With dry heat the bacteria are burned to death or oxidized (add a link). Dry, hot air is much less effective in transferring heat than moist heat. This is why microorganisms are much more able to withstand heat in a dry state. The dry heat sterilization process takes a long long time and is done in a high temperature (2 hours at 160°C). The total cycle time, including heating up and cooling down to 80°C can take about 10-11 hours, not the greatest solution for an active clinic that needs it's instruments to be readily available. With forced cooling the time may be reduced to five hours.