Use of 9.3μm CO 2 Laser for Removal of Zirconia Restorations

Objective: The primary aim of this study was to test if a 9.3μm Carbon Dioxide (CO 2 ) laser could be used to effectively separate a cemented zirconia restoration from dentin. The secondary aim was to compare shear bond strength (SBS) between RelyXTM Unicem 2 Automix Cement (3M ESPE) (RelyXTM Unicem 2) and RelyXTM Luting Plus Automix Cement (3M ESPE) (RelyX™ Luting Plus). Methods: 40 teeth were prepared to expose dentin and then randomized into four groups of 10 samples. Zirconia slices (non-glazed Yttrium stabilized zirconia samples (2.5 x 3 x 1.5 mm)) were sandblasted with 50 micron aluminum oxide at 30 psi and then cemented onto the dentin samples with RelyX™ Unicem 2 or RelyX™ Luting Plus, dependent on the group. The cements were applied to both the zirconia and dentin with a force of 20 g/mm2 for 30 seconds following manufacturer's recommendations. After 48 hours, the 9.3μm CO 2 laser was used on half the samples for 5 seconds. All 40 zirconia samples were removed with the Instron 5566A in a traditional SBS test. The groups were: 1A - RelyX™ Unicem 2 and Laser, 1B - RelyX™ Unicem 2 and Shear Bond, 2A - RelyX™ Luting Plus and Laser, and 2B - RelyX™ Luting Plus and Shear Bond. The Mann–Whitney U test was used for comparison. Results: Mean SBS of four groups ranged from 0.5 to 4.4 MPa. There was a significant difference in the SBS between 9.3μm CO2 laser and Shear Force methods for RelyX™ Luting Plus. However, the difference between the two methods was not significant for RelyX Unicem 2. RelyX™ Unicem 2 provided significantly higher SBS than RelyX™ Luting Plus for both the CO2 laser and shear force methods (Table 2). Conclusion: The 9.3μm CO 2 laser effectively separated the zirconia restoration cemented with RelyX™ Luting Plus from dentin. RelyX™ Unicem 2 provided significantly stronger SBS than RelyX™ Luting Plus