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.e4154
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Braz Dent Sci 2024 Jan/Mar;27 (1): e4154
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.
Marginal gap of zirconia and lithium disilicate frameworks
produced by the CAD-CAM technique through a comparator
microscope – in vitro analysis
Fenda marginal de estruturas de zircônia e dissilicato de lítio produzidas pela técnica CAD-CAM através de um microscópio
comparador – análise in vitro
Ellen Christine Rodrigues de ABREU1 , Vicente Colussi FERREIRA2 , Karina Andrea Novaes OLIVIERI2 ,
William Cunha BRANDT1
1 - Universidade Santo Amaro, Programa de Pós-graduação em Odontologia, Departamento de Implantodontia. São Paulo, SP, Brazil.
2 - Instituto e Centro de Pesquisas São Leopoldo Mandic, Departamento de Implantodontia. Campinas, SP, Brazil.
How to cite: Abreu ECR, Ferreira VC, Olivieri KAN, Brandt WC. Marginal gap of zirconia and lithium disilicate frameworks
produced by the CAD-CAM technique through a comparator microscope – in vitro analysis. Braz Dent Sci. 2024;27(1):e4154.
https://doi.org/10.4322/bds.2024.e4154
ABSTRACT
Objective: The aim of this study was to evaluate the marginal gap of frameworks produced using the CAD-CAM
system, from zirconia and lithium disilicate blocks, adapted to a tooth preparation and a gypsum die. Material and
Methods: For this study, a human rst molar tooth was used as a master model with a full crown preparation. It was
molded 20 times to obtain the gypsum die and randomly divided into 2 groups (n=10) for the fabrication of zirconia
and lithium disilicate frameworks. The frameworks were made using pre-sintered zirconia blocks and lithium disilicate
blocks, both CAD-CAM systems. The marginal gap was measured in µm at four points (buccal, palatal, mesial, and distal)
using a comparator microscope with 30x magnication, with the framework seated on the master model (tooth), and
on the gypsum die. Marginal gap data (µm) were evaluated using two-way analysis of variance and Tukey’s test with
a signicance level of 5%. Results: The results showed that there was no statistically signicant interaction between
the factors studied (p=0.223) or isolated factors (ceramic factor p=0.886 and die factor p=0.786). Conclusion: Both
ceramics produced using the CAD-CAM technique did not exhibit statistical differences in marginal adaptation on the
two types of substrates, both on tooth preparation and on the gypsum die.
KEYWORDS
CAD-CAM; Dental ceramics; Dental prosthesis; Lithium disilicate; Marginal adaptation; Zirconia.
RESUMO
Objetivo: O objetivo deste estudo foi avaliar o espaço marginal de estruturas produzidas usando o sistema CAD-CAM, a
partir de blocos de zircônia e dissilicato de lítio, adaptadas a um preparo sobre dente e a um troquel de gesso. Material e
Métodos: Para este estudo, um dente molar humano foi utilizado como modelo mestre com preparo para coroa total. Este
foi moldado 20 vezes para obter o troquel de gesso e dividido aleatoriamente em 2 grupos (n=10) para a fabricação de
estruturas de zircônia e dissilicato de lítio. As estruturas foram feitas usando blocos de zircônia pré-sinterizados e blocos de
dissilicato de lítio, ambos sistemas para CAD-CAM. O espaço marginal foi medido em µm, em quatro pontos (bucal, palatal,
mesial e distal), utilizando um microscópio comparador com ×30 de ampliação e com a estrutura assentada no modelo mestre
(dente) e no troquel de gesso. Os dados de espaço marginal (µm) foram avaliados usando análise de variância bidirecional
e teste de Tukey com um nível de signicância de 5%. Resultados: Os resultados mostraram que não houve interação
estatisticamente signicativa entre os fatores estudados (p=0,223) ou isoladamente (fator cerâmica p=0,886 e fator troquel
p=0,786). Conclusão: Ambas as cerâmicas produzidas usando a técnica CAD-CAM não apresentaram diferenças estatísticas
em relação à adaptação marginal nos dois tipos de substratos, tanto na preparação dentária quanto no troquel de gesso.
PALAVRAS-CHAVE
CAD-CAM; Cerâmicas odontológicas; Prótese dentária; Dissilicato de lítio; Adaptação marginal; Zircônia.
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Abreu ECR et al.
Marginal gap of zirconia and lithium disilicate frameworks produced by the CAD-CAM technique through a comparator microscope – in vitro analysis
Abreu ECR et al. Marginal gap of zirconia and lithium disilicate frameworks
produced by the CAD-CAM technique through a comparator
microscope – in vitro analysis
INTRODUCTION
The growing demand for aesthetic dental
procedures has driven the use of pure ceramics
as biocompatible and functional alternatives to
conventional restorative materials [1]. In addition
to aesthetics, factors such as mechanical strength,
color stability, and precision in marginal
adaptation are essential for the success of these
restorations [2]. Dental ceramics have a variety
of shades similar to natural teeth, providing high
aesthetics, as well as mechanical strength and
durability [3].
The introduction of digital systems, such as
scanners and milling machines, for the fabrication
of prosthetic restorations from ceramic blocks has
allowed the standardization of the work process
and the use of materials with better performance
and aesthetic quality [4-6]. Tetragonal zirconia
partially stabilized with yttrium oxide (Y-TZP)
has been incorporated into dentistry as a material
for all-ceramic restorations using the CAD-CAM
(Computer-Aided Design/Computer-Aided
Manufacturing) system [7,8]. Zirconia has
made a name for itself as a dental material due
to its biocompatibility, hardness, mechanical
strength, wear resistance, and excellent
chemical and dimensional stability, enabling
the fabrication of xed partial prostheses with
three or more elements, including posterior teeth
and abutments on implants [9-13]. However,
the opacity of this material, due to its high
crystallinity and density, historically required
the use of feldspathic ceramics to achieve the
desired aesthetics [14,15]. Nevertheless, chipping
and debonding of the veneering material were
common failures [13]. Recently, translucent
zirconia has been introduced to the market,
enabling monolithic restorations with superior
strength and aesthetics [16,17].
Lithium disilicate-reinforced ceramics stand
out due to their excellent optical properties. This
vitreous material offers options for both CAD-
CAM systems and pressing techniques. Due to
its favorable translucency and variety of colors,
it is possible to make single-layer (monolithic)
structures, which can subsequently be built up
or simply glazed [18]. Clinical applications of
the lithium disilicate-based system include inlay,
onlay, overlay, laminate veneers, full crowns, and
xed partial prostheses of up to three elements
in the anterior and premolar regions [14,18-20].
The marginal adaptation of ceramic
restorations is one of the crucial factors for
the clinical success and longevity of these
rehabilitations [20,21]. Therefore, maladaptation
that exceeds clinically acceptable limits (up to
120 µm) can result in biofilm accumulation,
predisposing to periodontal disease, recurrent
caries, and pulpal inammation [22]. In addition,
exposure of the luting agent to intraoral uids
can accelerate cement dissolution, leading
to restoration failure [23,24]. Zirconia and
lithium disilicate restorations seem to offer
excellent marginal adaptation with reduced
microgaps, thereby maintaining the health
of periodontal structures and ensuring long-
term clinical success [25-27]. To achieve this,
obtaining the denitive mold, either physically
or digitally, through conventional molding or
digitalization is necessary to provide information
for adequate marginal adaptation [28-33]. While
both materials are classied as dental ceramics,
there are differences between them, such as
resistance, translucency, aesthetics, and hardness.
The latter characteristic poses challenges in
occlusal and proximal adjustments with diamond
burs, potentially causing microcracks after the
crystallization process [34,35].
Although the tips used in milling machines
are specic to each material type, the hardness
of zirconia and the size of the tip can result in
restorations with fewer details when compared
to lithium disilicate restorations [36]. Similarly,
the number of milling machine axes can lead
to marginal gaps with statistically significant
differences [37,38].
Therefore, the objective of this study was
to evaluate the marginal microgap of CAD-
CAM infrastructures made with zirconia and
lithium disilicate blocks when adapted to dental
preparations and gypsum dies. The working
hypothesis is that there are differences in the
marginal microgap between the materials and
their variables.
MATERIAL AND METHODS
This study was submitted to the Research
Ethics Committee of São Leopoldo Mandic
University, (Campinas, SP, Brazil) and registered
under the number 2.270.526.
For this study, an extracted human left lower
rst molar [39] was selected according to the
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Abreu ECR et al.
Marginal gap of zirconia and lithium disilicate frameworks produced by the CAD-CAM technique through a comparator microscope – in vitro analysis
Abreu ECR et al. Marginal gap of zirconia and lithium disilicate frameworks
produced by the CAD-CAM technique through a comparator
microscope – in vitro analysis
following inclusion criteria: absence of enamel
or dentin fracture; dimensions and morphology
of the crown consistent with the size of the
preparation to be performed.
The element was included in a gypsum
base (Durone, Dentsply, Pennsylvania, USA),
leaving 1mm of the cervical area exposed
for crown preparation, denominated master
model (Figure 1). The crown preparation was
performed manually, under visual inspection,
in high rotation under abundant cooling, using
spherical diamond burs #1012 and cylindrical
#3216 (KG Sorensen, São Paulo, SP, BR), with
the following settings: 1.2 mm circumferential
reduction in chamfer, occlusal reduction of
2 mm, and convergence angle of the axial walls
of 6°(degrees).
Twenty impressions of the master model
were made with heavy-body and light-body
polyvinyl siloxane (Futura AD, Nova DFL Produtos
Odontológicos, Taquara, Rio de Janeiro) using
the compression molding method in 1 step to
obtain the gypsum casts, with the aid of an
individual adapted tray. Then the molds was
poured with Type IV gypsum (Durone, Dentsply,
Pensilvânia, EUA) for die casting. The handling
and proportioning of the materials used followed
the guidelines of their respective manufacturers.
As well as the master model, the casts were
included in a gypsum base, leaving the cervical
exposed for better visualization of the end of
the preparation (Figure 2). The 20 gypsum
casts obtained were divided into 2 groups with
10 samples each, according to the infrastructure
ceramic:
Group 1 - zirconia-based frameworks;
Group 2 - lithium disilicate frameworks.
To obtain the frameworks, 10 blocks of
pre-sintered zirconia (ICE Zirkon Transluzent
Plus, Zirkonzahn®, Gais, Itália) and 10 blocks
of lithium disilicate (Rosetta SM, OdontoMega,
Ribeirão Preto, São Paulo, BR) in LT W2 shade
were used and prepared in the CAD-CAM system
from Zirkonzahn®. The master model and the
gypsum dies were scanned (Scanner S600 ARTI,
Zirkonzahn®, Gais, Itália), which features two
high-resolution cameras, allowing a faster and
more accurate scanning. The software used
for digital design (CAD) was Zirkonzahn.Scan
(Zirkonzahn®, Gais, Itália) and the les were
sent to the milling software Zirkonzahn Fräsen
(Zirkonzahn®, Gais, Itália) (Figure 3). The milling
process was performed in the M1 5-Axis milling
machine (Zirkonzahn®, Gais, Itália) and then
Figure 1 - Master model.
Figure 2 – Gypsum die.
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Abreu ECR et al.
Marginal gap of zirconia and lithium disilicate frameworks produced by the CAD-CAM technique through a comparator microscope – in vitro analysis
Abreu ECR et al. Marginal gap of zirconia and lithium disilicate frameworks
produced by the CAD-CAM technique through a comparator
microscope – in vitro analysis
the blocks were sintered according to each of
the manufacturer’s recommendation using the
Zirkonofen 600 oven (Zirkonzahn®, Gais, Itália)
(Figure 4).
The gap were measured by passively placing the
frameworks on the master model and the gypsum
die on half of each side of the samples, that is, in
the middle of the buccal, lingual, mesial, and distal
faces (Figure 5), from the margin to the cervical end
of the preparation. The measurement points were
marked with colored graphite for better visualization
under the microscope. The measurements were
performed with a comparator microscope (Olympus
Corporation - USA) at ×30 magnification, and
the measurement system was the OLYMPUS
MMDC 201. Each face was measured in triplicate,
obtaining, thus, the average.
Statistical analysis
Prior to the analyses, the marginal gap
data (µm) were evaluated as for their normality
by the Shapiro-Wilk test (p=0,071). They
were then submitted to ANOVA two-way
analysis of variance. The study factors were
the ceramics (lithium disilicate and zirconia)
and the different dies (tooth and gypsum).
Statistical calculations were conducted using a
5% signicance level (α = 0.05) in SigmaPlot
Figure 3 - Master model scan (A); margin delimitation with Zirkonzahn Fräsen software (B) (Zirkonzahn®, Gais, Italy).
Figure 4 - Frameworks (A) Zirconia (B) lithium disilicate.
Figure 5 - The measurement points.
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Marginal gap of zirconia and lithium disilicate frameworks produced by the CAD-CAM technique through a comparator microscope – in vitro analysis
Abreu ECR et al. Marginal gap of zirconia and lithium disilicate frameworks
produced by the CAD-CAM technique through a comparator
microscope – in vitro analysis
14.0 software (Systat Software Inc., San Jose,
California, USA).
RESULTS
Table I shows the mean values and the
standard deviation of the marginal gap of the
different ceramics in relation to the different
dies.
The two-factor analysis of the variance
showed no statistically signicant interaction
between the studied factors (p=0.223), as there
was no statistically significant result for the
isolated factors - ceramic factor (p=0.886) and
die factor (p=0.786).
DISCUSSION
In the present study, the results demonstrated
that there was no difference in adaptation
between zirconia and lithium disilicate using the
CAD-CAM technique, nor between the evaluation
of the adaptation of the master model (tooth)
and the gypsum die; therefore, the experimental
hypothesis was rejected.
The standardization of processes and the use
of the CAD-CAM system for the manufacture of
both types of ceramics resulted in similar gaps,
especially in the gypsum die, which presented
average values of 74 µm ±47 for lithium disilicate
and 55 µm ±19 for zirconia. Other studies that
evaluated gaps using CAD-CAM technology
obtained results without statistical differences
between materials, as shown in the present
study [1,27].
The milling machine used in this study had
a 5-axis system (Zirkonzhan M1). The number
of axes on the milling machine can compensate
for differences in the t of ceramic restorations.
This observation aligns with the results of our
study, emphasizing the importance of the milling
machine’s axis count in ceramic restoration
precision and indicating that a higher axis count
correlates with increased accuracy. Studies have
demonstrated that a 5-axis milling machine
produced better fits than the results from a
3-axis milling machine, regardless of the type of
ceramic [27,37,38]. However, a study comparing
3-axis and 5-axis milling machines highlighted
that the 3-axis milling machine produced crowns
with smaller marginal discrepancies. This nding
suggests that, despite the significance of the
axis count, other factors, such as the diameter
of the milling tool tips, play a crucial role in the
precision of marginal adaptation. According to
the authors, the difference may be because the
3-axis milling machine used a 1 mm diameter
diamond bur to cut the internal surface of the
crown, while the 5-axis milling machine uses
burs with diameters of 3 mm, 2 mm, and 1 mm
in sequence to cut the surface of the crown
notch, contributing to the discrepancy in the
margin [35]. In addition to these results, a study
observed that zirconia restorations exhibited
the least occlusal contact delity during milling
and post-processing, along with the lowest need
for occlusal adjustment, advocating for reduced
occlusal compensation [36]. Collectively, these
studies offer a comprehensive perspective on
the impact of various variables on the quality
of ceramic restorations produced by CAD-CAM
milling machines. Furthermore, the effect of
the CAD-CAM technique used to produce the
structure in this study resulted in acceptable
marginal gaps that were smaller than the value
established in the literature (120 µ) [40,41].
An important factor to be considered after
milling is the sintering of these ceramics. This
must be controlled for each type of ceramic, as
this process provides the mechanical resistance
and translucency of each material [39,42].
In this study, zirconia was sintered for 2 hours
(8 ºC/min), until a nal temperature of 1500ºC,
and lithium disilicate for 10 minutes (95ºC/min),
reaching a nal temperature of 850ºC. Studies
demonstrate that sintering can significantly
interfere with the marginal and internal
adaptation of ceramic crowns [18,39,42].
Therefore, it is extremely important to follow
the protocols recommended by manufacturers,
especially the time x temperature relationship
to achieve the potential of glass ceramics [42].
The materials used in the master model
(tooth, metal or resin) and in the production
of dies (gypsum or resin) can contribute to the
marginal gap values. In the present study, the
master model was obtained from the preparation
Table I - Mean values of marginal gap ±standard deviation (μm)
Master
model Gypsum die Overall
average
Lithium
disilicate 54 ±19 74 ±47 64 ±37
Zirconia 68 ±63 55 ±19 61 ±43
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Abreu ECR et al.
Marginal gap of zirconia and lithium disilicate frameworks produced by the CAD-CAM technique through a comparator microscope – in vitro analysis
Abreu ECR et al. Marginal gap of zirconia and lithium disilicate frameworks
produced by the CAD-CAM technique through a comparator
microscope – in vitro analysis
of an extracted human tooth and after molding,
a type IV gypsum was used to create the die.
These factors did not affect the gap, as there
was no difference in the values between the
master model (tooth) and the gypsum die. Even
taking into account the dimensional changes that
gypsum can undergo, the study demonstrates
that, if the processes are carried out properly,
favorable results can be achieved. Studies that
used the metal master model and type IV gypsum
models concluded that the different materials
did not inuence the accuracy of the marginal
adaptation [43,44]. Furthermore, a comparative
study of accuracy between conventional printing
and digital printing concluded that gypsum
models still had more details in grooves and
ssures compared to CAD-CAM models [45].
The dimensional accuracy of an impression
is decisive in the adaptation of a xed prosthetic
work; therefore, the choice of technique and
impression material can contribute to marginal
discrepancies [29,30]. Some studies show
superior accuracy in the 2-step technique (double
mixing) [29,30], while others prefer the 1-step
technique [31]. In this study, the double-mix
(one-step) molding technique was applied, based
on studies that demonstrated superiority in
terms of marginal adaptation [31]. It should be
considered that this study was conducted in vitro,
and clinical factors such as gingival retraction,
bleeding, and saliva were not considered. With
the advancement of digital dentistry, digital
impressions made with intraoral scanners
have presented models with greater precision
than conventional impression techniques [32].
Furthermore, the procedure is faster and shortens
the operative time, in addition to being more
comfortable for the patient [33].
Both ceramics produced by CAD-CAM
technology exhibited similar results in terms of
marginal adaptation on the tooth preparation
and gypsum die. Thus, the ceramics did not
present statistical differences as materials
for the infrastructure (disilicate vs. zirconia).
In addition, the adaptation of the margin
was within acceptable values. Most of the
literature considers acceptable values of up
to 120µm, a value initially determined for
metallic structures [43]. Regarding zirconia,
a systematic review concluded that marginal
integrity presented high success values for
different observation periods [26], and another
study presented satisfactory results in relation to
marginal adaptation in its in vivo study, reaching
a survival rate of 100% for crowns made of
monolithic zirconia, monitored for 2 years [15].
These results highlight the increasing accuracy
of these systems, with some studies indicating
statistical differences between ceramics [44].
Other variables, such as scanner, software,
and operator, did not inuence the results of this
study. However, the importance of technology,
its development, and understanding, in addition
to fundamental knowledge in prosthetics and
dental materials, cannot be underestimated.
According to previous research, these variables
signicantly affect the results obtained through
intraoral scanning [46].
Since this study was conducted in vitro,
the mentioned variables, which could inuence
the clinical outcome of the restorations, were
considered limitations. Therefore, controlled
in vivo studies are needed to evaluate scanning
accuracy in conjunction with clinical factors and
the application of current technologies.
CONCLUSION
According to the results, it can be concluded
that both ceramics produced through CAD-
CAM technique showed no statistical differences
regarding marginal adaptation on the two types of
substrates, both on the tooth preparation and on the
gypsum die, and that the gap values are acceptable.
Author’s Contributions
ECRA: Conceptualization, Resources, Writing
– Review & Editing. VCF: Conceptualization,
Resources, Methodology, Data Curation, Formal
Analysis, Writing – Original Draft Preparation.
KANO: Supervision, Methodology, Validation.
WCB: Supervision, Methodology, Formal Analysis,
and Writing – Review & Editing.
Conict of Interest
The authors have no conicts of interest to
declare.
Data availability
Datasets related to this article will be
available upon request to the corresponding
author.
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Abreu ECR et al.
Marginal gap of zirconia and lithium disilicate frameworks produced by the CAD-CAM technique through a comparator microscope – in vitro analysis
Abreu ECR et al. Marginal gap of zirconia and lithium disilicate frameworks
produced by the CAD-CAM technique through a comparator
microscope – in vitro analysis
Funding
This research did not receive any specic
grant from funding agencies in the public,
commercial, or not-for-prot sectors.
Regulatory Statement
This study protocol was reviewed and
approved by the Research Ethics Committee of
São Leopoldo Mandic University (Campinas,
SP, Brazil), and registered under the number
2.270.526.
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William Cunha Brandt
(Corresponding address)
Universidade Santo Amaro, Programa de Pós-graduação em Odontologia, Departamento
de Implantodontia. São Paulo, SP, Brazil.
Email: williamcbrandt@yahoo.com.br
Date submitted: 2023 Nov 14
Accept submission: 2024 Mar 03
