title: Degree of conversion and microhardness of TPO-containing resin-based composites cured by polywave and monowave LED units.
abstract: OBJECTIVE
  To determine the degree of conversion (DC) and Knoop microhardness (KHN) of resin-based composites (RBCs) containing trimethylbenzoyl-diphenylphosphine oxide (TPO) cured by polywave or monowave LED light-curing units (LCUs).
  
  
  METHODS
  Three groups (each n = 5) of Tetric EvoCeram (Ivoclar Vivadent), Vit-l-escence (Ultradent) and Herculite XRV Ultra (Kerr) were prepared in Teflon moulds (5mm in diameter and 2mm thick) and cured with polywave Bluephase(®) G2 (Ivoclar Vivadent), polywave Valo (Ultradent) or monowave Bluephase(®) (Ivoclar Vivadent; control) resulting in 9 groups. DC and KHN were determined using micro-Raman spectroscopy and Knoop microhardness, respectively. High-performance liquid chromatography and nuclear magnetic resonance spectroscopy were used to confirm the presence or absence of TPO in the three uncured materials. Data were statistically analysed using two-way and one-way ANOVA and DC and KHN were correlated using Pearson's correlation (α = 0.05).
  
  
  RESULTS
  TPO was confirmed in Tetric EvoCeram and Vit-l-escence but not in Herculite XRV Ultra. All three LCUs produced comparable KHN for Tetric EvoCeram and Herculite XRV Ultra (p > 0.05). Both polywave LCUs resulted in significantly higher KHN for Vit-l-escence and higher DC in Tetric EvoCeram and Vit-l-escence than the monowave Bluephase(®) (p < 0.05). Conversely, Bluephase(®) showed higher DC than the two polywave LCUs in Herculite XRV Ultra (p < 0.05). Pearson's correlation coefficient was r = 0.818.
  
  
  CONCLUSIONS
  Polywave LED LCUs improved monomer to polymer conversion and KHN in the two TPO-containing RBCs, but not in Herculite XRV Ultra. DC and KHN were linearly correlated in all three RBCs. Vit-l-escence showed the highest DC and KHN of the three materials tested.
  
  
  CONCLUSIONS
  The use of polywave LEDs significantly improves both the DC and KHN of materials which contain TPO. This should be taken into account when curing bleached shades of RBCs even if the manufacturers do not indicate the presence of TPO in their materials.
authors.affiliation: The University of Edinburgh, Edinburgh Postgraduate Dental Institute, Lauriston Place, Edinburgh EH3 9HA, UK. ariosantini@hotmail.com
authors.forename: Ario
authors.initials: A
authors.lastname: Santini
authors.forename: Vesna
authors.initials: V
authors.lastname: Miletic
authors.forename: Michael D
authors.initials: MD
authors.lastname: Swift
authors.forename: Mark
authors.initials: M
authors.lastname: Bradley
mesh_terms: D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002164:Camphor / Q000031:analogs & derivatives / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental / Q000145:classification*; D003764:Dental Materials / Q000737:chemistry* / Q000528:radiation effects; D006244:Hardness; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D015591:Microspectrophotometry; D010720:Phosphines / Q000737:chemistry*; D058567:Photoinitiators, Dental / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry; D013059:Spectrum Analysis, Raman
chemical_list: C520678:(2,4,6-trimethylbenzoyl) diphenylphosphine oxide; D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; D010720:Phosphines; D058567:Photoinitiators, Dental; D011109:Polymethacrylic Acids; D011140:Polyurethanes; D019279:Resin Cements; C501891:Tetric EvoCeram; C515948:Vit-l-escence Trans Ice; C065770:Herculite XR; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; C041979:2,2-bis-(4-(2-methacryloxyethoxy)phenyl)propane; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; D002164:Camphor; C553149:camphorquinone