Reduction of polymerization contraction stress for dental composites by two-step light-activation

Objectives: The goal of this study was to assess the reduction of polymerization contraction stress of composites during a two-step light-activation process and to relate this reduction to the process of polymerization shrinkage and specimen thickness. Methods: Three test procedures were performed t...

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Bibliographic Details
Published in:Dental materials 2002-09, Vol.18 (6), p.436-444
Main Authors: Lim, B.-S, Ferracane, J.L, Sakaguchi, R.L, Condon, J.R
Format: Article
Language:English
Subjects:
Acrylic Resins - chemistry
Analysis of Variance
Composite Resins - chemistry
Composite Resins - radiation effects
Dental composite
Dentistry
Humans
Light
Materials Testing - instrumentation
Polymerization contraction stress
Polymers - chemistry
Polymers - radiation effects
Polyurethanes - chemistry
Resin Cements - chemistry
Shrinkage
Silicon Dioxide
Spectroscopy, Fourier Transform Infrared
Statistics as Topic
Stress, Mechanical
Surface Properties
Time Factors
Transducers
Two-step light-activation
Zirconium
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Summary:Objectives: The goal of this study was to assess the reduction of polymerization contraction stress of composites during a two-step light-activation process and to relate this reduction to the process of polymerization shrinkage and specimen thickness. Methods: Three test procedures were performed to compare two-step light-activation with delay with one-step continuous irradiation of composites: polymerization contraction stress using a closed-loop servohydraulic testing instrument, polymerization shrinkage by a mercury dilatometer, and degree of conversion by FTIR. For the one-step continuous curing method, the samples were light-activated for 60 s at 330 mW/cm 2. For the two-step curing method, a 5 s light exposure at 60 mW/cm 2 was followed by 2 min without light exposure, and then a second light exposure for 60 s at 330 mW/cm 2. The same light parameters were used for measurements of stress, shrinkage, and degree of conversion. Three composites, Heliomolar, Herculite and Z100 were evaluated. The contraction stress experiments were repeated with varying thickness for Herculite using the one-step and two different two-step techniques. Results: Polymerization contraction stress 10 min after light-activation was significantly reduced ( P
ISSN:0109-5641
1879-0097
DOI:10.1016/S0109-5641(01)00066-5