Bacteriological examination of fissure plaques from seriously mentally retarded adults.

The microfloras of fissure plaque samples removed from a total of 23 seriously mentally retarded adults, resident in two institutions, were examined and compared with the fissure microfloras found in 17 control subjects who were employees in both institutions. The samples were collected from both an intact fissure and a fissure with brown-stained defective enamel surface of the premolars of the lower jaw. Mutans streptococci, selected with MSB medium, were recovered from only one of the defective fissures of 13 patients who became retarded younger than 2 years of age, whereas 14 defective fissures of 17 controls harbored mutans streptococci. Four of 8 patients who became retarded older than 3 years of age harbored mutans streptococci. Lactobacilli were infrequently recovered from both patients and controls. The results are discussed in terms of the microbiological aspect of caries development in adults who became mentally retarded when young.