Teeters, Christopher Andrew2013-11-142013-11-142013-08https://hdl.handle.net/11299/160305University of Minnesota Master of Science thesis. August 2013. Major: Dentistry. Advisor: Nanci De Felippe. 2 computer files (PDF); 57, 1 pages.Introduction: Facial considerations are important in any contemporary cephalometric analysis based on a soft-tissue paradigm, and head position is often an important component of these soft-tissue measurements. Natural head position (NHP) has long been used as the reference position for craniofacial morphology and it has been subject to great scrutiny due to its inherent variability. This study aims to determine if there is an operator-defined optimal head position (OHP) that is deemed the most pleasant, universal to all skeletal classifications, and parallel to Frankfort Horizontal (FH). Methods: 31 subjects (10 orthodontists, 10 orthodontic residents, and 11 orthodontic staff members) were asked to take an online survey evaluating 9 soft-tissue rendering profile positions (2.5 degrees apart) of 30 different models (N=31, Power = 0.92). They were asked to indicate the most pleasant profile orientation and to disclose whether they were orthodontists, residents, or staff members. Results: Chi-square tests and two one-sided t-test procedure (TOST) tests were performed to test the null hypotheses. All null hypotheses were rejected, therefore: (1) not all profile orientations were chosen with equal frequency. The most commonly chosen angle was 0 (about 30% of the choices, p < 0.0001) corresponding to the Helion-Canthion line (HC line) parallel to the floor and about 70% of the choices were within 2.5 degrees of the angle 0. There was no significant difference in the head orientations chosen by orthodontists, orthodontic residents, and staff members; (2) the three skeletal classes demonstrated a very similar pattern of angle choice, which was most often 0 (p < 0.05); and (3) the soft-tissue HC line and hard-tissue FH deviation resulted in a mean of deviation range of values within the limits of ±0.5° (p< 0.001) denoting very high concordance between HC line and FH. Conclusions: 70% of responders chose the orientation within one standard deviation consistent with HC parallel to the floor (p < 0.001). We noticed that the most commonly chosen angle was 0 for each of the three skeletal groups (p < 0.05), and that their frequency distributions of angle choice had very similar shapes. The suggested OHP reference plane proved to be parallel to FH and it was deemed to be an esthetically pleasing and easily determined soft-tissue head orientation. We believe that OHP can be confidently and meaningfully used in contemporary cephalometric analyses. This head orientation may be obtained prior to taking pictures and radiographs (including CBCTs) or after the exposure, by rotating the picture or soft tissue rendering until the HC line is parallel to the floor.en-USDentistryCephalometricsDiagnosisHead positionOrthodonticsTreatment planningThesis or Dissertation