Abstract
Objectives
Air-abrasion as bonding conditioning method for zirconia ceramic might compromise the mechanical strength of zirconia restorations. The purpose of this study was to evaluate the influence of surface conditioning parameters, i.e., air-abrasion with reduced pressure or no air-abrasion and priming with adhesive primers on the long-term resin bond strength to zirconia ceramic.
Methods
Zirconia ceramic disks were polished with 600 grit abrasive paper. Plexiglas tubes filled with composite resin were bonded with RelyX Unicem luting composite resin to the conditioned zirconia disks. Three surface conditions (unconditioned, air-born particle abrasion at 0.05 or 0.25 MPa) and four priming conditions (no priming, priming with Metal/Zirconia Primer, priming with Alloy Primer, priming with Clearfil Ceramic Primer) were tested. Sixteen specimens of each combination were bonded. Subgroups of eight bonded samples were stored in water either for 3 days or 150 days with 37,500 thermocycling. Tensile bond strengths (TBSs) were determined with a universal testing machine at a crosshead speed of 2 mm/min.
Results
Without priming, RelyX Unicem showed durable bond strength to 0.25 MPa airborne-particle abraded ceramic. When combined with 10-methacryloyloxy-decyl dihydrogenphosphate containing primers, air-abrasion resulted in a durable TBS to zirconia ceramic even at a reduced abrasion pressure. However, combined with Metal/Zirconia Primer air-abrasion did not provide a durable TBS to zirconia ceramic.
Significance
Using a self-adhesive luting resin composite (RelyX Unicem), air-abrasion at 0.25 MPa or the combination of low pressure air-abrasion and priming with MDP-containing primers seems to be useful to achieve durable long-term bonding to zirconia ceramic.
1
Introduction
Air-abrasion seems to be a prerequisite to achieve high and durable bond strengths to zirconia ceramics . Air-abrasion with silica containing particles (named as silica-coating) followed by silanating has been used on zirconia ceramics with varying results. It produced durable resin bonding for some zirconia ceramics , while on other zirconia ceramics reduced bond strengths after artificial aging were found . An explanation might be that the silica layer to a large extent was not firmly attached to the zirconia surface . However increasing the blasting pressure during silica-coating from 0.15 MPa to 0.45 MPa increased the bond strength from 11.2 MPa up to 30.5 MPa suggesting that tribochemical silica-coating requires a high blasting pressure.
In several studies on zirconia ceramic bonding, air-abrasion with 50 μm Al 2 O 3 at 0.25 MPa at 10 mm operation distance was used to condition the ceramic surface in order to increase the surface roughness, as well as to clean and to activate the surface . This method can significantly improve resin–zirconia ceramic bond strength and its durability by increasing surface roughness, cleaning and activating the ceramic surface when combined with adhesive monomer-containing primers such as 4-methacryloxyethyl-trimellitate-anhydride (4-META) or 10-methacryloxydecyl-dihydrogenphosphate (MDP) .
However, air-abrasion might compromise the mechanical strength of ceramic itself by initiating surface defects although the critical defect size in zirconia ceramic varies between 15 and 40 μm depending on the nature of the critical flaw produced in the manufacturing process . Therefore, reducing the pressure during air-abrasion or omitting air-abrasion completely might be recommended in combination with new ceramic primers in order to improve the bonding durability and reduce the negative influence of high-pressure air-abrasion on the mechanical properties of zirconia ceramic. Up to now, this assumption has not been investigated or reported.
Recently, RelyX Unicem has been recommended as one-step self-adhesive luting composite resin for dental materials bonding. Adhesive monomer with phosphoric acid groups and effective function of initiators in the initially acidic cement paste bring about to RelyX Unicem self-adhesion and a high degree of cross-linking between the monomers after setting. For dental oxide ceramics with RelyX Unicem, only 0.25 MPa air-abrasion pretreatment of ceramic bonding surface without priming was recommended and proven to contribute to a durable resin–ceramic bonding . However, the effects of reduced blasting pressure and/or the primer application on bonding of Unicem to zirconia ceramic are not known.
In order to find one suitable surface treatment to improve bonding durability without impairing mechanical properties of zirconia ceramic restorations, the influence of various surface conditioning parameters, i.e., air-abrasion and priming, on the long-term resin bond strength to zirconia ceramic with RelyX Unicem was investigated in this study. The null hypotheses tested were that there is no influence of properly reducing air-abrasion pressure on resin–zirconia ceramic bond durability with RelyX Unicem, that there is no influence of surface condition with primers on resin–zirconia ceramic bond, and that there is no influence of the combination of reducing air-abrasion pressure and using different primers on resin–zirconia ceramic bonding durability.
2
Materials and methods
Zirconia ceramic disks were made from Cercon ceramic (Cercon, DeguDent, Hanau, Germany) and polished with 600 grit abrasive paper. Three surface conditions (polished, air-abrasion with alumina particles at 0.05 MPa, or at 0.25 MPa) and four priming conditions including no priming (NP), priming with Metal/Zirconia Primer (MZP, Ivoclar-Vivadent, Schaan, Liechtenstein), priming with Alloy Primer (AP, Kuraray Medical, Osaka, Japan) or Clearfil Ceramic Primer (CCP, Kuraray Medical, Osaka, Japan) according to the manufacturers’ instructions were tested ( Fig. 1 ). Air-abrasion was done with 50 μm Al 2 O 3 particles (Edelkorund weiß 50 μm, Pluradent, Offenbach, Germany) using a spot blasting unit (P-G 400, Harnisch + Rieth, Winterbach, Germany) at a distance of 10 mm from the bonding surface. Then the specimens were cleaned ultrasonically in 96% ethanol for 2 min to remove the debris of Al 2 O 3 particles from the ceramic surface.
2.1
Tensile bond strength (TBS) testing
The protocols of bonding the conditioned zirconia ceramic specimens with RelyX Unicem composite luting resin (3 M ESPE, Seefeld), aging simulations with water storage and thermal cycling, and TBS testing followed the protocol described by Kern and Thompson which was used as standard protocol in numerous studies and therefore allows valid comparisons to previously obtained results. Briefly, RelyX Unicem was bonded in light curing mode according to the manufacturer’s instruction. The bonded specimens were stored in 37 °C water for 3 days or 150 days with 37,500 thermal cycles from 5 °C and 55 °C prior to TBS testing with a universal testing machine (Zwick Z010/TN2A, Zwick, Germany) at a crosshead speed of 2 mm/min ( Fig. 1 ).
2.2
Surface topography examination and fractographic examination
A scanning electron microscope (SEM, XL 30 CP, Philips, Kassel, Germany) operating at 10–25 KV was used to observe ceramic surfaces after mechanical conditions with polishing, air-abraded with 0.05 MPa and 0.25 MPa and fractographic analysis of representative debonded ceramic specimens. Failure modes of debonded ceramic specimens after tensile testing were classified into : (A) adhesive failure at ceramic surface; (C) cohesive failure in the RelyX Unicem luting composite resin or in the tube filling composite resin with or without primer residue on ceramic surface. Failure areas of each mode were calculated and expressed as a percentage of the total bonding surface area for each test group. All debonded ceramic surfaces were examined using a light microscope at 40× magnification to calculate the area of each failure mode.
2.3
Statistical analysis
As data was not normally distributed, statistical analysis was performed using the Wilcoxon rank sum test adjusted according to Bonferroni–Holm for multiple testing at α = 5%.
2
Materials and methods
Zirconia ceramic disks were made from Cercon ceramic (Cercon, DeguDent, Hanau, Germany) and polished with 600 grit abrasive paper. Three surface conditions (polished, air-abrasion with alumina particles at 0.05 MPa, or at 0.25 MPa) and four priming conditions including no priming (NP), priming with Metal/Zirconia Primer (MZP, Ivoclar-Vivadent, Schaan, Liechtenstein), priming with Alloy Primer (AP, Kuraray Medical, Osaka, Japan) or Clearfil Ceramic Primer (CCP, Kuraray Medical, Osaka, Japan) according to the manufacturers’ instructions were tested ( Fig. 1 ). Air-abrasion was done with 50 μm Al 2 O 3 particles (Edelkorund weiß 50 μm, Pluradent, Offenbach, Germany) using a spot blasting unit (P-G 400, Harnisch + Rieth, Winterbach, Germany) at a distance of 10 mm from the bonding surface. Then the specimens were cleaned ultrasonically in 96% ethanol for 2 min to remove the debris of Al 2 O 3 particles from the ceramic surface.
2.1
Tensile bond strength (TBS) testing
The protocols of bonding the conditioned zirconia ceramic specimens with RelyX Unicem composite luting resin (3 M ESPE, Seefeld), aging simulations with water storage and thermal cycling, and TBS testing followed the protocol described by Kern and Thompson which was used as standard protocol in numerous studies and therefore allows valid comparisons to previously obtained results. Briefly, RelyX Unicem was bonded in light curing mode according to the manufacturer’s instruction. The bonded specimens were stored in 37 °C water for 3 days or 150 days with 37,500 thermal cycles from 5 °C and 55 °C prior to TBS testing with a universal testing machine (Zwick Z010/TN2A, Zwick, Germany) at a crosshead speed of 2 mm/min ( Fig. 1 ).
2.2
Surface topography examination and fractographic examination
A scanning electron microscope (SEM, XL 30 CP, Philips, Kassel, Germany) operating at 10–25 KV was used to observe ceramic surfaces after mechanical conditions with polishing, air-abraded with 0.05 MPa and 0.25 MPa and fractographic analysis of representative debonded ceramic specimens. Failure modes of debonded ceramic specimens after tensile testing were classified into : (A) adhesive failure at ceramic surface; (C) cohesive failure in the RelyX Unicem luting composite resin or in the tube filling composite resin with or without primer residue on ceramic surface. Failure areas of each mode were calculated and expressed as a percentage of the total bonding surface area for each test group. All debonded ceramic surfaces were examined using a light microscope at 40× magnification to calculate the area of each failure mode.
2.3
Statistical analysis
As data was not normally distributed, statistical analysis was performed using the Wilcoxon rank sum test adjusted according to Bonferroni–Holm for multiple testing at α = 5%.
3
Results
SEM photographs of different topographic surface structure produced by polishing (a), 0.05 MPa (b) and 0.25 MPa (c) air-abrasion are illustrated in Fig. 2 . Air-abrasion of zirconia ceramic surface created at 0.25 MPa produced a rougher surface than air-abrasion at 0.05 MPa, while only polishing resulted in the smallest roughness.
The means and standard deviations of TBS in MPa of experimental groups after different surface treatments and different storage conditions are shown in Table 1 . In groups without air-abrasion—although specimens showed acceptable TBS after 3 days storage—all specimens debonded spontaneously during water storage and thermal cycling regardless of primers. In groups 05, no priming and the Metal/Zirconia Primer priming did not result in long-term stable TBS, while Alloy Primer and Clearfil Ceramic Primer priming led to a durable long-term TBS. For groups 25, only Metal/Zirconia Primer priming showed decreased long-term TBS, no priming, Alloy Primer and Clearfil Ceramic Primer resulted in long-term stable TBS.
Stay updated, free dental videos. Join our Telegram channel
VIDEdental - Online dental courses
