Bond strength of veneer ceramic and zirconia cores with different surface modifications after microwave sintering

PURPOSE: To evaluate the effects of surface treatments on shear bond strength (SBS) between microwave and conventionally sintered zirconia core/veneers. MATERIALS AND METHODS: 96 disc shaped Noritake Alliance zirconia specimens were fabricated using YenaDent CAM unit and were divided in 2 groups with respect to microwave or conventional methods (n=48/group). Surface roughness (Ra) evaluation was made with a profilometer on randomly selected microwave (n=10) and conventionally sintered (n=10) cores. Specimens were then assessed into 4 subgroups according to surface treatments applied (n=12/group). Groups for microwave (M) and conventionally (C) sintered core specimens were as follows; M(C),C(C): untreated (control group), M1,C1:Al2O3 sandblasting, M2,C2:liner, M3,C3:Al2O3 sandblasting followed by liner. Veneer ceramic was fired on zirconia cores and specimens were thermocycled (6000 cycles between 5degrees-55degrees C). All specimens were subjected to SBS test using a universal testing machine at 0.5 mm/min, failure were evaluated under an optical microscope. Data were statistically analyzed using Shapiro Wilk, Levene, Post-hoc Tukey HSD and Student's t tests, Two-Way-Variance-Analysis and One-Way-Variance-Analysis (alpha=.05). RESULTS: Conventionally sintered specimens (1.06 +/- 0.32 microm) showed rougher surfaces compared to microwave sintered ones (0.76 +/- 0.32 microm)(P=.046), however, no correlation was found between SBS and surface roughness (r=-0.109, P=.658). The statistical comparison of the shear bond strengths of C3 and C1 group (P=.015); C(C) and M(C) group (P=.004) and C3 and M3 group presented statistically higher (P=.005) values. While adhesive failure was not seen in any of the groups, cohesive and combined patterns were seen in all groups. CONCLUSION: Based on the results of this in-vitro study, Al2O3-sandblasting followed by liner application on conventionally sintered zirconia cores may be preferred to enhance bond strength.

The bond characteristics of porcelain fused by titanium surface modification / 대한치과보철학회지

STATEMENT OF PROBLEM: Titanium is well known as a proper metal for the dental restorations, because it has an excellent biocompatibility, resistance to corrosion, and mechanical property. However, adhesion between titanium and dental porcelains is related to the diffusion of oxygen to the reaction layers formed on cast-titanium surfaces during porcelain firing and those oxidized layers make the adhesion difficult to be formed. Many studies using mechanical, chemical and physical methods to enhance the titanium-ceramic adhesion have been actively performed. PURPOSE: This study meant to comparatively analyse the adhesion characteristics depending on different titanium surface coatings after coating the casts and wrought titanium surfaces with Au and TiN. MATERIAL AND METHOD: In this study, the titanium specimens (CP-Ti, Grade 2, Kobe still Co. Japan) were categorized into cast and wrought titanium. The wrought titanium was cast by using the MgO-based investment(Selevest CB, Selec). The cast and wrought titanium were treated with Au coating(ParaOne(R), Gold Ion Sputter, Model PS-1200) and TiN coating(ATEC system, Korea) and the ultra low fusing dental porcelain was fused and fired onto the samples. Biaxial flection test was done on the fired samples and the porcelain was separated. The adhesion characteristics of porcelain and titanium after firing and the specimen surfaces before and after the porcelain fracture test were observed with SEM. The atomic percent of Si on all sample surfaces was comparatively analysed by EDS. In addition, the constituents of specimen surface layers after the porcelain fracture and the formed compound were evaluated by X-ray diffraction diagnosis. RESULT: The results of this study were obtained as follows : 1. The surface characteristics of cast and wrought titanium after surface treatment(Au, TiN, Al2O3 sandblasting) were similar and each cast and wrought titanium showed similar bonding characteristics. 2. Before and after the biaxial flection test, the highest atomic weight change of Si component was found in Al2O3 sandblasted wrought titanium(28.6at.% --> 8.3at.%). On the other hand, the least change was seen in Au-Pd-In alloy(24.5at.%--> 19.1at.%). 3. Much amount of Si components was uniformly distributed in Au and TiN coated titanium, but less amount of Si's was unevenly dispersed on Al2O3 sandblasting surfaces. 4. In X-ray diffraction diagnosis after porcelain debonding, we could see Au2Ti compound and TiN coating layers on Au and TiN coated surfaces and TiO2, typical oxide of titanium, on all titanium surfaces. 5. Debonding of porcelain on cast and wrought titanium surface after the biaxial flection is considered as a result of adhesion deterioration between coating layers and titanium surfaces. We found that there are both adhesive failure and cohesive failure at the same time. CONCLUSION: These results showed that the titanium-ceramic adhesion could be improved by coating cast and wrought titanium surfaces with Au and TiN when making porcelain fused to metal crowns. In order to use porcelain fused to titanium clinically, it is considered that coating technique to enhance the bonding strength between coating kKlayers and titanium surfaces should be developed first.