Optimizing the Fitting-Surface Preparation of Zirconia Restorations

e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476

Available online at www.sciencedirect.com

ScienceDirect

jo urnal homepage: www.intl.elsevierhealth.com/journals/dema

Optimizing the ﬁtting-surface preparation of

zirconia restorations for bonding to dentin

a a a a

Alexander Franz , Olivia Winkler , Stefan Lettner , Simon Öppinger ,

a a a b

Anna Hauser , Marwan Haidar , Andreas Moritz , David C. Watts , a,∗ Andreas Schedle

University Clinic of Dentistry, Medical University of Vienna, Austria

School of Medical Sciences and Photon Science Institute, University of Manchester, Manchester, UK

a r a

t b

i c s t

l e i n f o r a c t

Article history: Objectives. The aim of this study was to identify the relative strengths and weaknesses of

Accepted 7 December 2020 different interfaces within the multilayer structure of a zirconia crown restoration when

applying different surface pretreatments. These include the inﬂuence on shear strengths

of different air abrasion protocols, glaze-on techniques, zirconia primers and self-adhesive

Keywords: cements for either the complex structure: zirconia / self adhesive resin composite cement

Zirconia restorations (RCC) / bovine dentin substrate (part 1) or the RCC / zirconia substrate (part 2).

Adhesive cementation Methods. In Part 1, zirconia discs, pretreated by either glaze-on techniques or air abrasion

Zirconia-cement-interface using Rocatec Soft, were bonded to bovine dentin substrates with different self-adhesive

Glaze-on-technique RCCs. In Part 2, steel-cylinders were bonded to zirconia cuboid substrates, pretreated by

Air abrasion either different protocols for air-abrasion or a glaze-on-technique, with different self-

adhesive RCCs. Shear bond strengths (SBS) were measured for all interfacial combinations.

Results. In part 1, application of air abrasion using Rocatec Soft signiﬁcantly increased

the SBS of zirconia to dentin compared to control specimens without pretreatment, while

glaze-on techniques did not increase the SBS. Pretreatment of zirconia surfaces with two

primers (either Clearﬁl Ceramic Primer, or Monobond S) showed signiﬁcantly higher SBS

than the controls. Cementations with RelyX Unicem 2 Automix showed signiﬁcantly higher

SBS than with MaxCem Elite. In Part 2, all air abrasion protocols increased the SBS, but there

was no signiﬁcant difference between these protocols. Again the glaze-on technique did

not increase SBS. A signiﬁcant difference between the two RCCs was again observed. When

zirconia substrates were air abraded, regardless of which protocol was applied, the highest

SBS were obtained by Calibra with P&B active followed by Panavia with or without Clearﬁl

Ceramic Primer Plus. Calibra applied without P&B active exhibited the lowest SBS.

Signiﬁcance. Pretreatment of zirconia substrates using air abrasion and/or ceramic primers

increased the SBS of the zirconia cement interface. For all tested glaze-on treatments, in our

experimental setting no effect was observed.

article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

∗

Corresponding author.

E-mail address: [email protected] (A. Schedle).

https://doi.org/10.1016/j.dental.2020.12.001

d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476 465

the ceramic surface and microdefects are created, resulting

1. Introduction

in surface enlargement. The extent of these surface changes

depends on particle size, jet pressure, angle of incidence,

Over the last 20 years, material-related advances have led to

duration and working distance [11–13]. Multiple studies have

a signiﬁcant increase in the use of all-ceramic restorations.

established the value of grit blasting [4,14]. Largely unexplored

These improvements are in biocompatibility, mechanical

- or insufﬁciently well documented - are comparisons of dif-

properties and aesthetics. The procedure for cementation of

ferent grit blasting protocols with regard to the resultant bond

glass-ceramics has become standardized, involving: (i) etch-

strength. Likewise, the combined effect of grit blasting grain

ing the restoration with HF, then (ii) silanization to ensure

size and pressure is still largely unexplored. Furthermore,

a durable bond between restoration and composite cement

there is insufﬁcient data on whether primer addition can fur-

via chemical and micromechanical mechanisms. However, in

ther improve the SBS.

contrast to glass ceramics, there is no uniform “gold standard”

In order to achieve the aim of this study, to optimize the

for cementation of oxide ceramics such as zirconium oxide,

ﬁtting surface preparation of zirconia restorations for bonding

for which zinc phosphate, glass ionomer and self-adhesive

to dentin, the following objectives were investigated:

composite cements can be used. But these lack the advanta-

geous properties (increased fracture resistance and improved Part 1:

retention) of composite cements which adhere to etched and

silanized glass ceramics [1]. a) Coating of zirconia with glass ceramic using Zenostar

This leads to low retention between zirconia restorations, Magic Glaze Spray (ZM), IPS e.max Ceram Glaze Spray (IPS)

luting cement and tooth structure. Since zirconia does not or Hotbond zirconnect Spray (HB) followed by etching with

contain silicates, it is neither etchable nor can an effective HF and silanization.

bond be achieved with silanes between restoration and luting b) Pretreatment of zirconia with Rocatec Soft followed by

cement [2,3]. This means that conventional luting protocols the application of a ceramic primer versus an universal

of glass ceramics cannot be applied to oxide ceramics [4]. primer.

Another problem is the low wettability of the zirconia surface,

which is hydrophobic [5]. However, successful cementation of Both issues were investigated using zirconia discs bonded

oxide ceramic restorations is an important factor for long- via RCC to bovine dentin substrates.

term clinical success [3,4,6]. But stronger micromechanical

Part 2:

retention can be achieved via a rougher, larger or more ener-

getic surface that changes the wetting capacity and facilitates

a) Coating of zirconia with glass ceramic (HB) followed by

the ﬂow of cement into the roughened surface [7]. There have

etching with HF and silanization.

been many attempts over the last 2 decades to increase the

b) Pretreatment of zirconia substrates with air abrasion using

roughness of zirconia surface to improve cement bonding

different protocols followed by application of two universal

[2,4]. Proposed methods include grit blasting with different

primers with and without MDP monomer and two RCCs

materials and grain sizes, so-called “tribochemical coating”,

with and without MDP.

laser treatments [4], grinding, primer and acid treatment [3,7],

“plasma spraying” or silanization [1]. Alternative strategies

Both issues were investigated using stainless steel discs

include establishing a glass layer on the zirconia surface,

bonded via RCC to zirconia substrates. The logic of using stain-

known as “Internal Coating”, “Selective Inﬁltration Etching”

less steel (SS) discs is that adhesive failure will occur between

or “Glaze-on Techniques” [2,7–9]. Whereas, in “Selective Inﬁl-

RCC/zirconia, rather than at the SS/RCC interface.

tration Etching”, a thin glass layer is applied to the surface

by means of a conditioning agent and then completely dis- The following null-hypotheses were formulated:

solved [2], in the “Internal Coating” and “Glaze-on” technique

the glass or porcelain layer is preserved as the “inner lining” (i) Coating of zirconia surfaces with glass-ceramic does not

of the restoration. In the latter two methods [7,9] HF is applied improve bonding of composite cements to zirconia com-

to the ﬁred glass layer of the oxide ceramics to roughen the pared to the control (untreated zirconia surfaces).

surface. The silicates contained in the glass layer enable bond- (ii) Air abrasion of zirconia surfaces does not increase bond-

ing with silanes. The aforementioned “glaze-ontechnique¨ has ing via composite cements, regardless of grain size and

led to signiﬁcantly increased bonding in some studies, which pressure.

were also considered in some systematic reviews and meta- (iii) Primers do not increase the bonding of composite

analyses [3,7,10]. In the “glaze-on” studies examined in these cements to zirconia.

reviews this technique was only tested in combination with (iv) Self-adhesive RCCs, with or without MDP, do not show

metals or composites, but not with dentin. similar bond strenths for the bovine dentin/RCC/zirconia

Another possibility for surface treatment is air abrasion interfaces (part 1) versus the RCC/zirconia interface (part

(grit blasting) with small particles of silica (SiO2) and/or 2).

alumina (Al2O3) particles. Speciﬁcally in the Rocatec ,

TM TM

Rocatec Plus and Rocatec Soft systems (3M), particles

2. Materials and methods

of aluminium oxide with a silica coating are blasted at high

speed onto a ceramic workpiece. According to the manufac-

Materials are listed in Tables 1A, 1B, 1C. Study variables are

turer during this process components of the particles melt on

presented in Tables 2A, 2B and Fig. 1A, 1B.

466 d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476

Table 1A – Surface glazing agents.

Glaze Code Material Manufacturer Lot Numbers Formulation

HB DCMhotbond Dental Creativ Management 13-04-16 SiO2, Al2O3, K2O, Na2O,

zirconnect spray GmbH, Rostock, Germany CaO, B2O3

ZM Zenostar Magic Wieland Dental + Technik 3/11 ZrO2,HfO2,Y2O3,Al2O3,other

Glaze Spray GmbH & Co. KG, Pforzheim, oxides ≤ 1.0 %

Germany

IPS IPS e.max Ceram Ivoclar Vivadent, Schaan, U42646 SiO2, Al2O3, ZnO, Na2O,

Glaze Spray Liechtenstein K2O, ZrO2, CaO and P2O5

propellent, isobutane

Table 1B – Surface etching/priming/bonding.

Function Code Material Manufacturer Lot Numbers Formulation

Etching HF Hydroﬂuoric acid Ultradent Porcelain BDVSC Buffered gelled hydroﬂuoric acid

9% Etch, Ultradent

Products GmbH,

Köln, Germany

Silane CS Calibra Silane Dentsply Sirona, 170124 Ethyl alcohol, acetone, water

Coupling Agent Bensheim, Germany

Bonding CUBQ Clearﬁll Kuraray Noritake 1H0018 10-Methacryloyloxydecyl dihydrogenphosphate

Universal Bond Dental Inc., Tokyo, (MDP), BisphenolA diglycidylmethacrylate,

Quick Japan 2-Hydroxyethylmethacrylate (HEMA),

hydrophilic amide monomers, colloidal silica,

silan coupling agent, sodium ﬂuoride,

dl-Camphorquinon, ethanol, water,k-Etchant,

phosphoric acid, water, colloidal silica, pigment

MBP Monobond-Plus Ivoclar Vivadent, V30663 10-Methacryloyloxydecyl dihydrogen phosphate,

Schaan, Methacrylated phosphoric acid ester, adhesive Primer

Liechtenstein monomers, ethanol

CCP Clearﬁl Ceramic 3M ESPE, Seefeld, 650011 10-Methacryloyloxydecyl dihydrogen phosphate,

Primer Germany 3-trimethoxysilylpropyl (3-MPS) methacrylate,

sulphide methacrylates ethanol

CCPP Clearﬁll Ceramic Kuraray Noritake 3L0025 3-Methacryloxypropyl trimethoxysilane,

Primer Plus Dental Inc., Tokyo, 10-Methacryloyloxydecyl dihydrogenphosphate,

Japan Ethanol

PBA Prime & Bond Dentsply Sirona, 1706000937 Phosphoric acid modiﬁed acrylate resin,

active Bensheim, Germany multifunctional Acrylate, bifunctional acrylate,

acidic acrylate, isopropanol, water, initiator,

stabilizer

Table 1C – Cementation with RCCs.

RCC Material Manufacturer Lot Number Formulation Code

RXU RelyX Unicem 3M ESPE, Seefeld, 670242 Methacrylate monomers containing phosphoric acid groups,

2 Automix Germany Methacrylate monomers, Alkaline (basic) ﬁllers, silanated

ﬁllers, Initiator components, Stabilizers, Rheological additives, Pigments

MCE Maxcem Elite Kerr Dental, 5495743 1,6-hexanediyl bismethacrylate, 2-hydroxy-1,3-propanediyl

Orange, USA bismethacrylate, 7,7,9(or 7,9,9)-trimethyl-4,13-dioxo-3,14-

dioxa5,12-diazahexadecane-1,16-diyl bismethacrylate,

3-trimethoxysilylpropyl methacrylate, 1,1,3,3-tetramethylbutyl hydroperoxide

PSA Panavia SA Kuraray Noritake 2A0218 Paste A:10-Methacryloyloxydecyl dihydrogen phosphate,

Cement Plus Dental Inc., bisphenol A diglycidylmethacrylate, triethyleneglycol

Automix Tokyo, Japan dimethacrylate (TEGDMA), hydrophobic aromatic

dimethacrylate, 2-Hydroxyethylmethacrylate, silanated

barium glass ﬁlter, silanated colloidal silica,

dl-Camphorquinone, peroxide, catalysts, pigments

CAU Calibra Universal Dentsply Sirona, 170222 Urethane Dimethacrylate, Di-and Tri-Methacrylate resins,

Bensheim, phosphoric acid, modiﬁed acrylate resin, Barium Boron Flouro

Germany Alumino Silicate Glass, organic peroxide Initiator,

camphorquinone, phosphene oxide, accelerators, butylated

hydroxy toluene,UV stabilizer, titaniumdioxide, iron oxide,

hydrophobic amorphous silicon dioxide

d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476 467

Table 2A – Surface preparation of zirconia substrates and cementation.

Part 1 Part 2

® ®

Zirconia cylinders or 480 cylinders of Prettau Zirconia 480 cuboids of Y-TZP Cercon ht

zirconia cuboids (6 mm diameter / 3 mm height). (12 mm edge length / 2 mm thickness)

Glazing Air abrasion Glazing Air abrasion

Air abrasion Pure Al2O3: Rocatec SOFT Pure Al2O3: Pure Al2O3:

Particle size 110 ␮m (R-TEC): Particle size 110 ␮m Group 1: Particle size 110

Pressure 2 bar Particle size 30 ␮m Pressure 2 bar ␮m, pressure 3.5 bar

Duration 15 s Pressure 2 bar Duration 5 sec Group 2: Particle size 110

Distance 10 mm Duration 15 s Distance 10 mm, ␮m, pressure 2 bar

◦

Distance 10 mm Angle 45 Group 3: Particle size 50

␮m, pressure 2 bar

Group 4: Particle size 50

␮m, pressure 0.5 bar

For all four subgroups:

◦

Distance 10 mm, angle 45 ,

duration 5−7 sec

Glazing HB, ZM or IPS: HB:

Sprayed in circular movement, Distance 10 cm

◦

angle 90 , distance 10 cm

Air abrasion after HB and ZM: Pure Al2O3

glazing Pure Al2O3 Particle size 110 ␮m,

Particle size 110 ␮m Pressure 0.1 MPa

Pressure 1 bar Distance 10 mm

◦

Duration 5 s. Angle 45

Distance 10 mm IPS:

Pure Al2O3,

Particle size 50 ␮m

Pressure 0.75 bar

Duration 5 s.

Distance 10 mm

HF-Treatment Hydroﬂuoric acid 9% Hydroﬂuoric acid 10%

60 s, rinsed for 30 s 60 s, rinsed for 60 s

Silanization/Priming Monobond Plus or Monobond Plus or Calibra Silane 60s P&B active or

Clearfill Ceramic Primer Clearfill Ceramic or Clearfil CCP plus

60 s Primer 60 s Clearﬁl CCP plus 60 s 20 s

For half of the specimens

Bonding P&B active or

Clearﬁl universal bond

for half of the

specimens

Self-adhesive Maxcem Elite or Maxcem Elite or Calibra Universal or Calibra Universal or

composite RelyX Unicem 2 Automix RelyX Unicem 2 Panavia SA Cement Plus Panavia SA Cement Plus

cements Automix

2.1. Part 1: Shear bond strength of zirconia cylinders

Table 2B – Pretreatment of steel cylinders (Part 2).

with different surface treatments luted to bovine dentin

Steel cylinders 480 steel cylinders ex. Dentsply

Sirona

2.1.1. Zirconia cylinders and tooth substrates

(6 mm dia. / 2 mm height)

480 cylinders of pre-sintered Prettau Zirconia (Zirkonzahn

RocatecTM Plus

GmbH, Gais, Italy) were used in this study (see Table 2A). Three

High-purity Al2O3 110 ␮m, modiﬁed

different types of surface pretreatment of zirconia cylinders

Air abrasion of steel with silica (SiO2)

were applied:

cylinders Pressure 3.5 bar

Duration 5−7 s (i) a group using tribochemical silica coating using air abra-

Distance 10 mm sion with “Rocatec Soft” (see 2.1.2), (ii) a group where the

◦

Angle 45 “glaze on technique” with additional air abrasion was applied

Priming of Rocatec Clearﬁl Ceramic Primer Plus (CCPP)

(see 2.1.3.), and (iii) a control group with no surface pretreat-

Plus treated steel Applied with an applicator brush for

ment (see 2.1.4.). Groups (i) and (iii) received a coating with cylinders 20 s

468 d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476

Fig. 1 – (A) Test variables of part 1 (B) Test variables of part 2.

either a ceramic primer, an universal primer or no coating s and dried carefully with air, making sure they were not over-

before the application of the RCCs. dried.

480 bovine teeth were embedded in round small plas-

tic moulds with Epoxy Resin (EpoFix Resin, Struers GmbH,

2.1.2.2. Self-adhesive resin composite cements (RCCs). Zirconia

Sarasota, Florida, USA). Specimens were stored dry under

cylinders were luted with the RCCs Maxcem Elite (MCE) (Kerr

a laboratory exhaust hood until they were fully hardened.

Dental, Orange, USA) or RelyX Unicem 2 Automix (RXU) (3M

Thereafter the embedded teeth were ground on the buccal

ESPE, Seefeld, Germany) to bovine dentin. During the setting

side with a grinder/polisher (Metaserv 2000 Grinder/Polisher, 2

period of the cements a constant pressure of 20 g/mm was

Buehler, Lake Bluff, Illinois) until an adequate dentin surface

applied onto the specimens using a custom-made device. For

was exposed. Papers of different granulation size (P80, P600

MCE this pressure was applied for 4 min, for RXU for 6 min,

and P1200, CarbiMet , Buehler, Lake Bluff, Illinois, USA) were

according to manufacturer’s instructions. First, cements were

used.

irradiated just for 1 s with a light-curing unit (Elipar Deep

Cure-S, 3M ESPE, St. Paul, USA) to remove excess cement.

2.1.2. Surface treatment of zirconia cylinders using

Thereafter the cements were cured at the contact surface

tribochemical silica coating

from three different directions for a total of 60 s. Irradiance

Zirconia cylinders were air-abraded with Rocatec Soft (R- TM

of the curing unit was veriﬁed with a MARC-RC device (Blue

TEC) (Rocatec, 3M ESPE, Seefeld, Germany) (see Table 2A).

Light Analytics, Halifax, NS, Canada). The zirconia cylinders

luted to dentin were stored in an incubator (Heraeus incubator

2.1.2.1. Primers. A ceramic primer (Clearﬁl Ceramic Primer B6200, Thermo Fisher Scientiﬁc Inc., Waltham, Massachusetts,

◦

[CCP], Kuraray Noritake Dental Inc., Tokio, Japan) or a univer- USA) at 37 C and kept under 100% relative humidity for

sal primer (Monobond-Plus [MBP], Ivoclar Vivadent, Schaan, 24 h to create test conditions similar to the oral environ-

Liechtenstein), was applied onto the zirconia cylinders for 60 ment.

d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476 469

2.1.3. Surface treatment of zirconia cylinders using “glaze (i) four different air abrasion protocols (see 2.2.2), (ii) one

on” techniques “glaze on” technique (see 2.2.3) and (iii) a control group with

2.1.3.1. Air abrasion. Zirconia cylinders were initially air- no surface pretreatment (see 2.2.4.). Groups (i) and (iii) received

abraded (protocol see Table 2A) and afterwards cleaned in an a coating with two different universal primers or no coat-

ultrasonic bath (Sonorex digitec, BANDELIN electronic GmbH ing before the application of the self-adhesive composite

& Co. KG, Berlin, Germany) with distilled water for 10 min and cements.

then dried with air. Steel cylinders (ø 6 mm, cylinder height 2 mm, Dentsply

Sirona, Bensheim, Germany) were pretreated with Rocatec

2.1.3.2. Glazing. The surfaces of the zirconia cylinders were Plus (3M ESPE, Seefeld, Germany) followed by treatment with

sprayed until the surface had a uniform layer of glaze. Hotbond Clearﬁl Ceramic Primer Plus (CCPP) (Kuraray Noritake Dental

zirconnect Spray (HB) (Dental Creativ Management GmbH, Inc., Tokyo, Japan), which also serves as a metal primer, for

Rostock, Germany), Zenostar Magic Glaze Spray (ZM) (Wieland 20 s. Cylinders were then cleaned with oil-free air followed by

Dental + Technik GmbH & Co. KG, Pforzheim, Germany) and treatment in an ultrasonic bath for 10 min. Afterwards steel

IPS e.max Ceram Glaze Spray (IPS) (Ivoclar Vivadent, Schaan, cylinders were ﬁxed on the zirconia cuboids, following Wiedig

Liechtenstein) were used for glazing. Zirconia cylinders were et al. [15] (Table 2B), using two different composite cements as

then ﬁred in a dental ceramic furnace (Programat CS2, described below.

Ivoclar Vivadent, Schaan, Liechtenstein) according to the man-

ufacturer’s speciﬁcations. After cooling, the cylinders were 2.2.2. Surface treatment of zirconia cuboids with air

air-abraded again, using a different protocol depending on the abrasion

test group (see Table 2A) and cleaned again in an ultrasonic Zirconia cuboids were air-abraded using 4 different protocols

bath. During the experimental study, ZM was removed from (see Table 2A), cleaned in an ultrasonic bath with distilled

the market without prior notice. Therefore, the experiments water for 10 min and then dried again with oil-free air.

were continued with a similar product, IPS e.max Ceram Glaze

Spray (IPS).

2.2.2.1. Electron microscope examination. Randomly selected

zirconia cylinders were examined using an environmental

2.1.3.3. HF-treatment. Surfaces of zirconia cylinders of the

scanning electron microscope (FEI ESEM Quanta 200, FEI Com-

groups HB and ZM were etched with hydroﬂuoric acid 9%

pany, Hillsboro, Oregon, USA) before and after air abrasion

(Ultradent Porcelain Etch, Ultradent Products GmbH, Köln,

(Fig. 2A–E).

Germany) for 60 s and rinsed under running water for 30 s and

dried with air. Specimens of IPS were etched for 30 s.

2.2.2.2. Universal primers. Half of the air-abraded zirconia

cuboids were treated with the respective primer of the

2.1.3.4. Universal primers. After HF-treatment zirconia cylin-

adhesive system, Prime&Bond active (PBA) (Dentsply Sirona,

ders received coating with one of the two universal primers

Bensheim, Germany) or CCPP for 20 s followed by air drying.

used in this study (see 2.1.2.1.)

2.2.2.3. Self-adhesive resin composite cements. After surface

2.1.3.5. Self-adhesive resin composite cements. Thereafter zir-

conditioning, the steel cylinders were bonded onto the zir-

conia cylinders were bonded with one of the two RCCs used in

conia cuboids using either Calibra Universal (CAU) (Dentsply

this study (see 2.1.2.2).

Sirona, Bensheim, Germany) or PANAVIA SA Cement Plus

(PSA) (Kuraray Noritake Dental Inc., Tokyo, Japan). For bond-

2.1.4. Controls

ing procedure, again a custom-made device was used as

2.1.4.1. Surface treatment. None of the three surface treat-

described above (2.1.2.2.). Cements were photo-activated

ments applied elsewhere in this study (tribochemical coating,

using an Elipar S10 curing light (3M ESPE, St. Paul, USA)

air abrasion, glaze on technique with HF-treatment) were

as described above (2.1.2.2.). Again, irradiance of the curing

applied to the controls.

unit was veriﬁed with a MARC-RC device. To ensure curing

even on the non-exposed surfaces, the luted test specimens

2.1.4.2. Universal primers. For the control groups, zirconia

(including the weighting device) were placed in an incubator

cylinders were treated either with the primers used in this ◦

at 37 C for 6 min, and afterwards stored in distilled water at

experiment (see 2.1.2.1.) or received no primer treatment. ◦

37 C in the incubator for 7 days before shear bond strength

measurements according to Bielen et al. [16].

2.1.4.3. Self adhesive resin composite cements. See 2.1.2.2

2.2. Part 2: Inﬂuence of different surface treatments of 2.2.3. Surface treatment of zirconia cuboids with glaze-on

zirconia cuboid substrates on the adhesion of technique

self-adhesive cements Zirconia cuboids were air-abraded using only one protocol

(see Table 2A), and afterwards cleaned as described above (see

2.2.1. Steel cylinders bonded to zirconia cuboid substrates 2.2.2.).

480 zirconia cuboid substrates (Y-TZP CERCON ht, Dentsply

Sirona, Bensheim, Germany) were used in this study (Table 2.2.3.1. Glazing. In part 2 all zirconia cuboids were sprayed

2A). Again, three different types of surface pretreatments of only with HB. Application and ﬁring protocols were applied

the zirconia substrates were applied: according to the manufacturer’s instructions (see Table 2A). In

470 d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476

Fig. 2 – (A–E) SEM images of zirconia surfaces after air abrasion with Al2O3 using four different protocols and without air

abrasion (control).

(A) Group 1: Particle size 110 ␮m; Pressure 3.5 bar.

(B) Group 2: Particle size 110 ␮m; Pressure 2 bar.

(D) Group 4: Particle size 50 ␮m; Pressure 0.5 bar.

(E) Control group without air abrasion.

the next step, the glass-ceramic coating was again air-abraded 2.2.3.3. Silanization/Priming. Silanization of HF-treated zirco-

and cuboids were cleaned again in an ultrasonic bath. nia cuboids was carried out using Calibra Silane (CAS) for 30

s or CCPP for 20 s. A moist wetting of the entire surface was

ensured continuously by means of a microbrush, if necessary,

2.2.3.2. HF-treatment. All zirconia cuboids glaced with HB

the amount of adhesion promoter was increased during the

were subsequently air-abraded and etched with HF.

d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476 471

exposure time. Subsequently, the solvent residues were dried 2.2.4. Controls

with a multifunctional syringe. 2.2.4.1. Surface treatment. None of the surface treatments

applied in this study (air abrasion or glace-on technique) were

2.2.3.4. Bonding. In the next step an adhesive, Prime&Bond conducted for the controls.

active (PBA) or Clearﬁl universal bond quick (CUBQ) was

applied to half of the zirconia cuboids. Continuous wetting

was maintained for 20 s using a microbrush. Excess solvent

2.2.4.2. Universal primers. In the control group, zirconia

was blown off with a multifunctional syringe

cuboids were either treated with the primers used in this

experiment (see 2.2.2.2.) or received no primer treatment.

2.2.3.5. Self-adhesive resin composite cements. After surface

conditioning, the metal cylinders were bonded to the zirconia

cuboids either with CAU or PSA and stored before measure-

2.2.4.3. Self adhesive resin composite cements. See 2.2.2.3.

ments as described in 2.2.2.3.

Fig. 3 – (A) Schematic of shear device for part 1. (B) Schematic of shear device for part 2.

472 d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476

2.3. Shear bond strength measurements

The shear bond strength measurements for both parts were

operated with a Zwick universal testing machine (Type 1486,

Zwick Roell, Ulm, Germany). The luted specimens were ﬁxed

in a shear testing device (Fig. 3A and B) [17] and afterwards

loaded with a crosshead speed of 0.8 mm/min until failure.

The breaking load was measured and stated in stress units

(MPa).

2.4. Statistical methods

Two-way ANOVAs were applied evaluating shear bond

strength (SBS) by the factors pretreatment, primer, bonding,

or cement respectively, as well as their interaction. Residual

diagnostics showed reasonable approximation of normality,

but considering the relatively high sample size (total 480 for

each part of the study, at least 20 in any sub-group) even relying

on the central limit theorem should be sensible.

Post-hoc tests were done using Tukey’s Honest Signiﬁcant

Difference (HSD) method, thereby controlling for multiple test-

ing.

All computations were done using R version 4.0.2 (R Core

Team 2020)

3. Results

3.1. Part 1: Shear bond strength of zirconia cylinders

with different surface treatments luted to bovine dentin

Shear bond strengths of the interface when zirconia surfaces

were treated with Rocatec Soft were signiﬁcantly higher

than the controls (specimens without pretreatment) (p < 0.001,

Fig. 4A). Values from all “glaze on” techniques were not signif-

icantly different from each other and from controls (Fig. 4A).

Pretreatment of zirconia surfaces with both primers showed

signiﬁcantly higher SBS than the controls (p < 0.01, control vs

CCP p < 0.001; control vs MBS p = 0.007 (Fig. 4B). Cementations

with RXU showed signiﬁcantly higher SBS than with MCE (p <

0.001, Fig. 4C).

to bovine dentin after air abrasion with Rocatec Soft or

without air abrasion, treated with the respective primer

(Clearﬁl Ceramic Primer or Monobond-S) or without primer.

Comparison of the two applied self-adhesive composite

cements Maxcem Elite (MCE) or RelyX Unicem 2 Automix

(RXU).

Fig. 4 – (A) Shear bond strengths (MPa) of zirconia cylinders

R-TEC = Rocatec Soft

with different surface treatments luted to bovine dentin. (B)

Control = No surface treatment

Shear bond strengths (MPa) of zirconia cylinders, luted to

TM IPS = IPS e.max Ceram Glaze Spray

bovine dentin after air abrasion with Rocatec Soft or

ZM = Zenostar Magic Glaze Spray

without air abrasion, treated with the respective primer

HB = Hotbond zirconnect Spray

(Clearﬁl Ceramic Primer or Monobond-S) or without primer.

CCP = Clearﬁl Ceramic Primer

MBS = Monobond-S

d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476 473

3.2. Part 2: Inﬂuence of different surface treatments of

zirconia cuboid substrates on the adhesion of

self-adhesive cements

Shear bond strength between RCC-bonded steel cylinders and

zirconia surfaces glazed with HB was not signiﬁcantly dif-

ferent from controls (Fig. 5A). All investigated air abrasion

protocols increased the SBS (p < 0.0001), but there was no sig-

niﬁcant difference between the protocols (Fig. 5A). Examples

for the different air abrasion protocols are shown in Fig. 2A–E.

Again, pretreatment of zirconia surfaces with both primers

showed signiﬁcantly higher SBS than the controls (p < 0.001,

Fig. 5B). A signiﬁcant difference between the cements with dif-

ferent formulations was observed. When zirconia specimens

were air abraded regardless of which protocol was applied,

highest SBS were obtained with CAU with PBA. CAU without

PBA exhibited the lowest SBS (Fig. 5C). When zirconia spec-

imens were glazed with HB, PSA with CCPP with or without

bonding (CUBQ) showed higer SBS than CAU with CAS with or

without bonding (PBA) (Fig. 5D). When specimens were treated

with HB and hydroﬂuoric acid and silane (CCPP or CAS) after-

wards, additonal coating with a bonding (CUBQ or PBA) did not

inﬂuence the SBS.

3.2.1. Failure mode

In 98% of all tested specimens failures occurred between zirco-

nia and cement, in 0.8% between cement and metal cylinders

and in 1.2% mixed failures were detected.

4. Discussion

It has been shown that results achieved by bond strength

tests (e.g. tensile or shear bond methods) depend not only

on the materials involved but also on the geometry of the

test arrangement [18]. Usually important details of the test

arrangement are not reported so that accurate analysis of the

applied method, reproduceability and comparison with other

studies in the literature are not possible [18–20]. Following

different protocols, or without air abrasion, treated with the

respective primer (Prime&Bond active or Clearﬁl Ceramic

Primer Plus) or without primer. (C) Shear bond strengths

(MPa) of zirconia cuboids luted to steel cylinders after air

abrasion, using four different protocols, or without air

abrasion. Comparison of the two applied self-adhesive

cements in combination with their respective primers or

without primer. (D) Shear bond strengths (MPa) of zirconia

cuboids luted to steel cylinders. All zirconia cuboids were

initially treated with Hotbond zirconnect Spray (HB).

Comparison of the two applied self-adhesive cements in

combination with their respective primers with bonding

Fig. 5 – (A) Shear bond strengths (MPa) of zirconia cuboids applied after priming or without bonding.

luted to steel cylinders. Cuboids were treated with Hotbond CAU = Calibra Universal

zirconnect Spray (HB) or air-abraded using four different PSA = PANAVIA SA Cement Plus

protocols concerning applied pressure and particle size of CCPP = Clearﬁl Ceramic Primer Plus

Al2O3. (B) Shear bond strengths (MPa) of zirconia cuboids PBA = Prime&Bond active

luted to steel cylinders after air abrasion, using four CAS = Calibra Silane

CUBQ = Clearﬁl universal bond quick

474 d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476

these recommendations, we have presented all variables of using either overglazes, glazes, glass-bead gel, medium fusing

this study in Tables 2A and 2B. In part 1 of this study we porcelain or a paste liner.

used bovine teeth, which have been shown, by meta-analysis, In this study (both in parts 1 and 2), no difference was found

to function as a reliable substitute for human teeth for bond between the different glaze-on techniques and the control,

strength studies [21]. in line with Thammajaruk et al. [36]. In contrast, Valentino

◦

In part 1 of this study, specimens were stored at 37 C et al. [37] and Vanderlei et al. [38] determined signiﬁcantly

under 100% relative humidity for 24 h before testing, but increased adhesion with a glass-ceramic glaze in comparison

the failures were mixed, i.e. failures occurred partly between to conventional grit blasting protocols.

cement/dentin and between cement/zirconia in the same The considerable additional effort involved in the applica-

test specimens. Therefore, in part 2, a different experimen- tion of the “glaze on” techniques, compared to air abrasion,

tal protocol was chosen, using stainless steel discs bonded with no signiﬁcant effect indicates a low practical beneﬁt.

to zirconia with RCCs, expecting that adhesive failures would Air abraded specimens were tested with or without zirconia

occur mainly between RCC/zirconia, rather than at the SS/RCC primers. In part 2, Panavia SA applied without its respective

interface, which was the case in 98% of all shear tests. Adhe- primer (CCPP) shows siginiﬁcatly higher SBS than Calibra uni-

sive bond strength is most commonly evaluated by Macro versal without primer (PBA). This might be caused by the fact

SBS or TBS tests [22,23], with the option to rank the mate- that Panavia SA contains MDP, whereas Calibra does not. On

rials [3], although their interpretation is often questioned the other hand, Calibra applied with PBA showed signiﬁcantly

[18,22,23]. higher SBS than Panavia SA with CCPP.

In part 2, for the minimal storage time of specimens before Three out of four primers, which have been used for

testing, a different protocol of 7 days was considered beneficial this present study: Clearfil Ceramic Primer, Clearfil Ceramic

and more clinically relevant [10,16]. This allowed for complete Primer Plus and Monobond Plus, contain MDP and also a spe-

curing of the resin cements. The increase in hardness after cial bi-functional molecule for silanization. Applying primers

irradiation (a measure of curing) is rapid in the ﬁrst hour; containing silanes can modify the bond strength, since two

thereafter it slows down reaching a maximum value within 24 studies, which used a technique similar to the “glaze-on” tech-

h [24]. However, it has been shown that long-term water stor- nique, also investigated the failure mode and concluded that

age or even thermocycling (e.g 10000 cycles) only had a small a silane coupling agent could successfully establish a bond

effect on bonding to zirconia [10,25]. Rough surfaces with dif- between the silica containing layer and the used resin lut-

ferent proﬁles may contribute differently to the magnitudes of ing cements by creating a durable siloxane network [6,33].

shear bond strengths as these evalute more the micromechan- According to Martins et al., the silane molecules are able to

ical retention at the interface than any chemically promoted bond to the hydroxyl groups (OH) of the silica-based surface

adhesion. Practically speaking, however, it is the increased dis- and are co-polymerized within the matrix of resin composite

ruption force that matters, rather than the speciﬁc interfacial cements [33]. In this study, according to the results of But-

bonding mechanism. ler et al. [39], the use of a primer increased SBS compared to

The results of parts 1 and 2 gave complementary insights. groups that were bonded without a primer. Without consid-

In both parts “Glaze on” techniques did not improve SBS (null ering RCCs and surface treatments of the materials, surfaces

hypothesis (i) was accepted), while all applied air abrasion pro- treated with primers had signiﬁcantly higher SBS than sur-

tocols resulted in higher SBS (null hypothesis (ii) was rejected). faces bonded without primers.

Pretreatments of surfaces with zirconia primers also led to By air abrading the zirconia specimens with aluminium

higher SBS (null hypothesis (iii) was rejected). The different oxide corundum, in different grain sizes and with different

brands of the cements also had a signiﬁcant impact on the air pressures, signiﬁcantly higher SBS could be achieved com-

SBS (null hypothesis (iv) was accepted). pared to the untreated control groups, in line with Byeon

Due to the aesthetic demands of patients, zirconia restora- et al. [40]. This is due to a supposed surface enlargement by

tions are increasingly replacing precious metal restorations the corundum particles, which abrade part of the homoge-

[26]. Compared to precious metal restorations, the friction of neous smooth surface of the zirconia, depending on the grit

zirconia workpieces is usually lower. Therefore, conventional blasting protocol. As a desirable side effect, the surface was

cementation with zinc phosphate cement is in some cases also cleaned and possible contaminations were eliminated, as

insufﬁcient [27–32]. There have been several attempts to create described in Yang et al. [41].

a strong and durable bond between oxide ceramic restorations A controversial point of surface treatment with grit blasting

and dentin. Various surface treatments of zirconia have been is the transformation of the phase. The microdefects men-

developed for more than 20 years [4]. tioned above cause compressive stress zones on the surface

Zirconia cannot be etched or treated with silanization alone of the zirconia, which were observed by Özcan et al. [11] to

due to its lack of silica phases [10,33]. Decisive for success- increase the ﬂexural strength of the ceramic. However, such a

ful long-term bonding of composite luting cements to oxide phase transformation from tetragonal to monoclinic can only

ceramic restorations is the micromechanical and chemical occur once and is an irreversible effect that serves as a kind

retention and interaction between these two surfaces [3,7,10]. of buffer against sudden overload [13]. Aurelio et al. [42] found

One approach is surface coating to establish a silica layer, that an increase in ﬂexural strength is a positive effect, which,

either by grit blasting, plasma spraying, glass fusing (Inter- however, has not yet been sufﬁciently researched in clini-

nal coating and “Glaze-On”), or Selective Inﬁltrative Etching cal cases. Furthermore, it is described that ﬂexural strength

and nanostructured alumina coating [1,7]. Several studies with increased independent of grain size, air pressure, duration and

glaze-on techniques showed promising results [6,9,33–35], aging compared to an untreated control group [42].

d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476 475

In addition to SBS obtained by Byeon et al. [40], it was [5] Kaimal A, Ramdev P, Shruthi CS. Evaluation of effect of

found in this study that there were no signiﬁcant differences zirconia surface treatment, using plasma of argon and

silane, on the shear bond strength of two composite resin

between the various grit blasting protocols applied. Özcan

cements. J Clin Diagn Res 2017;11:39–43.

et al. [12] recommended not to use grain sizes larger than 50

[6] Kitayama S, Nikaido T, Ikeda M, Alireza S, Miura H, Tagami J.

␮m and to apply air pressure with a maximum of 2.5 bar due

Internal coating of zirconia restoration with silica-based

to the danger of phase change. For Aurelio et al. [42], however,

ceramic improves bonding of resin cement to dental

this risk was not considered critical. zirconia ceramic. Biomed Mater Eng 2010;20:77–87.

Overall, this means that pre-treatment with grit blasting [7] Papia E, Larsson C, du Toit M. Vult von Steyern P. Bonding

between oxide ceramics and adhesive cement systems: a

(air abrasion) protocols achieves signiﬁcantly higher SBS. Due

systematic review. J Biomed Mater Res B Appl Biomater

to the risk of phase transformation described in Özcan et al.

2014;102:395–413.

[11], the grit blasting protocol with 50 ␮m particle size and an

[8] Saker S, Ibrahim F, Ozcan M. Effect of different surface

air pressure of 0.5 bar is probably the best choice, also consid-

treatments on adhesion of In-Ceram Zirconia to enamel and

ering that in this study all applied grit blasting protocols gave dentin substrates. J Adhes Dent 2013;15:369–76.

good and comparable results. [9] Everson P, Addison O, Palin WM, Burke FJT. Improved

bonding of zirconia substructures to resin using a

glaze-on¨ technique.¨ J Dent 2012;40:347–51.

5. Conclusion [10] Inokoshi M, De Munck J, Minakuchi S, Van Meerbeek B.

Meta-analysis of bonding effectiveness to zirconia ceramics.

J Dent Res 2014;93:329–34.

Both complex systems studied: zirconia / RCC / bovine dentin

[11] Ozcan M, Melo RM, Souza RO, Machado JP, Felipe Valandro L,

(part 1) and the RCC / zironia interface (part 2) led to consistent

Bottino MA. Effect of air-particle abrasion protocols on the

results.

biaxial ﬂexural strength, surface characteristics and phase

All applied air abrasion protocols improved the bond transformation of zirconia after cyclic loading. J Mech Behav

strengths, whereas “Glaze-on” surface treatments did not Biomed Mater 2013;20:19–28.

demonstrate any signiﬁcant improvement. Air abrasion with [12] Ozcan M, Raadschelders J, Vallittu P, Lassilla L. Effect of

particle deposition parameters on silica coating of zirconia

Al2O3, 0.5 bar and 50 ␮m particle size might be the best choice

using a chairside air-abrasion device. J Adhes Dent

with minimal risk for phase transformation. Coating zirconia

2013;15:211–4.

with primers (with or without MDP) led to a further increase

[13] Wang H, Aboushelib MN, Feilzer AJ. Strength inﬂuencing

of shear bond strengths.

variables on CAD/CAM zirconia frameworks. Dent Mater

2008;24:633–8.

[14] Martins SB, de Oliveira Abi-Rached F, Adabo GL, Baldissara P,

Acknowledgements et al. Inﬂuence of particle and air-abrasion moment on

Y-TZP surface characterization and bond strength. J

We would like to thank Sonia Arellano, Nikolaus Maderbacher Prosthodont 2019;1:271–8.

[15] Wiedig CA, Hecht R, Ludsteck M, Rennschmid H, Raia G,

and Hassan Ali Shokoohi Tabrizi for skilful technical support

Wanek E. Shear bond strength of resin cements to high

and Dentsply Sirona Deutschland GmbH for supporting this

strength ceramics. J Dent Res 2010;(Spec Iss B):

study in part and Zirkonzahn GmbH for supporting this study

680.

with materials in part.

[16] Bielen V, Inokoshi M, De Munck J, Zhang F, Vanmeensel K,

Minakuchi S, et al. Bonding effectiveness to differently

sandblasted dental zirconia. J Adhes Dent 2015;17:

Appendix A. Supplementary data 235–42.

[17] ISO 10477:2018, Dentistry – Polymer-based crown and

veneering materials.

Supplementary material related to this article can be

[18] Van Noort R, Noroozi S, Howard IC, Cardew G. A critique of

found, in the online version, at doi:https://doi.org/10.1016/

bond strength measurements. J Dent 1989;17:61–7.

j.dental.2020.12.001.

[19] Roeder L, Pereira PNR, Yamamoto T, Ilie N, Armstrong S,

Ferracane J. Spotlight on bond strength testing—unraveling

the Complexities. Dent Mater 2011;27:1197–203.

r e f e r e n c e s

[20] Franz A, Lettner S, Watts DC, Graf A, Moritz A, Schedle A.

Analysis of pre-test failures and bond-strengths of seven

adhesive systems to bovine dentine: A nine-year

[1] Derand T, Molin M, Kvam K. Bond strength of composite

novice/beginner operator study. Dent Mater

luting cement to zirconia ceramic surfaces. Dent Mater 2018;34:1599–609.

2005;21:1158–62.

[21] Soares FZ, Follak A, da Rosa LS, Montagner AF, Lenzi TL,

[2] Aboushelib MN, Kleverlaan CJ, Feilzer AJ. Selective

Rocha RO. Bovine tooth is a substitute for human tooth on

inﬁltration-etching technique for a strong and durable bond

bond strength studies: A systematic review and

of resin cements to zirconia-based materials. J Prosthet Dent

meta-analysis of in vitro studies. Dent Mater

2007;98:379–88. 2016;32:1385–93.

[3] Özcan M, Bernasconi M. Adhesion to zirconia used for

[22] Braga RR, Meira JB, Boaro LC, Xavier TA. Adhesion to tooth

dental restorations: a systematic review and meta-analysis.

structure: a critical review of “macro” test methods. Dent

J Adhes Dent 2015;17:7–26.

Mater 2010;26:38–49.

[4] Usumez A, Hamdemirci N, Koroglu BY, Simsek I, Parlar O,

[23] Scherrer SS, Cesar PF, Swain MV. Direct comparison of the

Sari T. Bond strength of resin cement to zirconia ceramic

bond strength results of the different test methods: a critical

with different surface treatments. Lasers Med Sci

literature review. Dent Mater 2010;26:78–93. 2013;28:259–66.

476 d e n t a l m a t e r i a l s 3 7 ( 2 0 2 1 ) 464–476

[24] Pilo R, Cardash HS. Post-irradiation polymerization of zirconia-based ceramic with an alternative surface

different anterior and posterior visible light-activated resin treatment. Braz Oral Res 2015;29:54.

composites. Dent Mater 1992;8:299–304. [34] Ntala P, Chen X, Niggli J, Cattell M. Development and testing

[25] Komine F, Kobayashi K, Blatz MB, Fushiki R, Koizuka M, of multi-phase glazes for adhesive bonding to zirconia

Taguchi K, et al. Durability of bond between an indirect subtrates. J Dent 2010;38:773–81.

composite veneering material and zirconium dioxide [35] Cheung GC, Botelho MG, Matinlinna JP. Effect of surface

ceramics. Acta Odontol Scand 2013;71:457–63. treatments of zirconia ceramics on the bond strength to

[26] Vagkopoulou T, Koutayas SO, Koidis P, Strub JR. Zirconia in resin cement. J Adhes Dent 2014;16:49–56.

dentistry: part 1. Discovering the nature of an upcoming [36] Thammajaruk P, Buranadham S, Thanatvarakorn O, Ferrari

bioceramic. Eur J Esthet Dent 2009;4:130–51. M, Guazzato M. Inﬂuence of glass-ceramic coating on

[27] Zidan O, Ferguson GC. The retention of complete crowns composite zirconia bonding and its characterization. Dent

prepared with three different tapers and luted with four Mater 2019;35:105–13.

different cements. J Prosthet Dent 2003;89:565–71. [37] Valentino TA, Borges GA, Borges LH, Platt JA,

[28] Wandscher VF, Prochnow C, Rippe MP, Dorneles LS, Callegari Correr-Sobrinho L. Inﬂuence of glazed zirconia on dual-cure

GL, Baldissara P, et al. Retentive strength of Y-TZP crowns: luting agent bond strength. Oper Dent 2012;37:181–7.

comparison of different silica coating methods on the [38] Vanderlei AD, Queiroz JR, Bottino MA, Valandro LF. Improved

Intaglio surfaces. Oper Dent 2017;42:121–33. adhesion of Y-TZP ceramics: a novel approach for surface

[29] Antunes MCF, Miranda JS, de Carvalho RLA, de Carvalho RF, modiﬁcation. Gen Dent 2014;62:22–7.

Kimpara ET, de Assuncao E, et al. Can low-fusing glass [39] Butler S, Linke B, Torrealba Y. Effect of MDP-based primers

application affect the marginal misﬁt and bond strength of on the luting agent bond to Y-TZP ceramic and to dentin.

Y-TZP crowns? Braz Oral Res 2018;32:e34. Biomed Res Int 2018;16:2438145.

[30] Simon JF, de Rijk WG, Hill J, Hill N. Tensile bond strength of [40] Byeon SM, Lee MH, Bae TS. Shear bond strength of Al2O3

ceramic crowns to dentin using resin cements. Int J Comput sandblasted Y-TZP ceramic to the orthodontic metal

Dent 2011;14:309–19. bracket. Materials (Basel) 2017;10:148.

[31] Shahin R, Kern M. Effect of air-abrasion on the retention of [41] Yang B, Wolfart S, Scharnberg M, Ludwig K, Adelung R, Kern

zirconia ceramic crowns luted with different cements before M. Inﬂuence of contamination on zirconia ceramic bonding.

and after artiﬁcial aging. Dent Mater 2010;26:922–8. J Dent Res 2007;86:749–53.

[32] Sudheer A, Shetty G. An in vitro study to compare the effect [42] Aurelio IL, Marchionatti AME, Montagner AF, May LG, Soares

of two etching techniques on the tensile bond strength of FZM. Does air particle abrasion affect the ﬂexural strength

resin cement bonded to base metal alloy and enamel. J and phase transformation of Y-TZP? A systematic review

Indian Prosthodont Soc 2013;13:486–93. and meta-analysis. Dent Mater 2016;32:827–45.

[33] Martins AR, Gotti VB, Shimano MM, Borges GA, Goncalves

Lde S. Improving adhesion between luting cement and