The Mechanical and Thermal Effects of a High Speed Rotary Bur on Bovine Bone

Power drills and saws in ortheopeadic surgery are being used more and more to make the surgery go faster and easier, but the use of a power tool has some disadvantages over hand tools. The major problem with the power cutting tools is the thermal damage to the osteocytes caused by a temperature rise in the bone due to cutting. To date the majority of the studies performed in the area have only been the effects of temperature on the regeneration of bone cells and on the properties of strength of the bone. Most of the studies show for temperatures between 40°C and 50°C damage does occur to the osteocytes in the bone. There has been little work done in trying to relate the different cutting parameters to the temperature rise in bone due to cutting. This study will show by experimental results that relationship the cutting tool\u27s rotational speed and feed rate have with the temperatures and forces measured while cutting bone specimens and also the relationship of the depth of cut to the cutting temperatures and forces. The mid-shaft of fermurs taken from mature bulls was the source of the bone specimens. The specimens were cut into prisms with dimensions of approximately 1/2 x 1/4 x 3/8 inches. The osteons of the bone ran parallel with the length of the specimen. A cooperconstantan thermocouple was implanted in the specimen to measure the temperature in the specimen, and the specimen was clamped to a dynamometer so the cutting forces could be measured. The dynamometer was bolted to the cutting table of a milling machine and a Hall air turbine was also mounted on the millling machine. The feed rate of the cutting table and the depth of cut could be adjusted on the milling machine. Two different types of cutting burs were used (Hall number 21 and Hall number 07) at two different rotational speeds (100,00 RPM and 20,000 RPM). Temperature and forces were measured at three different feed rates at three different depths of cut. The cuts were made parallel to the osteons in the specimen and without a water coolant. The results showed that as the feed rate increased the temperature elevation decreased and as the depth of cut increased the temperature increased. Increasing the rotational speed of the number 21 bur showed no significant differences in the average temperatures measured, but the number 07 bur showed that the temperatures increased win and increase in rotational speed. The cutting forces were observed to increase when the feed rate and depth of cut incrased, but decrased with an incrase in rotational speed of the bur. It was determined that a more efficient cut could be made at the faster feed rates and larger depths of cut and it is suggested that with short periods of cuts and the use of a water collant the temperatures in the bone from cutting could be reduced