Improving dental grinding technology

Tooth cooling during grinding process for cavity or crown preparation is very essential for keeping tooth vitality. In vivo experiments done by Zach and Cohen in 1965 show that 15% of the teeth failed to recover when heated by 5.50C and if the interpulpal temperature was increased by 11.10C then in about 60% of the cases the teeth didn't recover. Since then many in vitro experiments were carried out in order to determine the water flow needed to maintain the temperature rise below 5.50C. The widespread cooling method is based on a number of water jets or water spray directed to the center of the dental bur. With this method excessive amount of water has to be applied in order to guarantee that enough coolant will be introduced into the grinding area. This leads to an unpleasant feeling of the patient and formation of mist obstructing the dentists working area visibility. A new concept of inner cooling method where the cooling water is entered to a hollow bur and comes out at the tip of the bur close to the grinding area was tested by the modification of an air turbine driven handpiece allowing water supply through the air turbine into a hollow bur. Special hollow burs were designed and manufactured for those experiments. Two kinds of experiments were conducted comparing the common outer cooling method and the internal cooling method; in the first experimental series the comparison was done by grinding glass ceramic material while in the second series the two cooling methods were applied while grinding extracted teeth. The results show significant improvement when using the internal cooling system. There was a reduction of about 20C while using the internal cooling system with the same water flow. The grinding of the extracted tooth was carried out by a dentistry student reporting improved visibility while using the internal cooling method. Further research and experiments will focus on developing a miniature system for entering the water into the high speed rotating bur, optimizing the cooling water flow rate with the internal cooling system, optimizing the position of the outlet holes at the tip of the bur, and developing a method for diamond coating of the hollow bur while keeping the holes in the tip of the bur open.