Enamel demineralisation assessed by computerised image analysis of clinical photographs

Objectives: To investigate the use of computerised image analysis to measure the area of demineralisation on the buccal surface of a tooth and to analyse the effect on that measurement of varying the angle at which a photographic image of the buccal surface of a tooth is taken. Methods: Twenty-two teeth with areas of incremental demineralisation on the buccal surface were photographed perpendicular to the buccal surface and at angles of 20 and 40°, above (Cuspal) and below (Gingival) the perpendicular. The images were captured and analysed using computerised image analysis. Results: The Gingival views showed lower limits of agreement than the Cuspal views, probably due to the positioning of the masking on the lower part of the flash, to reduce reflection. There was a significant difference between the areas of demineralisation measured for the three angles from the Gingival views (p<0.001). The mean differences in areas measured were not linear, but there was a significantly greater reduction in area measured for the 40° views. Conclusions: Computerised image analysis to measure areas of demineralisation from a captured 35 mm slide is reproducible. The position of the masking on the camera flash and the angle of the camera makes a difference to the area measured and the grey scales recorded. Images taken at a larger angle than 20° to the perpendicular will record a significantly reduced area of demineralisation. Standardisation of photographs with the use of calibration markers and manipulation of images is discussed.