Bonding characteristics of low-fusing porcelain bonded to pure titanium and palladium-copper alloy.

This study compared bond strengths among palladium-copper alloy/VMK 68 porcelain, cast titanium/Duceratin porcelain, and machine-milled titanium/Procera porcelain combinations and investigated the mode of bond failure of these combinations. The effect of multiple firings on the bond strength of porcelain bonded to machine-milled pure titanium was then examined. A uniform thickness of 1 mm of porcelain was applied along an 8 mm length in the central portion of metal specimens measured 25 x 3 x 0.5 mm. The specimens were subjected to a three-point bending test on a load-testing machine with a span distance of 20 mm, and the load of bond failure was recorded and statistically analyzed. Two completely debonded specimens and two longitudinally sectioned specimens of each group were studied with a scanning electron microscope to determine the mode of bond failure. The bond strength of Pd-Cu/VMK 68 porcelain was significantly greater than two titanium/porcelain combinations. There was no significant difference in the bond strengths of porcelain bonded to machine-milled pure titanium among the five porcelain firing schedules.

A study of the surface hardness and dimensional stability of several intermaxillary registration materials.

This study compared the surface hardness, the effect of time on surface hardness, and the dimensional stability of various intermaxillary relationship registration materials. The Shore hardness values of one zinc oxide-eugenol material, one polyether, and seven poly(vinyl siloxane) materials were obtained at 30 minutes and 24 hours after the start of mixing. The dimensional stability of one polyether and seven poly(vinyl siloxane) materials was measured using a standard mold as described in American Dental Association (ADA) Specification No. 19. All materials exhibited relatively high surface hardness despite some statistical differences among them. Four materials possessed higher surface hardness at 24 hours than at 30 minutes. Although the polyether showed significantly lower dimensional stability than the other materials, all materials satisfied the minimum requirement for Type I elastomeric impression material.

An investigation of the rheological properties of several interocclusal registration materials.

PURPOSE: To study the viscosities of eight interocclusal registration materials at 30 seconds after the start of mixing and to compare the time (Tcv) required for various interocclusal registration materials to reach a proposed critical viscosity of 5,000 poise. MATERIALS AND METHODS. One zinc-oxide eugenol, one polyether, and six vinyl-polysiloxane interocclusal registration materials were studied. The viscosities of the polymerizing materials were monitored with a cone and plate viscometer. RESULTS: One-way analysis of variance showed significant difference in the viscosity at 30 seconds and in the Tcv among the materials. A zinc oxide eugenol interocclusal registration material was found to possess the lowest viscosity at 30 seconds and the longest Tcv. CONCLUSIONS: The criteria for the selection of an interocclusal registration material should include its viscous properties because all materials behaved differently.

The effect of a shear load on the viscosities of 10 vinyl polysiloxane impression materials.

The viscosities of 10 vinyl polysiloxane impression materials with and without the effect of a shear load were studied. Samples of each impression material were divided into two groups. An initial shear load of 5.12 rpm was applied to group A samples for 10 seconds. No shear load was applied to group B samples during the same interval of time. The viscosities of two groups of samples were compared at 60 seconds. Results indicated that there were statistically significant differences among the group A or B samples of the impression materials. There were no statistically significant differences between the group A and B samples of five impression materials. The group A samples displayed significantly lower viscosities than group B samples for two impression materials. The group A samples also displayed significantly higher viscosities than group B samples for three impression materials. It was concluded that the effect of a shear load had no consistent effect on the viscosities of a group of vinyl polysiloxane impression materials.

A study of the "thixotropic" property of elastomeric impression materials.

Shear-thinning, the decrease in the apparent viscosity of an impression material under a shear load, is a characteristic of many elastomeric impression materials and improves handling properties. However, it is unknown whether the subsequent viscosity of such material continues to be lower. This study compared the apparent viscosities of five elastomeric impression materials under two conditions. One group of the materials was manually spatulated and injected through an impression syringe before being tested; the other group of materials was manually spatulated only. It was found that the viscosities of these materials were not affected by the shear load applied during syringing.

Alternative restorative techniques of the CeraOne single-tooth abutment: a technical note.

The screw-joint stability of single-tooth implant-supported restorations has been shown to be significantly improved with an abutment system (CeraOne) that uses a gold-alloy screw tightened at a prescribed amount of torque. The abutment system requires the cementation of the restoration to the abutment. This negates the possibility of accessing the abutment screw when the removal of the restoration is desired. This article described two alternative restorative techniques to maintain accessibility to the screw joint.

An investigation of the rheological properties of 10 vinyl-polysiloxane impression materials.

PURPOSE: The time required for 10 vinyl-polysiloxane impression materials to reach a viscosity of 5000 poise (Tcv) was estimated. This viscosity was selected based on previous work that suggested that an impression material might not be workable if its viscosity exceeded this limit. The effect of variations in the time of placement of the impression materials into a simulated oral-temperature environment was also studied. MATERIALS AND METHODS: The change in the viscosity of the impression materials was recorded with a viscometer at oral temperature. Impression materials were placed at either 20 seconds, 30 seconds, or 40 seconds from the start of mixing. RESULTS: There were statistically significant differences in Tcv among various impression materials. Variations in placement time significantly affected the Tcv of six impression materials. CONCLUSIONS: Knowledge of the viscosity change of an impression material is beneficial in the clinical selection of an impression material.

In vitro consistency of the Periotest instrument.

PURPOSE: The consistency of measuring the damping characteristics using the Periotest (Siemens AG, Bensheim, Germany) was studied. MATERIALS AND METHODS: Periotest values (PTV) of three rods embedded in various depths of impression material were recorded by seven dentists. RESULTS: There is no statistically significant difference among the subjects in measuring PTV of any of the three rods. However, the variation in the occlusal-gingival position of impact resulted in statistically significant different PTV measurements of each of the three rods. Assessment of mobility of the same objects using a clinical criterion was found to be less consistent as the mobility of the object increased. CONCLUSION: In vitro PTV measurements are consistent provided that the position of impact is controlled.