Zirconia blocks fracture resistance against grinding

In our research, 35 piece of zirconia blocks suitable to ISO standardizations (wideness of used zirconia blocks are 5 mm, thickness are 2mm and lengthiness are 21mm) which have been made by zirkonzahn (Zirkonzahn GmbH, Gais, Germany) were used. Zirconia blocks were divided into 3 groups. Each group has 5 piece of zirconia blocks. One of the groups was used as control group without any process. Second group, was grinded disregarding the time 1mm by cylindrical bur attached micromotor. Thirth group, without keeping any time was grinded 1mm by cylindrical bur.For our research, mechanism were designed that consist of 4mm diameter steal balls to use in Instron(Model3345,InstronCorp,Canton, Massachusetts, USA) machine to place the zirconia blocks suıtable to ISO standardization and for breaking bar that suıtable to ISO standardization were prepared with 1.4mm apex. The mechanismand the bar were placed in Instron machine and were fixed for our experiment. One by one we put the zirconia blocks horizontaly to the mechanism which consist of 4mm diameter steal balls.We positioned 1.4mm diameter breaking bar to the center of zirconia blocks. Speed regulated to 0.5mm/min. For instron machine and force applied until the blocks has broken.As a result of the experiment, fracture has been occured in control group =975 MPa. Disregarding the time 1mm grinded zirconia blocks by micromotor fractured =742 MPa, 10 second and 1mm grinded zirconia blocks fractured =903 MPa, 5second and 1mm grinded zirconia blocks fractured =839 MPa. Disregarding the time 1mm grinded zirconia blocks by aerotor fractured =833 MPa, 10 second and 1mm grinded zirconia blocks fractured =735 MPa, 5 second and 1mm grinded zirconia blocks fractured =892 MPa.Compared to the control group:1: Both of two grinding methods fracture resistance of blocks decreased.2: Fracture resistance affacted more than the others at 1mm grinding process disregarding the time by micromotor.3: In 10 second grinding by aerotor has been occured more than the others.4: In 5 second grinding by micromotor group grinding has been occured more than the others.As a result, we need long-term researches to obtain information for clinic applications of zirconia blocks.?