Evidence
Lactobacillus counts have been used to predict the incidence of new carious lesions.
Crossner (1981) studied a group of children, who had been given dental treatment at baseline so that no open lesions were present at the bacterial sampling. Two subgroups in this material are of special interest: those with very low or very high lactobacillus counts. Very few individuals in the low lactobacillus group developed new carious lesions over a 64-week period. In the high lactobacillus group, many, but not all, developed new lesions.
Some studies have shown that caries incidence is significantly increased when MS and lactobacilli occur in the same individual: During a 3-year longitudinal study, Alaluusua et al (1990) showed that teenagers with high salivary values for both MS and lactobacilli developed several times more new carious surfaces than did those with lower counts of either. The percentages of children who developed 0, 1 to 3, and more than 3 new carious surfaces were correlated to the total scores of MS and lactobacilli (Fig 37). Similar findings were reported by Stecksen-Blicks et al (1985).
In a 2-year study by Crossner et al (1989), samples from saliva, the tongue, and 276 interdental spaces were obtained from 23 7 year olds to (1) relate the presence of lactobacilli at various oral sites to the occurrence of lactobacilli in saliva, and (2) relate the presence of mutans streptococci and various types of lactobacilli interdentally to the development of proximal carious lesions. The results showed that the number of interdental samples containing lactobacilli increased as the number of salivary lactobacilli increased. Furthermore, lactobacilli were never found
interdentally without the presence of mutans streptococci, and lactobacilli proved to be the more suitable microorganism for prediction of proximal carious lesions.
Neither the number nor the differentiation into different species of interdental lactobacilli seemed to be of importance, merely their presence or absence. The presence of lactobacilli probably reflects a caries-inducing environment (etiologic microflora plus fermentable carbohydrates), thus explaining their high predictive ability despite their rather limited etiologic importance in the initiation of caries.
Lactobacilli are also implicated in root surface caries. Fure and Zickert (1990a) studied a group of 208 randomly selected 55, 65, and 75 year olds. To estimate the number of root caries lesions, an index, DFS%(R), was used, indicating the number of decayed and filled root surfaces as a percentage of the exposed root surfaces. The mean DFS%(R) was 13 for the 100 subjects with low lactobacillus counts (less than104), and 23 for the 52 subjects with high counts (more than 105). In crosssectional and longitudinal studies, it has been demonstrated that lactobacillus counts
are among the factors with a significant correlation to the development of root caries lesions (Ravald and Birkhed, 1991, 1994; van Houte et al, 1990). Ellen et al (1985) also showed that root surfaces harboring both MS and lactobacilli are most likely to develop root caries.
A number of studies have tried to clarify the prevalence of lactobacilli in various populations, eg, two Swedish studies, one comprising 646 9 to 12 year olds (Klock and Krasse, 1977) and the other a group of 101 13 to 14 year olds (Zickert et al, 1982b). About 50% showed low salivary counts (less than 10,000 CFUs/mL of saliva) and 10% to 20% had high counts (100,000 to 1 million CFUs/mL of saliva).
Generally the MS counts were 10 times greater than the lactobacillus counts. Most children with low mutans streptococci levels also had low numbers of lactobacilli, but there were situations where one type of bacterium was high and the other low.
In a dentate Swedish population of 80 and 85 year olds, Kohler and Persson (1991) found that 95% of the subjects had detectable salivary lactobacilli counts and 35% very high levels (more than 100,000 CFUs/mL of saliva). Almost 90% were MS positive, and 30% had more than 1 million CFUs/mL of saliva.
