Concentration of solutions for electrolytically etching Rexillium III

An aqueous solution of 10% H₂SO₄ is recommended for electrolytically etching Rexillium III. The reports do not specify whether this solution is 10% by weight or by volume. Instructions for preparing the etching solution produce approximately an 8% by volume solution. This study evaluated the tensile bond strengths of composite to metal etched by 1) a 10 weight % solution, 2) a 10 weight % solution with 10 volume % methanol added, and 3) an 8 volume % solution with 10 volume % methanol added. The 8 volume % solution provided significantly higher bond strengths (p≤.0003) than either of the two 10 weight % solutions. The average tensile bond strength for the 8 volume % solution (39.2 MPa) was nearly double that of the average bond strength of the 10 weight % solutions (20.6 MPa and 21.1 MPa). There was a large variation in bond strength within all the groups. An important observation is that all samples etched with the 8 volume % solution had bond strengths greater than the reported composite to enamel bond strengths (8-14 MPa). One fifth of the samples etched with each of the 10 weight % solutions fell in or below this level. This could result in significantly more clinical failures. The formulation of etching solutions has a significant effect on the bond strength and should be carefully specified in each report in order to evaluate results.