Influence of rapid palatal expansion on maxillary incisor alignment stability Luiz Filiphe Gonc¸alves Canuto,a Marcos Roberto de Freitas,b Guilherme Janson,c Karina Maria Salvatore de Freitas,d and Patrıcia Paschoal Martinse Bauru, Brazil Introduction: The purpose of this retrospective study was to compare the long-term stability of maxillary incisor alignment in patients treated with and without rapid maxillary expansion (RME). Methods: The sample comprised 48 subjects with Class I and Class II malocclusions, treated without extractions with fixed edgewise appliances, divided into 2 groups according to the treatment protocol: group 1 comprised 25 patients (15 girls, 10 boys) at a mean initial age of 13.53 years (SD, 1.63), who had RME during orthodontic treatment. Group 2 comprised 23 patients (13 girls, 10 boys) at a mean initial age of 13.36 years (SD, 1.81 years), treated with fixed appliances without RME. Maxillary dental cast measurements were obtained at the pretreatment, posttreatment, and long-term posttreatment stages. Variables assessed were the irregularity index and maxillary arch dimensions. Intergroup comparisons were made with independent t tests. Results: Greater transverse increases were found during treatment in the group treated with RME. However, during the long-term posttreatment period, no significant difference was observed in the amount of incisor crowding relapse between the groups. Conclusions: RME did not influence long-term maxillary anterior alignment stability. (Am J Orthod Dentofacial Orthop 2010;137:164.e1-164.e6)
here are indications that the amount of maxillary incisor irregularity in the long term out of retention is less than before treatment,1-4 and that rotational relapse of individual teeth rarely exceeds 20 .1,4 Some studies have concluded that rotational relapse is proportional to orthodontic correction, and that there might be an association between crowding and postretention reductions in arch length and width.1,4 Rapid maxillary expansion (RME) with fixed expansion appliances is primarily used to correct maxillary transverse discrepancies, but other applications include increasing arch perimeter to relieve moderate tooth size-arch length discrepancies and facilitate nonextraction edgewise treatment in borderline patients.5-9 Expansion through maxillary suture widening with a
Graduate student, Department of Orthodontics, Bauru Dental School, University of Sa˜o Paulo, Bauru, Sa˜o Paulo, Brazil. b Professor, Department of Orthodontics, Bauru Dental School, University of Sa˜o Paulo, Bauru, Sa˜o Paulo, Brazil. c Professor and head, Department of Orthodontics, Bauru Dental School, University of Sa˜o Paulo, Bauru, Sa˜o Paulo, Brazil. d Private practice, Bauru, Sa˜o Paulo, Brazil. e Private practice, Piracicaba, Sa˜o Paulo, Brazil. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requests to: Luiz Filiphe Gonc¸alves Canuto, Department of Orthodontics, Bauru Dental School, University of Sa˜o Paulo, Alameda Octa´vio Pinheiro Brisolla 9-75, Bauru, Sa˜o Paulo, 17012-901, Brazil; e-mail, luizfiliphecanuto@ yahoo.com.br. Submitted, April 2009; revised and accepted, June 2009. 0889-5406/$36.00 Copyright Ó 2010 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2009.06.017
RME has been claimed to promote dimensional stability after retention.10 This stability was attributed to the skeletal component of arch enlargement from the expansion appliance rather than to dental expansion after edgewise appliance mechanotherapy.10-13 However, no previous study has investigated whether long-term maxillary incisor alignment and dimensional arch stabilities are greater in nonextraction patients treated with RME than in those treated without RME. Studies on the immediate treatment effects of RME have reported increases in maxillary arch width after combined skeletal and dental expansion.9,14-17 Longterm changes in posttreatment maxillary arch dimensions are less well established, particularly in relation to the expected dimensional changes in untreated subjects with normal occlusion.5,18,19 Some long-term follow-ups have indicated a rebound effect of the dental component, yet there is relative dimensional stability of the skeletal aspect of expansion, resulting in maxillary arch dimension net gains.7,8,10,20,21 However, there are reports from complete stability to considerable relapse after maxillary arch expansion.21-24 Marshall et al5 found weak indirect evidence for long-term stability of maxillary expansion with either fixed or removable expansion appliances. Despite favorable arguments about RME effectiveness in correcting maxillary transverse discrepancies and the common use of RME followed by fixed appliances as an option to relieve modest tooth size-arch length discrepancies, a possible influence of this 164.e1
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procedure on long-term maxillary incisor alignment stability has not yet been investigated.7-9 The purpose of this study was to evaluate the influence of RME on maxillary incisor alignment stability by comparing dental arch measurements from nonextraction patients treated with edgewise appliances, with and without RME. MATERIAL AND METHODS
The sample, obtained from the files of the Department of Orthodontics of Bauru Dental School, University of Sa˜o Paulo, Bauru, Sa˜o Paulo, Brazil, included 144 dental casts of 48 patients treated without extractions. Dental casts were obtained at 3 times: pretreatment (T1), immediately after treatment (T2), and a mean of 5.2 years after treatment (T3). In addition to the availability of dental casts, other inclusion criteria were the clinical records that described sex, ages at T1 and T2, length of treatment, length of retention, and long-term posttreatment time. After active treatment, all patients wore a modified Hawley retainer in the maxillary arch, full time for the first 6 months and during sleep for the next 6 months. A lingual canine-to-canine mandibular bonded retainer was placed and left for a mean period of 3 years. The sample was divided into 2 groups according to the treatment protocol (with or without RME). Group 1 consisted of 75 dental casts of 25 patients (15 girls, 10 boys; initial mean age, 13.53 years; SD, 1.63 years) who had RME during orthodontic treatment. Sixteen patients had Class I molar relationships, 7 had quarter-cusp Class II molar relationships, and 2 had half-cusp Class II molar relationships.25 All had a combination of orthopedic-orthodontic treatment for a mean period of 2.07 years (SD, 0.55) and finished treatment at a mean age of 15.51 years (SD, 1.74). The mean T3 evaluation was 5.60 years (SD, 1.41). The patients in this group were treated without extractions and had RME with the Haas or Hyrax appliance and subsequent fixed orthodontic appliances. The decision to use RME therapy was based on at least 1 preexisting criterion: maxillary crowding, posterior crossbite, or esthetics.26 All patients had some crowding, generally associated with narrow dental arches. Sixteen subjects exhibited posterior crossbites. The patients underwent a standardized protocol of RME with 2 turns a day (0.25 mm per turn) until overcorrection of the transverse relationship.20 This overcorrection involved approximation of the palatal cusp tips of the maxillary posterior teeth and the buccal cusp tips of the mandibular posterior teeth in the transverse dimension.8
Fig 1. Maxillary incisor irregularity 5 A 1 B 1 C 1 D 1 E.
Fig 2. Variables studied on dental casts: A, intercanine width; B, interfirst-premolar width; B’, intersecondpremolar width; C, intermolar width; D 1 E, arch length; F, arch perimeter.
The expander was kept on the teeth as a passive retainer for a mean period of 90 days. After expansion, the patients wore a simple palatal plate with bilateral posterior clasps for stabilization.8 The plate was worn full time for 6 months; in 9 patients, however, the plate was not used. Immediately after the expanders were removed, fixed edgewise appliances were placed.6 Group 2 comprised 69 dental casts of 23 subjects (13 girls, 10 boys; initial mean age, 13.36 years; SD, 1.81 years) who had nonextraction orthodontic treatment without RME. They received full maxillary and mandibular fixed edgewise appliances. Ten patients had Class I, 8 had quarter-cusp Class II, and 5 had half Class II anteroposterior molar relationships.25 These patients underwent orthodontic treatment for a mean period of 2.18 years (SD, 0.93) and finished at a mean age of 15.54 years (SD, 1.86). The T3 study models were taken after a mean of 4.92 years (SD, 1.11).
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Table I. Intergroup compatibility evaluation for ages at T1 and T2, treatment time, long-term posttreatment time, and initial maxillary incisor irregularity (t tests) Group 1 Group 2 (with RME) (without RME) n 5 25 n 5 23 Variable
T1 age (y) T2 age (y) Treatment time (y) Long-term posttreatment time (y) Initial irregularity (mm)
13.53 15.51 2.07 5.60 7.65
1.63 13.36 1.74 15.54 0.55 2.18 1.41 4.92 2.96 6.56
1.81 1.86 0.93 1.11 2.84
0.729 0.956 0.625 0.072 0.201
5. Intergroup sex distribution compatibility evaluation at T1 (chi-square test)
Group 1 (with RME) Group 2 (without RME) Total
15 13 28
10 10 20
25 23 48
Chi-square 5 0.06; df 5 1; P 5 0.807.
Intergroup malocclusion severity compatibility evaluation at T1 (chi-square test) Table III.
Severity Class I 1/4 Class II 1/2 Class II Total
Group 1 (with RME)
Group 2 (without RME)
16 7 2 25
10 8 5 23
26 15 7 48
Chi-square 5 2.658; df 5 2; P 5 0.2647.
T1, T2, and T3 maxillary dental casts were used. All dental cast measurements were made with a precision digital caliper (Mitutoyo America, Aurora, Ill). The assessed variables were Little’s irregularity index; intercanine, interpremolar, and intermolar widths; and arch length and perimeter (Figs 1 and 2). Maxillary dental casts were measured by 1 investigator (L.F.G.C.) to the nearest 0.01 mm, with the digital caliper. Measurements were made on the cusp tips of the canines and the mesial buccal cusps of the first molars of each patient. When there was a facet, the cusp tip was estimated.10 Measurements were blindly and randomly made for all patients. All were linear measurements, in millimeters, described as follows. 1.
Maxillary incisor irregularity: the sum of the 5 distances between the anatomic contacts from the
mesial aspect of the right canine through the mesial aspect of the left canine; this is similar to Little’s method for evaluating mandibular incisor irregularity (Fig 1).27 Intercanine width: the linear distance between the cusp tips of the maxillary canines (Fig 2). Interfirst-premolar width: the linear distance between the central fossae of the maxillary first premolars (Fig 2). Intersecond-premolar width: linear distance between the central fossae of the maxillary second premolars (Fig 2). Intermolar width: the linear distance between the mesiobuccal cusps tips of the maxillary first molars (Fig 2). Arch length: the linear distance along the midline from the interincisal midline to the mesial contact of the first molars (Fig 2). Arch perimeter: the sum of the distances from the mesial contacts of the first molars to the distal contact points of the canines plus the mesiodistal widths of the canines plus the distance from the mesial contact point of the canines to the interproximal contact between the central incisors (Fig 2).8
Within 3 weeks from the first measurements, 15 dental casts were randomly selected and remeasured by the same examiner (L.F.G.C.). The casual error was calculated according to Dahlberg’s formula (Se2 5 Sd2/2n), where Se is the error variance and d is the difference between 2 determinations of the same variable.28 The systematic error was calculated with dependent t tests at P \0.05.29 Statistical analysis
The intergroup compatibility evaluation regarding initial and final ages, treatment time, long-term posttreatment time, and pretreatment incisor irregularity were evaluated with t tests. The sex distribution and the initial malocclusion severity compatibility between the 2 groups were assessed with chi-square tests. Means and standard deviations were calculated for all variables at T1, T2, and T3 for the whole sample. Treatment changes were also evaluated and calculated by subtracting the initial from the final values (T2 – T1). The amount of relapse was calculated by subtracting the final from the long-term posttreatment values (T3 – T2). The total changes were calculated by subtracting the initial from the long-term posttreatment values (T3 – T1). The intergroup comparisons at the several stages and observation periods were made with t tests.
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Table IV. Intergroup comparison of maxillary incisor irregularity and arch dimensions at T1, T2, and T3 (t tests) Group 1 (with RME) n 5 25 Measurement (mm) T1 Little’s index 3-3 width 4-4 width 5-5 width 6-6 width Arch length Arch perimeter T2 Little’s index 3-3 width 4-4 width 5-5 width 6-6 width Arch length Arch perimeter T3 Little’s index 3-3 width 4-4 width 5-5 width 6-6 width Arch length Arch perimeter
Group 2 (without RME) n 5 23
7.65 34.16 33.26 38.39 49.46 70.97 74.41
2.96 2.41 2.12 2.98 4.15 4.35 3.54
6.56 34.08 34.71 40.20 51.13 72.09 75.18
2.84 3.08 1.86 2.31 2.62 4.08 3.77
0.201 0.914 0.015* 0.024* 0.106 0.362 0.471
1.42 35.04 36.90 42.20 52.43 73.47 77.10
1.05 1.41 1.64 2.04 2.55 2.91 2.77
1.60 34.66 36.34 41.35 51.52 73.76 76.52
0.73 1.44 1.81 2.15 2.50 2.49 2.66
0.497 0.351 0.260 0.166 0.219 0.709 0.459
2.93 34.46 35.76 41.43 52.24 71.90 75.45
1.97 1.70 1.82 2.24 2.92 3.12 2.79
3.12 34.55 35.76 41.09 51.94 72.07 75.32
1.42 1.87 1.81 2.16 2.51 2.58 2.55
0.713 0.876 0.990 0.587 0.709 0.838 0.868
3-3,Intercanine; 4-4, interfirst-premolar; 5-5, intersecond-premolar; 6-6, intermolar. *Statistically significant at P \0.05.
The percentage of relapse was calculated as the rate between the relapse and the correction amounts. The results were considered significant at P \0.05. All statistical analyses were performed with Statistica software (release 6.0, Statistica for Windows, Statsoft, Tulsa, Okla).
Table V. Intergroup comparisons of maxillary incisor irregularity and arch dimensions for treatment (T2 – T1), long-term posttreatment (T3 – T2), and net changes (T3 – T1) (t tests) Group 1 (with RME) n 5 25 Measurement (mm)
Treatment changes Little’s index –6.23 2.90 3-3 width 0.88 1.89 4-4 width 3.65 1.84 5-5 width 3.82 2.12 6-6 width 2.97 3.56 Arch length 2.50 2.85 Arch perimeter 2.69 2.48 Long-term posttreatment changes Little’s index 1.52 1.60 3-3 width –0.58 0.72 4-4 width –1.14 0.90 5-5 width –0.77 1.05 6-6 width –0.20 1.64 Arch length –1.57 1.24 Arch perimeter –1.65 1.29 Net changes Little’s index –4.72 3.27 3-3 width 0.30 1.53 4-4 width 2.51 1.67 5-5 width 3.05 1.82 6-6 width 2.78 3.19 Arch length 0.93 2.41 Arch perimeter 1.04 2.57
Group 2 (without RME) n 5 23 Mean
–4.97 0.58 1.62 1.15 0.39 1.67 1.34
3.11 2.52 1.70 2.15 2.57 3.73 3.20
0.151 0.639 0.000* 0.000* 0.006* 0.390 0.107
1.52 –0.11 –0.58 –0.27 0.42 –1.69 –1.20
1.38 1.00 0.98 0.99 1.16 1.26 1.09
0.992 0.066 0.045* 0.095 0.146 0.732 0.194
–3.44 0.47 1.04 0.89 0.81 –0.02 0.14
2.73 2.47 1.52 1.95 1.87 3.25 3.29
0.152 0.778 0.003* 0.000* 0.013* 0.252 0.296
3-3, Intercanine; 4-4, interfirst-premolar; 5-5, intersecond-premolar; 6-6, intermolar. *Statistically significant at P \0.05.
cantly greater maxillary interfirst-premolar width decrease in group 1. There was no significant difference in the amount of maxillary crowding relapse between the groups (Table V).
The casual errors ranged from 0.08 (intersecondpremolar width) to 0.57 mm (Little irregularity). Paired t tests showed no statistically significant systematic errors. The groups were similar regarding ages at T1 and T2, treatment times, long-term posttreatment times, initial maxillary incisor irregularity, sex, and initial malocclusion severity distributions (Tables I to III). Group 2 (without RME) had greater first and second interpremolar widths at T1 (Table IV). Group 1 (with RME) had greater maxillary arch width increases than did group 2 during the treatment and the overall observation periods (Table V). During the long-term posttreatment period, there was a signifi-
The groups were similar regarding several parameters that could influence this comparison (Tables I to III). However, group 2 had significantly larger interfirst-premolar and intersecond-premolar widths (Table IV). Some transverse differences were expected between the groups because transverse deficiency and posterior crossbite were factors that motivated the patients in group 1 to have RME.20,30,31 Nevertheless, it is unlikely that this would affect the anterior irregularity comparison because both groups had similar maxillary anterior crowding. Perphaps it could influence the transverse dimension stability.7,8,10,20
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The RME group had greater transverse increases during treatment than did group 2, as expected.17 However, there were no significant differences in maxillary arch dimensions between the groups at T2 (Tables IV and V). This might have been consequent to some slow expansion that group 1 also experienced with treatment provided by using wider archwires to aid in correcting the crowding in these patients.10 Also, these patients were studied at the end of treatment and not at the end of expansion. Usually, some expansion is lost during fixed appliance treatment; this might also explain the absence of differences in the transverse dimensions at the end of treatment between the groups.7,21,32,33 Expansion was greater in the posterior than in the anterior aspect of the arch, as previously reported.7,9,11,14,34 Group 1 (with RME) had a maxillary arch perimeter increase of 0.74 mm for every 1 mm of interfirst-premolar expansion, corroborating a previous report.16 Decreases in maxillary incisor irregularity during treatment, similar to those observed in this study, have been previously reported for nonextraction patients treated with RME and fixed appliances.7,10 Although both groups had some crowding relapse, there was no significant difference in the amount of maxillary crowding relapse between the groups (Table V). Some relapse occurred in most patients, with mean percentages of 24.39% and 30.64% for groups 1 and 2, respectively. The amount of maxillary anterior crowding relapse is considered to be small-to-moderate by Little.27 Nevertheless, in this study, it was greater than in previous reports.8,10,20,35 The greater relapse was probably because the patients had a relatively shorter retention with the Hawley plate. Those authors used the Hawley retainer for 2 and 8.4 years, respectively,10,35 or some patients still used their retainers for an extended time.8,20 Others did not report the retention protocol after treatment.5,21 This suggests that, similar to the mandibular arch, a prolonged retention time might be important for long-term stability.35,36 However, the most important part of a stability study is to evaluate the posttreatment changes after some time without artificial retention. Additionally, comparisons among different investigations are difficult because clinical studies vary widely in sample sizes and age ranges, amounts of expansion, and retention methods.20,21 As in previous reports, the maxillary arch had longterm posttreatment dimensional decreases in both groups, with group 1 showing a significantly greater reduction only in interfirst-premolar width (Table V).7,8,32,37 Similar decreases as in group 1 have been reported.7,8,10
Despite a greater decrease in interfirst-premolar width, group 1 still had a significantly greater net increase in the interfirst-premolar, intersecond-premolar, and intermolar transverse distances than did group 2 (Table V). However, this did not contribute to greater anterior tooth alignment stability in that group. At the end of the overall observation period, the increases in maxillary arch length and perimeter for both groups were minimal, without statistical and clinical significance, corroborating a previous report.8 Based on these results, the use of RME only to relieve mild to moderate maxillary crowding in the permanent dentition might be unnecessary because incisor alignment stability is similar without the procedure, when crowding is corrected by slow dental arch expansion with wider archwires. The use of RME to correct crowding could cause an unnecessary increase of treatment time, reducing treatment efficiency. However, the effectiveness of RME in treating maxillary transverse discrepancies, with or without posterior crossbites, is unquestionable.9,13,17,21,23 CONCLUSIONS
The long-term stability of maxillary incisor alignment was similar in nonextraction groups treated with and without RME. Therefore, RME did not influence the alignment stability in the long term.
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