Comparison of microhardness, surface roughness and water sorption of conventional pressure-packed vertex acrylic resins and injection vertex acrylic resins

Abstract

Background and objective: One of the most widly used materials in prosthetic dentistry is poly methyl methacrylate, a material which has been used for denture base manufacturing , one of its main defects is the polymerization shrinkage that frequently leads in time consuming clinical problems. Several ways have been suggested to solve this problem; among them is "injection molding method". The properties such as microhardness, surface roughness and water sorption affect the quality of a prosthesis. The objective of this study was to investigate and compare microhardness, surface roughness and water sorption of a Conventional Pressure-Packed Acrylic Resin with a Injection Acrylic Resin. Materials and methods: Two groups of PMMA (n=10), consisting of one group of conventional pressure-packed PMMA (Vertex,Vertex Dental,Zeist,Netherlands) was used for the conventional pressure-packed technique and one group of injection molded PMMA samples (Vertex Castavaria,Vertex Dental,Zeist,Netherlands) was used for injection molding technique. For each test 20 specimens(10 specimens from each materials) was fabricated. Hardness testing was conducted using a Vickers hardness tester. The surface roughness test was performed by a profilometer ; And he water sorption test was performed by a digital scale. The independent sample t-test was used for comparing microhardness, surface roughness and water sorption between two groups. Data was analyzed using SPSS17 software. The significance level is considered to be P<0.05. Findings: The mean microhardness values of conventional pressure-packed vertex acrylic resin and injection vertex acrylic resin were 11.86±1.28 and 25.18±4.30 kg/m2 respevtively. Also the mean surface roughness values of conventional pressure-packed vertex acrylic resin and injection vertex acrylic resin were7.58±2.69 and 4.90±1.12μm. The mean water sorption values of conventional pressure-packed vertex acrylic resin and injection vertex acrylic resin were 25.00±2.54 and 21.29±2.68 μgr/mm3. The results of independent T test showed that the microhardness of injection vertex acrylic resin samples was significantly higher than that of conventional pressure-packed vertex acrylic resin samples (p value<0.05). Also the surface roughness and water sorption of injection vertex acrylic resin samples were significantly lower than those of conventional pressure-packed vertex acrylic resin samples (p value<0.05). Conclusion: Processing acrylic resin with injection molding technique can increase the microhardness of denture bases and also can decrease the surface roughness and water sorption of denture bases. Therefore molding denturebase with this method can improve the quality and durability of denture.