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.
Editor’s summary
When treating nonextraction patients, some clinicians believe that there is greater stability of maxillary incisor alignment if RME is part of the treatment plan. But is there any evidence to support this belief? We know that RME initially causes increases in the dental and skeletal transverse dimensions, but studies also show that much of this expansion is lost over time. What does this long-term change mean for the stability of the maxillary incisors? The purpose of this study was to evaluate the influence of RME on the stability of maxillary incisor alignment by comparing dental arch measurements after nonextraction treatment with edgewise appliances, with and without RME.
The records of 48 nonextraction patients were gathered at 3 times: pretreatment, end of treatment, and 5.2 years posttreatment. Group 1, including 25 subjects who had RME, was compared with group 2, consisting of 23 subjects who did not have RME. Study casts were used for all measurements (Little’s irregularity index; intercanine, interpremolar, and intermolar widths; and arch length and perimeter). At the end of the overall observation period, the increases in maxillary arch length and perimeter in both groups were minimal. It seems obvious from this study that using RME to relieve mild to moderate maxillary crowding in the permanent dentition might be unnecessary because incisor alignment stability is similar to treatment without it. The long-term stability of maxillary incisor alignment was similar in the nonextraction groups treated with and without RME.
| Group 1 (with RME) n = 25 |
Group 2 (without RME) n = 23 |
||||
|---|---|---|---|---|---|
| Measurement (mm) | Mean | SD | Mean | SD | P |
| Treatment changes | |||||
| Little’s index | –6.23 | 2.90 | –4.97 | 3.11 | 0.151 |
| 3-3 width | 0.88 | 1.89 | 0.58 | 2.52 | 0.639 |
| 4-4 width | 3.65 | 1.84 | 1.62 | 1.70 | 0.000 ∗ |
| 5-5 width | 3.82 | 2.12 | 1.15 | 2.15 | 0.000 ∗ |
| 6-6 width | 2.97 | 3.56 | 0.39 | 2.57 | 0.006 ∗ |
| Arch length | 2.50 | 2.85 | 1.67 | 3.73 | 0.390 |
| Arch perimeter | 2.69 | 2.48 | 1.34 | 3.20 | 0.107 |
| Long-term posttreatment changes | |||||
| Little’s index | 1.52 | 1.60 | 1.52 | 1.38 | 0.992 |
| 3-3 width | –0.58 | 0.72 | –0.11 | 1.00 | 0.066 |
| 4-4 width | –1.14 | 0.90 | –0.58 | 0.98 | 0.045 ∗ |
| 5-5 width | –0.77 | 1.05 | –0.27 | 0.99 | 0.095 |
| 6-6 width | –0.20 | 1.64 | 0.42 | 1.16 | 0.146 |
| Arch length | –1.57 | 1.24 | –1.69 | 1.26 | 0.732 |
| Arch perimeter | –1.65 | 1.29 | –1.20 | 1.09 | 0.194 |
| Net changes | |||||
| Little’s index | –4.72 | 3.27 | –3.44 | 2.73 | 0.152 |
| 3-3 width | 0.30 | 1.53 | 0.47 | 2.47 | 0.778 |
| 4-4 width | 2.51 | 1.67 | 1.04 | 1.52 | 0.003 ∗ |
| 5-5 width | 3.05 | 1.82 | 0.89 | 1.95 | 0.000 ∗ |
| 6-6 width | 2.78 | 3.19 | 0.81 | 1.87 | 0.013 ∗ |
| Arch length | 0.93 | 2.41 | –0.02 | 3.25 | 0.252 |
| Arch perimeter | 1.04 | 2.57 | 0.14 | 3.29 | 0.296 |
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