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