Control of polymerization shrinkage and stress in nanogel-modified monomer and composite materials

Abstract

Objectives This study demonstrates the effects of nano-scale prepolymer particles as additives to model dental monomer and composite formulations. Methods Discrete nanogel particles were prepared by solution photopolymerization of isobornyl methacrylate and urethane dimethacrylate in the presence of a chain transfer agent, which also provided a means to attach reactive groups to the prepolymer. Nanogel was added to triethylene glycol dimethacrylate (TEGDMA) in increments between 5 and 40 wt% with resin viscosity, reaction kinetics, shrinkage, mechanical properties, stress and optical properties evaluated. Maximum loading of barium glass filler was determined as a function of nanogel content and composites with varied nanogel content but uniform filler loading were compared in terms of consistency, conversion, shrinkage and mechanical properties. Results High conversion, high molecular weight internally crosslinked and cyclized nanogel prepolymer was efficiently prepared and redispersed into TEGDMA with an exponential rise in viscosity accompanying nanogel content. Nanogel addition at any level produced no deleterious effects on reaction kinetics, conversion or mechanical properties, as long as reactive nanogels were used. A reduction in polymerization shrinkage and stress was achieved in proportion to nanogel content. Even at high nanogel concentrations, the maximum loading of glass filler was only marginally reduced relative to the control and high strength composite materials with low shrinkage were obtained. Significance The use of reactive nanogels offers a versatile platform from which resin and composite handling properties can be adjusted while the polymerization shrinkage and stress development that challenge the adhesive bonding of dental restoratives are controllably reduced.

Improved Dental Adhesive Formulations Based on Reactive Nanogel Additives

“…The passive solvent evaporation testing suggests that nanogel addition may restrict oxygen diffusion rates at the material surface, which may reduce oxygen inhibition during adhesive layer polymerization. The increase in bulk monomer viscosity with nanogel addition has been shown to be fairly limited up to loading levels of 20 to 30 wt% (Morães et al, 2011), above which particle-particle interactions dominate (percolation threshold; Rubinstein and Colby, 2008). The effective concentrations of nanogels in the ethanol-solvated materials (ca.…”

“…The size and globular structure of individual nanogel particles (Szaloki et al, 2008;Morães et al, 2011) are such that their dispersion into dentinal tubules and interfibrillar collagen spaces is practical. Crosslinked particles not only impair water percolation and swelling but also provide mechanical reinforcement (Sahiner et al, 2006;Szaloki et al, 2008).…”

“…One example of such prepolymers has been described recently (Morães et al, 2011). Nanogels are 10-to 100-nm crosslinked globular particles synthesized through a versatile route allowing for adjustable hydrophobic character and level of methacrylate functionalization.…”

“…Nanogels are 10-to 100-nm crosslinked globular particles synthesized through a versatile route allowing for adjustable hydrophobic character and level of methacrylate functionalization. Nanogels can be swollen by and dispersed in monomers such as BisGMA and HEMA (Morães et al, 2011) and solvents (de Groot et al, 2001), which, in dentin bonding, are anticipated to carry the nanoparticles into demineralized dentin. Since this approach allows for retention of the basic adhesive monomer formulation, the water-chasing capacity, which depends on both resin and solvent composition, is expected to be maintained.…”

Polymerization shrinkage stress of composite resins and resin cements – What do we need to know?

“…Over the past 15 years, much effort has been dedicated to developing low-shrinking formulations, either by virtue of using a ring-opening polymerization mechanism (as is the case with the product containg epoxide-based silorane monomers) or by using monomers with higher molecular weight (as is the case for composites using dimer-acid dimethacrylates, or DX-511, a monomer developed by DuPont, both with Mw greater than 800 g/mol), or even pre-polymerized additives. 73 The structures for all of these monomers are shown in Figure 5. In the case of the ringopening monomers, the rationale for decreased shrinkage is their inherent lower molar shrinkage coefficient in comparison with methacrylates.…”