The purposes of the study were: (1) to assess the prevalence and distribution of smooth-bordered tooth wear in teenagers, and (2) to investigate the relationship between smooth-bordered tooth wear and social background, dietary pattern, drinking habits, oral hygiene practices and caries prevalence. In The Hague, The Netherlands, a sample of 345 10- to 13-year-olds and 400 15- and 16-year-olds was clinically examined. The criteria for the assessment of smooth-bordered tooth wear (‘smooth wear’) were in line with the diagnostic criteria for erosion developed by Lussi (1996). In the age group 10–13 years, the percentage of subjects with visible smooth wear (SW1 threshold) was 3% and in 1 subject (0.3%), deep smooth enamel wear was found. Due to the low prevalence, the results for this age group were not analysed further. In the age group 15–16 years, the proportion of subjects with visible smooth wear (SW1 threshold) was 30% and that with at least deep smooth enamel wear (SW2 threshold) 11%. Smooth wear into dentine was found in 1 subject. First molars and upper anterior teeth were affected predominantly. A significant effect on visible smooth wear (SW1 threshold) was found for gender and social background. At mouth level, no significant influence was found for dietary patterns, drinking habits or oral hygiene practices. The caries prevalence was similar in subjects with and without smooth wear.

A meta-analysis was performed on published data on the caries-inhibiting effect of chlorhexidine treatment. The results of the various studies are difficult to evaluate because of various treatment procedures, dissimilar features of participants, and different presentations of study results. A meta-analysis provides a more structured approach than the traditional review, due to systematic analysis and numerical processing of the available information. The objectives of this meta-analysis were: (1) to assess a more accurate estimate of the caries-inhibiting effect of chlorhexidine treatment than provided by individual studies, and (2) to explore factors potentially modifying the effect of chlorhexidine treatment in caries prevention, i.e., the application method, application frequency, target population, the fluoride regime, and caries criteria. Caries reduction was expressed by the prevented fraction, indicating the percentage reduction of caries incidence in the chlorhexidine group. For all prevented fractions, 95% confidence intervals were calculated. The overall caries-inhibiting effect of the chlorhexidine treatment studies was 46% (95% CI = 35% - 57%). Multiple-regression analysis showed no significant influence on the prevented fractions for the variables "application method", "application frequency", "caries risk", "fluoride regime", "caries diagnosis", and "tooth surface".

In 2002 a dental survey amongst 6- and 12-year-old schoolchildren (n = 832) in The Hague was carried out. The caries findings were compared with findings from earlier studies in The Hague. Caries prevalence (% of caries-free children) and caries experience (mean dmfs scores) among 6-year-old children had not changed significantly in the period 1996–2002. However, a significant increase of caries-free 12-year-old children of low socio-economic status was found in the period 1996–2002. The proportions of caries-free 12-year-old Dutch, Turkish and Moroccan children of low socio-economic status were 88, 69 and 78%, respectively, in 2002. The average DMFT score of 12-year-olds reached a minimum of 0.2. In 2002, 24% of the 12-year-olds exhibited signs of erosion, indicating that the presence of erosive wear was high among youngsters in The Hague.

A meta-analysis was performed on published data on the caries-inhibiting effect of fluoride gel treatment in 6- to 15-year-old children. The purposes of this meta-analysis were: (1) to calculate the overall caries-inhibiting effect of clinical fluoride gel treatment studies, based on explicit selection criteria, and (2) to explore factors potentially modifying the effect of fluoride gel treatment in caries prevention, concerning the baseline caries prevalence of the target population, the general fluoride regimen, and application features. The caries-inhibiting effect of fluoride gel application was assessed by the prevented fraction and the ‘number needed to treat’. The overal prevented fraction of the fluoride gel treatment studies, indicating the reduction of caries incidence by fluoride gel treatment relative to the incidence in the control group, was 22% (95% CI = 18–25%). Multiple regression analysis showed no significant influence on the prevented fractions for the variables ‘baseline caries prevalence’, ‘general fluoride regimen’, ‘application method’, and ‘application frequency’. The ‘number needed to treat’ (NNT), indicating the number of patients that need to be treated in order to prevent 1 DMFS, estimated the efficiency of fluoride gel treatment according to the caries incidence of the target population, including cost/effect relations. It was found that the NNT = 18 in a population with caries incidence 0.25 DMFS per year, and NNT = 3 in a population with caries incidence = 1.5 DMFS per year (treatment duration 1 year). From the standpoint of cost-effectiveness, the additional effect of fluoride gel treatment in current low and even moderate caries incidence child populations must be questioned.

The results suggest that the periodontal health of Dutch adults aged 25-54 years has improved since 1983.