Objectives: The purpose of this pilot study was to determine if QLF could detect, and longitudinally monitor, demineralisation adjacent to a range of restorative materials in vitro.  Methods: 15 previously extracted molars were selected.  A single burr hole was placed on the buccal surface and the cavity restored with amalgam, composite, compomer, glass ionomer or a temporary filling material.  Each material was placed in three teeth.  The buccal surface was then coated in an acid resistant nail varnish leaving an exposed area around the restoration and also a similar sized control region.  The teeth had QLF images taken at baseline and were then subjected to a demineralising buffer, further QLF images were taken at 72 hours and 144 hours.  Dye penetration was used to confirm the presence of lesions at the completion of the cycle (144 hours). QLF images were analysed, and DQ recorded. Results: When compared with surrounding enamel amalgam, glass ionomer and the temporary material all exhibited reduced fluorescence, while composite and compomer showed increased fluorescence.  There was no change in fluorescence of the materials when subjected to experimental demineralising conditions. Readings at 72 and 144 hours demonstrated demineralisation adjacent to all of the restorations and at the exposed control.  Significant differences were detected between baseline, 72 and 144 hours using ANOVA on all restorations with the exception of compomer where significance was noted between baseline and 144 hours, p<0.05.  Readings at 144 hours (DQ (SD)); Compomer (-3.7 (1.7)), Amalgam (-10.733 (2.542)), Temporary (-4.5 (2.364)), Composite (-13.533 (3.245)), Glass ionomer (-7.566 (4.909)). Conclusions: This study has demonstrated the ability for QLF to detect and monitor secondary caries in vitro.  Analysis techniques should be based upon the subtraction of baseline DQ scores from subsequent images.