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Au interface effect on Ti-dental porcelain bond strength investigated by spectroscopic methods and mechanical tests
Journal Pre-proof Au interface effect on Ti-dental porcelain bond strength investigated by spectroscopic methods and mechanical tests Malgorzata Lubas PII:
S0022-2860(20)30194-0
DOI:
https://doi.org/10.1016/j.molstruc.2020.127870
Reference:
MOLSTR 127870
To appear in:
Journal of Molecular Structure
Received Date: 20 December 2019 Revised Date:
3 February 2020
Accepted Date: 6 February 2020
Please cite this article as: M. Lubas, Au interface effect on Ti-dental porcelain bond strength investigated by spectroscopic methods and mechanical tests, Journal of Molecular Structure (2020), doi: https:// doi.org/10.1016/j.molstruc.2020.127870. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
The article has one author. To the author include: the concept, methodology and discussion of the results.
Au interface effect on Ti-dental porcelain bond strength investigated by spectroscopic methods and mechanical tests Malgorzata Lubas Czestochowa University of Technology, Department of Materials Engineering, 19 Armii Krajowej Ave., 42-200 Czestochowa, [email protected]
Abstract The article presents the results of the titanium 99.2/ceramic system interface bond strength investigated by mechanical tests and Raman spectroscopy. The titanium substrate was activated with sandblasting (Al2O3), an Au interlayer and finally covered with low fusing porcelain (GC Initial, Duceratin). In order to investigate the effects of the Au layer on the interface bond strength, mechanical testing (three-point bending) was conducted. Surface characterizations of the specimens were carried out with scanning electron microscopy (SEM/EDX) and spectroscopic (RS) study. The applied Au interface layer for substrate preparation improves the effects of porcelain adhesion to Ti 99.2, which was confirmed by bond strength improvement in the area of the titanium/bioceramic interface. The results indicated that the bond strengths of all the Ti/porcelain systems were greater than the minimal requirement (25 MPa) of ISO 9696. Surface activation with sandblasting and gold sputtering treatment of the Ti surfaces prior to porcelain sintering significantly strengthens the bond between the metal (Ti 99.2) and the dental porcelain.
Keywords: surface preparation, Au interlayer, titanium 99.2, bond strength, dental porcelain
Introduction A range of metallic and ceramic materials is used in dental prosthetics, which must work together long-term and fulfill specific functions. Dental prosthetics is a field in which many factors influence the satisfactory end result. Titanium is one of the most commonly used metal biomaterials in dentistry in the last few years. It gained its popularity due to its physical and chemical properties. It is characterized by excellent quality, high corrosion resistance and good mechanical properties [1 - 3]. Dental ceramics with a metal foundation are joined by physical, mechanical and chemical bonds. For a proper physical bond, it is necessary to choose the appropriate thermal expansion coefficients (WRC) for both materials to be joined. This is due to the formation of
compressive stresses during the ceramics firing process. The ceramics should have a lower WRC value than the metal, which is associated with an increase in strength that is responsible for adhering to the porcelain substrate when the ceramics is cooling down [4,5]. For mechanical bonds, proper preparation of the metal substrate is of great importance. Creating recesses on the substrate surface causes retention and micro retention, thanks to which the contact surface of the ceramic mass on the substrate is increased [6,7]. The most popular mechanical treatment improving the metal-ceramic bond is sandblasting using alumina with the appropriate grain size, pressure and angle of inclination of the sample. Properly selected parameters of this treatment allow micro retention to
be obtained.
Parameters such as sand thickness and pressure must be taken into account [8 - 12]. However, the obtained bond strength values do not always meet the requirements of industrial standards [13]. Studies on titanium surface modification are carried out on a large scale in order to improve the quality and bond strength of the metal-dental porcelain system, which do not explain in detail the bond formation mechanism [14 - 20]. The work investigates the influence of the intermediate gold layer on the strength of the titanium-porcelain bond in prosthetic applications. Tests were carried out using technically pure titanium 99.2 (Grade 2), sandblasted with Al2O3, on the surface of which an intermediate Au layer was sprayed and then the appropriate layers of dental ceramics (bond, opaque, dentine) were fired.
Research materials and methods The influence of the intermediate layer of Au on the strength of the titanium-dental porcelain bond was determined. Technically pure titanium (Ti 99.2) was used as the substrate. Titanium samples were prepared in accordance with ISO 9693 in the form of plates with dimensions of 25 (± 1) mm x 3 (± 1) mm x 0.5 (± 1 mm) [13]. The substrates were prepared by sandblasting with 110 µm alumina particles at 3 bar pressure for a time not exceeding 15 seconds. The samples were sandblasted at the angle of 45° and with the distance from the nozzle of 7 mm. Next the samples were cleaned in an ultrasonic cleaner for 5 minutes and divided into two groups: Ti/Al2O3/porcelain – control samples (20 pcs) and Ti/Al2O3/Au/porcelain – samples with an intermediate Au layer (20 pcs). These samples were sputtered with pure Au in an ion sputtering device (E-1010; Hitachi, Tokyo, Japan) at 15 mA for 60 seconds. In the next stage, low-melting porcelain from GC Initial and Duceratin were applied to the titanium surfaces in accordance with ISO 9693. The parameters and stages realized for surface activation treatment of the Ti samples and their results are presented in Table 1 and Figure 1. Table 1. Surface activation treatment stages conducted for titanium surface preparation
Samples Ti/Al2O3/porcelain
Surface treatment stage 1. Sandblasting Al2O3 with 110 µm particles 2. Ultrasonic cleaning in distilled water for 5 minutes 3. Firing porcelain layers (bond, opaque, dentin) 3a. GC Initial 3b. Duceratin Ti//Al2O3/Au/porcelain 1. Sandblasting Al2O3 with 110 µm particles 2. Ultrasonic cleaning in distilled water for 5 minutes 3. Gold sputter coating for 60 sec. At 15 mA 4. Firing porcelain layers (bond, opaque, dentin) 4a. GC Initial 4b. Duceratin
Fig. 1. SEM/EDX micrographs and analysis of titanium surface: a) after sandblasting, b) after sandblasting and Au interface spraying, c) after sandblasting, Au interlayer and application of subsequent porcelain layers (bond-opaque-dentin)
The porcelains were fired according to the manufacturers' requirements (Table 2) and their total thickness was about 1.1 mm (bond-opaque-dentine). Table 2. Low-melting GC Initial and Duceratin porcelain firing parameters [21,22] Parametry wypalania porcelany niskotopliwej GC Initial oraz Duceratin [21,22] Firing parameters Porcelain GC Initial Type of
Heating
Drying and
Increase
Firing
Drying
layer
temperature,
heating time,
temperature,
temperature,°C
time, min
Vacuum, hPa
°C
min
°C/min
bond
450
4:00
55
810
1:00
50
opaque
450
4:00
55
810
1:00
50
dentin
400
6:00
45
780
1:00
50
Porcelain Duceratin bond
600
6:00
100
750
1:00
50
opaque
450
10:00
100
760
0:30
50
dentin
450
9:00
55
760
1:00
50
Bond strength tests were performed using a universal Zwick Z100 strength testing machine with equipment set according to the requirements of ISO 9693 [13]. During the three-point bending tests, the porcelain side of the sample was placed faced down and the load was increased at a rate of 1.5 mm/min. The load as a result of which the Ti/porcelain bond was broken at one end of the sample was considered a destructive force. The titanium-porcelain bond strength with and without an intermediate layer was calculated based on the following relationship: τ = F ⋅ k, where: F – destructive force, k = f (dM), [13].
The study characterizes the surface of titanium samples after surface modification processes and bending tests. The basic roughness parameters of the titanium substrate after the sandblasting process and application of the Au layer were determined using a Hommel Tester T1000 profilometer. The microstructure and chemical composition of the surface of the samples after bending tests were determined by SEM/EDX (scanning electron microscope JOEL JSM-6610LV). Spectroscopic tests, aimed at determining the resistance of the titanium substrate to oxidation during the firing of subsequent porcelain layers were performed using Raman spectroscopy (RS Witec Alpha 300M + spectroscope with 488 nm laser and 600 gr/mm grid). Results and discussion
The results of the roughness measurements (Ra and Rz parameters), both for the surfaces of the pure titanium (99.2), titanium after the sandblasting process (Al2O3 - 110 µm) and titanium with an Au interlayer are presented in Table 3.
Table 3. Results of roughness measurements (Ra and Rz parameters) Sample
Ra, µm
Rz, µm
Titanium, 99.2
0.43 ±0.02
3.01 ±0.03
Titanium after sandblasting Al2O3
1.26 ±0.03
8.87 ±0,02
Titanium after sandblasting and Au layer
1.12 ±0.02
8.36 ±0.03
Analyzing the results, it was found that the values of the Ra and Rz parameters differ depending on the treatment used. The lowest Ra and Rz values were exhibited by the samples of technically pure titanium (99.2), and the highest by the samples after the sandblasting process. In the literature describing the impact of machining on the strength of the metal-dental porcelain bond, it was found that in adequate metal surface roughness in this system is one of the main factors leading to the uneven application of ceramic masses. As a result, this leads to the formation of voids, which can cause blistering during porcelain firing and weakening of the metal-ceramic bond [23, 24]. The gold layer used on the sandblasted titanium substrate reduces the roughness from Ra = 1.26µm to Ra = 1.12µm. Thus, it increases the contact surface of the veneering ceramic mass on the foundation and guarantees a better, more even application of the porcelain layers. The results of spectroscopy studies on the titanium-porcelain cross-section showed the presence of a TiO2 oxide layer for the samples without the intermediate Au layer (Fig. 2). It should be noted that the tested samples were not subjected to the oxidation process before applying the porcelain layers. The obtained results confirm that titanium oxidizes when applying and firing subsequent layers of porcelain. Similar conclusions were made in [25.26]. The obtained results confirm the share of two oxide varieties - rutile and anatase. No oxide layers were observed in the samples with the sprayed intermediate layer of gold (Fig. 3). The gold layer therefore affects the oxidation of titanium when firing subsequent layers of porcelain. The research shows that a very thin layer of gold (Fig. 3,4) inhibits the oxidation of titanium surfaces.
Fig. 2. Raman spectra of Ti/Al2O3/Duceratin porcelain system
Fig. 3. Raman spectra of Ti/Al2O3/Au interlayer/Duceratin porcelain system interface
Fig. 4. Cross section of titanium/Au/porcelain system, SEM/EDX
Based on the literature data, it is known that an excessively thick oxide layer, above 10 µm, formed on the surface of titanium at the sintering temperature of porcelain, is porous and does not adhere well to titanium. Damage to the titanium-porcelain bond occurs most often in the oxide layer [25 - 28]. The spectroscopic research shows that a very thin layer of gold in the metal-ceramic system is a factor that blocks the growth of the oxide layer that can contribute to improvement of the titanium-porcelain bond, as a result of mutual interdiffusion of the gold and dental porcelain components. A. Katz and S. Nakahara suggest bonding between Au and Si as early as 370°C, which improves the metal-gold-porcelain bond compared to the metal-porcelain system [29]. The results of the mechanical tests (three-point bending) of the titanium-intermediate gold layer-porcelain bond (Table 4) correlate with the obtained results of the spectroscopic tests. All the samples obtained values above 25 MPa and met the requirements of EN ISO 9693:2012. The samples with the intermediate layer of gold for Duceratin porcelain obtained almost 1.5 times higher flexural strength (25 MPa without Au and 40 MPa with Au). For the titanium samples with GC Inital porcelain, a slightly smaller difference was obtained between the samples subjected to traditional sandblasting (24 MPa) and with the layer of gold (34 MPa). Table. 4. Results of bond strength of Ti/porcelain samples after three-point bending mechanical tests
Lp.
1. 2.
Variant of titanium surface treatment Ti 99.2
Bond strength, τ [MPa]
Standard deviation
GC Initial
Duceratin
GC Initial
Duceratin
Ti/Al2O3/Porcelain
28.02±6
25.67±7
2.61
1.80
Ti/Al2O3/Au/Porcelain
34.65±5
40.18±6
1.84
1.61
The morphology studies and chemical composition of SEM/EDS after the bending tests for both series of samples with layers of GC Initial dental porcelain showed the presence of so called "craters" – areas after detachment of porcelain from the titanium substrate. The results of the SEM/EDX analysis also showed the presence of: La, B, Ce, Sn, Si, Al, Na and Ti for the samples without the gold layer (Fig. 5). For the samples with the Au layer, the presence of titanium was not observed, which indicates that is bonding of the system occurred only on the porcelain side, which adheres very well to titanium (Fig. 6). Based on the obtained results, it can be concluded that the Au layer significantly improves porcelain adhesion to titanium. In the case of Duceratin porcelain, the surface after the bending tests is fairly uniform, smooth with no clear residue of the ceramic layers (Fig.8), both for the sandblasted samples and the samples with the applied intermediate Au layer. The SEM/EDX analyses showed the presence of Ti and residual amounts of Si and Al, which suggests that the failure of the bond was adhesive [16, 30÷32].
Fig. 5. SEM/EDX microstructure and chemical composition analysis of Ti/GC Initial porcelain surface after three-point bending test
Fig. 6. SEM/EDX microstructure and chemical composition analysis of Ti/Au layer/GC Initial porcelain surface after three-point bending test
Fig. 7. SEM/EDX microstructure and chemical composition of Ti/ Duceratin porcelain surface after three-point bending test
Fig. 8. SEM/EDX microstructure and chemical composition of Ti/Au layer/Duceratin porcelain surface after three-point bending test
Summary The paper presents a method to improve the dental porcelain and titanium substrate bond strength. The proposed method is a combination of surface activation (sandblasting with Al2O3) with a thin Au layer sprayed on the titanium surface before sintering the porcelain.
Based on the results of Raman spectroscopy, it was found that titanium undergoes oxidation during firing of the porcelain layers, the effect of which is unfavorable as it can cause the formation of too thick an oxide layer and greatly reduce the titanium-porcelain bond strength. In this work it is shown that an intermediate Au layer sprayed on the Ti substrate greatly inhibits its oxidation and improves the bond strength of the titanium–dental porcelain system. It was also shown that a thin layer of gold ( diffusion zone, Fig. 4) applied as an interface in the titanium–porcelain system, significantly increases the bond strength from 28.02 MPa to 34.65 MPa for GC Initial porcelain and with 25.67 MPa up to 40.18 MPa for Duceratin porcelain. References [1] M. Rack, H.J.; Qazi, J.J. Titanium alloys for biomedical applications. Mater. Sci. Eng. C 2006, 26, 1269–1277 [2] B. Walkowiak: Biomedyczne skutki kontaktu tkanki z implantem. Inżynieria Biomateriałów, 38–43, 2004, 200–205 [3] X. Liu†, S. Chen†, J. K.H. Tsoi,J. P. Matinlinna, Binary titanium alloys as dental implant materials— a review, Regenerative Biomaterials, 2017, p. 315–323 [4] S. Zinelis, A. Tsetsekou, T. Papadopoulos, Thermal expansion and microstructural analysis of experimental metalceramic titanium alloys, The Journal of Prosthetic Dentistry, Vol. 90, No 4, p. 332338, 2003 [5] B. Surowska: Biomateriały metalowe oraz połączenia metal-ceramika stomatologicznych. Wyd. Politechniki Lubelskiej, 2009
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[6] H. Akin, F. Tugut, S. Topcuoglu, O. Kirmali: Effects of sandblasting and laser irradiation on shear Bond strength of low-fusing porcelain to titanium. J Adhes Dent, 15, 2013, 55-63 [7] M. Hajduga, D. Danel: Charakter połączenia faz metal – ceramika w obecności opakera. „Aktualne Problemy Biomechaniki”, 2010 [8] A. I. Moldi, K. S. Bhandari, S. Nagral,1 S. Deshpandey, P.Kulkarni, Effect of sandblasting on fracture load of titanium ceramic crowns, J. Indian Prosthodont, Soc. 15 (3), 2015, 224-228 [9] J. Jasinski, M. Lubas, J.J. Jasinski, P. Wieczorek, Titanium oxidation effects after various surface modyfication methods, Engineering of Biomaterials, No 120 , 2013, p. 41-47 [10] MG Jr Troia, GE Henriques, MF Mesquita, et al: The effect of surface modifications on titanium to enable titanium-porcelain bonding. Dent Mater, 24, 2008, 28-33 [11] ¨O.˙Inan, A. Acar, S. Halkacı: Effects of sandblasting and electrical discharge machining on porcelain adherence to cast and machined commercially pure titanium. J Biomed Mater Res B 2006;78:393-400 [12] Che-Shun Wang, Ker-Kong C Hen, K. Tajima, Y. Nagamatsu, H. Kakigawa, Y. Kozono, Effects of sandblasting media and steam cleaning on Bond strength of titanium-porcelain, Dental Materials Journal, Vol. 29 (4) , 2010, p. 381-391 [13] EN ISO 9693:2012, Dentistry Compatibility testing, Part 1, Metal-ceramic system, Geneva, 2012 [14] I. Hussaini, KA. Wazzan: Effect of surface treatment on Bond strength of low-fusing porcelain to commercially pure titanium. J Prosthet Dent, 94, 2005, p. 350-356
[15] S. Zhog, Y. Wang, FM. Zhang, et al: Effect of silicon coating on bonding strength of ceramics and titanium, 27, 2009, p. 276-279 [16] Mau-Chin Lin, Her-Hsiung Huang, Improvement in Dental Porcelain Bonding to Milled, Noncast Titanium Surfaces by Gold Sputter Coating, Journal of Prosthodontics 23, 2014, p. 540–548 [17] HJ. Almilhatti, KH. Neppelenbroek, CE. Vergani, AL. Machado, AC. Pavarina, ET. Giampaolo: Adhesive bonding of resin composite to various titanium surfaces using different metal conditioners and a surface modification system. J Appl Oral Sci 2013; 21: 5906 [18] M. Lubas, J.J. Jasinski, P. Jelen, M. Sitarz, Effect of ZrO2 sol-gel coating on the Ti 99.2 porcelain Bond strength investigated with mechanical testing and Raman spectroscopy, J. of Mol. Struc., 1168, 2018, p. 316-321 [19] SSH. Shayegh, P. Amini, K. Yaghmai, F. Massoumi, K. Abbasi: Comparison of the Effect of Three methods of Porcelain Surface Treatment on Shear Bond Strength of Composite to Porcelain. J Islam Dent Assoc Iran, 28, 2016, p. 72-77 [20] B. Dündar Yılmaz, A. Meşe, E. Kaya, The Comparison of Different Surface Preparation Methods in Terms of Shear Bond Strength of Tri-ceram Porcelain titanium Alloy, Meandros Med Dent J, 20, 2019, 137-143 [21] Technical Manual GC Initial Ti – November 2018 [22] Duceratin Kiss – instructions for use – multilingual [23] M. Walczak: Wpływ wybranych zabiegów technologicznych na trwałość użytkową układów metal – ceramika stosowanych w protetyce stomatologicznej. Wyd. Politechniki Lubelskiej, Lublin, 2014 [24] T. Egoshi, Y. Taira, K. Soeno, T. Sawase: Effects of sandblasting, H2SO4/HCl etching, and phosphate primer application on bond strength of veneering resin composite to commercially pure titanium grade 4. Dent Mater J, 32, 2013; 219-27 [25] RR. Wang, KK. Fung: Oxidation behavior of surface-modified titanium for titaniumceramic restorations. J Prosthet Dent , 77, 1997, 423-434 [26] Y.S. Al Jabbari, X. Barbagadaki, K.A. Al. Wazzan, et all, Shear bond strength and characterization of interfaces between electroformed gold substrates and porcelain, Materials Chemistry and Physics, 137, 2013, 825-833 [27] J. Howe, Bonding, structure, and properties of metal/ceramic interface: part 1chemical, bonding, chemical reaction, and interfacial structure, Int. Mater. Rev., 38, 1993, 233 [28] Y. Tanaka, I. Watanabe, T. Okabe: Cross-sectional TEM analysis of porcelain fused to goldcoated titanium. Dent Mater J 2007;26:84-88 [29] A. Katz, S. Nakahara, M. Geva, In situ stress measurements of gold films on glass substrates during thermal cycling, J. Appl. Phys. 70, 1991, 7342 [30] E. Miura, T. Tabaru, J. Liu, et al: Effect of gold coating on interfacial reaction between dental porcelain and titanium. Mater Trans 2004;10:3044-3049 [31] S. Zinelis, X. Barmpagadaki, V. Vergos, M. Chakmakchi, G. Eliade: Bond strength and interfacial characterization of eight low fusing porcelains to cp Ti, Dental Materials, 26 (3), 2010, 264-273 [32] SY. Sung, YJ. Kim: Alpha-case formation mechanism on titanium investment castings. Mater Sci Eng A 2005;405:173-177
Au interface effect on Ti–dental porcelain bondstrength investigated by spectroscopic method and mechanical tests MalgorzataLubas, Czestochowa University of Technology, Department of Materials Engineering,19 Armii Krajowej Ave., 42-200 Czestochowa, [email protected]
Highlights:
- Investigated the influence of an Au interlayer on the Ti–porcelain bond strength. - Intermediate Au layer sprayed on the Ti substrate inhibits oxidation titanium. - The applied Au layer for Ti substrate improves the effects of porcelain adhesion
S0022-2860(20)30194-0
DOI:
https://doi.org/10.1016/j.molstruc.2020.127870
Reference:
MOLSTR 127870
To appear in:
Journal of Molecular Structure
Received Date: 20 December 2019 Revised Date:
3 February 2020
Accepted Date: 6 February 2020
Please cite this article as: M. Lubas, Au interface effect on Ti-dental porcelain bond strength investigated by spectroscopic methods and mechanical tests, Journal of Molecular Structure (2020), doi: https:// doi.org/10.1016/j.molstruc.2020.127870. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.
The article has one author. To the author include: the concept, methodology and discussion of the results.
Au interface effect on Ti-dental porcelain bond strength investigated by spectroscopic methods and mechanical tests Malgorzata Lubas Czestochowa University of Technology, Department of Materials Engineering, 19 Armii Krajowej Ave., 42-200 Czestochowa, [email protected]
Abstract The article presents the results of the titanium 99.2/ceramic system interface bond strength investigated by mechanical tests and Raman spectroscopy. The titanium substrate was activated with sandblasting (Al2O3), an Au interlayer and finally covered with low fusing porcelain (GC Initial, Duceratin). In order to investigate the effects of the Au layer on the interface bond strength, mechanical testing (three-point bending) was conducted. Surface characterizations of the specimens were carried out with scanning electron microscopy (SEM/EDX) and spectroscopic (RS) study. The applied Au interface layer for substrate preparation improves the effects of porcelain adhesion to Ti 99.2, which was confirmed by bond strength improvement in the area of the titanium/bioceramic interface. The results indicated that the bond strengths of all the Ti/porcelain systems were greater than the minimal requirement (25 MPa) of ISO 9696. Surface activation with sandblasting and gold sputtering treatment of the Ti surfaces prior to porcelain sintering significantly strengthens the bond between the metal (Ti 99.2) and the dental porcelain.
Keywords: surface preparation, Au interlayer, titanium 99.2, bond strength, dental porcelain
Introduction A range of metallic and ceramic materials is used in dental prosthetics, which must work together long-term and fulfill specific functions. Dental prosthetics is a field in which many factors influence the satisfactory end result. Titanium is one of the most commonly used metal biomaterials in dentistry in the last few years. It gained its popularity due to its physical and chemical properties. It is characterized by excellent quality, high corrosion resistance and good mechanical properties [1 - 3]. Dental ceramics with a metal foundation are joined by physical, mechanical and chemical bonds. For a proper physical bond, it is necessary to choose the appropriate thermal expansion coefficients (WRC) for both materials to be joined. This is due to the formation of
compressive stresses during the ceramics firing process. The ceramics should have a lower WRC value than the metal, which is associated with an increase in strength that is responsible for adhering to the porcelain substrate when the ceramics is cooling down [4,5]. For mechanical bonds, proper preparation of the metal substrate is of great importance. Creating recesses on the substrate surface causes retention and micro retention, thanks to which the contact surface of the ceramic mass on the substrate is increased [6,7]. The most popular mechanical treatment improving the metal-ceramic bond is sandblasting using alumina with the appropriate grain size, pressure and angle of inclination of the sample. Properly selected parameters of this treatment allow micro retention to
be obtained.
Parameters such as sand thickness and pressure must be taken into account [8 - 12]. However, the obtained bond strength values do not always meet the requirements of industrial standards [13]. Studies on titanium surface modification are carried out on a large scale in order to improve the quality and bond strength of the metal-dental porcelain system, which do not explain in detail the bond formation mechanism [14 - 20]. The work investigates the influence of the intermediate gold layer on the strength of the titanium-porcelain bond in prosthetic applications. Tests were carried out using technically pure titanium 99.2 (Grade 2), sandblasted with Al2O3, on the surface of which an intermediate Au layer was sprayed and then the appropriate layers of dental ceramics (bond, opaque, dentine) were fired.
Research materials and methods The influence of the intermediate layer of Au on the strength of the titanium-dental porcelain bond was determined. Technically pure titanium (Ti 99.2) was used as the substrate. Titanium samples were prepared in accordance with ISO 9693 in the form of plates with dimensions of 25 (± 1) mm x 3 (± 1) mm x 0.5 (± 1 mm) [13]. The substrates were prepared by sandblasting with 110 µm alumina particles at 3 bar pressure for a time not exceeding 15 seconds. The samples were sandblasted at the angle of 45° and with the distance from the nozzle of 7 mm. Next the samples were cleaned in an ultrasonic cleaner for 5 minutes and divided into two groups: Ti/Al2O3/porcelain – control samples (20 pcs) and Ti/Al2O3/Au/porcelain – samples with an intermediate Au layer (20 pcs). These samples were sputtered with pure Au in an ion sputtering device (E-1010; Hitachi, Tokyo, Japan) at 15 mA for 60 seconds. In the next stage, low-melting porcelain from GC Initial and Duceratin were applied to the titanium surfaces in accordance with ISO 9693. The parameters and stages realized for surface activation treatment of the Ti samples and their results are presented in Table 1 and Figure 1. Table 1. Surface activation treatment stages conducted for titanium surface preparation
Samples Ti/Al2O3/porcelain
Surface treatment stage 1. Sandblasting Al2O3 with 110 µm particles 2. Ultrasonic cleaning in distilled water for 5 minutes 3. Firing porcelain layers (bond, opaque, dentin) 3a. GC Initial 3b. Duceratin Ti//Al2O3/Au/porcelain 1. Sandblasting Al2O3 with 110 µm particles 2. Ultrasonic cleaning in distilled water for 5 minutes 3. Gold sputter coating for 60 sec. At 15 mA 4. Firing porcelain layers (bond, opaque, dentin) 4a. GC Initial 4b. Duceratin
Fig. 1. SEM/EDX micrographs and analysis of titanium surface: a) after sandblasting, b) after sandblasting and Au interface spraying, c) after sandblasting, Au interlayer and application of subsequent porcelain layers (bond-opaque-dentin)
The porcelains were fired according to the manufacturers' requirements (Table 2) and their total thickness was about 1.1 mm (bond-opaque-dentine). Table 2. Low-melting GC Initial and Duceratin porcelain firing parameters [21,22] Parametry wypalania porcelany niskotopliwej GC Initial oraz Duceratin [21,22] Firing parameters Porcelain GC Initial Type of
Heating
Drying and
Increase
Firing
Drying
layer
temperature,
heating time,
temperature,
temperature,°C
time, min
Vacuum, hPa
°C
min
°C/min
bond
450
4:00
55
810
1:00
50
opaque
450
4:00
55
810
1:00
50
dentin
400
6:00
45
780
1:00
50
Porcelain Duceratin bond
600
6:00
100
750
1:00
50
opaque
450
10:00
100
760
0:30
50
dentin
450
9:00
55
760
1:00
50
Bond strength tests were performed using a universal Zwick Z100 strength testing machine with equipment set according to the requirements of ISO 9693 [13]. During the three-point bending tests, the porcelain side of the sample was placed faced down and the load was increased at a rate of 1.5 mm/min. The load as a result of which the Ti/porcelain bond was broken at one end of the sample was considered a destructive force. The titanium-porcelain bond strength with and without an intermediate layer was calculated based on the following relationship: τ = F ⋅ k, where: F – destructive force, k = f (dM), [13].
The study characterizes the surface of titanium samples after surface modification processes and bending tests. The basic roughness parameters of the titanium substrate after the sandblasting process and application of the Au layer were determined using a Hommel Tester T1000 profilometer. The microstructure and chemical composition of the surface of the samples after bending tests were determined by SEM/EDX (scanning electron microscope JOEL JSM-6610LV). Spectroscopic tests, aimed at determining the resistance of the titanium substrate to oxidation during the firing of subsequent porcelain layers were performed using Raman spectroscopy (RS Witec Alpha 300M + spectroscope with 488 nm laser and 600 gr/mm grid). Results and discussion
The results of the roughness measurements (Ra and Rz parameters), both for the surfaces of the pure titanium (99.2), titanium after the sandblasting process (Al2O3 - 110 µm) and titanium with an Au interlayer are presented in Table 3.
Table 3. Results of roughness measurements (Ra and Rz parameters) Sample
Ra, µm
Rz, µm
Titanium, 99.2
0.43 ±0.02
3.01 ±0.03
Titanium after sandblasting Al2O3
1.26 ±0.03
8.87 ±0,02
Titanium after sandblasting and Au layer
1.12 ±0.02
8.36 ±0.03
Analyzing the results, it was found that the values of the Ra and Rz parameters differ depending on the treatment used. The lowest Ra and Rz values were exhibited by the samples of technically pure titanium (99.2), and the highest by the samples after the sandblasting process. In the literature describing the impact of machining on the strength of the metal-dental porcelain bond, it was found that in adequate metal surface roughness in this system is one of the main factors leading to the uneven application of ceramic masses. As a result, this leads to the formation of voids, which can cause blistering during porcelain firing and weakening of the metal-ceramic bond [23, 24]. The gold layer used on the sandblasted titanium substrate reduces the roughness from Ra = 1.26µm to Ra = 1.12µm. Thus, it increases the contact surface of the veneering ceramic mass on the foundation and guarantees a better, more even application of the porcelain layers. The results of spectroscopy studies on the titanium-porcelain cross-section showed the presence of a TiO2 oxide layer for the samples without the intermediate Au layer (Fig. 2). It should be noted that the tested samples were not subjected to the oxidation process before applying the porcelain layers. The obtained results confirm that titanium oxidizes when applying and firing subsequent layers of porcelain. Similar conclusions were made in [25.26]. The obtained results confirm the share of two oxide varieties - rutile and anatase. No oxide layers were observed in the samples with the sprayed intermediate layer of gold (Fig. 3). The gold layer therefore affects the oxidation of titanium when firing subsequent layers of porcelain. The research shows that a very thin layer of gold (Fig. 3,4) inhibits the oxidation of titanium surfaces.
Fig. 2. Raman spectra of Ti/Al2O3/Duceratin porcelain system
Fig. 3. Raman spectra of Ti/Al2O3/Au interlayer/Duceratin porcelain system interface
Fig. 4. Cross section of titanium/Au/porcelain system, SEM/EDX
Based on the literature data, it is known that an excessively thick oxide layer, above 10 µm, formed on the surface of titanium at the sintering temperature of porcelain, is porous and does not adhere well to titanium. Damage to the titanium-porcelain bond occurs most often in the oxide layer [25 - 28]. The spectroscopic research shows that a very thin layer of gold in the metal-ceramic system is a factor that blocks the growth of the oxide layer that can contribute to improvement of the titanium-porcelain bond, as a result of mutual interdiffusion of the gold and dental porcelain components. A. Katz and S. Nakahara suggest bonding between Au and Si as early as 370°C, which improves the metal-gold-porcelain bond compared to the metal-porcelain system [29]. The results of the mechanical tests (three-point bending) of the titanium-intermediate gold layer-porcelain bond (Table 4) correlate with the obtained results of the spectroscopic tests. All the samples obtained values above 25 MPa and met the requirements of EN ISO 9693:2012. The samples with the intermediate layer of gold for Duceratin porcelain obtained almost 1.5 times higher flexural strength (25 MPa without Au and 40 MPa with Au). For the titanium samples with GC Inital porcelain, a slightly smaller difference was obtained between the samples subjected to traditional sandblasting (24 MPa) and with the layer of gold (34 MPa). Table. 4. Results of bond strength of Ti/porcelain samples after three-point bending mechanical tests
Lp.
1. 2.
Variant of titanium surface treatment Ti 99.2
Bond strength, τ [MPa]
Standard deviation
GC Initial
Duceratin
GC Initial
Duceratin
Ti/Al2O3/Porcelain
28.02±6
25.67±7
2.61
1.80
Ti/Al2O3/Au/Porcelain
34.65±5
40.18±6
1.84
1.61
The morphology studies and chemical composition of SEM/EDS after the bending tests for both series of samples with layers of GC Initial dental porcelain showed the presence of so called "craters" – areas after detachment of porcelain from the titanium substrate. The results of the SEM/EDX analysis also showed the presence of: La, B, Ce, Sn, Si, Al, Na and Ti for the samples without the gold layer (Fig. 5). For the samples with the Au layer, the presence of titanium was not observed, which indicates that is bonding of the system occurred only on the porcelain side, which adheres very well to titanium (Fig. 6). Based on the obtained results, it can be concluded that the Au layer significantly improves porcelain adhesion to titanium. In the case of Duceratin porcelain, the surface after the bending tests is fairly uniform, smooth with no clear residue of the ceramic layers (Fig.8), both for the sandblasted samples and the samples with the applied intermediate Au layer. The SEM/EDX analyses showed the presence of Ti and residual amounts of Si and Al, which suggests that the failure of the bond was adhesive [16, 30÷32].
Fig. 5. SEM/EDX microstructure and chemical composition analysis of Ti/GC Initial porcelain surface after three-point bending test
Fig. 6. SEM/EDX microstructure and chemical composition analysis of Ti/Au layer/GC Initial porcelain surface after three-point bending test
Fig. 7. SEM/EDX microstructure and chemical composition of Ti/ Duceratin porcelain surface after three-point bending test
Fig. 8. SEM/EDX microstructure and chemical composition of Ti/Au layer/Duceratin porcelain surface after three-point bending test
Summary The paper presents a method to improve the dental porcelain and titanium substrate bond strength. The proposed method is a combination of surface activation (sandblasting with Al2O3) with a thin Au layer sprayed on the titanium surface before sintering the porcelain.
Based on the results of Raman spectroscopy, it was found that titanium undergoes oxidation during firing of the porcelain layers, the effect of which is unfavorable as it can cause the formation of too thick an oxide layer and greatly reduce the titanium-porcelain bond strength. In this work it is shown that an intermediate Au layer sprayed on the Ti substrate greatly inhibits its oxidation and improves the bond strength of the titanium–dental porcelain system. It was also shown that a thin layer of gold ( diffusion zone, Fig. 4) applied as an interface in the titanium–porcelain system, significantly increases the bond strength from 28.02 MPa to 34.65 MPa for GC Initial porcelain and with 25.67 MPa up to 40.18 MPa for Duceratin porcelain. References [1] M. Rack, H.J.; Qazi, J.J. Titanium alloys for biomedical applications. Mater. Sci. Eng. C 2006, 26, 1269–1277 [2] B. Walkowiak: Biomedyczne skutki kontaktu tkanki z implantem. Inżynieria Biomateriałów, 38–43, 2004, 200–205 [3] X. Liu†, S. Chen†, J. K.H. Tsoi,J. P. Matinlinna, Binary titanium alloys as dental implant materials— a review, Regenerative Biomaterials, 2017, p. 315–323 [4] S. Zinelis, A. Tsetsekou, T. Papadopoulos, Thermal expansion and microstructural analysis of experimental metalceramic titanium alloys, The Journal of Prosthetic Dentistry, Vol. 90, No 4, p. 332338, 2003 [5] B. Surowska: Biomateriały metalowe oraz połączenia metal-ceramika stomatologicznych. Wyd. Politechniki Lubelskiej, 2009
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Au interface effect on Ti–dental porcelain bondstrength investigated by spectroscopic method and mechanical tests MalgorzataLubas, Czestochowa University of Technology, Department of Materials Engineering,19 Armii Krajowej Ave., 42-200 Czestochowa, [email protected]
Highlights:
- Investigated the influence of an Au interlayer on the Ti–porcelain bond strength. - Intermediate Au layer sprayed on the Ti substrate inhibits oxidation titanium. - The applied Au layer for Ti substrate improves the effects of porcelain adhesion