Evaluation of the effect of Poly Vinyl Pyrrolidone addition on the shear bond strength of acrylic resin artificial teeth to heat cured acrylic resin denture base material

Abstract

Background: The most common materials used for fabrication of denture bases are poly methyl methacrylate (PMMA). Fracture or debonding of plastic teeth from denture base are common clinical problems which are facing both the patient and the dentist. The aim of this study is to evaluate and compare the shear bond strength of acrylic resin artificial teeth treated by different chemical surface treatments (solvents like acetone & thinner) to the experimental prepared material and to the control material before and after thermocycling. Materials and methods: Preparation of modified heat cured denture base acrylic resin was carried out by preparing of (PMMA) (80%) and poly vinyl pyrrolidone (PVP) (20%) and the liquid part composed of methyl methacrylate (MMA) monomer. Control: poly methyl methacrylate (PMMA) + methyl methacrylate ( MMA ) as control group ( 2.5 : 1 ) by weight (1). Experimental: PMMA (80% ) + PVP ( 20% ) + MMA as experimental group ( 2.5 : 1 ) by weight. Sixty artificial acrylic teeth were prepared and cured by control and experimental denture base acrylic resin, then teeth were divided into three groups and treated with different surface treatment; first group received no further treatment (control), second group treated with acetone and third group treated with thinner. The denture teeth were flasked and wax was eliminated with running hot water. Denture resin was packed and cured according to manufacturer's instructions and specimens were deflasked upon the completion of resin processing. Then half of specimens from all surface treatments were tested by using Instron machine and subjected to shear force until failure. The other half of specimens which also include the surface treatments groups were thermocycled. Teeth surfaces after treatment and fracture sites were examined and photographed visually and under reflecting light microscope. Results: The results showed that all surface treatments produced significantly high improvement in shear bond strength (SBS). Control group had shown significantly lower (SBS) than experimental group bonded to artificial acrylic teeth. On the other hand, experimental denture base resin bonded to artificial acrylic teeth were affected more significantly by thermocycling than the same teeth bonded to control denture base resin. Results indicated that thinner treatment for acrylic teeth is recommended prior to denture base processing. Conclusion: higher SBS of artificial acrylic teeth bonded to experimental denture bases rather than to control denture bases.