title: Effect of gamma irradiation and restorative material on the biomechanical behaviour of root filled premolars.
abstract: OBJECTIVE
  To investigate ex vivo the influence of gamma irradiation therapy and restorative material on fracture resistance, fracture mode and strain of root filled human premolars.
  
  
  METHODS
  Sixty extracted human maxillary premolar teeth were randomly divided into six groups (n = 10) determined by two study factors: (i) restorative materials: sound teeth, root filled teeth restored with composite resin, root filled teeth restored with amalgam; (ii) gamma irradiation: irradiated (subjected to 60 Gy of gamma irradiation in daily increments of 2 Gy) and nonirradiated. For the strain gauge test, two strain gauges per sample were attached on the buccal and palatal cusp surfaces (n = 5). Strain values were recorded during loading of 0-150 N. Fracture resistance (N) was assessed in a mechanical testing machine (n = 10). Strain gauge for each cusp and fracture resistance data were analysed by two-way anova (3 × 2) followed by the Tukey's honestly significant difference test (α = 0.05). The failure mode was evaluated using an optical stereomicroscope and classified according to the location of the failure.
  
  
  RESULTS
  Gamma radiation therapy significantly reduced the fracture resistance of intact teeth. The strain was higher for teeth restored with amalgam than for those restored with composite resin. The teeth restored with composite resin had similar strain values to sound teeth. Nonirradiated teeth had more restorable failures than irradiated teeth.
  
  
  CONCLUSIONS
  Gamma irradiation significantly reduced fracture resistance and increased cusp strain. The use of composite resin resulted in better biomechanical behaviour than amalgam for restoring root filled teeth whether or not they were submitted to radiotherapy.
authors: Operative Dentistry and Dental Materials Department, School of Dentistry, Federal University of Uberlândia, Uberlândia, Brazil. carlosjsoares@umuarama.ufu.br
authors: C J
authors: CJ
authors: Soares
authors: M G
authors: MG
authors: Roscoe
authors: C G
authors: CG
authors: Castro
authors: F R
authors: FR
authors: Santana
authors: L H A
authors: LH
authors: Raposo
authors: P S
authors: PS
authors: Quagliatto
authors: V R
authors: VR
authors: Novais
mesh_terms: D000704:Analysis of Variance; D001641:Bicuspid / Q000473:pathology / Q000528:radiation effects; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D003188:Composite Resins / Q000528:radiation effects; D003723:Dental Amalgam / Q000528:radiation effects; D003764:Dental Materials / Q000528:radiation effects*; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent; D003799:Dental Stress Analysis; D005720:Gamma Rays / Q000009:adverse effects*; D006801:Humans; D008437:Maxilla; D011878:Radiotherapy / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D012016:Reference Values; D012390:Root Canal Therapy; D018709:Statistics, Nonparametric; D014082:Tooth Fractures / Q000209:etiology* / Q000473:pathology; D019553:Tooth, Nonvital / Q000150:complications*
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D003723:Dental Amalgam