Donna L. Dixon

The curing potential of light-activated composite resin luting agents

This study determined the effect of different light exposure times on the polymerization of three composite resins used as cements (Heliosit, Visio-Fil, and Dual) through various thicknesses and shades of two preprocessed composite resins (Isosit and Visio-Gem). The Knoop hardness of the surface of the luting resin was measured after polymerization and selected samples were remeasured at 24 hours to evaluate continued cure. Results indicated that polymerization of light-activated composite resin luting agents cannot predictably be accomplished through a restoration exceeding 2 mm in thickness using a light exposure of 90 seconds or less. The combined chemical and light-activated cure of Dual cement recorded the highest percentage of acceptable hardness values.

The transverse strengths of three denture base resins reinforced with polyethylene fibers

This investigation compared the transverse strengths of three denture base resins with and without polyethylene reinforcement fibers. These fibers were incorporated in 10 specimens each of a high-impact strength resin, a rapid heat-polymerized resin, and a light-activated resin. Each specimen was broken on an Instron universal testing machine using a three-point load after processing and air drying. The values obtained were then compared with values previously recorded for the same type of specimens without incorporated fibers. Only the light-activated denture base resin specimens exhibited a significantly higher mean transverse strength after polyethylene fiber reinforcement.

Linear dimensional variability of three denture base resins after processing and in water storage

It has been shown that denture base resins shrink during curing and expand during storage in water. This investigation measured and compared linear dimensional changes of three denture base resins that occurred during processing and after storage in water for 30, 60, and 90 days. Triad, Accelar 20, and Lucitone 199 long- and short-cured resins were studied, and it was found that Accelar 20 resin exhibited the least curing shrinkage and Lucitone 199 resin short-cured exhibited the most. However, no significant differences occurred between the groups. After 90 days of water storage, the only resin that exhibited a shrinkage from the processed state was Accelar 20. All of the expansion or shrinkage changes were so small that they were not statistically significant and should not be clinically detectable.

The transverse strengths of three denture base resins

Ten specimens each of (1) Lucitone 199, short- and long-cured, (2) Accelar 20, and (3) Triad materials were broken using a 3-point load on an Instron Universal testing machine after processing and air drying. Five specimens of each resin also were broken after storage in deionized distilled water at 37 degrees C for 30, 60, and 90 days. Triad material demonstrated the lowest transverse strengths of all three materials overall. However, Triad material was unaffected by water storage. The other resins all showed decreased strengths with water storage.

Accuracy of three interocclusal recording materials used to mount a working cast

When remaining occlusal contacts of a dental posterior quadrant have been prepared to receive complete or partial coverage restorations, it is necessary to use an interocclusal recording material to approximate the casts for laboratory mounting procedures. Inaccuracy in working cast approximation leads to occlusal discrepancies in the fabricated restorations that require correction by the dentist at the time of insertion. Traditionally waxes, impression compounds, plasters, and zinc oxide-eugenol pastes have been used intraorally to record maxillomandibular relationships. Elastomeric materials have also been advocated. Manufacturers of thermoplastic resins have recently suggested that these materials may be used with ease and accuracy for interocclusal records. This investigation measured and compared the accuracies of a thermoplastic resin, an acrylic resin, and a vinyl polysiloxane interocclusal recording material. A measuring method was developed in which a computerized axiograph was used to record positional errors in three planes, next to the posterior teeth, with the interocclusal recording materials listed.

The effect of connector design on cement retention in an implant and natural tooth-supported fixed partial denture*

This study investigated the effect of connector design, rigid or nonrigid, on cement retention in a combined implant and natural tooth-supported fixed partial denture. A prepared natural tooth was placed in a Plexiglas block in a manner that it could move approximately the same as a healthy premolar. An endosseous implant was placed in the block so that it was immobile. Joining the prepared tooth and implant was a fixed partial denture that could be made rigid or nonrigid. The natural tooth retainer was cemented to the prepared tooth, and the implant retainer was affixed to the implant fixture with a gold screw. One year of stress was applied to the fixed partial denture by a force simulation machine. Twenty randomly ordered tests were completed, 10 of each connector design. Retentive values for the cemented retainers were recorded and statistically compared by use of Students independent t test. No significant difference in cement retentive strength between designs was found (p less than 0.05).

Comparison of shear bond strengths of two resin luting systems for a base and a high noble metal alloy bonded to enamel

Researchers are investigating the use of noble metals for the fabrication of resin-bonded prostheses because of concerns about health hazards of nickel and beryllium in base metal alloys. Tin-plating has been advocated to improve the bond of resin luting agents to noble metal alloys. Some manufacturers have suggested that tin-plating is unnecessary to bond noble metal alloys to etched enamel with their products. In this study, Rexillium base metal and Olympia noble metal alloy specimens were bonded to extracted human teeth with the use of two resin luting agents (F21 and Panavia OP). One third of the noble metal specimens were tin-plated, one third were oxidized, and one third were oxidized and sandblasted. Each of the bonded specimens were thermocycled and subjected to a shear force until bond failure. The base metal specimens bonded with Panavia OP luting agent exhibited the greatest mean shear bond strengths. The tin-plating surface treatment significantly increased the mean shear bond strengths of Olympia noble metal specimens.

Compression resistance of four interocclusal recording materials

Elastomeric impression materials are popular for making interocclusal records to mount casts on dental articulators. The resistance of these materials to compressive forces is critical, because any deformation during the recording or mounting process could result in inaccurate articulation of casts and faulty fabrication of restorations. This investigation compared the deformation of designated thicknesses (2 mm, 5 mm, 10 mm, and 20 mm) for four elastomeric interocclusal recording materials (Blu-Mousse, Stat BR, Ramitec, and Regisil) when subjected to a 25 N compressive load. Compressive distortions of clinical significance were recorded for all of the materials with various thicknesses. The Blu-Mousse vinyl polysiloxane registration material exhibited the greatest resistance to compression for the designated thicknesses, and these resistance values were significantly lower than those of the other recording materials with thicknesses of 5, 10, and 20 mm (alpha < 0.05).

THE EFFECT OF METAL SURFACE TREATMENT ON THE SHEAR BOND STRENGTHS OF BASE AND NOBLE METALS BONDED TO ENAMEL

Adhesive resin luting agents provide a way for bonding metal surfaces to teeth through a combination of micromechanical retention to the rough metal surface and chemical adherence to metal oxides. The purpose of this study was to measure the effect of metal alloy surface treatments that would produce different textures and oxide layers on the shear bond strength of three alloys luted to etched enamel with one adhesive resin luting agent (Panavia). After a simulated porcelain firing sequence, high noble (Olympia), noble (Jelstar), and base metal (Rexillium III) alloy specimens were subjected to one of the following treatments: (1) sandblasting and simulated glazing, (2) simulated glazing only, (3) simulated glazing and sandblasting, or (4) simulated glazing, sandblasting, and tin plating. The specimens were bonded to extracted teeth and subjected to shear testing after water storage for 2 weeks, thermocycling for 500 cycles, and water storage for an additional 2 weeks. Data were analyzed with a two-way analysis of variance (alpha = 0.05). The base metal specimens and the tin-plated high noble and noble metal specimen groups exhibited similar mean shear bond strengths that were greater than the other groups. Those high noble and noble metal alloys sandblasted after simulated porcelain firing cycles and before the simulated glaze cycle exhibited nonsignificant increases in shear bond strengths compared with the groups that were either sandblasted after the simulated glaze cycle or not sandblasted at all.

Custom impression trays: Part I—Mechanical properties

Dimensional stability of custom impression trays is an important factor in determining the degree of accuracy achieved in forming a master cast. Such trays must remain stable over time and must not exhibit permanent deformation when a completed impression is removed from the oral cavity. Measurement of the mechanical properties allows comparison between various tray materials and is useful in interpreting data on stresses incurred during removal of the completed impression. In Part I of this three-part series, the various mechanical properties of five tray resins: one autopolymerizing polymethyl methacrylate, one light-polymerizing, and three brands of thermoplastic resins were recorded and compared. The thermoplastic resins studied in this investigation exhibited lower measured values for the strength and elastic modulus properties than the light-polymerizing resin and the autopolymerizing polymethyl methacrylate resin studied.