Effect of different metal surface treatments and thermocycling on shear bond strength of heat cure and light cure at Co/Cr and Ni/Cr interface

Abstract

Background Optimum bond strength at the metal – resin interface of prosthesis is essential for the success of thatprosthesis. The junction between metal alloy and acrylic resin is an area of clinical concern .Failure of a R.P.D. maybe linked to this interface. The main objective of this study were to determine the effect of different metal surfacetreatment and thermocycling on the shear bond strength of Co/Cr alloy and Ni/Cr alloy to heat cure acrylic resinand light cure acrylic resin.Materials and methods: 120 metal samples were prepared, 60 Co/Cr samples and 60 Ni/Cr of square flat plate (30mm x 30mm x 2 mm) that incorporated a central area (8mmx 12mm) of a large retentive mesh to simulate dentureframework. The samples were cleaned, finished and electropolished. Sixty samples of each type of metals weredivided into two groups according to the type of acrylic resin received each one 30 samples (A and group C) forheat cure, B and group D for light cure) which were furtherly subdivided according to the type of surface treatmentinto 3 subgroups each one 10 samples(A1 ,B1 ,C1and D1 )for no surface treatment, no thermocycling as a controlgroup (A2, B2 ,C2 and D2 )for Metal Prime II application with thermocycling (A3, B3 ,C3 and D3) for combination ofAir Abrasion and Metal Primer II application with thermocycling. The acrylic block were then prepared as arectangular block(12mm length ,8 mm width ,6 mm high )that was placed on a central area of metal plates, theacrylic was fabricated in the same conventional way of denture construction. All the sample were mounted onspecially test fixture that would hold them rigid at a 90-degree angle from the horizontal plane of the crosshead ofthe Instron machine .A tangent shear force was created by applying vertical load to the specimen .All of thespecimen were tested with Instron machine using stainless steel chisel shaped road at a constant crosshead speed of5 mm min until failure of the bond occurred The specimen were stressed to failure .The force of bond failure wasrecorded in Newton, which was divide by the surface of the bonded area (96 mm2 )to obtain the shear bondstrength calculated in Mpa.Result: The results showed that the subgroup that received no surface treatment and without thermocycling for bothtwo type of resins heat cure and light cure (A1, B1, C1and D1) had the highest shear bond values, followed bysubgroups that received Air Abrasion + Metal Primer II surface treatments and thermocycling (A3, B3, C3,D3).Subgroups that received Metal Primer II alone (A2, B2, C2 and D2) showed the least shear bond value than theother subgroups.Conclusion: All metal samples of Co/Cr and Ni/Cr with heat cure acrylic resin showed higher SBS mean values thanthat light cure resin whether with surface treatment and thermocycling or without thermocycling concluded higherbinding of heat cure acrylic resin with the metal surface