- Email: [email protected]
Effect of incorporating BisGMA resin on the bonding properties of silane and zirconia primers
Effect of incorporating BisGMA resin on the bonding properties of silane and zirconia primers Liang Chen, PhD,a Hong Shen, PhD,b and Byoung In Suh, PhDc Bisco, Schaumburg, Ill Statement of problem. Some silane primers and some zirconia primers contain extra resins such as bisphenol A glycol dimethacrylate (BisGMA) in their formulations for better wetting. No studies exist on the bonding properties of zirconia and silane primers, which contain extra resins. Purpose. The purpose of this study was to investigate the effect of incorporating BisGMA resin on the bonding properties of silane and zirconia primers. Material and methods. Silica-base lithium disilicate was etched and treated with BisGMA-incorporated Porcelain Primer, unmodified Porcelain Primer, or resin-containing Kerr Silane. Zirconia ceramic was airborne-particle abraded and treated with BisGMA-incorporated Monobond Plus, unmodified Monobond Plus, or BisGMA-containing ZPrime Plus. After primer treatment and cleaning with ethanol, the contact angles were measured to determine surface change (n¼10). Shear bond strength tests were also performed to measure the adhesion strength between resin cements and ceramic surfaces (n¼10). Data were statistically analyzed by 1-way ANOVA followed by the Tukey multiple comparison as a post hoc test (significance level .05). Results. The incorporation of BisGMA resin did not significantly influence the bond strength or contact angle of the zirconia primer (P>.05), but it did significantly reduce those of the silane primer (P<.05). Resin-containing Kerr Silane (22 degrees, 23 MPa) had a similar contact angle and higher bond strength than the control (21 degrees, 18 MPa), but lower than Porcelain Primer (88 degrees, 34 MPa). Resin-containing ZPrime Plus (75 degrees, 29 MPa) had a similar contact angle and higher bond strength than both Monobond Plus (74 degrees, 18 MPa) and the control (15 degrees, 4 MPa). Conclusions. The addition of BisGMA resin significantly inhibited the efficacy of silane-containing porcelain primers but did not affect that of phosphate-containing zirconia primers. (J Prosthet Dent 2013;110:402-407)
Clinical Implications The incorporation of extra resin reduced the priming efficacy of silane primers on silica-based ceramics but did not significantly influence that of phosphate-based zirconia primers on zirconia ceramics. BisGMAresin-containing ZPrime Plus showed a high priming efficacy on zirconia, whereas resin-containing Kerr Silane had almost no effect on lithium disilicate priming. Many factors (such as saliva contamination, adhesion between teeth, and cements) might affect bonding in clinical situations.
Interest in the use of ceramic materials has increased because of their nonmetallic nature, improved esthetics, and biocompatible features.1,2 Two types of ceramic core materials are available: silica-based glass ceramics1
such as lithium disilicate, feldspathic porcelain, and leucite; and silica-free high-strength ceramics such as zirconia and alumina.2 A strong and durable resin/ceramic bond improves marginal adaption and
retention rate.3 For silica-based ceramics, surface roughening with hydrofluoric acid etching (mechanical bonding) followed by silane priming (formation of chemical bond Si-O-Si by means of condensation reaction) is well
a
Chief Scientist, Department of Research and Development. Scientist, Department of Research and Development. c President. b
The Journal of Prosthetic Dentistry
Chen et al
November 2013
403
understood and is considered reliable.3-5 However, this traditional technique is not effective for zirconia. In the past several years, zirconia primers containing phosphate monomers, such as 10-methacryloyloxydecyl dihydrogen phosphate (MDP), have been developed and shown to improve resin/ zirconia bond strength.4,6-9 A study using secondary ion mass spectrometry (SIMS) indicated a chemical bond (ZrO-P) formation between zirconia ceramics and an MDP-containing zirconia primer.6 Other studies showed the surface treatment combining airborne-particle abrasion and phosphate monomer-containing primers improved the durability of resin/zirconia bond strength.10,11 The application of an additional bonding resin layer on primer-treated restoration surfaces improves the adaptation12 and bond strength13-15 of resin cements to the surface of the indirect restoration. The increase in bond strength is thought to be due to the better wetting of the low-viscosity bonding resin, which allows the resin cement to spread in a more uniform layer.13 In recent years, manufacturers have developed several commercial zirconia or silane primers (Kerr Silane, Kerr Corp ZPrime Plus, Bisco; Table I), which contain extra resin such as BisGMA in order to eliminate the additional step of applying a bonding resin layer. However, little information is available about the bonding properties (such as bond strength and contact angle) of the primers that contain an extra resin.
Table I.
The purpose of this study was to evaluate the bond strengths and contact angles of zirconia and silane primers with and without BisGMA resin. The null hypothesis tested was that the incorporation of BisGMA resin would not change the bond strengths or contact angles of silane or zirconia primers.
MATERIAL AND METHODS All materials were used according to the manufacturers’ instructions. Porcelain Primer and Monobond Plus were modified by adding 10 wt% of BisGMA resin (bisphenol A diglycidyl methacrylate). Other silane primers and zirconia primers tested are described in Table I. Zirconia disks (97% zirconia stabilized with 3% yttrium, Cercon; Dentsply Intl) and lithium disilicate (IPS e.max; Ivoclar Vivadent) cylinders were polished with 320-grit silicon carbide paper for 15 seconds in a figure-8 pattern under water cooling and manual pressure. The polished zirconia specimens were treated with airborne-particle abrasion (0.3 MPa, 5 s/50 mm2) with alumina particle (50 mm), and lithium disilicate specimens were etched with 4% HF Porcelain Etchant (Bisco) for 25 seconds. They were rinsed with water and dried before the shear bond strength and contact angles were measured. The shear bond strength on the ceramic surface was tested by using a special device6 with a bonding area 4.5 mm2 (Ultradent). According to the manufacturers’ instructions, the lithium
Compositions of ceramic primers used in bond strength and contact
angle tests
Primer Porcelain Primer Porcelain Primer-BisGMA
Major Components Silane
Batch No. (Manufacturer) 1100006537 (Bisco)
Silane, BisGMA
NB711180b (Bisco)
Silane, Resin
3409037 (Kerr Corp)
MDP
N75725 (Ivoclar Vivadent)
Monobond Plus-BisGMA
MDP, BisGMA
NB711180a (Bisco)
ZPrime Plus
MDP, BisGMA
1200006916 (Bisco)
Kerr Silane Monobond Plus
Silane, 3-methacryloxypropyltrimethoxysilane; BisGMA. bisphenol A diglycidyl methacrylate; MDP, 10-methacryloyloxydecyl dihydrogen phosphate. Composition information was provided by manufacturers.
Chen et al
disilicate specimens were treated with a silane primer and the zirconia specimens with a zirconia primer. In the control group, no surface chemical treatment was performed. The silane primer included Porcelain Primer or BisGMAModified Porcelain Primer (surfaces were coated with 1 application with a microbrush, allowed to stand for 30 seconds, and then lightly air dried for 5 seconds) and Kerr Silane (Kerr Corp) (surfaces were coated with 1 application with a microbrush, allowed to stand for 60 seconds, then lightly air dried for 5 seconds). Zirconia ceramics were treated with a zirconia primer. In the control group, no surface chemical treatment was performed. The zirconia primer included Monobond Plus or BisGMAModified Monobond Plus (surfaces were coated with 1 application with a microbrush, allowed to stand for 60 seconds, then lightly air dried for 5 seconds) and ZPrime Plus (surfaces were coated with 1 application with a microbrush and lightly air dried for 5 seconds). A resin composite cement (Duolink, Bisco) was then used to fabricate the posts (2 mm high) with the Ultradent device mold and light polymerized from the top for 40 seconds with an output of 500 mW/cm2 of a halogen polymerization light (wavelength 400 to 500 nm; VIP Junior Dental Curing Light; Bisco). The mold was then removed and the polymerized specimens were stored in deionized water at 37 C. After 24 hours’ storage, the specimens were stressed to failure in a universal testing machine (model 4466; Instron) with a crosshead speed of 1 mm/min. The data (in kgf) were then converted to bond strength (in MPa) (n¼10 each group). The failure modes of the bond were analyzed visually at 80 with a stereomicroscope (SZX10; Olympus Corp) (n¼10 each group). Failure modes were classified as adhesive failure between ceramic and resin cement, mixed failure, and cohesive failure within resin cement. The difference in primed ceramic surfaces was determined by measuring the contact angle (a higher contact angle value indicates a more hydrophobic
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Table II.
RESULTS
Shear bond strength (in MPa) on primed ceramic surface
Silane Primer
Lithium Disilicate
Zirconia Primer
Zirconia
Control (no primer)
18.0 (4.2)
c;3
Control (no primer)
4.2 (2.9)
C;3
Porcelain Primer
34.3 (7.6)
a;1
Monobond Plus
18.2 (5.0)
B;2
BisGMA-Modified Porcelain Primer
27.8 (6.1)
b;1,2
BisGMA-Modified Monobond Plus
22.0 (6.0)
B;2
Kerr Silane
23.1 (5.6)
b;2
ZPrime Plus
29.0 (6.3)
A;1
Data are presented as mean (standard deviation). Means followed by a different letter in same column are statistically different (P<.05). Logarithm-transformed shear bond strength data were also subjected to statistical analysis. Means of logarithm-transformed data followed by different number in same column are statistically different (P<.05).
Table III.
Mode of failure presented by lithium disilicate and zirconia specimens
Lithium Disilicate (AF/MF/CF)
Zirconia Primer
Control (no primer)
6/4/0
Control (no primer)
10/0/0
Porcelain Primer
3/6/1
Monobond Plus
5/4/1
BisGMA-Modified Porcelain Primer
5/5/0
BisGMA-Modified Monobond Plus
5/5/0
Kerr Silane
5/5/0
ZPrime Plus
2/7/1
Silane Primer
Zirconia (AF/ MF/CF)
AF, adhesive failure at cement/lithium disilicate interface; CF, cohesive failure within cement; MF, mixed failure.
Table IV.
Contact angle (degrees) on primed ceramic surface
Silane Primer
Lithium Disilicate
Zirconia Primer
Zirconia
Control (no primer)
20.9 (6.8)
c
Control (no primer)
15.1 (4.0)
B
Porcelain Primer
88.3 (9.5)
a
Monobond Plus
74.1 (6.7)
A
BisGMA-Modified Porcelain Primer
32.9 (8.1)
b
BisGMA-Modified Monobond Plus
71.7 (3.8)
A
Kerr Silane
22.5 (7.4)
c
ZPrime Plus
75.0 (6.1)
A
Data are presented as mean (standard deviation). Means followed by different letter in same column are statistically different (P<.05).
surface). Before contact angle measurement, airborne-particle-abraded zirconia was treated with a zirconia primer (Monobond Plus, BisGMA-Modified Monobond Plus or ZPrime Plus), and etched lithium disilicate specimens were treated with a silane primer (Porcelain Primer, BisGMA-Modified Porcelain Primer, or Kerr Silane). Control groups were not treated. After 5 minutes, ceramic specimens were ultrasonically cleaned in ethanol solvent for 2 minutes to remove any nonchemically
bonded compounds, rinsed with deionized water, and air dried. Contact angles were then measured by placing a deionized water droplet (40 mL) over the specimen surface with a goniometer (NRL Contact Angle Goniometer; Rame-Hart Inc) (n¼10 each group). Shear bond strength and contact angle data were statistically analyzed by 1-way ANOVA. The Tukey multiple comparison was used as a post hoc test. The level of significance was set at .05.
The Journal of Prosthetic Dentistry
Mean shear bond strength results are shown in Table II. In the lithium disilicate group, Porcelain Primer had significantly higher shear bond strength than BisGMA-Modified Porcelain Primer and Kerr Silane (P<.05), both of which had higher bond strength than the control (P<.05). In the zirconia group, ZPrime Plus had a higher bond strength than BisGMA-Modified and unmodified Monobond Plus (P<.05), both of which had higher bond strength than the control (P<.05). Failure modes are presented in Table III. In the lithium disilicate group, adhesive failures were observed more frequently for the control, Kerr Silane, and BisGMA-Modified Porcelain Primer than for unmodified Porcelain Primer. In the zirconia group, the control had 100% adhesive failure, and the other 3 groups had 20% to 50% adhesive failure. The results of contact angle measurements are presented in Table IV. In the lithium disilicate group, Porcelain Primer, which contains no BisGMA resin in its formulation, displayed a contact angle (88.3 degrees) significantly higher than the control (20.9 degrees) (P<.05). BisGMA-Modified Porcelain Primer showed a lower contact angle (32.9 degrees) than unmodified Porcelain Primer (P<.05). Resin-containing Kerr Silane had a similar contact angle as the control. In the zirconia group, both Monobond Plus (which contains no BisGMA resin) and ZPrime Plus (which contains BisGMA resin) demonstrated contact angle values higher than the control (P<.05). BisGMA-Modified Monobond Plus had a contact angle similar to the unmodified control (P¼.32). Singlefactor ANOVA analysis revealed a significant difference in mean contact angles and shear bond strengths in both the zirconia and lithium disilicate groups (Table V).
DISCUSSION This study evaluated the effect of incorporating BisGMA resin on the
Chen et al
November 2013
Table V.
405
Summary of serial 1-way ANOVAs
Source
Sum of Squares
df
Mean Square
F
P
1455
3
485
13.5
<.001
39.8
<.001
Silane primer bond strength Between groups Within groups
1293
36
Total
2748
39
3259
3
35.9
Zirconia primer bond strength Between groups Within groups Total
982
36
4241
39
1086 27.3
Silane primer contact angle Between groups Within groups Total
30447
3
10149
2305
36
64
32752
39
159
<.001
305
<.001
Zirconia primer contact angle Between groups Within groups Total
25721
3
1011
36
26732
39
bond strengths and contact angles of silane primers and zirconia primers (phosphate-monomer-based primers). The results indicated that the incorporation of 10 wt% BisGMA resin did not significantly influence the bond strength or contact angle of the zirconia primer, while it significantly reduced those of the silane primer. Therefore, the null hypothesis, which assumed the incorporation of BisGMA resin would not change bond strengths or contact angles of zirconia or silane primers, was partially rejected (Fig. 1). Measuring contact angle is a simple way to determine the hydrophilicity/hydrophobicity of a surface.16 The hydrophobic surface has a high water-contact angle, while a hydrophilic surface has a low water-contact angle. Dental adhesion usually involves strong bonding such as chemical bonds (or covalent bonds) and weak bonding such as electrostatic attraction or van der Waals forces.16 A simple evaluation of strong chemical bonds is an ultrasonic cleansing in organic solvents like ethanol, which would remove the weakly bound primers.6 The unremoved chemically bonded primers would convert
Chen et al
8574 28.1
hydrophilic (low contact angle) etched lithium disilicate or airborne-particleabraded zirconia surfaces into hydrophobic surfaces (high contact angle). As shown in the data, Porcelain Primer, a prehydrolyzed silane primer, displayed a much higher contact angle than that of unprimed etched lithium disilicate (control), suggesting a strong chemical attachment (bond) to lithium disilicate surfaces; this was confirmed by its high bond strength. The incorporation of BisGMA resin significantly reduced the contact angle and bond strength, suggesting that BisGMA resin inhibited the chemical reaction between the silane primer and the lithium disilicate ceramic. Kerr Silane, a resincontaining silane primer, displayed a contact angle similar to that of unprimed etched lithium disilicate (control), indicating that limited or no chemical bonding to the substrate surface is present. The low contact angle and bond strength values of Kerr Silane and BisGMA-Modified Porcelain Primer may be because the BisGMA resin inhibited the condensation reaction5 between the silanol (Si-OH) of the silane primer and the substrate (OH) of
the ceramic. The condensation reaction slowly liberates a water molecule to form a stable siloxane (Si-O-Si) bond.5 Because this reaction involves the liberation of water molecules, the reaction can be inhibited by extra resin, which slows down water evaporation (Le Chatelier principle).17 Kerr Silane had a significantly higher shear bond strength than the control, probably due to the wetting of its resin.13-15 The contact angle on the unprimed airborne-particle-abraded zirconia surface was low (15 degrees), representative of a hydrophilic surface. This finding is in agreement with the previously reported values (22 to 39 degrees).18,19 The application of Monobond Plus and BisGMA-containing ZPrime Plus followed by ultrasonic cleansing significantly increased the contact angle values, suggesting a strong chemical attachment of zirconia primers to zirconia surfaces. Incorporating BisGMA into Monobond Plus did not influence the contact angle. The results indicate that BisGMA resin did not inhibit the chemical reaction between zirconia primers (phosphate monomers) and zirconia ceramics. This is in sharp contrast to silane primers, suggesting that the mechanism of the zirconia primer reaction (formation of chemical bond -Zr-O-P-)6,19 is different from the condensation reaction of the silane primer. The bond strength data showed that incorporating BisGMA resin increased the bond strength of Monobond Plus (although not significantly), possibly due to the better wetting of extra BisGMA resin.13-15 The previous studies showed ZPrime Plus had a higher bond strength than other commercial zirconia primers such as Monobond Plus and Clearfil Ceramic Primer (Kuraray, Kurashiki).6-8 This was confirmed by the bond strength data in this study, which demonstrated that ZPrime Plus had a higher bond strength than either BisGMA-Modified or unmodified Monobond plus. The bond strength result was also supported by failure mode studies showing ZPrime Plus had fewer adhesive failures and more cohesive/ mixed failures than Monobond Plus. The
Volume 110 Issue 5 50
Zirconia Primer Bond Strength, MPa
Silane Primer Bond Strength, MPa
406
45 40 35
+
30
+
25
+
20
+
15 10 5 0
Porcelain P Porcelain P / Kerr Silane BisGMA
No Primer
40 35 30
20
+ 80 60 40
+
20 0
+
+
Porcelain P Porcelain P / Kerr Silane BisGMA
No Primer
C
Zirconia Primer Contact Angle, Degree
Silane Primer Contact Angle, Degree
100
+
+
15 10 5 0
A 120
+
25
+ Monobond Monobond Plus Plus / BisGMA
ZPRIME Plus
No Primer
B
100 90 80 70
+
+
+
60 50 40 30 20
+
10 0
Monobond Monobond Plus Plus / BisGMA
ZPRIME Plus
No Primer
D
1 Summary of box plots. A, Silane primer bond strength. B, Zirconia primer bond strength. C, Silane primer contact angle. D, Zirconia primer contact angle. Median (þ), 25% quartile (bottom line), 75% quartile (top line), maximum (plus error bar), and minimum (minus error bar). previous SEM studies confirmed that cohesive failures occurred when ZPrime Plus was used for resin-zirconia bonding.9 The higher bond strength of ZPrime Plus is attributed to its proprietary formula of both phosphate (MDP) and carboxylate monomers.6-8 Another possible reason is that ZPrime Plus contains extra BisGMA resin, which has better wetting to allow the resin cement to spread in a more uniform layer.13-15 This study evaluated the contact angle and short-term bond strength of silane and zirconia primers with and without the incorporation of BisGMA resin. Within the limited scope of the specimens evaluated here, the data suggest that the incorporation of BisGMA resin significantly inhibited the
efficacy of silane-containing porcelain primers, while it did not affect that of phosphate-containing zirconia primers. Future studies should explore long-term adhesion in more clinically relevant environments.
CONCLUSION This study analyzed the contact angle and shear bond strength of zirconia (phosphate-based) and silane primer with and without BisGMA resin. The results showed that incorporating BisGMA resin reduced the contact angle and bond strength values of silane primers, suggesting an inhibiting effect of BisGMA resin on silane primers. In contrast, incorporating BisGMA resin did not significantly influence the contact
The Journal of Prosthetic Dentistry
angles or bond strengths of zirconia (phosphate-based) primers, indicating BisGMA resin did not inhibit phosphatemonomer-containing zirconia primer.
REFERENCES 1. Conrad HJ, Seong WJ, Pesun IJ. Current ceramic materials and systems with clinical recommendations: a systematic review. J Prosthet Dent 2007;98:389-404. 2. Denry I, Kelly JR. State of the art of zirconia for dental applications. Dent Mater 2008;24: 299-307. 3. Blatz MB, Sadan A, Kern M. Resineceramic bonding: a review of the literature. J Prosthet Dent 2003;89:268-74. 4. Chen L, Suh BI. Bonding or resin materials to all-ceramics: a review. Curr Res Dent 2012;3: 7-17. 5. Lung CYK, Matinlinna JP. Aspects of silane coupling agents and surface conditioning in dentistry: an overview. Dent Mater 2012;28: 467-77.
Chen et al
November 2013 6. Chen L, Suh BI, Brown D, Chen X. Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths. Am J Dent 2012;25:103-8. 7. Magne P, Paranhos MP, Burnett LH. New zirconia primer improves bond strength of resinbased cements. Dent Mater 2010;26:345-52. 8. Piascik JR, Swift EJ, Braswell K, Stoner BR. Surface fluorination of zirconia: adhesive bond strength comparison to commercial primers. Dent Mater 2012;28:604-8. 9. Chen L, Suh BI, Kim J, Tay FR. Evaluation of silica-coating techniques for zirconia bonding. Am J Dent 2011;24:79-84. 10. Kern M, Barloi A, Yang B. Surface conditioning influences zirconia ceramic bonding. J Dent Res 2009;88:817-22. 11. Akgungor G, Sen D, Aydin M. Influence of different surface treatments on the shortterm bond strength and durability between a zirconia post and a composite resin core material. J Prosthet Dent 2008;99:388-99.
Chen et al
407 12. Stangel I, Nathanson D, Hsu CS. Shear strength of the composite bond to etched porcelain. J Dent Res 1987;66: 1460-5. 13. El Zohairy AA, De Gee AJ, Hassan FM, Feilzer AJ. The effect of adhesives with various degrees of hydrophilicity on resin ceramic bond durability. Dent Mater 2004;20:778-87. 14. Hisamatsu N, Atsuta M, Matsumura H. Effect of silane primers and unfilled resin bonding agents on repair bond strength of a prosthodontic microfilled composite. J Oral Rehabil 2002;29: 644-8. 15. Matsumura H, Hisamatsu N, Atsuta M. Effect of unfilled resins and a silane primer on bonding between layers of a light-activated composite resin veneering material. J Prosthet Dent 1995;73:386-91. 16. Marshall SJ, Bayne SC, Baier R, Tomsia AP, Marshall GW. A review of adhesion science. Dent Mater 2010;26:e11-6.
17. Callen HB. Thermodynamics. Hoboken, NJ: John Wiley & Sons; 1965. p. 135-205. 18. Shojai F, Pettersson A, Mäntylä TA, Rosenholm J. Detection of carbon residue on the surface of 3Y-ZrO2 powder and its effect on the rheology of the slip. Ceramics Int 2000;26:133-9. 19. Carrière D, Moreau M, Barboux P, Boilot JP. Modification of the surface properties of porous nanometric zirconia particles by covalent grafting. Langmuir 2004;20: 3449-55. Corresponding author: Dr Liang Chen Department of Research and Development Bisco, 1100 W Irving Park Rd Schaumburg, IL 60193 E-mail: [email protected] Copyright ª 2013 by the Editorial Council for The Journal of Prosthetic Dentistry.
Clinical Implications The incorporation of extra resin reduced the priming efficacy of silane primers on silica-based ceramics but did not significantly influence that of phosphate-based zirconia primers on zirconia ceramics. BisGMAresin-containing ZPrime Plus showed a high priming efficacy on zirconia, whereas resin-containing Kerr Silane had almost no effect on lithium disilicate priming. Many factors (such as saliva contamination, adhesion between teeth, and cements) might affect bonding in clinical situations.
Interest in the use of ceramic materials has increased because of their nonmetallic nature, improved esthetics, and biocompatible features.1,2 Two types of ceramic core materials are available: silica-based glass ceramics1
such as lithium disilicate, feldspathic porcelain, and leucite; and silica-free high-strength ceramics such as zirconia and alumina.2 A strong and durable resin/ceramic bond improves marginal adaption and
retention rate.3 For silica-based ceramics, surface roughening with hydrofluoric acid etching (mechanical bonding) followed by silane priming (formation of chemical bond Si-O-Si by means of condensation reaction) is well
a
Chief Scientist, Department of Research and Development. Scientist, Department of Research and Development. c President. b
The Journal of Prosthetic Dentistry
Chen et al
November 2013
403
understood and is considered reliable.3-5 However, this traditional technique is not effective for zirconia. In the past several years, zirconia primers containing phosphate monomers, such as 10-methacryloyloxydecyl dihydrogen phosphate (MDP), have been developed and shown to improve resin/ zirconia bond strength.4,6-9 A study using secondary ion mass spectrometry (SIMS) indicated a chemical bond (ZrO-P) formation between zirconia ceramics and an MDP-containing zirconia primer.6 Other studies showed the surface treatment combining airborne-particle abrasion and phosphate monomer-containing primers improved the durability of resin/zirconia bond strength.10,11 The application of an additional bonding resin layer on primer-treated restoration surfaces improves the adaptation12 and bond strength13-15 of resin cements to the surface of the indirect restoration. The increase in bond strength is thought to be due to the better wetting of the low-viscosity bonding resin, which allows the resin cement to spread in a more uniform layer.13 In recent years, manufacturers have developed several commercial zirconia or silane primers (Kerr Silane, Kerr Corp ZPrime Plus, Bisco; Table I), which contain extra resin such as BisGMA in order to eliminate the additional step of applying a bonding resin layer. However, little information is available about the bonding properties (such as bond strength and contact angle) of the primers that contain an extra resin.
Table I.
The purpose of this study was to evaluate the bond strengths and contact angles of zirconia and silane primers with and without BisGMA resin. The null hypothesis tested was that the incorporation of BisGMA resin would not change the bond strengths or contact angles of silane or zirconia primers.
MATERIAL AND METHODS All materials were used according to the manufacturers’ instructions. Porcelain Primer and Monobond Plus were modified by adding 10 wt% of BisGMA resin (bisphenol A diglycidyl methacrylate). Other silane primers and zirconia primers tested are described in Table I. Zirconia disks (97% zirconia stabilized with 3% yttrium, Cercon; Dentsply Intl) and lithium disilicate (IPS e.max; Ivoclar Vivadent) cylinders were polished with 320-grit silicon carbide paper for 15 seconds in a figure-8 pattern under water cooling and manual pressure. The polished zirconia specimens were treated with airborne-particle abrasion (0.3 MPa, 5 s/50 mm2) with alumina particle (50 mm), and lithium disilicate specimens were etched with 4% HF Porcelain Etchant (Bisco) for 25 seconds. They were rinsed with water and dried before the shear bond strength and contact angles were measured. The shear bond strength on the ceramic surface was tested by using a special device6 with a bonding area 4.5 mm2 (Ultradent). According to the manufacturers’ instructions, the lithium
Compositions of ceramic primers used in bond strength and contact
angle tests
Primer Porcelain Primer Porcelain Primer-BisGMA
Major Components Silane
Batch No. (Manufacturer) 1100006537 (Bisco)
Silane, BisGMA
NB711180b (Bisco)
Silane, Resin
3409037 (Kerr Corp)
MDP
N75725 (Ivoclar Vivadent)
Monobond Plus-BisGMA
MDP, BisGMA
NB711180a (Bisco)
ZPrime Plus
MDP, BisGMA
1200006916 (Bisco)
Kerr Silane Monobond Plus
Silane, 3-methacryloxypropyltrimethoxysilane; BisGMA. bisphenol A diglycidyl methacrylate; MDP, 10-methacryloyloxydecyl dihydrogen phosphate. Composition information was provided by manufacturers.
Chen et al
disilicate specimens were treated with a silane primer and the zirconia specimens with a zirconia primer. In the control group, no surface chemical treatment was performed. The silane primer included Porcelain Primer or BisGMAModified Porcelain Primer (surfaces were coated with 1 application with a microbrush, allowed to stand for 30 seconds, and then lightly air dried for 5 seconds) and Kerr Silane (Kerr Corp) (surfaces were coated with 1 application with a microbrush, allowed to stand for 60 seconds, then lightly air dried for 5 seconds). Zirconia ceramics were treated with a zirconia primer. In the control group, no surface chemical treatment was performed. The zirconia primer included Monobond Plus or BisGMAModified Monobond Plus (surfaces were coated with 1 application with a microbrush, allowed to stand for 60 seconds, then lightly air dried for 5 seconds) and ZPrime Plus (surfaces were coated with 1 application with a microbrush and lightly air dried for 5 seconds). A resin composite cement (Duolink, Bisco) was then used to fabricate the posts (2 mm high) with the Ultradent device mold and light polymerized from the top for 40 seconds with an output of 500 mW/cm2 of a halogen polymerization light (wavelength 400 to 500 nm; VIP Junior Dental Curing Light; Bisco). The mold was then removed and the polymerized specimens were stored in deionized water at 37 C. After 24 hours’ storage, the specimens were stressed to failure in a universal testing machine (model 4466; Instron) with a crosshead speed of 1 mm/min. The data (in kgf) were then converted to bond strength (in MPa) (n¼10 each group). The failure modes of the bond were analyzed visually at 80 with a stereomicroscope (SZX10; Olympus Corp) (n¼10 each group). Failure modes were classified as adhesive failure between ceramic and resin cement, mixed failure, and cohesive failure within resin cement. The difference in primed ceramic surfaces was determined by measuring the contact angle (a higher contact angle value indicates a more hydrophobic
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Volume 110 Issue 5
Table II.
RESULTS
Shear bond strength (in MPa) on primed ceramic surface
Silane Primer
Lithium Disilicate
Zirconia Primer
Zirconia
Control (no primer)
18.0 (4.2)
c;3
Control (no primer)
4.2 (2.9)
C;3
Porcelain Primer
34.3 (7.6)
a;1
Monobond Plus
18.2 (5.0)
B;2
BisGMA-Modified Porcelain Primer
27.8 (6.1)
b;1,2
BisGMA-Modified Monobond Plus
22.0 (6.0)
B;2
Kerr Silane
23.1 (5.6)
b;2
ZPrime Plus
29.0 (6.3)
A;1
Data are presented as mean (standard deviation). Means followed by a different letter in same column are statistically different (P<.05). Logarithm-transformed shear bond strength data were also subjected to statistical analysis. Means of logarithm-transformed data followed by different number in same column are statistically different (P<.05).
Table III.
Mode of failure presented by lithium disilicate and zirconia specimens
Lithium Disilicate (AF/MF/CF)
Zirconia Primer
Control (no primer)
6/4/0
Control (no primer)
10/0/0
Porcelain Primer
3/6/1
Monobond Plus
5/4/1
BisGMA-Modified Porcelain Primer
5/5/0
BisGMA-Modified Monobond Plus
5/5/0
Kerr Silane
5/5/0
ZPrime Plus
2/7/1
Silane Primer
Zirconia (AF/ MF/CF)
AF, adhesive failure at cement/lithium disilicate interface; CF, cohesive failure within cement; MF, mixed failure.
Table IV.
Contact angle (degrees) on primed ceramic surface
Silane Primer
Lithium Disilicate
Zirconia Primer
Zirconia
Control (no primer)
20.9 (6.8)
c
Control (no primer)
15.1 (4.0)
B
Porcelain Primer
88.3 (9.5)
a
Monobond Plus
74.1 (6.7)
A
BisGMA-Modified Porcelain Primer
32.9 (8.1)
b
BisGMA-Modified Monobond Plus
71.7 (3.8)
A
Kerr Silane
22.5 (7.4)
c
ZPrime Plus
75.0 (6.1)
A
Data are presented as mean (standard deviation). Means followed by different letter in same column are statistically different (P<.05).
surface). Before contact angle measurement, airborne-particle-abraded zirconia was treated with a zirconia primer (Monobond Plus, BisGMA-Modified Monobond Plus or ZPrime Plus), and etched lithium disilicate specimens were treated with a silane primer (Porcelain Primer, BisGMA-Modified Porcelain Primer, or Kerr Silane). Control groups were not treated. After 5 minutes, ceramic specimens were ultrasonically cleaned in ethanol solvent for 2 minutes to remove any nonchemically
bonded compounds, rinsed with deionized water, and air dried. Contact angles were then measured by placing a deionized water droplet (40 mL) over the specimen surface with a goniometer (NRL Contact Angle Goniometer; Rame-Hart Inc) (n¼10 each group). Shear bond strength and contact angle data were statistically analyzed by 1-way ANOVA. The Tukey multiple comparison was used as a post hoc test. The level of significance was set at .05.
The Journal of Prosthetic Dentistry
Mean shear bond strength results are shown in Table II. In the lithium disilicate group, Porcelain Primer had significantly higher shear bond strength than BisGMA-Modified Porcelain Primer and Kerr Silane (P<.05), both of which had higher bond strength than the control (P<.05). In the zirconia group, ZPrime Plus had a higher bond strength than BisGMA-Modified and unmodified Monobond Plus (P<.05), both of which had higher bond strength than the control (P<.05). Failure modes are presented in Table III. In the lithium disilicate group, adhesive failures were observed more frequently for the control, Kerr Silane, and BisGMA-Modified Porcelain Primer than for unmodified Porcelain Primer. In the zirconia group, the control had 100% adhesive failure, and the other 3 groups had 20% to 50% adhesive failure. The results of contact angle measurements are presented in Table IV. In the lithium disilicate group, Porcelain Primer, which contains no BisGMA resin in its formulation, displayed a contact angle (88.3 degrees) significantly higher than the control (20.9 degrees) (P<.05). BisGMA-Modified Porcelain Primer showed a lower contact angle (32.9 degrees) than unmodified Porcelain Primer (P<.05). Resin-containing Kerr Silane had a similar contact angle as the control. In the zirconia group, both Monobond Plus (which contains no BisGMA resin) and ZPrime Plus (which contains BisGMA resin) demonstrated contact angle values higher than the control (P<.05). BisGMA-Modified Monobond Plus had a contact angle similar to the unmodified control (P¼.32). Singlefactor ANOVA analysis revealed a significant difference in mean contact angles and shear bond strengths in both the zirconia and lithium disilicate groups (Table V).
DISCUSSION This study evaluated the effect of incorporating BisGMA resin on the
Chen et al
November 2013
Table V.
405
Summary of serial 1-way ANOVAs
Source
Sum of Squares
df
Mean Square
F
P
1455
3
485
13.5
<.001
39.8
<.001
Silane primer bond strength Between groups Within groups
1293
36
Total
2748
39
3259
3
35.9
Zirconia primer bond strength Between groups Within groups Total
982
36
4241
39
1086 27.3
Silane primer contact angle Between groups Within groups Total
30447
3
10149
2305
36
64
32752
39
159
<.001
305
<.001
Zirconia primer contact angle Between groups Within groups Total
25721
3
1011
36
26732
39
bond strengths and contact angles of silane primers and zirconia primers (phosphate-monomer-based primers). The results indicated that the incorporation of 10 wt% BisGMA resin did not significantly influence the bond strength or contact angle of the zirconia primer, while it significantly reduced those of the silane primer. Therefore, the null hypothesis, which assumed the incorporation of BisGMA resin would not change bond strengths or contact angles of zirconia or silane primers, was partially rejected (Fig. 1). Measuring contact angle is a simple way to determine the hydrophilicity/hydrophobicity of a surface.16 The hydrophobic surface has a high water-contact angle, while a hydrophilic surface has a low water-contact angle. Dental adhesion usually involves strong bonding such as chemical bonds (or covalent bonds) and weak bonding such as electrostatic attraction or van der Waals forces.16 A simple evaluation of strong chemical bonds is an ultrasonic cleansing in organic solvents like ethanol, which would remove the weakly bound primers.6 The unremoved chemically bonded primers would convert
Chen et al
8574 28.1
hydrophilic (low contact angle) etched lithium disilicate or airborne-particleabraded zirconia surfaces into hydrophobic surfaces (high contact angle). As shown in the data, Porcelain Primer, a prehydrolyzed silane primer, displayed a much higher contact angle than that of unprimed etched lithium disilicate (control), suggesting a strong chemical attachment (bond) to lithium disilicate surfaces; this was confirmed by its high bond strength. The incorporation of BisGMA resin significantly reduced the contact angle and bond strength, suggesting that BisGMA resin inhibited the chemical reaction between the silane primer and the lithium disilicate ceramic. Kerr Silane, a resincontaining silane primer, displayed a contact angle similar to that of unprimed etched lithium disilicate (control), indicating that limited or no chemical bonding to the substrate surface is present. The low contact angle and bond strength values of Kerr Silane and BisGMA-Modified Porcelain Primer may be because the BisGMA resin inhibited the condensation reaction5 between the silanol (Si-OH) of the silane primer and the substrate (OH) of
the ceramic. The condensation reaction slowly liberates a water molecule to form a stable siloxane (Si-O-Si) bond.5 Because this reaction involves the liberation of water molecules, the reaction can be inhibited by extra resin, which slows down water evaporation (Le Chatelier principle).17 Kerr Silane had a significantly higher shear bond strength than the control, probably due to the wetting of its resin.13-15 The contact angle on the unprimed airborne-particle-abraded zirconia surface was low (15 degrees), representative of a hydrophilic surface. This finding is in agreement with the previously reported values (22 to 39 degrees).18,19 The application of Monobond Plus and BisGMA-containing ZPrime Plus followed by ultrasonic cleansing significantly increased the contact angle values, suggesting a strong chemical attachment of zirconia primers to zirconia surfaces. Incorporating BisGMA into Monobond Plus did not influence the contact angle. The results indicate that BisGMA resin did not inhibit the chemical reaction between zirconia primers (phosphate monomers) and zirconia ceramics. This is in sharp contrast to silane primers, suggesting that the mechanism of the zirconia primer reaction (formation of chemical bond -Zr-O-P-)6,19 is different from the condensation reaction of the silane primer. The bond strength data showed that incorporating BisGMA resin increased the bond strength of Monobond Plus (although not significantly), possibly due to the better wetting of extra BisGMA resin.13-15 The previous studies showed ZPrime Plus had a higher bond strength than other commercial zirconia primers such as Monobond Plus and Clearfil Ceramic Primer (Kuraray, Kurashiki).6-8 This was confirmed by the bond strength data in this study, which demonstrated that ZPrime Plus had a higher bond strength than either BisGMA-Modified or unmodified Monobond plus. The bond strength result was also supported by failure mode studies showing ZPrime Plus had fewer adhesive failures and more cohesive/ mixed failures than Monobond Plus. The
Volume 110 Issue 5 50
Zirconia Primer Bond Strength, MPa
Silane Primer Bond Strength, MPa
406
45 40 35
+
30
+
25
+
20
+
15 10 5 0
Porcelain P Porcelain P / Kerr Silane BisGMA
No Primer
40 35 30
20
+ 80 60 40
+
20 0
+
+
Porcelain P Porcelain P / Kerr Silane BisGMA
No Primer
C
Zirconia Primer Contact Angle, Degree
Silane Primer Contact Angle, Degree
100
+
+
15 10 5 0
A 120
+
25
+ Monobond Monobond Plus Plus / BisGMA
ZPRIME Plus
No Primer
B
100 90 80 70
+
+
+
60 50 40 30 20
+
10 0
Monobond Monobond Plus Plus / BisGMA
ZPRIME Plus
No Primer
D
1 Summary of box plots. A, Silane primer bond strength. B, Zirconia primer bond strength. C, Silane primer contact angle. D, Zirconia primer contact angle. Median (þ), 25% quartile (bottom line), 75% quartile (top line), maximum (plus error bar), and minimum (minus error bar). previous SEM studies confirmed that cohesive failures occurred when ZPrime Plus was used for resin-zirconia bonding.9 The higher bond strength of ZPrime Plus is attributed to its proprietary formula of both phosphate (MDP) and carboxylate monomers.6-8 Another possible reason is that ZPrime Plus contains extra BisGMA resin, which has better wetting to allow the resin cement to spread in a more uniform layer.13-15 This study evaluated the contact angle and short-term bond strength of silane and zirconia primers with and without the incorporation of BisGMA resin. Within the limited scope of the specimens evaluated here, the data suggest that the incorporation of BisGMA resin significantly inhibited the
efficacy of silane-containing porcelain primers, while it did not affect that of phosphate-containing zirconia primers. Future studies should explore long-term adhesion in more clinically relevant environments.
CONCLUSION This study analyzed the contact angle and shear bond strength of zirconia (phosphate-based) and silane primer with and without BisGMA resin. The results showed that incorporating BisGMA resin reduced the contact angle and bond strength values of silane primers, suggesting an inhibiting effect of BisGMA resin on silane primers. In contrast, incorporating BisGMA resin did not significantly influence the contact
The Journal of Prosthetic Dentistry
angles or bond strengths of zirconia (phosphate-based) primers, indicating BisGMA resin did not inhibit phosphatemonomer-containing zirconia primer.
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Chen et al
November 2013 6. Chen L, Suh BI, Brown D, Chen X. Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths. Am J Dent 2012;25:103-8. 7. Magne P, Paranhos MP, Burnett LH. New zirconia primer improves bond strength of resinbased cements. Dent Mater 2010;26:345-52. 8. Piascik JR, Swift EJ, Braswell K, Stoner BR. Surface fluorination of zirconia: adhesive bond strength comparison to commercial primers. Dent Mater 2012;28:604-8. 9. Chen L, Suh BI, Kim J, Tay FR. Evaluation of silica-coating techniques for zirconia bonding. Am J Dent 2011;24:79-84. 10. Kern M, Barloi A, Yang B. Surface conditioning influences zirconia ceramic bonding. J Dent Res 2009;88:817-22. 11. Akgungor G, Sen D, Aydin M. Influence of different surface treatments on the shortterm bond strength and durability between a zirconia post and a composite resin core material. J Prosthet Dent 2008;99:388-99.
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407 12. Stangel I, Nathanson D, Hsu CS. Shear strength of the composite bond to etched porcelain. J Dent Res 1987;66: 1460-5. 13. El Zohairy AA, De Gee AJ, Hassan FM, Feilzer AJ. The effect of adhesives with various degrees of hydrophilicity on resin ceramic bond durability. Dent Mater 2004;20:778-87. 14. Hisamatsu N, Atsuta M, Matsumura H. Effect of silane primers and unfilled resin bonding agents on repair bond strength of a prosthodontic microfilled composite. J Oral Rehabil 2002;29: 644-8. 15. Matsumura H, Hisamatsu N, Atsuta M. Effect of unfilled resins and a silane primer on bonding between layers of a light-activated composite resin veneering material. J Prosthet Dent 1995;73:386-91. 16. Marshall SJ, Bayne SC, Baier R, Tomsia AP, Marshall GW. A review of adhesion science. Dent Mater 2010;26:e11-6.
17. Callen HB. Thermodynamics. Hoboken, NJ: John Wiley & Sons; 1965. p. 135-205. 18. Shojai F, Pettersson A, Mäntylä TA, Rosenholm J. Detection of carbon residue on the surface of 3Y-ZrO2 powder and its effect on the rheology of the slip. Ceramics Int 2000;26:133-9. 19. Carrière D, Moreau M, Barboux P, Boilot JP. Modification of the surface properties of porous nanometric zirconia particles by covalent grafting. Langmuir 2004;20: 3449-55. Corresponding author: Dr Liang Chen Department of Research and Development Bisco, 1100 W Irving Park Rd Schaumburg, IL 60193 E-mail: [email protected] Copyright ª 2013 by the Editorial Council for The Journal of Prosthetic Dentistry.