title: II. Risk factors for crown fractures of permanent incisors in children from Plovdiv.
abstract: OBJECTIVE
  The present study considers gender, age, overjet and lip competence as risk factors for children to sustain crown fractures to their permanent incisors.
  
  
  METHODS
  A total of 2572 children aged 7-11 years were included in the epidemiological study. They were randomly recruited from the schools in Plovdiv. A modified WHO classification for reporting crown fractures was used. The examiners collected data about children's age, gender, and age at sustaining the trauma; the overjet size was measured and the lip competence assessed. The obtained information was entered into a specially designed statistical proforma. The incisor overjet, lip competence, gender, age, and age at sustaining the fracture were encoded as variables as follows: overjet: 1 = normal (< 3 mm), 2 = increased (3-5 mm), 3 = highly increased (> 5mm); lip competence: 1 = adequate lip competence, 2 = lip incompetence; gender: 1 = male, 2 = female; fractures: 0 = no evidence of fractures, 1 = presence of fractures. On the basis of the obtained regression coefficients we developed a logistic regression model to determine the likelihood of sustaining crown fractures to the incisors.
  
  
  RESULTS
  The results clearly suggest that boys are twice more likely to sustain crown fractures of the incisors. The calculated ratio of boys to girls affected by crown fractures of incisors was 1.79:1 (odds ratio = 1.88). The greatest number of children with crown fractures of incisors were in the age range of 7-9 years (86.10 +/- 2.32%). These data suggest that there is a greater risk of experiencing crown fractures of the permanent incisors when the overjet exceeds 3 mm. The children with inadequate lip coverage were statistically significantly more at risk of sustaining crown fracture of the incisors in comparison with the children with normal lip competence (P < 0.001, chi2 = 122.54).
  
  
  CONCLUSIONS
  Children with inadequate lip coverage and overjet greater than 3 mm are significantly more at risk of sustaining crown fracture of the incisors. Boys are twice more likely to experience incisor crown fracture. The age period between 7 and 9 years is the most risky for fractures.
authors.affiliation: Department of Pediatric Dentistry, Faculty of Dental Medicine, Medical University, Plovdiv, Bulgaria.
authors.forename: Ani B
authors.initials: AB
authors.lastname: Belcheva
authors.forename: Kalina N
authors.initials: KN
authors.lastname: Indzhova
authors.forename: Rumen St
authors.initials: RS
authors.lastname: Stefanov
mesh_terms: D002031:Bulgaria / Q000453:epidemiology; D002648:Child; D005260:Female; D006801:Humans; D007180:Incisor / Q000293:injuries*; D008046:Lip / Q000503:physiopathology; D016015:Logistic Models; D008297:Male; D008310:Malocclusion / Q000150:complications* / Q000453:epidemiology / Q000503:physiopathology; D015995:Prevalence; D012307:Risk Factors; D019228:Tooth Crown / Q000293:injuries*; D014082:Tooth Fractures / Q000145:classification / Q000453:epidemiology / Q000209:etiology*; D014944:World Health Organization