Evaluation of sub-critical fatigue crack propagation in a restorative composite

Galyna M. Loughran, Antheunis Versluis, William H Douglas

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Objectives: Fracture is a major reason for clinical failure of dental restorations. Many clinical fractures are likely to be preceded by a slow sub-critical crack propagation. The purpose of this study was to determine slow crack propagation in a restorative composite. Methods: Notched composite (Z100, 3M ESPE) specimens were fatigued in a four-point bending test. The notch (1 mm) was created by embedding a sharpened razor blade in the specimen mold. The specimens were load-cycled at 5 Hz between -5 and -30 N until failure. Displacement and load were recorded during the fatigue tests and used to derive crack propagation based on beam-compliance. Results: The number of cycles until failure ranged between 34 and 82,481. In the last 1500 cycles prior to final fracture, the beam compliance increased consistently, indicating sub-critical crack propagation. It was calculated from the compliance change that the crack length increased 8% (77±14 μm) before final failure. The crack growth rate during sub-critical crack propagation was determined as a function of the stress intensity for the last 1500 cycles before fracture. Significance: A method is presented to determine slow crack propagation using a four-point bending test. Although fatigue lifetime varied widely, stable crack growth prior to fracture was consistent. This consistency allowed formulation of stress-based crack propagation relationships that can be used in concert with numerical simulations to predict composite restoration performance. The large variation found for specimen lifetime was attributed to the initiation process that precedes sub-critical crack propagation.

Original languageEnglish (US)
Pages (from-to)252-261
Number of pages10
JournalDental Materials
Issue number3
StatePublished - Mar 2005

Bibliographical note

Funding Information:
The results of this study were presented in part at the 2003 IADR meeting in Göteborg, Sweden: Loughran GM, Versluis A and Douglas WH. Experimental determination of fatigue crack propagation in a restorative composite resin. J Dent Res, 2003;82:B59, Abstr. No. 370. The authors thank Dr D. Tantbirojn for her contributions and Ms M.R. Pintado for the SEM images. This study was supported by the Minnesota Dental Research Center for Biomaterials and Biomechanics. The composite material was donated by 3M ESPE, St Paul, MN.


  • Compliance
  • Crack growth
  • Dental material
  • Fatigue
  • Four-point bending
  • Fracture mechanics
  • Restorative composite
  • Stress intensity


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