Does a low-shrinking composite induce less stress at the adhesive interface?
Introduction
The majority of composites used in restorative dentistry have their common basis in the radical polymerization of methacrylates. By conversion of monomer molecules into a polymer network, van der Waals spaces are exchanged for shorter covalent bindings. This causes considerable shrinkage of the resin composite, basically due to a closer packing of molecules. This shrinkage is clinically undesirable as it puts stress to the vulnerable interface. The magnitude of the resultant stress depends in the first place upon the cavity configuration [1], [2], [3], the elastic modulus of the composite and the polymerization conversion rate [4], [5]. Clinically, the effects of polymerization shrinkage stress can be minimized using techniques as layering and incremental curing [4], but none of these techniques can eliminate the stress completely. Naturally, the surest way to avoid shrinkage stress is to use non-shrinking resins.
Recently, a low-shrinking composite, commercialized as Filtek Silorane (3M ESPE, Seefeld, Germany), was introduced. So-called siloranes replace the methacrylates in the resin matrix of dental composites [6], [7], [8]. The ring-opening chemistry of the resin reduces shrinkage of the composite below 1 vol% [9]. Filtek Silorane comes with a two-step self-etch adhesive, commercialized as ‘Silorane System Adhesive’ (SSA). First, a hydrophilic self-etch primer (Silorane System Adhesive Self-Etch Primer, SSA-Primer) is applied and light-cured separately prior to the application of a hydrophobic adhesive resin (Silorane System Adhesive Bond, SSA-Bond). SSA-Bond is methacrylate-based and is therefore compatible with conventional methacrylate composites as well. Further details on how SSA-Bond links to the silorane composite is currently not known, but according to the technical information provided by 3M-ESPE, SSA-Bond contains a hydrophobic bifunctional monomer in order to match the hydrophobic silorane resin [10], [11]. In addition, TEM adhesive–composite interfacial characterization [12] did not disclose any separations between SSA-Bond and the silorane composite, while a clear incompatibility existed with the experimental precursor of SSA (before being referred to as ‘Hermes Bond’, 3M ESPE) [13].
Because of the low-shrinking nature of this silorane composite, the cavity configuration and the need for an incremental application technique is expected to be less critical. The hypotheses tested were therefore that (1) the cavity configuration and (2) the composite application technique do not affect the bonding effectiveness of a low-shrinking silorane-based composite to dentin. We determined the micro-tensile bond strength (μTBS) of Filtek Silorane in two different cavity configurations and using five different application techniques in comparison to that of a conventional resin composite (control).
Section snippets
Materials and methods
The study set-up is illustrated in Fig. 1. Non-carious human third molars were stored in 0.5% chloramine solution at 4 °C and used within 1 month after extraction. The cusps of the crown were flattened using a gypsum trimmer, to have a flat reference plane for the standardized cavities. All teeth were mounted in gypsum blocks in order to ease manipulation. The teeth were randomly divided in eight experimental groups, with at least five teeth per group. In five groups, a standard box-type class-I
Results
The μTBS and respective failure analysis are summarized per experimental condition in Table 3 and Fig. 2. The parametric statistical analysis showed that the different groups (p < 0.0001) as well as the different teeth (p < 0.0001) contributed significantly to the statistical model. When bonded to a flat dentin surface, no statistical difference in μTBS was recorded between Filtek Z100 and Filtek Silorane (Z100 ‘flat’(1) vs. FS ‘flat’(3), p = 0.9540). Bonding to cavity dentin lowered the μTBS in both
Discussion
The first hypothesis that cavity configuration does not affect the μTBS of a silorane composite, was rejected, as a significant decrease of the μTBS was observed (p = 0.0001). The second hypothesis that the composite application technique does not affect the μTBS, was rejected as well, since significant differences were observed between the different application protocols tested (for example between FS ‘cavity/bulk-filled’(5) and FS ‘cavity/flowable cured’(7), p = 0.0156). Altogether, it is obvious
Conclusion
The low-shrinking silorane composite and the methacrylate-based composite bonded equally well to flat dentin using the Silorane System Adhesive. From the different application techniques evaluated in this study can be concluded that adequate polymerization, especially at the bottom of the cavity, is more important than the cavity configuration. Therefore, a layering technique remains recommended, even for these low-shrinking composites.
Acknowledgements
This paper is part of a thesis submitted by A. Van Ende to the School of Dentistry, Oral Pathology and Maxillo-facial Surgery, Catholic University of Leuven, in partial fulfillment of the requirements to obtain the Flemish degree of Master in Dentistry. This study was supported in part by the FWO No. G.0206.07 and the KULeuven OT/06/55 research grants. 3M ESPE (Seefeld, Germany) is gratefully acknowledged for the generous donation of materials used in this study.
References (31)
Developing a more complete understanding of stresses produced in dental composites during polymerization
Dent Mater
(2005)- et al.
Polymerization shrinkage and elasticity of flowable composites and filled adhesives
Dent Mater
(1999) - et al.
Properties of silorane-based dental resins and composites containing a stress-reducing monomer
Dent Mater
(2007) - et al.
Stability of silorane dental monomers in aqueous systems
J Dent
(2006) - et al.
Siloranes in dental composites
Dent Mater
(2005) - et al.
Comparison of the hybrid layer formed by silorane adhesive, one-step self-etch and etch and rinse systems using confocal micro-Raman spectroscopy and SEM
J Dent
(2008) - et al.
Marginal integrity of class V restorations: SEM versus dye penetration
Dent Mater
(2008) - et al.
Dynamics of composite polymerization mediates the development of cuspal strain
Dent Mater
(2006) - et al.
Polymerization shrinkage and contraction stress of dental resin composites
Dent Mater
(2005) - et al.
Effect of cavity configuration and aging on the bonding effectiveness of six adhesives to dentin
Dent Mater
(2005)
Incremental layers bonding of silorane composite: the initial bonding properties
J Dent
The influence of water storage and C-factor on the dentin-resin composite microtensile bond strength and debond pathway utilizing a filled and unfilled adhesive resin
Dent Mater
Bond strength and ultimate tensile strength of resin composite filled into dentine cavity; effect of bulk and incremental filling technique
J Dent
The effects of cavity size and incremental technique on micro-tensile bond strength of resin composite in class I cavities
Dent Mater
In vitro cuspal deflection and microleakage of maxillary premolars restored with novel low-shrink dental composites
Dent Mater
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