Epidemiological assessment of predictors of caries increment in 7-10-year-olds: a 2-year cohort study

Objective The aim of this 2-year cohort study (2003 to 2005) was to investigate how caries experience, at initial lesions (early or non-cavited lesions) and cavited stages, predicts caries increment in permanent teeth in 7-10- year-olds. Material and Methods The random sample of 765 children attending public schools in the city of Piracicaba, SP, Brazil, was divided into two groups: 423 children aged 7-8 years and 342 children aged 9-10 years. All subjects were examined by a calibrated examiner, using dental mirror and ball-ended probes, after tooth brushing and air-drying in an outdoor setting, based on the World Health Organization criteria. Active caries with intact surfaces were also recorded as initial lesion (IL). Univariate analysis was used for statistical analysis (Odds Ratios and Chisquare). Results The association between the DMFT (decayed, missing and filled teeth) increment and the presence of IL was significant only for 9-10-year-old children. The children with DMFT>0 at baseline were more prone to have DMFT increment, with the highest risk for caries increment occurring in children aged 7-8 years. Conclusion The predictors of caries increment were the presence (at baseline) of caries experience in permanent teeth for both age groups (7-8; 9-10-year-olds) and the presence of the IL (at baseline) for 9-10-year-olds.


INTRODUCTION
Several epidemiological studies have discussed the changes in dental caries diagnosis criteria 6,7,18 .
Evidence from literature has shown that the early detection of initial caries lesions and the preventive approach are both the main aims for maintaining a good oral health status 2,6,7,14 . In fact, detecting initial caries lesions in epidemiological studies is important to estimate the real disease prevalence and to know the treatment needs, targeting either invasive or non invasive procedures, to subjects and/or groups of populations at risk.
Since recent scientific studies have reported that initial caries lesions are significantly more prevalent than cavitated caries lesions 7 , it is also important to determine the impact of initial caries lesions in caries risk assessment, verifying its influence as a predictor of caries increment, as assessed by some studies 8,20,23 . Therefore, the aim of this cohort study was to investigate how 2010;18(2):116-20 caries experience, at initial caries lesions (early lesions) and cavitated stages, predicts caries increment in permanent teeth over a two-year period.

Ethical Aspects
The study was approved by the Research In 2005, 765 children aged 9 to 12 years were reexamined for dental caries.
All the schools selected in this study are run by the municipality and are situated in low-income urban communities from the outskirts of Piracicaba. The schoolchildren were similar concerning socioeconomic characteristics.

Examination Methodology
The dental examinations carried out in 2003

Diagnostic Thresholds, Criteria and Codes
The criteria and codes used in this study were those based on the WHO recommendations 25 that consider a tooth as decayed only when cavitations are present. Active caries with intact surfaces were also recorded as ILs, following an adaptation of the criteria proposed by Nyvad, et al. 15 (1999) and Fyffe, et al. 5 (2000). Thus, an IL is defined as a presumably active carious lesion which, upon visual assessment by a calibrated examiner, has Epidemiological assessment of predictors of caries increment in 7-10-year-olds: a 2-year cohort study an intact surface with no clinically detectable dental tissue loss, with a whitish/yellowish area of increased opacity, roughness and loss of luster.
When the probe is used, its tip should move gently across the surface. For the smooth surfaces, caries lesion is typically located close to gingival margin. For the occlusal surface, the lesion extends along the fissure walls. In this study, localized surface defects (active microcavities) restricted to enamel were also included in the IL group. IL and microcavities contiguous to sealants, restorations and cavitations were also recorded.
Two diagnostic thresholds were used in the study: WHO diagnostic thresholds (DMFTdecayed, missing and filled permanent teethindex) and WHO+IL diagnostic threshold (DMFT index + initial caries active lesions).

Calibration of the Examiner
One examiner with epidemiological experience in surveys using the World Health Organization

Data Analysis
In data analysis the dependent variable was DMFT increment>0 over the 2-year period (DMFT at final examination subtracted from DMFT at baseline, according to the WHO). First the influence of ILs on caries increment was tested according to age groups (7-8-year-olds and 9-10-year-olds) by the Chi-square test.

RESULTS
The response rate in this 2-year cohort study was 77.8%, as from the 983 children who were examined at baseline, 765 completed the study.
The reasons for children dropout were: moving to another school and refusal to participate in the final examination.

DISCUSSION
In this prospective cohort study investigating how caries experience predicts caries increment in permanent teeth, the presence of IL at baseline was associated with caries increment in permanent dentition after 2 years for 9-10-yearold children (Table 1). This indicates that this variable is an important clinical finding and that these children should be assisted regularly.
Another important result is that all the children with DMFT>0 and dfmt>0 were significantly more prone to develop caries in permanent dentition in comparison to those caries-free in both dentitions ( Table 2). The children aged 7-8 years were probably in a dentition transition phase, with eruption of several permanent teeth, especially the first molars and incisors, when data were collected. As pointed out by Carvalho et al. 4 (1989), teeth in eruption process are more susceptible to develop dental caries because the biofilm finds favorable conditions for accumulation as these teeth are not yet in function. Moreover, children may present poor dental cleaning, becoming a more susceptible group for dental caries in permanent dentition.
An unexpected result was that a child with caries experience in permanent dentition at baseline presented statistically higher probability of developing DMFT increment (Table 2), since many studies about caries prediction have shown that caries in primary dentition is a good predictor of the disease in permanent dentition 10-12,21,22,24 .
In general, children aged 7-8 years are in a period of dentition transition, with many primary teeth exfoliating and permanent teeth in eruption.
Especially the last condition may increase the caries risk due to some characteristics such as: a) a higher carbonate content in dental enamel, which causes changes in the hydroxyapatite crystal lattice, resulting in a more acid-susceptible enamel surface; and b) teeth in eruption have no functional occlusal contact, which may increase dental biofilm accumulation and hinder toothbrushing 1 .
Regarding the lack of association between the DMFT increment and the presence of ILs for younger children (

CONCLUSION
The predictors of caries increment were the presence (at baseline) of caries experience in permanent teeth for both age groups (7-8; 9- 10-year-olds) and the presence of the IL (at baseline) for 9-10-year-olds.