Journal of Dental Research, Vol 55, 115-120, Copyright © 1976 by International & American Associations for Dental Research Online Journals
Effects of cement bases on the stresses and deflections in composite restorations
J. W. Farah, J. M. Powers, J. B. Dennison, R. G. Craig and J. Spencer
A model was used to investigate stresses and deflections in cement bases
and in a composite restorative material induced in a posterior Class I
restoration. Deflections in the composite were highest when it was
supported by a base with a low modulus; however, the maximum tensile stress
(12 MN/meter2) occurring in the composite restoration at the interface with
the base was well below the maximum tensile strength of most composite
materials (30 to 40 MN/ meter2). Tensile and shear stresses occurring in
the cement bases were of sufficient magnitude to exceed the strength of the
cement when a 1.5-mm layer of zinc phosphate cement (base consistency) was
supported by a 0.5-mm layer of ZOE lining material. Lowest values of stress
were observed when a 2-mm layer of a zinc polyacrylate base was used to
support the composite restoration. An ideal situation would be to have a
cement base with a modulus of elasticity equal to that of the composite
material. Finally, the maximum stress and deflection values obtained here
can be easily exceeded in a clinical situation when wider variations can be
easily introduced, making the choice of a cement with the proper modulus
even more critical.
