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...
This study evaluated the effect of abutment materials on the fracture resistance of composite crowns for premolars. Composite crowns were fabricated using two different indirect composite resin materials (Meta Color Prime Art or Estenia C&B) and cemented onto either a metal (Castwell M.C. 12) or composite resin (Build-It FR and FibreKor) abutment with resin cement (Panavia F2.0). Twenty-four specimens were fabricated for four groups (n=6 each) and subjected to 280-N cyclic impact loading at 1.0 Hz. The number of cycles which caused the composite crown to fracture was defined as its fracture resistance. All data were statistically analyzed using ANOVA and the Bonferroni test (α=0.05). Composite crowns cemented onto resin abutments showed higher fracture resistance than those cemented onto metal abutments.
INTRODUCTIONResin-based adhesive systems, which mostly involve the use of metal primers to improve the bond strength of resin cements to metals, are used in diverse ways in dentistry. Intraorally, these adhesive systems are used for direct filling procedures and cementation of indirect restorations. For such cases in the oral cavity, the adherend temperature is about 37°C. Extraorally, these adhesive systems are used in the fabrication and repair of indirect restorations. For such cases outside the oral cavity, the adherend would typically assume the ambient room temperature, which is about 23°C.The bonding procedure begins with the contact of adhesive resin to the adherend surface and completes at resin cement polymerization. It is a process which combines the diffusion of monomers in primers and resin cements and the chemical reaction between adhesive resin and adherend. Amongst the key factors that affect the diffusion process and chemical reaction is the adherend temperature, and which thus affects the bonding performance.In a study by Miyazaki et al. 1) , it was reported that the shear bond strengths of several dentin bonding systems decreased with increasing relative humidity but were not influenced by environmental temperature. In another report by Brackett et al.2) which studied the effect of temperature on the shear bond strength of three commercial resins to dentin, they reported that significant differences were observed between 20°C and 55°C for all resins, and that one adhesive resin exhibited a significant difference between 20°C and 37°C2) . Numerous studies have investigated the effects of varied resin cement temperatures, with mostly comparing between room temperature [1][2][3][4][5][6] and intraoral temperature 1,3) . On the choice of adherend, it was limited to either dentin [1][2][3][4][5][6] or enamel 7) . To the best of the authors' knowledge, the effect of adherend temperature on bonding has not been studied. In this study, a heat-polymerizing denture base resin and a silver-palladium-copper-gold (Ag-Pd-Cu-Au) alloy were selected as the adherend materials. Since the focus was on the effect of adherend temperatures, bonding procedures were carried out at four different adherend temperatures to simulate a wide range of intraoral and extraoral conditions: 10°C, 23°C, 37°C, and 55°C. Bond strength before and after thermocycling were then evaluated using specimens fabricated by bonding an auto-polymerizing resin to each adherend at each of the four designated temperatures.The null hypothesis of this study was that the shear bond strengths of auto-polymerizing resin to denture base resin and 4-META/MMA-TBBO resin to Ag-Pd-Cu-Au alloy would not be affected by adherend temperature. Table 1 presents the materials used in this study. For the adherends, the selected materials were a heatpolymerizing denture base resin (Acron, GC Corp., Tokyo, Japan; AC) and an Ag-Pd-Cu-Au alloy (Castwell M.C. 12, GC Corp., Tokyo, Japan; MC). For the adhesive resin cements, an auto-polymerizing repair resin (Unifast...
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