title: Thermo-mechanical degradation of composite restoration photoactivated by modulated methods-a SEM study of marginal and internal gap formation.
abstract: OBJECTIVE
  To evaluate the influence of thermal-mechanical degradation on superficial and internal gap formation of composite restorations photoactivated using modulated methods.
  
  
  METHODS
  An experimental composite was prepared using a resin matrix containing 65wt% Bis-GMA and 35wt% TEGDMA. Camphorquinone (0.5wt%) and dimethylaminoethyl-methacrylate (0.5wt%) were dissolved in the resin as a photo-initiator system and 65wt.% silanized glass fillers were added to the matrix. Ground buccal surfaces of bovine lower incisors were used to make 160 preparations (3 mm × 3 mm × 2 mm in depth). An adhesive system (Adper Single Bond 2) was applied and the specimens were assigned into 16 groups (n = 10), according to the photoactivation method [high intensity (HI), low intensity (LI), soft-start (SS) and pulse-delay (PD)] and the degradation protocol [(control/no degradation; thermal cycling (TC); mechanical loading (ML); thermo-mechanical loading (TC+ML)]. Marginal and internal interfaces of bonded restorations were replicated in epoxy resin and analyzed by SEM. Gaps were expressed as a percentage of the total length of the margins. Data were submitted to 2-way ANOVA and Tukey's test (α = 0.05).
  
  
  RESULTS
  For the control group no significance was noted among the photoactivation methods. TC had no effect in gap formation. ML and TC+ML increased the incidence of superficial gaps for both HI and SS groups as well as increased the internal gaps for all groups.
  
  
  CONCLUSIONS
  Although photoactivation methods do not influence gap formation at first, composite restoration photoactivated by low intensity or modulated methods showed improved resistance to thermo-mechanical degradation. Mechanical loading is determinant for interfacial degradation of composite restorations, while thermal cycling has no effect on gap formation.
authors: Biomaterials, Bandeirante University of São Paulo (ANHANGUERA UNIBAN), São Paulo, SP, Brazil. robalonso@yahoo.com
authors: Roberta Caroline
authors: RC
authors: Alonso
authors: Boniek Castillo Dutra
authors: BC
authors: Borges
authors: Paulo Henrique Perlatti
authors: PH
authors: D'Alpino
authors: Camillo
authors: C
authors: Anauate-Netto
authors: Regina Maria
authors: RM
authors: Puppin-Rontani
authors: Mario Alexandre Coelho
authors: MA
authors: Sinhoretti
mesh_terms: D000818:Animals; D002417:Cattle; D003188:Composite Resins; D008855:Microscopy, Electron, Scanning / Q000379:methods*
chemical_list: D003188:Composite Resins