Abstract
Accelerating orthodontic tooth movement is a topical issue. Despite the different techniques described in the literature, the corticotomy is the only effective and safe means of accelerating orthodontic tooth movement. Although effective, the corticotomy presents significant postoperative discomfort. The aggressive nature of these particular methods, related to the elevation of mucoperiosteal flaps and to the length of the surgery, has resulted in reluctance to proceed with this technique among both patients and the dental community. To overcome the disadvantages of the corticotomy, this technical note describes an innovative, minimally invasive, flapless procedure combining piezoelectric surgical cortical micro-incisions with the use of a 3D Printed CAD/CAM surgical guide.
The mean duration of fixed orthodontic treatment poses a high risk of caries, external root resorption, and decreasing patient compliance. Accelerating orthodontic tooth movement, with the resulting shortened treatment duration, is therefore a topical issue. Despite the different techniques described in the literature, the corticotomy is the only effective and safe means of accelerating orthodontic tooth movement; however, there are few published reports on this subject. It has been suggested that the biological basis of accelerated orthodontic tooth movement is mediated by a regional acceleratory phenomenon. The hypothesis is that the corticotomy can lead to intensified osteoclastic activity, resulting in osteopaenia and increased bone remodeling.
The corticotomy used in accelerating orthodontic tooth movement, also termed corticotomy-assisted orthodontic treatment (CAOT), consists of small perforations on the alveolar bones along the way by which the tooth would be moved. Although effective, CAOT presents significant postoperative discomfort. The aggressive nature of these particular methods, related to the elevation of mucoperiosteal flaps and to the length of the surgery, has resulted in reluctance to proceed with this technique among both patients and the dental community. Initially the cortical incisions were performed using a bone bur, which had the potential to damage the roots of neighbouring teeth; more recently the corticotomy has been performed by means of a piezoelectric surgical micro-saw.
An innovative, minimally invasive, flapless procedure combining piezoelectric surgical cortical micro-incisions with the use of a 3D Printed CAD/CAM (computer-aided design and computer-aided manufacturing) surgical guide, which overcomes the disadvantages of the corticotomy, removing the need for flap elevation, is described herein.
Materials and methods
Manufacture of the surgical template
The subject treated with this technique was referred to the Department of Oral and Maxillofacial Science of “Sapienza” University of Rome. The patient was a 20-year-old female, who presented a bilateral class I molar malocclusion with severe crowding. A corticotomy was indicated to facilitate the treatment. The patient did not present any systemic contraindications to this treatment and provided written informed consent to undergo the procedures. The guidelines of the Declaration of Helsinki were followed.
After taking a first impression, a custom impression tray was manufactured on the plaster cast to make an impression as wide as possible of the fornix. Once the impression was taken and a cast built, an acrylic radiological template that covered the occlusal surface of the molars and premolars and the margins of the canines and incisors, extending as deep as possible into the vestibular fornix between the first right upper premolar and first left upper premolar, was manufactured. Gutta-percha markers were inserted into the acrylic radiological template. This template was used as a guide for the construction of the surgical guide in a CAD environment.
The patient, with the templates in place, underwent a cone beam computed tomography (CBCT) scan of each arch separately; the radiological templates were also CBCT scanned separately. DICOM images were acquired using Mimics software (Materialise, Leuven, Belgium), which allows for the segmentation of three-dimensional (3D) medical images obtained from CT or CBCT scans. Images of the arches, teeth, and radiological templates were transformed into 3D models and saved in an STL file. STL files were acquired using the 3D modelling software application Rhinoceros 3D (Robert McNeel & Associates, Seattle, WA, USA), and the models of the templates acquired were aligned with a point-to-point registration on the 3D bone models. The software allows the 3D model to be viewed from different perspectives and planes with a perfect rendering.
The space between the roots of each tooth from the first right premolar to the first left premolar was evaluated, and a longitudinal axis parallel to each root was designed. Following the direction of the pre-determined longitudinal axis, the 3D model of the radiological template was modified in the software, performing cuts of the same dimension as the piezoelectric cutting insert (1 mm) ( Fig. 1 ). Cuts were performed at a distance of 2 mm from the papilla up to the vestibular fornix, 2 mm above the apex of the tooth. The 3D STL model of the radiological template was transformed into a surgical guide, with the slots designed to guide first the scalpel blade and then the piezoelectric cutting insert ( Figs. 2 and 3 ). The 3D STL model of the surgical guide was printed using an Alaris 30 Desktop 3D Printer (Objet Geometries Ltd., Rehovot, Israel).
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