Original article

Skeletal and dental changes accompanying rapid midpalatal suture opening☆

In growing children with transverse malocclusion problems, various types of rapid maxillary expanders (RMEs) have been effectively used in skeletal and dental expansions. We evaluated 3-dimensional dentopalatal changes in growing children who underwent maxillary expansion using RMEs and bonded RMEs.

We investigated dentopalatal changes in 20 patients treated with bonded RMEs, 19 with RMEs, and 38 control patients. Dental plaster models before and after expansion were scanned 3-dimensionally and superimposed to evaluate transverse expansion, expansion ratio, angular expansion, and palatal expansion height ratio.

Using bonded RMEs, similar anterior and posterior dental expansions were achieved with an efficiency of 69%-76% (expansion ratio), and palatal soft-tissue expansion occurred more apically in the posterior area (palatal expansion height ratio, 1.00) than in the anterior area (palatal expansion height ratio, 0.64). Using RMEs, a larger posterior dental expansion was achieved, with an efficiency of 106%-117% (expansion ratio), than anterior dental expansion (55%-60%), and palatal soft-tissue expansion occurred more apically in the posterior area (palatal expansion height ratio, 0.99) than anterior area (palatal expansion height ratio, 0.23).

Dental expansions in the anterior and posterior areas were similar using bonded RMEs, whereas the posterior dental expansions were larger than those of the anterior area using RMEs. The entire palatal soft-tissue slope expanded in the posterior area, whereas the occlusal part expanded in the anterior area using RMEs and bonded RMEs.

Various designs of mini-implants assisted rapid palatal expander (MARPE) appliances can impact treatment effectiveness through their biomechanical effects. The purpose of the study was to study the stress distribution and displacement with four different designs of the MARPE appliance on the craniofacial complex.

A 3D finite element model of the craniofacial complex was created from CBCT DICOM data, comprising four distinct groups. Each group consisted of one 4-hole expansion screw positioned between the second premolar and first molar in all models. Group 1 used four single-cortical mini-implants (1.5 × 8 mm) engaging only the palatal cortex. Group 2 employed four mini-implants (1.5 × 11 mm) engaging both the palatal and nasal cortices. Group 3 had monocortical implants on the palatal slopes, while Group 4 was similar to group 3 with implants in the acrylic wings. Comparisons between groups were made for anchorage (groups 1 and 2), mini-implant position (groups 1 and 3) and surface effect (groups 3 and 4). Von Mises stresses and displacements at various skeletal and dental points were evaluated using ANSYS software.

The highest stresses were observed in the maxillary, pterygoid and zygomatic bones, as well as in the mid- palatal suture in all four groups. Downward and forward rotation of the craniofacial complex was noted. Group 2 showed greater skeletal expansion than group 1. Among groups 1 and 3, group 3 showed a better stress distribution. Group 4 showed less dentoalveolar rotation than group 3.

The MARPE appliances had an impact on the craniofacial complex with stresses on the mid-palatal suture, maxillary bone, pterygoid bones and anterior teeth. Clockwise rotation of the maxilla, zygomatic bones and dentition was noted, while the pterygoid bones and pterygoid suture were displaced backwards. MARPE with bicortical anchorage produces better skeletal expansion. Placing implants on the palatal slopes with acrylic wings results in better skeletal expansion with less clockwise rotation of the dentition.

This study aimed to compare the effects of 3 different bone-borne type expansion appliances used in the surgically-assisted rapid palatal expansion (SARPE) by finite element analysis.

Three different miniscrew-supported palatal expansion appliances were modeled. Median and lateral osteotomies were performed without pterygomaxillary suture separation. Model I consisted of a palatal expander with 2 miniscrews placed 4 mm far from the midpalatal suture. In model II, 2 miniscrews were located at the alveolar ridge between the first molar and the second premolar. In model III, 4 miniscrews were placed as a combination of the first and second models. Stress distributions and amount of displacements were evaluated with Ansys software (version 19.2; Ansys, Canonsburg, Pa) for 5-mm expansion in a symmetrical finite element analysis model to reflect the clinical situation.

SARPE simulation using miniscrew-assisted maxillary expanders for all models showed a rotation and tipping of the maxilla. The largest displacement was found for the anterior part of the palate in model II and the posterior part in model III. Although a wedge-shaped expansion pattern was observed in all models, this form was more prominent in model II. The highest stress value (0.91 MPa) was measured in model I, and the lowest value (0.004 MPa) was measured in model II for the anterior nasal spine region. The highest stress value (0.51 MPa) was measured in model III, and the lowest value (0.12 MPa) was measured in model II for the posterior nasal spine region. The lowest stress values were measured in model II for all the craniofacial and maxillofacial structures.

Among the models, the lowest stress distribution conditions for craniofacial and maxillofacial structures were found in model II. The largest displacement was found at the incisors and anterior part of the maxilla for model II. The greatest displacement was found at the posterior region for model III.

This study aimed to analyze the variation of dentoskeletal effects after rapid maxillary expander therapy in subjects with different vertical growth patterns.

The study sample consisted of 94 patients (32 males, 62 females; mean age 8.9 ± 1.5 years) treated with rapid maxillary expander (RME) anchored on first permanent molars. For each subject, lateral cephalograms and maxillary digital dental casts were available before RME, immediately after appliance removal, and 1 year after appliance removal. All the subjects were divided into 3 groups according to their vertical facial patterns (low-angle, normal-angle, and high-angle). Cephalometric analysis was conducted on lateral cephalograms. The virtual 3-dimensional models were used to analyze the torque of the first permanent molars and intercanine and intermolar width. The differences between the vertical facial subgroups were contrasted by analysis of variance multicomparison test (P <0.05).

In the short-term (from before to immediately after RME removal), high-angle subjects showed a mandibular clockwise rotation compared with other groups. No significant long-term vertical and sagittal skeletal changes (from before to 1 year after RME removal) were found between the groups. A greater increase in maxillary molar torque was observed in high-angle subjects than in the other groups. The low-angle patients showed a greater increase in the intercanine diameter.

Hyperdivergent subjects showed increased buccal tipping of the anchor molars after the expansion. Hypodivergent and normodivergent subjects showed lower buccal tipping after the expansion and an increased expansion effect in the anterior region.

This review aims to provide current knowledge about the efficacy, mechanism, and multidisciplinary collaboration of rapid maxillary expansion (RME) treatment in pediatric obstructive sleep apnea (OSA). OSA is a chronic disease characterized by progressively increasing upper airway resistance, with various symptoms and signs. Increasingly the evidence indicates that RME is a non-invasive and effective therapy option for children with OSA. Besides, the therapeutic mechanism of RME includes increasing upper airway volume, reducing nasal resistance, and changing tongue posture. Recent clinical researches and case reports also show that a multidisciplinary approach improves sleep-disordered breathing in children. Applied with adenotonsillectomy, mandibular advancement, continuous positive airway pressure, and comprehensive orthodontic treatment, RME can be more effective in recurrent or residual OSA.

This study aimed to verify a finite element (FE) model for bone-anchored rapid maxillary expansion. In addition, the stage of ossification of the midpalatal and circummaxillary sutures and their impact on expansion were analyzed.

Six patients were treated for maxillary transverse deficiency using the maxillary skeletal expansion appliance in an in vivo study. Preexpansion and postexpansion cone-beam computed tomography images were superimposed to analyze the expansion pattern of the midpalatal suture and maxilla displacement. In FE stimulation, the material property of the midpalatal suture was verified using a simple model, and the impact of 3 surrounding sutures was evaluated using a 3-dimensional skull model.

All patients demonstrated a parallel pattern of expansion in the midpalatal suture, with the movement of the maxilla in an upward and forward direction. In the FE simple model, the maximal reaction force on the expander was significantly decreased to the values approximated to the clinical findings when Young’s modulus of the midpalatal suture was 0.15 MPa and ν was 0.1 or 0.3. Three different deformation patterns were observed in the skull model when the settings of the 3 surrounding sutures were assigned with various ossification stages.

The material properties of the midpalatal suture play a crucial role in determining the reaction force on the expander. The ossification stage or the assumptions of material properties in surrounding sutures has a decisive influence on the expansion pattern of bone-anchored rapid maxillary expansion.