Optimizing the fitting-surface preparation of zirconia restorations for bonding to dentin

Abstract

Objectives

The aim of this study was to identify the relative strengths and weaknesses of different interfaces within the multilayer structure of a zirconia crown restoration when applying different surface pretreatments. These include the influence on shear strengths of different air abrasion protocols, glaze-on techniques, zirconia primers and self-adhesive cements for either the complex structure: zirconia / self adhesive resin composite cement (RCC) / bovine dentin substrate (part 1) or the RCC / zirconia substrate (part 2).

Methods

In Part 1, zirconia discs, pretreated by either glaze-on techniques or air abrasion using Rocatec™ Soft, were bonded to bovine dentin substrates with different self-adhesive RCCs. In Part 2, steel-cylinders were bonded to zirconia cuboid substrates, pretreated by either different protocols for air-abrasion or a glaze-on-technique, with different self-adhesive RCCs. Shear bond strengths (SBS) were measured for all interfacial combinations.

Results

In part 1, application of air abrasion using Rocatec™ Soft significantly increased the SBS of zirconia to dentin compared to control specimens without pretreatment, while glaze-on techniques did not increase the SBS. Pretreatment of zirconia surfaces with two primers (either Clearfil Ceramic Primer, or Monobond S) showed significantly higher SBS than the controls. Cementations with RelyX Unicem 2 Automix showed significantly higher SBS than with MaxCem Elite. In Part 2, all air abrasion protocols increased the SBS, but there was no significant difference between these protocols. Again the glaze-on technique did not increase SBS. A significant difference between the two RCCs was again observed. When zirconia substrates were air abraded, regardless of which protocol was applied, the highest SBS were obtained by Calibra with P&B active followed by Panavia with or without Clearfil Ceramic Primer Plus. Calibra applied without P&B active exhibited the lowest SBS.

Significance

Pretreatment of zirconia substrates using air abrasion and/or ceramic primers increased the SBS of the zirconia cement interface. For all tested glaze-on treatments, in our experimental setting no effect was observed.

Introduction

Over the last 20 years, material-related advances have led to a significant increase in the use of all-ceramic restorations. These improvements are in biocompatibility, mechanical properties and aesthetics. The procedure for cementation of glass-ceramics has become standardized, involving: (i) etching the restoration with HF, then (ii) silanization to ensure a durable bond between restoration and composite cement via chemical and micromechanical mechanisms. However, in contrast to glass ceramics, there is no uniform “gold standard” for cementation of oxide ceramics such as zirconium oxide, for which zinc phosphate, glass ionomer and self-adhesive composite cements can be used. But these lack the advantageous properties (increased fracture resistance and improved retention) of composite cements which adhere to etched and silanized glass ceramics [ ].

This leads to low retention between zirconia restorations, luting cement and tooth structure. Since zirconia does not contain silicates, it is neither etchable nor can an effective bond be achieved with silanes between restoration and luting cement [ , ]. This means that conventional luting protocols of glass ceramics cannot be applied to oxide ceramics [ ]. Another problem is the low wettability of the zirconia surface, which is hydrophobic [ ]. However, successful cementation of oxide ceramic restorations is an important factor for long-term clinical success [ , , ]. But stronger micromechanical retention can be achieved via a rougher, larger or more energetic surface that changes the wetting capacity and facilitates the flow of cement into the roughened surface [ ]. There have been many attempts over the last 2 decades to increase the roughness of zirconia surface to improve cement bonding [ , ]. Proposed methods include grit blasting with different materials and grain sizes, so-called “tribochemical coating”, laser treatments [ ], grinding, primer and acid treatment [ , ], “plasma spraying” or silanization [ ]. Alternative strategies include establishing a glass layer on the zirconia surface, known as “Internal Coating”, “Selective Infiltration Etching” or “Glaze-on Techniques” [ , ]. Whereas, in “Selective Infiltration Etching”, a thin glass layer is applied to the surface by means of a conditioning agent and then completely dissolved [ ], in the “Internal Coating” and “Glaze-on” technique the glass or porcelain layer is preserved as the “inner lining” of the restoration. In the latter two methods [ , ] HF is applied to the fired glass layer of the oxide ceramics to roughen the surface. The silicates contained in the glass layer enable bonding with silanes. The aforementioned “glaze-on” technique has led to significantly increased bonding in some studies, which were also considered in some systematic reviews and meta-analyses [ , , ]. In the “glaze-on” studies examined in these reviews this technique was only tested in combination with metals or composites, but not with dentin.

Another possibility for surface treatment is air abrasion (grit blasting) with small particles of silica (SiO 2 ) and/or alumina (Al 2 O 3 ) particles. Specifically in the Rocatec™, Rocatec™ Plus and Rocatec™ Soft systems (3M), particles of aluminium oxide with a silica coating are blasted at high speed onto a ceramic workpiece. According to the manufacturer during this process components of the particles melt on the ceramic surface and microdefects are created, resulting in surface enlargement. The extent of these surface changes depends on particle size, jet pressure, angle of incidence, duration and working distance [ ]. Multiple studies have established the value of grit blasting [ , ]. Largely unexplored – or insufficiently well documented – are comparisons of different grit blasting protocols with regard to the resultant bond strength. Likewise, the combined effect of grit blasting grain size and pressure is still largely unexplored. Furthermore, there is insufficient data on whether primer addition can further improve the SBS.

In order to achieve the aim of this study, to optimize the fitting surface preparation of zirconia restorations for bonding to dentin, the following objectives were investigated:

Part 1:

  • a)

    Coating of zirconia with glass ceramic using Zenostar Magic Glaze Spray (ZM), IPS e.max Ceram Glaze Spray (IPS) or Hotbond zirconnect Spray (HB) followed by etching with HF and silanization.

  • b)

    Pretreatment of zirconia with Rocatec™ Soft followed by the application of a ceramic primer versus an universal primer.

Both issues were investigated using zirconia discs bonded via RCC to bovine dentin substrates.

Part 2:

  • a)

    Coating of zirconia with glass ceramic (HB) followed by etching with HF and silanization.

  • b)

    Pretreatment of zirconia substrates with air abrasion using different protocols followed by application of two universal primers with and without MDP monomer and two RCCs with and without MDP.

Both issues were investigated using stainless steel discs bonded via RCC to zirconia substrates. The logic of using stainless steel (SS) discs is that adhesive failure will occur between RCC/zirconia, rather than at the SS/RCC interface.

The following null-hypotheses were formulated:

  • (i)

    Coating of zirconia surfaces with glass-ceramic does not improve bonding of composite cements to zirconia compared to the control (untreated zirconia surfaces).

  • (ii)

    Air abrasion of zirconia surfaces does not increase bonding via composite cements, regardless of grain size and pressure.

  • (iii)

    Primers do not increase the bonding of composite cements to zirconia.

  • (iv)

    Self-adhesive RCCs, with or without MDP, do not show similar bond strenths for the bovine dentin/RCC/zirconia interfaces (part 1) versus the RCC/zirconia interface (part 2).

Materials and methods

Materials are listed in Tables 1A , 1B , 1C . Study variables are presented in Tables 2A , 2B and Fig. 1 A, 1B.

Table 1A
Surface glazing agents.
Glaze Code Material Manufacturer Lot Numbers Formulation
HB DCMhotbond zirconnect spray Dental Creativ Management GmbH, Rostock, Germany 13-04-16 SiO 2 , Al 2 O 3 , K 2 O, Na 2 O, CaO, B 2 O 3
ZM Zenostar Magic Glaze Spray Wieland Dental + Technik GmbH & Co. KG, Pforzheim, Germany 3/11 ZrO 2 ,HfO 2 ,Y 2 O 3 ,Al 2 O 3 ,other oxides ≤ 1.0 %
IPS IPS e.max Ceram Glaze Spray Ivoclar Vivadent, Schaan, Liechtenstein U42646 SiO 2 , Al 2 O 3 , ZnO, Na 2 O, K 2 O, ZrO 2 , CaO and P 2 O 5 propellent, isobutane

Table 1B
Surface etching/priming/bonding.
Function Code Material Manufacturer Lot Numbers Formulation
Etching HF Hydrofluoric acid 9% Ultradent® Porcelain Etch, Ultradent Products GmbH, Köln, Germany BDVSC Buffered gelled hydrofluoric acid
Silane CS Calibra Silane
Coupling Agent
Dentsply Sirona, Bensheim, Germany 170124 Ethyl alcohol, acetone, water
Bonding CUBQ Clearfill Universal Bond Quick Kuraray Noritake Dental Inc., Tokyo, Japan 1H0018 10-Methacryloyloxydecyl dihydrogenphosphate (MDP), BisphenolA diglycidylmethacrylate,
2-Hydroxyethylmethacrylate (HEMA), hydrophilic amide monomers, colloidal silica, silan coupling agent, sodium fluoride, dl-Camphorquinon, ethanol, water,k-Etchant, phosphoric acid, water, colloidal silica, pigment
Primer MBP Monobond-Plus Ivoclar Vivadent, Schaan, Liechtenstein V30663 10-Methacryloyloxydecyl dihydrogen phosphate, Methacrylated phosphoric acid ester, adhesive monomers, ethanol
CCP Clearfil Ceramic Primer 3M ESPE, Seefeld, Germany 650011 10-Methacryloyloxydecyl dihydrogen phosphate, 3-trimethoxysilylpropyl (3-MPS) methacrylate, sulphide methacrylates ethanol
CCPP Clearfill Ceramic Primer Plus Kuraray Noritake Dental Inc., Tokyo, Japan 3L0025 3-Methacryloxypropyl trimethoxysilane,
10-Methacryloyloxydecyl dihydrogenphosphate,
Ethanol
PBA Prime & Bond active Dentsply Sirona, Bensheim, Germany 1706000937 Phosphoric acid modified acrylate resin, multifunctional Acrylate, bifunctional acrylate, acidic acrylate, isopropanol, water, initiator, stabilizer

Table 1C
Cementation with RCCs.
RCC
Code
Material Manufacturer Lot Number Formulation
RXU RelyX™ Unicem 2 Automix 3M ESPE, Seefeld, Germany 670242 Methacrylate monomers containing phosphoric acid groups, Methacrylate monomers, Alkaline (basic) fillers, silanated fillers, Initiator components, Stabilizers, Rheological additives, Pigments
MCE Maxcem Elite™ Kerr Dental, Orange, USA 5495743 1,6-hexanediyl bismethacrylate, 2-hydroxy-1,3-propanediyl bismethacrylate, 7,7,9(or 7,9,9)-trimethyl-4,13-dioxo-3,14-dioxa5,12-diazahexadecane-1,16-diyl bismethacrylate, 3-trimethoxysilylpropyl methacrylate, 1,1,3,3-tetramethylbutyl hydroperoxide
PSA Panavia™ SA Cement Plus Automix Kuraray Noritake Dental Inc., Tokyo, Japan 2A0218 Paste A:10-Methacryloyloxydecyl dihydrogen phosphate, bisphenol A diglycidylmethacrylate, triethyleneglycol dimethacrylate (TEGDMA), hydrophobic aromatic dimethacrylate, 2-Hydroxyethylmethacrylate, silanated barium glass filter, silanated colloidal silica, dl-Camphorquinone, peroxide, catalysts, pigments
CAU Calibra Universal Dentsply Sirona, Bensheim, Germany 170222 Urethane Dimethacrylate, Di-and Tri-Methacrylate resins,
phosphoric acid, modified acrylate resin, Barium Boron Flouro Alumino Silicate Glass, organic peroxide Initiator, camphorquinone, phosphene oxide, accelerators, butylated hydroxy toluene,UV stabilizer, titaniumdioxide, iron oxide,
hydrophobic amorphous silicon dioxide

Table 2A
Surface preparation of zirconia substrates and cementation.
Part 1 Part 2
Zirconia cylinders or zirconia cuboids 480 cylinders of Prettau® Zirconia
(6 mm diameter / 3 mm height).
480 cuboids of Y-TZP Cercon ht®
(12 mm edge length / 2 mm thickness)
Glazing Air abrasion Glazing Air abrasion
Air abrasion Pure Al 2 O 3 :
Particle size 110 μm
Pressure 2 bar
Duration 15 s
Distance 10 mm
Rocatec SOFT (R-TEC):
Particle size 30 μm
Pressure 2 bar
Duration 15 s
Distance 10 mm
Pure Al 2 O 3 :
Particle size 110 μm
Pressure 2 bar
Duration 5 sec
Distance 10 mm,
Angle 45°
Pure Al 2 O 3 :
Group 1: Particle size 110 μm, pressure 3.5 bar
Group 2: Particle size 110 μm, pressure 2 bar
Group 3: Particle size 50 μm, pressure 2 bar
Group 4: Particle size 50 μm, pressure 0.5 bar
For all four subgroups:
Distance 10 mm, angle 45°, duration 5−7 sec
Glazing HB, ZM or IPS:
Sprayed in circular movement, angle 90°, distance 10 cm
HB:
Distance 10 cm
Air abrasion after glazing HB and ZM:
Pure Al 2 O 3
Particle size 110 μm
Pressure 1 bar
Duration 5 s.
Distance 10 mm
IPS:
Pure Al 2 O 3,
Particle size 50 μm
Pressure 0.75 bar
Duration 5 s.
Distance 10 mm
Pure Al 2 O 3
Particle size 110 μm,
Pressure 0.1 MPa
Distance 10 mm
Angle 45°
HF-Treatment Hydrofluoric acid 9%
60 s, rinsed for 30 s
Hydrofluoric acid 10% 60 s, rinsed for 60 s
Silanization/Priming Monobond Plus or
Clearfill Ceramic Primer
60 s
Monobond Plus or
Clearfill Ceramic Primer 60 s
Calibra Silane 60s
or
Clearfil CCP plus 60 s
P&B active or
Clearfil CCP plus
20 s
For half of the specimens
Bonding P&B active or
Clearfil universal bond
for half of the specimens
Self-adhesive composite cements Maxcem Elite or
RelyX Unicem 2 Automix
Maxcem Elite or
RelyX Unicem 2 Automix
Calibra Universal or
Panavia SA Cement Plus
Calibra Universal or
Panavia SA Cement Plus
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Mar 21, 2021 | Posted by in Dental Materials | Comments Off on Optimizing the fitting-surface preparation of zirconia restorations for bonding to dentin
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