Influence of the ceramic translucency on the relative degree of conversion of a direct composite and dual-curing resin cement through lithium disilicate onlays and endocrowns

Highlights

• Relative DC was not affected under high translucent onlays and endocrowns.

• Microhybrid resin composite performed with higher DC than resin cement under onlays.

• There was no difference in relative DC of both resins under low translucent endocrowns.

• Relative DC increased with prolonged polymerization time under glass ceramic restorations.

Abstract

Introduction

The goal of this study was to investigate the influence of the ceramic translucency, restoration type and polymerization time on the relative degree of conversion of a dual-curing resin cement and a conventional microhybrid resin composite using a high-power light-curing device.

Methods and materials

Two 4.0 mm thick onlay (O) and two 7.5 mm thick endocrown (E) lithium disilicate restorations in high and low translucency (HT/LT) were fabricated on a decapitated molar. The pulp chamber was prepared to accommodate a 2 mm layer of a microhybrid resin composite (MHC) or dual-curing resin cement (DCC). Composite specimens were light-cured (n = 15; 1200 mW/cm²) without or through an onlay or endocrown restoration. Fourier-transform infrared spectroscopy (FTIR) absorbance curves were collected for the same composite specimen after 3 × 20, 3 × 40, 3 × 60 and 3 × 90 s of light-curing. The relative degree of conversion (DC%) was calculated and results analyzed using Kruskal-Wallis test and Friedman's ANOVA. Alpha was set at 0.05.

Results

After 3 × 60 s, the DC of MHC was significantly lower (p = 0.03; r = 0.61) under LT/EC restorations (Mdn: 77.8%) than HT/EC restorations (Mdn: 95.2%). DC of the DCC was not significantly affected by the ceramic translucency or restoration type. MHC had a significant higher DC than DCC under the HT/O, LT/O and HT/E restorations. There were no significant differences between MHC and DCC cured through LT/E restorations.

Conclusion

DC for DCC was not significantly affected by the ceramic translucency or restoration type. DC for MHC was significantly lower for LT/EC than HT/EC restorations after 3 × 60s polymerization, but not different for the high translucent restorations and low translucent onlays.

Clinical relevance

the use of light-curing microhybrid composite for bonding high translucent onlays and endocrowns and low translucent onlays seems feasible.

Introduction

Adhesive cementation of glass ceramic restorations increases the survival rate and fracture strength of indirect restorations (Burke et al., 2002; Van den Breemer et al., 2015). Dual-curing (DC) resin cements are widely employed in the luting of indirect composite and glass ceramic restorations and are considered as the golden standard for luting thick or opaque indirect restorations (Kameyama et al., 2015; Van den Breemer et al., 2015). They have some possible drawbacks related to their susceptibility to color change due to an oxidation process of the reactive groups in the tertiary amines (Pissaia et al., 2019). They also have a shorter working time as compared to conventional light-curing (LC) direct resin composites. Furthermore, some clinicians prefer the ease of removal of the excess composite due to its higher viscosity (Van den Breemer et al., 2021). Studies also show that indirect restorations luted with a direct composite perform with higher fracture strength (Gresnigt et al., 2017) and bond strength (Kameyama et al., 2015) when compared to dual-curing resin cements.

Concerns have been raised about the use of a direct resin composite under glass ceramic restorations because of compromised light transmittance through the ceramic, which may result in an insufficient degree of conversion (Archegas et al., 2012; Martins et al., 2019). Results from a recent meta-analysis showed that a thickness of 1.0 mm of porcelain significantly reduced the degree of conversion of both dual- and light-curing only resin cements as compared to no restoration (Martins et al., 2019). Light-curing resin cements have therefore been used mainly in the cementation of thin indirect laminate veneers (Peumans et al., 2004). However, new generations of light-curing devices based on light-emitting diode (LED) technology with increased irradiance might broaden the indications for the use of light-curing resin composite as a luting material (Faria-e-Silva and Pfeifer, 2017). Second and third generations of high power light-curing devices can produce an irradiance from 1100 mW/cm² up to as much as 3200 mW/cm² (Martins et al., 2019). This increased irradiance might aid in the polymerization of resin cements under thick glass ceramic restorations. Furthermore, after a prolonged polymerization time, the mechanical properties and in vivo performance of composite resins under thick glass ceramic restorations seems to be adequate (Bindl et al., 2005; Gregor et al., 2014; Van den Breemer et al., 2021).

For endodontically treated teeth, adhesive rehabilitation using partial indirect restorations promotes tissue preservation. In case of severe coronal destruction, endocrown restorations could be a viable alternative to the conventional post-and-core covering crown, especially in molar teeth (Bindl et al., 2005). Endocrowns are adhesively bonded indirect restorations with an extension into the pulp chamber (Bindl and Mörmann, 1999). One in vitro study investigated the Vickers microhardness under 7.5 mm thick feldspathic and composite endocrowns, comparing a dual-curing resin cement with a conventional microhybrid composite (Gregor et al., 2014). The microhybrid composite performed with significantly higher microhardness than the dual-curing resin cement. However, more research is needed to corroborate the feasibility of bonding lithium disilicate endocrowns using a conventional microhybrid composite alone. Variables that influence the degree of conversion are, amongst others, the translucency of the ceramic restoration, ceramic thickness and the polymerization time (Archegas et al., 2012; Martins et al., 2019).

The goal of this in vitro study is to investigate the influence of the ceramic translucency, restoration type and polymerization time on the relative degree of conversion of a dual-curing resin cement and a conventional microhybrid composite using a high-power light-curing device. The null hypothesis is that the translucency would have no effect on the relative degree of conversion of the dual-curing resin cement and the microhybrid composite. The secondary hypothesis is that the restoration type would not influence the relative degree of conversion. The third and fourth hypotheses would be that respectively the cement type and polymerization time would not affect the relative degree of conversion.