The effect of different viewing media in assessing the patients with dentofacial deformities

Abstract

The current goal of treatment for dentofacial deformities has moved toward an emphasis on both intra- and extra-oral features. The intra- and extra-oral three-dimensional (3D) surface topography can be captured using 3D surface-imaging systems and intraoral scanners (IOS). Visual depth perceptions for these 3D images are recreated using monocular cues; however, true binocular depth perception cannot be experienced unless stereoscopic 3D is utilized. The aims of this study were therefore to explore the applications of stereoscopic 3D in assessment of intra- and extra-oral features in patients with dentofacial deformities.

Stereoscopic 3D was found to be a valid alternative method to assess dental arch relationships in patients with unilateral cleft lip and palate (UCLP). The dental arch relationships of 29 subjects were rated on plaster models, conventional 3D, and stereoscopic 3D by three calibrated orthodontists using Great Ormond Street, London and Oslo, Norway (GOSLON) Yardstick on two occasions at 1-month interval. The intra- and inter-rater reliability were all above “good”, as well as the agreement between plaster models and stereoscopic 3D images.

For the purpose of assessing facial features in patients with dentofacial deformities i.e. cleft lip and palate (CLP), a systematic review was carried out and highlighted the need for a standardized rating panel of professionals to include those who are part of the interdisciplinary care team even though they are from different disciplines. The recommendations for study designs and outcome measures deriving from this review, i.e. full facial images of a homogeneous type of patients assessed by the standardized rating panel using visual analogue scale (VAS) on two occasions after calibration, could be applied in future studies.

When assessing facial features using 3D images, it was noteworthy that natural head position (NHP) should be recorded by using physical reference (RNHP) rather than subjective estimation by clinicians (ENHP). Six clinicians were asked to estimate the NHP of 15 pre-surgical Class III orthognathic patients without facial asymmetry; however, the results suggested that estimation of natural head position (ENHP) was possible in roll and yaw, but not in pitch.

Stereoscopic 3D was thought to be superior to conventional 3D and 2D photographs by the majority of the raters providing additional visual information when assessing facial features in Class III orthognathic patients. Eight professionals evaluated the 2D photographs, conventional 3D, and stereoscopic 3D of 40 pre-surgical subjects in NHP using a VAS; 20 patients were randomly selected and reassessed for each viewing media at a minimum of 1-week interval. Results showed that the intra- and inter-rater reliability for three viewing media were dependent upon the specific feature being assessed. 2D images may not allow consistent evaluation of facial symmetry, though routinely used in clinical practice.

In conclusion, the studies reported in this thesis supported the use of stereoscopic 3D in longitudinal treatment and evaluation of outcomes in patients with dentofacial deformities. Stereoscopic 3D was preferred to 2D photographs and conventional 3D for rating facial features but these findings should be further investigated in relation to the “gold standard” (clinical assessment) in future studies. (Total words: 500)