In vitro evaluation of the oxidation efficacy of transgingival photodynamic therapy

Objective. To evaluate the capability of soft laser light to penetrate blood, serum, gingival connective tissue and pure collagen type I. Materials and methods. A 1: 1 mixture of methylene blue (MB) and diphenylisobenzofuran (DPBF) was irradiated for 60 s with a diode laser (670 nm, 0.3 W) through blood, serum, gingival connective tissue and collagen type I (2 mm transillumination thickness). The oxidation of DPBF by MB was determined spectrophotometrically by measuring the optical density (oD) at 410 nm. The absorption spectra of DPBF/MB irradiated through MB (1%) and strawberry red solution (3%) served as control. Results. The mean oD of non-irradiated DPBF/MB was 1.98 +/- 0.04. Irradiation through MB showed no oxidation of DPBF (1.98 +/- 0.02; p > 0.05), while interposition of strawberry red and serum resulted in almost complete oxidation of DPBF (0.13 +/- 0.09, 0.06 +/- 0.03; p <= 0.0001). Irradiation through gingiva and collagen reduced the oxidation of DPBF significantly (1.0 +/- 0.04, 0.7 +/- 0.04; p <= 0.0001), accounting for 50% to 35% of the non-irradiated DPBF/MB solution. Conclusion. Red light from a diode laser can penetrate blood and gingival tissues. However, light absorption for collagen and connective tissue can hamper the oxidation process.