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Long-term stability of rapid palatal expander treatment and edgewise mechanotherapy
Long-term stability of rapid palatal expander treatment and edgewise mechanotherapy Raed Moussa, DDS,
DIP, a
Maria T. O'Reilly, DMD, MDS, PhD, b and John M. Close, MA, PMS °
Pittsburgh, Pa. Previous studies on long-term stability of orthodontic treatment primarily have focused on the stability of the lower arch treated with edgewise appliances. The aim of this study was to evaluate the long-term stability of the upper and the lower dental arches of patients treated with a rapid palatal expander. The sample comprised of 165 dental casts randomly selected from patients who had been out of retention for 8 to 10 years at a mean age of 30 years. Measurements were made directly on dental casts obtained at the three time intervals: before treatment, after treatment, and after retention. Differences over time between the upper and the lower dental arches and between intervals were analyzed by a two-way multivariate analysis of variance (MANOVA) and post hoc Bonferroni t tests. Differences between after treatment and after retention were statistically significant (P < 0.006) for all except lower intermolar width. However, only for lower and upper arch lengths and perimeters were the differences greater than 2.0 mm. Treatment with the rapid palatal expander presented good stability for upper intercanine width, upper and lower intermolar widths and incisor irregularity. Lower intercanine, arch length, and perimeter presented poor stability. (AM J ORTHOD DENTOFACORTHOP 1995;108:478-88.)
Many theories have been postulated regarding the cause of relapse. Orthodontists have proposed treatment strategies involving concepts/philosophies as to what enhance stability, such as overcorrection of the malocclusion, 1 avoidance of excessive arch expansion by extraction, 2'3 expansion with palatal expander, 4'~ placing teeth over basal bone, 3"~ prolonged retention, TM maintenance of arch form during treatment, 9,a° and type of mechanotherapy. 4'5'11 Previous studies have often noted a decrease in arch length and width, while also showing that increases in incisor crowding, overbite, and overjet occur after retention? 22' Attempts to correlate observed postretention changes with pretreatment and posttreatment conditions have failed to provide useful associations. '''22 Untreated normal subjects also have been examined to determine whether changes seen during development differ from those in treated subjects. 23 Expansion through maxillary suture widening by rapid maxillary expanders has been claimed to promote stability after retention. Stability has been attributed to the skeletal component of arch en~Assistant Professor, Department of Orthodontics, Baath University. bAssociate Professor, Department of Orthodontics, School of Dental Medicine, University of Pittsburgh. CAssistant Professor, Division of Learning Resources, School of Dental Medicine, University of Pittsburgh. Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$5.00 + 0 8/1/55445
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largement obtained by the expansion appliance as opposed to dental expansion as a result of edgewise appliance mechanotherapy. Studies on immediate treatment effects of rapid palatal expansion have reported increases in arch width as a result of combined skeletal and dental expansion. Short-term follow-up has indicated a rebound effect of the dental component, yet a relative stability of the skeletal aspect of the expansion.4.5.11,24-28 The implant studies by Krebs 29 during a 7-year observation period found a substantial reduction in dental arch width after discontinuation of retention which continued for as long as 4 to 5 years. The 5-year posttreatment study by LinderAronson and Lindgren 3° noted that only 45% of the initially achieved expansion was maintained. These findings concur with those of Stockfish, 31 who found 50% of relapse within 3 to 5 years after retention. Herold 32 reported that the increase in intercanine and intermolar widths observed during treatment was followed by relapse, with a residual increase of 2.1 mm (62.5%) and 3.1 mm (56.4%), respectively. Linder-Aronson and Lindgren 3° found a residual expansion of 38% and 59% for intercanine and intermolar widths, respectively, over a period of observation similar to that of Herold? 2 Midpalatal suture opening can be accomplished in both children and adults, but with advancing maturity the rigidity of the skeletal components
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Table h Sample characteristics m e a n and range for age (year-month) and gender
Males (16) Females (39) Total (55)
Pretreatment (T1)
Posttreatment (T2)
End of retention
13.6 ± 3.1 (8.1-19.3) 12.6 ± 2.2 (8.4-16.7) 12.1 ± 2.6 (8.4-19.3)
16.2 ± 2.8 (12.1-20.7) 15.4 +_ 2.5 (10.6-20.5) 15.7 + 2.6 (10.6-20.7)
22.7 ± 3.8 (15.5-30.9) 21:1 ± 2.8 (17.1-30.2) 22.0 _ 4.0 (15.5-30.1)
limits the extent and the stability of the expansion, which may involve fracturing of the bony interdigitations.2S, 33-35 Differences in immediate treatment outcome and stability also have been attributed to appliance design and rate of expansion. H a a s 5 maintains that rapid palatal expansion with a soft tissue-borne appliance is superior to a totally tooth borne palatal expander (i.e., Hyrax). H e believes that the former delivers a m o r e parallel expansive force on the two maxillary segments that is distributed evenly to both the teeth and alveolar processes. Further, he argues that in older patients where the suture usually does not open, the force delivered to the palatal vault by the acrylic sections of the appliance tends to compress the palatine arteries. This compression, in turn, stimulates the connective tissue surrounding these vessels to differentiate into osteoclasts that serve to resorb underlying bone and thus protect the arteries from injury. In so doing, the vault is "hollowed out" and a true apical base expansion is induced. T M According to Haas, the p e r m a n e n t widening of the maxillary palatal arch and base also allows the mandibular teeth to upright and expand. A review of the literature thus supports the contention that the rapid palatal expander (RPE) device, in addition to its other effects, can provide additional space in the arch to relieve crowding. Studies on long-term stability of orthodontic treatment 3'7"12'14-~s'2°-22 have focused primarily on the mandibular arch and the strength of association between dental and cephalometric p a r a m e t e r s that may be used as predictive of postretention changes. In these studies, the m e c h a n o t h e r a p y used was reported to be edgewise appliances. The purpose of this study therefore was to assess the long-term changes of maxillary and mandibular dental arch m e a s u r e m e n t s in patients who were treated with the soft tissue-borne palatal expander and edgewise appliances. Changes in intercanine width, intermolar width, arch length,
I
I Postretention I (T3)
Duration of retention (lower)
Years postretention
6.4 _+ 2.3 (5.0-10.1) 6.7 ± 2.3 (5.1-15.9) 6.6 ± 2.3 (5.0-15.9)
8.1 ± 5.4 (5.0-20.4) 7.9 ± 3.1 (5.0-16.6) 8 . 0 2 3.1 (5.6-20.4)
31.5 ± 7.5 (20.8-51.1) 29.7 +- 3.91 (21.5-39.7) 30.2 ± 5.3 (20.8-51.1)
arch perimeter, and Irregularity Index were examined. METHODS AND MATERIALS The sample consisted of 165 dental casts of 55 patients, 16 males and 39 females. They were selected randomly from records of patients who had been treated with a soft tissue-borne RPE and edgewise appliances at Andrew Haas' private practice in Cuyahoga Falls, Ohio, between 1960 and 1980. To be included in the study, dental casts at pretreatment and posttreatment had to be available, and all permanent teeth had to be present (except third molars). Of 400 patients, 60 were contacted by two office staff members (I.W. and J.P.) for obtaining the postretention records. Two patients could not be reached, and three were eliminated because of missing anterior teeth (Table I). The mean age at treatment completion and at end of retention was 15.7 and 22 years, respectively. At the time postretention records were obtained, the mean age was 30 years. The incisor relationship was Class I in 40 patients, Class II in 9, and edge-to-edge in 6. Of the 55 patients, two patients had extractions , maxillary right first premolar and mandibular first premolars. Clinical management The appliance was activated 1 mm (four turns) and 0.25 mm (quarter turn) each 5 minutes for 15 minutes at the time the appliance was placed. Thereafter it was activated a quarter turn in the morning and a quarter turn in the evening. The patients were seen at weekly intervals and during each visit, the screw was extended an additional 1 to 1.5 mm (4 to 6 turns). The desired expansion was achieved when the mandibular arch was completely contained by the maxillary arch, the screw being opened at least 11 mm and up to 14 mm. At that time, the appliance was stabilized with brass wire and maintained in place for a minimum of 3 months. On the same day the expander was removed, a removable acrylic plate was inserted and worn throughout the remainder of active treatment. Retention protocol The maxillary retainer consisted of a removable appliance that was worn for 2 years after treatment, and the
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Fig, 1. Measurements: A, Arch width; B, arch perimeter; C, arch length; and D, Irregularity Index.
mandibular retainer was a fixed lingual arch from canine to canine worn for approximately 61/2 years.
displacement of adjacent anatomic contact points of the six anterior teeth (Fig. 1, D).
Methods of measurements
Statistical analysis
The following measurements were made directly on the dental casts (Fig. 1):
To assess whether the changes that occurred over time were different between maxillary and the mandibular measurements, a two-way multivariate analysis of variance (MANOVA) for a within-subject design was performed. Post hoc Bonferroni t tests were used for pairwise comparisons to test for differences between each of the intervals.
1. 2. 3. 4. 5.
Maxillary and mandibular Maxillary and mandibular Maxillary and mandibular Maxillary and mandibular Irregularity Index 37
intercanine width intermolar width arch perimeter 36 arch length 2
The intercanine width was measured as the distance between cusp tips and the intermolar width as the distance between mesiobuccal cusps tips bilaterally (Fig. 1,A). All measurements were made with a two-pointed caliper approximated to the nearest 0.01 ram. Before making the measurements, the cusp tips of the canines and the mesial buccal cusps of the first molars for each patient were marked simultaneously with a No. 0.3 pencil. In cases where a facet existed, the cusp tip was estimated. Measurements were made randomly for all the patients without knowledge as to the phase of treatment. Arch perimeter was measured by finding the sum of the lengths of segments connecting the mesial contact points of first molars and premolars, the premolar mesial contact point and that of the canine and mesial contact point of the canine to that of the lateral incisor for both sides of arch (Fig. 1, B). Mandibular and maxillary arch lengths were measured as the summed inside measurement from first permanent molars to the central incisor contact point (Fig. 1, C). The Irregularity Index was the summed
RESULTS M e a s u r e m e n t e r r o r was e v a l u a t e d by r a n d o m l y selecting 15 casts, e a c h m e a s u r e d twice on s e p a r a t e occasions. T h e s t a n d a r d d e v i a t i o n s w e r e f o u n d to b e in t h e 0.07 to 0.17 m m for all m e a s u r e m e n t s . T h e M A N O V A r e s u l t e d in significant (p < .001) m a i n effects for site (maxilla versus m a n d i b l e ) a n d t i m e ( p r e t r e a t m e n t , p o s t t r e a t m e n t ) for all five dep e n d e n t variables. T h e i n t e r a c t i o n b e t w e e n site a n d t i m e was significant for f o u r of t h e five d e p e n d e n t v a r i a b l e s ( p < 0.02). T h e i n t e r a c t i o n effect for arch l e n g t h was n o t significant ( p = 0.69). Post hoc c o m p a r i sons using B o n f e r r o n i t tests w e r e as follows ( T a b l e s II a n d III): Intercanine width Maxillary i n t e r c a n i n e w i d t h i n c r e a s e d 3.6 +_ 3.0 m m f r o m b e f o r e t r e a t m e n t to a f t e r t r e a t m e n t a n d
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Table II. Mean and standard deviations of measurements (mm)
Variable
Pretreatment T1
Posttreatment T2
Postretention T3
Mean ± SD
Mean +_ SD
Mean ± SD
31.4 ± 3.0 25.5 +_ 2.4
35.0 + 2.2 27.0 ± 1.8
34.1 _+ 2.2 25.9 ± 2.0
46.5 ± 4.6 42.8 _+ 3.4
53.4 -- 3.0 44.9 +_ 3.0
52.1 + 3.0 45.3 _+ 3.1
70.8 ± 5.0 62.9 +- 4.4
74.9 -+ 6.8 65.6 ± 4.7
72.4 + 6.1 62.3 -+ 5.2
68.4 ± 5,0 59.2 _+ 6,3
71.6 ± 6.4 62.3 ± 5.0
68.4 -+ 7.9 59.8 ± 4.6
6.7 ± 5.5 4.5 +- 3.4
0.8 ± 0.7 0.6 ± 0.6
1.5 ± 1.5 1.4 ± 1.3
Intercanine width U L
Intermolar width U L
Arch perimeter U L
Arch length U L
Irregularity index U L
decreased 0.8 + 1.3 mm from after treatment to after retention. This resulted in a net increase of 2.7 -+ 2.8 mm. In the mandible the increase was 1.8 + 1.7 m m at the end of treatment. At postretention there was a decrease of 1.1 +_ 0.9 mm, leaving a net increase of 0.7 +_ 1.7 mm.
Intermolar width The increase for the maxilla was 6.7 +_ 4.1 mm during treatment and the decrease was 1.2 + 1.7 mm after retention. This resulted in a net increase of 5.5 _+ 4.0 mm. For the mandible, there was an increase of 2.0 +_ 3.0 mm during treatment, followed by an increase of 0.3 _+ 2.2 mm after retention. The net increase was 2.3 +_ 2.7 ram.
Irregularity index The mean pretreatment value was 6 . 7 _ 5.5 mm for the maxilla and 4.5 +_ 3.4 mm for the mandible. In the maxilla incisor alignment was improved greatly during treatment with the mean decrease from before treatment to after treatment being 5.8 _ 5.5 mm. During the postretention period there was an increase of 0.6 + 1.3 mm, leaving a net improvement of 5.3 + 5.4 mm. For the mandible, there also was a decrease from before treatment to after treatment of 3.9 +_ 3.3 mm. During the postretention period, an increase of 0.8 _+ 1.2 mm occurred leaving a net improvement of 3.0 _ 3.3 ram.
Arch perimeter
DISCUSSION
The mean increase in the maxilla during treatment was 4.1 _+ 6.6 mm followed by a decrease after retention of 2.5 + 3.8 mm, resulting in a net increase of 1.6 _+ 5.4 ram, which was not statistically significant. The mean increase for the mandible was 2.7 _+ 4.0 mm and the mean decrease was 3.5 +_ 1.8 mm. The net decrease was 0.6 +_ 4.1 mm, which was also not statistically significant.
Rapid palatal expansion is an accepted procedure to relieve deficiencies in arch perimeter and/or length. With the increasing emphasis on nonextraction therapy, the procedure has gained popularity because of the relief of crowding it provides. Rapid palatal expansion compensates for arch deficiencies through transverse expansion of the palate and dental arches. The principal objective of this study was to determine the long-term stability of treatment with the soft tissue R P E and edgewise appliances.
Arch length Arch length changed similarly for both arches. The maxilla increased 3.3 _+ 5.9 mm during treatment and decreased 3.2 _+ 4.4 after retention, which resulted in no treatment gain. The mandible measured 3.2 + 6.4 mm and decreased 2.4 ___ 2.3 mm with a net increase of 0.6 _+ 5.9 mm also not statistically significant.
Intercanine width Although studies on long-term stability of intercanine width in the lower arch have been numerous, the problem of stability of upper intercanine width has been addressed with less frequency.
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Table IlL Mean differences and standard deviations of measurements Intercanine width T2 > T,
T3 > T2
Intermolar width
] T3 > T 1
T2 > T1
T3 > T2
T3 > T 1
T2 > T1
T3>T2
T3 > T 1
6.7 _+ 4.1" 2.0 _+ 3.0*
- 1 . 2 --- 1.7" 0.3 -+ 2.2
5.5 _+ 4.0* 2.3 _+ 2.7*
4.1 _ 6.6* 2.7 _+ 4.0*
- 2 . 5 _+ 3.8* - 3 . 5 -+ 1.8"
1.6 -+ 5.4 - 0 . 6 - 4.1
T3 > T2 = Postretention/posttreatment;
T3 > r~ =
r
Maxilla Mandible
3.6 _+ 3.0* 1.8 -_ 1.7'
- 0 . 8 _+ 1.3" - 1 . 1 _+ 0.9*
2.7 -+ 2.8* 0.7 -+ 1.7"
Arch perimeter
*p < 0.006. ( - ) = decrease; ( + ) = increase; Te > T1 = Posttreatment/Pretreatment; Postretention/Pretreatment (net change).
Table IV. Intercanin, and intermolar width measurement changes Intercanine width References
Treatment~sample size
1"2>1"1
T3 > T2
Intermolar width T3 > T 1
7"2 > r l
7"3 > T2
- 0 . 8 (1.3) - i . 8 (1.7)
2.7 (2.8)
6.7 (4.1)
- 1 . 2 (1.7)
T3 > T1
Maxilla This study U h d e et al. 21 Herold 32 Linder-Aronson and Lindgren 3°
5.5 (4.0)
R P E (56) E (27) NE (45) R P E (19) R P E (17)
3.6 (3.0)
3.2 (2.7) 2.1 (1.6)
- 1 . 3 (1.0) - 1 . 3 (1.1)
1.9 (2.3) 0.8 (1.2)
3.9 (3.3) 5.9 (3.5)
R P E (56) E (29)
1.8 (1.7) 1.9 (2.1)
- 1 . 1 (0.9) - 1 . 1 (1.1)
0.7 (1.7) 0.7 (1.9)
2.0 (3.0) - 1 . 4 (1.5)
0.3 (2.2) - 0 . 0 3 (1.3)
2.4 (2.7) - 1 . 4 (1.7)
2.0 0.9 -1.0 1.4 0.5 0.8
0.0 -0.5 -1.1 -0.5 -0.3 -1.0
(1.6) (1.3) (1.5) (1.4)
1.9 (1.8) 0.4 - 2 . 1 (2.1) 1.0 (1.9) 0.2 -0.2
- 1.3
(1.6)
- 1.0
(1.9)
- 1.5 ( 1 . 8 ) - 1.3
(1.8)
-1.8 (1.6) -2.2 (2.4)
2.1 (3.4) 3.5 (2.7)
Mandible This study G a r d n e r and Chaconas TM Glen et al. 2° Shapiro Is Riedel et al. 4° U h d e et al. ~ Sinclair and Little 23
NE (74) NE (28) E (58) NE ( 2 2 ) E1 (24) E2 (18) E (27) N E (45) U N (65) F M
1.2 0.5 1.7 0.7 - 1.6 -5.2
- 0.3 - 0.08 -0.5
(1.6) (1.8) (2.3) (2.2) (3.1)
- 0 . 7 (1.1) - 1.0 - 1 . 9 (1.3) - 1 . 4 (1.4) - 1.1 (0.95) - 1 . 4 (1.2) - 2 . 1 (1.3) - 2 . 3 (1.7) - 0.44 - 0.7 (0.78) - 0 . 1 6 (0.9)
0.5 (1.7) - 0.4 - 0 . 3 (1.8) - 0 . 7 (1.9) -2.7 -6.6
- 0.7
(1.7) (2.3) (1.8) (1.4) (2.1)
-0.5 - 0 . 0 4 (1.3) - 0 . 7 (1.7)
(1.1)
-0.1 - 0 . 4 1 (0.8) - 0 . 7 (1.7)
-0.1
T 2 > T 1 = T r e a t m e n t change; /12 > T3 = posttreatment change; T3 > T 1 = treatment gain. E = Extraction; N E = nonextraction; UN = untreated normal; F = female; M = male.
Maxilla
Herold's long-term study of stability of intercanine width treated with the Hyrax palatal expander 32 reported a mean treatment increase similar to that of this study (3.2 and 3.6 mm, respectively). Linder-Aronson and Lindgren, 3° also using a Hyrax appliance, reported a smaller mean increase (2.1 ram) than that of Herold's study and this study. At postretention intercanine width decreased, however, in this study its magnitude was smaller (0.8 mm) than that reported by Herold 32 and Linder-Aronson and Lindgren 3° (1.3 mm) (Table IV). The differences in final intercanine width be-
tween this study and those reported by the studies of Herold 32 and Linder-Aronson and Lindgren 3° were in the magnitude of the loss at postretention. In this study, intercanine width experienced the largest increase during treatment but, also the smallest decrease in post-retention. The mean net gain in this study was double that reported by Herold 32 and triple that reported by LinderAronson and Lindgren 3° (Table IV). Considering that the patients in this study had been out of retention for a much longer period, ranging from 5.6 to 20.4 years, and were at least 10 years older than those of Herold's 32 and Linder-Aronson and Lindgren's, 3° a greater loss would have been ex-
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Arch length 7"2>7"1 3.3 +- 5.9* 3.2 ± 6.4*
I
7"3>7"2 - 3 . 2 -+ 4.4* - 2 . 4 ± 2.3*
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Irregularity Index I
T3 > T1
7"2 > T1
7"3 >7"2
0.6 -+ 7.6* 0.6 ± 5.9*
- 5 . 8 +-5.5* - 3 . 9 ± 3.3*
0.6 ± 1.3" 0.8 ± 1.2"
pected in this study. Results in untreated normal subjects 23 reported a loss in intercanine dimension of 0.7 mm from 13.6 to 20.6 years, approximately three times less than the gain reported in this study. Final intercanine width closely approximated the posttreatment dimension in this study. Therefore treatment with the soft tissue-borne palatal expander provided better stability than the Hyrax. Mandible
Studies on long-term stability of intercanine width changes in the lower arch during treatment have shown that regardless of the direction of change induced by the treatment, often a decrease occurred after retention. The decrease after retention resulted in final intercanine width that was either smaller than the pretreatment value or closely approximated it. Treatment modality (extractions versus expansion) was not related to the magnitude of the changes induced by treatment. 14-16,2o,21.38,39,4o In this study, a mean increase in intercanine width (1.8 _+ 1.7 ram) was observed at the posttreatment mean age of 15.7 _+ 2.6 years (Table IV). This increase was very similar to those reported for extraction cases by Gardner and Chaconas 14 and Shapiro is (1.2 and 1.7 mm, respectively) and double that reported by Glenn, Sinclair, and Alexander 2° for nonextraction cases (0.5 mm). The mean increase during treatment in this study was followed by a decrease after retention (1.1 _ 9.2) at age 30.2 _+ 5.3 years. The extent of this decrease closely approximated (within 1.0 mm) those reported for premolar extraction cases, 14 and nonextraction treated cases, 2° and was slightly less than that found by the extraction and nonextraction cases of Shapiro ~5 (1.4 and 1.9 ram, respectively) (Table IV). The net gain of 0.7 +_ 1.7 mm in this study was similar to the Gardner and Chaconas 14 extraction (0.7 _ 1.9 mm) and nonextraction (0.5 _+ 1.7 ram) cases. Postretention intercanine width was either
[
7"3 > T1 - 5 . 3 ± 5.4* - 3 . 0 ± 3.3*
smaller or closely approximated within 2 mm of the pretreatment values regardless of treatment modality. Studies of untreated normal subjects 23 showed intercanine width to be a very stable dimension in male subjects, with only minor decreases (less than 1.0 mm) in female subjects from 9 to 20 years (Table IV). Although in this study, a mean gain of 0.7 mm was observed at final age measured the magnitude of this change was not of clinical significance. The final width in this study (25.9 -4- 2.0 mm) was within that found for normal untreated 23 (24.7 +_ 2.4 ram) and closely approximated that reported for nonextraction and extraction cases by Gardner and Chaconas. 14 The larger and faster rates of decrease after retention reported for the treated groups may be attributed to the older ages of the treated cases. Also, the nature of the two groups may not have been representative of the same population. Final mandibular intercanine width in this study, as well as previous ones, either closely approximated pretreatment dimensions or was slightly smaller regardless of the treatment modality. Intermolar width has been the most frequent measure of posterior arch dimension. Longitudinal studies of untreated cases have shown either slight increases or decreases in this dimension with inc r e a s i n g age. 1°'41-43 Maxilla
The stability of maxillary intermolar width longterm after retention has not been the subject of investigation to the same extent as the mandibular arch. Effects of expansion with R P E and other expansion devices have focused on short-term effects after appliance stabilization or shortly thereafter, zS'3z Long-term follow-up has either been limited to case studies or small sample sizes followed for less than 5 years. 3°-32 H e r o l & 2 reported about half the amount of expansion during treatment to that found in this study (3.9 and 6.7 mm, respectively). After retention, the decrease reported by Herold was slightly larger as
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Table V. Irregularity index m e a s u r e m e n t s
Pretreatment (T1) References This Study Little et al. ~6
Little et al. 38 Glen et al.2° Riedel et al.4° Little and RiedeP 9 Sinclair and Little 23
Sample size RPE MX (56) MD E P (65) C1 I
Mean [ SD 6.7 4.5 7.3 8.1
(5.5) (3.4) (0.6) (0.6)
C1 II
6.7
(3.8)
EP (30) C1 I C1 II NE P (28) C1 1(14) C1 II(14) E 1 (24) (42) 2 (18) NE UN P (65) V M
4.1 3.2 6.0 2.9 3.3 2.4 1.7 2.3 2.5 2.2 2.5 1.8
(2.0) (0.9) (2.7) (1.4) (1.2) (1.4) (0.8) (0.9)
Posttreatment (T2)
Range
1.9-9.7
0.9-1.7 (1.2) (1.4) (0.9)
Mean I SD
Range
Postretention (T3) Mean[
SD
0.8
(0.7)
1.5
(1.5)
0.6 1.7 1.7 1.6
(0.6)
1.4 4.6 4.8 4.5
(1.3)
1.8 1.5 1.9 1.0 0.8 1.0 0.9 0.4 1.5 2.0
(0.6) (0.6) (0.6) (0.9) (0.8) (0.5) (0.5) (0.4) (0.5) (0.1) (0.2)
0.4-4.2
0.3-3.0 (1.1)
4.3 4.5 3.9 2.2 2.6 1.8 0.6 0.7 3.8 2.7 3.1 2.2
(1.9) (2.0) (1.9) (1.6) (4.5) (3.9) (1.7) (1.6) (1.9) (0.3) (0.2)
1.8-8.6
1.3-9.3 (1.6) (1.7) (1.4)
E = Extraction; MD = mandible; UN = untreated normal; NE = nonextraction; MX = maxilla; RPE = palatal P = pooled; F - female; M = male. 1 = One lower incisor extraction; 2 = two lower incisor extractions.
that in this study (1.8 m m as o p p o s e d to 1.2 m m ) (Table IV). T h e L i n d e r - A r o n s o n and L i n d g r e n 3° t r e a t m e n t increase closely approximated that o f this study (5.9 and 6.7 ram, respectively). T h e greater a m o u n t of expansion during t r e a t m e n t and the smaller loss after retention contributed to the larger net gain in this study. Final intermolar width was 5.5 m m larger than its p r e t r e a t m e n t dimension and closely approximated its p o s t t r e a t m e n t dimension (Table II). T h e patients in this study had b e e n out of retention for a m i n i m u m of 5 years, ranging from 5.6 to 20.4 years. H e r o l d ' s cases ~2 had b e e n out of active t r e a t m e n t for approximately 5 years and those of L i n d e r - A r o n s o n ~° for 1.7 years at the time final records were obtained. Thus the differences in the time interval between end of retention and after retention, as well as age at final measurements, m a k e it difficult to c o m p a r e the results of these studies. However, on the basis of the findings for u n t r e a t e d subjects in w h o m intermolar width decreased with aging and t h o s e of patients treated with the Hyrax R P E , in w h o m greater losses were reported, it may be inferred that the better stability was due either to the type of expander used and duration of retention in the present study, or a combination of the two factors.
Range
expander;
Mandible
Mandibular intermolar width stability after retention has b e e n a subject of m a n y studies. In the present study, a m e a n increase during t r e a t m e n t o c c u r r e d (2.0 __+ 3.0 ram) and was similar to that of the nonextraction cases of G a r d n e r and C h a c o n a s 14 (2.0 _+ 1.7 ram) and slightly larger than that of the nonextraction cases of Shapiro 15 (1.4 -+ 1.8 ram). A f t e r retention a small m e a n increase o c c u r r e d (0.3 + 2.2 m m ) in this study as o p p o s e d to a small m e a n decrease o f approximately less than 1.0 m m observed in previous studies. It is important to take into consideration the large s t a n d a r d deviations w h e n interpreting these findings. T h e y were twice the mean, ranging f r o m 1.0 to 1.3 mm, in previous studies and approximately seven times the m e a n in this study. Sinclair and coworkers 23 r e p o r t e d a decrease in intermolar width for u n t r e a t e d n o r m a l subjects observed from ages 9 to 20 years. T h e m e a n intermolar width at age 9 years was 43.7 m m and at age 20 years, 43.5 ram. In the treated subjects of this study, examined f r o m ages 12 to 30 years, and increase o c c u r r e d for this dimension. T h e m e a n intermolar widths at ages 12 and 30 years were 42.8 and 45.3 mm, respectively. T h e interval between m e a s u r e m e n t s was larger and the subjects were m u c h older at the final m e a s u r e m e n t in this study
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than the untreated subjects. The increase observed in this study may be attributed to treatment. Whether the stability of treatment increase in this study was the result of the soft tissue-borne palatal expansion, the prolonged retention period, or a combination of the two factors cannot be determined because a control group was not available. Previous studies with edgewise appliances, however, have reported smaller net gains (0.4 to 1.9 m m ) . 14'15"2° Irregularity Index
Increase in lower incisor irregularity after retention has been reported by several authors. 16'18'2°'38'39'4° The stability of upper incisor irregularity correction long-term after retention has not previously been investigated. The significant improvement in upper incisor alignment observed at the end of treatment in this study was, however, similar to that reported previously for the lower arch (Table V). After retention, however, there were differences between the results of this study for both arches and those previously reported for the lower arch. Postretention incisor irregularity was minimum, less than 1.5 mm for the both upper and lower arches in this study. Pretreatment irregularity in this study was severe for the upper incisors and moderate for the lower incisors. Previous studies 16'38 with similar, as well as less pretreatment irregularity2°'39 showed more severe irregularity postretention irregularity (1.8 to 4.8 mm) than that of this study (1.4_ 1.3 ram) despite similar improvements with treatment, time interval between measurements, and age at postretention evaluation to those of this study (Table V). The extent of incisor irregularity in this study also was less than that reported by Sinclair and Little23 for untreated normal subjects with minimum irregularity at beginning of their observation period and at a much younger age (Table V). The long-term study of Little, Riedel, and Artun 18 on postretention changes in mandibular anterior alignment from age 10 to 20 years and beyond suggested that cases continue to worsen as they age, but with less significant deterioration after age 30. There were two factors that may have contributed to better stability of incisor alignment in this study: the type of expander used and the prolonged retention into mid and late twenties. The wide individual variability observed requires caution in interpretation of the results of this study, as well as previous ones. Also, the lack of
485
control sample with similar characteristics to those of the treated make it impossible to attribute the results solely to treatment effects. ARCH LENGTH Maxilla
Arch length stability in the maxilla has not been examined to the same extent as that in the mandibular arch. In the two short-term studies35'36 that examined this parameter, the methods of measurement differed from that of this study. Adkins and coworkers,35 reported a decrease for this dimension of 0.4 (0.5) mm. In the current study, a mean increase of 3.3 mm was followed by a decrease of 3.2 mm at postretention evaluation, with large individual variability among the subjects (Table VI). Final arch length was similar to its pretreatment dimension. Mandible
Mandibular arch length during treatment either decreased or remained approximately the same as its pretreatment dimensions, a4'15"2°'39 After retention further decreases were observed that resulted in final arch length being smaller than its pretreatment measurement (Table VI). Similar direction of changes were also reported for untreated normal persons at a much younger age23 (Table VI). In the present study, the mean mandibular arch length increase during treatment was 3.2 mm. A large individual variability, however, prevailed. After retention the mean decrease was similar in magnitude to those observed in previous studies. 14'15"z°'39 Although final arch length in the current study was slightly larger than its pretreatment dimension, it was neither statistically nor clinically significant (Table VII). ARCH PERIMETER
The magnitude of change in arch perimeter with transverse expansion of the maxillary dental arch has not been evaluated to the same degree as in other arch dimensions. The short-term studies of Adkins et alY and Berlocher et al. 36 reported an increase in maxillary arch perimeter during treatment. The treatment mean increase reported by Adkins et al. was similar to that of this study (4.7 and 4.1 mm). In this study, arch perimeter decreased after retention 0.6 mm in the mandible and increased 1.6 mm for the maxilla with a large individual
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Table VI. Measurement change for arch length
T2>T1 Sources This study
G a r d n e r and Chaconas 14 Glenn et al. 2° Shapiro 18 Riedel et al. 4°
Sinclair and Little 23
Treatment~sample size R P E (56) MX MD E (29) N E (74) N E (28) E (48) N E (22) E (42) 1 (24) 2 (18) U N (65) P F M
T2>T3
T3>TI
Mean
SD
Mean
SD
Mean
SD
3.3 3.2 - 6.4 -1.2 0.2 -8.3 - 0.7
(5.9) (6.4) (2.2) (1.4)
- 3.2 -2.4 - 0.8 -0.9 - 2.4 -3.1 - 2.6
(4.4) (2.3) (0.8) (0.8)
0.0 0.6 - 7.3 -2.1 - 2.2 - 11.4 - 3.2
(7.6) (5.9) (1.9) (1.4) (5.7) (2,6)
-2.3 -2.4 -1.9 - 1.6 -2.2
(1.9) (4.1)
-2.6 -7.7 -4.8
(1.8)
-0.2 -5.2 -2.8 - 3.5 -2.2
(3.7) (2.8) (2.8) (4.1) (1.6) (1.7)
(4.5) (1.7)
(2.2) (1.4)
E = Extraction; NE = nonextraction; UN = untreated; MD = mandible; MX = maxilla; F = female; M = male. 1 = O n e lower incisor; 2 = two lower incisor.
Table VII. Arch length measurements Sources This study
G a r d n e r and Chaconas ~4
Sinclair and Little ~3
Treatment/sample size
Pretreatment (T1)
RPE (56) MX MD E (29) NE (74) CII (14) CIII (14) UN (65)
I
Posttreatment (T2)
Postretention (T3)
71.3 (6.3) 62.3 (5.0) 18.5 (1.4) 23.7 (1.2) 61.5 (3.1) 60.0 (3.6) 60.2 (3.4)
68.4 (7.9) 59.8 (4.5) 17.6 (1.1) 22.7 (1.3) 59.1 (3.6) 57.8 (3.5) 58.2 (3.1)
68.3 (5.0) 59.1 (6.2) 25.0 (2.1) 24.9 (1.7) 61.5 (3.7) 60.0 (3.6) 63.1 (6.2)
NE = Nonextraction; E = extraction; UN = u n t r e a t e d normal; MD = mandible; MX = maxilla; P = pooled.
variability present. Although final arch perimeter was longer than its pretreatment dimension, it was neither statistically nor clinically significant (Table III). The relationship between the direction of change in arch length and perimeter during treatment to postretention stability of the incisors was not examined in this study. Mandibular incisor irregularity after retention was, however, minimum compared with the findings of previous studies that examined patients treated with edgewise appliances, 16'2°'37-39as well as untreated normal subjects. 23Similar assessments have not been conducted for the maxillary arch. Judging by the lower values for incisor irregularity found in this study after retention, the treatment increase in arch length and
perimeter during treatment, do not appear to have been influential. However, this needs further investigation. CONCLUSIONS
1. Maxillary intercanine width and maxillary and mandibular intermolar widths after retention closely approximated the P0streat ment dimensions and were larger than their pretreatment dimensions. 2. Mandibular intercanine width, arch length, and arch perimeter after retention closely approximated pretreatment dimensions. 3. Incisor irregularity after retention was minimum for both maxillary and mandibular arch.
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W e express our appreciation to Dr. A n d r e w Haas for his willing cooperation in supplying the material from his office. W e would also like to acknowledge Joann Pianelli and Irene Williams for their effort i n recalling and collecting the long-term records used in the study. Without their cooperation, this work could not have been accomplished. REFERENCES 1. Ricketts RM. Bioprogressive therapy as an answer to orthodontic needs. AM J ORTHOD 1976;70:241-68. 2. Nance HN. The limitations of orthodontic treatment. Diagnosis and treatment in the permanent dentition. AM J ORTHOD ORAL SURG 1947;33:253-301. 3. Arnold M. A study of changes of the mandibular intercanine and intermolar widths during orthodontic treatment and following a post-retention period of 5 or more years. [Master's thesis.] Seattle: University of Washington, School of Dentistry, 1963. 4. Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. AM J ORTHOD 1970;57:219-55. 5. Haas AJ. Long-term post-treatment evaluation of rapid palatal expansion. Angle Orthod 1980;50:189-218. 6. Tweed CJ. Indications for the extraction of teeth in orthodontic procedures. AM J ORTHOD ORAL SURG 1944;30: 405-28. 7. Walter DC. Changes in the form and dimensions of dental arches resulting from orthodontic treatment. Angle Orthod 1953;23:3-18. 8. Walter DC. Comparative changes in mandibular canine and first molar widths. Angle Orthod 1962;32:232-41. 9. Riedel RA. A review of the retention problem. Angle Orthod 1960;30:179-99. 10. Moorrees CFA. The dentition of the growing child. Cambridge: Harvard University Press, 1959. 11. Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening of the midpalatal suture. Angle Orthod 1961;31:73-90. 12. Dona A. An analysis of dental casts of patients made before and after orthodontic treatment. [Master's thesis.] Seattle: University of Washington, School of Dentistry, 1962. 13. Gallerano R. Mandibular anterior crowding-a post-retention study. [Master's thesis.] Seattle: University of Washington, School of Dentistry, 1976. 14. Gardner SD, Chaconas SJ. Post-treatment and post-retention changes following orthodontic therapy. Angle Orthod 1976;46:151-61. 15. Shapiro PA. Mandibular dental arch form and dimension. AM J ORTHOD 1974;66:58-70. 16. Little RM, Wallen TR, Riedel RA. Stability and relapse of mandibular anterior alignment-first premolar cases treated by traditional edgewise orthodontics. AM J ORTHOD 1981; 80:349-64. 17. Sandusky WC. A long-term post-retention study of Tweed extraction treatment. [Master's thesis.] Memphis: University of Tennessee, 1983. 18. Little RM, Riedel RA, Artun J. An evaluation of changes in mandibular anterior alignment from 10 to 20 years postretention. AM J ORTHOD DENTOFAC ORTHOP 1988;93:423-8.
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19. Mew J. Relapse following maxillary expansion. A study of 25 consecutive cases. AM J ORTHOD 1983;83:56-61. 20. Glen G, Sinclair PM, Alexander RG. Nonextraction orthodontic therapy: posttreatment dental and skeletal stability. AM J ORTHOD DENTOFAC ORTHOP 1987;92:321-8. 21. Uhde MD, Sadowsky C, BeGole EA. Long-term stability of dental relations after orthodontic treatment. Angle Orthod 1983;53:240-52. 22. Shields TM, Little RM, Chapko MK. Stability and relapse of mandibular anterior alignment-a cephalometric appraisal of first premolar extraction cases treated by traditional edgewise orthodontics. AM J ORTHOD 1985;87:27-38. 23. Sinclair PM, Little RM. Maturation of untreated normal occlusions. AM J ORTHOD 1983;88:146-56. 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. Mossaz-Joelson K, Mossaz CF. Slow maxillary expansion: a comparison between banded and bonded appliances. Eur J Orthod 1989;11:67-76. 26. Casto CM. Slow maxillary expansion: a clinical study of the skeletal and dental response during and following the application of a low magnitude force. [Master's thesis.] Seattle: University of Washington, School of Dentistry, 1979. 27. Cotton LA. Slow maxillary expansion: skeletal versus dental response to low magnitude force in Macaca mulatta. AM J ORTHOD 1978;73:1-23. 28. Wertz RA. Skeletal and dental changes accompanying rapid maxillary suture opening. AM J ORTHOD 1980;58:41-66. 29. Krebs AA. Rapid expansion of the midpalatal suture by a fixed appliance. An implant study over a 7-year period. Trans Eur Orthod Sco 1964:141. 30. Linder-Aronson A, Lindgren J. The skeletal and dental effects of rapid maxillary expansion. Br J Orthod 1979;6: 25-9. 31. Stockfish H. Rapid expansion of the maxilla-success and relapse. Trans Eur Orthod Soc 1969:469-81. 32. Herold JS. Maxillary expansion: a retrospective study of three methods of expansion and their long-term sequelae. Br J Orthod 1989;16:195-200. 33. Krebs AA. Expansion of the midpalatal suture studied by means of metallic implants. Eur Orthod Soc Rep 1958;34: 163-71. 34. Zimring JF, Isaacson RJ. Forces produced by rapid maxillary expansion. III. Forces present during retention. Angle Orthod 1965;35:178-86. 35. Berlocher WC, Mueller BH, Tinaoff N. The effect of maxillary palatal expansion on the primary dental circumference. Pediatr Dent 1980;2:27-30. 36. Adkins MD, Nanda RS, Currier GF. Arch perimeter changes on rapid palatal expansion. AM J ORTHOD 1965; 35:178-86. 37. Little RM. The irregularity index: a quantitative score of mandibular anterior alignment. AM J ORTHOD 1975;68:55463. 38. Little RM, Riedel RA, Engst ED. Serial extraction of first premolars-post-retention evaluation of stability and relapse. Angle Orthod 1990;60:255-62. 39. Little RM, Riedel RA. Postretention evaluation of stability and relapse--mandibular arches with generalized spacing. AM J ORTHOD DENTOFAC ORTHOP 1989;95:37-41.
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40. Riedel RA, Little RM, Bui TD. Mandibular incisor extraction-post-retention evaluation of stability and relapse. Angle Orthod 1992;62:103-16. 41. Barrow GV, White JR. Developmental changes of the maxillary and mandibular dental arches. Angle Orthod 1952;22: 41-6. 42. Brown VP, Daugarrd-Jensen I. Changes in the dentition from the early teens to the early twenties. Acta Odont Scan 1951;9:177-92.
American Journal of Orthodontics and Dentofacial Orthopedics November 1995
43. Cryer S. Lower arch changes during the early teens. Trans Eur Orthod Soc 1966;87:99-107. Reprint requests to: Dr. Maria O'Reilly University of Pittsburgh School of Dental Medicine Department of Orthodontics 3501 Terrace St. Pittsburgh, PA 15261
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DIP, a
Maria T. O'Reilly, DMD, MDS, PhD, b and John M. Close, MA, PMS °
Pittsburgh, Pa. Previous studies on long-term stability of orthodontic treatment primarily have focused on the stability of the lower arch treated with edgewise appliances. The aim of this study was to evaluate the long-term stability of the upper and the lower dental arches of patients treated with a rapid palatal expander. The sample comprised of 165 dental casts randomly selected from patients who had been out of retention for 8 to 10 years at a mean age of 30 years. Measurements were made directly on dental casts obtained at the three time intervals: before treatment, after treatment, and after retention. Differences over time between the upper and the lower dental arches and between intervals were analyzed by a two-way multivariate analysis of variance (MANOVA) and post hoc Bonferroni t tests. Differences between after treatment and after retention were statistically significant (P < 0.006) for all except lower intermolar width. However, only for lower and upper arch lengths and perimeters were the differences greater than 2.0 mm. Treatment with the rapid palatal expander presented good stability for upper intercanine width, upper and lower intermolar widths and incisor irregularity. Lower intercanine, arch length, and perimeter presented poor stability. (AM J ORTHOD DENTOFACORTHOP 1995;108:478-88.)
Many theories have been postulated regarding the cause of relapse. Orthodontists have proposed treatment strategies involving concepts/philosophies as to what enhance stability, such as overcorrection of the malocclusion, 1 avoidance of excessive arch expansion by extraction, 2'3 expansion with palatal expander, 4'~ placing teeth over basal bone, 3"~ prolonged retention, TM maintenance of arch form during treatment, 9,a° and type of mechanotherapy. 4'5'11 Previous studies have often noted a decrease in arch length and width, while also showing that increases in incisor crowding, overbite, and overjet occur after retention? 22' Attempts to correlate observed postretention changes with pretreatment and posttreatment conditions have failed to provide useful associations. '''22 Untreated normal subjects also have been examined to determine whether changes seen during development differ from those in treated subjects. 23 Expansion through maxillary suture widening by rapid maxillary expanders has been claimed to promote stability after retention. Stability has been attributed to the skeletal component of arch en~Assistant Professor, Department of Orthodontics, Baath University. bAssociate Professor, Department of Orthodontics, School of Dental Medicine, University of Pittsburgh. CAssistant Professor, Division of Learning Resources, School of Dental Medicine, University of Pittsburgh. Copyright © 1995 by the American Association of Orthodontists. 0889-5406/95/$5.00 + 0 8/1/55445
478
largement obtained by the expansion appliance as opposed to dental expansion as a result of edgewise appliance mechanotherapy. Studies on immediate treatment effects of rapid palatal expansion have reported increases in arch width as a result of combined skeletal and dental expansion. Short-term follow-up has indicated a rebound effect of the dental component, yet a relative stability of the skeletal aspect of the expansion.4.5.11,24-28 The implant studies by Krebs 29 during a 7-year observation period found a substantial reduction in dental arch width after discontinuation of retention which continued for as long as 4 to 5 years. The 5-year posttreatment study by LinderAronson and Lindgren 3° noted that only 45% of the initially achieved expansion was maintained. These findings concur with those of Stockfish, 31 who found 50% of relapse within 3 to 5 years after retention. Herold 32 reported that the increase in intercanine and intermolar widths observed during treatment was followed by relapse, with a residual increase of 2.1 mm (62.5%) and 3.1 mm (56.4%), respectively. Linder-Aronson and Lindgren 3° found a residual expansion of 38% and 59% for intercanine and intermolar widths, respectively, over a period of observation similar to that of Herold? 2 Midpalatal suture opening can be accomplished in both children and adults, but with advancing maturity the rigidity of the skeletal components
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479
Table h Sample characteristics m e a n and range for age (year-month) and gender
Males (16) Females (39) Total (55)
Pretreatment (T1)
Posttreatment (T2)
End of retention
13.6 ± 3.1 (8.1-19.3) 12.6 ± 2.2 (8.4-16.7) 12.1 ± 2.6 (8.4-19.3)
16.2 ± 2.8 (12.1-20.7) 15.4 +_ 2.5 (10.6-20.5) 15.7 + 2.6 (10.6-20.7)
22.7 ± 3.8 (15.5-30.9) 21:1 ± 2.8 (17.1-30.2) 22.0 _ 4.0 (15.5-30.1)
limits the extent and the stability of the expansion, which may involve fracturing of the bony interdigitations.2S, 33-35 Differences in immediate treatment outcome and stability also have been attributed to appliance design and rate of expansion. H a a s 5 maintains that rapid palatal expansion with a soft tissue-borne appliance is superior to a totally tooth borne palatal expander (i.e., Hyrax). H e believes that the former delivers a m o r e parallel expansive force on the two maxillary segments that is distributed evenly to both the teeth and alveolar processes. Further, he argues that in older patients where the suture usually does not open, the force delivered to the palatal vault by the acrylic sections of the appliance tends to compress the palatine arteries. This compression, in turn, stimulates the connective tissue surrounding these vessels to differentiate into osteoclasts that serve to resorb underlying bone and thus protect the arteries from injury. In so doing, the vault is "hollowed out" and a true apical base expansion is induced. T M According to Haas, the p e r m a n e n t widening of the maxillary palatal arch and base also allows the mandibular teeth to upright and expand. A review of the literature thus supports the contention that the rapid palatal expander (RPE) device, in addition to its other effects, can provide additional space in the arch to relieve crowding. Studies on long-term stability of orthodontic treatment 3'7"12'14-~s'2°-22 have focused primarily on the mandibular arch and the strength of association between dental and cephalometric p a r a m e t e r s that may be used as predictive of postretention changes. In these studies, the m e c h a n o t h e r a p y used was reported to be edgewise appliances. The purpose of this study therefore was to assess the long-term changes of maxillary and mandibular dental arch m e a s u r e m e n t s in patients who were treated with the soft tissue-borne palatal expander and edgewise appliances. Changes in intercanine width, intermolar width, arch length,
I
I Postretention I (T3)
Duration of retention (lower)
Years postretention
6.4 _+ 2.3 (5.0-10.1) 6.7 ± 2.3 (5.1-15.9) 6.6 ± 2.3 (5.0-15.9)
8.1 ± 5.4 (5.0-20.4) 7.9 ± 3.1 (5.0-16.6) 8 . 0 2 3.1 (5.6-20.4)
31.5 ± 7.5 (20.8-51.1) 29.7 +- 3.91 (21.5-39.7) 30.2 ± 5.3 (20.8-51.1)
arch perimeter, and Irregularity Index were examined. METHODS AND MATERIALS The sample consisted of 165 dental casts of 55 patients, 16 males and 39 females. They were selected randomly from records of patients who had been treated with a soft tissue-borne RPE and edgewise appliances at Andrew Haas' private practice in Cuyahoga Falls, Ohio, between 1960 and 1980. To be included in the study, dental casts at pretreatment and posttreatment had to be available, and all permanent teeth had to be present (except third molars). Of 400 patients, 60 were contacted by two office staff members (I.W. and J.P.) for obtaining the postretention records. Two patients could not be reached, and three were eliminated because of missing anterior teeth (Table I). The mean age at treatment completion and at end of retention was 15.7 and 22 years, respectively. At the time postretention records were obtained, the mean age was 30 years. The incisor relationship was Class I in 40 patients, Class II in 9, and edge-to-edge in 6. Of the 55 patients, two patients had extractions , maxillary right first premolar and mandibular first premolars. Clinical management The appliance was activated 1 mm (four turns) and 0.25 mm (quarter turn) each 5 minutes for 15 minutes at the time the appliance was placed. Thereafter it was activated a quarter turn in the morning and a quarter turn in the evening. The patients were seen at weekly intervals and during each visit, the screw was extended an additional 1 to 1.5 mm (4 to 6 turns). The desired expansion was achieved when the mandibular arch was completely contained by the maxillary arch, the screw being opened at least 11 mm and up to 14 mm. At that time, the appliance was stabilized with brass wire and maintained in place for a minimum of 3 months. On the same day the expander was removed, a removable acrylic plate was inserted and worn throughout the remainder of active treatment. Retention protocol The maxillary retainer consisted of a removable appliance that was worn for 2 years after treatment, and the
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Fig, 1. Measurements: A, Arch width; B, arch perimeter; C, arch length; and D, Irregularity Index.
mandibular retainer was a fixed lingual arch from canine to canine worn for approximately 61/2 years.
displacement of adjacent anatomic contact points of the six anterior teeth (Fig. 1, D).
Methods of measurements
Statistical analysis
The following measurements were made directly on the dental casts (Fig. 1):
To assess whether the changes that occurred over time were different between maxillary and the mandibular measurements, a two-way multivariate analysis of variance (MANOVA) for a within-subject design was performed. Post hoc Bonferroni t tests were used for pairwise comparisons to test for differences between each of the intervals.
1. 2. 3. 4. 5.
Maxillary and mandibular Maxillary and mandibular Maxillary and mandibular Maxillary and mandibular Irregularity Index 37
intercanine width intermolar width arch perimeter 36 arch length 2
The intercanine width was measured as the distance between cusp tips and the intermolar width as the distance between mesiobuccal cusps tips bilaterally (Fig. 1,A). All measurements were made with a two-pointed caliper approximated to the nearest 0.01 ram. Before making the measurements, the cusp tips of the canines and the mesial buccal cusps of the first molars for each patient were marked simultaneously with a No. 0.3 pencil. In cases where a facet existed, the cusp tip was estimated. Measurements were made randomly for all the patients without knowledge as to the phase of treatment. Arch perimeter was measured by finding the sum of the lengths of segments connecting the mesial contact points of first molars and premolars, the premolar mesial contact point and that of the canine and mesial contact point of the canine to that of the lateral incisor for both sides of arch (Fig. 1, B). Mandibular and maxillary arch lengths were measured as the summed inside measurement from first permanent molars to the central incisor contact point (Fig. 1, C). The Irregularity Index was the summed
RESULTS M e a s u r e m e n t e r r o r was e v a l u a t e d by r a n d o m l y selecting 15 casts, e a c h m e a s u r e d twice on s e p a r a t e occasions. T h e s t a n d a r d d e v i a t i o n s w e r e f o u n d to b e in t h e 0.07 to 0.17 m m for all m e a s u r e m e n t s . T h e M A N O V A r e s u l t e d in significant (p < .001) m a i n effects for site (maxilla versus m a n d i b l e ) a n d t i m e ( p r e t r e a t m e n t , p o s t t r e a t m e n t ) for all five dep e n d e n t variables. T h e i n t e r a c t i o n b e t w e e n site a n d t i m e was significant for f o u r of t h e five d e p e n d e n t v a r i a b l e s ( p < 0.02). T h e i n t e r a c t i o n effect for arch l e n g t h was n o t significant ( p = 0.69). Post hoc c o m p a r i sons using B o n f e r r o n i t tests w e r e as follows ( T a b l e s II a n d III): Intercanine width Maxillary i n t e r c a n i n e w i d t h i n c r e a s e d 3.6 +_ 3.0 m m f r o m b e f o r e t r e a t m e n t to a f t e r t r e a t m e n t a n d
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Table II. Mean and standard deviations of measurements (mm)
Variable
Pretreatment T1
Posttreatment T2
Postretention T3
Mean ± SD
Mean +_ SD
Mean ± SD
31.4 ± 3.0 25.5 +_ 2.4
35.0 + 2.2 27.0 ± 1.8
34.1 _+ 2.2 25.9 ± 2.0
46.5 ± 4.6 42.8 _+ 3.4
53.4 -- 3.0 44.9 +_ 3.0
52.1 + 3.0 45.3 _+ 3.1
70.8 ± 5.0 62.9 +- 4.4
74.9 -+ 6.8 65.6 ± 4.7
72.4 + 6.1 62.3 -+ 5.2
68.4 ± 5,0 59.2 _+ 6,3
71.6 ± 6.4 62.3 ± 5.0
68.4 -+ 7.9 59.8 ± 4.6
6.7 ± 5.5 4.5 +- 3.4
0.8 ± 0.7 0.6 ± 0.6
1.5 ± 1.5 1.4 ± 1.3
Intercanine width U L
Intermolar width U L
Arch perimeter U L
Arch length U L
Irregularity index U L
decreased 0.8 + 1.3 mm from after treatment to after retention. This resulted in a net increase of 2.7 -+ 2.8 mm. In the mandible the increase was 1.8 + 1.7 m m at the end of treatment. At postretention there was a decrease of 1.1 +_ 0.9 mm, leaving a net increase of 0.7 +_ 1.7 mm.
Intermolar width The increase for the maxilla was 6.7 +_ 4.1 mm during treatment and the decrease was 1.2 + 1.7 mm after retention. This resulted in a net increase of 5.5 _+ 4.0 mm. For the mandible, there was an increase of 2.0 +_ 3.0 mm during treatment, followed by an increase of 0.3 _+ 2.2 mm after retention. The net increase was 2.3 +_ 2.7 ram.
Irregularity index The mean pretreatment value was 6 . 7 _ 5.5 mm for the maxilla and 4.5 +_ 3.4 mm for the mandible. In the maxilla incisor alignment was improved greatly during treatment with the mean decrease from before treatment to after treatment being 5.8 _ 5.5 mm. During the postretention period there was an increase of 0.6 + 1.3 mm, leaving a net improvement of 5.3 + 5.4 mm. For the mandible, there also was a decrease from before treatment to after treatment of 3.9 +_ 3.3 mm. During the postretention period, an increase of 0.8 _+ 1.2 mm occurred leaving a net improvement of 3.0 _ 3.3 ram.
Arch perimeter
DISCUSSION
The mean increase in the maxilla during treatment was 4.1 _+ 6.6 mm followed by a decrease after retention of 2.5 + 3.8 mm, resulting in a net increase of 1.6 _+ 5.4 ram, which was not statistically significant. The mean increase for the mandible was 2.7 _+ 4.0 mm and the mean decrease was 3.5 +_ 1.8 mm. The net decrease was 0.6 +_ 4.1 mm, which was also not statistically significant.
Rapid palatal expansion is an accepted procedure to relieve deficiencies in arch perimeter and/or length. With the increasing emphasis on nonextraction therapy, the procedure has gained popularity because of the relief of crowding it provides. Rapid palatal expansion compensates for arch deficiencies through transverse expansion of the palate and dental arches. The principal objective of this study was to determine the long-term stability of treatment with the soft tissue R P E and edgewise appliances.
Arch length Arch length changed similarly for both arches. The maxilla increased 3.3 _+ 5.9 mm during treatment and decreased 3.2 _+ 4.4 after retention, which resulted in no treatment gain. The mandible measured 3.2 + 6.4 mm and decreased 2.4 ___ 2.3 mm with a net increase of 0.6 _+ 5.9 mm also not statistically significant.
Intercanine width Although studies on long-term stability of intercanine width in the lower arch have been numerous, the problem of stability of upper intercanine width has been addressed with less frequency.
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Table IlL Mean differences and standard deviations of measurements Intercanine width T2 > T,
T3 > T2
Intermolar width
] T3 > T 1
T2 > T1
T3 > T2
T3 > T 1
T2 > T1
T3>T2
T3 > T 1
6.7 _+ 4.1" 2.0 _+ 3.0*
- 1 . 2 --- 1.7" 0.3 -+ 2.2
5.5 _+ 4.0* 2.3 _+ 2.7*
4.1 _ 6.6* 2.7 _+ 4.0*
- 2 . 5 _+ 3.8* - 3 . 5 -+ 1.8"
1.6 -+ 5.4 - 0 . 6 - 4.1
T3 > T2 = Postretention/posttreatment;
T3 > r~ =
r
Maxilla Mandible
3.6 _+ 3.0* 1.8 -_ 1.7'
- 0 . 8 _+ 1.3" - 1 . 1 _+ 0.9*
2.7 -+ 2.8* 0.7 -+ 1.7"
Arch perimeter
*p < 0.006. ( - ) = decrease; ( + ) = increase; Te > T1 = Posttreatment/Pretreatment; Postretention/Pretreatment (net change).
Table IV. Intercanin, and intermolar width measurement changes Intercanine width References
Treatment~sample size
1"2>1"1
T3 > T2
Intermolar width T3 > T 1
7"2 > r l
7"3 > T2
- 0 . 8 (1.3) - i . 8 (1.7)
2.7 (2.8)
6.7 (4.1)
- 1 . 2 (1.7)
T3 > T1
Maxilla This study U h d e et al. 21 Herold 32 Linder-Aronson and Lindgren 3°
5.5 (4.0)
R P E (56) E (27) NE (45) R P E (19) R P E (17)
3.6 (3.0)
3.2 (2.7) 2.1 (1.6)
- 1 . 3 (1.0) - 1 . 3 (1.1)
1.9 (2.3) 0.8 (1.2)
3.9 (3.3) 5.9 (3.5)
R P E (56) E (29)
1.8 (1.7) 1.9 (2.1)
- 1 . 1 (0.9) - 1 . 1 (1.1)
0.7 (1.7) 0.7 (1.9)
2.0 (3.0) - 1 . 4 (1.5)
0.3 (2.2) - 0 . 0 3 (1.3)
2.4 (2.7) - 1 . 4 (1.7)
2.0 0.9 -1.0 1.4 0.5 0.8
0.0 -0.5 -1.1 -0.5 -0.3 -1.0
(1.6) (1.3) (1.5) (1.4)
1.9 (1.8) 0.4 - 2 . 1 (2.1) 1.0 (1.9) 0.2 -0.2
- 1.3
(1.6)
- 1.0
(1.9)
- 1.5 ( 1 . 8 ) - 1.3
(1.8)
-1.8 (1.6) -2.2 (2.4)
2.1 (3.4) 3.5 (2.7)
Mandible This study G a r d n e r and Chaconas TM Glen et al. 2° Shapiro Is Riedel et al. 4° U h d e et al. ~ Sinclair and Little 23
NE (74) NE (28) E (58) NE ( 2 2 ) E1 (24) E2 (18) E (27) N E (45) U N (65) F M
1.2 0.5 1.7 0.7 - 1.6 -5.2
- 0.3 - 0.08 -0.5
(1.6) (1.8) (2.3) (2.2) (3.1)
- 0 . 7 (1.1) - 1.0 - 1 . 9 (1.3) - 1 . 4 (1.4) - 1.1 (0.95) - 1 . 4 (1.2) - 2 . 1 (1.3) - 2 . 3 (1.7) - 0.44 - 0.7 (0.78) - 0 . 1 6 (0.9)
0.5 (1.7) - 0.4 - 0 . 3 (1.8) - 0 . 7 (1.9) -2.7 -6.6
- 0.7
(1.7) (2.3) (1.8) (1.4) (2.1)
-0.5 - 0 . 0 4 (1.3) - 0 . 7 (1.7)
(1.1)
-0.1 - 0 . 4 1 (0.8) - 0 . 7 (1.7)
-0.1
T 2 > T 1 = T r e a t m e n t change; /12 > T3 = posttreatment change; T3 > T 1 = treatment gain. E = Extraction; N E = nonextraction; UN = untreated normal; F = female; M = male.
Maxilla
Herold's long-term study of stability of intercanine width treated with the Hyrax palatal expander 32 reported a mean treatment increase similar to that of this study (3.2 and 3.6 mm, respectively). Linder-Aronson and Lindgren, 3° also using a Hyrax appliance, reported a smaller mean increase (2.1 ram) than that of Herold's study and this study. At postretention intercanine width decreased, however, in this study its magnitude was smaller (0.8 mm) than that reported by Herold 32 and Linder-Aronson and Lindgren 3° (1.3 mm) (Table IV). The differences in final intercanine width be-
tween this study and those reported by the studies of Herold 32 and Linder-Aronson and Lindgren 3° were in the magnitude of the loss at postretention. In this study, intercanine width experienced the largest increase during treatment but, also the smallest decrease in post-retention. The mean net gain in this study was double that reported by Herold 32 and triple that reported by LinderAronson and Lindgren 3° (Table IV). Considering that the patients in this study had been out of retention for a much longer period, ranging from 5.6 to 20.4 years, and were at least 10 years older than those of Herold's 32 and Linder-Aronson and Lindgren's, 3° a greater loss would have been ex-
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Arch length 7"2>7"1 3.3 +- 5.9* 3.2 ± 6.4*
I
7"3>7"2 - 3 . 2 -+ 4.4* - 2 . 4 ± 2.3*
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Irregularity Index I
T3 > T1
7"2 > T1
7"3 >7"2
0.6 -+ 7.6* 0.6 ± 5.9*
- 5 . 8 +-5.5* - 3 . 9 ± 3.3*
0.6 ± 1.3" 0.8 ± 1.2"
pected in this study. Results in untreated normal subjects 23 reported a loss in intercanine dimension of 0.7 mm from 13.6 to 20.6 years, approximately three times less than the gain reported in this study. Final intercanine width closely approximated the posttreatment dimension in this study. Therefore treatment with the soft tissue-borne palatal expander provided better stability than the Hyrax. Mandible
Studies on long-term stability of intercanine width changes in the lower arch during treatment have shown that regardless of the direction of change induced by the treatment, often a decrease occurred after retention. The decrease after retention resulted in final intercanine width that was either smaller than the pretreatment value or closely approximated it. Treatment modality (extractions versus expansion) was not related to the magnitude of the changes induced by treatment. 14-16,2o,21.38,39,4o In this study, a mean increase in intercanine width (1.8 _+ 1.7 ram) was observed at the posttreatment mean age of 15.7 _+ 2.6 years (Table IV). This increase was very similar to those reported for extraction cases by Gardner and Chaconas 14 and Shapiro is (1.2 and 1.7 mm, respectively) and double that reported by Glenn, Sinclair, and Alexander 2° for nonextraction cases (0.5 mm). The mean increase during treatment in this study was followed by a decrease after retention (1.1 _ 9.2) at age 30.2 _+ 5.3 years. The extent of this decrease closely approximated (within 1.0 mm) those reported for premolar extraction cases, 14 and nonextraction treated cases, 2° and was slightly less than that found by the extraction and nonextraction cases of Shapiro ~5 (1.4 and 1.9 ram, respectively) (Table IV). The net gain of 0.7 +_ 1.7 mm in this study was similar to the Gardner and Chaconas 14 extraction (0.7 _ 1.9 mm) and nonextraction (0.5 _+ 1.7 ram) cases. Postretention intercanine width was either
[
7"3 > T1 - 5 . 3 ± 5.4* - 3 . 0 ± 3.3*
smaller or closely approximated within 2 mm of the pretreatment values regardless of treatment modality. Studies of untreated normal subjects 23 showed intercanine width to be a very stable dimension in male subjects, with only minor decreases (less than 1.0 mm) in female subjects from 9 to 20 years (Table IV). Although in this study, a mean gain of 0.7 mm was observed at final age measured the magnitude of this change was not of clinical significance. The final width in this study (25.9 -4- 2.0 mm) was within that found for normal untreated 23 (24.7 +_ 2.4 ram) and closely approximated that reported for nonextraction and extraction cases by Gardner and Chaconas. 14 The larger and faster rates of decrease after retention reported for the treated groups may be attributed to the older ages of the treated cases. Also, the nature of the two groups may not have been representative of the same population. Final mandibular intercanine width in this study, as well as previous ones, either closely approximated pretreatment dimensions or was slightly smaller regardless of the treatment modality. Intermolar width has been the most frequent measure of posterior arch dimension. Longitudinal studies of untreated cases have shown either slight increases or decreases in this dimension with inc r e a s i n g age. 1°'41-43 Maxilla
The stability of maxillary intermolar width longterm after retention has not been the subject of investigation to the same extent as the mandibular arch. Effects of expansion with R P E and other expansion devices have focused on short-term effects after appliance stabilization or shortly thereafter, zS'3z Long-term follow-up has either been limited to case studies or small sample sizes followed for less than 5 years. 3°-32 H e r o l & 2 reported about half the amount of expansion during treatment to that found in this study (3.9 and 6.7 mm, respectively). After retention, the decrease reported by Herold was slightly larger as
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Close
Table V. Irregularity index m e a s u r e m e n t s
Pretreatment (T1) References This Study Little et al. ~6
Little et al. 38 Glen et al.2° Riedel et al.4° Little and RiedeP 9 Sinclair and Little 23
Sample size RPE MX (56) MD E P (65) C1 I
Mean [ SD 6.7 4.5 7.3 8.1
(5.5) (3.4) (0.6) (0.6)
C1 II
6.7
(3.8)
EP (30) C1 I C1 II NE P (28) C1 1(14) C1 II(14) E 1 (24) (42) 2 (18) NE UN P (65) V M
4.1 3.2 6.0 2.9 3.3 2.4 1.7 2.3 2.5 2.2 2.5 1.8
(2.0) (0.9) (2.7) (1.4) (1.2) (1.4) (0.8) (0.9)
Posttreatment (T2)
Range
1.9-9.7
0.9-1.7 (1.2) (1.4) (0.9)
Mean I SD
Range
Postretention (T3) Mean[
SD
0.8
(0.7)
1.5
(1.5)
0.6 1.7 1.7 1.6
(0.6)
1.4 4.6 4.8 4.5
(1.3)
1.8 1.5 1.9 1.0 0.8 1.0 0.9 0.4 1.5 2.0
(0.6) (0.6) (0.6) (0.9) (0.8) (0.5) (0.5) (0.4) (0.5) (0.1) (0.2)
0.4-4.2
0.3-3.0 (1.1)
4.3 4.5 3.9 2.2 2.6 1.8 0.6 0.7 3.8 2.7 3.1 2.2
(1.9) (2.0) (1.9) (1.6) (4.5) (3.9) (1.7) (1.6) (1.9) (0.3) (0.2)
1.8-8.6
1.3-9.3 (1.6) (1.7) (1.4)
E = Extraction; MD = mandible; UN = untreated normal; NE = nonextraction; MX = maxilla; RPE = palatal P = pooled; F - female; M = male. 1 = One lower incisor extraction; 2 = two lower incisor extractions.
that in this study (1.8 m m as o p p o s e d to 1.2 m m ) (Table IV). T h e L i n d e r - A r o n s o n and L i n d g r e n 3° t r e a t m e n t increase closely approximated that o f this study (5.9 and 6.7 ram, respectively). T h e greater a m o u n t of expansion during t r e a t m e n t and the smaller loss after retention contributed to the larger net gain in this study. Final intermolar width was 5.5 m m larger than its p r e t r e a t m e n t dimension and closely approximated its p o s t t r e a t m e n t dimension (Table II). T h e patients in this study had b e e n out of retention for a m i n i m u m of 5 years, ranging from 5.6 to 20.4 years. H e r o l d ' s cases ~2 had b e e n out of active t r e a t m e n t for approximately 5 years and those of L i n d e r - A r o n s o n ~° for 1.7 years at the time final records were obtained. Thus the differences in the time interval between end of retention and after retention, as well as age at final measurements, m a k e it difficult to c o m p a r e the results of these studies. However, on the basis of the findings for u n t r e a t e d subjects in w h o m intermolar width decreased with aging and t h o s e of patients treated with the Hyrax R P E , in w h o m greater losses were reported, it may be inferred that the better stability was due either to the type of expander used and duration of retention in the present study, or a combination of the two factors.
Range
expander;
Mandible
Mandibular intermolar width stability after retention has b e e n a subject of m a n y studies. In the present study, a m e a n increase during t r e a t m e n t o c c u r r e d (2.0 __+ 3.0 ram) and was similar to that of the nonextraction cases of G a r d n e r and C h a c o n a s 14 (2.0 _+ 1.7 ram) and slightly larger than that of the nonextraction cases of Shapiro 15 (1.4 -+ 1.8 ram). A f t e r retention a small m e a n increase o c c u r r e d (0.3 + 2.2 m m ) in this study as o p p o s e d to a small m e a n decrease o f approximately less than 1.0 m m observed in previous studies. It is important to take into consideration the large s t a n d a r d deviations w h e n interpreting these findings. T h e y were twice the mean, ranging f r o m 1.0 to 1.3 mm, in previous studies and approximately seven times the m e a n in this study. Sinclair and coworkers 23 r e p o r t e d a decrease in intermolar width for u n t r e a t e d n o r m a l subjects observed from ages 9 to 20 years. T h e m e a n intermolar width at age 9 years was 43.7 m m and at age 20 years, 43.5 ram. In the treated subjects of this study, examined f r o m ages 12 to 30 years, and increase o c c u r r e d for this dimension. T h e m e a n intermolar widths at ages 12 and 30 years were 42.8 and 45.3 mm, respectively. T h e interval between m e a s u r e m e n t s was larger and the subjects were m u c h older at the final m e a s u r e m e n t in this study
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than the untreated subjects. The increase observed in this study may be attributed to treatment. Whether the stability of treatment increase in this study was the result of the soft tissue-borne palatal expansion, the prolonged retention period, or a combination of the two factors cannot be determined because a control group was not available. Previous studies with edgewise appliances, however, have reported smaller net gains (0.4 to 1.9 m m ) . 14'15"2° Irregularity Index
Increase in lower incisor irregularity after retention has been reported by several authors. 16'18'2°'38'39'4° The stability of upper incisor irregularity correction long-term after retention has not previously been investigated. The significant improvement in upper incisor alignment observed at the end of treatment in this study was, however, similar to that reported previously for the lower arch (Table V). After retention, however, there were differences between the results of this study for both arches and those previously reported for the lower arch. Postretention incisor irregularity was minimum, less than 1.5 mm for the both upper and lower arches in this study. Pretreatment irregularity in this study was severe for the upper incisors and moderate for the lower incisors. Previous studies 16'38 with similar, as well as less pretreatment irregularity2°'39 showed more severe irregularity postretention irregularity (1.8 to 4.8 mm) than that of this study (1.4_ 1.3 ram) despite similar improvements with treatment, time interval between measurements, and age at postretention evaluation to those of this study (Table V). The extent of incisor irregularity in this study also was less than that reported by Sinclair and Little23 for untreated normal subjects with minimum irregularity at beginning of their observation period and at a much younger age (Table V). The long-term study of Little, Riedel, and Artun 18 on postretention changes in mandibular anterior alignment from age 10 to 20 years and beyond suggested that cases continue to worsen as they age, but with less significant deterioration after age 30. There were two factors that may have contributed to better stability of incisor alignment in this study: the type of expander used and the prolonged retention into mid and late twenties. The wide individual variability observed requires caution in interpretation of the results of this study, as well as previous ones. Also, the lack of
485
control sample with similar characteristics to those of the treated make it impossible to attribute the results solely to treatment effects. ARCH LENGTH Maxilla
Arch length stability in the maxilla has not been examined to the same extent as that in the mandibular arch. In the two short-term studies35'36 that examined this parameter, the methods of measurement differed from that of this study. Adkins and coworkers,35 reported a decrease for this dimension of 0.4 (0.5) mm. In the current study, a mean increase of 3.3 mm was followed by a decrease of 3.2 mm at postretention evaluation, with large individual variability among the subjects (Table VI). Final arch length was similar to its pretreatment dimension. Mandible
Mandibular arch length during treatment either decreased or remained approximately the same as its pretreatment dimensions, a4'15"2°'39 After retention further decreases were observed that resulted in final arch length being smaller than its pretreatment measurement (Table VI). Similar direction of changes were also reported for untreated normal persons at a much younger age23 (Table VI). In the present study, the mean mandibular arch length increase during treatment was 3.2 mm. A large individual variability, however, prevailed. After retention the mean decrease was similar in magnitude to those observed in previous studies. 14'15"z°'39 Although final arch length in the current study was slightly larger than its pretreatment dimension, it was neither statistically nor clinically significant (Table VII). ARCH PERIMETER
The magnitude of change in arch perimeter with transverse expansion of the maxillary dental arch has not been evaluated to the same degree as in other arch dimensions. The short-term studies of Adkins et alY and Berlocher et al. 36 reported an increase in maxillary arch perimeter during treatment. The treatment mean increase reported by Adkins et al. was similar to that of this study (4.7 and 4.1 mm). In this study, arch perimeter decreased after retention 0.6 mm in the mandible and increased 1.6 mm for the maxilla with a large individual
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Table VI. Measurement change for arch length
T2>T1 Sources This study
G a r d n e r and Chaconas 14 Glenn et al. 2° Shapiro 18 Riedel et al. 4°
Sinclair and Little 23
Treatment~sample size R P E (56) MX MD E (29) N E (74) N E (28) E (48) N E (22) E (42) 1 (24) 2 (18) U N (65) P F M
T2>T3
T3>TI
Mean
SD
Mean
SD
Mean
SD
3.3 3.2 - 6.4 -1.2 0.2 -8.3 - 0.7
(5.9) (6.4) (2.2) (1.4)
- 3.2 -2.4 - 0.8 -0.9 - 2.4 -3.1 - 2.6
(4.4) (2.3) (0.8) (0.8)
0.0 0.6 - 7.3 -2.1 - 2.2 - 11.4 - 3.2
(7.6) (5.9) (1.9) (1.4) (5.7) (2,6)
-2.3 -2.4 -1.9 - 1.6 -2.2
(1.9) (4.1)
-2.6 -7.7 -4.8
(1.8)
-0.2 -5.2 -2.8 - 3.5 -2.2
(3.7) (2.8) (2.8) (4.1) (1.6) (1.7)
(4.5) (1.7)
(2.2) (1.4)
E = Extraction; NE = nonextraction; UN = untreated; MD = mandible; MX = maxilla; F = female; M = male. 1 = O n e lower incisor; 2 = two lower incisor.
Table VII. Arch length measurements Sources This study
G a r d n e r and Chaconas ~4
Sinclair and Little ~3
Treatment/sample size
Pretreatment (T1)
RPE (56) MX MD E (29) NE (74) CII (14) CIII (14) UN (65)
I
Posttreatment (T2)
Postretention (T3)
71.3 (6.3) 62.3 (5.0) 18.5 (1.4) 23.7 (1.2) 61.5 (3.1) 60.0 (3.6) 60.2 (3.4)
68.4 (7.9) 59.8 (4.5) 17.6 (1.1) 22.7 (1.3) 59.1 (3.6) 57.8 (3.5) 58.2 (3.1)
68.3 (5.0) 59.1 (6.2) 25.0 (2.1) 24.9 (1.7) 61.5 (3.7) 60.0 (3.6) 63.1 (6.2)
NE = Nonextraction; E = extraction; UN = u n t r e a t e d normal; MD = mandible; MX = maxilla; P = pooled.
variability present. Although final arch perimeter was longer than its pretreatment dimension, it was neither statistically nor clinically significant (Table III). The relationship between the direction of change in arch length and perimeter during treatment to postretention stability of the incisors was not examined in this study. Mandibular incisor irregularity after retention was, however, minimum compared with the findings of previous studies that examined patients treated with edgewise appliances, 16'2°'37-39as well as untreated normal subjects. 23Similar assessments have not been conducted for the maxillary arch. Judging by the lower values for incisor irregularity found in this study after retention, the treatment increase in arch length and
perimeter during treatment, do not appear to have been influential. However, this needs further investigation. CONCLUSIONS
1. Maxillary intercanine width and maxillary and mandibular intermolar widths after retention closely approximated the P0streat ment dimensions and were larger than their pretreatment dimensions. 2. Mandibular intercanine width, arch length, and arch perimeter after retention closely approximated pretreatment dimensions. 3. Incisor irregularity after retention was minimum for both maxillary and mandibular arch.
American Journal of Orthodontics and Dentofacial Orthopedics Volume 108, No. 5
W e express our appreciation to Dr. A n d r e w Haas for his willing cooperation in supplying the material from his office. W e would also like to acknowledge Joann Pianelli and Irene Williams for their effort i n recalling and collecting the long-term records used in the study. Without their cooperation, this work could not have been accomplished. REFERENCES 1. Ricketts RM. Bioprogressive therapy as an answer to orthodontic needs. AM J ORTHOD 1976;70:241-68. 2. Nance HN. The limitations of orthodontic treatment. Diagnosis and treatment in the permanent dentition. AM J ORTHOD ORAL SURG 1947;33:253-301. 3. Arnold M. A study of changes of the mandibular intercanine and intermolar widths during orthodontic treatment and following a post-retention period of 5 or more years. [Master's thesis.] Seattle: University of Washington, School of Dentistry, 1963. 4. Haas AJ. Palatal expansion: just the beginning of dentofacial orthopedics. AM J ORTHOD 1970;57:219-55. 5. Haas AJ. Long-term post-treatment evaluation of rapid palatal expansion. Angle Orthod 1980;50:189-218. 6. Tweed CJ. Indications for the extraction of teeth in orthodontic procedures. AM J ORTHOD ORAL SURG 1944;30: 405-28. 7. Walter DC. Changes in the form and dimensions of dental arches resulting from orthodontic treatment. Angle Orthod 1953;23:3-18. 8. Walter DC. Comparative changes in mandibular canine and first molar widths. Angle Orthod 1962;32:232-41. 9. Riedel RA. A review of the retention problem. Angle Orthod 1960;30:179-99. 10. Moorrees CFA. The dentition of the growing child. Cambridge: Harvard University Press, 1959. 11. Haas AJ. Rapid expansion of the maxillary dental arch and nasal cavity by opening of the midpalatal suture. Angle Orthod 1961;31:73-90. 12. Dona A. An analysis of dental casts of patients made before and after orthodontic treatment. [Master's thesis.] Seattle: University of Washington, School of Dentistry, 1962. 13. Gallerano R. Mandibular anterior crowding-a post-retention study. [Master's thesis.] Seattle: University of Washington, School of Dentistry, 1976. 14. Gardner SD, Chaconas SJ. Post-treatment and post-retention changes following orthodontic therapy. Angle Orthod 1976;46:151-61. 15. Shapiro PA. Mandibular dental arch form and dimension. AM J ORTHOD 1974;66:58-70. 16. Little RM, Wallen TR, Riedel RA. Stability and relapse of mandibular anterior alignment-first premolar cases treated by traditional edgewise orthodontics. AM J ORTHOD 1981; 80:349-64. 17. Sandusky WC. A long-term post-retention study of Tweed extraction treatment. [Master's thesis.] Memphis: University of Tennessee, 1983. 18. Little RM, Riedel RA, Artun J. An evaluation of changes in mandibular anterior alignment from 10 to 20 years postretention. AM J ORTHOD DENTOFAC ORTHOP 1988;93:423-8.
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43. Cryer S. Lower arch changes during the early teens. Trans Eur Orthod Soc 1966;87:99-107. Reprint requests to: Dr. Maria O'Reilly University of Pittsburgh School of Dental Medicine Department of Orthodontics 3501 Terrace St. Pittsburgh, PA 15261
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