Novel High Intensity Focused Ultrasound in Debriding Ti Dental Implant-Attached Streptococcus mutans Biofilms

Effective management of PI depends on removing the colonised microbial biofilms to preserve osseointegration, yet thorough debridement remains difficult. HIFU offers a novel, non-invasive approach that uses contact-free acoustic energy while minimising aerosol and debris. This in vitro study evaluates the effectiveness of HIFU in removing Streptococcus mutans biofilms from titanium implants. Biofilm reduction was visualised via DCLSM and quantified using FCM.

Two Ti dental implants were characterised via SEM. S. mutans biofilms were grown over 10 days on the coronal 5mm section of another 18 implants. Implants in the test group (n = 6) were treated with optimised HIFU through a glass beaker in water-based medium for 2 minutes. Residual biofilms were stained and visualised under DCLSM at 4×, 10×, and 20× magnifications and quantified using FCM for live/dead bacterial images and counts. The data from the test and the control samples (untreated and Airflow® treated) were subjected to ANOVA followed by post-hoc Tukey's test to determine the statistical differences between the groups.

DCLSM Z-stacks using a 10× objective and 512-pixel resolution yielded the optimal balance between image clarity and field coverage. HIFU-treated implants showed scattered bacterial clusters with surrounding biofilm-free zones, while Airflow®-treated samples retained a thin, continuous biofilm primarily along thread walls and root junctions. Both Airflow® and HIFU significantly reduced total bacterial loads compared to untreated controls (p < .05). (Airflow: 40,021 ± 17,253; HIFU: 254,000 ± 124,000; control: 731,000 ± 211,000).

HIFU acoustic waves were uniquely able to penetrate a solid (glass) barrier and create localised biofilm-free regions. HIFU shows potential as a physical method for biofilm disruption; however, further studies - including multispecies, in vivo, and pre-clinical models - are required to evaluate its clinical applicability.