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Available online at www.sciencedirect.com

jo u rn al hom epa ge : www.int l .e lsev ierhea l th .com/ journa ls /dema

new modified laser pretreatment for porcelain zirconiaonding

an Liua, Jukka P. Matinlinnaa,∗, James Kit-Hon Tsoia, Edmond H.N. Powa,akashi Miyazakib, Yo Shibatab, Chi-Wai Kanc

Faculty of Dentistry, University of Hong Kong, Hong Kong Special Administrative RegionDepartment of Oral Biomaterials & Technology, School of Dentistry, Showa University, Tokyo, JapanInstitute of Textiles and Clothing, The Hong Kong Polytechnic University, Hong Kong Special Administrative Region

r t i c l e i n f o

rticle history:

eceived 26 April 2012

eceived in revised form

7 December 2012

ccepted 4 March 2013

eywords:

aser irradiation

andblasting

egeneration firing

urface treatment

eneering porcelain

irconia

ental ceramics

a b s t r a c t

Objectives. The aim of this study was to compare the effects of three different surface treat-

ments in enhancing porcelain zirconia bonding.

Methods. Totally, 160 densely sintered zirconia specimens were prepared and randomly

divided into four study groups: control (no treatment, Group C), sandblasting (Group S),

sandblasting followed by regeneration firing (Group SH), and laser irradiation (pulse mode)

on a CO2 laser system (Group L). After surface treatment, porcelain powders were veneered

on zirconia surface. Half of the specimens in each group were evaluated without aging (ini-

tial shear bond strength – initial SBS), and the other half was tested after being stored in

water for one month (aging SBS). X-ray diffractometry (XRD) was used to observe any crys-

tallographic transformation at zirconia surface. Results were statistically analyzed using

analysis of variance (ANOVA) and Turkey test (=0.05).

Results. The initial average SBS values of Group S, Group SH, and Group L were 31.3 ± 5.7 MPa,

29.2 ± 7.0 MPa and 32.1 ± 7.5 MPa, respectively. The differences among these three groups

were not significant. The control group had significantly lower value, 24.8 ± 6.7 MPa, than

those of Group S and Group L. Furthermore, there was no significant difference between

initial and aging values in each group. XRD analysis showed that sandblasting caused

tetragonal to monoclinic phase transformation. Regeneration firing reversed such a trans-

formation. However, crystallographic transformation could not be detected in laser treated

specimens.

Significance. Both sandblasting and laser irradiation increased porcelain zirconia bond

strength. The presented new modified laser pre-treatment might be an alternative way to

rovin

emy

sandblasting for imp

© 2013 Acad

. Introduction

lthough zirconia, especially yttria-stabilized tetragonal zir-onia polycrystal (Y-TZP), has been widely used in the

∗ Corresponding author at: Department of Dental Materials Science, Faing Pun, Hong Kong Special Administrative Region. Tel.: +852 2859038

E-mail address: jpmat@hku.hk (J.P. Matinlinna).109-5641/$ – see front matter © 2013 Academy of Dental Materials. Puttp://dx.doi.org/10.1016/j.dental.2013.03.002

g zirconia/porcelain integration.

of Dental Materials. Published by Elsevier Ltd. All rights reserved.

production of all-ceramic restorations nowadays, the rel-

culty of Dentistry, University of Hong Kong, 34 Hospital Road, Sai0; fax: +852 25489464.

atively higher failure rate of zirconia-based prosthesescompared with porcelain-fused-to-metal (PFM) restoration isstill concerned [1]. The bonding between zirconia and porce-lain was also reported to be inferior to that between metal and

blished by Elsevier Ltd. All rights reserved.

l s 2

on a flat surface. Twenty randomly selected zirconia samples

560 d e n t a l m a t e r i a

porcelain [2]. Such weak bonding might be due to some fac-tors, e.g. a mismatch in the coefficients of thermal expansion,surface treatment, lack of chemical bonding, unintentionalformation of microporosities at the interface, etc. [3].

Several in vitro studies on zirconia surface treatment havebeen carried out aiming at improving the quality of porce-lain to zirconia bonding. Since zirconia is chemically inert,it cannot be etched by some commonly used mineral acids,such as HF, H3PO4, under normal atmospheric conditions[4]. Thus, acid etching may not be an effective and conve-nient method. It has been reported that the application ofsandblasting would help to produce a durable bonding at zir-conia/porcelain interface [5]. However, such a finding has notbeen supported by all published studies. One study found that,although sandblasting could significantly increase the surfaceroughness of zirconia, it did not result in improving the zir-conia/porcelain porcelain integration [6]. Furthermore, duringthe process of sandblasting, surface flaws may also be pro-duced which might be detrimental to the clinical survival ofzirconia-based restorations [7].

Light Amplification by Stimulated Emission of Radiation(laser) technology has been utilized as one of the indus-trial surface treatment methods for more than forty years.Laser beam has some advanced properties, includes highand precise monochromaticity, coherence, collimation, greatbrightness and output efficiency [8]. The use of laser energyin zirconia surface treatment has now been of interest andreported in several studies. It was found that the values of zir-conia surface roughness had been significantly increased afterbeing processed with Nd:YAG laser (pulse mode) as well asthe surface wettability [9]. Another study compared the shearbond strengths of resin zirconia bonding among four differ-ent pre-treatment groups (untreated, HF etching, sandblastingand laser irradiation) and claimed that CO2 laser irradiation(pulse mode) at the 3 W power induced higher bond strength.Such improvement in bond strength was ascribed to the gen-eration of micro-cracks on zirconia superficial layer induced bylaser treatment. Thus, the author proposed the laser irradia-tion as an alternative way to surface pre-treatment of zirconia[10]. Nevertheless, the application of laser irradiation as amethod of zirconia surface conditioning is still lack of inves-tigation. Since the same effects generated in resin zirconiabonding may not work in the same way in porcelain zirco-nia bonding, the final word of the influence of laser treatmenton porcelain to zirconia bonding still remains questionable.

The aim of this study was to investigate the effects oflaser irradiation on zirconia before veneering procedure on theshear bond strength between zirconia and veneering porce-lain. The hypothesis of the study was that laser irradiationwould improve bonding at zirconia/veneering porcelain inter-face compared to sandblasting.

2. Materials and methods

2.1. Preparation of zirconia specimens

One hundred and sixty Y-TZP (Cercon base, DeguDent GmbH,Hanau, Germany) planar specimens with a half moon shapeand initial dimensions of 25 mm in diameter and 6 mm in

9 ( 2 0 1 3 ) 559–565

thickness were sectioned from pre-sintered zirconia blocks(containing 3 mol% yttria) using a cutting machine (Microslice,Metal Research limited company, England) under runningwater. These pre-sintered discs were then polished with SiCpaper (1000-grit) under running water on a polishing device(Lumn Major, Struers, Denmark). All the specimens were thendensely sintered in a furnace (Cercon heat, DeguDent GmbH,Hanau, Germany) under the conditions (1350 ◦C for 6 h) accord-ing to the manufacturer’s instructions. After the sinteringprocedure, dimensional change occurred (about 24 vol%) ineach disc and the size of each slice was finally determined as:19.2 mm in diameter, and 4.5 mm in thickness. Subsequently,all the zirconia specimens were divided into four experimen-tal study groups (n = 40) using the method of randomization,according to the surface treatments as follows:

Group C (control): no special treatment was carried out tomodify the zirconia specimen surfaces in this control group.

Group S (sandblasting): in this group, the bonding areas onzirconia specimens were sandblasted with 50 �m alumina par-ticles (Vacumat 300, Vita zahnfabrik, Germany) for 15 s at thepressure level of 3.5 bar and the working distance was set as10 mm. The direction of this air abrasion process was perpen-dicular to the specimen surface.

Group SH (sandblasting followed by regeneration firing):the specimens were sandblasted using the same settings asdescribed above and the particles used as those in Group S.Then, after being ultrasonically cleaned in a 70% ethanol solu-tion (Ethanol 70% Technisolv® Pure, VWR International, USA)for 10 min and air dried, they were further heated in a porce-lain furnace (Cobra 15941205, Renfert GmbH, Germany) at thetemperature of 1000 ◦C for 15 min with a 500 ◦C pre-dryingtemperature and 100 ◦C/min increasing firing rate.

Group L (laser irradiation): laser surface treatment of zir-conia surface was adjusted according to authors’ designand conducted using a commercial scale CO2 laser system(GFK Marcatex Flexi-150, Eurotrend Group, Spain). This CO2

laser was operated using a pulse mode and a wavelength of10,600 nm. The output laser light was set as 60 dpi in resolu-tion and 300 �s in pixel time. The actual output power was15.1 W/cm2. The entire surface of each zirconia disc was mod-ified with laser beam directly without any coating for threetimes. After each period of laser irradiation, the specimenswere rotated at 90◦ clockwise. The interval time between twoirradiations was 20 s.

2.2. Analysis of surface roughness

The surface roughness of all groups was analyzed with aprofilometer (Surtronic 3+, Taylor Hobson Ltd, UK). Arithmeti-cal mean roughness, Ra, was determined as the indicationof surface roughness. The higher Ra value is the roughersurface. Before each test, the profilometer was calibrated witha standard sample (6.02 �m) provided by the manufacturerand the cut off length was 0.80 mm. The tests were performed

in each group were measured after surface modification.For each sample, the measurement of surface roughnesswas performed three times and the mean value of the threereadings was adopted.

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.3. Scanning electron microscope (SEM) examination

our zirconia specimens conditioned with the four differentethods of surface treatments respectively were randomly

elected and gold-sputtered using a sputter coater (Ion SputterFC-1100, JEOL, Tokyo, Japan). Surface topography of zirconiapecimens was observed using a scanning electron micro-cope (LEO 1530 Gemini, Zeiss, USA) at the magnification of000×.

.4. Evaluation of crystallographic changes

-ray diffractometry (Thin Film-XRD, XRD-6100, Shimadzu,yoto, Japan) examination was carried out to determine theonstitution of crystalline phase at surface and identify thenfluence of surface conditioning, if any, on the crystal-ographic structure at zirconia surface. The scanning waserformed at a voltage of 40 kV and a current of 40 mA. Thecanning was set at 1.00 ◦/min in scanning and 0.02◦ in sam-ling pitch.

.5. Procedure of veneering

ll the specimens were ultrasonically cleansed in a 70%thanol solution for 15 min and dried using oil-free air afterhe application of any listed surface treatments. A thin layerf liner porcelain (Cercon Ceram Kiss Paste Liner, DeguDentmbH, Germany), which is used for modifying the color of zir-onia framework, was veneered on each sample and then, theorresponding dentin porcelain (Cercon Ceram Kiss Dentineorcelain DA 3.5, DeguDent GmbH, Germany) was fired on theurface with the dimensions as 3.6 mm in diameter and 3 mmn thickness, following strictly a dental laboratory procedure.

plastic mold was utilized in this veneering procedure. Theixture of porcelain powders and modeling liquid with an

ppropriate recommended ratio was filled into the mold andurned into the required form. After vibration, the superfluousiquid which came out of the surface was carefully removedsing tissue paper. All the firing procedures were carried out inhe porcelain furnace according to the manufacturer’s direc-ions.

.6. Evaluation of shear bond strength betweenirconia and porcelain

alf of the specimens in each group were evaluated for thenitial shear bond strengths in a Universal Testing MachineElectroPulsTM E3000, Instron, USA). The specimens were

ounted on the machine with a positioning: the loading unitt the same level as the zirconia/porcelain interface and paral-el to the veneering surface. The speed of crosshead was set at.0 mm/min. The loading was applied until the failure of eachpecimen occurred. Shear bond strength of each specimenas obtained by dividing the load causing the failure with the

irconia/porcelain interfacial area (3.6 mm in diameter). Theracture surfaces were investigated using a microscope (Leica

Z6, Leica Microsystems Ltd, USA) and the failure modes wereecorded and defined as an adhesive failure (i.e. separation oforcelain and zirconia), a cohesive failure (failure in porce-

ain or zirconia), and a mixed mode of failure (combination

( 2 0 1 3 ) 559–565 561

of these two modes). The other half of the specimens werestored in 37 ◦C water for 4 weeks and thereafter, subjected tothe shear bond strength test.

2.7. Statistical analysis

The final results were statistically analyzed using a statisticalsoftware (SPSS 16.0, SPSS Inc, USA) with two-way ANOVA testfor two factors (surface treatment and aging method), thenone-way ANOVA test for comparison of four groups under twoaging conditions (with and without water storage) and Tukeymultiple comparison test for comparing the mean initial andaging shear bond strength values in each group. Statistical sig-nificance was set at p = 0.05. The difference in the effects ofsurveyed surface treatments and the effects of water storagewere then evaluated.

3. Results

Table 1 shows that in Group C, the mean value of sur-face roughness was 0.196 ± 0.026 �m, while in Group S, ithad increased to 1.314 ± 0.138 �m, and in Group SH it was1.230 ± 0.175 �m. For the laser irradiation group the meanvalue was 0.980 ± 0.170 �m. There was no significant differ-ence between Groups S and SH (p > 0.05).

Tables 2 and 3 demonstrate the values of shear bondstrength in the four different surface treatment groups.Results showed that the lowest initial mean shear bondstrength was obtained in the control group (24.8 ± 6.7 MPa)which was significantly lower than Group S (31.3 ± 5.7 MPa)and Group L (32.1 ± 7.5 MPa). However, the differences amongGroup S (31.3 ± 5.7 MPa), Group SH (29.2 ± 7.0 MPa), and GroupL were not significant (p > 0.05). After water storage, Group Lstill exhibited the highest mean strength, 29.7 ± 6.1 MPa, andcontrol group the lowest, 25.6 ± 5.2 MPa. In each group, the ini-tial mean bond strength value was not significantly differentfrom that after storage in water.

In Table 4, most of the specimens (90%) in Group C showeda mixed mode of failure and the remaining specimens hadshown adhesive failures. All the specimens in the other threegroups exhibited a mixed mode of failure. The fractures werefound to start from the veneering porcelain and propagatealong the zirconia/porcelain interface. None of the zirconiabase was found to be damaged.

XRD analysis (Figs. 1 and 2) showed that only tetragonal(T) phase existed on zirconia surface before surface treatment(Group C) and after sandblasting, some peaks representativefor monoclinic (M) phase of zirconia appeared (Group S). Whenthe heat treatment was performed after sandblasting, thepeaks for monoclinic content disappeared (Group SH), and thespectrogram of laser treatment (Group L) was similar to thatof the control group.

Surface changes on the zirconia surfaces after being sand-blasted and laser irradiated were revealed by SEM examination(Fig. 3). In Group C, only some shallow grooves could be found

on zirconia surfaces and the surface was relatively smooth. InGroups S and SH, more irregularities were observed on sand-blasted zirconia surfaces, the grooves also disappeared due tothe loss of the surface material. Some surface flaws, such as

562 d e n t a l m a t e r i a l s 2 9 ( 2 0 1 3 ) 559–565

Table 1 – Values of surface roughness after surface treatment in different groups (Ra) (n = 20).

Group Surface treatment Mean (�m) Standard deviation

C Control 0.196a 0.026S Sandblasting 1.314b 0.138SH Sandblasting followed by heating 1.230b 0.175L Laser irradiation 0.980c 0.170

Values marked with identical letters did not differ significantly (p > 0.05).Key: C = control; S = sandblasting; SH = sandblasting followed by regeneration firing; and L = laser irradiation.

Table 2 – Tests of between-subjects effects.

Dependent variable: shear bond strength

Source Type III sum of squares df Mean square F Sig.

Corrected model 899.733a 7 128.533 3.524 .002Intercept 130815.321 1 130815.321 3.586E3 .000Treatment 729.441 3 243.147 6.666 .000Aging 88.503 1 88.503 2.426 .121Treatment × aging 81.789 3 27.263 .747 .525Error 5544.123 152 36.474Total 137259.177 160Corrected total 6443.856 159

a R squared = .140 (adjusted R squared = .100).

Table 3 – Mean shear bond strength (SBS) of four groups before and after water storage (n = 20).

Group Initial shear bond strength Shear bond strength after water storage

Mean (MPa) Standard deviation Mean (MPa) Standard deviation

C 24.8a,e ± 6.7 25.6d,e ± 5.3S 31.3b,f ± 5.7 28.3d,f ± 5.1SH 29.2a,b,g ± 7.0 27.9d,g ± 4.6L 32.1b,h ± 7.5 29.7d,h ± 6.1

Values marked with identical letters did not differ significantly (p > 0.05) (key: see Table 1).

Table 4 – Percentage of failure types in each group (%) (n = 40).

C S SH L

Adhesive 10 0 0 0100

0

Mixed 90

Cohesive 0

some voids due to the loss of the surface material, could alsobe found. In Group L, laser irradiation caused the formation ofa flake-type surface topography.

4. Discussion

The aim of surface treatment on zirconia surface is, in additionto clean the surface from any debris, to increase the surfaceroughness at the microscopic level, which will then result inthe promotion of high surface energy and thereby better wet-tability [11,12].

Sandblasting is one of the most frequently used meth-ods of surface treatment. However, the scientific communityis still not unanimous about whether sandblasting should

be carried out before veneering procedure to increase thebond strength between zirconia and porcelain. Some den-tal zirconia manufacturers recommend the sandblasting asa routine pre-treatment method. In one study, the author

100 100 0 0

compared the effects of sandblasting at the pressures of0.2 MPa, 0.4 MPa, 0.6 MPa and without sandblasting. Sand-blasting at 0.4 MPa was found to produce the highest shearbond strength, and at the same time, the flexural strengthof zirconia was not significantly influenced. Thus, the authorsuggested that sandblasting at the pressure of 0.4 MPa shouldbe adopted in the production of zirconia-based restorations[5]. This positive effect of sandblasting in increasing porce-lain to zirconia shear bond strength was also confirmed in thecurrent study. However, according to another study, althoughsandblasting caused the increase in the surface roughness ofzirconia, such treatment did not result in stronger porcelainzirconia bonding [6].

Several studies investigated the influence of sandblast-ing on the mechanical properties and bonding reliability of

zirconia. It was shown that sandblasting could lead to theformation of a compressive layer on zirconia surface andthus increased the flexural strength, accompanied with T → Mphase transformation of the surface grains [13]. Even so, the

d e n t a l m a t e r i a l s 2 9 ( 2 0 1 3 ) 559–565 563

Fig. 1 – Results of XRD analysis before and after threedifferent surface treatments (full scale). Key: C = control;S = sandblasting; SH = sandblasting followed byregeneration firing; and L = laser irradiation.

Fig. 2 – Results of XRD analysis before and after threedifferent surface treatments (low degree range) (key: see

Fig. 3 – Results of SEM examination (original magnification 1000(C) SH: sandblasting followed by regeneration firing; and (D) L: la

Fig. 1).

×) on zirconia surfaces: (A) C: control; (B) S: sandblasting;ser irradiation.

l s 2

564 d e n t a l m a t e r i a

existence of the M phase was concluded to be limited in thedepth within about 0.33 �m [14], the occurrence of such acrystallographic transformation might impair the long-termreliability and stability of zirconia-based restorations. Fur-thermore, sandblasting could also act as a critical factor inthe development of surface flaws and voids, which wouldsubsequently impair the clinical performance and reliabilityof zirconia-based restorations [15]. Consequently, althoughthe effect of sandblasting in improving zirconia/porcelaininterfacial integration has also been proved in our study, analternative method of surface treatment which is not onlyeffective but also less detrimental to the stability of zirconiabase may be in need of development.

Heat treatment after sandblasting was reported to reversethe crystallographic transformation due to the sandblasting.Monoclinic contents on zirconia surface which were gener-ated during sandblasting would be turned back into tetragonalstructures. The compressive layer on zirconia was also elimi-nated and this also led to the decreasing in flexural strengthcompared with sandblasted zirconia [16]. This process wasaimed at the offset of the deleterious effects induced by sand-blasting. Moreover, sandblasting followed by heat treatmentwas found to produce higher debonding strength in zirco-nia/porcelain composite compared with merely sandblastingtreatment [17]. However, there was a controversial consider-ing on such process, the adverse influence of regenerationfiring was reported in a shear bond strength test. This nega-tive effect was ascribed to the reduction in compression forceof veneering porcelain as well as the presence of flaws on zir-conia surface since these surface flaws could not be healedby heating at 1000 ◦C [6]. Even so, in the current study, theresults showed that such regeneration firing had not reducedthe enhancing effect of sandblasting, though its influence inlong-term stability of zirconia base may need a further inves-tigation in the near future.

Laser has already been utilized in dental practice and sur-face treatment of dental materials for many years [18,19].For tooth hard tissue ablation, the primary mechanism isexplained as when water contents in tooth tissue absorb laserenergy, they will be turned into steam instantly and the follow-ing volume expansion will lead to the micro-explosion whichthen removes the ambient tissues and makes surface rougher[20]. However, in zirconia specimens, no water content exists.The main effects of laser irradiation on zirconia surface maybe the melting and rehardening of surface material due to theample absorption of laser energy [21]. Such changes in zirco-nia surface topography will consequently result in differentsurface roughness values.

Recently, some research results of laser application inzirconia-based prostheses have been reported. The values ofzirconia surface roughness were claimed to be significantlypromoted after being irradiated with an Er:YAG laser beam(pulse mode). Although high levels of output energy had pro-duced distinct effects on zirconia surface, low output energywas found to cause less destructive effects and suggested as amethod worth of further investigation [22]. For resin zirconia

bonding, one study declared that both Er:YAG (pulse mode)and CO2 lasers (continuous mode) could enhance the shearbond strength [23]. In addition, the rate of microleakage inthe resin/zirconia interface was significantly reduced using

9 ( 2 0 1 3 ) 559–565

Er:YAG laser (pulse mode) [24]. The effects of laser surfacetreatment on porcelain to zirconia bonding, however, havenot been reported before. The laser systems used in previousstudies were designed solely for dental clinical applications,in which, the maximum output energy of these systems wasrelatively lower than the present system. Most of these stud-ies also need to coat zirconia surface with a graphite powder,which obviously complicated the procedure and diffused thelaser energy acting on zirconia surface. Additionally, differ-ent types of laser beams may not have the same influenceon zirconia bonding properties due to the difference in laserenergy adsorption, e.g. CO2 [10] and Er:YAG laser systems(pulse mode) were reported to be more efficient in strengthen-ing resin zirconia bonding while a Nd:YAG laser (pulse mode)reduced the bond strength [23]. The present results using amodified laser treatment proved the effectiveness of CO2 laserin porcelain zirconia bonding and the higher output powerused without the coating of graphite powders had simplifiedthe preparation process.

In the current study, it was also found that the adsorp-tion of laser energy caused the remodeling of zirconia surfacesand resulted in the promotion of surface roughness. Although,both sandblasting and CO2 laser irradiation increased the sur-face roughness of zirconia specimens, the increase in thesandblasting group (Group S) was higher than that in thelaser group (Group L). This was supposed to be due to the dif-ferent mechanisms of energy transmission and adsorption.However, a higher surface roughness did not result in thehigher shear bond strength. Such finding may be explainedwith the results of SEM examination. It is noteworthy thatin this study, small laser beams were subjected onto zirco-nia surfaces and they produced a lot of regular shallow pitsand flake-type structures. These pits and flake-type structuresmight act as the mechanical retentive understructures whichstrengthened the integration between zirconia and porcelain.The number of pits and flake-type structures can be controlledby adjusting the setting of laser light intensity; also the depthand width of each pit can be modified by changing the dura-tion of irradiation time. Accordingly, the output energy maybe modulated by changing these two parameters.

XRD analysis showed that after sandblasting, some of thegrains on zirconia surface were transformed to monoclinicphase. When heat treatment was performed after sandblast-ing, monoclinic content was reversed back to tetragonal phase.This was in accordance with the previous studies [16]. Laserirradiation did not cause the crystallographic changes of zir-conia grains. The stability in crystalline structure may alsobe a positive factor in the maintenance of zirconia/porcelainintegration.

As shown in this study, only one selected setting of laserirradiation was evaluated. Further investigation should be car-ried out to find out what is the optimal setting that mayproduce preferable effects in enhancing porcelain to zirco-nia bonding. Also, the influence of laser irradiation on themechanical properties of zirconia, especially the fatigue tol-erance properties and aging resistance, should be furtherexamined. It is necessary to determine whether the new mod-

ified laser treatment will impair the degradation-resistance ofzirconia frameworks because the results of SEM observationshowed that the settings adopted in this study produced a

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ake-type appearance on the zirconia surfaces. Such patternsn zirconia may also indicate that the output power selected

n our study might be needed to be optimized in order to obtain more effective surface topography and thereby an adequatehear bond strength for porcelain zirconia bonding. Therefore,

more applicable setting should be developed in further studynd the possible changes in chemical composition shouldlso be investigated. Moreover, in the future investigation ofEM and XRD, more specimens should be adopted. So far, theypothesis of this study was still accepted and a new modified

aser-treatment of zirconia for porcelain zirconia bonding waseveloped.

. Conclusions

ithin the limitation of this in vitro study, the following con-lusions were drawn:

Both sandblasting and new laser irradiation increased porce-lain zirconia bond strength.The laser irradiation used might be a new potential way ofsurface treatment for enhancing the zirconia/porcelain inter-facial adhesion and integration.The second firing after sandblasting did not influence porce-lain zirconia bonding significantly.

cknowledgments

he authors are grateful to Dentsply International for gener-usly providing the experimental materials in this study, andong Kong Polytechnic University, Laser Engraving Laboratory,

or access to their research laboratory.

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