Detection of Streptococcus mutans by PCR amplification of the spaP gene in teeth rendered caries free

Objectives: To investigate the degree of association between tactile and optical criteria as used to assess the carious status of the enameldentine junction (EDJ) during cavity preparation, assessment with a caries detector dye and detection of Streptococcus mutans using culture and polymerase chain reaction (PCR) techniques. Methods: Twenty-nine teeth, extracted within the previous 30 min, and 15 teeth prepared under rubber dam in vivo, were clinically assessed at the EDJ after the removal of evident carious tissue. Demineralisation was then assessed using a caries detector dye (1% acid red in propylene glycol; Cavex™). A rosehead bur was used to remove tissue at the EDJ for culture and PCR analysis. Culture was carried out on a tryptone yeast cystine sucrose bacitracin selective medium, and PCR used to amplify a sequence (192 bp) of the spaP gene, which encodes the surface protein antigen I/II of S. mutans. Results: Demineralised tissue at the EDJ, as shown using the dye, was found in 52% of teeth. Removed tissue was culture and PCR positive for S. mutans in 2 and 47% of teeth, respectively. A highly significant association (77% of cases; P < 0.001) was shown between dye and PCR assessment methods. No association was found between any other combination of assessment methods. Conclusions: Culture methods may underestimate the presence of S. mutans. Removal of sufficient dye-stained tissue is therefore recommended to prevent further carious assault from residual S. mutans.