title: Effect of remaining dentine structure and thermal-mechanical aging on the fracture resistance of bovine roots with different post and core systems.
abstract: OBJECTIVE
  To evaluate the influence of remaining dentine thickness around post and core systems and the thermo-mechanical stresses on fracture resistance of bovine roots.
  
  
  METHODS
  This study involved 288 bovine incisor roots with standardized dimensions. Roots were randomly distributed into 24 groups (n = 12) according to root conditions [intact, semi-weakened, or weakened] and post and core systems [custom cast core, composite resin core, prefabricated metallic post, or prefabricated carbon fibre post], submitted or not to thermomechanical aging [5000 thermal cycles and 100 000 mechanical cycles at a 135-degree angle to the long axis of the root]. Specimens were submitted to a tangential compressive load (135 degrees angle) at a crosshead speed of 0.5 mm min(-1) until failure. Fracture resistance data were analyzed using 3-way anova and Tukey test: alpha = 5%.
  
  
  RESULTS
  Roots restored with composite resin cores demonstrated no resistance to mechanical aging. No statistically significant difference was observed between aged and nonaged specimens involving all post-systems. Roots restored with custom cast cores had the highest fracture strength, followed by prefabricated metallic posts and carbon fibre posts, regardless of root conditions and thermomechanical aging. The remaining dentine thickness affected significantly roots restored with custom cast cores; weakened roots had a lower fracture resistance.
  
  
  CONCLUSIONS
  Although custom cast cores had a higher fracture resistance when compared to the other techniques, the results were highly dependent on remaining dentine thickness. Prefabricated posts performed in a similar manner in intact, semi-weakened and weakened roots reinforced with composite resin.
authors.affiliation: Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas Piracicaba, SP, Brazil. gimarchi@fop.unicamp.br
authors.forename: G M
authors.initials: GM
authors.lastname: Marchi
authors.forename: F H O
authors.initials: FH
authors.lastname: Mitsui
authors.forename: A N
authors.initials: AN
authors.lastname: Cavalcanti
mesh_terms: D000134:Acid Etching, Dental; D000818:Animals; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002244:Carbon / Q000737:chemistry; D000077482:Carbon Fiber; D002417:Cattle; D003188:Composite Resins / Q000737:chemistry; D003722:Dental Alloys / Q000737:chemistry; D003764:Dental Materials / Q000737:chemistry; D017267:Dental Prosthesis Design; D003804:Dentin / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry; D008422:Materials Testing; D063065:Organophosphonates / Q000737:chemistry; D010165:Palladium / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D011109:Polymethacrylic Acids / Q000737:chemistry; D011176:Post and Core Technique / Q000295:instrumentation; D011897:Random Allocation; D019279:Resin Cements / Q000737:chemistry; D012834:Silver / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014082:Tooth Fractures / Q000503:physiopathology; D014092:Tooth Root / Q000648:ultrastructure*
chemical_list: D000077482:Carbon Fiber; D003188:Composite Resins; D003722:Dental Alloys; D003764:Dental Materials; D017220:Dentin-Bonding Agents; C444701:Filtek Z250; D063065:Organophosphonates; D011109:Polymethacrylic Acids; C462240:RelyX ARC; D019279:Resin Cements; C454540:Scotchbond etchant; C115612:single bond; D012834:Silver; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D010165:Palladium; D002244:Carbon