Rheological Properties, Surface Microhardness, and Dentin Shear Bond Strength of Resin-Modified Glass Ionomer Cements Containing Methacrylate-Functionalized Polyacids and Spherical Pre-Reacted Glass Fillers

Abstract

The aim of this study was to prepare experimental resin-modified glass ionomer cements (RMGICs) containing low levels of hydroxyethyl methacrylate (HEMA) for pulp protection. Liquid and powder phases of the experimental RMGICs were polyacid functionalized with methacrylate groups and spherical pre-reacted glass fillers (SPG). Two types of liquid phase containing 0 wt. % HEMA (CM liquid) or 5 wt. % HEMA (CMH liquid) were formulated. The experimental RMGICs were prepared by mixing SPG fillers with CM liquid (F1) or CMH liquid (F2). Rheological properties were examined using a strain-controlled rheometer (n = 5). The Vickers microhardness (n = 5) and dentin shear bond strength (SBS) (n = 10) of the materials were tested. Commercial pulp protection materials (Vitrebond and TheraCal LC) were used as comparisons. The viscosity and surface microhardness of F1 (22 m Pa·s, 18 VHN) and F2 (18 m Pa·s, 16 VHN) were significantly higher than those of Vitrebond (6 mPa·s, 6 VHN) and TheraCal (0.1 mPa·s, 7 VHN). The SBS of F1 (10.7 MPa) and F2 (11.9 MPa) was comparable to that of Vitrebond (15.4 MPa) but higher than that of TheraCal LC (5.6 MPa). The addition of 5 wt. % HEMA showed no significant effect on viscosity, surface microhardness, or SBS of the experimental RMGICs. The experimental materials showed higher viscosity and microhardness but similar SBS when compared with the commercial RMGIC.

Monomer Conversion, Dimensional Stability, Biaxial Flexural Strength, Ion Release, and Cytotoxicity of Resin-Modified Glass Ionomer Cements Containing Methacrylate-Functionalized Polyacids and Spherical Pre-Reacted Glass Fillers

“…A previous study successfully prepared resin-modified glass ionomer cements containing polyacid functionalized with methacrylate groups [ 21 ]. The use of different liquid phases containing HEMA (0 or 5 wt%) showed negligible effects on the rheological properties, surface microhardness, and shear bond strength to dentin.…”

“…This could be because the HEMA enhanced water sorption, plasticizing the polymer network and thus reducing the strength and modulus of the elasticity of the materials [ 51 ]. A previous study demonstrated that F1 and F2 showed higher surface microhardness than VB [ 21 ]. However, the biaxial flexural strength of VB was comparable with that of F1 but higher than that of F2.…”

“…In terms of clinical applications, the experimental RMGICs exhibited acceptable rheological properties and shear bond strength to dentin comparable with the commercial RMGIC for pulp protection [ 21 ]. The strength of the materials at 24 h was also higher than that required by the ISO standard, which may suggest that the materials can withstand occlusal forces.…”

“…Polyacids functionalized with methacrylate groups were prepared according to the protocol used in previous studies [ 21 , 24 ]. Briefly, the co-polymer of acrylic acid (Acros Organics, Fair Lawn, NJ, USA) and maleic acid (Sigma-Aldrich, St. Louis, MO, USA) was prepared using potassium persulphate (Honeywell Fluka, Charlotte, NC, USA) and isopropanol (RCI Labscan Limited, Bangkok, Thailand) as the initiator and chain transfer agent, respectively.…”

“…Previous studies have therefore developed the liquid phase for RMGICs containing polyacids that were functionalized with methacrylate groups to enable light-curing mechanisms without the need for HEMA. A recent study prepared experimental RMGICs by mixing spherical pre-reacted glass fillers (SPG) and methacrylate-functionalized polyacids with added HEMA at 0 or 5 wt% [ 21 ]. The use of pre-reacted fillers was expected to enhance cross-linking between the polymer and the glass fillers, enhancing the mechanical properties [ 22 , 23 ].…”