A patient returns with a composite restoration placed years ago. The margins appear slightly stained. The explorer catches in one area. The bitewing hints at a questionable radiolucency.
Is it secondary caries?
Or is it simply an ageing restoration that doesn't need to be replaced?
Making the wrong call has consequences either way. Replace a restoration too early, and healthy tooth structure is sacrificed. Leave secondary caries untreated, and the lesion continues to progress beneath the restoration.
A new clinical study suggests that fluorescence imaging may help bridge this diagnostic gap—not by replacing clinical judgement, but by making it more confident.
Looking Beyond What the Eye Can See
Researchers evaluated the performance of the QrayPen C, a fluorescence imaging device designed to detect demineralized tooth structure around existing restorations.
The study included 120 posterior composite restorations that clinicians had already decided required repair or replacement. After recording clinical findings, bitewing radiographs and fluorescence images, the restorations were removed to determine whether secondary caries was actually present beneath them.
Two out of every three restorations were found to have dentinal secondary caries after removal.
When the lowest fluorescence threshold was used, the device correctly identified most of these lesions, demonstrating an overall diagnostic accuracy of nearly 87%, with high sensitivity and specificity.
More importantly, increasing the fluorescence threshold reduced false-positive findings but also increased the likelihood of missing true lesions—a reminder that every diagnostic test involves a balance between sensitivity and specificity.
A Helpful Guide, Not the Final Decision
The authors do not suggest replacing restorations simply because the fluorescence image appears positive.
Likewise, a negative fluorescence finding should not be interpreted as proof that the underlying dentin is healthy.
Instead, the QrayPen should be viewed as another piece of diagnostic information—similar to a bitewing radiograph or transillumination—that helps clinicians localize suspicious areas and strengthen their overall assessment.
In other words, the device may improve diagnostic confidence, but it should never replace clinical judgement.
What This Means Chairside
Secondary caries remains one of the leading reasons for replacing composite restorations worldwide. Yet diagnosing it accurately continues to be surprisingly difficult. Marginal staining, discoloration and wear can all mimic disease, while early lesions often remain hidden beneath apparently intact restorations.
This is where adjunctive technologies are becoming increasingly relevant.
Rather than encouraging more intervention, tools such as fluorescence imaging may actually support more conservative decision-making by helping clinicians distinguish restorations that genuinely require treatment from those that can continue to be monitored.
That distinction matters because every replacement restoration begins another cycle of restoration enlargement, increasing the likelihood of future complications.
The question is no longer whether technology can detect secondary caries.
The more important question is whether it can help dentists preserve more natural tooth structure by making better restorative decisions.
This study suggests we may be moving one step closer—but the final diagnosis still belongs to the clinician, not the device.