Prevalence of dental caries in children born prematurely or at full term

The objective of this study was to evaluate the prevalence of dental caries in 192 children, 96 born prematurely and 96 at full term, in a regional hospital in Brazil. Mean age at clinical examination was 40.72 months in the full-term group (G1) and 30.44 months in the premature group (G2). The children were divided in two age subgroups: 0 to 3 and 4 to 6 years. Statistical results (Student's t and Kruskal-Wallis tests) showed that dmft was 0.43 for G1 and 0.01 for G2 in the 0-3 age subgroup, and 1.7 for G1 and 1.1 for G2 in the 4-6 age subgroup. Differences were significant between G1 and G2 only in the 0-3 age subgroup (p = 0.047). Caries evaluation showed that, of the 96 children in G1, 75 were caries free, while in G2, 84 did not have the disease. These differences were not significant (p = 0.088). The lower mean dmft found in the 0-3 age subgroup in G2 may be attributed to routines established by the hospital's neonatology staff, such as frequent dental visits and preventive instructions about oral habits, oral hygiene and diet. After this age, with the completion of the primary dentition, values increased and became similar between the G1 and G2 groups. Results also suggested a highly skewed distribution since most caries were found in only a small number of children.


INTRODUCTION
The number of dental caries has declined significantly in the last few years.However, caries distribution is still skewed because a small number of children account for a large number of caries.Some risk groups have been identified, and attention should be focused on them so that preventive and health promotion measures are taken in an attempt to reverse this situation.One of these risk groups is composed of children born prematurely. 5,17rematurity may be a predisposing factor for the development of caries. 3,4,10,19However, other factors, such as diet, oral hygiene habits, and bacteria in the oral cavity, cannot be left out of any study about this disease.In a study of the effects of diet, breast-feeding and weaning, Davenport et al. 4 (2004) and Burt, Pai 3 (2001) concluded that prematurely born, low-birthweight children had a greater intake of sugar than children born at full term, and had, consequently, a greater number of caries.
Several authors report that children born prematurely have a higher prevalence of enamel defects in the primary dentition than children born at full term. 1,6,9This prevalence varies greatly according to study criteria, indices and study sample.Enamel hypoplasia may indicate a greater risk of caries. 7,8,14,16Rough surfaces promote plaque formation by Streptococcus mutans adhesion and colony forming, and may lead to quick progression of the disease. 12,13Less mineralized enamel is more susceptible to caries.In a symposium on early childhood caries, Seow 15 (1998) called attention to the fact that enamel defects are an important but currently little investigated area in caries research.
Fadavi et al. 5 (1993) reported a high prevalence of caries in prematurely born children, and associated it with low birthweight.Children whose birthweight was below 1,000 g had a prevalence rate of 56%; those whose birthweight was between 1,000 and 1,500 g and those whose weight was above 1,500 g had prevalence rates of 47% and 43%, respectively.They concluded that low birthweight is a risk factor for the development of dental caries.Similar results were reported by Maatouk et al. 11 (1996), who also found a significant association between caries and low birthweight.
Conversely, Fearne et al. 6 (1990) found a greater prevalence of cavitated lesions in children born at full term than in children born prematurely.Their results were assigned to the fact that the premature children evaluated in their study came from a more privileged social and economic group and received fluoride supplementation.
In a systematic review of literature, Burt, Pai 3 (2001) did not find enough evidence to support the assertion that children whose birthweight was low were at a greater risk of caries.However, those authors suggested that findings be cautiously interpreted due to the scarcity of studies; they also underscored the need for further studies to investigate the association between prematurity and/or low birthweight and dental caries.
Predisposition to dental caries in premature children is somewhat controversial.Several factors should be evaluated together, such as oral hygiene, diet, fluoride supplementation, dental visits, and other secondary or adjuvant factors.The purpose of this study was to evaluate the prevalence of dental caries in children who were born prematurely or at full term.

MATERIAL AND METHODS
One hundred and ninety-two children (96 born at full term and 96 born prematurely) with primary teeth were included in the study.Children's ages ranged from 10 to 72 months, and mean ages were 40.72 months for the full term group (G1) and 30.44 months for the premature group (G2).Mean birthweight for children born prematurely was 1,421 g, and for children born at full term, 3,294 g.The premature group (G2) was classified according to birthweight into three subgroups: very low birthweight (VLBW < 1,500 g), low birthweight (LBW ≥ 1,500 and ≤ 2,500 g) and normal birthweight (NBW > 2,500 g) (Tables 1 and  2).Both G1 and G2 groups were subdivided according to two age subgroups: 0 to 3 and 4 to 6 years.Clinical examination was performed in the pediatric outpatient clinic of a regional hospital in Brazil, by one single examiner.This hospital provides health care to pregnant women and children, and is a reference hospital for extended health care of children born prematurely.Only children that came to the hospital for routine consultations were examined.The children re-examined for calibration were randomly chosen among children that had to return for a control visit.The examiner conducted the visual inspection under natural lighting and with the aid of a mouth mirror and dental probe after cleaning and drying dental surfaces with a piece of gauze while the child was lying down on a hospital stretcher.Caries were diagnosed according to the criteria proposed by the WHO, 18 and the index used for the diagnosis of caries was the dmft.All data were recorded and noted down on a clinical form by the examiner.Before examinations, intraobserver agreement for the diagnosis of caries was checked: two clinical examinations were performed in 10% of the sample at a mean interval of one week.Values obtained were k = 1.00 and p = 0.02.Calibration was conducted with this sample in the first study time point.

Data collection
Data about the study subjects, such as birthweight and gestational age at birth, were collected from hospital records.

Ethical considerations
This study was conducted in accordance with Resolution 196/96 of the Brazilian National Health Board and its complements.An informed consent term was signed by parents or legal guardians expressing agreement to answer the questionnaire and granting authorization for the child's participation in the study.This study was approved by the Ethics in Research Committee of the Health Department, Distrito Federal, Brazil, under number 005/2004.

Data analysis
Student's t test for independent samples, the Fisher exact test, and the chi-square test were used for comparison of variables.The Kruskal-Wallis test was used to check the prevalence of caries in birthweight subgroups of the group of prematurely born children.For the two tests, the null hypothesis was that measures were equal, and level of significance was p ≤ 0.05.The Kappa coefficient was used to check intraobserver reproducibility.

RESULTS
Table 3 shows the dmft values for children in the premature and full term groups according to age subgroups.
Table 4 shows the dmft values in the group of prematurely born children according to birthweight in the different age subgroups.
Table 5 shows the number of children free of caries in G1 and G2 according to age subgroups.

DISCUSSION
Children born prematurely had a lower dmft than children born at full term in this study.In the 0-to-3 age subgroup, dmft was 0.43 for G1 and 0.01 for G2, with a statistically significant difference in G2 (p = 0.047; Table 3).In the 4-to-6 age  subgroup, the values were 1.71 for G1 and 1.1 for G2 (Table 3).These results are in agreement with those reported by Fearne et al. 6 (1990), who attributed the low prevalence of caries in the group of prematurely born children evaluated in their study to the fact that they came from a more privileged social and economic group and received fluoride supplementation.Fadavi et al. 5 (1993) reported a high prevalence of caries in prematurely born children, and associated it with low birthweight.However, their study did not include a control group, and the classification by weight was different from the one adopted here, which complicates comparison of results.The scarcity of similar studies in the literature makes comparisons with our results difficult.More studies in the area of cariology with children born prematurely should be conducted, and results should be used to establish preventive measures and health promotion programs to give children a better quality of life.The low dmft found in this study for the group of prematurely born children may be explained by the fact that these children were routinely followedup and received instructions about diet and oral hygiene habits from the neonatology team in the hospital, and were discharged according to individual needs.However, the group of children born at term did not receive pediatric follow-up in the same hospital, but were referred to health stations close to their homes instead.They only returned to this hospital when they had more complicated health problems, such as allergies, ophthalmologic problems, or problems that required tests that the health stations were not prepared to conduct.After 3 years of age, dmft increased to 1.7 and 1.1 in the full term and premature groups, respectively, but no statistically significant difference was found between groups (Table 3).Although mean dmft values increased in the 4-to-6 age subgroup, results were still satisfactory according to Brazilian standards.From 4 years of age on, values were similar between groups, maybe due to a series of factors that are inherent to the child's age.At 4 the child becomes more independent and chooses foods with a greater cariogenic potential.Also, they experience more freedom and less diet control by parents.This correlation between age and a higher dmft indicates that the development of caries increases with age and is probably associated with the fact that, from 3 years on, children already have a complete primary dentition, that is, a larger number of teeth.These results are in agreement with those reported by Fadavi et al. 5 (1993) and Bezerra 2 (1990), who also found this same association.
Fadavi et al. 5 (1993) studied 31 prematurely born children classified by birthweight and found that 16 were free of caries, which corresponded to 51.16%.However, they studied only a small sample and did not have a control group.The comparison of dmft with birthweight in the 0-3 age group revealed greater dmft values for children with normal birth weight than for children with low birthweight or very low birthweight.However, in the 4-6 age group, no statistically significant difference was found in the comparison of birthweight subgroups.The lack of similar studies make comparison of results difficult.
Most caries were found in only a small number of the children participating in our study, which suggests a highly skewed distribution of the disease.In the 0-to-3 age subgroup of G1 (40 children), only 5 children were responsible for the dmft value found, and in the same age subgroup in G2 (66 children), only one child, who met the characteristics of this study group, was responsible for the value found (Tables 4 and 5).Although this study was conducted in one single hospital, the results described here are in agreement with the current falling trend in the prevalence of caries in Brazil, which may be attributed to factors such as the increase in the number of people with access to water fluoridation programs in many cities in the Southeastern, Southern and Mid-Western regions, addition of fluoride to toothpaste, and changes in dental practice paradigms, with priority being attributed to preventive and health promotion programs.Reports in the literature show a high prevalence of enamel defects in children born prematurely and point out that these defects may be predisposing factors for a higher number of caries in these children. 7However, our results showed that a high prevalence of caries was not found in these children, and this may be attributed to early dental assistance and to frequent follow-up that contributed to minimize risk factors.Instructions about dental health and the development of healthy dietary and oral hygiene habits, as well as the adoption of efficient preventive measures, are relevant and important factors in achieving and maintaining oral health.Longitudinal studies with larger samples should be conducted to determine actual dental health conditions in this population.

CONCLUSION
Under the conditions of this study, a lower dmft value was found in the group of premature children than in the group of children born at term.No significant association was found between prematurity and a higher prevalence rate of caries in primary dentition.

TABLE 2 -
Characteristics of the two groups.

TABLE 1 -
Characteristics of the two groups.

TABLE 3 -
Comparison of dmft between the two groups (Student's t test).

TABLE 4 -
Comparison of dmft for prematurely born children according to age and birthweight subgroups (Kruskal-Wallis test).

TABLE 5 -
Comparison of children free of caries in the two groups (chi square test).