Longitudinal Effects of Rapid Maxillary ExpansionA Retrospective Cephalometric Study
Objective: To evaluate the long-term effects of rapid maxillary expansion (RME) via banded expanders in the sagittal and vertical facial planes.
Materials and Methods: The sample consisted of 25 patients who had undergone RME (with either Haas-type or Hyrax hygienic expanders) followed by standard edgewise orthodontic therapy. This sample was compared with a group of 25 patients who had edgewise treatment only and with a control nontreatment group of 26 subjects, matched by age and gender with the patients of the other two groups. Lateral cephalograms were taken before treatment (T1), at the end of treatment (T2), and at 3 years posttreatment (T3), comprising a 5-year average time of observation.
Results: RME treatment, in the long-term, did not influence the sagittal position of the apical jaw bases or the facial vertical dimension.
Conclusion: Unfavorable cephalometric changes resulting immediately after RME are temporary, and therefore concerns about using RME in patients with vertical growth patterns or an extremely convex facial profile are not substantiated.Abstract
INTRODUCTION
Rapid maxillary expansion (RME) constitutes a routine clinical procedure in orthodontics, with its main purpose to normalize the constricted maxillary arch. Forces of large magnitude delivered during activation of an expansion screw1 open the intermaxillary suture,2–4 increasing the basal bone width245 and the dental arch perimeter.6 In addition to the desirable transverse alterations, RME produces perceptible changes in the sagittal and vertical facial planes. The literature clearly demonstrates that, immediately after expansion, there is downward maxillary displacement and extrusion of the supporting teeth, leading to downward and backward mandibular rotation.247–15 The opening rotation of the mandible induces cephalometric changes, such as increases in inclination of the mandibular plane, in lower anterior facial height, and in facial convexity, in addition to evident bite opening in the anterior region.
In this context, some orthodontists have advised against performing RME in patients with predominantly vertical growth patterns and convex facial profiles1617 to prevent worsening of the malocclusion. Other clinicians have recommended the simultaneous use of other appliances, such as high-pull chin caps,18–20 occlusal plates,21 or expanders with acrylic occlusal coverage,822–25 to minimize the undesirable anteroposterior and vertical effects of RME.
Most cephalometric studies of RME performed to date are limited to short-term evaluations, which have revealed partial relapse of the vertical and sagittal effects following the retention period.412 These results led to uncertainties regarding the longitudinal behavior of these cephalometric changes. Do the undesirable sagittal and vertical effects of RME become negligible over time, or are they maintained, justifying professional care to prevent them? Few lateral cephalometric investigations have been conducted longitudinally on RME,1526–28 and the majority of studies had no control group against which to make adequate comparisons.152728
In light of these facts, this study was designed to evaluate the longitudinal cephalometric changes caused by RME followed by edgewise mechanics and to compare them to the changes caused by edgewise mechanics without previous expansion. Changes resulting from craniofacial growth and development were also compared with those of a control nontreatment group.
MATERIALS AND METHODS
All patients were selected retrospectively and consecutively. Three groups of subjects were analyzed. Group 1 (RME group) was composed of 25 white patients (11 male, 14 female) with a mean age of 13.5 years (varying from 11 to 17.3 years) at treatment onset who presented with either Angle Class I (I) or Class II, division 1 (II/1), malocclusions (14 and 11 patients, respectively) and posterior crossbite.
Approval was received for the use of human subjects in this study by the human subjects committee of the authors' university.
Group 1 underwent RME with either tooth-tissue– supported (Haas type) or tooth-supported (Hyrax or Hygienic) expanders, followed by standard edgewise therapy. The expanders were activated 5 to 9 mm over a period of approximately 2 weeks until the posterior crossbite was overcorrected. After completion of the active expansion phase, the expander was kept as a retainer for 3 months. During edgewise therapy, 6 patients had four first premolar extractions and 19 patients were treated with no extractions. Lateral cephalograms taken before treatment (T1), after active orthodontic treatment (T2), and 3 years after treatment (T3) were used in this study, comprising a mean observation period of 5 years.
Group 2 (edgewise group) consisted of 25 white patients (11 male, 14 female), with a mean age of 13.1 years (ranging from 10.6 to 18.7 years) at treatment onset, presenting with Class I or II/1 malocclusion (11 and 14 patients, respectively). The treatment of these patients did not involve RME and was limited to the use of edgewise fixed appliances. Extraction of four first premolars was performed in 9 of the 25 patients, and the remaining 16 were treated without extractions. Three lateral cephalograms were obtained for each patient at the same stages described for group 1.
Group 3 (control group) comprised 26 white (13 male and 13 female) subjects who did not undergo orthodontic treatment and who were selected from the records of Bauru Growth Center29 and matched by age to the patients in groups 1 and 2. Three lateral cephalograms of each individual were traced, obtained at ages 13, 15, and 18 years, corresponding to the mean ages at each treatment stage in the other groups (Table 1). Although the majority of this sample had normal occlusion, subjects with Class I or II/1 malocclusion were also included.
Anatomic tracings and location of dentoskeletal landmarks were manually conducted by a single investigator for all three groups and then digitized (Numonics AccuGrid XNT, model A30TL.F, Numonics Corporation, Montgomeryville, Penn). These data were then stored on a 166 Pentium II computer and analyzed with Dentofacial Planner 7.02 Plus (Dentofacial Software Inc, Toronto, Ontario, Canada). This software corrected the magnification factor (6% to 9%) of the radiographic images and calculated the angular and linear cephalometric variables employed in this study (Figures 1 and 2).
Citation: The Angle Orthodontist 77, 3; 10.2319/0003-3219(2007)077[0442:LEORME]2.0.CO;2
Citation: The Angle Orthodontist 77, 3; 10.2319/0003-3219(2007)077[0442:LEORME]2.0.CO;2
Statistical Analyses
Descriptive statistics (means and standard deviations) were obtained for each cephalometric measurement at T1, T2, and T3 as well as for the changes between stages (T1 to T2, T2 to T3, T1 to T3). Analysis of variance (ANOVA) and Tukey test were used to identify intergroup differences regarding both initial values and changes over time (P < .05).
Eighteen radiographs were randomly selected, retraced, redigitalized, and remeasured by the same examiner after a 30-day interval. Casual and systematic errors were calculated comparing the first and second measurements with Dahlberg's formula and dependent t-test, respectively, at a significance level of 5%. Only one variable analyzed (SN.PP) had a statistically significant systematic error (mean = −0.3°), and no variable showed an error greater than 0.5° or 0.5 mm.
RESULTS
A comparison of anatomic form at baseline (Table 2) revealed that the three groups had similar characteristics for 11 of the 15 cephalometric measures analyzed. Group 2 showed greater ANB angle than group 3 and greater overjet than groups 1 and 3. Other significant differences included greater FMA angle and smaller overbite in group 1 compared to group 3. The number of patients with high mandibular angle (FMA angle greater than 30°) in groups 1, 2, and 3 were 10, 7, and 4, respectively.
During the treatment period (T1 to T2), there were no statistical differences between the groups regarding vertical changes (Table 3). Only facial convexity (ANB and NAP) showed a larger reduction in group 2 in comparison with the other two groups, which was the result of a decrease in the SNA angle in that group.
Posttreatment changes (T2 to T3) are detailed in Table 4. There were no differences between groups during this period.
Considering the whole observation period (T1 to T3), the majority of measurements that expressed facial vertical dimensions and growth patterns showed similar changes in all groups (Table 5).
Between-group differences were restricted to sagittal features, with the edgewise group (group 2) displaying a significantly larger decrease in both facial convexity and SNA angle compared with the RME (group 1) and control groups (group 3).
DISCUSSION
Precise evaluation of the longitudinal cephalometric effects of RME, which was the primary goal of this study, required identification of alterations related to craniofacial growth and orthodontic mechanics performed after RME in the study sample. In this way, a group of patients who underwent RME before mechanical treatment with fixed appliances was compared to a sample of patients whose corrective orthodontic treatment did not include RME. A control group of untreated subjects was also used to identify confounding factors such as the expression of craniofacial growth and development during the study period.
Sagittal Changes
Considering the changes in SNA angle, it seems evident that the maxilla in group 1 behaved similar to that of the control group throughout the study period (Tables 3 to 5). Group 2 was treated with edgewise mechanics only and was significantly different from the other groups. In groups 1 and 3, the maxillary sagittal position remained unchanged in relation to the cranial base, considering the slight changes in SNA angle, whereas group 2 revealed maxillary retrusion during the treatment period (T1 to T2), probably a result of backward displacement of point A secondary to tooth extractions (Table 3). Analysis of the initial measurements in Table 2 reveals that group 2 presented higher values for ANB angle and overjet. Thus, in this group, dental compensation of the malocclusion required a larger amount of maxillary incisor retraction, which should be enough to cause remodeling of the maxillary anterior region and retrusion of point A.
The contradictory data in the literature on the effects of RME on maxillary anteroposterior positioning, obtained from short-term observations, require critical analysis of longitudinal studies. Haas2 was the first to mention the occurrence of anterior displacement of the maxilla after expansion. Thereafter, some cephalometric studies corroborated these results,8–101330 whereas other studies did not observe such displacement, instead noting variable sagittal behavior of the maxilla that was clinically insignificant.41214152331 The findings of the present study revealed that RME did not yield any relevant long-term effect on the maxilla in the anteroposterior dimension. Other authors who applied longitudinal methodologies found similar results.1526–28
Interpretation of SNB angle changes showed no significant differences among the three study groups regarding mandibular sagittal behavior (Tables 3 to 5). In both treated groups, as well as in the control group, the mandible presented forward displacement in relation to the cranial base. Thus, it can be concluded that neither RME nor corrective orthodontics influenced anteroposterior mandibular growth. Chin retropositioning observed soon after RME owing to downward and backward mandibular rotation247–15 constitutes a temporary effect of RME. Studies that followed patients during the 3-month retention period after expansion had already demonstrated partial relapse of these alterations, with the cephalometric variables tending to return to their initial values.412 The current findings confirm the results of previous longitudinal studies.2627
The variables that indicate the anteroposterior relationship between the maxilla and the mandible (ANB) and bony profile convexity (NAP) were reduced throughout the study period (T1 to T3) (Tables 3 to 5). This reduction in facial convexity was similar in the RME and the control groups, confirming that RME does not influence the sagittal relationship between the apical jaw bases. Thus, the alterations that occur immediately after expansion and are frequently reported in the literature, such as increases in facial convexity and overjet,28912–143233 should be considered ephemeral phenomena.
These results do not provide a basis to contraindicate RME in patients with a convex profile based on the side effects observed soon after expansion. Only group 2 exhibited a statistically significantly greater reduction in ANB and NAP angles compared to the other groups (Table 3). Since these angles are related to sagittal changes of the apical jaw bases, the greater reduction in facial convexity in group 2 is secondary to the retropositioning of point A previously discussed.
Vertical Changes
The palatal plane inclination (SN.PP angle) remained unchanged in the control group over the entire evaluation period (Table 5). Groups 1 and 2, which were treated, showed similar responses yet were statistically different from group 3, showing mild anteroinferior rotation of the palatal plane, with a mean of 0.6°. The literature presents varied responses of the palatal plane secondary to RME, from anteroinferior rotation to anterosuperior rotation.414 However, considering the lack of differences between groups 1 and 2, it does not seem reasonable to assign any longitudinal influence in palatal plane inclination to the effects of RME.
The changes observed for upper anterior and posterior facial heights (UAFH and UPFH) should also be emphasized, since there were no statistically significant differences between the study groups (Tables 3 to 5). These data reveal that, even though RME causes vertical maxillary displacement, as demonstrated by several studies,249111415 this vertical alteration is not significant in the long term.
The results related to vertical facial changes in the RME group are of extreme clinical importance. It is known that RME increases lower anterior facial height (LAFH) and inclination of the mandibular plane and leads to anterior bite opening because of the downward maxillary displacement and extrusion of anchorage teeth.247–15 Furthermore, overcorrection of 2 to 3 mm during activation of the screw gives rise to occlusal interferences when the lingual cusps of maxillary teeth occlude against the buccal cusps of mandibular teeth,20 contributing to vertical increases. Even though cephalometric studies show partial relapse of such alterations during the retention period,412 the uncertainties of the longitudinal behavior of vertical facial dimensions could constitute a concern when performing RME in patients with a long face and/or an excessively retrognathic profile.1617
Surprisingly, a comparison of the three study groups during the observation period did not demonstrate significant differences between them regarding changes in facial growth pattern, facial height, maxillary first molar extrusion, and overbite (Tables 3 to 5). These findings corroborate the studies of Chang et al26 and Velásquez et al,27 which revealed that the vertical skeletal changes in patients treated with RME were not different after consideration of natural alterations resulting from individual facial growth.
CONCLUSION
-
Undesirable cephalometric effects observed immediately after RME with banded appliances were not significant in the long term and thus do not contraindicate this procedure in patients with a vertical growth pattern or an extremely convex facial profile.
Cephalometric variables for sagittal and vertical evaluation. 1 indicates SNA angle; 2, SNB angle; 3, ANB angle; 4, NAP angle, skeletal profile convexity (Downs); 5, overjet; 6, SN.PP; 7, SN.GoGn; And 8, FMA.
Linear cephalometric variables for vertical evaluation. 9 indicates upper anterior facial height (UAFH); 10, lower anterior facial height (LAFH); 11, total anterior facial height (TAFH); 12, upper posterior facial height (UPFH); 13, total posterior facial height (TPFH); 14, U6-PP; and 15, overbite
Contributor Notes
Corresponding author: Dr Daniela Gamba Garib, University of São Paulo City, Department of Orthodontics, R. Rio Branco 19-18, Bauru, São Paulo 17040-480, Brazil (dgarib_boston@hotmail.com)