Scanning resolution and the detection of approximal caries.
OBJECTIVE
To determine a proper scanning resolution for digitizing bitewing radiographs in the detection of approximal caries.


METHODS
Fifty-two premolars and 48 molars were mounted in blocks and imaged on conventional film (Ektaspeed Plus, Eastman-Kodak, Rochester, NY USA) simulating a bitewing projection. The 15 bitewing radiographs were then scanned with a flatbed scanner at three resolutions 150, 300 and 600 d.p.i. The digitized images were displayed in random order on a high-resolution cathode ray tube monitor. Ten observers assessed the caries status of 200 approximal 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 the results from a histological examination. Data were analysed using analysis of variance, by calculating signed observer error, absolute observer error and observer confidence.


RESULTS
Lesion depth had a significant effect on confidence of lesion recognition. The main effect of resolution and the interaction between resolution and lesion depth were significant. Pair-wise comparison showed a significant difference between resolutions in case of sound surfaces and surfaces with dentinal lesions for absolute error. The confidence increased as the resolution increased but no significant difference was found between 300 and 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 digital file size is manageable without significant loss of the information necessary for caries diagnosis.
Janhom
A
A
Department of Oral Radiology, Academic Centre for Dentistry Amsterdam (ACTA), Louwesweg 1, 1066 EA, Amsterdam, The Netherlands.
van Ginkel
F C
FC
van Amerongen
J P
JP
van der Stelt
P F
PF
D015502:Absorptiometry, Photon; D000704:Analysis of Variance; D001641:Bicuspid / Q000000981:diagnostic imaging / Q000473:pathology; D016001:Confidence Intervals; D003626:Data Display; D003731:Dental Caries / Q000145:classification / Q000000981:diagnostic imaging* / Q000473:pathology; D003743:Dental Enamel / Q000000981:diagnostic imaging / Q000473:pathology; D003804:Dentin / Q000000981:diagnostic imaging / Q000473:pathology; D006801:Humans; D008963:Molar / Q000000981:diagnostic imaging / Q000473:pathology; D015999:Multivariate Analysis; D015588:Observer Variation; D011856:Radiographic Image Enhancement / Q000295:instrumentation / Q000379:methods*; D016300:Radiography, Bitewing / Q000379:methods*; D013223:Statistics as Topic; D014962:X-Ray Film