Effect of imaging geometry on evaluating natural white-spot lesions using quantitative light-induced fluorescence

The objective of this study was to determine the effect of imaging geometry on evaluating natural white-spot lesions with quantitative light-induced fluorescence (QLF). A total of 34 specimens were prepared from extracted human premolars and permanent molars with white spots on the interproximal surface. The specimens were each adjusted to a final thickness of 3.0 mm. Images were acquired with the QLF system perpendicular to the white spots and at 5degrees intervals up to 30degrees above and below the perpendicular. The specimens were rotated around the buccolingual axis of the tooth ( pitch angle) and around the long axis of the tooth ( roll angle). The averages of fluorescence loss (DeltaF, %) and lesion size (mm(2)) were determined with QLF. Another variable, DeltaQ, which was defined as the fluorescence loss integrated over the lesion size (% x mm(2)), was also calculated. DeltaF was smaller when lesions were viewed from the cervical direction (angles less than 90degrees), and became bigger when viewed from the coronal direction. Roll angle did not significantly affect DeltaF. Apparent lesion size diminished with deviations from 90degrees in both directions for pitch and roll angles. DeltaQ was affected by pitch and roll angles with the largest value at 90degrees and values decreasing in both directions from 90degrees. In general, there were significant differences for angles larger than 20degrees from the perpendicular for all three QLF variables. This study suggests that angle is an important factor to control when performing QLF studies; however, small changes ( deviations within 20degrees) have a minimal effect on QLF variables.