Year : 2007 | Volume
: 18 | Issue : 4 | Page : 186--189
Eruption age of permanent mandibular first molars and central incisors in the south Indian population
Rakhi Gupta, B Sivapathasundharam, A Einstein
Department of Oral and Maxillo Facial Pathology, Meenakshi Ammal Dental College and Hospital, Chennai - 600 095, India
Department of Oral and Maxillo Facial Pathology, Meenakshi Ammal Dental College and Hospital, Chennai - 600 095
Objective: The existing eruption schedules for permanent and deciduous dentition are based on studies in the Western population. Since Indians differ from Westerners racially, genetically, and environmentally, these studies fail to provide relevant guidance on the eruption schedule in the Indian population. This study aims at determining the eruption pattern of permanent mandibular molars and central incisors in the south Indian population.
Materials and Methods: 10,156 apparently healthy Indian children in the age-group of 6-9 years were examined with mouth mirror and probe under adequate illumination for the status of the eruption of the permanent mandibular first molar and permanent mandibular central incisor. Pearson«SQ»s Chi-square test with Yates«SQ» continuity correction was used to calculate the P -value for comparison of proportion between girls and boys. The values obtained in our study were compared with the standard values. The Z-test with continuity correction was used to calculate the P -value.
Results: As per our study, the permanent mandibular first molars and central incisors erupted one to two years later compared to the values reported in Westerners. The earlier eruption of the permanent mandibular first molars compared to the permanent mandibular central incisors, as well as the earlier eruption of both the teeth in girls compared to boys, were in accordance with the existing literature.
Conclusion: The eruption age reported by us may form a standard reference for eruption age in Indians.
|How to cite this article:|
Gupta R, Sivapathasundharam B, Einstein A. Eruption age of permanent mandibular first molars and central incisors in the south Indian population.Indian J Dent Res 2007;18:186-189
|How to cite this URL:|
Gupta R, Sivapathasundharam B, Einstein A. Eruption age of permanent mandibular first molars and central incisors in the south Indian population. Indian J Dent Res [serial online] 2007 [cited 2022 Nov 29 ];18:186-189
Available from: https://www.ijdr.in/text.asp?2007/18/4/186/35830
'Eruption,' derived from the Latin word 'erumpere,' means to break out. Histologically, the term eruption has been used to denote the emergence of a tooth through the alveolar mucosa. It can be defined as the axial or occlusal movement of a tooth from its developmental position within the jaws to its functional position in the occlusal plane.
Eruption of deciduous teeth, their shedding, and the subsequent eruption of the permanent dentition are orderly, sequential, and age-specific events. The transition from primary to permanent dentition begins with the emergence and eruption of the first permanent molars and the shedding of the deciduous incisors, which is followed by eruption of the permanent incisors. The permanent or succedaneous teeth replace the exfoliated deciduous teeth in a sequence of eruption that exhibits great variation.
The subjects surveyed in almost all studies of dental development in the past ,, are essentially of Western derivation. This chronology of eruption based on Western subjects fails to provide relevant guidelines regarding the Indian population, as Indians differ from them racially, culturally, and environmentally.
Population differences can only be established by studies in non-Western populations. Therefore in the present study, we have examined 10,156 south Indian children for the emergence (eruption) of the permanent mandibular first molars and permanent mandibular central incisors. As per the existing literature, ,, these are the first permanent teeth to erupt into the oral cavity, with the permanent mandibular first molars erupting at 6 years of age and the permanent mandibular central incisors erupting at 6 to 7 years of age.
Materials and Methods
10,156 students in the age-group of 6-9 years, from primary schools in various parts of Chennai, comprised the subjects for the study. Only apparently healthy students were included in the study and their ages were confirmed from the birth certificates submitted to the school authorities.
The study sample comprised two groups: group 1 consisted of 5104 boys and group 2 consisted of 5052 girls. Each of these groups was further divided into three subgroups based on their age, namely 6-7 years, 7-8 years, and 8-9 years [Table 1].
The subjects were examined using sterilized mouth mirror and probe under adequate illumination, for the eruption of the permanent mandibular first molar and the permanent mandibular central incisor. For the purpose of this study, an erupted tooth was defined as any tooth with any part of its crown penetrating the gingiva and becoming visible in the oral cavity.
The observed values were subjected to statistical analysis. Pearson's Chi-square test with Yates' continuity correction was used to calculate the P-value for the differences in proportions between girls and boys.
The eruption values reported by Logan and Kronfeld in 1933  are widely used as a guideline for eruption dates of permanent mandibular first molars and permanent central incisors. The values obtained in our study were compared with these values. Z-test with continuity correction was used to calculate the P-value.
[Table 2],[Table 3] enumerate the observations from both the study groups.
A comparison of the values obtained from groups 1 and 2 showed that permanent mandibular first molars erupted earlier than permanent mandibular central incisors, and girls had earlier eruption of both these teeth as compared to boys [Figure 1],[Figure 2]; the differences were statistically significant.
Comparison of the eruption values in our study with the values obtained in the study by Logan and Kronfeld revealed statistically significant differences [Table 4],[Table 5].
Eruption is the movement of the tooth through the bone of the jaws and the overlying mucosa, to appear and function in the oral cavity.  Eruptive movements begin with the onset of root formation, well before the tooth is seen in the oral cavity. The emergence of the tooth through the alveolar mucosa is the first clinical sign of the eruption. Following emergence, the tooth moves further, to reach the occlusal plane and later undergos functional eruptive movements to compensate for jaw growth and occlusal wear. Movement leading to tooth eruption can be divided into the preeruptive, the eruptive/prefunctional eruptive, and the functional eruptive/posteruptive phases. 
Several theories have been postulated to explain the mechanism by which a tooth moves through its surrounding tissues as it erupts into the oral cavity. These include the root formation, hydrostatic pressure, bone remodelling, and periodontal ligament traction theories.  Other suggested causes are the activity of the pulp, including constriction by dentinogenesis and increase in the volume area of Hertwig's epithelial root sheath and the diaphragm, pressure exerted by muscles, and hormonal influence, particularly by pituitary and thyroid hormones.
Various studies carried out in Western populations have reported the age of eruption of deciduous and permanent teeth. ,,, This age range is considered as the standard reference age for eruption of human dentition and is quoted in all the standard textbooks of oral physiology. Delayed or premature eruption of teeth is defined based on this reference age.
Indians form one-sixth of the global population and differ from the Western population genetically, racially, and environmentally. Considering this, the standard eruption age based on Western populations cannot be applied to the Indian population. Further, defining disturbances in eruption in Indian patients based on the Western age range will not be justified. Studies in the past have noted significant differences in the eruption age among different populations. , Therefore, large scale studies in the Indian population are necessary. Very few studies have been carried out in the past on the eruption schedule of dentition in the Indian population. ,,
In this study, the eruption age of permanent mandibular molars and central incisors were studied. As per the existing Western literature, ,, these two are the first permanent teeth to erupt into the oral cavity, with the permanent mandibular first molars erupting at 6 years of age and the permanent mandibular central incisors erupting at 6 to 7 years of age.
The eruption of the permanent mandibular first molars earlier than the permanent mandibular central incisors as well as the earlier eruption age of both in girls compared to boys, as observed in our study, are in accordance with the studies in Western populations. ,,
However, the permanent mandibular first molars and central incisors erupted 1 to 2 years later in our study subjects compared to the Western population. With no reference eruption age existing for Indian populations, this cannot be regarded as delayed eruption. It is interesting to note, at this point, the observations of Blankenstein et al. that the teeth of Indian children erupt 5-7 months later than those of Black children, a difference that was statistically significant. Steggerda and Hill suggested that the chronological age of Asians was more as compared to children in the US. 
Among the few Indian studies is the one by Tandon et al.,  which showed differences in eruption of deciduous dentition in a south Indian population as compared to the data given by Logan and Kronfeld  that was based on Western populations.Though Indians have a lower nutritional status as compared to Westerners, the variations in teeth eruption do not seem to be decided by this. This strongly suggests that racial differences between the two populations is the main factor underlying the variations in eruption timings. ,
Population differences in the body build, head form, and dentition are the result of genetic and environmental interactions. An appreciation of this genotype-phenotype relationship as a source of physical variation in humans is important in the recognition and establishment of correct standards for any given population. The variations in Indians may be attributed to genetic, racial, socioeconomic, and maternal factors, which vary considerably between Indians and the rest of the world. So this study reporting a significant difference in eruption timings of permanent mandibular central incisor and permanent mandibular first molar, in Indians as compared to Westerners, may form a standard reference for eruption age in Indians.
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