Residual stress due to polymerization shrinkage of restorative dental materials has been associated with a number of clinical symptoms, ranging from post-operative sensitivity to secondary caries to fracture. Although the concept of shrinkage stress is intuitive, its assessment is complex. Shrinkage stress is the outcome of multiple factors. To study how they interact requires an integrating model. Finite element models have been invaluable for shrinkage stress research because they provide an integration environment to study shrinkage concepts. By retracing the advancements in shrinkage stress concepts, this chapter illustrates the vital role that finite element modeling plays in evaluating the essence of shrinkage stress and its controlling factors. The shrinkage concepts discussed in this chapter will improve clinical understanding for management of shrinkage stress, and help design and assess polymerization shrinkage research.
Shrinkage Stress Model: Correlation With Shrinkage
The most simple model for shrinkage stress is that the residual stress is related to shrinkage. This intuitive model is based on the observation that without shrinkage there will be no shrinkage stress. The observation is subsequently extrapolated into a positive correlation between shrinkage and stress, because it appears credible that when shrinkage increases, shrinkage stress increases too. This intuitive model is probably the most common and practical expression of our understanding of the nature of polymerization shrinkage stress. Manufacturers, clinicians, and researchers alike have the same initial response when confronted with shrinkage data: “a composite with higher shrinkage values must cause higher stresses”. To validate this model, the relationship between shrinkage and stress will be considered more closely.