Antimicrobial effect of 1064 nm Nd:YAG laser with flat-top homogeneous beam profile on oral fungal and bacterial biofilms: an in vitro study

PURPOSE: This in vitro study aimed to evaluate the antimicrobial effects of a 1064 nm Nd:YAG laser delivered through a novel handpiece designed to provide a flat-top, homogeneous energy distribution profile (MarcoM handpiece) against key oral pathogens: Candida albicans, Candida glabrata, and Streptococcus mutans, in both planktonic and biofilm forms, in single- and dual-species cultures. METHODS: Microorganisms were cultured individually and in dual-species combinations and irradiated using two irradiance settings (T1: 0.2 W/cm², T2: 0.6 W/cm²) corresponding to clinically established photobiomodulation parameters for wound healing and analgesia. Colony-forming units (CFU/mL) were quantified immediately and 24 hours post-irradiation to assess laser-induced antimicrobial effects. RESULTS: Streptococcus mutans exhibited the highest susceptibility in planktonic form, with CFU reductions of 79.0 ± 5.6% (T1) and 86.3 ± 4.2% (T2) immediately after irradiation (p < 0.05). After 24 hours, a 92.0 ± 3.5% reduction was observed, though viability partially recovered in dual-species cultures with C. albicans (T1: 4.7 ± 6.6%, T2: 0.0 ± 0.0%). C. albicans showed greater reduction after 24 hours (T2: 68.2 ± 9.7%) than immediately post-irradiation (32.1 ± 6.7%) (p < 0.05). In biofilm forms, the greatest effect was observed for C. albicans at T2 (91.7 ± 2.8%), while C. glabrata biofilms showed no significant difference between settings (p > 0.05). Dual-species biofilms required higher irradiance (T2, p < 0.05) for significant eradication. CONCLUSION: Under the specific in vitro conditions tested, 1064 nm Nd:YAG irradiation delivered with a flat-top, homogeneous beam profile reduced CFU counts and biofilm biomass of the tested oral microbial isolates. The effect depended on laser parameters, microbial species, culture model, and time point. Because only one clinical isolate per species was used and no positive antimicrobial comparator was included, these findings should be interpreted as preliminary proof-of-concept data requiring validation in expanded strain panels and comparator-controlled studies.