Determining the temporal development of dentin-composite bond strength during curing.
As composite restorations cure a competition develops between bond formation and shrinkage stress at the composite-dentin interface. Thus, understanding the temporal development of tooth-composite bond strength should enable better assessment of tooth-composite debonding.



In this study, bond strengths of composite-dentin specimens obtained from tensile test at different curing times were used to determine the bond formation rate. By varying the composite thickness and output from the curing light, their effects on the rate of bond formation for two different materials (a conventional and a bulk-fill composite) were also investigated. The proportions of cohesive and adhesive failure were determined by analysis of electron micrographs of the fractured surfaces.



The development of dentin-composite bond strength (S) with time (t) can be described by the equation: S=Smax(1-exp(-αt)), where Smax is the final bond strength (∼12MPa for both composites) and α the rate of bond formation. Using bulk-fill and thinner specimens gave faster bond formation. In fact, the higher the irradiance at the interface, the higher the rate of bond formation. However, α had a maximum value of ∼0.6s(-1) and the rule of reciprocity did not hold. A minimum dose of ∼2J/cm(2) was required to achieve adequate bond strength. The predominant failure mode changed from cohesive in the composite and adhesive to interfacial at the adhesive-dentin interface, indicating the latter to be the weakest link in the cured dentin-composite assemblies considered.



When combined with the temporal development of shrinkage stress, the current results will help determine the likelihood of tooth-composite debonding.
State Key Laboratory of Military Stomatology, Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, Xi'an 710032, China. Electronic address: never0@126.com.
Jiawen
J
Guo
Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB), School of Dentistry, University of Minnesota, MN 55455, USA. Electronic address: bholmes@umn.edu.
Brian
B
Holmes
Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-sen University, Guangzhou 510080, China. Electronic address: yangbo9011@foxmail.com.
Bo
B
Yang
Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB), School of Dentistry, University of Minnesota, MN 55455, USA. Electronic address: lixx1191@umn.edu.
Yuping
Y
Li
Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB), School of Dentistry, University of Minnesota, MN 55455, USA. Electronic address: heoxx002@umn.edu.
Young Cheul
YC
Heo
State Key Laboratory of Military Stomatology, Department of Prosthodontics, School of Stomatology, Fourth Military Medical University, Xi'an 710032, China. Electronic address: jhchen@fmmu.edu.cn.
Jihua
J
Chen
Minnesota Dental Research Center for Biomaterials and Biomechanics (MDRCBB), School of Dentistry, University of Minnesota, MN 55455, USA. Electronic address: alexfok@umn.edu.
Alex
A
Fok
D003188:Composite Resins; D001840:Dental Bonding; D003738:Dental Cements; D003804:Dentin; D017220:Dentin-Bonding Agents; D006801:Humans; D008422:Materials Testing; D019279:Resin Cements; D013499:Surface Properties; D013718:Tensile Strength
D003188:Composite Resins; D003738:Dental Cements; D017220:Dentin-Bonding Agents; D019279:Resin Cements
Composite resins; Dentin bond strength; Rule of reciprocity; Temporal development