Effects of curing protocols on fluid kinetics and hardness of resin cements

Abstract

The effects of polymerization protocols on water sorption/solubility, the diffusion coefficient (D), the flux (J), and the hardness (KH) of two resin cements were evaluated. The materials were manipulated and divided into three groups (n=6) according to the curing protocol: PA=photoactivation (40 s); DP=delayed photoactivation (10 min self-curing plus 40 s photoactivated); CA=chemical activation. After desiccation, the specimens were weighed, stored in water (37ºC), evaluated over 28-days, and hardness recorded. Chemical activation resulted in lower net water uptake, D, and J for RelyX ARC (RX). For Variolink II (VL), CA yielded equivalent D and lower J; however, photoactivation resulted in lower net water uptake. Hardness of VL was less affected by the water storage, irrespective of the polymerization protocol. Considering the water diffusion parameters, VL demonstrated immediate photoactivation dependence; for RX, a chemical activation. Different polymerization protocols affect the fluid kinetics and the hardness of the resin cements tested.

Influence of curing protocols on water sorption and solubility of a self-adhesive resin-cement

“…Svizero et al verified water sorption daily for 2 weeks and found that the greatest increase of mass was observed in the first day in water for the cements analysed after three curing protocols 12 . During seven…”

“…Therefore, the polymerization protocols of 10 min-delay and no light-activation may have disturbed the conversion of the dual-cured resin cement producing shorter chains, resulting in significantly higher water sorption. It should be noted that a 10-min delay was proven to be harmful in another study 12 and it is a time too long for a clinical procedure. The expansion promoted by the solvent inside the resin matrix, separating the polymer chains, promotes plastification of the material and diffusion of the unreacted monomer, called elution 16,18 .…”

“…Light-activation delay of 5 min, was suggested as being advantageous to reduce shrinkage stress during polymerization, without impairing the degree of conversion, the extent of polymerization and hardness of some dual-cured cements [9][10][11] . It was also demonstrated that a 6-minute delay after the manipulation of resin cements may result in increased color stability 2 , but a 10-minute delay may be harmful 12 . During polymerization, individual polymer chains are formed by covalent bonds, which are crosslinked by secondary bonds.…”

“…The high water sorption and solubility influence negatively the resinous materials, indicating lower chemical stability, lower biocompatibility, higher expansion and lower mechanical properties. Sorption, solubility and mass variation are considered indicators of the chemical, physical and mechanical properties observed in the structure of the polymeric network 12,21 . Alterations of these properties can lead to deleterious clinical effects.…”

“…The expansion resulting from water sorption favours the release of the monomers not linked into chains, reduction of mechanical properties 18 and the cement plasticisation can generate unsupported areas, causing fracture to indirect restorations 19 . Sorption and solubility tests are used for in vitro evaluation of resin-based materials 20 , including dual-cured resin cements 12 , to evaluate and recommend the materials with lower sorption and solubility for indirect restorations 21 . The water absorption measured by sorption, influences negatively the material, causing expansion, weakening of matrix and filler bonding, discoloration and reduction of mechanical properties 20 .…”