Does expander design influence the risk of asymmetric palatal expansion? A retrospective cohort study.

Background: Unplanned asymmetric palatal expansion following Surgically Assisted Rapid Maxillary Expansion (SARME) can result in a poor esthetic outcome or an unstable occlusion. The purpose of this study was to analyze the association between expander design and asymmetric expansion.

Methods: In this retrospective cohort study, preoperative and postoperative cone beam computed tomography (CBCT) scans of patients treated with SARME were randomly selected from the Radboud University medical imaging database. Patients were divided into two groups according to the used expander: (1) bone-borne distractor (TPD); (2) tooth-borne expander (Hyrax). Transverse dental and skeletal maxillary expansion were quantified using landmark-based measurements. A left-right difference of more than one millimeter was considered as asymmetric. Paired and independent t-tests were performed to analyze the asymmetry within and between the groups. Linear regression analyses were used to identify predictor variables for asymmetric expansion.

Results: 60 patients were enrolled into the study (mean age 30.3 ± 9.1 years; 24 male and 36 female), 30 in the TPD group and 30 in the hyrax group. The mean anterior maxillary dental and skeletal expansion was 3.9 ± 2.7 mm and 2.2 ± 1.4 mm. The mean posterior maxillary dental and skeletal expansion was 5.2 ± 2.7 mm and 2.3 ± 1.6 mm. No differences in dental and skeletal expansion were found between the TPD and hyrax groups (p > 0.05). 18 patients in the TPD group and 21 patients in the hyrax group exhibited anterior dental asymmetry (p = 0.42) whereas 10 and 11 patients exhibited anterior skeletal asymmetry (p = 0.79). Linear regression analyses demonstrated that the type of expander does not appear to be a predictor variable for asymmetric expansion.

Conclusion: Asymmetric maxillary opening occurred frequently after SARME irrespective of the type of expander used. Considering the similar postoperative outcome of hyrax and TPD, SARME with a hyrax expander may be preferred as it is less surgically invasive and more cost effective.