Dental and Skeletal Changes Following Bone- and Tooth-borne Maxillary Protraction with Miniscrews and Class III Elastics

The intervention involves placing four miniscrews (9mm or 7mm (PSM Medical Solutions, Tuttlingen, Germany)) – two on the anterior palate of the maxilla and two on the buccal surfaces of the mandible (one on each side between the permanent first and second premolar, or between the permanent canine and first premolar). They will be placed under local anaesthesia by orthodontic postgraduate students or orthodontists. Miniscrew insertion will be followed by an intraoral scan (TRIOS; 3Shape, Copenhagen, Denmark). The intraoral scan will be sent to the dental technician, who will design the maxillary and mandibular frameworks that will be fitted over the miniscrews, under instruction of the chief investigator/supervisor. The duration of the procedure will take 45 minutes. After 2 weeks, the frameworks will be cemented. Two weeks is the usual turnover time for dental laboratories. The maxillary framework will join the metal bands around the permanent first premolar and molar, bilaterally. There will be a traction button on the buccal surface of permanent first molar's metal band, to allow placement of Class III elastics to the lower framework, exerting a force to move the maxilla forward. A Hyrax screw (Forastadent, Pforzheim, Germany – 10mm) will be incorporated if needed, in patients with transverse maxillary deficiency. Similarly, the mandibular framework will join the metal bands around the permanent canines or first premolars (in the case where the canine has not erupted yet) and first molars. A traction button will be located on the anterior buccal surfaces of the framework, for placement of Class III elastics. The final metal framework designs will be printed by selective laser melting process using the material Remanium Star (Dentaurum, Ispringen, Germany), electro-polished, and the bonding surfaces will be sandblasted. The dental surfaces will be acid etched with 37% phosphoric acid gel for 30 seconds. After rinsing and air drying, Rely X Unicem (3M ESPE, St Paul, Minn) will be used to cement the appliances and will be light-cured for 30 seconds. Finally, fixation screws will be placed, to secure the frameworks over the miniscrews. The patient will then be instructed to use 6 oz 3/16-in Class III elastics full-time (i.e. at all times besides meals and brushing teeth), to be replaced at least three times a day. The cementation of the framework will take 45 minutes. Patients will be monitored 3-4 weeks after the appliances have been placed, followed by every 2 months subsequently. The total duration of the study for each participant will be a maximum of 12 months. Once the Class III malocclusion has been corrected, the miniscrews and elastics will be removed/discontinued. Dental measurements will be measured on the intra-oral scans, to assess the dental effects. Radiographically, cephalometric analysis of pre- and post-treatment lateral cephalograms will be conducted to assess the skeletal effects. Both pre- and post-treatment lateral cephalograms will also be superimposed to provide a visual aid of the skeletal and dental changes that occur over time. Before and after comparisons will be made with subsequent data analysis processed using SPSS statistical software with the aid of a statistician.