Influence of activation modes on diametral tensile strength of dual-curing resin cements

Abstract

In metallic restorations, the polymerization of dual-curing resin cements depends exclusively on chemical activation. The effect of the lack of photoactivation on the strength of these cements has been rarely studied. This study evaluated the influence of activation modes on the diametral tensile strength (DTS) of dual-curing resin cements. Base and catalyst pastes of Panavia F, Variolink II, Scotchbond Resin Cement, Rely X and Enforce were mixed and inserted into cylindrical metal moulds (4 x 2 mm). Cements were either: 1) not exposed to light (chemical activation = self-cured groups) or 2) photoactivated through mylar strips (chemical and photo-activation = dual-cured groups) (n = 10). After a 24 h storage in 37 masculineC distilled water, specimens were subjected to compressive load in a testing machine. A self-curing resin cement (Cement-It) and a zinc phosphate cement served as controls. Comparative analyses were performed: 1) between the activation modes for each dual-curing resin cement, using Students t test; 2) among the self-cured groups of the dual-curing resin cements and the control groups, using one-way ANOVA and Tukeys test (alpha = 0.05). The dual-cured groups of Scotchbond Resin Cement (53.3 MPa), Variolink II (48.4 MPa) and Rely X (51.6 MPa) showed higher DTS than that of self-cured groups (44.6, 40.4 and 44.5 MPa respectively) (p< 0.05). For Enforce (48.5 and 47.8 MPa) and Panavia F (44.0 and 43.3 MPa), no significant difference was found between the activation modes (p > 0.05). The self-cured groups of all the dual-curing resin cements presented statistically the same DTS as that of Cement-It (44.1 MPa) (p > 0.05), and higher DTS than that of zinc phosphate (4.2 MPa). Scotchbond Resin Cement, Variolink II and Rely X depended on photoactivation to achieve maximum DTS. In the absence of light, all the dual-curing resin cements presented higher DTS than that of zinc phosphate and statistically the same as that of Cement-It (p > 0.05).

Effect of different photo-initiators and light curing units on degree of conversion of composites

“…These results show that even when maintaining the total radiant exposure constant (in the present study it was maintained at approximately 35.5 J/cm²) different results will be found in different areas of the spectrum due to the different emission profiles of each LCU. Therefore, although radiant exposure has enormous importance, 23 the correlation between the absorption spectrum of the photo-initiator and the emission spectrum of the LCU also plays an essential role. Previous studies show similar outcomes.…”

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

“…Furthermore, the effect of the assembly stability during the delayed light-activation and the chemical activation periods must be known. Two studies describe that finger pressure and 0.5 kg weight were applied to permit extrusion of excess material 13,21 , while another 9 used clamps during light-activation delay periods. Most studies do not use any device for stability, with constant support.…”

“…Most studies do not use any device for stability, with constant support. Even though constant pressure during these periods was not employed by other authors [4][5][6]10,12,13,[22][23][24]29 , and it is not clinically appropriate, this parameter may have influenced the results, because any loss of stability may favour the formation of microvoids and consequently increase water sorption and solubility.…”

“…The polymer network of a resin-based material is composed by crosslinked molecules and unreacted monomers not linked to the chains. Inadequate polymerization, in addition to reducing the mechanical properties 10,13 , may have biological consequences 14,15 related to the unreacted free monomers. 16 Water sorption and hydrogen bonds with the polar groups of polymers produce separation of the molecules and reduction of hydrogen bonds between them 17 .…”

Microtensile bond strength of a newly developed resin cement to dentin

“…Several studies reported lower µTBS of dual cure resin cements when the light curing procedure was omitted 1,27,28) . However, ECD produced higher bond strength in comparison with the two self-adhering systems under both light and dark conditions.…”