Associations between orthodontic treatment need and oral health-related quality of life among young adults: does it depend on how you assess them?

Objective: To determine the association between orthodontic treatment need (OTN) and oral health-related quality of life (OHRQoL).

Methods:   A cross-sectional study involving 273 young adults seeking orthodontic care. OHRQoL was assessed by the short-form Oral Health Impact Profile (OHIP-14) and United Kingdom oral health-related quality of life measure (OHQoL-UK). Study casts were assessed for OTN by: Dental Aesthetic Index (DAI), Index of Orthodontic Treatment Need (IOTN)-Aesthetic Component (IOTN-AC) and Dental Health Component (IOTN-DHC) and Index of Complexity, Outcome and Need (ICON). Variations in OHIP-14 and OHQoL-UK were determined with respect to OTN, and the magnitude of differences was calculated (effect size: ES).

Results: There were significant but weak correlations between occlusal indices scores and OHIP-14 scores (P<0.05, r<0.3) and between occlusal indices scores and OHQoL-UK scores (P<0.05, r<0.4). The magnitude of the statistical difference in OHQoL-UK scores was moderate to large with respect to OTN (ES: 0.36-0.87) and largest when DHC (ES=0.87) and ICON (ES=0.74) were used. The magnitude of the statistical difference in OHIP-14 scores was relatively lower (ES: 0.21-0.69), but also greatest when DHC and ICON were used to determine OTN (ES 0.69 and 0.50, respectively).

Conclusions: Orthodontic treatment need was associated with OHRQoL. The magnitude of the statistical difference between those with and without an orthodontic treatment need was larger when OHRQoL was assessed using OHQoL-UK compared to OHIP-14. DHC and ICON were more useful indices in identifying greater differences in OHRQoL with respect to orthodontic treatment need.