3D Photogrammetry Versus Commercial Scanners for Accurate Repositioning of the Maxilla for Correction of the Dentofacial Deformity.

In orthognathic surgery, the precise repositioning of the maxilla after Le-fort I osteotomy is a challenging procedure because there is no room for error in this step if the procedure is to be accurate.Transferring the virtual position of the maxilla to the real operative field via the intermediate occlusal splint fabrication, which is the most commonly used method, ensures only the intended position of the maxilla in the transverse, sagittal planes and cannot guarantee its vertical position in relation to the skull base. The vertical maxillary repositioning usually relies on a manual intraoperative adjustment using either intra-oral or extraoral reference points and affected by the degree of autorotation of the mandible that occur as a result of the surgical maneuvers operated by the surgeon intraoperatively. This makes the reliability of and precision in transferring virtual surgical plans to the operative field is still unpredictable defeating the main advantages of 3D technology. Moreover, it can be time consuming.

Many attempts to obtain a more reliable method for positioning the maxilla, independent of the mandible, have been made such as a series of maxillary reposition templates, patient specific osteosynthesis plates and navigation assisted surgery and it yielded satisfactory results. Also, intraoperative occlusal-based devices that transfer virtual surgical planning to the operating field for repositioning of the osteotomized segments was introduced. Most of the time the surgeon looks for new modalities to optimize his surgical results, simplify the execution of the surgery and at the same time to meet the patients' demands and expectations.

Photogrammetry is a versatile, readily available technique that allows for creating a 3D model from 2D photographs in an affordable manner and with a high levels of precision equivalent to other tools that are generally more expensive and less available such as a commercial scanner. It has several applications in the life and earth sciences, medicine, osteological studies, architecture, topography, archaeology, crime scene investigation, cinematography, and engineering. So, the present study aims to assess the accuracy gained and the feasibility of using this technique for transferring the virtually intended maxillary segment position to the real operation compared with the commercial scanners.

Trial design:

Randomized Controlled Clinical Trial. Parallel group, two arm with allocation ratio 1:1.

Sample size:

This study will be conducted for 24 patients, 12 patients per group.

Patients will be selected from the outpatient clinics of Oral and Maxillofacial Surgery Department and Orthodontic Department, Faculty of Dentistry, Cairo University. The trial is to be conducted in the Oral and Maxillofacial Surgery Department, Cairo University.

The eligible patients will be randomly allocated into 2 groups:

Intervention group; Maxillary segment repositioning using positioning guide for the maxilla and the pre-bent plates that is fabricated by the reverse engineering technology utilizing the 3D photogrammetry technique.

Comparator group; Maxillary segment repositioning using positioning guide for the maxilla and the pre-bent plates that is fabricated by the reverse engineering technology utilizing the commercial scanners.

General operative procedures:

Patients of both groups will be subjected to:

• Comprehensive clinical and radiographic examination.
• Pre-operative photographs will be taken.
• Primary upper and lower impressions will be made for the selected patients and the impression material will be poured using hard dental stone to make dental models.

Surgical planning / Preoperative workup;

For both groups:

• Virtual planning: Using dedicated software, 3D digitized bony maxilla will be virtually osteotomized and repositioned to the new intended postoperative position.
• Printing of the corrected 3D model and plate pre-bending (2.0 titanium mini plates will be selected and perfectly adapted over the corrected and printed 3D model).
• Scanning of plate adapted on the printed 3D model to generate a virtual model.
• For the intervention group; Pre-bent plates will be scanned using 3D photogrammetry technique and a specific software dedicated for image acquisition will be used.
• For the Comparator group; Pre-bent plates will be scanned using the commercial scanners and imported for virtual designing of the positioning and locating guide.
• A guide will be designed on the reproduced virtual model. This guide will be used intraoperative as a locating and positioning guide for the maxilla and the plates.
• To ensure a more precise location of the positioning guide, the cutting guide will be also constructed and act as a cutting and screw hole locating guide as well. This will be done by incorporating the drill holes to be used for final placement and fixation of the maxilla, in the cutting guide.

Surgical procedure:

• The procedure will be performed under general anesthesia with nasotracheal intubation and controlled hypotension.
• Lidocaine Hydrochloride with 1:200,000 of Epinephrine solution will be utilized for hemostasis.
• Scrubbing and draping of the patient will be carried out in a standard fashion.
• Intra-oral maxillary vestibular incision will be used, elevation of the flap and dissection will be performed exposing the antero-lateral and posterior-lateral aspects of the maxilla.
• Cutting surgical guide will be adapted over the maxilla, the screw holes incorporated in the surgical guide will be drilled and then the osteotomy will be performed and completed using chisels.
• Mobilization of the maxilla will be done. Finally, the positioning and locating guide for the maxilla and the plates will be used. While the guide in place, the plates will be fixed into their position.
• After fixation of the plates, the guide will be removed.
• The rest of the orthognathic surgery (mandibular osteotomy, genioplasty if needed) will be completed in a conventional fashion.
• Debridement, irrigation of the surgical field followed by wound closure and suturing using 3-0 resorbable suture.

Postoperative care:

• Ice packs will be applied for 20 minutes every 1 hour for the first 24 hours to minimize the edema.
• High caloric soft diet will be instructed.
• Good oral hygiene will be emphasized.
• All patients will be kept on the following regimen;
• Ampicillin/sulbactam 1500 mg vial Intra-muscular( IM) injection every 12 hours for 5 days.
• Oral Metronidazole 500 mg every 8 hours for 5 days.
• Diclofenac sodium75 mg IM injection whenever needed.
• Diclofenac Potassium 50 mg tablets will be given every 8 hours for control of pain.
• Dexamethasone sodium phosphate 8 mg/2ml IM injection on 8 doses, the first 4 doses will be given every 6 hours, and then it will be tapered on next 4 doses to half the dose every 6 hours.
• Methylprednisolone acetate 80 mg/ml IM injection will be given with the last dose of Dexamethasone sodium phosphate.
• The oral antibiotic regimen (Amoxicillin/Clavulanic acid 1000 mg everym12 hours) will be continued for 5-7 days postoperatively to guard against infection.

Number of visits \& follow up period:

• All patients will be advised to stay on a soft diet for 4-6 weeks to avoid any undue forces on the surgical site.
• Postoperative CT will be obtained one week postoperatively.