Effect of air abrasives on marginal configurations of porcelain-fused-to-metal alloys: an SEM analysis

The Effect of Temporary Cement Cleaning Methods on the Retention of Crowns

PURPOSE

To evaluate the effect of temporary cement cleaning methods on the retention of cemented crowns using zinc phosphate cement and resin-modified glass ionomer cement.

MATERIALS AND METHODS

Forty titanium specimens were fabricated to simulate prepared molars with minimally retentive taper. The Ni-Cr cast crowns were fabricated, temporarily cemented, and separated. The specimens were divided into four groups according to the temporary cement cleaning method (n = 10) as follows: control group (no temporary cementation), orange solvent group, ultrasonic cleaning group, and air-abrasion group. After the cleaning procedures, the specimens were cemented with definitive cements (zinc phosphate cement and resin-modified glass ionomer, RMGI, cement) and subjected to thermocycling (5000 cycles, 5-55°C, dwell time, 10 seconds). The tensile bond strength of each specimen was measured using a universal testing machine, and the results were analyzed using the Kruskal-Wallis and Mann-Whitney U test (α = 0.05).

RESULTS

When cemented with zinc phosphate cement, the statistical analysis showed that the value of the air-abrasion group was significantly higher than those of the other groups (p < 0.01). There was no statistically significant difference among the other groups. When cemented with RMGI cement, the air-abrasion group showed the lowest value, and the control group showed the highest value (p < 0.01). The difference between the ultrasonic cleaning group and the orange solvent group was not statistically significant.

CONCLUSION

The use of temporary cement did not have a significant influence on retention of permanently cemented crowns when zinc phosphate cement was used for permanent cementation. Airborne-particle abrasion after provisional cementation improved retention of crowns cemented with zinc phosphate cement; however, the use of temporary cement significantly decreased retention of permanently cemented crowns when RMGI cement was used regardless of the temporary cement cleaning method.

Microabrasion of Cast Metal Margins?A Warning

Plastic test patterns were milled to simulate casting margins and were cast in a variety of dental alloys. The cast specimens were exposed to horizontal and vertical streams of low-pressure microabrasion with 50 microm aluminum oxide particles. Post-exposure measurements show all specimens were affected by microabrasion. Dentists and laboratory technicians who use microabrasion must be aware of the potential damage to casting margins.

The Effects of a Commercial Aluminum Airpolishing Powder on Dental Restorative Materials

INTRODUCTION

JET-Fresh (Dentsply International, York, PA), a new airpolishing powder that contains aluminum trihydroxide as the abrasive agent, has been introduced for use with Prophy-Jet trade mark (Dentsply International).

PURPOSE

The aim of this study was to investigate the surface effects of aluminum trihydroxide airpolishing powder on a series of restorative materials.

MATERIALS AND METHODS

A total of 6 Class V preparations with enamel margins were created on the buccal surface of extracted human molars. The preparations were restored with Type III gold, a high copper spherical alloy amalgam, porcelain, a light-activated hybrid composite material, a light-activated microfilled composite material, and a light-activated, resin-modified glass ionomer material. The distal half of each restoration was covered with fiberglass tape and the mesial half subjected to treatment with the aluminum trihydroxide powder via the Prophy-Jet for 5 seconds. After removal of the protective tape, the buccal surface of each treated tooth was replicated with impression material. Replicas were generated using epoxy resin and prepared for evaluation with scanning electron microscopy.

RESULTS

The aluminum trihydroxide produced surface alterations that were apparent visually and when viewed by a scanning microscope of the hybrid and microfilled composites and the glass ionomer restorations. The surfaces of the amalgam and gold restorations were altered, but not to the extent that the resin-based materials were. No disruption of the surface characterization of the porcelain was detected; however, with gold and porcelain materials, the aluminum trihydroxide removed notable amounts of the luting cements (the results are consistent with the data gathered with sodium bicarbonate powder).

CONCLUSION

Aluminum trihydroxide as the abrasive agent in an airpolishing system should be avoided on resin composites, resin-modified composites, and around the margins of cemented restorations.

Report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The committee screened several hundred articles, citing 518 published papers. Some are present quality in research, others provide clinical interest, and some are identified as misleading. New techniques in pulp physiology and pathology are reported. Laser use and techniques in prevention, restorative dentistry, and materials use are reported. Epidemiology of selected diseases and the results of various formulations for treatment are cited. Diagnosis of craniomandibular dysfunction is well represented as well as references to literature reviews and other sophisticated scientific investigation. Research on adhesives is presented in respect to bonding agents for dentin and enamel. Several clinical studies are included, along with customary laboratory reports on several materials.