Mechanical manifestation of the C-factor in relation to photopolymerization of dental resin composites

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Abstract

Objective: This study aims to assess the validity of a recent theory which proposes that (1) the magnitude of the shrinkage stress of resin composites depends on the thickness of the boundary layer under triaxial constraints relative to the total thickness of the specimen and (2) the boundary-layer thickness is proportional to the diameter of the specimen. Methods: Cylindrical specimens of three commercially available resin composites, three diameters (4, 5 and 6.3 mm) and four thicknesses (2, 3, 5 and 6.5 mm) were tested. Curing was applied using a LED light for 40 s. Microscopic images (32×) of the specimens before and after curing were analyzed to determine the lateral shrinkage profile along the vertical axis. Boundary-layer thickness was determined from the point where lateral shrinkage displacement first reached the maximum value found at mid-thickness. Results: Lateral shrinkage displacement at mid-thickness was close to the theoretical value based on published shrinkage-strain data, with the ratio between experimental and theoretical values being 1.04 ± 0.06. The boundary-layer thickness was found to be proportional to specimen diameter only, independent of material, C-factor, and specimen thickness. The proportionality constant was 0.64 ± 0.07, which was approximately 3 times that of the effective value indicated by shrinkage strain/stress calculations. Significance: This study validates the assumption made in the shrinkage-stress theory recently proposed and provides a more precise and mechanistic interpretation for the C-factor, i.e. the C-factor, as a measure of a specimen's constraint, is the ratio between the boundary-layer thickness and the total thickness of the specimen.

Original languageEnglish (US)
Pages (from-to)1108-1114
Number of pages7
JournalDental Materials
Volume36
Issue number8
DOIs
StatePublished - Aug 2020

Bibliographical note

Funding Information:
The materials used in this study were kindly donated by 3M OCSD, USA and DMG, Germany. Jing Fu would like to thank the Minnesota Dental Research Center for Biomaterials and Biomechanics for providing her with a 3Mgives KOL scholarship to support her visit, during which this study was performed. She would also like to thank Nicholas G. Fischer for his help with her English in preparing the first draft of this manuscript. This work was also supported by the National Natural Science Foundation of China [grant number 51703106] and the Natural Science Foundation of Shandong Province [grant number ZR2016EMQ05]. The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article.

Funding Information:
The materials used in this study were kindly donated by 3M OCSD, USA and DMG, Germany. Jing Fu would like to thank the Minnesota Dental Research Center for Biomaterials and Biomechanics for providing her with a 3Mgives KOL scholarship to support her visit, during which this study was performed. She would also like to thank Nicholas G. Fischer for his help with her English in preparing the first draft of this manuscript. This work was also supported by the National Natural Science Foundation of China [grant number 51703106 ] and the Natural Science Foundation of Shandong Province [grant number ZR2016EMQ05 ]. The authors declare no potential conflicts of interest with respect to the authorship and/or publication of this article.

Publisher Copyright:
© 2020 The Academy of Dental Materials

Keywords

  • Boundary layer
  • C-factor
  • Composite resins
  • Shrinkage strain

PubMed: MeSH publication types

  • Journal Article
  • Research Support, Non-U.S. Gov't

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