title: Etiological factors in second mandibular molar impaction.
abstract: OBJECTIVE
  The impaction of the second mandibular molar (MM2) has recently become more prevalent. Several etiological hypothesis have been proposed to investigate the association between skeletal features and impaction of MM2. The aims of this study were to analyze the skeletal features in patients with MM2 impaction and the association between arrested eruption of MM2 and the presence of the third mandibular molar (MM3).
  
  
  METHODS
  In this retrospective study 48 subjects from 3,530 Caucasian orthodontic patients with MM2 impaction were included in a study group (SG) and compared to a control group (CG) of 200 subjects without MM2 impaction. Panoramic radiographs evaluated the presence or absence of the MM3 germ. Cephalometric analysis was performed to evaluate linear and angular skeletal values. For the statistical analysis, descriptive statistics, Student's t-test, χ2 test and odds ratio (OR) were used.
  
  
  RESULTS
  The paired comparisons between SG and CG showed in cephalometric analysis both a reduced mandibular gonial angle (ArGoMe) and lowered Jarabak's polygon value with a statistically significant difference (P≤ 0.05). MM3 was statistically significant associated (P≤ 0.05) with MM2 impaction but it is not a risk factor (OR 0.817).
  
  
  CONCLUSIONS
  Subjects with MM2 impaction show a vertical condylar growth direction. MM3 is not a risk factor for MM2 impaction. Key words:Impacted mandibular second molar, skeletal features, orthodontic.
authors.affiliation: DDS PhD, Assistant Professor. Department of Oral and Maxillofacial Sciences, School of Dentistry, "Sapienza" University of Rome, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Cassetta
authors.affiliation: DDS, Assistant Researcher. Department of Oral and Maxillofacial Sciences, School of Dentistry, "Sapienza" University of Rome, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Altieri
authors.affiliation: DDS, Assistant Researcher. Department of Oral and Maxillofacial Sciences, School of Dentistry, "Sapienza" University of Rome, Italy.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Calasso