Dual-curing, self-adhesive resin cement: influence of the polymerization modes on the degree of conversion and microhardness

Abstract

RelyXTM Unicem, dual-curing self-adhesive resin cement, was tested in order to evaluate the degree of conversion (DC) and Vickers microhardness (VMH). The specimens were prepared into 4 groups (GR). For GR1, the specimens were irradiated with 500 mW.cm -2 during 20 seconds while for GR3 the same intensity was used but the irradiation time was 40 seconds. The GR2 followed the same polymerization mode of the GR1 but a ceramic disk was applied as a light barrier. For the last group, only the chemical polymerization was carried out. The DC and VMH were measured immediately after the irradiation time and again after 24 hours. Dual-polymerization (light and chemical polymerization) showed higher DC and VMH than the chemical polymerization (dark cure). The presence of a ceramic disk did not affect the DC but reduced the VMH. Increasing the exposure to light, the DC remained almost constant whereas the VMH raised slightly indicating that the VMH is quite dependent on the incident energy. Additionally, the powder/liquid portions of the cement were also characterized. The TG showed that the solid fraction was constituted of 96% of inorganic matter and 4% of vinyl-silane, a coupling agent. Regarding the liquid part, it was found that 84% was related to the mixture of monomers. The SEM revealed that the size particle of the inorganic fillers were between 400 and 11.000 nm. Factors such as energy density, size and distribution of inorganic fillers and the low effectiveness of the chemical cure contributed to the low values of the DC and VMH.

In Vitro Shear Bond Strength of Three Self-adhesive Resin Cements and a Resin-Modified Glass Ionomer Cement to Various Prosthodontic Substrates

“…4 A number of studies have reported higher degree of conversion under light-polymerization conditions for resin-based materials. 17,18,22 …”

The effect of elapsed time following alumina blasting on adhesion of CAD/CAM resin block to dentin

“…Many studies reported that light curing could improve the photo-polymerization of dual cure resin cements, while chemical curing was insufficient for polymerization 31,32) . The light curing increased the degree of conversion and the microhardness compared to chemical cured ones 33) . This study reported that light curing significantly improved the µTBS over the chemical curing mode, by which the hypothesis (b) was rejected as well.…”

In-Vitro behavior of resin luting cement material polymerized with different light sources under different hybrid CAD/CAM materials thicknesses

“…Although the used CAD/CAM materials acts as a light barrier during photo initiation of resin luting cements, yet their translucency may play a major role, allowing sufficient delivery of curing wave length to the under lying maturing material. Therefore, a greater degree of conversion leading to harder resin with a more stable color after polymerization (21,22,23,24) .…”