Number and Type of Primary Teeth in the Oral Cavity among Thai Children Aged 9-30 Months at the Well Baby Clinic, Srinagarind Hospital, Faculty of Medicine, Khon Kaen University

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Supawich Morkmued
Siwanon Rattanakanokchai
Prapassara Sirikarn
Patimaporn Pungchanchaikul


In Thailand, an estimation of the eruption age of the primary dentition in Thai children is based on international studies using references criteria that apply to different ethnic groups.  Certain discrepancies, due to ethnic factors, may bias the evaluation of normal tooth eruption age in Thai children. This study aims to estimate number and describe the types of primary teeth that erupted in preschool children aged 9, 12, 18, 24, and 30 months. Results were based on retrospective analysis of oral examination records of healthy children, aged 9-30 months, who attended the Well Baby Clinic, Srinagarind Hospital, Khon Kaen University, for their scheduled vaccinations during the years 2014-2018. Seven hundred and nine records were included for data analysis. Records were divided into five age groups: 9, 12, 18, 24, and 30 months. Descriptive statistics included mean, frequency, and percentage were used for describing erupted primary teeth. We also estimated with a 95 percent confidence interval (95% CI) the number of primary teeth according to the tooth type. Our results showed the average number of primary teeth detected in children aged 9, 12, 18, 24 and 30 months, was 3.6 (95% CI: 3.3, 3.9), 5.5 (95% CI: 5.2, 5.8), 12.0 (95% CI: 11.4, 12.5), 16.2 (95% CI: 16.0, 16.6) and 18.5 (95% CI: 18.1, 18.9), respectively. The lower central incisor was the most often detected tooth in every age range. It was found beginning at 9 months in 96.0% of infants (95% CI: 90.8, 98.7) on the right side and in 94.4% of infants (95% CI: 88.7, 97.7) on the left side. The detected number of primary teeth observed between boys and girls in each age range were similar. Overall eruption patterns appeared symmetrical. The highest increase in number of erupted teeth occurred during the period from 12 to 18 months old. Most of the study group at age 1 year had primary central incisor and at age 2 years had the first primary molar. At age 30 months, half of the study group had the presence of the second primary molar.


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Morkmued S, Rattanakanokchai S, Sirikarn P, Pungchanchaikul P. Number and Type of Primary Teeth in the Oral Cavity among Thai Children Aged 9-30 Months at the Well Baby Clinic, Srinagarind Hospital, Faculty of Medicine, Khon Kaen University. Khon Kaen Dent J [Internet]. 2020 Aug. 25 [cited 2023 Jan. 29];23(2):66-73. Available from:
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