Streptococcus mutans and Streptococcus sobrinus are known to be associated with the development of dental caries. In this study these bacteria were detected in pre-school children (each with primary dentition, age range 3-5 years, n ¼ 60) using a PCR method, and then their presence was compared with the incidence of dental caries over a 1-year period. Plaque samples were collected from all erupted tooth sites using a sterile toothbrush. Dental examinations at the beginning of the study (baseline) and after 1 year were also performed to determine decayed, missing, filled teeth (dmft) scores using WHO caries diagnostic criteria. The prevalences of S. mutans and S. sobrinus across all the subjects were 61 . 7 % and 56 . 6 %, respectively; 13 subjects (21 . 7 %) were positive for S. mutans alone, 10 (16 . 6 %) were positive for S. sobrinus alone and 24 (40 . 0 %) were positive for both S. mutans and S. sobrinus, whereas 13 (21 . 7 %) were negative for both S. mutans and S. sobrinus. dmft scores of subjects positive for both S. mutans and S. sobrinus at baseline and after 1 year were significantly higher than of those positive for S. mutans alone at the same stages (P , 0 . 01 and P , 0 . 001, respectively). The caries incremental increase was also significantly greater in those with both bacteria detected (P , 0 . 05). Our results indicate that pre-school children harbouring both S. mutans and S. sobrinus have a significantly higher incidence of dental caries than those with S. mutans alone.
INTRODUCTIONMutans streptococci (Streptococcus mutans and Streptococcus sobrinus) are considered to be major dental caries aetiologic agents. They are the most common pathogens isolated from human dental plaque and their prevalence has been reported in epidemiological studies (Hamada & Slade, 1980;Whiley & Beighton, 1998). S. mutans has been shown to be more prevalent than S. sobrinus in dental plaque samples (Loesche, 1986; Carlsson et al., 1987), while several epidemiological studies have shown that the prevalence of S. sobrinus is more closely associated with high caries activity (Fujiwara et al., 1991;Hirose et al., 1993).In several epidemiological studies, identification of S. mutans and S. sobrinus on selective media such as mitis-salivarius (MS) or MS-bacitracin (MSB) agar has been performed using colonial morphology (Wade et al., 1986;Svanberg & Krasse, 1990). However, accurate differentiation between S. mutans and S. sobrinus is not easy, and is also timeconsuming and laborious (de Soet et al., 1990). Further, it has been reported that S. sobrinus from dental plaque samples is especially difficult to culture directly on MSB selective medium (Jordan 1986;de Soet et al., 1990). Thus, it is of great importance to distinguish the presence of these two species separately in children for accurate prediction and effective prevention of dental caries.Thus far, several methods used for detecting and identifying mutans streptococci have been reported, including direct microscopy, cultivation, enzyme tests, mAbs, ELISAs and specie...