In vitro evaluation of color, hardness and surface roughness of a heat-polymerized acrylic resin after immersion in Ricinus communis solution

• Grant number: 12/19017-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: October 01, 2013
• End date: September 30, 2014
• Field of knowledge: Health Sciences - Dentistry - Dental Materials
• Principal Investigator: Helena de Freitas Oliveira Paranhos
• Grantee: Isabela Maria Dal Rovere
• Host Institution: Faculdade de Odontologia de Ribeirão Preto (FORP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil

Abstract

The hygiene methods employed by denture wearers should be effective and not harmful to the constituent materials of prosthetic devices. The objective of this study is to evaluate the adverse effects caused by solutions based on castor oil (Ricinus communis - 3,3%, 5% e 10%) on a heat-polymerized acrylic resin. To obtain the specimens, circular metallic matrices (16 X 6mm) will be invested in metallic flasks (type III dental stone and condensation silicone) and the acrylic resin (Lucitone 550) will be manipulated, packed, pressed into the mold, and polymerized according to the manufacturer's instructions. After divesting of the specimens, the excess will be eliminated ( micromotor and cutter) and both flat sides of each specimen will be polished (sandpaper - 180, 320, 400, 600, 1200). In one of the flat faces of each specimen, polishing was performed with cloth for polishing and white of Spain in the horizontal lathe spindle. The specimens (n=100) will be distributed into following groups (n = 20): C1 - no immersion; C2 - Immersion in distilled water; EX1: Immersion in 3,3% Ricinus communis solution; EX2 - Immersion in 10% Ricinus communis solution; EX3 - Immersion in 15% Ricinus communis solution. The immersions will be performed for 15 (T15) and 183 (T183) days, simulating three (immersion's routine of 20 minutes per day) and one and a half (immersion's routine of 08 hours per day) years of use, respectively. The specimens were evaluated for color, hardness, and surface roughness at the baseline and after the immersions. The color alterations will be measured with a colorimeter (Color Guide 45/0, BYK), with a standardized lighting D65, observation angle of 10 °, and the light source with visible spectrum (400 to 700nm). The measurement geometry was 45/0. The color measurements will be obtained with the use of CIELab color system, with the calculation of the total color alteration (”E) from the following equation: E* = [(L*)² + (a*)² + (b*)²]½. To relate the color alterations (E) to the clinical environment, data will be quantified by the National Bureau of Standards (NBS) units through the formula: NBS units = E * 0.92. The Knoop hardness changes will be measured using a microhardness tester (Microhardness Tester Shimadzu) with a load of 25g for 5 seconds, by obtaining the arithmetic mean from 08 measurements over the surfaces of the specimens. The surface roughness changes will be quantitatively evaluated with a dosimeter (Surftest SJ-201P, Mitutoyo Corporation) by performing three readings (4.0 mm in length and "cut off" value of 0.8 mm with the speed of 0.5 mm/s) in each specimen and calculating the arithmetic mean (µm). The qualitative evaluation will be performed with a scanning electron microscope (JSM-6610LV Scanning Electron Microscope). The data will be statistically analyzed in software (SPSS Statistics 17.0). (AU)