Chairside CAD/CAM materials. Part 1: Measurement of elastic constants and microstructural characterization

Abstract

Objective

A deeper understanding of the mechanical behavior of dental restorative materials requires an insight into the materials elastic constants and microstructure. Here we aim to use complementary methodologies to thoroughly characterize chairside CAD/CAM materials and discuss the benefits and limitations of different analytical strategies.

Methods

Eight commercial CAM/CAM materials, ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Elastic constants were evaluated using three methods: Resonant Ultrasound Spectroscopy (RUS), Resonant Beam Technique (RBT) and Ultrasonic Pulse-Echo (PE). The microstructures were characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Raman Spectroscopy and X-ray Diffraction (XRD).

Results

Young’s modulus (E), Shear modulus (G), Bulk modulus (B) and Poisson’s ratio ( ν ) were obtained for each material. E and ν reached values ranging from 10.9 (Lava Ultimate) to 201.4 (e.max ZirCAD) and 0.173 (Empress CAD) to 0.47 (Lava Ultimate), respectively. RUS showed to be the most complex and reliable method, while the PE method the easiest to perform but most unreliable. All dynamic methods have shown limitations in measuring the elastic constants of materials showing high damping behavior (hybrid materials). SEM images, Raman spectra and XRD patterns were made available for each material, showing to be complementary tools in the characterization of their crystal phases.

Significance

Here different methodologies are compared for the measurement of elastic constants and microstructural characterization of CAD/CAM restorative materials. The elastic properties and crystal phases of eight materials are herein fully characterized.

Introduction

Dental aesthetic indirect restoratives, formally supplied mainly as powders (glassy veneers) or pastes (resin composites), now find their way to the user in a ready-to-use pre-processed state, whether in block (cuboid) or blank (disc) geometries. The change in the form in which restorative materials were made available for processing constituted nothing but a natural – and inevitable – step ensuing from the development and establishment of CAD/CAM technology in dentistry. Most materials are now fully produced in an ideal industrial environment, ensuring quality standards hardly achieved under laboratorial/clinical conditions. Their processing diverges from traditional additive techniques, in that blocks and blanks are machined down to the final shape using the subtractive route. This concept allowed the unprecedent application of densely sintered high-strength glass-free polycrystalline ceramics in dentistry, such as zirconium dioxide (ZrO 2 ), aluminum oxide (Al 2 O 3 ) and their composites, whose powders are isostatically pressed in block/blank form and pre-sintered prior to machining (green bodies). Some monolithic glassy products are also offered in a meta-sintered stage to facilitate grinding, and the later piece is subjected to a final crystallization firing, such as with lithium disilicate (LS 2 ) and lithium silicate (LS) glass-ceramics.

Although easier for users, the form in which materials are now delivered pose new challenges for those who test them (i.e., scientists and manufacturers looking for quality control). Especially for small partial- and single-unit restorations, CAD/CAM material blocks come only in diminute blocks of approximately 18 mm × 16 mm × 18 mm 3 (e.g., C16 blocks) or smaller (e.g., C14, I12, I10, etc.). From such block sizes test specimens cannot be produced in common beam geometries recommended by appropriate testing standards for the measurement of typical mechanical properties. To name a few examples, the European standard EN 843-1 for testing the uniaxial flexural strength of ceramics in four-point bending recommends a minimum outer span length of 20 mm , as does ASTM C 1161 for advanced ceramics , a condition that requires specimens of at least 22 mm in length. Many other national and international standards for strength testing of ceramics impose similar restrictions. For polymerizable resin composites the dental standard ISO 4049 advocates 25 mm-long specimens for a 20 mm span length in the three-point bending set-up . Most standards standardizing the test of fracture toughness in bending, such as , also advocate span lengths between 20 and 40 mm. Some controversial exceptions exist, such as ISO 6872 for dental ceramics, allowing spans of 12 mm for three-point bending and 16 mm for four-point bending strength testing . Although feasible, the miniaturization of bending tests come with wider error margins in tow , requiring custom fixtures of increased sophistication and extra caution in specimen preparation and testing . The technique sensitivity involved in miniaturized set-ups is not addressed in ISO 6872, a standard broadly used by manufacturers for testing and advertising new products due to its flexible dimension requirements. Alternatively to uniaxial tests using bars, reduced specimen dimensions can be prepared out of small CAD/CAM blocks and tested in biaxial flexure, using set-ups like the piston-on-ring, ring-on-ring, piston-on-three-balls, and many other variations. These configurations use a disc-shaped geometry due to its rotational symmetry, which requires grinding of cuboid blocks into cylinders before sectioning them in discs, an inconvenient step for ordinary labs.

Set out to facilitate the mechanical testing of dental restorative materials available as CAD/CAM blocks, the authors devised a series of contributions aimed to introduce to the dental materials field the test method of biaxial flexural strength based on the ball-on-three-balls set-up developed by Börger et al. . The test is scalable for small specimen sizes , adaptable for rectangular plate geometries , and intended also for fracture toughness testing . The stresses in discs and plates using the ball-on-three-balls test is biaxial in nature, requiring the knowledge of the material’s elastic constants (i.e., Poisson’s ratio and Young’s modulus) as parameters for the numerical solutions. The Poisson’s ratio ( ν ) is a fundamental parameter in biaxial stress state problems by means of the biaxial (or effective) Elastic modulus ( E ), expressed as E ′ = E /(1 − ν ), even though the importance of accurate measurements of ν are not always appreciated. For example, again in ISO 6872, ν is required in the analytical solution for the pinston-on-three-balls biaxial flexural strength test, but the standard lets off easy, suggesting: “ If the value for the ceramic concerned is not known , use Poisson s ratio = 0.25 ” . This obviously leads to errors in strength determination using the solution given therein, from ∼0.67% for a variation in ν of 0.01, up to ∼3.38% for an error of ±0.05 in the value for ν . As will be shown later, the Poisson’s ratio of most dental ceramics varies between 0.20 and 0.25. A disregard of material specific Poisson’s ratio has also been shown to result in inaccuracies in determining the fracture toughness of ceramic materials using the surface crack in flexure method by means of erroneous estimations of the crack geometry factor, Y . The classical Newman and Raju formula is used to derive Y for a general case of ν = 0.3, leading to errors up to 40% in extreme cases, according to a recent analysis by Strobl et al. (in general the Newman and Raju solution for Y results in an overestimation of K Ic by 8–10% [own observations]). Clearly there is no place for approximations, as often perpetrated in the dental literature, and accurate measurements of elastic constants are mandatory prior to any mechanical testing.

Elastic properties are mainly dictated by the microstructure and material composition. Unfortunately, information provided by the manufacturers are often incomplete or labeled with misleading terminologies regarding phase constituents. Terms like “Polymer-infiltrated Ceramic Network”, “Resin Nano-Ceramic” or “Zirconia-reinforced Lithium Silicate Ceramic” have been used to advertise recent CAD/CAM restoratives, but deeper microstructural analyses performed by independent scientific peers are generally missing.

The present study focuses on the methodological aspects of the determination of elastic constants in dental materials supplied as CAD/CAM chairside blocks. Materials of different classes were selected, and a thorough microstructural/phase characterization was conducted using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), Raman Spectroscopy and X-ray Diffraction (XRD). Structure-property relationships are ultimately discussed within the frame of phase constituents and elastic constants for different restorative classes.

Background

Elastic constants

Materials under mechanical stress deform, resulting in changes in their original volume and shape. Within the limits of linear elasticity, the ratio between the relative deformation in the transverse direction (Δ T / T = ε t ) and in that taking place in the longitudinal direction (Δ L / L = ε l ) during a longitudinal uniaxial loading is a constant expressed by ν = − ε t / ε l , the Poisson’s ratio. Depending on the loading nature (tension or compression), one of the terms will be negative, resulting in a positive value for most isotropic materials within 0 ≤ ν ≤ ½. Compliant behaviors are characteristic of incompressible materials, exhibiting a large volume change when loaded, determined by the Bulk modulus B , typical for materials with high atomic density. Less dense materials are usually more compressible, undergoing shape changes more easily than volume changes, a behavior determined by the shear modulus G . The relationship between these three constants is expressed by:

ν=(3B2G)/(2G+6B)
ν = ( 3 B − 2 G ) / ( 2 G + 6 B )

This relation sets the maximum limit of ν at ½ for materials with B G , that is, B/G ≫ 1, being rubber a classical example. Polymers in general tend to ν > 0.3, while ceramics lay between 0.25–0.3 and glasses slightly lower, in the range of 0.15–0.3 . Some materials may exhibit contraction or expansion in both directions when loaded uniaxially, showing negative Poisson’s ratios (i.e., ν −1), meaning that B / G approaches 0. This behavior has little relation to the material’s atomic arrangement per se, but are rather common for materials with network-like configurations with cellular structures exhibiting folding or rotational capabilities . Performing laborious measurements for each individual elastic constant is generally not necessary, since they are, for isotropic materials, all interrelated:

E=2G(1+ν)=3B(12ν).
E = 2 G ( 1 + ν ) = 3 B ( 1 − 2 ν ) .

Beside static test methods (tension, compression, bending), three main dynamic measurement methods are widely used: The Resonant Beam Technique (RBT) uses freely suspended beams, which are subjected to vibrations to measure a set of resonance frequencies . The evaluation is based on the solution of the frequency equation from Timoshenko’s beam theory. Higher modes are increasingly influenced by shear deformation, which is taken into account by the shear correction factor k . For this factor, analytical expressions are available for isotropic and anisotropic materials . By fitting theoretical to experimental frequencies, Young’s and shear modulus are obtained.

Similar to RBT, in Resonant Ultrasound Spectroscopy (RUS) small samples are excited to resonance vibrations . The difference to RBT is that RUS samples usually exhibit a cube- or disc-shaped geometry. The second difference concerns the theory, which is in case of RUS a full description of mechanical vibrations of a solid. This allows the determination of the full elastic tensor from one single measurement . The disadvantage is that the number of resonance frequencies is sometimes very high, which requires pre-knowledge of the sample in order to uniquely attribute experimental to theoretical frequencies.

Ultrasonic Pulse Echo (PE) methods offer a cheap and fast approach to measure elastic constants: The time span between pulse and echo is determined to result in values for quasi-longitudinal and quasi-transverse acoustic wave velocities (“quasi” for the anisotropic case) with respect to different crystal directions. Elastic constants are derived from these velocities .

We present in the following data for each of these dynamic methods and discuss advantages and limitations of the respective technique.

Background

Elastic constants

Materials under mechanical stress deform, resulting in changes in their original volume and shape. Within the limits of linear elasticity, the ratio between the relative deformation in the transverse direction (Δ T / T = ε t ) and in that taking place in the longitudinal direction (Δ L / L = ε l ) during a longitudinal uniaxial loading is a constant expressed by ν = − ε t / ε l , the Poisson’s ratio. Depending on the loading nature (tension or compression), one of the terms will be negative, resulting in a positive value for most isotropic materials within 0 ≤ ν ≤ ½. Compliant behaviors are characteristic of incompressible materials, exhibiting a large volume change when loaded, determined by the Bulk modulus B , typical for materials with high atomic density. Less dense materials are usually more compressible, undergoing shape changes more easily than volume changes, a behavior determined by the shear modulus G . The relationship between these three constants is expressed by:

ν=(3B2G)/(2G+6B)
ν = ( 3 B − 2 G ) / ( 2 G + 6 B )

This relation sets the maximum limit of ν at ½ for materials with B G , that is, B/G ≫ 1, being rubber a classical example. Polymers in general tend to ν > 0.3, while ceramics lay between 0.25–0.3 and glasses slightly lower, in the range of 0.15–0.3 . Some materials may exhibit contraction or expansion in both directions when loaded uniaxially, showing negative Poisson’s ratios (i.e., ν −1), meaning that B / G approaches 0. This behavior has little relation to the material’s atomic arrangement per se, but are rather common for materials with network-like configurations with cellular structures exhibiting folding or rotational capabilities . Performing laborious measurements for each individual elastic constant is generally not necessary, since they are, for isotropic materials, all interrelated:

E=2G(1+ν)=3B(12ν).
E = 2 G ( 1 + ν ) = 3 B ( 1 − 2 ν ) .

Beside static test methods (tension, compression, bending), three main dynamic measurement methods are widely used: The Resonant Beam Technique (RBT) uses freely suspended beams, which are subjected to vibrations to measure a set of resonance frequencies . The evaluation is based on the solution of the frequency equation from Timoshenko’s beam theory. Higher modes are increasingly influenced by shear deformation, which is taken into account by the shear correction factor k . For this factor, analytical expressions are available for isotropic and anisotropic materials . By fitting theoretical to experimental frequencies, Young’s and shear modulus are obtained.

Similar to RBT, in Resonant Ultrasound Spectroscopy (RUS) small samples are excited to resonance vibrations . The difference to RBT is that RUS samples usually exhibit a cube- or disc-shaped geometry. The second difference concerns the theory, which is in case of RUS a full description of mechanical vibrations of a solid. This allows the determination of the full elastic tensor from one single measurement . The disadvantage is that the number of resonance frequencies is sometimes very high, which requires pre-knowledge of the sample in order to uniquely attribute experimental to theoretical frequencies.

Ultrasonic Pulse Echo (PE) methods offer a cheap and fast approach to measure elastic constants: The time span between pulse and echo is determined to result in values for quasi-longitudinal and quasi-transverse acoustic wave velocities (“quasi” for the anisotropic case) with respect to different crystal directions. Elastic constants are derived from these velocities .

We present in the following data for each of these dynamic methods and discuss advantages and limitations of the respective technique.

Materials and methods

Materials and specimen preparation

The evaluated restoratives were selected to encompass materials of different classes and clinical indications ( Table 1 ). Due to its wide range of application and the decreased interest in alumina ceramics in dentistry, a 3 mol% yttria-stabilized tetragonal zirconium dioxide (3Y-TZP) material (e.max ZirCAD) was chosen as the solely representative of glass-free polycrystalline ceramics. The 3Y-TZP powder is combined with a binder and isostatically pressed to form blocks, which are later pre-sintered before machining. The material e.max CAD is delivered in blocks of partially crystallized lithium metasilicate precursory phase, and tinted with bluish pigment. A single or a two-stage heat-treatment (depending on the oven used) of the material follows from that, resulting in needle-shaped lithium disilicate crystals of 2 μm in length randomly orientated embedded in a 30 vol% residual Li 2 O·2SiO 2 glass phase. The materials Suprinity and Celtra Duo are essentially the same material, developed by both manufacturers in conjunction with the Fraunhofer Institute for Silicate Research (ISC) in Würzburg, Germany. They consist of a lithium silicate glass containing ZrO 2 that uses diphosphorus pentoxide (P 2 O 5 ) as nucleation agent for crystallization of lithium metasilicate. To date the manufacturer of Suprinity supplies the material as a pre-crystallized version that needs to undergo a crystallization firing after machining. The company Dentsply DeTrey in turn, supplies the material in both pre-crystallized (Celtra CAD) and fully crystallized (Celtra Duo) stages as blocks for machining. For our study the pre-crystallized version Suprinity and the fully crystallized version Celtra Duo were selected. Vitablocs Mark II and Empress CAD are well established materials derived from early generations of CAD/CAM blocks, containing feldspar or leucite crystals up to 40 vol% embedded in an aluminosilicate (feldspathic) glass matrix. Enamic is a hybrid material containing a reinforced glass phase (86 wt%, 75 vol%, according to the manufacturer) and a polymeric phase (urethane dimethacrylate and triethylene glycol dimethacrylate). The glassy phase of Enamic is sintered to a porous structure, which is later infiltrated with resin monomers under high pressure. Lava Ultimate is a typical resin composite based on the polymerizable Filtek Supreme Ultra (3M, St. Paul, MN, USA) product, containing dispersed nanometric colloidal silica and ZrO 2 spherical particles in agglomerated and non-agglomerated form (80 wt%, 65 vol%) embedded in a dimethacrylate resin, being industrially pre-polymerized in block form under ideal temperature and pressure conditions.

Table 1
Evaluated materials, their manufacturers, material class and clinical indication.
Material Manufacturer Class/terminology Clinical indication a
e.max ZirCAD Ivoclar-Vivadent 3 mol% Yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) Framework for single- and multi-unit (3–12 elements) fixed-partial dentures.
e.max CAD Ivoclar-Vivadent Lithium disilicate (LS 2 ) glass-ceramic Veneers; inlays; onlays; anterior and posterior crowns; anterior and posterior implant abutments; three-unit bridges up to premolars; overlay veneers for multi-unit frameworks.
Celtra Duo Dentsply DeTrey Fully-sintered lithium silicate/phosphate (LSP) glass-ceramic Veneers; inlays; onlays; anterior and posterior crowns.
Suprinity VITA Zahnfabrik Pre-sintered lithium silicate/phosphate (LSP) glass-ceramic Veneers; inlays; onlays; anterior and posterior crowns.
Vitablocs Mark II VITA Zahnfabrik Feldspar-reinforced aluminosilicate glass (FAG) Veneers; inlays; onlays; anterior and posterior crowns; overlay veneers for multi-unit frameworks.
Empress CAD Ivoclar-Vivadent Leucite-based glass-ceramic (LG) Veneers; inlays; onlays; anterior and posterior crowns.
Enamic VITA Zahnfabrik Polymer-infiltrated reinforced-glass network (PIRGN) Veneers; inlays; onlays; anterior and posterior crowns.
Lava ultimate 3M ESPE Nano-particulate pre-polymerized resin composite (RC) Veneers; inlays; onlays.

a Clinical indication as given by the manufacturer.

The respective CAD/CAM blocks were sectioned using a precision cutting machine (Buehler, USA) and a diamond-embedded copper disc under water irrigation. For the measurement of elastic constants, two specimen geometries were used: a parallelepiped (14 mm × 12 mm × 10 mm) and a beam (2 mm × 4 mm × 15 mm) ( Fig. 1 ). Parallel walls were ensured by grinding the sides with a diamond wheel in a grinding machine, up to 0.01 mm toleration. The materials e.max ZirCAD was sintered at 1550 °C for 2 h and cooled overnight. The materials e.max.CAD and Suprinity were crystallized according to the manufacturers instructions in a Vacumat 4000 oven (Vita Zahnfabrik). All other materials were not further treated.

Fig. 1
(a) Chairside CAD/CAM blocks selected for this study. (b) Specimen sizes and geometries used for the measurements of the elastic constants (RUS = Resonant Ultrasound Spectroscopy, PE = Pulse-echo, RBT = Resonant Beam Technique).

Measurement of elastic properties

For RBT, prismatic samples were carefully machined to the dimension 15 × 4 × 2 mm 3 . The beams were suspended in alumina fiber loops attached to piezoelectric transducers. One transducer excites vibrations, the other detects the resonance answer of the sample. Signal processing is performed with the aid of a network analyzer (HP 8751A) with a signal to noise ratio of up to −140 dBm. In extension of the European standard EN-15335:2007 not only bending, but also torsional vibrations were used for evaluation. For RUS, nearly cuboid samples with an edge length of approximately 10 mm were machined. These samples were placed directly between two piezoelectric transducers. Signal processing is the same as described above, and evaluation is performed according to the literature . For pulse echo measurements, the same samples as for RUS were used and directly contacted with honey. The wave velocities were derived from thickness measurement using an Olympus MG2 equipped with a longitudinal and a torsional transducer (V112-RM and V156-RM). From the longitudinal and transverse wave velocities, Young’s and shear modulus were calculated.

Material characterization

Since the chemical structure and the microstructural features both define the mechanical behavior of materials, a thorough characterization is in order. Samples of all materials were obtained from blocks and prepared for Scanning Electron Microscopy (SEM) and Raman Spectroscopy as described above. Polished (SiC paper, up to 4000 grit in water) and etched specimens (5% Hydrofluoric acid, from 0 to 40 s) were gold sputtered an inserted in a SEM (Auriga, Zeiss, Germany) for microstructural imaging and qualitative Energy Dispersive X-ray Spectroscopy (EDX). To collect their Raman spectra, polished specimens were excited with a 532 nm wavelength Ar + laser through a 50× objective with a 100 μm pinhole aperture in 6 successive measurements of 60 s integration time each (Nicolet Almega XR, Thermo Fischer Scientific, Waltham, USA). Step-scan powder diffraction data were recorded using a Siemens D500 diffractometer (Siemens AG, Munich, Germany) with a Cu X-ray tube operating at 30 kV and 30 mA. The spectra were recorded in the 2-theta range from 5° to 70° with a 0.02° step and 1 s counting time. For e.max ZirCAD the powder was obtained from pulverizing the pre-sintered block.

Results

Elastic constants

Depending on the material tested the methods used to measure the elastic constants agreed well or showed significant differences. The results are summarized in Table 2 . Apart from the hybrid materials (Enamic and Lava Ultimate), RBT and RUS methods showed a good agreement within measurement errors. For these methods the Poisson’s ratio of dental ceramics fell within the range 0.20 < ν < 0.25, with upper and lower B / G bounds of 1.86 and 1.26, respectively, set by Enamic and Empress CAD ( Fig. 2 ). Compared to RBT and RUS, PE tended to overestimate ν values for e.max ZirCAD and e.max CAD, while underestimating it for Vitablocs Mark II. For the glass-ceramics Suprinity, Celtra Duo and Empress CAD all methods seemed in accord. For Lava Ultimate the damping behavior of the polymeric portion led to unreliable values for RUS and PE especially. For Enamic this effect was observed to a lesser extent, and lead to an overestimation of ν using the RBT method. See details in Section 5 .

Table 2
Density and elastic constants obtained using RBT, RUS and PE methods.
ρ (g/cm 3 ) E (GPa) G (GPa) B (GPa) ν
E.max ZirCAD RBT #1 5.970 ± 0.041 206.3 ± 3.4 82.9 ± 1.4 134.3 0.244 ± 0.03
RBT #2 5.981 ± 0.041 207.1 ± 3.6 82.9 ± 1.5 137.5 0.249 ± 0.03
RUS #1 6.059 204.1 82.2 131.8 0.242
RUS #2 6.051 208.9 81.9 155.4 0.276
PE #1 210.4 80.6 178.9 0.304
PE #2 210.3 80.9 175.2 0.300
E.max CAD RBT #1 2.466 ± 0.017 102.5 ± 1.6 42.2 ± 0.7 60.1 0.216 ± 0.01
RBT #2 2.441 ± 0.017 100.7 ± 1.4 41.7 ± 0.6 57.4 0.208 ± 0.01
RUS #1 2.472 102.8 42.3 59.9 0.214
RUS #2 2.468 103.1 42.4 60.5 0.216
PE #1 105.1 41.7 72.9 0.260
PE #2 107.0 42.7 72.5 0.254
Celtra Duo RBT #1 2.623 ± 0.019 107.6 ± 1.6 44.1 ± 0.7 64.0 0.220 ± 0.01
RBT #2 2.627 ± 0.019 108.6 ± 1.6 44.5 ± 0.7 64.6 0.220 ± 0.01
RUS #1 2.630 108.2 44.2 65.3 0.224
RUS #2 2.624 108.2 44.2 65.3 0.224
PE #1 106.6 44.1 61.0 0.209
PE #2 106.5 43.8 62.2 0.215
Suprinity RBT #1 2.604 ± 0.018 102.9 ± 1.5 43.0 ± 0.7 56.2 0.195 ± 0.01
RBT #2 2.574 ± 0.018 103.9 ± 1.5 43.0 ± 0.7 59.3 0.208 ± 0.01
RUS #1 2.643 105.8 43.8 60.2 0.207
RUS #2 2.641 106.0 43.7 61.3 0.212
PE #1 103.4 42.8 59.0 0.208
PE #2 104.7 43.3 60.1 0.210
Vitablocs Mark II RBT #1 2.424 ± 0.017 70.1 ± 1.0 28.4 ± 0.5 43.5 0.232 ± 0.01
RBT #2 2.45 ± 0.018 72.2 ± 1.1 29.9 ± 0.5 42.2 0.215 ± 0.01
RUS #1 2.461 72.4 29.4 44.7 0.230
RUS #2 2.460 71.8 29.3 43.7 0.226
PE #1 69.6 28.8 39.6 0.207
PE #2 70.3 29.1 40.0 0.207
Empress CAD RBT #1 2.434 ± 0.017 65.3 ± 0.64 27.2 ± 0.6 36.4 0.201 ± 0.01
RBT #2 64.4 ± 0.5 27.5 ± 0.4 32.8 0.173 ± 0.01
RUS #1 2.438 65.8 27.3 37.4 0.207
RUS #2 65.6 27.2 36.8 0.203
PE #1 65.5 27.5 35.3 0.191
PE #2 64.7 27.2 34.5 0.188
Enamic RBT #1 2.128 ± 0.015 37.4 ± 0.6 15.4 ± 0.3 25.9 0.260 ± 0.01
RBT #2 2.130 ± 0.015 37.6 ± 0.6 14.6 ± 0.03 29.8 0.290 ± 0.01
RUS #1 2.142 38.11 15.33 24.7 0.243
RUS #2 2.146 38.05 15.57 22.8 0.222
PE #1 37.3 15.3 22.2 0.220
PE #2 37.0 15.0 23.0 0.232
Lava Ultimate RBT #1 1.968 ± 0.028 12.7 ± 0.3 4.3 ± 0.3 70.5 0.47 ± 0.05
RBT #2 1.959 ± 0.028 12.6 ± 0.3 4.5 ± 0.3 23.3 0.41 ± 0.05
RUS #1 1.977 11.05 4.04 13.9 0.368
RUS #2 1.975 10.9 4.02 12.3 0.353
PE #1 17.9 7.1 12.3 0.258
PE #2 17.8 7.1 12.2 0.258
# Refers to the specimen number. For RUS and PE the same specimens were used for both measurements.

Fig. 2
Plot Bulk modulus vs. Shear modulus showing the data points for the eight materials measured with RUS, RBT and PE methods.

Microstructural and phase characterization

SEM images of the investigated materials are illustrated in Figs. 3 and 4 at low and high magnifications. To bring out contrast between phases most materials were etched with 5% Hydrofluoric acid (HF), with exception of e.max ZirCAD. Materials containing finer microstructure, such as Celtra Duo and Suprinity, a highly diluted solution of 0.5% HF was used.

Nov 22, 2017 | Posted by in Dental Materials | Comments Off on Chairside CAD/CAM materials. Part 1: Measurement of elastic constants and microstructural characterization
Premium Wordpress Themes by UFO Themes