Jung-Yun Ha

Effect of heat treatment of dental zirconia ceramic treated with three different primers on the bonding durability of resin cement

AbstractEstablishing a durable bond with dental zirconia ceramic remains difficult. This study investigated the effect of heat treatment of primer-coated dental zirconia on the bonding durability of resin cement to the zirconia. Each of three types of primers (silane primer, acidic monomer-containing primer, and silane/acidic monomer containing two-component primer) was applied to sandblasted zirconia surfaces. For subsequent heat treatment, half were then put in a furnace for 60 min at 150 °C. All specimens were bonded with resin cement and aged using thermocycling (0, 5,000, and 20,000 cycles) prior to a shear test. The surface energy parameters of the zirconia were also calculated from the contact angle measurements based on the acid-base theory. The heat treatment enhanced the bonding durability of the zirconia pre-treated with the silane primer and the acidic monomer-containing one, the shear test and Weibull analysis results showed that the former performed better than the latter. In contrast, the twocomponent primer-coated zirconia showed poor bonding durability after the heat treatment. The bonding performance was related to the surface characteristics of the zirconia. Thus, we suggest that heat treatment of zirconia pretreated with silane primer effectively improves bonding durability with resin cement.

Preliminary Evaluation of Mechanical Properties of Co-Cr Alloys Fabricated by Three New Manufacturing Processes.

A preliminary tensile test was performed to evaluate the mechanical properties of cobalt-chromium (Co-Cr) alloys fabricated by three new manufacturing processes: metal milling, milling for soft metal, and rapid prototyping (n=6). For comparison, the three alloy materials were also used to fabricate specimens by a casting procedure. In all groups tested, the proof strength and elongation were over 500 MPa and 2%, respectively. The milled soft alloy in particular showed a substantially greater elongation, whereas the alloy fabricated by rapid prototyping exhibited a higher proof strength.

Effects of Prepolymerized Particle Size and Polymerization Kinetics on Volumetric Shrinkage of Dental Modeling Resins

Dental modeling resins have been developed for use in areas where highly precise resin structures are needed. The manufacturers claim that these polymethyl methacrylate/methyl methacrylate (PMMA/MMA) resins show little or no shrinkage after polymerization. This study examined the polymerization shrinkage of five dental modeling resins as well as one temporary PMMA/MMA resin (control). The morphology and the particle size of the prepolymerized PMMA powders were investigated by scanning electron microscopy and laser diffraction particle size analysis, respectively. Linear polymerization shrinkage strains of the resins were monitored for 20 minutes using a custom-made linometer, and the final values (at 20 minutes) were converted into volumetric shrinkages. The final volumetric shrinkage values for the modeling resins were statistically similar (P > 0.05) or significantly larger (P < 0.05) than that of the control resin and were related to the polymerization kinetics (P < 0.05) rather than the PMMA bead size (P = 0.335). Therefore, the optimal control of the polymerization kinetics seems to be more important for producing high-precision resin structures rather than the use of dental modeling resins.