The primary aim of the study is to compare the bacterial reduction in pulpectomy of primary molars using a single rotary file system versus conventional manual instrumentation.

This study aims to compare the antibacterial effectiveness of a single rotary file system with conventional manual instrumentation during pulpectomy of primary molars. The study will evaluate bacterial reduction by microbiological culture techniques using colony-forming units per milliliter (CFU/mL) before and after chemo-mechanical preparation.

This investigation will include both in vitro and in vivo components to provide a comprehensive evaluation of bacterial reduction. In the clinical part of the study, children aged 4 to 6 years with restorable mandibular second primary molars diagnosed with irreversible pulpitis will be recruited from the outpatient clinic of the Pediatric Dentistry and Dental Public Health Department at the Faculty of Dentistry, Cairo University. Eligible teeth will undergo pulpectomy and will be randomly assigned to one of two groups:

Group 1: Pulpectomy using a single rotary file system. Group 2: Pulpectomy using conventional manual stainless-steel K-files.

Microbiological samples will be collected from the root canals before instrumentation and after completion of chemo-mechanical preparation using sterile paper points. The samples will be transferred to brain-heart infusion broth and cultured on agar plates under aerobic and anaerobic conditions. Bacterial growth will be quantified by counting colony-forming units to determine the degree of bacterial reduction produced by each instrumentation technique.

The findings of this study will contribute to evidence-based decision-making in pediatric endodontics by clarifying whether rotary instrumentation provides superior bacterial reduction compared with manual instrumentation in primary molar pulpectomy. Improved understanding of the antimicrobial effectiveness of these techniques may help clinicians select instrumentation methods that enhance treatment success, reduce chairside time, and improve patient cooperation during pediatric dental procedures.

Inclusion Criteria:

• Children age 4 to 6 years
• Medically free children
• Cooperative children
• Restorable mandibular second primary molars with signs or symptoms of irreversible pulpitis
• No internal root resorption on radiograph
• No external root resorption on radiograph
• No periapical radiolucency
• No inter-radicular radiolucency

Exclusion Criteria:

• Uncooperative children
• Children with systemic disease
• Children with physical disability
• Children with mental disability
• Refusal to participate
• Inability to attend follow-up visits
• Refusal to sign consent form
• Previously accessed teeth
• Mobile mandibular primary molars
• Pain on percussion
• Swelling on palpation or in the vestibule

The blinding of operator is not possible due to the nature of the technique used