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Effects of substrate, ceramic thickness, translucency, and cement shade on the color of CAD/CAM lithium‐disilicate crowns

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Objective: The aim of this in vitro study was to evaluate the effects of substrate colors, different levels of ceramic thickness and translucency, and cement shades on the color difference from a reference color of lithium-disilicate crowns. Materials and methods: A premolar tooth preparation was made on a study model for 1.0 and 1.5 mm thick full-ceramic crowns. Digital impressions were taken (3Shape TRIOS) and crowns designed in a CAD program (DentalDesigner). Shade A1 crowns were milled (Everest, Kavo) from high-translucency (HT) and low-translucency IPS e.max (Ivoclar Vivadent) blocks. Twelve substrates were made of different colors and materials (Natural Die Material, Co-Cr, zirconia, and gold-colored alloy). Three different shades of try-in pastes were used to simulate the effect of cements (Variolink Esthetic try-in paste; Ivoclar). Shade measurement was done three times for each crown by a spectrophotometer (VITA Easyshade Advance); averages were compared to a reference crown (A1, HT, 1.5 mm, ND2 abutment, neutral try-in paste) with ΔE00 (CIEDE2000, according to the CIE latest standard) calculated. Results: All the examined parameters influenced the ΔE00 of the crowns. The weakest effect was exerted by the try-in paste. Conclusions: All examined parameters influenced the final color of e.max CAD lithium-disilicate ceramic crowns. Clinical significance: Matching the shade of ceramic crowns to the natural tooth color is a great challenge in dentistry. To meet patients' increasing esthetical expectations, CAD/CAM methods are very popular for full-ceramic crowns. However, several factors such as the shade of the abutment, luting cement color, ceramic thickness, and translucency may influence the final color. Our objective was to measure the optical effect of these factors on the final shade of CAD/CAM lithium-disilicate ceramic crowns.
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RESEARCH ARTICLE
Effects of substrate, ceramic thickness, translucency,
and cement shade on the color of CAD/CAM
lithium-disilicate crowns
Alexandra Czigola DMD
1
| Emese Abram DMD
1
| Zoltan I. Kovacs DMD
2
|
Krisztina Marton DMD, PhD
2
| Peter Hermann DMD, PhD
1
| Judit Borbely DMD, PhD
1
1
Department of Prosthodontics, Faculty of
Dentistry, Semmelweis University, Budapest,
Hungary
2
Department of General Dental Preclinical
Practice, Faculty of Dentistry, Semmelweis
University, Budapest, Hungary
Correspondence
Alexandra Czigola, DMD, Department of
Prosthodontics, Faculty of Dentistry,
Semmelweis University, Szentkirályi Street
47, 1088 Budapest, Hungary.
Email: czigola.alexandra@dent.semmelweis-
univ.hu
Abstract
Objective: The aim of this in vitro study was to evaluate the effects of substrate colors, different
levels of ceramic thickness and translucency, and cement shades on the color difference from a
reference color of lithium-disilicate crowns.
Materials and Methods: A premolar tooth preparation was made on a study model for 1.0 and
1.5 mm thick full-ceramic crowns. Digital impressions were taken (3Shape TRIOS) and crowns designed
in a CAD program (DentalDesigner). Shade A1 crowns were milled (Everest, Kavo) from high-
translucency (HT) and low-translucency IPS e.max (Ivoclar Vivadent) blocks. Twelve substrates were
made of different colors and materials (Natural Die Material, Co-Cr, zirconia, andgold-coloredalloy).
Three different shades of try-in pastes were used to simulate the effect of cements (Variolink Esthetic
try-in paste; Ivoclar). Shade measurement was done three times for each crown by a spectrophotome-
ter (VITA Easyshade Advance); averages were compared to a reference crown (A1, HT, 1.5 mm, ND2
abutment, neutral try-in paste) with ΔE
00
(CIEDE2000, according to the CIE latest standard) calculated.
Results: All the examined parameters influenced the ΔE
00
of the crowns. The weakest effect
was exerted by the try-in paste.
Conclusions: All examined parameters influenced the final color of e.max CAD lithium-disilicate
ceramic crowns.
Clinical Significance
Matching the shade of ceramic crowns to the natural tooth color is a great challenge in dentistry.
To meet patients' increasing esthetical expectations, CAD/CAM methods are very popular for full-
ceramic crowns. However, several factors such as the shade of the abutment, luting cement color,
ceramic thickness, and translucency may influence the final color. Our objective was to measure the
optical effect of these factors on the final shade of CAD/CAM lithium-disilicate ceramic crowns.
KEYWORDS
CAD/CAM, ceramic, colorimetry, crown, optical phenomena
1|INTRODUCTION
New CAD/CAM (Computer Aided Design/Computer Aided Manufactur-
ing) technologies are being introduced in the dental marketplace, and
most companies investing into restorative dentistry are also on the mar-
ket to develop materials for digital systems. CAD/CAM systems are
based on three factors: data collection, data processing, and manufactur-
ing. Nowadays, open systems make it possible to use the constituent
parts separately.
1
Based on a 2015 AACD (American Academy of Cosmetic Dentistry)
survey, 1/3 of dentists currently use a CAD/CAM system in their prac-
tice, while another 1/3 are considering to invest into such technology.
2
Received: 16 July 2018 Revised: 31 January 2019 Accepted: 6 March 2019
DOI: 10.1111/jerd.12470
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium,
provided the original work is properly cited.
© 2019 The Authors. Journal of Esthetic and Restorative Dentistry published by Wiley Periodicals, Inc.
J Esthet Restor Dent. 2019;18. wileyonlinelibrary.com/journal/jerd 1
The abundance of new systems facilitates the use of superior
dental ceramics besides conventional techniques. This strictly con-
trolled industrial ceramic processing means increased micro-
structural uniformity, higher density, lower porosity, and decreased
residual stress. CAD/CAM systems have the potential to improve clinical
predictability. These ceramic materials are perfect for manufacturing all
types of all-ceramic restorations, such as inlays, onlays, crowns, and brid-
ges.
3
The final goal is a quick, reliable, and predictable esthetic result.
Together with the development of CAD/CAM systems, intraoral
scanners are also available on the dental market. With laboratory
scanners, it is possible to create a 3D model of the oral cavity without
taking an impression and digitizing a model. Technicians can use these
intraoral scan based digital models to design the restorations.
4
Digital
impressions offer speed, efficiency, storability of captured informa-
tion, and an easier way of communication between the dental office
and the laboratory through digital images.
5
Newer generations of all-ceramic systems and adhesive cements
allow dentists to use a minimally invasive approach and make thinner
restorations (1.0-1.5 mm). It is a great task to preserve as much tooth
structure as we can and obtain a superior esthetic result. The goal is to
achieve the desired color, especially the VITA Classical A1 shade, which
is the most commonly selected shade tab for ceramic restorations.
6
By allowing greater light transmission, all-ceramic materials improve
the translucency of the restoration; however, a perfect natural-like color
cannot be ensured.
7
Lithium disilicate-reinforced glass-ceramic restora-
tions are in the focus of interest due to their low refractive index, which
makes the material very translucent despite its high crystalline content.
This characteristic makes them suitable for full contour restorations and
the highest of esthetic demands.
8,9
In the 2015 AACD survey, when
the question which restoration material would you use in your own
mouth?was asked, the majority (84%) of responding dentists chose
lithium-disilicate (eg, IPS e.max) with zirconia trailing.
2
Natural tooth color is defined by the optical properties of enamel
and dentin. It is a great challenge in dentistry to match the color of
natural teeth with ceramic restorations.
It has been described that the shade of the restorations is highly
influenced by the prepared die. If a ceramic restoration is placed on a
dark underlying tooth structure, for example, an endodontically treated
tooth, the color beneath the crown might result in discoloration and
shadowing of the restoration, particularly in the cervical areas.
9
In addition to the prepared die, luting cements can also be a modi-
fying factor. Composite resin cements are produced in different shades
by manufacturers to influence the final appearance of full-ceramic res-
torations. Their aim is to enhance the final appearance of the crowns or
veneers. It has been demonstrated that controlling the thickness of the
ceramic might allow clinicians to manage the overall translucency of the
restoration, while the choice of cement color has less of an effect.
9
In
another study, using different shaded try-in pastes did not bring the
crowns a perceptible color change from their original crown color.
10
The purpose of this study therefore was to evaluate the color
difference of different substrate colors, different levels of ceramic
thickness and translucency, and different cement shades of lithium-
disilicate crowns (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechten-
stein) produced by CAD/CAM technology based on intraoral scans
(3shape TRIOS, Copenhagen, Denmark) from a reference color.
2|MATERIALS AND METHODS
An upper right first premolar tooth #14 on a study model was prepared
with a chamfer finishing line for 1.0 and 1.5 mm thick full-ceramic
crowns. A silicone index was made of the upper right quadrant to
control the depth of the preparation.
Digital impression was taken using a 3Shape TRIOS intraoral
scanner (Figure 1). Pre-preparation scan
11
was made in intercuspal
position of the jaws for occlusion. The digital impression of the origi-
nal tooth shape was used to design the ceramic crowns.
Crowns were designed for the prepared tooth #14 and for the
adjacent teeth #13 and 15 with the DentalDesigner (3Shape, Copenha-
gen, Denmark) CAD program in the Dental Laboratory of the Univer-
sity. The CAD/CAM method ensured that all crowns were identical in
shape and size.
Even thicknesses of 1.0 and 1.5 mm were secured on the buccal
sides of the ceramic crowns (Figure 2), taking into consideration a
5-mm diameter of the Easyshade probe (VITA Easyshade Advance 4.0).
The influence of different cement shades on the final color was
also investigated. The marginal gap for the cement was set to
0.01 mm; a uniform layer of 0.04 mm gap (3Shape DentalDesigner
program original set up) was used on the inner surface (Figure 3).
Test crowns were milled from polymethyl-methacrylate material
to check the design.
When satisfied with all settings and parameters, the CAD files
were sent to an Everest KaVo CAM unit (KaVo, Bieberach, Germany).
The crowns were milled from IPS e.max CAD (Ivoclar Vivadent)
lithium-disilicate ceramic blocks.
Maxillary right first premolar (14): 10 copies of 1.0 mm and 10
copies of 1.5 mm thick A1 crowns were milled from low-translucency
(LT) and high-translucency (HT) blocks.
Adjacentteeth#13and15crownswerealsomilledtosecure
the approximal contact points. Figure 4 shows the crowns before
crystallization.
FIGURE 1 Scan of prepared dies in the DentalDesigner CAD program
2CZIGOLA ET AL.
Crystallization firing and glazing of the crowns was done according
to the manufacturers' instructions.
IPS Natural Die (Ivoclar Vivadent) composite material of nine dif-
ferent shades was used to create the core part of the substrates fused
together with replaceable plastic posts of the study model. CAD/CAM
method was used to mill Co-Cr alloy, gold painted alloy, and sup-
erwhite zirconia substrate cores. Substrates were made in 12 different
colors (Figure 5).
Variolink Esthetic (Ivoclar Vivadent) try-in cement was used for
cementation. The advantage of the try-in paste is that it can be easily
wiped off crowns. Opaque light plus, yellowish warm, and translucent
neutral shades were used.
VITA Easyshade Advance 4.0 device was used for shade measure-
ment. To measure the color, spectrophotometers can be used. The
VITA company's first spectrophotometer was the Easyshade in 2004.
Dozic et al found that Easyshade was the most reliable instrument of
FIGURE 2 The buccal surface designed and controlled for equal thicknesses (1.0 mm and 1.5 mm)
FIGURE 3 The cementation gap (40 μm)
CZIGOLA ET AL.3
shade matching in both in vitro and in vivo circumstances.
12
The posi-
tion of the Easyshade probe was standardized on the buccal surface
of the crowns. Each crown-shade was measured three times. CIELAB
values were recorded. Easyshade measurements were performed by
two trained dental students. The spectrophotometer was calibrated
before each measurement. External light sources such as daylight
were not excluded during all measurements and they were taken in a
room with artificial lightening conditions. According to the Commission
internationale de l'éclairage (CIE) standard Easyshade uses the D65
(6500 K, daylight) illuminant for shade matching.
12
As it is described by
CIE in 1931 for determining the color of an object the size of tooth the
2Observer is needed. The 2Observer is used in the Easyshade for
CIELAB color space.
13
Easyshade advance 4.0 screen can display the Labcoordinates for
the measured shade. We can calculate a modified chroma C0and hue
angle h0from L0,a0,andb0coordinates to define the numerical color dif-
ference (ΔE
00
) between two pairs of samples by using CIEDE2000
equitation.
14
ΔE
00
(color difference in the coordinate system according to
CIEDE2000) was calculated by comparison to the reference crown:
high translucent, A1, 1.5 mm thick crown placed on the ND2 substrate
with neutral try-in paste. Many studies have selected shade A1 for
their research, as this tooth shade is the most commonly selected for
ceramic restorations.
6,19,2225,28,30
For reference abutment we have
chosen ND2 shade acting as a non-discolored prepared healthy dentin
and neutral try-in paste, that we would not want to affect the final
color of the crown by a colored luting cement.
CIEDE 2000 (ΔE
00
) equation
15
was used to calculate color
difference:
ΔE00 =ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ΔL0
kLSL

2
+ΔC0
kCSC

2
+ΔH0
kHSH

2
+RT
ΔC0
kCSC
ΔH0
kHSH
:
s
CIELAB is classically the standard parameter for total color differ-
ence between two objects, but to improve the correction between
computed and perceived color differences, it is recommended to use
the CIEDE2000 color-difference formula (ΔE
00
). CIEDE2000 (ΔE
00
)
includes specific corrections for nonuniformity of CIELAB space (so-
called weighting functions S
L
,S
C
,andS
H
) and the parametric factors for
the influence of illuminating and viewing conditions in color-difference
evaluation (K
L
,K
C
,andK
H
). The values of K
L
,K
C
,andK
H
in the
CIEDE2000 formula were all set to 1.
15
R
T
means rotation function, the
interaction between chroma and hue differences in the blue region.
16
The CIEDE2000 formula is the latest international standard
according to CIE.
15
It provides better adjustments in color-difference
evaluation.
17,18
For CIEDE 2000 formula, the perceptibility threshold (PT) was set
at 0.8 and an acceptability threshold (AT) of ΔE
00
= 1.8 was set.
19
Measurement procedure steps taken included cement application,
crown positioning on the substrate, cement excess removal, spectro-
photometer calibration and measurement.
3|STATISTICAL ANALYSIS
We used the four-way interaction model for statistical analysis. We
estimated the goodness of the model's fit by subtracting the ratio of
the residual sum of squares and the total sum of squares from one (ie,
calculating the coefficient of determination, R
2
), and also looked at the
proportion of residuals under the perceptibility and ATs. The model's fit
was remarkably good at R
2
=0.9798forΔE
00
(with R
2
= 0.9860 achiev-
able in a complete four-way interaction structure). Residuals were
under the PT/ATs in 91.5%/99.7% of observations. The parameter
FIGURE 4 IPS e.max CAD crowns before crystallization
FIGURE 5 The 12 different substrates
4CZIGOLA ET AL.
values of Cand hfor each observation were calculated from L,a,and
bfollowing published formulae. L,a,b,C,andhwere then averaged
across each measurement triplet. This averaged dataset was then used
to calculate ΔE
00
. A crown identifier was generated to group observa-
tions of identical crown thickness and translucency (but varying sub-
strate and cement material). Multilevel mixed-effects linear regression
was used to evaluate the effects of technical parameters on color
match. The outcome variable was ΔE
00
based on the CIEDE2000 for-
mula. Fixed-effect explanatory variables included crown translucency,
crown thickness, substrate type, and cement type (all categorical), plus
interaction terms between: thickness and translucency; thickness and
substrate; translucency and substrate; cement and substrate; translu-
cency and thickness and substrate (three-way). Interactions between
cement and thickness, and between cement and translucency, were not
used because they were observed to be negligible size compared to
other interactions. The model included the random effect of crown
identifier and allowed heteroskedastic variability across different sub-
strates. Modeling results were expressed as adjusted predictions with
95% confidence intervals (CI) or adjusted effects with 95% CI. The sig-
nificance criterion was set at α= 0.05. The statistical package Stata
20
was used for data handling and analysis.
4|RESULTS
Working with the recent CIEDE 2000 equation (Figure 6) 41 of the
144 measured combinations were within the acceptable range (under
AT); however, only 13 of these were below the PT.
The smallest ΔE
00
values were measured on 1.5 mm thick LT
crowns. With Co-Cr and gold alloy substrates, there was no combi-
nation under the PT. The greatest color difference compared to the
reference crown could be detected on 1 mm HT crowns on Co-Cr
substrates.
Negative range data presented in Figure 7 indicate that the
respective ΔE
00
values (ie, shade discrepancy) were lower for 1.5 mm
than for 1.0 mm crowns. It can be concluded that thicker crowns pro-
vide better coverage, as expected, unless the material is highly translu-
cent, in which case thickness seems to play a less accentuated role.
It is interesting to note that thickness has no effect when applying
HT crowns with zirconium dioxide substrates. However, in case of LT
crowns, inferior results were obtained with the thicker formulation.
As it is represented in Figure 8, crowns with greater translucency
have higher ΔE
00
values resulting in a lower quality shade match.
Nonetheless, the results of HT crowns on yellowish substrates show
decreasing ΔEdespite the decreasing lightness of the shade
(ND1-ND6)though ΔE
00
increase was expected since HT crowns are
more translucent. This phenomenon demonstrates the complexity of
the optical properties of these materials.
In Figure 9, the Values in the negative range indicate better
results having been achieved with a type of cement different from the
neutral. ΔE
00
differences greater in absolute value than 1 can be con-
sidered clinically significant; such effects are exclusive to the ND9 and
Co-Cr substrates when applying light plus cement, and to the zirconia
substrates when applying warm cement.
5|DISCUSSION
Results of the present study showed that the color difference (ΔE
00
)
of a CAD/CAM glass-ceramic lithium-disilicate full-ceramic crown is
influenced by ceramic thickness and translucency, substrate color, and
cement color. Data of this investigation are in agreement with previ-
ous studies in the literature.
9,10,2131
FIGURE 6 Model predictions as a function of restoration technical parameters (ΔE00 based on CIEDE2000 formula). The y-axis represents ΔE
shade of substrate. Markers indicate point estimate and 95% confidence interval. The green and black lines are the acceptability threshold and
the perceptibility threshold, respectively. The reference crown (A1 crown/low translucency/1.5 mm thick/neutral cement/ND2 substrate) is also
represented here
CZIGOLA ET AL.5
If a ΔE
00
value less than 0.8 (with the recent CIEDE2000 for-
mula) is regarded a clinically imperceptible color change, only 13 of
the measured combinations of LT crowns were below this visibility
threshold. None of the HT crowns was in this range. The reason
might be the material's optical properties: LT blocks have more
lithium-disilicate crystals than HT blocks. Crystals reduce the internal
scattering of light as it passes through the material. That means when
the substrate has a dark color or the underlying tooth is highly dis-
colored, the application of a CAD/CAM glass-ceramic lithium dis-
ilicate with a HT ceramic block may result in limited success.
9,24,28,29
However, translucent ceramics have been more frequently used to
fabricate anterior restorations than opaque ones, for example,
medium-opacity and low-opacity (LO) blocks. Pires et al compared
HO (high-opacity) and LO ceramics and found ΔE
00
values of ceramic
HO to be lower than those of ceramic LT. Clinicians should consider
increasing the thickness and opacity of the ceramic to mask the
underlying color.
30
In many studies, increasing ceramic thickness is
accompanied by better color results.
9,21,22,28
We found that ceramic
thickness has less of an effect if the material is highly translucent
(HT crowns, Figure 7).
FIGURE 7 Comparison of 1.0 and 1.5 mm ceramic thickness. The x-axis represents substrate shades while yrepresents ΔE
00
differences of
1.5 mm crowns in relation to their 1.0 mm counterparts. The red reference line represents mean values for 1.0 mm crowns
FIGURE 8 Low-translucency (LT) crowns' ceramic translucency compared to high-translucency (HT) crowns. The red line demonstrates the
values of the LT crowns
6CZIGOLA ET AL.
Besides translucency, crown chromacity also plays an important
role in final color. A limitation of our study therefore is that we mea-
sured A1 shaded crowns only. Al Ben Ali et al confirmed that increasing
chromacity (high-opacity ceramics) can reduce the color effect of the
underlying tooth structure.
22
Previous studies agreed that the underlying substructure affects
the final color of the restoration.
9,10,2123,28
Chaiyabutr et al found
that dark-colored abutment teeth had the greatest ΔEvalues com-
pared to other configurations.
9
Changing the underlying color from a
lighter to a darker background resulted in increased color differ-
ences.
9,22
Ge et al found that using gold shaded posts and cores did
not influence the color of 1.5 mm thick full-ceramic crowns (Empress
2), with all measurements being under the patients' average percep-
tion level (ΔE= 1.8). The greatest color change was caused by the Ni-
Cr post core.
10
The present study found that there was no combina-
tion under the AT (ΔE
00
= 1.8) with gold alloy substrates, and only one
measured combination was below the AT (ΔE
00
= 1.8) with Co-Cr sub-
strates (1.5 mm LT crown, light plus try-in paste). As we expected, the
lowest ΔEvalues were found with LT 1.5 mm thick crowns (Figure 6).
Only a few studies can be found about the color modifying effect
of luting cements, but they agree that the choice of cement color has
less of an effect on the final color of restorations.
9,23,28
According to Niu, the final shade of a 1.5-mm thick lithium-
disilicate crown is affected not only by the cement's shade but also by
its layer thickness (300, 100, 50 μm). In this study, white opaque
cements (Multilink white opaque; Nexus3 white opaque) demon-
strated better masking ability than cements of other colors.
31
When
we used opaque cement (Variolink Esthetic light plus), it significantly
influenced the crown-shade on ND9 and Co-Cr substrates (Figure 9).
Another parameter of interest is luting cement layer thickness.
Increasing white opaque cement layer thickness from 100 to 300 μm
did not affect the shade of lithium-disilicate restorations.
31
Neither any
measured ceramic layer thickness (1.0, 1.5, 2.0, 2.5 mm), nor increased
cement thickness (300 vs 100 μm) had significant modifying effects.
9
It should be plausible that the layer thickness we used (40 μm)
results in no more than a minuscule color change. However,
increasing the amount of luting cement causes a loss of bond
strength between the crown and the die, and increases the possibil-
ity of ceramic fractures.
6|CONCLUSION
Within the limitations of this study, all examined parameters play an
important role in changing the color of a monolithic CAD/CAM full-
ceramic crown compared to the reference crown. In case of HT crowns,
the crown wall thickness has limited influence. Data show that the opti-
cal properties of these ceramic materials are highly complex, but of the
two examined e.max CAD block translucency levels (LT and HT), LT
crowns produced better color outcomes. Cement color has less of an
effect, but in some cases (ND9, Co-Cr substrates) opaque cement
shades can help mask the underlying darker substrate color.
ORCID
Alexandra Czigola https://orcid.org/0000-0002-3543-5237
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00
of test cements in comparison to the
neutral cement, with the red line (zero) representing mean ΔE
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CZIGOLA ET AL.7
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How to cite this article: Czigola A, Abram E, Kovacs ZI,
Marton K, Hermann P, Borbely J. Effects of substrate, ceramic
thickness, translucency, and cement shade on the color of
CAD/CAM lithium-disilicate crowns. J Esthet Restor Dent.
2019;18. https://doi.org/10.1111/jerd.12470
8CZIGOLA ET AL.
... Recently, digital dentistry has widely spread allowing fabrication of CAD/CAM ceramic restorations that have superior properties such as high translucency and esthetics. This helps in minimizing chairside time, facilitating shade selection and communication between dentist and lab technician, and reducing the fabrication defects produced from conventional fabrication methods such as voids, cracks, and firing problems [9][10][11]. ...
... Recent types of dental ceramics enable clinicians to fabricate monolithic esthetic restorations with a conservative tooth preparation achieving the required shade [9]. However, translucency of the restoration depends on the amount of light transmission through the restoration, which is affected by the shade of underlying tooth structure, cement, and thickness of the ceramic used, and its composition [15,16]. ...
... However, thinner samples show higher ∆E (LD: 11.36,8.21 and LR: 12.58,9.51 for 0.5 and 1 mm thicknesses, respectively), indicating poor masking ability. ...
Article
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Shade matching is a common challenge that dentists face during fabrication of esthetic dental restoration. Thus, the aim of the current study was to assess the masking ability of two types of CAD/CAM ceramics for gaining high esthetic prosthesis. This in vitro study used a total sample size of 66 lithium disilicate (LD) and leucite reinforced (LR) CAD/CAM ceramics sub-grouped into three thicknesses: 0.5, 1, and 1.5 mm. Nine shades of natural dentin die materials were prepared as a replica of the underlying tooth structure. The difference in color (ΔE) and translucency parameter (TP) were assessed for both tested ceramics at the three thicknesses. One-way ANOVA was performed to compare the three thicknesses of each ceramic, followed by multiple pairwise comparisons between both ceramics. LR had significantly higher ΔE than LD at all thicknesses used unlike the case in TP. Thickness of 0.5 mm exhibited the highest ΔE and TP, while 1.5 mm thickness showed the lowest ΔE and TP in both ceramics. Increase in ceramic thickness had a great impact on both color masking ability of the underlying tooth structure and its translucency. The higher the ceramic thickness, the better the masking ability and the lower the translucency was reported.
... The influence of the above-mentioned factors on translucency has been reported for felspathic ceramic [7], lithium-disilicate [8,9], and zirconia materials [10,11]. However, few studies and limited clinical guides correlating the luting cement and the background substrate shade on translucency and color of lithium disilicate compared to last generation cubic zirconia are present in the literature. ...
... [39,40,43,44]. This effect is implemented by the intrinsic translucency of the material [8]. In addition to the translucency variation, the material's thickness may have consequences on light irradiation intensity through the material, which could, therefore, affect the conversion degree of the underlining luting cement [8,34,36]. ...
... This effect is implemented by the intrinsic translucency of the material [8]. In addition to the translucency variation, the material's thickness may have consequences on light irradiation intensity through the material, which could, therefore, affect the conversion degree of the underlining luting cement [8,34,36]. A recent study by Tafur Zelada et al. [45] pointed out that the decrease of light irradiation intensity through thick zirconia frameworks could lead to color instability and poor mechanical properties. ...
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The aim of this in vitro study was to evaluate the effects of substrate and cement shades on the translucency and color of lithium-disilicate and zirconia CAD/CAM materials. Two light-cured resin cements (RelyX Veneer Cement; 3M; Choice 2 Veneer Cement; Bisco Dental) with a standardized thickness (0.1 mm) were tested in combination with two different monolithic CAD/CAM materials (E-Max CAD (LI2SI2O5); Ivoclar Vivadent; Katana (ZrO2); Kuraray-Noritake Dental) on two different colored composite substrates used as a dentin (Filtek Supreme XTE; 3M); for a total of 12 combinations (n = 10). The specimens’ color was measured with a spectrophotometer (Spectroshade; MHT). Measurements were taken using the CIELAB color coordinate system (L*a*b*) against black and white backgrounds. L*a*b* values were statistically analyzed for the variables Substrate, Ceramic, and Cement by applying a Three-Way ANOVA followed by the Tukey Test for post-hoc comparison (p < 0.05). Translucency Parameter (TP) and Constant Ratio (CR) were assessed to evaluate translucency; acceptability and perceptibility thresholds (ΔE00 1.8 and 0.8) were used. Statistically significant influence was found for factors ceramic material, cement shade, and substrate color (p < 0.05). Unacceptable color differences were reported for Li2Si2O5. Opacity was significantly higher when white opaque cement shade was employed. Ceramic type and cement shade significantly influenced L*a*b* color coordinates. The final translucency and color of ceramic restorations can, therefore, be influenced by ceramic material, cement shade, and substrate color
... [8,9,25] It has been reported that, if the thickness of the restoration is between 1.0 and 2.0 mm, the color of cement has the least effect on final shade rather than other variables. [8,26,27] While we did not investigate the impact of luting cement on masking ability of ceramic restorations, Pires [14] and Bacchi [11] took into account this important factor in their studies. Laís et al. compared the masking ability in different thicknesses of LT and HO types of lithium disilicate placed on composite resin and metal alloy substrates with the translucent shade of variolink II resin cement using spectrophotometry and reported that the color, type, and thickness of ceramic and using a cement have a significant influence on the resultant color. ...
Article
Background: Masking dark tooth structure or darkness of oral cavity with ceramic restorations is an important concern. The aim of this study was to determine the minimum thickness of a multilayer all-ceramic restoration (IPS-emax Press) required for a proper masking in these situations. Materials and Methods: In this experimental in vitro study, 36 multilayer ceramic disks of IPS e.max Press (IvoclarVivadent, Schaan, Liechtenstein) with the diameter of 13 mm were prepared and allocated in six groups of different core/veneer thicknesses: 0.4/0.4 mm (G1), 0.5/0.5 mm (G2), 0.6/0.6 mm (G3), 0.8/0.7 mm (G4), 1.0/0.8 mm (G5), and 1.1/0.9 mm (G6). For backgrounds, the standard black tile of spectrophotometer (B) was used to stimulate the darkness of oral cavity, and an opaque ceramic (OC) of IPS-emax Press (OC) was fabricated to determine the masking ability. CIELAB values of all disks on B and OC backgrounds were measured, and ΔE was calculated between two backings. One-way ANOVA and post hoc tukey test were used to analyze the data. ΔE ≤3.3 and P < 0.05 were considered, respectively, as the clinically acceptable limit and the level of statistical significancy. Results: The mean ΔE between B and OC of groups 4 (2.83 ± 0.80) and 5 (1.46 ± 0.36) were within the range of the clinically acceptable color difference (ΔE ≤3.3); thus these groups could properly mask the black background. A trend was existed in the results as by increasing the thickness, ΔE was decreased. Conclusion: A thickness of 1.5 mm of a multilayer ceramic restoration (IPS e.max Press) is required to mask a dark discoloration.
... Due to its discriminating power, the metric has been adopted in many scenarios, especially in industry applications. In dentistry, it is used to compare teeth whitening efficacy [18,20] and cement shades [3]. It is also used to study the coating process of pharmaceutical tablets [15]. ...
Article
Full-text available
Color comparison is a key aspect in many areas of application, including industrial applications, and different metrics have been proposed. In many applications, this comparison is required to be closely related to human perception of color differences, thus adding complexity to the process. To tackle this, different approaches were proposed through the years, culminating in the CIEDE2000 formulation. In our previous work, we showed that simple color properties could be used to reduce the computational time of a color similarity decision process that employed this metric, which is recognized as having high computational complexity. In this paper, we show mathematically and experimentally that these findings can be adapted and extended to the recently proposed CIEDE2000 PF metric, which has been recommended by the CIE for industrial applications. Moreover, we propose new efficient models that not only achieve lower error rates, but also outperform the results obtained for the CIEDE2000 metric.
... Metal-free ceramic restorations have been widely used in dentistry due to their excellent aesthetic, biocompatibility and durability (1)(2)(3). Lithium disilicate glass-ceramics have a high mechanical strength and aesthetic besides their capacity of adhesive bonding to resin cements (4) and the possibility of obtaining CAD/CAM (computer-aided-design/ computer-aided-manufacturing) restorations (5,6). Ideally, to promote the stress distribution through the tooth structure, ceramic restorations should be adhesively cemented and the most reliable performance is achieved with light-cured, self-cured or dual-cured resin cements. ...
Article
Background: To assess whether glass-ceramic shade, thickness and translucency affect degree of conversion (DC) and Knoop microhardness (KHN) of resin cements photoactivated using light-emitting diode (LED) or quartz-tungsten-halogen (QTH) units. Material and methods: Glass-ceramic blocks were cut (2, 3 and 4mm) and sintered. For DC FT Raman spectroscopy (n=3), film specimens of cements (RelyX ARC, U200, Veneer, C&B) were obtained. For KHN test (n=3), cements were inserted in cylindrical matrix and covered by polyester strip. Specimens were photoactivated (30s) using LED or QTH according to each group: direct photoactivation (DP), interposing ceramic specimens or no photoactivation (NP). Data were analysed by ANOVA and Tukey's test, Kruskal-Wallis and Dunn's tests (p<0.05). Results: Ceramic features had significant effect on DC of RelyX ARC, U200 and Veneer (p<0.0017). Light source had no effect (p=0.9512). C&B and Veneer had higher DC, followed by dual cements. NP dual cements showed the lowest DC. For KHN, ceramic shade (p=0.1717) and light source (p=0.1421) were not significant, but ceramic translucency, thickness and resin cement were significant (p=0.0001). KHN was higher for U200 followed by ARC, and lowest for Veneer. Conclusions: DC was affected by ceramic shade, translucency and thickness. KHN was dependent on ceramic translucency and thickness. Higher DC and KHN were achieved for dual-cured cements photoactivated through 2mm-thick low translucent or 3mm-thick high translucent glass-ceramic. Key words:Cementation, composite resin cements, dental curing lights, glass ceramics.
Article
Statement of problem Information regarding the masking ability of computer-aided design and computer-aided manufacture (CAD-CAM) resin-matrix ceramic materials with different compositions is scarce. Purpose The purpose of this in vitro study was to evaluate the effects of background color and thickness on the optical properties (color and translucency) of CAD-CAM resin-matrix ceramics. Material and methods Twelve rectangular specimens were fabricated at a different thickness (1, 1.5, and 2 mm) (n=12) from each of the resin-matrix ceramic materials: Shofu block (SB), Lava Ultimate (LU), CERASMART (CS), VITA ENAMIC (VE), Crystal Ultra (CU), and the VITABLOCS Mark II feldspathic ceramic (VB). The color of the specimens over amalgam, titanium, enamel, and dentin backgrounds was measured with a spectrophotometer, and the color differences (ΔE∗ab) were calculated by using the Commission Internationale de l’Eclairage (CIE) 76 formula. The difference in color of the specimen over the black and white backgrounds was used to calculate the translucency parameter (TP). ANOVA was used to statistically test whether material, background, and thicknesses influenced ΔE∗ab and TP values. Post hoc comparisons were performed to determine the significant difference among the groups (α=.05). Results The interaction with 2 between factors demonstrated that the material was a factor that significantly influenced ΔE∗ab (P<.001). The highest mean ±standard deviation of ΔE∗ab was recorded in the combination of VB material and 2-mm thickness (1.84 ±0.37), and the lowest with CS material with 1.5-mm thickness (0.47 ±0.24). The type of material and specimen thickness significantly influenced TP (P<.001). The highest and lowest mean ±standard deviation of TP were recorded for the 1-mm-thick CS (14.20 ±0.90) and 2-mm-thick SB (4.91 ±0.42) specimens, respectively. Conclusions CERASMART resin-matrix ceramic and VITABLOCS Mark II feldspathic ceramic exhibited high and low masking abilities over the investigated background substrates, respectively. However, irrespective of the thickness, all study materials exhibited acceptable masking abilities.
Article
Statement of problem Achieving accurate tooth color is important in esthetic dental treatments; however, clinical studies evaluating how ceramic veneer procedures affect color alterations are lacking. Purpose The purpose of this clinical study was to assess the color alteration during treatment with ceramic veneers and to correlate these changes with the tooth treated and veneer thickness. Material and methods Ten patients who underwent esthetic treatment were enrolled as participants. Color analysis with the VITA spectrophotometer was performed at baseline, after tooth preparation, immediately after cementation (Final 1), and after 6 to 12 months of follow-up (Final 2). Data of L∗, a∗, b∗, shade guide unit (SGU), ΔEab, ΔE00, and variation in SGU (ΔSGU) were obtained. Thickness of the veneer was also recorded. Each participant was considered as a statistical block, and the mean results for each tooth (maxillary central incisors, lateral incisors, and canines) were presented. Data were evaluated by the mixed model for repeated measures and Tukey-Kramer post hoc test (L∗, a∗, b∗), generalized linear models (thickness, ΔEab, ΔE00, SGU), Friedman test (ΔSGU), and the Pearson test was used to correlate veneer thickness and color change (ΔEab, ΔE00, ΔSGU) (α=.05). Results Among the teeth treated, no differences were found in ceramic thicknesses. The mean thickness was 1.03 mm for central incisors, 0.96 for lateral incisors, and 0.89 for canines. The b∗ values increased significantly after preparation and decreased after cementation (P<.001). For ΔEab, ΔE00, and ΔSGU, there was no statistically significant difference between the types of tooth at each respective time of analysis (P>.05). Regardless of the tooth, a decrease in the SGU score was detected after cementation (P=.015). After tooth preparation, there was significant correlation (P<.05) between ceramic thickness and ΔSGU (r=0.36). Conclusions Treatment with ceramic veneers resulted in color change, mainly with respect to the b∗ axis (yellow), producing objective differences in the ΔE analysis. Although ceramic thickness correlated with the VITA scale change (ΔSGU) after tooth wear or preparation, ceramic thickness did not differ among tooth types and did not correlate with changes in color parameters after cementation. (P>.05).
Article
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Objective The purpose of this study is to evaluate the color changes of lithium disilicate ceramics when cemented with different brands of cement by varying the thickness of the ceramic. Materials and Methods Forty ceramic discs, shade A2, were fabricated with 0.5 and 0.8 mm thickness. Forty composite resin discs, shade A3, were also produced. The ceramic samples were cemented to the composite resin discs, with two colors of resin cement, Neutral and Warm. A spectrophotometer evaluation was made. Translucency and color change analysis was performed by calculating the ΔE. A two-way analysis of variance test and multiple comparisons were performed using the Bonferroni method with a 95% confidence interval. Results There are statistically significant differences between the two ceramic thicknesses with different brands of cement (p < .001). In addition, using the translucency analysis it was found that there are statistically significant differences between the two ceramic thicknesses in both types of cement (p < .001). Conclusions The use of different cementation materials on lithium disilicate ceramics appears to have little visible influence at the clinical level. Different ceramic thicknesses have a clinically visible influence on the final restoration color.
Article
The present study aimed to determine how spectrophotometer type and background blackness affect the optical evaluation of resin composites. Cylindrical specimens were built using one resin composite, provided with translucencies named Effect, Enamel, Body, and Dentin (n = 3). The CIELAB color coordinates were assessed over black and white backgrounds using a handheld spectrophotometer designed for laboratory readings (SP60, X-Rite) and a spectrophotometer designed for clinical application (Easyshade V5, Vita Zahnfabrik). The black portion of a grayscale target (ColorChecker) and the black trap portion of the calibration reference of the spectrophotometer were used. Color differences between the devices were calculated, as well as the translucency parameter and contrast ratio. Data were analyzed by repeated-measures ANOVA and linear regressions (α = .05). In general, Easyshade resulted in higher values for all color coordinates than the SP60, irrespective of the background. Easyshade was unable to measure the color of composite Effect over black backgrounds. For other composite translucencies, both spectrophotometers yielded similar values of translucency parameter and contrast ratio, and the blackness of the black background did not affect these results. The highest agreement for the translucency parameter and contrast ratio values was observed for the composite Dentin. High agreement was observed between the two spectrophotometers regarding the translucency parameter and contrast ratio values. However, the clinical spectrophotometer was unable to measure the color of the more translucent composite over a black background and overestimated the color coordinates.
Article
Statement of problem Achieving excellent esthetics with monolithic self-glazed zirconia crowns in anterior teeth is challenging, and the impact of different surface treatments and abutment shades on the final color is unclear. Purpose The purpose of this in vitro study was to evaluate the effects of different external surface treatments (self-glazed, milled, polished, and glazed), different intaglio surface treatments (milled and airborne-particle abraded), and different abutment shades on the color difference of high-translucency self-glazed zirconia crowns. Material and methods Sixty shade A1 and 60 shade A3 crowns were fabricated with a thickness of 0.80 ±0.02 mm and randomly divided into 12 groups (n=10). Different external and intaglio surface treatments were applied. Shade A1 and A3 abutments were made with composite resin. Color was measured with a spectrophotometer and expressed in CIELab coordinates, and color differences (ΔE00) between specimens and references were calculated. The data were analyzed with ANOVA and the Tukey post hoc test. The impact of different surface treatments and abutment shades on the color difference were compared by using multiple linear regression (α=.05). Results The effects of external surface treatments, intaglio airborne-particle abrasion, and abutment shades on the L∗, a∗, b∗ and ΔE00 values of the final color of the crowns were significantly different (P<.001). Polishing resulted in the greatest ΔE00 value among all external surface treatments (P<.001). The average ΔE00 values of all crowns on the A3 abutment were higher than those of all crowns on the A1 abutment (P<.001). The influence on the color difference was abutment>external surface treatment>intaglio surface treatment. Conclusions Different surface treatments affected the final color of zirconia crowns, and a greater impact was seen with external surface treatments than with intaglio surface treatments. External polishing resulted in the greatest color difference. The abutment shade had the most effect on the color difference, as the darker the abutment color, the greater the color difference.
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Objectives: To compare visual and instrumental shade matching performances using two shade guides and three color difference formulas. Methods: One hundred dental students (DS) volunteers (35 males and 65 females) with normal color vision participated in the study. The spectral reflectance of 4 extracted human upper central incisors (UCI) and shade tabs from Vita Classical (VC) and Vita Toothguide 3D-Master (3D) shade guides were measured using a spectroradiometer (SP) under D65 illuminant (diffuse/0° geometry) inside a viewing booth with a gray background. Color coordinates (CIE L*, a*, b*, C* and h°) were calculated according to CIE D65 illuminant and CIE 2° Standard Observer. Color coordinates of UCI were also evaluated using a dental spectrophotometer (EA - Easyshade Advance). DS used VC and 3D to visually select the best shade match for each UCI, under same experimental conditions used for the SP evaluation. Three color difference metrics (CIELAB, CIEDE2000(1:1:1) and CIEDE2000(2:1:1)) were used to calculate the best instrumental shade matching based on minimum color difference. Results: The agreement between visual and instrumental shade matching was greater using SP (25-75%) than EA (0-25%). The percentage of best match for the visual assessment was more consistent using VC (23-55%) than 3D (19-34%). Considering the best performance (using SP and VC), the CIEDE2000(2:1:1) color difference formula showed the best estimate to the visual perception from DS. Significance: Within the limitations of this study, combining the use of SP, CIEDE2000(2:1:1) and Vita Classical shade guide most closely represented the visual perception of DS. Instrumental shade determination should be accompanied by experienced human visual assessment.
Article
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The aim of this prospective multicenter study was to determine 50:50% perceptibility threshold (PT) and 50:50% acceptability threshold (AT) of dental ceramic under simulated clinical settings. The spectral radiance of 63 monochromatic ceramic specimens was determined using a non-contact spectroradiometer. A total of 60 specimen pairs, divided into 3 sets of 20 specimen pairs (medium to light shades, medium to dark shades, and dark shades), were selected for psychophysical experiment. The coordinating center and seven research sites obtained the Institutional Review Board (IRB) approvals prior the beginning of the experiment. Each research site had 25 observers, divided into five groups of five observers: dentists-D, dental students-S, dental auxiliaries-A, dental technicians-T, and lay persons-L. There were 35 observers per group (five observers per group at each site ×7 sites), for a total of 175 observers. Visual color comparisons were performed using a viewing booth. Takagi-Sugeno-Kang (TSK) fuzzy approximation was used for fitting the data points. The 50:50% PT and 50:50% AT were determined in CIELAB and CIEDE2000. The t-test was used to evaluate the statistical significance in thresholds differences. The CIELAB 50:50% PT was ΔEab = 1.2, whereas 50:50% AT was ΔEab = 2.7. Corresponding CIEDE2000 (ΔE00 ) values were 0.8 and 1.8, respectively. 50:50% PT by the observer group revealed differences among groups D, A, T, and L as compared with 50:50% PT for all observers. The 50:50% AT for all observers was statistically different than 50:50% AT in groups T and L. A 50:50% perceptibility and ATs were significantly different. The same is true for differences between two color difference formulas ΔE00 /ΔEab . Observer groups and sites showed high level of statistical difference in all thresholds. Visual color difference thresholds can serve as a quality control tool to guide the selection of esthetic dental materials, evaluate clinical performance, and interpret visual and instrumental findings in clinical dentistry, dental research, and subsequent standardization. The importance of quality control in dentistry is reinforced by increased esthetic demands of patients and dental professionals. © 2015 Wiley Periodicals, Inc.
Article
Statement of problem: Reproducing the characteristics of natural teeth in ceramic crowns remains a complex and difficult process. Purpose: The purpose of this in vitro study was to evaluate the effect of the substrate, cement, type, and thickness of the ceramic on the resulting color of a lithium disilicate ceramic. Material and methods: Forty ceramic disks were prepared from IPS e.max Press LT (low translucency) and HO (high opacity) in 2 different thicknesses (1.5 and 2 mm). The LT groups were composed of monolithic ceramic disks, and the HO groups were composed of disks fabricated with a 0.5-mm thickness combined with a 1- or 1.5-mm veneering ceramic thickness. Disks made of composite resin (R) and alloy (A) were used as substrate structures. The resin cement used was Variolink II. Color was measured with a spectrophotometer and expressed in CIELab coordinates. Color differences (ΔE) were calculated. The data were analyzed with ANOVA and the Tukey HSD test (α=.05). Results: When the ΔE of ceramic disks with both substrates, with and without cement, were compared, the lowest value (3) was obtained for ceramic HO with a 2-mm thickness/alloy substrate/without cement; the highest value (10) was obtained for ceramic LT with a1.5-mm thickness/alloy substrate/with cement. This difference was statistically significant. When the effect of cement on the ΔE of ceramics in both substrates was compared, the lowest value (1.1) occurred with ceramic HO with a 1.5-mm thickness/resin substrate, and the highest was observed for ceramic LT with a 1.5-mm thickness/alloy substrate (6.4). This difference was statistically significant. Conclusions: The substrate color, type and thickness of ceramic, and presence of the cement significantly influenced the resulting optical color. The ΔE values of cemented HO ceramics were lower than that of the LT ceramic.
Article
Statement of problem: Many color specification systems and color differences have been proposed to improve the correlation between color measurement and visual perception. Although color differences can be quantified using either the CIELab formula (ΔE*ab) or the recently introduced CIEDE2000 formula (ΔE00), which captures the perceived color difference better is unknown. Purpose: The purpose of this study was to evaluate the CIELab and CIEDE2000 formulas to determine which best reflects the difference in color perception and whether color perception differs by sex. Material and methods: Forty participants grouped 18 dental resin disks (color range: from 73.6 to 87.5 for L*; from -1.6 to 3.4 for a*; from 18.1 to 36.6 for b*), the only requirement being that each group was formed of disks with chromatically indistinguishable colors. Each participant was free to choose the number and composition of the groups. With the results obtained, a dissimilarity matrix was generated, and nonmetric multidimensional scaling (MDS) was applied to it to obtain the coordinates of the disks within a Euclidean space. Results: The linear correlation coefficient between the interpoint distances of the MDS configuration (MDS_total sample) and the color differences with the CIELab formula (ΔE*ab) was 0.176 (P =.029), whereas with the CIEDE2000 formula (ΔE00) it was 0.289 (P<.001). For the configuration obtained in the women's group (MDS_w), the correlation between the interpoint distances and the CIELab color differences was 0.230 (P=.004), and the CIEDE2000 color difference was 0.328 (P<.001). For the configuration obtained in the men's group (MDS_m), the color differences calculated with both formulas reflected the perceived differences more poorly. Conclusions: Within the limitations of this study, the CIEDE2000 formula reflected the color differences perceived by the human eye better than the CIELab formula (ΔE*ab). In addition, women were confirmed to be more sensitive than men to color differences.
Article
To evaluate the cumulative effect of the abutment tooth and resin cement color on the resultant optical properties of porcelain laminate veneers (PLVs) fabricated with leucite-based CAD/CAM blocks with different shades and thicknesses. A total of 224 ceramic specimens were prepared from the IPS Empress CAD with four different shades of HT-A1, LT-A1, MT-A1 and Bl-1. Resin composite discs were prepared with shade A3.5. For the cementation, 4 different shades of light-cure resin cements were chosen. L*, a*, and b* values, as well as the chroma (C) and hue (h) values of each cemented ceramic and the A1 shade tab, were recorded. L*, Cab* and hab* values of the cemented ceramics were influenced by ceramic shade, ceramic thickness, cement shade, and interaction terms of the three variables. There were significant differences between the 1-mm-thick ceramic veneers that exhibited higher L* and lower Cab* values compared with veneers that were 0.5mm in thickness. Using the Tr shade cement resulted in lower L* and higher Cab* values for all thicknesses and ceramic shades, whereas the WO shade cement resulted in higher values. Conclusions: The selected color of a laminate restoration is significantly affected by the ceramic shade, ceramic thickness and resin cement shade. Using the WO shade resin cement seems to be more effective in masking the discolored abutment tooth. Clinicians should also select the translucency level of the ceramic block with the shade when a leucite-based CAD/CAM system is chosen to treat a discolored tooth.
Article
The effects of cement color and thickness on the color of machinable lithium disilicate (MLD) ceramic luted on metal foundation restorations is unknown. The purpose of this study was to evaluate the effects of cement color and thickness on the shade matching of MLD restorations luted on silver-palladium (Ag-Pd) foundations. Fifteen 1.5-mm-thick ceramic specimens were made from shade A1 LT lithium disilicate blocks. Five resin cements with different colors and opacities (Multilink Automix white opaque, Multilink Automix yellow, Nexus3 white opaque, Nexus3 white, Nexus3 yellow) of 3 thicknesses (300 μm, 100 μm, 50 μm) were sequentially luted to a roughened Ag-Pd alloy foundation restoration block. Five shade measurements were made with a portable spectrophotometer after optically connecting the ceramic specimen to each cement foundation block. The color differences (ΔE) between each specimen assembly and the target block (a 14×14×12-mm shade A1 LT crystalized e.max block) were recorded with the CIE (Commission internationale de l'éclairage) L*a*b* system. Clinical significance was determined by comparing color differences to perceptibility and acceptability thresholds with the 1-sample t test (α=.05). Both cement color and cement thickness significantly affected the mean values of the color difference (ΔE) of lithium disilicate ceramic assemblies to the target block (P<.001). Among the 5 cements tested, the lowest mean ΔE was observed for Nexus3 white opaque cement. Overall, the combination of Nexus3 white opaque cement and 100-μm thickness led to the lowest mean ΔE. The means of ΔE were below the clinically perceptible level (ΔE<2.6) for combinations of Nexus3 white opaque of 100-μm and 300-μm cement thicknesses (P<.001 and P=.022, respectively). The means of ΔE were below the clinically acceptable level (ΔE<5.5) for the following combinations: Nexus3 white opaque of 50-μm thickness, Nexus3 white, and Nexus3 yellow for all tested cement thicknesses and Multilink white opaque or Multilink yellow of either 50-μm or 100-μm cement thickness (P<.001). The means of ΔE were above the clinically acceptable level (ΔE>5.5) for Multilink white opaque and Multilink yellow of 300-μm cement thickness. The colors of machinable lithium disilicate ceramic restorations placed on Ag-Pd foundation were affected by both the color and thickness of cements. Among the 5 cements tested in this study, Nexus3 white opaque cement of 100 μm or 300 μm yielded shade matches below the clinical perceptible threshold (ΔE<2.6) relative to the target block.
Article
Metal or white opaque foundation restorations may negatively affect the color of machinable lithium disilicate (MLD) ceramic restorations. The purpose of this study was to evaluate the effects of ceramic thickness and foundation restoration materials on the color of MLD restorations. Forty-five ceramic slices in 3 thicknesses (1.0 mm, 1.5 mm, 2.0 mm; 15 slices in each group) were made from low-translucency (LT) shade A1 IPS e.max CAD blocks. Resin cement (Multilink yellow) of 100-μm cement thickness was bonded to 3 different foundation restoration materials: silver-palladium (Ag-Pd) (Albacast) alloy, type III gold (Midas), and white opaque core resin (Paracore white) to make the cement-foundation blocks. After optically connecting each ceramic specimen to the cement-foundation block, the color of each laminated combination was measured with a portable spectrophotometer (Vita EasyShade Compact). The color differences (ΔE) between the specimen assemblies and a control target block (a 12×14×14-mm crystalized shade A1 LT e.max CAD block) were calculated. Two-way ANOVA and general linear model were used to assess the effects of ceramic thickness, foundation materials, and their interactions to the resultant ΔE (α=.05). Clinical significance was determined by comparing color differences to perceptibility and acceptability thresholds by using the t test (α=.05). Both ceramic thickness and foundation materials significantly affected the mean values of color difference (ΔE) of MLD restorations (P<.001). The mean value of ΔE decreased as the ceramic thickness increased. At a ceramic thickness of 1 mm, the color difference was above the clinically perceptible level (ΔE>2.6) with the 3 tested foundation materials (P<.001). As for the foundation materials, the ΔE was the lowest for type III gold alloy, followed by Ag-Pd, then white opaque core resin. The color differences for type III gold and a ceramic thickness of 1.5 or 2.0 mm were below the clinically perceptible level (ΔE<2.6) (P<.001). For Ag-Pd alloy or white opaque core resin, the color differences were above the clinically perceptible level (ΔE>2.6) (P<.001). Ag-Pd alloy reduced, the values of L* and b* parameters of MLD complexes, whereas the white opaque resin increased them. Based on the results of the study, the colors of MLD ceramic restorations were affected by both the ceramic thickness and foundation restoration materials. Increasing ceramic thickness improved the resultant shade matching. Ag-Pd alloy made the ceramic restorations darker and bluish, whereas white opaque core resin made restorations brighter and yellowish.
Article
The purpose of this study was to compare the effect of variations in translucency and background on color differences (ΔE) for different shades of computer-aided design and computer-aided manufacturing (CAD/CAM) lithium disilicate glass ceramics. A pilot study suggested n = 10 as an appropriate sample size for the number of lithium disilicate glass ceramic cylinders per group. High-transparency (HT) and low-transparency (LT) cylinders (diameter, 12 mm; length, 13 mm) were fabricated in three ceramic shades (BL1, A2, C3) using CAD/CAM technology and were cut into specimen disks (thickness, 1.2 mm; diameter, 12 mm) for placement on Natural Die (ND1 and ND4) backgrounds. Four combinations of translucency and background color were evaluated in terms of color differences for the three ceramic shades: group 1 (HT ND1, reference), group 2 (HT ND4), group 3 (LT ND1), and group 4 (LT ND4). A spectrophotometer was used to measure the color differences. Nonparametric tests (Kruskal-Wallis tests) were used to evaluate the color differences among the tested groups, and Mann-Whitney U tests with Bonferroni correction were used as post hoc tests. Furthermore, for each ceramic shade, the HT groups were compared to the LT groups using the Mann-Whitney U test. Significant differences were present among the tested groups of the same ceramic shade (p < 0.001). The highest ΔE values were observed in the HT ND4 group for BL1, while the lowest ΔE values were found in the LT ND1 group for both A2 and C3. Further, the HT groups and the groups with a darker background (ND4) showed increased ΔE values compared with the other groups (p < 0.001). Within the limitations of this study, the results suggested that the translucency and background color significantly influenced the lithium disilicate glass ceramic color among the BL1, A2, and C3 ceramic shades. Changing the underlying color from a lighter background to a darker background resulted in increased color differences.
Article
The increased use of esthetic restorations requires an improved understanding of the translucent characteristics of ceramic materials. Ceramic translucency has been considered to be dependent on composition and thickness, but less information is available about the translucent characteristics of these materials, especially at different thicknesses. The purpose of this study was to investigate the relationship between translucency and the thickness of different dental ceramics. Six disk-shaped specimens of 8 glass ceramics (IPS e.max Press HO, MO, LT, HT, IPS e.max CAD LT, MO, AvanteZ Dentin, and Trans) and 5 specimens of 5 zirconia ceramics (Cercon Base, Zenotec Zr Bridge, Lava Standard, Lava Standard FS3, and Lava Plus High Translucency) were prepared following the manufacturers' instructions and ground to a predetermined thickness with a grinding machine. A spectrophotometer was used to measure the translucency parameters (TP) of the glass ceramics, which ranged from 2.0 to 0.6 mm, and of the zirconia ceramics, which ranged from 1.0 to 0.4 mm. The relationship between the thickness and TP of each material was evaluated using a regression analysis (α=.05). The TP values of the glass ceramics ranged from 2.2 to 25.3 and the zirconia ceramics from 5.5 to 15.1. There was an increase in the TP with a decrease in thickness, but the amount of change was material dependent. An exponential relationship with statistical significance (P<.05) between the TP and thickness was found for both glass ceramics and zirconia ceramics. The translucency of dental ceramics was significantly influenced by both material and thickness. The translucency of all materials increased exponentially as the thickness decreased. All of the zirconia ceramics evaluated in the present study showed some degree of translucency, which was less sensitive to thickness compared to that of the glass ceramics.