The effect of the disc support system on biaxial tensile strength of a glass ionomer cement

Abstract

Objective: This was to examine how varying the type of support, from a complete ring to a series of point supports, affected the biaxial tensile strength of one glass ionomer cement.

Method: Three support diameters from 11.5 to 28.6 mm were achieved using 3 mm ball bearings as point supports equidistantly spaced around the diameter. From 3-30 point supports were used depending on diameter. At the maximum number of point supports for each diameter the support points were 3 mm apart. After 24h storage in water at 37 degrees C the biaxial tensile strength of 1 mm thick glass ionomer restorative cement discs was measured using a loading rate of 1 mm min(-1). The load at break was converted to biaxial tensile strength using the Timoschenko and Woinowsky-Kreiger equation using a Poisson's ratio value of 0.30. The mean strength of six specimens tested per support regime was calculated.

Results: Comparison with the mean result obtained from using a continuous knife-edge support showed there to be no significant difference (unpaired t-test) between the different support systems except in two cases, both being when a four-point support was used. Neither the support diameter nor the number of point supports was crucial.

Significance: Results from studies where different systems have been used to support brittle cement discs may be compared.