Sometimes the presence of caries is easy to detect. Other times the process is more challenging as we balance conserving tooth structure, being cautious about proximity to the pulp and removing all of the affected dentin. One of the tools that we have to add precision to this process is caries detection dye. The science behind the dye is simple as the organic matrix of less mineralized dentin takes up the stain. The idea being that healthy dentin is unaffected and retains a natural color, while carious dentin will be discolored. The challenge is that mineralization is not directly correlated with bacterial infiltration and caries. The circumpulpal dentin and that at the dentino-enamel junction is less mineralized. Therefore the dentin at the depth of the prep and close to the pulp often takes up the dye, resulting in a false positive result and potentially over preparation and increased risk of pulpal trauma.
There are numerous studies that have addressed this lack of specificity of caries detection dyes. Despite our uncertainty at times tactile and visual examination have proven to be effective modalities for accurate caries removal, so trust your senses. If you are going to use caries detection dye here are some things to consider. First, the tooth should be well isolated before placement. Utilize an explorer or spoon excavator to assess the density of the dentin and determine caries. When placing the dye rinse away quickly and thoroughly. The dye is less accurate as the prep depth approaches the pulp and at the junction of the dentin and enamel. I prefer the green dye to red, as this can become confusing with being able to visualize the pulpal tissue.