MINIMALLY INVASIVE SURGERY TO FACILITATE MICRO-IMPLANT SUPPORTED MAXILLARY SKELETAL EXPANSION IN ADULT PATIENTS.

Introduction The aim of the present study is to evaluate the skeletal modifications induced by maxillary expansion supported by palatal micro-implants and localized osteotomies produced with minimally invasive surgical technique in young-adult and adult patients. In the present investigation, osteotomies had a lower extension than the ones used in conventional surgically assisted rapid palatal expansion (SARPE), to adopt a minimally invasive surgical technique that can be performed with greater comfort for the patient and less post-operative sequelae. More in detail, the localized osteotomies were executed only in the anterior part of the midpalatal suture and bilaterally at the basis of the zygomatic process of the maxilla without involvement of the piriform rim. These areas represent a great resistance to the lateral maxillary movement. Furthermore, they are of simple surgical access and don’t present important arterial plexuses. Patients requiring micro-implant supported maxillary expansion and/or SARPE routinely undergo a pre-treatment cone-beam computed tomography (CBCT) of the skull, to plan the surgical operation and, one month after treatment a secondary CBCT for a surgical and orthodontic control. CBCT is a low radiation tomography, extensively used in maxillofacial surgery and in dentistry. For the implementation of this study, that aims at evaluating the efficacy of micro-implant-supported maxillary expansion in combination with localized osteotomies, only radiologic exams that are anyway needed for the planning and post-treatment evaluation were used. Aim The aim of the present study is to evaluate the advantages introduced in the treatment of maxillary constriction by the therapy with micro-implant supported Maxillary Skeletal Expander (MSE) and localized osteotomies in young-adult and adult patients. The main objective is to evaluate the efficacy of the technique, by measuring the movement of skeletal landmarks in the midface, particularly on the maxillary and zygomatic bones, and on the lateral wall of the nose, by comparing the pre-treatment and post-treatment CBCT. For this particular technique, a new methodology for digital planning of position of MSE and miniscrews on patient CBCT was developed. Furthermore, incorporation of 2 additional miniscrews to the original MSE design, which conventionally features only 4 miniscrews, was developed with the aid of computer aided design – computer aided manufactured (CAD-CAM) technology. Methods The study presented the following steps: ▪ Development of a digital planning methodology for positioning the miniscrews and MSE appliance on pre-treatment CBCT ▪ Development of a CAD-CAM methodology for incorporating 2 additional miniscrews to the original MSE design with 4 miniscrews ▪ Selection of patients with age above 17 years, without congenital craniofacial syndromes, who require intervention of maxillary skeletal expansion ▪ Acquisition of initial CBCT with 17 x 13.5 cm field of view (FOV) ▪ Intervention of maxillary expansion supported by palatal micro-implants and localized osteotomies executed with minimally invasive surgical technique ▪ One month after treatment, acquisition of post-treatment CBCT with 17 x 13.5 cm FOV ▪ Analysis of skeletal modifications in the midface (maxillary bone, sphenoid bone, zygomatic arch, nasal cavity, etc.), by comparing the pre- and post- treatment CBCT with a 3D software (OnDemand software by Cybermed) Results The new methodology allowed the digital planning of MSE and miniscrews positioning on patients’ CBCTs, and the incorporation of two additional miniscrews to the original MSE design through CAD-CAM technology. In the clinical trial, a total of four patients had an average age of 27.6 years (range 22.1 – 39.9 years). MSE appliance was activated by an average of 6.0 mm and generated a parallel split of the midpalatal suture of 3.4 mm, 3.0 mm and 3.6 mm at anterior nasal spine (ANS), nasopalatine foramen (NPF) and posterior nasal spine (PNS), respectively. Skeletal modifications were found in all CBCT sections evaluated in the study (axial palatal, upper nasal, coronal zygomatic, axial zygomatic), indicating that all midfacial bones are affected by maxillary expansion with MSE and localized osteotomies. Particularly, skeletal changes were noticed also in CBCT sections above the lateral maxillary osteotomies (LMOs), in the maxilla, zygomatic bone, zygomatic arches, and nasal cavity. In the upper nasal section (UNS) the maxilla was laterally displaced by 2.4 mm and 0.9 mm, at its anterior and posterior extremities, respectively. The frontozygomatic angle (FZA) increased by 1.9° (average of right and left side), while the lower interzygomatic distance increased by 2.9 mm, indicating a rotation of the zygomatic bone in a lateral direction. The zygomatic arch was affected by bone bending phenomena and was deflected in an outward direction, with increase in the anterior intermaxillary distance by 1.7 mm and in the posterior inter-zygomatic distance by 1.6 mm. The nasal width (NW) parameter increased by 2.9 mm with treatment: this anatomical finding is the basis for a potential improvement in nasal breathing for patients suffering from increased nasal airway resistance. The cited modifications in skeletal structures above lateral maxillary osteotomies (LMOs) are most likely due to the fact that LMOs didn’t involve the piriform rim of the maxilla, and this point needs further investigations. Regarding dentoalveolar modifications, the inter-molar distance increased by 7.4 mm, and molars underwent a small dentoalveolar tipping in a buccal direction by 1.1° (average of right and left side), as evidenced by the change in molar basal bone angle (MBBA). No intra-operatory hemorrhage nor post-operatory bleeding was reported in treated patients, probably due to the lack of pterygopalatine suture surgical disjunction. A limitation of the study is its small sample size, represented by 4 patients. A larger number of patients is required to confirm the above results.