Longitudinal Restoration of Regulatory Compliance in Dental Unit Waterlines Following Continuous Hypochlorous Acid Disinfection: A Real-World Evaluation

Abstract Background: Dental unit waterlines (DUWLs) are prone to biofilm formation and recurrent microbial amplification, frequently resulting in heterotrophic plate counts exceeding regulatory thresholds. Continuous hypochlorous acid (HOCl) disinfection has been proposed as a strategy to achieve sustained microbiological control; however, longitudinal real-world evidence under regulated European clinical conditions remains limited. This study evaluated microbiological evolution and regulatory compliance following implementation of continuous HOCl disinfection in a German pediatric dental clinic. Methods: A longitudinal environmental microbiological evaluation was conducted in two dental units (BE1, BE2) under routine clinical conditions. Water samples were collected at three predefined timepoints: baseline (T0), early follow-up at 3 weeks (T1), and late follow-up at ≥4 months (T2). Heterotrophic plate counts at 36°C and Legionella spp. detection were performed by an ISO 17025-accredited laboratory according to DIN EN ISO 11731. Percentage and log₁₀reductions were calculated relative to baseline. Regulatory compliance was defined according to Robert Koch Institute (RKI) standards (