II treatment it is recommended that perioral muscle function be analyzed by means of electromyographic registrations of the mentalis muscle activity. REFERENCES
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S.: Adenoids: Their effect on mode of breathing and nasal Linder-Aronson, and their relationship to characteristics of the facial skeleton and dentition, Otolaryngol., Supp. 265, 1970. of adenoidectomy on dentition and nasopharynx, 21. Linder-Aronson, S. : Effects
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ORTHOD. 65: l-15, 1974. 22. Winders, R. V.: Forces exerted on the dentition by the perioral and lingual musculature during swallowing, Angle Orthod. 28: 226235, 1958. 23. Marx, R.: The circumoral muscles and the incisor relationship-An electromyographic study, Trans. Eur. Orthod. Sot., pp. 187.201, 1965. 24. Ahlgren, J., and Laurin, C.: Late results of activator treatment: A cephalometric study, Br. J. Orthod. 3: 181-187, 1976. 25. BjGrk, A.: Prediction of mandibular growth rotation, AM. J. ORTHOD. 56: 585-599, 1969. 26. Proffit, W. R.: Muscle pressures and tooth position: North American whites and Australian .aborgines, Angle Orthod. 45: l-11, 1975. 27. BjSrk, A., and Skieller, V.: Facial development and tooth eruption, AM. J. ORTHOD. 62:
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Trayfoot, J., and Richardson, A.: Angle Class II, Division 1 malocclusions treated by the Andresen method, Br. Dent. J. 124: 516-519, 1968. 30. Parkhouse, R. C.: A cephalometric appraisal of cases of Angle’s Class II, Division 1 malocclusions treated by the Andresen appliance, Trans. Br. Sot. Orthod. 55: 61-70, 1969. 31. Woodside, D. G.: The activator. In Salzmann, J. A. (editor): Orthodontics in daily practice, Philadelphia, 1974, J. B. Lippincott Company, pp. 556-591. and orbicularis oris activity in children with 32. Gustafsson, M. ,and Ahlgren, J.: Mentalis incompetent lips, Acta Odontol. Stand. 33: 355-363, 1975. Carl