The primary aims of this longitudinal study were to (1) determine the prevalence and timing of predentate and post-dentate colonization of the cariogenic bacteria Streptococcus mutans in preterm and fullterm infants, (2) investigate maternal and infant factors which affect colonization of S. mutans and (3) investigate the effectiveness of once weekly toothbrushing of 0.2% chlorhexidine gluconate gel in dentate infants for suppression of S. mutans colonization.
Three hundred and twelve (93 preterm, 219 fullterm) infant-mother pairs were randomly recruited at Mater Mothers' Hospitals at birth. Dental examination and saliva collections were performed for infant-mother pairs at the hospital and then every 3 months at the School of Dentistry, the University of Queensland until infants reached the age of 24 months. Mothers were interviewed at birth and every 3 monthly regarding
demographic details, medical and dental health, feeding, dietary, oral hygiene and other habits. Hospital medical records were used to verify medical information obtained from mothers. Sterile swabs were used to collect unstimulated whole saliva from mothers and infants, for isolation of S. mutans using selective tryptone-yeast-cysteine-sucrose-bacitracin (TYCSB) agar and for estimating total salivary IgA, IgG and IgM levels using enzyme-linked immunosorbent assays (ELISA).
S. mutans was isolated from a total of 246 (79%) infants during the study period (0 to 24 month-old). The overall prevalence of predentate S. mutans colonization in this study was 64% (153/238). The prevalence increased to 84% (93/111) post-eruption.
At 3 months of age, the prevalence of S. mutans infection among infants without teeth was 30% (56/188). Fullterm infants showed a higher prevalence of
S. mutans than preterm infants (34% vs, 20%), p<0.05). Oral developmental nodules associated with predentate colonization of S. mutans at 3 months in a dose-response relationship (p<0.01). At the age of 6 months, the prevalence of S. mutans colonization was 56% (97/112) in infants without teeth (preterm 50% vs. fullterm 60%), p>0.05). The three most significant factors associated with colonization of S. mutans before the eruption of teeth were frequency of sugar intake (p<0.001), breastfeeding (p<0.001) and habits that encouraged maternal saliva transfer (p<0.01). The most significiant correlation for predentate colonization of S. mutans in preterm infants was frequent sugar exposure from solids (rs= 0726, p<0.001) and in fullterm infants, on-demand breast and/or bottle feeding (rs= 0.484,
Prevalence of S. mutans colonization after tooth eruption were 1%, 12%, 37%, 54%, 58%, 71% and 85% at 6-, 9-, 12-, 15-, 18-, 21- and 24 months of age respectively (total 93/111 infants). The median age of colonization after tooth eruption in fullterm was lower compared to preterm infants (15.0 month-old vs. 16.5 month-old, p<0.017). The three most significant associating factors were being cared for by adults other than mothers before 12 months of age (p<0.001), on-demand and/or night feeding (p<0.001) and sleeping next to mother (p<0.001). Preterm infants were 4.4 times (95% CI = 1.0-20.3) more at-risk of post-dentate colonization of S. mutans (is = 0.198, p<0.045). Reasons for the increased risk may be due to the fact that infected preterm infants were 26.2 times (95% CI = 7.8- 88.1) more likely to possess enamel defects and 7.9 times (95%) CI = 3.4- 18.7) more likely
to be frequently exposed to sugar in solids than infected fullterm infants.
In addition, a placebo-controlled double-blind clinical trial was carried out on dentate infants who harbored S. mutans. The 3 months trial compared once weekly toothbrushing of 0.2% chlorhexidine gluconate gel (Periogard, Colgate, Australia) (n = 50) to placebo (n = 46) and no gel (n = 210) controls. These infants were followed until the age of 18 months. Saliva samples were obtained at three monthly recall appointments for microbiological assays.
In the clinical trial using chlorhexidine gluconate gel, infants with initially low S. mutans levels of less than 300 CFU/mL, showed significant percentage reduction in S. mutans in the chlorhexidine group compared to the placebo and no-gel control groups immediately after three months of weekly gel application (p<0.025). S.
mutans reductions in the chlorhexidine and placebo gel groups were not significantly different after 15 months of follow-up. In addition, a significant percentage (39/96,41%) of all the infants in the trial showed reduction of S. mutans to undetectable levels. Compared to infants who retained S. mutans, these infants had higher toothbrushing frequencies (p<0.001), regular use of fiuoridated toothpaste (p<0.001), lower frequencies of daily feeds (p<0.01) and lower frequencies of sugar consumption (p<0.001).
In conclusion, predentate colonization of S. mutans occurred in preterm and fullterm infants as young as 3 months of age. Dentate colonization occurred most frequently at 15-16 months of age (mean 15.7 ± 5.1 month old). By 24 months of age, S. mutans can be isolated from most preterm and fullterm infants in this study. The prevalence
of S. mutans increased significantly after tooth eruption (64% vs. 84%, p<0.01). The use of 0.2% chlorhexidine gluconate gel once a week for three months significantly reduced S. mutans in infants with low initial levels (less than 300 CFU/mL) for three months after cessation of treatment. However, there was no significant long-term suppression of S. mutans colonization once the use of chlorhexidine gel was ceased. More frequent applications using higher concentrations of chlorhexidine may be required.
Although the prevalence of neonatal complications and long-term medical problems were greater in preterm than fullterm infants, there were relatively few factors which were significantly different in their risk for S. mutans colonization. The additional risk factors in the preterm infants include their high predisposition to enamel hypoplasia and their increased consumption of
sugar in solid foods. In both groups of infants, the most significant factors associated with colonization of S. mutans were high frequency of sugar exposure, feeding habits, habits that facilitate saliva transfer from adults and the presence of oral developmental nodules. These factors may be useful in the identification of infants at-risk of early colonization of S. mutans which in turn may help to identify those at-risk for early childhood caries.