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Caries Rates Related to Approximal Caries at Ages 11-13: A 10-year Follow-up Study in Sweden
1 Department of Public Health and Clinical Medicine, Epidemiology, Umeå University, S-901 85 Umeå, Sweden; and Correspondence: * corresponding author, hans.stenlund{at}epiph.umu.se
Predicting future caries risk is a difficult but important clinical task. The aim of this study was to analyze radiographically the relationship between approximal caries (4d-7m) at ages 11-13 (baseline) and future approximal caries. We followed 534 individuals prospectively through annual bitewing radiographs from 11 to 22 years of age. Two measures were used: individual-based incidence of the first new approximal caries lesion and surface-based incidence of approximal lesions. In the group with no approximal caries lesions at baseline, the individual-based incidence was 19 first new approximal lesions/100 person-years; the corresponding value for those with 3 approximal lesions at baseline was 71. Individuals with no approximal lesions at baseline developed 3.1 new lesions/100 tooth surface-years; the corresponding value for those with 3 lesions at baseline was 7.7. The highest risk for developing new approximal lesions was within the first 2 years after baseline.
Key Words: adolescents • approximal caries • caries rate • cohort • prediction • young adults
Several studies have shown that previous caries in adolescents can be used to predict new caries (Gröndahl et al., 1984; Honkala et al., 1984; Seppä and Hausen, 1988; Wilson and Ashley, 1989; Alaluusua et al., 1990; Russel et al., 1991; Disney et al., 1992; Lith and Gröndahl, 1992; Mattiasson-Robertsson and Twetman, 1993; Mejàre et al., 1999; Gustafsson et al., 2000). Most of these studies used sensitivity and specificity measures to assess the accuracy of the prediction. Although hardly any of them reached the proposed level of acceptable accuracy—a combined sensitivity and specificity of 160% (Kingman, 1990)—a consistent finding was that past caries experience is the most powerful single predictor of future caries. Since efforts to predict future caries are made every day in the clinical setting—for deciding recall intervals, at the very least—it is necessary to try to distinguish between those who do and those who do not run a risk of developing new caries lesions. In this respect, a reasonable number of misclassifications must be accepted. Few studies have focused on approximal caries as a risk marker for future approximal caries (Gröndahl et al., 1984; Lith and Gröndahl, 1992; Mejàre et al., 1999; Gustafsson et al., 2000). The results suggest that 1 or 2 approximal dentin lesions and/or restorations present at ages 12-14 constitute a useful cut-off for separating individuals with from those without a substantial risk of developing new approximal dentin lesions during adolescence. In two of the studies, enamel lesions were included as a predictor of future approximal caries. Risk assessment has not, however, been performed by comparing individuals who are caries-free on approximal surfaces at ages 12-14 as judged radiographically in comparison with those who are not. This is of clinical importance, particularly in populations with a generally low caries prevalence. In a previous study (Mejàre et al., 1999), the enamel and dentin caries incidences for posterior approximal surfaces were assessed prospectively in individuals from 11 to 22 yrs of age. Our aim was, using these data, to explore the relationship between approximal caries at ages 11-13 and future approximal caries, with special attention to comparing individuals who were radiographically caries-free at baseline with those who were not and to analyze the impact of follow-up time on caries incidence.
Subjects The children derived from a cohort of 536 children, 11-13 yrs old at baseline (mean = 12.5; SD = 0.7) (Mejàre et al., 1998). All the children born in 1972-73 in the catchment area of the Västerhaninge clinic, a southern suburb of Stockholm, were included. Socio-economically, the catchment area is comprised of families with high-, medium-, and low-level income status. The cohort was followed up to 21-22 yrs of age. The examinations were carried out as part of routine practice. All the children and their parents gave informed consent. The Review Board of the Public Dental Health Service, Stockholm County Council, gave ethical approval. The children had received organized dental care on an annual basis in the Public Dental Health Service from the age of three. The caries-preventive activities directed toward this cohort, including individually adjusted measures for those considered caries-active, have been described earlier (Mejàre et al., 1998). The material consisted of annual bitewing radiographs from 536 children. Two children were excluded for technical reasons, reducing the study group to 534 children, 279 boys and 255 girls. During the study, 82 children moved from the area, 20 switched to private dentists, and 55 were partially non-attendant. The mean number of sets of bitewing radiographs of each individual was 8.7.
Methods
Twenty-four mesial and distal surfaces of posterior teeth were analyzed (4d –7m). For each surface, the entry date was the first time the surface was observed in a caries-free state. The exit date was either the last examination in a caries-free state or the estimated date of transition into a caries state. If a surface was in a caries state at an examination, the date of transition was set to 6 months earlier. The exit date of an individual was either the first occasion when one of the originally caries-free surfaces was observed in a caries state or at the last examination. At baseline, 4.9% of all approximal surfaces were in a caries state or restored. Of these carious/restored surfaces, 58% were score 2 lesions, 17% were score 3 lesions, 0.2% score 4 or 5 lesions, and the rest were restored.
Data Analysis
Statistics Cox regression was used to model the individual-based caries rates. The dependence between the surfaces due to clustering within the mouth was considered: Poisson regression with over-dispersion was used to model the surface-based caries rates (Agresti, 1996). The statistical calculations were done with the SPSS 9.0 and STATA 7.0.
Caries Rates Related to Baseline Status The median follow-up time was 9 yrs (mean = 8.1; SD = 2.0). The mean individual-based caries rate was 27 new approximal caries lesions per 100 person-years (range, 19-114). The relative risk of getting at least one new approximal caries lesion increased as the number of lesions at baseline increased (Table 1  ). The surface-based caries rates (mean = 4.5) also increased as the number of lesions at baseline increased (Table 1).
Caries Rates Related to Time
The main reason for children leaving the study was moving from the area. Partial non-attendants were not lost but did not appear every year for examination. Therefore, most probably, these individuals did not cause any distortion of the results. In accordance with Lith and Gröndahl (1992), the present results suggest that enamel lesions can be included and used as a predictor of future approximal caries. Those without any radiographic signs of approximal caries at baseline had a low caries rate during adolescence and young adulthood. However, even in this group, the probability of at least one new caries lesion developing was 80% (Fig. 2 ). Thus, even in a low-caries-prevalence population, it seems that approximal caries has not disappeared. Rather, approximal caries is characterized by a slow rate of lesion progression (Mejàre et al., 1999). Notably, in spite of intensified preventive measures for those considered caries-active, individuals who were caries-active at baseline continued to be so. The conventional high-risk strategies may therefore be questioned (Disney et al., 1989; Hausen et al., 2000).
The caries rates decreased as the time after baseline increased (Table 2 In conclusion, a strong impact of the baseline status on caries rates was found. For all the groups, the first 2 yrs after baseline constituted the highest risk period for developing new approximal caries. The clinical implications would therefore be to focus on preventing approximal caries during this period. Recall intervals could be lengthened for those who have no radiographic signs of approximal caries at ages 11-13.
The Public Dental Health Service in Stockholm, the Swedish Patent Revenue Research Fund, and the Swedish Dental Society supported this study. Received for publication September 24, 2001. Revision received April 23, 2002. Accepted for publication May 13, 2002.
Journal of Dental Research, Vol. 81, No. 7,
455-458 (2002)
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