A 21-year-old male patient presented to our department with a complaint of maxillary retrusion following bilateral cleft lip and palate. Computer-assisted preoperative simulation with 2-stage procedure combining maxillary advancement by employing distraction technique and mandibular setback surgery was planned. The patient was subjected to CT scan of the face using 320-row area detector CT scanner (Aquilion ONE, Toshiba, Tokyo, Japan), which acquired CT scans (slice thickness, 0.5 mm) of the maxilla. Based on the CT data, 3D surface models of the maxilla were constituted from image processing software (Mimics 16.0; Materialise, Leuven, Belgium). The cephalometric analysis and 3D planning were done using simulation software to obtain a normal profile and occlusal relationship. The 3D inspection and metrology of the maxilla was constituted using Geomagic Qualify (Geomagic, North Carolina, USA) and FreeFrom plus 2014 software (Geomagic, North Carolina, USA). The 3D models were built and superimposed through a fully automated voxel-wise method using the pre-surgery cranial base as reference. The 3D scanner (Rexcan DS2, Solutionix, Seoul, Korea) was used to obtain 3D surface data of the titanium plate (KLS Martin, Umkirch, Germany). The 3D surface data of titanium plate were imported to the Freeform Plus software (Rock Hill, USA).
In the preoperative simulation planning; the computer-assisted bone movement and positioning of the plate were carried out using 3D images (Fig. 1). The virtual Le Fort I osteotomy on the maxilla and forward movement of the virtual maxillary fragment was carried out using the Freeform Plus software. The hole was created using the virtual drill at the 3D position as computed by the preoperative simulation prior to the bone movement. The displacement distance between the points before and after the bone movement (Fig. 1A & B) and distance between the points which superimposed Lefort titanium plate of 11 mm (right) and 9 mm (left) were calculated using FreeFrom plus software. (Fig. 2). In the second step, the mandible was moved backward till the occlusal relationship was achieved.
During the real-time surgery (1st stage) Lefort type I osteotomy was carried out and the zurich pediatric maxillary distractors were placed. The distractors were adjusted on a day to day basis and the predetermined advance movement of maxilla was obtained on the 23rd day. In the 2nd stage (i.e on 23rd day) the distractor was removed and the maxillary bone was fixed using Lefort titanium plate (one Lefort plates of 9 mm, one Lefort plates of 11 mm and two Lefort plates). This enabled holding the maxilla at its advanced position and kept it stable by fixing the titanium plated to the screw holes created at the pre-designated site. The mandibular setback surgery (intraoral vertical ramus osteotomy) was performed, which manipulated the mandible and maxilla to obtain a planned normal occlusal relationship. The plate and screw position during the actual surgery and after the completion has been shown in Figs. 3-4 .
The accuracy of the simulation results was analyzed using "3D comparison" with Geomagic Qualify (Rock Hill, USA). The cranial base and zygomatic arch were used as base to superimpose the virtual plan and postoperative scan images as the base bone were unaltered during the surgery. The differences between the virtual plans and postoperative results are shown in Fig. 5. In Fig. 3A and B, the arrows show the screw positions prior to the movement of the bone while the arrows in Fig. 4A and B show the screw positions after the movement of the bone. The error of the maxillary position was noted to be less than 1 mm. The preoperative planning employing a virtual plate was found to be more reliable and less time consuming. The required time for virtual surgical planning was about 60 min.