Objectives: The objective was to evaluate the magnitude, incidence and possible factors of asymmetric expansion with a customized microimplant-supported rapid palatal expander (MARPE) in non-growing patients.
Setting and sample population: This retrospective study included a sample of 49 patients (mean age: 23.9 ± 3.9 years) treated with a customized microimplant-supported rapid palatal expander. Based on the symmetry of expansion, the sample was divided into Group S (symmetric expansion group, n = 26) and Group A (asymmetric expansion group, n = 23).
Methods: Pre- and post-treatment cone-beam computed tomography (CBCT) images were superimposed to assess skeletal change in both studied groups. Seven variables were tested: unilateral crossbite, maxillary base cant, chin deviation, the initial asymmetrical position of the mid-palatal suture, split pattern of frontomaxillary suture, Angle's classification and dental arch crowding. Paired t-test and logistic regression analyses were utilized to evaluate the possible factors behind the asymmetric expansion.
Results: There was a significant difference (P < .01) between the studied groups. The average expansion was 4.26 mm at the anterolateral maxillary walls (BB) and 3.83 mm at the greater palatine foramen region (GPF). The average expansion at the GPF was 90% of that at the BB. The frequency of asymmetric expansion was 46.9%. Among the seven tested variables, the presence of the initial asymmetric position of the mid-palatal suture is the only variable that showed correlation with asymmetric expansion.
Conclusion: Initial asymmetric position of the mid-palatal suture is considered a contributing factor of skeletal asymmetric expansion following microimplant-supported rapid palatal expansion in skeletally comparable patients.
Keywords: asymmetric expansion; microimplant-supported rapid palatal expansion; non-growing patients; symmetric expansion.
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