Influence of Photodynamic Therapy on Bacterial Attachment to Titanium Surface

In periodontitis and peri-implantitis, plaque-forming microorganisms develop biofilms in which the microbes become protected from washing and antibiotics. While the antibiotics often become partially ineffective and traditional scaling to implant surface becomes challenging on such biofilm, Photodynamic Therapy (PDT) can be a useful option against these protected microorganisms. In this investigation, a unique combination of PDT and water rinsing force representing physical removal (using jet impingement techniques) were applied to biofilms of Streptococcus mutans (ATCC strain 27351) grown on commercially pure titanium (Ti). The experiment examined the force required to detach a biofilm (shear stress) as a way to determine changes in the biofilm's attachment strength after applying PDT. Colony-forming-unit (CFU) counts and Alamar Blue (A.B.) assays were used to measure the vitality and metabolism of the bacteria before and after the treatment. Multiple Attenuated Internal Reflection Infrared (MAIR-IR) spectra of identical biofilms grown on germanium prisms having surface properties similar to those of Ti were used to test differences in biofilm removal susceptibility. Using independent samples t-test, PDT-treated biofilms were significantly (p<0.05) more susceptible to removal from their substrata by water-jet impingement forces in comparison to the untreated biofilms. Varying thicknesses of untreated control biofilms required more shear stress (144 and 228 dynes/cm²) to delaminate from titanium surfaces when compared to less shear stress (90 to 140 dynes/cm²) required to removed PDT-treated companion biofilms. Moreover, an exopolymer matrix of polysaccharide (P.S.s) within layers of biofilm required less shear stress when compared to the force needed to detach biofilm from substrata. However, also needing further less force for treated biofilm (between 39 and 51 dynes/cm²) and (57 and 68 dynes/cm²) for PDT treated and control, respectively. Multiple Attenuated Internal Reflection Infrared (MAIR-IR) results confirmed the superiority of PDT-induced removal, predominantly of the protective polysaccharide part of the biofilm. These results suggest that PDT can weaken biofilms at different levels of maturity, allowing easier detachment using simple rinsing forces, which has promising future application in the dental practice where traditional scaling of implant surfaces is challenging.