title: Effects of light exposure time on composite resin hardness after root reinforcement using translucent fibre post.
abstract: OBJECTIVE
  The purpose of this in vitro study was to evaluate the Vickers hardness (VHN) of a Light Core (Bisco) composite resin after root reinforcement, according to the light exposure time, region of intracanal reinforcement and lateral distance from the light-transmitting fibre post.
  
  
  METHODS
  Forty-five 17-mm long roots were used. Twenty-four hours after obturation, the root canals were emptied to a depth of 12 mm and the root dentine was artificially flared to produce a 1mm space between the fibre post and the canal walls. The roots were bulk restored with the composite resin, which was photoactivated through the post for 40s (G1, control), 80 s (G2) or 120 s (G3). Twenty-four hours after post-cementation, the specimens were sectioned transversely into three slices at depths of 2, 6 and 10mm, corresponding to the coronal, middle and apical regions of the reinforced root. Composite VHN was measured as the average of three indentations (100g/15 s) in each region at lateral distances of 50, 200 and 350 microm from the cement/post-interface.
  
  
  RESULTS
  Three-way analysis of variance (alpha=0.05) indicated that the factors time, region and distance influenced the hardness and that the interaction timexregion was statistically significant (p=0.0193). Tukey's test showed that the mean VHN values for G1 (76.37+/-8.58) and G2 (74.89+/-6.28) differed significantly from that for G3 (79.55+/-5.18).
  
  
  CONCLUSIONS
  Composite resin hardness was significantly lower in deeper regions of root reinforcement and in lateral areas distant from the post. Overall, a light exposure time of 120 s provided higher composite hardness than the shorter times (40 and 80s).
authors.affiliation: School of Dentistry, University of Ribeirão Preto (UNAERP), Ribeirão Preto, SP, Brazil.
authors.forename: Cleonice da Silveira
authors.initials: CS
authors.lastname: Teixeira
authors.forename: Yara C
authors.initials: YC
authors.lastname: Silva-Sousa
authors.forename: Manoel Damião de
authors.initials: MD
authors.lastname: Sousa-Neto
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry / Q000528:radiation effects; D002484:Cementation; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects*; D017267:Dental Prosthesis Design; D003786:Dental Pulp Cavity / Q000033:anatomy & histology; D003804:Dentin / Q000033:anatomy & histology; D017220:Dentin-Bonding Agents / Q000737:chemistry / Q000528:radiation effects; D004853:Epoxy Resins / Q000737:chemistry / Q000528:radiation effects; D006244:Hardness; D006801:Humans; D006813:Humidity; D008027:Light; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry / Q000528:radiation effects; D011176:Post and Core Technique / Q000295:instrumentation*; D019279:Resin Cements / Q000737:chemistry / Q000528:radiation effects; D012387:Root Canal Filling Materials; D018915:Root Canal Preparation; D013696:Temperature; D013997:Time Factors; D019227:Tooth Apex / Q000033:anatomy & histology; D019553:Tooth, Nonvital / Q000628:therapy
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D017220:Dentin-Bonding Agents; C431350:Duo-Link; D004853:Epoxy Resins; D008689:Methacrylates; D019279:Resin Cements; D012387:Root Canal Filling Materials; C534916:epoxy resin-based root canal sealer; C100742:All-Bond 2; C074277:ethoxylated bis-phenol A dimethacrylate; D017438:Bisphenol A-Glycidyl Methacrylate