A longitudinal study of caries onset in initially caries-free children and baseline salivary mutans streptococci levels: a Kaplan-Meier survival analysis

A Prospective Longitudinal Study of Early Childhood Caries Onset in Initially Caries-Free Children

INTRODUCTION

Early childhood caries (ECC) is a complex oral disease that is prevalent in US children.

OBJECTIVES

The purpose of this 2-y prospective cohort study was to examine baseline and time-dependent risk factors for ECC onset in initially caries-free preschool children.

METHODS

A cohort of 189 initially caries-free children aged 1 to 3 y was recruited. At each 6-mo study visit, children were examined using the ICDAS index; salivary samples were collected to assess mutans streptococci (MS), lactobacilli, Candida species, salivary cortisol (prior and after a stressor), and salivary IgA. Diet and oral health behavior were assessed from parent report. Child and family stress exposure was assessed from measures of psychological symptoms, stressful life event exposure, family organization and violence exposure, and social support. Sociodemographic factors were also considered. A Kaplan-Meier estimator of survival function of time to ECC and a Cox proportional hazards model were used to identify predictors of ECC onset.

RESULTS

Onset of ECC was associated with high salivary MS levels at baseline (log-rank test, P < 0.0001). Cox proportional hazards regression showed that the risk of dental caries significantly increased with salivary MS in log scale over the 6-mo period (hazard ratio, 1.08; P = 0.01). Other risk factors in the model did not reach statistical significance.

CONCLUSION

Our results provide prospective evidence that an increase in salivary MS predicts ECC onset in young, initially caries-free children, confirming that a high salivary MS count likely plays a causal role in ECC onset, independent of covariates.

KNOWLEDGE TRANSFER STATEMENT

These results suggest that we must focus on reducing salivary MS counts in young children and preventing or delaying MS colonization in infants and young children determined to be at risk for ECC.

Influence of caries risk on the retention of a resin-modified glass ionomer used as occlusal sealant: a clinical trial

Abstract Introduction Little is known whether caries risk influence occlusal sealants retention. Objective To determine the retention rates (RR) of the resin-modified glass ionomer cement used as occlusal sealant in permanent first molars of 6-8-year old schoolchildren and to analyze the influence of caries risk at baseline on the RR of the sealant, over a 24-month period. Material and method The sealant application was performed in a dental office at the beginning of the study, after children being allocated into high caries risk group (HR) and low caries risk group (LR). The examinations were performed by the same calibrated dentist at 0, 6, 12, 18 and 24 months. Retention rates were estimated, the Kaplan-Meier method was used to estimate the survival probabilities; and the comparison between HR and LR groups was evaluated by Wilcoxon and log-rank test. Result The results showed that 14% of sealed teeth showed total loss (16% for HR and 12% for LR) and 46% showed partial loss during the study (51% for HR and 41% for LR), in relation to the baseline sample. No difference could be demonstrated by the survival analysis between HR and LR groups (p>0.05). Conclusion Caries risk did not influence the retention rates of a resin-modified glass ionomer cement used as occlusal sealant in 6-8-year old schoolchildren.

Relationship among α amylase and carbonic anhydrase VI in saliva, visible biofilm, and early childhood caries: a longitudinal study

AIM

This longitudinal study investigated the relationship among early childhood caries (ECC), α amylase, carbonic anhydrase VI (CA VI), and the presence of visible biofilm, besides detecting if these variables could predict risk for ECC.

DESIGN

One hundred children were divided into two groups: caries group (n = 45) and caries-free group (n = 55). Visible biofilm on maxillary incisors was recorded, followed by caries diagnosis in preschoolers at baseline and at follow-up. Saliva samples were collected, and activities of CA VI and α amylase were determined. Data normality was assessed by Shapiro-Wilk test and then Mann-Whitney, Spearman correlation, and chi-square tests followed by multiple logistic regression analysis (α = 0.05, 95% confidence interval).

RESULTS

CA VI activity was significantly higher in saliva of children with caries (P ≤ 0.05), and α amylase activity was significantly higher in saliva of caries-free children (P < 0.0001). Children with α amylase activity in saliva lower than 122.8 U/mL (OR = 3.33 P = 0.042) and visible biofilm on maxillary incisors (OR = 3.6 P = 0.009) were more likely to develop ECC than caries-free children. A negative correlation between caries and α amylase activity was found (P = 0.0008).

CONCLUSIONS

The presence of visible biofilm and low salivary activity of α amylase may be considered risk predictors for ECC.

Longitudinal study of caries progression in 2- and 3-year-old German children

OBJECTIVE

This 2-year longitudinal study in 2- and 3-year-old kindergarten children investigated lesion progression on different surfaces of primary teeth.

METHODS

The study was conducted between September 2008 and September 2010 on a sample of 400 children from the Kyffhäuser district (Thuringia, Germany). A calibrated investigator recorded (non)cavitated caries lesions according to World Health Organization (WHO), International Caries Detection and Assessment System (ICDAS) and Universal Visual Scoring System (UniViSS) criteria. Nonparametric methods and linear regression using a mixed-effects model with an unbalanced design were used for data analysis.

RESULTS

There was a significant increase in the prevalence of noncavitated caries lesions during the 2-year period, with the highest chance for change on all surfaces compared to cavitated lesions. First visible sign lesions on occlusal surfaces had the highest chance for change (estimate 0.38), whereas established lesions revealed the highest chance for change on proximal (estimate 1.05) and smooth surfaces (estimate 0.62). Proximal lesions exhibited the greatest chance for change irrespective of severity level.

CONCLUSION

Our study demonstrated that each type of carious lesion had different changing rates. Greater lesion severity correlated with greater chances to change and receive treatment. This information is crucial for dental practitioners in decision-making processes.

Unraveling the hidden heterogeneities of breast cancer based on functional miRNA cluster

It has become increasingly clear that the current taxonomy of clinical phenotypes is mixed with molecular heterogeneity, which potentially affects the treatment effect for involved patients. Defining the hidden molecular-distinct diseases using modern large-scale genomic approaches is therefore useful for refining clinical practice and improving intervention strategies. Given that microRNA expression profiling has provided a powerful way to dissect hidden genetic heterogeneity for complex diseases, the aim of the study was to develop a bioinformatics approach that identifies microRNA features leading to the hidden subtyping of complex clinical phenotypes. The basic strategy of the proposed method was to identify optimal miRNA clusters by iteratively partitioning the sample and feature space using the two-ways super-paramagnetic clustering technique. We evaluated the obtained optimal miRNA cluster by determining the consistency of co-expression and the chromosome location among the within-cluster microRNAs, and concluded that the optimal miRNA cluster could lead to a natural partition of disease samples. We applied the proposed method to a publicly available microarray dataset of breast cancer patients that have notoriously heterogeneous phenotypes. We obtained a feature subset of 13 microRNAs that could classify the 71 breast cancer patients into five subtypes with significantly different five-year overall survival rates (45%, 82.4%, 70.6%, 100% and 60% respectively; p = 0.008). By building a multivariate Cox proportional-hazards prediction model for the feature subset, we identified has-miR-146b as one of the most significant predictor (p = 0.045; hazard ratios = 0.39). The proposed algorithm is a promising computational strategy for dissecting hidden genetic heterogeneity for complex diseases, and will be of value for improving cancer diagnosis and treatment.

Dynamics of oral microbial community profiling during severe early childhood caries development monitored by PCR-DGGE

OBJECTIVE

To monitor the longitudinal changes in oral microbial diversity of children with severe early childhood caries (S-ECC) compared to caries free (CF) controls.

METHODS

Dental plaque samples of 12 children in each group at 8, 14, 20, 26 and 32 months of age were analysed. Total microbial genomic DNA was isolated from each sample, and PCR-denaturing gradient gel electrophoresis (DGGE) analyses were carried out.

RESULTS

The number of bands was significantly higher in the CF group (18.17±4.91 bands) than in the S-ECC group (14.54±5.56 bands) at 32 months of age (P<0.05). A total of 21 genera were identified in all subjects, and there were no significant differences between the two groups at genus level. DGGE profiles showed that most of the clusters were constructed from one individual over time in the both groups.

CONCLUSIONS

The onset of S-ECC is accompanied by a decrease in microbial diversity. The overall composition of the microbiota is highly similar within an individual over time.

A longitudinal study of occlusal caries in Newark New Jersey school children: relationship between initial dental finding and the development of new lesions

OBJECTIVE

Dental caries is a significant public health problem especially amongst children from low-income backgrounds. This longitudinal study examined the development of new occlusal caries in 227 Newark, NJ children ages 10-18. The role of previous caries experience and the presence of occlusal white and dark lesions in predicting the development of new lesions were examined.

DESIGN

At each visit, the patient's teeth were given a visual-tactile examination and the subject's decayed, missing and filled (DMFS) score was determined. Next, molars lacking probeable caries or restorations were examined using transillumination for occlusal white and dark spots. This examination was repeated periodically. A Cox proportional hazard was used to analyse data concerning the development of new occusal caries in molars.

RESULTS

The longitudinal data indicates that patients who were caries free at visit-1 developed significantly fewer occlusal caries during the longitudinal study. The hazard ratio for subjects who had first-visit caries was 2.27 compared to caries free subjects. Intact molars with occlusal white or dark lesions had caries hazard ratios of 0.78 and 1.49 respectively, compared to molars lacking initial colour changes.

CONCLUSION

Having a prior caries history places the subject at increased risk of developing future caries. Teeth with dark lesions but not white lesions are at significantly increased risk for developing decay. White lesions may represent remineralizing or slowly progressing lesions. The results of this study can help identify patients and tooth surfaces at risk for future occlusal decay.

Timing of colonization of caries-producing bacteria: an approach based on studying monozygotic twin pairs

Findings are presented from a prospective cohort study of timing of primary tooth emergence and timing of oral colonization of Streptococcus mutans (S. mutans) in Australian twins. The paper focuses on differences in colonization timing in genetically identical monozygotic (MZ) twins. Timing of tooth emergence was based on parental report. Colonization timing of S. mutans were established by plating samples of plaque and saliva on selective media at 3 monthly intervals and assessing colony morphology. In 25% of individuals colonization occurred prior to emergence of the first tooth. A significant proportion of MZ pairs (21%) was discordant for colonization occurring before or after first tooth emergence, suggesting a role of environmental or epigenetic factors in timing of tooth emergence, colonization by S. mutans, or both. These findings and further application of the MZ co-twin model should assist in development of strategies to prevent or delay infection with S. mutans in children.

Urease activity as a risk factor for caries development in children during a three-year study period: a survival analysis approach

Recent cross-sectional studies suggest that reduced ability to generate alkali via the urease pathway in dental plaque may be an important caries risk factor, but it has not been assessed prospectively.

OBJECTIVE

To evaluate the effect of plaque and saliva urease activity on the risk for developing new caries over a three-year period in children.

METHODS

A panel of 80 children, three to six years of age at recruitment, was followed prospectively for three years. Plaque urease activity, saliva urease activity and dental caries were measured every six months. Survival analysis methodology was used to evaluate the effect of urease on caries development during the study period adjusted for gender, age, baseline caries levels, sugar consumption, amount of plaque, and mutans streptococci levels.

RESULTS

The risk for developing new caries increased in a dose-responsive manner with increasing levels of urease activity in saliva (adjusted HR(Q4 vs. Q1): 4.98; 95% CI: 1.33, 18.69) and with decreasing urease activity in plaque (adjusted HR(Q4 vs. Q1): 0.29; 95% CI: 0.11, 0.76). Multiple measurements of urease activity were conducted to overcome the variability of urease activity in this study. Baseline caries and mutans streptococci in saliva were also important predictors of caries risk.

CONCLUSIONS

Increased urease activity in saliva can be an indicator of increased caries risk in children, whilst increased urease activity in plaque may be associated with reduced caries risk. The reproducibility of urease measurements must be improved before these findings can be further tested and clinically applied.

The relationship between levels of income inequality and dental caries and periodontal diseases

The objective of this study was to evaluate the association between income inequality at a lagged time of 2 and 11 years with two short latency outcomes (untreated dental caries and gingivitis) and two long latency outcomes (edentulism and periodontal attachment loss > 8mm). We used data from the Brazilian oral health survey in 2002-2003. Our analysis included 13,405 subjects aged 35-44 years. Different lagged Gini at municipal level were fitted using logistic and negative binomial multilevel analyses. Covariates included municipal per capita income, equivalized income, age, sex, time since last dental visit and place of residence (rural versus urban). Crude estimates showed that only untreated dental caries was associated with current and lagged Gini, but in adjusted models only current Gini remained significant with a ratio of 1.19 (95%CI: 1.09-1.30) for every ten-point increase in the Gini coefficient. We conclude that lagged Gini showed no association with oral health; and current income Gini was associated with current dental caries but not with periodontal disease.

Urease activity in dental plaque and saliva of children during a three-year study period and its relationship with other caries risk factors

Bacterial urease activity in dental plaque and in saliva generates ammonia, which can increase the plaque pH and can protect acid-sensitive oral bacteria. Recent cross-sectional studies suggest that reduced ability to generate ammonia from urea in dental plaque can be an important caries risk factor. In spite of this proposed important clinical role, there is currently no information available regarding important clinical aspects of oral ureolysis in children.

OBJECTIVE

The objective of this study was to evaluate the distribution and pattern of urease activity in the dental plaque and in the saliva of children during a three-year period, and to examine the relationship of urease with some important caries risk factors.

METHODS

A longitudinal study was conducted with repeated measures over a three-year period on a panel of 80 children, aged 3-6 years at recruitment. The dynamics of change in urease activity were described and associated with clinical, biological, and behavioural caries risk factors.

RESULTS

Urease activity in plaque showed a trend to remain stable during the study period and was negatively associated with sugar consumption (P<0.05). Urease activity in unstimulated saliva increased with age, and it was positively associated with the levels of mutans streptococci in saliva and with the educational level of the parents (P<0.05).

CONCLUSIONS

The results of this study reveal interesting and complex interactions between oral urease activity and some important caries risk factors. Urease activity in saliva could be an indicator of mutans infection in children.

Association between caregiver behaviours to prevent vertical transmission and dental caries in their 3-year-old children

BACKGROUND

It has been suggested that oral organisms in children are mainly those transmitted from their mothers. That may account for the relationship between caries levels in children and their parents. However, few studies have investigated the effect of trying to prevent vertical transmission of oral organisms on dental caries levels in children, and the findings in the studies are controversial. The aim of this study was to investigate the association between measures to prevent vertical transmission of oral organisms and the caries experience in 3-year-old children.

METHODS

Data were collected from dental examinations for 3-year-old children and a self-administered questionnaire for their caregivers. Absence of maternal sharing of utensils and mouth-to-mouth feeding between caregivers and children was used as the variable about behaviour to prevent vertical transmission of oral organisms. Sex, age in months, dietary behaviour, oral health behaviour and sociodemographic factors were used as covariates.

RESULTS AND CONCLUSION

Data for 3,035 children (73.5% of the subjects) were analysed. Caregivers who practised vertical transmission prevention tended to have better oral health behaviours. Multivariate logistic regression analysis did not show any significant association between behaviour to prevent vertical transmission and caries experience (OR = 1.10, 95% CI = 0.86-1.41). This study suggests that caregiver behaviour to prevent vertical transmission was not effective in reducing levels of childhood caries.

The individual and contextual pathways between oral health and income inequality in Brazilian adolescents and adults

We evaluate the association between income inequality (Gini index) and oral health and in particular the role of alternative models in explaining this association. We also studied whether or not income at the individual level modifies the Gini effect. We used data from an oral health survey in Brazil in 2002-2003. Our analysis included 23,568 15-19 and 22,839 35-44 year-olds nested in 330 municipalities. Different models were fitted using multilevel analysis. The outcomes analysed were the number of untreated dental caries (count), having at least one missing tooth (dichotomous) and being edentulous (dichotomous). To assess interaction as a departure from additivity we used the Synergy Index. For this, we dichotomized the Gini coefficient (high vs low inequality) by the median value across municipalities and the individual income in the point beyond which it showed roughly no association with oral health. Adjusted rate ratio of mean untreated dental caries, respectively for the 15-19 and 35-44 age groups, was 1.12 and 1.16 for each 10 points increase in Gini scale. Adjusted odds ratio of a 15-19 year-old having at least one missing tooth or a 35-44 year-old being edentulous was, respectively, 1.19 and 1.01. High income inequality had no statistically significant synergistic effect with being poor or living in a poor municipality. Higher levels of income inequality at the municipal level were associated with worse oral health and there was an unexplained residual effect after controlling for potential confoundings and mediators. Municipal level income inequality had a similar, detrimental effect, among individuals with lower or higher income.

Allospecific CD154+ T cells associate with rejection risk after pediatric liver transplantation

Antigen-specific T cells, which express CD154 rapidly, but remain untested in alloimmunity, were measured with flow cytometry in 16-h MLR of 58 identically-immunosuppressed children with liver transplantation (LTx), to identify Rejectors (who had experienced biopsy-proven rejection within 60 days posttransplantation). Thirty-one children were sampled once, cross-sectionally. Twenty-seven children were sampled longitudinally, pre-LTx, and at 1-60 and 61-200 days after LTx. Results were correlated with proliferative alloresponses measured by CFSE-dye dilution (n = 23), and CTLA4, a negative T-cell costimulator, which antagonizes CD154-mediated effects (n = 31). In cross-sectional observations, logistic regression and leave-one-out cross-validation identified donor-specific, CD154 + T-cytotoxic (Tc)-memory cells as best associated with rejection outcomes. In the longitudinal cohort, (1) the association between CD154 + Tc-memory cells and rejection outcomes was replicated with sensitivity/specificity 92.3%/84.6% for observations at 1-60 days, and (2) elevated pre-LTx CD154 + Tc-memory cell responses were associated with significantly increased incidence (p = 0.02) and hazard (HR = 7.355) of rejection in survival/proportional hazard analysis. CD154 expression correlated with proliferative alloresponses (r = 0.835, p = 7.1e-07), and inversely with CTLA4 expression of allospecific CD154 + Tc-memory cells (r =-0.706, p = 3.0e-05). Allospecific CD154 + T-helper-memory cells, not CD154 + Tc-memory, were inhibited by increasing Tacrolimus concentrations (p = 0.026). Collectively, allospecific CD154 + T cells provide an estimate of rejection risk in children with LTx.

A long-term effect of caries-related factors in initially caries-free children

AIM

The aim of this study was to examine the rate and pattern of early childhood caries development in caries-free children based on their dental plaque accumulations, salivary Streptococcus mutans levels, maternal sharing, oral hygiene, and feeding attitudes at baseline and at 24-month follow-up period.

DESIGN

A total of 92 children, aged between 15 to 35 months, comprised the study group. The children's dental examinations were first carried out at baseline, and 56 of them were re-examined 24 months later to determine the changes in dental status. The mothers were also interviewed at each examination based on a prepared questionnaire.

RESULTS

The prevalence of caries incidence was 45% at 24-month evaluation period among initially caries-free children. The new caries formation was mostly observed on occlusal and aproximal surfaces of maxillary molars (28% and 26%) followed by mesial, distal and buccal surfaces of anterior teeth, respectively. Significant correlations between dental caries formation and maternal sharing, S. mutans levels, and plaque scores were found.

CONCLUSION

The results indicated that early S. mutans colonization, high plaque accumulation, and maternal sharing were important factors on a child's caries development.

Unravelling the hidden heterogeneities of diffuse large B-cell lymphoma based on coupled two-way clustering

BACKGROUND

It becomes increasingly clear that our current taxonomy of clinical phenotypes is mixed with molecular heterogeneity. Of vital importance for refined clinical practice and improved intervention strategies is to define the hidden molecular distinct diseases using modern large-scale genomic approaches. Microarray omics technology has provided a powerful way to dissect hidden genetic heterogeneity of complex diseases. The aim of this study was thus to develop a bioinformatics approach to seek the transcriptional features leading to the hidden subtyping of a complex clinical phenotype. The basic strategy of the proposed method was to iteratively partition in two ways sample and feature space with super-paramagnetic clustering technique and to seek for hard and robust gene clusters that lead to a natural partition of disease samples and that have the highest functionally conceptual consensus evaluated with Gene Ontology.

RESULTS

We applied the proposed method to two publicly available microarray datasets of diffuse large B-cell lymphoma (DLBCL), a notoriously heterogeneous phenotype. A feature subset of 30 genes (38 probes) derived from analysis of the first dataset consisting of 4026 genes and 42 DLBCL samples identified three categories of patients with very different five-year overall survival rates (70.59%, 44.44% and 14.29% respectively; p = 0.0017). Analysis of the second dataset consisting of 7129 genes and 58 DLBCL samples revealed a feature subset of 13 genes (16 probes) that not only replicated the findings of the important DLBCL genes (e.g. JAW1 and BCL7A), but also identified three clinically similar subtypes (with 5-year overall survival rates of 63.13%, 34.92% and 15.38% respectively; p = 0.0009) to those identified in the first dataset. Finally, we built a multivariate Cox proportional-hazards prediction model for each feature subset and defined JAW1 as one of the most significant predictor (p = 0.005 and 0.014; hazard ratios = 0.02 and 0.03, respectively for two datasets) for both DLBCL cohorts under study.

CONCLUSION

Our results showed that the proposed algorithm is a promising computational strategy for peeling off the hidden genetic heterogeneity based on transcriptionally profiling disease samples, which may lead to an improved diagnosis and treatment of cancers.

Factors influencing oral colonization of mutans streptococci in young children

This paper aims to critically review current knowledge about the key factors involved in oral colonization of the cariogenic group of bacteria, mutans streptococci (MS) in young children. MS, consisting mainly of the species Streptococcus mutans and Streptococcus sobrinus, are commonly cultured from the mouths of infants, with prevalence of infection ranging from around 30 per cent in 3 month old predentate children to over 80 per cent in 24 month old children with primary teeth. MS is usually transmitted to children through their mothers, and the risk of transmission increases with high maternal salivary levels of MS and frequent inoculation. Factors that affect the colonization of MS may be divided into bacterial virulence, host-related and environmental factors. Complex interaction among these factors determine the success and timing of MS colonization in the child. As clinical studies have shown that caries risk is correlated with age at which initial MS colonization occurred, strategies for the prevention of dental caries should include timely control of colonization of the cariogenic bacteria in the mouths of young children.

A seven-year survival analysis of caries onset in primary second molars and permanent first molars in different caries risk groups determined at age two years

OBJECTIVE

To investigate in a group of children (n=183) the effect of possible risk factors registered at the age of 2 years on caries development in 7 years of follow-up, and to study associations between risk groups.

MATERIAL AND METHODS

Consumption of candies, use of a nursing bottle at night, use of fluorides, toothbrushing, pacifier sucking, and prolonged breastfeeding (>or=12 months) were recorded at the age of 2 years. The timing of caries onset in different groups was compared by applying a survival analysis method--the survival curves produced separately for selected teeth in different risk groups.

RESULTS

The survival curves of caries onset for both primary and permanent molars were consistently lower for children who consumed candies more than once a week, did not brush their teeth daily, were given a nursing bottle at night or a pacifier at age 2 years. The multivariate survival analysis confirmed that consumption of candies and lack of daily toothbrushing were the factors that had the major impact on caries onset in both primary and permanent molars. Prolonged pacifier sucking (>or=2 years) was related only with short duration of breastfeeding. Children with prolonged use of a nursing bottle at night also consumed candies more than once a week, did not brush their teeth regularly, and did not use fluoride tablets.

CONCLUSIONS

Consumption of candies and inadequate oral hygiene at age 2 years are important long-term risk factors for caries development in both primary and permanent molars.

Application of nonhomogenous Markov models for analyzing longitudinal caries risk

OBJECTIVES

Markov modeling is a useful mathematical procedure for calculating probabilities of disease prognosis. Increasingly, Markov models are being applied in medical and health services research and also in social sciences research. The purpose of our study was to use the Markov process to determine time-dependent transition probabilities for caries-free children to convert to a caries-active state and to assess the impact of salivary mutans streptococci (MS) levels on caries status.

METHODS

Our analysis was based on data obtained from a 6-year longitudinal study of risk factors associated with caries onset in children.

RESULTS

Based on a two-state Markov model, the probability that a caries-free child would convert to a caries-active state during the study ranged between 0.0046 and 0.0471. The highest probability of converting from a caries-free state to a caries-active state was 0.0471 at age 8.5 years.

CONCLUSIONS

In addition to standard statistical methods of analyzing longitudinal caries data, Markov models show promise for use in the analysis of caries risk.

Caries-Preventive Effect of Chlorhexidine Gel Applications among High-Risk Children

Evidence on the caries-preventive effect of chlorhexidine (CHX) among high-risk children is inconclusive, possibly because obscured by fluoride exposure. We investigated the effect of CHX among initially 3-year-old subjects whose baseline d(3)ft was = 0 and whose only regular fluoride exposure came from toothpaste. The subjects were assigned to three groups: high-risk test (HRT, n = 70), high-risk control (HRC, n = 71), and low-risk control (LRC, n = 70). Risk classification was based on salivary mutans streptococcal levels (MS, </>or=1.0 x 10(5) cfu/ml). Basic measures (oral hygiene, dietary counselling every 4 months) were given to all groups. HRT also underwent CHX gel applications for 3 consecutive days at 3-month intervals for 15 months. Eighteen months after baseline d(3)ft increments and proportions of children with d(3)ft increment >or=1 (%d(3)ft increment >or=1) among all groups were assessed. Anti-MS effect on high-risk children and caries-preventive effect on all children were statistically analysed by residual change analysis (MS), non-parametric tests and logistic regression analysis (caries). No differences were found between the groups in basic programme compliance. CHX significantly reduced MS levels. %d(3)ft increment >or=1 and mean d(3)ft increments were 34.3%, 0.56 (HRT), 32.4%, 0.54 (HRC) and 11.4%, 0.11 (LRC), with HRT/HRC values statistically significantly higher than LRC values and no significant difference between HRT and HRC. HRT children were not less likely to show new lesions than HRC children (OR = 1.09; 95% confidence interval 0.54-2.19), while high-risk children were 4 times more likely to show new lesions than low-risk children (OR = 3.71; 95% confidence interval 1.53-9.03). CHX gel applications showed moderate anti-MS effect but negligible caries-preventive effect.