Effect of airborne-particle abrasion on retentive strength in overtapered fixed prosthodontic restorations

Objective: To evaluate retentive strength and film thickness of complete metal crowns cemented to overtapered teeth with 3 different cements after the application of airborne-particle abrasion. Method and Materials: Sixty extracted maxillary molar teeth were embedded in autopolymerizing resin. Crowns were prepared with 30-degree overtapered axial walls and a 1-mm shoulder margin using a water-cooled cylindrical airborne-particle abrasion device. Then, 60 complete crowns were made from a nickel-chromium alloy. Teeth and crowns were assigned to 2 groups, 30 to the control group and 30 to the experimental group to undergo airborne-particle abrasion. In the first part of study, 30 teeth from the experimental group were submitted to the silicon-replica technique and their buccolingual cross sections were measured so that cement film thickness could be measured before airborne-particle abrasion. Three measurements using a light microscope were made in 7 regions of each tooth. In the second part of study, complete metal crowns with and without airborne-particle abrasion were distributed into 3 groups with 10 teeth each to be cemented with zinc phosphate, polycarboxylate, or resin-modified glass ionomer. All specimens were subjected to a tensile bond test in an universal testing machine at a crosshead speed of 0.1 mm/min until failure. The results were then evaluated with Student t test at a 5% level of significance. Results: The film thickness showed no statistically significant differences among groups (P > .05). There was a significant difference between the control and experimental groups, with an increase in all 3 cements after airborne-particle abrasion (P .05). The highest retentive strength in the control group was found with resin-modified glass ionomer (141.4 ± 56.7 N), but there was no significant difference between the resin-modified glass ionomer (141.4 ± 56.7 N) and zinc phosphate (121.4 ± 24.2 N) (P > .05). Retentive strength of polycarboxylate was the lowest (78.03 ± 16 N) (P .05). For the experimental group, the difference among the zinc phosphate (220.5 ± 83.8 N), polycarboxylate (185.4 ± 60.8 N), and resin-modified glass ionomer (228.9 ± 62.4 N) was not statistically significant (P > .05). Conclusion: Airborne-particle abrasion had a positive effect on the retention of complete metal crowns when the crowns were cemented with zinc phosphate cement, polycarboxylate cement, or resin-modified glass-ionomer cement. Keywords: airborne-particle abrasion, film thickness, overtapered restoration, resin-modified glass-ionomer cement, retentive strength, zinc phosphate cement