Orthodontic pain: an interaction between age and sex in early and middle adolescence. 
To investigate the age and sex interaction effect on orthodontic pain in adolescence during the initial phase of fixed orthodontic treatment.  Three hundred participants (mean age 13.85 ± 1.98 years; 152 female, 148 male) met all inclusion criteria and enrolled in the study designed as 2 × 2 factorial trial with two levels each for age (11-14 years; 14-17 years) and sex (male; female).  A 0.16-inch superelastic NiTi wire was used in a 0.022-inch slot (Roth's prescription) preadjusted edgewise appliance for initial leveling and alignment of mandibular anterior dentition.  The follow-up period was 7 days.  Pain was assessed by using 100 mm visual analog scale for one baseline and nine follow-up repeated measurements at prespecified time points.  Data were analyzed by using generalized linear mixed effect model analysis.  Three participants were lost to follow-up, and 17 participants were not considered for analysis due to incomplete or improperly completed questionnaire.  Therefore, 280 participants (mean age 13.96 ± 2.01 years; 138 female, 142 male) were analyzed for results.  Results showed that age and sex interaction had statistically significant effect on pain (F = 3.56; P = .0151; df 3/218).  In the 11-14 year age group, there was no significant difference for pain between male and female.  In the 14-17 year age group, girls reported significantly greater pain compared to 14- to 17 year-old boys (t = 2.76; P = .0209).  Pain reported by 14- to 17-year-old girls was also significantly greater compared to 11- to 14-year-old boys (t = 2.91; P = .0206).  Age and sex interaction has significant effect on orthodontic pain during adolescence, and 14- to 17-year-old girls experienced maximum pain.