Effect of x-ray beam vertical angulation on radiographic alveolar crest level measurement

Utilizing intraoral radiographs of human skulls taken at known vertical angulation, we have demonstrated that expression of the crest level as a distance between cej and the crest is as accurate as a ratio of bone height to root length. The degree of inaccuracy of either of these measures is related to the magnitude of the angular deviation of the x-ray beam from 90 degrees. Angular deviation can be estimated from calculation of a cusp height score (ratio of lingual cusp height to buccal cusp height x 100). Based on the analysis of cusp height scores it was determined that the x-ray beam angulation for posterior bitewings ranged between 90 degrees and 80 degrees whereas for posterior periapicals the angulation range was between 90 degrees and 70 degrees. Therefore, it is recommended that, for longitudinal studies of bone height, measurements of the crest to cej distance, particularly in the region of the molars, be made utilizing bitewing radiographs. For the premolar and incisor regions, deviation of the vertical angulation of an x-ray of up to 20 degrees from a 90 degrees baseline resulted in little, if any, change in crest level by either one of the two measures used. An appendix is provided for the theoretical modeling of the types and magnitude of change in crest level observed for projection images of different anatomical configurations.