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Muscle activity with the mandibular lip bumper
ORIGINAL ARTICLE Muscle activity with the mandibular lip bumper Arndt Klocke, Drmeddent, MS,a Ram S. Nanda, DDS, MS, PhD,b and Joydeep Ghosh, DDS, MSc Hamburg, Germany, Oklahoma City, Okla, and Dallas, Tex This prospective study was designed to measure muscle activity with lip bumper treatment. Surface electromyography was used to measure upper and lower lip activity with and without the appliance in place. Measurements were taken on a sample of 25 adolescent patients (age range, 10 to 17 years) before and after 12 months of lip bumper treatment. Recordings included a closed lip rest position, swallowing of water, and speech of the words “church,” “phone,” and “pop.” Insertion of the lip bumper at the pretreatment recording resulted in significantly increased activity of the upper and lower lips at rest (P < .001) and while swallowing (P < .05), whereas the response for speech was variable. Pretreatment and posttreatment muscle activity measurements of the lower lip were compared to determine whether 12 months of treatment with the appliance resulted in muscle adaptation. The initial increase of muscle activity with insertion of the appliance for the closed lip rest position and for swallowing was not followed by a decrease during the treatment period. There were significant differences in muscle activity when comparing the “new” equilibrium introduced by the lip bumper to the “old” pretreatment equilibrium without the appliance. Although it was shown that the insertion of the appliance had a significant influence on muscle activity of the lips, the results of this study did not indicate adaptation of the lower lip to the appliance over the treatment period. (Am J Orthod Dentofacial Orthop 2000;117:384-90)
The mode of action of the lip bumper has been explained as an alteration of the functional pattern as well as a stretching of the lower labial musculature,1 resulting in proclination of the incisors, uprighting of the anchor molars, and an increase in arch width.2-10 As opposed to conventional expansion techniques, the lip bumper appliance introduces an alteration of the functional pattern.1 The shielding effect not only allows the dental arch to expand but also encourages adaptation of the lips and cheeks so that the pressure exerted on the teeth is less than it would have been if the teeth had been moved labially with routine orthodontic treatment.11 A relatively slow expansion of the dental arch is the result of “natural forces” with the lip bumper.9 Attempts have been made to quantify the forces on the lip bumper that result from the new environment created with the appliance.12-17 Sakuda and Ishikawa13 measured higher pressure in the midline area of the lip bumper during swallowing than during speech or chewing. Sather et al14 found no correlation between tooth movement and forces From the Department of Orthodontics, University of Oklahoma. aFormer graduate student. Currently Associate Professor, Department of Orthodontics, College of Dentistry, University of Hamburg, Germany. bProfessor and Chair, Department of Orthodontics, College of Dentistry, University of Oklahoma, Oklahoma City. cIn Private Practice, Dallas, Tex. Reprint requests to: Dr Ram Nanda, Department of Orthodontics, University of Oklahoma, College of Dentistry, 1001 Stanton L. Young Blvd, Oklahoma City, OK 73190 Copyright © 2000 by the American Association of Orthodontists. 0889-5406/2000/$12.00 + 0 8/1/104688 doi.10.1067/mod.2000.104688
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with lip bumper treatment. Soo and Moore15 showed a decrease in forces on the lip bumper, starting at 1 month of appliance wear. This decrease was dependent on the location of the measuring gauge, with less decrease of force in the modiolus than in the midline area. The authors speculated that the adaptive response of the lip varied with the anatomic location, with the modiolus being less adaptable than the mentalis muscle. Hodge et al16 evaluated forces with specially designed strain gauges at the mandibular molars on a sample of 38 adolescent patients. They investigated forces with different types of lip bumpers (wire and acrylic shield) and found that the forces on the mandibular molars varied with vertical and horizontal positioning of the lip bumper relative to the mandibular incisors. The acrylic shield lip bumper produced higher resting forces than the wire lip bumper. The forces were higher with the lip bumper in a position 4 mm anterior as compared with a position 2 mm anterior to the mandibular incisors. In addition, positioning the lip bumper at the height of the gingival margin produced higher forces than a position at the middle of the clinical crown. O’Donnell et al17 measured forces before and after lip bumper treatment. They found no decrease in force at the posttreatment recording. Stavridi and Ahlgren18 pointed out that although the influence of the perioral musculature on the position of teeth and growth and development of craniofacial structures has been very extensively discussed, questions with regard to muscle behavior during various orthodontic treatment methods remain unanswered.
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Lip Bumper Treatment
Fig 1. Lip bumper used during treatment period.
Although the lip bumper is a muscle-activated appliance, limited information is available on the underlying muscular activity with the lip bumper. With a sample of 8 children, Bundgaard et al19 used a shield lip bumper and measured muscle activity with surface electromyography with and without the appliance in place, at rest and in function. They concluded that similarities in occlusion and facial morphology do not account for similarities in functional pattern. Reproducibility of the method was a problem in this study. An illogical relationship between morphologic and electromyographic changes was attributed to the weakness of the methods applied. The purpose of this prospective study was to measure muscle activity of the lips in the new environment created by the lip bumper. Comparisons between pretreatment and posttreatment muscle activity were used to indicate a possible adaptation of the lips to the appliance. MATERIAL AND METHODS Sample
Twenty-five patients were selected for treatment with the lip bumper appliance and were followed for a 12-month period. The criteria for treatment with the lip bumper were a mild to moderate arch length deficiency and a nonextraction orthodontic treatment plan in the mandibular arch. All 25 patients received 12 months of lip bumper treatment with no other appliances in the mandibular arch while regular orthodontic treatment proceeded in the maxillary arch with bands, brackets, expanders, and transpalatal arches. The sample consisted of 16 females and 9 males with a mean initial age of 13 years 1 month and an age range from 10 years 6 months to 17 years 4 months.
The lip bumper used for the 12 months of treatment was an 0.045 inch stainless steel lip bumper (American Orthodontics, Sheboygan, Wis) with adjustment loops mesial to the mandibular first molars and hooks (for ligatures) mesial to the adjustments loops (Fig 1). The lip bumper was inserted passively into the molar tubes and positioned to be 2 mm anterior to the facial surface of the mandibular incisor teeth at the level of the gingival margin. To ensure a permanent wear during the 12 months of treatment, the lip bumper was tied passively to the mandibular first molars via elastomeric or steel ligatures. During the treatment period, the lip bumper was inspected regularly; minor adjustments were made, if necessary, to maintain its position relative to the mandibular incisors. Electromyography
Electromyographic (EMG) data were collected with the K6-I Diagnostic System (Myo-tronics, Tukwila, Wash). The processed (integrated) electromyographic output of the muscles was investigated with the amount of magnification set to 100 µV. Fifteen seconds of muscle activity could be measured continuously and the recording of activity could be started and stopped at any time during these 15 seconds. From the graphic display, the operator could determine the exact point of beginning and end for each functional exercise. All other data points were then discarded, and EMG activity was calculated by the K6-I system for the data segment specified. EMG raw data were sampled at 240 samples per second, the average electromyographic activity (µV) was calculated from the integrated EMG activity from beginning to end of the functional exercise. Duo-trode electrodes (Myo-tronics, Tukwila, Wash) were used to record the muscle activity. These were bipolar surface electrodes (silver/silver chloride) with an interelectrode distance of 20 mm; they were placed over the upper and lower lip. The electrodes were cut in the middle to increase the interelectrode distance from 20 to 30 mm. This was done to allow close adaptation and improve mobility of the lips. To ensure a consistent interelectrode distance of 30 mm and enable reproducible placement of the electrodes, a template was constructed. A grounding electrode was placed on the skin below the ear lobe. The electrode sites were prepared by cleaning the skin with ethanol. The electrodes were placed symmetrically to the facial midline at the vermilion border. Recording Procedure
Muscle activity recordings were taken on the same day lip bumper treatment was initiated and again after 12 months of treatment with continuous wear of the appli-
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Table I. Average
muscle activity (µV) of the upper and lower lips (Means and standard deviations for the pretreatment and posttreatment recordings with and without the lip bumper are shown for the different functional exercises.) Pretreatment recording With lip bumper Muscle Upper lip Rest (lips closed) Speech (church) Speech (pop) Speech (phone) Swallow Lower lip Rest (lips closed) Speech (church) Speech (pop) Speech (phone) Swallow
Mean
SD
13.60 29.18 37.82 26.21 39.02
10.33 19.85 14.07 13.01 24.13
13.78 34.29 38.65 52.64 44.75
6.94 22.52 15.79 24.10 27.63
Posttreatment recording
Without lip bumper Mean
With lip bumper
Without lip bumper
SD
Mean
SD
Mean
SD
4.99 25.50 26.89 23.91 22.11
3.31 18.00 10.85 13.15 15.27
10.08 21.39 31.89 20.99 33.25
7.41 16.85 16.26 11.59 21.56
4.22 24.43 28.88 22.07 20.38
3.48 15.85 15.18 13.41 12.96
5.79 52.17 38.21 52.29 33.65
3.64 26.17 15.71 21.56 23.91
14.07 34.78 35.35 51.53 41.52
7.95 18.57 16.62 19.92 26.46
6.04 49.36 37.18 47.90 27.42
5.38 23.96 14.62 22.90 23.04
ance. Measurements were taken with the patient seated upright in a chair with firm back support in a relaxed position with the head unsupported in a natural position (per Moorrees20). The muscle activity recording procedures were done for each patient with and without the lip bumper in place. Activity was recorded at a closed lip rest position, during speech (“phone,” “church,” and “pop”), and while swallowing 5 ml of water. During the recording session every activity recording was repeated 5 times. The first of the 5 readings was eliminated from the data collection because of anticipated higher initial readings due to the patient’s tension and anxiety (per Burdette and Gale21 and Ingervall and Thüer22). The experimental condition was repeated to reduce intraindividual variation of the electromyographic readings.21,23,24 Forces were recorded at the mandibular molars at the same time as the muscle activity measurements.16,17 Statistical Analysis
Means and standard deviations were calculated for each functional exercise for each muscle. This was done for the recordings both without the lip bumper and with the lip bumper inserted. Paired t tests were performed to determine if any significant differences were present between the pretreatment and the posttreatment muscle activity measurements. RESULTS Muscle Activity Before Treatment (Table I)
Muscle activity without the lip bumper. Resting activity was 4.99 ± 3.31 µV for the upper lip and 5.79 ± 3.64 µV for the lower lip. The speech exercises showed the highest activity in the lower lip (“church”
52.17 ± 26.17 µV, “pop” 38.21 ± 15.71 µV, “phone” 52.29 ± 21.56 µV). The upper lip muscle activity for speech was measured at 25.50 ± 18.00 µV for “church,” at 26.89 ± 10.85 µV for “pop,” and at 23.91 ± 13.15 µV for “phone.” The swallowing exercise was recorded at 22.11 ± 15.27 µV for the upper and 33.65 ± 23.91 µV for the lower lip. Muscle activity with the lip bumper. The comparison of pretreatment muscle activity with and without the lip bumper is shown in Table II (column I). The activity at rest and while swallowing increased with insertion of the appliance; rest activity for the upper lip was measured at 4.99 ± 3.31 µV without the lip bumper and at 13.60 ± 10.33 µV with the appliance in place (P < .001). Lower lip activity at rest increased from 5.79 ± 3.64 µV to 13.78 ± 6.94 µV (P < .001). Swallowing showed significant increases from 22.11 ± 15.27 µV to 39.02 ± 24.13 µV for the upper lip (P < .001) and from 33.65 ± 23.91 µV to 44.75 ± 27.63 µV for the lower lip. The speech activity exhibited a rather variable response: “church” showed a significant decrease in lower lip activity with the lip bumper (P < .001), “pop” exhibited less activity of the upper lip with the bumper (P < .001). Effect of Lip Bumper Treatment on Muscle Activity of the Lips
Comparison of muscle activity with the lip bumper before and after treatment (Table II, column II). The lower lip showed virtually no differences between pretreatment and posttreatment values, and the corresponding P values were not statistically significant. The upper lip showed a trend to lower activity at the posttreatment recording. However, only the activity
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Table II. Comparison
of activity recordings before (T1) and after (T2) treatment and with (LB) and without (No LB) the lip bumper appliance in place Mean difference (µV) Muscle Upper lip Rest (lips closed) Speech (church) Speech (pop) Speech (phone) Swallow Lower lip Rest (lips closed) Speech (church) Speech (pop) Speech (phone) Swallow
I (T1 LB - T1 No LB)
8.61*** 3.68 10.93*** 2.30 16.91*** 7.99*** –17.88*** 0.44 0.35 11.11*
II (T1 LB - T2 LB)
3.51 7.79* 5.93 5.22* 5.76 –0.29 –0.49 3.31 1.12 3.23
III (T1 No LB - T2 No LB)
IV (T1 No LB - T2 LB)
0.77 1.07 2.00 1.84 1.73
–5.09** 4.11 –5.00 2.92 –11.15**
–0.25 2.81 1.03 4.39 6.22
–8.28*** 17.39*** 2.86 0.77 –7.88
*Significant at P < .05; **significant at P < .01; ***significant at P < .001. I, Before treatment with the lip bumper - before treatment without the lip bumper (T1 LB - T1 no LB). II, Before treatment with the lip bumper - after treatment with the lip bumper (T1 LB - T2 LB). III, Before treatment without the lip bumper - after treatment without the lip bumper (T1 no LB - T2 no LB). IV, Before treatment without the lip bumper - after treatment with the lip bumper (T1 no LB - T2 LB).
for speech of the words “church” and “phone” was significantly lower (P < .05) for the posttreatment measurement. Resting and swallowing activity, as well as speech of the word “pop” showed lower values at the posttreatment recording, but these differences were not statistically significant. Comparison of muscle activity without the lip bumper before and after treatment (Table II, column III). The resting activity for the lower lip was 5.79 ± 3.64 µV before treatment and 6.04 ± 5.38 µV after treatment, the upper lip activity at rest was 4.99 ± 3.31 µV before treatment and 4.22 ± 3.84 µV after treatment. No statistically significant differences between pretreatment and posttreatment values were found. Comparison of pretreatment muscle activity without the lip bumper to posttreatment muscle activity with the lip bumper (Table II, column IV). Pretreatment activity without the lip bumper was compared with posttreatment activity with the lip bumper for the upper and lower lip. Activity at rest was significantly higher at the posttreatment recording with the lip bumper (P < .01 for the upper lip and P < .001 for the lower lip). Speech activity showed no significant differences except for speech of the word “church” for the lower lip, which was significantly lower at the posttreatment recording with the lip bumper (P < .001). Swallow activity was higher both for the upper and lower lip at the posttreatment recording with the lip bumper inserted but was only found to be statistically significant for the upper lip (P < .01).
DISCUSSION Variability of the Electromyographic Method
Reliability of electromyography for evaluating orofacial musculature has been controversial in the past; Cecere et al25 concluded that quantitative electromyography of the masticatory muscles has a limited value as a diagnostic tool and in the assessment of individual treatment outcomes because of problems with reproducibility. However, when analyzing a large enough study sample, valuable information can be gained. Harradine and Kirschen23 as well as Simpson and Richardson26 demonstrated that it is possible to reliably evaluate lip activity for functional exercises. Past studies that investigated the reliability of muscle activity over a shorter period of time have used templates that attached to the teeth for a reliable replacement of the electrodes.27-29 Because of the long-term nature of the present study and the actively growing nature of the sample, this was not possible. However, a template was used to ensure a reproducible placement of the electrodes relative to the facial midline and vermilion border at a constant interelectrode distance. Furthermore, the variability of the electromyographic method can be decreased in different ways that were used in the present study. Providing a quiet environment with avoidance of patient distractions has been found to be important to reduce patient anxiety.26 Burdette and Gale17 and Ingervall and Thüer22 have shown that the effect of patient anxiety can be minimized by discarding the first of the recordings for each experimental
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condition. Thüer et al30 suggested repeated observations to reduce intraindividual variability. They based their recordings on 2 observations and reported on a reduction of the intraindividual variation of about 30%. In the present study, averaging 4 measurements led to a measurement error for the average of the 4 measurements that was 50% less than the measurement error of the single observation. Using the aforementioned procedures and the fact that Harradine and Kirschen23 as well as Simpson and Richardson26 have demonstrated that it is possible to reliably evaluate lip activity for functional exercises, the use of electromyography in a carefully designed experiment is considered valid. All electromyographic recordings were characterized by high standard deviation values. The standard deviation increased with the actual value of activity that was measured. Large variability with quantitative electromyography is not unique. Other related studies have also reported large standard deviation values. Thüer and Ingervall31 found large interindividual and intraindividual variability for electromyographic variables of the upper and lower lip during recording of lip pressure. They reported on standard deviations up to 160% of the mean value and suggested making repeated observations on the same individual to overcome the adverse effect of the large intraindividual variation. An explanation for the large standard deviations might also lie in the physiology of the lips. Thüer et al30 attributed large experimental errors in lip strength and lip pressure recordings mainly to biologic intraindividual variation. Lip pressure was found to be highly variable also by Gould and Picton,32,33 McNulty et al,34 Soo and Moore,15 and Hodge et al.16 Therefore, it seems that both the experimental method used (electromyography) and the physiologic environment contribute to the variability that was observed.
cult. Bundgaard et al19 recorded muscle activity at rest and while functioning with and without a lip bumper inserted and found a pronounced variability in muscle activity among their 8 patients. They did, however, mention that there was little variation in resting muscle activity in the relaxed position before and after wearing the lip bumper. Stavridi and Ahlgren18 tested the effect of an oral screen on the mentalis, buccinator, and masseter muscle activity. For rest with closed lip posture, they found a statistically significant increase in mentalis activity with the activator in place. Therefore, it may seem that the shielding effect of the lip bumper and of the vestibular elements of the oral screen activator leads to increased lower lip activity necessary to enable lip closure at rest. Stavridi and Ahlgren showed a statistically significant decrease in swallowing activity of the mentalis muscle with the oral screen activator in place, whereas this study measured increased activity of the lower lip with the lip bumper in place. A possible explanation is the difference in the experimental procedure: Stavridi and Ahlgren used an “empty” swallowing of saliva, and the subjects in the present study were instructed to swallow 5 ml of water. Stavridi and Ahlgren reported that the subjects usually had their lips open, which is contrary to the swallowing observed in the present study. In addition, the sample used by Stavridi and Ahlgren consisted of Class II Division 1 patients. Six of 10 of their patients had lip incompetence, which is often associated with mentalis hyperactivity. Therefore, insertion of a shielding appliance is more likely to reduce mentalis activity. The sample in the present study had competent and no discernible mentalis hyperactivity. And Stavridi and Ahlgren measured mentalis muscle activity whereas this study recorded activity mainly of the lower portion of the orbicularis oris muscle.
Effect of Insertion of the Lip Bumper Appliance on Muscle Activity
Muscle Adaptation to the Lip Bumper
The comparison between activity with and without the lip bumper showed markedly different activity of the upper and lower lips with the appliance in place (see Tables I and II). The speech exercises exhibited both significant increases and decreases; rest and swallowing were significantly higher with the appliance inserted. The increase in rest activity of the lower lip is crucial for the mode of action of the appliance because the lips are at rest for the majority of the time, and increased activity at rest is probably related to the dental changes. There is a lack of information in the orthodontic literature about the influence of inserting a shielding appliance on the muscle activity of the lips, which makes a comparison of the results of this study diffi-
This discussion will focus on muscle adaptation of the lower lip. Comparisons of pretreatment and posttreatment muscle activity measurements were used as an indicator of muscle adaptation. Insertion of the lip bumper was found to increase muscle activity at rest and for swallowing (Table I). It is hypothesized that if adaptation occurred over the treatment period, muscle activity, which increased initially with insertion of the appliance (at rest and for swallow), should decrease again and be significantly lower than at the beginning of treatment. However, no significant changes between pretreatment and posttreatment muscle activity with the lip bumper were found for the lower lip. Because the lips are at a closed lip rest position in lip competent subjects for the longest duration of time during the day,
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adaptation of muscle function should have resulted in decreased posttreatment activity. In case of muscle adaptation over the treatment period, posttreatment activity without the appliance in place should be significantly lower than pretreatment activity without the appliance in place. This would indicate that the equilibrium has changed and a different environment has been established that might provide stability of the dental arch at the new and expanded arch position. The comparison of pretreatment and posttreatment activity without the lip bumper revealed no pretreatment to posttreatment differences in muscle activity for the lower lip. None of the corresponding P values was statistically significant. This suggests an unchanged soft tissue environment. Comparing the “old” equilibrium without the lip bumper with the “new” equilibrium with the lip bumper can also be used as an indicator of muscle adaptation. It can be assumed that in case of muscular adaptation the new equilibrium introduced by the appliance over the treatment period provides stability by establishing similar muscular activity levels as before treatment without an appliance in place, resulting in similar pressures on the teeth in the new position as before treatment. However, rest activity of the lower lip was found to be significantly different (P < .001). Speech activity was not used as an indicator because insertion of the lip bumper before treatment did not consistently show a significant increase in muscle activity. Therefore, comparison of pretreatment activity without the lip bumper and posttreatment activity with the lip bumper could not be expected to be significantly different from each other in the case of muscle adaptation. The swallow exercise exhibited a difference in response between upper and lower lip. Although the upper lip showed significant differences, this could not be measured for the lower lip (P = .1042). It has to be stated that the insertion of the lip bumper at the pretreatment measurement only resulted in significantly higher measurements at the P < .05 level when compared with the measurements without the appliance. The actually recorded pretreatment and posttreatment values with the appliance in place were only marginally different from each other. Emphasis on muscle adaptation was on the lower lip musculature for two reasons: (1) upper lip activity changed to a certain degree with the insertion of the lip bumper, but this activity is not likely to contribute significantly to pressures on the mandibular lip bumper; and (2) at the recording after 12 months of lip bumper treatment, fixed appliances (brackets, bands, palatal arches, expanders) had been placed in the maxillary arch and had probably influenced upper lip activity.
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Thus far, the extent of muscle and soft tissue adaptation to the lip bumper has not been thoroughly studied. Grossen and Ingervall9 stated that it is not known whether the relatively slow expansion of the dental arch by “natural forces” with the lip bumper brings about adaptations in surrounding structures that decrease the risk for relapse. Shellhart et al11 pointed out that vestibular shields not only allow the dental arch to expand, they also are meant to encourage adaptation of the lips and cheeks so that the pressure they exert on the teeth is less than it would have been if the teeth had been moved labially with routine orthodontic treatment. Theoretically, this decrease in pressure should result in improved stability of treatment. Soo and Moore15 found a decrease in pressure especially in the midline area of the lip bumper and suggested that an adaptive response of the lip muscles to lip bumper treatment occurred that varied according to anatomic location. O’Donnell et al17 did not find a decrease in pressure on the mandibular lip bumper over the treatment period that would indicate an adaptive process. Bundgaard et al19 recorded lip muscle activity electromyographically before and after 7 months of lip bumper treatment. However, they did not try to analyze muscle adaptation to the appliance. The findings of the present study on muscle activity are in concordance with the results by O’Donnell et al17; both studies suggest an unchanged environment after 12 months of lip bumper treatment and do not indicate soft tissue adaptation. The proposed increased stability11 due to the slow and “physiologic” expansion with the lip bumper with a decreased risk for relapse cannot be supported by the results of our study. Renfroe35 and Subtelny and Sakuda36 pointed out that loss of alveolar bone on the labial aspect of lower incisor roots was due to the influence of the pressure of a tight or hyperfunctional lip. They advocated the protection of the vestibular attachment of the mandibular incisors by the lip bumper. This protection might only be a temporary effect. The vestibular tissue seems to be subjected to the same muscle forces before and after lip bumper treatment, with the lip bumper influencing the pressure of the lower lip only during the actual treatment period. Therefore, stability of the treatment results cannot depend on a change in soft tissue environment but might require a retention protocol similar to that for conventional arch expansion treatment. Dental changes in the mandibular arch due to lip bumper treatment necessitated minor periodic adjustments of the bumper to maintain a constant distance of the anterior part of the bumper from the incisor teeth. It can be argued that these adjustments made for a chang-
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ing relationship of the lip bumper with the soft tissue environment. However, the adjustments cannot be considered a major source of bias because the lower incisors proclined only 4.37° and protruded 0.9 mm with lip bumper treatment (as measured by O’Donnell et al17) and resulted in a minor advancement only at the gingival margin. The necessary adjustments accounted mainly for the uprighting and distal tipping of the molars (4.73° distal tipping, 0.95 mm distal movement). It has to be kept in mind that the patients investigated in this study had an age range of 10 to 17 years. The muscular response could be different in a younger age group that receives treatment over a longer time period in the transitional dentition. Future research should determine if treatment at earlier ages can permanently alter the soft tissue environment with lip bumper treatment. If adaptation was observed in such a study with this mechanism of physiologic expansion, one may even wish to compare the stability of teeth in these patients with those treated with conventional expansion.
apia ortodontica senza estrazioni: indagine clinico-statistica. Mondo Ortodontico 1989;14:325-32. Nevant CT, Buschang PH, Alexander RG, Steffen JM. Lip bumper therapy for gaining arch length. Am J Orthod Dentofacial Orthop 1991;100:330-6. Osborn WS, Nanda RS, Currier FG. Mandibular arch perimeter changes with lip bumper treatment. Am J Orthod Dentofacial Orthop 1991;99:527-32. Werner SP, Shivapuja PK, Harris EF. Skeletodental changes in the adolescent accruing from use of the lip bumper. Angle Orthod 1994;64:13-22. Grossen J, Ingervall B. The effect of a lip bumper on lower dental arch dimensions and tooth positions. Eur J Orthod 1995;17:129-34. Davidovitch M, McInnis D, Lindauer SJ. The effects of lip bumper therapy in the mixed dentition. Am J Orthod Dentofacial Orthop 1997;111:52-8. Shellhart WC, Moawad MI, Matheny J, Paterson RL, Hicks EP. A prospective study of lip adaptation during six months of simulated mandibular dental arch expansion. Angle Orthod 1997;67:47-54. Lindeman DE, Moore RN. Measurement of intraoral muscle forces during functional exercises. Am J Orthod Dentofacial Orthop 1990;97:289-300. Sakuda M, Ishizawa M. Study of the lip bumper. J Dent Res 1970;49:677. Sather AH, Mayfield SB, Nelson DH. Effects of muscular anchorage appliances on deficient mandibular arch length. Am J Orthod 1971;60:68-78. Soo ND, Moore RN. A technique for measurement of intraoral lip pressures with lip bumper therapy. Am J Orthod Dentofacial Orthop 1991;99:409-17. Hodge JJ, Nanda RS, Ghosh J, Smith D. Forces produced by lip bumpers on mandibular molars. Am J Orthod Dentofacial Orthop 1997;111:613-22. O’Donnell SA, Nanda RS, Ghosh J. Perioral forces and dental changes resulting from mandibular lip bumper treatment. Am J Orthod Dentofacial Orthop 1998;113:247-55. Stavridi R, Ahlgren J. Muscle response to the oral-screen activator: an EMG study of the masseter, buccinator, and mentalis muscles. Eur J Orthod 1992;14:339-49. Bundgaard M, Bjerregaard J, Melsen B, Terp S. An electromyographical study of the effect of a mandibular lipbumper. Eur J Orthod 1983;5:149-56. Moorrees CFA. Natural head position. Am J Orthod Dentofacial Orthop 1994;105:512-3. Burdette BH, Gale EN. Reliability of surface electromyography of the masseteric and anterior temporal areas. Archs Oral Biol 1990;35:747-51. Ingervall B, Thüer U. Temporal muscle activity during the first year of Class II, Division 1 malocclusion treatment with an activator. Am J Orthod Dentofacial Orthop 1991;99:361-8. Harradine N, Kirschen R. Lip and mentalis activity and its influence on incisor position: a quantitative electromyographic study. Br J Orthod 1983;10:114-27. Throckmorton GS, Ellis E, Sinn DP. Functional characteristics of retrognathic patients before and after mandibular advancement surgery. J Oral Maxillofac Surg 1995;53:898-908. Cecere F, Ruf S, Pancherz H. Is quantitative electromyography reliable? J Orofacial Pain 1996;10:38-47. Simpson M, Richardson A. The reproducibility of electromyographic data. Br J Orthod 1975;2:41-6. Burdette BH, Gale EN. Reliability of surface electromyography of the masseteric and anterior temporal areas. Archs Oral Biol 1990;35:747-51. Garrett NR, Kapur KK. Replicability of electromyographic recordings of the masseter muscle during mastication. J Pros Dent 1986;55:352-6. Nouri A, Rothwell P, Duxbury A. The reproducibility of electromyographic recordings of the masseter muscle in humans. J Oral Rehab 1976;3:189-200. Thüer U, Janson T, Ingervall B. Application in children of a new method for the measurement of forces from the lips on the teeth. Eur J Orthod 1985;7:63-78. Thüer U, Ingervall B. Pressure from the lips on the teeth and malocclusion. Am J Orthod Dentofacial Orthop 1986;90:234-42. Gould MCE, Picton DCA. A study of pressures exerted by the lips and cheeks on the teeth of subjects with normal occlusion. Arch Oral Biol 1964;9:469-78. Gould MCE, Picton DCA. A study of pressures exerted by the lips and cheeks on the teeth of subjects with Angle’s Class II Division 1, Class II Division 2, and Class III malocclusions compared with those of subjects with normal occlusions. Archs Oral Biol 1968;13:527-41. McNulty EC, Lear CSC, Moorrees CFA. Variability in lip adaptation to changes in incisor position. J Dent Res 1968;47:537-47. Renfroe EW. The factor of stabilization in anchorage. Am J Orthod 1956;42:883-97. Subtelny JD, Sakuda M. Muscle function, oral malformation, and growth changes. Am J Orthod 1966;52:495-517.
6. 7. 8. 9. 10. 11.
12. 13. 14. 15. 16. 17. 18. 19. 20.
CONCLUSIONS 21.
1. Insertion of the lip bumper led to increased activity during rest and swallowing of the upper and lower lips. The response for the speech exercises was variable. 2. The lower lip musculature did not show any differences between pretreatment and posttreatment activity that would indicate muscle adaptation to the lip bumper appliance. 3. Lip bumper treatment in the adolescent patient might not result in increased posttreatment stability. It is suggested that a retention protocol similar to that for conventional arch expansion is used.
22.
23. 24.
25. 26. 27. 28.
We thank Dr Wolfram Hussels for his ideas and suggestions, Drs John J. Hodge and Scot A. O´Donnell for their help and advice with this research project, and Dr David W. Smith for his statistical advice and support. REFERENCES 1. Bjerregaard J, Bundgaard AM, Melsen B. The effect of the mandibular lip bumper and maxillary bite plane on tooth movement, occlusion, and space conditions in the lower dental arch. Eur J Orthod 1980;2:257-65. 2. Bergersen EO. A cephalometric study of the clinical use of the mandibular labial bumper. Am J Orthod 1972;61:578-601. 3. Aru G, Colli S, Falconi A, Zappa G. Il lip-bumper in ortodonzia. Mondo Ortodontico 1985;10:25-32. 4. Cetlin, NM, Ten Hoeve A. Nonextraction treatment. J Clin Orthod 1983;17:396-413. 5. Nidoli G, Lazzati M, Macchi A, Carloni L, Raso M. Il ruolo del lip-bumper nella ter-
29. 30. 31. 32. 33.
34. 35. 36.
The mode of action of the lip bumper has been explained as an alteration of the functional pattern as well as a stretching of the lower labial musculature,1 resulting in proclination of the incisors, uprighting of the anchor molars, and an increase in arch width.2-10 As opposed to conventional expansion techniques, the lip bumper appliance introduces an alteration of the functional pattern.1 The shielding effect not only allows the dental arch to expand but also encourages adaptation of the lips and cheeks so that the pressure exerted on the teeth is less than it would have been if the teeth had been moved labially with routine orthodontic treatment.11 A relatively slow expansion of the dental arch is the result of “natural forces” with the lip bumper.9 Attempts have been made to quantify the forces on the lip bumper that result from the new environment created with the appliance.12-17 Sakuda and Ishikawa13 measured higher pressure in the midline area of the lip bumper during swallowing than during speech or chewing. Sather et al14 found no correlation between tooth movement and forces From the Department of Orthodontics, University of Oklahoma. aFormer graduate student. Currently Associate Professor, Department of Orthodontics, College of Dentistry, University of Hamburg, Germany. bProfessor and Chair, Department of Orthodontics, College of Dentistry, University of Oklahoma, Oklahoma City. cIn Private Practice, Dallas, Tex. Reprint requests to: Dr Ram Nanda, Department of Orthodontics, University of Oklahoma, College of Dentistry, 1001 Stanton L. Young Blvd, Oklahoma City, OK 73190 Copyright © 2000 by the American Association of Orthodontists. 0889-5406/2000/$12.00 + 0 8/1/104688 doi.10.1067/mod.2000.104688
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with lip bumper treatment. Soo and Moore15 showed a decrease in forces on the lip bumper, starting at 1 month of appliance wear. This decrease was dependent on the location of the measuring gauge, with less decrease of force in the modiolus than in the midline area. The authors speculated that the adaptive response of the lip varied with the anatomic location, with the modiolus being less adaptable than the mentalis muscle. Hodge et al16 evaluated forces with specially designed strain gauges at the mandibular molars on a sample of 38 adolescent patients. They investigated forces with different types of lip bumpers (wire and acrylic shield) and found that the forces on the mandibular molars varied with vertical and horizontal positioning of the lip bumper relative to the mandibular incisors. The acrylic shield lip bumper produced higher resting forces than the wire lip bumper. The forces were higher with the lip bumper in a position 4 mm anterior as compared with a position 2 mm anterior to the mandibular incisors. In addition, positioning the lip bumper at the height of the gingival margin produced higher forces than a position at the middle of the clinical crown. O’Donnell et al17 measured forces before and after lip bumper treatment. They found no decrease in force at the posttreatment recording. Stavridi and Ahlgren18 pointed out that although the influence of the perioral musculature on the position of teeth and growth and development of craniofacial structures has been very extensively discussed, questions with regard to muscle behavior during various orthodontic treatment methods remain unanswered.
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Lip Bumper Treatment
Fig 1. Lip bumper used during treatment period.
Although the lip bumper is a muscle-activated appliance, limited information is available on the underlying muscular activity with the lip bumper. With a sample of 8 children, Bundgaard et al19 used a shield lip bumper and measured muscle activity with surface electromyography with and without the appliance in place, at rest and in function. They concluded that similarities in occlusion and facial morphology do not account for similarities in functional pattern. Reproducibility of the method was a problem in this study. An illogical relationship between morphologic and electromyographic changes was attributed to the weakness of the methods applied. The purpose of this prospective study was to measure muscle activity of the lips in the new environment created by the lip bumper. Comparisons between pretreatment and posttreatment muscle activity were used to indicate a possible adaptation of the lips to the appliance. MATERIAL AND METHODS Sample
Twenty-five patients were selected for treatment with the lip bumper appliance and were followed for a 12-month period. The criteria for treatment with the lip bumper were a mild to moderate arch length deficiency and a nonextraction orthodontic treatment plan in the mandibular arch. All 25 patients received 12 months of lip bumper treatment with no other appliances in the mandibular arch while regular orthodontic treatment proceeded in the maxillary arch with bands, brackets, expanders, and transpalatal arches. The sample consisted of 16 females and 9 males with a mean initial age of 13 years 1 month and an age range from 10 years 6 months to 17 years 4 months.
The lip bumper used for the 12 months of treatment was an 0.045 inch stainless steel lip bumper (American Orthodontics, Sheboygan, Wis) with adjustment loops mesial to the mandibular first molars and hooks (for ligatures) mesial to the adjustments loops (Fig 1). The lip bumper was inserted passively into the molar tubes and positioned to be 2 mm anterior to the facial surface of the mandibular incisor teeth at the level of the gingival margin. To ensure a permanent wear during the 12 months of treatment, the lip bumper was tied passively to the mandibular first molars via elastomeric or steel ligatures. During the treatment period, the lip bumper was inspected regularly; minor adjustments were made, if necessary, to maintain its position relative to the mandibular incisors. Electromyography
Electromyographic (EMG) data were collected with the K6-I Diagnostic System (Myo-tronics, Tukwila, Wash). The processed (integrated) electromyographic output of the muscles was investigated with the amount of magnification set to 100 µV. Fifteen seconds of muscle activity could be measured continuously and the recording of activity could be started and stopped at any time during these 15 seconds. From the graphic display, the operator could determine the exact point of beginning and end for each functional exercise. All other data points were then discarded, and EMG activity was calculated by the K6-I system for the data segment specified. EMG raw data were sampled at 240 samples per second, the average electromyographic activity (µV) was calculated from the integrated EMG activity from beginning to end of the functional exercise. Duo-trode electrodes (Myo-tronics, Tukwila, Wash) were used to record the muscle activity. These were bipolar surface electrodes (silver/silver chloride) with an interelectrode distance of 20 mm; they were placed over the upper and lower lip. The electrodes were cut in the middle to increase the interelectrode distance from 20 to 30 mm. This was done to allow close adaptation and improve mobility of the lips. To ensure a consistent interelectrode distance of 30 mm and enable reproducible placement of the electrodes, a template was constructed. A grounding electrode was placed on the skin below the ear lobe. The electrode sites were prepared by cleaning the skin with ethanol. The electrodes were placed symmetrically to the facial midline at the vermilion border. Recording Procedure
Muscle activity recordings were taken on the same day lip bumper treatment was initiated and again after 12 months of treatment with continuous wear of the appli-
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Table I. Average
muscle activity (µV) of the upper and lower lips (Means and standard deviations for the pretreatment and posttreatment recordings with and without the lip bumper are shown for the different functional exercises.) Pretreatment recording With lip bumper Muscle Upper lip Rest (lips closed) Speech (church) Speech (pop) Speech (phone) Swallow Lower lip Rest (lips closed) Speech (church) Speech (pop) Speech (phone) Swallow
Mean
SD
13.60 29.18 37.82 26.21 39.02
10.33 19.85 14.07 13.01 24.13
13.78 34.29 38.65 52.64 44.75
6.94 22.52 15.79 24.10 27.63
Posttreatment recording
Without lip bumper Mean
With lip bumper
Without lip bumper
SD
Mean
SD
Mean
SD
4.99 25.50 26.89 23.91 22.11
3.31 18.00 10.85 13.15 15.27
10.08 21.39 31.89 20.99 33.25
7.41 16.85 16.26 11.59 21.56
4.22 24.43 28.88 22.07 20.38
3.48 15.85 15.18 13.41 12.96
5.79 52.17 38.21 52.29 33.65
3.64 26.17 15.71 21.56 23.91
14.07 34.78 35.35 51.53 41.52
7.95 18.57 16.62 19.92 26.46
6.04 49.36 37.18 47.90 27.42
5.38 23.96 14.62 22.90 23.04
ance. Measurements were taken with the patient seated upright in a chair with firm back support in a relaxed position with the head unsupported in a natural position (per Moorrees20). The muscle activity recording procedures were done for each patient with and without the lip bumper in place. Activity was recorded at a closed lip rest position, during speech (“phone,” “church,” and “pop”), and while swallowing 5 ml of water. During the recording session every activity recording was repeated 5 times. The first of the 5 readings was eliminated from the data collection because of anticipated higher initial readings due to the patient’s tension and anxiety (per Burdette and Gale21 and Ingervall and Thüer22). The experimental condition was repeated to reduce intraindividual variation of the electromyographic readings.21,23,24 Forces were recorded at the mandibular molars at the same time as the muscle activity measurements.16,17 Statistical Analysis
Means and standard deviations were calculated for each functional exercise for each muscle. This was done for the recordings both without the lip bumper and with the lip bumper inserted. Paired t tests were performed to determine if any significant differences were present between the pretreatment and the posttreatment muscle activity measurements. RESULTS Muscle Activity Before Treatment (Table I)
Muscle activity without the lip bumper. Resting activity was 4.99 ± 3.31 µV for the upper lip and 5.79 ± 3.64 µV for the lower lip. The speech exercises showed the highest activity in the lower lip (“church”
52.17 ± 26.17 µV, “pop” 38.21 ± 15.71 µV, “phone” 52.29 ± 21.56 µV). The upper lip muscle activity for speech was measured at 25.50 ± 18.00 µV for “church,” at 26.89 ± 10.85 µV for “pop,” and at 23.91 ± 13.15 µV for “phone.” The swallowing exercise was recorded at 22.11 ± 15.27 µV for the upper and 33.65 ± 23.91 µV for the lower lip. Muscle activity with the lip bumper. The comparison of pretreatment muscle activity with and without the lip bumper is shown in Table II (column I). The activity at rest and while swallowing increased with insertion of the appliance; rest activity for the upper lip was measured at 4.99 ± 3.31 µV without the lip bumper and at 13.60 ± 10.33 µV with the appliance in place (P < .001). Lower lip activity at rest increased from 5.79 ± 3.64 µV to 13.78 ± 6.94 µV (P < .001). Swallowing showed significant increases from 22.11 ± 15.27 µV to 39.02 ± 24.13 µV for the upper lip (P < .001) and from 33.65 ± 23.91 µV to 44.75 ± 27.63 µV for the lower lip. The speech activity exhibited a rather variable response: “church” showed a significant decrease in lower lip activity with the lip bumper (P < .001), “pop” exhibited less activity of the upper lip with the bumper (P < .001). Effect of Lip Bumper Treatment on Muscle Activity of the Lips
Comparison of muscle activity with the lip bumper before and after treatment (Table II, column II). The lower lip showed virtually no differences between pretreatment and posttreatment values, and the corresponding P values were not statistically significant. The upper lip showed a trend to lower activity at the posttreatment recording. However, only the activity
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Table II. Comparison
of activity recordings before (T1) and after (T2) treatment and with (LB) and without (No LB) the lip bumper appliance in place Mean difference (µV) Muscle Upper lip Rest (lips closed) Speech (church) Speech (pop) Speech (phone) Swallow Lower lip Rest (lips closed) Speech (church) Speech (pop) Speech (phone) Swallow
I (T1 LB - T1 No LB)
8.61*** 3.68 10.93*** 2.30 16.91*** 7.99*** –17.88*** 0.44 0.35 11.11*
II (T1 LB - T2 LB)
3.51 7.79* 5.93 5.22* 5.76 –0.29 –0.49 3.31 1.12 3.23
III (T1 No LB - T2 No LB)
IV (T1 No LB - T2 LB)
0.77 1.07 2.00 1.84 1.73
–5.09** 4.11 –5.00 2.92 –11.15**
–0.25 2.81 1.03 4.39 6.22
–8.28*** 17.39*** 2.86 0.77 –7.88
*Significant at P < .05; **significant at P < .01; ***significant at P < .001. I, Before treatment with the lip bumper - before treatment without the lip bumper (T1 LB - T1 no LB). II, Before treatment with the lip bumper - after treatment with the lip bumper (T1 LB - T2 LB). III, Before treatment without the lip bumper - after treatment without the lip bumper (T1 no LB - T2 no LB). IV, Before treatment without the lip bumper - after treatment with the lip bumper (T1 no LB - T2 LB).
for speech of the words “church” and “phone” was significantly lower (P < .05) for the posttreatment measurement. Resting and swallowing activity, as well as speech of the word “pop” showed lower values at the posttreatment recording, but these differences were not statistically significant. Comparison of muscle activity without the lip bumper before and after treatment (Table II, column III). The resting activity for the lower lip was 5.79 ± 3.64 µV before treatment and 6.04 ± 5.38 µV after treatment, the upper lip activity at rest was 4.99 ± 3.31 µV before treatment and 4.22 ± 3.84 µV after treatment. No statistically significant differences between pretreatment and posttreatment values were found. Comparison of pretreatment muscle activity without the lip bumper to posttreatment muscle activity with the lip bumper (Table II, column IV). Pretreatment activity without the lip bumper was compared with posttreatment activity with the lip bumper for the upper and lower lip. Activity at rest was significantly higher at the posttreatment recording with the lip bumper (P < .01 for the upper lip and P < .001 for the lower lip). Speech activity showed no significant differences except for speech of the word “church” for the lower lip, which was significantly lower at the posttreatment recording with the lip bumper (P < .001). Swallow activity was higher both for the upper and lower lip at the posttreatment recording with the lip bumper inserted but was only found to be statistically significant for the upper lip (P < .01).
DISCUSSION Variability of the Electromyographic Method
Reliability of electromyography for evaluating orofacial musculature has been controversial in the past; Cecere et al25 concluded that quantitative electromyography of the masticatory muscles has a limited value as a diagnostic tool and in the assessment of individual treatment outcomes because of problems with reproducibility. However, when analyzing a large enough study sample, valuable information can be gained. Harradine and Kirschen23 as well as Simpson and Richardson26 demonstrated that it is possible to reliably evaluate lip activity for functional exercises. Past studies that investigated the reliability of muscle activity over a shorter period of time have used templates that attached to the teeth for a reliable replacement of the electrodes.27-29 Because of the long-term nature of the present study and the actively growing nature of the sample, this was not possible. However, a template was used to ensure a reproducible placement of the electrodes relative to the facial midline and vermilion border at a constant interelectrode distance. Furthermore, the variability of the electromyographic method can be decreased in different ways that were used in the present study. Providing a quiet environment with avoidance of patient distractions has been found to be important to reduce patient anxiety.26 Burdette and Gale17 and Ingervall and Thüer22 have shown that the effect of patient anxiety can be minimized by discarding the first of the recordings for each experimental
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condition. Thüer et al30 suggested repeated observations to reduce intraindividual variability. They based their recordings on 2 observations and reported on a reduction of the intraindividual variation of about 30%. In the present study, averaging 4 measurements led to a measurement error for the average of the 4 measurements that was 50% less than the measurement error of the single observation. Using the aforementioned procedures and the fact that Harradine and Kirschen23 as well as Simpson and Richardson26 have demonstrated that it is possible to reliably evaluate lip activity for functional exercises, the use of electromyography in a carefully designed experiment is considered valid. All electromyographic recordings were characterized by high standard deviation values. The standard deviation increased with the actual value of activity that was measured. Large variability with quantitative electromyography is not unique. Other related studies have also reported large standard deviation values. Thüer and Ingervall31 found large interindividual and intraindividual variability for electromyographic variables of the upper and lower lip during recording of lip pressure. They reported on standard deviations up to 160% of the mean value and suggested making repeated observations on the same individual to overcome the adverse effect of the large intraindividual variation. An explanation for the large standard deviations might also lie in the physiology of the lips. Thüer et al30 attributed large experimental errors in lip strength and lip pressure recordings mainly to biologic intraindividual variation. Lip pressure was found to be highly variable also by Gould and Picton,32,33 McNulty et al,34 Soo and Moore,15 and Hodge et al.16 Therefore, it seems that both the experimental method used (electromyography) and the physiologic environment contribute to the variability that was observed.
cult. Bundgaard et al19 recorded muscle activity at rest and while functioning with and without a lip bumper inserted and found a pronounced variability in muscle activity among their 8 patients. They did, however, mention that there was little variation in resting muscle activity in the relaxed position before and after wearing the lip bumper. Stavridi and Ahlgren18 tested the effect of an oral screen on the mentalis, buccinator, and masseter muscle activity. For rest with closed lip posture, they found a statistically significant increase in mentalis activity with the activator in place. Therefore, it may seem that the shielding effect of the lip bumper and of the vestibular elements of the oral screen activator leads to increased lower lip activity necessary to enable lip closure at rest. Stavridi and Ahlgren showed a statistically significant decrease in swallowing activity of the mentalis muscle with the oral screen activator in place, whereas this study measured increased activity of the lower lip with the lip bumper in place. A possible explanation is the difference in the experimental procedure: Stavridi and Ahlgren used an “empty” swallowing of saliva, and the subjects in the present study were instructed to swallow 5 ml of water. Stavridi and Ahlgren reported that the subjects usually had their lips open, which is contrary to the swallowing observed in the present study. In addition, the sample used by Stavridi and Ahlgren consisted of Class II Division 1 patients. Six of 10 of their patients had lip incompetence, which is often associated with mentalis hyperactivity. Therefore, insertion of a shielding appliance is more likely to reduce mentalis activity. The sample in the present study had competent and no discernible mentalis hyperactivity. And Stavridi and Ahlgren measured mentalis muscle activity whereas this study recorded activity mainly of the lower portion of the orbicularis oris muscle.
Effect of Insertion of the Lip Bumper Appliance on Muscle Activity
Muscle Adaptation to the Lip Bumper
The comparison between activity with and without the lip bumper showed markedly different activity of the upper and lower lips with the appliance in place (see Tables I and II). The speech exercises exhibited both significant increases and decreases; rest and swallowing were significantly higher with the appliance inserted. The increase in rest activity of the lower lip is crucial for the mode of action of the appliance because the lips are at rest for the majority of the time, and increased activity at rest is probably related to the dental changes. There is a lack of information in the orthodontic literature about the influence of inserting a shielding appliance on the muscle activity of the lips, which makes a comparison of the results of this study diffi-
This discussion will focus on muscle adaptation of the lower lip. Comparisons of pretreatment and posttreatment muscle activity measurements were used as an indicator of muscle adaptation. Insertion of the lip bumper was found to increase muscle activity at rest and for swallowing (Table I). It is hypothesized that if adaptation occurred over the treatment period, muscle activity, which increased initially with insertion of the appliance (at rest and for swallow), should decrease again and be significantly lower than at the beginning of treatment. However, no significant changes between pretreatment and posttreatment muscle activity with the lip bumper were found for the lower lip. Because the lips are at a closed lip rest position in lip competent subjects for the longest duration of time during the day,
American Journal of Orthodontics and Dentofacial Orthopedics Volume 117, Number 4
adaptation of muscle function should have resulted in decreased posttreatment activity. In case of muscle adaptation over the treatment period, posttreatment activity without the appliance in place should be significantly lower than pretreatment activity without the appliance in place. This would indicate that the equilibrium has changed and a different environment has been established that might provide stability of the dental arch at the new and expanded arch position. The comparison of pretreatment and posttreatment activity without the lip bumper revealed no pretreatment to posttreatment differences in muscle activity for the lower lip. None of the corresponding P values was statistically significant. This suggests an unchanged soft tissue environment. Comparing the “old” equilibrium without the lip bumper with the “new” equilibrium with the lip bumper can also be used as an indicator of muscle adaptation. It can be assumed that in case of muscular adaptation the new equilibrium introduced by the appliance over the treatment period provides stability by establishing similar muscular activity levels as before treatment without an appliance in place, resulting in similar pressures on the teeth in the new position as before treatment. However, rest activity of the lower lip was found to be significantly different (P < .001). Speech activity was not used as an indicator because insertion of the lip bumper before treatment did not consistently show a significant increase in muscle activity. Therefore, comparison of pretreatment activity without the lip bumper and posttreatment activity with the lip bumper could not be expected to be significantly different from each other in the case of muscle adaptation. The swallow exercise exhibited a difference in response between upper and lower lip. Although the upper lip showed significant differences, this could not be measured for the lower lip (P = .1042). It has to be stated that the insertion of the lip bumper at the pretreatment measurement only resulted in significantly higher measurements at the P < .05 level when compared with the measurements without the appliance. The actually recorded pretreatment and posttreatment values with the appliance in place were only marginally different from each other. Emphasis on muscle adaptation was on the lower lip musculature for two reasons: (1) upper lip activity changed to a certain degree with the insertion of the lip bumper, but this activity is not likely to contribute significantly to pressures on the mandibular lip bumper; and (2) at the recording after 12 months of lip bumper treatment, fixed appliances (brackets, bands, palatal arches, expanders) had been placed in the maxillary arch and had probably influenced upper lip activity.
Klocke, Nanda, and Ghosh 389
Thus far, the extent of muscle and soft tissue adaptation to the lip bumper has not been thoroughly studied. Grossen and Ingervall9 stated that it is not known whether the relatively slow expansion of the dental arch by “natural forces” with the lip bumper brings about adaptations in surrounding structures that decrease the risk for relapse. Shellhart et al11 pointed out that vestibular shields not only allow the dental arch to expand, they also are meant to encourage adaptation of the lips and cheeks so that the pressure they exert on the teeth is less than it would have been if the teeth had been moved labially with routine orthodontic treatment. Theoretically, this decrease in pressure should result in improved stability of treatment. Soo and Moore15 found a decrease in pressure especially in the midline area of the lip bumper and suggested that an adaptive response of the lip muscles to lip bumper treatment occurred that varied according to anatomic location. O’Donnell et al17 did not find a decrease in pressure on the mandibular lip bumper over the treatment period that would indicate an adaptive process. Bundgaard et al19 recorded lip muscle activity electromyographically before and after 7 months of lip bumper treatment. However, they did not try to analyze muscle adaptation to the appliance. The findings of the present study on muscle activity are in concordance with the results by O’Donnell et al17; both studies suggest an unchanged environment after 12 months of lip bumper treatment and do not indicate soft tissue adaptation. The proposed increased stability11 due to the slow and “physiologic” expansion with the lip bumper with a decreased risk for relapse cannot be supported by the results of our study. Renfroe35 and Subtelny and Sakuda36 pointed out that loss of alveolar bone on the labial aspect of lower incisor roots was due to the influence of the pressure of a tight or hyperfunctional lip. They advocated the protection of the vestibular attachment of the mandibular incisors by the lip bumper. This protection might only be a temporary effect. The vestibular tissue seems to be subjected to the same muscle forces before and after lip bumper treatment, with the lip bumper influencing the pressure of the lower lip only during the actual treatment period. Therefore, stability of the treatment results cannot depend on a change in soft tissue environment but might require a retention protocol similar to that for conventional arch expansion treatment. Dental changes in the mandibular arch due to lip bumper treatment necessitated minor periodic adjustments of the bumper to maintain a constant distance of the anterior part of the bumper from the incisor teeth. It can be argued that these adjustments made for a chang-
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ing relationship of the lip bumper with the soft tissue environment. However, the adjustments cannot be considered a major source of bias because the lower incisors proclined only 4.37° and protruded 0.9 mm with lip bumper treatment (as measured by O’Donnell et al17) and resulted in a minor advancement only at the gingival margin. The necessary adjustments accounted mainly for the uprighting and distal tipping of the molars (4.73° distal tipping, 0.95 mm distal movement). It has to be kept in mind that the patients investigated in this study had an age range of 10 to 17 years. The muscular response could be different in a younger age group that receives treatment over a longer time period in the transitional dentition. Future research should determine if treatment at earlier ages can permanently alter the soft tissue environment with lip bumper treatment. If adaptation was observed in such a study with this mechanism of physiologic expansion, one may even wish to compare the stability of teeth in these patients with those treated with conventional expansion.
apia ortodontica senza estrazioni: indagine clinico-statistica. Mondo Ortodontico 1989;14:325-32. Nevant CT, Buschang PH, Alexander RG, Steffen JM. Lip bumper therapy for gaining arch length. Am J Orthod Dentofacial Orthop 1991;100:330-6. Osborn WS, Nanda RS, Currier FG. Mandibular arch perimeter changes with lip bumper treatment. Am J Orthod Dentofacial Orthop 1991;99:527-32. Werner SP, Shivapuja PK, Harris EF. Skeletodental changes in the adolescent accruing from use of the lip bumper. Angle Orthod 1994;64:13-22. Grossen J, Ingervall B. The effect of a lip bumper on lower dental arch dimensions and tooth positions. Eur J Orthod 1995;17:129-34. Davidovitch M, McInnis D, Lindauer SJ. The effects of lip bumper therapy in the mixed dentition. Am J Orthod Dentofacial Orthop 1997;111:52-8. Shellhart WC, Moawad MI, Matheny J, Paterson RL, Hicks EP. A prospective study of lip adaptation during six months of simulated mandibular dental arch expansion. Angle Orthod 1997;67:47-54. Lindeman DE, Moore RN. Measurement of intraoral muscle forces during functional exercises. Am J Orthod Dentofacial Orthop 1990;97:289-300. Sakuda M, Ishizawa M. Study of the lip bumper. J Dent Res 1970;49:677. Sather AH, Mayfield SB, Nelson DH. Effects of muscular anchorage appliances on deficient mandibular arch length. Am J Orthod 1971;60:68-78. Soo ND, Moore RN. A technique for measurement of intraoral lip pressures with lip bumper therapy. Am J Orthod Dentofacial Orthop 1991;99:409-17. Hodge JJ, Nanda RS, Ghosh J, Smith D. Forces produced by lip bumpers on mandibular molars. Am J Orthod Dentofacial Orthop 1997;111:613-22. O’Donnell SA, Nanda RS, Ghosh J. Perioral forces and dental changes resulting from mandibular lip bumper treatment. Am J Orthod Dentofacial Orthop 1998;113:247-55. Stavridi R, Ahlgren J. Muscle response to the oral-screen activator: an EMG study of the masseter, buccinator, and mentalis muscles. Eur J Orthod 1992;14:339-49. Bundgaard M, Bjerregaard J, Melsen B, Terp S. An electromyographical study of the effect of a mandibular lipbumper. Eur J Orthod 1983;5:149-56. Moorrees CFA. Natural head position. Am J Orthod Dentofacial Orthop 1994;105:512-3. Burdette BH, Gale EN. Reliability of surface electromyography of the masseteric and anterior temporal areas. Archs Oral Biol 1990;35:747-51. Ingervall B, Thüer U. Temporal muscle activity during the first year of Class II, Division 1 malocclusion treatment with an activator. Am J Orthod Dentofacial Orthop 1991;99:361-8. Harradine N, Kirschen R. Lip and mentalis activity and its influence on incisor position: a quantitative electromyographic study. Br J Orthod 1983;10:114-27. Throckmorton GS, Ellis E, Sinn DP. Functional characteristics of retrognathic patients before and after mandibular advancement surgery. J Oral Maxillofac Surg 1995;53:898-908. Cecere F, Ruf S, Pancherz H. Is quantitative electromyography reliable? J Orofacial Pain 1996;10:38-47. Simpson M, Richardson A. The reproducibility of electromyographic data. Br J Orthod 1975;2:41-6. Burdette BH, Gale EN. Reliability of surface electromyography of the masseteric and anterior temporal areas. Archs Oral Biol 1990;35:747-51. Garrett NR, Kapur KK. Replicability of electromyographic recordings of the masseter muscle during mastication. J Pros Dent 1986;55:352-6. Nouri A, Rothwell P, Duxbury A. The reproducibility of electromyographic recordings of the masseter muscle in humans. J Oral Rehab 1976;3:189-200. Thüer U, Janson T, Ingervall B. Application in children of a new method for the measurement of forces from the lips on the teeth. Eur J Orthod 1985;7:63-78. Thüer U, Ingervall B. Pressure from the lips on the teeth and malocclusion. Am J Orthod Dentofacial Orthop 1986;90:234-42. Gould MCE, Picton DCA. A study of pressures exerted by the lips and cheeks on the teeth of subjects with normal occlusion. Arch Oral Biol 1964;9:469-78. Gould MCE, Picton DCA. A study of pressures exerted by the lips and cheeks on the teeth of subjects with Angle’s Class II Division 1, Class II Division 2, and Class III malocclusions compared with those of subjects with normal occlusions. Archs Oral Biol 1968;13:527-41. McNulty EC, Lear CSC, Moorrees CFA. Variability in lip adaptation to changes in incisor position. J Dent Res 1968;47:537-47. Renfroe EW. The factor of stabilization in anchorage. Am J Orthod 1956;42:883-97. Subtelny JD, Sakuda M. Muscle function, oral malformation, and growth changes. Am J Orthod 1966;52:495-517.
6. 7. 8. 9. 10. 11.
12. 13. 14. 15. 16. 17. 18. 19. 20.
CONCLUSIONS 21.
1. Insertion of the lip bumper led to increased activity during rest and swallowing of the upper and lower lips. The response for the speech exercises was variable. 2. The lower lip musculature did not show any differences between pretreatment and posttreatment activity that would indicate muscle adaptation to the lip bumper appliance. 3. Lip bumper treatment in the adolescent patient might not result in increased posttreatment stability. It is suggested that a retention protocol similar to that for conventional arch expansion is used.
22.
23. 24.
25. 26. 27. 28.
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