Comparison of Ultrasonic vs 980-nm Diode Laser Irrigant Activation for Reducing Residual Bacterial DNA in Necrotic Teeth

Pulp necrosis is associated with microbial colonization and biofilm formation within the root canal system. Residual bacteria that persist after root canal treatment may contribute to persistent infection and unfavorable clinical outcomes. Although chemomechanical preparation and sodium hypochlorite irrigation are essential components of endodontic disinfection, anatomical complexities may limit complete bacterial elimination. Therefore, irrigant activation techniques have been introduced to improve irrigant penetration, biofilm disruption, and antimicrobial effectiveness. Ultrasonic activation enhances irrigant movement through acoustic streaming and cavitation, whereas diode laser activation may produce additional photothermal antibacterial effects and deeper penetration into dentinal tubules. However, evidence comparing residual bacterial detection after these activation methods remains limited, particularly when evaluated using molecular identification techniques. This exploratory randomized clinical trial compared ultrasonic irrigant activation and 980-nm diode laser irrigant activation in necrotic single-rooted teeth using 16S rRNA PCR sequencing. The study was conducted at the Dental and Oral Hospital of Hasanuddin University and the Hasanuddin University Medical Research Center, Indonesia. Sixteen necrotic single-rooted teeth were randomly allocated into two groups: ultrasonic activation (n = 8) and 980-nm diode laser activation (n = 8). After rubber dam isolation and access preparation under aseptic conditions, initial microbial samples were collected before chemomechanical preparation. Root canal instrumentation was performed using ProGlider and ProTaper Gold rotary instruments up to F2. In both groups, canals were irrigated using 3% sodium hypochlorite. In the ultrasonic group, irrigant activation was performed using ultrasonic activation at 45 kHz for 20 seconds per cycle for three cycles. In the diode laser group, activation was performed using a 980-nm diode laser at 1.5 W for 20 seconds per cycle for three cycles. Post-treatment microbial samples were then collected. Bacterial DNA was extracted and amplified using universal 16S rRNA primers, followed by sequencing and taxonomic identification. The primary outcome was the presence or absence of detectable oral bacterial DNA after treatment. Secondary outcomes included identification of bacterial taxa detected before and after treatment and comparison of bacterial profile reduction between activation methods. The study was designed as an exploratory clinical-molecular investigation intended to generate preliminary evidence regarding the antibacterial effects of ultrasonic and diode laser irrigant activation in root canal disinfection.