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Effect of ambient light and monitor brightness and contrast settings on the detection of approximal caries in digital radiographs: an in vitro study

¹Department of Oral and Maxillofacial Radiology, Faculty of Odontology, Malmö University, Malmö, Sweden; ²Department of Oral Pathology, Faculty of Odontology, Malmö University, Malmö, Sweden

*Correspondence to: Kristina Hellén-Halme, Department of Oral and Maxillofacial Radiology, Malmö University, SE-205 06 Malmö, Sweden. E-mail: Kristina.Hellen-Halme{at}od.mah.se

Received 1 February 2007; revised 21 August 2007; accepted 19 September 2007

Objectives: The aim of this study was to investigate how brightness and contrast settings of the display monitor and ambient light level (illuminance) in the viewing room affect the clinician's ability to diagnose carious lesions in digital radiographs.

Methods: Standardized radiographs were taken of 100 extracted teeth. Seven observers evaluated the images for approximal carious lesions twice, once under 50 lux and once under 1000 lux room illumination. Monitor brightness and contrast were varied ±50% and ±6%, respectively, to mimic the normal limits of monitor adjustment by an inexperienced user and one optimal setting. This was done by adjusting radiograph brightness and contrast by ±25%. Thus, five radiographs of each tooth were evaluated. Receiver operating characteristic (ROC) analyses were performed. Histological examinations of the teeth served as the criterion standard. A paired t-test was used to evaluate whether differences in the areas under the ROC curves were significant and kappa was used to evaluate intraobserver agreement.

Results: When a monitor with optimal brightness and contrast settings was used to detect approximal carious lesions, ambient light levels less than 50 lux were significantly better than levels above 1000 lux (dentin and enamel lesions, P < 0.01; dentin lesions, P < 0.02). Increasing the contrast setting of the monitor by 6% did not change these results; 50 lux was still significantly better than 1000 lux (enamel lesions, P < 0.01; dentin and enamel lesions, P < 0.02) for evaluating radiographs. Intraobserver agreement differed from fair to good.

Conclusions: Reducing ambient light to less than 50 lux significantly increased the accuracy of diagnosing approximal carious lesions on a monitor with an optimal brightness setting and an optimal or slightly higher than optimal contrast setting.

Keywords: display monitor, digital radiography, dental caries, receiver operating characteristic curve