Effect of diode laser irradiation on bacterial viability in an in vivo biofilm formed on a titanium surface

Abstract

Dental implant treatment is a popular option to replace missing teeth; an estimated one in one hundred New Zealand (NZ) adults have a dental implant. In the past 50 years, implants have revolutionised the dental industry, however between 5-43% may have significant biological complications due to bacterial colonisation of the implant surface. Bacteria colonise all non-shedding oral surfaces and whilst initially there may be host compatibility, disease is marked by tissue breakdown initiated by a shift towards pathogenic bacteria. Therefore, techniques are required to minimise biofilm formation on the implant fixture and, when required, to decontaminate the implant surface. Currently, due to the macro and micro irregularities of the implant shape and surface texture, current decontamination protocols fail to completely clean the implant surface. At this time there is insufficient evidence to support recommendation of a specific decontamination protocol. Diode lasers are a promising method for implant surface decontamination due to the bactericidal effect demonstrated in vitro. Diode lasers do not damage the implant surface, irrespective of the power applied. However, the bactericidal effect of the diode laser on a natural biofilm has not been elucidated.

Objective The study’s primary objective was to assess the effects of an 810 nm diode laser on a natural biofilm in periodontally healthy participants; quantifying both the bactericidal and physical changes. Initially, a technique for cultivating an intraoral biofilm on a titanium disc was developed as a model to compare implant decontamination methods. Secondly, calibration of the bacterial viability fluorescence stain (LIVE/DEAD® BaclightTM), for use on roughened titanium surfaces was undertaken. Finally, bacterial viability and assessment of biofilm thickness following laser irradiation was assessed to establish a minimum effective clinical dosage recommendation.

Methods Participants received customised intraoral appliances containing six titanium discs with a moderately rough surface (Ra= 0.96 +/- 0.23 um) to replicate dental implant surfaces. Four periodontally healthy participants wore their intraoral appliances continuously for four-days (96 hours). A single disc was removed at 24, 48, 72 and 96 hours and viewed immediately under SEM to assess biofilm development. Subsequently, as 96 hours was established as the optimal intraoral time required for in vivo development of a mature biofilm, ten periodontally healthy participants wore intraoral appliances continually for 96 hours. Discs were sequentially removed and irradiated using various laser protocols. Following irradiation the discs were immediately stained using bacterial viability stain and viewed under confocal laser scanning microscopy to assess changes in bacterial viability and biofilm thickness.

Results Following 96 hours in vivo, biofilms had established on moderately rough titanium discs. The biofilm consisted of bacteria with various morphologies and the entire surface was covered with a homogeneous plaque. Diode laser irradiation resulted in a dose-dependent bactericidal effect. Fluence was measured based on a standard curve. Maximum antimicrobial efficacy occurred at 75 J/cm2 laser fluence and above this level the bactericidal effect plateaued. No damage to the implant surface was evident with scanning electron microscopy following up to 150 J/cm2 laser fluence. Biofilm mass was not completely removed but was significantly reduced with irradiation up to 100 J/cm2.

Conclusion A diode laser (810 nm) has an effective bactericidal effect on intraoral biofilms formed on roughened titanium surfaces and did not show damage to the titanium surface at any energy level delivered in this study. There were biofilm remnants remaining on the titanium surface following irradiation and the consequence of this upon healing remains to be determined.