The purposes of this study were twofold: (1) to examine the effects of bleaching on the bond strength of an adhesive to bovine tooth surfaces; and (2) to explore the effectiveness of an ascorbic acid application in preventing the deterioration of bonding ability due to bleaching. In the experimental groups, ascorbic acid was applied to the bleached bovine tooth surfaces. In the control groups, the tooth specimens were bleached but no ascorbic acid application was carried out. All bonded specimens were subjected to shear bond test, and the data were statistically analyzed with twoway ANOVA and Bonferroni' s test (p＝0.05). Bond strengths to the bleached specimens were significantly lower than those of non-bleached specimens. No statistical differences were found in bond strength between the bleached and non-bleached groups when the ascorbic acid treatment was carried out. Results of this study suggested that ascorbic acid application was effective in preventing the reduction of bonding ability to bleached teeth.

The purpose of this study was to evaluate the effect of thermal cycling on the surface texture of restorative materials. Disk-shaped specimens made of seven resin composites (Beautifil: BF; Esthet-X: EX; Filtek Supreme: FS; Inten-S: IS; Point 4: PT; Solare: SR; and Venus: VS) were finished with 1-μm alumina suspension, and then thermocycled between 4 and 60 ℃ in distilled water for 20,000 or 50,000 cycles with a dwell time of 60 seconds. Staining susceptibility and mean surface roughness, Ra, were examined, and surface texture was observed by scanning electron microscopy. Dye penetration test showed that the surfaces of all resin composites were more stained after thermal cycling. Mean Ra of all resin composites, except PT, significantly increased after 50,000 thermal cycles. Dislodgement of filler particles was observed for all resin composites after thermal cycling, except FS. It was concluded that thermal cycling significantly affected the surface texture of the seven examined resin composites.

The purpose of the present study was to evaluate the efficacy of pretreatment on the bonding durability between titanium casting and two acrylic adhesives. Cast titanium disk specimens treated with four polymer-metal bonding systems as follow: 1) air-abraded with 50-70 μm alumina, 2) 1)+Alloy Primer, 3) 1)+M.L. Primer and 4) tribochemical silica/silane coating system (Rocatec System). The specimens were bonded with M bond or Super-bond C&B adhesive. The shear bond strengths were determined before and after thermocycling (20,000 cycles). The surface characteristics after polishing, and for the 1) and 4) preparations were determined. The bond strengths for all combinations significantly decreased after thermocycling. The combination of Super-bond C&B adhesive and 2) led to significantly higher bond strength than the other preparations after thermocycling. The maximum height of the profile parameters for the polishing group was lower than other preparations.

No abstract

INTRODUCTIONResin-bonded fixed partial dentures with cast metal frameworks have emerged as a minimally invasive, aesthetically pleasing, and predictable treatment option for abutment teeth [1][2][3] . Two key factors contribute to this emerging trend: improvement in retainer design [4][5][6] and availability of metal primers which react directly and chemically with the bonding surfaces of noble metal alloys, such as silver-containing gold-palladium alloys 7,8) and type IV gold alloy [8][9][10] . Noble metal alloys are not suitable for cases that require high-quality aesthetic appearance. To satisfy both aesthetic and functional demands, the optimal alternative is resin-bonded fixed partial dentures fabricated with metal alloy frameworks and porcelainfaced pontics. Traditionally, nickel-chromium [11][12][13] and cobalt-chromium 12,14) alloys are used for the retainers. This is largely because of well-established, durable bonding of adhesive resin cements to nickel-chromium 15,16) and cobalt-chromium 17,18) alloys. However, noble metal ceramic alloys are preferable and superior in terms of castability, workability, corrosion resistance, and biocompatibility 19,20) . Macro-mechanical retention and micro-mechanical retention are two critical factors that influence the clinical success and longevity of fixed partial dentures. Macro-mechanical retention depends on abutment preparation and precision of fit of retainers. Micromechanical retention is achieved by chemical bonding, which in turn can be achieved with surface modification of metal substrates or application of metal primers [7][8][9][10] .On the former, currently available surface treatment methods range from tin (Sn) plating 13,21,22) to thermal silica coating (Silicoater MD) 22) and tribochemical silica coating (Rocatec) 23) . On the latter, adhesion promoting monomers play an important role in improving bonding, which is especially vital for restorations with compromised retention form.For base metals, it was shown that the presence of both TBBO initiator and 4-META functional monomer at the resin-metal interface during the setting reaction improved the bonding to cobalt-chromium alloy 18) . For noble metals, inclusion of thiirane monomers as an adhesive monomer component of MMA-TBBO resin improved the bonding to dental precious metal alloys 24) . Studies 25,26) have also shown the positive effect of metal primers on the bonding of 4-META/MMA-TBBO resin to high-gold-content metal ceramic alloys. At the same time, these studies 25,26) revealed the inadequacy of these primers on bonding to pure palladium (Pd) and highpalladium-content metal ceramic alloys. Although some studies 7-9) have reported on the efficacy of metal primers in improving the bond strength to Pd-containing alloys, it must be highlighted that these alloys contained other metals such as Ag and Cu, which are compatible with numerous primers 25) . The purpose of this study was to evaluate the effect of adhesion promoting monomers on bonding of MMA-TBBO resin to Pd. Although pure Pd is not use...