A microbiological study of recurrent dentinal caries.

A cross-sectional microbiological study of recurrent (secondary) dentinal caries was conducted. Freshly extracted human teeth containing amalgam restorations judged to be clinically intact were scrubbed with chlorhexidine soap and soaked in povidone-iodine solution. The teeth were then split to remove the fillings and examined for dentinal caries. Of 54 teeth examined, 22 (40%) were free of dentinal caries in the restored site. The remainder were assigned to arbitrary groups of questionable (15), initial (8) and active caries (9), based on the amount of dentinal decay observed. Comparison of pre-extraction bite-wing radiographs with the in situ findings revealed the sensitivity for secondary caries detection to be only about 50%. In contrast, the specificity for absence of caries was 73%. There was considerable variation in the numbers and types of micro-organisms found in dentine samples from lesions of comparable severity. Facultatively, anaerobic streptococci were the most numerous and most prevalent micro-organisms in the affected dentine, but no single species was significantly associated with recurrent caries. Mutans streptococci were found in 40% of sites with any degree of caries and in only 3 of the 9 sites with the most caries. Homofermentative lactobacilli were present in 18 of the 54 dentine samples, including 4 from caries-free sites. While the prevalence and numbers of lactobacilli increased with the degree of caries, they occurred in less than half of the affected dentine samples. Actinomyces occurred in 15 of 32 affected sites but only in 2 of the 9 most active sites. Their numbers never exceeded 3 x 10(3) CFU/mg.(ABSTRACT TRUNCATED AT 250 WORDS)