Objective: (1) To assess the need for orthodontic treatment (OT) using the Index of Orthodontic Treatment Need (IOTN) to analyze the relationship between demand and need for OT, and (2) to compare the demand and need for OT between genders.

Material and Method: A cross-sectional study was conducted on 450 students aged 12- to 14-years-old in three government high schools in Bangkok. A constructed questionnaire was used to assess demand for OT. Clinical examination was done by two orthodontists to determine the need for OT using the IOTN.

Results: Most of the students (74.0%) wished to have OT, while only one-third (37.5%) had severe need, and one-third (34.4%) had moderate need for OT as judge by the DHC of the IOTN. The AC of the IOTN indicated that most students (55.8%) had mild or no need for OT. Females (79%) demanded OT more than males (66% p-value = 0.033) but the need was similar in both sexes. Most functional factors had strong relationships with the demand for OT except lower teeth bite on palate, but none was found to be associated with need for OT. All of the aesthetic factors had strong relationships with demand for OT. There were significant relationships with needs in five categories, 1) crooked, crowded, or spacing teeth, 2) worried when speaking or smiling, 3) had suggested for OT, 4) breath smell and halitosis, and 5) wanted to put on braces to be like other people or for fashionable reasons.

Conclusion: Most of the students requested OT but females had significantly higher demand for OT than males. Most of the samples needed to have OT. The aesthetic factors that had strong relationships with the need for OT were 1) crooked, crowded, or spacing teeth, 2) worried when speaking or smiling, 3) had suggested for OT, 4) breath smell and halitosis, and 5) wanted to put on braces to be like other people or for fashionable reasons.

Keywords: Orthodontic treatment (OT), The index of orthodontic treatment need (IOTN), The dental health component (DHC), The aesthetic component (AC)