الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The fabrication of optimum restoration is dependent on the clinicians skilles in selection of the type of the restoration and restorative material which is required for the patient.
The material most commonly employed in the construction of dentures is polymethyl methacrylate resin,but, it is still far from the requirements of ideal denture base materials. Physico-mechanical properties of acrylic resin are still a cause for concern in order to overcome the high incidence of material fracture, lack of dimensional stability and improper patient satisfaction. To overcome these disadvantages a new types of plastic materials have been introduced one of them is thermoplastic acrylic resin(vertex thermosens). Thermosens is formed by injection mold technique with preheating of the cylinder of the thermoject machine to 290oC for 18 min using a pressure of 6.5 bar.
This study was conducted to evaluate thermoplastic acrylic resin material (thermosens) and compare with conventional heat cure acrylic resin denture base materials as regards the followings:
1. Impact strength.
2. Flexure strength.
3. Warpage.
A total (70)Specimens that were prepared according to the international standers specifications for each test (28 specimens for impact , 28 for flexural and 14specimens for warpage). The specimens were divided into two groups as following:
group (A) (control group): Specimens of conventional heat cure acrylic resin denture base material (PMMA) (14 specimens for impact , 14 for flexural and 7specimens for warpage).
group (B)(study group): Specimens of thermoplastic resin material (Vertex TM Thermosens) (14 specimens for impact, 14 for flexural and 7specimens for warpage).
Each group was divided into 2 subgroups:
Subgroup I: 7 specimens for each test were thermocycled to examine the effects of temperature variations.
Subgroup II: 7 specimens were stored in the incubator at 37 0C for 24 hours.
N.B: For the warpage test the same number of specimens (14) after stored in distilled water and examined by stereomicroscope would be thermocycling in thermocycling machine because the specimens were not destructed.
1. Impact strength test
A total of 28 specimens were prepared according to the method described in the ISO standard (ISo179-2:2010) Bar shaped specimens75 mm length,10mm wide and 4mm thick ,notched at the center.
14 specimens were thermocycled in the thermocycling machine for 500 cycles between 50 C and 550C indistilled water. The remaining of specimens (14specimens) were stored in distilled water at 370C for 24 hours as a state Known as thermocycle zero. Measurement were conducted using a charpey impact testerand the strength was calculated according to standard equation.
2. Flexure strength test
Atotal of 28 specimens were prepared with 65mm length,10mm width and 2.5 mm thickness according the ADA specification No.12.
14 specimens were thermocycled in the thermocycling machine for 500 cycles between 50C and 550C in distilled water. The remaining of specimens (14 specimens) were stored in distilled water at 370C for 24 hours as a state Known as thermocycle zero.
Each specimen were mounted on an universal testing machine .Three point bending test will be carried out with a distance of 50mm between the two supporting points and a crosshead speed of 0.5mm/min.
3. Warpage test
7 identical plate specimens from each group) atotal of 14 specimens) were prepared for testing the adaptation accuracy of acrylic resin on the stone cast at the posterior palatal seal area.
14 specimens were stored in distilled water at 37oC for 24 hours as state of thermocycle zero. As the warpage test is non destructive,so the same specimens were thermocyled in thermocycling machine.
The measurment carried out by using stero-microscope:
1. Immediately after processing, deflasking and finishing of plates.
2. After stored in distilled water at 37 0C in the incubator for 24 hours.
3. After thermocycling the specimens for 500 cycles between 550C and 50C.