Zirconia

Review Article

Clinical trials in zirconia: a systematic review

B. AL-AMLEH, K. LYONS & M. SWAIN Department of Oral Rehabilitation, Faculty of Dentistry, University of

Otago, Dunedin, New Zealand

SUMMARY Zirconia is unique in its polymorphic crys-

talline makeup, reported to be sensitive to manu-

facturing and handling processes, and there is debate

about which processing method is least harmful to

the final product. Currently, zirconia restorations are

manufactured by either soft or hard-milling

processes, with the manufacturer of each claiming

advantages over the other. Chipping of the veneering

porcelain is reported as a common problem and has

been labelled as its main clinical setback. The objec-

tive of this systematic review is to report on the

clinical success of zirconia-based restorations fabri-

cated by both milling processes, in regard to frame-

work fractures and veneering porcelain chipping. A

comprehensive review of the literature was com-

pleted for in vivo trials on zirconia restorations in

MEDLINE and PubMed between 1950 and 2009. A

manual hand search of relevant dental journals was

also completed. Seventeen clinical trials involving

zirconia-based restorations were found, 13 were

conducted on fixed partial dentures, two on single

crowns and two on zirconia implant abutments, of

which 11 were based on soft-milled zirconia and six

on hard-milled zirconia. Chipping of the veneering

porcelain was a common occurrence, and framework

fracture was only observed in soft-milled zirconia.

Based on the limited number of short-term in vivo

studies, zirconia appears to be suitable for the

fabrication of single crowns, and fixed partial den-

tures and implant abutments providing strict proto-

cols during the manufacturing and delivery process

are adhered to. Further long-term prospective stud-

ies are necessary to establish the best manufacturing

process for zirconia-based restorations.

KEYWORDS: zirconia, fracture, porcelain chipping,

crowns, fixed partial dentures, implant abutments

Accepted for publication 13 March 2010

Introduction

In dentistry, gold and metal-alloys have passed the test

of time and are recognized as predictable and well-

established clinical materials for the restoration of

various fixed prostheses (1). Indeed, metal-ceramic

systems require relatively little special knowledge for

their routine use which has led to their worldwide

acceptance and use since their inception. Nevertheless,

the increasing aesthetic demand in dentistry has driven

the development of a number of ceramics for their

aesthetic capability, biocompatibility, colour stability,

wear resistance and low thermal conductivity (2). As

far back as 1885, porcelain jacket crowns were first used

for single crowns for the anterior teeth because of

their aesthetic and natural appearance (3). However,

ceramics cannot withstand deformation strain of more

than 0Æ1%–0Æ3% without fracturing and are susceptible

to fatigue fracture. It is this brittleness, because of the

ionic-covalent atomic bonding, which has limited their

use in dentistry for decades (4).

The most recent introduction to the dental ceramics

family is zirconia, which in its pure form is a polymor-

phic material that occurs in three temperature-depen-

dant forms that are: monoclinic (room temperature to

1170 �C), tetragonal (1170 �C–2370 �C) and cubic

(2370 �C – up to melting point) (5). However, when

stabilizing oxides such as magnesia, ceria, yttria and

calcium are added to zirconia, the tetragonal phase is

retained in a metastable condition at room tempera-

ture, enabling a phenomenon called transformation

toughening to occur. The partially stabilized crystalline

ª 2010 Blackwell Publishing Ltd doi: 10.1111/j.1365-2842.2010.02094.x

Journal of Oral Rehabilitation 2010 37; 641–652

J o u r n a l o f Oral Rehabilitation

tetragonal zirconia, in response to mechanical stimuli,

such as tensile stress at crack tips, transforms to the

more stable monoclinic phase with a local increase in

volume of approximately 4%. This increase in volume

closes the crack tips, effectively blunting crack propa-

gation. It is this transformation-toughening process

which gives zirconia its strength and toughness,

exceeding all currently available sintered ceramics.

Compared to alumina, zirconia has twice the flexural

strength, partly because of its grain size and the

transformation-toughening mechanism. (6).

To date, there are three types of zirconia-containing

ceramics which are used in dentistry. Glass-infiltrated

zirconia-toughened alumina ceramics, magnesium-

doped partially stabilized zirconia and 3 mol% yttria

containing tetragonal zirconia polycrystalline (Y-TZP),

with the latter being the most utilised form in dentistry

because of its higher flexural strength reported to range

from 900 to 1200 MPa (7). Y-TZP has been used in root

canal posts (8), frameworks for all-ceramic posterior

crowns and fixed partial dentures (FPDs) (9–12),

implant abutments (13, 14) and dental implants (15).

Advances in CAD ⁄ CAM technology has made it

possible to more readily use zirconia in dentistry. This

technology enables complex shapes to be milled out of

pre-made zirconia blanks (or blocks), where the

prepared abutment is first scanned, then using com-

puter software, the desired framework is designed prior

to milling (16).

There are two types of zirconia milling processes

available: (i) soft-milling and (ii) hard-milling. Soft-

milling involves machining enlarged frameworks out of

pre-sintered blanks of zirconia, also called the ‘‘green’’

state. These are then sintered to their full strength,

which is accompanied by shrinkage of the milled

framework by approximately 25% to the desired

dimensions. Hard-milling involves machining the

framework directly to the desired dimension out of

densely sintered (higher strength and more homoge-

nous) zirconia blanks, typically these have been hot

isostatic pressed (HIPed). However, because of the

extreme hardness of sintered zirconia, a robust milling

system is required that needs an extended milling

period compared to the soft-milling process as well as

placing heavy demands on the rigidity of the cutting

instruments. The relative ease and speed of soft-milling

may be why more manufacturers chose this method to

fabricate their dental zirconia products, while only a

smaller number have used HIPed zirconia. Among the

common representative systems utilizing soft-milling

are Lava,* Procera zirconia,† IPS e.max ZirCAD‡ and

Cercon.§ Systems that utilize hard-milling of HIPed

zirconia include DC-Zirkon¶ and Denzir.**

Supporters of soft-milling claim that hard-milling

may introduce microcracks in the framework during

the milling process. In contrast, hard-milling supporters

claim a superior marginal fit because no shrinkage is

involved in their manufacturing process. Nevertheless,

in vitro studies support the use of both HIPed and non-

HIPed zirconia for all-ceramic FPDs, crowns and

implant abutments for the posterior of the mouth

because of their high flexural strength and fracture

toughness (17).

The most utilized zirconia in dentistry, Y-TZP, has

been found to withstand cyclic fatigue testing, where

posterior all-ceramic FPDs spanning up to 5-units, had a

lifetime comparable to that achieved with metal-

ceramic restorations (2), and it has been predicted,

based on the results of this study, to have a lifetime

longer than 20 years (18). However, early clinical

findings show that there are two main drawbacks for

zirconia restorations compared to metal-ceramics. The

first is a high incidence of veneering porcelain fracture,

manifesting clinically as chipping fractures, and the

other is an inherent accelerated ageing problem that

has been identified to occur in zirconia in the presence

of water. This ageing phenomenon is known as

low-temperature degradation (LTD), which causes a

decrease in physical properties by spontaneous phase

transformation of the zirconia crystals from the tetrag-

onal phase to the weaker monoclinic phase putting

zirconia frameworks at risk of spontaneous catastrophic

failure (19).

The objective of this systematic review is to report

on the clinical success of HIPed and non-HIPed Y-TZP-

based restorations (single crowns, FPDs and implant

abutments), focusing on the incidence of framework

fracture and chipping of the veneering porcelain in

both groups. In addition, recent in vitro studies con-

ducted in an attempt to solve some of the reported

problems in zirconia-based restorations are also dis-

cussed.

*3M ESPE, Seefeld, Germany.†Nobel Biocare AB, Carolinsk, Sweden.‡Vivadent-Ivoclar, Ellwangen, Germany.§Dentsply-Degudent, Hanau, Germany.¶DCS Dental AG, Allschwil, Germany.

**Decim AB, Skelleftea, Sweden.

B . A L - A M L E H et al.642

ª 2010 Blackwell Publishing Ltd

Materials and methods

A search was performed in MEDLINE and PubMed

for in vivo trials on zirconia restorations published

between 1950 and June 2009. The main keywords

used for the search and the number of articles

produced were:

1 ‘‘zirconia AND clinical’’- 329 articles

2 ‘‘zirconia AND fixed partial dentures’’- 130 articles

3 ‘‘zirconia AND FPD’’- 23 articles

4 ‘‘zirconia AND implant abutments’’- 61 articles

5 ‘‘zirconia AND single crowns’’- 73 articles

In addition, a manual hand search was conducted

through the literature to identify any possible clinical

trials on Y-TZP which may have not been listed on

MEDLINE and PubMed. The articles found were read to

identify ones which satisfied the following inclusion

and exclusion criteria:

Inclusion Criteria:

1 Human in vivo only

2 Conducted on Y-TZP

3 Fixed prosthetics (single

crowns, FPDs or implant abutments)

4 Study has a set inclusion and exclusion criteria

5 Study has a materials and methods

6 In the English language

Exclusion Criteria:

1 Case reports

2 In vitro trials

3 Animal studies

4 Trials <12 months

The search yielded 19 articles and abstracts involving

Y-TZP restorations in clinical trials which satisfied the

inclusion criteria. Following this, one final search was

done by inspecting the bibliographies of the 19

reviewed articles for any additional studies, however,

none were found.

Results

In total, only 17 clinical trials involving Y-TZP-based

restorations were found in the literature, of which only

three are randomized control trials (14, 20, 21). The

majority of studies investigated all-ceramic FPDs in the

posterior mouth (4, 9–12, 20, 22–29), while a small

number investigated single crowns (21, 30), implant

abutments (13, 14, 31), and only one study was

available on implant-supported zirconia FPDs (20).

Eight different brands of Y-TZP were identified among

the 17 studies with Cercon zirconia being the most

investigated brand (Table 1).

The longest follow-upperiod found was 5 years, where

two papers reported results on patients restored with

zirconia all-ceramic FPDs (9, 10). Both studies involved 3

to 5-unit FPDs on natural teeth in thepremolar and molar

regions, except for one 3-unit FPD that replaced a lateral

incisor (9). The survival rate of Y-TZP FPDs over 5 years

was 100% (9) and 74% (10), and in the latter study, a

5-unit FPD framework fracture occurred, reportedly

because of accidental biting of a stone in a piece of bread.

While the incidence of chipping of the veneering ceramic

was 15Æ2%, in this study, secondary caries was found to

be the most common cause of failure (21Æ7%). This was

attributed to the poor marginal fit produced by a

prototype milling technique used to fabricate the zirconia

restorations in this particular study.

Four studies reported data on 1-year follow-up

periods for four different treatment modalities. These

were zirconia FPDs on natural teeth (27), FPDs restored

on titanium implant abutments (20), inlay-retained

FPDs (28) and zirconia implant abutments(31), two of

which are randomized control trials (20, 31). The

highest incidence of framework fracture and chipping

veneering porcelain was both reported in 1-year follow-

up studies (10%(28) and 54%(20), respectively) when

compared to longer follow-up periods.

Zirconia implant abutments

Zirconia implant abutments demonstrated encouraging

early results in the only two studies conducted on

single-tooth implant abutments using both HIPed and

non-HIPed zirconia. Glauser et al. reported no fractures

of the 38 HIPed-based zirconia abutments in the

anterior and premolar regions in 18 patients evaluated

after 4 years (13), and favourable hard and soft tissue

responses were also reported. All abutments were

restored with Empress I (Leucite reinforced) crowns

and cemented with Panavia TC†† resin cement. How-

ever, screw loosening of two zirconia abutments at 8

and 27 months was reported, nevertheless no frame-

work fracture occurred during the follow-up period.

In a randomized controlled trial, 20 customized non-

HIPed-based zirconia single-tooth implant abutments

(Procera†) and 20 customized titanium single-tooth

implant abutments (Procera†) were followed for

††Kuraray, Okayama, Japan.

C L I N I C A L T R I A L S I N Z I R C O N I A 643


3 years, with no fractures or loosening of abutments in

either group, and a 100% survival rate reported (14). In

this study, the abutments were restored in the canine to

molar regions. There was no difference in the soft tissue

health around both abutment groups, nevertheless

using spectrophotometric analysis, both zirconia and

titanium abutments induced similar amount of discol-

ouration of the mucosa when compared to the gingiva

of natural teeth.

Both trials on zirconia implant abutments were

conducted on regular platform, externally hexed

implants (Branemark system- RP†)were used for sin-

gle-tooth replacement. The Branemark implant system

was the first titanium dental implant introduced in the

mid 1970s, nevertheless recently introduced internal

type connections have been shown to improve the

fracture resistance and stability of the implant-

abutment system (32). However, so far there are no

published clinical trials using internal type zirconia

implant abutments, so no comparison could be made of

the long-term stability of both systems using zirconia

abutments.

Zirconia single crowns

Single crowns have a small representation in pub-

lished clinical trials on Y-TZP. In a 2-year randomized

control trial, 1 of 15 Cercon zirconia crowns§ fractured

in half only 1 month after cementation on a maxillary

second molar (21), so that the success rate for this

study was 93% after 2-years. There was no significant

difference in soft tissue health adjacent to the Cercon

crowns and the control crowns made with In-Ceram

zirconia (Vita). No chipping of the veneering porcelain

was reported after 2 years. In the mean time, no

framework fracture have been reported after 3 years

in a study with 204 single crowns fabricated with

Procera zirconia† in a private practice setting (30).

However, 16% of the crowns had some type of

complication, and 6% were recorded as a failure. Loss

Table 1. List of in vivo trials conducted in yttria-stabilized tetragonal zirconia polycrystalline

Type of

zirconia Brand Study

Follow-up

periods

Type of

restorations

Sample

size

Framework

fracture, %

Veneering

porcelain

fracture,

%

Non-HIPed Cercon zirconia

(Dentsply)

Sailer et al. 2007 (10) 5 years 3–5 units FPD 33 8 15

Beuer et al. 2009 (22) 3 years 3 units FPD 21 5 0

Cehreli et al. 2009 (21) 2 years Single crowns 15 7 0

Schimitter et al. 2009 (23) 2 years 4–7 units FPD 30 3 3

Bornemann et al. 2003 (24) 1Æ5 years 3–4 units FPD 59 0 3

Lava (3M ESPE) Raigrodski et al. 2006 (25) 2Æ5 years 3 units FPD 20 0 25

Pospeich et al. 2003 (26) 2 years 3 units FPD 38 0 3

Crisp et al. 2008 (27) 1 year 3–4 units FPD 38 0 3

Procera zirconia

(Nobel Biocare)

Zembic et al. 2009 (14) 3 years Implant

abutments

18 0 –

Ortrop et al. 2009 (30) 3 years Single crowns 204 0 2

IPS e.max Zir ⁄ CAD

(Vivadent-Ivoclar)

Ohlmann et al. 2008 (28) 1 year IRFPD 30 10 13

HIPed Denzir (Cadesthetics

AB)

Molin & Karlsson 2008 (9) 5 years 3 units FPD 19 0 36

Larsson et al. 2006 (20) 1 year 2–5 units

FPD ⁄ Ti abut

13 0 54

DC- Zirkon

(DCS Dental AG)

Tinschert et al. 2008 (29) 3 years 3–10 units

+cantilever

65 0 6

Vult von Steyern et al.

2005 (4)

2 years 3–5 units FPD 23 0 15

Digizon Edelhoff et al. 2008 (12) 3 years 3–6 units FPD 21 0 9Æ5Wohlwend Glauser et al. 2004 (13) 4 years Implant

abutments

54 0 –

HIPed, hot isostatic pressed zirconia; FPD, fixed partial denture; IRFPD, inlay-retained fixed partial denture; Ti abut, titanium implant

abutment.



of retention (12 ⁄ 204 = 6%), extraction of abutment

tooth (5 ⁄ 204 = 2Æ5%), persistent pain (10 ⁄ 204 = 5%)

and chipping of veneering porcelain (4 ⁄ 204 = 2%)

were some of the complications reported in this study

which had a cumulative survival rate of 93% at

3 years.

Although zirconia single crowns appear to demon-

strate good short-term success rates of 93% after

2 years and a survival rate of 93% after 3 years, these

must be viewed with caution as they reflect data from a

study with a small sample size of 15, and the other

study reported data from a private practice setting that

was mainly based on patients records rather than

clinical evaluation.

Zirconia-fixed partial dentures

The most investigated treatment modality are the

zirconia-fixed partial dentures, with 13 different clinical

trials reporting data on FPD spans ranging from 3 to

10-units. Except for one study, all FPDs used natural

teeth as abutments; the exception used titanium

implant abutments. Zirconia PFDs demonstrated

favourable results, exhibiting a high success rate in

most studies. A relatively small number of framework

fractures have been reported in the clinical trials and do

not appear to have occurred spontaneously, but rather

an initiating factor was determined to have contributed

to the fractured framework. The longest FPD spanned

10-units (5 pontics on 5 abutments) with the frame-

work made with DC-Zirkon¶ and the veneering porce-

lain was Vita D (29). This study also included two

cantilever posterior FPDs. No framework fractures were

reported after 3 years of follow-up; however, chipping

of the veneering porcelain was reported in 4 posterior

FPDs of the 65 FPDs placed in the anterior and posterior

regions.

Zirconia framework fracture

Fracture of Y-TZP substructures mostly occurred in

FPDs, nevertheless this was found to be rare, and was

only reported in five studies on two zirconia brands

(Table 2). The incidence of framework fracture was

directly related to the design of the FPD, where inlay-

retained FPDs (IRFPD) showed the highest failure rate

of 10% after only 12 months. These IRFPDs were made

with IPS e.max ZirCAD‡, where debonding of the inlay

pontic has been concluded to be the cause of the

framework fractures. In the review, Cercon zirconia

suffered the majority of frameworks fractures compared

to the other investigated zirconia brands; however, it

must be kept in mind that it is also the most investi-

gated brand (5 of 18 trials), followed by Lava* (3 of 18

trials). Both IPS e.max ZirCAD and Cercon zirconia are

a non-HIPed zirconia manufactured by the soft-milling

process.

Veneering porcelain fracture

The most common complication observed in zirconia-

based restorations was fracture of the veneering porce-

lain, manifesting clinically as chipping fractures of the

veneering ceramic with or without exposing the

underlying Y-TZP framework. All eight of the investi-

gated zirconia brands exhibited chipping fractures, even

when using specifically manufactured veneering

porcelains with modified coefficients of thermal

expansions compatible with zirconia (>11 · 10)6 K)1)

(10, 25). These chipping fractures were found to occur

in non-load-bearing areas, such as the mesio-lingual

cusps on a mandibular second molars (23), and the

lingual aspect of FPD pontics (10). Possible trends in the

location of the chipping have been identified by some

authors and included the premolar and molar regions

Table 2. In vivo studies which reported Y-TZP framework fracture and the time until fracture

Study Brand of Zirconia

Type of

restoration

Follow-up

periods

Time until

fracture

Number of units

fractured

Incidence,

%

Sailer et al. 2007 (10) Cercon zirconia 3–5 unit FPD 5 years 38 months 1 out of 13 8

Beuer et al. 2009 (22) Cercon zirconia 3 unit FPD 3 years 30 months 1 out of 21 5

Schimitter et al. 2009 (23) Cercon zirconia 4–7 unit FPD 2 years 1 month 1 out of 30 3

Cehreli et al. 2009 (21) Cercon zirconia Single crowns 2 years 1 month 1 out of 15 7

Ohlmann et al. 2008 (28) IPS e.max ZirCAD IR FPD 1 year Not specified

(<12months)

3 out of 30 10



(30), particularly the second molars on FPDs (25) and

the connector area in mandibular posterior FPDs (29).

Denzir zirconia‡‡ frameworks veneered with Espri-

dent Triceram,§§ demonstrated the highest incidence of

veneering porcelain fracture at 1 year of 54% when

FPDs were using titanium implant abutments (20). In

addition, there was a 36% incidence of roughness ⁄ pit-

ting on occlusal surfaces of 3-unit FPDs on natural teeth

after 5 years with Denzir zirconia frameworks veneered

with either a feldspathic porcelain Vita Veneering

Ceramic D (Vita) or leucite reinforced pressed ceramic

IPS Empress‡ (9).

Cementation and bonding

Because of its high flexural strength, zirconia can be

conventionally cemented, just like metal-ceramic res-

torations, without the need for any pretreatment;

although bonding of zirconia is possible provided

special conditioning, treatment of the zirconia is carried

out first because zirconia is not etchable. Indeed,

cementation of zirconia all-ceramic restorations is a

simpler process compared to other all-ceramic systems

which require added steps for bonding. This was

evident in the range of cements used by the various

authors in the published clinical trials; zinc phosphate

cement (4, 9, 20, 24, 29, 30), glass–ionomer cements

(GIC) (21–23, 26), resin-modified GIC (12, 25) and

resin cements (9–13, 27–30).

Loss of retention was seen in 7 of 16 studies involving

the cementation of zirconia restorations. One 3-unit

FPD cemented with Panavia F lost retention after

12 months (9), a 4-unit FPD cemented with Variolink

lost retention after 33Æ3 months in service (10), while

two 3-unit FPDs in the molar region cemented with

zinc phosphate lost retention at 17 and 32 months (29).

Ketac Cem* glass–ionomer cement had one posterior 3-

unit FPD decemented after 38 months (22), in addition

to two long-span FPDs at 8Æ8 and 14Æ2 months in service

(23). All debonded zirconia restorations were rece-

mented successfully for the duration of the follow-up

period in each of the studies.

In contrast, six cases of debonded inlay-retained

zirconia FPDs were seen with Panavia F (dual-cured

resin cement) and Multilink (automix self-curing resin

cement), despite the pretreatment of the zirconia with

tribochemical air abrasion (Rocatec*). Fracture of the

framework occurred in three of the six debonded

restorations (28). Similarly, in a study on single Procera

zirconia crowns, 12 of 204 crowns lost retention of

which 4 could not be recemented (30). Unfortunately,

the type of cement used for the crowns which lost

retention was not reported, as both zinc phosphate and

resin cement (Rely-X Unicem*) where used.

Despite the encouraging retentive capacity of zinc

phosphate-cemented zirconia restorations, after 5-years

follow-up of 3-unit FPDs that were cemented with

either resin cement (Panavia F) or zinc phosphate

(De Trey Zinc§), visible evidence of ditching along the

margins was only seen in the zinc phosphate-cemented

group. Ditching was reported in 5% of mesial abut-

ments and 26% in distal abutments in this study,

however, this problem was not reported in the other

trials using zinc phosphate cement.

Discussion

With the limited number of published clinical trials, one

can conclude that Y-TZP has the potential for being

accepted as a suitable material for fixed prosthodontic

dental treatment; however, larger sample sizes and

longer in vivo studies are needed. The majority of

published studies are prospective clinical trials, with the

longest follow-up period being 5 years. In addition,

only three randomized control trials exist, with 1 to

3-year follow-up periods. Long-span multi-unit FPDs

have also been included in a number of studies

demonstrating confidence in the structural potential

of zirconia frameworks (4, 10, 12, 20, 23, 29).

Certainly, the published clinical trials demonstrate a

careful and meticulous approach in their treatments,

with steps taken to insure that the zirconia frameworks

are delivered at their best possible condition before final

cementation. Furthermore, it was interesting to note

that all 17 studies included bruxism in their exclusion

criteria, and therefore this should alert a potential

limitation of this all-ceramic system that is not being

investigated clinically.

Zirconia framework fracture

The probability of fracture of zirconia FPDs has been

estimated to be almost 0% after a simulated 10-year

clinical service study (33), however, framework fracture

has been reported in several in vivo trials of less than

‡‡Cadesthetics AB, Skelleftae, Sweden.§§Dentaurum, Ispringen, Germany.



5-years (10, 21–23, 28). Four of 5 studies involving

Cercon zirconia reported framework fractures both in

single crowns and FPDs. In an in vitro trial, it was reported

that a force of 379 to 501 MPa was needed to load Cercon

zirconia 4-unit FPDs to failure which is higher than the

average human bite, confirming its suitability as a

substructure framework for FPDs (34). Cercon zirconia

is a non-HIPed Y-TZP, and it is too early to say whether it

is a weaker brand of zirconia compared to others because

of the limited number of trials published so far, and

keeping in mind that Cercon zirconia has been the most

clinically investigated brand of Y-TZP so far.

A 5-unit Cercon zirconia maxillary FPD fractured at

the connector between two pontics at the first and second

premolars after 38 months in service (10). The dimen-

sion of the fractured connector was 19Æ28 mm2, well

above the recommended connector area of 9–16 mm2 by

Raigrodski (2004) (35). Accidental biting on a stone was

reported to be the primary reason for failure. Scanning

electron microscopy (SEM) analysis revealed the pri-

mary crack initiation site on a Cercon zirconia FPD that

failed 29 days after insertion to be from the gingival

aspect of the connector that was around 10Æ5 mm2 in

surface area (23). It was claimed by the authors to be

because of inappropriate alteration performed by a

dental technician during the veneering of the FPD. This

confirms reports that the most susceptible part of fracture

in all-ceramic FPDs is the connector area (36, 37). In fact,

fractographic analyses of five failed 4-unit Cercon zirco-

nia FPDs confirmed all the connector failures were

initiated from the gingival surface; where tensile stresses

were the greatest (34). In contrast, lithium disilicate-

based FPDs were found to fracture from the occlusal

surface of the failing connector (38).

As for single crowns, one Cercon zirconia crown

restoring a non-vital maxillary second molar fractured

in half after 1 month in service (21). This tooth did not

have a post, and although bruxism was part of their

exclusion criteria, the patient reportedly had nocturnal

bruxism, for which he had been undertaking muscle-

relaxation splint therapy.

Despite the promising results reported in vitro (39),

IRFPDs made with IPS e.max ZirCAD‡ also a non-HIPed

Y-TZP, demonstrated the highest incidence of fractured

frameworks in just 1-year, with a survival rate of 57%

(28). These FPDs had inlays, partial and full-crowns as

retainers with at least one retainer being an inlay.

Debonding of 20% of the retainers resulted in a 10%

framework fracture primarily when one retainer

debonded, which subsequently overloaded the connec-

tors to failure. Bonding procedures in the study used

the generally recommended bonding method for Y-TZP,

namely using tribochemical silica-coating air abrasion

(Rocatec*) pretreatment of the inner surface of the

copings, followed by silanization and cementation using

phosphate monomer resin cements, Panavia F†† and

Multilink Automix‡. Debonding was explained by the

reduced area of adhesion, either because of the small

surface area of the inlay retainers or because of voids in

the resin cement. No other in vivo study investigated the

longevity of inlay-retained FPDs, and furthermore, it is

the only in vivo study conducted on IPS e.max ZirCAD.

The physical properties of IPS e.max ZirCAD are no

lower than the average Y-TZP (40), hence the high

failure rate seen could only be explained by the design

of the inlay-retained framework. Wolfart & Kern

reported two case studies on IRFPDs. These IRFPDs

had modified wrap-around wing retainers resembling

metal winged resin-bonded retainers to increase the

bonding surface area that also had full thickness

zirconia that omitted any veneering ceramic for max-

imum strength (41). Nevertheless, in contrast to other

treatment modalities, Y-TZP IRFPDs cannot yet be

recommended and should not be clinically prescribed

until improvements in bonding of zirconia is achieved

and further long-term clinical trials are published.

An in vitro study of five framework-designed canti-

lever zirconia FPDs made of Lava* showed poor fracture

resistance, where most fractures occurred at the distal

wall of the terminal abutment (42). As a consequence,

cantilever FPDs made of zirconia were not recom-

mended by the authors; nevertheless, a 3-unit and a

4-unit cantilever Y-TZP FPDs survived 3 years in

function in the posterior region of the mouth (29).

These cantilever FPDs were made from DC-Zirkon¶

HIPed densely sintered blanks and cemented with zinc

phosphate cement. Further larger sample sizes and

longer follow-up periods are necessary before zirconia

cantilever FPDs can be recommended.

Chipping of veneering porcelain

Zirconia has a white opaque colour, which needs

masking by veneering it with a more translucent, and

aesthetic porcelain to achieve an acceptable aesthetic

result, as with porcelain-fused-to-metal restorations

(PFM). The most striking finding which has been

reported in the literature is the high incidence of



cohesive failure of the veneering porcelain, manifesting

clinically as chipping of the veneering ceramic with or

without exposing the underlying Y-TZP framework.

The incidence of chipping fractures ranged from 0% in

two studies, both on Cercon zirconia at 2 years (21) and

3 years(22), to as high as 54% in just 1 year (20). No

brand of Y-TZP has escaped this problem, and it has

been reported in all seven brands of zirconia investi-

gated for crowns and bridges as follows: Cercon [15% in

5 years (10), 3% in 2 years (23), 3% in 1Æ5 years (24)];

Lava [25% in 2Æ5 years (25), 3% in 1 year (27) and 3%

in 2 years (26)]; IPS e.max ZirCAD [13% in 1 year

(28)]; Procera [2% in 3 years (30)]; DC-Zirkon [6% in

3 years(29), 15% in 2 years (4)]; Denzir [36% in

5 years (9), 54% in 1 year (20)] and Digizon [9Æ5% in

3 years (12)]. In some occasions, they occur at non-

load-bearing areas, and no set pattern has been iden-

tified so far, although the second molars have been

reported to have a higher incidence than the rest of the

dentition because of higher forces found at the posterior

of the mouth (25, 29).

It is important to appreciate that a large number of

chip fractures reported were undetected by the patients

and were an incidental finding during review appoint-

ments (4, 20, 27), and some patients were satisfied with

simply polishing the rough margins (23, 27), or repair-

ing the fracture with composite resin (12), while in

some cases, the patients chose not to have them

polished at all (25). Nevertheless, some restorations

did require total replacement because of major chipping

fractures which could not be polished or because they

posed aesthetic concerns (10, 30).

Chipping fractures can be a disappointment to both

the clinician and patient, and it has been noted in the

literature as a serious problem (43), instigating a large

number of studies investigating this phenomenon in

an attempt to solve it. Numerous reasons have been

suggested, such as mismatch of the CTE between the

veneering porcelain and the zirconia substructure

(44), mechanically defective micro-structural regions

in the porcelain, areas of porosities (28), surface

defects or improper support by the framework (43),

overloading and fatigue (45), low fracture toughness

of the veneering porcelain (46) and finally the low

thermal conductivity of zirconia (47). Delamination,

as opposed to chip fractures, has also been proposed as

a cause of failure. Delamination is the adhesive failure

between the veneering ceramic and zirconia, mani-

festing clinically as the complete loss of porcelain

partially exposing the substructure, although Ohl-

mann et al. (2008) argued that delamination can only

be confirmed after microscopic examination, which is

impossible if the restoration remains in situ, and

therefore it is quite possible that many fractures that

have been classified as delamination may in fact be

chipping fractures. This speculation is supported by

the evidence that the bond strength between zirconia

and a large number of veneering porcelains with

varying CTEs was higher than the cohesive strength of

the porcelain itself (44, 48, 49). Consequently, it has

been concluded that the veneering porcelain is the

weakest link, and improving its strength could reduce

the incidence of veneering porcelain chipping (44,

50). This was attempted by using high-strength heat-

pressed ceramics which have shown to have better

bond strengths to zirconia frameworks compared to

traditional layering ceramics and have been receiving

support in the literature (51). Aboushelib et al.(52)

described a ‘‘double veneering’’ technique which

combines the high bond strength of heat-pressed

ceramics with the superior aesthetics of layered

porcelain in an effort to improve the overall strength

and aesthetics of the veneering porcelain. Unfortu-

nately, chipping fractures have also been reported in

pressed porcelain in clinical trials on zirconia FPDs

and do not appear to have solved this chipping

problem (9, 28).

Swain (2009) (47) proposed that tempering residual

stress was the basis for the preponderance of chipping of

porcelain bonded to zirconia. He concluded that there

are three factors which contribute these residual

stresses and the unstable chipping fractures in zirconia:

mismatch of the higher thermal expansion coefficient

of porcelains bonded to zirconia; thickness of the

veneering porcelain and cooling rate. The cooling rate

after the removal of the sintered restoration from the

furnace, while the restoration is still at elevated

temperatures, generates significant thermal gradients

within the porcelain and is directly related to the low

thermal conductivity of zirconia, which is much lower

than that of metal-alloys and even alumina ceramic,

which has not experienced similar incidences of chip-

ping fractures. He suggests that by more slowly cooling

the restoration above the glass transition temperature

of the porcelain, it is possible to prevent the develop-

ment of high tensile subsurface residual stresses in the

porcelain which may result in unstable cracking or

chipping. This approach of a reduced cooling rate after



the final firing or glazing procedure is now recom-

mended by most dental material producers.

Improper design of the zirconia framework has also

been suggested to be a contributing factor in chipping

fractures, because of the inadequate support provided

by the thin zirconia copings commonly milled. Re-

cently, an improved customised zirconia-coping design

has been recommended by bulking out the substructure

to provide adequate support to the veneering porcelain.

This was demonstrated in a case report by Marchack

and colleagues (43), where the design of their zirconia

crowns was taken from the conventional PFM tech-

nique of a full contour wax-up which was then cut back

to allow for the veneering porcelain. An aesthetic

drawback would be the visible opaque white zirconia

along the palatal or lingual surfaces; however, the

authors argue that patient acceptance is high as soon as

they are given the choice between the appearance of a

metal margin or a white ceramic. Tinschert et al. (29)

adopted this modified framework design in their FPDs,

however, chipping fractures still occurred in 4 of 65

FPDs in their clinical trial spanning 3 years. Alteration

of the zirconia crystalline structures during sandblasting

prior to the veneering process was suggested by the

authors to be a possible reason why they had chipping

fractures, however, if that was the case, then complete

delamination of the porcelain would be expected rather

than chipping fracture of the superficial porcelain.

A novel approach in veneering zirconia copings has

been described by Beuer and colleagues (46) by

sintering a CAD ⁄ CAM-milled lithium disilicate veneer

cap onto the zirconia coping significantly increasing the

mechanical strength of the restoration. Other than

improved strength, they claimed this method to be a

cost-effective way of fabricating all-ceramic restora-

tions. To date, there are no clinical trials that have

adopted this method, and further in vitro studies are

needed before they can be clinically trialed.

Low-temperature degradation

Catastrophic failure of zirconia restorations has been a

major concern because of the inherent spontaneous

ageing problem of zirconia in the presence of water.

Low-temperature degradation (LTD) was first described

by Kobayashi in 1981 (53), where in a humid envi-

ronment, spontaneous slow transformation from the

tetragonal phase to the more stable monoclinic phase

occurred in zirconia grains at relatively low tempera-

tures of 150–400 �C. This ageing process initiates at

surface grains and then later progresses towards the

bulk material causing a reduction in flexural strength of

the material, putting it at risk of spontaneous cata-

strophic failure. How great a problem this ageing

process is going to be for zirconia restorations is

currently unknown. The vulnerability of zirconia to

ageing is exacerbated by the fact that its severity has

been shown to differ between different zirconias from

different manufacturers, and even in zirconia from the

same manufacturer but which have been processed

differently (54). This may be reflected clinically, for

example, in the fractured zirconia frameworks reported

with Cercon zirconia, suggesting a possible weakness of

this brand compared to others, however, before this can

be confirmed, further studies with larger sample sizes

and following a longer review period must be com-

pleted; especially that each case of framework fracture

was caused by an initiating factor, such as accidentally

biting a stone, improper laboratory technique, insuffi-

cient thickness of the zirconia coping and poor design,

which if avoided, a longer restoration life-time may

have been expected.

HIPed vs. non-Hiped zirconia

The type of blanks with which the zirconia restorations

are milled from have been suggested to have a direct

affect on the final outcome of the restoration. Support-

ers of soft-milling using the non-HIPed zirconia claim

that hard-milling of HIPed zirconia could introduce

microcracks to the framework during the milling pro-

cess, reducing its overall physical strength and longevity

of the prosthesis (16). This was not evident in the

published clinical trials; in contrast, zirconia cata-

strophic fractures have only been reported in non-

HIPed zirconia and not in HIPed zirconia. On the other

hand, HIPed zirconia supporters claim superior marginal

fit because no shrinkage is involved in the manufactur-

ing process, and precise margins are not possible with

non-HIPed zirconia, giving rise to recurrent caries,

periodontal conditions and unaesthetic margins. Sailer

et al. (2007) reported the highest incidence of secondary

caries (22%) in a non-HIPed zirconia¶¶ FPDs after a 5-

year follow-up, suggested to be because of using a

prototype soft-milling method which has since been

improved. Notably, no other study reported a high

¶¶Cercon zirconia, Dentsply Degudent, Hanau, Germany.



incidence of caries, even when using non-HIPed zirco-

nia. Reich and colleagues (55) examined the clinical fit

of 4-unit posterior FPDs made by non-HIPed zirconia

and found a median marginal gap of 77 lm in 24 FPDs,

well within the clinically acceptable marginal gap limit

of 100–120 lm (56). Further, in vivo studies with larger

sample sizes and longer follow-up periods are needed to

establish any significant differences between HIPed and

non-HIPed zirconia restorations; and although more

dental zirconia manufacturers supply non-HIPed Y-

TZP, so far clinical results are in favour of HIPed

zirconia because of the absence of any framework failures

in the short-term.

The future of zirconia

Case reports of large multi-unit tooth and implant FPDs

suggest that the dental community may have some

confidence in zirconia as a restorative material, with

some authors restoring full mouth rehabilitations using

zirconia abutments and frameworks despite limited

scientific evidence (57–59).

The issue of porcelain chipping appears to be germane

to zirconia frameworks despite their intrinsic superior

mechanical properties and that porcelain mechanical

properties are almost framework independent. Despite

this apparent anomaly methods of strengthening the

veneering porcelain are being developed to control the

unstable chipping fractures. These include novel con-

cepts that are being reported in the literature, such as

the high-strength CAD ⁄ CAM-fabrication of the veneer-

ing porcelain (46) and the ‘‘double veneering’’ tech-

nique (52). Other approaches include bulking out the

zirconia framework and omitting veneering porcelain at

non-aesthetic areas such as the lingual and palatal

aspects of the restoration.

At this time, investigations appear to have been

directed towards zirconia materials with stabilisers

other than yttria which are less prone to LTD, such as

magnesia partially stabilized zirconia (Mg-PSZ) (60) and

ceria-stabilized zirconia ⁄ alumina nanocomposites

(Ce-TZP ⁄ A) (61). These non-yttria-stabilized zirconia

materials may be less susceptible to LTD and spontane-

ous phase transformation, however, their fracture

toughness and flexural strengths are not as high as Y-

TZP and so they may not be suitable for medium to

long-span FPDs. Therefore, long-term in vivo studies

must be carefully evaluated before non-yttria-stabilized

zirconia materials could be recommended.

Conclusion

1 Based on the limited short-term studies available,

zirconia can be said to be suitable for the fabrication

of all-ceramic posterior single crowns, long-span

FPDs and implant abutments.

2 Inlay-retained FPDs cannot be recommended in light

of published in vivo trials.

3 Chipping of the veneering porcelain is confirmed to

be an ongoing problem with zirconia all-ceramic-

based restorations.

4 Zirconia framework fractures have only been reported

in soft-milled non-HIPed zirconia, with a possible

advantage being seen in hard-milling HIPed zirconia.

5 Zirconia-based all-ceramic restorations can be

cemented with conventional luting cements, how-

ever, bonding to tooth structure is also possible but

with limited success.

Conflicts of interest

The authors declare no conflicts of interests.

References

1. Spear F. The metal-free practice: myth? Reality desirable goal?

J Esthet Restor Dent. 2001;13:59–67.

2. Studart AR, Filser F, Kocher P, Gauckler LJ. In vitro lifetime of

dental ceramics under cyclic loading in water. Biomaterials.

2007;28:2695–2705.

3. McLean JW, Hughes TH. The reinforcement of dental

porcelain with ceramic oxides. Br Dent J. 1965;119:

251–267.

4. Vult von Steyern P, Carlson P, Nilner K. All-ceramic fixed

partial dentures designed according to the DC-Zirkon

technique. A -year clinical study. J Oral Rehabil. 2005;32:

180–187.

5. Denry I, Kelly J. State of the art zirconia for dental applica-

tions. Dent Mater. 2008;24:299–307.

6. Piconi C, Maccauro G. Zirconia as a ceramic biomaterial.

Biomaterials. 1999;20:1–25.

7. Christel P, Meunier A, Heller M, Torre J, Peille C. Mechanical

properties and short-term in vivo evaluation of yttrium-oxide-

partially-stabilized zirconia. J Biomed Mater Res. 1989;23:

45–61.

8. Meyenberg K, Luthy H, Scharer P. Zirconia posts: a new all-

ceramic concept for nonvital abutment teeth. J Esthet Dent.

1995;7:73–80.

9. Molin MK, Karlsson SL. Five-year clinical prospective evalu-

ation of zirconia-based Denzir 3-unit FPDs. Int J Prosthodont.

2008;21:223–227.

10. Sailer I, Feher A, Filser F, Gauckler LJ, Luthy H, Hammerle

CH. Five-year clinical results of zirconia frameworks for



posterior fixed partial dentures. Int J Prosthodont.

2007;20:383–388.

11. Sailer I, Feher A, Filser F, Luthy H, Gauckler LJ, Scharer P

et al. Prospective clinical study of zirconia posterior fixed

partial dentures: 3-year follow-up. Quintessence Int.

2006;37:685–693.

12. Edelhoff D, Florian B, Florian W, Johnen C. HIP zirconia fixed

partial dentures–clinical results after 3 years of clinical service.

Quintessence Int. 2008;39:459–471.

13. Glauser R, Sailer I, Wohlwend A, Studer S, Schibli M, Scharer

P. Experimental zirconia abutments for implant-supported

single-tooth restorations in esthetically demanding regions: 4-

year results of a prospective clinical study. Int J Prosthodont.

2004;17:285–290.

14. Zembic A, Sailer I, Jung R, Hammerle C. Randomized-

controlled clinical trial of customized zirconia and titanium

implant abutments for single-tooth implants in canine and

posterior regions: 3-year results. Clin Oral Implants Res.

2009;20:802–808.

15. Wenz H, Bartsch J, Wolfart S, Kern M. Osseointegration and

clinical success of zirconia dental implants: a systematic

review. Int J Prosthodont. 2008;21:27–36.

16. Raigrodski AJ. Contemporary all-ceramic fixed partial den-

tures: a review. Dent Clin North Am. 2004;48:531–544.

17. Guazzato M, Albakry M, Ringer SP, Swain MV. Strength,

fracture toughness and microstructure of a selection of all-

ceramic materials. Part II. Zirconia-based dental ceramics.

Dent Mater. 2004;20:449–456.

18. Studart AR, Filser F, Kocher P, Luthy H, Gauckler LJ. Cyclic

fatigue in water of veneer-framework composites for

all-ceramic dental bridges. Dent Mater. 2007;23:177–185.

19. Kelly J, Denry I. Stabilized zirconia as a structural ceramic: an

overview. Dent Mater. 2008;24:289–298.

20. Larsson C, Vult von Steyern P, Sunzel B, Nilner K. All-ceramic

two- to five-unit implant-supported reconstructions. A

randomized, prospective clinical trial. Swed Dent J. 2006;30:

45–53.

21. Cehreli M, Kokat A, Akca K. CAD ⁄ CAM Zirconia vs. slip-cast

glass-infiltrated Alumina ⁄ Zirconia all-ceramic crowns: 2-year

results of a randomized controlled clinical trial. J Appl Oral

Sci. 2009;17:49–55.

22. Beuer F, Edelhoff D, Gernet W, Sorensen J. Three-year

clinical prospective evaluation of zirconia-based posterior

fixed dental prostheses (FDPs). Clin Oral Investig.

2009;13:445–451.

23. Schmitter M, Mussotter K, Rammelsberg P, Stober T, Ohl-

mann B, Gabbert O. Clinical performance of extended zirconia

frameworks for fixed dental prostheses: two-year results.

J Oral Rehabil. 2009;36:610–615.

24. Bornemann G. Prospective Clinical Trial with Conventionally

Luted Zirconia-based Fixed Partial Dentures–18-month Re-

sults. J Dent Res. 2003;82:117 (Sp issue B).

25. Raigrodski AJ, Chiche GJ, Potiket N, Hochstedler JL, Moham-

ed SE, Billiot S et al. The efficacy of posterior three-unit

zirconium-oxide-based ceramic fixed partial dental prosthe-

ses: a prospective clinical pilot study. J Prosthet Dent.

2006;96:237–244.

26. Pospiech P, Rountree P, Nothdurft F. Clinical evaluation of

zirconia-based all-ceramic posterior bridges: two-year results.

J Dent Res. 2003;82:114.

27. Crisp RJ, Cowan AJ, Lamb J, Thompson O, Tulloch N, Burke

FJ. A clinical evaluation of all-ceramic bridges placed in UK

general dental practices: first-year results. Br Dent J.

2008;205:477–482.

28. Ohlmann B, Rammelsberg P, Schmitter M, Schwarz S,

Gabbert O. All-ceramic inlay-retained fixed partial dentures:

preliminary results from a clinical study. J Dent. 2008;36:

692–696.

29. Tinschert J, Schulze KA, Natt G, Latzke P, Heussen N,

Spiekermann H. Clinical behavior of zirconia-based fixed

partial dentures made of DC-Zirkon: 3-year results. Int J

Prosthodont. 2008;21:217–222.

30. Ortorp A, Kihl M, Carlsson G. A 3-year retrospective and

clinical follow-up study of zirconia single crowns performed in

a private practice. J Dent. 2009;37:731–736.

31. Sailer I, Zembic A, Jung R, Siegenthaler D, Holderegger C,

Hammerle C. Randomized controlled clinical trial of custom-

ized zirconia and titanium implant abutments for canine and

posterior single-tooth implant reconstructions: preliminary

results at 1 year of function. Clin Oral Implants Res.

2009;20:219–225.

32. Norton MR. An in vitro evaluation of the strength of an

internal conical interface compared to a butt joint interface

in implant design. Clin Oral Implants Res. 1997;8:

290–298.

33. Fischer H, Weber M, Marx R. Lifetime prediction of all-

ceramic bridges by computational methods. J Dent Res.

2003;82:238–242.

34. Taskonak B, Yan J, Mecholsky JJ Jr, Sertgoz A, Kocak A.

Fractographic analyses of zirconia-based fixed partial den-

tures. Dent Mater. 2008;24:1077–1082.

35. Raigrodski A. Contemporary materials and technologies for

all-ceramic fixed partial dentures: a review of the literature.

J Prosthet Dent. 2004;92:557–562.

36. Kelly JR, Tesk JA, Sorensen JA. Failure of all-ceramic fixed

partial dentures in vitro and in vivo: analysis and modeling.

J Dent Res. 1995;74:1253–1258.

37. Oh W, Gotzen N, Anusavice KJ. Influence of connector design

on fracture probability of ceramic fixed-partial dentures.

J Dent Res. 2002;81:623–627.

38. Taskonak B, Mecholsky JJ Jr, Anusavice KJ. Fracture surface

analysis of clinically failed fixed partial dentures. J Dent Res.

2006;85:277–281.

39. Ohlmann B, Gabbert O, Schmitter M, Gilde H, Rammelsberg

P. Fracture resistance of the veneering on inlay-retained

zirconia ceramic fixed partial dentures. Acta Odontol Scand.

2005;63:335–342.

40. Giordano R. Materials for chairside CAD ⁄ CAM-produced

restorations. J Am Dent Assoc. 2006;137:14S–21S.

41. Wolfart S, Kern M. A new design for all-ceramic inlay-

retained fixed partial dentures: a report of 2 cases. Quintes-

sence Int. 2006;37:27–33.

42. Ohlmann B, Marienburg K, Gabbert O, Hassel A, Gilde H,

Rammelsberg P. Fracture-load values of all-ceramic cantile-



vered FPDs with different framework designs. Int J Prosth-

odont. 2009;22:49–52.

43. Marchack BW, Futatsuki Y, Marchack CB, White SN. Cus-

tomization of milled zirconia copings for all-ceramic crowns: a

clinical report. J Prosthet Dent. 2008;99:169–173.

44. Fischer J, Stawarzcyk B, Trottmann A, Hammerle CH.

Impact of thermal misfit on shear strength of veneering

ceramic ⁄ zirconia composites. Dent Mater. 2009;25:419–423.

45. Coelho PG, Silva NR, Bonfante EA, Guess PC, Rekow ED,

Thompson VP. Fatigue testing of two porcelain-zirconia

all-ceramic crown systems. Dent Mater. 2009;25:1122–1127.

46. Beuer F, Schweiger J, Eichberger M, Kappert HF, Gernet W,

Edelhoff D. High-strength CAD ⁄ CAM-fabricated veneering

material sintered to zirconia copings–a new fabrication mode

for all-ceramic restorations. Dent Mater. 2009;25:121–128.

47. Swain MV. Unstable cracking (chipping) of veneering porce-

lain on all-ceramic dental crowns and fixed partial dentures.

Acta Biomater. 2009;5:1668–1677.

48. Al-Dohan HM, Yaman P, Dennison JB, Razzoog ME, Lang BR.

Shear strength of core-veneer interface in bi-layered ceramics.

J Prosthet Dent. 2004;91:349–355.

49. Tsalouchou E, Cattell MJ, Knowles JC, Pittayachawan P,

McDonald A. Fatigue and fracture properties of yttria partially

stabilized zirconia crown systems. Dent Mater. 2008;24:

308–318.

50. Ashkanani HM, Raigrodski AJ, Flinn BD, Heindl H, Mancl LA.

Flexural and shear strengths of ZrO2 and a high-noble alloy

bonded to their corresponding porcelains. J Prosthet Dent.

2008;100:274–284.

51. Aboushelib MN, Kleverlaan CJ, Feilzer AJ. Microtensile bond

strength of different components of core veneered all-ceramic

restorations. Part II: Zirconia veneering ceramics. Dent Mater.

2006;22:857–863.

52. Aboushelib MN, Kleverlaan CJ, Feilzer AJ. Microtensile bond

strength of different components of core veneered all-ceramic

restorations. Part 3: double veneer technique. J Prosthodont.

2008;17:9–13.

53. Kobayashi K, Kuwajima H, Masaki T. Phase change and

mechanical properties of ZrO2-Y2O3 solid electrolyte after

aging. Solid State Ionics. 1981;3:489–493.

54. Chevalier J. What future for zirconia as a biomaterial?

Biomaterials. 2006;27:535–543.

55. Reich S, Kappe K, Teschner H, Schmitt J. Clinical fit of four-

unit zirconia posterior fixed dental prostheses. Eur J Oral Sci.

2008;116:579–584.

56. McLean JW, von Fraunhofer JA. The estimation of cement

film thickness by an in vivo technique. Br Dent J. 1971;131:

107–111.

57. Dunn DB. The use of a zirconia custom implant-supported

fixed partial denture prosthesis to treat implant failure in the

anterior maxilla: a clinical report. J Prosthet Dent.

2008;100:415–421.

58. Chang PP, Henegbarth EA, Lang LA. Maxillary zirconia

implant fixed partial dentures opposing an acrylic resin

implant fixed complete denture: a two-year clinical report. J

Prosthet Dent. 2007;97:321–330.

59. Nam J, Raigrodski AJ, Heindl H. Utilization of multiple

restorative materials in full-mouth rehabilitation: a clinical

report. J Esthet Restor Dent. 2008;20:251–263.

60. Sundh A, Sjogren G. Fracture resistance of all-ceramic

zirconia bridges with differing phase stabilizers and quality

of sintering. Dent Mater. 2006;22:778–784.

61. Fischer J, Stawarczyk B, Trottmann A, Hammerle CH. Impact

of thermal properties of veneering ceramics on the fracture

load of layered Ce-TZP ⁄ A nanocomposite frameworks. Dent

Mater. 2009;25:326–330.

Correspondence: Basil Al-Amleh, Department of Oral Rehabilitation,

Faculty of Dentistry, University of Otago, PO Box 647, Dunedin 9054,

New Zealand. E-mail: [email protected]



Zirconia

Documents

Transcript of Zirconia