Elsevier

Materials Letters

Volume 65, Issues 23–24, December 2011, Pages 3586-3589
Materials Letters

Shrinkage properties of a modified dental resin composites containing a novel spiro-orthocarbonate expanding monomer

https://doi.org/10.1016/j.matlet.2011.07.097Get rights and content

Abstract

Objectives

This study investigated the photopolymerization-induced shrinkage properties of conventional methacrylate-based composites modified by a novel spiro-orthocarbonate (SOC) expanding monomer.

Methods

The epoxy monomer and SOC expanding monomer were added to a methacrylate-based resin matrix at five different ratios ranging from 20 wt.% (SOC + Epoxy) (group 1) to 60 wt.% (SOC + Epoxy) (group 5). Volumetric shrinkage and contraction stress developing after polymerization were measured using X-ray micro-computed tomography and a universal testing machine, respectively.

Results

The volumetric shrinkage of the resin composite samples ranged from 0.92% (group 5) to 3.85% (control group) 30 min after light curing. Group 5 had the lowest volumetric shrinkage (p < 0.05), followed by groups 4, 3, 2 and 1. The contraction stress of the materials ranged from 1.86 MPa (group 5) to 3.56 MPa (control group). The lowest contraction stress was also observed in group 5, 30 min after curing (p < 0.05).

Conclusion

Including SOC expanding monomer reduced volumetric shrinkage and contraction stress of composites in comparison with conventional methacrylate-based composites.

Highlights

► Spiro-orthocarbonate (SOC) as expanding monomer. ► The volumetric shrinkage of composites can be examined precisely using Micro-CT. ► Including SOC can modify shrinkage properties of conventional methacrylate-based composites.

Introduction

Current dental resin composite systems are generally based on dimethacrylate monomers such as 2,2′-bis[4(2-hydroxy-3-methacryloylpropyloxy)phenyl]propane (Bis-GMA) and triethyleneglycoldimethacry-late (TEGDMA). Bis-GMA is the primary organic ingredient in nearly every commercial restorative resin due to its superior aesthetic quality, simple administration, and enhanced mechanical strength. However, there are still problems with this material, namely polymerization-induced volumetric shrinkage [1]. Shrinkage can induce stress in the resin composite and at the bonding interface, which may lead to debonding, microleakage [2], post-operative sensitivity [3], a compromise in the material's physical properties, and damage to the tooth substrate [4], [5], [6].

Resin composites exhibiting minimal to no volume shrinkage after polymerization are highly desirable in the field of restorative dentistry. Some recent developments in dental composite materials have used light-activated oxirane (epoxide) -based dental resins [7], [8], since compared to conventional dimethacrylate resins, the cationic ring-opening polymerizations of oxiranes (epoxides) exhibit less shrinkage [9]. Spiro-orthocarbonates (SOCs) are monomers that can be combined with other monomers such as epoxy resins, to produce a non-shrinking dental matrix for dental composites [10]. These polymerizing mixtures of epoxides with SOCs have been shown to have good biocompatibility profiles and promising physical properties [9]. However, the mass increase in water at 37 °C was almost double that of conventional dimethacrylate matrices, and cracking was observed in some samples during hydration [8]. It is worth noting that little work has been conducted to establish the degree of shrinkage-mitigation epoxy-SOC may have on conventional dimethacrylate resin composites.

In this study, we synthesized a SOC expanding monomer according to a method described in a previous study [11], and characterized a low-shrinkage resin composite based on the commonly used dimethacrylate resin, BISGMA, modified by epoxy-SOC formulations.

Section snippets

Preparation of visible light-curing resin composites

The chemical structure and formulas of materials used in the composites are depicted in Fig. 1. The epoxy resin, 3,4-Epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (ECHM-ECHC), was obtained from Sigma-Aldrich Co., Milwaukee, WI. Conventional dental matrix resins, BISGMA and TEGDMA, were derived from Esstech, Linwood, PA, USA. The spiro-orthocarbonate expanding monomer 3,9-Diethyl-3,9-bis(allyloxymethy)-1,5,7,11-tetraoxa-spiro[5,5]undecane (SOC), was synthesized in the laboratory

Results and discussion

The greatest concern in this study was determining if the experimental materials would expand upon polymerization. Fig. 3 presents a summary of the volumetric polymerization-shrinkage and contraction stress of the various composite resins investigated in this study. Values for all SOC-containing test materials exhibited statistically significant (p < 0.05) lower shrinkage values (ranging from 3.06% to 0.92%) in comparison to the B/T methacrylate control group (exhibiting shrinkage of 3.85%). The

Conclusion

This study determined that the addition of spiro-orthocarbonate (SOC) expanding monomer and epoxy monomer mixtures reduced the photopolymerization-shrinkage and contraction stress in comparison with conventional methacrylate-based composites.

Acknowledgements

The oral science research center of The Fourth Military Medical University is gratefully acknowledged for the technological support and equipment providing. This study was financially supported by a grant (No. 30801309 & No. 81070861) from the Natural Science Foundation of China. We also thank Esstech Company for generously supplying the precious materials for our research.

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Yuncong Li and Xiang Sun equally contributed to this work as co-first authors.

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