|Year : 2020 | Volume
| Issue : 1 | Page : 70-76
Association of eruption timing of first permanent molars and incisors with body mass index of children in Bengaluru City
Priya Subramaniam, Raksha Pagadala
Department of Pedodontics and Preventive Dentistry, The Oxford Dental College and Hospital, Bengaluru, Karnataka, India
|Date of Submission||22-Jul-2019|
|Date of Decision||02-Jan-2020|
|Date of Acceptance||06-Feb-2020|
|Date of Web Publication||2-Mar-2020|
Dr. Priya Subramaniam
Department of Pedodontics and Preventive Dentistry, The Oxford Dental College and Hospital, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Tooth eruption is influenced by various factors which include physiological and genetic factors. The first permanent teeth to erupt are the permanent first molars at the age of 6 years. The timing of eruption of permanent teeth can be affected by the body mass index (BMI) which is a predictor of the overall growth of the child. Aim: The aim of the study was to determine the association of eruption timing of the mandibular and maxillary first permanent molars and incisors with BMI of children in Bengaluru city. Materials and Methods: In this cross-sectional study, 3166 schoolchildren (1636 boys and 1530 girls) between the ages of 5 and 10 years were selected. Oral examination was carried out to record the presence of the permanent first molars and incisors. The height in meters and weight in kilograms of each child were recorded and the BMI was calculated. Statistical Package for Social Sciences for Windows, Version 22.0, Released 2013, IBM Corp., Armonk, NY, USA, was used to analyze the data. The median age of eruption was calculated by using Probit analysis. Independent sample Student's t-test was used to compare the distribution of erupted teeth between girls and boys at different age groups. The association between BMI and eruption timing was derived using Pearson's correlation coefficient. Results: The first permanent tooth to erupt was the mandibular first molar at the age of 5.76 ± 1.3 years. Girls showed an earlier age of eruption of all the teeth except the mandibular central incisors. A statistically significant inverse association was seen between BMI and eruption timing of the teeth examined (P < 0.05). Conclusion: The median eruption timing of the mandibular permanent first molar and incisors was earlier than that of the maxillary counterparts. Children with higher BMI values showed earlier eruption timing of the permanent teeth examined.
Keywords: Body mass index, eruption, incisor, molar, permanent, tooth
|How to cite this article:|
Subramaniam P, Pagadala R. Association of eruption timing of first permanent molars and incisors with body mass index of children in Bengaluru City. J Indian Assoc Public Health Dent 2020;18:70-6
|How to cite this URL:|
Subramaniam P, Pagadala R. Association of eruption timing of first permanent molars and incisors with body mass index of children in Bengaluru City. J Indian Assoc Public Health Dent [serial online] 2020 [cited 2020 Oct 31];18:70-6. Available from: https://www.jiaphd.org/text.asp?2020/18/1/70/279826
| Introduction|| |
Eruption of a tooth occurs when the forming tooth migrates from its intraosseous location in the jaw to its functional position within the oral cavity., Permanent teeth are biological markers of maturity and their eruption is an important milestone in a child's development. The clinical maturation stage of permanent dentition is determined by the number of permanent teeth that have erupted in a child's mouth by a specific age.
The chronology of eruption as given by Logan and Kronfeld in 1933 is still being widely used as a standard of reference for eruption timing of permanent teeth. The existing eruption schedule for permanent and deciduous dentition is based on studies conducted on Caucasians. These standards of eruption cannot be applied to the Indian population as the eruption timings were derived from a very small sample of Caucasian population. The Indian population differs from the Western population genetically, racially, and environmentally. The timing of tooth emergence in the oral cavity can be attributed to genetic and environmental causes. They can be further divided into two categories: general and local factors. The general factors include body composition, nutrition, fluoride intake, socioeconomic status, and season of birth. Early loss of primary teeth and its sequelae, dental caries, and trauma to both primary and developing permanent teeth are the local factors.,,
Tooth eruption is also influenced by pituitary growth hormone-, thyroid hormone-, and parathyroid hormone-related proteins. Tooth calcification correlates positively with height, weight, body fat, and ossification of wrist bones. The overall physical growth of the child influences the development and eruption of teeth. Body mass index (BMI) can be considered an alternative to direct measures of the overall physical growth of the child as well.
BMI estimates the overall physical development of a child and provides an insight into his or her dental development. A high body fat content affects hormonal metabolism and growth, suggesting that obese children have an accelerated linear growth. Changes in BMI could influence the eruption timing of permanent teeth.
The first permanent tooth to erupt into the oral cavity is the lower first molar between the ages of 6 and 7 years followed by the upper first molar around the same age. The next teeth to erupt are the central and lateral incisors in the lower arch followed by the incisors in the upper arch. The most commonly found sequence of eruption of permanent teeth is first molar followed by the central incisor and then the lateral incisor.,,,
The factors affecting the timing and sequence of eruption can be divided into systemic and local factors. The systemic factors include the genetic background, growth of the child, nutritional status of the child, and presence or absence of any systemic disease. The local factors include the status of the predecessor primary tooth, trauma, or presence of any cyst or tumor., Both the sequence and timing of eruption seem to be largely gene determined. Further, there are sequences and timings of eruption that are typical for certain racial groups; for example, in Europeans and Americans of European origin, teeth tend to erupt later than African Americans and American Indians. Most studies of eruption, in humans, are based on the radiographic data or intraoral visualization of the effects of the basic biologic mechanisms. There are important racial differences in the timing of permanent tooth emergence, differences apart from socioeconomically caused variations. North American Black boys and girls showed systematically earlier emergence of all teeth when compared with North American White children of European ancestry.
Except for third molars, girls erupt their permanent teeth on an average of approximately 5 months earlier than boys. This difference in the eruption timings of the teeth can be attributed to the difference in the timing of the growth spurts that occur in both the genders.
Mechanical disturbances can alter the genetic plan of eruption. If the primary tooth is extracted after the permanent successor has begun active eruptive movements, the permanent tooth will erupt earlier. If the primary tooth is extracted prior to the onset of permanent eruptive movements (prior to root formation), the permanent tooth is very likely to be delayed in its eruption. The nutritional influences on calcification and eruption are relatively much less significant than the genetic, for it is only at the extremes of nutritive variation that the effects tooth eruption can be observed evidently. This should not be surprising, as it is well known that both calcification and eruption are less responsive to endocrine disturbances than skeletal development.
As the permanent incisors and first molars erupt during the initial years of formal schooling, they play an important role in esthetics, function, and overall health and psychological well-being of a child. Very often, parents express concern about “unerupted permanent teeth” as they associate emergence of the permanent teeth with the chronological age of the child.
Eruption timing can vary among different populations. Earlier studies on eruption timing of permanent teeth in the Indian population are diverse with regard to geographical area and methodology followed.,,,, An up-to-date population-specific standard can provide additional information on eruption timing of these teeth in India. Therefore, this study was carried out with an aim to know the eruption timing of permanent first molars and incisors in children from Bengaluru city and its association with their BMI.
| Materials and Methods|| |
The study was conducted on schoolchildren between the ages of 5 and 10 years from various schools in the city of Bengaluru, Karnataka. The sample size was estimated based on the life expectancy of the population and prevalence of the particular age group from that population.
The sample size was estimated using the following formula:
N = Z2 × p (1 − p)/M2
where n = sample size for infinite population,
Z = Z value (e.g., 1.96 for 95% confidence level),
p = population proportion (expressed as decimal) (assumed to be 0.08–0.1)
(life expectancy = 60–65 years in general in India, so 5–10 years form 8% to 10% of the total population),
hence, P = 0.8–1,
M = margin of error at 5% of prevalence (0.008–0.01).
By substituting the above values in the formula, a sample size ranging from 2800 to 3450 was obtained. The sample size was rounded off to 3000 for convenience.
Prior to commencement of the study, ethical clearance to conduct the study was obtained from the institutional ethics review board and written consent was obtained from the school authorities to conduct the study. Healthy cooperative children with no developmental disorders or systemic diseases were recruited for the study. The children were asked to rinse thoroughly prior to the oral examination. The teeth were cleaned of any food debris with sterile cotton swabs for better visibility. Oral examination was done using a sterile mouth mirror and Community Periodontal Index for Treatment Needs (CPITN) probe by a single-trained, calibrated examiner under adequate illumination. A permanent tooth was considered as “erupted” if any part of its crown had penetrated the gingiva and was visible in the oral cavity. For examining if a tooth had erupted or not, a CPITN probe was used in cases where the erupted tooth was covered with a gingival flap. Recording of erupted permanent first molars and incisors in all the four quadrants was done for each child.
Each child was asked to remove his/her shoes prior to the recording of his/her height and weight. For measuring weight, a standardized portable glass digital weighing scale (model: HSB1, Hesley Inc., Germany) was used. The child was made to stand on the weighing scale and the reading was recorded once it was stable for 5 s. The weight was recorded in kilograms and rounded off to the nearest two decimal points.
The BMI was then calculated for each child using the following formula: BMI = weight in kilograms/height in meters. Based on the BMI, the children were divided into the following four BMI groups: underweight, normal weight, overweight, and obese. This was done using the gender-specific BMI-for-age growth charts of the Centers for Disease Control and Prevention (CDC) of the United States. According to the CDC, a child whose BMI is less than the 5th percentile is underweight, between the 5th and 85th percentile is normal weight, between the 85th percentile and 95th percentile is overweight, and above the 95th percentile is obese.
The Statistical Package for Social Sciences for Windows, version 22.0 (released 2013, IBM Corp., Armonk, NY, USA) was used to perform the statistical analyses in this study.
For the estimation of the eruption age of the permanent teeth, Probit analysis was performed. Independent sample Student's t-test was performed to compare the mean values of distribution of erupted teeth between girls and boys at different age groups. P <0.05 was considered statistically significant. The association between the eruption age and the BMI was calculated using the Pearson's correlation coefficient.
| Results|| |
A total of 3166 children were examined, of which 1636 (51.6%) were boys and 1530 (48.4%) were girls [Table 1]. The first permanent molar was seen in 63 (21.1%) boys and 69 (27.2%) girls in the 5-year age group. There was a statistically significant difference between the boys (97%) and girls (92.8%) in the 7-year age group, with more number of boys (259) having erupted first molar than compared to girls (233) (P = 0.029). All the children belonging to the 9- and 10-year age group had the mandibular central incisor. All the boys (254) had the mandibular lateral incisor at 10 years, whereas in girls, 255 (99.6%) had the tooth erupted [Table 2].
|Table 2: Distribution of children with eruption of mandibular first permanent molars and incisors|
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In the 7-year age group, the permanent first molar was seen in 253 (94.7%) boys and 227 (90.4%) girls. The permanent first molar was seen in 99% of both boys and girls in the 8-year age group. All the children in the 9- and 10-year age group showed an erupted permanent first molar. None of the children in the 5-year age group had an erupted maxillary central or lateral incisor. All the children in the 10-year age group had their maxillary central incisor, while 251 (98.8%) boys and 249 (97.2%) girls had their maxillary lateral incisor [Table 3].
|Table 3: Distribution of children with eruption of maxillary first permanent molars and incisors|
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Using the Probit analysis, the median age of eruption of the mandibular first molar was 5.76 ± 1.3 years, the mandibular central incisor was 6.58 ± 1.2 years, and the mandibular lateral incisor was 7.27 ± 1.4 years. For the maxillary teeth, the median age of eruption of the permanent first molar was 6.63 ± 1.3 years, the central incisor was 7.49 ± 1.4 years, and the lateral incisor was 8.68 ± 1.2 years [Table 4].
|Table 4: Median age of eruption of permanent maxillary and mandibular teeth|
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The mandibular permanent first molar erupted statistically significantly earlier in girls (5.46 ± 1.4 years) than boys (5.88 ± 1.2 years) (P = 0.046). In comparison to boys, girls showed an earlier age of eruption in all the teeth, except for the mandibular central incisors which erupted statistically significantly earlier in boys (6.20 ± 1.3 years) (P = 0.044) [Table 5].
In both boys and girls, the median age of eruption of most teeth decreased with an increase in BMI. Children in the underweight category showed a higher mean age of eruption compared to those of all other BMI categories [Graphs 1] and [Graphs 2]. Using Pearson's correlation coefficient, there was a statistically significant inverse association between tooth eruption timing (in years) and BMI in both boys and girls for all the teeth that were examined (P < 0.05) [Table 6].
|Table 6: Correlation between eruption timing and body mass index according to gender|
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| Discussion|| |
Permanent teeth are biological markers of maturity and their eruption is an important milestone in a child's development. Many biological and environmental factors affect the timing and pace of eruption of permanent teeth. The chronological standards which are followed worldwide for the eruption timing of the permanent teeth are dated back to the 1930s. These standards of eruption cannot be applied to the Indian population as the eruption timings were derived from a very small sample of Caucasian population. The Indian population differs from the Western population genetically, racially, and environmentally. Earlier studies on eruption timing of permanent teeth in the Indian population are diverse with regard to geographical area and methodology followed.,,,,, These studies were done in other districts of Karnataka and other states of India and reported of different ages for eruption of the permanent teeth. As Bengaluru is a cosmopolitan city, the eruption age is expected to vary. Due to the paucity in studies for standards of eruption timings for the population of Bengaluru city, this study was carried out to determine the eruption timing of permanent first molars and incisors in children from Bengaluru.
A cross-sectional study design was used to study the eruption timing because in comparison to the longitudinal method, it is amenable to include larger samples, thereby yielding results that are more representative of a population. In the present study, the teeth examined were the maxillary and mandibular permanent first molar and incisors. The permanent first molar is the first permanent tooth to erupt into the oral cavity. It is also considered the key to occlusion. The teeth to erupt around the same time are the permanent incisors.
The overall physical growth of a child influences the development and eruption of dentition. The measurement of BMI provides an insight into the overall physical development of the child. BMI is largely influenced by the genetic makeup of an individual. Globally, higher values of BMI are noticed in the European, African, and North American populations, whereas populations of Asian, Mongoloid, and South American descents have lower BMI values. Studies on the influence of BMI on the eruption timing of permanent teeth have shown varying results across the globe.,,,,
If a tooth is to be considered as “erupted” only if it is in occlusion, it would result in an overestimation in the eruption age of that particular tooth. Therefore, in this study, a tooth was considered to be erupted if any part of the tooth had penetrated through the gingiva and was visible in the oral cavity., Few studies have further graded eruption timing based on the area of tooth surface visible in the oral cavity.,
The present study found the mandibular first molar to be the first permanent tooth to erupt, which is similar to the chronology given by Logan and Kronfeld. Similar findings were reported in various studies during the past decade stating that the mandibular first molar was the first permanent tooth to erupt into the oral cavity.,,, Various studies conducted on the Indian population were in accordance with this finding.,,,,
However, other studies have reported that the mandibular central incisor is the first permanent tooth to erupt prior to the first molar.,,,, A study conducted in an Iranian population indicated that there are higher chances of the mandibular first molar to erupt earlier than any other permanent tooth. In our study, the first permanent tooth to erupt was the mandibular first molar in both boys and girls. Studies conducted in the Czech and Greek population have shown that the first permanent tooth to erupt was the mandibular first molar in girls, whereas in boys, the first tooth to erupt was the mandibular central incisor.,
According to the well-established chronology of tooth eruption by Logan and Kronfled, the mandibular first permanent molar erupts between the ages of 6 and 7 years. Studies on children from across the world have also shown similar timing of eruption of the mandibular first molar.,,, However, in our study, the eruption time of the mandibular first molar was earlier, at around 5 years and 8 months. Even most studies in India have reported the eruption age to be only after 6 years,,,, except for a study in Mysore that reported the eruption age of the mandibular first molar to be around 5.2 years. Similarly, a study conducted on children in Uganda also showed a much earlier eruption of the mandibular first molar at the age of 5.2 years. However, in our study, the eruption time of the mandibular first molar was earlier, at around 5 years and 8 months.
The eruption of teeth is a complex process which is dependent on the osteoclastic and osteoblastic activities, especially in teeth which have a primary tooth as a predecessor. The amount of bone covering the permanent tooth prior to its eruption decides the timing of eruption. The bone structure of the mandible and maxilla differs, with the former being thinner and less denser, especially in the anterior region. This could result in the earlier eruption of the mandibular teeth compared to the maxillary teeth. The median eruption timing of all the mandibular teeth examined was earlier than that of the maxillary permanent teeth, which was in accordance with various studies.,,, This finding was also supported by other studies conducted earlier in India, where the mandibular teeth erupt earlier than the maxillary teeth in both the sexes.,,, Shaweesh reported that there was no significant difference between eruption timing of mandibular and maxillary first molars in Iranian children. All mandibular teeth compared to the maxillary teeth were seen to erupt earlier in Greek children, with an exception of the maxillary first permanent molars which erupted earlier in boys. According to the rate of tooth formation, the time taken for the mandibular teeth crowns to be completed is lesser than that of the maxillary teeth. The permanent mandibular incisor tooth buds are placed lingual to the primary incisors, allowing them to erupt into the oral cavity prior to the exfoliation of the primary incisors.,, This could also result in the earlier eruption of the mandibular incisors in comparison to the maxillary incisors.
It has been well documented that girls have an earlier eruption age than boys.,,, The timing of growth spurts occurs earlier in girls, resulting in early dental development and eruption of teeth. In the present study, girls showed an earlier age of eruption of all teeth except for mandibular central incisor which erupted earlier in boys. No difference in the eruption timings between boys and girls has been reported in a Pakistani population.
It has been previously shown that children in higher BMI categories have an earlier eruption of permanent teeth.,,,,,,, Unhealthy dietary practices and lifestyle during childhood may lead to hyperinsulinemia and may result in the increase in insulin-like growth factor-1 (IGF-1). The IGF-1 hormone plays an important role in the acceleration of bone maturation, resulting in an early eruption of the permanent teeth in these children. Similarly, the age of eruption was found to be earlier in overweight and obese children.
The children belonging to the underweight category showed a late eruption time of all the teeth irrespective of their gender. This finding is also in agreement with studies that report of a delay in eruption in children with lower BMI.,,,
The present study shows an association between BMI and tooth eruption. In clinical practice, the calculation of BMI can be relevant in the estimation of eruption time rather than only relying on chronological age. In children reporting with delayed eruption, an initial recording of their BMI could indicate eruption timing and probably minimize the need for taking several radiographs. The estimation of BMI is an inexpensive and an easy-to-perform method of screening for weight categories. Often, parents exhibit anxiety if the interviewing period between exfoliation of primary incisors and eruption of permanent incisors is prolonged. In these situations, the values obtained from the present study could be of clinical relevance to the clinicians in Bengaluru.
As tooth eruption is a complex process, further studies on the association of eruption timing with other factors such as nutritional status, age of exfoliation of the predecessor tooth, developmental disturbances, and trauma to the primary dentition should be carried out. As radiographs were not taken for the children in this study, congenitally missing or impacted incisors may have been overlooked and considered as not yet erupted. Further longitudinal studies on children through adolescence can be carried out to provide more accurate eruption timing of permanent teeth.
| Conclusion|| |
The present epidemiological study concluded that:
- The median eruption timing of the mandibular permanent first molar and incisors was earlier than that of the maxillary permanent first molar and incisors
- The first permanent tooth to erupt was the mandibular first molar at the age of 5.76 ± 1.3 years. The median age of eruption in girls was 5.46 ± 1.4 years, which was statistically significantly earlier than boys (5.88 ± 1.2 years) (P < 0.05)
- There was earlier eruption of all the teeth examined in girls, except for the mandibular central incisor which erupted statistically significantly earlier in boys (P < 0.05)
- Children with higher BMI values appeared to have early eruption timing. The median age of eruption was higher in children who were underweight
- A statistically significant inverse relation was seen between BMI of children and eruption timing of maxillary and mandibular permanent first molars and incisors (P < 0.05).
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]