Rheological properties and dentine shear bond strength of resin-modified glass ionomer cement containing pre-reacted spherical glass fillers and polyacid functionalized with methacrylate groups

Objective: The main limitation of current resin-modified glass ionomer cements for pulp protection is the use of 2-hydroxyethyl methacrylate (HEMA) in the materials. This study developed novel RMGICs containing spherical pre-reacted glass fillers (SPG) andpolyacid functionalized with methacrylate groups (CM liquid) to reduce the need for HEMA. The effect of rising PLR and using different liquids (0 or 5 wt% HEMA) on rheological properties, shear bond strength to dentin, and surface microhardness was examined.Materials and methods: Polyacids functionalized with methacrylate groups with 0 wt% (CM) or 5 wt% 2-hydroxyethyl methacrylate (HEMA) (CMH) were prepared. The powder phase was spherical pre-reacted fluoroaluminosilicate glass fillers (SPG).Initially, rheological properties of experimental RMGICs mixing with different powder to liquid ratios (0.5:1, 1:1, 1.5:1, and 2:1) were assessed using a strain-controlled rheometer (n=5). Macro shear bond strength (SBS) to dentin was assessed using themechanical testing frame (n=10). Fracture modes were examined under SEM-EDX. microhardness was also tested (n=5). Commercial pulp protection materials (VitrebondTM; VB and TheraCal LC; TC) were used as the comparisons. Result: Rising PLR linearly increased the viscosity but reduced gelation time and setting time of the materials. Using PLR of 1.5:1 (CM-1.5 and CMH-1.5) showed acceptablerheological properties for handling compared with other experimental materials. However, CM-1.5 (21.7 mPa·s) and CMH-1.5 (17.8 mPa·s ) showed significantly higher viscosity than VB (5.6 mPa·s ) and TC (0.01 mPa·s ) (p < 0.01). The highest and lowest5 SBS were obtained from VB (15.4 MPa) and TC (5.1 MPa). SBS of CM-1.5 (10.8 MPa)and CMH-1.5 (11.9 MPa) and VB were comparable (p > 0.05). The surface microhardness after immersion in water for 24 h of CM-1.5 (17.5 VHN) and CMH-1.5(15.6 VHN) were comparable (p > 0.05) but significantly higher than VB (6.34 VHN)and TC (7.5 VHN) (p < 0.05). Conclusions: The increase of PLR from 0.5:1 to 2:1 increased viscosity but reduced the setting time for the experimental material. The selected formulations (CM-1.5, CMH-1.5) exhibited shear bond strength to dentin comparable to the commercial material but withhigher surface hardness. The novel RMGICs could be alternative pulp protection materials.