Does Rinsing Following Particle Deposition Methods Have a Negative Effect on Adhesion to Titanium? Mutlu Özcana / Gurel Pekkanb / Ashkan Khanc Purpose: This study evaluated whether air blasting or rinsing particle remnants with water would impair adhesion of resin composite to metal. Materials and Methods: Commercially pure titanium plates (1 mm x 25 mm x 50 mm) were wet polished down to 1200-grit silicone carbide abrasive and ultrasonically cleaned. They were then embedded in auto-polymerizing acrylic with the bonding surfaces exposed. Specimens were randomly assigned to one of the following particle deposition protocols (N = 60, n = 10 per group): group 1: particle deposition with aluminum trioxide (50 μm Al2O3) (AL) + air blasting + silane (ESPE-Sil); group 2: particle deposition with 30 μm SiO2 (CoJet) (CSC) + air blasting + silane; group 3: particle deposition with Rocatec Pre 110 μm Al2O3+Rocatec Plus 110 μm SiO2 (LSC) + air blasting + silane. In groups 4 (AL-W), 5 (CSC-W) and 6 (LSC-W), the same protocols were used, but instead of air blasting only, particle-deposited specimen surfaces were rinsed with water and air blasted. Adhesive resin (VisioBond) was applied and resin composite (Quadrant Posterior, Cavex) was bonded using polyethylene molds and photopolymerized. The specimens were then submitted to thermocycling (6000 cycles, 5°C–55ºC, dwell time: 30 s, transfer time: 5 s). Pre-test failures during thermocycling were assigned a value of 0 MPa. Failure modes were identified using an optical microscope. SEM images of particles were obtained. Bond strength data (MPa) were statistically analyzed using two-way ANOVA and Tukey’s post-hoc tests (_= 0.05). Results: Particle type significantly affected the bond results (p < 0.001). AL groups presented significantly lower results (air blasting: 4.3 ± 3.3, rinsing: 11.8 ± 6.5) compared to those of CSC (air blasting: 27.7 ± 6.6, rinsing: 30.4 ± 9.3) and LSC (air blasting: 31.4 ± 8.7, rinsing: 28.7 ± 7.0). AL groups presented 5 spontaneous debondings during thermocycling in the air-blasted group. Rinsing with water as opposed to air blasting only did not decrease the results with any of the particle types (p > 0.05). While AL groups showed exclusively adhesive failure between the resin composite and the substrate, the incidence of cohesive failures in the composite was more frequent in groups CSC and LSC after either air blasting or rinsing. SEM images of particles showed sharp morphology of the particles in AL compared to CSC and LSC. Conclusion: Rinsing and air blasting following particle deposition methods did not impair adhesion of resin composite to titanium. Particle deposition with silica particles provided better adhesion of resin composite to this substrate compared to the use of alumina particles. Key words: adhesion, air abrasion, bond strength, composite resin, particle deposition, repair, silane coupling agent, surface conditioning, titanium. J Adhes Dent 2013; 15: 307–310. doi: 10.3290/j.jad.a30163
a
Professor, University of Zurich, Dental Materials Unit, Center for Dental and Oral Medicine, Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, Zurich, Switzerland. Designed the study, analyzed the data, wrote the manuscript, discussed the results and commented on the manuscript at all stages.
b
Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Dumlupinar University, Kutahya, Turkey. Analyzed the data, performed the experiments while guest researcher in Groningen, discussed the results and commented on the manuscript at all stages.
c
Dental Student, University Medical Center Groningen, Department of Dentistry and Oral Hygiene, Groningen, The Netherlands. Performed the experiments, discussed the results and commented on the manuscript at all stages.
Correspondence: Professor Mutlu Özcan, University of Zürich, Dental Materials Unit, Center for Dental and Oral Medicine, Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, Plattenstrasse 11, CH-8032, Zürich, Switzerland. Tel: +41-44-63 45600, Fax: +41-44-63 44305. e-mail:
[email protected]
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Submitted for publication: 29.12.12; accepted for publication: 09.05.13
P
article deposition protocols using abrasives of different sizes increases the surface area and contributes to micromechanical retention of resin-based materials to metals during repair of metal-ceramic fixed dental prostheses (FDP),6 cementation of metal posts,12 frameworks,8,11,13 or veneering indirect composites to metal frameworks. 4 Particle deposition methods increase wetting properties of adhesion promoters and improve interfacial bonding between the resin-based materials and the substrate.5 Today, it is possible to activate the surface energy and increase the surface roughness of metals using either alumina or silica-coated alumina particles.10 Particle deposition methods applied under propelled compressed air removes unfavorable oxides and contaminants, thereby cleaning the surface. One 307
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rationale for the use of abrasive particles is to form covalent bonds between the resin and the hydroxyl groups on the metal.3 The particle-deposited surfaces are then coated with silane coupling agents for improved adhesion of the resin-based materials.2,7 Silane coupling agents improve wettability and promote covalent bonds, thus enhancing the chemical adhesion between the metals and resin composite.9 After particle deposition on a given substrate, part of the particles penetrate the surface due to the impact and some particles bounce back from the surface.10 The loose particles create undesirable debris in the mouth and may also impair wettability of the silane and the successive adhesive resin depending on the size of the abrasive. Thus, the loose particles are typically air blasted, but this procedure does not completely eliminate the particles from the working environment. This is an important aspect as the minimum space required at the bonding interface is crucial to avoid clinical debonding failures and microleakage.5 Clinically, there are concerns whether removal of particle remnants with water followed by air blasting would impair adhesion compared to air blasting only. The objectives of this study therefore were a) to evaluate the effect of air blasting alone vs rinsing and then air blasting of abrasives after particle deposition methods on the adhesion of resin composite to metal and b) to identify the failure modes after debonding. The null hypothesis tested was air blasting alone or rinsing and air blasting of abrasives after particle deposition methods would not show significant differences in adhesion of resin composite to metal.
MATERIALS AND METHODS Commercially pure titanium plates (Permascand; Ljungaverk, Sweden) (1 mm × 25 mm × 50 mm) were wet polished to 1200-grit silicone carbide abrasive (SiC) (Struers; Willich, Germany) and ultrasonically cleaned (Vitasonic II, Vita Zahnfabrik; Bad Säckingen, Germany) in distilled water for 5 min and allowed to dry at room temperature for 5 min. They were then embedded in autopolymerizing acrylic (Autoplast, Condular; Wangen, Switzerland) with the bonding surfaces exposed. Specimens were randomly assigned to one of the following particle deposition protocols (Nplates = 15, Nspecimens = 60, n = 10 per group): y Group 1 (AL): The specimens were particle deposited with 50 μm Al2O3 (Korox, Bego; Bremen, Germany) using an intraoral air-abrasion device (Dento-Prep, RØNVIG; Daugaard, Denmark) perpendicular to the surface from a distance of approximately 10 mm for 20 s/cm2 in circling motions at 2.8 bar. y Group 2 (CSC): In this group, instead of ordinary alumina particles, 30-μm alumina particles coated with silica (SiO2) were used (CoJet Sand, 3M ESPE; Seefeld, Germany). The particle deposition protocol was as described in group 1. y Group 3 (LSC): In this group, 110-μm Al2O3 (Rocatec Pre, 3M ESPE) followed by 110-μm SiO 2 (Rocatec 308
Plus, 3M ESPE) was used (Rocatec System, 3M ESPE). Deposition parameters were as described in group 1. y After particle deposition in groups 1 to 3, the remnants of the abrasive particles were gently air blasted for 20 s. y In groups 4 (AL-W), 5 (CSC-W), and 6 (LSC-W), the same protocols were performed, but instead of air blasting, particle-deposited specimen surfaces were rinsed with water using a multifunctional tip for 20 s and air blasted for 20 s. All specimens received one coat of silane coupling agent (ESPE-Sil, 3M ESPE) which was left to react for 5 min. Subsequently, one coat of adhesive resin (VisioBond, 3M ESPE) was applied with a microbrush, air thinned and photopolymerized (650 mW/cm2) for 40 s using a photopolymerization device (Astralis 5, Ivoclar Vivadent; Schaan, Liechtenstein). Resin composite (Quadrant Posterior, Cavex Holland BV; Haarlem, The Netherlands) was then placed and bonded incrementally using polyethylene molds (height: 3 mm) and photopolymerized from the top for 40 s. The specimens were then submitted to thermocycling (6000 cycles, 5°C–55ºC, dwell time: 30 s, transfer time: 5 s). Pre-test failures during thermocycling were assigned a value of 0 MPa. Specimens were mounted in the jig of the universal testing machine (Zwick ROELL Z2.5 MA 18-1-3/7; Ulm, Germany) and shear force (crosshead speed: 1 mm/min) was applied to the bonded interface until failure occurred. Failure modes were identified using an optical microscope (Stemi 2000-C, Carl Zeiss; Göttingen, Germany) at 100X magnification. SEM (JSM-5500, JEOL; Tokyo, Japan) images of abrasive particles were obtained. Failure types were categorized according to the modified Adhesive Remnant Index (ARI):1 score 0 = no composite left on the surface, score 1 = < 1/2 of the surface covered with composite, score 2 = >1/2 of the surface covered with composite, score 3 = surface completely covered with composite. Bond strength data (MPa) were analyzed statistically using two-way ANOVA and Tukey’s post-hoc tests _ = 0.05).
RESULTS Particle type significantly affected the bond strength results (p < 0.001). AL groups presented significantly lower results (air blasting: 4.3 ± 3.3, rinsing: 11.8 ± 6.5) compared to those of CSC (air blasting: 27.7 ± 6.6, rinsing: 30.4 ± 9.3) and LSC (air blasting: 31.4 ± 8.7, rinsing: 28.7 ± 7.0). AL groups presented 5 spontaneous debondings during thermocycling in the airblasted group (Fig 1). Rinsing with water did not decrease the results with any of the particle types as opposed to air blasting only (p > 0.05). While AL groups showed exclusively adhesive failures between the resin composite and titanium, the incidence of cohesive failures in the composite was more frequent The Journal of Adhesive Dentistry
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in groups CSC and LSC after either air drying or rinsing, respectively (Table 1). SEM images of particles showed sharp morphology of the particles in AL compared to CSC and LSC (Fig 2).
Shear Bond Strength (MPa) 45 40 35
DISCUSSION
30
Since rinsing with water and air blasting after particle deposition with all particle types did not have an adverse effect on the bond results, the null hypothesis could be accepted. Yet bond strengths with the alumina particles (AL) were significantly lower than with alumina particles coated with silica (CoJet-CSC and Rocatec Systems-LSC), indicating that particle morphology affects the adhesion to metal. Although ordinary alumina particles and CoJet particles present similar particle sizes, the higher bond strengths with the latter imply a greater importance of the chemical aspect of adhesion than the micromechanical characteristics. Principally, silane (oligomers) monomers or molecules, being chemically bifunctional, react with each other forming siloxane bonds, -Si-O-Si-. With an
25 30.4 20 27.7
15
31.4 28.4
10
11.8
5 0
4.3
Al
CSC
LSC
Dry Rinse
Fig 1 Means and standard deviations of the bond strength (MPa) of resin composite to titanium after air-particle abrasion protocols where the particles were only air dried (Dry) or rinsed and dried after deposition (Rinse).
Table 1 Distribution of the frequencies of failure types according to modified Adhesive Remnant Index (ARI) for experimental groups (n = 10 per group) Groups
Score 0
Score 1
Score 2
Score 3
Dislodged*
AL
10/10
0/10
0/10
0/10
5/10
AL-W
10/10
0/10
0/10
0/10
0/10
CSC
0/10
4/10
4/10
2/10
0/10
CSC-W
0/10
2/10
6/10
2/10
0/10
LSC
0/10
1/10
5/10
4/10
0/10
LSC-W
0/10
1/10
5/10
4/10
0/10
Score 0 = no composite left on the surface, score 1 = 1/2 of the surface covered with composite, score 3 = surface completely covered with composite. *Dislodged during thermocycling.
a
b
c
Figs 2a to 2c Typical SEM images of a) Al2O3 (10,000X), b) CoJet Sand (10,000X) and c) Rocatec Plus (3500X) particles. Note the rough surface of individual Al2O3 particles compared to silica-coated Al2O3 particles in b and c. Morphology of individual particles shows great variation.
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inorganic substrate (resin matrix) (ie, silica, metal oxides that contain basic hydroxyl OH groups), they can form -Si-O-M- bonds (M = metal).3 Hydrolytic degradation of -Al-O-Si- compared to -Si-O-Si- has been previously reported.7 Thus, the higher incidence of pre-test failures during thermocycling in the alumina deposited group can be explained based on this phenomenon. Similarly, even though the particle size was much higher in Rocatec (110 μm) as opposed to CoJet (30 μm), the non-significant difference in all conditions between these two systems cancels out the significance of micromechanical retention when better wettability of the silane is achieved on less rough surfaces. Future studies should look at the wettability aspect of silanes and their hydrolytic stability on different rough topographies. Also, the necessary amount of Si vs Al needs to be established, as the surfaces are not completely coated with Si in silicacoating systems.10 Hydrolyzed alkoxy groups, ie, they have reacted with water, turn into silanol groups; as a byproduct, corresponding alcohol molecules are yielded. The silanol groups bond covalently to the hydroxyl groups (-OH) on titanium dioxide of the titanium surface.2 The available amount of alumina or alumina particles coated with silica on the titanium surface even after rinsing was sufficient to obtain durable adhesion of the resin composite tested. The embedded Si and Al particles on the substrate surface, after deposition under the applied parameters, do not seem to be removed by rinsing or were sufficient to react with the silane. The rinsing and subsequent air-blasting approach could to be implemented after clinical particle abrasion protocols during intraoral repair of metal-ceramic FDPs, cementation of metal posts or veneering metal frameworks. In this study, titanium was used as a screening metal. Certainly, the results may change when a noble alloy is used.
3. The particle size of 30 or 110 μm in silica deposition systems tested did not affect the bond strength results.
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CONCLUSIONS 1. Rinsing with water after particle deposition of alumina and alumina particles coated with silica did not impair the adhesion of resin composite to titanium. 2. Both laboratory and chairside silica deposition systems delivered higher bond strength than particle deposition with alumina, with which more hydrolytic degradation and exclusively adhesive failures were experienced.
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Clinical relevance: Rinsing loose particle remnants after particle deposition methods did not impair the adhesion of resin composite to titanium. Chairside or laboratory silica particle deposition should be preferred to alumina particles for conditioning this substrate.
The Journal of Adhesive Dentistry
