Accuracy of dimensional and angular measurements from panoramic and lateral oblique radiographs

Dimensional and angular measurements from radiographs can be used in clinical dentistry to determine the inclination of impacted teeth, the relative position of roots and restorative abutments, and for implant site assessment. This study was carried out to assess the in-vitro accuracy of such measurements obtained from three rotational panoramic systems and two standardized lateral oblique projections (45 degrees and 60 degrees) using two cephalometric systems.

Acrylic test models with wires positioned to represent the position and angulations of the teeth were used. Ten images were taken with Oralix Pan DC/1, Panelipse and Orthophos panoramic machines. Fourteen lateral oblique radiographs were also taken using two cephalometric units: an Orthophos and a Quint Sectograph. The models were repositioned between each exposure. Horizontal, vertical and angular dimensions of every tooth position on each radiograph were measured by three evaluators and compared using ANOVA at an a priori significance level of alpha = 0.05.

Assessment of vertical dimensions was consistently more accurate on lateral oblique projections than on the panoramic radiographs. In general, the most accurate horizontal measurements could also be made with the lateral oblique projections. No differences in angular measurement accuracy were found between any of the projections. The use of statistical means and standard deviations can be misleading in ranking accuracy where a consistent conversion factor can be applied.

While panoramic radiography is convenient for dimensional and angular assessments, lateral oblique radiographs taken with a standard cephalometric apparatus are an alternative when greater clinical accuracy is needed.