Bacteria Found in Root Caries: Common Culprits and New Associations

Objectives: This study identified bacteria associated with root caries in geriatric patients. Previous studies have found Streptococcus mutans, Lactobacillus species and Actinomyces species can be associated with root caries. We determined whether these species, along with four additional species, are present in higher concentrations on carious root surfaces compared to healthy control teeth.
Methods: Up to twenty patients, 65 years and older, with root caries were recruited. Supragingival plaque was collected from both a carious root and a healthy contralateral root surface from the same patient. Plaque samples were placed in sterile buffered-saline with 10% glycerol for storage. Bacteria were lysed, DNA purified using a Qiagen DNA purification kit. DNA was then amplified using PCR primers specific for selected organisms. Levels of each species were quantified using Real-Time PCR. Results between paired carious and non-carious plaque samples were statistically analyzed to determine whether differences in bacterial colonization between the two groups were significant.
Results: Results with 14 pairs of plaque samples suggest high levels of S. mutans or Actinomyces can result in root caries or that a combination of more modestly increased levels of both S. mutans and Actinomyces at a single site may lead to root caries. Some carious teeth with no increase in S. mutans or Actinomyces had increased levels of Olsenella uli. There was no consistent inverse correlation between S. sanguinis colonization and S. mutans colonization. Furthermore, elevated levels of V. parvula correlated with increased S. mutans and caries in several cases.
Conclusions: Our analyses suggest S. mutans and Actinomyces species are major contributors to root caries and Olsenella uli may also play a role. Furthermore, S. sanguinis does not appear to readily compete with S. mutans on root surfaces. Finally we found no cases (0/14) where increased colonization by Lactobacillus casei showed an association with root caries.