## 4 Discussion  
While preparing implant bed various factors need to be taken into consideration, including the drill's shape, drilling technique, cooling material and drilling speed and torque, as well as the implant system used [23; 24; 25; 26]. In some systems there is a tendency to minimize the number of drills to simplify the procedure and lower the overall costs [27; 28]. In other systems, a large number of drills allows for safe and precise bed preparation in risky recipients [29]. As far as the heat production is concerned, [PERSON] et al. [30] reported that maximum heat temperature without irrigation was higher than that with irrigation, which contradicts our observations, whereas [PERSON] et al. [23] suggested that the double irrigation technique produced a significantly smaller increase in the temperature in the cortical bone during both continuous and intermittent drilling movement. It is worth highlighting that while using disc drills the temperature decreased in proportion to the increasing drilling speed, which, so far, has not been described in the literature. This may have some clinical implications as disk implants are used in cranio-facial surgery for epithesis anchorage in auricular and orbital regions [31; 32]. Since in these regions there  
Figure 9: **(a). ** Vertical, 2.7 mm- thick slot for cutting discs. (**b**). Horizontal and vertical slot from cutting disc #6 in PUR foam. is a close vicinity of anatomical structures and the bone often undergoes irradiation, high temperature during bed preparation may be undesirable. [PERSON] et al. [25] showed that the effects of the bone preparation by low speed drilling (50 rpm) without irrigation and conventional drilling (800 rpm) with irrigation are similar, which means that both drilling techniques are successful in keeping bone cells alive. In our study, one drill fractured during drilling and the experiment with drill 4 was stopped so that the drill would not break. It might have been due to the fact that the PUR foam is harder than the real bone of the mandible, or cylindrical part of these drills were not sharp enough for radial drill cutting. In our opinion the radial movement 5 mm/min is very slow to be performed in clinical environment while drilling into the patient's bone. In this study, the drill without a hole (1) provided better results than the drill with a hole (2) even if the cooling medium was flowing throughout the hole. These results confirm findings presented by [PERSON] et al. [15] for twist drills with 2 mm diameter and 10 mm drilling depth. They reported the lowest temperature change of 20.45 \({}^{\circ}\)C for external irrigation in comparison with internal irrigation where the temperature rose to 28.30 \({}^{\circ}\)C. We have concluded that the amount of metal-mass in the drill helps to absorb and distribute the heat better than the through-and-through irrigation of the cutting part of the drill. There are also numerous articles regarding the importance and differences between simplified and conventional drilling techniques in regards to their numbers, which show that the outcome on the bone is the same [10]. [PERSON] et al. [33] evaluated the combined effect of drilling sequence and implant diameter. It turned out that the simplified technique did not influence bone formation. What is more, studies conducted by [PERSON] and [PERSON] [34] showed that a simplified drilling technique generates as much heat as the conventional one. To prove their hypothesis they used 80 implants with 2 different diameters placed in bovine ribs. [PERSON] et al. [35] tested implants placed in sites prepared with a simplified protocol with one drill and multiple conventional drilling steps. Their results showed that both drilling techniques are successful, but single-bur technique was less time consuming and caused less pain. Additionally, [PERSON] et al. [36] compared simplified protocols with conventional ones in terms of biological response.