Evaluation the Effect of Fibers Addition on Mechanical Properties of Flexible Acrylic Resin

Abstract

Background: In chemistry the development of polymer has produced another material to poly methyl methacrylate such as epoxy resins, polyamides (nylon), acetyl resins -----etc. All these resins are suited for thermoplastic processing. Polyamide materials are more flexible than the commonly used polymethylmethacrylate. The flexibility of polyamide allows partial dentures to be pressed in one piece including clasps. Glass fibers are the most widely used reinforcing materials forming about 90 % of the reinforcement in resins. The addition of fibers to provisional restorative resin increases tensile strength, fracture toughness and surface hardness. Objective of the study: An evaluation of the surface roughness, modulus of elasticity and tensile strength improvement of flexible denture bases after adding of glass fibers and altering in powder – monomer ratio. Material and Methods: Eighty samples of flexible acrylic were made and divided into two main groups according to the type of test to be used. Forty samples for surface roughness and forty samples for tensile strength and (modulus of elasticity). Each group is divided into four subgroups according to fibers addition and to the alteration in powder-liquid ratio as follows: group (A) consists of (10 specimens) without the addition of glass fibers and with (3:1) powder- monomer ratio. Group (B) consists of (10 specimens) with addition of glass fibers and with (3:1) powder- monomer ratio, group (C) consists of (10 specimens) without addition of glass fibers and with (2.5:1) powder- monomer ratio and group (D) consists of (10 specimens) with glass fibers and with (2.5:1) powder- monomer ratio. The tensile strength and modulus of elasticity were determined by Instron testing machine at cross speed of 0.5mm/min. The T.R 200 device was used to indicate the values of surface roughness specimens before and after finishing and polishing. Results: In the present study, ANOVA test showed a significant difference at (P<0.05) between all the groups of tensile strength test.Least significant difference( LSD) test showed a non-significant difference at (P>0.05) between most of the tested groups except the groups of 3:1 powder–monomer ratio with and without fibers addition and groups of 3:1 ratio without fibers addition in comparison with the groups of 2.5:1 ratio with fibers addition which showed highly significant . The modulus of elasticity revealed a non-significant difference between all the tested groups at (P>0.05). While there were highly significant difference at (p<0.01) between groups of surface roughness test before and after polishing, except the group of 2.5:1 ratio with and without fibers addition which showed a non-significant difference at (P>0.05.). Conclusion: Conclusion was derived that fibers addition significantly affects tensile strength. The modulus of elasticity was not significantly affected by fibers addition or by powder-monomer ratio. Regarding surface roughness, it was improved after fibers addition and alteration in powder-liquid ratio.