Soft tissue morphology of the naso-maxillary complex following surgical correction of maxillary hypoplasia

Abstract

Orthognathic surgery is undergone to improve facial and dental aesthetics and to improve function. Three dimensional (3D) soft tissue analysis based on stereophotogrammetry provides a realistic measurement of facial morphology. There is a need for objective assessment of surgery outcomes. The study aim was to evaluate the 3D naso-maxillary complex soft tissue morphology following Le Fort I maxillary advancement and compare the findings with a local reference group. 3D images of 112 volunteers were captured using stereophotogrammetry and viewed by 8 lay people; 40 images (16 males and 24 females) were chosen as the reference group to have harmonious facial appearance. The linear and angular measurements of this group were compared with 35 patients (19 female and 16 male) who had maxillary advancement in the post-surgical group. Facial morphology post-surgery was similar to the reference group, except the nasal base width which was wider by 2.3 mm in males and 2.6 mm in females. In the orthognathic group, the females had a smaller nasolabial angle by 9.7° than the reference group. In conclusion, 3D imaging is a sensitive tool for analysing facial appearance. Compared with a control group, statistical differences were identified in soft tissue morphology which should be considered in surgical planning and patient consent.

The primary objective of orthognathic surgery is to improve facial and dental aesthetics to an acceptable clinical standard often with the secondary objective of improving function. For the majority of patients the improvement in their soft tissue appearance is the prime motivating factor for seeking surgical treatment.

At present the use of cephalometric ‘normal’ values aid diagnosis, treatment planning and assessing outcome. The values should be representative of the individual being treated (i.e. ethnicity) and be a true representation of the patient. The available cephalometric values are two dimensional (2D) measurements of three dimensional (3D) facial morphology and therefore lack geometric accuracy. In addition cephalometric measurements are poorly correlated with the perception of facial appearance and they are often not gender specific. 3D soft tissue analysis based on stereophotogrammetry provides a realistic, meaningful measurement of facial morphology, which informs the clinical evaluation of dentofacial deformity. To date no ‘normal’ soft tissue 3D data have been published to characterise facial morphology adequately for the British population.

Subjective assessment of the face showed wide variations amongst clinicians and clear diversity when compared with lay assessors. There is a need for a reliable method to assess facial appearance in an objective manner. Previous studies have used the visual analogue score (VAS) as a method of subjectively assessing facial appearance. The VAS is a simple, quick to construct, valid, reliable, convenient, easily understood, readily accepted and easy to administer measurement method that can be used by both lay persons and professionals. There is a growing amount of evidence that showed the VAS to be a fairly reliable, valid and sensitive tool in the measurement of subjective phenomena, allowing scores on a large number of variables to be readily assessed by a panel of judges.

This study was designed to test the hypothesis that following surgical correction of class III skeletal patterns, by maxillary advancement, the final soft tissue appearance of the naso-maxillary complex was similar to an untreated reference group. The aim of the study was to evaluate the 3D facial appearance following the surgical correction of maxillary hypoplasia with a Le Fort I osteotomy and compare the findings with the 3D facial aesthetic norms of a local reference group.

Materials and methods

Ethical approval was obtained from the Local Area Ethics Committee.

Sample size calculation

The clinical significance of the difference in landmark location was derived from the results of a previous study and was set at 3 mm. A search of the literature indicated that the majority of soft tissue facial landmarks of potential interest had a standard deviation of ±3.0 mm. Applying a significance level of 0.05 and a power of 80% a sample size of 16 subjects was required. This meant that within each group a minimum of 16 patients was required.

Orthognathic group sample selection

In this retrospective study the records of patients who were 18–35 years of age and non-syndromic were selected from the multi-disciplinary dentofacial planning clinic over a two and a half-year period from October 2005 to June 2008. All patients were diagnosed with maxillary deficiency based on a comprehensive clinical and radiographic assessment and treated with a standard Le Fort I advancement procedure. The final position of the maxilla was determined by conventional 2D profile prediction methods and model surgery. None of the patients required any change in the vertical position of the maxilla or had facial asymmetry that required surgical intervention. A cinch stitch was applied if the alar base width had increased more than 3 mm peri-operatively. All patients were followed up postoperatively and full records including 3D images had been taken 1 year following surgery.

The records of 35 (19 female and 16 male) surgically managed cases, which had Le Fort I advancement for correction of maxillary hypoplasia in the anterior–posterior direction, were selected. The mean planned maxillary advancement was 7.5 mm (range 6–11 mm), there was no difference between the male and female groups. Vertical surgical changes were minimal.

Reference group

112 volunteers were recruited from within the local population from April 2008 to January 2009. Subjects were 18–35 years of age, non-syndromic, had no previous history of facial surgery or facial trauma and were Caucasian with both parents from the same geographic location.

A panel of 4 male and 4 female lay assessors generated the reference group. None of the lay panel had a dental or medical background. Prior to viewing the images, the lay panel were given basic instructions on how to rate them. They were instructed to ignore skin complexion, hair, position of ears and to concentrate on facial appearance with respect to facial balance and harmony. Each lay panel member viewed a PowerPoint presentation, which included an embedded 3D standard facial video clip of each of the participants, in a single sitting. The lay assessors rated each image for overall facial harmony on a 100 mm horizontal VAS scale marked with the anchors ‘least attractive’ and ‘most attractive’.

The VASs were ranked from most attractive to least attractive for each subject. Individuals who were ranked in the top two tertiles by at least 6 lay panel members were chosen to be part of the reference group which generated 40 cases (16 males and 24 females) as the reference group.

Imaging

Each individual from the reference and surgically managed groups were imaged, by the same operator (BSK) using the Di3D system (Di3D, Dimensional Imaging, Hillington Park, Glasgow, UK), which consisted of two camera stations placed at each side of the face to take a stereo image. Each station contained only a pair of colour high-resolution digital cameras (Eastman Kodak Company, Rochester, NY, USA). The face was simultaneously illuminated by commercial white-light studio flash units (Esprit Digital DX1000, Bowens, Essex, UK). For all captures, subjects were seated on a dental chair directly in front of the camera system ( Fig. 1 ). To standardise the images, the face of each subject was captured in natural head position and lip repose; this was achieved by asking the individuals to say ‘Mississippi’, and then told to swallow once and say ‘N’. It took 1 ms to capture the full face using the two camera stations. A personal computer required less than 5 minutes to produce a 3D model of the captured subject. Prior to image capture, the Di3D system was calibrated. A 3D model of the subjects face was built using Di3D software (Di3D, Dimensional Imaging, Hillington Park, Glasgow, UK).

Fig. 1
The Di3D system.

For each case, the face was captured according to the protocol above. Each image was viewed in the frontal view and then rotated slowly to the left and then to the right using GLview software ( home.snafu.de/hg/ ). During the viewing, the screen was captured as a video clip using screen recording software, Auto Screen Recorder (Wisdom Software Inc., Victoria, Canada). Each image was recorded for 30 s and the video clip was saved as an Audio Video Interleaved file (*.avi) for viewing later. This procedure was repeated for all 112 individuals. Each video file was embedded into a PowerPoint presentation (Microsoft ® PowerPoint 2000, Microsoft Corporation, USA). Images were embedded alternately male and female were possible. The presentation was saved onto a DVD (Imation, Schiphol, The Netherlands).

3D measurements

The 40 reference group images were viewed using software which allowed landmark digitisation (DiView4, Dimensional Imaging, Hillington Park, Glasgow, UK). The software allowed simultaneous viewing of the single image in three different windows, allowing rotation and magnification of the image ( Fig. 2 ).

Fig. 2
The screen capture when an image is viewed simultaneously in three windows, showing magnification and rotation.

The landmarks and measurements recorded are shown in Fig. 3 and Tables 1 and 2 . This procedure was carried out for 40 reference group images and for each of the orthognathic cases, by the same operator (TUN).

Fig. 3
Landmark locations.

Table 1
Landmark definitions (* bilateral left and right landmarks).
Landmark Definition
Nasion (N) The point in the midline of both the nasal root and the nasofrontal suture, always above the line that connects the two inner canthi, identical to bony nasion.
Exocanthion (Exc)* The point at the outer commissure of the eye fissure, located slightly medial to bony exocanthion.
Endocanthion (Enc)* The point at the inner commissure of the eye fissure, located lateral to the bony landmark.
Subtragion (Sbtr)* The most anterior inferior point on the anterior inferior margin of the helix attachment to the face, just above the earlobe.
Alar curvature (Ac)* The most lateral point on the curved base line of each ala, indicating the facial insertion of the nasal wingbase.
Pronasale (Prn) The most protruded point of the apex nose identified in lateral view of the rest position of the head.
Subnasale (Sn) The midpoint of the angle at the columella base where the lower border of the nasal septum and surface of the upper lip meet.
Cheilion (Ch)* The point located at each labial commissure.
Crista philtre (Cphi)* The peak of Cupid’s bow of the upper lip inferior.
Labrale superius (Ls) A point indicating the muco-cutaneous junction of the upper lip and philtrum.

Table 2
Landmarks used to define clinical linear and angular measurements.
Landmarks Clinical measurement
Linear
N-Sn Upper anterior face height
Ex(R)-Ex(L) Upper face width
Sbtr(R)-Sbtr(L) Middle face width
Ac(R)-Ac(L) Nasal base width
Sn-Prn Columella length
Ch(R)-Ch(L) Mouth width
En(R)-En(L) Nasal bridge width
Cphil(R)-Cphil(L) Philtrum width
Sn-LS Philitrum length
AcR-Prn Right nasal length
AcL-Prn Left nasal length
N-Prn Dorsal nasal length
Sn-LS Upper lip length
Angular
Ex(R)-N-Ex(L) Upper facial convexity
Sbtr(R)-Sn-Sbtr(L) Mid facial convexity
Ac(R)-Prn-Ac(L) Nasal tip convexity
Prn-Sn-LS Nasolabial angle
N-Prn-Sn Angle of facial convexity
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Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Soft tissue morphology of the naso-maxillary complex following surgical correction of maxillary hypoplasia
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