The intra- and inter-examiner reliability of quantitative light-induced fluorescence (QLF) analyses

Objective: To assess the reliability of the analysis stage of quantitative light-induced fluorescence (QLF), The QLF analysis involves subjective input from the user and this study examines the influence of this on the reproducibility of the QLF data. Method: QLF images were taken of 20 human molar teeth that had been previously subjected to a demineralising solution (phosphoric acid 37%) to create artificial white spot lesions on their buccal surfaces. Following examination of the images, 16 were chosen to represent a range of lesion size and severity. Three copies were made of the images and each was allocated a different filename. 10 examiners in three centres were asked to analyse each of the 16 images on three occasions, with at least seven days between each attempt. Simple instructions describing the analysis procedure were supplied and examiners were asked to adhere to these directions. Examiners were asked to rate each of the 16 teeth on their first attempt both quantitatively (5 point scale) and qualitatively in terms of difficulty of analysis. Data reported were the ΔQ at 5% threshold for each tooth on each of three attempts. Results: Using ANOVA and paired t-tests to detect statistical differences, the three attempts of each examiner were used to determine intra-examiner reliability. Only one examiner (a novice at the technique) demonstrated differences between all three attempts and two demonstrated difference between one attempt. When the mean scores were compared to determine the inter-examiner reliability, only one examiner's results were statistically different when compared with two others Conclusion: This study has demonstrated that the analysis stage of QLF is reliable between examiners and within multiple attempts by the same examiner, when analysing in vitro lesions. Novices at the technique should be trained before analysing experimental data.