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