Statement of problem: In an effort to control postoperative sensitivity, dentin sealers are being applied following crown preparation with little knowledge of how crown retention might be affected. A previous study demonstrated no adverse effect when using a glutaraldehyde-based sealer, and existing studies have shown conflicting results for resin-based products.
Purpose: This study determined if a resin sealer applied to prepared dentin affected retention of cemented castings when using 3 common types of luting agents.
Material and methods: Extracted human molars (n=55) were prepared with a flat occlusal, 20-degree taper, and 4-mm axial length. The axial surface area of each preparation was determined and specimens were distributed equally among groups (n=11). A 2-step, single-bottle adhesive system (One Step) was used to seal dentin following tooth preparation. Sealer was not used on the control specimens except for the modified-resin cement (Resinomer) specimens that required use of adhesive with cementation. Using ceramometal high noble alloy (Olympia), a casting was produced for each specimen and cemented with a seating force of 20 Kg using either zinc phosphate (Fleck's), glass ionomer (Ketac-Cem) or modified-resin cement (Resinomer) with the single-bottle adhesive. Castings were thermal cycled at 5 degrees C and 55 degrees C for 2500 cycles; then removed along the path of insertion using a universal testing machine at 0.5 mm/min. A single-factor ANOVA was used with alpha=.05. The nature of failure was also recorded and the data analyzed with a chi-square test.
Results: Mean dislodgment stresses for unsealed and sealed conditions were 3.7 +/- 1.0 and 2.2 +/- 0.8 MPa for zinc phosphate; 2.7 +/- 1.2 and 4.2 +/- 0.9 MPa for glass ionomer, respectively (P<.001). Retentive stress of castings cemented with modified-resin cement was 6.4 +/- 1.7 MPa. With resin sealer in combination with zinc phosphate, cement resided totally on castings in 82% of the situations and was on both surfaces without sealer. The tooth failed before casting dislodgment in 9 of 11 specimens cemented with modified-resin cement.
Conclusions: Resin sealer decreased casting retentive stress by 42% when used with zinc phosphate. However, sealer use resulted in 55% increased retention when used with glass ionomer. The modified-resin cement produced the highest mean dislodgment stress, nearly always exceeding the strength of the tooth.