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QLF is designed to study caries development. Caries on a tooth surface is analysed for integrated fluorescence loss (.Q) using the surrounding sound enamel as reference. To ensure the same spot is analysed each time, proper repositioning of the tooth surface in the images is necessary. Images of tooth surfaces are repositioned by eye by looking at the baseline image. Variations in orientation, size and location are considered the main source of error when computing .Q. Recently, video repositioning (VID-REP) and an ambient light shield (ALS) clipping onto the camera were introduced. The ALS should also allow easier repositioning. VID-REP displays the baseline and live image simultaneously and computes the correlation between them. Images are stored in a list when correlation c0.92. This study evaluates the use of VID-REP and ALS in vivo. A full-mouth examination of 60 surfaces was repeated on 3 separate occasions using repositioning by eye and a camera handpiece with mirror. The same was done using VID-REP, and VID-REP combined with ALS. Images of 12 surfaces with decalcifications were analysed for .Q. The average correlation between baseline and follow-up images was 0.71 (SD 0.19) for repositioning by eye, 0.97 (SD 0.01) using VID-REP and 0.99 (SD 0.01) using VID-REP and ALS. All three methods were found to be significantly different from each other (pd0.01). The relative standard deviation for .Q was improved from 30% for repositioning by eye to 23% for VID-REP and to 7% using VID-REP and ALS. In conclusion VID-REP in combination with ALS allows changes in teeth to be followed more reliably than without, so changes in .Q can be detected earlier than without video repositioning. |