Introduction This in vitro study assessed how shade changes induced by endodontic medicaments affect the transmission of single and multiples wavelengths of infrared light through enamel and dentin.

Methods Eighteen extracted single-rooted permanent teeth were prepared, removing all extrinsic staining, and cementum. Tooth slices were treated for 4 weeks with UltraCal XS, Ledermix, or were untreated controls. Light transmission through enamel-dentin and dentin regions was assessed using diode lasers (660, 808, 904 nm) and a multi-wavelength light-emitting diode (LED) light source (700–1100 nm). Absorption studies were performed to evaluate light absorption by components of medicaments.

Results Samples treated with Ledermix showed the greatest shade change, with a corresponding reduction in visible and near infrared light transmission (P < .001) in dentin, whereas UltraCal XS had a milder effect (P < .01). Across different substrates, the greatest light transmission was seen for the multi-wavelength LED light source, followed by 904 nm, 808 nm, and finally 660 nm. Spectrophotometric studies revealed light absorption by turbid and saturated calcium hydroxide solutions.

Conclusions This study shows that medicaments may influence transmission of visible red and near infrared light. Photobiomodulation protocols used in regenerative endodontics should take this effect into account, by incorporating longer near infrared wavelengths (up to 1100 nm) and using multi-wavelength light sources to account for this absorption.