Rapid-maxillary-expansion induced rhinological effects: a retrospective multicenter study.

Conventional dental-borne rapid maxillary expansion (RME) leads to a widening of the airways, followed by improved nasal breathing. Although combined skeletal-dental appliances are nowadays being inserted increasingly often and provide a force at the center of resistance in the nasomaxillary complex, no study exists so far that shows whether this treatment may improve the expansionary effect on the airways. In this study, low-dose computed tomography (CT) images from 31 patients (average age 14.63 ± 0.38 years) were examined retrospectively. Both records (T0 = before expansion and T1 = immediately after maximum expansion) were taken in a time interval of 25 days to avoid growth influence. Five patients were treated with Hyrax RME, 6 patients with Hybrid RME, and 20 patients with acrylic cap RME. The total airway volume increased highly significantly (mean +7272.6 mm(3); P < 0.001, power = 0.998), representing an average airway expansion of +11.54 % (2.35 %/mm activation). While the nasopharynx and oropharynx showed highly significant expansion (P < 0.000, power = 0.999), the airway at the laryngopharynx did not change significantly (P > 0.779, power = 0.05). Although the patients were significantly older in the Hybrid RME group (P = 0.006), the positive rhinological effects were comparable within all groups of different appliances (P > 0.316). Hybrid RME may, therefore, be an advisable procedure in patients with nasomaxillary impairment and pronounced patient's age.

Application of a new viscoelastic finite element method model and analysis of miniscrew-supported hybrid hyrax treatment.

INTRODUCTION: In this study, we aimed to assess the ability of a new viscoelastic finite element method model to accurately simulate rapid palatal expansion with a miniscrew-supported hybrid hyrax appliance. METHODS: A female patient received 3-dimensional craniofacial imaging with computed tomography at 2 times: before expansion and immediately after expansion, with the latter serving as a reference model for the analysis. A novel approach was applied to the finite element method model to improve simulation of the viscoelastic properties of osseous tissue. RESULTS: The resulting finite element method model was a suitable approximation of the clinical situation and adequately simulated the forced expansion of the midpalatal suture. Specifically, it demonstrated that the hybrid hyrax appliance delivered a force via the 2 mini-implants at the center of resistance of the nasomaxillary complex. CONCLUSIONS: The newly developed model provided a suitable simulation of the clinical effects of the hybrid hyrax appliance, which proved to be a suitable device for rapid palatal expansion.

Evaluation of 3-dimensional superimposition techniques on various skeletal structures of the head using surface models.

OBJECTIVES: To test the applicability, accuracy, precision, and reproducibility of various 3D superimposition techniques for radiographic data, transformed to triangulated surface data. METHODS: Five superimposition techniques (3P: three-point registration; AC: anterior cranial base; AC + F: anterior cranial base + foramen magnum; BZ: both zygomatic arches; 1Z: one zygomatic arch) were tested using eight pairs of pre-existing CT data (pre- and post-treatment). These were obtained from non-growing orthodontic patients treated with rapid maxillary expansion. All datasets were superimposed by three operators independently, who repeated the whole procedure one month later. Accuracy was assessed by the distance (D) between superimposed datasets on three form-stable anatomical areas, located on the anterior cranial base and the foramen magnum. Precision and reproducibility were assessed using the distances between models at four specific landmarks. Non parametric multivariate models and Bland-Altman difference plots were used for analyses. RESULTS: There was no difference among operators or between time points on the accuracy of each superimposition technique (p>0.05). The AC + F technique was the most accurate (D<0.17 mm), as expected, followed by AC and BZ superimpositions that presented similar level of accuracy (D<0.5 mm). 3P and 1Z were the least accurate superimpositions (0.790.05), the detected structural changes differed significantly between different techniques (p<0.05). Bland-Altman difference plots showed that BZ superimposition was comparable to AC, though it presented slightly higher random error. CONCLUSIONS: Superimposition of 3D datasets using surface models created from voxel data can provide accurate, precise, and reproducible results, offering also high efficiency and increased post-processing capabilities. In the present study population, the BZ superimposition was comparable to AC, with the added advantage of being applicable to scans with a smaller field of view.

Density of the midpalatal suture after RME treatment - a retrospective comparative low-dose CT-study.

INTRODUCTION: Rapid maxillary expansion (RME) is a common technique to improve the dental and skeletal transverse width in cases of constricted maxillary arches. Although retention after RME has been widely examined, there is still no clear statement about the minimal retention time in postpubertal patients and many practitioners have retention concepts varying between three and six months. METHODS: This retrospective study consisted of 14 patients who were either treated with a Haas-type RME (6 patients) or a Hybrid-RME (8 patients). The average age was 15.8 years (min. 13.5 years, max. 23.0 years).Low-dose CT scans were taken initially before placement of the RME (T0), directly after maximal activation (T1) and (in six cases) also in retention after 6 months (T2). Using a 3D-software ("OnDemand3D"/Cybermed Inc.) in analogy to the method published by Franchi et al. (AJODO Volume 137/ Number 4) all values were measured twice at an interval of 1 month to assess the method error and the intraoperator reliability.Statistical analysis was performed using SPSS 21 for Mac. Possible influences of the RME-type were assessed using the univariate ANOVA. Changes in the sutural density between the different points of time were examined using paired t-tests. RESULTS: The density of the suture decreased significantly after expansion (T0-T1) with both types of RME (p = 0.000). In the retention period there was a significant increase of the sutural density (p = 0.007) although it did not achieve the initial level (p = 0.002). CONCLUSIONS: 1. The midpalatal suture was opened in all analysed patients.2. In postpubertal patients a retention time of six months does not allow sufficient reorganization of the suture.3. Therefore, a retention period longer than six months seems to be beneficial to prevent relapses in postpubertal patients.