title: Physical and adhesive properties of dental enamel after radiotherapy and bonding of metal and ceramic brackets.
abstract: BACKGROUND
  The increasing success rates for cancer patients treated with radiotherapy and the frequent occurrence of tooth loss during treatment have led to an increased demand for orthodontic treatment after radiotherapy. The aim of this study was to evaluate tooth enamel of irradiated teeth after the bonding and debonding of metal and ceramic brackets.
  
  
  METHODS
  Ten permanent molars were cut into enamel fragments measuring 1 mm(2) and divided into an irradiated group (total dose of 60 Gy) and a nonirradiated group. The fragments were subjected to microshear testing to evaluate whether radiotherapy altered the strength of the enamel. Furthermore, 90 prepared premolars were divided into 6 groups and subgroups (n = 15): group 1, nonirradiated and nonaged; group 2, nonirradiated and aged (thermal cycled); group 3, irradiated and aged; each group was divided into 2 subgroups: metallic and ceramic brackets. After thermal cycling and radiotherapy, the brackets were bonded onto the specimens with Transbond XT (3M Unitek, Monrovia, Calif). After 24 hours, the specimens were subjected to the shear tests. Images of the enamel surfaces were classified using the adhesive remnant index. The composite resin-enamel interface was also evaluated.
  
  
  RESULTS
  Enamel fragments subjected to radiation had lower strength than did the nonirradiated samples (P <0.05). The groups and subgroups submitted to radiation and bonded ceramic brackets had the lowest strength values. Groups 1 and 2 with metallic brackets had less adhesive on the surface, whereas groups 1 and 2 with ceramic brackets and group 3 with both metallic and ceramic brackets had more adhesive on the surfaces. On the images of the composite resin-enamel interface, resin tags were more extensive on irradiated tooth enamel.
  
  
  CONCLUSIONS
  Radiation decreased tooth enamel strength, and the specimens treated with radiotherapy had higher frequencies of adhesive failure between the bracket and the composite resin as well as more extensive tags.
authors.affiliation: Postgraduate student, Department of Pediatric Dentistry, School of Dentistry, University of São Paulo, Ribeirão Preto, São Paulo, Brazil. Electronic address: gabsantin@usp.br.
authors.forename: Gabriela Cristina
authors.initials: GC
authors.lastname: Santin
authors.affiliation: Professor, Department of Restorative Dentistry, School of Dentistry, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Regina Guenka
authors.initials: RG
authors.lastname: Palma-Dibb
authors.affiliation: Professor, Department of Pediatric Dentistry, School of Dentistry, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Fábio Lourenço
authors.initials: FL
authors.lastname: Romano
authors.affiliation: Professor, Department of Medical Clinics, School of Medicine, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Harley Francisco
authors.initials: HF
authors.lastname: de Oliveira
authors.affiliation: Professor, Department of Pediatric Dentistry, School of Dentistry, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Paulo
authors.initials: P
authors.lastname: Nelson Filho
authors.affiliation: Professor, Department of Pediatric Dentistry, School of Dentistry, University of São Paulo, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Alexandra Mussolino
authors.initials: AM
authors.lastname: de Queiroz
mesh_terms: D000268:Adhesiveness; D002516:Ceramics / Q000737:chemistry*; D003722:Dental Alloys / Q000737:chemistry*; D001840:Dental Bonding; D003743:Dental Enamel / Q000528:radiation effects* / Q000648:ultrastructure; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D019583:Dose Fractionation, Radiation; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D016910:Orthodontic Brackets; D011879:Radiotherapy Dosage; D019279:Resin Cements / Q000737:chemistry; D033081:Shear Strength; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D003722:Dental Alloys; D003764:Dental Materials; D019279:Resin Cements; C477790:Transbond XT