EVALUATION OF DIFFERENT SURFACE CONDITIONING METHODS ON THE BOND STRENGTH OF ZIRCONIA CERAMIC TO A RESIN CEMENT

Surface conditioning methods used for resin bonding to conventional silica base dental ceramics are not dependable for zirconium ceramic. The aim of this study was to evaluate the effect of different surface conditioning methods on the shear bond strength of zirconia ceramic to resin cement. Twenty eight Zirconia ceramic specimens were fabricated from (IPS e.max Zir CAD), and randomly assigned to four groups (n=7). Each group was subjected to the following surface treatments: Control (no treatment), sandblasting with 110 μm aluminum oxide, Silica coating and silanization (CoJet system), and Nd: YAG laser irradiation. A composite resin discs were fabricated and bonded to the treated ceramic surfaces using resin luting agent (Panavia F 2.0) and stored for 24 hours in distilled water at 37 OC. Specimens then subjected to thermocycling for 1000 cycles between 5O C and 55O C with a 30 s dwell time. All specimens were subjected to shear bond strength test by a universal testing machine at a crosshead speed of 0.5 mm/minute. The shear bond strength values were analyzed with ANOVA to compare between groups using SPSS software . The level of significance was 0.05. Results obtained showed that silica coating and silanization (CoJet system) is an effective method for achieving an acceptable bond between zirconia and resin cement. The use of Nd: YAG laser enhance the bond strength between the zirconia and resin cement. (3668) Tarek R. Abdelrehim E.D. J. Vol. 63, No. 4 The success of all ceramic restorations is extremely dependent on achieving a bond of resin with the underlying tooth structure as well as with the restoration. Bonding is required for enhancement of retention, fracture resistance, marginal adaptation and bond strength of the restorations (4). A proper use of ceramic surface conditioning methods is necessary for the strength of ceramic restorations that depends on the integrity of luting cement to ceramic (5,6). A strong resin ceramic bond depends on the chemical bond between the ceramic and the luting cement also on the micromechanical retention produced by surface roughening . There are different surface treatment methods as grinding with diamond rotary instruments, air abrasion with alumina, acid etching by hydrofluoric acid, silica coating, coupling with silane and combination of any of these methods (7, 8). However, in case of zirconia ceramics because the limited glass phase and the absence of silica in zirconia structure, it is not susceptible to hydrofluoric acid etching and the formation of a siloxane network with the siloxane groups contained in bifunctional primers (9,10). According to this findings, alternative techniques such as silica coating (11), use of phosphate acidic monomers on cements or primers(12-13), laser irradiation (14-15), and other techniques to modify the zirconia ceramic surfaces has been introduced for the treatment of the zirconia surfaces to be bonded to the resin based cements (16-17). There are different studies comparing different surface treatment techniques but the best method for achieving the bond between zirconia and resin cement is still undefined. Therefore the purpose of this in vitro study was to evaluate the effect of different surfaces conditioning methods on the shear bond strength between zirconia ceramic and resin cement. MATERIAL AND METHODS Twenty eight zirconia ceramic specimens (IPS e.max ZirCAD; Ivoclar Vivadent , Schaan, Liechtenstein) were fabricated from pre-sintered blocks by means of water cooled diamond disc. The specimens were sintered in Programat S1 high temperature furnace following the manufactures instructions. The sintered specimens were then ultrasonically cleaned with 96% isopropyl alcohol for 3 min and 10 min in distilled water. The zirconia specimens were randomly divided into four groups (n=7) as follows: Group 1, Control (CO)-no treatment. Group 2 (SB) sandblasted with 110 μm aluminum oxide (Al2O3) particles (Korox, Bego, Germany) for 15 seconds at 35 psi from a distance of 10 mm, Group 3 (SC), silica coated with 30 μm CoJet Sand ( 3 M -ESPE, Germany) at a 2.8 Psi pressure for 10 s at a distance of 10 mm , and then a silane coupling agent (ESPE-Sil;3M ESPE) was applied and allowed to dry for 60 s . Group 4(L) Laser irradiation by Nd: YAG laser system (Continuum NY 81-30 USA) at the infrared wave length (p =1064). The laser beam was reflected at 90 O angle on the specimen which was fixed on a special holder via a special flat fully reflected dielectric mirror (Melles Groit 02 MPG) held at 45O incident angle. The exposure power densities (210 MW /cm2) and the number of pulses was 1800 per minute (30 pulses /second). Transparent plastic tubes , 3mm high were filled with composite resin ( Filtek Z 350 XT,3M ESPE ), light polymerized (Heliolux DXL ,Ivoclar Vivadent, Schann Liechtenstein) for 40 seconds on each side before bonding to the treated zirconia ceramic specimens. A dual polymerizing adhesive resin luting agent (Panavia F 2.0, Kuraray America, Inc) was used according to the manufactures instructions to bond the filled plastic tubes to the pretreatment zirconia ceramic specimens. A static load of 1Kg was applied to the specimens until polymerization was achieved. Excess resin cement was removed with a brush. The luting agent was polymerized with a light EVALUATION OF DIFFERENT SURFACE CONDITIONING METHODS (3669) polymerizing system from two different directions for 40 seconds on each side. The polymerization light tip was placed at a distance of 5 mm from the specimen surface. Oxyguard II (Kuraray America, Inc) was applied for 10 minutes before removing the specimens from the press. The specimens were washed with air water spray and stored in distilled water at 37O for 24 hours . Specimens then subjected to thermocycling for 1000 cycles between 5O C and 55O C with a 30 s dwell time. Shear bond strength was tested by the universal testing machine (Instron, Canton, USA) at a crosshead speed of 0.5 mm/minute until failure occurred. The maximum force (MPa) to produce fracture was recorded using corresponding software. The data was collected and entered into personal computer. Statistical analysis was done using Statistical Package for Social Sciences (SPSS/version 20) software. Arithmetic mean and standard deviation, for the numerical data to compare between more than two groups ANOVA test was used. The level of significant was 0.05.