International Journal of Dental Sciences and Research
ISSN (Print): 2333-1135 ISSN (Online): 2333-1259 Website: http://www.sciepub.com/journal/ijdsr Editor-in-chief: Marcos Roberto Tovani Palone
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International Journal of Dental Sciences and Research. 2015, 3(3), 64-71
DOI: 10.12691/ijdsr-3-3-6
Open AccessArticle

Effect of Varying Curing Regimes and Powder-liquid Ratios on the Flexural Strength and Surface Porosities of Heat Cure Acrylic: An In-vitro Experiment

Saleha Nisar1, Faisal Moeen2, and Uzma Hasan1

1Student of MPhil Dental Materials, Islamic International Dental College, Riphah University, Islamabad, Pakistan

2Department of Dental Materials, Islamic International Dental College, Riphah University, Islamabad, Pakistan

Pub. Date: May 14, 2015

Cite this paper:
Saleha Nisar, Faisal Moeen and Uzma Hasan. Effect of Varying Curing Regimes and Powder-liquid Ratios on the Flexural Strength and Surface Porosities of Heat Cure Acrylic: An In-vitro Experiment. International Journal of Dental Sciences and Research. 2015; 3(3):64-71. doi: 10.12691/ijdsr-3-3-6

Abstract

Objectives: To evaluate and compare the effect of varying curing regimes and powder-liquid ratios on flexural strength and surface porosities in heat cure acrylic denture base resin. Methodology: Heat cured acrylic specimens (18 x 10 x 3mm) were made according to four powder-liquid ratio groups(2.22, 2.00, 1.80 and student-ratio) and polymerized according to four different curing cycles. Each group consisted of 16 samples with a total of 64 acrylic discs. Curing cycles 1A and 1B initiated curing of specimens at room temperature followed by a terminal boil for 60 and 30 minutes respectively. Cycles 2A and 2B initiated curing at 70°C and 100°C respectively, without any terminal boil. All discs were tested for flexural strength by the ‘short beam’ testing method after immersion in water at 37°C for 28 days. Perimeter of each surfacepore was outlined and area of each pore was measured by a SEM. Total area of surface pores was calculated and expressed in percentage form. Results: Regression analysis indicated a very weak negative correlation (-0.085) between the powder-liquid ratios and the flexural strength values (p =0.252), indicating that variations in powder-liquid ratio does not affect the flexural strength of the acrylic specimens. Placing the curing assembly directly in the water bath at 100°C for 30 minutes showed the lowest over-all flexural strength and highest porosity percent, while immersing the flask in water bath at room temperature, gradually increasing the temperature from 70°C to 100°C and maintaining it for 60 minutes displayed the lowest over-all percent porosity and highest flexural strength values. A weak positive correlation (0.286) between the groups and percent porosity values (p=0.025) indicate a poor effect of powder-liquid ratio on porosities. Conclusions: Flexural strength and percent porosity of acrylic resins are affected more by changes in curing regimes rather than variations in powder-liquid ratio. Increasing the terminal boil period by 30 minutes had a significant effect on reducing percent porosity however did not enhance flexural strength of heat cure acrylic specimens.

Keywords:
Polymethyl-methacrylate (PMMA) polymerization method flexural strength porosity terminal boil

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