Polymerization stress of resin composites as a function of system compliance

Gonçalves, Flavia; Pfeifer, Carmem S.C.; Meira, Josete B.C.; Ballester, Rafael Y.; Lima, Raul G.; Braga, Roberto R.

doi:10.1016/j.dental.2007.06.032

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Volume 24, Issue 5 , Pages 645-652, May 2008

Polymerization stress of resin composites as a function of system compliance

Flavia Gonçalves
- University of São Paulo, Department Biomaterials and Oral Biochemistry, São Paulo, Brazil
Carmem S.C. Pfeifer
- University of São Paulo, Department Biomaterials and Oral Biochemistry, São Paulo, Brazil
Josete B.C. Meira
- University of São Paulo, Department Biomaterials and Oral Biochemistry, São Paulo, Brazil
Rafael Y. Ballester
- University of São Paulo, Department Biomaterials and Oral Biochemistry, São Paulo, Brazil
Raul G. Lima
- University of São Paulo, Department of Mechanical Engineering, São Paulo, Brazil
Roberto R. Braga
- University of São Paulo, Department Biomaterials and Oral Biochemistry, São Paulo, Brazil
- Corresponding author at: Departamento de Materiais Dentários da FOUSP, Av. Prof. Lineu Prestes, 2227, São Paulo, SP 05508-900, Brazil. Tel.: +55 11 3091 7840; fax: +55 11 3091 7840.

Received 6 December 2006; accepted 7 June 2007.

Abstract

Objectives

Evaluate the effect of testing system compliance on polymerization stress and stress distribution of composites.

Methods

Composites tested were Filtek Z250 (FZ), Herculite (HL), Tetric Ceram (TC), Helio Fill-AP (HF) and Heliomolar (HM). Stress was determined in 1-mm thick specimens, inserted between two rods of either poly(methyl methacrylate), PMMA, or glass. Experimental nominal stress (σ_exp) was calculated by dividing the maximum force recorded 5min after photoactivation by the cross-sectional area of the rod. Composites’ elastic modulus (E) was obtained by three-point bending. Data were submitted to one-way ANOVA/Tukey's test (α=0.05). Stress distribution on longitudinal (σ_y) and transverse (σ_x) axes of models representing the composites with the highest and lowest E (FZ and HM, respectively) were evaluated by finite element analysis (FEA).

Results

σ_exp ranged from 5.5 to 8.8MPa in glass and from 2.6 to 3.4MPa in PMMA. Composite ranking was not identical in both substrates, since FZ showed σ_exp statistically higher than HM in glass, while in PMMA FZ showed values similar to the other composites. A strong correlation was found between stress reduction (%) from glass to PMMA and composite's E (r²=0.946). FEA revealed that system compliance was influenced by the composite (FZ led to higher compliance than HM). σ_x distribution was similar in both substrates, while σ_y distribution showed larger areas of compressive stresses in specimens built on PMMA.

Significance

σ_exp determined in PMMA was 53–68% lower than in glass. Composite ranking varied slightly due to differences in substrates’ longitudinal and transverse deformation.

Keywords: Resin composite, Polymerization stress, Finite element analysis, Three-point bending