Examination at 1 year

Each year, parents of all the about 170 children per year, who had their 1-year birthday, and lived in the catchment area of the Vidablick Public Dental Clinic, between 2002 and 2010 were invited by regular mail to a meeting including information about child dental care and possible participation in the study. Parents of the 1-year-olds received a questionnaire (Table 1) on caries-associated and other relevant factors before visiting the clinic and were asked not to brush their child’s teeth the morning of the visit. Children who did not turn up or whose parents had not completed the questionnaire were excluded from the study. During the visit, parents received information on oral health, including how to avoid dental caries.

The clinical examination comprised a visual inspection of the teeth, an assessment of visible dental plaque, and collection of one bacterial sample with a Quick-Stick^® (Dentsolv AB, Saltsjö-Boo, Sweden). If a tooth – preferably an upper incisor – had emerged, a bacterial sample was taken from the buccal surface close to the marginal gingival sulcus. If no tooth had emerged, the bacterial sample was taken – in a similar way as from the teeth – from the tongue and cheek on one side of the mouth. Plaque on the Quick-Stick^® was transferred to an incubation strip and cultivated according to the manufacturer’s instructions for the Dentocult^® Strip Mutans test (Orion Diagnostica, Espoo, Finland). The sample was incubated in a heat chamber (model; Memmert GmbH, Hannover, Germany) at the clinic for 48 h at 37 °C before analysis. A dental hygienist assessed the number of adherent colonies according to a chart supplied by the manufacturer and assigned a score between 0 and 3 to indicate low to high levels of MS. An MS score of 0 included all MS bacterial samples with less than 10⁴ CFU/ml.[18]

Only one dental professional, a dental hygienist or a dental assistant, was present at each visit and examined the child. In total, four experienced dental professionals were involved in the examinations during the study period. The four examiners were well trained in the examination procedures and bacterial sample evaluation. Assessment of caries risk followed the recommendations of the Östergötland County Council caries risk programme, including medical-, family- or social factors and visual plaque. Caries risk was considered to be present if the child was expected to develop dental caries during the next 2 years. Caries risk was evaluated based on clinical and anamnestic findings including responses from the questionnaire (Table 1). If the child was assessed to have a caries risk, a caries preventive programme with further information to the parents was implemented.

Examination at 3 years

At age 3 years, the children were invited for a dental examination at the Public Dental Service Clinic. A dental hygienist or a dentist recorded the findings from this dental examination in the clinic’s electronic patient file system. The clinical examination was done in the dental chair; no X-rays were taken. The clinician diagnosed dentin caries (d₃) using visual tactile inspection with a dental mirror and a dental explorer, according to the criteria of Koch.[19] Enamel caries was not taken into account.

Children who had been assessed at the Public Dental Service Clinic at the age of 1 year and who were examined in the Public Dental Service in Östergötland County at the age of 3 years (2004–2012) were included in the study.

Children, whose families had moved from the county, who had chosen a private dental clinic, or who for other reasons had not been examined in the Public Dental Service in Östergötland County during the year of their 3rd birthday, or whose dental records from the visit to the Public Dental Service Clinic at age 3 years were incomplete, were excluded from the study.

The Regional Ethics Board at Linköping University, Linköping, Sweden approved the study.

Statistical analysis

Simple and multiple logistic regression analyses were used to identify which caries risk factors at age 1 year were associated with dentin caries prevalence (deft > 0) at age 3 years. The significance level was set to 5%.

Study group

Due to ethical considerations, we did not investigate the reasons for not participating at the 1-year visit. Possible reasons for nonparticipation at baseline could be: parents who had previously attended a 1-year appointment with an older sibling may have considered it less important to attend the 1-year appointment again, since the focus of the visit was information; parents may have had difficulties planning their schedules; and some parents may simply have been uninterested in their child’s oral health, which other studies found.[20] This last group may include parents who neglected their children to some extent in several areas of life. Children from such families have been found to suffer a high risk of dental caries.[21] One reason for the lower proportion of children with dentin caries in our group of children compared to county-wide statistics could be that the proportion of parents who were interested and engaged in their children’s dental care was higher among those who decided to participate than among those who did not participate, a relationship observed in a previous study.[20] These circumstances should be kept in mind when assessing the results from the present study. While some of the children, who dropped out between the examinations at 1- and 3-year, may have dropped out due to the same reasons as mentioned above regarding the non-participating 1-year-olds, some families had moved away from the county council and were not available for the 3-year examination. The major reason for drop-outs during the study period was anyhow the parents’ choice to leave the Public Dental Service and bring their child to a private dental clinic, why they were not invited to the 3-year examination at the Public Dental Clinic. Approximately 15% of the children in the county council chose private dental care for their children. Only children who participated in the examinations at both 1- and 3-year age were included in the study.

Various dentists and dental hygienists who had not been calibrated performed the dental examinations of the 3-year-olds. This is a limitation of the study. But because the regional clinical guidelines includes clear, well-established, well-known and internationally accepted criteria for the diagnosis of dentin caries, and since dentin caries lesions often occur in sites simple to detect and are easier to detect than initial/enamel caries lesions, and since the examiners were well trained according to the methods, we consider the methods used for the diagnosis of dental caries reliable. Epidemiological data for 2012 from the County of Östergötland, the site of the present study, show that ECC (not including enamel caries) occurred in 6% of the 3-year-olds, which is a higher prevalence than we found for the 3-year-olds in our study.[22] The lower dentin caries prevalence found in the study group as compared to the population (according to registrations of the epidemiological data from the county) is reflecting the better oral health found among those who attend and complete a dental scientific study. It also indicates that the non-attenders and drop-outs have a worse dental health than those we manage to include in scientific dental studies. The low caries prevalence in our study should be taken into account when comparing our results with other studies.

The strong association between the caries risk assessment at the age of 1 year and dentin caries (deft > 0) at the age of 3 years indicates that the assessment of caries risk at the age of 1 year was reliable. The higher OR for the caries risk assessment than for most of the other variables indicates that it is better to perform a risk assessment comprising several factors than rely on separate factors for the evaluation. This is in accordance with the known multi-factorial aetiology of caries disease, which gives a higher accuracy in determining caries risk when a variety of risk factors are included in the assessment.[23–25] The importance of the ‘gut-feeling’ among dental professionals has previously been discussed and our study supports the findings of other authors.[17,25,26]

Gender

Gender differences in oral health have been found among both adults and children.[27,28] Caries prevalence is usually reported to be higher in females, a finding that our study did not support.[28] Our results agree with Mohebbi et al. [29], who found no difference between the genders in the prevalence of ECC among 1- to 3-year-old Iranian children. On the other hand, Peressini et al. [30] found that 3- to 5-year-old American boys had a higher prevalence of ECC than girls, which is in contrast to the findings of Declerck et al. [28], who found a higher caries prevalence among 3- to 5-year-old Belgian girls. We assume that cultural differences influence oral hygiene habits and habits for food and beverage intake, which could explain the different outcomes in the association between caries and gender in studies from various countries. The different caries prevalence reported for varying international regions makes comparisons of studies from different cultures and population subgroups challenging.[31]

Siblings with caries

We found that the 1-year-old children, who had siblings with caries, had a higher risk of developing caries during the next 2 years, which confirms the results of other studies that describe caries as a family-related disease.[24,32] Poureslami et al. [24] described caries as a transmissible disease with both vertical (from mother to child) and horizontal (between members of a group) transmission of caries-related bacteria.[33] Our findings agree with Kawashita et al. [34], who found that children with siblings, who had severe dental caries, have a higher risk of development of dental caries. Although the similarities regarding caries prevalence between siblings has been regarded as a transmission of bacteria and sharing of habits between siblings, there is always an additional vertical transmission with the parents.[24,34,35] Other familial characteristics are associated with caries in siblings. The parents’ lifestyle will influence the care for their child regarding e.g. dental awareness, dental hygiene and food habits.[24,32]

Night meal

Our finding in both the simple and multiple regression analyses, that Night meals (most commonly breastfeeding or bottle feeding) at 1 year of age were associated with dental caries at 3 years of age, agrees with the findings of Prakash et al. [36], who found that night meals including breastfeeding and bottle feeding increased the prevalence of ECC in Indian children. Declerck et al. [28] presented similar results, that sweetened drinks at night were associated with dental caries in 3- to 5-year-old Belgian children. Mohebbi et al. [37], who studied 1- to 3-year-old Iranian children, stated that bottle feeding of milk at night should be avoided; our findings support this.

Breastfeeding

Breastfeeding was often occurring together with Night meal. The possible influence of breastfeeding on ECC is contradictory.[38] Breast feeding at age one was not associated with dentin caries at 3 years of age, which is in agreement with studies from Brazil,[39] USA [40] and Iran.[37] Contrary to these studies, Chaffee et al. [41] found a higher prevalence of ECC in Brazilian 3-year-olds from low income families when breastfeeding had been prolonged until the age of 2 years. The relationship between breastfeeding and ECC is complex and confounded by several behavioural factors, such as sugar intake and social variables,[42] which are more likely – than the breastfeeding per se – to be etiological factors when studying the relationship between breastfeeding and ECC.[42]

Beverage other than water between meals

Our finding that Beverage other than water between meals at the age of 1 year was associated with dentin caries at the age of 3 years agrees, for example, with Declerck et al. [28], who found that sweetened drinks were associated with caries prevalence among Belgian preschool children. Beverage other than water between meals had the highest OR (7.1) in our multiple regression analyses, which is why preventive dental care programmes for preschool children should highlight this.

No toothbrushing

The finding that toothbrushing had not yet started in 5% of the 1-year-olds shows that not all parents in Sweden follow the generally accepted recommendation to begin toothbrushing when the first tooth appears. The finding that No toothbrushing at the age of 1 year was not significantly associated with the development of dentin caries at the age of 3 years is contrary to Wendt et al. [43], who found an association between enamel and dentin caries and oral hygiene in Swedish 1-year-olds. Mattila et al. [44] also described an association between dental plaque and the prevalence of dental caries in Finnish 3- to 5-year-olds. The correlation between neglected toothbrushing and dental caries, which Hsieh et al. [45] found among Taiwanese 2- to 5-year-olds, also disagreed with our findings. The inclusion of enamel caries and the higher caries prevalence among the participants in the study by Wendt et al. [43] and the older age of the children participating in the studies of Mattila et al. [44] and Hsieh et al. [45] may explain their disagreements with our results.

Mutans streptococci

In a simple regression model, we found that, independent of the MS score, Presence of MS at 1 year of age was associated with dentin caries at 3 years of age (Table 3). (This finding is supported by Köhler and Andréen,[46] who found that children who were colonized by MS at an early age developed more caries than those who were colonized with MS later in life.) Thorild et al. [47] reported similar results; they found that caries prevalence at age 3 years was significantly related to MS colonization at the age of 18 months. Thus, it is useful to analyse Presence of MS, even though cultivation and analysis methods vary. We did not analyse if the different microbial sampling techniques used before and after tooth emergence had any impact on the results, which could be considered when interpreting the results of the microbial analyses.

Assessments of an association between the MS score at the age of 1 year and caries at 3-years-age, anyhow, found a higher OR (Table 3) for a high level of MS (score 2–3) than for the Presence of MS variable. Thus, we excluded Presence of MS from the multiple regression analysis (Table 4) to avoid bias. Our findings are in line with Parisotto et al., who found that high MS levels are strong risk indicators for ECC.[16] The use of topical antimicrobial treatment (e.g. with chlorhexidine-containing gel, toothpaste or varnish) in mothers with high levels of MS could be considered as an additional caries preventive treatment option to prevent or delay infant infection by cariogenic microorganisms.[23]

Number of teeth

In a previous study, we found that the Number of teeth among 1-year-olds was correlated to the MS score, a finding confirmed by others.[18,48] Although development of dental caries is closely related to the level of MS,[16] we found no association between Number of teeth at 1 year of age and caries at 3 years of age in our study, which is in agreement with results from a previous study in Sweden.[49]

Other factors

Socio-economic factors are known to influence the prevalence of dental caries.[32,43,49,50] In our study, we included no socio-economic variables in the analysis, which limits the impact of the results. There was a concern about that parents would find questions about family income and education level offensive, why socioeconomic factors were excluded from the questionnaire. We assume that the caries risk assessment of the dental assistant or dental hygienist included knowledge about the home address of the family and factors influencing their ‘gut feeling’, including possible social factors.[51]

The presence of illness and intake of medication was recorded at the age of 1 year, but could have changed considerably before the age of 3 years, which in turn could influence the caries risk considerably. Possible changes regarding environmental and social influencing factors should always be kept in mind when planning the individual caries preventive programme for each individual child.

Risk assessment

Our finding that the caries risk assessment of 1-year-olds made by a dental hygienist or dental assistant had a higher OR than all other individual variables – with the exception of Beverage other than water and Sibling with caries – shows the importance of a multivariate approach to risk assessment. Mejàre et al. [17] and Hallet,[51] for example, have discussed the importance of ‘gut feeling’ when assessing caries risk, and this intuitive evaluation probably contributed to the good risk assessment found in our study. However, the hypothesis was rejected, since the caries risk assessment made by a dental hygienist or a dental assistant had a lower OR than two of the independent variables used for caries risk assessment.

Several studies from various regions around the world with differing prevalence of ECC have stressed the importance and success of screening and early caries risk assessment.[6,17,52,53] Interactions between the different risk factors in the multifactorial caries disease makes it necessary to include several variables in the risk analysis.[23,24] The multiple regression analysis used in our study is one way to find out which factors are most closely associated to ECC. Individual variations are in any case present, and should always be considered when designing caries preventive programmes.