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Effect of thickness of zirconia framework on fracture strengthand fracture mode of ceria-stabilized tetragonal zirconia
polycrystals/alumina ceramic restoration on resin tooth abutment
Vibul Paisankobrit, DDS, Satoshi Omori, DDS, PhD, Rie Fujita, DDS, PhD, Yoji Ueda,
DDS, PhD, Reina Nemoto, DDS, PhD, and Hiroyuki Miura, DDS, PhD
Fixed Prosthodontics, Department of Restorative Sciences, Division of Oral Health Sciences, Graduate
School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan
Purpose: This study aimed to evaluate the fracture strength and fracture mode of ceria-stabilized tetragonal
zirconia polycrystals/alumina (Al2O3) nanocomposites (Ce-TZP/A) and yttria-stabilized tetragonal zirconia
polycrystals (Y-TZP) ceramic restorations in different thicknesses of frameworks on resin tooth abutments andto assess the usability of Ce-TZP/A ceramic restoration with thin zirconia frameworks.
Materials and Methods: Artificial maxillary second premolars were prepared for all-ceramic and metal-ceramic
restoration. Then resin tooth abutments were duplicated. Four groups of zirconia-ceramic restoration framework
were fabricated (n = 10): standard 0.5 mm thickness frameworks (Y-TZPs, Ce-TZP/As) for all-ceramic
restoration preparation, and modified 0.3 mm thickness with palatal support frameworks (Y-TZPm,
Ce-TZP/Am) for metal-ceramic restoration preparation. Porcelains were pressed. The restorations were fixed toresin abutment teeth and loaded vertically until fracture. The maximum fracture loads were recorded as fracture
strengths. One-way ANOVA and post hoc test (Tukey’s HSD) were performed. The fracture modes wereobserved and statistically analyzed with Fisher’s exact test. All tests were used at a significant level of 0.05.
Results: The fracture strength of Ce-TZP/Am (2,824.1 ± 320.8 N) was significantly higher than Y-TZPm(2,399.7 ± 188.8 N) but was not significantly different from Ce-TZP/As (3,056.4 ± 337.1 N). There was no
significant difference in fracture mode between groups.
Conclusion: Within the limitations of this study, Ce-TZP/A can be use with the thin modified design framework.
Ce-TZP/Am provided good fracture strength and sufficiency for clinical use.
(Asian Pac J Dent 2017; 17: 31-40.)
Key Words: Ce-TZP/A, fracture strength, framework thickness, zirconia-ceramic restoration

Introduction
Nowadays, esthetic dentistry has become popular. All-ceramic restorations or metal-free restorations are being
used increasingly instead of metal-ceramic restorations for many reasons such as esthetic capability [1,2], color
stability, low thermal conductivity [3], low risk of metal allergy, and low plaque accumulation [4].
Metal-ceramic restorations were used and recommended for more than 50 years due to their durability and fit to
the abutment, but their esthetics were not satisfied as compared to all-ceramic restorations (metal-freerestorations). It is difficult to cover metal and create natural tooth color, due to its dark color. In addition, metals
may cause bluish appearance of the surrounding soft tissues [5,6].
Recently, all-ceramic restorations are often preferred to metal-ceramic restorations. The increasing esthetic
demand has driven the development and enhancement of dental ceramics [2,3]. One of the most recent dental
ceramics is zirconia [3], which is a high strength ceramic. In the past, due to its high strength and limited
manufacturing technology, dental zirconia was fabricated with difficulty, and milling machines could not attainsatisfied accuracy and marginal adaptation. Hence, dental zirconia has rarely been acceptable. However, recent
advancements in the CAD-CAM technology have made dental zirconia affordable for restorations such as fixed
partial dentures (FPDs) [7], removable partial dentures, and complete dentures [8].
Zirconia has been played an important role in all-ceramic restorations due to its superior mechanicalproperties including high fracture strength, high fracture toughness, and high biocompatibility [6]. Zirconia canbe used as frameworks of restorations and FPDs instead of metal framework, while maintaining their sufficient31

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strength, but without metallic colored appearance. In addition, the use of zirconia-ceramic restorations canprovide better esthetic appearance from outer porcelain and high strength from inner zirconia framework [6].
Currently, yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) are used widely in clinics due to their
good flexural strength (1,000 MPa), but they have moderate fracture toughness (7 MPa) [9]. While
ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP) are very high fracture toughness zirconia (23 MPa),
they have some disadvantages such as lower flexural strength (450 MPa) when compared to Y-TZP [9], and they
are not available for use in the dental field. Therefore, Ce-TZP was developed into ceria-stabilized tetragonal
zirconia polycrystals/alumina (Al2O3) nanocomposites (Ce-TZP/A) that have both high flexural strength andfracture toughness (1,000 MPa and 18 MPa) [9] to improve the low strength of Ce-TZP [10].
Ce-TZP/A was developed by integrating nanometer-sized Al2O3 and Ce-TZP particles in grains of the othercomponent. Al2O3 particles were dispersed within the Ce-TZP grains and grain boundaries, and Ce-TZP particles
were dispersed within the Al2O3 grains and grain boundaries. This homogeneous dispersion of Al2O3 particles in
the Ce-TZP matrix resulted in increased hardness, flexural strength, hydrothermal stability, and suppressed grain
growth of tetragonal zirconia while preserving its toughness [10,11].
The strength of zirconia comes from stress-induced transformation toughening that the tetragonal phasetransforms into monoclinic phase. This transformation is associated with an increase in volume (3-5%) and local
compressive stress fields are made and tend to stop crack propagation [12]. However, some zirconia such as
Y-TZP have a few problems concerning low temperature aging degradation (LTAD) [10,13-16]. The LTAD iscaused by unintentional phase transformation induced by fatigue at low-temperatures and exposure to moist
environments such as water or saliva in the oral cavity [14,16,17], which may decrease the strength in thelong-term and may lead to catastrophic failure of zirconia [18]. On the other hand, Ce-TZP/A has total resistanceto LTAD [8,15,16,19], and can thus maintain its strength for a longer period. From the many excellent properties
described above, Ce-TZP/A has an advantage over Y-TZP, but usability needs to be studied further.
Tooth preparation design of all-ceramic restorations requires more spaces than metal-ceramic restorations,which limits usability and is a significant disadvantage. Due to superior mechanical properties of Ce-TZP/A, it
may be possible to reduce the thickness of Ce-TZP/A ceramic restoration framework from the usual standard of
Y-TZP ceramic restoration framework, which is commonly used in many restorations. Thinner zirconia
framework would require less tooth reduction, which follows the concept of minimal intervention [20]. This
would lead to better preservation of pulp vitality, especially in young age patients who have large pulp cavities[21,22]. From these improved mechanical properties, the clinical applications of zirconia-ceramic restorations
were supposed to expand. We have already reported that thin Ce-TZP/A frameworks gave a good result [23], but
the effect of thickness of Ce-TZP/A ceramic restoration framework combined with pressed porcelain has notbeen studied in detail.
The aims of this study were to evaluate the fracture strength and fracture mode of Ce-TZP/A and Y-TZP
ceramic restorations in different thicknesses of zirconia frameworks on resin tooth abutments and to assess theusability of Ce-TZP/A ceramic restorations with thin Ce-TZP/A frameworks.

Materials and Methods
Abutment tooth preparations
Artificial maxillary second premolar teeth (Simple Root Tooth Model A5A-500 #15, Nissin Dental Product Inc.,

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Kyoto, Japan) were prepared for two types of preparations: metal-ceramic restoration preparation andall-ceramic restoration preparation. The metal-ceramic restoration abutment was prepared with a 1.0 mm heavy
chamfer finish line at buccal margin, 0.5 mm chamfer finish line at palatal margin, 1.3 mm occlusal reduction of
buccal cusp (non-functional cusp), and 1.8 mm occlusal reduction of palatal cusp (functional cusp). The
all-ceramic restoration abutment was prepared with a 1.0 mm overall heavy chamfer finish line, 1.5 mm occlusal
reduction of buccal cusp (non-functional cusp), and 2.0 mm occlusal reduction of palatal cusp (functional cusp).
Both types of preparations had an axial convergence angle of approximately 6-degrees, and the palatal surfacesof the functional cusp were reduced in two planes. (Fig. 1)

Fig. 1
Proximal view ofabutment toothpreparations(A) all-ceramic
restoration
preparation,(B) metal-ceramic
restoration
preparation

Fabrication of resin tooth abutments
After preparing both the artificial teeth, their impressions were made with transparent vinyl polysiloxane
impression material (Memosil 2, Heraeus Kulzer GmbH, Hanau, Germany). The impressions were used as
duplicating molds for resin tooth abutments. After that, an auto-mixed composite resin (Clearfil DC coreautomix, Kuraray Noritake Dental Inc., Tokyo, Japan) was injected into the transparent duplicating molds. The
composite resin paste was cured using a light curing unit (Optilux 501, Sybron Dental Specialties Japan Inc.,Tokyo, Japan) for 15 s on each side (buccal, palatal, mesial, and distal). After the resin tooth abutments were
cured, they were removed from the molds. After 30 minutes, the procedure was repeated for the next resin
abutment. Twenty resin tooth abutments for metal-ceramic restoration preparation and twenty resin tooth
abutments for all-ceramic restoration preparation were fabricated.
Fabrication of dies
The impressions of the prepared teeth were made with hydrophilic vinyl polysiloxane impression material(Exafine, GC Corp., Tokyo, Japan). The impressions were poured with type IV die stone (New Fujirock, GC
Corp.). The metal-ceramic restoration preparation die and all-ceramic restoration preparation die were thus
fabricated.
Fabrication of zirconia-ceramic restoration frameworks
In this study, two zirconia materials were used for fabricating zirconia-ceramic restoration frameworks, whichwere Y-TZP (Cercon base, DeguDent, Hanau, Germany) and Ce-TZP/A (NANOZR, Panasonic Healthcare,
Tokyo, Japan). Moreover, two different framework designs were used. First one was standard zirconia-ceramic
restoration framework design, which was 0.5 mm overall wall thickness framework used for all-ceramic
restoration preparation. The other was modified zirconia-ceramic restoration framework design, consisting of 0.3
mm wall thickness framework with additional palatal support (1.0 mm thick and 2.0 mm high) at palatal margin
extending to the proximal surfaces, used for metal-ceramic restoration preparation (Fig. 2).

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Fig. 2 Proximal view of framework designs and restoration thicknesses(A) Standard design framework zirconia-ceramic restoration (Y-TZPs, Ce-TZP/As); 0.5 mm overall thickness
framework(B) Modified design framework zirconia-ceramic restoration (Y-TZPm, Ce-TZP/Am); 0.3 mm overall thickness
framework with additional palatal support (1.0 mm thick and 2.0 mm high) at palatal margin extending to theproximal surfaces(A), (B) Pressed-over porcelain 1.0 mm thickness on the occlusal surface of non-functional cusp and 1.5 mm
thickness on the occlusal surface of functional cusp

Stone dies from the previous step were used as master dies for making four groups of zirconia-ceramic
restoration frameworks as follows; 1 Standard Y-TZP framework (Y-TZPs), 2 Standard Ce-TZP/A framework(Ce-TZP/As), 3 Modified Y-TZP framework (Y-TZPm), and 4 Modified Ce-TZP/A framework (Ce-TZP/Am).
Ten frameworks were fabricated for each group (total = 40). Y-TZPs and Y-TZPm were fabricated by using
CAD-CAM system (Cercon smart ceramics, DreguDent). The dies were scanned (Cercon eye, DeguDent),
frameworks were designed (Cercon art, DeguDent), milled (Cercon brain, DeguDent), and sintered (Cercon heat,
DeguDent) according to the manufacturer's recommendations. Ce-TZP/As and Ce-TZP/Am were fabricated byusing another CAD-CAM system (C-Pro system, Panasonic Healthcare). The dies were scanned, designed,
milled, and sintered according to the manufacturer's recommendations. All frameworks were checked andadjusted for internal fit with resin tooth abutment by using fit checking vinyl polysiloxane material (Fit checker,
GC Corp.) for ensuring acceptable internal fit and no difference within each group.
Fabrication of restorations
For all zirconia-ceramic restoration frameworks, outer surfaces of the frameworks were treated using
air-abrasion with 70 µm alumina particles (Hi Aluminas, Shofu Inc., Kyoto, Japan) at 0.2 MPa for 10 s at a
distance of 10 mm. Then, the frameworks were cleaned by using ultrasonic cleaner in an acetone solution for 10
minutes, followed by cleaning in deionized water for 5 minutes twice, and drying with air. Shade base stain(Cerabian ZR Press shade base stain SSA3, Kuraray Noritake Dental Inc.) was applied twice.
Maxillary second premolar restorations were formed with wax-up (Inlay wax Medium, GC Corp.). The wax
patterns of all frameworks were made 1.0 mm thick on the occlusal surface of non-functional cusp and 1.5 mm
thick on the occlusal surface of functional cusp by using a silicone jig of the anatomical form. The thickness wasverified by periodic caliper measurement at several areas.
After that, wax patterns of the frameworks were invested using pressable ceramic investment (Ceravety press
and cast, Shofu Inc.). Pressable ceramics (Cerabian ZR press A3, Kuraray Noritake Dental Inc.) were pressed on
the zirconia frameworks. Zirconia-ceramic restorations were fabricated, adjusted, and polished.

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Cementation
All zirconia-ceramic restorations were cemented to resin tooth abutments using an adhesive technique.
Pre-treatment was performed on both inner surfaces of restorations and resin abutments. Inner surfaces ofzirconia-ceramic restorations were treated using air-abrasion with 70 µm alumina particles at 0.2 MPa for 10 s at
a distance of 10 mm, cleaned with ultrasonic cleaner in deionized water for 5 minutes, and dried with air. Then,
silane-coupling agent (Clearfil ceramic primer, Kuraray Noritake Dental Inc.) was applied, followed by drying
with air. The resin abutment tooth surfaces were cleaned with 40% phosphoric acid (K-etchant gel, Kuraray
Noritake Dental Inc.) for 5 s, rinsed with water for 10 s, and air-dried. The silane-coupling agent (Clearfil
ceramic primer, Kuraray Noritake Dental Inc.) was applied, and dried with air. Next, the zirconia-ceramic
restorations were luted to the resin tooth abutments with adhesive resin cement (Panavia F2.0, Kuraray Noritake
Dental Inc.) according to the manufacturer's recommendations. The restorations were pressed with firm handpressure on resin tooth abutment until the restoration seated properly. Excess cement was removed before curingwith a light curing unit (Optilux 501, Sybron Dental Specialties Japan Inc.) for 5 s on each buccal and palatalside. One hour after cementation, the specimens were stored in deionized water at 37˚C for 24 hours in darkness.
After that, the specimens were embedded into stainless steel rings (20 mm length, 20 mm diameter) using acrylic
resin (Palapress Vario, Heraeus Kulzer GmbH) at the position where the restorations’ marginal line were placed
0.2 mm above the resin to mimic the biological width. The fracture loads were tested after polymerization of theresin.
Measurement of fracture load
Fracture loads of all specimens were tested using a universal testing machine (Autograph AGS-H, Shimadzu
Corp., Kyoto, Japan). The specimens were tested with a 4.0 mm diameter ball-ended stainless steel rod at
cross-head speed of 1.0 mm/min, loading along the axis at the central fossa until fracture. The maximum fractureloads were recorded as fracture strengths.
Fracture modes
After the fracture load test, all specimens were observed for the fracture modes and classified into two groups:
Type A, fracture of zirconia-ceramic restoration limited to the pressing porcelain; and Type B, fracture of
zirconia-ceramic restoration extending to zirconia framework and resin abutment.
Statistical analyses
The results of fracture load of zirconia-ceramic restorations were statistically analyzed with one-way analysis ofvariance (ANOVA) at a significant level of 0.05. After that, multiple comparison post hoc test was performed
with Tukey’s HSD test at a significant difference probability level of 0.05. The results of the fracture mode were
statistically analyzed with Fisher’s exact test at a significant level of 0.05.

Results
The means and standard deviations of fracture strength for each group are presented in Table 1. The one-way
analysis of variance (ANOVA) showed statistically significant differences among groups (p < 0.05). The post
hoc test (Tukey’s HSD) revealed that the fracture strength of Ce-TZP/Am (2,824.1 ± 320.8 N) was significantly
higher than Y-TZPm (2,399.7 ± 188.8 N), but was not significantly different from Ce-TZP/As (3,056.4 ± 337.1
N). No significant difference between Y-TZPs (3,338.8 ± 359.3 N) and Ce-TZP/As was observed. The fracturemodes for all groups are presented in Table 2. The Fisher’s exact test showed no significant difference between

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groups. The representative fracture modes of all groups are shown in Fig. 3.
Table 1 Fracture strength (N) of zirconia-ceramic restorations
Experimental group Framework material Framework design, thickness (mm)Y-TZPsY-TZPStandard (0.5)
Ce-TZP/As
Ce-TZP/A
Y-TZPmY-TZP
Modified with palatal support (0.3)
Ce-TZP/Am
Ce-TZP/A
The different superscript letter showed statistical difference (p < 0.05).

Mean (SD) of fracture strength
3,338.80 (359.38)a
3,056.40 (337.13)a,c
2,399.70 (188.86)b
2,824.10 (320.83)c

Table 2 Fracture mode of zirconia-ceramic restorations (n = 40)
Fracture mode
Type A
Type BY-TZPsd
1
9
Ce-TZP/Asd
0
10
Y-TZPmd
1
9
Ce-TZP/Amd
3
7
Type A, Fracture of zirconia-ceramic restoration limited to the pressing porcelain
Type B, Fracture of zirconia-ceramic restoration extending to zirconia framework and resin abutment
The different superscript letter showed statistical difference (p < 0.05).
Experimental group

Fig. 3 Occlusal view of representative fracture modes of zirconia-ceramic restorations
Type A: Facture of zirconia-ceramic restoration limited to the pressing porcelain;(A) Y-TZPs, (B) Y-TZPm, (C) Ce-TZP/Am
Type B: Fracture of zirconia-ceramic restoration extending to zirconia framework and resin abutment:(D) Y-TZPs, (E) Ce-TZP/As, (F) Y-TZPm, (G) Ce-TZP/Am

Discussion
In this study, the aims were to evaluate the fracture strength and fracture mode of Ce-TZP/A and Y-TZP ceramic
restorations in different thicknesses of zirconia frameworks on resin tooth abutments and to assess the usabilityof thin Ce-TZP/A framework with palatal support.

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According to the conventional guidelines, minimum thickness of the metal framework of porcelain fused tometal restoration should be 0.3 mm [24]. However, nowadays, when the patients’ demands have shifted towards
metal-free restorations, the zirconia-ceramic restoration is one of the alternative choices and Y-TZP is the mostcommonly used zirconia for this restoration [25]. The minimum thickness of Y-TZP framework ofzirconia-ceramic restoration in the posterior region is 0.5 mm [23,26]. Increase in this thickness requires greater
tooth preparation. However, Ce-TZP/A has superior mechanical properties than Y-TZP, and can potentiallyreduce the thickness of the framework. In this study, 0.3 mm thick Ce-TZP/A framework was used to assess theusability of Ce-TZP/A ceramic restoration frameworks. This 0.3 mm thickness was based on the standard
minimum thickness of metal framework of porcelain fused to metal restoration which has long term reliability
history [6].
A modified framework design with palatal or lingual support on the porcelain fused to metal restoration has
been suggested to improve the strength of veneered porcelain by creating support and providing good esthetic
appearance without compromising on strength. Besides, the modified framework of zirconia-ceramic restoration
is becoming more popular in clinical use [27]. Moreover, this modification also provides porcelain support, good
esthetic appearance, and improves the characteristic strength of zirconia-ceramic restoration as well [28-30].
Therefore, the modified zirconia-ceramic restoration framework with palatal support was selected for this study.
In the previous study, modified Ce-TZP/A ceramic restoration framework was evaluated the fracture strength[23]. However, modified Ce-TZP/A ceramic restoration framework with pressed-over porcelain has not beenstudied in detail. Thus, for this study, modified Ce-TZP/A ceramic restoration framework with pressed-overporcelain was used in an attempt to be examined in actual restorations.
Fracture strength of Ce-TZP/Am was significantly higher than Y-TZPm. This implies that the strength of
Ce-TZP/A ceramic restoration with modified framework makes it a better alternative choice for use with thinner
zirconia frameworks, and reduce tooth preparation for zirconia-ceramic restorations. Although Y-TZPs showed
higher fracture strength than Ce-TZP/Am, Y-TZPs ceramic restoration framework was thicker than Ce-TZP/Am
ceramic restoration framework and would require more tooth reduction. Ce-TZP/Am and Ce-TZP/As showed nosignificant differences when tested for fracture strength. These results assume that Ce-TZP/A ceramic restoration
framework can maintain its strength when reduced its thickness to 0.3 mm.
In general, the strength of zirconia comes from the transformation of the tetragonal phase to monoclinic phase,when external stresses are applied. This is called stress-induced transformation toughening. Consequently, 3-5%
volume expansion occurs and induces local compressive stresses around the micro crack areas. As a result, theopening of the crack is stopped and crack propagation is resisted [12]. The tetragonal phase can spontaneouslytransform to monoclinic phase when exposed to humid environment, which is known as low temperature aging
degradation (LTAD) [14,16,17]. For this reason, some zirconia materials have reduced strength and durability.
Y-TZP materials are susceptible to LTAD [10,13-16]. On the other hand, Ce-TZP/A materials are completely
resistance to LTAD [8,15,16,19]. Complete resistance to LTAD of Ce-TZP/A would be one of requirement
property for use with modified frameworks with palatal or lingual support, as this palatal or lingual support is
exposed to the moist environment of the oral cavity, which leads to creation of LTAD [8]. LTAD may shorten
the durability in long-term evaluation of zirconia material. This phenomenon is a weakness and undesired
property of zirconia.
Practically, tooth preparation for the conventional Y-TZP ceramic restoration requires shoulder finish line

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with rounded internal angles [23]. When compared to porcelain fused to metal restoration, the amount of tooth
reduction is considereble. Therefore, the conventional Y-TZP ceramic restoration may have some difficulties in
use in cases of vital teeth, especially in young patients, who have relatively large pulp cavities [21,22]. The use
of Ce-TZP/A framework in case of zirconia-ceramic restorations would require less tooth reduction, because
preparation can result in a chamfer finish line from proximal to palatal side, and reduced occlusal reduction [31].
This preparation would preserve tooth structure, minimize chances of damaging the pulp tissue, and would be
preferable as per the minimal intervention concept.
Even though zirconia can provide tooth-color simulation, but it is still highly opaque [32]. This property may
limit the esthetic outcomes of zirconia restorations. Therefore, veneering porcelain on zirconia-ceramic
restorations would provide the enhancement of translucency to fulfill the esthetic outcomes [32] when comparedto monolithic zirconia restorations. Both monolithic zirconia restorations and zirconia-ceramic restorations havetheir own advantages. Monolithic zirconia restorations have no chipping problem of veneering porcelain, but
their esthetic outcomes are limited due to lack of translucency. In case of zirconia-ceramic restorations, esthetic
capability is achieved by using esthetic veneering porcelain to cover the high strength zirconia framework.
Therefore, monolithic zirconia restorations may be suitable for non-esthetic areas such as molar region, while
porcelain veneered zirconia restorations can be used in esthetic areas such as anterior and premolar regions[3,33].
Maximum bite force can reach approximately 650 N in males and 540 N in females [34,35]. Thus, thefracture strength of Ce-TZP/Am would be high enough for clinical use. Numerous studies suggest that thechipping problems of veneering porcelain can be reduced by using an anatomically designed [18,36,37]
modified framework with palatal or lingual support [29,30]. Moreover, porcelain pressing technique, which hasa higher survival rate and better clinical outcomes than conventional layering technique can also be useful [18].
In a short-term clinical study, the porcelain veneer chipping rate of zirconia-ceramic restorations was not foundto be significantly higher than metal-ceramic restorations [38]. Thus, zirconia-ceramic restorations may become
an acceptable alternative choice of treatment [18].
The fracture mode of Ce-TZP/Am showed three specimens that fracture limited to the pressing porcelain, but
Y-TZPm showed only one specimen. The fracture limited to the pressing porcelain and was not extending tozirconia framework and resin abutment referring to prevent a catastrophic failure of the abutment and can bere-treated with conventional treatment procedure.
Due to all the above stated advantages of Ce-TZP/A including high fracture strength, it can be fabricated as athin framework while maintaining its strength, reduced tooth reduction, and complete resistance to LTAD. Thesesuggest that Ce-TZP/A would be one of the most recommended alternative choices for frameworks inzirconia-ceramic restorations.
Resin cement was used in this study due to its many advantages when used with zirconia restorations such as
its high compressive strength, high tensile strength, high bonding strength, sufficient marginal adaptation, lowstress concentration in cement layer, and low solubility [39,40]. In addition, resin cement is preferred and isgaining popularity for use in zirconia restorations [40]. The abutment used in this study was created from resin
composite material as its Young’s modulus is similar to dentin, making it widely used in clinics [41]. Therefore,
resin cement and resin abutments were used in this study, in an attempt to simulate a practical clinical treatment
for zirconia-ceramic restorations.

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Within the limitations of this in vitro study, it can be concluded that Ce-TZP/A can be use with the thin
modified design framework (0.3 mm thickness with palatal support) in zirconia-ceramic restorations. For thisreason, the amount of tooth reduction can be reduced. Ce-TZP/A ceramic restorations with thin modified
framework had higher fracture strength than Y-TZP ceramic restorations with thin modified framework. In
addition, they provide sufficient strength for use in cases of vital or non-vital abutment teeth restored by resin
composite material.
Acknowledgments
This study was partly supported by Grants-in-Aid for Scientific Research (JSPS KAKENHI Grant Number 16K20490).

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Correspondence to:
Dr. Satoshi Omori
Fixed Prosthodontics, Department of Restorative Sciences, Division of Oral Health Sciences,
Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University,
1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8549, Japan
Fax: +81-3-5803-0201 E-mail: s.omori.fpro@tmd.ac.jp
Accepted May 24, 2017.
Copyright ©2017 by the Asian Pacific Journal of Dentistry.
Online ISSN 2185-3487, Print ISSN 2185-3479

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