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Mechanical Properties and DIC Analyses of CAD/CAM Materials J Clin Exp Dent-AHEAD OF PRINT Properties of CAD/CAM materials Journal section: Prosthetic Dentistry doi:10.4317/jced.53014 Publication Types: Research http://dx.doi.org/10.4317/jced.53014 Mechanical properties and DIC analyses of CAD/CAM materials Thiago Porto 1,2, Renato Roperto 2, Anna Akkus 3, Ozan Akkus 3, Sizenando Porto-Neto 1, Sorin Teich 4, Lisa Lang 4, Edson Campos 1 1 DDS, MSc, PhD, Department of Restorative Dentistry, Faculty of Dentistry, Sao Paulo State University, Araraquara, SP–Brazil 2 DDS, MSc, PhD, Department of Comprehensive Care, School of Dental Medicine, Case Western Reserve University, Cleveland, OH – USA 3 PhD, Department of Comprehensive Care, School of Dental Medicine, Case Western Reserve University, Cleveland, OH–USA 4 DDS, MBA, Department of Comprehensive Care, School of Dental Medicine, Case Western Reserve University, Cleveland, OH–USA Correspondence: Case Western Reserve University, School of Dental Medicine 2124 Cornell RD, 44106, Cleveland OH, USA [email protected] Received: 04/02/2016 Please cite this article in press as: Porto T, Roperto R, Akkus A, Akkus O, Accepted: 17/02/2016 Porto-Neto S, Teich S, Lang L, Campos E. Mechanical properties and DIC analyses of CAD/CAM materials. J Clin Exp Dent. (2016), doi:10.4317/ jced.53014 Abstract Background: This study compared two well-knowncomputer-aided-design/computer-aided-manufactured (CAD/ CAM) blocks (Paradigm MZ100 [3M ESPE] and Vitablocs Mark II [Vita] in terms of fracture toughness (Kic), index of brittleness (BI) and stress/strain distributions. Material and Methods: Three-point bending test was used to calculate the fracture toughness, and the relationship between the Kic and the Vickers hardness was used to calculate the index of brittleness. Additionally, digital image correlation (DIC) was used to analyze the stress/strain distributionon both materials. Results: The values for fracture toughness obtained under three-point bending were 1.87Pa√m (±0.69) for Pa- radigm MZ100 and 1.18Pa√m (±0.17) for Vitablocs Mark II. For the index of brittleness, the values for Para- digm and Vitablocs were 73.13μm-1/2(±30.72) and 550.22μm-1/2 (±82.46). One-way ANOVA was performed to find differences(α=0.05) and detected deviation between the stress/strain distributions on both materials. Conclusions: Both CAD/CAM materialstested presented similar fracture toughness, but, different strain/stress dis- tributions. Both materials may perform similarly when used in CAD/CAM restorations. Key words: Ceramic, CAD/CAM, hybrid materials, composite resin, fracture toughness. Introduction perties have been made during the past few years, some The progress of dental technology has lead develop- concerns still remain, such as fracture susceptibility to ment of strong materials, such as ceramics, for indirect thermal and mechanical loading, and marginal misfit restorations. However, structural components of these (1-3). Since the introduction of the first dental ceramic materials have one obvious weakness: they tend to be materials in the 19th century (4), different manufacturing brittle. Ceramics are brittle materials and susceptible to techniques have been used in their fabrication. The tradi- chipping. Although improvements in mechanical pro- tional ceramic lost wax technique caused microcracks at E1 J Clin Exp Dent-AHEAD OF PRINT Properties of CAD/CAM materials the intaglio surface during the cooling phase. This is the of feldsphatic ceramic uniformly embedded into a glassy reason why the technique was replaced for the porcelain- matrix (19). Table 1 shows the mechanical properties of fused-to-metal (PFM) technique. Currently, metal-free both materials. ceramic restorations are being used because of advances Six composite and six ceramic CAD/CAM blocks in mechanical properties such as better material strength (17.5mm x 14.8mm x 12mm) were first serially cut in and better aesthetics (5,6). rectangles (14.8mm x 12mm x 3mm) using a slow-speed Ceramics is by far the most common material used to fa- saw (Isomet 1000; Buehler, Lake Bluff, USA), then cut bricate CAD/CAM blocks (7), however, due to ceramic again to create the beam size samples (14mm x 3.5mm x inherent characteristics as brittleness, low tensile streng- 3mm). In order to smooth out rough corners, beams were th, and low fracture toughness (8-10), in recent years polished with a finishing and polishing machine (Eco- new composite resin-based blocks have been developed met 6, Buehler, Lake Bluff, IL, USA) using a sequence (11,12). Resin composite CAD/CAM blocks seem to of sandpapers #240, #400, #800 and #1200. Final beam have on advantage over ceramic CAD/CAM blocks in shape was confirmed with a digital calipers and had the terms of resilience and less abrasion on the antagonist dimensions of 14mm x 3mm x 2.5mm. enamel, helping to preserve overall balance of the den- The beam samples were polished,thenanalyzed by mi- tition, and can also be easily adjusted or repaired (13). croscopy (Optical microscopy: 35x magnification, In contrast, all ceramic restorations have a high clinical Nikon SMZ445, Melville, NY, USA) so every sample failure rate in posterior sites (14,15), and are frequently with any chipping defect was disposed of. After the se- replaced because of bulk fracture (2,16). Crack propaga- lection procedure, beams were centrally positioned in tion of ceramic materials during mechanical deformation circular plastic matrix molds of 16mm diameter and normally occurs differently from plastic materials (17). 10mm height, filled with microstoneplaster (Golden However,CAD/CAM materials have not been fully in- Type 3, Whip Mix, Louisville, KY, USA) and left for vestigated in terms of mechanical properties. The aim 15 min until it had set. In order to make the V-notch, of this study was to compare the fracture toughness of specimens were positioned in the device by using spe- CAD/CAM composite versus ceramic materials and cial clips. The device had three axes: X-axis (horizontal) to analyze the stress distribution through Digital Ima- was where the ensemble was fixed with the clips; Y-axis ge Correlation (DIC) around the stress area. The null (vertical) was connected a hand-piece (Henry Schein, hypothesis is that there is no difference between fracture Melville, NY, USA) with a diamond point 862-016FC toughness, index of brittleness of both materials and no (SS White, New Jersey, USA) needle shape. Finally, the difference around the stress/strain concentration. V-notch was created using the tip of the diamond point along the Z-axis (width) with an approximate depth of Material and Methods 1.0mm (Fig. 1); further specimens were cleaned using -Materials Selection deionized water in a sonic bath (Boekel Analog Model In this study, composite CAD/CAM block (Paradigm 139400, PA, USA) for 30min. MZ100 – 3M ESPE, St. Paul, MN, USA) and feldspa- -Fracture toughness (three-point bending test) and index thicceramic CAD/CAM block (Vitablocs Mark II –Vita of brittleness Zahnfabrik, Essen, Germany) were used. The Paradigm The three-point bending test to calculate the fracture MZ100 blocks are manufactured with the same 3M™ toughness was made following the methods given by Z100™ composite resin restorative material. It has ASTM C1421-10 ‘Standard test methods for determina- a highly polymeric matrix reinforced with 85 wt% of tion of fracture toughness of advanced ceramics at am- ultrafine (0.6μm) zirconia-silica ceramic particles that bient temperature’ (20). With the V-notch facing down, when synthesized, results in a resilient structure of nano- beam samples were positioned following the schematic crystallinezirconia (18). In contrast, the CAD/CAM Vi- in figure 1a. With a span (S0) of 12mm the three-pointing tablocs Mark II is manufactured with fine-particle (4μm) bend test was performed in a Universal testing machine Table 1. Mechanical properties and filler components. Material Manufacturer Flexural Strength Young’s Modulus Filler content Paradigm MZ 100 3M ESPE 150 Mpa 8 Gpa Ultrafine zirconia-silica ceramic particles Vitablocs Mark II Vita Zahnfabrik 113 Mpa 65 Gpa Fine feldspar ceramic particle E2 J Clin Exp Dent-AHEAD OF PRINT Properties of CAD/CAM materials Fig. 5. (a) The first photographbefore the three-point bendingthe green area without strain/stress concentration is visible. (b) On the second when the test starts some strain/stress concentration around the tip of the crack is visible. (c) With more pressure on the specimen Fig. 1. a) Schematic of beam samples positioned under three-point- strain/stress concentration in front of the tip increases. (d) The last bending test. b) Schematic of DIC camera lenses focused on beam photograph before failure show clearly the increase of the red area samples. around the tip of the crack, moreover there is a big area of stress distribution at the bottom of the sample. (Test Resources, Shakopee, MN, USA) at a crosshead speed of 0.5mm/min until failure. The fracture tough- ness (Kic) of each material was calculated following equations (1) and (2): (Figs. 2,3) -6 3/2 1/2 3/2 Kic = g[PmaxS010 / BW ] [3(a / W) / 2(1-a / W) Fig. 2. Equation 1. g = [1.99 – (a / W)(1 – a / W){2.15 – 3.93 (a / W) + 2.7 (a / W)2}] / [1 + 2 (a / W)] Fig. 3. Equation 2. In equation (1) Kic is the fracture toughness, while g is a function of the ratio a/W, Pmax is the maximum load Fig. 6. (a) The first photograph before the three-point bending the (N) at the moment of the fracture, B (m) is the sample green area without strain/stress concentration is visible.(b) At the side to side parallel to the support, W (m) is sample top moment of the test starts, at the top of the crack tip a stress/strain to bottom perpendicular to the support, and a (m) is dep- concentration is seeable.
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