The Impact of Transgingival Laser Irradiation on Antimicrobial Photodynamic Therapy (aPDT)

Objectives: Diode lasers are commonly used for antimicrobial photodynamic therapy (aPDT) regiments. The aim of the study was to assess the possibility of transgingival laser irradiation during an aPDT procedure and to evaluate if an activation of the photosensitizer might be induced.
Methods: Four laser settings of a diode laser device (Helbo, Bredent, Walldorf, Germany) were assessed for their performance in transgingival irradiation: (I) 120mW, (II) 80mW, (III) 60mW and (IV) 40mW. 15 pieces of soft tissue from a pig's lower jaw were prepared. The thickness of the specimens was measured in three points of the marginal gingiva. Subsequently laser irradiation was performed transgingivally in these three points from the buccal aspect. Laser energy was measured on the other side of the soft tissue employing a digital power meter (PM100D, Thorlabs, Dachau, Germany). Afterwards, the same study protocol was used to assess the power outcome after staining the non-buccal aspect of the tissue with a photosensitizer dye (phenothiazine-chloride, Helbo, Bredent, Walldorf, Germany).
Results: Transgingivally applied laser irradiation (average soft tissue thickness: 0.84mm +/- 0.1) resulted in different energy outcomes depending on the power settings under study and the photosensitizer. Lowest values could be observed for the 40mW setting and applied photosensitizer (median: 3.3mW, max: 5.0, min: 2.3). Highest values were measured for the 120mW setting without photosensitizer (median: 41.3mW, max: 42.7, min: 38.0).
Conclusions: The present study indicates that transgingival irradiation might be suitable for antimicrobial photodynamic therapy as an energy transmission through gingival tissue could be observed in all specimens. However, a decrease of laser energy caused by both soft tissue and photosensitizer has to be considered.