J. Matyas

Effects of disinfectants on dimensional accuracy of impression materials

There is a continuing concern over the potential for cross-contamination of viral infections such as AIDS by means of dental impressions. This investigation compared the effects of various viricidal agents on the accuracy of irreversible hydrocolloid and silicone impressions made of single-unit and full mandibular arch models. Measurements on casts made from the treated impressions were compared with the corresponding measurements on casts made from untreated impressions. The results of this study led to the conclusions that there was no preferred disinfectant with respect to dimensional stability for the irreversible hydrocolloid, condensation silicone, or vinyl polysiloxane impression materials tested, and there was no difference in the accuracy of the casts obtained either by spraying with or immersion in any of the disinfectants tested. Therefore using the disinfectants described with either the immersion or spray techniques will not significantly affect the dimensional accuracy of cats made from treated impressions.

The accuracy of highly filled elastomeric impression materials

Summary A specific test was used to determine the accuracy of the highly filled silicone impression materials. They proved to be as accurate as the other standard impression materials tested. Two of the three highly filled silicone systems had the advantage of showing the lowest variability of accuracy. This study supports the use of the Class IV silicones for dental duplication procedures when such materials are used in conjunction with a corrective wash. This procedure obviates the need for making a custom impression tray.

Effectiveness of porcelain repair systems

The study indicates that the repair system using a bonding agent with acrylic resin is significantly stronger than the repair system using a specific composite resin. On the basis of this study, the acrylic resin repair system has the best potential for clinical success in porcelain-to-porcelain repairs.

Effect of metal surface treatment on ceramic bond strength

This study indicates that the unaltered specimens of both alloys produced the lowest bond values; for the gold-palladium alloy, a short degassing period (manufacturers recommendation) and a 10-minute degassing period resulted in significantly lower bond strengths than those observed with the aluminum oxide and the steam cleaning treatments; and all treatments of the silver-palladium alloy gave comparable bond strengths to that obtained with the manufacturers recommendation for surface treatment. Because the simplified methods gave equivalent or higher bond strength values than the manufacturers recommendations, and because of the time saving, we recommend the following procedures for the porcelain-alloy systems tested: After casting and investment removal, use an abrasive to remove casting irregularities and to modify or correct the surface that will receive porcelain. Create a uniform matte finish on the surface that is to receive porcelain by pressure blasting with 50 micron aluminum oxide particles, or steam clean the surface for 30 seconds, or both. Proceed with opaquing.

Effect of opaque porcelain application on strength of bond to silver-palladium alloys.

The opaque porcelain layer for porcelain-fused-to-metal restorations is critical for success. This investigation examined opaque porcelain application using one- and two-layer techniques with respect to their effect on the strength of bond to three silver-palladium alloys. There were no significant differences in the flexural bond strengths of the three alloys for the one- and two-layer opaque application techniques. With respect to bond strength, these results afford flexibility in the choice of the one- or two-layer techniques.

Reuse of silver-palladium ceramic metal

The effect of various percentages of reused silver-palladium alloy on the bond strength of porcelain was considered. All-new metal and once-cast alloy with the addition of 50% new metal produced the highest bond values. Once-cast alloy with less than 50% new metal produced bond strength values that were significantly lower. When using this silver-palladium alloy, 50% new alloy should be added to each casting button, and buttons with questionable casting history should not be used.

Magnetizable abutment crowns for distal-extension removable partial dentures

A study of the retention and load-distributing characteristics of bilateral distal-extension dentures with magnetizable abutment crowns revealed the following findings: Comparable retention was obtained with the horizontal and oblique pedestals. Decreased retention was noted when there was space between the magnet and pedestal. The retention values were substantially higher than reported values for the I-bar retainer. For the space and no-space situations, the horizontal pedestal design provided better stress results than the oblique design. Better stress-distributing properties for horizontal and oblique pedestals were obtained with the presence of a space between the magnets and pedestals. Of all the designs tested, the horizontal pedestal with a space demonstrated the best load-transmission characteristics.

The interaction of a magnetically retained denture with osseointegrated implants

A replica of an atrophied mandible was constructed in which two Brånemark implants were embedded to simulate osseointegration. Ferromagnetic keepers were then attached to the implants. A complete overdenture was constructed which had magnets positioned directly over the keepers. The denture was then subjected to different loads and the stresses were photographically recorded. The denture was also tested for its retention capabilities. Because of the equitable stress distribution with the absence of high foci of concentration, a magnetically-retained overdenture with osseointegrated supports lends itself well as a prosthetic replacement. In addition, the magnets exhibit sufficient retention without unduly loading the implants or residual ridge. It may be concluded that in a similar in vivo situation, magnets could be an alternative to other attachment systems; however, there are many variables to be considered on an individual patient basis.

Retention magnets in guiding plates of distal-extension removable partial dentures

This investigation studied vertically placed magnets that act simultaneously as guiding plates and retentive devices. The retention of vertically placed magnets was less than that of horizontally or obliquely placed magnets, but comparable to that of I-bar retainers. Load-induced stresses were lower, transmitted more axially to the abutments and were generally more equitably distributed than stresses produced by magnets in other orientations to the abutment tooth. The force distribution characteristics were less stressful than those of a comparable RPD with distal guiding plates, mesial rests, and I-bar retainers. Although the investigators were initially concerned about the relative capabilities of the vertically placed magnets, in vitro and in vivo studies demonstrated that retention was as good if not better than that of conventional clasp designs.