Objectives: The aims of this thesis were to: 1) describe the caries experience and caries-related factors in mothers and their preschool and school children, 2) correlate quantified supragingival plaque bacteria between mothers and their children and identify possible microbial associations, 3) examine whether bacteria in pooled supragingival plaque samples, quantified using a “checkerboard DNA-DNA hybridisation”-based panel of caries-related bacteria, could reflect the caries experience in a manner similar to saliva samples analysed using chair-side methods, 4) measure the effects of six weeks’ use of a 5,000 ppm fluoride toothpaste on caries-related factors in dental plaque and saliva and 5) consecutively assess the caries risk following six weeks’ use of 5,000 ppm fluoride toothpaste using the “Cariogram”. Materials and methods: A total of 258 individuals (86 mothers and two of their children, 4-6 and 12-16 years old) were examined cross-sectionally (Studies I, II & III) out of which 17 families were enrolled (mothers and 13- to 17-year-old children) a year later in a longitudinal six weeks trial (Studies IV & V) in which 5,000 ppm fluoride toothpaste was administered. In Study I, anamnestic data were collected, and clinical oral examinations and chair-side tests were performed. In Studies II and III, pooled interproximal supragingival plaque samples were analysed for their content of bacterial strains using the checkerboard DNA-DNA hybridisation technique. In Study II, microbial associations for all three age groups together were sought using cluster analysis, while principal components analysis (PCA) was used for each of the three age groups separately. In Study III, relationships between the bacterial scores and the caries experience (DMFT/dmft and D/d groups) were assessed. In Study IV, the participants were assessed on four (two weeks apart) visits. Sampling of approximal fluid for fluoride analysis and approximal plaque for organic acid analysis was performed. Chair-side tests were performed to register the lactic acid production rate on the tongue, approximal plaque pH, salivary buffer capacity and counts of cariogenic microorganisms. In Study V, caries-risk assessment following the use of 5,000 ppm fluoride toothpaste was performed consecutively on each of the four visits using the “Cariogram” software. Results: In Study I, the mean caries experience (DMFT/dmft) was high in the mothers and their younger and older children (12.4 ± 5.3, 9.0 ± 5.0 and 5.8 ± 4.1, respectively). The DMFT/dmft increased with higher salivary mutans streptococci counts in all age groups (p<0.05). The caries experiences of the children were positively correlated with those of their mothers (R24-6=0.12, R212-16=0.18, p<0.01). A positive association between mothers and both children was evident for toothbrushing habits, snacking frequency and gingival health (p<0.05). An association between plaque scores, salivary buffer capacity and mutans streptococci (MS) counts was found between mothers and older children (p<0.05). In Study II, three complexes were formed from the dendrogram. PCA results were similar in all three groups. The correlation analyses of bacterial counts between mothers and their children showed a significant association for most of the bacterial strains (p<0.05 or 0.01). In Study III, no significant relationships were found between the bacterial scores and DMFT/dmft or D/d groups. In Study IV, the six weeks’ use of 5,000 ppm fluoride toothpaste significantly increased the approximal fluid fluoride concentration, and salivary buffer capacity. It also decreased the lactic acid production rate, plaque acideogenicity (AUC5.7, AUC6.2, maximum pH fall) and salivary mutans streptococci counts. In Study V, the use of 5,000 ppm fluoride toothpaste resulted in a statistically significant modification of the caries-risk profile, increasing the actual chance of avoiding caries in the future among the mothers and teenagers at each visit following baseline (p<0.01). The changes essentially related to the salivary parameters [buffer capacity, MS, and lactobacilli (LB) counts]. A statistically significant linear trend was observed for MS counts (p<0.01) and the number of individuals with a salivary concentration of MS < 103 increased on each visit. The same trend was also observed for LB and buffer capacity scores (p=0.04 and p=0.03 respectively). Conclusions: The caries experience in Saudi mothers and their children is high, with similar contributory caries-related factors. Supragingival plaque microbiota are correlated between the mothers and their children with similar supragingival plaque microbial associations present in all three family members. The analysed pooled plaque samples did not reveal any significant relationships between the bacterial counts and the caries experience in any of the family members. The 5,000 ppm fluoride toothpaste has the ability to reduce the cariogenic potential of dental plaque and saliva, as well as the caries-risk profile
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