Emergence of the first permanent molar in 5-6-year-old children: implications from a longitudinal analysis for occlusal caries prevention



Paulo Frazão

Departamento de Prática de Saúde Pública da Faculdade de Saúde Publica da Universidade de São Paulo





The timing of tooth emergence is of considerable importance in the planning of prevention of occlusal caries.
OBJECTIVE: The aim was to estimate the trends of emergence of the first permanent molars in girls and boys between 5-6 years of age, since more children are included in the first grade after Brazilian elementary education has been extended from eight to nine years of duration.
METHODS: Dental spaces of 497 children aged 60 months or older were examined four times by a calibrated dentist (kappa > 0.97) during 18 months in a longitudinal study. The first permanent molar was considered emerged when any tooth surface could be reached by a ball point probe. Participants' age was measured in months; 95% confidence intervals were obtained for prevalence and incidence values for each sex in three age groups - 60.0 to 65.9; 66.0 to 71.9; 72.0 to 77.9 months. Incidence rate ratios were estimated by Poisson regression analysis.
RESULTS: The majority of children from 66.0 to 71.9 months and 72.0 to 77.9 months presented at least one emerged permanent molar. For each three children in the 66.0-71.9-month group, at least one had all four permanent molars emerged.
CONCLUSION: The emergence trends observed justify the need for specific protection and surveillance measures for occlusal caries prevention.

Keywords: Epidemiology. Tooth eruption. Permanent dentition. Molar. Age. Gender.




The majority of caries lesions in school-aged population is concentrated on the masticatory surfaces of the first permanent molars, whose pits and fissures are less benefited by treatment with fluoride than smooth surfaces1,2. Initial oclusal caries lesions occur during the first 36 months after emergence of this tooth group3-5. Given this intra-oral distribution and the challenges to control it in the population groups that are more vulnerable to this disease, knowledge about the timing of tooth emergence is essential to plan diagnostic, preventive and therapeutic measures6.

Several factors can be associated with the timing of permanent tooth emergence, such as gender, ethnicity, environment and socioeconomic level7. As these factors can vary from one area to another, there is not a standard table applicable to all children. In a city of Southern Brazil, a longitudinal study with 359 children showed that tooth emergence depends on nutritional and developmental characteristics measured at birth and during the first year of life. Children showing a height-for-age deficit at six months of age had a higher probability of their first molars not emerging at the age of six years8. Given the variability of emergence patterns, they should be originated from the populations to which they will be applied9.

In Brazil, with the extension of primary education from eight to nine years of duration, a higher number of children aged six years have been found in the first grade. Official Report CNE/CEB 6/2005, approved on June 8th 2005, defines that "educational systems must establish the conditions for the enrollment of six-year-old children in primary education, according to their chronological age: those aged six years or those who are going to turn six years at the beginning of the school year". Brazilian states were obliged by law to implement this change in primary education by 201010.

With this extension, specific programs aimed at the prevention of oclusal caries in the first permanent molars could be directed towards newly enrolled children (aged six years) who had one or more partially or completely emerged first permanent molars. In this sense, information about first permanent molar emergence in the oral cavity and the effect of demographic factors can be useful to guide the planning of studies on the activities and materials aimed at oclusal caries prevention and to subsidize the implementation of oral health actions in primary health care.

The present study, part of the broader research project entitled "Custo-efetividade da Escovação Dental Supervisionada na Prevenção da Cárie Dentária Infantil" (Cost-effectiveness of Supervised Toothbrushing in Child Dental Caries Prevention), aimed to estimate the emergence trends of first permanent molars in children aged from 5 to 6 years and to quantify the differences between boys and girls in this life cycle.



The main research project was approved by the Comitê de Ética em Pesquisa da Universidade Católica de Santos (Catholic University of Santos Research Ethics Committee - Process 4843-20-2005).

The study population was comprised of all children aged 60 months of age or more, enrolled in the six public primary education units situated in an impoverished area of the city of São Vicente, SP, Brazil.

In a longitudinal study, dental spaces corresponding to the first permanent molars were analyzed four times by a calibrated dentist (kappa>0.97) during 18 months (from May 2007 to November 2008). The dentist was calibrated by a standard-examiner before the first and third exam cycles. Training courses lasted 20 hours and were held in a primary education unit not selected for this study. Individuals were examined in the supine position, under natural lighting conditions, on the schoolyard, using a wooden spatula, flat mirror and ball point probe. The first permanent molar was considered emerged when any part of its surface could be reached by the ball point probe. Age was measured in days between the date of birth and the exam day. The year was standardized as 360 days and 12 months and the value was converted into the month unit. In the present study, data on children aged between 60.0 and 77.9 months in any of the exams were analyzed.

As the emergence incidence values are not constant throughout time, varying according to each individual's age, the study population was stratified into three age cohorts: between 60.0 and 65.9 months; between 66.0 and 71.9 months; and between 72.0 and 77.9 months. Population size characteristics in each age cohort enabled estimation with a margin of error between 5.0 and 7.5%. Pearson's chi-square test was applied in each age cohort to evaluate the differences in composition between sexes.

The prevalence of individuals was estimated according to the number of molars emerged in each age cohort. Incidence rate was analyzed and 95% confidence intervals were compared according to sex and age. Incidence rate ratio was estimated to compare tooth emergence between boys and girls in each age cohort, using Poisson regression model. A value of p<0.05 was adopted to reject the null hypothesis. Stata 10.0 software was used.



A total of 497 children aged between 5 and 6 years participated in this study, of which 311 were evaluated in the first exam, 473 in the second exam, and 497 in the third exam. Of these, 24 participated in only one follow-up, 162 in two follow-ups, and 311 in three follow-ups, comprising 1,281 observations. Table 1 shows the distribution of observations according to sex and age cohort in each follow-up. There was a balance between sexes in all age cohorts (p>0.05).



Figure 1 shows the proportion of girls and boys in each age cohort, according to the number of emerged permanent molars in each follow-up. A higher proportion of emerged teeth were observed in older age groups. Less than 40% of children had two or more molars emerged between the ages of 60.0 to 65.9 months.



Table 2 shows the distribution of girls and boys according to the number of molars emerged. In the younger age cohort, half of the children did not have any emerged molars. Between 66.0 and 71.9 months of age, 60.1% of girls had two or more molars emerged, whereas 50.4% of boys showed this condition. Between 66.0 and 71.9 months and between 72.0 and 77.9 months, the majority of children were found to have at least one permanent molar emerged. Among girls, rates varied from 76.9% to 89.7%, for each age cohort respectively, whereas these rates varied between 60.8% and 77.7% among boys.



Mean values and respective confidence intervals of emerged molar incidence are shown in Table 3. There was a slight and not statistically significant advantage for girls in the two younger age cohorts (between 60.0 and 65.9 months and between 66.0 and 71.9 months). This trend was then inverted, favoring boys in the age cohort from 72.0 to 77.9 months, thus revealing that these trends do not have the same direction in short time intervals, such as those considered in the present study.



Differences in incidence as a function of demographic characteristics were estimated using Poisson regression model to check these trends. Thus, the effect of sex in the incidence rate of first permanent molar emergence was evaluated in each age cohort, considering girls as the reference category. Boys and girls showed incidence values that were statistically different in the age cohorts included in the interval from 60.0 to 77.9 months of age. The results are shown in Table 4. The incidence of tooth emergence was 29% and 25% higher in girls, when compared to boys, in the age cohorts from 60.0 to 65.9 months and 66.0 to 71.9 months, respectively, whereas this incidence was 50% higher in boys in the oldest age cohort.




Knowledge about the time of first permanent molar emergence is essential to plan diagnostic, preventive and therapeutic measures6, given the fact that a higher dental caries burden in a relevant number of children is concentrated in this tooth group.

With the extension of primary education from eight to nine years of duration, a higher number of children aged six years tend to be included in the first grade of primary education, thus making it necessary to evaluate the relevance of specific programs aimed at oclusal caries prevention in first permanent molars. When tooth emergence is investigated, it is impossible to assess the exact moment this occurs. One alternative is to analyze this phenomenon between two exams. The collected data enabled the production of valid information about the presence of first permanent molars, according to the age cohorts defined in intervals of six months, separated into boys and girls. In certain studies, this information was produced from annual exams11,12.

Using the data obtained in conjunction with the educational system, it is possible to estimate the number of children and emerged molars that require attention and surveillance, using specific measures which must be object of more in-depth studies. By providing resources for future studies and for the planning of oral health actions in primary health care, the main findings were the prevalence rates of two or more emerged molars in each age cohort and the incidence rates estimating differences between boys and girls.

With the use of a longitudinal study, researchers investigated the emergence of the first permanent molars in a group of 69 children13. Tooth emergence was observed in intervals not longer than four months, until functional occlusion was obtained. In girls, the first molar emerged at the age of 73.6 months (6.1 years), whereas mean age was 75.2 months among boys (6.3 years), without statistically significant differences. A great variation in age of tooth emergence was found (in girls, between 63 and 92 months of age; in boys, between 62 and 94 months), with the duration of emergence of the four molars corresponding to a total time of 15.4 months in girls (variation from 5 to 32 months) and 15.0 months in boys (variation from 7 to 28 months).

In a different study11, which followed the same type of design, although with a much larger sample (more than 30,000 records of children from the public dental service of Denmark), emergence of all permanent teeth was described. Authors concluded that teeth emerge firstly in girls, rather than in boys - the difference varied between two to ten months, without a clear dependence on the age of tooth emergence or type of tooth. Age distribution during tooth emergence corresponded to a normal curve for teeth with a low proportion of aplasia. In the present study, there was also a trend towards earlier tooth emergence in girls. First permanent molar emergence was compared in three age cohorts, with a higher emergence incidence trend in girls, in the two younger age cohorts. In the oldest age cohort, this trend inverted, showing that such trends do not have the same direction in short time intervals.

Differences in mean age of permanent tooth emergence between girls and boys was also observed in other studies7,12,14. In addition, hereditary factors, ethnicity, place of residence (urban or rural), and nutritional and hormonal characteristics are aspects that have been investigated in the literature7,9.

Although socioeconomic condition can have an effect on general body growth, its impact on tooth emergence remains controversial9,15. A longitudinal analysis with Brazilian children did not show an association between socioeconomic variables and tooth emergence8. For this reason, the fact that this study was conducted with a population living in a low-income area may not represent a limitation to the generalization of the results.

It is admitted that there is an uncertainty of 4 to 5 months as to the emergence age corresponding to the mean time interval (in months) between exams. However, as this interval was similar in both sexes, the comparison shown between girls and boys can be considered valid. In addition to this gender difference, the prevalence rate values of emerged molars in the three age cohorts studied were an important result found. Between 66.0 and 71.9 months of age and between 72.0 and 77.9 months, two age groups that begin to be included in the first grade due to the primary education extension, the majority of children were found to have at least one emerged permanent molar, a fact that justifies the adoption of surveillance measures and specific protection against oclusal caries lesion.

Children with four emerged molars can require more individualized measures towards oclusal caries lesion. In the age group between 66.0 and 71.9 months, at least one of each three children had their four first permanent molars emerged. In the age group between 72.0 and 77.9 months, 69.1% [CI95% 59.8 - 78.3] of girls and 50% [CI95% 39.8 - 60.2] of boys were in this condition.

In recent years, a reduction in caries has been observed among Brazilian schoolchildren. One of the reasons pointed out are supervised tooth-brushing programs, where fluoride toothpaste is used16. São Vicente and several other cities have maintained supervised tooth-brushing programs funded by the Fundo Nacional de Saúde (Brazilian Health Fund)17. Many dental assistants are involved and a large amount of resources is spent annually. This action consists of oral health education and dental plaque observation, followed by supervised tooth-brushing with fluoride toothpaste, conducted by dental assistants every three months18. Oral health care has been considered one of the dimensions of primary health care and coverage of the above mentioned action has been one of the indicators established in the primary health care statement19. The majority of programs focus on the first grades of primary school, the period when the first permanent teeth emerge, among which the first molar is most frequently affected by caries, reason why protection measures are needed20. The results shown justify the efforts aimed at the newly enrolled schoolchildren, with the extension of primary education.



The incidence of tooth emergence was 29% and 25% higher in girls, when compared to boys, in the age cohorts of 60.0 to 65.9 months and 66.0 to 71.9 months, respectively, whereas this incidence was 50% higher in boys, in the oldest age cohort. Between 66.0 and 71.9 months and between 72.0 and 77.9 months, the two age groups that begin to be included in the first grade with the extension of primary education, the majority of children were found to have at least one emerged permanent molar, a fact that has important repercussions for the adoption of specific surveillance and protection measures against oclusal caries lesion.



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Prof. Paulo Frazão
Departamento de Prática de Saúde Pública
Faculdade de Saúde Pública
Universidade de São Paulo
Av. Dr Arnaldo 715
São Paulo, SP, CEP 01246-904
E-mail: pafrazao@usp.br

Received: 27/05/10
Final version: 23/11/10
Approved: 10/01/11



* Parte da pesquisa "Custo-efetividade da escovação dental supervisionada na prevenção da cárie dentária infantil" financiada pela FAPESP (Processo 06/51300-0).

Associação Brasileira de Pós -Graduação em Saúde Coletiva São Paulo - SP - Brazil
E-mail: revbrepi@usp.br