Cutting effectiveness of diamond burs on dental zirconia.

摘要

Monolithic zirconia restorations are popular but removing these crowns is difficult. The purpose of the study is to measure and compare the cutting effectiveness of 10 types of diamond burs through monolithic sintered zirconia. Ten types of diamond burs (n=8) were compared for the cutting effectiveness in Zirconia (CERCON; DeguDent) using a high speed computer controlled cutting device with water spray (5.45L/min). The turbine used to cut the blocks rotated at 150,000 rpm and with the burs at a depth of 2mm into the zirconia during cutting. A 100 gm load was applied during cutting for each bur which made 2-9minute cuts. In the second part of the experiment, we tested 2 representative diamond burs with the same conditions as described before except the bur rotation was resuced to 40,0000rpm. This part of the experiment was performed to evaluate manufacturer's claims some diamonds are more effective at lower cutting speeds. After each cut, zirconia blocks were ultrasonically cleaned (10 minutes-acetone), dried in an oven at 200°C for 5 minutes before and after each cut and weighed (OHAUS Discovery Balances). The length of the cut was also recorded with a 3D digital microscope (Keyence VHX6000). The data were analyzed with ANOVA and Turkey/Kramer post-hoc tests (p=0.05). In conclusions the volumetric loss and cutting length of zirconia produced during the first 9 minute cut was significantly greater than the second 9 minute cut for all grit sizes. Zirconia surface chipping increased with increased diamond grit size. Four types of wear patterns were observed on the diamond bur: particle fracture, particle pullout, particle wear and matrix damage. In general, super coarse and coarse diamond produced better cutting effectiveness. Higher cutting efficacy was found with higher motor rotary speed.