title: Radiation therapy alters microhardness and microstructure of enamel and dentin of permanent human teeth.
abstract: OBJECTIVE
  To evaluate, in vitro, the effects of ionizing radiation on the mechanical and micro-morphological properties of enamel and dentin of permanent teeth.
  
  
  METHODS
  Enamel and dentin microhardness (n=12 hemi-sections) was evaluated at three depths (superficial, middle and deep) prior to (control) and after every 10Gy radiation dose up to a cumulative dose of 60Gy by means of longitudinal microhardness. Data were analyzed using two-way analysis of variance and Tukey's test at a significance level of 5%. Enamel and dentin morphology was assessed by scanning electron microscopy (SEM) for semi-quantitative analysis (n=8 hemi-sections). Data were analyzed using Kruskal-Wallis and Dunn's or Fisher exact tests at a significance level of 5%.
  
  
  RESULTS
  The application of ionizing radiation did not change the overall enamel microhardness, although an increase in superficial enamel microhardness was observed. The micro-morphological analysis of enamel revealed that irradiation did not influence rod structure but interprismatic structure became more evident. Dentin microhardness decreased after 10, 20, 30, 50 and 60Gy cumulative doses (p<0.05) compared with non-irradiated dentin, mainly in the middle portion of the tissue. The micro-morphological analysis revealed fissures in the dentin structure, obliterated dentinal tubules and fragmentation of collagen fibers after 30 and 60Gy cumulative doses.
  
  
  CONCLUSIONS
  Although ionizing radiation did not affect the enamel microhardness of permanent teeth as a whole, an increase in superficial enamel microhardness was observed. Dentin microhardness decreased after almost all radiation doses compared with the control, with the greatest reduction of microhardness in the middle depth region. The morphological alterations on enamel and dentin structures increased with the increase of the radiation dose, with a more evident interprismatic portion, presence of fissures and obliterated dentinal tubules, and progressive fragmentation of the collagen fibers.
  
  
  CONCLUSIONS
  This study shows that irradiation affects microhardness and micro-morphology of enamel and dentin of permanent teeth. The effects of gamma irradiation on dental substrate might contribute to increased risk of radiation tooth decay associated with salivary changes, microbiota shift and high soft and carbohydrate-rich food intake.
authors.affiliation: School of Dentistry of Ribeirao Preto at University of Sao Paulo, Brazil.
authors.forename: Ligia Maria Napolitano
authors.initials: LM
authors.lastname: Gonçalves
authors.affiliation: School of Dentistry of Ribeirao Preto at University of Sao Paulo, Brazil.
authors.forename: Regina Guenka
authors.initials: RG
authors.lastname: Palma-Dibb
authors.affiliation: School of Dentistry of Ribeirao Preto at University of Sao Paulo, Brazil.
authors.forename: Francisco Wanderley Garcia
authors.initials: FW
authors.lastname: Paula-Silva
authors.affiliation: School of Medicine of Ribeirao Preto at University of Sao Paulo, Brazil.
authors.forename: Harley Francisco de
authors.initials: HF
authors.lastname: Oliveira
authors.affiliation: School of Dentistry of Ribeirao Preto at University of Sao Paulo, Brazil.
authors.forename: Paulo
authors.initials: P
authors.lastname: Nelson-Filho
authors.affiliation: School of Dentistry of Ribeirao Preto at University of Sao Paulo, Brazil.
authors.forename: Léa Assed Bezerra da
authors.initials: LA
authors.lastname: Silva
authors.affiliation: School of Dentistry of Ribeirao Preto at University of Sao Paulo, Brazil. Electronic address: amqueiroz@forp.usp.br.
authors.forename: Alexandra Mussolino de
authors.initials: AM
authors.lastname: Queiroz
mesh_terms: D003037:Cobalt Radioisotopes; D003094:Collagen / Q000528:radiation effects / Q000648:ultrastructure; D003743:Dental Enamel / Q000528:radiation effects* / Q000648:ultrastructure; D003804:Dentin / Q000528:radiation effects* / Q000648:ultrastructure; D019583:Dose Fractionation, Radiation; D006244:Hardness; D006801:Humans; D066298:In Vitro Techniques; D008855:Microscopy, Electron, Scanning; D008963:Molar / Q000528:radiation effects / Q000648:ultrastructure; D011879:Radiotherapy Dosage; D011882:Radiotherapy, High-Energy
chemical_list: D003037:Cobalt Radioisotopes; D003094:Collagen
keywords: Microhardness; Permanent dentition; Radiotherapy; Scanning electron microscopy