Development of New Precious Metal Alloys for Resin Bonding with Adhesive Metal Primer

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New dental precious metal alloys containing In Zn, or Sn for resin bonding have been developed. Excellent adhesive ability with dental adhesive was obtained by using a thiophosphate metal primer. The authors have presented Japanese Patent (Adhesive Dental Precious Metal Alloys, H6-204145,1994). In the present project, adhesion mechanism was investigated by analytical methods including quartz crystal microbalance method, FT-IR,and ESCA.The application for clinical use was also studied in the field of prosthodontic and restorative dentistry. The results obtained were as follows :1) Excellent water durability at adhesion interface between adhesive resin and new precious metal alloys was obtained with adhesive primer. Corrosion resistant of alloys containing 60-70% gold was not decreased by adding of base metal up to 18% with copper. The corrosion resistance was comparable to commercial 14 K gold alloy. Aging behavior did not change by adding base metals.2) The Au-In alloy surface was analyzed by ESCA to establish the relationship with adhesive ability. It is considered that chemisorbed and/or physisorbed H_2O molecules on the surface caused the poor adhesive ability of 4-META resin to pure gold. To obtain excellent adhesion the element of an oxide having chemical affinity for 4-META must cover at least 50% on the alloy surface.3) Chemical interaction, based on Bolger's acid-base interaction, of 4-META with oxides such as In_2O_3, ZnO,and Sio formed on gold alloys was investigated to better understand the adhesion mechanism between metal and 4-META resin. Polar surface interaction was discussed with the isoelectric point of oxides and pK_A of adhesive monomer. The interaction of 4-META with In_2O_3, ZnO,and SnO was considered to be ionic, and hydrogen bonds were assumed with SiO_2.