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j o u r n a l o f t h e m e c h a n i c a l b e h a v i o r o f b i o m e d i c a l m a t e r i a l s 5 5 ( 2 0 1 5 ) 1 – 1 1

http://dx.doi.org/101751-6161/& 2015 El

nCorresponding autE-mail address:

Research Paper

Evaluation of mechanical and optical behaviorof current esthetic dental restorativeCAD/CAM composites

Bogna Stawarczykn, Anja Liebermann, Marlis Eichberger, Jan-Frederik Guth

Department of Prosthodontics, Dental School, Ludwig-Maximilians-University Munich, Goethestrasse 70,80336 Munich, Germany

a r t i c l e i n f o

Article history:

Received 20 August 2015

Received in revised form

6 October 2015

Accepted 12 October 2015

Available online 19 October 2015

Keywords:

CAD/CAM composite

Three-point flexural strength

Two-body wear

Discoloration

Optical and mechanical properties

.1016/j.jmbbm.2015.10.004sevier Ltd. All rights rese

hor. Tel./fax: þ49 4400 59bogna.stawarczyk@med.

a b s t r a c t

Objectives: To determine the mechanical and optical properties of CAD/CAM composites

(LAVA Ultimate, Cerasmart, Shofu Block and two exp. CAD/CAM composites), a hybrid

material (VITA Enamic), a leucite (IPS Empress CAD) and a lithium disilicate glass-ceramic

(IPS e.max CAD).

Materials and methods: Three-point flexural strength (FS) was investigated according ISO

6872:2008 (N¼240/n¼30). Two-body wear (TBW) was analyzed in a chewing simulator

(1,200,000 cycles, 50 N, 51/55 1C) using human teeth as antagonists (N¼120/n¼15). Quanti-

tative analysis of wear was carried out with a 3D-scanner and associated matching

software. Discoloration rate (DR) after 14 days of storage in cress, curry, red wine, and

distilled water (N¼384/n¼12), and translucency (T) (N¼384/n¼48) of CAD/CAM materials

were measured in a spectrophotometer (400–700 nm wavelength). Data were analyzed

using two-/one-way ANOVA with Scheffé post-hoc test, Kruskal–Wallis-H test, and linear

mixed models (α¼0.05).

Results: IPS e.max CAD showed the highest FS (po0.001), followed by LAVA Ultimate;

however, not different from the remaining CAD/CAM composites (exception: Shofu Block).

The lowest FS showed VITA Enamic and IPS Empress CAD (po0.001). IPS Empress CAD,

VITA Enamic, exp. CAD/CAM composite 2, followed by IPS e.max presented lower material

TBW than the remaining CAD/CAM materials (po0.001). The highest antagonist wear was

observed for the tested glass-ceramics and the hybrid material (po0.001). Storage medium

(red wine4curry4cress4distilled water) exerted the highest influence on DR (po0.001),

closely followed by CAD/CAM material. Glass-ceramics showed lower DR than CAD/CAM

composites (po0.001).

Conclusions: CAD/CAM composites presented moderate FS, high T and antagonist friendly

behavior. Glass-ceramic demonstrated the most favorable DR and lowest TBW on the

material side.

& 2015 Elsevier Ltd. All rights reserved.

rved.

573.uni-muenchen.de (B. Stawarczyk).

j o u r n a l o f t h e m e c h a n i c a l b e h a v i o r o f b i o m e d i c a l m a t e r i a l s 5 5 ( 2 0 1 5 ) 1 – 1 12

1. Introduction

Numerous dental manufacturers recently offer high-performancepolymers (HPP) for CAD/CAM application for permanent restora-tions. Those industrially prefabricated polymers or acrylates offermechanical qualities superior to those of direct temporaryrestorations (Alt et al., 2011; Stawarczyk et al., 2013). Thepolymerization-process under industrial conditions with standar-dized high pressure and temperature parameters, leads to ahighly homogeneous internal structure of the blanks, offeringnumerous advantages. First studies showed an increased long-term stability, better biocompatibility and a more favorable wearbehavior compared to manually processed polymers (Jakob et al.,2010). A further study additionally investigated the color stabilityof PMMA-based temporary HPPs and conventional polymerscompared to glass-ceramics, where comparable color stability toglass-ceramics and a significantly better color stability thanconventional resins could be observed (Stawarczyk et al., 2012).

A further study additionally investigated the color stabilityof PMMA-based temporary HPPs and conventional polymerscompared to glass-ceramics, where comparable color stabilityto glass‐ceramics and a significantly better color stability thanconventional resins could be observed (Stawarczyk et al., 2012).

The application of high-performance permanent CAD/CAM polymers as long-term temporaries offers new innova-tive treatment strategies and restorative approaches. Forexample, extended pre-treatment phases, using minimallyinvasive HPP CAD/CAM polymer restorations significantlysimplifies clinical procedures in complex cases with loss ofvertical dimension of occlusion VDO (Edelhoff et al., 2012;Güth et al., 2012, 2014). Furthermore, they offer more favor-able CAD/CAM processing characteristics and can be used inlower thickness than ceramic materials (Magne and Belser,2003); Edelhoff et al., 2012).

In the meanwhile, some manufacturers have alreadyaccredited the use of their HPP-materials for permanentsingle-tooth restorations. In the meanwhile, some manufac-turers have already accredited the use of their HPP-materialsfor permanent single-tooth restorations. While long termclinical evaluations do not become available, in vitro compar-isons to already well-known and clinically proven materialsmay provide some information on their suitability for longterm clinical use. Therefore, the mechanical and opticalproperties of HPPs have to be compared to already well-known and scientifically proven concepts using ceramicmaterials, which currently mean the accepted standard fortooth-colored single tooth restorations. Therefore, themechanical and optical properties of HPPs have to be com-pared to already well-known and scientifically proven con-cepts using ceramic materials, which currently mean theaccepted standard for tooth-colored single tooth restorations.Mechanical and optical properties of the HPPs are influencedby monomer composition, chemical composition as well asfiller size or arrangement of the materials itself.

Basically, PMMA-based, mostly unfilled materials for theuse as long-term temporaries (e.g. Telio CAD or VITA CAD-Temp) have to be distinguished from materials that areaccredited for definite use and feature a high amount ofinorganic fillers. Examples for this group are the polymer-

infiltrated-feldspathic ceramic-network material (VITAEnamic) with 86% ceramic by weight or the resin nanocera-mic material (LAVA Ultimate) with 80 wt% silica and zirconiananoparticles and nanoclusters.

This shows that the composition of HPP – materials canreasonably vary, which makes it almost impossible to classifythe HPP-materials into groups so far. This again leads to thefact, that every single material has to be evaluated individu-ally in regards to its mechanical behavior and esthetical/optical properties. Currently insufficient information is avail-able about the mechanical and optical properties of HPP CAD/CAM composites. The null hypothesis stated that flexuralstrength, two-body wear rate as well as translucency anddiscoloration of CAD/CAM composites are comparable withglass-based ceramic materials.

2. Material and methods

Five different CAD/CAM composites namely, LAVA Ultimate,Cerasmart, Shofu Block and two exp. CAD/CAM compositesand a hybrid material VITA Enamic were tested and com-pared with a leucite-reinforced (IPS Empress CAD) and alithium disilicate-reinforced glass-ceramic (IPS e.max CAD)(Table 1).

2.1. Three-point flexural strength

Three-point flexural strength of CAD/CAM materials wasmeasured (ISO 6872:2008). The CAD/CAM blanks were cutwith a low-speed diamond saw (Secutom-50, Struers, Bal-lerup, Denmark) in bars and then ground to the final dimen-sions of 15 mm�4 mm�3 mm using silicon carbide (SiC)paper disks P500, P1200, P2400, and P4000 (Struers). Asrequired by the standards, the two surfaces of the specimensdid not differ more than 0.05 mm in parallelism. In summary,240 bars were prepared and this resulted in thirty specimensper each material group. The specimens were tested imme-diately after preparation.

Before the flexural strength measurements, the dimen-sions of the specimens were measured with a digital micro-meter (Mitutoyo, Andover, England) to the next 0.01 mm. Thespecimens were tested dry at room temperature. They wereplaced on two rollers with a diameter of 2 mm and set at adistance of 10 mm. The specimens were loaded axially with acylinder (diameter of 2 mm) in a Universal Testing Machine(Zwick/Roell 1445, Zwick, Ulm, Germany) at a cross-headspeed of 1 mm/min until failure. The three-point flexuralstrength was calculated according to the following formula:

s¼3Nl/2bd2

s: flexural strength, N: fracture load (N), l: distancebetween supports (mm), b: width of the specimen (mm),and d: thickness of the specimen (mm).

2.2. Two-body wear

Specimens were manufactured by cutting standardized geo-metries of 10 mm�10 mm�2 mm under constant water-cooling using a low-speed diamond saw (Secutom-50). Thespecimens were then embedded in an acrylic resin

Tab

le1–Them

anufacturer,

com

pos

ition,an

dLo

t-No.

ofalltested

CAD/C

AM

materials.

CAD/C

AM

material

Man

ufacturers

Lot-No

Com

pos

ition

Res

inco

mpos

ite

LAVA

Ultim

ateA2-HT

14L

3MES

PE,Se

efeld,German

yN52

5997

Composite

resin

material(BisGMA,UDMA,BisEM

A,TEG

DMA)with

80wt%

silica

andzirconia

nan

oparticles

andzirconia/silicanan

oclusters

Ceras

martA2-HT/14

GC

Den

talProductsEu

rope,

Leuve

n,

Belgium

1407

231

Composite

resin

material(BisMEP

P,UDMA,DMA)with

71wt%

silica

andba

rium

glas

snan

oparticles

Shofu

Block

HC

A2-HT/M

Shofu

,Kyo

to,Japan

0914

01Composite

resin

material(U

DMA,TEG

DMA)with

61wt%

silica

-powder,zirconium

silica

te,

micro

fumed

silica

Exp.CAD/C

AM

composite

1HT

A2/C14

Ivoclar

Vivad

ent,

Schaa

n,

Liec

htenstein

2892

3Composite

resin

material(N

.N.)with

80wt%

nan

oparticles

Exp.CAD/C

AM

composite

2HT

A2/C14

Colten

e/W

haled

ent,

Altstätten,

Switze

rlan

dCK14

0901

Composite

resin

material(N

.N.)with

71wt%

barium

glas

san

dsilica

particles

Hyb

ridmaterial

VITA

Enam

ic2M

2-HT

EM-14

VITA

Zah

nfabrik,Bad

Säck

inge

n,

German

y43

000

Polymer-infiltrated-feldsp

atic

ceramic-n

etwork

material(U

DMA,TEG

DMA)with

86wt%

ceramic

Glass

-ceram

icIPSEm

press

CAD

HT

A2/C14

Ivoclar

Vivad

ent,

Schaa

n,

Liec

htenstein

M13

643

Leucite-reinforced

glas

s-ce

ramic

ofth

eSiO

2–Al 2O

3–K2O-m

aterials

system

IPSe.max

CAD

HT

A2/C14

Ivoclar

Vivad

ent,

Schaa

n,

Liec

htenstein

T18

85Lith

ium

disilicatereinforced

glas

s-ce

ramic

ofth

eLi

2O–K2O–P 2O5–MgO

-materialsy

stem

BisGMA:b

isphen

olA

diglycidylether

dim

ethac

rylate;U

DMA:u

reth

anedim

ethac

rylate;B

isEM

A:e

thoxy

latedbisp

hen

olA

dim

ethac

rylate;T

EGDMA:triethylen

eglyc

oldim

ethac

rylate;B

isMEP

P:2,2-Bis

(4-m

ethya

cryloxy

polyethoxy

phen

yl)pro

pane;

DMA:dodec

yldim

ethac

rylate.

j o u r n a l o f t h e m e c h a n i c a l b e h a v i o r o f b i o m e d i c a l m a t e r i a l s 5 5 ( 2 0 1 5 ) 1 – 1 1 3

(Scandiform/ScandiQuick, SCAN-DIA, Hagen, Germany) andpolished with ascending SiC papers applying four steps underwater-cooling up to P4000.

For the artificial aging in the chewing simulator, mesio-buccal cusps of maxillary human molars fixed in amalgam(Dispersalloy, Dentsply DeTrey, Konstanz, Germany, LOT:120823) were used as antagonists. All teeth originated froman anonymous collection of several dentists located in south-ern Germany area. All teeth were disinfected and stored byimmersing them in a 0.5% chloramine T solution (Chlora-mine-T; Sigma-Aldrich Laborchemikalien, Seelze, Germany,LOT 53110, CAS No. 7080-50-4) at room temperature for amaximum of 7 days after extraction. Afterwards, they werestored in distilled water at 5 1C for a maximum time period of6 months (ISO 11405/TR). The cusp-tips were adjusted to aspherical shape. Therefore, the separated mesiobuccal cuspswere prepared using a bench drill (BT-BD 1020 D, EinhellGermany, Landau/Isar, Germany) with 40 mm and 8 mm grit(custom-made product, Komet Dental, Gebr. Brasseler,Lemgo, Germany) to obtain spherical-shaped cusp-tips witha diameter of 1 mm. Subsequently, the cusp-tips werepolished with a goat hair brush (Abraso-Starglanz, bredent,Senden, Germany). In order to allow optimal wear quantifica-tion and superimposition, each antagonist received threenotches using a diamond disc (924.104.180, Komet Dental,Gebr. Brasseler). Each group consisted of 15 specimens. Then,one tooth antagonist was randomly assigned to one CAD/CAM material specimen. In summary, 120 combinations ofCAD/CAM material specimens and tooth antagonists wereprepared, resulting in 15 specimen combinations per eachCAD/CAM material group.

Specimens and antagonists were mounted in a computersupported chewing simulator (Chewing Simulator CS-4, SDMechatronik, Feldkirchen-Westerham, Germany). The speci-mens were loaded with a vertical load of 50 N and a slidingmovement of 0.7 mm until 1,200,000 chewing cycles. Wearsimulation with simultaneous thermal stress was applied indistilled water at changing temperatures of 5 1C and 55 1Cwith a duration of 60 s for each cycle.

The surfaces of the specimens and antagonists weredigitized before aging (baseline) and after 120,000, 240,000,640,000, and 1,200,000 masticatory cycles, respectively. Alldatasets before (baseline) and after wear simulation weresuperimposed using a three-notch alignment and match-3Dprocedure and images were generated to display the differ-ences. The vertical material and antagonist loss were com-puted (Debian, Match 3D, developed by Dr. Wolfram Gloger,Ludwig-Maximilians University, Munich).

2.3. Translucency and discoloration

For the translucency and discoloration measurement, rectan-gular specimens were fabricated and analyzed with a spectro-photometer (Lambda 35 Perkin Elmer, Perkin Elmer Inc.,Massachusetts, USA). All tested CAD/CAM materials exhibitedcolor A2 high translucency (HT) according to the manufacturer.The CAD/CAM blocks were cut (Secutom-50) under water-cooling to produce 12 disks with a width of 12mm, a lengthof 14 mm and a thickness of 1.2 mm. The specimens were fixedto a plate index and polished sequentially by using a series of

j o u r n a l o f t h e m e c h a n i c a l b e h a v i o r o f b i o m e d i c a l m a t e r i a l s 5 5 ( 2 0 1 5 ) 1 – 1 14

diamond grinding sheets (up to SiC P4000) on a grindingmachine (Abramin, Struers). The grinding and polishing proce-dures were performed on both sides of all specimens, up to thefinal thickness of 170.005 mm. Then, all specimens wereultrasonically cleaned in distilled water for 5min (SonorexRK102H; Bandelin electronic, Berlin, Germany). In summary,368 disk-shaped specimens were prepared and this resulted in48 specimens per each CAD/CAM material group. The translu-cency of all specimens was measured before artificial aging.

Then, the specimens were randomly divided into four sub-groups (n¼12) with regard to the different storage media:

(1) Cress-solution (174 g tamped fresh cress was boiled up in1 l of water for 10 min and filtrated through a fine teastrainer); pH¼6.0.

(2) Curry-solution (Ostmann, Dissen a.T.W., 40 g curry pow-der was boiled up with 1 l of water for 10 min and filtratedthrough a fine tea strainer); pH¼5.9.

(3) Red wine (Rioja, Spain), pH¼3.8.(4) Distilled water (Aqua Bidest., Kerndl, Weissenfeld, Germany);

pH¼6.7.

The storage took place at 37 1C and the different pH-valueswere measured on a daily basis (Voltcraft PH-100 ATC,Conrad Electronic, Hirschau, Germany).

Quantitative measurements of translucency and discolora-tion were made, analyzing the definite transmission of lightthrough each specimen. The spectrophotometer, using a dualbeam system, records the light transmission with the help of asensor in comparison to the light intensity from a split beam.The light source provided a wavelength varying between 400and 700 nm. Initial translucency was calculated by the intensityof the monochromatic light I0, and the light I, transmittedthrough the specimen. The transmission coefficients tc [%] werecalculated by the equation: I/I0¼tc

x. The overall light transmis-sion for each material [T] was calculated as the integration (tc (λ)dλ [10�5]) of all tc values for the wavelengths from 400 to700 nm. To analyze the light transmission, the overall lighttransmission value of each material was divided by the overalllight transmission value with no specimen in the spectro-photometer (baseline), to receive light transmission in %.

The measurements were carried out at baseline and after14 days of storage. The parameter L* (brightness), a* (red–green axis) and b* (yellow–blue axis) were examined byilluminant D65 with the UV WinLabTM 2.8 Software (PerkinElmer Inc.) against a white background. The ΔE values werecalculated using the Color Application Software V1.00 (PerkinElmer Inc.) according to the following formula:

ΔE¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiΔa2 þ Δb2�ΔL2

q

ΔE: general difference in color changes, Δa: difference incolor change in the red–green-axis, Δb: difference in colorchange in the yellow–blue-axis. ΔL: difference in brightness.

2.4. Statistical analysis

Data were analyzed using the statistical software SPSS Ver-sion 23 (SPSS INC, Chicago, IL, USA). Firstly, descriptivestatistics for all groups were calculated. Normality of data

distribution was tested using the Kolmogorov–Smirnov test.Two- and one-way ANOVA followed by Scheffé post-hoc testas well as Kruskal–Wallis-H and Mann–Whitney-U tests wereused for analyze the effect of CAD/CAM material and storagemedium. Linear mixed models were applied to investigatethe influence of the number of masticatory cycles. Addition-ally, Weibull distribution parameter (Weibull modulus) wascalculated using the maximum likelihood estimation methodat 95% confidence level (Bütikofer et al., 2015). The results ofstatistical analyses with p-values less than 0.05 were inter-preted as statistically significant.

3. Results

3.1. Three-point flexural strength

According to the Kolmogorov–Smirnov test, the values in 2 of8 measured material groups were not normally distributed(25%). Therefore, the statistical comparisons were madeusing the non-parametric tests. Significant differences wereobserved between the tested materials in respect to theflexural strength values (po0.001) (Fig. 1). The lithium dis-ilicate ceramic IPS e.max CAD showed the highest flexuralstrength values, followed by LAVA Ultimate. However, theflexural strength values of LAVA Ultimate was not statisti-cally different compared to the CAD/CAM composites such asexp. CAD/CAM composite 1 and 2 as well as Cerasmart. Incontrast, Shofu Block showed significantly lower values thanLAVA Ultimate. The lowest flexural strength was observed forthe hybrid material VITA Enamic and the leucite-reinforcedglass-ceramic IPS Empress CAD.

The highest Weibull modulus was observed for VITAEnamic, followed by the CAD/CAM composites LAVA Ulti-mate and exp. CAD/CAM composite 1 and 2 (Table 2). Thelowest Weibull modulus showed IPS e.max CAD. The highestcharacteristic strength showed IPS e.max CAD, followed byLAVA Ultimate and the both exp. CAD/CAM composites. Thelowest characteristic strength was measured for VITA Enamicand IPS Empress CAD (Table 2).

3.2. Two-body wear

According to the Kolmogorov–Smirnov test, all group valueswere normally distributed. The descriptive statistics arepresented in Table 3. Fig. 2 depicts the vertical material lossdepending on the chewing cycles. All CAD/CAM materialsand their antagonists showed a significantly increase ofmaterial loss with the increase of chewing cycles (po0.001).

After 120,000, 240,000, 600,000 as well as 1,200,000 chewingcycles, the tested materials and their corresponding antago-nist showed significantly impact on the wear results (po0.001).

After 120,000 chewing cycles, the lowest material lossesfor VITA Enamic and the highest for Shofu Block wereobserved (po0.001). However, VITA Enamic was in samevalue range with exp. CAD/CAM composite 2, IPS EmpressCAD, and IPS e.max CAD. These groups showed significantlylower material loss than the CAD/CAM composite ShofuBlock. VITA Enamic caused a higher antagonist material lossthan exp. CAD/CAM composite 2 and Shofu Block (po0.001).

Fig. 1 – Bar graph of 3-point flexural strength values of tested CAD/CAMmaterials after 14 days. Different letters (abcd) presentsignificant differences between the tested material groups.

Table 2 – Weibull statistics, such as Weibull modulus andcharacteristic strength of measured flexuralstrength data.

Groups Weibull modulus Characteristic strength(MPa)

LAVA Ultimate 17.3 (11.7;25.2)de 205 (198;210)b

Cerasmart 10.2 (6.9;14.9)ab 184 (176;192)c

Shofu Block 11.2 (7.6;16.4)abc 180 (172;187)c

Exp. CAD/CAMcomposite 1

12.2 (8.2;17.8)bcd 192 (185;199)bc

Exp. CAD /CAMcomposite 2

15.2 (10.3;22.2)bcd 197 (191;203)bc

VITA Enamic 22.8 (15.5;33.2)e 146 (142;149)d

IPS Empress CAD 12.0 (8.0;17.2)abcd 151 (145;157)d

IPS e .max CAD 8.0 (5.3;11.7)a 356 (337;374)a

Different letters abcd represent a significant difference between thetested materials.

j o u r n a l o f t h e m e c h a n i c a l b e h a v i o r o f b i o m e d i c a l m a t e r i a l s 5 5 ( 2 0 1 5 ) 1 – 1 1 5

Mean values of material- and respective antagonistic-wear

are displayed in Fig. 3.After 240,000 chewing cycles, Shofu Block showed the

highest and VITA Enamic with exp. CAD/CAM composite

2 the lowest material loss values (po0.001). The highest

antagonist loss showed VITA Enamic, followed by IPS e.max

CAD, and IPS Empress CAD (po0.001). In contrast, the lowest

antagonist loss was observed for exp. CAD/CAM composite

2 and Cerasmart, followed by Shofu Block, exp. CAD/CAM

composite 1, and LAVA Ultimate (po0.001).After 600,000 chewing cycles, Shofu Block, LAVA Ultimate,

exp. CAD/CAM composite 1, and IPS e.max CAD showed

significantly higher material loss compared to IPS Empress

CAD, VITA Enamic, and exp. CAD/CAM composite 2

(po0.001). Within the antagonist values, all CAD/CAM resin

composites showed lower values than VITA Enamic, and IPS

e.max CAD materials (po0.001). LAVA Ultimate caused same

antagonistic wear as IPS Empress CAD (p40.194).

After 1,200,000 chewing cycles, LAVA Ultimate, ShofuBlock, Cerasmart, and exp. CAD/CAM composite 1 showedsignificantly higher material loss compared to IPS EmpressCAD, VITA Enamic, and exp. CAD/CAM composite 2(po0.001). Both glass-ceramics and VITA Enamic showedsignificantly higher antagonist loss compared to all testedCAD/CAM resin composites (po0.001).

3.3. Translucency

On the basis of the not normal distribution of 2 (25%) of8 groups, the data were non-parametric analyzed. VITAEnamic, followed by both glass-ceramics showed the signifi-cantly lowest translucencies. The highest translucency wasobserved for exp. CAD/CAM composite 1, followed by Cer-asmart, LAVA Ultimate, and Shofu Block (Fig. 3).

3.4. Discoloration

Kolmogorov–Smirnov test indicated no violation of theassumption of normality in 4 of 32 tested groups. Hence,87.5% of all tested groups were normally distributed (Table 4)and two-/one-way-ANOVA were applied. Storage mediumexerted the highest influence on the discoloration values(po0.001, partial eta squared ηP2¼0.919), closely followed byCAD/CAM material (po0.001, ηP2¼0.649). The interactioneffect of the binary combinations of the 2 independent para-meters (storage medium, and CAD/CAM material) was alsosignificant (po0.001, ηP2¼0.705). Subsequently, the data wassplitted and analyzed with respect to the test hypothesesindividually (Fig. 4).

According to the 1-way ANOVA (po0.001), materials storedin distilled water, followed by cress and curry solutionshowed the lowest discoloration. The highest discolorationrate was observed in the groups stored in red wine, regardlesson the CAD/CAM material group.

Table 3 – Two-body wear mean values after 120,000, 240,000, 600,000 and 1,200,000chewing cycles with standard deviation (SD) and 95% confidence interval (95% CI). Allvalues are presented in lm.

Wear materials Wear antagonists

Mean7SD 95% CI Mean7SD 95% CI

120,000 chewing cyclesLAVA Ultimate �191.7738.0ab �211;�171 �250.87158.6ab �339;�161Cerasmart �181.4733.8ab �201;�161 �171.0796.5ab �225;�116Shofu Block �231.5734.8a �251;�211 �167.07107.0b �227;�106Exp. CAD/CAMcomposite 1

�189.7736.0ab �208;�170 �200.87100.6ab �309;�181

Exp. CAD/CAMcomposite 2

�157.1739.6bc �180;�134 �117.7747.1b �144;�90

VITA Enamic �127.1730.5c �142;�109 �350.67144.7a �431;�269IPS EmpressCAD

�161.9750.3bc �188;�135 �257.67191.3ab �364;�150

IPS e.max CAD �170.6743.8bc �1957�145 �285.17152.5ab �370;�199240,000 chewing cyclesLAVA Ultimate �207.6751.4ab �237;�178 �229.57107.6bcd �290;�168Cerasmart �208.1741.6ab �232;�184 �191.3795.3cd �245;�137Shofu Block �254.1748.0a �281;�226 �190.1772.2cd �231;�149Exp. CAD/CAMcomposite 1

�207.8748.6ab �238;�179 �199.57106.6bcd �240;�178

Exp. CAD/CAMcomposite 2

�180.1747.8b �207;�152 �142.7746.9d �169;�115

VITA Enamic �177.0739.6b �199;�154 �455.17152.4a �540;�369IPS EmpressCAD

�200.4748.5ab �228;�172 �308.37173.1abc �405;�211

IPS e.max CAD �227.3746.0ab �253;�200 �366.17128.7ab �438;�293600,000 chewing cyclesLAVA Ultimate �352.07115.2a �416;�287 �284.57109.0cd �345;�223Cerasmart �312.1756.6ab �344;�279 �223.37118.6d �289;�156Shofu Block �355.8752.3a �385;�325 �237.4765.3d �274;�200Exp. CAD/CAMcomposite 1

�342.07105.2a �406;�267 �204.57101.0d �305;�213

Exp. CAD/CAMcomposite 2

�210.3743.5c �233;�185 �203.8772.0d �244;�162

VITA Enamic �230.9746.9bc �257;�203 �578.57138.7a �656;�500IPS EmpressCAD

�236.0742.2bc �260;�211 �414.07163.8bc �505;�322

IPS e.max CAD �310.1758.7ab �341;�276 �452.277133.3ab �527;�3771,200,000 chewing cyclesLAVA Ultimate �480.87158.1a �569;�392 �319.7798.0b �374;�264Cerasmart �421.6776.8ab �465;�378 �247.97151.3b �332;�163Shofu Block �475.0792.2a �527;�422 �319.0791.4b �370;�267Exp. CAD/CAMcomposite 1

�425.0752.2ab �503;�402 �329.0784.2b �380;�247

Exp. CAD/CAMcomposite 2

�276.0741.2c �299;�252 �271.5781.4b �317;�225

VITA Enamic �296.6762.8c �332;�260 �659.37171.4a �755;�563IPS EmpressCAD

�297.2765.4c �334;�260 �545.57161.4a �635;�455

IPS e.max CAD �356.5765.8bc �393;�319 �519.17124.5a �589;�449

Different letters abcd represent a significant difference according to one-way ANOVA followed by post-hoc Scheffé test between the tested materials, within one chewing cycle level.

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In general, IPS e.max CAD, followed by IPS Empress CADshowed the lowest discoloration rates compared to the testedCAD/CAM composites, regardless of the storage medium(po0.001). Within materials stored in cress solution, thehighest discoloration rate was observed for exp. CAD/CAMcomposite 1 and VITA Enamic, followed by LAVA Ultimate

(po0.001). For specimens stored in curry solution, the highestdiscoloration was observed for Shofu Block and LAVA Ulti-mate, followed by Cerasmart (po0.001). Within the CAD/CAMcomposite groups, Cerasmart and Shofu Block presentedhigher red wine discoloration rate than VITA Enamic(po0.001). Within groups stored in distilled water, IPS e.max

Fig. 2 – Material loss characteristics of tested CAD/CAM materials and their corresponding human tooth antagonistsdependent on the chewing cycles after 14 days. (A) CAD/CAM material side; (B) human tooth side.

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CAD, exp. CAD/CAM composite 1 and 2 as well as LAVAUltimate showed significantly lower color change comparedto Shofu Block and VITA Enamic (po0.001).

4. Discussion

The research interest of mechanical and optical properties ofHPP CAD/CAM composites is increasing, especially concern-ing newly introduced materials. Therefore, this study inves-tigated three commercial and two experimental CAD/CAMcomposites and compared them with a hybrid material, aleucite ceramic and a lithium disilicate ceramic. Main proper-ties of these materials, including their low abrasiveness toantagonist and their low elastic modulus, enable moreabsorption of functional stresses through deformation

(Magne et al., 2002; Schlichting et al., 2011). Furthermore,CAD/CAM composites increased the fatigue resistance ofultra-thin occlusal veneers when compared to leucite andlithium disilicate ceramics (Schlichting et al., 2011). In thisstudy, the CAD/CAM composites presented lower flexuralstrength values than lithium disilicate ceramic, but highervalues than leucite ceramic and the hybrid material VITAEnamic. In contrast, the lowest Weibull modulus wasobserved for the lithium disilicate ceramic and the highestWeibull Modulus showed the hybrid material VITA Enamic,followed by the CAD/CAM composites. Therefore, it can beassumed, that brittle materials, such as lithium disilicateceramic, on the one hand showed higher initial flexuralstrength and on the other hand could lead to spontaneousfracture due to the brittle behavior of ceramics. Composite,however, show higher deformation of the material, which

Fig. 3 – Mean values for two-body wear of materials and enamel antagonists respectively.

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reduces the eventual spontaneous fracture probability(Schlichting et al., 2011). These mechanical properties playan important role, especially for thin expiring restorations.Fiber-reinforced composite resin blocks additionally revealedthe highest load-bearing capacity (21637246 N), whereascommercial composite resin blocks showed the lowest(12907172 N) (Başaran et al., 2013). Furthermore, a studyanalyzed the fracture resistance of computer-aided design/computer-assisted manufacture (CAD/CAM)-fabricated fiber-reinforced composite (FRC) denture retainers and stated thatpolymerized dentures with FRC showed greater mean finalfracture load than the CAD/CAM dentures with FRC (Nagataet al., 2013).

VITA Enamic is a polymer-infiltrated-glass-ceramic andshould include both properties, i.e. high flexural strength aswell as better elastic properties than ceramics. The elasticmodulus of VITA Enamic presented values of approximately30 GPa, whereas CAD/CAM composites range between 10 and15 GPa and glass-ceramic about 55 GPa (Coldea et al., 2013;Lauvahutanon et al., 2014). Thus, VITA Enamic is, withrespect to the elastic modulus, closer to human tooth struc-ture values which was underlined with a very good reliabilityseen in the high Weibull modulus in the current study. Insummary, the hypothesis, that the CAD/CAM compositesshowed comparable flexural strength results to ceramics,have to be rejected.

In general, Weibull statistics is considered to characterizethe structural reliability of dental materials. Lower Weibullmodulus indicates greater variability and thereby less relia-bility in the strength, due to flaws and defects (size, distribu-tion and frequency) in the material. In the Weibull statistics,the characteristic strength represents the 63.21 percentile ofstrength distribution (Weibull, 1951). In this study, VITAEnamic (22.8) showed the highest Weibull modulus. There-fore, it can be concluded that the structure of this material isvery homogeneous. In contrast, CAD/CAM composites pre-sented lower Weibull modulus and showed only slightdifferences among themselves (17.3–10.2). Presumably theparticle sizes and distribution of these composites are

comparable. Unfortunately, there is very little informationin respect thereto. IPS e.max CAD showed a Weibull Modulusof 8.0, in the literature most dental ceramics are reported tohave Weibull modulus values in the range of 5–15 (Johnson,1982).

A disadvantage of the CAD/CAM composites (exception:exp. CAD/CAM composite 2) in comparison with glass-ceramics is their lower material abrasion resistance. Therefore,the hypothesis, that the wear resistance of CAD/CAM compo-sites and glass-ceramics is similar, was rejected. The results ofthis study confirmed the results of a previously publishedstudy (Stawarczyk et al., 2013). In this study, however, differ-ences between the CAD/CAM composites could be elaborated.A new experimental CAD/CAM composite (exp. CAD/CAMcomposite 2) exhibited comparable abrasion rates with theglass-ceramics and the hybrid material. This can be attributedto the type of polymerization of the CAD/CAM blank. Knownmanner, the type of polymerization has an effect on theproperties of the materials (Nguyen et al., 2012). Unfortunately,the information that is provided by the manufacturer con-cerning the composition of the CAD/CAM composite are somodest that, in this respect, no further comparison can bemade. One advantage is, advised at the high material loss ofthe CAD/CAM composites, that the antagonists are onlyslightly damaged when compared to ceramics. Several studieshave already dealt with this problem (Stawarczyk et al., 2015;Wiegand et al., 2015) and showed that the material losses ofCAD/CAM composites, that is caused during the clinical periodof wear, can be repaired to allow an extended clinical use. Seenfrom a biomimetic point of view, saving biological tissuesseems to make sense. However, clinical stability of the verticaldimension of occlusion (VDO), has to be ensured, to preventfunctional side-effects, especially when quadrants or even fulljaws are restored. Regarding the material and antagonisticwear properties all over, it has to be mentioned, that ceramicmaterials (IPD empress and e.max) and VITA Enamic causedthe highest overall wear. Besides other clinical parametersclinicians should consider this fact during material choicewhen placing restorations against enamel anatagonists.

Table 4 – ΔE mean values for discoloration after 14 daysstorage in different storage media with standard devia-tion (SD) and 95% confidence interval (95% CI).

Mean7SD 95% CI

CressLAVA Ultimate 3.370.4d 3.0;3.6Cerasmart 1.470.4b 1.0;1.7Shofu Block 2.270.5c 1.8;2.6Exp. CAD/CAM composite 1 4.770.5e 4.3;5.1Exp. CAD/CAM composite 2 2.570.4c 2.1;2.8VITA Enamic 4.370.9* 3.6;4.9IPS Empress CAD 0.870.2ab 0.5;0.9IPS e.max CAD 0.670.2a 0.4;0.8CurryLAVA Ultimate 7.870.3de 7.5;8.0Cerasmart 6.570.9*cd 5.8;7.2Shofu Block 8.771.1e 7.9;9.4Exp. CAD/CAM composite 1 6.270.5*c 5.7;6.6Exp. CAD/CAM composite 2 6.371.0c 5.5;7.0VITA Enamic 5.471.0c 4.6;6.1IPS Empress CAD 3.970.9b 3.2;4.5IPS e.max CAD 1.770.4a 1.3;2.0Red wineLAVA Ultimate 15.171.2bc 14.2;15.9Cerasmart 19.775.0c 16.3;22.8Shofu Block 18.673.7*c 16.1;20.9Exp. CAD/CAM composite 1 15.770.8bc 15.1;16.3Exp. CAD/CAM composite 2 17.474.4bc 14.5;20.2VITA Enamic 13.671.1b 12.7;14.3IPS Empress CAD 6.972.4a 5.2;8.5IPS e.max CAD 3.170.4a 2.7;3.4Distilled waterLAVA Ultimate 1.070.1a 0.8;1.1Cerasmart 1.170.2ab 0.9;1.3Shofu Block 1.570.1b 1.3;1.7Exp. CAD/CAM composite 1 0.970.2a 0.6;1.0Exp. CAD/CAM composite 2 0.870.2a 0.5;1.0VITA Enamic 1.670.3b 1.2;1.8IPS Empress CAD 1.070.6*ab 0.6;1.5IPS e.max CAD 0.770.4a 0.3;1.0

Different letters abcd represent a significant difference according toone-way ANOVA followed by post-hoc Scheffé test between thetested materials, within one storage medium.* not normally distributed groups.

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In regard to the optical appearance of a dental restoration,the translucency of the applied material is considered to be acrucial factor during material selection to achieve estheticallyappealing restorations. The longer the HPP-restorations areused in clinical service, the more important becomes theirway of luting. For both, esthetics and luting procedures, thetranslucency of the material plays a decisive role (Kelly et al.,1996). Therefore, the knowledge of the translucency of dif-ferent materials is essential to tailor the restoration indivi-dually to the patients' individual needs, even more whenrestorations are milled from monolithic and monocoloredblanks. In the current study, different inner structures andcompositions of the tested materials seemed to influence thetranslucency. The total transmission varied from 44.1% up to59.7% and exhibited significant differences, rejecting the null-hypothesis particularly. Thus, the hybrid material VITAEnamic showed the lowest translucency, followed by thelithium disilicate ceramic together with the leucite glass-

ceramic. The highest translucency was observed for the CAD/CAM composites, with an organic matrix and inorganic fillers.The light transmission of resin materials is influenced by thedifference of refraction index between the filler particle andmatrix (Nakajima et al., 2012). This means, that the differ-ences in between the composite resins are supposedly causedby the composition of the matrix and different filler char-acter, content, amount, and size (Azzopardi et al., 2009; DelMar Perez et al., 2009; Dos Santos et al., 2008). For most of thetested materials no previous data regarding the light trans-mission is available. However, a previous study using thesame methodology and sample-size, reports a lower lighttransmission for Lava Ultimate compared to the outcome ofthe current study (Güth et al., 2013). This can be explained bythe fact, that samples from color A3 were used previously,whereas the present study used A2-colored specimens.Knowledge about the translucency of HPP-materials and thepossibility of comparison to already known ceramic materi-als, enables clinicians to improve the optical adjustment of amonolithic restoration and the luting mode to the individualclinical situation.

Additionally to the initial optical behavior of a material,the color stability plays a decisive role during materialselection especially for anterior restorations. In the presentstudy, the storage media presented higher influence on thediscoloration values with generally higher discoloration ratefor red wine, independent of tested CAD/CAM materials.Therefore, the null hypothesis was consequently rejected.The highest discoloration rate for specimen stored in redwine was followed by curry, cress, and distilled water. Thisfinding confirms findings of previous studies (Stober et al.,2001; Guler et al., 2005; Stawarczyk et al., 2011). In the presentstudy, red wine showed the lowest pH value with an acidicpH value of 3.8, also followed by curry with a neutral pH of5.9, cress with the neutral pH value of 6.0 and distilled waterwith the most obvious neutral pH value of 6.7. The pH valuesof the storage solutions possibly promote the discolorationrates during the entire 14 days storage. However, a previousstudy stated, that diverse pH values of the different storagemedia (red wine, coca cola, coffee, and artificial saliva) had noimpact on the discoloration behavior of composite materials(Güth et al., 2013). Further studies would be necessary.

ΔE values greater than 3.3 ΔE are considered to beclinically observable (Imazato et al., 1995; Robinson et al.,1997). In the present study, all materials stored in red wineand curry showed ΔE values greater than 3.3, except thelithium disilicate ceramic specimens. In general, both glass-ceramics showed lower ΔE values than all tested CAD/CAMcomposites, regardless which storage medium was used(po0.001) with some small differences dependent on theparticular media. This could be explained with the specialcompositions of each material mentioned above causingdifferent sensitivity for special discoloration solutions. Incontrast, a previous study showed similar color stability offour of the five tested CAD/CAM resins compared to a glass-ceramic (Stawarczyk et al., 2011). However, that study testedthe discoloration rate until 180 days of storage. Our studymeasured the discoloration after 14 days.

From the clinical point of view and in contrast to commonclinical opinions, all tested CAD/CAM composites showed

Fig. 4 – Bar graph of translucency values of tested CAD/CAM materials after 14 days. Different letters (abcdef) presentsignificant differences between the tested material groups.

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satisfactory mechanical and optical properties. Despite up todate no clinical data regarding the clinical longevity of thesematerials is available, mechanical and optical properties letassume, that they may at least be used for medium-termrestorations. However, the indications, like crowns, partialcrowns and inlays, as well as the possibilities for luting arealso decisive for the clinical success. Final prove can only begiven by clinical long-term studies, that are urgently needed.

5. Conclusions

Within the limitations of this in-vitro study, it can beconcluded that:

1. CAD/CAM composites showed higher flexural strengthsthan leucite ceramic and the hybrid material VITA Enamic,but lower ones than lithium disilicate ceramic.

2. The highest Weibull modulus was observed for the hybridmaterial VITA Enamic, followed by the CAD/CAM compo-sites and the lowest one for lithium disilicate ceramic.

3. Only one CAD/CAM composite (exp. CAD/CAD composite 2)showed comparable wear properties with the tested glass-ceramics and the hybrid material. Remaining CAD/CAMcomposites presented higher material loss than glass-ceramics.

4. Glass-ceramics and the hybrid material showed higherhuman tooth antagonist wear than CAD/CAM composites.

5. Specimens stored in red wine, followed by curry and cressshowed higher discoloration rate than specimens stored indistilled water.

6. Glass-ceramics showed lower discoloration rate than CAD/CAM composites.

Acknowledgments

The authors would like to thank all companies for providingthe materials, especially Coltene/Whaledent.

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