ESCA study on dental alloy surfaces modified by Ga-Sn alloy

Bonding behavior and chemical and mechanical properties of silver-based dental alloys

This article presents a review of silver-based dental alloys, with a focus on their bonding behavior and their chemical and mechanical properties. The most effective pretreatment for bonding silver-based alloys involves alumina air-abrasion followed by the application of a metal adhesive primer containing both the vinyl-thione monomer and a hydrophobic phosphate monomer. Silver-based alloys are readily sulfurized, making it clinically important to limit their use to cast post and core restorations to avoid direct exposure to salivary components. Fracture of the post and core restorations can be prevented by reinforcing their mechanical properties by applying the cast joining technique with tougher metals.

Visualization study on distortion of a metal frame by polymerization shrinkage and thermal contraction of resin

Three types of metal specimens (ring-shaped, plate-shaped, and a simulated anterior arch) for distortion observations were made from Au-Ag-Pd-Cu alloy. Distortion due to polymerization shrinkage and thermal contraction of a heat-curing acrylic resin containing 4-META (4-methacryloyloxyethyl trimellitate anhydride, 4-META resin) could be visualized for the ring-shaped specimen, which showed increasing distortion of the metal frame upon adhesion of the resin to the outer metal surface. Distortion of the plateshaped specimen adhering to 4-META resin decreased with increasing thickness of the cured resin. The distortion of the metal frame simulating an anterior arch of a six-unit bridge with a facing composite resin showed that the curvature of the metal frame was larger after curing of the facing composite resin. However, it recovered most of its original curvature with an associated increase in the number of cracks between the crowns after trimming the resin to a tooth profile.

Analysis of residual stress in the resin of metal-resin adhesion structures by scanning acoustic microscopy

The residual stress caused by polymerization shrinkage and thermal contraction of a heat-curing resin containing 4-META on a metal-resin structure was measured by a scanning acoustic microscope. The tensile residual stress in the resin occurred within 70 µm of the adhesion interface with a flat plate specimen. The maximum tensile stress was about 58 MPa at the interface. On a metal plate specimen with retention holes, ring-like cracks in the resin occurred around the retention holes with the adhesive specimen and many linear cracks occurred in the resin vertical to the longitudinal direction of the metal frame with the non-adhesive specimens. There was tensile residual stress on the resin surface at the center of the retention holes of the adhesion specimen, indicating that the stress in the specimen with surface treatment for adhesion was higher than in that without surface treatment.

Surface analysis of porcelain fused to metal systems

OBJECTIVE

The effect of four different, commonly performed, metal-ceramic alloy, surface preparation stages, were investigated to observe surface compositional changes.

METHODS

Two metal-ceramic alloys were examined (Pd/Ag alloy and a Ni/Cr alloy). Discs 12 mm diameter and 2mm thick were produced using the lost wax casting process. Prior to casting alloy ingots were examined using X-ray fluorescence spectrometry (XRF) to determine bulk composition. The four preparation stages were (1) devesting and Al2O3 blasted; (2) ground smooth and Al2O3 blasted; (3) oxidation firing; (4) firing cycle for opaque porcelain application. X-ray photoelectron spectroscopy (XPS) surface analysis was performed after each surface preparation stage to determine changes in surface composition. SEM with EDS was also used to identify surface composition.

RESULTS

XRF and manufacturers compositional analysis of the alloys showed similar findings for the major elements. XPS analysis showed that at preparation stages 3 and 4 evidence of elemental migration to the surface (In with Pd/Ag alloy and Cr and Mn with Ni/Cr alloy). Alumina was also seen on the alloy surfaces, with SEM/EDS confirming Al2O3 particles embedded in the surface of the alloys.

SIGNIFICANCE

Surface composition is very different from the batch composition. Surface preparation stage 3 is essential in bringing to the alloy surface elements which could be directly involved in the metal-ceramic bond. Elements and their oxides, in various forms, cover the surface of the alloys. Al2O3 particles can remain embedded in the alloy surface during porcelain application.

Direct bonding to Adlloy-treated amalgam

The purpose of this study was to test the bond-enhancing effect by modifying amalgam surfaces with Adlloy (a gallium-tin liquid alloy) and bonding brackets by using two different resin systems. Bond strength and location of bond failure was assessed by using (1) Concise (3M Dental Products) and (2) C&B Metabond (Parkell) systems with and without the use of Adlloy alloy. Class V buccal amalgam restorations (n = 132) were subjected to one of two surface treatments: (1) sandblasting or (2) sandblasting plus Adlloy treatment. Mandibular premolar brackets were bonded with Concise composite resin or C&B Metabond (adhesive) to amalgam surfaces. All specimens were stored in 37 degrees C water for 10 weeks and subjected to thermocycling before bond strength testing. The laboratory shear bond strength of Concise material to amalgam was not improved after Adlloy modification. However, Adlloy-treated amalgam significantly increased the laboratory shear bond strength of orthodontic brackets bonded with C&B Metabond material. The majority (58%) of the bond failures of C&B Metabond bonded to non-Adlloy treated-amalgam occurred at the amalgam-adhesive interface, whereas the majority (58%) of the bond failure of C&B Metabond bonded to Adlloy-treated amalgam failed within the adhesive. Fracture within the amalgam during debonding was observed with C&B Metabond bonded to sandblasted amalgam (21%) and Adlloy-treated amalgam (15%). Regardless of Adlloy treatment, C&B Metabond would appear to provide adequate orthodontic bonding to amalgam; however, there may exist a potential risk of amalgam restoration fracture upon debonding.

A new method for promoting adhesion between precious metal alloys and dental adhesives

A new, simple method of modifying the adherend metal surface by a liquid Ga-Sn alloy (Adlloy) was applied to dental precious and base-metal alloys for adhesion with 4-META adhesive resin. Adhesions of 4-META resin to three other surface states--as-polished, oxidized at high temperature, and electroplated tin--were also performed for comparison with the adhesion on Adlloy-modified surfaces. Bond strength measurements were made, and the durability against water at the adhering interface was evaluated. The Adlloy-modified gold alloys (Type IV and 14 K) and silver-based alloys (Ag-Pd and Ag-Cu) showed not only high bond strengths but also excellent water durability at the adhesion interface. Surface modification by Adlloy, however, did not affect adhesion to Ag-In-Zn and base-metal (SUS, Co-Cr, and Ni-Cr) alloys. Adhesion to the tin-electroplated specimens was comparable with that to the Adlloy-modified specimens.