796 Journal of the College of Physicians and Surgeons Pakistan 2014, Vol. 24 (11): 796-801 INTRODUCTION Dental biofilm, more commonly known as dental plaque is an intricate composition of multiform, well-organized and mutually benefitting community of microorganisms that forms naturally on tooth surfaces. Accumulation of dental plaque, if not under control can give rise to detrimental effects on teeth, gums and oral supporting tissues which manifests in the form of dental caries, gingivitis and periodontitis respectively. 1,2 Its development involves a number of stages: (i) formation of acquired pellicle on tooth surface; (ii) successful adherence of bacteria to this pellicle; (iii) successful colonization of the pioneer bacteria that finally leads to the formation of dental plaque; (iv) co-adhesion of secondary colonizers; (v) maturation of plaque and (vi) detachment of bacteria. 2 Dental plaque agglomerates preferentially at stagnant sites that afford protection from the vigorous removal forces that apply in the mouth. Many commercially available mouthrinses have been claimed to be efficient in controlling the development of dental plaque in the stagnation areas. Among them is the mouthrinse that incorporates chlorhexidine as the antibacterial ingredient. However, chlorhexidine is expensive and has unwanted side effects such as extrinsic tooth staining, alteration of the taste sensation, irritation of the oral mucosa and oral hypersensitivity reactions. 3 Combinations with other antibacterial agents such as tetracycline mouthrinses is also available. However, tetracycline been reported to alter the composition of dental plaques, thereby favouring bacteria resistant to tetracycline and other unrelated agents to predominate. 4 In addition, most of the commercially available mouthrinses contain alcohol. McCullough and Farah reported that using alcohol-containing mouthrinses may promote the development of oral cancer. 5 It has been reported that extracts from plants such as Piper betle and Psidium guajava, Sygzium aromaticum, Mangifera indica and Mentha piperita have antibacterial effect towards oral bacteria. 6,7 This leads to the suggestion of incorporating the extracts as antibacterial agent in mouthrinses. Leaves of Psidium guajava in the form of paste have been used in folklore practices as toothpaste to maintain the oral hygiene. The extracts of Piper betle and Psidium guajava were also known for their anti- adhering activities towards oral bacteria and the effect varies with the bacterial species. 8 In previous studies, the antibacterial effect of the extracts were determined in planktonic conditions. 6,7 ORIGINAL ARTICLE The Effect of Selected Plant Extracts on the Development of Single-Species Dental Biofilms Zubaidah Haji Abdul Rahim 1 , Sameer Shaikh 1 , Wan Nordini Hasnor Wan Ismail 2 , Wan Himratul-Aznita Wan Harun 1 and Fathilah Abdul Razak 1 ABSTRACT Objective: To determine the effect of a mixture of plant extracts on the adherence and retention of bacteria in dental biofilm. Study Design: Experimental study. Place and Duration of Study: Department of Oral Biology, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia, from December 2009 to December 2011. Methodology: For determination of adhering ability, experimental pellicle was first treated with the Plant Extracts Mixture (PEM) before inoculating it with individual bacterial species (S. mitis / S. sanguinis / S. mutans). For the determination of retention ability, the procedure was repeated with the experimental pellicle being inoculated first with the individual bacterial species and then treating it with the PEM. These two experiments were repeated with deionized distilled water (negative control) and Thymol (0.64%) (positive control). The bacterial populations in biofilms for the two experiments were expressed as Colony Forming Unit (CFU) / mL x 10 4 and the corresponding values were expressed as mean ± SD. Results: The effect of the Plant Extracts Mixture (PEM) for the two experiments was compared with that of Thymol and deionized distilled water. It was shown that there is a reduced adherence of bacteria to PEM-treated and Thymol (0.064%) treated experimental pellicle compared with the negative control (p < 0.001). It was also found that the retention of bacteria in both treated biofilms is also lower than that of negative control (p < 0.001). Conclusion: Plant Extracts Mixture (PEM) may influence the development of dental biofilm by affecting the adhering and retention capacities of the bacterial species in the dental biofilms. Key Words: Plant extracts. Thymol (0.064%). Anti-plaque. Dental biofilm. 1 Department of Oral Biology, Faculty of Dentistry, University of Malaya, Kuala Lumpur, Malaysia. 2 Faculty of Pharmacy, Campus Bukit Mertajam, Universiti Teknologi MARA (UiTM), 13500 Sebrang Perai, Penang, Malaysia. Correspondence: Dr. Sameer Shaikh, Flat No. C-402, Mustafa Heights (Opp. Naheed Super Mkt., Above Pizza Hut), Block 3 DMCHS, Off Shaheed-e-Millat Road, Karachi. E-mail: smrshaikh@gmail.com Received: May 09, 2013; Accepted: July 19, 2014.