Adhesion promotion between metadent and a high palladium alloy with a pyrolytically fused porcelain opaque layer

Several authors have reported a preference for the use of high palladium alloys in the construction of implant-fixed partial denture (IFPD) substructures. Heat-polymerized polymethyl methacrylate resins (PMMR) are used to secure denture teeth to IFPD substructures. Metadent (Sun Medical Co, Kyoto, Japan), a heat-polymerized PMMR containing 5% 4-methacryloxyethyl trimellitate anhydride (4-META), could possibly improve the overall design of the prosthesis because this resin adheres to resin and ceramic denture teeth and noble metals. However, adhesive bonding between Metadent and elemental palladium has been shown to be poor. The purpose of this study was to evaluate the potential for adhesive bonding between Metadent, titanate primers, and a ceramic layer pyrolytically fused to a high palladium alloy.

Five groups of 10 specimens were prepared. A layer of opaque porcelain was baked on all of the specimens under vacuum at 1760 degrees F. The specimens were grouped as follows: (1) Metadent resin processed on ceramic with no primer, (2) Metadent resin with 10% ethyl acetoacetate titanate (DC) processed on ceramic with no primer, (3) Metadent resin with 10% DC processed to ceramic with a 2% tetraisopropyl (TPT) surface primer, (4) 4-Metadent resin with 10% DC processed to ceramic with a 2% isopropyl dimethacryloyl isostearoyl titanate (KR-7) surface primer, and (5) Metadent resin with 10% DC processed to ceramic with a titanium dioxide layer on the opaque and a KR-7 surface primer. The primers were in a methyl methacrylate (MMA) solution. All of the specimens were heat-polymerized under pressure at 212 degrees F for 1 hour. One-half (25) of the specimens (5 from each group) were hydro-thermocycled at 4 degrees C to 55 degrees C, 0.5 minute dwell per bath for 3,000 cycles. All specimens were tested in shear on an MTS Universal machine at cross head speeds of 0.5/mm/min.

The results showed adhesion between the resin-ceramic layer in virtually all groups regardless of thermocycling effects. The control (heat cure without 10% DC and no primer) and the 10% DC with KR-7 and TPT primer groups had an average MPa of 7.5, 7.7, and 7.0, respectively. The failure mode of the specimens was adhesive, with the site of failure being the porcelain-metal interface.

It was concluded that adhesion between palladium alloy and Metadent was possible when a ceramic layer was used as an intermediary interface. The limitation seemed to be the adhesion of the ceramic to the metal.