Abstract
A tapered mandibular contour is popular with Far Eastern Asians. This study describes a safe and accurate method of using preoperative virtual surgical planning (VSP) and an intraoperative ostectomy guide to maximize the esthetic outcomes of mandibular symmetry and tapering while mitigating injury to the inferior alveolar nerve (IAN). Twelve subjects with chief complaints of a wide and square lower face underwent this protocol from January to June 2015. VSP was used to confirm symmetry and preserve the IAN while maximizing the surgeon’s ability to taper the lower face via mandibular inferior border ostectomy. The accuracy of this method was confirmed by superimposition of the perioperative computed tomography scans in all subjects. No subjects complained of prolonged paresthesia after 3 months. A safe and accurate protocol for achieving an esthetic lower face in indicated Far Eastern individuals is described.
In Far East Asia, a wide lower face resulting from skeletal or masseteric hypertrophy is generally considered unesthetic, particularly in females. A tapered and oval-shaped face, accentuated with a lower jaw contour frequently referred to as the ‘V-line’, is particularly popular with Far Eastern Asians. Mandibular tapering and contouring surgery has become one of the most popular facial esthetic procedures in recent years.
There are generally two ways to achieve a desirable tapered lower face via skeletal surgery: (1) mandibular inferior border ostectomy (the V-line procedure), and (2) mandibular outer cortex splitting ostectomy. Both can be combined with narrowing and lengthening genioplasties. These procedures are highly effective in achieving the desired lower facial contour. However, avoiding injury to the neurovascular bundle and achieving symmetry of the facial skeleton during this process remain challenging even for the most skilled surgeons.
While virtual surgical planning (VSP) and the use of intraoperative guides have been popularized in reconstructive surgery, their uses in esthetic procedures are less discussed. A safe and accurate protocol of using VSP and an intraoperative ostectomy guide that is specific to mandibular tapering and contouring surgery for esthetic indications is described herein.
Patients and methods
Twelve subjects attending an aesthetic surgery center in Taipei, Taiwan, who ranged in age from 19 to 43 years, underwent the study protocol for mandibular tapering and contouring surgery from January to June 2015. There were two male and 10 female subjects. Subjects were ASA physical status I or II (American Society of Anesthesiologists) and devoid of any concurrent congenital or acquired dentofacial deformity. Subjective complaints included a wide lower face, a ‘square’ look, an ‘angry look,’ and inadequacy of botulinum A toxin tapering of the lower face. Mandibular angle hypertrophy was the diagnosis for the subjects. In addition to mandibular tapering and contouring, nine subjects also underwent unilateral angle sagittal ostectomy, five underwent malar reduction, and seven underwent narrowing and lengthening genioplasties. The reason for the additional procedures was to further taper the mandibular contour while maintaining the overall facial balance. The study protocol was approved by the Institutional Review Board of Cathay General Hospital, and signed informed consent was obtained from all subjects.
Virtual surgical planning
Image acquisition
Facial scans were acquired by cone beam computed tomography (CBCT) (i-CAT; Imaging Sciences International, Hatfield, PA, USA) and were performed with patients in natural head position (NHP). NHP was ascertained by asking the patient to look themselves in the eye in a mirror positioned 1.5 m in front of the scanner. NHP was adjusted and confirmed by the surgeon. DICOM files of the facial skeleton (0.25 mm in thickness) were then imported into Simplant software (Materialise, Leuven, Belgium) for processing.
Design of the ostectomy guide
Mimics software (Materialise, Leuven, Belgium) was used to design the virtual ostectomy. First, the inferior alveolar nerve (IAN) canal was traced from the lingula to the mental foramen, and then reconstructed in three dimensions ( Fig. 1 a) . The ostectomy border was designed by the surgeon virtually while maintaining a minimum distance of 2.0 mm from the neurovascular bundle ( Fig. 1 b). The side of the mandible with the IAN canal closer to the lateral bony cortex dictated the maximum extent of the ostectomy bilaterally. The mandibular contour was then examined in all orientations to ensure symmetry. An ostectomy guide was designed with the superior edge following the virtually designed ostectomy and the inferior edge cupping the mandibular body and ramus. The virtual ostectomy guide was exported as stereolithography files and fabricated by a rapid prototyping machine (Formiga P110; EOS, Munich, Germany) ( Fig. 1 c).
Intraoperative use of the ostectomy guide
The esthetic mandibular tapering and contouring operations were performed under general anesthesia via intraoral approach. A stable and accurate fit of the ostectomy guides at the mandibular angle was achieved after sub-periosteal dissection; these were secured with 2.0 × 6.0 mm screws via trocar access ( Fig. 2 a) . The anterior part of the ostectomy was performed with a reciprocating saw, while the posterior ostectomy with its acute curvature at the angle region was performed with an oscillating saw. Neither saw by itself will adequately complete the ostectomy due to surgical access and mandibular contour. The bone specimen was removed together with the ostectomy guide ( Fig. 2 b).
