title: Evaluation of Vickers hardness and depth of cure of six composite resins photo-activated with different polymerization modes.
abstract: OBJECTIVE
  The current in vitro study evaluated Vickers hardness (VK) and depth of cure (hardness ratio) of six resin composites, polymerized with a light-emitting diode (LED) curing unit by different polymerization modes: Standard 20 s, Standard 40 s, Soft-start 40 s.
  
  
  METHODS
  SIX RESIN COMPOSITES WERE SELECTED FOR THE PRESENT STUDY: three microhybrid (Esthet.X HD, Amaris, Filtek Silorane), two nanohybrid (Grandio, Ceram.X mono) and one nanofilled (Filtek Supreme XT). The VK of the surface was determined with a microhardness tester using a Vickers diamond indenter and a 200 g load applied for 15 seconds. The mean VK and hardness ratio of the specimens were calculated using the formula: hardness ratio = VK of bottom surface / VK of top surface.
  
  
  RESULTS
  For all the materials tested and with all the polymerization modes, hardness ratio was higher than the minimum value indicated in literature in order to consider the bottom surface as adequately cured (0.80). Curing time did not affect hardness ratio values for Filtek Silorane, Grandio and Filtek Supreme XT.
  
  
  CONCLUSIONS
  The effectiveness of cure at the top and bottom surface was not affected by Soft-start polymerization mode.
authors.affiliation: Department of Operative Dentistry, University of Pavia, Policlinico "San Matteo", Piazzale Golgi 2, 27100 Pavia, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Poggio
authors.forename: M
authors.initials: M
authors.lastname: Lombardini
authors.forename: S
authors.initials: S
authors.lastname: Gaviati
authors.forename: M
authors.initials: M
authors.lastname: Chiesa