Three-dimensional analysis of the facial soft tissues.

Hren, Natasa Ihan ; Pogacar, Vojko

1. INTRODUCTION

Maxillofacial surgeon, as esthetic plastic surgeon and orthodontist for the diagnostic procedures and treatment planning of facial deformities use standard diagnostic procedures as x-ray images and computer tomography scans, plaster models of their teeth and standard photography of the face. Plaster models of teeth are good tool for planning esthetic and functional bite after treatment, but they are not sufficient for whole facial area. Standard roentgenographs as lateral and posterior projection of the head with standard analysis (lateral cephalogram) had been developed to good golden standard for diagnostic, but the difficult cases need also computer tomography scans with significant radiation risk (Khambay et al., 2002). Also these x-ray pictures are mainly for bone analysis and they offer only little information about the soft tissues of the face (for example there is the good information of the nose, upper lip and chin, but only in lateral view). So the analysis of the face as integrity is problem partially solved by standard photography (Moss et al., 2003). The analysis of the face photos is very difficult and subjective, routinely evaluate transverse discrepancy clinically and on 2D photographs. However, 2D photograph analysis of a 3D structure as the face is, provides incomplete data and does not account for differences in facial depth and shape (Moss et al., 1994, Miller et al., 2007). So the modern technology is developing the computer system for face soft tissue analysis on the basis of digital facial scans of the face surface. With this method we can reproduce the facial form in 3D to a greater precision. The whole face or different parts of the face can be evaluated for asymmetry and other facial characteristics (Da Silveira et al., 2003). These facial surface images are done by laser or optical scanners and by three-dimensional digitizing method.

2. METHOD

The innovative method of three-dimensional scanning and digital analysis of the face is developing together by Faculty department of maxillofacial and oral surgery, Medical faculty in Ljubljana with Engineering Design Lab of the University of Maribor, Faculty of Mechanical Engineering.

The three-dimensional scanning is done by optical white-light-scanner Atos II. The precision of that technologic scanner is very high for facial surface structure. Taking scans is very fast, only one scan is necessary for analysis and all that is advantage for patients. There is also very few unwanted data. Only the heavy light is a little disturbing but for very short period. The posture of the head is natural (Chiu & Clark 1991). The two examples of these face images are presented on fig. 1.

[FIGURE 1 OMITTED]

The 3D data was imported to a reverse modeling software Atos II. and Polyworks, but later we planed to develop more focused user friendly software for maxillofacial analysis. Each scan of the face (left and right images) was processed in order to remove unwanted data, registered and merged to produce a complete facial image. The facial shell was aligned to two planes: the mid-sagittal plane (Y-Z) and the inner cantus of the eyes (X-Z). The facial shell was divided into three parts; the upper part was defined as the part of the face above the inner cantus plane, the middle part ranged from the inner cantus plane to the plane through the outer commissures of the lips and the lower part was below this plane. To check for left/right symmetry the face was mirrored on the mid-sagittal plane.

3. DISCUSSION

Similar methods as our developing one are using in some medical centres in the world (Nute & Moss 2000, Ji et al., 2002). The Konica/Minolta Vivid 910 (20) is the example of laser scanner (Da Silveira et al., 2003) and these methods are disadvantaged because of possible laser damages. Also photo scanner as 3DMD is commercially available.

The 3D data also can be analysed by reverse modeling software package, Rapidform[TM] 2006 (@ INUS Technology Inc, Seoul, Korea). But in spite off that we decided to develop our own method comparable by them. The main reason is to use the advantages of cooperation of people of two very different faculty departments and that relationship can produce in the future not only the system for facial scanning, but also user-friendly software for a lot of research and clinical work; to determine the normal standards for women' and man' faces in Slovenia. This could be the base for assessment of facial deformities, better treatment planning and assessment of the surgical methods and clinical results.

4. CONCLUSIONS

The medical needs and contemporary technological development are the fields that will be in close relation in the future. The analysis of facial soft tissues in safe way for patients will be developing. Our innovative method is one example of these solutions. It respects the basal postulations and enables to develop individual needs as research method and treatment modality.

5. REFERENCES

Chiu, CS. & Clark, RK. (1991). Reproducibility of natural head position. J Dent 19., pp. 130,

Da Silveira, AC.; Daw Jr, JL.; Kusnoto, B.; Evans, C. & Cohen, M. (2003). Craniofacial application of three-dimensional laser surface scanning. Journal of Craniofacial Surgery 14., pp. 449-456.

Ji, Y.; Zhang, F.; Schwartz, J.; Stile, F. & Lineaweaver, WC. (2002). Assessment of facial tissue expansion with three-dimensional digitizer scanning. Journal of Craniofacial Surgery 13., pp. 687-92,

Khambay, B.; Nebel, JC.; Bowman, J.; Walker, F.; Hadley, DM. & Ayoub, A. (2002). 3D stereophotogrammetric image superimposition onto 3D CT scan images: the future of orthognathic surgery. A pilot study. International Journal of Adult Orthodontic and Orthognatic Surgery 17., pp. 331-341,

Marmulla, R.; Hassfeld, S.; Luth, T. & Muhling, J. (2003). Laser-scan-based navigation in cranio-maxillofacial surgery. Journal of Craniomaxillofacial Surgery 31., pp. 267-277,

Miller, L.; Morris, DO. & Berry, E. (2007). Visualizing three dimensional facial soft tissue changes following orthognathic surgery. Eurpean Journal of Orthodontics 29., pp. 14-20,

Moss, JP.; Linney, AD.; McCance, AM. & James, DR. (1994). The use of three-dimensional optical scanning techniques in dental and related fields. Dental Update 21., pp. 386-390,

Moss, JP.; Ismail, SF. & Hennessy, RJ. (2003). Three-dimensional assessment of treatment outcomes on the face. Orthodontics and Craniofacial Research 1., pp. 126-131,

Nute, SJ. & Moss, JP. (2000). Three-dimensional facial growth studied by optical surface scanning. Journal of Orthodontics 27., pp. 31-38,