The influence of resin coating on the shear punch strength of a high strength auto-cure glass ionomer

Abstract

Objectives. The aim of this study is to examine the influence of early water contact on the shear punch strength of a modern, high strength, auto-cure glass ionomer (Fuji IX GP). Methods. Specimens, 8.0 mm in diameter and approximately 1.25 mm thick, were prepared in metal washers, and allowed to remain covered by polyester strips for 7 min, to ensure completion of the initial set. A minimum of 32 specimens was prepared for each set of experiments and they were divided into two equal groups. Following removal of the strips, the surfaces of the specimens in Group 1 were immediately coated on both sides with Fuji Coat LC and light cured for 10 s. In Group 2 the specimens were left uncoated. All specimens were then placed in distilled water at 37 °C, and stored for periods of 24 h, 1, 2, 5, or 8 weeks. The strength of the specimens was measured at each time interval in the shear mode by a punch test in a universal testing machine. Results. The mean strength of the coated specimens in Group 1, which had been protected against exposure to water, increased significantly on ageing from 67.1 (24 h) to 78.0 MPa (1 week), with no further significant change in strength. The mean strength of the specimens in Group 2 increased significantly from 75.7 (24 h) to 83.3 (1 week) and 91.9 MPa (2 weeks), with no further significant change in strength. Uncoated specimens were stronger at all points of time. The difference was statistically significant at 24 h, 2, 5, and 8 weeks ( P<0.05), but not at 1 week ( P=0.061). Significance. The results suggest that, contrary to the usual instructions for placement of glass ionomer, early access to water will positively influence the shear punch strength of Fuji IX GP.