Abstract
During a reduction malarplasty, precise sectioning of the zygomatic arch according to the plan formulated in the diagnostic stage is very important, because differences in the locations of the osteotomies in the left and right zygomatic arch will result in facial asymmetry, and arch osteotomies that are placed at locations other than those specified during planning elicit unwanted results. A method for the precise planning and sectioning of the zygomatic arch involving the use of computed tomography (CT) and a viewer program is presented herein. Furthermore, a case in which this method was applied during reduction malarplasty via a combined intraoral and external incision is described.
The reduction malarplasty is a common surgery among Asian populations, in which a wide bizygomatic width is often seen . The wide bizygomatic width is often due to a prominent zygomatic body and arch, and this problem can be solved via osteotomy of the zygomatic body with a technique that involves a wedge-section osteotomy in combination with a greenstick fracture of the arch . However, this technique is only applicable if there is a protrusion of the zygomatic body, and a protrusion of the zygomatic arch requires an osteotomy of the arch to relocate it inward.
During such osteotomies of the zygomatic arch, the location of the osteotomy is considered to be vital, because an osteotomy at a point that is far more anterior on the arch than optimal will result in an excess amount of the zygomatic process at the anterior part of articular eminence, which in turn will result in an inadequate reduction of the zygoma. If the osteotomy is performed at a point on the zygomatic arch that is far more posterior than optimal, sectioning may occur at the articular eminence and may result in interference that makes the inward movement of the zygomatic arch difficult. An additional reason that precise sectioning of the zygomatic arch exactly at the planned location is required is that osteotomies that are at different points on the left and right zygomatic arches result in facial asymmetry.
A method for the precise planning and sectioning of the zygomatic arch involving the use of computed tomography (CT) and a viewer program is reported herein. Furthermore, a case in which this method was applied for reduction malarplasty via a combined intraoral and external incision is described.
Technique
In this technique, the surgical planning for each patient is performed based on preoperative photographs, radiographs, and cone beam computed tomography (CBCT) images (3D eXam; Kavo Dental GmbH, Biberach, Germany). CBCT data of the craniomaxillofacial skeleton were obtained with 0.7 mm resolution. The patient data were stored in DICOM format (Digital Imaging and Communications in Medicine) and reconstructed into three-dimensional (3D) bone images using the software Invivo 5 (Anatomage, San Jose, CA, USA). The required amount of zygomatic reduction and the location of the osteotomy on the zygomatic arch were determined based on an analysis of the patient’s clinical photographs and the 3D images that were constructed using Invivo 5. Additionally, the location of the osteotomy on the zygomatic arch was placed as far posterior as possible to allow the zygoma to move inward easily.
Following determination of the sectioning location, the left and right points were chosen on the unchanged anatomy based on the soft tissue images using Invivo software. In practise, the uppermost part of the external auditory meatus is often used as point ‘A’. Additionally, point ‘B’, which is selected for zygomatic arch sectioning, was set on the arch on the bone images. All of the points were then translated into 3D coordinates. Based on these coordinates, the distances between the points were measured. The absolute value unit of the coordinate system in Invivo 5 is the millimetre. Also, with Invivo 5 it is possible to measure the distance between two points directly ( Fig. 1 ). The measured values were then reflected on the device (paper ruler, compass etc.), and the device with the measured value settings from surgical planning were applied to the operation field through an external incision ( Fig. 2 ).
