Bergman Gašparić, Lana

Mehulić, Ketij

Schauperl, Zdravko

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Coll. Antropol. 37 (2013) 1: 121–125Original scientific paperShear Bond Strength in Zirconia VeneeredCeramics Using Two Different SurfaceTreatments Prior VeneeringLana Bergman Ga{pari}1, Zdravko Schauperl2 and Ketij Mehuli}1,31 University of Zagreb, School of Dental Medicine, Department of Fixed Prosthodontics, Zagreb, Croatia2 University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Zagreb, Croatia3 University of Zagreb, Zagreb University Hospital Center, Dental Clinic, Zagreb, CroatiaA B S T R A C TAim of the study was to assess the effect of different surface treatments on the shear bond strength (SBS) of the veneer-ing ceramics to zirconia core. In a shear test the influence of grinding and sandblasting of the zirconia surface on bond-ing were assessed. Statistical analysis was performed using SPSS statistical package (version 17.0, SPSS Inc., Chicago,IL, USA) and Microsoft Office Excel 2003 (Microsoft, Seattle, WA, USA). There was a significant difference between thegroups considering shear bond strength (SBS) values, i.e. ground and sandblasted samples had significantly higherSBS values than only ground samples (mean difference=–190.67; df=10, t=–6.386, p<0.001). The results of the presentstudy indicate that ground and sandblasted cores are superior to ground cores, allowing significantly higher surfaceroughness and significantly higher shear bond strength between the core and the veneering material.Key words: shear bond strength, zirconia, veneering ceramics, surface treatmentIntroductionAlthough conventional metal-ceramic restorationshave demonstrated superior fracture resistance overother types of ceramic restorations, due to the opaque ap-pearance it may not be the first choice in patients withhigh aesthetic demands1–3. Kelly et al. identified coretranslucency as one of the primary factors in controllingaesthetics in ceramic materials4,5. Zirconia core allowssome light transmission, and thus, veneering ceramicscan be applied directly to the core without masking6. Zir-conia is a crystalline dioxide of zirconium. Its mechanicalproperties are very similar to those of metals but its col-our is similar to tooth colour7. Zirconia based all-ceramicrestorations can be manufactured both in the anterior, aswell as in the posterior dentition, which is an advantageto the lithium disilicate ceramics, which cannot with-stand high forces and is therefore limited only to anteriordentition and for a short-span fixed partial dentures(FPD).The zirconium-oxide all-ceramic material provides se-veral advantages, including a high flexural strength(1000 MPa) and desirable optical properties, such asshading adaptation to the basic shades and a reduction ina layer thickness (compared to conventional ceramics) ofthe veneer ceramic required to achieve the desired co-lour8,9. Appropriate veneering ceramic can be appliedonto zirconia core by either a hand-layered powder buildup or a pressed technique10. Zirconia based ceramics maybe used in posterior region where high occlusal forces areexpected due to the high strength of a zirconia core mate-rial, but delamination (chipping) of veneering porcelainis described to be the most frequent failure reason. It isreported that chipping is multi-factorial. It may be causedby insufficient bond strength11, excessive tensile stressdue to a thermal mismatch between veneering porcelainand underlying zirconia framework12, firing shrinkage ofceramics13, the framework/veneer thickness ratio14, res-toration geometry and inadequate framework design15.There is not much information available about thebond quality between veneering ceramics and zirconiacore. It has been reported that the bonding strength and121Received for publication November 23, 2011the mode of failure were significantly affected by somesurface treatments, such as airborne particles abrasionor use of liners and however a type of zirconia frameworkmaterial14,16. Different manufacturers recommend dif-ferent surface treatments.The aim of the present study was to evaluate shearbond strength between veneering ceramics bonded to zir-conia with two different methods of preparing zirconiasurface prior to applying veneer ceramic material.Materials and MethodsA total number of 12 zirconia core-veneer samplesneeded for the study was divided in two groups and pre-pared according to the following procedures:Presintered Y-TZP IPS e.max ZirCAD blocks (IvoclarVivadent AG, Schaan, Lichtenstein) were used for thisstudy. Sintering to full density in the Programat S1 fur-nace (Ivoclar Vivadent AG, Schaan, Lichtenstein) during6 hours at the temperature of 1500 °C, the blocks gaineddimensions of 10´10´10 mm needed for the study, soCAD/CAM grinding was not necessary.All samples were ground under water spray jet incor-porated in the hand-piece with a 90 mm grit diamond bur(Komet, Salzburg, Austria). Surface grinding was carriedout at the maximum revolutions/min (200,000 rpm) andwith minimal pressure to ensure a consistent grindingspeed. The cubes were cleaned with 70% ethanol by wip-ing their surfaces with cotton, then steam cleaned during10 seconds and air dried. Six samples were left for ve-neering and other six samples were additionally sand-blasted (Renfert duo pro, GmbH, Hilzingen, Germany)with 110 mm Al2O3 particles (Cobra; Renfert, GmbH,Hilzingen, Germany) at 2.5 bar pressure for a period of 5seconds, steam-cleaned and air-dried.All samples were submitted to the Surface ElectronMicroscope (SEM) analysis (TESCAN VEGA TS. 5136LS,Tescan, Brno, Czech Republic). Zirconia surface wasevaluated under different magnifications to assess thesurface topography (Figure 1a, b, c and d). SEM measure-ments were performed at the Department of Materialo-graphy, (Faculty of machine and naval engineering, Uni-versity of Zagreb, Croatia). Measurement of surfaceroughness was performed using the Stylus instrumentPerthometer S8P (Perthen, Mahr, Göttingen, Germany).During the measurement the stylus was moved at a con-stant speed across the samples with a measuring force of1.3 mN. Measurements were performed by using Gaussfilter with cut-off value of lc = 0.8 mm and the evalua-tion length ln = 5.6 mm. Mean roughnes (Ra) and Z val-ues (the distance from the highest to the lowest point ofmeasurement along the observed line) were recorded foreach sample and were statistically analysed.After the SEM analysis and determination of surfaceroughness, all zirconia samples were veneered using alayering technique. The veneering ceramic IPS e.maxCeram powder (Ivoclar Vivadent AG, Schaan, Lichten-stein) was mixed with an appropriate amount of the re-spective liquid according to the manufacturer`s instruc-tions and the obtained slurry was plotted with absorbentpaper to draw excess water. After that, the samples werefired according to the firing program of the manufac-turer in a firing furnace Programat P700 (Ivoclar Viva-dent AG, Schaan, Lichtenstein). To compensate for theporcelain shrinkage during the sintering process, twoseparate firings under the same conditions were requiredto establish the correct dimensions of the veneering ce-ramics (10´5´3 mm).After the veneer porcelain was sintered to zirconiacubes, each sample was embedded in the customizedpolytetrafluoroethylene (PTFE) molds using the PMMAresin AcryFix (Struers Co, Ballerup, Denmark) to allowshear bond testing (Figure 2a). The samples were in-serted in the holder of the universal testing machineL. Bergman Ga{pari} et al.: Shear Bond Strength in Zirconia Veneered Ceramics, Coll. Antropol. 37 (2013) 1: 121–125122Fig. 1. a and b. SEM micrographs: a and b = ground samples; c andd = ground and sandblasted samples; a and c = magnification 100x;b and d = magnification 1000x.Fig. 2. a = sample in a mold, b = sample placed in a shear bond test-ing machine.(model LRX, Lloyd Instruments, Fareham, Great Brit-ain) which had the same diameter as the above men-tioned molds, with the core-veneer interface positionedat the level of the jig. Then shear force was applied asclose as possible to the veneer-core interface at acrosshead speed of 1 mm/min until fracture occurred(Figure 2b). Load deflection curves and ultimate load tofailure were recorded automatically and displayed by thecomputer software of the testing machine (Nexygen,Lloyd Instruments, Fareham, Great Britain).Statistical analysis was performed using SPSS statis-tical package (version 17.0, SPSS Inc., Chicago, IL, USA)and Microsoft Office Excel 2003 (Microsoft, Seattle, WA,USA). Independent samples t-test was used to test thedifference between ground samples and ground andsandblasted samples. P value of less than 0.05 was con-sidered statistically significant.ResultsMean roughness (Ra) of ground zirconia core samples(N=6) and ground and sandblasted zirconia core samples(N=6) are presented in Figure 3. T test for independentsamples revealed that there was a statistically significantdifference between two sample groups (mean differen-ce= 0.1933; df=10, t=–9.522, p<0.001). Ground andsandblasted samples had significantly higher values.Mean Z values of ground zirconia core samples (N=6)and ground and sandblasted zirconia core samples (N=6)are presented in Figure 4. There was a significant differ-ence between the groups considering Z values, i.e.ground and sandblasted samples had significantly higherz values than only ground samples (mean differ-ence=–1.491; df= 10, t=–26.11, p<0.001).Shear bond strength values of ground zirconia coresamples (N=6) and ground and sandblasted zirconia coresamples (N=6) are presented in Figure 5.There was a significant difference between the groupsconsidering shear bond strength (SBS) values, i.e. groundand sandblasted samples had significantly higher SBSvalues than only ground samples (mean difference=–190.67; df=10, t=–6.386, p<0.001).DiscussionDental ceramic materials exhibit many desirable ma-terial properties, including biocompatibility, aesthetics,diminished plaque accumulation, low thermal conductiv-ity, abrasion resistance, surface smoothness and colourstability. The popularity of metal-ceramic restorations islarge, due to predictable strength with reasonable aes-thetics. Zirconia based ceramics have been introduced inprosthodontics due to superior aesthetic properties. In afield of restorative dentistry, zirconia has been used forroot canal posts since 1989, for implant abutments since1995, and for all-ceramic posterior FPDs since 199817.Among all-ceramic materials, zirconia-based ceramicsare gaining popularity due to their superior biocompa-tibility, chemical stability, flexural strength, fracturetoughness, and the development of CAD/CAM technolo-gies which allow fabrication of all-ceramic crowns andfixed partial dentures16,18–20. High strength core materi-als are used to reinforce veneering ceramics and also allowclinicians to use a wide range of conventional or adhesiveluting protocols during fixation of the restoration21,22. Itshould also be emphasized that adequate tooth prepara-tion and carefully managed laboratory procedures, in-cluding maintaining a smooth, uniform thickness of theveneering ceramic on the cores, are also important23.The layering technique has been the principal methodof applying veneering ceramics to the core material. Suf-ficient bond strength is a concern for long term clinicalsuccess of zirconia restorations and many studies haveaddressed the associated high failure rate of zirconia-ve-neering ceramics12,24–28. Clinical failures of veneered yt-tria-stabilized tetragonal zirconia polycristal (Y-TZP)L. Bergman Ga{pari} et al.: Shear Bond Strength in Zirconia Veneered Ceramics, Coll. Antropol. 37 (2013) 1: 121–125123Fig. 3. Ra values of ground and ground + sandblasted samples.Fig. 4. Z values of ground and ground + sandblasted samples.Fig. 5. Shear bond strength values of ground and ground +sandblasted samples.frameworks were reported in 15% of patients after 2years, and in 13.0% and 15.2% after 3 and 5 years,respectively15,29–31. In contrast, failure rates of metal ce-ramic FDPs were between 8 and 10% after 10 years32,33.In a survey of the literature, few articles utilized variousbond strength test methods for all-ceramic core and ve-neering ceramic such as the shear bond strength test16,24–27,34–37, three and four point loading test38, biaxial flex-ure strength test39 and the microtensile bond strengthtest12,26,35.Using the SBS test to determine the core-veneer bondstrength results in more standardized data than usingthree or four point flexure and biaxial flexure strengthtest, because the applied forces are perpendicular to thebonding area, and the small cross-sectional area of thebonded surfaces eliminates the incorporation of thestructural flaws, which significantly affects testreadings12,40,41. Therefore the SBS test was used in thisstudy. Surface of the core material was treated in twoways prior layering: zirconia cubes were ground only andground + sandblasted. After the surface analysis and sta-tistical analysis of the obtained values, it was obviousthat ground and sandblasted specimen from the secondgroup had significantly increased surface roughness incomparison to ground samples (Figures 3 and 4). More-over, second group samples had also significantly highershear bond strength values than the first group samples(p< 0.01, Figure 5). It seems that increased surfaceroughness enabled consequently an increase of shearbond strength values. Posterior occlusal forces are usu-ally not over 600 N42,43. However, the SBS forces can onlybe of a smaller amount, as they are formed through man-dibular excursions during masticatory process. The SBSvalues for ground and sandblasted samples are probablyhigh enough to withstand many chewing cycles withoutchipping, even in posterior dentition.Further studies will be needed to validate recent re-sults and to provide additional information of long termclinical performance.ConclusionThe results of the present study indicate that groundand sandblasted cores are superior to ground cores, al-lowing significantly higher surface roughness and signif-icantly higher shear bond strength between the core andthe veneering material.AcknowledgementsThis research was supported by the Ministry of Sci-ence, Education and Sports of the Republic of Croatiaunder the Project 065-0650446-0435.R E F E R E N C E S1. MEHULI] K, SVETLI^I] V, [EGOTA S, VOJVODI] D, KOVA-^I] I, KATANEC D, PETRI^EVI] N, GLAVINA D, ^ELEBI] A, CollAntropol, 34 (2010) 235. — 2. PER[I] S, MILARDOVI] S, MEHULI] K,^ELEBI] A, Int J Prosthodont, 24 (2011) 523. — 3. 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CHOI BK, HAN JS, YANG JH,LEE JB, KIM SH, J Adv Prosthodont, 1 (2009) 129. — 38. WHITE SN,MIKLUS VG, MCLAREN EA, LANG LA, CAPUTO AA, J Prosthet Dent,94 (2005) 125. — 39. ISGRO G, PALLAV P, VAN DER ZEL JM, FEILZERAJ, J Prosthet Dent, 90 (2003) 465. — 40. ABOUSHELIB MN, KLEVER-LAAN CJ, FEILZER AJ, J Prosthodont, 17 (2008) 13. — 41. FISCHER J,STAWARCZYK B, HAMMERLE CHF, J Dent, 36 (2008) 316. — 42. ]E-LI] R, BRAUT V, PETRI^EVI] N, Coll Antropol, 35 (2011) 709. — 43.LAJNERT V, FRAN^I[KOVI] T, GR@I] R, KOVA^EVI] PAVI^I] D,BAKAR^I] D, BUKOVI] D, ^ELEBI] A, BRAUT V, FUGO[I] V, CollAntropol, 34 (2010) 1415.L. Bergman Ga{pari} et al.: Shear Bond Strength in Zirconia Veneered Ceramics, Coll. Antropol. 37 (2013) 1: 121–125124L. Bergman Ga{pari}University of Zagreb, School of Dental Medicine, Department of Fixed Prosthodontics, Gunduli}eva 5, 10000 Zagrebe-mail: bergman@sfzg.hrUTJECAJ OBRADE POVR[INE CIRKONIJEVOG OKSIDA PRIJE NANO[ENJA OBLO@NEKERAMIKE NA VEZNU ^VRSTO]US A @ E T A KSvrha istra`ivanja bila je testom vezne ~vrsto}e utvrditi utjecaj poliranja dijamantnim svrdlom i pjeskarenja povr-{ine cirkonij oksidne keramike na veznu ~vrsto}u s oblo`nom keramikom. Statisti~ka analiza provedena je koriste}iSPSS statisti~ki program (17.0, SPSS Inc., Chicago, IL, USA) i Microsoft Office Excel 2003 (Microsoft, Seattle, WA,USA). Postoji zna~ajna razlika u veznoj ~vrsto}i me|u uzorcima, polirani i pjeskareni uzorci imali su zna~ajno ve}uveznu ~vrsto}u od samo poliranih uzoraka (aritmeti~ka sredina razlike=–190.67; df=10, t=–6.386, p<0.001). Rezultatisu pokazali da se pjeskarenjem dobiva hrapavija povr{ina cirkonijevog dioksida {to omogu}uje bolju vezu s oblo`nomkeramikom.L. Bergman Ga{pari} et al.: Shear Bond Strength in Zirconia Veneered Ceramics, Coll. Antropol. 37 (2013) 1: 121–125125

Utjecaj obrade površine cirkonijevog oksida prije nanošenja obložne keramike na veznu čvrstoću

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