BACKGROUND: There is a lack of cohort studies on the influence factors of oral 
health-related quality of life (OHRQoL). This study aimed to follow subjects 
from age 12 to 18 to analyse the sociodemographic and clinical factors that may 
influence OHRQoL.
METHODS: This cohort study selected a representative sample from Hong Kong. 
Periodontal status and caries were examined according to WHO criteria. Four 
orthodontic indices were used to assess malocclusion. Child Perceptions 
Questionnaires (CPQ11-14) with 8 items (CPQ11-14-ISF: 8) and 37 items were used 
to assess OHRQoL at age 12 and age 15, respectively; Oral Health Impact Profile 
(OHIP-14) was used to assess OHRQoL at age 18. Wilcoxon signed ranks test and 
Friedman's test were used to analyse the age-related change of OHRQoL and 
malocclusion from age 12 to 18. Generalized estimating equations were used to 
analyse the influence factors of OHRQoL and to calculate adjusted risk ratio 
(RR).
RESULTS: Subjects recruited in this study were 589 (305 females, 284 males), 364 
(186 females, 178 males) and 300 (165 females, 135 males) at age 12, 15 and 18, 
respectively. Among them, 331 subjects (172 females, 159 males) were followed 
from age 12 to 15, and 118 subjects (106 females, 82 males) were followed from 
age 12 to 18. Subjects had less severe malocclusion at age 12 than at ages 15 
and 18 (p = 0.000, measured by Dental Aesthetic Index). Age, periodontal status, 
and malocclusion had an effect on OHRQoL. When compared with OHRQoL at age 12, 
worse OHRQoL was observed at age 15 (adjusted RR = 1.06, 95%CI = 1.01-1.12, 
p = 0.032), but not at age 18 (adjusted RR = 1.01, 95%CI = 0.95-1.08, 
p = 0.759). Unhealthy periodontal conditions had a negative effect on OHRQoL 
(adjusted RR = 1.14, 95%CI = 1.04-1.25, p = 0.007). Only severe malocclusions 
had a negative effect on OHRQoL; a more severe malocclusion was associated with 
a higher effect on OHRQoL (adjusted RR = 1.09, 95%CI = 1.01-1.18, p = 0.032 for 
severe malocclusion, and adjusted RR = 1.17, 95%CI = 1.07-1.28, p = 0.001 for 
very severe malocclusion measured by Dental Aesthetic Index).
CONCLUSION: Age, periodontal status, and malocclusion had an influence on OHRQoL 
from age 12 to 18. When clinicians attempt to improve subjects' OHRQoL, it is 
necessary to consider these factors.