UNIVERSIDADE ESTADUAL PAULISTA

“JÚLIO DE MESQUITA FILHO”

Instituto de Ciência e Tecnologia

Campus de São José dos Campos

ORIGINAL ARTICLE DOI: https://doi.org/10.4322/bds.2024.e4356

Braz Dent Sci 2024 Apr/June;27 (2): e4356

This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in

any medium, provided the original work is properly cited.

The optical behavior of pressable lithia-based glass-ceramics under

two diﬀerent heat treatment protocols

O comportamento óptico de vitrocerâmicas prensadas à base de lítio sob dois protocolos diferentes de tratamento térmico

Iman Haggag Elnagar AHMED1 , Amr EL-ETREBY2,3 , Sara Mehanna FOUDAH2 

1 - October 6 University, Faculty of Dentistry, Fixed Prosthodontics. Cairo, Egypt.

2 - Ain Shams University, Faculty of Dentistry, Fixed Prosthodontics. Cairo, Egypt.

3 - Tallinn Health Care College. Tallinn, Estonia.

How to cite: AHMED IHE, El-Etreby A, Foudah SM. The optical behavior of pressable lithia-based glass-ceramics under two different heat

treatment protocols. Braz Dent Sci. 2024;27(2):e4356. https://doi.org/10.4322/bds.2024.e4356

ABSTRACT

Objective: This study aimed to evaluate the optical behavior of pressable lithia-silicate and lithia-zirconia-

silicate glass ceramics toward additional heat treatment protocols. Material and Methods: 40 lithia-silicate discs

(15mm x 1mm) were heat pressed following the manufacturers’ instructions. Discs were divided into four groups

(n=10) according to type as follows: two groups of lithia-silicate-glass ceramics; Gp(E) (IPS e.max Press; Ivoclar

Vivadent AG), Gp(L) (GC Initial LiSi Press, GC), two lithia-zirconia-silicate pressable glass ceramics; Gp(C) (Celtra

Press, Dentsply Sirona) and Gp(A) (VITA Ambria, VITA Zahnfabrik). Each group was subdivided into (n=5):

Subgroup(T1): the thermal tempering temperature was set 9% below the pressing temperature, Subgroup(T2):

the temperature was set 5% below the pressing temperature. Optical properties: color, translucency parameter

(TP), and contrast ratio (CR) were evaluated by spectrophotometer (Aglient Cary 5000 UV-Vis–NIR) after

pressing and after thermal tempering. Results: Thermal tempering regardless of temperature resulted in a color

shift within the acceptability level as ΔE for Gp(E) (3.18±2) followed by ΔE for Gp(L) (2.47±0.19) by ΔE for

Gp(C) (2.26±0.14) and the last ΔE for Gp(A) (1.62±0.13). Subgroup(T2) showed a signicantly higher color

shift with mean ΔE(2.55±0.63) compared to Subgroup(T1) ΔE(2.35±0.59). There was a statistically signicant

increase in TP after tempering for all tested groups parallelled with a decrease in CR values. Conclusion: Heat

tempering of the tested lithia-silicate pressable ceramics had a signicant effect on the optical outcome of these

materials, being lithia-zirconia-silicate ceramics more stable and less affected optically than other lithia-silicate-

glass ceramics.

KEYWORDS

Ceramics; Glass ceramics; Hot temperature; Silicates; Zirconium oxide.

RESUMO

Objetivo: Avaliar o comportamento óptico de cerâmicas pressionáveis de vidro de litia-silicato e litia-zircônia-

silicato sob protocolos adicionais de tratamento térmico. Materiais e métodos: 40 discos de litia-silicato (15mm

x 1mm) foram prensados a quente conforme instruções dos fabricantes. Material e Métodos: 40 discos de litia-

silicato (15mm x 1mm) foram prensados e divididos em quatro grupos (n=10): dois de lithia-silicato-vidro,

Gp(E) (IPS e.max Imprensa) e Gp(L) (GC inicial LiSi Press), e dois de vidro prensado de litia-zircônia-silicato,

Gp(C) (Celtra Press) e Gp(A) (VITA Ambria). Cada grupo foi subdividido em (n=5): Subgrupo(T1): amostras

temperadas a 9% abaixo da temperatura de prensagem, e Subgrupo(T2): a temperatura foi ajustada 5% abaixo

da temperatura de prensagem. As propriedades ópticas, incluindo cor, translucidez (TP) e contraste (CR), foram

avaliadas com um espectrofotômetro (Aglient Cary 5000 UV-Vis-NIR) após prensagem e temperagem térmica.

Resultados: O tratamento térmico resultou em mudança de cor dentro do nível aceitável, com ΔE mais alto para

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

INTRODUCTION

Lithium silicate-based ceramics (LSCs) stand

out among the many all-ceramic materials that

have entered the dental market in recent years

and have the potential to establish themselves

as the preferred choice, particularly for single

restorations [1,2]. Dental manufacturers have

frequently attempted to combine mechanical

efciency and aesthetic quality, making lithium

silicate materials an exemplar that meets both

requirements [3]. The introduction of such

materials that are effectively used in monolithic

mode rendered the necessity for bilayer restoration

redundant [4]. Nevertheless, these materials

were produced in a versatile manner using the

well-known earlier heat pressing technology or

the following digital production using CAD/CAM,

which made them tempting and easy to use [5].

A material with visual qualities comparable

to glass ceramics and superior mechanical

performance was a revolutionary breakthrough

when it was rst introduced to the dental market

in the 1990s as IPS Empress II (Ivoclar Vivadent,

Schaan, Liechtenstein) utilizing the hot-press

technology [6,7]. The next generation was

around 2001 with the release and patenting

of IPS e.max Press (Ivoclar Vivadent, Schaan,

Liechtenstein) [8]. This moldable version utilized

the lost wax technology based on the viscous ow

of glass-ceramics with the advantages of net-

shape processing, decreased porosity, increased

Weibull modulus, increased exural strength, and

providing excellent marginal t [9]. Early around

the year 2005 the introduction of IPS e.max CAD®

(Ivoclar Vivadent, Schaan, Liechtenstein) [10],

took place as the machinable CAD/CAM version

for the chair side delivery of such restorations

utilizing the digital workow. These moldable

and machinable glass-ceramics that precipitate

lithium disilicate have been utilized to create more

than one hundred eight million dental restoration

pieces over 8 years of exclusive presence in

the dental market with recorded excellence of

clinical durability [11,12]. This encouraged

producers and scientists to continue developing

this kind of material to increase its potential

applications, especially once the material’s patent

expired. In 2013 just after the launching of a

second lithium silicate-based ceramic material by

Glidewell Laboratories [13], reinforcements of

these materials by adding zirconia to its chemical

structure was pioneered by lithia-zirconia silicate

glass ceramics such as Celtra Duo (Dentsply

Sirona, York, PA, USA) and Suprenity PC (Vita

Zahnfabrik, Bad Sӓckingen, Germany) with

addition of around 8-12% zirconium oxide to

the structure. The trend of creating novel lithia

silicates with reducing crystal dimensions while

maintaining around 50 vol% crystallinity - to

aid in millability and subsequent processing

capability - is being driven by the inclusion of

ZrO2 as an auxiliary nucleate center [14]. This

resulted in lithium (mono)-silicate crystals and

the presence of biphasic variants with lithium

meta-silicate and lithium disilicate is evident [15].

Variations in the manufacturing techniques and

different microstructural forms of the material

were noticed to have consequences for the nal

material properties [15]. Heat application is

an essential process required during the whole

process of manufacturing. Starting with the early

preprocessing stages of ingot fabrication and

reaching the further treatments involved to create

the final tooth-shaped restoration [6,15,16].

An essential second round of heat application at the

laboratory level is needed as follows; for moldable

versions, these ingots are being subjected to high

pressing temperature dictated by the manufacturer

at the dental lab. Typically, machinable versions

are supplied in a pre-crystallized state that eases the

machinability but needs an essential crystallization

firing cycle. Additional third levels of firing

cycles may be recommended for some esthetic

characterizations, corrections, glazing, or healing

and reinforcements. These tuning procedures with

variable temperatures, heating rates, holding times,

Gp(E) (3,18±2), seguido por Gp(L) (2,47±0,19), Gp(C) (2,26±0,14), e Gp(A) (1,62±0,13). No subgrupo (T2),

houve uma mudança de cor mais signicativa, com ΔE médio de (2,55±0,63), comparado ao subgrupo (T1) com

ΔE médio de (2,35±0,59). Houve aumento signicativo na TP e redução nos valores de RC após o tratamento

térmico em todos os grupos testados. Conclusão: O tratamento térmico das cerâmicas prensadas de litia-silicato

teve um efeito signicativo na sua qualidade ótica, com as cerâmicas de litia-zircônia-silicato mostrando-se mais

estáveis e menos afetadas visualmente em comparação com outras cerâmicas de litia-silicato-vidro.

PALAVRAS-CHAVE

Cerâmica; Cerâmica de vidro; Temperatura quente; Silicatos; Óxido de zircónio.

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

or cooling rates have been evidenced to affect the

material structure, crystallization formation, and

growth [17]. Consequently, the mechanical, and

physical impacts of such treatments were reported

in the literature with controversial conclusions.

While some discussed how applying heat can

elevate internal stresses [18,19], affecting the

strength negatively [18,20], and increasing the

chairside time with post-processing additional

firings required, others have noted that it can

also have a strengthening impact [21,22]. While

speed firing has been attempted to facilitate

crystallization [23], prefacing of such lithia-

silicate based restoration was introduced so

that restorations could be milled, polished, and

delivered with the elimination of the post-mill

crystallization firing needed and substitution

by a minor post-mill glaze ring that inherently

heals any machining aws like in Cerec Tessera

(Dentsply Sirona, York, PA, USA). Moreover

grinding fully crystallized materials without any

post-grind heat treatment was nally introduced

with the launching of materials such as GC Initial

LiSi Block (GC, Tokyo, Japan) [24], and N!CE

(Straumann, Basel, Switzerland) [25]. On the

other hand, manufacturers reported an increase

of about 160 MPa in exural strength for the LSCs

subjected to an additional ring cycle over that of

the machined one [26]. Not only for mechanical

benet, optical optimization for the translucency

level of a material like Amber mill (HASSBio,

Kangneung, Korea) [27], was recommended

by the manufacturer through changing the

temperature of the crystallization cycle. For a

recently introduced lithia-zirconia silicate ceramic

in 2021, VITA Ambria (VITA Zahnfabrik, Bad

Säckingen, Germany) [28], an additional third

step of heat tempering at 800 °C is recommended

by the manufacturer to increase the strength of

the pressed restorations [29]. The effect of such

heat treatments on optical properties such as

translucency and color duplication does not have

a cutting end in the literature up to the authors’

knowledge [6,30,31]. This study simulates two

of the third-level thermal tempering protocols

in the laboratory and explores their impact

on aesthetic parameters such as the color and

translucency of four lithia-silicate pressed glass

ceramics, providing recommendations for the

clinical implications of such tempering protocols

regarding esthetics. The null hypothesis was that

no significant difference in optical properties

between two lithia-silicate and two lithia-zirconia

silicate pressable glass ceramics tested and that the

thermal tempering procedures had no signicant

impact on these properties.

MATERIAL AND METHODS

Sample preparation

Out of 40 pressable lithia-silicate ceramic

ingots, 40 rounded discs measuring 15 mm in

diameter and 1 mm in thickness were created.

These discs were then categorized into 4 groups

(n=10) according to the composition of the

material used;

Two lithia-silicate glass ceramics (LSGCs)

used in this study were:

• Gp (E) (IPS e.max Press; Ivoclar Vivadent AG),

• Gp (L) (GC Initial LiSi Press, GC).

While the two Lithia-zirconia silicate (LZSCs)

glass ceramics used in this study were:

• Gp (C) (Celtra Press, Dentsply Sirona) and

• Gp (A) (VITA Ambria, VITA Zahnfabrik).

For construction of these samples, Wax

patterns (Elastiwax; Keram & Keramik) were

made in a special Teon mold with the desired

geometry, sprued and invested (IPS e.max Special

Investment Material; Ivoclar Vivadent AG), the

wax eliminated at 850 °C for 1 hour, and the

ingots were pressed in a furnace (EP600; Ivoclar

Vivadent AG) as per the protocol recommended

by each manufacturer as shown in Table I.

The specimens were divested by sandblasting

with 50 μm alumina particles at 4 bars of

atmospheric pressure. Then smooth divesting was

used at 2 bars till complete removal of investment

material from discs. After sprues were separated by

separating diamond discs, each attachment point

was smoothened by a diamond disc. The samples

were nally nished and polished using (Optrane

Ceramic Polishing System) sequentially, using the

rst tip for 60 seconds with a speed of 10000 rpm.

While the next tip was used for the same duration

Table I - Recommended pressing temperatures of ceramics

Group (T0)

Gp (A) 880 °C

Gp (C) 870 °C

Gp (E) 917 °C

Gp (L) 910 °C

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

of 60 seconds, but with a slower speed of 6000 rpm

to simulate the clinical situation.

First phase measurements

Optical properties measurements

The color was measured on both a black

and white background using Aglient Cary

5000 UV-Vis-NIR spectrophotometer (Agilent

Technologies, Santa Clara, USA) where the discs

were aligned in the device that is considered

a PC and a spectrophotometer unit. The light

beam passes from the tungsten lamp through

a double monochromator to allow being

monochromatic. Then passes through the

sample to the detector. The passing light beam is

detected by a photomultiplier that is sensitive to

ultraviolet regions. The wavelength ranged from

380 to 780 nm. CIE L*a*b* color values for each

sample were then calculated from the diffuse

reectance using color software which is available

through the Cary WinUV instrument and supports

extensive color standards and calculations.

* Is a measure of the lightness-darkness of

material (perfect black has an

* = 0, and perfect

white has an

= 100).

The

* coordinate is a measure of the redness

(positive value) or the greenness (negative

value), while the

* coordinate is a measure of

the yellowness (positive value), or the blueness

(negative value).

The translucency parameter (TP) was

obtained by calculating the color difference

between specimens over black and white

backgrounds.

( ) ( ) ( )

2 2 2 ½TP Lb Lw ab aw bb bw= − + +−





−

(1)

where: (b) refers to color coordinated over a

black background; (w) refers to color coordinated

over a white background.

While Contrast ratio (CR) was calculated

through;

/CR YB YW=

(2)

[ ]

( )

½ 16 116 100YL= +− ×

(3)

And the CR range was defined from

0 (transparent) to 1 (totally opaque).

Scanning electron microscope (SEM)

A Field Emission Scanning Electron

Microscope (FESEM, Carl Zeiss Ultra, Oberkochen,

Germany) was used to analyze the microstructure.

The glass-ceramics microstructure was examined

using the specimens. Using an etched specimen,

the crystallite microstructure was investigated.

The specimens were cleaned with distilled water

and then etched for 20 seconds using a 9.5%

hydrouoric acid gel. The operating distance was

8 mm, and the acceleration voltage was 5 kV.

Before SEM examination, all specimens were gold

sputter-coated to avoid charging effects during

imaging.

X-ray diffraction analysis

Bruker’s AXS D8 Advance X-ray

diffractometer was used to examine the samples’

mineralogy using monochromatic Cu K α x-ray

angle (= 1.5406 Å). With a counting time of two

seconds per step and a step size of 0.006◦(2),

X-ray diffractograms were obtained between 10◦

and 60◦(2). ICSD reference data served as the

basis for phase identication.

Energy dispersive X-ray analysis (EDX)

A non-destructive X-ray technology termed

energy dispersive X-ray analysis (EDX) was

implemented to gure out the elemental makeup

of materials. The specimen of interest was

identied by the microscope imaging on Electron

Microscopy instruments, which have been

equipped with EDX systems. The obtained EDX

ndings are provided as spectra that display the

peaks of the analysis’s compositional constituents.

Thermal tempering

Following that, each major group of the

four LSCs was split into two groups (n = 5)

in accordance with the thermal tempering

procedure, as follows:

• Sub gp T1 (n = 10), where specimens were

red at a temperature 9% below the pressing

temperature;

• Sub gp T2 (n = 10) the specimens underwent

a ring cycle at a temperature 5% below the

pressing temperature based on the following

re charts for each material.Recommended

tempering temperatures are shown in

Table II.

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

Second phase measurements

Optical properties measurements, Scanning

Electron Microscopic analysis (SEM), X-ray

Diffraction analysis (XRD), and Energy Dispersive

X-ray Analysis (EDX) were repeated for all

samples after thermal tempering the same way

discussed earlier.

Statistical analysis

Using tests of normality (Kolmogorov-

Smirnov and Shapiro-Wilk tests) and examining

the data distribution, numerical data were

examined in preparation for statistical analysis.

The data were all parametrically distributed.

The mean and standard deviation (SD) values of

the data were displayed. Two-way ANOVA testing

and repeated measures ANOVA were employed.

When the ANOVA test was signicant, pairwise

comparisons were performed using Bonferroni’s

post-hoc test.

RESULTS

Translucency: at T0 Pairwise comparisons

between LSCs types revealed there was a

statistically signicant difference between them

(

-value <0.001, Effect size = 0.998). that

Gp (E) showed the statistically significantly

highest mean TP. Gp (L) showed a statistically

signicantly lower mean TP followed by Gp (A)

with a statistically signicant difference between

the two ceramics. Gp (C) showed the statistically

signicantly lowest mean as shown in Table III.

After heat treatment whether with T1 or

T2, in all groups and subgroups, there was a

statistically signicant increase in mean TP after

thermal tempering. Comparing the two tempering

protocols, T1 showed statistically signicantly

lower TP mean values than T2. The difference

was signicantly highest recorded for Gp (E).

In terms of CR mean values, the results

showed that LSCs type had a statistically

signicant effect on mean CR (

-value <0.001,

Effect size = 0.995). recorded the signicantly

highest CR mean values for (LZSC) in Gp (C)

and Gp (A), followed by Gp (L) and Gp (E)

respectively. The selected thermal tempering

whether T1 or T2 had a statistically signicant

decrease in mean CR (

-value <0.001, Effect

size = 0.96). while the effect of changing the

temperature of the thermal tempering procedure

had no statistically signicant effect on mean CR

(

-value = 0.694, Effect size = 0.005).

Color changes

Table IV shown a signicant shift in color in

all groups witnessed after the selected thermal

tempering procedures, being highest evidenced

in Gp (E) with ΔE values of (3.18± 0.2) followed

by Gp (L) ΔE of (2.47± 0.19) then Gp (C) ΔE of

(2.26 ±0.14) and the last Gp (A) ΔE (1.62 ±0.13).

The T2 thermal tempering procedure

provided a noticeably greater color shift ΔE mean

value of (2.55 ± 0.63) against ΔE of (2.35 ±

0.59) with the T1 protocol.

With thermal tempering, the shift was

caused by an increase in L* parameter values and

moving positively toward redness in a* parameter

consistently with moving toward the yellow

direction in b* as shown in Table V.

Scanning electron microscopy

Typically, Gp (ET0) showed multilayered

crystals in the form of rods lying parallel to the

direction of pressing with the average crystal’s

length × width diameters of 3 μm × 680 nm

(Figure 1A). For Gp (ET1), the length and width

grew to 4.5 μm and 700 nm, respectively

(Figure 1B). Further growth to 4 μm length and

870 nm width with Gp (ET2) (Figure 1C).

Table II - Recommended tempering temperatures of ceramics

Group (T0) (T1) (T2)

Gp (A) 880 °C 800 °C 836 °C

Gp (C) 870 °C 790 °C 826 °C

Gp (E) 917 °C 835 °C 872 °C

Gp (L) 910 °C 828 °C 865 °C

Table III - The mean, standard deviation (SD) values and results of repeated measures ANOVA test for comparison between TP of ceramic types

Gp (E) Gp (L) Gp (A) Gp (C)

-value Eﬀect size

(Partial eta squared)

Mean SD Mean SD Mean SD Mean SD

17.53A0.89 15.5B0.7 13.69C0.54 12.24D0.4 <0.001* 0.998

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

Comparing the Gp (LT0) group to the Gp

(ET0) group, there is a noticeable difference in the

microstructure; An interlocking microstructure

was formed by layering platelet-shaped crystals

embedded in the glass matrix. The crystals were

not oriented parallel to the direction of pressing

as compared to Gp (ET0). The crystals in the Gp

(LT0) featured an average length of 2 um and a

diameter of 600 nm (Figure 2A). In contrast, Gp

(LT1) (Figure 2B) displayed 2.5 um in length

Table IV - The mean, standard deviation (SD) values and results of the two-way ANOVA test for comparison between ΔE of ceramic types

regardless of temperature

Gp (E) Gp (L) Gp (C) Gp (A)

-value Eﬀect size

(Partial

eta squared)

Mean SD Mean SD Mean SD Mean SD

3.18 A0.2 2.74 B0.19 2.26 C0.14 1.62 D0.13 <0.001* 0.957

*: Signiﬁcant at P ≤ 0.05

Table V - Average change values of L* a* b* after heat treatments

ΔL Δa Δb ΔE

Gp E T1 1.47 1.17 2.40 3.05

T2 1.56 1.40 2.55 3.30

Gp L T1 1.26 1.10 2.02 2.63

T2 1.40 1.09 2.23 2.85

Gp C T1 1.20 0.67 1.69 2.18

T2 1.28 0.84 1.76 2.34

Gp A T1 0.92 0.67 1.04 1.55

T2 1.02 0.70 1.14 1.69

Figure 1 - (A) SEM IPS e.max Press without tempering; (B) SEM showing IPS e.max Press after the ﬁrst heat tempering at 9%; (C) SEM showing

IPS e.max Press after the second heat tempering at 5%.

A B

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

and 630 nm in width. Meanwhile, reaching a

length of 2.4 um and 985 nm width with Gp

(LT2) (Figure 2C).

The microstructure of Gp (CT0) was found

to be interlocking, with an average crystal length

of 1.8 um and a width of 500 nm (Figure 3A).

The crystal’s length shrank to 1.3 um and its width

expanded to 600 nm in Gp (CT1) (Figure 3B).

The length increased to 2 um as well as its width

signicantly increased to 770 nm in the (GpC)

T2 (Figure 3C).

Figure 4A of Gp (AT0) revealed needle-like

crystals with an average length of 3 um and a

width of 380 nm. Figure 4B of Gp (AT1) revealed

an additional increase in the length and width

of the crystals, measuring 4.5 um and 530 nm,

respectively. The lithium disilicate crystals in Gp

(AT2) solidied and shrank in size (Figure 4C),

which made it challenging to estimate grain sizes

with any degree of accuracy.

X-ray diffraction

Major peaks of lithium disilicate (LisSi2O5)

were observed at 2Ɵ values of 24.7°, and

40 degrees. Traces of lithium phosphate (Li3PO4)

were detected in all groups while traces of

Lithium metasilicate (Li2SiO3) traces were

detected with Gp (C) and Gp (A). The dominant

peak (highest peak) was at 24.7 degrees. The XRD

data showed the highest peak intensity in Gp (E)

equally in T0, T1, and T2, while for Gp (L) highest

peak intensity was at T1 with equal intensities

in T0 and T2. For Gp (C) the highest peak is

with T2 and the least was with T0. For Gp (A)

the highest intensity was at T0 and the lowest

intensity at T1 (Figures 5, 6, 7 and 8).

Energy dispersive X-ray analysis (EDAX)

Minor differences in compositions

between materials and thermal tempering

protocols were analyzed as shown in the

Figures 9, 10, 11 and 12 below.

DISCUSSION

The study aimed to assess how specific

thermal tempering techniques affect the optical

characteristics of pressable LSCs whether

with LSGCs or LZSCs. The selection of those

specific two thermal protocols was based on

the ’manufacturer’s recommendation of one

Figure 2. (A) SEM GC Initial LiSi Press without tempering); (B) SEM showing GC Initial LiSi Press after the second heat tempering at 9%; (C)

SEM showing GC Initial LiSi Press after the second heat tempering at 5%.

A B

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

Figure 3 - (A) SEM Celtra Press without tempering; (B) SEM showing Celtra Press after the second heat tempering at 9%; (C) SEM showing

Celtra Press after the second heat tempering at 5%.

A B

Figure 4 - (A) SEM VITA Ambria Press without tempering; (B) SEM showing VITA Ambria Press after the second heat tempering at 9%; (C) SEM

showing VITA Ambria Press after the second heat tempering at 5%.

A B

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

of the selected materials for an additional

firing cycle at a temperature of 9% below

the pressing temperature [29]. The second

protocol was selected with 5% below the pressing

temperature which is the maximum limit for

temperature deviations below the pressing and

should not be exceeded by any means [32,33].

The obtained results demonstrated that the

chosen thermal tempering processes could have a

considerable impact on the optical result of these

chosen materials, rejecting the null hypothesis.

Translucency is a vital key optical property that

can be employed to replicate the appearance

of natural teeth and precisely match with the

surrounding structure, particularly in the anterior

and esthetic zones [34]. The translucency

of lithium disilicate glass-ceramics depends

on several factors such as: thermal history,

pressure, time (for heat-pressed), amount and

type of nucleating agent, crystal morphology,

microstructure, glass matrix, volume ratio

crystal/glass and difference in the refractive index

between these phases, phase composition and

chemical composition including grain boundaries,

pores, second-phase component, additives, and

light scattering from the surface [35].

Effect on translucency

Before any thermal process: at T0

The translucency was greatly impacted

by the type of LSCs utilized, as seen by the TP

mean values. The LSCs recorded signicantly

higher translucency than the LZSCs as; Gp

(E) recorded the significantly highest mean

TP value (TP=17.52), according to published

literature [36], this is within the same translucency

range of 1 mm for human enamel and dentin,

which are 18.7 and 16.4, respectively. This

implies this material is best suited as an aesthetic

material for anterior cases. Gp(L), with a mean

Figure 5 - XRD analysis of IPS E.max Press, (T0) control group, (T1)

tempering at 9% below pressing temperature, and (T2) tempering at

5% below pressing temperature.

Figure 6 - XRD analysis of LiSi Press (T0) control group, (T1)

tempering at 9% below pressing temperature and (T2) tempering at

5% below pressing temperature

10 20 30 40 50 60 70

Counts

80 X-2022-679 (12)

10 20 30 40 50 60 70

Counts

100

200

X-2022-678 (11)

10 20 30 40 50 60 70

Counts

X-2022-677 (10)

Intensity

°2θ

Intensity

°2θ

Intensity

°2θ

(○) Li2Si2O3 () Li3PO4 (▲) Li2SiO3

P i i [°2θ] (C (C ))

10 20 30 40 50 60 70

Counts

100 X-2022-676 (9)

P i i [°2θ] (C (C ))

10 20 30 40 50 60 70

Counts

100

X-2022-675 (8)

10 20 30 40 50 60 70

Counts

100

X-2022-674 (7)

Intensity

°2θ

Intensity

°2θ

Intensity

°2θ

(○) Li2Si2O3 () Li3PO4 (▲) Li2SiO3

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

TP value of (TP=15.5), came next. Even though

both materials have considerable crystallinity,

the matching of refractive indices between their

crystalline phase 1.55 and glassy phase 1.50,

which permits greater light transmission, was

considered one of the main causes for their

unique translucency [37].

Since it has been shown that lithium disilicate

crystals obstruct light transmission, varying the

size of the crystals in these materials can result

in varying levels of translucency. An earlier

investigation comparing the translucencies of IPS

e.max CAD LT, MT, and HT concluded that the

larger crystal sizes of the IPS e.max HT reduced

its dispersion and lowered its crystal density,

which in turn led to its higher translucency [38].

SEM analysis showed that GP (E) has larger rod-

shaped crystals with an average measured length

of 2.762-3.293 μm and an average measured width

of 533.5-687.9 nm, while GP (L) has more rounded

smaller platelet-shaped crystals with an average

measured length of 2.2μm and an average width

of 580nm. Similar crystal sizes for both materials

were reported by Ohashi et al. [39]. Further

differences in spatial crystal arrangement were

revealed by the SEM analysis. For example, the

crystals in Gp (E) aligned parallel to the sample

surface in an interlocking arrangement, indicating

the pressing direction. Conversely, the scanning

image of GP (L) revealed platelet-shaped crystals

that were randomly oriented, densely fused and

had a highly interlocking microstructure with

irregular edges. In contrast to (Gp E), the crystals’

orientation was not parallel to the pressing plane.

Higher transmittance values may be explained

by the linear, more ordered crystalline structure,

whereas the noticeably lower transmittance values

for the Gp (L) may be explained by the irregular

crystal arrangement, which increases scattering

and reflectance in addition to increasing the

incidence of porosities, which negatively affects

translucency due to the mismatch between the

Figure 7 - XRD analysis of Celtra Press, (T0) control group, (T1)

tempering at 9% below pressing temperature, and (T2) tempering

at 5% below pressing temperature.

Figure 8 - XRD analysis of VITA ambria, (T0) Control group, (T1)

tempering at 9% below pressing temperature, and (T2) Tempering

at 5% below pressing temperature

P i i [°2θ] (C (C ))

10 20 30 40 50 60 70

Counts

X-2022-673 (6)

10 20 30 40 50 60 70

Counts

X-2022-672 (5)

10 20 30 40 50 60 70

Counts

100

X-2022-671 (4)

Intensity

°2θ

Intensity

°2θ

Intensity

°2θ

(○) Li2Si2O3 () Li3PO4 (▲) Li2SiO3

10 20 30 40 50 60 70

Counts

100

200

X-2022-670 (3)

10 20 30 40 50 60 70

Counts

X-2022-669 (2)

P i i [°2θ] (C (C ))

10 20 30 40 50 60 70

Counts

X-2022-668 (1)

Intensity

°2θ

Intensity

°2θ

Intensity

°2θ

(○) Li2Si2O3 () Li3PO4 (▲) Li2SiO3

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

air refractive index and the other phases. Similar

microstructural observations were found when

Hallman et al. [35] investigated the microstructure

of the same materials following pressing.

The pressing temperature for both ceramics

was above 900 °C where a complete transformation

to lithium disilicate Li2Si2O5 occurred with only

minor traces of lithium orthophosphate Li3PO4.

This was evident with the XRD analysis at T0.

In terms of the lowest TP mean values for

the LSCs; the two LZSCs were ordered as follows;

GP (A) and Gp (C) (TP = 13.69 and 12.24,

respectively). As mentioned by Yan et al. [40],

the 8-12% zirconia content in these materials may

seem to be the cause of the increased dispersion

and decreased transmission. This reason could

not be fully depended upon in our investigation

because hardly any phases containing zirconia

were found, either in XRD or in EDAX analysis,

which outweighed the dissolution during the

crystallization procedure. The Zr role was evident

in modifying the crystallization process and

increasing the viscosity of the glassy matrix.

It proved that the presence of ZrO and AlO allowed

the precipitation and domination of the lithium

metasilicate Li2SiO3 phase at a temperature of

around 700 °C as stated by Zhang et al. [15], which

is then reacted again, at higher temperatures of

pressing at 880-870 °C, with the silica in the glass

matrix to form the lithium disilicate crystal phase.

This nal reaction was not complete with both

LZSCs tested materials as traces of the lithium

metasilicate phase were evident in XRD analysis at

T0. This is logically one of the reasons for hindering

the translucency of these materials. Besides the

smaller crystal sizes were evident through SEM

analysis as the crystals were narrower and more

irregularly arranged.

Figure 9 - Microanalysis by EDAX of Gp(E), (T0) Control group, (T1) tempering 9% below pressing temperature and (T2) tempering 5% below

pressing temperature.

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

Consistently the signicantly highest CR

mean value was for LZSCs: GP (C) followed by

GP (A) with no signicant difference between

them, and then the two other groups of LSCs;

Gp (L) and GP (E) the significantly lowest.

The non-significance between both LZSCs

groups may be attributed to that the CR is

mainly for measuring opacity and small light

transmittance differences can’t be detected

through such measurement, while TP is

calculated through the color parameters that

give a more accurate indication about the light

transmittance.

Effect of thermal tempering on translucency

Regardless of the ceramic type and

temperature of the tempering process there was

a signicant increase in translucency with thermal

tempering expressed in a considerable increase

in TP mean value paralleled with a signicant

decrease in CR values. This is consistent with

Farahnaz Nejatidanesh et al. [41] study results

that a signicant increase in translucency with

repeated firing was reported. This might be

explained by the fact that heat treatment causes

the crystals to grow larger while also changing

Figure 10 - Microanalysis by EDAX of Gp(L), (A) Control group, (B) tempering 9% below pressing temperature, and (C) tempering 9% below

pressing temperature.

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

the pore size, crystal distribution, and crystal

orientation. The growth of crystals followed

distinct axes based on the nature of ceramic

and microstructure, leading to a phenomenon

known as “

Ostwald ripening

” in published

works [35], where tiny crystals are sacriced

in favor of bigger ones. This was evident by

the SEM analysis that revealed an increase in

length and width measurements of crystal size

after thermal tempering. For the non-zirconia

reinforced LGSCs, these were considered the

main reasons for increasing translucency. While

for the other two LZSCs Gp (A) (T1, T2) and

Gp (C) (T1, T2) we could include the reason

for further crystallization of the remaining glass

matrix. The pressing temperature for these two

types was lower than that of the others which

might have caused incomplete maturation of

lithium metasilicate crystals as mentioned before

concerning XRD analysis. Subjecting these

materials to a second hit of thermal treatment at a

temperature somewhat lower than their pressing

temperature provided the opportunity for full, as

evidenced by higher peaks of LI2SI2O5 in XRD.

Comparing the tempering temperature

T1 and T2, in terms of TP mean values, Our

research’s findings indicated that selecting a

Figure 11 - Microanalysis by EDAX of Gp(C), (T0) Control group, (T1) tempering 9% below pressing temperature and (T2) tempering 5% below

pressing temperature.

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

tempering temperature T2 of 5% below the

pressing temperature T0 would signicantly boost

the translucency of LSCs compared to T1 of 9%

below the pressing temperature T0. GP (E) was the

greatest expression of it. This was about the same

heat-treated microstructural and compositional

modifications that were previously discussed.

It makes sense for these changes to be more

pronounced at higher temperatures that are closer

to pressing, as shown by the T2 groups. While in

terms of CR values the decrease in opacity recorded

was statistically insignicant in all groups for both

tempering protocols. This was related to the nature

of the CR parameter as mentioned before.

Change in color parameters

The glass-ceramics utilized in this

investigation had the same translucency (medium,

MT) and color (A2), per manufacturer data.

All Groups showed a signicant shift in color

after thermal tempering regardless of tempering

temperature, being ordered from the most stable

material with minimal ΔE of 1.62 (just above

the Perceptibility thresholds) that was GP (A),

followed by GP (C) of ΔE=2.26, then GP Lisi

of ΔE= 2.44 and the greatest shift in color was

with GP (E) with ΔE= 3.18. Thresholds for

acceptability and perceptibility were established

Figure 12 - Microanalysis by EDAX of Gp(A), (T0) Control group, (T1) tempering 9% below pressing temperature and (T2) tempering 5% below

pressing temperature.

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

based on information from published literature

on these values [42].

For the temperature effect, the T1 group

expressed signicantly less shift in ΔE than Group

T2 both being in the range of acceptability.

The formation of a new crystal phase, or the size

change of the original crystal, the disappearance

of impurities and other low-melting substances,

resulting in the fusion of the main crystal phase

and the change of the ceramic surface structure.

Thus, the color changes accordingly. It had been

found that this color shift was attributed to the

shift in all the color parameters. An increase in

L* values of color parameters which means an

increase in the brightness of the material [43],

was recorded with an average increase of

ΔL=1.25 being mostly expressed in Gp (ET2)

with ΔL=1.47 and least in Gp (AT1) with

ΔL= 0.9. This was not expected consistently

with the increase in translucency that implies

usually increase in the amount of transmission.

A previous study by Dong-Dong et al. [44]

pointed out a total downward L* value with

repeated sintering however in the same work

they pointed out an initial increase in value

level with the first three additional sintering

cycles which was then decreased with the

increase in number of sintering cycles. So it is

consistent with our results as we added a single

tempering cycle with different temperatures

in each subgroup (T1 & T2). According to the

pre-discussed microstructural changes with heat

application, crystal size at growth at the expense

of the glassy phase volume and the pores size

and distributional changes lead to increased

translucency. A combination of reducing the

porosity and decreasing boundaries and interfaces

may have caused an increase in the homogeneity

of its crystalline structure, which promoted higher

specular reectance and optical transmission with

minimized refraction and absorption, this may

have been due to the grain and pore distribution

volume reduction, this new scattering pattern

increased in specular reflectance elevating

the L* value yet allowing more transmission.

The highest value indicating the largest shift in

color parameters was with Δb values toward the

yellow direction with maximum value for Gp

(ET2) Δb = 2.55 and lowest with Gp (AT1) Δb=

1.04. The metallic pigment particles infused in the

parent ceramic formula are primarily responsible

for the variation in chroma [45]. By incorporating

various kinds and concentrations of pigment

particles, ceramic materials may exhibit a range

of hues. Typically, pigments are made of metal

oxides that can withstand high temperatures, such

as manganese oxides, zinc, iron red, chromium

red, and titanium yellow [46]. The pigment’s

chemical structure may alter as a result of thermal

tempering, changing the hue [47]. Furthermore,

the dissolution or melting of pigment particles

upon tempering may alter the ceramic’s hue as

well as how the particles react to incident light.

The shift toward redness was the least among

all color parameters being most recorded to GP

(ET2), Δa= 1.40, and least equal with GP (CT1)

and Gp (AT1), Δa=0.67, in all cases, the most

shift in color was recorded to non-reinforced

LGSCs, with IPS emax being the highest affected

specially with T2 tempering protocol where the

temperature was 5% lower than the pressing

temperature, while for zirconia reinforced LZSCs

color shift was minimal being least apparent with

Vita Ambria at T1 tempering temperature.

CONCLUSION

Within the limitations of the present study,

the following conclusions could be made:

1) The most translucent lithium disilicate

types (E. Max Press – LiSi Press) are the

most susceptible to change in color and

translucency with exposure to thermal

tempering protocols;

2) Zr-reinforced lithium silicate-based ceramics

are less sensitive to optical changes with

additional heat treatments;

3) Increasing the tempering temperature near

the pressing temperature had a greater

positive impact on the color and translucency

of pressable lithium disilicates.

Author’s Contributions

IHEA: Formal Analysis, Investigation, Writing

– Review & Editing. AEE: Conceptualization,

Methodology, Data Curation. SMF: Writing –

Original Draft Preparation, Supervision.

Conict of Interest

The authors have no conict of interest.

Funding

The authors have no funding for this article.

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

Regulatory Statement

The authors have no proprietary, nancial,

or other personal interest of any nature or kind

in any product, service, and/or company that is

presented in this article.

REFERENCES

1. van den Breemer CR, Vinkenborg C, van Pelt H, Edelhoff D, Cune

MS. The clinical performance of monolithic lithium disilicate

posterior restorations after 5, 10, and 15 years: a retrospective

case series. Int J Prosthodont. 2017;30(1):62-5. http://doi.

org/10.11607/ijp.4997. PMid:28085983.

2. Meleka N, El-Banna A, El-Korashy D. Color stability and degree

of conversion of amine-free dual cured resin cement used with

two different translucencies of lithium disilicate ceramics. Braz

Dent Sci. 2023;26(2):e3614. http://doi.org/10.4322/bds.2023.

e3614.

3. Huettig F, Gehrke UP. Early complications and performance of

327 heat-pressed lithium disilicate crowns up to five years. J

Adv Prosthodont. 2016;8(3):194-200. http://doi.org/10.4047/

jap.2016.8.3.194. PMid:27350853.

4. Makhija SK, Lawson NC, Gilbert GH, Litaker MS, McClelland JA,

Louis DR,etal. Dentist material selection for single-unit crowns:

findings from the National Dental Practice-Based Research

Network. J Dent. 2016;55:40-7. http://doi.org/10.1016/j.

jdent.2016.09.010. PMid:27693778.

5. Mounajjed R, Layton D, Azar B. The marginal fit of E.max Press

and E.max CAD lithium disilicate restorations: a critical review.

Dent Mater J. 2016;35(6):835-44. http://doi.org/10.4012/

dmj.2016-008. PMid:27546857.

6. Abd El-Moniem H, El-Etreby A, Salah T. Color and translucency

of repressed lithium disilicate glass ceramic subjected to

multiple firings and aging: color and translucency of ceramics.

Braz Dent Sci. 2022;25(3):e3226. http://doi.org/10.4322/

bds.2022.e3226.

7. Schweiger M, Höland W, Frank M, Drescher H, Rheinberger V.

IPS Empress 2: a new pressable high-strength glass-ceramic for

esthetic all-ceramic restorations. Quintessence Dent Technol.

1999;22:143-51.

8. Ivoclar [Internet]. 2017 [cited 2024 apr 27]. Available from:

https://www.ivoclarvivadent.com/en_US/downloadcenter/?

dc=us&lang=en#search-info-212=106005%2C1&search-info-

210=106203%2C1&details=15136

9. Li RW, Chow TW, Matinlinna JP. Ceramic dental biomaterials

and CAD/CAM technology: state of the art. J Prosthodont Res.

2014;58(4):208-16. http://doi.org/10.1016/j.jpor.2014.07.003.

PMid:25172234.

10. Google [Internet]. 2024 [cited 2024 apr 27]. Available

from: lang=en#search-info-210=106202%2C1&search-info-

211=279006%2C1&search-info-212=106007%2C1&details=4857

11. Dental Products Report [Internet]. 2024 [cited 2024 apr 27].

Available from: https://www.dentalproductsreport.com

12. Garling A, Sasse M, Becker MEE, Kern M. Fifteen-year outcome

of three-unit fixed dental prostheses made from monolithic

lithium disilicate ceramic. J Dent. 2019;89:103178. http://doi.

org/10.1016/j.jdent.2019.08.001. PMid:31394121.

13. Ortiz AL, Borrero-Lopez O, Guiberteau F, Zhang Y. Microstructural

development during heat treatment of a commercially available

dental-grade lithium disilicate glass-ceramic. Dent Mater.

2019;35(5):697-708. http://doi.org/10.1016/j.dental.2019.02.011.

PMid:30827800.

14. Ortiz AL, Rodrigues CS, Guiberteau F, Zhang Y. Microstructural

development during crystallization firing of a dental-

grade nanostructured lithia-zirconia glass-ceramic. J Eur

Ceram Soc. 2021;41(11):5728-39. http://doi.org/10.1016/j.

jeurceramsoc.2021.04.036.

15. Zhang Y, Vardhaman S, Rodrigues CS, Lawn BR. A critical review of

dental lithia-based glass-ceramics. J Dent Res. 2023;102(3):245-

53. http://doi.org/10.1177/00220345221142755. PMid:36645131.

16. Phark JH, Duarte S Jr. Microstructural considerations for novel

lithium disilicate glass ceramics: A review. J Esthet Restor

Dent. 2022;34(1):92-103. http://doi.org/10.1111/jerd.12864.

PMid:34995008.

17. Miranda JS, Barcellos ASP, Campos TMB, Cesar PF, Amaral

M, Kimpara ET. Effect of repeated firings and staining on

themechanical behavior and composition of lithiumdisilicate.

Dent Mater. 2020;36(5):e149-57. PMid:32061444.

18. Gorman CM, Horgan K, Dollard RP, Stanton KT. Effects of repeated

processing on the strength and microstructure of a heat-pressed

dental ceramic. J Prosthet Dent. 2014;112(6):1370-6. http://doi.

org/10.1016/j.prosdent.2014.06.015. PMid:25258270.

19. Gozneli R, Kazazoglu E, Ozkan K. Effects of repeated firings on

colour of leucite and lithium di-silicate ceramics. Balkan Journal

of Stomatology. 2013;17(3):122-7.

20. Cho SH, Nagy WW, Goodman JT, Solomon E, Koike M. The effect

of multiple firings on the marginal integrity of pressable ceramic

single crowns. J Prosthet Dent. 2012;107(1):17-23. http://doi.

org/10.1016/S0022-3913(12)60011-0. PMid:22230912.

21. Aurélio IL, Dorneles LS, May LG. Extended glaze firing on ceramics

for hard machining: crack healing, residual stresses, optical and

microstructural aspects. Dent Mater. 2017;33(2):226-40. http://

doi.org/10.1016/j.dental.2016.12.002. PMid:28069245.

22. Aurelio IL, Fraga S, Dorneles LS, Bottino MA, May LG. Extended

glaze firing improves flexural strength of a glass ceramic.

Dent Mater. 2015;31(12):e316-24. http://doi.org/10.1016/j.

dental.2015.10.012. PMid:26599302.

23. Miranda JS, Barcellos ASP, Martinelli Lobo CM, Caneppele TMF,

Amaral M, Kimpara ET. Effect of staining and repeated firing on

the surface and optical properties of lithium disilicate. J Esthet

Restor Dent. 2020;32(1):113-8. http://doi.org/10.1111/jerd.12558.

PMid:31854512.

24. GC America Inc. [Internet]. 2024 [cited 2024 apr 27]. Available

from: https://www.gc.dental/america/products/digital/

gc_initial_lisi_block/GCA_Initial_LiSi_ Block_Brochure-digital.

pdf

25. Straumann. Straumann® n!ce® Glass-Ceramic nice to meet you

[Internet]. 2019 [cited 2024 apr 27]. Available from: https://

www.straumann.com/content/dam/media-center/straumann/

en/documents/brochure/product-information/490.396-en_low.

pdf

26. Saint-Jean SJ. Dental glasses and glass-ceramics. In: Shen JZ,

editor. Advanced ceramics for dentistry. Netherlands: Elsevier;

2014. p. 255-77.

27. HASSBio [Internet]. 2024 [cited 2024 apr 27]. Available

from: https://www.hassbio.com/common/download.

php?fullpath=board/14/364_0.pdf&ﬁlename=%5BEN%5D+Am

ber+Mill_Manual_English.pdf

28. VITA Ambria [Internet]. 2024 [cited 2024 apr 27]. Available from:

https://mam.vita-zahnfabrik.com/portal/ecms_mdb_download.

php?id=100097&sprache=en&fallback=de&cls_session_

id=&neuste_version=1

29. Google [Internet]. 2024 [cited 2024 apr 27]. Available from:

https://id=94347&sprache=en&fallback=de&cls_session_

id=&neuste_version=1

Braz Dent Sci 2024 Apr/June;27 (2): e4356

Ahmed IHE et al.

The optical behavior of pressable lithia-based glass-ceramics under two different heat treatment protocols

Ahmed IHE et al. The optical behavior of pressable lithia-based glass-ceramics

under two diﬀerent heat treatment protocols

30. Li S, Pang L, Yao J. The effects of firing numbers on the

opening total pore volume, translucency parameter and color

of dental all-ceramic systems. Hua Xi Kou Qiang Yi Xue Za Zhi.

2012;30(4):417-9. PMid:22934503.

31. Gonuldas F, Yilmaz K, Ozturk C. The effect of repeated firings

on the color change and surface roughness of dental ceramics.

J Adv Prosthodont. 2014;6(4):309-16. http://doi.org/10.4047/

jap.2014.6.4.309. PMid:25177475.

32. Haag P. Porcelain veneering of titanium: clinical and technical

aspects. Malmö: Faculty of Odontology, Malmö University; 2011.

33. Haag P, Ciber E, Derand T. Firing temperature accuracy of four

dental furnaces. Swed Dent J. 2011;35(1):25-31. PMid:21591597.

34. Vichi A, Ferrari M, Davidson CL. Influence of ceramic and cement

thickness on the masking of various types of opaque posts. J

Prosthet Dent. 2000;83(4):412-7. http://doi.org/10.1016/S0022-

3913(00)70035-7. PMid:10756290.

35. Hallmann L, Ulmer P, Gerngross MD, Jetter J, Mintrone M,

Lehmann F, et al. Properties of hot-pressed lithium silicate

glass-ceramics. Dent Mater. 2019;35(5):713-29. http://doi.

org/10.1016/j.dental.2019.02.027. PMid:30853210.

36. Spink LS, Rungruanganut P, Megremis S, Kelly JR. Comparison

of an absolute and surrogate measure of relative translucency

in dental ceramics. Dent Mater. 2013;29(6):702-7. http://doi.

org/10.1016/j.dental.2013.03.021. PMid:23618557.

37. Schaefer O, Watts DC, Sigusch BW, Kuepper H, Guentsch A.

Marginal and internal fit of pressed lithium disilicate partial

crowns in vitro: a three-dimensional analysis of accuracy and

reproducibility. Dent Mater. 2012;28(3):320-6. http://doi.

org/10.1016/j.dental.2011.12.008. PMid:22265824.

38. Fabian Fonzar R, Carrabba M, Sedda M, Ferrari M, Goracci C,

Vichi A. Flexural resistance of heat-pressed and CAD-CAM

lithium disilicate with different translucencies. Dent Mater.

2017;33(1):63-70. http://doi.org/10.1016/j.dental.2016.10.005.

PMid:27855994.

39. Ohashi K, Kameyama Y, Wada Y, Midono T, Miyake K, Kunzelmann

K-H,etal. Evaluation and comparison of the characteristics of

three pressable lithium disilicate glass ceramic materials. Int J

Dev Res. 2017;7:16711-6.

40. Yan ZL, Xian SQ, Tan T, Liao YM, Yang XY. Influence of zirconia

content on translucency of zirconia-toughened alumina

glass-infiltrated ceramic. West China Journal of Stomatology.

2011;29(2):191. PMid:21598497.

41. Nejatidanesh F, Azadbakht K, Savabi O, Sharifi M, Shirani M.

Effect of repeated firing on the translucency of CAD-CAM

monolithic glass-ceramics. J Prosthet Dent. 2020;123(3):530.

e1. http://doi.org/10.1016/j.prosdent.2019.10.028.

PMid:31916977.

42. Gaidarji B, Perez BG, Ruiz-Lopez J, Perez MM, Durand LB.

Effectiveness and color stability of bleaching techniques

on blood-stained teeth: an in vitro study. J Esthet Restor

Dent. 2022;34(2):342-50. http://doi.org/10.1111/jerd.12850.

PMid:34859941.

43. Wahba MM, Sherif AH, El-Etreby AS, Morsi TS. The effect of

different surface treatments on color and translucency of

bilayered translucent nano-crystalline zirconia before and after

accelerated aging. Braz Dent Sci. 2019;22(2):203-12. http://doi.

org/10.14295/bds.2019.v22i2.1622.

44. Dong-Dong Q, Lei Z, Xiaoping L, Wenli C. Effect of repeated

sintering on the color and translucency of dental lithium

disilicate-based glass ceramic. Hua Xi Kou Qiang Yi Xue Za Zhi.

2015;33(1):50-3. PMid:25872299.

45. Cho MS, Lee YK, Lim BS, Lim YJ. Changes in optical properties

of enamel porcelain after repeated external staining. J

Prosthet Dent. 2006;95(6):437-43. http://doi.org/10.1016/j.

prosdent.2006.04.002. PMid:16765156.

46. El-Khayat H, Katamish H, El-Etreby A, Aboushahba M. Effect of

varying thickness and artificial aging on color and translucency

of cubic zirconia and lithium disilicate ceramics. Braz Dent Sci.

2021;24(3):1-9. http://doi.org/10.14295/bds.2021.v24i3.2623.

47. Pires-de-Souza FCP, Casemiro LA, Garcia LFR, Cruvinel DR.

Color stability of dental ceramics submitted to artificial

accelerated aging after repeated firings. J Prosthet Dent.

2009;101(1):13-8. http://doi.org/10.1016/S0022-3913(08)60282-

6. PMid:19105987.

Iman Haggag Elnagar Ahmed

(Corresponding address)

October 6 University, Faculty of Dentistry, Fixed Prosthodontics,

Cairo, Egypt

Email: memohaggag93@gmail.com Date submitted: 2024 Apr 27

Accept submission: 2024 May 27