They are highly acidogenic and acid tolernt, and are associated with advanced caries lesion and carious dentine. Simple tese with selective media have been designed for estimating the numbers of lactobacili in patients saliva to give an indication of the cariogenic potential of a mouth. Although these tests are often unreliable,they are useful for monitioring the dietary behaviour of a patient because levels of lactobacilli correlate closely with the intake of dietary carbohydrate. Some lactobacilli are being considered as possible oral probiotic strains