Can poly(acrylic) acid molecular weight mixtures improve the compressive fracture strength and elastic modulus of a glass-ionomer restorative?

Abstract

Objectives To optimize the compressive fracture strength ( σ) and elastic modulus ( E) of a glass-ionomer (GI) restorative using poly(acrylic) acid (PAA) weight average molecular weight ( M w ) mixtures. Methods 174 PAA solutions were prepared (four control PAA M w s at three PAA concentrations (25, 35 and 45%) ( n = 12) and six M w mixtures (Groups A–F at nine blend ratios and three PAA concentrations ( n = 162))). The viscosity ( η) of each PAA solution was determined using a digital viscometer. The PAA solutions were hand-mixed with a commercial GI restorative powder (Ionofil Molar; Voco, Cuxhaven, Germany) and σ and E were determined using cylindrical (6 mm height, 4 mm diameter) specimens ( n = 20) at 24 h. Data were analyzed using analyses of variance (ANOVA) (three-, two- and one-way) and regression analyses at p < 0.05. Results The three- and two-way ANOVAs highlighted significant effects of M w mixture, blend ratio and PAA concentration (all p < 0.0001) on the η, σ and E data. Regression analyses showed significant increases in η, σ and E ( p < 0.0001) with increasing M w from Groups A to F. There was no significant effect of blend ratio on the σ data for Groups A ( p = 0.178), D ( p = 0.747) and F ( p = 0.107) and on the E data ( p > 0.083). Significance The current approach to improving the mechanical properties of GI restoratives using PAA M w mixtures is encouraging, however, further manipulation of the GI restorative system by optimizing PAA M w mixtures, blend ratios and PAA concentrations is required to elicit further improvements in σ and E without impacting upon the η of the PAA solution.