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Changes concurrent with orthodontic treatment when maxillary expansion is a primary goal
Changes concurrent with orthodontic treatment when maxillary expansion is a primary goal Paul T. Ladner, DDS, MS," and Zane F. Muhl, DDS, PhD b
Galesburg and Chicago, Ill. A retrospective study of dental and maxillary skeletal changes occurring during a period of orthodontic treatment was made from pretreatment and posttreatment dental casts. Sixty maxillary expansion cases were examined. Thirty cases had maxillary expansion accomplished with a fixed rapid palatal expander and 30 were expanded with a quadhelix appliance. All cases were finished with full fixed edgewise appliances. Multiple linear regression analyses were completed for both groups with upper molar width change as the criterion and age, tipping of the upper molars, palatal width change and maxillary tipping as the predictors. All predictors were included in the analysis for the quadhelix group with a significant R2 value of 0.55. For the rapid expansion group, a significant R2 value of 0.33 was achieved with the inclusion of palatal width change and age only. The other variables did not meet the level of significance for entry into the model. Although both groups demonstrated similar amounts of maxillary dental expansion, the rapid expansion group demonstrated greater average skeletal expansion. In addition, there was a significant relationship between skeletal and dental expansion for the rapid expansion group, but not the quadhelix group. Palatal depth increased more on average in the rapid expansion group suggesting that there was greater dental eruption in that group. Expansion across the mandibular molars was greater on average in the quadhelix group. There was no difference in the degree of upper molar rotation or final upper and lower arch forms between the two groups. (AM J ORTHOD DENTOFACORTHOP 1995;1 08:1 84-93.)
T h e rapid palatal expander as described by Haas I is a rigid appliance designed for maximum dental anchorage that uses a jackscrew to produce expansion in 10 to 14 days (Fig. 1). The basis for the rapid expansion procedure is to produce immediate midpalatal suture separation by disruption of the sutural connective tissue. Haas I believes this will maximize the orthopedic effects. Forces produced by this appliance have been reported in the range of 3 to 10 pounds. 2 The quadhelix has been introduced more recently.3 This lingual arch appliance is a modification of the " W " arch described by Coffin4 and has also been used to expand the maxillary dental arch (Fig. 1). It is less rigid and works more slowly than the rapid expander. It has been shown to develop force in the range of 221 to 1149 gm (0.5 to 2.5 pounds)? 8 The quadhelix has the ability to rotate molars and can be adjusted to expand the molars and anterior teeth differentially.9'!° This article is based on research submitted by Dr. Ladner in partial fulfillment of the requirements for the degree of Master of Science in Orthodontics, University of Illinois at Chicago. ~In private practice, Galesburg, Ill. bAssociate Professor, Department of Orthodontics, University of Illinois. Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$3.00 + 0 8/1/53683
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Fig. 1. Appliances studied. Rapid expander as described by HaasI includes jackscrew, buccal and lingual bars, and acrylic palate. Appliance is activated with key. Quadhelix is constructed from 0.036-inch diameter orthodontic wire with four helices in transpalatal section. Anterior arms are constructed from 0.025-inch diameter wire.
Both of these appliances can be used to expand the maxillary dental arch. In clinical practice they are often used as the initial appliance in a treatment plan that includes full fixed appliances, yet their influence on final treatment results is not clear. The transverse change seen across the upper dental arch can be the result of three factors: (1) separation of the midpalatal suture 1"11-26that allows the maxillae to separate; (2) tipping of the two
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maxillae and alveolar processes, 1'24'25'27and (3) tipping or bodily m o v e m e n t of the teeth with the alveolus and within the alveolar bone. 1'23-26'z8-32A g e m a y influence the a m o u n t of dental expansion achieved or m a y affect the relative contributions of t h e s e f a c t o r s . 5'9"1°'15'1s'2°'23 In addition, maxillary first m o l a r rotation, palatal d e p t h ~7'27 and final maxillary arch f o r m m a y be influenced by the use of one of these appliances. C h a n g e s in m a n d i b u l a r intermolar w i d t h 1'6"14'17'2°'33'34 and final m a n d i b u l a r arch f o r m m a y also be influenced. T h e p r e s e n t study seeks to d e t e r m i n e the relationship b e t w e e n u p p e r molar expansion and the three factors previously m e n t i o n e d in subjects t r e a t e d with either the rapid expander or the quadhelix appliance as part of full fixed appliance therapy.
MATERIALS AND METHODS The sample Pretreatment and posttreatment dental casts of 30 subjects treated with rapid palatal expansion and 30 subjects treated with a quadhelix appliance were used in this retrospective study. The treatment of both groups involved a phase of full fixed appliance therapy with a straight wire edgewise appliance with a Hilger's prescription. All subjects were treated without extraction or surgery and had been recently retained. The quadhelix subjects were chosen only if there were indications in the treatment plan or treatment record that maxillary expansion was a goal of treatment. The average ages for the rapid palatal expander and quadhelix groups were 11 years 8 months (SD = 2 years) and 11 years 11 months (SD = 2 years 1 month), respectively. There were 17 female and 13 male subjects in the rapid expansion group and 19 female and 11 male subjects in the quadhelix group. Twenty-three of the rapid expansion group and 10 of the quadhelix group had posterior crossbite involving at least one tooth in each arch. The other patients had varying degrees of buccal overjet. The active expansion for the rapid expansion subjects lasted an average of 23 days (SD = 10 days). The number of turns of the expansion screw per day has not been controlled in the group. At the end of active expansion, the appliance was stabilized with wire and worn as a fixed retainer for an average period of 77 days (SD = 33 days). An acrylic palatal appliance, as described by Haas 1 and Wertz 14was then worn by the patient through the duration of fixed appliance therapy. The quadhelix was worn an average 149 days (SD = 86 days). There was no record of the expansive force applied by the appliance. The clinician retained expansion with an inactive appliance much like the stabilized rapid expander. The mean total treatment time was 36 months
Fig, 2. Symmetrograph has recording plate perpendicular to sliding base with millimeter calibrations. Cast is held by three set screws attached to rotating platform in base. Tracings are drawn by pencil lead in pantograph arm that was guided by movement of stylus against cast.
(SD = 13 months) and 26 months (SD = 8 months) for the rapid palatal expander and quadhelix groups, respectively. Two distinct treatment phases were used in eight of the rapid expansion subjects, whereas only one quadhelix subject had two-phase treatment.
Descriptive variables Variables were measured that describe pretreatment and posttreatment characteristics, as well as changes occurring over the treatment period for the two groups.
Palatal width change Palatal width change, a measure of skeletal expansion, was assessed indirectly from dental casts. Coronal palatal contour tracings were obtained with the use of a symmetrograph 35 (Fig. 2) according to a description provided by Lebret? 6 The pretreatment and posttreatment palatal contour tracings were superimposed as described by Lebret 36 to attain a measurement of the transverse expansion across the midpalatal raphe (Fig. 3).
Tipping of the maxillary alveolus The tipping of the maxillary halves and their alveolus was measured on these same coronal palatal contour tracings (Fig. 4). A line was drawn tangent to the more vertical portion of one side of the posttreatment tracing. The pretreatment tracing was superimposed on that side of the posttreatment tracing and the same line was drawn on the pretreatment tracing. The pretreatment and post-
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x; E~'x2 A
B
C
Fig. 3. Superimpositions to measure palatal width change. Broken line: Pretreatment palatal contour. Solid line: Posttreatment palatal contour. Points X1 and )(2 indicate median palatal raphe for pretreatment and posttreatment tracings, respectively. Two tracings are (A) superimposed on median palatal raphes, (B) right side palatal contour and (C) left side palatal contour, Amount of expansion toward right (ER) and left (EL) are measured.
A
B
C
Fig. 4. Measurement of maxillary alveolar tipping. Broken line: Pretreatment contour tracing. Solid line: Posttreatment contour tracing. A, Tangent to palatal contour of posttreatment tracing was drawn, B, Pretreatment and posttreatment tracings were superimposed on palatal contours and tangent was drawn on pretreatment tracing. C, Tracings were superimposed on contralateral palatal contour and angle alpha was measured.
treatment tracings were then superimposed on the contralateral side of the tracing. The angle formed by the two lines was a measure of tipping of the maxillary alveolus.
Tipping of the upper molar teeth The change in buccoiingual angular orientation of the first molar teeth was measured with the use of a goniometer as described by Thorne. 28 Measurement of the tipping was made by superimposition of photographic negatives. A negative value indicated lingual tipping and a positive value buccal tipping (Fig. 5).
Rotation of the upper molar teeth Angular measurement of the upper first molar rotation was similar to that used for molar buccolingual angular relations (Fig. 6). Orthodontic wires were inserted into compound caps on the first molar teeth so
that they were parallel to the occlusal plane and crossed when observed from above. A photograph of the pretreatment cast with the caps in place was taken from above with the plane of the film and the occlusal plane parallel. The caps were removed from the pretreatment cast, placed on the posttreatment cast, and again photographed from above. The .amount of rotation was measured by superimposition of photographic negatives. A positive value indicated mesiobuccal rotation and a negative value mesiolingual rotation.
Palatal depth Palatal depth was measured with an instrument made of a piece of clear plastic with a length of rectangular orthodontic wire passing through it perpendicularly (Fig. 7). The wire passes through a tight fitting rectangular tube embedded in the plastic. A line across the plastic, which intersects the sliding wire, allows the wire
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Ladner and M u h l
./.
\
_
\e +
A
B
Fig. 5. Measurement of tipping of upper molar teeth. Goniometer wires were positioned so that they intersected when observed from heel of cast. A, Line was constructed perpendicular to right wire and angle (a) of pretreatment goniometer was measured. B, Angle (b) of posttreatment goniometer was also measured.
Fig. 6. Measurement of molar rotation. Goniometer wires were positioned so that they intersected when observed from occlusal. A, Line was constructed perpendicular to left wire and angle (c) of pretreatment goniometer was measured. B, Angle (d) of posttreatment goniometer was also measured.
to be positioned across the mesiolingual cusp tips of the first molar teeth. The plastic, which extends anteriorly beyond the incisors, was placed on the dental cast so that it contacted the most prominent cusps of the first molar teeth and the first contact mesial to the molars. The wire was extended to contact the median palatal raphe. The distance from the plastic to the end of the wire was measured with a Boley gauge.
Transverse dental measurements The pretreatment and posttreatment intermolar dimensions were measured between the mesiobuccal cusp tips of the upper and lower first molar teeth. Upper and lower posttreatment intercanine width was also measured between the incisal tips of these teeth. An index of buccal molar overjet was calculated as the ratio of upper to lower intermolar width. The ratios of upper intermolar to intercanine and lower intermolar to intercanine width were used as an index of upper and lower arch form. Fig. 7. Palatal depth gauge.
RESULTS All measurements were replicated twice for 10 sets of casts with 1 week between trials. Matched pair t tests were employed to test for significant differences between trials. The null hypothesis was that the mean difference between trials was equal to zero. No significant difference were found at p < 0.1, indicating that for this group the measurements were reproducible. Tables I and II show correlation matrices for the quadhelix and rapid expansion groups, respectively. All variables in these tables, other than age,
represent change occurring in the maxilla during treatment. Overall the correlations are low. Only 4 of 23 correlations calculated for the quadhelix group and 3 of 23 the correlations calculated for the rapid expansion group were found to be significantly different from zero at p < 0.05. To illustrate the relationship between dental expansion and the factors responsible for the expansion, a stepwise multiple regression analysis was performed for each group. U p p e r molar width change was used as the criterion and age, upper
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I. M a t r i x of P e a r s o n c o r r e l a t i o n coefficients for c h a n g e in t h e maxilla in t h e q u a d h e l i x s a m p l e ( N = 30)
Table
Age UMTP UMR PWC MXTP UMC PDC
-
Age
UMTP
UMR
1.00 0.32 0.32 0.35 0.05 0.40* 0.49*
1.00 0.17 - 0.36 0.07 0.31 - 0.38*
1.00 - 0.19 0.14 0.19 0.26
[
PWC
[
MXTP
UMC
1.00 0.16 -0.11
1.00 0.28
[
PDC
1.00
-0.19 0.34 0.37*
1.00
*Correlations significant at p < 0.05. UMTP, Tipping of the upper molar; UMR, rotation of the upper molar; PWC, palatal width change; MXTP, maxillary tipping; UMC, upper intermolar change; PDC, palatal depth change. Table II. M a t r i x o f P e a r s o n c o r r e l a t i o n coefficients for c h a n g e in t h e maxilla in t h e r a p i d e x p a n s i o n s a m p l e ( N = 30)
I Age UMTP UMR PWC MXTP UMC PDC
Age
UMTP
UMR
PWC
1.00 0.01 - 0.28 - 0.25 0.05 - 0.42* -0.61"
1.00 0.11 0.29 - 0.03 0.29 -0.15
1.00 0.00 - 0.26 0.30 0.11
-0.17 0.54* 0.09
MXTP
UMC
1.00 - 0.03 - 0.31
1.00 0.30
I
PDC
1.00
1.00
*Correlations significant at p < 0.05.
Table
Ill, S t e p w i s e m u l t i p l e r e g r e s s i o n for d e n t a l e x p a n s i o n in t h e q u a d h e l i x s a m p l e ( N = 30)
Step
I
1 2 3 4
Table
Variable entered
Partial R 2
Model R 2
Age Tipping of the upper molar Palatal width change Maxillary tipping
0.16 0.21 0.13 0.04
0.16 0.37 0.50 0.55
IV, S t e p w i s e m u l t i p l e r e g r e s s i o n for d e n t a l e x p a n s i o n in t h e r a p i d e x p a n s i o n s a m p l e ( N = 30)
Step 1 2
[
Variable entered
Partial R 2
Model R 2
Palatal width change Age
0.29 0.09
0.29 0.38
No other variables met the 0.15 level for significance.
m o l a r tip, p a l a t a l w i d t h c h a n g e a n d maxillary tip w e r e u s e d as p r e d i c t o r s . T a b l e I I I shows t h e results of t h e r e g r e s s i o n analysis for t h e q u a d h e l i x group. A g e was s e l e c t e d first, f o l l o w e d b y u p p e r m o l a r tip, p a l a t a l w i d t h c h a n g e a n d maxillary tip. T h e regression, c o n s i d e r ing all f o u r variables, e x p l a i n e d 55% of t h e vari-
ability in i n t e r m o l a r e x p a n s i o n for t h e q u a d h e l i x group. T h e r e g r e s s i o n was significant at p < 0.001. T a b l e I V shows t h e results of t h e r e g r e s s i o n analysis for t h e r a p i d e x p a n s i o n group. P a l a t a l w i d t h c h a n g e was s e l e c t e d first a n d was followed by age. T h e o t h e r v a r i a b l e s d i d n o t m e e t t h e 0.15 significance level for e n t r y into t h e m o d e l . T h e
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Table V. T tests for pretreatment means in the quadhelix and rapid expansion samples (?4 = 30) Quadhelix
RPE
Variab&
Mean
SD
Mean
SD
Age (months) Upper intermolar width (ram) Lower intermolar width (mm) Palatal depth (mm) Ratio of upper/lower intermolar width
143 48.0 43.0 18.8 1.12"
25 2.6 3.0 2.0 0.07
141 46.6 44.0 18.9 1.06"
24 3.1 3.2 1.8 0.07
0.7301 0.0566 0.2184 0.9098 0.0014
*Sample means are statistically different for these variables at p < 0.01.
Table VI. Matched pair t test for maxillary change during treatment for the quadhelix sample (N = 30) Variable
Mean change
Upper intermolar change (mm) Palatal depth change (ram) Tipping of the upper molar (degrees) Rotation of the upper molar (degrees) Palatal width change (ram) Maxillary tipping (degrees)
5.4* 1.0" 1.3
SD
Maximum
Minimum
p
2.0 1.2 8.2
9.8 4.1 18.2
0.5 -1.3 - 15.5
0.0001 0.0001 0.3934
23.8*
12.7
50.3
0.2
0.0001
1.3" 3.7*
0.9 4.3
4.3 20.1
0.0 0.5
0.0001 0.0001
*Change during treatment significant at p < 0.007.
Table VII. Matched pair t test for maxillary change during treatment for the rapid expansion sample (N = 30) Variable
Mean change
SD
Maximum
Minimum
p
Upper intermolar change (mm) Palatal depth change (ram) Tipping of the upper molar (degrees) Rotation of the upper molar (degrees) Palatal width change (mm) Maxillary tipping (degrees)
6.0* 2.3* - 4.6
2.6 1.6 11.3
11.4 5.4 16.2
0.7 -0.2 - 38.2
0.0001 0.0001 0.0349
16.5"
15.4
48.8
- 9.3
0.0001
2.6* 1.0
1.4 5.9
5.1 12.4
0.4 - 13.5
0.0001 0.3663
*Change during treatment significant at p < 0.007.
regression explained 38% of the variability in intermolar expansion for the rapid expansion group. The regression was significant at p < 0.005. The hypothesis that the two groups were alike before treatment was tested (Table V). The statistical level for significance was set at p < 0.05. This was adjusted for multiple t tests with the Bonferroni method resulting in a value of p < 0.01 for significance. Only the ratio of upper molar width to lower molar width was statistically different. Changes occurring in each group during treatment were examined with t tests (Tables VI and
VII). Adjustment for multiple t tests with the Bonferroni method resulted in a value ofp < 0.007 for significance. Most of the variables showed significant change. Changes occurring during treatment were compared (Table VIII). Adjustment for multiple t tests with the Bonferroni method resulted in a value of p < 0.006 for significance. The palate expansion group showed more change in palatal depth and width than the quadhelix group. Both groups showed significant increases in lower molar width (p < 0.05). The quadhelix group
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Table VIII. T test for comparison of maxillary changes during treatment for the quadhelix and rapid
expansion samples (N = 30) Quadhelix Variable
Upper intermolar change (mm) Palatal depth change (mm) Tipping of the upper molar (degrees) Rotation of the upper molar (degrees) Palatal width change (mm) Maxillary tip (degrees) Upper intercanine after treatment/Upper molar after treatment Palatal width change/Upper intermolar change
RPE
Mean
SD
Mean
SD
P
5.4 1.0" 1.3 23.8 1.3" 3.7 0.66
2.0 1.2 8.2 12.7 0.9 4.3 0.03
6.0 2.3* -4.5 16.5 2.6* 1.0 0.65
2.6 1.6 11.3 15.4 1.4 5.9 0.05
0.2612 0.0012 0.0254 0.0503 0.0001 0.0491 0.3406
0.32
0.49
0.46
0.24
0.1579
*Sample means are statistically different at p < 0.006.
had an average increase of 2.5 mm (SD = 2.3 mm) and the rapid expansion group 1.0 mm (SD = 2.0 ram) in this dimension. Lower molar width change was significantly greater (p < 0.05) for the quadhelix group than for the rapid expansion group. Clinically, the quadhelix was worn for an average total time of 149 days (SD = 86 days). This was significantly longer (p < 0.05) than total appliance wear for the rapid expander which was 100 days (SD = 35 days). The total treatment time was 26 months (SD = 8 months) for the quadhelix group and 36 months (SD = 13 months) for the rapid expansion group. These were found to be significantly different (p < 0.05). DISCUSSION Achievement of maxillary dental expansion
Although both regression models for upper molar expansion were significant, the predictors entered into the stepwise multiple regression analysis left a great deal of unexplained variability in both. The predictors explained more of the variability in the quadhelix group than in the rapid expansion group. Age was chosen first for the quadhelix regression, whereas it was chosen second, after skeletal expansion, for the rapid expansion regression. The indices of skeletal and dental tipping were not selected for the rapid expansion model, but were chosen for the quadhelix model. Upper molar width change had a significant negative correlation with age, but none of the three factors proposed to be responsible for the dental expansion demonstrated a significant relationship with age. There was no significant difference in upper
intermolar expansion between the two groups, but there was greater skeletal expansion in the rapid expansion group. In addition, there was a positive correlation between upper intermolar expansion and skeletal expansion for the rapid expansion group, but not for the quadhelix group. The average ratio of skeletal expansion to upper intermolar expansion in the present study was 0.32 and 0.46 for the quadhelix and rapid expansion groups, respectively. These were not statistically different. This ratio has been reported to be in the range of 0.17 to 0.53 for slow expansion9'22 and 0.38 to 0.62 for rapid expansion. 15'16"2aThe ratios in the present study fall within the range reported in the literature. Timms 16 reported the correlation between skeletal and dental expansion and between skeletal expansion and age for a rapid expansion sample (r = 0.55 and r = -0.33, respectively). The correlations found for the rapid expansion sample in the present study between these variables were surprisingly similar. Thorne 28 reported buccal tipping of the molar teeth in 75% of his rapid expansion sample measured immediately after expansion. Herold 29showed only minimal buccal tipping of the molars after rapid expansion with greater buccal tipping in a sample treated with a quadhelix. Hicks24reported 1.5 to 24° of upper molar tipping in a slow expansion sample. Even though tipping of the upper molars was able to account for some of the variability in upper molar expansion for the quadhelix group, tipping of the upper molars was not significant in either group and there was no difference in upper molar tipping between the two groups.
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American Journal of Orthodontics and Dentofacial Orthopedics Volume 108, No. 2 H i c k s 24 reported - 2° to 8° of skeletal tipping in a slow expansion study. Cotton 25 reported 4° to 7° of maxillary tipping with 2° to 17° of buccal molar tipping in a slow expansion study of monkeys. The present study showed significant buccal tipping of the maxillae in the quadhelix group but not in the rapid expansion group.
Palatal depth
The average increase in palatal depth was greater for the rapid expansion group than for the quadhelix group. Palatal depth change is due to an increase in dentoalveolar height? 9 The rapid expansion group therefore demonstrated greater dental eruption. A significant negative correlation existed between palatal depth change and age for both groups, but average age was not different for the two groups. Therefore age alone Could not have been responsible for the difference in palatal depth change. Longer treatment times would allow greater expression of the growth process. Because the rapid expansion group was in treatment significantly longer than the quadhelix group and palatal depth change was correlated with treatment time for both groups (r = 0.42 and r = 0.67 for the quadhelix and rapid expansion groups, respectively), it would appear that the longer treatment time could have allowed greater alveolar growth in the rapid expansion group. The increase in palatal depth was greater than would be expected from growth alone. Lowering of the palatal shelves of the maxilla on expansion has been suggested to o c c u r I and later was demonstrated in monkeys.27 Palatal shelf lowering would decrease the depth of the palate. A decrease in palatal depth was not demonstrated in the present groups. If lowering of the palatal shelves did occur, its effect has been more than offset by extrusion of the dentition because of orthodontic treatment and growth. Mandibular molar width
The lower intermolar expansion was greater for the quadhelix group and was correlated with the upper intermolar width change for the quadhelix group, but not the rapid expansion group. There was also a significant correlation between lower molar width change and the initial transverse discrepancy for both groups (r --- 0.44 and r = 0.36 for the quadhelix and rapid expansion groups, respectively). It appears that the difference in lower intermolar expansion may be due to the fact that
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there was less initial transverse discrepancy in the quadhelix group than in the rapid expansion group. For example, a patient presents with no posterior crossbite yet the clinician decides that it would be desirable to expand the upper arch. If the lower arch were not expanded a corresponding amount, the buccal segments would be treated into buccal crossbite. However, if a patient presents with a posterior crossbite and the clinician decides to treat with expansion of the upper arch, a corresponding amount of lower arch expansion would perpetuate the crossbite. In the present study the quadhelix group reflects the first of these possibilities and the rapid expansion group reflects the other. The present results cannot attribute the difference in lower intermolar width change to the use of one appliance over the other. The lower arch expansion is probably dependant on the amount of maxillary expansion and the initial transverse discrepancy regardless of the appliances used. Davis and Kronman 17 reported greater lower molar width change for a rapid expansion sample when a lower arch wire was used than when one was not. Evaluation of the other literature on rapid expansion reveals that the increase in lower molar width tends to be greater when a lower arch wire w a s u s e d . 1°'2s'33"36 Similar information is not available for a slow expansion sample. The lower molar width change for the rapid expansion group in the present study agrees very closely with that reported by Davis and Kronman 17 for the sample in which a lower arch wire was used. Gryson33 studied rapid expansion in a crossbite sample and found no correlation between upper and lower intermolar width change. This was true for the present rapid expansion group as well. Molar rotation
The quadhelix has the ability to rotate molars and the rapid expander has no such capability, yet there was no average difference in molar rotation for the two groups. The fixed appliance therapy that followed the expansion was likely responsible for molar rotation in the rapid expansion group. Arch form
The quadhelix appliance can expand differentially anteroposteriorly, whereas the rapid expander cannot. The final upper and lower arch forms were not different for the two groups. Presumably the fixed appliance therapy after expansion was responsible for standard~ing the arch form.
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CONCLUSIONS
1. The three factors proposed to account for the variability in upper intermolar width change explained a greater amount of the variability in the quadhelix group than the rapid expansion group. However, the factors left a great deal of variability unexplained in both groups. 2. Age was correlated only with maxillary intermolar expansion and not with any of the three factors proposed to be responsible for the dental expansion. 3. Although both appliances achieved similar amounts of maxillary dental expansion, the rapid expander produced greater skeletal expansion. In addition, there was a significant relationship between skeletal and dental expansion in the rapid expansion group, but not in the quadhelix group. 4. Both the quadhelix and rapid expansion groups demonstrated significant increases in lower intermolar width. The expansion was greater in the quadhelix group. The difference is most likely due to the difference in initial transverse discrepancy between the groups and not the appliances themselves. 5. Palatal depth increased more in the rapid expansion group suggesting greater dental eruption in the rapid expansion group. 6. Although the rapid expander does not have the ability to rotate molars that the quadhelix has, there was no difference in the degree of molar rotation at the end of full edgewise appliance therapy. 7. Although the rapid expander cannot expand the canines and molars differentially as the quadhelix can, there was no difference in the final upper or lower arch forms at the end of full edgewise appliance therapy. REFERENCES 1. Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening the midpalatal suture. Angle Orthod 1961;31:200-17. 2. Isaacson RJ, Wood JL, Ingram AH. Forces produced by rapid maxillary expansion. I and II. Angle Orthod 1964;34: 256-70. 3. Ricketts RM. Growth prediction: part 2. J Clin Orthod 1975;9:340-62. 4. Coffin WH. A generalized treatment of irregularities. Trans Int Cong Med London 1881;3:542-7. 5. Chaconas SJ, Caputo AA. Observation of orthopedic force distribution utilizing maxillary orthodontic appliances. J Dent Res 1975;54:45.
American Journal of Orthodontics and Dentofacial Orthopedics August 1995
6. Hermanson H, Kurol J, Ronnerman A. Treatment of unilateral posterior crossbite with quad-helix and removable plates. A retrospective study. Eur J Orthod 1985;7:97-102. 7. Urbaniak JA, Brantley WA, Prnhs R J, Zussman RL, Post AC. Effects of appliance size, arch wire diameter and alloy composition on the in vitro force delivery of the quad-helix appliance. AM J ORTHOD DENTOFAC ORTNOP 1988;94: 311-6. 8. Ranta R. Treatment of unilateral posterior crossbite: comparison of quad-helix and removable plate. J Dent Child 1988;Mar-Apr:102-4. 9. Frank SW, Engle GA. The effects of maxillary quad-helix appliance expansion on cephalometric measurements in growing orthodontic patients. AM J ORTHOD 1982;81:37889. 10. Chaconas SJ, de Alba y Levy JA. Orthopedic and orthodontic applications of the quad-helix appliance. AM J ORTHOD 1977;72:422-8. 11. Debbane EF. A cephalometric and histologic study of the effect of orthodontic expansion of the midpalatal suture of the cat. AM J ORTHOD 1958;44:187-218. 12. Haas AJ. The treatment of maxillary deficiency by opening the midpalatal suture. Angle Orthod 1965;35:200-17. 13. Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. AM J ORTHOD 1970;57:219-55. 14. Wertz RA. Skeletal and dental changes accompanying rapid midpalatal suture opening. AN J ORTHOD 1970;58:41-66. 15. Krebs A. Midpalatal suture expansion studies by the implant method studied over a seven year period. Eur J Orthod Soc Rep Congr 1964;40:131-42. 16. Timms RJ. A study of Basal movement with rapid maxillary expansion. AM J ORTHOD 1980;77:500-7. 17. Davis WM, Kronman JH. Anatomical changes induced by splitting of the midpalatal suture. Angle Orthod 1969;39: 126-32. 18. Gerlach HG. The apical base after rapid spreading of the maxillary bones. Eur Orthod Soc Rep 1956;32:266-78. 19. Harberson VA, Myers DR. Midpalatal suture opening during functional posterior cross-bite correction. AM J ORTHOD 1978;74:310-3. 20. Bell RA, LeCompte EJ. The effects of maxillary expansion using a quad-helix appliance during the deciduous and mixed dentitions. AM J ORTHOD 1981;79:152-61. 21. Korkhaus GA. Present orthodontic thought in Germany. AM J ORTHOD 1960;46:187-206. 22. Lebret ML. Changes in the palatal vault resulting from expansion. Angle Orthod 1965;35:97-105. 23. Skieller V. Expansion of the midpalatal suture by removable plates, analysed by the implant method. Eur Orthod Soc Trans 1964;143-57. 24. Hicks EP. Slow maxillary expansion, a clinical study of the skeletal versus dental response to low magnitude force. AM J ORTHOD 1978;73:121-41. 25. Cotton LA. Slow maxillary expansion: skeletal versus dental response to low magnitude force in the Macaca mulatta. AM J ORTHOD 1978;73:1-23. 26. Cleall JF, Bayne DI, Posen JM, Subtelny JD. Expansion of the midpalatal suture in the monkey. Angle Orthod 1965; 35:23-35. 27. Starnbach JK, Bayne DI, Cleall JF, Subtelny JD. Facioskeletal and dental changes resulting from rapid maxillary expansion. Angle Orthod 1966;36:152-64. 28. Thorne NH. Experiences on widening the median maxillary suture. Eur Orthod Soc Trans 1956;31:279-90.
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29. Herold JS. Maxillary expansion: a retrospective study of three methods of expansion and their long term sequelae. Br J Orthod 1989;16:195-200. 30. Starnbach JK, Cleall JF. Effects of splitting the midpalatal suture on the surrounding structures. AM J ORTHOD 1964; 50:923. 31. Odenrick L, Karlander EL, Pierce A, Kretschmar U. Surface resorption following two forms of rapid maxillary expansion. Trans Eur Orthod Soc 1991;13:265-70. 32. Adkins MD, Nanda RM, Currier G F . Arch perimeter changes on rapid palatal expansion. AM J ORTHOD 1990; 97:194-9. 33. Gryson JA. Changes in mandibular interdental distance concurrent with maxillary expansion. Angle Orthod 1977;47: 186-92. 34. Sandstrom RA, Klapper L, Papaconstantinou S. Expansion of the lower arch concurrent with rapid maxillary expansion. AM J ORTHOD DENTOFAC ORTHOP 1988;94:296-302.
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35. Korkhaus GA. A new orthodontic symmetrograph. Int J Orthod 1930;16:665-8. 36. Lebret ML. Growth changes of the palate. J Dent Res 1962;41:1391-404. 37. Knott VB, Johnson R. Height and shape of the palate in girls: a longitudinal study. Arch Oral Biol 1970;15:849-60. 38. Barrow GV, White JR. Developmental changes of the maxillary and mandibular dental arches. Angle Orthod 1952;22: 41-6. 39. Bjork A, Skieller V. Growth in width of the maxilla studied by the implant method. Scand J Plast Reconstr Surg 1974; 8:26-33. Reprint requests to:
Dr. Zane F. Muhl College of Dentistry Department of Orthodontics 801 S. Paulina St. Chicago, IL 60612
JOURNAL BACK ISSUES ON CD-ROM Back issues of the AMERICAN JOURNAL OF ORTHODONTICS AND DENTOFACIAL ORTHOPEDICS are now available on C D - R O M . The complete and full text of 1500 articles has been reproduced. Twenty-six volumes consisting of more than 13,000 pages, 10,000 black and white pictures and diagrams, 5000 tables, and 1000 color pictures have all been compressed onto compact disk. In addition, the disk will contain a Book of Abstracts and a Book of Landmark Articles as suggested by Editor-In-Chief, T.M. Graber. The new A J O - D O on C D - R O M will be of enormous benefit to education, research, and publication of articles. Direct all inquiries to a Gold O p t i m e d i a / O R M C O representative; 1-800-854-1741, ext. 777; international: (818) 852-0921, ext. 777.
Galesburg and Chicago, Ill. A retrospective study of dental and maxillary skeletal changes occurring during a period of orthodontic treatment was made from pretreatment and posttreatment dental casts. Sixty maxillary expansion cases were examined. Thirty cases had maxillary expansion accomplished with a fixed rapid palatal expander and 30 were expanded with a quadhelix appliance. All cases were finished with full fixed edgewise appliances. Multiple linear regression analyses were completed for both groups with upper molar width change as the criterion and age, tipping of the upper molars, palatal width change and maxillary tipping as the predictors. All predictors were included in the analysis for the quadhelix group with a significant R2 value of 0.55. For the rapid expansion group, a significant R2 value of 0.33 was achieved with the inclusion of palatal width change and age only. The other variables did not meet the level of significance for entry into the model. Although both groups demonstrated similar amounts of maxillary dental expansion, the rapid expansion group demonstrated greater average skeletal expansion. In addition, there was a significant relationship between skeletal and dental expansion for the rapid expansion group, but not the quadhelix group. Palatal depth increased more on average in the rapid expansion group suggesting that there was greater dental eruption in that group. Expansion across the mandibular molars was greater on average in the quadhelix group. There was no difference in the degree of upper molar rotation or final upper and lower arch forms between the two groups. (AM J ORTHOD DENTOFACORTHOP 1995;1 08:1 84-93.)
T h e rapid palatal expander as described by Haas I is a rigid appliance designed for maximum dental anchorage that uses a jackscrew to produce expansion in 10 to 14 days (Fig. 1). The basis for the rapid expansion procedure is to produce immediate midpalatal suture separation by disruption of the sutural connective tissue. Haas I believes this will maximize the orthopedic effects. Forces produced by this appliance have been reported in the range of 3 to 10 pounds. 2 The quadhelix has been introduced more recently.3 This lingual arch appliance is a modification of the " W " arch described by Coffin4 and has also been used to expand the maxillary dental arch (Fig. 1). It is less rigid and works more slowly than the rapid expander. It has been shown to develop force in the range of 221 to 1149 gm (0.5 to 2.5 pounds)? 8 The quadhelix has the ability to rotate molars and can be adjusted to expand the molars and anterior teeth differentially.9'!° This article is based on research submitted by Dr. Ladner in partial fulfillment of the requirements for the degree of Master of Science in Orthodontics, University of Illinois at Chicago. ~In private practice, Galesburg, Ill. bAssociate Professor, Department of Orthodontics, University of Illinois. Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$3.00 + 0 8/1/53683
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Fig. 1. Appliances studied. Rapid expander as described by HaasI includes jackscrew, buccal and lingual bars, and acrylic palate. Appliance is activated with key. Quadhelix is constructed from 0.036-inch diameter orthodontic wire with four helices in transpalatal section. Anterior arms are constructed from 0.025-inch diameter wire.
Both of these appliances can be used to expand the maxillary dental arch. In clinical practice they are often used as the initial appliance in a treatment plan that includes full fixed appliances, yet their influence on final treatment results is not clear. The transverse change seen across the upper dental arch can be the result of three factors: (1) separation of the midpalatal suture 1"11-26that allows the maxillae to separate; (2) tipping of the two
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maxillae and alveolar processes, 1'24'25'27and (3) tipping or bodily m o v e m e n t of the teeth with the alveolus and within the alveolar bone. 1'23-26'z8-32A g e m a y influence the a m o u n t of dental expansion achieved or m a y affect the relative contributions of t h e s e f a c t o r s . 5'9"1°'15'1s'2°'23 In addition, maxillary first m o l a r rotation, palatal d e p t h ~7'27 and final maxillary arch f o r m m a y be influenced by the use of one of these appliances. C h a n g e s in m a n d i b u l a r intermolar w i d t h 1'6"14'17'2°'33'34 and final m a n d i b u l a r arch f o r m m a y also be influenced. T h e p r e s e n t study seeks to d e t e r m i n e the relationship b e t w e e n u p p e r molar expansion and the three factors previously m e n t i o n e d in subjects t r e a t e d with either the rapid expander or the quadhelix appliance as part of full fixed appliance therapy.
MATERIALS AND METHODS The sample Pretreatment and posttreatment dental casts of 30 subjects treated with rapid palatal expansion and 30 subjects treated with a quadhelix appliance were used in this retrospective study. The treatment of both groups involved a phase of full fixed appliance therapy with a straight wire edgewise appliance with a Hilger's prescription. All subjects were treated without extraction or surgery and had been recently retained. The quadhelix subjects were chosen only if there were indications in the treatment plan or treatment record that maxillary expansion was a goal of treatment. The average ages for the rapid palatal expander and quadhelix groups were 11 years 8 months (SD = 2 years) and 11 years 11 months (SD = 2 years 1 month), respectively. There were 17 female and 13 male subjects in the rapid expansion group and 19 female and 11 male subjects in the quadhelix group. Twenty-three of the rapid expansion group and 10 of the quadhelix group had posterior crossbite involving at least one tooth in each arch. The other patients had varying degrees of buccal overjet. The active expansion for the rapid expansion subjects lasted an average of 23 days (SD = 10 days). The number of turns of the expansion screw per day has not been controlled in the group. At the end of active expansion, the appliance was stabilized with wire and worn as a fixed retainer for an average period of 77 days (SD = 33 days). An acrylic palatal appliance, as described by Haas 1 and Wertz 14was then worn by the patient through the duration of fixed appliance therapy. The quadhelix was worn an average 149 days (SD = 86 days). There was no record of the expansive force applied by the appliance. The clinician retained expansion with an inactive appliance much like the stabilized rapid expander. The mean total treatment time was 36 months
Fig, 2. Symmetrograph has recording plate perpendicular to sliding base with millimeter calibrations. Cast is held by three set screws attached to rotating platform in base. Tracings are drawn by pencil lead in pantograph arm that was guided by movement of stylus against cast.
(SD = 13 months) and 26 months (SD = 8 months) for the rapid palatal expander and quadhelix groups, respectively. Two distinct treatment phases were used in eight of the rapid expansion subjects, whereas only one quadhelix subject had two-phase treatment.
Descriptive variables Variables were measured that describe pretreatment and posttreatment characteristics, as well as changes occurring over the treatment period for the two groups.
Palatal width change Palatal width change, a measure of skeletal expansion, was assessed indirectly from dental casts. Coronal palatal contour tracings were obtained with the use of a symmetrograph 35 (Fig. 2) according to a description provided by Lebret? 6 The pretreatment and posttreatment palatal contour tracings were superimposed as described by Lebret 36 to attain a measurement of the transverse expansion across the midpalatal raphe (Fig. 3).
Tipping of the maxillary alveolus The tipping of the maxillary halves and their alveolus was measured on these same coronal palatal contour tracings (Fig. 4). A line was drawn tangent to the more vertical portion of one side of the posttreatment tracing. The pretreatment tracing was superimposed on that side of the posttreatment tracing and the same line was drawn on the pretreatment tracing. The pretreatment and post-
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x; E~'x2 A
B
C
Fig. 3. Superimpositions to measure palatal width change. Broken line: Pretreatment palatal contour. Solid line: Posttreatment palatal contour. Points X1 and )(2 indicate median palatal raphe for pretreatment and posttreatment tracings, respectively. Two tracings are (A) superimposed on median palatal raphes, (B) right side palatal contour and (C) left side palatal contour, Amount of expansion toward right (ER) and left (EL) are measured.
A
B
C
Fig. 4. Measurement of maxillary alveolar tipping. Broken line: Pretreatment contour tracing. Solid line: Posttreatment contour tracing. A, Tangent to palatal contour of posttreatment tracing was drawn, B, Pretreatment and posttreatment tracings were superimposed on palatal contours and tangent was drawn on pretreatment tracing. C, Tracings were superimposed on contralateral palatal contour and angle alpha was measured.
treatment tracings were then superimposed on the contralateral side of the tracing. The angle formed by the two lines was a measure of tipping of the maxillary alveolus.
Tipping of the upper molar teeth The change in buccoiingual angular orientation of the first molar teeth was measured with the use of a goniometer as described by Thorne. 28 Measurement of the tipping was made by superimposition of photographic negatives. A negative value indicated lingual tipping and a positive value buccal tipping (Fig. 5).
Rotation of the upper molar teeth Angular measurement of the upper first molar rotation was similar to that used for molar buccolingual angular relations (Fig. 6). Orthodontic wires were inserted into compound caps on the first molar teeth so
that they were parallel to the occlusal plane and crossed when observed from above. A photograph of the pretreatment cast with the caps in place was taken from above with the plane of the film and the occlusal plane parallel. The caps were removed from the pretreatment cast, placed on the posttreatment cast, and again photographed from above. The .amount of rotation was measured by superimposition of photographic negatives. A positive value indicated mesiobuccal rotation and a negative value mesiolingual rotation.
Palatal depth Palatal depth was measured with an instrument made of a piece of clear plastic with a length of rectangular orthodontic wire passing through it perpendicularly (Fig. 7). The wire passes through a tight fitting rectangular tube embedded in the plastic. A line across the plastic, which intersects the sliding wire, allows the wire
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Ladner and M u h l
./.
\
_
\e +
A
B
Fig. 5. Measurement of tipping of upper molar teeth. Goniometer wires were positioned so that they intersected when observed from heel of cast. A, Line was constructed perpendicular to right wire and angle (a) of pretreatment goniometer was measured. B, Angle (b) of posttreatment goniometer was also measured.
Fig. 6. Measurement of molar rotation. Goniometer wires were positioned so that they intersected when observed from occlusal. A, Line was constructed perpendicular to left wire and angle (c) of pretreatment goniometer was measured. B, Angle (d) of posttreatment goniometer was also measured.
to be positioned across the mesiolingual cusp tips of the first molar teeth. The plastic, which extends anteriorly beyond the incisors, was placed on the dental cast so that it contacted the most prominent cusps of the first molar teeth and the first contact mesial to the molars. The wire was extended to contact the median palatal raphe. The distance from the plastic to the end of the wire was measured with a Boley gauge.
Transverse dental measurements The pretreatment and posttreatment intermolar dimensions were measured between the mesiobuccal cusp tips of the upper and lower first molar teeth. Upper and lower posttreatment intercanine width was also measured between the incisal tips of these teeth. An index of buccal molar overjet was calculated as the ratio of upper to lower intermolar width. The ratios of upper intermolar to intercanine and lower intermolar to intercanine width were used as an index of upper and lower arch form. Fig. 7. Palatal depth gauge.
RESULTS All measurements were replicated twice for 10 sets of casts with 1 week between trials. Matched pair t tests were employed to test for significant differences between trials. The null hypothesis was that the mean difference between trials was equal to zero. No significant difference were found at p < 0.1, indicating that for this group the measurements were reproducible. Tables I and II show correlation matrices for the quadhelix and rapid expansion groups, respectively. All variables in these tables, other than age,
represent change occurring in the maxilla during treatment. Overall the correlations are low. Only 4 of 23 correlations calculated for the quadhelix group and 3 of 23 the correlations calculated for the rapid expansion group were found to be significantly different from zero at p < 0.05. To illustrate the relationship between dental expansion and the factors responsible for the expansion, a stepwise multiple regression analysis was performed for each group. U p p e r molar width change was used as the criterion and age, upper
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I. M a t r i x of P e a r s o n c o r r e l a t i o n coefficients for c h a n g e in t h e maxilla in t h e q u a d h e l i x s a m p l e ( N = 30)
Table
Age UMTP UMR PWC MXTP UMC PDC
-
Age
UMTP
UMR
1.00 0.32 0.32 0.35 0.05 0.40* 0.49*
1.00 0.17 - 0.36 0.07 0.31 - 0.38*
1.00 - 0.19 0.14 0.19 0.26
[
PWC
[
MXTP
UMC
1.00 0.16 -0.11
1.00 0.28
[
PDC
1.00
-0.19 0.34 0.37*
1.00
*Correlations significant at p < 0.05. UMTP, Tipping of the upper molar; UMR, rotation of the upper molar; PWC, palatal width change; MXTP, maxillary tipping; UMC, upper intermolar change; PDC, palatal depth change. Table II. M a t r i x o f P e a r s o n c o r r e l a t i o n coefficients for c h a n g e in t h e maxilla in t h e r a p i d e x p a n s i o n s a m p l e ( N = 30)
I Age UMTP UMR PWC MXTP UMC PDC
Age
UMTP
UMR
PWC
1.00 0.01 - 0.28 - 0.25 0.05 - 0.42* -0.61"
1.00 0.11 0.29 - 0.03 0.29 -0.15
1.00 0.00 - 0.26 0.30 0.11
-0.17 0.54* 0.09
MXTP
UMC
1.00 - 0.03 - 0.31
1.00 0.30
I
PDC
1.00
1.00
*Correlations significant at p < 0.05.
Table
Ill, S t e p w i s e m u l t i p l e r e g r e s s i o n for d e n t a l e x p a n s i o n in t h e q u a d h e l i x s a m p l e ( N = 30)
Step
I
1 2 3 4
Table
Variable entered
Partial R 2
Model R 2
Age Tipping of the upper molar Palatal width change Maxillary tipping
0.16 0.21 0.13 0.04
0.16 0.37 0.50 0.55
IV, S t e p w i s e m u l t i p l e r e g r e s s i o n for d e n t a l e x p a n s i o n in t h e r a p i d e x p a n s i o n s a m p l e ( N = 30)
Step 1 2
[
Variable entered
Partial R 2
Model R 2
Palatal width change Age
0.29 0.09
0.29 0.38
No other variables met the 0.15 level for significance.
m o l a r tip, p a l a t a l w i d t h c h a n g e a n d maxillary tip w e r e u s e d as p r e d i c t o r s . T a b l e I I I shows t h e results of t h e r e g r e s s i o n analysis for t h e q u a d h e l i x group. A g e was s e l e c t e d first, f o l l o w e d b y u p p e r m o l a r tip, p a l a t a l w i d t h c h a n g e a n d maxillary tip. T h e regression, c o n s i d e r ing all f o u r variables, e x p l a i n e d 55% of t h e vari-
ability in i n t e r m o l a r e x p a n s i o n for t h e q u a d h e l i x group. T h e r e g r e s s i o n was significant at p < 0.001. T a b l e I V shows t h e results of t h e r e g r e s s i o n analysis for t h e r a p i d e x p a n s i o n group. P a l a t a l w i d t h c h a n g e was s e l e c t e d first a n d was followed by age. T h e o t h e r v a r i a b l e s d i d n o t m e e t t h e 0.15 significance level for e n t r y into t h e m o d e l . T h e
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Table V. T tests for pretreatment means in the quadhelix and rapid expansion samples (?4 = 30) Quadhelix
RPE
Variab&
Mean
SD
Mean
SD
Age (months) Upper intermolar width (ram) Lower intermolar width (mm) Palatal depth (mm) Ratio of upper/lower intermolar width
143 48.0 43.0 18.8 1.12"
25 2.6 3.0 2.0 0.07
141 46.6 44.0 18.9 1.06"
24 3.1 3.2 1.8 0.07
0.7301 0.0566 0.2184 0.9098 0.0014
*Sample means are statistically different for these variables at p < 0.01.
Table VI. Matched pair t test for maxillary change during treatment for the quadhelix sample (N = 30) Variable
Mean change
Upper intermolar change (mm) Palatal depth change (ram) Tipping of the upper molar (degrees) Rotation of the upper molar (degrees) Palatal width change (ram) Maxillary tipping (degrees)
5.4* 1.0" 1.3
SD
Maximum
Minimum
p
2.0 1.2 8.2
9.8 4.1 18.2
0.5 -1.3 - 15.5
0.0001 0.0001 0.3934
23.8*
12.7
50.3
0.2
0.0001
1.3" 3.7*
0.9 4.3
4.3 20.1
0.0 0.5
0.0001 0.0001
*Change during treatment significant at p < 0.007.
Table VII. Matched pair t test for maxillary change during treatment for the rapid expansion sample (N = 30) Variable
Mean change
SD
Maximum
Minimum
p
Upper intermolar change (mm) Palatal depth change (ram) Tipping of the upper molar (degrees) Rotation of the upper molar (degrees) Palatal width change (mm) Maxillary tipping (degrees)
6.0* 2.3* - 4.6
2.6 1.6 11.3
11.4 5.4 16.2
0.7 -0.2 - 38.2
0.0001 0.0001 0.0349
16.5"
15.4
48.8
- 9.3
0.0001
2.6* 1.0
1.4 5.9
5.1 12.4
0.4 - 13.5
0.0001 0.3663
*Change during treatment significant at p < 0.007.
regression explained 38% of the variability in intermolar expansion for the rapid expansion group. The regression was significant at p < 0.005. The hypothesis that the two groups were alike before treatment was tested (Table V). The statistical level for significance was set at p < 0.05. This was adjusted for multiple t tests with the Bonferroni method resulting in a value of p < 0.01 for significance. Only the ratio of upper molar width to lower molar width was statistically different. Changes occurring in each group during treatment were examined with t tests (Tables VI and
VII). Adjustment for multiple t tests with the Bonferroni method resulted in a value ofp < 0.007 for significance. Most of the variables showed significant change. Changes occurring during treatment were compared (Table VIII). Adjustment for multiple t tests with the Bonferroni method resulted in a value of p < 0.006 for significance. The palate expansion group showed more change in palatal depth and width than the quadhelix group. Both groups showed significant increases in lower molar width (p < 0.05). The quadhelix group
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Table VIII. T test for comparison of maxillary changes during treatment for the quadhelix and rapid
expansion samples (N = 30) Quadhelix Variable
Upper intermolar change (mm) Palatal depth change (mm) Tipping of the upper molar (degrees) Rotation of the upper molar (degrees) Palatal width change (mm) Maxillary tip (degrees) Upper intercanine after treatment/Upper molar after treatment Palatal width change/Upper intermolar change
RPE
Mean
SD
Mean
SD
P
5.4 1.0" 1.3 23.8 1.3" 3.7 0.66
2.0 1.2 8.2 12.7 0.9 4.3 0.03
6.0 2.3* -4.5 16.5 2.6* 1.0 0.65
2.6 1.6 11.3 15.4 1.4 5.9 0.05
0.2612 0.0012 0.0254 0.0503 0.0001 0.0491 0.3406
0.32
0.49
0.46
0.24
0.1579
*Sample means are statistically different at p < 0.006.
had an average increase of 2.5 mm (SD = 2.3 mm) and the rapid expansion group 1.0 mm (SD = 2.0 ram) in this dimension. Lower molar width change was significantly greater (p < 0.05) for the quadhelix group than for the rapid expansion group. Clinically, the quadhelix was worn for an average total time of 149 days (SD = 86 days). This was significantly longer (p < 0.05) than total appliance wear for the rapid expander which was 100 days (SD = 35 days). The total treatment time was 26 months (SD = 8 months) for the quadhelix group and 36 months (SD = 13 months) for the rapid expansion group. These were found to be significantly different (p < 0.05). DISCUSSION Achievement of maxillary dental expansion
Although both regression models for upper molar expansion were significant, the predictors entered into the stepwise multiple regression analysis left a great deal of unexplained variability in both. The predictors explained more of the variability in the quadhelix group than in the rapid expansion group. Age was chosen first for the quadhelix regression, whereas it was chosen second, after skeletal expansion, for the rapid expansion regression. The indices of skeletal and dental tipping were not selected for the rapid expansion model, but were chosen for the quadhelix model. Upper molar width change had a significant negative correlation with age, but none of the three factors proposed to be responsible for the dental expansion demonstrated a significant relationship with age. There was no significant difference in upper
intermolar expansion between the two groups, but there was greater skeletal expansion in the rapid expansion group. In addition, there was a positive correlation between upper intermolar expansion and skeletal expansion for the rapid expansion group, but not for the quadhelix group. The average ratio of skeletal expansion to upper intermolar expansion in the present study was 0.32 and 0.46 for the quadhelix and rapid expansion groups, respectively. These were not statistically different. This ratio has been reported to be in the range of 0.17 to 0.53 for slow expansion9'22 and 0.38 to 0.62 for rapid expansion. 15'16"2aThe ratios in the present study fall within the range reported in the literature. Timms 16 reported the correlation between skeletal and dental expansion and between skeletal expansion and age for a rapid expansion sample (r = 0.55 and r = -0.33, respectively). The correlations found for the rapid expansion sample in the present study between these variables were surprisingly similar. Thorne 28 reported buccal tipping of the molar teeth in 75% of his rapid expansion sample measured immediately after expansion. Herold 29showed only minimal buccal tipping of the molars after rapid expansion with greater buccal tipping in a sample treated with a quadhelix. Hicks24reported 1.5 to 24° of upper molar tipping in a slow expansion sample. Even though tipping of the upper molars was able to account for some of the variability in upper molar expansion for the quadhelix group, tipping of the upper molars was not significant in either group and there was no difference in upper molar tipping between the two groups.
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American Journal of Orthodontics and Dentofacial Orthopedics Volume 108, No. 2 H i c k s 24 reported - 2° to 8° of skeletal tipping in a slow expansion study. Cotton 25 reported 4° to 7° of maxillary tipping with 2° to 17° of buccal molar tipping in a slow expansion study of monkeys. The present study showed significant buccal tipping of the maxillae in the quadhelix group but not in the rapid expansion group.
Palatal depth
The average increase in palatal depth was greater for the rapid expansion group than for the quadhelix group. Palatal depth change is due to an increase in dentoalveolar height? 9 The rapid expansion group therefore demonstrated greater dental eruption. A significant negative correlation existed between palatal depth change and age for both groups, but average age was not different for the two groups. Therefore age alone Could not have been responsible for the difference in palatal depth change. Longer treatment times would allow greater expression of the growth process. Because the rapid expansion group was in treatment significantly longer than the quadhelix group and palatal depth change was correlated with treatment time for both groups (r = 0.42 and r = 0.67 for the quadhelix and rapid expansion groups, respectively), it would appear that the longer treatment time could have allowed greater alveolar growth in the rapid expansion group. The increase in palatal depth was greater than would be expected from growth alone. Lowering of the palatal shelves of the maxilla on expansion has been suggested to o c c u r I and later was demonstrated in monkeys.27 Palatal shelf lowering would decrease the depth of the palate. A decrease in palatal depth was not demonstrated in the present groups. If lowering of the palatal shelves did occur, its effect has been more than offset by extrusion of the dentition because of orthodontic treatment and growth. Mandibular molar width
The lower intermolar expansion was greater for the quadhelix group and was correlated with the upper intermolar width change for the quadhelix group, but not the rapid expansion group. There was also a significant correlation between lower molar width change and the initial transverse discrepancy for both groups (r --- 0.44 and r = 0.36 for the quadhelix and rapid expansion groups, respectively). It appears that the difference in lower intermolar expansion may be due to the fact that
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there was less initial transverse discrepancy in the quadhelix group than in the rapid expansion group. For example, a patient presents with no posterior crossbite yet the clinician decides that it would be desirable to expand the upper arch. If the lower arch were not expanded a corresponding amount, the buccal segments would be treated into buccal crossbite. However, if a patient presents with a posterior crossbite and the clinician decides to treat with expansion of the upper arch, a corresponding amount of lower arch expansion would perpetuate the crossbite. In the present study the quadhelix group reflects the first of these possibilities and the rapid expansion group reflects the other. The present results cannot attribute the difference in lower intermolar width change to the use of one appliance over the other. The lower arch expansion is probably dependant on the amount of maxillary expansion and the initial transverse discrepancy regardless of the appliances used. Davis and Kronman 17 reported greater lower molar width change for a rapid expansion sample when a lower arch wire was used than when one was not. Evaluation of the other literature on rapid expansion reveals that the increase in lower molar width tends to be greater when a lower arch wire w a s u s e d . 1°'2s'33"36 Similar information is not available for a slow expansion sample. The lower molar width change for the rapid expansion group in the present study agrees very closely with that reported by Davis and Kronman 17 for the sample in which a lower arch wire was used. Gryson33 studied rapid expansion in a crossbite sample and found no correlation between upper and lower intermolar width change. This was true for the present rapid expansion group as well. Molar rotation
The quadhelix has the ability to rotate molars and the rapid expander has no such capability, yet there was no average difference in molar rotation for the two groups. The fixed appliance therapy that followed the expansion was likely responsible for molar rotation in the rapid expansion group. Arch form
The quadhelix appliance can expand differentially anteroposteriorly, whereas the rapid expander cannot. The final upper and lower arch forms were not different for the two groups. Presumably the fixed appliance therapy after expansion was responsible for standard~ing the arch form.
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CONCLUSIONS
1. The three factors proposed to account for the variability in upper intermolar width change explained a greater amount of the variability in the quadhelix group than the rapid expansion group. However, the factors left a great deal of variability unexplained in both groups. 2. Age was correlated only with maxillary intermolar expansion and not with any of the three factors proposed to be responsible for the dental expansion. 3. Although both appliances achieved similar amounts of maxillary dental expansion, the rapid expander produced greater skeletal expansion. In addition, there was a significant relationship between skeletal and dental expansion in the rapid expansion group, but not in the quadhelix group. 4. Both the quadhelix and rapid expansion groups demonstrated significant increases in lower intermolar width. The expansion was greater in the quadhelix group. The difference is most likely due to the difference in initial transverse discrepancy between the groups and not the appliances themselves. 5. Palatal depth increased more in the rapid expansion group suggesting greater dental eruption in the rapid expansion group. 6. Although the rapid expander does not have the ability to rotate molars that the quadhelix has, there was no difference in the degree of molar rotation at the end of full edgewise appliance therapy. 7. Although the rapid expander cannot expand the canines and molars differentially as the quadhelix can, there was no difference in the final upper or lower arch forms at the end of full edgewise appliance therapy. REFERENCES 1. Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening the midpalatal suture. Angle Orthod 1961;31:200-17. 2. Isaacson RJ, Wood JL, Ingram AH. Forces produced by rapid maxillary expansion. I and II. Angle Orthod 1964;34: 256-70. 3. Ricketts RM. Growth prediction: part 2. J Clin Orthod 1975;9:340-62. 4. Coffin WH. A generalized treatment of irregularities. Trans Int Cong Med London 1881;3:542-7. 5. Chaconas SJ, Caputo AA. Observation of orthopedic force distribution utilizing maxillary orthodontic appliances. J Dent Res 1975;54:45.
American Journal of Orthodontics and Dentofacial Orthopedics August 1995
6. Hermanson H, Kurol J, Ronnerman A. Treatment of unilateral posterior crossbite with quad-helix and removable plates. A retrospective study. Eur J Orthod 1985;7:97-102. 7. Urbaniak JA, Brantley WA, Prnhs R J, Zussman RL, Post AC. Effects of appliance size, arch wire diameter and alloy composition on the in vitro force delivery of the quad-helix appliance. AM J ORTHOD DENTOFAC ORTNOP 1988;94: 311-6. 8. Ranta R. Treatment of unilateral posterior crossbite: comparison of quad-helix and removable plate. J Dent Child 1988;Mar-Apr:102-4. 9. Frank SW, Engle GA. The effects of maxillary quad-helix appliance expansion on cephalometric measurements in growing orthodontic patients. AM J ORTHOD 1982;81:37889. 10. Chaconas SJ, de Alba y Levy JA. Orthopedic and orthodontic applications of the quad-helix appliance. AM J ORTHOD 1977;72:422-8. 11. Debbane EF. A cephalometric and histologic study of the effect of orthodontic expansion of the midpalatal suture of the cat. AM J ORTHOD 1958;44:187-218. 12. Haas AJ. The treatment of maxillary deficiency by opening the midpalatal suture. Angle Orthod 1965;35:200-17. 13. Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. AM J ORTHOD 1970;57:219-55. 14. Wertz RA. Skeletal and dental changes accompanying rapid midpalatal suture opening. AN J ORTHOD 1970;58:41-66. 15. Krebs A. Midpalatal suture expansion studies by the implant method studied over a seven year period. Eur J Orthod Soc Rep Congr 1964;40:131-42. 16. Timms RJ. A study of Basal movement with rapid maxillary expansion. AM J ORTHOD 1980;77:500-7. 17. Davis WM, Kronman JH. Anatomical changes induced by splitting of the midpalatal suture. Angle Orthod 1969;39: 126-32. 18. Gerlach HG. The apical base after rapid spreading of the maxillary bones. Eur Orthod Soc Rep 1956;32:266-78. 19. Harberson VA, Myers DR. Midpalatal suture opening during functional posterior cross-bite correction. AM J ORTHOD 1978;74:310-3. 20. Bell RA, LeCompte EJ. The effects of maxillary expansion using a quad-helix appliance during the deciduous and mixed dentitions. AM J ORTHOD 1981;79:152-61. 21. Korkhaus GA. Present orthodontic thought in Germany. AM J ORTHOD 1960;46:187-206. 22. Lebret ML. Changes in the palatal vault resulting from expansion. Angle Orthod 1965;35:97-105. 23. Skieller V. Expansion of the midpalatal suture by removable plates, analysed by the implant method. Eur Orthod Soc Trans 1964;143-57. 24. Hicks EP. Slow maxillary expansion, a clinical study of the skeletal versus dental response to low magnitude force. AM J ORTHOD 1978;73:121-41. 25. Cotton LA. Slow maxillary expansion: skeletal versus dental response to low magnitude force in the Macaca mulatta. AM J ORTHOD 1978;73:1-23. 26. Cleall JF, Bayne DI, Posen JM, Subtelny JD. Expansion of the midpalatal suture in the monkey. Angle Orthod 1965; 35:23-35. 27. Starnbach JK, Bayne DI, Cleall JF, Subtelny JD. Facioskeletal and dental changes resulting from rapid maxillary expansion. Angle Orthod 1966;36:152-64. 28. Thorne NH. Experiences on widening the median maxillary suture. Eur Orthod Soc Trans 1956;31:279-90.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 108, No. 2
29. Herold JS. Maxillary expansion: a retrospective study of three methods of expansion and their long term sequelae. Br J Orthod 1989;16:195-200. 30. Starnbach JK, Cleall JF. Effects of splitting the midpalatal suture on the surrounding structures. AM J ORTHOD 1964; 50:923. 31. Odenrick L, Karlander EL, Pierce A, Kretschmar U. Surface resorption following two forms of rapid maxillary expansion. Trans Eur Orthod Soc 1991;13:265-70. 32. Adkins MD, Nanda RM, Currier G F . Arch perimeter changes on rapid palatal expansion. AM J ORTHOD 1990; 97:194-9. 33. Gryson JA. Changes in mandibular interdental distance concurrent with maxillary expansion. Angle Orthod 1977;47: 186-92. 34. Sandstrom RA, Klapper L, Papaconstantinou S. Expansion of the lower arch concurrent with rapid maxillary expansion. AM J ORTHOD DENTOFAC ORTHOP 1988;94:296-302.
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35. Korkhaus GA. A new orthodontic symmetrograph. Int J Orthod 1930;16:665-8. 36. Lebret ML. Growth changes of the palate. J Dent Res 1962;41:1391-404. 37. Knott VB, Johnson R. Height and shape of the palate in girls: a longitudinal study. Arch Oral Biol 1970;15:849-60. 38. Barrow GV, White JR. Developmental changes of the maxillary and mandibular dental arches. Angle Orthod 1952;22: 41-6. 39. Bjork A, Skieller V. Growth in width of the maxilla studied by the implant method. Scand J Plast Reconstr Surg 1974; 8:26-33. Reprint requests to:
Dr. Zane F. Muhl College of Dentistry Department of Orthodontics 801 S. Paulina St. Chicago, IL 60612
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