Research ArticleEffect of Microarc Oxidation Treatment with DifferentConcentrations of MgSiF6 on Titanium-PorcelainBonding Strength

Jing Lv12 Mujie Yuan1 Pei Sun3 Changlei Wei3 Shaojun Zhang4 Yaozhong Wang4

Jie Liu 1 and Fei Tan 1

1Department of Prosthodontics e Affiliated Hospital of Qingdao University Qingdao 266003 China2School of Stomatology of Qingdao University Qingdao 266003 China3Department of Oral Medicine e Affiliated Hospital of Qingdao University Qingdao 266003 China4Qingdao Stomatological Hospital Qingdao 266001 China

Correspondence should be addressed to Jie Liu jennicalvoutlookcom and Fei Tan tanf-1984163com

Received 11 July 2020 Revised 15 September 2020 Accepted 23 September 2020 Published 8 October 2020

Academic Editor Hiroshi Yoshihara

Copyright copy 2020 Jing Lv et al 1is is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

1is study aims to evaluate the effects of different electrolyte concentrations on titanium-porcelain bonding strength aftermicroarc oxidation (MAO) treatment Four MgSiF6 electrolyte concentrations (10 gL 20 gL 30 gL and 40 gL) were chosen forthe MAO bath solutions According to ISO 9693 the bonding strengths of titanium-porcelain restorations were detected by thethree-point bending test Scanning electronmicroscopy (SEM) and energy-dispersive spectroscopy (EDS) were applied to evaluatethe morphologies and elemental compositions of the MAO coating titanium-porcelain fracture surfaces titanium-porcelaininterfaces and oxygen diffusion1e bonding strength of the 20 gLMgSiF6 group was significantly higher than that of the controlgroup However overly high MgSiF6 concentrations had a negative influence on the bonding strength between titanium andporcelain 1e results demonstrate that MAO treatment with only appropriate electrolyte concentration can improve the ti-tanium-porcelain bonding strength

1 Introduction

Porcelain-fused metal (PFM) prosthetic restoration is widelyapplied in clinic 1e metal substrate used for PFM shouldhave superior biocompatibility excellent physicochemicalproperties and relatively low cost Titanium appears to be aperfect candidate because of its corrosion resistance out-standing biocompatibility and low cost [1] However whenthe sintering temperature exceeds 800degC during porcelainfusion titanium strongly reacts with gaseous elements suchas oxygen [2] It has been repeatedly reported that titaniumoxidation is one of the most important reasons for titanium-porcelain bonding failure [3]

In clinic various treatments have been applied to improvethe titanium-porcelain bonding strength such as airborne-particle abrasion or acid etching However the effects of these

methods on the titanium-porcelain bonding strength are stillcontroversial For instance airborne-particle abrasion couldcontaminate the titanium surface with alumina particles whichmay weaken the interfacial bonding strength [4] To improvethe bonding strengths of titanium-porcelain restorationsvarious interlayers have been induced to prevent the formationof excessive titanium oxide layer such as silica coating [5]nanotitanium coating [6] and gold coating [7] For exampleGuo found that nanotitanium coating formed by sol-gel processcould prevent the oxidation of titanium substrate andsubsequently improve bonding strength between titanium andporcelain [6] It has been repeatedly proved that interlayerwould be an effective strategy to improve bonding strength oftitanium-porcelain restoration Microarc oxidation (MAO) isan electrochemical technology that involves an arc dischargereaction that forms a ceramic coating on the titanium substrate

HindawiAdvances in Materials Science and EngineeringVolume 2020 Article ID 9542471 7 pageshttpsdoiorg10115520209542471

in seconds AMAO coating includes a compact inner coating toserve as an oxygen-diffusion barrier and a porous outer coatingto increase the mechanical interlocking of the porcelain andtitanium In our previous study we found that MAO withappropriate electrolytes such as MgSiF6 can significantly im-prove the titanium-porcelain bonding strength [8] Howeverthe effect of MgSiF6 concentration on the titanium-porcelainbonding strength needs further investigation

1e physicochemical properties of MAO coatings areaffected by the concentration of the MAO electrolyte InMAO electrolyte anions are driven by the high voltagebombarding the titanium surface and fusing into the ceramiccoating On the one hand the quantity of anions fused intothe coating depends on the concentration of the MAOelectrolyte and then determines the chemical proportion ofthe MAO coating [9] In our previous study the elementalproportion of silicon and fluorine in bonding porcelain were212 and 26 respectively [10] 1us altering thechemical proportion of the MAO coating would alter thechemical bonding which is a major bonding force in tita-nium-porcelain restorations [11] On the other hand theconcentration of the electrolyte affects the conductivity ofthe MAO bath solution and the bombarding energy of theelectrolyte anions As a result the alterations of electrolyteconcentration impact the morphology and structure of theMAO coating on titanium [12]1erefore the concentrationof the electrolyte influences the physicochemical propertiesof the MAO coating and changes the bonding strengthbetween titanium and porcelain while the appropriateelectrolyte concentration for titanium-porcelain restorationsneeds further study

1is study aims to determine the effects of MgSiF6concentration on titanium-porcelain bonding strength andthe appropriate MAO electrolyte concentration In thisstudy four different concentrations of MgSiF6 were selectedfor the MAO electrolyte and the physicochemical propertiesof the MAO coatings were investigated 1e failure mode atthe interface the effect of the MAO coating on reducingtitanium oxidation and the influence of intermediatecoatings on the bond strength improvement were evaluated

2 Materials and Methods

21 Surface Treatment A total of 50 samples(25mmtimes 3mmtimes05mm) of milling commercial pure tita-nium (CP-Ti) of ASTM Grade II (Bego Bremen Germany)were randomly divided into five groups Four groups weretreated with MAO (MAO-100 College of Materials Scienceand Engineering QingdaoUniversity China) Four differentconcentrations of MgSiF6 (Shanghai Chemical ReagentShanghai China) were selected including 10 gL 20 gL30 gL and 40 gL 1e applied voltage pulse frequency andduty cycle were set to 300V 500Hz and 004 respectively Astainless steel disc was used as the MAO cathode and ti-tanium specimens were used as the anode 1e MAOtreatment was performed under water-cooled conditionskeeping the temperature of the entire process below 30degC1e arc discharges occurred on the titanium surface at280degV 1en arc discharges spread all over the titanium

substrate when the MAO applied voltage arrived at 300degV1e duration of the MAO treatment at 300degV was 3minAfter MAO treatment all the samples were cleaned con-tinuously for 10min with acetone ethanol and distilledwater in an ultrasonic cleaner1en they were dried at roomtemperature 1e control group was airborne-particleabraded with 150 μm aluminum oxide powder at a pressureof 02MPa from a distance of 5mm and at a 45deg angle for 5 s

22 Coating Morphology and Component Analysis Fivespecimens were randomly selected from each group toevaluate the titanium surface morphology by scanningelectron microscopy (SEM JMS-6460 JEOL Tokyo Japan)and the elemental composition of the MAO coating wasanalyzed using energy-dispersive spectroscopy (EDS INCA-sight Oxford Instruments London England)

23 Porcelain Application Porcelain was fused to dimen-sions of 8mmtimes 3mmtimes1mm according to ISO 9693 All thespecimens were ultrasonically cleaned in ethanol acetoneand deionized water for 15min and then dried at roomtemperature Low-fusing porcelain for titanium (Superporcelain Ti-22 Noritake Tokyo Japan) was used in thisstudy 1e bonding porcelain opaque porcelain and bodyporcelain were coated in the selected area with a short-bristled brush individually the thickness of the porcelainwas controlled by a self-made mold 1e porcelain-firingparameters were controlled automatically in a dental por-celain furnace (Vita Vacumat 6000M Sackingen Germany)according to the manufacturerrsquos instructions 1e thick-nesses of the porcelain coatings and the manufacturerrsquosinstructions are listed in Table 1

24 Bond Strength Testing Procedure In accordance withISO 9693 the titanium-porcelain bonding strengths wereevaluated by three-point bending tests with a universaltesting machine (Shimadzu AGS-J Tokyo Japan) Eachspecimen was placed on the supports (20 mm span dis-tance) A round loading piston with a radius of 1 mm waspressed to the center of the titanium specimen and theloading rate was set to 05 mmmin 1e load was appliedcontinuously until the load-deflection curve of the por-celain-titanium restoration was obtained Bond failurewas recorded digitally using the software provided by themanufacturer of the testing machine 1e bendingstrength was calculated according to the followingformula

1113944 k middot FN

mm21113890 1113891 (1)

where F is the maximum force k is the constant calculatedaccording to ISO 9693 and Σ is the bond strength in Nmm2After the three-point bending test the titanium fracturesurfaces of each group were observed by SEM to evaluate thefailure mode

2 Advances in Materials Science and Engineering

25 SEM and EDS Analysis of the Titanium-PorcelainInterface A specimen was randomly selected from eachgroup and embedded in auto polymerizing acrylic resin forthe exposure of the titanium-porcelain interface SiC paperswith different grits from 600 to 2000 were used to polish thesectioned specimens 1en the specimens were polishedwith 05 μm alumina on a flannelette and ultrasonicallycleaned with ethanol and distilled water for 10min Finallyafter coating the titanium-porcelain interface and elementalcomposition of the specimens with a layer of graphite thespecimens were evaluated using SEM coupled with EDS

26 Statistical Analysis All the data were reported as themeanplusmn standard deviation (SD) 1e statistically significantdifferences were analyzed by one-way analysis of variance(ANOVA) and Tukeyrsquos multiple range tests using SPSSsoftware 1e statistical significance was defined as plt 005

3 Results

31 Coating Morphology and Component AnalysisDuring the MAO treatment numerous wandering sparkleswere observed on the anode surfaces 1e reaction becamemore intense with increasing concentration of MgSiF6 1emorphology of each group is shown in Figure 1 1especimen surface of the control group was rough and ir-regular (Figure 1(a)) which was caused by airborne-particleabrasion 1e MAO coatings of the 10 gL MgSiF6 group(Figure 1(b)) and 20 gL MgSiF6 group (Figure 1(c)) wereboth porous and homogeneous However comparing withthe pore size of the 10 gL MgSiF6 group (05ndash1 μm diam-eter) larger pores (approximately 1ndash2 μm diameter) werefound on the MAO coating of the 20 gL MgSiF6 group 1eMAO coating morphologies of the 30 gL MgSiF6 group(Figure 1(c)) and 40 gL MgSiF6 group (Figure 1(d)) weredifferent from those of other MAO groups For example thecoating of the 40 gL MgSiF6 group was uneven with nu-merous distributed cracks and plaques

To further investigate the effect of electrolyte concen-tration on the MAO coating EDS was used to analyze thechemical proportion of the MAO coatings As listed inTable 2 the electrolyte concentration can significantly affectthe chemical proportion of the MAO coating With in-creasing electrolyte concentration a higher weight per-centage of fluorine was found in the MAO coating Forexample the weight percent of fluorine in the 40 gL MgSiF6group (7143plusmn 065 wt) was significantly higher than thatin the 10 gL MgSiF6 group (186plusmn 021 wt) However theweight percentage of silicon in the MAO coating decreasedwith increasing concentration of MAO electrolyte

32 Bonding Strength of Titanium-Porcelain Restorations1e bonding strengths of each group are presented in Ta-ble 3 We found that compared with the control groupMAO treatment with appropriate electrolyte concentrationcan significantly improve the bonding strengths For in-stance compared with the control group the 10 gL MgSiF6group and 20 gL MgSiF6 group showed 141-fold and 165-fold increases in the bonding strength respectively How-ever no significant difference in bonding strength was foundbetween the control and 40 gL MgSiF6 groups (pgt 005)

33 SEMAnalysis of the Titanium-Porcelain Fracture Surface1e titanium fracture surface of each group after the three-point bending test is shown in Figure 2 As shown there wasno residual porcelain on the specimens of the control(Figure 2(a)) and 40 gL MgSiF6 (Figure 2(e)) groups in-dicating that the titanium-porcelain bonding fracture oc-curred between the oxide layer and titanium substrate Incontrast we found a significant amount of residual porcelainat the titanium surface of the 10 gL MgSiF6 (Figure 2(b))and 20 gL MgSiF6 (Figure 2(c)) groups indicating thatcrack propagation occurred within the porcelain Mean-while only a small amount of residual porcelain was foundat the fracture surface of 30 gL MgSiF6 (Figure 2(d))

34 SEM and EDS Analysis of the Titanium-PorcelainInterface 1e morphologies of the titanium-porcelain in-terface of each group are shown in Figure 3 Noticeablecracks and pores can be found at the titanium-porcelaininterfaces of the control (Figure 3(a)) and 40 gL MgSiF6groups (Figure 3(e)) Meanwhile several tiny pores occurredat the interfaces of the 10 gL MgSiF6 (Figure 3(b)) and 30 gL MgSiF6 groups (Figure 3(d)) However the interface of the20 gL MgSiF6 group (Figure 3(c)) was uniformly compactand free of cracks and pores

To further evaluate the effect of interface morphology onoxygen diffusion linear elemental scanning was employed(Figure 4) It was found that the oxygen curves of the 20 gLMgSiF6 group declined sharply over a narrow range aftercrossing the titanium-porcelain interface (Figure 4(c)) whichindicates that the MAO coating can act as a barrier for oxygendiffusion of titanium-porcelain restorations In contrast theoxygen curves of other groups declined slowly after crossing theinterface of the titanium-porcelain restoration

4 Discussion

To improve titanium-porcelain bonding strength the idealcoating should (1) shield against oxygen diffusion into ti-tanium (2) increase the titanium-porcelain bonding

Table 1 Sintering condition of the porcelain

Porcelain Startingtemperature (degC)

Sinteringtemperature (degC)

Vacuum(MPa)

Sinteringtime (min)

Porcelain coatingthickness (mm)

Bonding agent 500 800 0099 3 02Opaque 500 780 0099 3 02Dentin 500 760 0096 5 06

Advances in Materials Science and Engineering 3

strength and (3) possess excellent biocompatibility In thisstudy different concentrations of MgSiF6 were used toevaluate their effects on the coatingrsquos physicochemicalproperties and titanium-porcelain bonding strength Wefound that MAO electrolyte concentration could signifi-cantly affect the coating physicochemical properties andsubsequent titanium-porcelain bonding strength 1e ap-propriate electrolyte concentration would be necessary toform a porous and homogeneous MAO coating which couldeffectively prevent oxygen diffusion and enhance bondingstrength However excessive electrolyte concentrationwould impact MAO coating homogeneousness 1e datademonstrated that MAO could improve titanium-porcelainbonding strength only with appropriate electrolyteconcentration

1e MAO electrolyte concentration could affect thecoating morphology In theory increasing the electrolyteconcentration could significantly enhance the bombardingenergy of anions because of increased anion volume andelectrolyte conductivity [13] In this study we found thatpore sizes on the coating of the 20 gL MgSiF6 group werelarger than that of the 10 gL MgSiF6 group indicating thehigher bombarding energy of the 20 gL MgSiF6 groupHowever excessively high MgSiF6 concentration wouldimpair the coating function For example we found manycracks on the coating of the 40 gL MgSiF6 group implyingthat an overly high bombarding energy of anions candamage the integrity of MAO coating On the other handfew pores were found on the 30 gL MgSiF6 and 40 gLMgSiF6 groups indicating that the pores were covered by theexcessive fused mass Moreover the MAO electrolyteconcentration could affect the coatingrsquos chemical propor-tion As the MAO electrolyte concentration was increased ahigher weight percentage of fluorine was found in the MAOcoating indicating that more anions were fused into theMAO coating However the weight percentage of silicondecreased with increasing MgSiF6 concentration which maybe caused by the high atom ratio of fluorine and silicon in theanion

Compared with the control group the 20 gL MgSiF6group exhibited bond strength enhancements of 653 1is

(a) (b) (c)

(d) (e)

Figure 1 SEMmicrophotographs of MAO coating (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group (d) 30 gL MgSiF6group and (e) 40 gL MgSiF6 group Bar 1 μm

Table 2 Effect of electrolyte concentrations on the Mao coating (wt n 6)Groups Ti Si O F10 gL MgSiF6 4065plusmn 060 891plusmn 051 4859plusmn 027 186plusmn 02120 gL MgSiF6 4059plusmn 092 316plusmn 024 3930plusmn 119 1695plusmn 20330 gL MgSiF6 2883plusmn 094 187plusmn 010 2423plusmn 074 4507plusmn 16840 gL MgSiF6 1392plusmn 044 076plusmn 013 1389plusmn 032 7143plusmn 265lowastplt 005 compared to the control group

Table 3 Bonding strength of different titanium-porcelain resto-rations (meanplusmn SD n 10)Group K Bond strength (MPa)10 gL MgSiF6 47 3818plusmn 265lowast20 gL MgSiF6 47 4475plusmn 221lowast30 gL MgSiF6 47 3144plusmn 204lowast40 gL MgSiF6 47 2804plusmn 259Control group 47 2708plusmn 316lowastplt 005 compared to the control group

4 Advances in Materials Science and Engineering

result can be indirectly proved by the fracture surface ob-servation 1e titanium-porcelain fracture of the 20 gLMgSiF6 group occurred in the interior of porcelain Itdemonstrates that the bonding strength of the 20 gL MgSiF6group had exceeded the mechanical strength of bondingporcelain 1e improved bonding strength of the 20 gLMgSiF6 group should stem from the coating morphologyprevention of oxygen diffusion and coating chemicalcomposition First the improved bonding strength can beattributed to the porous morphology of MAO coating 1epores (approximately 1-2 μmdiameter) on theMAO coating

of the 20 gL MgSiF6 group would enhance the interlockbetween titanium and porcelain According to results on thecoatingrsquos morphology more pores and larger pore diameterswere found on the MAO coating of the 20 gLMgSiF6 groupcompared to the other groups Other studies have provedthat porcelain can fuse into the porous coating and physi-cally interlock with titanium substrate [6] In addition tothis studies have demonstrated that interlocking is animportant bonding force for titanium-porcelain restorations[14 15] Second the improved bonding strength may stemfrom the protective effect of MAO coating on the oxygen

(a) (b) (c)

(d) (e)

Figure 2 SEM microphotographs of the fracture surface of titanium specimens (a) control group (b) 10 gL MgSiF6 group (c) 20 gLMgSiF6 group (d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group Bar 100 μm 1e residual porcelain is indicated by arrows

(a) (b) (c)

(d) (e)

Figure 3 SEMmicrophotographs of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group (d)30 gL MgSiF6 group and (e) 40 gL MgSiF6 group Bar 10 μm 1e pores and cracks are indicated by arrows

Advances in Materials Science and Engineering 5

diffusion As shown the oxygen curves of the 20 gL MgSiF6group declined rapidly in a narrow range after crossing theinterface indicating that the MAO coating effectivelycontrolled the diffusion of oxygen into titanium 1e oxy-gen-diffusion barrier of the 20 gL MgSiF6 group may haveresulted from the impact structure at the titanium-porcelaininterface For example many pores and cracks were found atthe interface of other groups In the porcelain applicationthe oxygen could diffuse into the titanium substrate throughthese structural defects between titanium and porcelain1ird the improved bonding strength may result fromchemical changes caused by anions bombarding at the ti-tanium-porcelain interface After MAO treatment siliconand fluorine were found on the surface of titanium substrateIt was found that the same element both in coating andporcelain would improve chemical bonding between tita-nium and porcelain for example silicon 1e chemicalbonding formed during porcelain sintering and played animportant role in the titanium-porcelain bond For exampleLin found a mutual diffusion of silicon formed at the tita-nium-porcelain interface 1e elemental silicon that diffused

to the titanium substrate comes from the silica coating madeby sol-gel dipping [5]

Furthermore excessively high MgSiF6 concentrationswould impair the bonding strength between titanium andporcelain When the MAO concentration of MgSiF6 wasabove 20 gL the bonding strength decreased with in-creasing MAO concentration 1e weakened bondingstrength may result from changes to the coatingrsquos chemicalcomposition Chemical bonding has been proved to be themajor bonding force of titanium-porcelain restorations [16]In our previous study we found that excluding oxygensilicon (212) and fluorine (26) are major nonmetallicelements in the bonding porcelain [10] However the weightpercent of silicon in the 40 gL MgSiF6 group (076plusmn 013 wt) was far lower than that in the bonding porcelainMoreover the weight percent of fluorine in the 40 gLMgSiF6 group (7143plusmn 065 wt) was far higher than that inthe bonding porcelain Change to the chemical proportionwould increase the mismatch of thermal expansion coeffi-cient (TEC) between titanium and porcelain It was dem-onstrated that the TEC mismatch would decrease the

Si

O

Ti1

05

0

k

0 50 100

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

(a)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(b)

Si

O

Ti

0 100 200

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

1

05

0

k

(c)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(d)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

k

1

05

0

(e)

Figure 4 Elemental line scanning of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group(d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group

6 Advances in Materials Science and Engineering

bonding strength between titanium and porcelain [17] Onthe other hand the weakened bonding strength may stemfrom the morphology of the 40 gL MgSiF6 group In con-trast with the 20 gL MgSiF6 group the coating of the 40 gLMgSiF6 group was uneven with numerous cracks and pla-ques distributed Decreased morphological integrity wouldincrease oxygen diffusion into titanium and impair thebonding strength

5 Conclusions

In this study we found that different concentrations of theMAO electrolyte can influence the morphology of the MAOcoating and result in different effects on the bondingstrength MAO treatment with 20 gL MgSiF6 can signifi-cantly improve the titanium-porcelain bonding strength

Although more anions were fused into the MAO coatingwith increasing electrolyte concentration the bondingstrength decreased when the concentration exceeded 20 gLIn addition it was demonstrated that overly high MgSiF6concentrations have a negative influence on the structuralhomogeneity of the coating interface integrity and oxygendiffusion 1erefore titanium-porcelain restorations treatedby MAO are suitable for clinical use when appropriateMgSiF6 concentrations are used

Data Availability

1e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

1e authors declare that there are no conflicts of interestregarding the publication of this paper

Authorsrsquo Contributions

1e authors Jing Lv and Mujie Yuan contributed equally tothis work

Acknowledgments

1e authors would like to thank Editage (httpwwweditagecom) for English language editing 1is study wassupported by Shandong Provincial Natural Science Foun-dation (ZR2018BH015) and Source Innovation Planning ofQingdao (19-06-02-45-cg)

References

[1] N Suansuwan and M V Swain ldquoAdhesion of porcelain totitanium and a titanium alloyrdquo Journal of Dentistry vol 31no 7 pp 509ndash518 2003

[2] H Kimura C J Horng M Okazaki et al ldquoOxidation effectson porcelain-titanium interface reactions and bond strengthrdquoDental Materials Journal vol 9 no 1 pp 91ndash99 1990

[3] J C Souza B Henriques E Ariza et al ldquoMechanical andchemical analyses across dental porcelain fused to CP tita-nium or Ti6Al4VrdquoMaterials Science and Engineering vol 37pp 76ndash83 2014

[4] S E Elsaka ldquoInfluence of surface treatments on adhesion ofporcelain to titaniumrdquo Journal of Prosthodontics vol 22no 6 pp 465ndash471 2013

[5] J Ye X Ye S Chang et al ldquoEffect of silica coating on the bondstrength of milled pure titanium to dental porcelainrdquo Euro-pean Journal of Oral Sciences vol 124 no 5 pp 498ndash5032016

[6] L Guo X Chen X Liu et al ldquoSurface modifications andNano-composite coatings to improve the bonding strength oftitanium-porcelainrdquo Materials Science and Engineering Cvol 61 no 1 pp 143ndash148 2016

[7] R Khung and N S Suansuwan ldquoEffect of gold sputtering onthe adhesion of porcelain to cast and machined titaniumrdquoeJournal of Prosthetic Dentistry vol 110 no 1 pp 41ndash46 2013

[8] X Yuan F Tan H Xu et al ldquoEffects of different electrolytesfor micro-arc oxidation on the bond strength between tita-nium and porcelainrdquo e Journal of Prosthetic Dentistryvol 61 no 3 pp 297ndash304 2017

[9] K Venkateswarlu N Rameshbabu D Sreekanth et al ldquoRoleof electrolyte chemistry on electronic and in vitro electro-chemical properties of micro-arc oxidized titania films on CpTirdquo Electrochimica Acta vol 105 no 30 pp 468ndash480 2013

[10] Z Zhang F Tan Y Ba and Y Zhang ldquoEffects of differentbond agents on commercially pure Ti-porcelain bondstrengthrdquo Materials Letters vol 109 pp 214ndash216 2013

[11] P Haag and K Nilner ldquoBonding between titanium and dentalporcelain A systematic reviewrdquo Acta Odontol Scand vol 68no 3 pp 154ndash164 2010

[12] Z Zhao X Chen A Chen et al ldquoSynthesis of bioactiveceramic on the titanium substrate by micro-arc oxidationrdquoJournal of Biomedical Materials Research Part A vol 90 no 2pp 438ndash445 2009

[13] A R Ribeiro F Oliveira L C Boldrini et al ldquoMicro-arcoxidation as a tool to develop multifunctional calcium-richsurfaces for dental implant applicationsrdquo Materials Scienceand Engineering C vol 54 pp 196ndash206 2015

[14] M G Troia G E Henriques M F Mesquita andW S Fragoso ldquo1e effect of surface modifications on titaniumto enable titanium-porcelain bondingrdquo Dental Materialsvol 24 no 1 pp 28ndash33 2008

[15] A Acar O Inan and S Halkaci ldquoEffects of airborne-particleabrasion sodium hydroxide anodization and electrical dis-charge machining on porcelain adherence to cast commer-cially pure titaniumrdquo Journal of Biomedical MaterialsResearch Part B Applied Biomaterials vol 82 no 1pp 267ndash274 2007

[16] J Yang J R Kelly O Bailey and G Fischman ldquoPorcelain-titanium bonding with a newly introduced commerciallyavailable systemrdquo Journal of Prosthetic Dentistry vol 116no 1 pp 98ndash101 2016

[17] K M Mahale and S J Nagda ldquoEffect of preoxidation on thebond strength of titanium and porcelainrdquo European Journal ofProsthodontics and Restorative Dentistry vol 22 no 2pp 76ndash83 2014

Advances in Materials Science and Engineering 7

25 SEM and EDS Analysis of the Titanium-PorcelainInterface A specimen was randomly selected from eachgroup and embedded in auto polymerizing acrylic resin forthe exposure of the titanium-porcelain interface SiC paperswith different grits from 600 to 2000 were used to polish thesectioned specimens 1en the specimens were polishedwith 05 μm alumina on a flannelette and ultrasonicallycleaned with ethanol and distilled water for 10min Finallyafter coating the titanium-porcelain interface and elementalcomposition of the specimens with a layer of graphite thespecimens were evaluated using SEM coupled with EDS

26 Statistical Analysis All the data were reported as themeanplusmn standard deviation (SD) 1e statistically significantdifferences were analyzed by one-way analysis of variance(ANOVA) and Tukeyrsquos multiple range tests using SPSSsoftware 1e statistical significance was defined as plt 005

3 Results

31 Coating Morphology and Component AnalysisDuring the MAO treatment numerous wandering sparkleswere observed on the anode surfaces 1e reaction becamemore intense with increasing concentration of MgSiF6 1emorphology of each group is shown in Figure 1 1especimen surface of the control group was rough and ir-regular (Figure 1(a)) which was caused by airborne-particleabrasion 1e MAO coatings of the 10 gL MgSiF6 group(Figure 1(b)) and 20 gL MgSiF6 group (Figure 1(c)) wereboth porous and homogeneous However comparing withthe pore size of the 10 gL MgSiF6 group (05ndash1 μm diam-eter) larger pores (approximately 1ndash2 μm diameter) werefound on the MAO coating of the 20 gL MgSiF6 group 1eMAO coating morphologies of the 30 gL MgSiF6 group(Figure 1(c)) and 40 gL MgSiF6 group (Figure 1(d)) weredifferent from those of other MAO groups For example thecoating of the 40 gL MgSiF6 group was uneven with nu-merous distributed cracks and plaques

To further investigate the effect of electrolyte concen-tration on the MAO coating EDS was used to analyze thechemical proportion of the MAO coatings As listed inTable 2 the electrolyte concentration can significantly affectthe chemical proportion of the MAO coating With in-creasing electrolyte concentration a higher weight per-centage of fluorine was found in the MAO coating Forexample the weight percent of fluorine in the 40 gL MgSiF6group (7143plusmn 065 wt) was significantly higher than thatin the 10 gL MgSiF6 group (186plusmn 021 wt) However theweight percentage of silicon in the MAO coating decreasedwith increasing concentration of MAO electrolyte

32 Bonding Strength of Titanium-Porcelain Restorations1e bonding strengths of each group are presented in Ta-ble 3 We found that compared with the control groupMAO treatment with appropriate electrolyte concentrationcan significantly improve the bonding strengths For in-stance compared with the control group the 10 gL MgSiF6group and 20 gL MgSiF6 group showed 141-fold and 165-fold increases in the bonding strength respectively How-ever no significant difference in bonding strength was foundbetween the control and 40 gL MgSiF6 groups (pgt 005)

33 SEMAnalysis of the Titanium-Porcelain Fracture Surface1e titanium fracture surface of each group after the three-point bending test is shown in Figure 2 As shown there wasno residual porcelain on the specimens of the control(Figure 2(a)) and 40 gL MgSiF6 (Figure 2(e)) groups in-dicating that the titanium-porcelain bonding fracture oc-curred between the oxide layer and titanium substrate Incontrast we found a significant amount of residual porcelainat the titanium surface of the 10 gL MgSiF6 (Figure 2(b))and 20 gL MgSiF6 (Figure 2(c)) groups indicating thatcrack propagation occurred within the porcelain Mean-while only a small amount of residual porcelain was foundat the fracture surface of 30 gL MgSiF6 (Figure 2(d))

34 SEM and EDS Analysis of the Titanium-PorcelainInterface 1e morphologies of the titanium-porcelain in-terface of each group are shown in Figure 3 Noticeablecracks and pores can be found at the titanium-porcelaininterfaces of the control (Figure 3(a)) and 40 gL MgSiF6groups (Figure 3(e)) Meanwhile several tiny pores occurredat the interfaces of the 10 gL MgSiF6 (Figure 3(b)) and 30 gL MgSiF6 groups (Figure 3(d)) However the interface of the20 gL MgSiF6 group (Figure 3(c)) was uniformly compactand free of cracks and pores

To further evaluate the effect of interface morphology onoxygen diffusion linear elemental scanning was employed(Figure 4) It was found that the oxygen curves of the 20 gLMgSiF6 group declined sharply over a narrow range aftercrossing the titanium-porcelain interface (Figure 4(c)) whichindicates that the MAO coating can act as a barrier for oxygendiffusion of titanium-porcelain restorations In contrast theoxygen curves of other groups declined slowly after crossing theinterface of the titanium-porcelain restoration

4 Discussion

To improve titanium-porcelain bonding strength the idealcoating should (1) shield against oxygen diffusion into ti-tanium (2) increase the titanium-porcelain bonding

Table 1 Sintering condition of the porcelain

Porcelain Startingtemperature (degC)

Sinteringtemperature (degC)

Vacuum(MPa)

Sinteringtime (min)

Porcelain coatingthickness (mm)

Bonding agent 500 800 0099 3 02Opaque 500 780 0099 3 02Dentin 500 760 0096 5 06

Advances in Materials Science and Engineering 3

strength and (3) possess excellent biocompatibility In thisstudy different concentrations of MgSiF6 were used toevaluate their effects on the coatingrsquos physicochemicalproperties and titanium-porcelain bonding strength Wefound that MAO electrolyte concentration could signifi-cantly affect the coating physicochemical properties andsubsequent titanium-porcelain bonding strength 1e ap-propriate electrolyte concentration would be necessary toform a porous and homogeneous MAO coating which couldeffectively prevent oxygen diffusion and enhance bondingstrength However excessive electrolyte concentrationwould impact MAO coating homogeneousness 1e datademonstrated that MAO could improve titanium-porcelainbonding strength only with appropriate electrolyteconcentration

1e MAO electrolyte concentration could affect thecoating morphology In theory increasing the electrolyteconcentration could significantly enhance the bombardingenergy of anions because of increased anion volume andelectrolyte conductivity [13] In this study we found thatpore sizes on the coating of the 20 gL MgSiF6 group werelarger than that of the 10 gL MgSiF6 group indicating thehigher bombarding energy of the 20 gL MgSiF6 groupHowever excessively high MgSiF6 concentration wouldimpair the coating function For example we found manycracks on the coating of the 40 gL MgSiF6 group implyingthat an overly high bombarding energy of anions candamage the integrity of MAO coating On the other handfew pores were found on the 30 gL MgSiF6 and 40 gLMgSiF6 groups indicating that the pores were covered by theexcessive fused mass Moreover the MAO electrolyteconcentration could affect the coatingrsquos chemical propor-tion As the MAO electrolyte concentration was increased ahigher weight percentage of fluorine was found in the MAOcoating indicating that more anions were fused into theMAO coating However the weight percentage of silicondecreased with increasing MgSiF6 concentration which maybe caused by the high atom ratio of fluorine and silicon in theanion

Compared with the control group the 20 gL MgSiF6group exhibited bond strength enhancements of 653 1is

(a) (b) (c)

(d) (e)

Figure 1 SEMmicrophotographs of MAO coating (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group (d) 30 gL MgSiF6group and (e) 40 gL MgSiF6 group Bar 1 μm

Table 2 Effect of electrolyte concentrations on the Mao coating (wt n 6)Groups Ti Si O F10 gL MgSiF6 4065plusmn 060 891plusmn 051 4859plusmn 027 186plusmn 02120 gL MgSiF6 4059plusmn 092 316plusmn 024 3930plusmn 119 1695plusmn 20330 gL MgSiF6 2883plusmn 094 187plusmn 010 2423plusmn 074 4507plusmn 16840 gL MgSiF6 1392plusmn 044 076plusmn 013 1389plusmn 032 7143plusmn 265lowastplt 005 compared to the control group

Table 3 Bonding strength of different titanium-porcelain resto-rations (meanplusmn SD n 10)Group K Bond strength (MPa)10 gL MgSiF6 47 3818plusmn 265lowast20 gL MgSiF6 47 4475plusmn 221lowast30 gL MgSiF6 47 3144plusmn 204lowast40 gL MgSiF6 47 2804plusmn 259Control group 47 2708plusmn 316lowastplt 005 compared to the control group

4 Advances in Materials Science and Engineering

result can be indirectly proved by the fracture surface ob-servation 1e titanium-porcelain fracture of the 20 gLMgSiF6 group occurred in the interior of porcelain Itdemonstrates that the bonding strength of the 20 gL MgSiF6group had exceeded the mechanical strength of bondingporcelain 1e improved bonding strength of the 20 gLMgSiF6 group should stem from the coating morphologyprevention of oxygen diffusion and coating chemicalcomposition First the improved bonding strength can beattributed to the porous morphology of MAO coating 1epores (approximately 1-2 μmdiameter) on theMAO coating

of the 20 gL MgSiF6 group would enhance the interlockbetween titanium and porcelain According to results on thecoatingrsquos morphology more pores and larger pore diameterswere found on the MAO coating of the 20 gLMgSiF6 groupcompared to the other groups Other studies have provedthat porcelain can fuse into the porous coating and physi-cally interlock with titanium substrate [6] In addition tothis studies have demonstrated that interlocking is animportant bonding force for titanium-porcelain restorations[14 15] Second the improved bonding strength may stemfrom the protective effect of MAO coating on the oxygen

(a) (b) (c)

(d) (e)

Figure 2 SEM microphotographs of the fracture surface of titanium specimens (a) control group (b) 10 gL MgSiF6 group (c) 20 gLMgSiF6 group (d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group Bar 100 μm 1e residual porcelain is indicated by arrows

(a) (b) (c)

(d) (e)

Figure 3 SEMmicrophotographs of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group (d)30 gL MgSiF6 group and (e) 40 gL MgSiF6 group Bar 10 μm 1e pores and cracks are indicated by arrows

Advances in Materials Science and Engineering 5

diffusion As shown the oxygen curves of the 20 gL MgSiF6group declined rapidly in a narrow range after crossing theinterface indicating that the MAO coating effectivelycontrolled the diffusion of oxygen into titanium 1e oxy-gen-diffusion barrier of the 20 gL MgSiF6 group may haveresulted from the impact structure at the titanium-porcelaininterface For example many pores and cracks were found atthe interface of other groups In the porcelain applicationthe oxygen could diffuse into the titanium substrate throughthese structural defects between titanium and porcelain1ird the improved bonding strength may result fromchemical changes caused by anions bombarding at the ti-tanium-porcelain interface After MAO treatment siliconand fluorine were found on the surface of titanium substrateIt was found that the same element both in coating andporcelain would improve chemical bonding between tita-nium and porcelain for example silicon 1e chemicalbonding formed during porcelain sintering and played animportant role in the titanium-porcelain bond For exampleLin found a mutual diffusion of silicon formed at the tita-nium-porcelain interface 1e elemental silicon that diffused

to the titanium substrate comes from the silica coating madeby sol-gel dipping [5]

Furthermore excessively high MgSiF6 concentrationswould impair the bonding strength between titanium andporcelain When the MAO concentration of MgSiF6 wasabove 20 gL the bonding strength decreased with in-creasing MAO concentration 1e weakened bondingstrength may result from changes to the coatingrsquos chemicalcomposition Chemical bonding has been proved to be themajor bonding force of titanium-porcelain restorations [16]In our previous study we found that excluding oxygensilicon (212) and fluorine (26) are major nonmetallicelements in the bonding porcelain [10] However the weightpercent of silicon in the 40 gL MgSiF6 group (076plusmn 013 wt) was far lower than that in the bonding porcelainMoreover the weight percent of fluorine in the 40 gLMgSiF6 group (7143plusmn 065 wt) was far higher than that inthe bonding porcelain Change to the chemical proportionwould increase the mismatch of thermal expansion coeffi-cient (TEC) between titanium and porcelain It was dem-onstrated that the TEC mismatch would decrease the

Si

O

Ti1

05

0

k

0 50 100

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

(a)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(b)

Si

O

Ti

0 100 200

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

1

05

0

k

(c)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(d)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

k

1

05

0

(e)

Figure 4 Elemental line scanning of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group(d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group

6 Advances in Materials Science and Engineering

bonding strength between titanium and porcelain [17] Onthe other hand the weakened bonding strength may stemfrom the morphology of the 40 gL MgSiF6 group In con-trast with the 20 gL MgSiF6 group the coating of the 40 gLMgSiF6 group was uneven with numerous cracks and pla-ques distributed Decreased morphological integrity wouldincrease oxygen diffusion into titanium and impair thebonding strength

5 Conclusions

In this study we found that different concentrations of theMAO electrolyte can influence the morphology of the MAOcoating and result in different effects on the bondingstrength MAO treatment with 20 gL MgSiF6 can signifi-cantly improve the titanium-porcelain bonding strength

Although more anions were fused into the MAO coatingwith increasing electrolyte concentration the bondingstrength decreased when the concentration exceeded 20 gLIn addition it was demonstrated that overly high MgSiF6concentrations have a negative influence on the structuralhomogeneity of the coating interface integrity and oxygendiffusion 1erefore titanium-porcelain restorations treatedby MAO are suitable for clinical use when appropriateMgSiF6 concentrations are used

Data Availability

1e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

1e authors declare that there are no conflicts of interestregarding the publication of this paper

Authorsrsquo Contributions

1e authors Jing Lv and Mujie Yuan contributed equally tothis work

Acknowledgments

1e authors would like to thank Editage (httpwwweditagecom) for English language editing 1is study wassupported by Shandong Provincial Natural Science Foun-dation (ZR2018BH015) and Source Innovation Planning ofQingdao (19-06-02-45-cg)

References

[1] N Suansuwan and M V Swain ldquoAdhesion of porcelain totitanium and a titanium alloyrdquo Journal of Dentistry vol 31no 7 pp 509ndash518 2003

[2] H Kimura C J Horng M Okazaki et al ldquoOxidation effectson porcelain-titanium interface reactions and bond strengthrdquoDental Materials Journal vol 9 no 1 pp 91ndash99 1990

[3] J C Souza B Henriques E Ariza et al ldquoMechanical andchemical analyses across dental porcelain fused to CP tita-nium or Ti6Al4VrdquoMaterials Science and Engineering vol 37pp 76ndash83 2014

[4] S E Elsaka ldquoInfluence of surface treatments on adhesion ofporcelain to titaniumrdquo Journal of Prosthodontics vol 22no 6 pp 465ndash471 2013

[5] J Ye X Ye S Chang et al ldquoEffect of silica coating on the bondstrength of milled pure titanium to dental porcelainrdquo Euro-pean Journal of Oral Sciences vol 124 no 5 pp 498ndash5032016

[6] L Guo X Chen X Liu et al ldquoSurface modifications andNano-composite coatings to improve the bonding strength oftitanium-porcelainrdquo Materials Science and Engineering Cvol 61 no 1 pp 143ndash148 2016

[7] R Khung and N S Suansuwan ldquoEffect of gold sputtering onthe adhesion of porcelain to cast and machined titaniumrdquoeJournal of Prosthetic Dentistry vol 110 no 1 pp 41ndash46 2013

[8] X Yuan F Tan H Xu et al ldquoEffects of different electrolytesfor micro-arc oxidation on the bond strength between tita-nium and porcelainrdquo e Journal of Prosthetic Dentistryvol 61 no 3 pp 297ndash304 2017

[9] K Venkateswarlu N Rameshbabu D Sreekanth et al ldquoRoleof electrolyte chemistry on electronic and in vitro electro-chemical properties of micro-arc oxidized titania films on CpTirdquo Electrochimica Acta vol 105 no 30 pp 468ndash480 2013

[10] Z Zhang F Tan Y Ba and Y Zhang ldquoEffects of differentbond agents on commercially pure Ti-porcelain bondstrengthrdquo Materials Letters vol 109 pp 214ndash216 2013

[11] P Haag and K Nilner ldquoBonding between titanium and dentalporcelain A systematic reviewrdquo Acta Odontol Scand vol 68no 3 pp 154ndash164 2010

[12] Z Zhao X Chen A Chen et al ldquoSynthesis of bioactiveceramic on the titanium substrate by micro-arc oxidationrdquoJournal of Biomedical Materials Research Part A vol 90 no 2pp 438ndash445 2009

[13] A R Ribeiro F Oliveira L C Boldrini et al ldquoMicro-arcoxidation as a tool to develop multifunctional calcium-richsurfaces for dental implant applicationsrdquo Materials Scienceand Engineering C vol 54 pp 196ndash206 2015

[14] M G Troia G E Henriques M F Mesquita andW S Fragoso ldquo1e effect of surface modifications on titaniumto enable titanium-porcelain bondingrdquo Dental Materialsvol 24 no 1 pp 28ndash33 2008

[15] A Acar O Inan and S Halkaci ldquoEffects of airborne-particleabrasion sodium hydroxide anodization and electrical dis-charge machining on porcelain adherence to cast commer-cially pure titaniumrdquo Journal of Biomedical MaterialsResearch Part B Applied Biomaterials vol 82 no 1pp 267ndash274 2007

[16] J Yang J R Kelly O Bailey and G Fischman ldquoPorcelain-titanium bonding with a newly introduced commerciallyavailable systemrdquo Journal of Prosthetic Dentistry vol 116no 1 pp 98ndash101 2016

[17] K M Mahale and S J Nagda ldquoEffect of preoxidation on thebond strength of titanium and porcelainrdquo European Journal ofProsthodontics and Restorative Dentistry vol 22 no 2pp 76ndash83 2014

Advances in Materials Science and Engineering 7

strength and (3) possess excellent biocompatibility In thisstudy different concentrations of MgSiF6 were used toevaluate their effects on the coatingrsquos physicochemicalproperties and titanium-porcelain bonding strength Wefound that MAO electrolyte concentration could signifi-cantly affect the coating physicochemical properties andsubsequent titanium-porcelain bonding strength 1e ap-propriate electrolyte concentration would be necessary toform a porous and homogeneous MAO coating which couldeffectively prevent oxygen diffusion and enhance bondingstrength However excessive electrolyte concentrationwould impact MAO coating homogeneousness 1e datademonstrated that MAO could improve titanium-porcelainbonding strength only with appropriate electrolyteconcentration

1e MAO electrolyte concentration could affect thecoating morphology In theory increasing the electrolyteconcentration could significantly enhance the bombardingenergy of anions because of increased anion volume andelectrolyte conductivity [13] In this study we found thatpore sizes on the coating of the 20 gL MgSiF6 group werelarger than that of the 10 gL MgSiF6 group indicating thehigher bombarding energy of the 20 gL MgSiF6 groupHowever excessively high MgSiF6 concentration wouldimpair the coating function For example we found manycracks on the coating of the 40 gL MgSiF6 group implyingthat an overly high bombarding energy of anions candamage the integrity of MAO coating On the other handfew pores were found on the 30 gL MgSiF6 and 40 gLMgSiF6 groups indicating that the pores were covered by theexcessive fused mass Moreover the MAO electrolyteconcentration could affect the coatingrsquos chemical propor-tion As the MAO electrolyte concentration was increased ahigher weight percentage of fluorine was found in the MAOcoating indicating that more anions were fused into theMAO coating However the weight percentage of silicondecreased with increasing MgSiF6 concentration which maybe caused by the high atom ratio of fluorine and silicon in theanion

Compared with the control group the 20 gL MgSiF6group exhibited bond strength enhancements of 653 1is

(a) (b) (c)

(d) (e)

Figure 1 SEMmicrophotographs of MAO coating (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group (d) 30 gL MgSiF6group and (e) 40 gL MgSiF6 group Bar 1 μm

Table 2 Effect of electrolyte concentrations on the Mao coating (wt n 6)Groups Ti Si O F10 gL MgSiF6 4065plusmn 060 891plusmn 051 4859plusmn 027 186plusmn 02120 gL MgSiF6 4059plusmn 092 316plusmn 024 3930plusmn 119 1695plusmn 20330 gL MgSiF6 2883plusmn 094 187plusmn 010 2423plusmn 074 4507plusmn 16840 gL MgSiF6 1392plusmn 044 076plusmn 013 1389plusmn 032 7143plusmn 265lowastplt 005 compared to the control group

Table 3 Bonding strength of different titanium-porcelain resto-rations (meanplusmn SD n 10)Group K Bond strength (MPa)10 gL MgSiF6 47 3818plusmn 265lowast20 gL MgSiF6 47 4475plusmn 221lowast30 gL MgSiF6 47 3144plusmn 204lowast40 gL MgSiF6 47 2804plusmn 259Control group 47 2708plusmn 316lowastplt 005 compared to the control group

4 Advances in Materials Science and Engineering

result can be indirectly proved by the fracture surface ob-servation 1e titanium-porcelain fracture of the 20 gLMgSiF6 group occurred in the interior of porcelain Itdemonstrates that the bonding strength of the 20 gL MgSiF6group had exceeded the mechanical strength of bondingporcelain 1e improved bonding strength of the 20 gLMgSiF6 group should stem from the coating morphologyprevention of oxygen diffusion and coating chemicalcomposition First the improved bonding strength can beattributed to the porous morphology of MAO coating 1epores (approximately 1-2 μmdiameter) on theMAO coating

of the 20 gL MgSiF6 group would enhance the interlockbetween titanium and porcelain According to results on thecoatingrsquos morphology more pores and larger pore diameterswere found on the MAO coating of the 20 gLMgSiF6 groupcompared to the other groups Other studies have provedthat porcelain can fuse into the porous coating and physi-cally interlock with titanium substrate [6] In addition tothis studies have demonstrated that interlocking is animportant bonding force for titanium-porcelain restorations[14 15] Second the improved bonding strength may stemfrom the protective effect of MAO coating on the oxygen

(a) (b) (c)

(d) (e)

Figure 2 SEM microphotographs of the fracture surface of titanium specimens (a) control group (b) 10 gL MgSiF6 group (c) 20 gLMgSiF6 group (d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group Bar 100 μm 1e residual porcelain is indicated by arrows

(a) (b) (c)

(d) (e)

Figure 3 SEMmicrophotographs of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group (d)30 gL MgSiF6 group and (e) 40 gL MgSiF6 group Bar 10 μm 1e pores and cracks are indicated by arrows

Advances in Materials Science and Engineering 5

diffusion As shown the oxygen curves of the 20 gL MgSiF6group declined rapidly in a narrow range after crossing theinterface indicating that the MAO coating effectivelycontrolled the diffusion of oxygen into titanium 1e oxy-gen-diffusion barrier of the 20 gL MgSiF6 group may haveresulted from the impact structure at the titanium-porcelaininterface For example many pores and cracks were found atthe interface of other groups In the porcelain applicationthe oxygen could diffuse into the titanium substrate throughthese structural defects between titanium and porcelain1ird the improved bonding strength may result fromchemical changes caused by anions bombarding at the ti-tanium-porcelain interface After MAO treatment siliconand fluorine were found on the surface of titanium substrateIt was found that the same element both in coating andporcelain would improve chemical bonding between tita-nium and porcelain for example silicon 1e chemicalbonding formed during porcelain sintering and played animportant role in the titanium-porcelain bond For exampleLin found a mutual diffusion of silicon formed at the tita-nium-porcelain interface 1e elemental silicon that diffused

to the titanium substrate comes from the silica coating madeby sol-gel dipping [5]

Furthermore excessively high MgSiF6 concentrationswould impair the bonding strength between titanium andporcelain When the MAO concentration of MgSiF6 wasabove 20 gL the bonding strength decreased with in-creasing MAO concentration 1e weakened bondingstrength may result from changes to the coatingrsquos chemicalcomposition Chemical bonding has been proved to be themajor bonding force of titanium-porcelain restorations [16]In our previous study we found that excluding oxygensilicon (212) and fluorine (26) are major nonmetallicelements in the bonding porcelain [10] However the weightpercent of silicon in the 40 gL MgSiF6 group (076plusmn 013 wt) was far lower than that in the bonding porcelainMoreover the weight percent of fluorine in the 40 gLMgSiF6 group (7143plusmn 065 wt) was far higher than that inthe bonding porcelain Change to the chemical proportionwould increase the mismatch of thermal expansion coeffi-cient (TEC) between titanium and porcelain It was dem-onstrated that the TEC mismatch would decrease the

Si

O

Ti1

05

0

k

0 50 100

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

(a)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(b)

Si

O

Ti

0 100 200

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

1

05

0

k

(c)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(d)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

k

1

05

0

(e)

Figure 4 Elemental line scanning of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group(d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group

6 Advances in Materials Science and Engineering

bonding strength between titanium and porcelain [17] Onthe other hand the weakened bonding strength may stemfrom the morphology of the 40 gL MgSiF6 group In con-trast with the 20 gL MgSiF6 group the coating of the 40 gLMgSiF6 group was uneven with numerous cracks and pla-ques distributed Decreased morphological integrity wouldincrease oxygen diffusion into titanium and impair thebonding strength

5 Conclusions

In this study we found that different concentrations of theMAO electrolyte can influence the morphology of the MAOcoating and result in different effects on the bondingstrength MAO treatment with 20 gL MgSiF6 can signifi-cantly improve the titanium-porcelain bonding strength

Although more anions were fused into the MAO coatingwith increasing electrolyte concentration the bondingstrength decreased when the concentration exceeded 20 gLIn addition it was demonstrated that overly high MgSiF6concentrations have a negative influence on the structuralhomogeneity of the coating interface integrity and oxygendiffusion 1erefore titanium-porcelain restorations treatedby MAO are suitable for clinical use when appropriateMgSiF6 concentrations are used

Data Availability

1e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

1e authors declare that there are no conflicts of interestregarding the publication of this paper

Authorsrsquo Contributions

1e authors Jing Lv and Mujie Yuan contributed equally tothis work

Acknowledgments

1e authors would like to thank Editage (httpwwweditagecom) for English language editing 1is study wassupported by Shandong Provincial Natural Science Foun-dation (ZR2018BH015) and Source Innovation Planning ofQingdao (19-06-02-45-cg)

References

[1] N Suansuwan and M V Swain ldquoAdhesion of porcelain totitanium and a titanium alloyrdquo Journal of Dentistry vol 31no 7 pp 509ndash518 2003

[2] H Kimura C J Horng M Okazaki et al ldquoOxidation effectson porcelain-titanium interface reactions and bond strengthrdquoDental Materials Journal vol 9 no 1 pp 91ndash99 1990

[3] J C Souza B Henriques E Ariza et al ldquoMechanical andchemical analyses across dental porcelain fused to CP tita-nium or Ti6Al4VrdquoMaterials Science and Engineering vol 37pp 76ndash83 2014

[4] S E Elsaka ldquoInfluence of surface treatments on adhesion ofporcelain to titaniumrdquo Journal of Prosthodontics vol 22no 6 pp 465ndash471 2013

[5] J Ye X Ye S Chang et al ldquoEffect of silica coating on the bondstrength of milled pure titanium to dental porcelainrdquo Euro-pean Journal of Oral Sciences vol 124 no 5 pp 498ndash5032016

[6] L Guo X Chen X Liu et al ldquoSurface modifications andNano-composite coatings to improve the bonding strength oftitanium-porcelainrdquo Materials Science and Engineering Cvol 61 no 1 pp 143ndash148 2016

[7] R Khung and N S Suansuwan ldquoEffect of gold sputtering onthe adhesion of porcelain to cast and machined titaniumrdquoeJournal of Prosthetic Dentistry vol 110 no 1 pp 41ndash46 2013

[8] X Yuan F Tan H Xu et al ldquoEffects of different electrolytesfor micro-arc oxidation on the bond strength between tita-nium and porcelainrdquo e Journal of Prosthetic Dentistryvol 61 no 3 pp 297ndash304 2017

[9] K Venkateswarlu N Rameshbabu D Sreekanth et al ldquoRoleof electrolyte chemistry on electronic and in vitro electro-chemical properties of micro-arc oxidized titania films on CpTirdquo Electrochimica Acta vol 105 no 30 pp 468ndash480 2013

[10] Z Zhang F Tan Y Ba and Y Zhang ldquoEffects of differentbond agents on commercially pure Ti-porcelain bondstrengthrdquo Materials Letters vol 109 pp 214ndash216 2013

[11] P Haag and K Nilner ldquoBonding between titanium and dentalporcelain A systematic reviewrdquo Acta Odontol Scand vol 68no 3 pp 154ndash164 2010

[12] Z Zhao X Chen A Chen et al ldquoSynthesis of bioactiveceramic on the titanium substrate by micro-arc oxidationrdquoJournal of Biomedical Materials Research Part A vol 90 no 2pp 438ndash445 2009

[13] A R Ribeiro F Oliveira L C Boldrini et al ldquoMicro-arcoxidation as a tool to develop multifunctional calcium-richsurfaces for dental implant applicationsrdquo Materials Scienceand Engineering C vol 54 pp 196ndash206 2015

[14] M G Troia G E Henriques M F Mesquita andW S Fragoso ldquo1e effect of surface modifications on titaniumto enable titanium-porcelain bondingrdquo Dental Materialsvol 24 no 1 pp 28ndash33 2008

[15] A Acar O Inan and S Halkaci ldquoEffects of airborne-particleabrasion sodium hydroxide anodization and electrical dis-charge machining on porcelain adherence to cast commer-cially pure titaniumrdquo Journal of Biomedical MaterialsResearch Part B Applied Biomaterials vol 82 no 1pp 267ndash274 2007

[16] J Yang J R Kelly O Bailey and G Fischman ldquoPorcelain-titanium bonding with a newly introduced commerciallyavailable systemrdquo Journal of Prosthetic Dentistry vol 116no 1 pp 98ndash101 2016

[17] K M Mahale and S J Nagda ldquoEffect of preoxidation on thebond strength of titanium and porcelainrdquo European Journal ofProsthodontics and Restorative Dentistry vol 22 no 2pp 76ndash83 2014

Advances in Materials Science and Engineering 7

result can be indirectly proved by the fracture surface ob-servation 1e titanium-porcelain fracture of the 20 gLMgSiF6 group occurred in the interior of porcelain Itdemonstrates that the bonding strength of the 20 gL MgSiF6group had exceeded the mechanical strength of bondingporcelain 1e improved bonding strength of the 20 gLMgSiF6 group should stem from the coating morphologyprevention of oxygen diffusion and coating chemicalcomposition First the improved bonding strength can beattributed to the porous morphology of MAO coating 1epores (approximately 1-2 μmdiameter) on theMAO coating

of the 20 gL MgSiF6 group would enhance the interlockbetween titanium and porcelain According to results on thecoatingrsquos morphology more pores and larger pore diameterswere found on the MAO coating of the 20 gLMgSiF6 groupcompared to the other groups Other studies have provedthat porcelain can fuse into the porous coating and physi-cally interlock with titanium substrate [6] In addition tothis studies have demonstrated that interlocking is animportant bonding force for titanium-porcelain restorations[14 15] Second the improved bonding strength may stemfrom the protective effect of MAO coating on the oxygen

(a) (b) (c)

(d) (e)

Figure 2 SEM microphotographs of the fracture surface of titanium specimens (a) control group (b) 10 gL MgSiF6 group (c) 20 gLMgSiF6 group (d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group Bar 100 μm 1e residual porcelain is indicated by arrows

(a) (b) (c)

(d) (e)

Figure 3 SEMmicrophotographs of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group (d)30 gL MgSiF6 group and (e) 40 gL MgSiF6 group Bar 10 μm 1e pores and cracks are indicated by arrows

Advances in Materials Science and Engineering 5

diffusion As shown the oxygen curves of the 20 gL MgSiF6group declined rapidly in a narrow range after crossing theinterface indicating that the MAO coating effectivelycontrolled the diffusion of oxygen into titanium 1e oxy-gen-diffusion barrier of the 20 gL MgSiF6 group may haveresulted from the impact structure at the titanium-porcelaininterface For example many pores and cracks were found atthe interface of other groups In the porcelain applicationthe oxygen could diffuse into the titanium substrate throughthese structural defects between titanium and porcelain1ird the improved bonding strength may result fromchemical changes caused by anions bombarding at the ti-tanium-porcelain interface After MAO treatment siliconand fluorine were found on the surface of titanium substrateIt was found that the same element both in coating andporcelain would improve chemical bonding between tita-nium and porcelain for example silicon 1e chemicalbonding formed during porcelain sintering and played animportant role in the titanium-porcelain bond For exampleLin found a mutual diffusion of silicon formed at the tita-nium-porcelain interface 1e elemental silicon that diffused

to the titanium substrate comes from the silica coating madeby sol-gel dipping [5]

Furthermore excessively high MgSiF6 concentrationswould impair the bonding strength between titanium andporcelain When the MAO concentration of MgSiF6 wasabove 20 gL the bonding strength decreased with in-creasing MAO concentration 1e weakened bondingstrength may result from changes to the coatingrsquos chemicalcomposition Chemical bonding has been proved to be themajor bonding force of titanium-porcelain restorations [16]In our previous study we found that excluding oxygensilicon (212) and fluorine (26) are major nonmetallicelements in the bonding porcelain [10] However the weightpercent of silicon in the 40 gL MgSiF6 group (076plusmn 013 wt) was far lower than that in the bonding porcelainMoreover the weight percent of fluorine in the 40 gLMgSiF6 group (7143plusmn 065 wt) was far higher than that inthe bonding porcelain Change to the chemical proportionwould increase the mismatch of thermal expansion coeffi-cient (TEC) between titanium and porcelain It was dem-onstrated that the TEC mismatch would decrease the

Si

O

Ti1

05

0

k

0 50 100

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

(a)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(b)

Si

O

Ti

0 100 200

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

1

05

0

k

(c)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(d)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

k

1

05

0

(e)

Figure 4 Elemental line scanning of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group(d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group

6 Advances in Materials Science and Engineering

bonding strength between titanium and porcelain [17] Onthe other hand the weakened bonding strength may stemfrom the morphology of the 40 gL MgSiF6 group In con-trast with the 20 gL MgSiF6 group the coating of the 40 gLMgSiF6 group was uneven with numerous cracks and pla-ques distributed Decreased morphological integrity wouldincrease oxygen diffusion into titanium and impair thebonding strength

5 Conclusions

In this study we found that different concentrations of theMAO electrolyte can influence the morphology of the MAOcoating and result in different effects on the bondingstrength MAO treatment with 20 gL MgSiF6 can signifi-cantly improve the titanium-porcelain bonding strength

Although more anions were fused into the MAO coatingwith increasing electrolyte concentration the bondingstrength decreased when the concentration exceeded 20 gLIn addition it was demonstrated that overly high MgSiF6concentrations have a negative influence on the structuralhomogeneity of the coating interface integrity and oxygendiffusion 1erefore titanium-porcelain restorations treatedby MAO are suitable for clinical use when appropriateMgSiF6 concentrations are used

Data Availability

1e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

1e authors declare that there are no conflicts of interestregarding the publication of this paper

Authorsrsquo Contributions

1e authors Jing Lv and Mujie Yuan contributed equally tothis work

Acknowledgments

1e authors would like to thank Editage (httpwwweditagecom) for English language editing 1is study wassupported by Shandong Provincial Natural Science Foun-dation (ZR2018BH015) and Source Innovation Planning ofQingdao (19-06-02-45-cg)

References

[1] N Suansuwan and M V Swain ldquoAdhesion of porcelain totitanium and a titanium alloyrdquo Journal of Dentistry vol 31no 7 pp 509ndash518 2003

[2] H Kimura C J Horng M Okazaki et al ldquoOxidation effectson porcelain-titanium interface reactions and bond strengthrdquoDental Materials Journal vol 9 no 1 pp 91ndash99 1990

[3] J C Souza B Henriques E Ariza et al ldquoMechanical andchemical analyses across dental porcelain fused to CP tita-nium or Ti6Al4VrdquoMaterials Science and Engineering vol 37pp 76ndash83 2014

[4] S E Elsaka ldquoInfluence of surface treatments on adhesion ofporcelain to titaniumrdquo Journal of Prosthodontics vol 22no 6 pp 465ndash471 2013

[5] J Ye X Ye S Chang et al ldquoEffect of silica coating on the bondstrength of milled pure titanium to dental porcelainrdquo Euro-pean Journal of Oral Sciences vol 124 no 5 pp 498ndash5032016

[6] L Guo X Chen X Liu et al ldquoSurface modifications andNano-composite coatings to improve the bonding strength oftitanium-porcelainrdquo Materials Science and Engineering Cvol 61 no 1 pp 143ndash148 2016

[7] R Khung and N S Suansuwan ldquoEffect of gold sputtering onthe adhesion of porcelain to cast and machined titaniumrdquoeJournal of Prosthetic Dentistry vol 110 no 1 pp 41ndash46 2013

[8] X Yuan F Tan H Xu et al ldquoEffects of different electrolytesfor micro-arc oxidation on the bond strength between tita-nium and porcelainrdquo e Journal of Prosthetic Dentistryvol 61 no 3 pp 297ndash304 2017

[9] K Venkateswarlu N Rameshbabu D Sreekanth et al ldquoRoleof electrolyte chemistry on electronic and in vitro electro-chemical properties of micro-arc oxidized titania films on CpTirdquo Electrochimica Acta vol 105 no 30 pp 468ndash480 2013

[10] Z Zhang F Tan Y Ba and Y Zhang ldquoEffects of differentbond agents on commercially pure Ti-porcelain bondstrengthrdquo Materials Letters vol 109 pp 214ndash216 2013

[11] P Haag and K Nilner ldquoBonding between titanium and dentalporcelain A systematic reviewrdquo Acta Odontol Scand vol 68no 3 pp 154ndash164 2010

[12] Z Zhao X Chen A Chen et al ldquoSynthesis of bioactiveceramic on the titanium substrate by micro-arc oxidationrdquoJournal of Biomedical Materials Research Part A vol 90 no 2pp 438ndash445 2009

[13] A R Ribeiro F Oliveira L C Boldrini et al ldquoMicro-arcoxidation as a tool to develop multifunctional calcium-richsurfaces for dental implant applicationsrdquo Materials Scienceand Engineering C vol 54 pp 196ndash206 2015

[14] M G Troia G E Henriques M F Mesquita andW S Fragoso ldquo1e effect of surface modifications on titaniumto enable titanium-porcelain bondingrdquo Dental Materialsvol 24 no 1 pp 28ndash33 2008

[15] A Acar O Inan and S Halkaci ldquoEffects of airborne-particleabrasion sodium hydroxide anodization and electrical dis-charge machining on porcelain adherence to cast commer-cially pure titaniumrdquo Journal of Biomedical MaterialsResearch Part B Applied Biomaterials vol 82 no 1pp 267ndash274 2007

[16] J Yang J R Kelly O Bailey and G Fischman ldquoPorcelain-titanium bonding with a newly introduced commerciallyavailable systemrdquo Journal of Prosthetic Dentistry vol 116no 1 pp 98ndash101 2016

[17] K M Mahale and S J Nagda ldquoEffect of preoxidation on thebond strength of titanium and porcelainrdquo European Journal ofProsthodontics and Restorative Dentistry vol 22 no 2pp 76ndash83 2014

Advances in Materials Science and Engineering 7

diffusion As shown the oxygen curves of the 20 gL MgSiF6group declined rapidly in a narrow range after crossing theinterface indicating that the MAO coating effectivelycontrolled the diffusion of oxygen into titanium 1e oxy-gen-diffusion barrier of the 20 gL MgSiF6 group may haveresulted from the impact structure at the titanium-porcelaininterface For example many pores and cracks were found atthe interface of other groups In the porcelain applicationthe oxygen could diffuse into the titanium substrate throughthese structural defects between titanium and porcelain1ird the improved bonding strength may result fromchemical changes caused by anions bombarding at the ti-tanium-porcelain interface After MAO treatment siliconand fluorine were found on the surface of titanium substrateIt was found that the same element both in coating andporcelain would improve chemical bonding between tita-nium and porcelain for example silicon 1e chemicalbonding formed during porcelain sintering and played animportant role in the titanium-porcelain bond For exampleLin found a mutual diffusion of silicon formed at the tita-nium-porcelain interface 1e elemental silicon that diffused

to the titanium substrate comes from the silica coating madeby sol-gel dipping [5]

Furthermore excessively high MgSiF6 concentrationswould impair the bonding strength between titanium andporcelain When the MAO concentration of MgSiF6 wasabove 20 gL the bonding strength decreased with in-creasing MAO concentration 1e weakened bondingstrength may result from changes to the coatingrsquos chemicalcomposition Chemical bonding has been proved to be themajor bonding force of titanium-porcelain restorations [16]In our previous study we found that excluding oxygensilicon (212) and fluorine (26) are major nonmetallicelements in the bonding porcelain [10] However the weightpercent of silicon in the 40 gL MgSiF6 group (076plusmn 013 wt) was far lower than that in the bonding porcelainMoreover the weight percent of fluorine in the 40 gLMgSiF6 group (7143plusmn 065 wt) was far higher than that inthe bonding porcelain Change to the chemical proportionwould increase the mismatch of thermal expansion coeffi-cient (TEC) between titanium and porcelain It was dem-onstrated that the TEC mismatch would decrease the

Si

O

Ti1

05

0

k

0 50 100

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

(a)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(b)

Si

O

Ti

0 100 200

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

1

05

0

k

(c)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

2

1

0

k

(d)

Si

O

Ti

0 50 100 150

Titanium Ka 1Silicon Ka 1Oxygen Ka 1

μm

k

1

05

0

(e)

Figure 4 Elemental line scanning of titanium-porcelain interface (a) control group (b) 10 gL MgSiF6 group (c) 20 gL MgSiF6 group(d) 30 gL MgSiF6 group and (e) 40 gL MgSiF6 group

6 Advances in Materials Science and Engineering

bonding strength between titanium and porcelain [17] Onthe other hand the weakened bonding strength may stemfrom the morphology of the 40 gL MgSiF6 group In con-trast with the 20 gL MgSiF6 group the coating of the 40 gLMgSiF6 group was uneven with numerous cracks and pla-ques distributed Decreased morphological integrity wouldincrease oxygen diffusion into titanium and impair thebonding strength

5 Conclusions

In this study we found that different concentrations of theMAO electrolyte can influence the morphology of the MAOcoating and result in different effects on the bondingstrength MAO treatment with 20 gL MgSiF6 can signifi-cantly improve the titanium-porcelain bonding strength

Although more anions were fused into the MAO coatingwith increasing electrolyte concentration the bondingstrength decreased when the concentration exceeded 20 gLIn addition it was demonstrated that overly high MgSiF6concentrations have a negative influence on the structuralhomogeneity of the coating interface integrity and oxygendiffusion 1erefore titanium-porcelain restorations treatedby MAO are suitable for clinical use when appropriateMgSiF6 concentrations are used

Data Availability

1e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

1e authors declare that there are no conflicts of interestregarding the publication of this paper

Authorsrsquo Contributions

1e authors Jing Lv and Mujie Yuan contributed equally tothis work

Acknowledgments

1e authors would like to thank Editage (httpwwweditagecom) for English language editing 1is study wassupported by Shandong Provincial Natural Science Foun-dation (ZR2018BH015) and Source Innovation Planning ofQingdao (19-06-02-45-cg)

References

[1] N Suansuwan and M V Swain ldquoAdhesion of porcelain totitanium and a titanium alloyrdquo Journal of Dentistry vol 31no 7 pp 509ndash518 2003

[2] H Kimura C J Horng M Okazaki et al ldquoOxidation effectson porcelain-titanium interface reactions and bond strengthrdquoDental Materials Journal vol 9 no 1 pp 91ndash99 1990

[3] J C Souza B Henriques E Ariza et al ldquoMechanical andchemical analyses across dental porcelain fused to CP tita-nium or Ti6Al4VrdquoMaterials Science and Engineering vol 37pp 76ndash83 2014

[4] S E Elsaka ldquoInfluence of surface treatments on adhesion ofporcelain to titaniumrdquo Journal of Prosthodontics vol 22no 6 pp 465ndash471 2013

[5] J Ye X Ye S Chang et al ldquoEffect of silica coating on the bondstrength of milled pure titanium to dental porcelainrdquo Euro-pean Journal of Oral Sciences vol 124 no 5 pp 498ndash5032016

[6] L Guo X Chen X Liu et al ldquoSurface modifications andNano-composite coatings to improve the bonding strength oftitanium-porcelainrdquo Materials Science and Engineering Cvol 61 no 1 pp 143ndash148 2016

[7] R Khung and N S Suansuwan ldquoEffect of gold sputtering onthe adhesion of porcelain to cast and machined titaniumrdquoeJournal of Prosthetic Dentistry vol 110 no 1 pp 41ndash46 2013

[8] X Yuan F Tan H Xu et al ldquoEffects of different electrolytesfor micro-arc oxidation on the bond strength between tita-nium and porcelainrdquo e Journal of Prosthetic Dentistryvol 61 no 3 pp 297ndash304 2017

[9] K Venkateswarlu N Rameshbabu D Sreekanth et al ldquoRoleof electrolyte chemistry on electronic and in vitro electro-chemical properties of micro-arc oxidized titania films on CpTirdquo Electrochimica Acta vol 105 no 30 pp 468ndash480 2013

[10] Z Zhang F Tan Y Ba and Y Zhang ldquoEffects of differentbond agents on commercially pure Ti-porcelain bondstrengthrdquo Materials Letters vol 109 pp 214ndash216 2013

[11] P Haag and K Nilner ldquoBonding between titanium and dentalporcelain A systematic reviewrdquo Acta Odontol Scand vol 68no 3 pp 154ndash164 2010

[12] Z Zhao X Chen A Chen et al ldquoSynthesis of bioactiveceramic on the titanium substrate by micro-arc oxidationrdquoJournal of Biomedical Materials Research Part A vol 90 no 2pp 438ndash445 2009

[13] A R Ribeiro F Oliveira L C Boldrini et al ldquoMicro-arcoxidation as a tool to develop multifunctional calcium-richsurfaces for dental implant applicationsrdquo Materials Scienceand Engineering C vol 54 pp 196ndash206 2015

[14] M G Troia G E Henriques M F Mesquita andW S Fragoso ldquo1e effect of surface modifications on titaniumto enable titanium-porcelain bondingrdquo Dental Materialsvol 24 no 1 pp 28ndash33 2008

[15] A Acar O Inan and S Halkaci ldquoEffects of airborne-particleabrasion sodium hydroxide anodization and electrical dis-charge machining on porcelain adherence to cast commer-cially pure titaniumrdquo Journal of Biomedical MaterialsResearch Part B Applied Biomaterials vol 82 no 1pp 267ndash274 2007

[16] J Yang J R Kelly O Bailey and G Fischman ldquoPorcelain-titanium bonding with a newly introduced commerciallyavailable systemrdquo Journal of Prosthetic Dentistry vol 116no 1 pp 98ndash101 2016

[17] K M Mahale and S J Nagda ldquoEffect of preoxidation on thebond strength of titanium and porcelainrdquo European Journal ofProsthodontics and Restorative Dentistry vol 22 no 2pp 76ndash83 2014

Advances in Materials Science and Engineering 7

bonding strength between titanium and porcelain [17] Onthe other hand the weakened bonding strength may stemfrom the morphology of the 40 gL MgSiF6 group In con-trast with the 20 gL MgSiF6 group the coating of the 40 gLMgSiF6 group was uneven with numerous cracks and pla-ques distributed Decreased morphological integrity wouldincrease oxygen diffusion into titanium and impair thebonding strength

5 Conclusions

In this study we found that different concentrations of theMAO electrolyte can influence the morphology of the MAOcoating and result in different effects on the bondingstrength MAO treatment with 20 gL MgSiF6 can signifi-cantly improve the titanium-porcelain bonding strength

Although more anions were fused into the MAO coatingwith increasing electrolyte concentration the bondingstrength decreased when the concentration exceeded 20 gLIn addition it was demonstrated that overly high MgSiF6concentrations have a negative influence on the structuralhomogeneity of the coating interface integrity and oxygendiffusion 1erefore titanium-porcelain restorations treatedby MAO are suitable for clinical use when appropriateMgSiF6 concentrations are used

Data Availability

1e data used to support the findings of this study areavailable from the corresponding author upon request

Conflicts of Interest

1e authors declare that there are no conflicts of interestregarding the publication of this paper

Authorsrsquo Contributions

1e authors Jing Lv and Mujie Yuan contributed equally tothis work

Acknowledgments

1e authors would like to thank Editage (httpwwweditagecom) for English language editing 1is study wassupported by Shandong Provincial Natural Science Foun-dation (ZR2018BH015) and Source Innovation Planning ofQingdao (19-06-02-45-cg)

References

[1] N Suansuwan and M V Swain ldquoAdhesion of porcelain totitanium and a titanium alloyrdquo Journal of Dentistry vol 31no 7 pp 509ndash518 2003

[2] H Kimura C J Horng M Okazaki et al ldquoOxidation effectson porcelain-titanium interface reactions and bond strengthrdquoDental Materials Journal vol 9 no 1 pp 91ndash99 1990

[3] J C Souza B Henriques E Ariza et al ldquoMechanical andchemical analyses across dental porcelain fused to CP tita-nium or Ti6Al4VrdquoMaterials Science and Engineering vol 37pp 76ndash83 2014

[4] S E Elsaka ldquoInfluence of surface treatments on adhesion ofporcelain to titaniumrdquo Journal of Prosthodontics vol 22no 6 pp 465ndash471 2013

[5] J Ye X Ye S Chang et al ldquoEffect of silica coating on the bondstrength of milled pure titanium to dental porcelainrdquo Euro-pean Journal of Oral Sciences vol 124 no 5 pp 498ndash5032016

[6] L Guo X Chen X Liu et al ldquoSurface modifications andNano-composite coatings to improve the bonding strength oftitanium-porcelainrdquo Materials Science and Engineering Cvol 61 no 1 pp 143ndash148 2016

[7] R Khung and N S Suansuwan ldquoEffect of gold sputtering onthe adhesion of porcelain to cast and machined titaniumrdquoeJournal of Prosthetic Dentistry vol 110 no 1 pp 41ndash46 2013

[8] X Yuan F Tan H Xu et al ldquoEffects of different electrolytesfor micro-arc oxidation on the bond strength between tita-nium and porcelainrdquo e Journal of Prosthetic Dentistryvol 61 no 3 pp 297ndash304 2017

[9] K Venkateswarlu N Rameshbabu D Sreekanth et al ldquoRoleof electrolyte chemistry on electronic and in vitro electro-chemical properties of micro-arc oxidized titania films on CpTirdquo Electrochimica Acta vol 105 no 30 pp 468ndash480 2013

[10] Z Zhang F Tan Y Ba and Y Zhang ldquoEffects of differentbond agents on commercially pure Ti-porcelain bondstrengthrdquo Materials Letters vol 109 pp 214ndash216 2013

[11] P Haag and K Nilner ldquoBonding between titanium and dentalporcelain A systematic reviewrdquo Acta Odontol Scand vol 68no 3 pp 154ndash164 2010

[12] Z Zhao X Chen A Chen et al ldquoSynthesis of bioactiveceramic on the titanium substrate by micro-arc oxidationrdquoJournal of Biomedical Materials Research Part A vol 90 no 2pp 438ndash445 2009

[13] A R Ribeiro F Oliveira L C Boldrini et al ldquoMicro-arcoxidation as a tool to develop multifunctional calcium-richsurfaces for dental implant applicationsrdquo Materials Scienceand Engineering C vol 54 pp 196ndash206 2015

[14] M G Troia G E Henriques M F Mesquita andW S Fragoso ldquo1e effect of surface modifications on titaniumto enable titanium-porcelain bondingrdquo Dental Materialsvol 24 no 1 pp 28ndash33 2008

[15] A Acar O Inan and S Halkaci ldquoEffects of airborne-particleabrasion sodium hydroxide anodization and electrical dis-charge machining on porcelain adherence to cast commer-cially pure titaniumrdquo Journal of Biomedical MaterialsResearch Part B Applied Biomaterials vol 82 no 1pp 267ndash274 2007

[16] J Yang J R Kelly O Bailey and G Fischman ldquoPorcelain-titanium bonding with a newly introduced commerciallyavailable systemrdquo Journal of Prosthetic Dentistry vol 116no 1 pp 98ndash101 2016

[17] K M Mahale and S J Nagda ldquoEffect of preoxidation on thebond strength of titanium and porcelainrdquo European Journal ofProsthodontics and Restorative Dentistry vol 22 no 2pp 76ndash83 2014

Advances in Materials Science and Engineering 7