A MICROBIOLOGICAL STUDY OF RECURRENT DENTINAL CARIES

A cross-sectional microbiological study of recurrent (secondary) denti nal caries was conducted. Freshly extracted human teeth containing ama lgam restorations judged to be clinically intact were scrubbed with ch lorhexidine soap and soaked in povidone-iodine solution. The teeth wer e then split to remove the fillings and examined for dentinal caries. Of 54 teeth examined, 22 (40%) were free of dentinal caries in the res tored site. The remainder were assigned to arbitrary groups of questio nable (15), initial (8) and active caries (9), based on the amount of dentinal decay observed. Comparison of pre-extraction bite-wing radiog raphs with the in situ findings revealed the sensitivity for secondary caries detection to be only about 50%. In contrast, the specificity f or absence of caries was 73%. There was considerable variation in the numbers and types of micro-organisms found in dentine samples from les ions of comparable severity. Facultatively, anaerobic streptococci wer e the most numerous and most prevalent micro-organisms in the affected dentine, but no single species was significantly associated with recu rrent 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. Ho mofermentative lactobacilli were present in 18 of the 54 dentine sampl es, including 4 from caries-free sites. While the prevalence and numbe rs of lactobacilli increased with the degree of caries, they occurred in less than half of the affected dentine samples. Actinomyces occurre d 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. The observed variation s in the numbers and types of organisms present in the dentinal lesion s, coupled with the relative scarcity of lactobacilli and mutans strep tococci, raised the possibility that other, less acidogenic, microorga nisms could be involved in the causation of recurrent dentinal caries. Support for this view came from observations that most of the types o f bacteria recovered from the lesions were capable of lowering the pH below the threshold of pH 5.7 for demineralization of dentine. More fo cussed studies to determine the issue of the etiology of recurrent den tinal caries are needed.