Effects of montmorillonite clay addition on the compressive fracture strength and wear resistance of glass-ionomer restoratives

Abstract

The aim of the present investigation was to investigate the influence of montmorillonite (MMT) clay, both as-found (un-modified calcium montmorillonite (Ca-MMT)) and pre-treated to encourage exfoliation (organically-modified MMT clay 12-amino-dodecanoic acid treated-montmorillonite (ADA-MMT)), on the compressive fracture strength, elastic modulus and in vitro wear resistance of a variety of commercial GI restorative products. Firstly, the MMT clays were added to the powder and liquid constituents of an anhydrous GI restorative (Chemfil Superior) at concentrations ranging from 0.5 to 2.5 wt.% (in 0.5 wt.% increments). Groups of 30 or more cylindrical specimens (6 mm height, 4 mm diameter) were prepared and the mean compressive fracture strength was determined. The in vitro wear resistance was assessed for groups of eight disc-shaped specimens using the OHSU oral wear simulator operating at 20 N abrasion and 90 N attrition forces for 50,000 cycles at a frequency of 1 Hz in the presence of a poppy seed and PMMA bead slurry. The addition of Ca-MMT clay to Chemfil Superior resulted in a steady decrease in the mean compressive fracture strength and in vitro wear resistance with increasing Ca- MMT clay concentration. Adding ADA-MMT clay to Chemfil Superior (at concentrations ranging from 0.25 to 1.25 wt.%) resulted in significant increases in the mean compressive fracture strength and in vitro wear resistance compared with the control. As a result, ADA-MMT clay was also added (at concentrations of 0.5 and 1.0 wt.%) to the powder and liquid constituents of a variety of conventional GI restoratives consisting of a separate glass containing powder and a polyalkenoic acid liquid solution. In general the addition of ADA-MMT clay to the powder and liquid constituents of the conventional GI restoratives did not increase the mean compressive