## 4 Discussion
In contrast, [PERSON] et al., who compared 32 mL/min, 44 mL/min, 56 mL/min, and 68 mL/min amounts of coolant, showed a visible reduction in thermal damages with volumes higher than 32 mL/min. They suggested that the most effective volume, which should be used to provide continuous cooling and limited thermal damage, is 56 mL/min [22]. Additionally, the temperature of the coolant may significantly impact the thermal necrosis and reduce its risk. [PERSON] et al. showed that a lower temperature of the coolant (10 \({}^{\circ}\)C compared to 25 \({}^{\circ}\)C) may sufficiently decrease the final temperature and lower the risk of thermal damage [19]. In our study, we compared thermal damage in three conditions: without cooling and with cooling by 3 \({}^{\circ}\)C, and 20 \({}^{\circ}\)C of the 0.9% NaCl, which revealed a notable higher thermal damage in cases without coolant compared to cases with coolant, but the differences in damage zone between cases with 3 \({}^{\circ}\)C and 20 \({}^{\circ}\)C coolant temperatures were irrelevant. According to many different results published, the optimal speed for bone drilling remains unidentified. There is no compromise regarding the relationship between the drilling speed and temperature. The first research carried out in 1958 in order to examine the correlation between drilling rate and temperature revealed that the increase in drilling speed increased the temperature while drilling [23]. Many years later, these results were confirmed by [PERSON] et al., who evaluated five drill speeds between 188 and 1820 rpm, [PERSON] et al., who used 600 and 1200 rpm drilling speeds, and [PERSON], who investigated 1200, 1800, and 2200 rpm drilling rates. They all received the same result--the higher the speed, the higher the temperature [20; 24; 25]. As opposed to previously mentioned investigations, [PERSON] et al. showed that the higher the speed, the lower the temperature. He obtained these research results using three different speeds: 1225, 1667, and 2500 rpm [26]. The latest results of the research carried out by [PERSON] et al. showed that the optimal rate that stimulates osteointegration and minimalizes thermal damage ranged from 1000 rpm to 1500 rpm [12]. In our study, we used three rotation speeds: suboptimal (800 rpm), optimal (1200 rpm), and maximal (1500 rpm). The force applied during the creation of the implant site remains one of the factors that may influence the temperature while drilling. The average force put on the implant site during its preparation is 1.2 kg [27]. [PERSON] et al. compared drilling at 1200 and 2400 rpm under loads of 1.2 and 2.4 kg. It turned out that drilling at the speed of 1800 rpm at the load of 1.2 kg generated an identical amount of heat as that of the 2400 rpm speed at the load of 2.4 kg. To obtain the same conditions while making all the implant sites, all of them were made by the same researcher with a synonymous force. Furthermore, an increase of one of the parameters (speed or load) caused an increased heat generation. On the other hand, increasing both parameters (speed and load) caused an unnoticeable rise in temperature and allowed for more effective implant site preparation [28]. In our study, we also used pre-drilling as the method that allows for broadening of the drilling site and causing heat dissipation. During implant site preparation, the drill diameter was increased gradually from the smallest to the largest diameter. The method of pre-drilling was introduced in 1983 by [PERSON] and later confirmed by many researchers, but remains a rarely used procedure [20; 29]. Our study showed that both speed and coolant used during drilling with constant force provoked significantly different changes in bone tissue. The bone tissue compression was visible after low speed (800 rpm), cooled drilling (Figure 2), and the lack of coolant caused only moderate destruction of bone tissue and bone marrow (Figure 3).