A computer assisted photogrammetric analysis of soft tissue changes after orthodontic treatment. Part I: Methodology and reliability.

The purpose of this study was to use standardized facial photographs to compare the soft tissue profile changes in persons with Class II, Division 1 malocclusions who were treated with either an extraction or a nonextraction treatment modality. Ninety-one patients (44 extraction and 47 nonextraction) were evaluated with standardized facial photographs, available at pretreatment, posttreatment, and 2 years in retention. The photographs were digitized and displayed on a computer monitor. Thirty-eight landmarks (18 frontal and 20 lateral) were located. From these landmarks, 29 angular and linear dimensions (8 frontal and 21 lateral) were constructed. Descriptive and analytical statistics were used to compare the absolute dimensions, as well as the incremental changes, between the extraction and nonextraction groups. The present findings indicate that (1) Photographs allow for measurement of structures from a profile, as well as frontal orientations. (2) Measurement of profile changes from facial photographs appear to be fairly reliable but also have significant limitations. (3) Certain landmarks tended to be less reliable than others, e.g., subnasale and gnathion. In general, measurements from frontal photographs were more reliable than those obtained from lateral photographs and linear measurements were more reliable than angular measurements. (4) Changes in head posture within the cephalostat have an impact on vertical facial dimensions measured from frontal photographs. Horizontal dimensions were effected to a lesser degree. (5) Facial structures that lie closer to the camera appeared to be relatively larger than structures located farther from the camera. (6) The overall process of evaluating facial changes from photographs is both technique and operator sensitive. (7) More research specifically testing the photogrammetric method in a clinical setting is needed.