DENTAL MATERIALS
Original Article
TOUGHNESS MEASUREMENT IN DIRECT RESIN COMPOSITES USING QUANTITATIVE FRACTOGRAPHIC ANALYSIS
Brendan M. Angus 1a *, John J. Mecholsky Jr. 1b, Nader Abdulhameed 2c
1
Materials Science and Engineering Department, College of Engineering, University of Florida, Gainesville FL, USA
2
College of Dentistry, University of Florida, Gainesville FL, USA a
BS, Research Assistant b
PhD, Professor and Associate Chair of the Materials Science and Engineering Department c
BDS, MS, PhD Student, Clinical Assistant Professor of Restorative Dental Science
ABSTRACT DOI: 10.25241 / stomaeduj. 2018.5( 1). art. 1
Objective: To outline a procedure to determine the fracture toughness of direct resin composites failing from“ natural” flaws. Methodology: Tensile( hour glass) tests( n = 30) of a conventional hybrid dental composite( Tetric EvoCeram, Ivoclar Vivadent) were fabricated and fractured in uniaxial tension loaded at a crosshead speed of 1 mm / min( ≥ 10 MPa / s). The fracture toughness of the material was then calculated using the stress at failure and measurement of the crack size from fractographic analysis using SEM. Hardness( H) measurements were taken using a Vickers pyramidal diamond indenter. Elastic modulus( E) was calculated from the E / H ratio using a Knoop indenter. Results: The values for fracture toughness found were similar to other Bis-GMA based dental composites 0.5 ± 0.2 MPa. The Vickers Hardness was 509 ± 27 MPa and the Knoop Hardness was 495 ± 14 MPa using 0.5 kg / 30 s, while the elastic modulus was 9.5 ± 1.4 GPa. Conclusion: The differences found in fracture toughness between this study and previous published studies are most likely due to variation in technique and material. Quantitative fractographic analysis offers a different method to evaluate the toughness of direct resin composites. Keywords: fracture toughness, resin composites, fractography, dental materials.
OPEN ACCESS This is an Open Access article under the CC BY-NC 4.0 license.
Peer-Reviewed Article
Citation: Angus BM, Mecholsky Jr JJ, Abdulhameed N. Toughness measurement in direct resin composites using quantitative fractographic analysis. Stoma Edu J. 2018; 5( 1): 18-23.
Academic Editor: Nicoleta Ilie, Dipl. Eng, PhD, Professor, University Hospital, Ludwig- Maximilians-Universität München, Munich, Germany
Received: January 09, 2018 Revised: February 04, 2018 Acccepted: February 22, 2018 Published: February 26, 2018
* Corresponding author: Brendan M. Angus, BS, Research Assistant, Materials Science and Engineering Department, College of Engineering, University of Florida, 1724 Gale Lemerand Dr, Gainesville, FL 32603, USA, Tel:( 561) 927-8584, e-mail: BrendanAngus @ ufl. edu
Copyright: © 2018 the Editorial Council for the Stomatology Edu Journal.
1. Introduction Dental composites are a mixture of polymers and glass particles used in dental restorations to mimic the appearance and performance of teeth and are often used to repair damaged teeth [ 1 ]. Their mechanical properties have improved over the last years and consequently a lot of research has been performed to assess these properties and how they are affected by variations in particle size, polymerization depth, and viscosity [ 2-4 ]. In one longitudinal study it was found that out of 926 restorations investigated, 8 % failed by fracture. This number increases to 18 % when considering the failure of only resin composites restorations [ 5 ]. In a review of prospective studies, it was found that fracture of dental restorations is the most common cause of restoration failures in the first 5 years. [ 6 ] Therefore fracture toughness is a property that has received a lot of attention in dental composites. Fracture toughness is a property that represents the ability of some materials to resist crack propagation [ 7 ]. The load continuously applied in different directions with temperature and humidity variation leads to the progressive degradation and failure of the restoration, mainly due to the crack propagation. The introduction of imperfections in the material during processing, finishing, and / or in service has a high impact on the restoration failure probability. The organic matrix of dental composites has viscoelastic properties, which means that the response to stress will
be time dependent. Under a rapid stressing rate, the stress-strain response will be primarily linearly elastic. Under a slow stressing rate, the stress-strain response will be viscoelastic [ 8 ]. The presence of filler also has a high impact on the mechanical properties [ 9 ]. The greater the amount of fillers, the greater the modulus of elasticity. The combination of the viscous matrix and greater modulus reinforcement leads to a tougher composite [ 10 ]. The main concern with the increase in fracture toughness of the restorative material is maintaining or improving the lifetime service in the oral environment while maintaining the esthetic value. The mechanical properties of dental composites have been highly improved in the last few years [ 11 ]. Even though there are many tests done to correlate in vitro data with the clinical behavior of dental composites, there still is a need to improve these methods to be more realistic and comparable to material behavior while in service [ 12 ]. There are several ways to measure fracture toughness such as the single edge notch test, compact tension test, or double torsion test [ 13 ]. However, the tests for toughness, in almost all cases for resin composites, involve large crack techniques. Resin composites mostly fail from small cracks so it is important to develop small crack techniques to determine fracture toughness. The quantitative fractography method offers the advantage of using flaw sizes of those encountered in service, i. e., small cracks. There are two approaches when using fractographic procedures to determine
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Stoma Edu J. 2018; 5( 1): 18-23. http:// www. stomaeduj. com