There are a variety of studies on investigating the effect of external cooling during drilling of bone and all of them emphasize its positive influence in limiting the maximum temperature elevation . Augustin et al  investigated the effect of external irrigation with water as coolant. They indicated that while there are several parameters that increase bone temperature during drilling, cooling (as external irrigation in their case) can be the only and the most important factor in limiting this increase in bone temperature and must be used for bone drilling. On the other hand, Shakouri et al , Sener et al , Al-Dabag and Sultan , and Sindel et al  determined the efficiency of external cooling with normal saline as coolant. They also indicated similar positive influence in limiting the maximum temperature elevation. Therefore, the lower maximum temperatures which are seen in Figure 2a and Figure 2b for external cooling with normal saline in comparison to the condition that there was no cooling, is not a surprise; the results thoroughly support the previous studies on external cooling.
Moreover, studies on the effect of drilling speed and feed-rate on temperature elevation are not consistent . This was also the case when external cooling was employed since in the experiments of Shakouri et al , there is no trend for temperature variations with changes in drilling speed, neither without cooling nor with external cooling. In spite of this, the external cooling efficiency in limiting the temperature rise is observed with all combinations of parameters in the current study.
According to Table 1 and Figure 2, using OpSite spray not only limited the maximum temperature elevation in our experiments, but also shows much better results in comparison to normal saline. It is more important if consider the lower risks of infection for this coolant since it is not liquid but rather is in the form of spray . Furthermore, according to the literature, for occurrence of thermal osteonecrosis, there is a reverse exponential relationship between thermal necrosis temperature and necrosis time. Whereas the exact threshold temperature for thermal osteonecrosis in human bone is unknown, heat transfer to the bone cells in an average temperature of 47 °C for 1 min is believed to be the threshold . However, OpSite successfully limited the temperature elevation and the highest recorded temperature for cooling with OpSite Spray was 37 °C. Thus, the risks of thermal osteonecrosis during drilling and consequent risks of loosening and failure in the implants and orthopaedic fixation screws are much lower when using OpSite as coolant.
With regard to the results of this study, it can be concluded that though employment of a cooling system has positive effects in controlling temperature rise during drilling of bone, using OpSite spray as coolant for external cooling is recommended in orthopaedic surgeries due to lower risks of thermal osteonecrosis (better subsequent osseointegration and thus more success rate) and infection.
However, more in-vivo studies on its clinical success are needed, both on animals and human. Moreover, to have a better conclusion, further osteonecrosis evaluations on histopathology of the surrounding tissue may be helpful.