title: Bonding resin thixotropy and viscosity influence on dentine bond strength.
abstract: To investigate the influence of bonding resin thixotropy and viscosity on dentine tubule penetration, blister formation and consequently on dentine bond strength as a function of air-blowing pressure (air-bp) intensity.
  
  
  
  Two HEMA-free, acetone-based, one-bottle self-etch adhesives with similar composition except disparate silica filler contents and different bonding resin viscosities were investigated. The high-filler-containing adhesive (G-Bond) featured a lower viscous bonding resin with inherent thixotropic resin (TR) properties compared to the low-filler-containing adhesive (iBond) exhibiting a higher viscous bonding resin with non-thixotropic resin (NTR) properties. Shear bond strength tests for each adhesive with low (1.5bar; 0.15MPa; n=16) and high (3.0bar; 0.30MPa; n=16) air-bp application were performed after specimen storage in distilled water (24h; 37.0±1.0°C). Results were analysed using a Student's t-test to identify statistically significant differences (p<0.05). Fracture surfaces of TR adhesive specimens were morphologically characterised by SEM.
  
  
  
  Statistically significant bond strength differences were obtained for the thixotropic resin adhesive (high-pressure: 24.6MPa, low-pressure: 9.6MPa). While high air-bp specimens provided SEM images revealing resin-plugged dentine tubules, resin tags and only marginally blister structures, low air-bp left copious droplets and open dentine tubules. In contrast, the non-thixotropic resin adhesive showed no significant bond strength differences (high-pressure: 9.3MPa, low-pressure: 7.6MPa).
  
  
  
  A pressure-dependent distinct influence of bonding resin thixotropy and viscosity on dentine bond strength has been demonstrated. Stronger adhesion with high air-bp application is explained by improved resin fluidity and facilitated resin penetration into dentine tubules.
  
  
  
  Filler particles used in adhesive systems may induce thixotropic effects in bonding resin layers, accounting for improved free-flowing resin properties. In combination with high air-bp this effect allows an easy plugging of dentine tubules and elimination of blister structures, both resulting in superior dentine bond strength.
authors.affiliation: Department of Prosthodontics, Justus-Liebig University, Schlangenzahl 14, D-35392 Giessen, Germany. Electronic address: thomas.niem@dentist.med.uni-giessen.de.
authors.forename: Thomas
authors.initials: T
authors.lastname: Niem
authors.affiliation: Department of Prosthodontics, Justus-Liebig University, Schlangenzahl 14, D-35392 Giessen, Germany. Electronic address: alexander.schmidt@dentist.med.uni-giessen.de.
authors.forename: Alexander
authors.initials: A
authors.lastname: Schmidt
authors.affiliation: Department of Prosthodontics, Justus-Liebig University, Schlangenzahl 14, D-35392 Giessen, Germany. Electronic address: bernd.woestmann@dentist.med.uni-giessen.de.
authors.forename: Bernd
authors.initials: B
authors.lastname: Wöstmann
mesh_terms: D003188:Composite Resins; D003804:Dentin; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D008422:Materials Testing; D019279:Resin Cements; D033081:Shear Strength; D013718:Tensile Strength; D014783:Viscosity
chemical_list: D003188:Composite Resins; D017220:Dentin-Bonding Agents; D019279:Resin Cements
keywords: Air-blowing pressure; Blister; Bonding resin layer; One-bottle self-etch adhesive; Phase separation; Resin tag