Effect on Shear-Bond Strength of Several Methods to Remove Temporary Cement

Objectives: Clinicians often need to remove “temporary” cement prior to delivery of a final restoration. This project measured shear bond strength of a self-etching resin cement to dentin after cleaning the tooth surface by three different methods.
Methods: 75 non-carious, extracted human molars were de-coronated to provide a flat dentin surface, embedded in acrylic, wet-polished through P1200 grit, and had Temp-Bond NE cement (Kerr, Orange, CA) applied and cured to the surface. After 24Hrs. at 37C/100% humidity, they were randomly assigned to three groups. Cement was removed by 1) pumice/prophy cup (Preppies, WhipMix, Kentucky) using a low-speed handpiece (5,000rpm); 2) air abrasion with 27μm aluminum oxide particles (Danville Materials, CA); and 3) air abrasion with particles of sol-gel bioactive glass (BAG). BAG (65 mol%SiO₂, 31mol%CaO, 4mol% P₂O₅) was synthesized in our laboratory, ground and sieved to obtain a size fraction of 10 to 70 μm. Air abrasions were performed with a Danville microetcher at 100 psi. After cement removal, samples were rinsed with water and air-dried. They were placed into an Ultradent jig (Ultradent, UT) and RelyX™ Unicem-2 Self-Adhesive Resin Cement (3M ESPE, MN) was added to produce 2mm-high posts. Samples were self-cured (2 min) and light cured (20 sec). Posts underwent shear bond-strength testing (24hrs, 1 month and 3 months after bonding) with an Electropuls E-3000 (Instron, MA) (crosshead speed == 0.5mm/min). Data were compared using ANOVA (with post-hoc Tukey) with α=0.05.
Results: No differences were detected between any of the cleaning methods at 24 hours. At one and three months, grit blasting with alumina showed bond strengths equivalent to 24-hour bond strength, while pumice and BAG treated samples demonstrated significant decreases in bond strength.
Conclusions: When cementing indirect ceramic restorations, grit blast removal with alumina yielded the highest bond strength and maintained durability of the bond up to 3 months.