Fracture strength of denture base resins is of great concern and many approaches have been made to improve the fracture resistance of acrylic resin dentures by strengthening them. Purpose of the study was to assess the effect of a Novel pre-impregnated glass fiber reinforcement system and nylon fiber reinforcement on the flexural strength of conventional heat-polymerized poly(methylmethacrylate) [PMMA] denture resin under dry and wet storage conditions. Forty specimens of standard dimensions were prepared for each of the four experimental groups; unreinforced conventional acrylic resin and the same reinforced with unidirectional Stick (S) glass fibers, woven Stick Net (SN) glass fibers and nylon fibers. Each group was further subdivided into two groups of 20 specimens each on the basis of storage conditions (dry and wet). All 160 specimens were then subjected to a 3-point bending test and flexural strength was calculated. Statistical analysis was carried out using student t test and 1-way analysis of variance (ANOVA). Stick and Stick Net glass fiber reinforcements enhanced the flexural strength of conventional heat-cured PMMA denture resin. Specimens reinforced with Stick glass fibers exhibited highest flexural strength followed by those reinforced with Stick Net glass fibers. Nylon fiber reinforcement decreased the flexural strength of acrylic resin. All the specimens in the four groups stored under wet conditions showed decrease in flexural strength in comparison to those stored in dry conditions. The reinforcement of denture base resin with pre-impregnated glass fibers may be a useful means of strengthening denture bases. Use of nylon as a reinforcement fiber is not desirable as it decreased the flexural strength of acrylic resin.

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To determine the effect of resin based sealer on retention of casting cemented with three different luting agents. 55 extracted molar teeth were prepared with a flat occlusal surface, 20° taper and 4 mm axial height. The axial surface of each specimen was determined. The specimen were then distributed into five groups based on decreasing surface area, so each cementation group contained 11 specimens with similar mean axial surface area. A two-step, single bottle universal adhesive system (One-Step-Resinomer, Bisco) was used to seal dentin after the tooth preparation. Sealer was not used on the control specimens except for the modified-resin cement (Resinomer, Bisco) specimens that required use of adhesive with cementation. Using ceramometal (Wirobond(®), BEGO), a casting was produced for each specimen and cemented with either zinc phosphate (Harvard), glass ionomer (Vivaglass) or modified resin cement (Resinomer) with single bottle adhesive. All the castings were cemented with a force of 20 kg. Castings were thermal cycled at 5 and 55 °C for 2,500 cycles and were then removed along the path of insertion using a universal testing machine at 0.5 mm/min. A single-factor ANOVA was used with a = 0.05. The nature of failure was also recorded. The mean stress removal for non sealed zinc phosphate, sealed zinc phosphate, non sealed glass ionomer, sealed glass ionomer and modified resin cement was found to be 3.56, 1.92, 2.40, 4.26, 6.95 MPa respectively. Zinc phosphate cement remained principally on the castings when the tooth surface was treated with the sealer and was found on both the tooth and the casting when the sealer was not used. Fracture of root before dislodgement was seen in 9 of 11 specimens with modified resin cement. Resin sealer decreases the retention of the castings when used with zinc phosphate and increases it when used with glass ionomer cement. The highest mean dislodgement force was measured with modified resin cement.

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