The factors that produce cervical burnout images in the film emulsion and Mach band effects in the retinal receptors have been discussed. In the former, overpenetration of thinner cervical tooth areas produces radiolucent areas that have rounded, diffuse inner borders, but that show intact tooth edges. Mach bands, produced by lateral inhibition of neural receptors in the eye, are optical illusions that may appear in the dentin along the proximal DEJ, or in dentinal peaks bounded by occlusal and proximal enamel. Not every observer has the same ability to perceive Mach bands, and perception is modified by projection, contour, and film and object density. A masking technique has been described to facilitate differential interpretation between the Mach apparition and actual tooth decalcification.
