Scanning resolution and the detection of approximal caries

Objective: To determine a propel scanning resolution for digitizing bitewin g radiographs in the detection of approximal caries, Methods: Fifty-two premolars and 48 molars were mounted in blocks and image d on conventional film (Ektaspeed Plus, Eastman-Kodak, Rochester, NY USA) s imulating a bitewing projection. The 15 bitewing radiographs were then scan ned with a flatbed scanner at three resolutions 150, 300 and 600 d.p.i. The digitized images M:eri displayed in random order on a high-resolution cath ode my tube monitor. Tell observers assessed tile caries status of 200 appr oximal surfaces. They scored lesion presence on a 5-point confidence scale and depth on a 3-point scale. The observer's scores were compared with tile results from a histological examination. Data were analysed using analysis of variance hv calculating signed observed error, absolute observer error and observer confidence. Results: Lesion depth had a significant effect on confidence of lesion reco gnition. Tile main effect of resolution and the intel action between resolu tion and lesion depth were significant. Pair-wise comparison showed a signi ficant difference between resolutions in case of sound surfaces and surface s with dentinal lesion for absolute error. The confidence increased as the resolution increased but no significant difference was found between 300 an d 600 d.p.i. The best score for depth estimation was obtained at the 300 d. p.i. scanning resolution. Conclusions: When bitewing radiographs are scanned with a flatbed scanner, a resolution of 300 d.p.i, seems the best choice. At this resolution the di gital file size is manageable without significant loss of the information n ecessary for caries diagnosis.