Kinetic measurements of photo-polymerization contraction in resins and composites

Abstract

An instrument for the reproducible measurement of polymerization shrinkage kinetics is described, constructed around a disc-shaped specimen sandwiched between two glass plates. Test specimens of light-activated resins were irradiated through the lower, rigid plate. The physical response of this measurement system, in relation to the characteristics of photo-polymerized materials, has been subject to an original detailed analysis and validation. The upper non-rigid plate was readily deflected by an increase of the adhesive stress from the polymerizing and shrinking sample. Deflection was measured by a LVDT transducer and computer recorded. Dimensional changes were confined to the specimen disc-thickness dimension, such that the fractional linear shrinkage approximated the volumetric shrinkage. Shrinkage data are reported for representative unfilled and composite resins. Equilibrium shrinkage magnitudes ranged from 1.3 to 7.9%. The kinetic behaviour was approximately characterized by an overall time constant, ranging from 12.5-27 s, associated with an exponential growth curve, although the initial shrinkage was nearly linear in time, for many materials, due to non-steady-state concentrations of polymer free radicals.

Polymerization shrinkage kinetics and shrinkage-stress in dental resin-composites

“…This could be due to the wide range of material tested from different groups which makes it difficult to isolate the effect of the polymerization rate on the stress generation. Several factors contribute to the amount of stress generation besides the polymerization kinetics, including the conversion kinetics which is closely affected by the material chemical composition [20,38,[55][56][57]. Moreover, some materials develop elastic modulus at a low conversion which means that even at a low reaction rate there is no further plastic deformation and the stress starts to build up [18,20,58].…”

Extended Setting Shrinkage Behavior of Endodontic Sealers

“…The investigation into the shrinkage kinetics could help to understand the phenomenon per se and/or give an estimation of the polymerization reaction pattern (18). Polymerization shrinkage-strain is a time-dependent phenomenon (21). The shrinkage behavior has not been thoroughly investigated.…”

Nondestructive quantification of leakage at the tooth–composite interface and its correlation with material performance parameters

“…Polymerization is believed to proceed in two stages, i.e., pre-gelation and post-gelation[2]. At the earlier stage, flow may occur to allow chain rearrangement and alleviate stress; beyond the gel point, chains are “locked” in place and stress develops.…”