Dimensional stability of injection and conventional processing of denture base acrylic resin

Abstract

C omplete denture fabrication is fraught with both extrinsic and intrinsic potential error. The greater part of this error can be controlled with careful clinical and laboratory technique. ’ Woelfel and Paffenbarge9 outlined the inaccuracies inherent to the use of poly(methy1 methacrylate) as a denture base material. Dimensional change during processing is one such source of error. The processing shrinkage of poly(methy1 methacrylate) resin is well documented.*” Injection processing of poly(methy1 methacrylate) denture bases was introduced by Pryor in an attempt to reduce processing shrinkage. More recently a continuous-pressure injection technique has been developed (SR-Ivocap, Ivoclar AG, Schaan, Liechtenstein). As discussed by Schmidt9 the process claims to deliver reduced processing error and increased resin density through layered curing of the resin and no processing flash. Trituration of the liquidpowder system is mechanically performed in prepackaged capsules in an attempt to produce a more even mix resulting in a homogeneous denture base. The mixed resin is injected into the flask under continuous pressure during the processing.” This study determined the dimensional changes of heat-cured poly(methy1 methacrylate) resin processed by the injection processing system compared with that processed by a conventional compression packing technique.