|Year : 2022 | Volume
| Issue : 5 | Page : 462-467
Comparison of tensile and shear bond strengths of layering porcelain with VITA Suprinity after different surface treatment methods: An in vitro study
Arash Shishehian1, Farnoush Fotovat1, Banafsheh Poormoradi2, Sara Khazaei1, Maryam Farhadian3, Hirbod Gilandoust4
1 Department of Prosthodontics, School of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran
2 Department of Periodontics, School of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran
3 Department of Biostatistics and Epidemiology, Faculty of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran
4 School of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran
|Date of Submission||01-Apr-2022|
|Date of Decision||24-Jul-2022|
|Date of Acceptance||25-Jul-2022|
|Date of Web Publication||31-Oct-2022|
Dr. Farnoush Fotovat
Department of Prosthodontics, School of Dentistry, Hamadan University of Medical Sciences, Hamadan
Source of Support: None, Conflict of Interest: None
Background: For all-ceramic restorations to last a long time, the ceramic veneering and substructure need to have a strong sufficient bond. This research compared how two different surface treatments affected the tensile and shear bond strengths of zirconium-reinforced lithium silicate and porcelain (Suprinity). Materials and Methods: A total of 120 samples were divided into three groups at random: control(no surface treatment),aluminium oxide sandblasting, Erbium, Chromium-doped Yttrium, Scandium, Gallium, and Garnet (Er, Cr: YSGG) laser irradiation, and 60 samples to evaluate tensile bond strength and 60 samples to evaluate shear bond strength. By using one-way ANOVA and the post-hoc Tukey’s test, the tensile and shear bond strength between Suprinity and porcelain (VITA VM 11) was analyzed in all groups. Results: The maximum and minimum tensile bond strength was seen in sandblasting group (7.86 ± 2.22 Mpa) and control group (4.88 ± 1.58 Mpa), respectively (P < 0.001). The amount of shear bond strength in the laser group, sandblast group, and control group was (5.16 ± 1.66 Mpa),(5.00 ± 1.34 Mpa),(4.39 ± 1.54 Mpa) respectively (P = 0.252). In tensile and shear bond strength tests, most failures were cohesive in VITA VM 11 layering porcelain (65.0% vs. 66.7%) followed by mixed failures (33.3% vs. 20%). Conclusion: Suprinity and layering porcelain produced higher tensile bonds as a result of Al2O3 sandblasting and Er, Cr: YSGG laser irradiation. While no pure adhesive failure was seen, cohesive failure was predominant.
Keywords: Dental Bonding, Dental Porcelain, Shear Strength, VITA Suprinity
|How to cite this article:|
Shishehian A, Fotovat F, Poormoradi B, Khazaei S, Farhadian M, Gilandoust H. Comparison of tensile and shear bond strengths of layering porcelain with VITA Suprinity after different surface treatment methods: An in vitro study. J Int Oral Health 2022;14:462-7
|How to cite this URL:|
Shishehian A, Fotovat F, Poormoradi B, Khazaei S, Farhadian M, Gilandoust H. Comparison of tensile and shear bond strengths of layering porcelain with VITA Suprinity after different surface treatment methods: An in vitro study. J Int Oral Health [serial online] 2022 [cited 2023 Nov 30];14:462-7. Available from: https://www.jioh.org/text.asp?2022/14/5/462/359971
| Introduction|| |
With the advancement of technology in dentistry, studies on ceramics are increasing for their better aesthetics, biocompatibility, abrasion resistance, and chemical stability., Despite the growing development of ceramics, various types of them have poor mechanical properties, including brittleness, so their use in posterior teeth is severely restricted. Porcelain is widely used to bond metals, glass-ceramics, and monoblock ceramic restorations. Most porcelains are feldspathic, lithium disilicate, mica, alumina, leucite glass-ceramics, or fluorapatite glass-ceramics. Despite their low strength, feldspars and leucite-ceramics are used in many ceramic restorations as a coating material to improve aesthetic properties and thermal compatibility., The main limitations of these porcelains are their low hardness, being brittle, and chipping.
With the development of zirconia ceramics, ceramics have been strengthened and used in posterior areas of the mouth with a greater force. Zirconia restorations are widely used in the reconstruction of different areas of the mouth and are less dependent on the size of the prosthesis and the amount of force due to their strong biomechanical properties. Several studies have shown that the application of zirconia has enhanced the mechanical properties of all-ceramic restorations., Also, better visual property and polishing have been reported for this material than porcelain fused to metal restoration. It is also significant to mention that the cooling rate and application methods have a significant impact on long-term success. For veneering all-ceramic crowns, the pressed technique combined with a slow-cooling protocol produces the best results..
One of the problems with using zirconia restorations is their opacity, limiting their use in areas with a high demand for aesthetics.
To overcome this problem, the use of lithium silicate reinforced zirconia ceramics (VITA Suprinity)(vita zahnfabrik H. RauterGmblt) has been suggested to provide better aesthetic properties. Since these ceramics come in one-piece blocks and layering ceramics should be applied on them if required, for example, for improving contour or proximal contact correction, they are associated with problems in porcelain bonding. Various surface treatments have been made to achieve better bonding of resin cement or layering porcelains to the underlying ceramics to obtain better mechanical properties and to reduce the failure of these restorations.
Ceramic sandblasting with aluminum oxide (Al2O3) particles is one of the common methods of surface treatment to boost the strength of the underlying ceramic bond with layering porcelain.,, Several studies have reported that laser irradiations could also enhance the bond strength., In addition, mechanical abrasion,, silica coating,, plasma spray, and hydrofluoric acid, are other methods of surface treatment. In light of this, the purpose of this study was to evaluate the tensile and shear bond strengths of layering porcelain with Suprinity that had undergone sandblasting and Ee,Cr:YSGG laser irradiation modifications. The tensile and shear bond strengths of veneering porcelain to VITA Suprinity were tested under the hypothesis that they would be influenced by the surface treatment techniques used.
| Materials and Methods|| |
This experimental study was approved by the Hamadan University of Medical Sciences’ Research and Ethics Committee in accordance with IR.UMSHA.REC. 1397.890.
Calculating method of sample size: The pwr software program (R version 5.3.1) was used to calculate the sample size needed for this study. The required number of samples in each group was 20, based on the Nikzadjamnani et al. study’s test power of 85% and significance level of 0.05. The total number of sample size required for this study was 120.
A total of 120 samples (60 samples to evaluate tensile bond strength and 60 samples to assess shear bond strength) were prepared from 2M2-T LS-14 translucent glass-ceramic blocks ((VITA Suprinity)(vita Zahnfabrik H. RauterGmblt) and they were mounted in self-cured acrylic resin (Acropars, Tehran, Iran) to obtain equal slices, where a checkered paper pattern was used on the blocks. The mounting blocks were cut to obtain samples of 5 mm height and 2.25 mm2 cross-section using a cutting machine (Novin, Mashhad, Iran) with air and water coolant to evaluate the tensile bond strength. For the shear bond strength test, the mounting blocks were cut transversely with dimensions of 4 × 4 × 12 mm. Next, The samples were then completely crystallized for 30 minutes at 850°C in a high-temperature furnace (Programat Ivoclar-Vivadent, Buffalo, NY) in accordance with the manufacturer’s instructions.
Experimental groups and surface treatment
As previously stated, 120 samples were separated into three groups of Er,Cr: YSGG laser irradiation, sandblasting with Al2O3, and control. Of these samples, 60 were used to evaluate the tensile bond strength and 60 were used to evaluate the shear bond strength (without surface treatment). The samples of Er,Cr:YSGG group (Bio lase, USA-California) were prepared at a wavelength of 2780 nm, 10 Hz frequency, power 2 W, 60% water, 50% air, and tip MZ5 (2 mm distance/ vertical, horizontal and spiral movements for 30 seconds). In the second group, the samples were prepared by sandblasting with Al2O3 particles (GD Carlo de Giorgi Sri, Italy) and dimensions of 30 µm for 15 seconds at a distance of 10 mm and a pressure of 3.5 bar. In the third group, no surface treatment was done.
A veneering porcelain cylinder was applied to each specimen’s prepared surface using a custom-made split silicone mold. A square shape measuring 4 mm in length, 4 mm in width, and 2 mm in height was created using distilled water and porcelain powder VITA VM 11 (VITA zahnfabrik H. RauterGmblt). Tissue paper was used to absorb excess water. As instructed by the manufacturer, firing was performed in a calibrated porcelain furnace. To make up for the porcelain shrinkage experienced during the initial firing, a second firing was required.
Evaluation of tensile bond strength
Inclusion criteria for measuring tensile bond strength included obtaining the desired cross-sectional area and no fracture or chipping after cutting. Exclusion criteria also included a distinct interface between Suprinity and coating porcelain. The dimensions of the micro-bars were measured by a digital caliper (Hi-Tech diamond 4, USA). The samples were fixed on the arms of the universal testing machine (Santam, Tehran, Iran) using adhesive bond ((Sana bond)(Alan Industry, Tehran, Iran)) and stretched at a speed of 1 mm/min until failure occurred [Figure 1]a. The force required to cause failure was electronically recorded and expressed in Newtons (N). The following equation was used to convert the obtained values to megapascal (Mpa):
|Figure 1: Tensile bond strength test by universal testing machine (a), Shear bond strength test by universal testing machine (b)|
Click here to view
The failure sites were examined at ×40 magnification to determine the type of failure by a stereomicroscope (Motic digital microscope DM-143, Hong Kong). The failures were classified as the layering porcelain cohesive failure, Suprinity cohesive failure, adhesive failure, and mixed failure (cohesive and adhesive failures).
Evaluation of shear bond strength
The inclusion and exclusion criteria were viewed as being similar to the tensile bond strength measurement in order to measure the shear bond strength. The diameter of the cylinders was measured by a digital caliper (Hi-Tech diamond 4, USA) to reduce measurement error. The samples were mounted in an acrylic resin for better stability and then fixed at the site of the universal testing machine (Santam, Tehran, Iran)) and pressed at a speed of 1 mm/min with the machine blade) until failure occurred [Figure 1]b. The force required to cause failure was electronically recorded and expressed in Newtons (N). The following equation was used to convert the obtained values to megapascal (Mpa):
Types of failures were examined by a stereomicroscope (Motic digital microscope DM-143, Hong Kong) at ×40 magnification. Failure types similar to those described above were classified.
The Statistical Package for Social Sciences (SPSS) version 21.0 software was used to conduct statistical analysis using the one-way variance (ANOVA) test. Tukey’s post hoc test was used to analyze the data when P values were found to be lower than 0.05. All information was presented as mean standard deviation (SD).
| Results|| |
The shear and tensile bond strength between Suprinity and layering/porcelain was determined by the Kolmogorov-Smirnov test to have a normal data distribution, so parametric tests were utilized for data analysis. The shear and tensile bond strengths between Suprinity and layering porcelain were analyzed in different groups of Al2O3 sandblasting (Ee,Cr:YSGG) laser irradiation and control using one-way ANOVA. The results indicated that the tensile bond strength of Suprinity with layering porcelain in different groups significantly changed among the groups (P < 0.001). Further data analysis by the post-hoc Tukey test revealed that the mean tensile bond strength between Suprinity and layering/ porcelain in the control group was 4.89 ± 1.58Mpa, which increased to 7.63 ± 1.87 Mpa due to Ee,Cr:YSGG laser irradiation (P < 0.001). The mean tensile bond strength between Suprinity and layering porcelain also increased in the group of Al2O3 sandblasting (, P < 0.001) compared to the control group (4.89 ± 1.58Mpa). However, the mean tensile bond strength of Suprinity with layering porcelain was not altered in the Ee,Cr:YSGG laser irradiation group to the Al2O3 sandblasting group (a, P = 0.920) (). Meanwhile, the one-way ANOVA analysis of the shear bond strengths of Suprinity with layering porcelain in different groups did not change significantly (P = 0.252) [Table 1].
[Table 2] reports the evaluation findings of the sample failure types in the shear and tensile bond strength in the various groups. The results indicated that the total percentages of cohesive failures of porcelain in the shear and tensile bond strength increased (65% and 66.7%, respectively) compared with the cohesive failures of Suprinity (1.7% and 13.3%, respectively) and mixed (cohesive and adhesive) failures (33.3% and 20%, respectively). In addition, no adhesive failure was observed in any of the groups.
|Table 2: Mode of failure of the samples in tensile and shear bond strength tests|
Click here to view
| Discussion|| |
In our study, the Al2O3 sandblasting and Er,Cr: YSGG-irradiated groups had higher tensile bond strengths of Suprinity with layering porcelain compared to the control group. The current study’s findings partially support the hypothesis that various surface treatment techniques will affect the shear and tensile bond strength of veneering porcelain to VITA Suprinity. Similar to our findings, a study by Nikzadjamnani et al. revealed that compared to the control group, sandblasting with Al2O3 and CO2 and Er:YAG laser irradiation strengthened the tensile bond between the zirconia core and veneering porcelain. Al2O3 sandblasting of the samples was recommended as the best surface treatment technique. Er:YAG and Er:Cr,YSGG lasers in the erbium family have wavelengths of 2940 nm and 2780 nm, respectively. These lasers have the highest water and hydroxyapatite absorption rates. Despite the many similarities between the two lasers, differences in wavelength, surface texture removal ability, heat generation potential, and penetration depth make these lasers unique.,
Mahmoodi et al. demonstrated, in contrast to our finding, that sandblasting the samples with Al2O3 particles and Nd:YAG laser irradiation could not increase the tensile bond strength of zirconia ceramics to coating material or resin cement. The highest absorption in water and pigments occurs at the Nd:YAG laser’s 1064 nm wavelength. The best option for homeostasis and soft tissue surgery is this laser. The Nd:YAG lasers could deform the surface of porcelain with zirconia pores, but fails to produce an acceptable bond, though some recent studies have reported acceptable results regarding the application of these lasers to porcelain-based zirconia and feldspathic porcelain., Henriques et al.’s study on zirconia (TZ-3YBE) showed that sandblasting of the specimens with Al2O3 particles and Nd:YAG laser irradiation boosted the shear bond strength zirconia. It is also suggested that the optimum surface treatment technique was Nd:YAG laser irradiation. Although surface treatment with Al2O3 particles could enhance porcelain bond strength with zirconia, it might have an adverse effect on the flexural strength of the prosthesis and reduce restoration long time prognosis. According to a study by Ataol et al., the shear bond strength of Vita Suprinity with resin cement was unaffected by the surface treatments methods of air abrasion with Al2O3 and Er,Cr:YSGG laser irradiation.
Clinical studies have shown that separation of the upper structure from the lower structure accounts for most failures of treatment with zirconia restorations. In our study, most of the failures were due to the porcelain structure. On the other hand, the bond strength between Suprinity and layering porcelain is stronger than the internal structure of the layering/ porcelain. This can be due to the lack of coordination in the thermal expansion coefficient of layering/ porcelain and Suprinity, which can cause separation between different phases of restoration. In addition, some studies have indicated that small cavities caused by Al2O3 particles could lead to long-term cracking and failure of joint prostheses. These effects are probably due to differences in the magnitude of the particle collisions. Nikzadjamnani et al. showed that 92.44% of failures were cohesive in the veneering porcelain. Mahmoodi et al.’s study indicated that most adhesive failures for the sandblasted specimens occurred in zirconia block and resin cement bonding. In addition, Piascik et al.’s study reported that 85% of the failures occurred after testing from the joint of ceramic block and resin cement.
According to our results, surface modiﬁcation could create deep holes in the ceramic surface, despite the increased strength of Suprinity bond with layering/ porcelain. These effects could lower the flexural strength of the restoration or cause cracking in the Suprinity substructure as well as reduce the prosthesis’s longevity. In order to elucidate the mechanical properties of zirconia, it is recommended to examine the surface treatment (sandblasting and laser irradiation) by scanning electron microscope (SEM). It is also advised that longer-term clinical studies be conducted to evaluate how long-lasting these repairs will be. Technical sensitivity, sample fracture and dimensional inaccuracy during the cutting of Suprinity blocks, veneering porcelain flexure and fracture during baking, and ceramic substrate fracture during testing were among the limitations of the current laboratory investigation. Additionally, we encountered limitations when applying clinical loading forces to restorations. The environment of the oral cavity was not simulated, and the loading was monotonic rather than cyclic. The specimens weren’t thermally cycled either. Therefore, ongoing clinical evaluations are advised.
| Conclusion|| |
In comparison to the control, sandblasting the specimens with Al2O3 particles and Er,Cr:YSGG laser irradiation may greatly increase the tensile bond strength between lithium silicate reinforced zirconia ceramics and porcelain. In addition, no adhesive failures occurred in lithium silicate reinforced zirconia ceramics joint with layering porcelain, and most of the cohesive failures were due to the layering porcelain structure.
This research was done as a part of prosthodontics undergraduate student thesis #9712147768. The Research Center of Dentistry at Hamadan University of Medical Sciences in Hamadan, Iran is acknowledged by the authors. This study was attributed to Dental Faculty,Hamadan University of Medical sciences,Hamadan,Iran.
Financial support and sponsorship
We would like to express our gratitude to the Hamadan University of Medical Sciences’ deputy for research and technology for providing financial support for this work (grant number:9712147768).
Conflict of interest
There are no conflicts of interest.
Manuscript preparation, editing and review by Arash Shishehian, Farnoush Fotovat
Study concept Sara Khazaei,Banafsheh Poormoradi
Statistical analysis Maryam Farhadian
Experimental procedures by Hirbod Gilandoust
Ethical policy and institutional review board statement
This experimental study was approved by the Hamadan University of Medical Sciences’ Research and Ethics Committee in accordance with IR.UMSHA.REC. 1397.890.
Patient declaration of consent
Data availability statement
Data is available upon reasonable request.
| References|| |
Salazar Marocho SM, Studart AR, Bottino MA, Bona AD Mechanical strength and subcritical crack growth under wet cyclic loading of glass-infiltrated dental ceramics. Dent Mater 2010;26:483-90.
Della Bona A, Mecholsky JJ Jr, Barrett AA, Griggs JA Characterization of glass-infiltrated alumina-based ceramics. Dent Mater 2008;24:1568-74.
Song X-F, Yin L, Peng J-H, Lin B Cutting characteristics of dental glass ceramics during in vitro dental abrasive adjusting using a high-speed electric handpiece. Ceramics International 2013;39:6237-49.
Griggs JA Recent advances in materials for all-ceramic restorations. Dent Clin North Am 2007;51:713-27, viii.
Malament KA, Socransky SS Survival of dicor glass-ceramic dental restorations over 20 years: Part IV. The effects of combinations of variables. Int J Prosthodont 2010;23:134-40.
Sailer I, Gottnerb J, Kanelb S, Hammerle CH Randomized controlled clinical trial of zirconia-ceramic and metal-ceramic posterior fixed dental prostheses: A 3-year follow-up. Int J Prosthodont 2009;22:553-60.
Raigrodski AJ, Hillstead MB, Meng GK, Chung KH Survival and complications of zirconia-based fixed dental prostheses: A systematic review. J Prosthet Dent 2012;107:170-7.
Elsaka SE Influence of surface treatments on the surface properties of different zirconia cores and adhesion of zirconia-veneering ceramic systems. Dent Mater 2013;29:e239-51.
Stawarczyk B, Frevert K, Ender A, Roos M, Sener B, Wimmer T Comparison of four monolithic zirconia materials with conventional ones: Contrast ratio, grain size, four-point flexural strength and two-body wear. J Mech Behav Biomed Mater 2016;59:128-38.
Júlia-Magalhães-da Costa Lima J, Tribst PM, Anami LC, de Melo RM, Dayanne-Monielle-Duarte Moura RO, Souza A, Bottino MA Long-term fracture load of all-ceramic crowns: Effects of veneering ceramic thickness, application techniques, and cooling protocol. Journal of Clinical and Experimental Dentistry 2020;12:1078.
Tuncel İ, Turp I, Üşümez A Evaluation of translucency of monolithic zirconia and framework zirconia materials. J Adv Prosthodont 2016;8:181-6.
Elsaka SE, Elnaghy AM Mechanical properties of zirconia reinforced lithium silicate glass-ceramic. Dent Mater 2016;32:908-14.
Alves LMM, Contreras LPC, Campos TMB, Bottino MA, Valandro LF, Melo RM In vitro wear of a zirconium-reinforced lithium silicate ceramic against different restorative materials. J Mech Behav Biomed Mater 2019;100:103403.
Akın H, Ozkurt Z, Kırmalı O, Kazazoglu E, Ozdemir AK Shear bond strength of resin cement to zirconia ceramic after aluminum oxide sandblasting and various laser treatments. Photomed Laser Surg 2011;29:797-802.
Akyıl MŞ, Uzun İH, Bayındır F Bond strength of resin cement to yttrium-stabilized tetragonal zirconia ceramic treated with air abrasion, silica coating, and laser irradiation. Photomedicine and Laser Surgery 2010;28:801-8.
Kim HJ, Lim HP, Park YJ, Vang MS Effect of zirconia surface treatments on the shear bond strength of veneering ceramic. J Prosthet Dent 2011;105:315-22.
Ural Ç, Külünk T, Külünk Ş, Kurt M The effect of laser treatment on bonding between zirconia ceramic surface and resin cement. Acta Odontol Scand 2010;68:354-9.
Usumez A, Hamdemirci N, Koroglu BY, Simsek I, Parlar O, Sari T Bond strength of resin cement to zirconia ceramic with different surface treatments. Lasers Med Sci 2013;28:259-66.
Kimyai S, Mohammadi N, Navimipour EJ, Rikhtegaran S Comparison of the effect of three mechanical surface treatments on the repair bond strength of a laboratory composite. Photomed Laser Surg 2010;28 Suppl 2:S25-30.
Guess PC, Zhang Y, Kim JW, Rekow ED, Thompson VP Damage and reliability of Y-TZP after cementation surface treatment. J Dent Res 2010;89:592-6.
Joulaei M, Bahari M, Ahmadi A, Savadi Oskoee S Effect of different surface treatments on repair micro-shear bond strength of silica- and zirconia-filled composite resins. J Dent Res Dent Clin Dent Prospects 2012;6:131-7.
Fischer J, Grohmann P, Stawarczyk B Effect of zirconia surface treatments on the shear strength of zirconia/veneering ceramic composites. Dent Mater J 2008;27:448-54.
Roy M, Bandyopadhyay A, Bose S Induction plasma sprayed nano hydroxyapatite coatings on titanium for orthopaedic and dental implants. Surf Coat Technol 2011;205: 2785-92.
Piwowarczyk A, Lauer HC, Sorensen JA In vitro shear bond strength of cementing agents to fixed prosthodontic restorative materials. J Prosthet Dent 2004;92:265-73.
Nikzadjamnani S, Zarrati S, Rostamzadeh M Microtensile bond strength between zirconia core and veneering porcelain after different surface treatments. J Dent (Tehran) 2017;14:303-12.
Kumar G, Rehman F, Chaturvedy V Soft tissue applications of er,cr:YSGG laser in pediatric dentistry. Int J Clin Pediatr Dent 2017;10:188-92.
Fekrazad R, Chiniforush N One visit providing desirable smile by laser application. J Lasers Med Sci 2014;5:47-50.
Mahmoodi N, Hooshmand T, Heidari S, Khoshro K Effect of sandblasting, silica coating, and laser treatment on the microtensile bond strength of a dental zirconia ceramic to resin cements. Lasers Med Sci 2016;31:205-11.
Paranhos MP, Burnett LH Jr, Magne P Effect of nd:YAG laser and CO2
laser treatment on the resin bond strength to zirconia ceramic. Quintessence Int 2011;42:79-89.
Maruo Y, Nishigawa G, Irie M, Yamamoto Y, Yoshihara K, Minagi S Effects of irradiation with a CO2
laser on surface structure and bonding of a zirconia ceramic to dental resin cement. Journal of Laser Micro Nanoengineering 2011;6:174.
Henriques B, Fabris D, Souza JCM, Silva FS, Carvalho Ó, Fredel MC, et al
. Bond strength enhancement of zirconia-porcelain interfaces via nd:YAG laser surface structuring. J Mech Behav Biomed Mater 2018;81:161-7.
Ataol AS, Ergun G Effects of surface treatments on repair bond strength of a new CAD/CAM ZLS glass ceramic and two different types of CAD/CAM ceramics. J Oral Sci 2018;60:201-11.
Aboushelib MN, de Jager N, Kleverlaan CJ, Feilzer AJ Microtensile bond strength of different components of core veneered all-ceramic restorations. Dent Mater 2005;21:984-91.
de Kler M, de Jager N, Meegdes M, van der Zel JM Influence of thermal expansion mismatch and fatigue loading on phase changes in porcelain veneered Y-TZP zirconia discs. J Oral Rehabil 2007;34:841-7.
[Table 1], [Table 2]