The Impact of Implementing an Enhanced Infection Control Protocol on Root Canal Treatment Outcomes: In vivo and Clinical Studies

Abstract

Aims: This thesis was intended to determine the effectiveness of implementing an enhanced infection control protocol on primary root canal treatment. First, the effect was studied on the outcome of root canal treatment of molar teeth clinically and radiographically; teeth were assigned to one of the two protocols: a standard root canal treatment protocol (SP), and an enhanced infection control protocol (EP). Moreover, this project examined the impact of the EP on the microbial load and the composition of the microbial community after chemomechanical preparation. Materials and methods: The pilot study involved samples obtained from teeth diagnosed with irreversible pulpitis (IP). Samples were collected from different sites such as files, endodontic ruler surface, rubber dam surface, gloves and instruments (tip of the tweezer, DG-16 endodontic explorer, plugger and flat plastic instrument), as well as intracanal samples. Microbial load was investigated by quantitative polymerase chain reaction (qPCR). The microbial composition was evaluated by targeting the 16S rRNA V3-V5 hypervariable regions of the 16S rRNA and subjecting to next-generation sequencing (NGS). Moreover, the microbial load and composition of intracanal samples of vital teeth were investigated by similar molecular methods. The randomised controlled clinical trial involved healthy patients at Guys’ Hospital receiving primary root canal treatments. The patients were block randomised to a standard protocol (SP) and an enhanced infection control protocol (EP). Both treatment arms adhered to current best practice recommendations, while the EP comprised additional steps included replacing rubber dams, gloves, files, all instruments and surface barriers at the time of obturation to reduce the chances of iatrogenic contaminations. CBCT and PA radiographs were taken at baseline and one-year follow-up to assess the outcome of treatment. The outcome was assessed clinically and radiographically using CBCT. In addition, intracanal samples were taken at baseline (S1) and after completion of chemomechanical preparation (S2). Microbial 16S rDNA copy numbers were enumerated by qPCR. Bacterial composition and identification were performed targeting the 16S rRNA V3-V4 hypervariable regions and subjected to NGS. Results: Findings of the pilot study showed that around half of the rubber dam surfaces were contaminated with bacteria at time of obturation and 38% of initial files introduced into the canal showed significant levels of bacteria. Bacteria were also detected in 20-30% of gloves, instruments and rulers prior to obturation. Streptococcus, Rothia, Propionibacterium, and Fusobacterium were among the taxa found in such contaminated surfaces. The pilot study findings suggested the risk of introducing bacteria into the root canal space after chemomechanical preparations; higher bacterial loads were more frequently present in intracanal samples before root canal filling when instruments and surfaces were found to be contaminated. Regarding the intracanal samples of IP teeth, half of the intracanal samples had a substantial bacterial load of bacteria within the vital pulp (≥104 16S rRNA copies), as determined by qPCR. NGS microbial identification yielded 187 bacterial OTUs mainly belonging to the genera Veillonella, Streptococcus, Corynebacterium, Cutibacterium, and Porphyromonas. At one-year follow-up, 115 teeth were analysed (54 in SP and 61 in EP), as a part of the clinical study. The probability of 12-month success was three times higher in the EP group compared to the SP group. The median bacterial reads were reduced to 3.5×103 in the SP group and to 1.3×103 in the EP group. The EP significantly reduced bacterial counts in pre-obturation samples when compared to the SP. Using a high-throughput sequencing approach, the findings showed a trend of reduced diversity obser