Multi-species bacterial-fungal biofilms are common in the spectrum of infectious diseases including root canal infections. In endodontic treatment, biofilm removal is accomplished by a chemo-mechanical process. Using existing medicaments and techniques, effective disinfection of dentine during root canal treatment remains a major challenge. There is an argument for development of novel antimicrobial agents with a different mode of action, but the potential tissue toxicity and allergic reactions of any alternative medicament must be considered. The work described in this thesis aims to evaluate the effectiveness of two novel antimicrobial agents, HICA and alpha-mangostin, against multi-species bacterial-fungal biofilms. Another objective is to study the potential of these agents as a root canal medicament. The planktonic susceptibility testing of HICA and alpha- mangostin against six bacterial strains and two Candida albicans was performed to decide the concentration of each agent to be used in biofilm experiments. The metabolic activity of single and multi-species biofilms after exposure to antimicrobial agents was analysed by a metabolic (XTT) assay. The alterations in the biofilm structure were then determined by bright field microscopy and BaclightTM LIVE/DEAD fluorescence microscopy. Time-kill assays were used to determine the antimicrobial activity of HICA and alpha-mangostin against the planktonic root canal microbes compared to commercial root canal medicaments. The ex vivo multi-species biofilms root canal model was developed to mimic the polymicrobial environment of root canal infections. The anti-biofilm activity of HICA and alpha-mangostin was evaluated against established root canal biofilms. Culture techniques were used to quantify biofilm biomass and viability whereas a qPCR method was used to investigate the viability and composition within the biofilms. Both HICA and alpha-mangostin demonstrated better efficacy against bacterial, fungal, and multi-species biofilms. These agents exerted superior anti- biofilm activity in infected human dental root canals compared to the commonly used inter-appointment intra-canal medicament (Ca(OH)2) as they reduced biofilm biomass and viability within biofilms effectively. This study showed that HICA and alpha-mangosin have the potential to be used as inter-appointment medications in the treatment of root canal infections, especially for persistent infections or retreatment cases.