Mandibular arch perimeter changes with bumper treatment William S. Osborn, DDS, MS,* Ram S. Nanda, DDS, MS, PhD,** and G. Fr~ins Currier, DDS, MSD, MEd*** Oklahoma City, Okla.
The effects of lip bumper treatment on the mandibular arch were observed in 32 patients with late transitional and early permanent dentitions. Dental cast measurements were made for arch perimeter, arch length, and a:rch width. Cephalometric radiographs were used to determine labial tipping of the incisors and distal movement of the molars. Arch circumference increased in all patients, ranging from 0.7 mm to 8.8 mm, with an average of 4.1 mm. The mean increase in arch length was 1.2 mm'and was largely attributed to anterior tipping of the mandibular incisors. Change in arch length was the most predictive variable for the increase in arch circumference. Passive changes in arch width were recorded, with a mean increase of 2.0 mm in the intercanine distance and 2.5 mm in the first premolar distance. Arch width increments contributed to the increase in arch circumference, but the increases in arch width were not found to be predictive of the change in arch circumference. Changes in either arch circumference or arch length were not related to the duration of treatment, age and sex of the patient, or the eruption status of the permanent second molars. (AM J ORTHOD DENTOFACORTHOP 1991;99:527-32.)
N o n e x t r a c t i o n approaches to treatment have increased interest in appliances and techniques that help create additional space within the dental arch. The lip bumper appliance, which is lip activated, has regained popularity in recent years for the treatment of crowding in the mandibular arch. ~-3 Lip bumper treatment has been used for molar anchorage, 4~ prevention of poor lip habits,79 and creation of increased space for the mandibular arch. ~3,9t~ The appliance has a stainless steel wire, usually 0.045 inch thick, that spans the facial surface of the mandibular arch without contacting the teeth and is inserted into tubes attached to the mandibular molars.L4"6'8"~' Anteriorly, the wire is sometimes covered by plastic tubing or a shield made of acrylic or plastic that holds the lower lip away from the mandibular incisors. Forces from the mentalis muscle are translated to the mandibular molars, enabling them to move to an upright and distal position. At the same time, the tongue may cause the mandibular incisors to tilt outward and the canines and premolars to move buccally. Thus mandibular arch length and width may increase, helping to alleviate crowding mesial to the mandibular molars. 1"4,9a3
From the Department of Orthodontics, University of Oklahoma. *Graduate Student. **Professor and Chairman, ***Associate Professor. 811119524
Previous studies on the effects of lip bumper treatment have largely focused on the movement of molars posteriorly and incisors anteriorly.4,9.~2.~3However, Cetlin and Ten Hoeve t and Ten Hoeve2 have stated that arch width increase is primarily responsible for increase in arch circumference. The purpose of our study was to evaluate the specific changes in mandibular arch length and width that affect increases in arch circumference associated with the use of the lip-bumper appliance.
MATERIALS AND METHODS Thirty-two patients, 19 female and 13 male, between the ages of 9 and 17 years, with a mean age of 12 years, were treated for mandibular crowding with a lip bumper inserted into tubes placed on mandibular permanent first molars. The distribution of the sample at the start of treatment--by sex, age, and presence or absence of mandibular permanent second molars and deciduous second molars--is given in Table I. The patients were consecutively treated persons from the practices of four orthodontists and the graduate orthodontic Clinic. Twelve patients were treated by orthodontist A, five by orthodontist B, six each by orthodontists C and D, and three in the graduate clinic. Lip bumpers were the only appliances used in the mandibular arch. They were worn full-time for a treatment time ranging from 6 to 33 months, with an average of I I months. A variety of maxillary appliances was 527
528
Osborn, Nanda, and Currier
Am. J. Orthod.Dentofac.Orthop. June 1991
Table i. Distribution of sample according to sex, age, and presence of mandibular permanent second molars and deciduous second molars at start of treatment
Age(Yr± too)
I
Malesttbiects
9---6 10±6 11---6 12±6 13±6 14±6 15---6 16±6 17±6 Total
I
Fema/esubjects
2 1 3 2 3 1 l 0 0 13
I
1 4 5 3 2 2 1 0 1 19
-7
I
0 1 1 1 3 3 2 0 1 12
Table II. Changes for mandibular arch after lip bumper treatment
Variable
No.
Mean change (mnO
SD
Arch perimeter Arch length 3 to 3 width 4 to 4 width 5 to 5 width e to e to 5 to 5 width 6 to 6 width
32 32 20 19 10 19 32
4.07* I. 17" 1.99" 2.50* 2.43* 3.39* 1.921"
2.03 1.25 1.31 1.74 1.42 1.94 2.74
I
Minimum Ohm) 0.70 - 0.84 0.21 0.40 0.21 0.54 -2.21
e 3 4 9 3 0 0 0 0 0 19
[
Mct~hnum (ram) 8.84 4.49 6.58 8.09 5.31 7.29 8.14
*Significant at p < 0.0001; lslgnificant at p < 0.001.
also used during the lip bumper treatment. Fifteen patients had maxillary Kloehn headgear, while 14 Patients had either a bonded or a banded edgewise appliance with an arch wire. Three of the patients wore high-pull facebow headgear, one wore a quadhelix device, and another wore a rapid palatal expansion device (Hyrax).
Clinical procedure A mandibular alginate impression and a cephalometric radiograph were taken immediately before the initiation of treatment. All lip bumpers were made o f 0.45-inch wire with a plastic, shrink-fit tubing, except for three, which had a wide plastic anterior shield. Loops were placed in the wire just mesial to the molar to serve as stops against the tubes. The wire was adjusted to be 3 to 5 mm away from the premolar and caanine teeth at the coronal level to hold the cheek away from the teeth. The anterior bow of the lip bumper was adjusted vertically at the level of the gingival margin and was held 1.5 to 2 mm away from the mz~ndibular incisor teeth. On completion of treatment, the' mandibular appliance was removed, and another alginate impression and a cephalometric radiograph were taken. The dental casts were poured in stone plaster, and
the landmarks were marked with a sharp lead pencil. The measurements on the dental casts were made directly with electronic-dial calipers accurate to 0.01 mm. The arch-circumference measurement was an aggregate of the following four measurements, as'described by Fisk 14 and Bjerregaardlt: mesial aspect of the right permanent first molar to distal aspect of the right permanent lateral incisor; distal aspect of the right permanent lateral incisor to midline; midline to distal aspect of left permanent lateral incisor and distal aspect of left permanent lateral incisor to mesial aspect of the left permanent first molar. Arch length was measured according to Moorrees ~5and Adkins t6 from a line drawn perpendicular.from the mesial contact points of the incisors to a line connecting the mesial contact points of the mandibular permanent first molars. No obvious asymmetry in the molar position was noticeable. Widths of molars and premolars were measured from a point marked on the central groove where it was bisected by the mesiodistal width of the tooth. Intercanine width was measured from cusp tips. Only 10 patients had all 14 mandibular permanent teeth. Nineteen patients had transitional dentitions with deciduous second molars present at the start of treatment. In the remaining three patients the second pre-
Volume 99 Number 6
Mandibular arch perimeter chtmges with lip bttmper treatment
529
1/ ;/7; Syrnp
stance
~
Fig. 1. Molar angle and molar distance from the lateral cephalometric radiographs.
molars were in varying stages of eruption; hence their width changes in the second premolar area could not be measured. Tile width changes for the first premolar and the permanent canine were not measured in cases where either one or both canines or premolars had not erupted at the time of initial records or at the end of the lip bumper treatment. The measurements from the lateral cephalometric tracings were (1) the incisor mandibular plane angle, or IMPA; (2) the angle of the lower incisor axis to the NB plane; and (3) the linear distance from the lower incisor to the NB plane. Additional measurements included (4) the anterior-superior angle formed by a line passing through the mesial cusp tip and the mesial root tip of the mandibular first molar and intersecting with the mandibular plane and (5) the molar distance, which was measured on the mandibular plane between the two points of intersection, M and SP (Fig. 1). We located point M by drawing a perpendicular line from the most distal point on the distal surface of the first molar, and we located point SP by drawing a perpendicular line from the most posterior point on the mandibular symphysis, or point SymP. This latter point was found to be stable during the period of lip bumper treatment and could be easily identified, thus providing a skeletal reference for measurement of the changes in position of the mandibular molars. The analysis of the data included computation of means and standard deviations. Paired Student's t tests were performed to determine whether an increase in arch circumference was significant. A correlation test between all the variables was performed to examine the strength of significant relationships. To determine the most predictive variable for increase in arch circumference and arch length, we applied stepwise multiple linear regression analyses, with increase in circumference and increase in length as the dependent variables. Analysis-of-variance tests were done to determine
whether there were any significant differences between changes in arch circumference and mandibular incisor position among patients treated by different orthodontists. RESULTS
The means, standard deviations, and range of changes in dental cast measurements on the mandibular arch are given in Table II. The mean increases in arch circumference and in arch length were found to be 4.07 mm and 1.17 ram, respectively, and were significant at p < 0.0001. The width between the first molars increased an average of 1.92 mm: In the premolar region, the width measurement for the 10 patients with mandibular second premolars increased an average of 2.43 mm, while the 19 patients who had both mandibular deciduous second molars at the initiation of treatment and second premolars that had erupted by the close of lip bumper treatment showed an average increase in width of 3.39 mm. The difference between the mean changes in width at the second premolar region in groups of patients with deciduous molars or premolars at the initiation of treatment was not significant (p >0.05). There were 19 patients who had mandibular first premolars and 20 who had.permanent canines at the end of treatment. These measurements showed that the interpremolar and intercanine widths had increased 2.5 mm and 1.99 mm, respectively. The mean changes in measurements for cephalometric radiographs are shown in Table III. In 25 patients (78%), the mandibular incisors tipped anteriorly. The average increase in incisor mandibular plane angle, or IMPA, was 2.92 °. Among the remaining seven patients (22%), three showed no change, whereas the other four had decreases in the angle ranging from 0.5 ° to 1.5 ° . The mean increase in molar angle was 3.09 ° . Twenty-six patients (81%) had a varying amount of
5:30 Osborn, Nanda, and Currier
Am. J. Orthod. Dentofac. Orthop. June 1991
Table III. Changes from the cephalometric radiographs after lip bumper treatment
I IMPA LI to N B LI to N B M o l a r angle M o l a r distance A r c h length
,,eonc, o,, e
I
2 . 9 2 °* 3.400* 1.12 r a m * 3.09°t 0.36 mm$ 1.34 r a m *
SO
I
3. I 1 3.42 1.20 3.89 0.99 ! .89
Ma.riraum - 1.50 ° -3.00 ° - i.42 mm - 3.50" -2.13 mm - 1.37 m m
12.00 ° 9.00 ° 3.35 mm 13.50 ° 2.21 m m 4.89 mm
*Significant at p < 0 . 0 0 0 1 ; "['significant at p < 0 . 0 0 1 ; :l:significant at p < 0 . 0 5 .
increase in this angle, signifying distal tipping of the permanent mandibular first molar. Six patients (19%) indicated small mesial tipping. Student's t test was applied to all of the posttreatment differences for all the measurements from the dental casts and the cephalometric radiograph (Tables II and III). It was found that all of the changes recorded with lip bumper treatment were statistically significant. Stepwise multiple linear regression analysis of the independent variables--i.e., the changes in arch length measured from dental casts and cephalometric radiographs: IMPA, LI to NB (in mm), molar angle, and molar distance--indicated that arch-length measurement from dental casts was the best predictor of increase in arch circumference with an R 2 value of 0.62 (p < 0.001). similarly, IMPA was found to be the most predictive measurement for change in arch length, with an R 2 value of 0.78 (p < 0.0001). The different archwidth changes were found to be correlated with each other, and therefore none of them stood out with higher R 2 values in the regression analysis for prediction of arch circumference. Since five orthodontists were participating in this study, there was a possibility of slight differences in the fabrication and application of the lip bumper appliances. Analysis of variance tests revealed no significant differences (p = 0.36) with respect to increases in arch circumference among patients being treated by different orthodontists. However, a significant difference was noted for changes of IMPA in the patients being treated by one orthodontist (p < 0.05), compared to the average IMPA changes for the other groups. When the sample was grouped by patients with second molars erupted before the initiation of treatment and those without, it was found that the changes in arch circumference, arch length, and the various arch widths were not significantly different between the two groups. No significant correlations were discovered with respect to changes in arch circumference, arch length, and length of treatment time, age, or sex of the patient.
DISCUSSION
The mandibular arch circumference increased in all patients during the course of treatment. This observation agrees with the conclusions from all the previous studies that indicate that lip bumper treatment yields increased arch circumference. However, most of the previous studies did not clarify whether this increase in arch circumference was attributable to increase in arch length or width. Cetlin and Ten Hoeve t have indicated increase in arch width as the primary cause of increased arch circumference. They reported an average increase of 5.5 mm at the permanent first molars. The average expansion at the molars in our study was 1.92 mm, substantially less than that reported by Cetlin and Ten Hoeve. The premolar width increases observed in our study were also less than those given by Cetlin and Ten Hoeve. We found 2.50 mm at the first premolar and 2.43 mm at the second premolar regions, while Cetlin and Ten Hoeve found 4 mm at the first premolars. However, the mean change in intercanine width was closer for the two studies (1.99 mm in our study, versus 2.5 mm in the Cetlin and Ten Hoeve study). The larger increases in arch width reported by Cetlin and Ten Hoeve t may have resulted from a force applied by the lip bumpers at the molar tubes, which caused expansion of the intermolar width and may also have indirectly contributed to the enhanced increases in the premolar widths. In the present study, an effort was made to maintain passive insertion of the lip bumper appliance in the molar tubes. However, there were a few cases in which appreciable expansion at the first molars was noted. In addition, treatment time for patients in the Cetlin and Ten Hoeve was longer (12 to 18 months) than the average treatment time for all patients in our study (11 months). A closer comparison with the Cetlin and Ten Hoeve ~ study is not possible, because they did not furnish details of their investigations. Our study indicated that passive changes from pressure of the tongue increased arch width in the premolar and canine regions and accounted for most of the gain in arch circumference.
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Mandibular arch perimeter changes with lip bumper treatment
531
T a b l e IV. R e s u l t s o f lip b u m p e r t r e a t m e n t o n m a n d i b u l a r arch p r e s e n t e d in d e s c e n d i n g o r d e r o f c h a n g e in arch circumference
Patient 29 2 22 17 1 15 5 6 12 11
20 3 10 16 30 19 18 21 32 8 26 4 14 25 9 31 7 23 27 13 28 24
Starting age (yr-mo) 11-6 13-9 9-9 9-10 13-1 1 I-7 15-2 13-2 11-1 9-5 11-2 12-1 12-7' 9-10 11-0 11-7 10-9 9-11 12-8 14-0 12-6 17-1 11-2 10-9 14-10 18-1 14-3 10-8 12-3 ! 1-10 13-2 10-2
Duration of treatment Ono)
Change in arch circumference (ram)
10.0 8.5 11.0 14.0 6.0 19.5 6.5 6.0 12.5 16.0 7.0 8.5 16.0 33.0 7.0 14.0 12.5 12.0 6.0 9.0 8.5 6.0 8.5 9.0 8.5 7.0 9.0 12.0 9.5 11.5 14.5 10.0
8.84 8.68 7.82 7.07 6.56 6.17 5.86 5.79 4.51 4.94 4.48 4.25 4.09 3.89 3.89 3.61 3.50 3.28 3.24 3.19 3.18 3.11 2.66 2.61 2.51 2.48 2.39 2.35 1.91 1.70 i.69 0.70
Change hz arch lbngth
Changes in arch widths (ram)
!. 15 4.49 3.75 0.89 3.09 2.51 3.03 2.36 0.95 0.45 0.09 -0.14 2.15 1.55 1.28 0.13 1.51 0.00 1.85 1.13 1.05 1.42 - 0.41 1.50 0.32 1.02 0.76 - 0.64 0.03 1.38 - 0.25
6.58 1.49 --1.18 -1.20 1.15 2.96 3.72 -3.22 2.74 ----2.98 2.53 1.08 2.03 1.90 I. 12 -1.81 . 0.21 -!.33 -1.27
- 0.84
1.09
.
8.09 0.40 --1.56 -i .88 1.75 ---3.71 2.92 -4.58 2.03 ---1.49 -1.45 2.98 2.22 1.72 . 1.0 -3.41 0.70 1.45 2.70
3.89* 0.21 3.41" 7.29* 2.29 5.13" 2.82 2.48 4.99* 6.67* 3.53* 5.31 3.10 3.31" -2.87* 5.21" 3.50* -1.74 2.60* I. 19 2.99* 2.00* 1.39 2.49" 1.50* 1.23" 0.54* 0.62*
- 0.47 - 0.71 3.46 7.13 2.91 5.44 0.20 0.78 4.93 6.58 2.23 4.28 0.46 3.51 8.14 0.05 3.03 2.27 3.49 0.87 - 0.07 2.87 5.72 - 0.95 0.34 0.24 - 1.31 0.25 0.36 0.30 - 2.21
2.70"
- 2.00
.
* Initial measurements were from e to e, but later changes were 5 to 5.
S a g i t t a l c h a n g e s in a r c h l e n g t h w e r e s m a l l e r t h a n in the t r a n s v e r s e d i m e n s i o n s , w i t h a m e a n c h a n g e o f 1.17 m m . M o s t o f this c h a n g e c o u l d b e a t t r i b u t e d to a n t e r i o r t i p p i n g o f the m a n d i b u l a r incisors. M e a n I M P A i n c r e a s e d 2 . 9 2 °. T h i s c h a n g e in t h e i n c i s o r position c o r r o b o r a t e s t h e findings o f several p r e v i o u s studies .4. t~., 3
Distal t i p p i n g o f t h e m o l a r s was n o t f o u n d to b e a p p r e c i a b l e . T h e m e a n a m o u n t o f c h a n g e in t h e m o l a r a n g l e w a s 3 . 0 9 ° . T h e l i n e a r d i s t a n c e f r o m the distal s u r f a c e o f the m o l a r ( M ) to the s y m p h y s i s p o s t e r i o r ( S P ) , m e a s u r e d o n the m a n d i b u l a r p l a n e , i n c r e a s e d b y a m e a n o f 0 . 3 6 m m , w h i c h is less t h a n e a r l i e r findings. 4'9'tz'z3 In t h e c u r r e n t study, r e a s o n a b l e c a r e w a s
T h e m o v e m e n t o f the i n c i s o r s d e p e n d s o n the pos i t i o n a n d t y p e o f l a b i a l b o w used. T h e labial b o w u s e d w i t h 2 9 p a t i e n t s o f this s t u d y w a s m a d e f r o m 0 . 0 4 5 i n c h w i r e , w i t h t u b i n g , a n d w a s a d j u s t e d at the level o f the g i n g i v a l m a r g i n o f the teeth. T h e lip b u m p e r u s e d o n the r e m a i n i n g t h r e e p a t i e n t s in this study, as well as b y B j e r r e g a a r d et a l . , " w a s f a b r i c a t e d w i t h a 6 m m p l a s t i c shield that c o m p l e t e l y b l o c k e d the i n c i s o r s ; this b u m p t e r p r o d u c e d a m o r e p r o n o u n c e d t i p p i n g o f the incisors.
t a k e n to m e a s u r e the c h a n g e s in m o l a r p o s i t i o n ; this p r e c a u t i o n m a y e x p l a i n the d i f f e r e n c e s in o u r o b s e r vations from those of previous investigators. It is i n t e r e s t i n g to n o t e that n o p o s i t i v e c o r r e l a t i o n w a s f o u n d b e t w e e n the m e a n c h a n g e s in a r c h c i r c u m ference or arch length and length of treatment. The p l a u s i b l e e x p l a n a t i o n is the fact that o n l y m i n o r c h a n g e s w e r e r e c o r d e d in d i s t a l i z a t i o n o f m o l a r s a n d that t h e c h a n g e s in a r c h c i r c u m f e r e n c e w e r e m a i n l y a t t r i b u t a b l e to arch w i d t h a n d a n t e r i o r t i p p i n g o f the incisors. T h e s e
532
Osborn, Nanda, attd C u r r i e r
changes m a y be produced optimally in a treatment time of about 1 year. The variability of changes in arch width and arch length was so large that no reliable equation to predict the increases in arch circumference could be derived. Table IV illustrates the increases in arch circumference and the changes in arch length and width for all the persons in the study. Patients 3, 11, 19, 20, and 21 all showed increases in arch circumference o f greater than 3 m m , with less than 0.5 mm increases in arch length. Except for Patients 19 and 20, whose canines were unerupted, each patient had an increase o f at least 3 m m in intercanine width. Patient 29 had. an 8.8 m m arch-circumference increase, with only a 1.2 m m increase in arch length; this patient also had the largest increase in arch width. In five cases (Patients 3, 14, 23, 24, and 28) archlength m~asurements decreased. This change would have caused a decrease in arch circumference except for the fact that the patients had some increases in intercanine and interpremolar arch width to allow for increases in arch circumference. However, these patients had relatively small increases in arch circumference. Only four patients (1, 2, 5, and 22) had increases in arch length greater than 3 mm. They also had the largest increases in arch circumference. It is likely that individual variations in arch form changed the effect o f increases in arch widths at the different teeth on arch circumference. CONCLUSIONS
Evaluation o f results from clinical studies is difficult at best. A number of factors m a y be involved in terms o f selection of the sample, fabrication and application of the appliance, length of treatment, number of participating clinicians, patient's age and response, and methods used in appraisal o f the results. This study includes many o f the variables but has attempted to document changes in both sagittal and transverse dimensions. It confirms that the lip bumper appliance may be used for gaining space in the mandibular dental arches. Appropriate adjustment of the appliance in the incisor region is needed when anterior movement o f
Am. J. Orthod. Dentofac. Orthop. June 1991
the incisors is not desired. Posterior movement o f the mandibular molars was found to be minimal. Therefore the anticipated changes in arch perimeter resulted from changes in arch width and anterior movement of the incisors. BIBLIOGRAPHY 1. Cetlin NM, Ten Hoeve A. Nonextraction treatment. J Clin Orthod 1983;17:396-413. 2. Ten Hoeve A. Palatal bar and lip bumper in nonextraction treatment. J Clin Orthod 1985;19:272-91. 3. Ghafari J. A lip activated appliance in early orthodontic treatment. J Am Dent Assoc 1985;1 ! 1:771-4. 4. Bergersen EO. A cephalometric study of the clinical use of the mandibular labial bumper. AM J ORTtIOD1972;61:578-602. 5. Bedell WR. The use of tissue-bearing anchorage alone and in conjunction with various techniques in treatment. AM J OBSTET GYNECOL1954;40:404-20. 6. Renfroe EW. The factor of stabilization in anchorage. AM J ORTHOD 1956;42:883-97. 7. Graber TM, Neumann B. Removable orthodontic appliances. 2nd ed. Philadelphia: WB Saunders,. 1984:80-4. 8. Denholtz M. A method of harnessing lip pressure to move teeth. J Am Soc Study Orihod 1963;1:16-35. 9. Subtelny JD, Sakuda M. Muscle function, oral malformation, and growth changes. AM J OR'roOD 1966;52:495-517. 10. Sather AH, Mayfield SB, Nelson. DH. Effects of muscular anchorage appliances on deficient mandibular arch length. AM J ORTtIOD 1971;60:68-78. I!. Bjerregaard J, Bundgaard ANt, Nielsen B. The effect of the mandibular lip bumper and maxillary bite plate on tooth movement, occlusion and space conditions in the lower dental arch. Eur J Orthod 1980;2:257-65. 12. Sakuda M, lshizawa M. Study of the lip bumper. I Dent Res 1970;49:677. 13. Anarzadeh F, Adenwalla ST. A cephalometric analysis of the clinical application of lip bumper. J Dent Res 1987;66:252. 14. Fisk RO. Normal mandibular arch changes between ages 9-16. J Can Dent Assoc 1966;32:652-658. 15. Moorrees CFA. The dentition of the growing child. Cambridge: Harvard University Press, 1959:87-8. 16. Adkins MA, Nanda RS, Currier GF. Arch perimeter changes on rapid palatal expansion. Ar~lJ ORTIIODDENTOFACORTHOP1990; 97:194-9. Reprint requests to:
Dr. William S. Osbom University of Oklahoma Department of Orthodontics P. O. Box 26901" 1001 Stanton L. Young Blvd. Oklahoma City, OK 73190
The effects of lip bumper treatment on the mandibular arch were observed in 32 patients with late transitional and early permanent dentitions. Dental cast measurements were made for arch perimeter, arch length, and a:rch width. Cephalometric radiographs were used to determine labial tipping of the incisors and distal movement of the molars. Arch circumference increased in all patients, ranging from 0.7 mm to 8.8 mm, with an average of 4.1 mm. The mean increase in arch length was 1.2 mm'and was largely attributed to anterior tipping of the mandibular incisors. Change in arch length was the most predictive variable for the increase in arch circumference. Passive changes in arch width were recorded, with a mean increase of 2.0 mm in the intercanine distance and 2.5 mm in the first premolar distance. Arch width increments contributed to the increase in arch circumference, but the increases in arch width were not found to be predictive of the change in arch circumference. Changes in either arch circumference or arch length were not related to the duration of treatment, age and sex of the patient, or the eruption status of the permanent second molars. (AM J ORTHOD DENTOFACORTHOP 1991;99:527-32.)
N o n e x t r a c t i o n approaches to treatment have increased interest in appliances and techniques that help create additional space within the dental arch. The lip bumper appliance, which is lip activated, has regained popularity in recent years for the treatment of crowding in the mandibular arch. ~-3 Lip bumper treatment has been used for molar anchorage, 4~ prevention of poor lip habits,79 and creation of increased space for the mandibular arch. ~3,9t~ The appliance has a stainless steel wire, usually 0.045 inch thick, that spans the facial surface of the mandibular arch without contacting the teeth and is inserted into tubes attached to the mandibular molars.L4"6'8"~' Anteriorly, the wire is sometimes covered by plastic tubing or a shield made of acrylic or plastic that holds the lower lip away from the mandibular incisors. Forces from the mentalis muscle are translated to the mandibular molars, enabling them to move to an upright and distal position. At the same time, the tongue may cause the mandibular incisors to tilt outward and the canines and premolars to move buccally. Thus mandibular arch length and width may increase, helping to alleviate crowding mesial to the mandibular molars. 1"4,9a3
From the Department of Orthodontics, University of Oklahoma. *Graduate Student. **Professor and Chairman, ***Associate Professor. 811119524
Previous studies on the effects of lip bumper treatment have largely focused on the movement of molars posteriorly and incisors anteriorly.4,9.~2.~3However, Cetlin and Ten Hoeve t and Ten Hoeve2 have stated that arch width increase is primarily responsible for increase in arch circumference. The purpose of our study was to evaluate the specific changes in mandibular arch length and width that affect increases in arch circumference associated with the use of the lip-bumper appliance.
MATERIALS AND METHODS Thirty-two patients, 19 female and 13 male, between the ages of 9 and 17 years, with a mean age of 12 years, were treated for mandibular crowding with a lip bumper inserted into tubes placed on mandibular permanent first molars. The distribution of the sample at the start of treatment--by sex, age, and presence or absence of mandibular permanent second molars and deciduous second molars--is given in Table I. The patients were consecutively treated persons from the practices of four orthodontists and the graduate orthodontic Clinic. Twelve patients were treated by orthodontist A, five by orthodontist B, six each by orthodontists C and D, and three in the graduate clinic. Lip bumpers were the only appliances used in the mandibular arch. They were worn full-time for a treatment time ranging from 6 to 33 months, with an average of I I months. A variety of maxillary appliances was 527
528
Osborn, Nanda, and Currier
Am. J. Orthod.Dentofac.Orthop. June 1991
Table i. Distribution of sample according to sex, age, and presence of mandibular permanent second molars and deciduous second molars at start of treatment
Age(Yr± too)
I
Malesttbiects
9---6 10±6 11---6 12±6 13±6 14±6 15---6 16±6 17±6 Total
I
Fema/esubjects
2 1 3 2 3 1 l 0 0 13
I
1 4 5 3 2 2 1 0 1 19
-7
I
0 1 1 1 3 3 2 0 1 12
Table II. Changes for mandibular arch after lip bumper treatment
Variable
No.
Mean change (mnO
SD
Arch perimeter Arch length 3 to 3 width 4 to 4 width 5 to 5 width e to e to 5 to 5 width 6 to 6 width
32 32 20 19 10 19 32
4.07* I. 17" 1.99" 2.50* 2.43* 3.39* 1.921"
2.03 1.25 1.31 1.74 1.42 1.94 2.74
I
Minimum Ohm) 0.70 - 0.84 0.21 0.40 0.21 0.54 -2.21
e 3 4 9 3 0 0 0 0 0 19
[
Mct~hnum (ram) 8.84 4.49 6.58 8.09 5.31 7.29 8.14
*Significant at p < 0.0001; lslgnificant at p < 0.001.
also used during the lip bumper treatment. Fifteen patients had maxillary Kloehn headgear, while 14 Patients had either a bonded or a banded edgewise appliance with an arch wire. Three of the patients wore high-pull facebow headgear, one wore a quadhelix device, and another wore a rapid palatal expansion device (Hyrax).
Clinical procedure A mandibular alginate impression and a cephalometric radiograph were taken immediately before the initiation of treatment. All lip bumpers were made o f 0.45-inch wire with a plastic, shrink-fit tubing, except for three, which had a wide plastic anterior shield. Loops were placed in the wire just mesial to the molar to serve as stops against the tubes. The wire was adjusted to be 3 to 5 mm away from the premolar and caanine teeth at the coronal level to hold the cheek away from the teeth. The anterior bow of the lip bumper was adjusted vertically at the level of the gingival margin and was held 1.5 to 2 mm away from the mz~ndibular incisor teeth. On completion of treatment, the' mandibular appliance was removed, and another alginate impression and a cephalometric radiograph were taken. The dental casts were poured in stone plaster, and
the landmarks were marked with a sharp lead pencil. The measurements on the dental casts were made directly with electronic-dial calipers accurate to 0.01 mm. The arch-circumference measurement was an aggregate of the following four measurements, as'described by Fisk 14 and Bjerregaardlt: mesial aspect of the right permanent first molar to distal aspect of the right permanent lateral incisor; distal aspect of the right permanent lateral incisor to midline; midline to distal aspect of left permanent lateral incisor and distal aspect of left permanent lateral incisor to mesial aspect of the left permanent first molar. Arch length was measured according to Moorrees ~5and Adkins t6 from a line drawn perpendicular.from the mesial contact points of the incisors to a line connecting the mesial contact points of the mandibular permanent first molars. No obvious asymmetry in the molar position was noticeable. Widths of molars and premolars were measured from a point marked on the central groove where it was bisected by the mesiodistal width of the tooth. Intercanine width was measured from cusp tips. Only 10 patients had all 14 mandibular permanent teeth. Nineteen patients had transitional dentitions with deciduous second molars present at the start of treatment. In the remaining three patients the second pre-
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Mandibular arch perimeter chtmges with lip bttmper treatment
529
1/ ;/7; Syrnp
stance
~
Fig. 1. Molar angle and molar distance from the lateral cephalometric radiographs.
molars were in varying stages of eruption; hence their width changes in the second premolar area could not be measured. Tile width changes for the first premolar and the permanent canine were not measured in cases where either one or both canines or premolars had not erupted at the time of initial records or at the end of the lip bumper treatment. The measurements from the lateral cephalometric tracings were (1) the incisor mandibular plane angle, or IMPA; (2) the angle of the lower incisor axis to the NB plane; and (3) the linear distance from the lower incisor to the NB plane. Additional measurements included (4) the anterior-superior angle formed by a line passing through the mesial cusp tip and the mesial root tip of the mandibular first molar and intersecting with the mandibular plane and (5) the molar distance, which was measured on the mandibular plane between the two points of intersection, M and SP (Fig. 1). We located point M by drawing a perpendicular line from the most distal point on the distal surface of the first molar, and we located point SP by drawing a perpendicular line from the most posterior point on the mandibular symphysis, or point SymP. This latter point was found to be stable during the period of lip bumper treatment and could be easily identified, thus providing a skeletal reference for measurement of the changes in position of the mandibular molars. The analysis of the data included computation of means and standard deviations. Paired Student's t tests were performed to determine whether an increase in arch circumference was significant. A correlation test between all the variables was performed to examine the strength of significant relationships. To determine the most predictive variable for increase in arch circumference and arch length, we applied stepwise multiple linear regression analyses, with increase in circumference and increase in length as the dependent variables. Analysis-of-variance tests were done to determine
whether there were any significant differences between changes in arch circumference and mandibular incisor position among patients treated by different orthodontists. RESULTS
The means, standard deviations, and range of changes in dental cast measurements on the mandibular arch are given in Table II. The mean increases in arch circumference and in arch length were found to be 4.07 mm and 1.17 ram, respectively, and were significant at p < 0.0001. The width between the first molars increased an average of 1.92 mm: In the premolar region, the width measurement for the 10 patients with mandibular second premolars increased an average of 2.43 mm, while the 19 patients who had both mandibular deciduous second molars at the initiation of treatment and second premolars that had erupted by the close of lip bumper treatment showed an average increase in width of 3.39 mm. The difference between the mean changes in width at the second premolar region in groups of patients with deciduous molars or premolars at the initiation of treatment was not significant (p >0.05). There were 19 patients who had mandibular first premolars and 20 who had.permanent canines at the end of treatment. These measurements showed that the interpremolar and intercanine widths had increased 2.5 mm and 1.99 mm, respectively. The mean changes in measurements for cephalometric radiographs are shown in Table III. In 25 patients (78%), the mandibular incisors tipped anteriorly. The average increase in incisor mandibular plane angle, or IMPA, was 2.92 °. Among the remaining seven patients (22%), three showed no change, whereas the other four had decreases in the angle ranging from 0.5 ° to 1.5 ° . The mean increase in molar angle was 3.09 ° . Twenty-six patients (81%) had a varying amount of
5:30 Osborn, Nanda, and Currier
Am. J. Orthod. Dentofac. Orthop. June 1991
Table III. Changes from the cephalometric radiographs after lip bumper treatment
I IMPA LI to N B LI to N B M o l a r angle M o l a r distance A r c h length
,,eonc, o,, e
I
2 . 9 2 °* 3.400* 1.12 r a m * 3.09°t 0.36 mm$ 1.34 r a m *
SO
I
3. I 1 3.42 1.20 3.89 0.99 ! .89
Ma.riraum - 1.50 ° -3.00 ° - i.42 mm - 3.50" -2.13 mm - 1.37 m m
12.00 ° 9.00 ° 3.35 mm 13.50 ° 2.21 m m 4.89 mm
*Significant at p < 0 . 0 0 0 1 ; "['significant at p < 0 . 0 0 1 ; :l:significant at p < 0 . 0 5 .
increase in this angle, signifying distal tipping of the permanent mandibular first molar. Six patients (19%) indicated small mesial tipping. Student's t test was applied to all of the posttreatment differences for all the measurements from the dental casts and the cephalometric radiograph (Tables II and III). It was found that all of the changes recorded with lip bumper treatment were statistically significant. Stepwise multiple linear regression analysis of the independent variables--i.e., the changes in arch length measured from dental casts and cephalometric radiographs: IMPA, LI to NB (in mm), molar angle, and molar distance--indicated that arch-length measurement from dental casts was the best predictor of increase in arch circumference with an R 2 value of 0.62 (p < 0.001). similarly, IMPA was found to be the most predictive measurement for change in arch length, with an R 2 value of 0.78 (p < 0.0001). The different archwidth changes were found to be correlated with each other, and therefore none of them stood out with higher R 2 values in the regression analysis for prediction of arch circumference. Since five orthodontists were participating in this study, there was a possibility of slight differences in the fabrication and application of the lip bumper appliances. Analysis of variance tests revealed no significant differences (p = 0.36) with respect to increases in arch circumference among patients being treated by different orthodontists. However, a significant difference was noted for changes of IMPA in the patients being treated by one orthodontist (p < 0.05), compared to the average IMPA changes for the other groups. When the sample was grouped by patients with second molars erupted before the initiation of treatment and those without, it was found that the changes in arch circumference, arch length, and the various arch widths were not significantly different between the two groups. No significant correlations were discovered with respect to changes in arch circumference, arch length, and length of treatment time, age, or sex of the patient.
DISCUSSION
The mandibular arch circumference increased in all patients during the course of treatment. This observation agrees with the conclusions from all the previous studies that indicate that lip bumper treatment yields increased arch circumference. However, most of the previous studies did not clarify whether this increase in arch circumference was attributable to increase in arch length or width. Cetlin and Ten Hoeve t have indicated increase in arch width as the primary cause of increased arch circumference. They reported an average increase of 5.5 mm at the permanent first molars. The average expansion at the molars in our study was 1.92 mm, substantially less than that reported by Cetlin and Ten Hoeve. The premolar width increases observed in our study were also less than those given by Cetlin and Ten Hoeve. We found 2.50 mm at the first premolar and 2.43 mm at the second premolar regions, while Cetlin and Ten Hoeve found 4 mm at the first premolars. However, the mean change in intercanine width was closer for the two studies (1.99 mm in our study, versus 2.5 mm in the Cetlin and Ten Hoeve study). The larger increases in arch width reported by Cetlin and Ten Hoeve t may have resulted from a force applied by the lip bumpers at the molar tubes, which caused expansion of the intermolar width and may also have indirectly contributed to the enhanced increases in the premolar widths. In the present study, an effort was made to maintain passive insertion of the lip bumper appliance in the molar tubes. However, there were a few cases in which appreciable expansion at the first molars was noted. In addition, treatment time for patients in the Cetlin and Ten Hoeve was longer (12 to 18 months) than the average treatment time for all patients in our study (11 months). A closer comparison with the Cetlin and Ten Hoeve ~ study is not possible, because they did not furnish details of their investigations. Our study indicated that passive changes from pressure of the tongue increased arch width in the premolar and canine regions and accounted for most of the gain in arch circumference.
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Mandibular arch perimeter changes with lip bumper treatment
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T a b l e IV. R e s u l t s o f lip b u m p e r t r e a t m e n t o n m a n d i b u l a r arch p r e s e n t e d in d e s c e n d i n g o r d e r o f c h a n g e in arch circumference
Patient 29 2 22 17 1 15 5 6 12 11
20 3 10 16 30 19 18 21 32 8 26 4 14 25 9 31 7 23 27 13 28 24
Starting age (yr-mo) 11-6 13-9 9-9 9-10 13-1 1 I-7 15-2 13-2 11-1 9-5 11-2 12-1 12-7' 9-10 11-0 11-7 10-9 9-11 12-8 14-0 12-6 17-1 11-2 10-9 14-10 18-1 14-3 10-8 12-3 ! 1-10 13-2 10-2
Duration of treatment Ono)
Change in arch circumference (ram)
10.0 8.5 11.0 14.0 6.0 19.5 6.5 6.0 12.5 16.0 7.0 8.5 16.0 33.0 7.0 14.0 12.5 12.0 6.0 9.0 8.5 6.0 8.5 9.0 8.5 7.0 9.0 12.0 9.5 11.5 14.5 10.0
8.84 8.68 7.82 7.07 6.56 6.17 5.86 5.79 4.51 4.94 4.48 4.25 4.09 3.89 3.89 3.61 3.50 3.28 3.24 3.19 3.18 3.11 2.66 2.61 2.51 2.48 2.39 2.35 1.91 1.70 i.69 0.70
Change hz arch lbngth
Changes in arch widths (ram)
!. 15 4.49 3.75 0.89 3.09 2.51 3.03 2.36 0.95 0.45 0.09 -0.14 2.15 1.55 1.28 0.13 1.51 0.00 1.85 1.13 1.05 1.42 - 0.41 1.50 0.32 1.02 0.76 - 0.64 0.03 1.38 - 0.25
6.58 1.49 --1.18 -1.20 1.15 2.96 3.72 -3.22 2.74 ----2.98 2.53 1.08 2.03 1.90 I. 12 -1.81 . 0.21 -!.33 -1.27
- 0.84
1.09
.
8.09 0.40 --1.56 -i .88 1.75 ---3.71 2.92 -4.58 2.03 ---1.49 -1.45 2.98 2.22 1.72 . 1.0 -3.41 0.70 1.45 2.70
3.89* 0.21 3.41" 7.29* 2.29 5.13" 2.82 2.48 4.99* 6.67* 3.53* 5.31 3.10 3.31" -2.87* 5.21" 3.50* -1.74 2.60* I. 19 2.99* 2.00* 1.39 2.49" 1.50* 1.23" 0.54* 0.62*
- 0.47 - 0.71 3.46 7.13 2.91 5.44 0.20 0.78 4.93 6.58 2.23 4.28 0.46 3.51 8.14 0.05 3.03 2.27 3.49 0.87 - 0.07 2.87 5.72 - 0.95 0.34 0.24 - 1.31 0.25 0.36 0.30 - 2.21
2.70"
- 2.00
.
* Initial measurements were from e to e, but later changes were 5 to 5.
S a g i t t a l c h a n g e s in a r c h l e n g t h w e r e s m a l l e r t h a n in the t r a n s v e r s e d i m e n s i o n s , w i t h a m e a n c h a n g e o f 1.17 m m . M o s t o f this c h a n g e c o u l d b e a t t r i b u t e d to a n t e r i o r t i p p i n g o f the m a n d i b u l a r incisors. M e a n I M P A i n c r e a s e d 2 . 9 2 °. T h i s c h a n g e in t h e i n c i s o r position c o r r o b o r a t e s t h e findings o f several p r e v i o u s studies .4. t~., 3
Distal t i p p i n g o f t h e m o l a r s was n o t f o u n d to b e a p p r e c i a b l e . T h e m e a n a m o u n t o f c h a n g e in t h e m o l a r a n g l e w a s 3 . 0 9 ° . T h e l i n e a r d i s t a n c e f r o m the distal s u r f a c e o f the m o l a r ( M ) to the s y m p h y s i s p o s t e r i o r ( S P ) , m e a s u r e d o n the m a n d i b u l a r p l a n e , i n c r e a s e d b y a m e a n o f 0 . 3 6 m m , w h i c h is less t h a n e a r l i e r findings. 4'9'tz'z3 In t h e c u r r e n t study, r e a s o n a b l e c a r e w a s
T h e m o v e m e n t o f the i n c i s o r s d e p e n d s o n the pos i t i o n a n d t y p e o f l a b i a l b o w used. T h e labial b o w u s e d w i t h 2 9 p a t i e n t s o f this s t u d y w a s m a d e f r o m 0 . 0 4 5 i n c h w i r e , w i t h t u b i n g , a n d w a s a d j u s t e d at the level o f the g i n g i v a l m a r g i n o f the teeth. T h e lip b u m p e r u s e d o n the r e m a i n i n g t h r e e p a t i e n t s in this study, as well as b y B j e r r e g a a r d et a l . , " w a s f a b r i c a t e d w i t h a 6 m m p l a s t i c shield that c o m p l e t e l y b l o c k e d the i n c i s o r s ; this b u m p t e r p r o d u c e d a m o r e p r o n o u n c e d t i p p i n g o f the incisors.
t a k e n to m e a s u r e the c h a n g e s in m o l a r p o s i t i o n ; this p r e c a u t i o n m a y e x p l a i n the d i f f e r e n c e s in o u r o b s e r vations from those of previous investigators. It is i n t e r e s t i n g to n o t e that n o p o s i t i v e c o r r e l a t i o n w a s f o u n d b e t w e e n the m e a n c h a n g e s in a r c h c i r c u m ference or arch length and length of treatment. The p l a u s i b l e e x p l a n a t i o n is the fact that o n l y m i n o r c h a n g e s w e r e r e c o r d e d in d i s t a l i z a t i o n o f m o l a r s a n d that t h e c h a n g e s in a r c h c i r c u m f e r e n c e w e r e m a i n l y a t t r i b u t a b l e to arch w i d t h a n d a n t e r i o r t i p p i n g o f the incisors. T h e s e
532
Osborn, Nanda, attd C u r r i e r
changes m a y be produced optimally in a treatment time of about 1 year. The variability of changes in arch width and arch length was so large that no reliable equation to predict the increases in arch circumference could be derived. Table IV illustrates the increases in arch circumference and the changes in arch length and width for all the persons in the study. Patients 3, 11, 19, 20, and 21 all showed increases in arch circumference o f greater than 3 m m , with less than 0.5 mm increases in arch length. Except for Patients 19 and 20, whose canines were unerupted, each patient had an increase o f at least 3 m m in intercanine width. Patient 29 had. an 8.8 m m arch-circumference increase, with only a 1.2 m m increase in arch length; this patient also had the largest increase in arch width. In five cases (Patients 3, 14, 23, 24, and 28) archlength m~asurements decreased. This change would have caused a decrease in arch circumference except for the fact that the patients had some increases in intercanine and interpremolar arch width to allow for increases in arch circumference. However, these patients had relatively small increases in arch circumference. Only four patients (1, 2, 5, and 22) had increases in arch length greater than 3 mm. They also had the largest increases in arch circumference. It is likely that individual variations in arch form changed the effect o f increases in arch widths at the different teeth on arch circumference. CONCLUSIONS
Evaluation o f results from clinical studies is difficult at best. A number of factors m a y be involved in terms o f selection of the sample, fabrication and application of the appliance, length of treatment, number of participating clinicians, patient's age and response, and methods used in appraisal o f the results. This study includes many o f the variables but has attempted to document changes in both sagittal and transverse dimensions. It confirms that the lip bumper appliance may be used for gaining space in the mandibular dental arches. Appropriate adjustment of the appliance in the incisor region is needed when anterior movement o f
Am. J. Orthod. Dentofac. Orthop. June 1991
the incisors is not desired. Posterior movement o f the mandibular molars was found to be minimal. Therefore the anticipated changes in arch perimeter resulted from changes in arch width and anterior movement of the incisors. BIBLIOGRAPHY 1. Cetlin NM, Ten Hoeve A. Nonextraction treatment. J Clin Orthod 1983;17:396-413. 2. Ten Hoeve A. Palatal bar and lip bumper in nonextraction treatment. J Clin Orthod 1985;19:272-91. 3. Ghafari J. A lip activated appliance in early orthodontic treatment. J Am Dent Assoc 1985;1 ! 1:771-4. 4. Bergersen EO. A cephalometric study of the clinical use of the mandibular labial bumper. AM J ORTtIOD1972;61:578-602. 5. Bedell WR. The use of tissue-bearing anchorage alone and in conjunction with various techniques in treatment. AM J OBSTET GYNECOL1954;40:404-20. 6. Renfroe EW. The factor of stabilization in anchorage. AM J ORTHOD 1956;42:883-97. 7. Graber TM, Neumann B. Removable orthodontic appliances. 2nd ed. Philadelphia: WB Saunders,. 1984:80-4. 8. Denholtz M. A method of harnessing lip pressure to move teeth. J Am Soc Study Orihod 1963;1:16-35. 9. Subtelny JD, Sakuda M. Muscle function, oral malformation, and growth changes. AM J OR'roOD 1966;52:495-517. 10. Sather AH, Mayfield SB, Nelson. DH. Effects of muscular anchorage appliances on deficient mandibular arch length. AM J ORTtIOD 1971;60:68-78. I!. Bjerregaard J, Bundgaard ANt, Nielsen B. The effect of the mandibular lip bumper and maxillary bite plate on tooth movement, occlusion and space conditions in the lower dental arch. Eur J Orthod 1980;2:257-65. 12. Sakuda M, lshizawa M. Study of the lip bumper. I Dent Res 1970;49:677. 13. Anarzadeh F, Adenwalla ST. A cephalometric analysis of the clinical application of lip bumper. J Dent Res 1987;66:252. 14. Fisk RO. Normal mandibular arch changes between ages 9-16. J Can Dent Assoc 1966;32:652-658. 15. Moorrees CFA. The dentition of the growing child. Cambridge: Harvard University Press, 1959:87-8. 16. Adkins MA, Nanda RS, Currier GF. Arch perimeter changes on rapid palatal expansion. Ar~lJ ORTIIODDENTOFACORTHOP1990; 97:194-9. Reprint requests to:
Dr. William S. Osbom University of Oklahoma Department of Orthodontics P. O. Box 26901" 1001 Stanton L. Young Blvd. Oklahoma City, OK 73190
