title: Frontal sinus dimensions can differ significantly between individuals within a monozygotic twin pair, indicating environmental influence on sinus sizes.
abstract: CONCLUSIONS
  The study showed that the size of the frontal sinus is not determined solely by genotype, but that other factors, e.g. environment, seem to affect the size as well. Environmental factors may include, for example diseases, trauma, allergies, acquired conditions, nutrition or medicine use.
  
  
  OBJECTIVE
  The purpose of the study was to compare sinus dimensions between individuals within a monozygotic twin pair.
  
  
  METHODS
  Profile radiographs were obtained from 42 pairs of monozygotic twins, 18 male and 24 female pairs (aged 18-23 years) with no known skeletal deviations in the cranium or general diseases. For each individual the size of the frontal sinus was analyzed on a profile radiograph and compared with the sinus size of the corresponding twin. The variation between twins was estimated using a random effects model for each gender.
  
  
  RESULTS
  The sinus sizes varied considerably between twins. The standard deviation between female pairs was 2.98 mm and between male pairs 5.36 mm. The variations in sinus sizes between females and males within twin pairs were not significantly different (p = 0.86 for height and p = 0.83 for width, F test). Still, within one female twin pair and within two male twin pairs, sinus sizes varied significantly between the two individuals.
authors.affiliation: Department of Orthodontics, Institute of Odontology, University of Copenhagen, Copenhagen, Denmark. ik@sund.ku.dk
authors.forename: Inger
authors.initials: I
authors.lastname: Kjær
authors.forename: Carsten
authors.initials: C
authors.lastname: Pallisgaard
authors.forename: Mette Toft
authors.initials: MT
authors.lastname: Brock-Jacobsen
mesh_terms: D000293:Adolescent; D002508:Cephalometry / Q000379:methods*; D005260:Female; D005626:Frontal Sinus / Q000033:anatomy & histology*; D005838:Genotype; D006801:Humans; D008297:Male; D012016:Reference Values; D012931:Social Environment; D014430:Twins, Monozygotic / Q000235:genetics*; D055815:Young Adult