Incremental Filling Technique and Composite Material—Part II: Shrinkage and Shrinkage Stresses

Abstract

Increasing the number of increments and high post-gel shrinkage and/or elastic modulus values caused higher stresses in the remaining tooth structure and tooth/restoration interface. Cuspal deformation measured with the strain gauge method validated the finite element analyses.

Polymerization shrinkage stress of composite resins and resin cements – What do we need to know?

“…17 To measure the effect of the polymerization shrinkage on surrounding structures, other methods have been used, such as photoelastic analysis, 18 shrinkage force via load cells, 19,20 and cuspal deflection. 8,10,21 Shrinkage stresses have also been analyzed using finite element methods 9,11,12,22 and enamel crack tracking. 10,23 Since different testing methods provide different information about shrinkage stress development, a more complete picture of the complex interactions during the polymerization process is likely obtained by a combination of different tests.…”

“…35 Cusp deflection can be measured using various methods, for example strain gauges ( Figure 4A), which measure strains (deformation) at the external cuspal surfaces. 8,9,10,35 Another simple method is the use of a digital micrometer to measure the distance between cusp tips before and after restoration. 36 Cuspal flexure has also been measured using 3D scanning techniques.…”

“…9,11,12,22 To calculate residual shrinkage stress in a tooth, a two-dimensional or Clinical techniques and their effect of shrinkage stress…”

“…11,13 A consequence of shrinkage stress can be debonding along the restoration/tooth interface or at the restoration margins, resulting in internal and marginal gaps, micro-cracking of either or both the restorative material and tooth structure, marginal stain cuspal movement (Figures 1 and 2). 6,7,8,9,10,11 When indirect restorations are cemented to a vital tooth, polymerization shrinkage may result in postoperative sensitivity or marginal debonding that contributes to marginal staining, 11 which is often erroneously used as a criterion for replacement of indirect and direct composite restorations ( Figure 2C). …”

“…After the polymerizing material looses its ability to flow, its elastic properties increase and, consequently, any restraints on the polymerization shrinkage (for example by the bonding between restoration and tooth structure) will generate residual shrinkage stresses. 6,7,8,9 Despite various developments in new restorative materials over the last years, drawbacks related to polymerization shrinkage of composites and resin cements remain a clinical problem. 1,10,11 Typically, dental composites used in restorative procedures exhibit volumetric shrinkage ranging from less than 1% up to 6%, depending on the formulation and curing conditions.…”