A review of polymerization contraction: the influence of stress development versus stress relief.

The insertion of bonded resin composites into cavity preparations leads to a competition between polymerization contraction forces and the strength of bonds to tooth structure. The degree of stress development can be controlled, to some extent, by the cavity design (C-factor), the use of bases, the size, shape, and position of increments of composite resins placed in the cavity, and whether the resin is light- or chemically cured. Stress relief can be accomplished by maintaining the C-factor as low as possible, using chemical-curing resins, low modulus liners, and, over time, by water sorption. A thorough understanding of these principles permits clinicians to exercise more control over these variables, thereby improving the quality of their bonded restorations.