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Understanding the Facial Changes Associated with Postoperative Swelling in Patients Following Orthognathic Surgery

Chung How Kau, Stephen Richmond, and Andrew Cronin

INTRODUCTION

Advancements in three – dimensional (3D) technology have accelerated at a tremendous pace over the last two decades, with newer machines and software support appearing rapidly in the marketplace. This now means that applications for the clinical settings can be created and used in routine diagnosis, treatment planning, and patient education.

Broadly, 3D imaging devices may be classified as internal soft and hard tissue devices or external surface scanners. Internal imaging devices consist of 3D conventional and cone beam computed tomography scanners,^1-3 magnetic resonance imagers and ultrasound devices. These provide a large amount of clinical data but are radiation dose-intensive and often costly. External surface scanners tend to be less invasive and less expensive to use. These include light- based scanners, moir é fringe techniques,^4,5 laser scanning,^6-11 and stereo-photogrammetry.^12,13

Due to the advantages of surface acquisition systems, many early studies tended to favor the use of external surface scanners. The variety of applications with these 3D devices has resulted in a better understanding of the craniofacial form. In recent times, 3D images have been created to establish databases for normative populations,14 facial averages,¹⁵ and cross-sectional growth changes,^16,17 as well as for assessing clinical outcomes in surgical18-24 and non-surgical^25-27 treatments in the craniofacial region.

One area of interest to head and neck clinicians, which include plastic surgeons, oral and maxillofacial surgeons, and orthodontists, is the study of soft tissue changes associated with orthognathic surgery. The traditional method of understanding post- operative soft tissue changes was to plot linear measurements on landmark-based points.²⁸ Other newer methods have compared treatment changes between groups of normal adults and those with facial disproportion29 by comparing the color codes on facial deviation maps. More recently studies have also compared facial asymmetry before and after surgery.³⁰

3D surface imaging has proven to be an effective tool in the study of facial morphology. The 3D images are obtained by laser triangulation when a distortion of the light pattern falls on the surface of a subject. The scanning process is noninvasive and normally completed within a few seconds. Previous studies have reported on the validity and accuracy of the commercially available Minolta scanners and found them to be highly accurate.10,31-33 Furthermore, 3D soft tissue capture is reliable and reproducible.³⁴

The application of 3D surface imaging to the understanding of facial swelling can result in answers that provide clinical information to both patient and clinician.

APPLICATION OF SURFACE IMAGING

This section describes the usefulness of 3D surface imaging for understanding facial swelling in a group of orthognathic post- operative subjects. Some of the information has previously been reported.³⁵

Subjects

12 subjects (seven males and five females) with a mean age of 28.5 years were studied. Each of the subjects required orthognathic surgery on either one or both jaws. Five patients presented with a Class II skeletal pattern and seven patients with a Class III pattern. Each patient received a routine drug regime that consisted of three doses of 1.3 g Augmentin and 8 mg Dexametasone, one dose at the induction of anesthesia and two other postoperative doses in the hospital during the recovery period. All subjects were discharged within 3–5 days following surgery.

Three – dimensional imaging system

The laser imaging scanning system previously described was used, only a brief introduction will be made here. The system consisted of two high – resolution Minolta VIVID VI900 3D (Konica Minolta Sensing, Inc, Osaka, Japan) cameras, with a reported manufacturing accuracy of 0.3 mm, operating as a stereo- pair. Each of these cameras emits an eye- safe Class I laser (US Food and Drug Administration) of wavelength 690 nm at 30 mW with an object-to- scanner distance of 600–2500 mm and a fast- mode scan time of 0.3 seconds. The system uses a one- half-frame transfer charge- coupled device and can acquire 307,000 datapoints. The scanners were placed at a distance of 1350 mm from the head frame.

The scanners were controlled with multi- scan software (Cebas Computer GmBH, Eppelheim, Germany), and data coordinates were saved in a VIVID file format (.vvd). Information was transferred to a reverse modeling software package Rapidform 2006 PP2 (RF6; INUS Technology Inc, Seoul, Korea) for analysis. This software provides nine different 3D work activities together, which allow high- quality polygon meshes, accurate freeform nonuniform rational B – spline surfaces and geometrically perfect solid models to be created. RF6 generates data as absolute mean shell deviations, standard deviations of the errors during shell overlaps, maximum and minimum range maps, histogram plots, and color maps. All linear measurements are made in millimeters.

Data capture technique

A custom- built studio facilitated standardized light conditions. Natural head posture was adopted for this study, as this has been shown to be clinically reproducible.37 The subjects sat on a self- adjustable stool and were asked to look into a mirror with standard horizontal and vertical lines simulating a cross marked on it. They were asked to level their eyes to the horizontal line, and the midline of the face was aligned to the vertical line. Adjustments to seating heights were made to assist the subjects in achieving natural head posture. The subjects were also instructed to swallow hard and to keep their jaws in a relaxed position just before the scans were taken. The total scan time was approximately 7.5 seconds.

Data processing of left and right facial scans

Extraneous data were removed by an in- house- developed software subroutine.38 This automatic and systematic process further reduced the scanned images into shells and identified those small shells that represented minor scanning distortions. These images were smoothed out, while preserving all shape and volume, and the left and right scans were aligned to one another based on the areas of overlap of the faces. The pre- merged scans were carefully checked individually. and unwanted areas that could not be automatically removed were done so manually by dividing the unwanted areas from the main shell before proceeding to the next stage. Recorded in millimeters, the mean score for left and right scans gave an indication of the data reliability. Finally, one whole face was generated for each subject.

Facial analysis

3D laser scans were recorded over six time periods (T1 – presurgical scan; postoperatively: T2 – 1 day, T3 – 1 week, T4 – 1 month, T5 – 3 months, and T6 – 6 months). To facilitate the study of surface changes associated with facial swelling after surgery, the surface scan recorded at the sixth month (T6) was used as the baseline to compare all the surface changes after surgery.

Each individual’ s surface scan for the time period was overlaid on the baseline by aligning five points on the facial scans (four points at the outer and inner canthus of th/>