title: Quantitative histological features and ultrastructure of opercula of human teeth showing normal and delayed eruption.
abstract: BACKGROUND
  Failure of eruption of human permanent molars has been attributed to opercular lesions, although comparisons with specimens from normally erupting teeth are scarce. The aim of this study was to quantitatively analyse opercula associated with normal and delayed tooth eruption.
  
  
  METHODS
  Twenty opercula covering permanent molars delayed in eruption were obtained from 13 patients aged 7.3-18.1 years. Six opercula from normally erupting molars of five 7.3-17.5-year-old subjects served as controls. Specimens were analysed light and electron microscopically and morphometrically.
  
  
  RESULTS
  In addition to features recognized previously, prominent numbers of nerves, high endothelial-like venules and mast cells were observed. Ultrastructurally, large multinucleated cells did not reveal cell boundaries running between the nuclei, and mast cells seemed belonging to the MC(TC)-type. None of the features differed significantly between opercula from cases of delayed and normal tooth eruption.
  
  
  CONCLUSIONS
  Disturbances of tooth eruption that are attributed to opercular lesions may represent retentions resulting from the failure of the eruption mechanism, rather than impactions because of a physical barrier.
authors.affiliation: Institute of Oral Biology, Section of Orofacial Structures and Development, Center of Dental and Oral Medicine, University of Zurich, Zurich, Switzerland.
authors.forename: D K
authors.initials: DK
authors.lastname: Verma
authors.forename: P N R
authors.initials: PN
authors.lastname: Nair
authors.forename: H U
authors.initials: HU
authors.lastname: Luder
mesh_terms: D000293:Adolescent; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D002648:Child; D005260:Female; D005881:Gingiva / Q000033:anatomy & histology* / Q000648:ultrastructure; D006801:Humans; D008297:Male; D008854:Microscopy, Electron; D018709:Statistics, Nonparametric; D013997:Time Factors; D014078:Tooth Eruption; D014097:Tooth, Unerupted / Q000473:pathology / Q000648:ultrastructure