Support of occlusal enamel provided by bonded restorations.

In this in vitro study, the resistance to fracture of occlusal enamel supported by a bonded tooth-colored restorative material was compared to unsupported enamel and enamel supported by sound dentin. Eighty extracted human lower molars were sorted into five groups of 16 teeth each. Lingual cusps were removed. In Groups 2-5, dentin was removed from the facial cusps, leaving a shell of enamel. In Group 1, dentin was not removed. Group 2 remained unrestored. The groups in which a restorative material was inserted to replace missing dentin were as follows: composite (Scotchbond MP/Filtek Z250 [A2] in capsules, 3M); Group 4-resin-modified glass-ionomer (Fuji II LC [A2] in capsules, GC); Group 5-conventional glass ionomer (Fuji IX [A2] in capsules, GC). Specimens were thermocycled (1500 cycles, 6 degrees-60 degrees C, dwell 30 seconds), then mounted in die stone with lingual inclines of facial cusps approximately horizontal. The cusp ridges of the lingual inclines were flattened slightly using a horizontally mounted separating disk. Specimens were loaded evenly on flattened inclines in an Instron with a flat rectangular rod at a crosshead speed of 5 mm/minute. Data analysis was with one-way ANOVA and Student-Newman-Keul's test (F = 50.30, p < 0.0001). The bonded restorations provided significantly less enamel support than natural dentin and significantly more than when the enamel was left without support by dentin or a restorative material. There was no difference in support provided by the three restorative materials.

Support of undermined occlusal enamel provided by restorative materials.

OBJECTIVE: The purpose of this study was to test the support of occlusal enamel by amalgam (Dispersalloy), bonded amalgam (AmalgamBond Plus adhesive system with high-performance additive powder and Dispersalloy amalgam), and a bonded resin composite (Scotchbond Multi-Purpose adhesive system and Z100 resin composite). METHOD AND MATERIALS: For each material, 16 human molars were prepared. The lingual cusps were removed, and the dentin supporting the facial cusps was cut away, leaving a shell of enamel. Each group of prepared teeth was restored using the materials according to manufacturers' instructions. All specimens were thermocycled (1,500 cycles, 6 degrees C to 60 degrees C, dwell time 30 seconds), then mounted vertically in cast stone. A separating disk, mounted horizontally, was used to create a flat horizontal surface approximately 1.5 mm wide at the tips of both remaining enamel cusps of each specimen. Specimens were loaded evenly across the cusp tips at a crosshead speed of 10 mm/min until the fracture occurred. RESULTS: Data were analyzed using analysis of variance and Tukey A post hoc analysis. No significant difference was detected among amalgam, bonded amalgam, and bonded resin composite in their ability to support occlusal enamel. Support provided for occlusal enamel by the materials, whether bonded or not, was intermediate between no support and that provided by dentin. CONCLUSION: Without further development of materials technology and evidence of efficacy, restorative materials should not be relied upon to support undermined occlusal enamel.

Almost two centuries with amalgam: where are we today?

Amalgam has provided valuable and comparatively inexpensive service to patients for a longer time than any other restorative material. Despite the excitement surrounding the use of each new restorative material, each has a shortcoming that amalgam hasn't.

Making an instrument for smoothing the detailed occlusal anatomy of a wax pattern.

A smooth wax pattern is imperative to reduce the polishing time of the subsequent casting. The detailed occlusal anatomy is often the most difficult portion of the wax pattern to smooth. This article describes a procedure for making a device that can be used to smooth the detailed anatomy of a wax pattern. It also describes how to use the device.

An indicator for fitting castings to a die.

This article describes a procedure for making an indicator to be used in fitting a casting to a die. It also describes how to use the indicator in the laboratory. The materials for making the indicator are inexpensive, present no health hazard, and are readily available at any arts and crafts store.

Making a coping for an esthetic veneer crown.

Esthetic veneer crowns should be waxed to full contour before the veneer surface is cut back. This procedure ensures that patterns and metal copings will have the proper contours. A technique is described for making a coping that has an ideal thickness of 0.3 to 0.5 mm, that is stable, and that is unlikely to fracture.

Equipping a dental laboratory: fabricating a pressure pot.

A pressure pot has many applications in dentistry. This article describes a simple method of converting an everyday kitchen pressure cooker into one that can be used in dentistry. The technique is simple, and the components needed are readily available at a local hardware or department store. The advantage of this pressure pot is that it can be made for one third to one half the cost of purchasing one from a manufacturer.

Equipping a dental laboratory: making a shell blaster.

A shell blaster has many uses in a dental laboratory. However, because of the size and expense of this piece of equipment, it is not often found in many office laboratories. This article describes a method for making a relatively small, fully functional shell blaster for less than one hundred dollars. The shell blaster can be changed into a sandblaster by removing the walnut shells and refilling it with 26-grit aluminous oxide.

Film thickness of four disclosing media.

The use of disclosing media has been recommended to enhance the fit of castings. This study evaluated the film thickness of four disclosing media: (1) disclosing wax, (2) Net spray, (3) G-C Check Fit material, and (4) Extrude polyvinylsiloxane (low viscosity) impression material. ADA Specification No. 8 for zinc phosphate cement gives a maximum film thickness for the cement that was used as the control for these four media. The results demonstrated that the film thicknesses of all four disclosing media were less than the 25 microns maximum allowed for zinc phosphate cement.

Equipping a dental laboratory: making a plaster trap.

A plaster trap is a necessity for any dental laboratory. This article describes a technique for making an inexpensive plaster trap from a 3 1/2 gallon bucket and two trap adaptors. The materials are readily available and the armamentarium necessary to assemble the plaster trap is minimal. Making a plaster trap has two advantages. First, it can be made for a fraction of the cost of those purchased commercially and second, the plaster trap is easily cleaned by replacing the bucket without remaking the lid portion.

Equipping a dental laboratory: making a dust and particle container.

A particle container has many uses in the dental laboratory and operatory. This article describes a method of making such a container from a 3 1/2 gallon bucket with a lid. Such a container can be easily and inexpensively made from materials that are readily available.

Surface detail reproduction of Type IV dental stones with selected polyvinyl siloxane impression materials.

Four polyvinyl siloxane impression materials and 14 modified Type IV dental stones were evaluated for their abilities to reproduce surface detail. Each combination of impression material and dental stone was used to duplicate a 20-microns-wide line. Surface detail reproduction was observed by two paired-rater groups. The line was reproduced in all impression material specimens, but in only 32% of the stone cast specimens. Some combinations of impression material/dental stone reproduced the line all or most of the time, but 12 combinations did not reproduce the line at all.

Temporary replacement of missing maxillary incisors.

A technique has been described in which a polycarbonate crown form was used as a temporary replacement for a missing central incisor. As with the other techniques of temporary replacement using acid etching, little chair time is required for the procedure. Additional advantages of this technique are that polycarbonate crown forms are inexpensive and readily available in most dental offices, and filling the crown form with composite resin and opening up the embrasures allows maximum bulk of resin at the connector surface without encountering the staining problems associated with composite resin pontics.

A simple method of boxing rubber base impressions.

The advantages of boxing an impression are better adaptation of stone around dowel pins, control over the level of the second pour of stone, and minimal cast trimming. This article describes a simplified boxing technique that offers the following additional advantages: Parts of the impression that are inadequate in length can be extended to ensure a die of adequate length (Fig. 6). Boxmat adheres to the rubber base and facilitates application. Contouring the palatal or lingual part of the impression is greatly simplified and provides access for sawing out dies. The material is reusable.