Evaluation of the Influence of Er:YAG Laser Parameters on the Effectiveness of Growth Inhibition of Candida Biofilms: An In Vitro Study

<b>Background/Objectives</b>: <i>Candida</i> biofilms exhibit high resistance to antifungal treatment, motivating investigation of adjunctive physical disinfection methods. To quantitatively assess the effect of Er:YAG laser fluence on growth inhibition and viability of single-species <i>Candida</i> biofilms in vitro using a 7 mm full-beam handpiece. <b>Methods</b>: Biofilms of <i>Candida albicans</i> ATCC 10231, <i>C. glabrata</i> ATCC 90030, <i>C. parapsilosis</i> ATCC 22019, and <i>C. krusei</i> ATCC 6258 were grown on Sabouraud agar. In phase 1, growth inhibition zones (GIZs) were evaluated after non-contact Er:YAG irradiation (2 Hz, 300 µs, 10 mm distance, no air or water spray) at fluences from 0.3 to 3.4 J/cm², with incubation for 24 to 96 h. In phase 2, 96 h mature biofilms were irradiated for 120 s at 0.8, 1.0, 1.5, or 2.0 J/cm², and viability was quantified by colony-forming unit (CFU) imprinting. All experimental conditions were tested in quadruplicate. <b>Results</b>: GIZ diameters increased significantly with fluence for all species (<i>p</i> < 0.05) and remained stable up to 96 h. At the highest fluence, mean GIZs reached approximately 8.0 mm for <i>C. albicans</i>, 7.7 mm for <i>C. parapsilosis</i>, 7.0 mm for <i>C. krusei</i>, and 5.2 mm for <i>C. glaxfbrata</i>. In mature biofilms, CFU counts decreased significantly with increasing fluence (<i>p</i> < 0.05). For <i>C. albicans</i>, CFUs were reduced from 164.0 ± 25.1 at 0.8 J/cm² to 16.5 ± 5.2 at 2.0 J/cm², while <i>C. glabrata</i> decreased from 103.5 ± 5.4 to 20.8 ± 1.7. <i>C. parapsilosis</i> and <i>C. krusei</i> showed maximal reductions at 1.0-1.5 J/cm², followed by partial CFU rebound at 2.0 J/cm². <b>Conclusions</b>: Er:YAG irradiation delivered over a large, uniformly illuminated area induces stable, fluence-dependent inhibition and significant reduction of <i>Candida</i> biofilm viability in vitro. Optimal fluence ranges are species specific, underscoring the need for parameter optimization and further evaluation in more complex biofilm models before clinical extrapolation.