title: The influence of irradiation potential on the degree of conversion and mechanical properties of two bulk-fill flowable RBC base materials.
abstract: OBJECTIVE
  To assess the depth of cure claims of two bulk-fill flowable RBC bases (SDR and x-tra base) using Fourier transform infrared (FTIR) spectroscopy, biaxial flexure strength (BFS), and Vickers hardness number (VHN) for specimen depths of 8mm (in 1mm increments).
  
  
  METHODS
  The degree of conversion (DC) was measured by monitoring the peak height (6164cm(-1)) of specimens (11.0±0.1mm diameter, 1.0±0.1mm thickness) during light irradiation for 20s using a quartz tungsten halogen light curing unit at 650±26mW/cm(2). DC was measured up to 120s post irradiation and repeated (n=3) for irradiation depths up to 8mm (in 1mm increments). Further series (n=20) of eight discs were prepared, stacked, light irradiated and numbered from one to eight (distance from the LCU). The specimens were stored at 37±1°C for 24h and BFS tested with the fracture fragments used to determine the VHN for each specimen.
  
  
  RESULTS
  X-tra base can be irradiated to 8mm without a change in DC, something the SDR material cannot claim. However, the DC results confirm both bulk-fill flowable RBC bases have a depth of cure in excess of 4mm. One-way ANOVAs of BFS and VHN data showed significant differences between irradiation depths for x-tra base and SDR with increasing irradiation depth (4mm) resulting in significant reductions in mean BFS and VHN.
  
  
  CONCLUSIONS
  The claims that the bulk-fill flowable RBC bases have a depth of cure in excess of 4mm can be confirmed but the differing chemistry of the resin formulations and filler characteristics contribute to significant differences in DC, BFS and VHN data between the two materials tested.
authors.affiliation: Materials Science Unit, Division of Oral Biosciences, Dublin Dental University Hospital, Trinity College Dublin, Ireland.
authors.forename: Leah
authors.initials: L
authors.lastname: Finan
authors.forename: William M
authors.initials: WM
authors.lastname: Palin
authors.forename: Natalia
authors.initials: N
authors.lastname: Moskwa
authors.forename: Emma Louise
authors.initials: EL
authors.lastname: McGinley
authors.forename: Garry J P
authors.initials: GJ
authors.lastname: Fleming
mesh_terms: D000465:Algorithms; D002626:Chemistry, Pharmaceutical; D003188:Composite Resins / Q000737:chemistry / Q000528:radiation effects*; D055117:Curing Lights, Dental / Q000145:classification; D003764:Dental Materials / Q000737:chemistry / Q000528:radiation effects*; D003799:Dental Stress Analysis / Q000295:instrumentation; D006244:Hardness; D006801:Humans; D055115:Light-Curing of Dental Adhesives / Q000295:instrumentation / Q000379:methods*; D008422:Materials Testing; D055595:Mechanical Phenomena; D018583:Pliability; D058105:Polymerization; D011829:Radiation Dosage; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013997:Time Factors
chemical_list: D003188:Composite Resins; D003764:Dental Materials
keywords: Biaxial flexure strength; Bulk-fill flowable; Fourier transform infrared spectroscopy; RBC base materials; Vickers hardness number