Porosity reduction and its associated effect on the diametral tensile strength of activated acrylic resins.

Each acrylic resin tested is basic to the armamentarium of the clinical dentist. From this study it is apparent that there exist several possible mechanisms that will aid in the reduction of porosity and subsequently enhance the tensile strength properties of chemically activated acrylic resins. With the manufacturer's recommended powder to liquid ratio mixtures, indications are that only small increases in curing pressure (approximately 0.68 MPa) are required to substantially enhance strength levels of the test materials. Therefore, when cured under conditions that avoid residual stress buildup, the small increases in pressure attainable by modified pressurization devices may indeed be of benefit in reducing porosity and enhancing the tensile strength of the acrylic resins. Similar increases in strength appear possible with various combinations of powder particle sizes and powder/liquid ratios used in an effort to reduce the monomer concentration in clinically desirable acrylic mixtures. It is important to realize that alteration of powder/liquid ratio and powder particle size mixtures offers a method of reducing porosity without the addition of external pressure. However, at this time it is not recommended that these sophisticated alterations of the basic resin components be performed by the clinician.