Possibility for keyhole surgery to enhance periapical healing using laser photodynamic therapy : physical and biological considerations

Abstract

ABSTRACT The inability to resolve periapical pathosis is a crucial determinant of clinical failures of root canal treatment. Presence of intricate and inaccessible areas within the root canal system has made the disinfection of these anatomical sites rather difficult. The use of antimicrobial photodynamic therapy (aPDT) offers an innovative, non-invasive modality which was the subject of this thesis. Before a clinically applicable protocol could be proposed, it was necessary to examine the physical parameters and related issues for its application.

First, the transmission of laser that involved modification of the optical fiber tips was investigated for any losses of power transmitted. It was found that manual polishing of the fiber tip resulted in a significant reduction in the losses of emitted power and with a more consistent beam profile.

Then, the effect of dentin thickness, mineral density and dentinal tubule orientation on the transmitted laser power was examined. Except for mineral density, the dentin thickness and orientation of dentinal tubules relative to the incident beam showed a significant reduction in laser transmission through the dentin slab.

As indocyanine green (ICG) seems to be a promising photosensitizer for aPDT in dentistry, it is necessary to delineate the effect on healing being derived from the aPDT, but not the photosensitizer alone, or from the photobiomodulation (PBM) effect of the laser itself. For that, various concentrations of ICG irradiated with 10 J/cm2 laser 810 nm for 60 seconds was tested, with an optimum concentration (0.1µM) found to produce the highest amount of ROS as measured with a luminol assay. Then, the antimicrobial effect of 0.1µM ICG, with or without laser irradiation, was tested on planktonic cultures of E. fecalis (ATCC® 29212™). Results showed a reduction in CFUs for both groups; however, the difference was not statistically significant. A simulated infected/inflamed condition on cell culture was prepared by adding bacterial lipopolysaccharide (LPS) to a pre-osteoblastic cell line MC3T3, to examine the safety of laser-irradiated 0.1µM ICG using the AlamarBlue cell viability assay. Cell differentiation to mineralized phenotype was assessed with Alizarin red staining and RT-qPCR for expression of alkaline phosphatase, bone sialophosphoprotein, osteocalcin and Runt-related transcription factor 2. The aPDT parameters were shown not to be detrimental to the viability and mineralization of the pre-osteoblast cells in both healthy and inflamed condition.

Finally, it was hoped to evaluate the diffusion pattern of a photosensitizer in bone. A radiopaque dye and ribs of swine were used to build the model (with limitations). The diffusion was evaluated using C-arm digital radiography (2D) and cone-beam computerized tomography for 3D imaging. The radiopaque dye was injected at two rates: (i) slow using a 27G hypodermic needle and (ii) rapid deposition using a needleless injection system (Comfort-in™). The former seemed to produce a denser deposit of dye than the needleless system; however, the amount had not been quantified and the extent appeared qualitatively similar. Further studies using animal models with localized bone infection are needed to examine the aPDT versus PBM effect to yield more clinically relevant data.