title: Orthodontic pain trajectories in adolescents: Between-subject and within-subject variability in pain perception.
abstract: BACKGROUND
  The objective of this study was to assess the effects of age, sex, and the age-sex interaction on mean pain trajectories and individual variations in the pain experienced by adolescents after orthodontic separator placement.
  
  
  METHODS
  We included 115 subjects (mean age, 14.99 years; SD, ±1.90 years; 56 boys, 48.7%; 59 girls, 51.3%) in this study. Orthodontic separators were placed in the mesial and distal contact points of the maxillary and mandibular first molars. A 100-mm visual analog scale was used for pain assessment at 11 prespecified times: 1 hour and 2, 4, 12, 24, 36, 48, 72, 96, 120, and 144 hours. A mixed-effects location scale model was used for the data analysis to directly model between-subject and within-subject variabilities in pain in addition to the usual modeling of mean pain as a function of age, sex, and time.
  
  
  RESULTS
  Mean initial pain after 1 hour of separator placement for the 12- to 15-year-old male group was 13.52 mm on the visual analog scale, which initially increased rapidly (linear estimate, 9.16; P = 0.000; 95% confidence interval [CI], -8.65 to 9.67) but decelerated with time (quadratic estimate, -0.95; P = 0.000; 95% CI, -1.0 to -0.90), suggesting an inverted U-shaped mean pain trajectory. Age, sex, and age-sex interaction effects did not significantly influence initial pain. Compared with the 12- to 15-year-old male group, the 15- to 18-year-old female group reported the steepest rise in pain (estimate, 8.55; P = 0.00; 95% CI, 7.40 to 9.70) and, as a result, experienced the most overall pain. The 12- to 15-year-old male group reported minimum between-subjects variations (SD, ±4.6 mm) as well as within-subjects variations (SD, ±5.5 mm). The between-subjects variations were highest for the 12- to 15-year-old female group (SD, ±9.8 mm), whereas the within-subjects variations were highest for the 15- to 18-year-old female group (SD, ±10.1 mm).
  
  
  CONCLUSIONS
  The 12- to 15-year-old boys reported the lowest mean average pain intensity and a minimum subjective variation in between-subject and within-subject variances. The 15- to 18-year-old girls experienced maximum mean pain intensity and the highest daily fluctuations in pain intensity. The 12- to 15-year-old girls were the most different from one another in their overall pain experience.
authors.affiliation: Professor, Department of Orthodontics and Dentofacial Orthopedics, Genesis Institute of Dental Sciences and Research, Ferozepur, Punjab, India. Electronic address: drsatpalsandhu@yahoo.co.in.
authors.forename: Satpal S
authors.initials: SS
authors.lastname: Sandhu
authors.affiliation: Senior lecturer in Social Statistics, Centre for Multilevel Modelling, Graduate School of Education, University of Bristol, Bristol, United Kingdom.
authors.forename: George
authors.initials: G
authors.lastname: Leckie
mesh_terms: D000293:Adolescent; D000367:Age Factors; D000700:Analgesics / Q000627:therapeutic use; D002648:Child; D002940:Circadian Rhythm; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008963:Molar / Q000503:physiopathology; D009967:Orthodontic Appliances; D010147:Pain Measurement / Q000379:methods; D058748:Pain Perception / Q000502:physiology*; D012737:Sex Factors; D013314:Stress, Mechanical; D014087:Tooth Movement Techniques / Q000295:instrumentation
chemical_list: D000700:Analgesics