Shrinkage behaviors of dental composite restorations-The experimental-numerical hybrid analysis.
To investigate the effects of light curing protocols on the shrinkage behaviors, contraction stress, and microleakage in composite restorations by an experimental-numerical hybrid analysis.



Three groups of human molars were collected to receive different light-curing protocols: vertical or oblique curing at regular intensity, and vertical curing at reduced intensity. For each tooth, the composite fillings were consecutively placed under unbonded and bonded states, and their shrinkage behaviors were examined with a digital image correlation (DIC) technique. The strains of the unbonded restorations were input into two finite element analysis (FEA) models with settings of the composite as either homogeneous or hardened along polymerization gradients. The preliminary solutions were verified by their individual deformations in the bonded restorations. The interfacial microleakage of restorations was also determined by micro-CT scanning and compared with the FEA results.



The bonded restorations showed centripetal shrinkage patterns with greater downward displacements than their unbonded restorations. Vertical curing at regular intensity caused the greatest shrinkage strain, contraction stress, and microleakage among the three protocols. Low-intensity curing reduced overall shrinkage strain and displacements at cervical margin, but did not prevent the formation of microleakage. Oblique curing caused asymmetric shrinkage with the tooth-shielded side revealing less deformation. Setting the polymerization-dependent elastic moduli of the composite enhanced the reliability of FEA.



This hybrid analysis comprehensively examined the polymerization shrinkage behaviors. Both the light intensity and direction affect the shrinkages and contraction stress. Oblique curing decreases shrinkage due to the attenuated irradiation by tooth-shielding rather than modulations of shrinkage direction.
Institute of Oral Medicine and Department of Stomatology, College of Medicine and Hospital, National Cheng Kung University, 138 Sheng-Li Road, Tainan 70403, Taiwan. Electronic address: sfchuang@mail.ncku.edu.tw.
Shu-Fen
SF
Chuang
Department of Mechanical Engineering, National Cheng Kung University, Taiwan.
Pin-Sheng
PS
Huang
Department of Mechanical Engineering, National Cheng Kung University, Taiwan.
Terry Yuan-Fang
TY
Chen
Department of Mechanical Engineering, National Cheng Kung University, Taiwan.
Lo-Hao
LH
Huang
Department of Medical Research, Taichung Veterans General Hospital, Taiwan.
Ko-Chih
KC
Su
Department of Biomedical Engineering, National Cheng Kung University, Taiwan.
Chi-Han
CH
Chang
D003188:Composite Resins; D055117:Curing Lights, Dental; D018772:Dental Marginal Adaptation; D003793:Dental Restoration, Permanent; D008422:Materials Testing; D008963:Molar; D058105:Polymerization; D015203:Reproducibility of Results
D003188:Composite Resins
Digital image correlation; Finite element analysis; Interfacial debonding; Light-curing; Polymerization shrinkage; Resin composite