Method: 49 patients, recently evaluated for treatment at a private orthodontic practice, were randomly selected. Only angular, not linear, measurements were chosen to minimize errors of photographic distance variation. The six diagnostic angles chosen for this study are: (1)nasolabial, (2)mentolabial, (3)upper-lip-position-a, (4)upper-lip-position-b, (5)lower-lip-position, and (6)upper-to-lower-lip relationship. A commercially available software system, OrthoTrac, produced a digital protractor that created the measurements on the lateral photograph and then on the cephalogram. A total of twelve measurements were carried out for each patient. Next, statistical analysis was performed to evaluate the data against the null hypothesis (Ho = no difference in results by measurement method).
Result: A statistically significant difference was found with three of the six diagnostic angles. Using a paired T-test to compare the means (critical P-value 0.05), a significant difference was found between the cephalometric and photographic measurements for three diagnostic angles: upper-to-lower-lip relationship (p<0.001), upper-lip-position-b (p<0.001), and mentolabial (p=0.001). For these angles, we reject the null hypothesis. For the remaining diagnostic angles, no significant difference was found.
Conclusion: Soft-tissue profiles attained via cephalometric radiography appear to vary from those gathered via photograph. Further research is needed to more thoroughly describe the nature and extent of the discrepancies, to determine the potential causes, and to evaluate the relevance of these discrepancies with regard to treatment decisions and outcomes.