title: Thio-urethanes improve properties of dual-cured composite cements.
abstract: This study aims at modifying dual-cure composite cements by adding thio-urethane oligomers to improve mechanical properties, especially fracture toughness, and reduce polymerization stress. Thiol-functionalized oligomers were synthesized by combining 1,3-bis(1-isocyanato-1-methylethyl)benzene with trimethylol-tris-3-mercaptopropionate, at 1:2 isocyanate:thiol. Oligomer was added at 0, 10 or 20 wt% to BisGMA-UDMA-TEGDMA (5:3:2, with 25 wt% silanated inorganic fillers) or to one commercial composite cement (Relyx Ultimate, 3M Espe). Near-IR was used to measure methacrylate conversion after photoactivation (700 mW/cm(2) × 60s) and after 72 h. Flexural strength and modulus, toughness, and fracture toughness were evaluated in three-point bending. Polymerization stress was measured with the Bioman. The microtensile bond strength of an indirect composite and a glass ceramic to dentin was also evaluated. Results were analyzed with analysis of variance and Tukey's test (α = 0.05). For BisGMA-UDMA-TEGDMA cements, conversion values were not affected by the addition of thio-urethanes. Flexural strength/modulus increased significantly for both oligomer concentrations, with a 3-fold increase in toughness at 20 wt%. Fracture toughness increased over 2-fold for the thio-urethane modified groups. Contraction stress was reduced by 40% to 50% with the addition of thio-urethanes. The addition of thio-urethane to the commercial cement led to similar flexural strength, toughness, and conversion at 72h compared to the control. Flexural modulus decreased for the 20 wt% group, due to the dilution of the overall filler volume, which also led to decreased stress. However, fracture toughness increased by up to 50%. The microtensile bond strength increased for the experimental composite cement with 20 wt% thio-urethane bonding for both an indirect composite and a glass ceramic. Novel dual-cured composite cements containing thio-urethanes showed increased toughness, fracture toughness and bond strength to dentin while demonstrating reduced contraction stress. All of these benefits are derived without compromising the methacrylate conversion of the resin component. The modification does not require changing the operatory technique.
authors.affiliation: Piracicaba Dental School, Campinas State University, Piracicaba, SP, Brazil Meridional Faculty, Prosthodontics and Dental Materials, Passo Fundo, RS, Brazil.
authors.forename: A
authors.initials: A
authors.lastname: Bacchi
authors.affiliation: Oregon Health and Science University, Biomaterials and Biomechanics, Portland, OR, USA.
authors.forename: A
authors.initials: A
authors.lastname: Dobson
authors.affiliation: Oregon Health and Science University, Biomaterials and Biomechanics, Portland, OR, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Ferracane
authors.affiliation: Piracicaba Dental School, Campinas State University, Piracicaba, SP, Brazil.
authors.forename: R
authors.initials: R
authors.lastname: Consani
authors.affiliation: Oregon Health and Science University, Biomaterials and Biomechanics, Portland, OR, USA pfeiferc@ohsu.edu.
authors.forename: C S
authors.initials: CS
authors.lastname: Pfeifer
mesh_terms: D015097:3-Mercaptopropionic Acid / Q000737:chemistry; D001585:Benzoyl Peroxide / Q000737:chemistry; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002516:Ceramics / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry*; D001840:Dental Bonding; D003804:Dentin / Q000648:ultrastructure; D055119:Elastic Modulus; D006801:Humans; D017953:Isocyanates / Q000737:chemistry; D055115:Light-Curing of Dental Adhesives / Q000379:methods; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D018583:Pliability; D011092:Polyethylene Glycols / Q000737:chemistry; D058105:Polymerization; D011109:Polymethacrylic Acids / Q000737:chemistry; D011140:Polyurethanes / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D055116:Self-Curing of Dental Resins / Q000379:methods; D012821:Silanes / Q000737:chemistry; D013314:Stress, Mechanical; D013457:Sulfur Compounds / Q000737:chemistry*; D013499:Surface Properties; D013718:Tensile Strength; D014520:Urethane / Q000737:chemistry*; D062366:para-Aminobenzoates / Q000737:chemistry
chemical_list: D003188:Composite Resins; D017953:Isocyanates; D008689:Methacrylates; D011109:Polymethacrylic Acids; D011140:Polyurethanes; C528569:Rely-X; D019279:Resin Cements; D012821:Silanes; D013457:Sulfur Compounds; C523330:ethyl 4-N,N-dimethylaminobenzoate; D062366:para-Aminobenzoates; C029824:urethane dimethacrylate luting resin; C020946:triethylene glycol dimethacrylate; D014520:Urethane; D011092:Polyethylene Glycols; D017438:Bisphenol A-Glycidyl Methacrylate; C023506:Glass ceramics; D015097:3-Mercaptopropionic Acid; D001585:Benzoyl Peroxide
keywords: delayed gelation; fracture toughness; kinetics of conversion; polymerization stress; prepolymerized additives; volumetric shrinkage