# Direct Measurement of Heat Produced during Drilling for Implant Site Preparation
## 4 Discussion  
In dental implant procedures, understanding and minimizing the heat generated by friction at the interface between the drill and bone based on a well-designed experiment is important to avoid the potential damage to native bone tissue because thermally damaged osseous tissues around the implant constrain osseointegration, and may lead to implant failures and revisions that are painful to both patients and clinicians [3; 4; 7; 9; 19]. Many previous studies have tried to evaluate the excessive heat during drilling bones, but the methods to measure the temperature changes are somewhat irrelevant to clinical situations. For examples, most previous studies measure the temperature at a \(>\)0.5 mm distance from the bone surface in contact with the drill, but the heat damages occur at the superficial tissues at the contact [5]. Despite recent efforts to measure the temperature directly from the drill, heat produced from the friction between the thermocouple and drill was ignored in the previous studies [14; 15]. In this study, we have custom-built a drill equipped with a rotating thermocouple to eliminate the friction. We then measured the temperature from the inside of the bone being drilled via heat flow in real time. The temperature was attained under several conditions that vary in drilling speeds and depths. The resulting measurements were different among various drilling speeds and depths, which rejects the null hypothesis. Considering the temperature changes based on bone depth, the heat was produced mostly at the drill tip where most friction and compressive forces are applied [20]. The infrared ray sensor method used in previous reports does not fully reflect the actual temperature changes during implant drilling because the temperature on the upper part of the drill did not increase in the same manner as the lower portion of the drill inside the bone during drilling, and the infrared ray sensor measured the temperature at the entrance of the drill hole only at the onset of drilling [21]. In this study, an 800 g weight was used according to previous drilling studies (when an oral maxillofacial surgeon drilled bone, a 6-24 N pressure was applied) [22; 23]. Implantation torque was set at 30 N cm as this was shown to be the minimum torque that did not place excessive pressure on the bone around the implant but fixed it sufficiently in place [24; 25]. The drill rotating speed recommended by manufacturers differs from 1000 to 1500 rpm, and we used from 500 to 2000 rpm [21]. As we increased the rotating speed, friction force and minimal temperature also increased, but the drilling time needed for reaching the intended depth decreased [26]. In this study, at higher rotation speed, the temperature increased more rapidly and the maximum temperature was also higher as shown in previous studies, indicating that the temperature of bone increased when the drill rotating speed increased [27]. The patterns of temperature change observed herein were consistent at all three rotating speeds. A stainless steel drill, frequently used for dental drilling, has a 14-fold greater thermal conductivity and a 30-fold greater thermal diffusion disparity compared to compact bones [13; 28]. Evaluating the heat with a thermocouple located in bone where the distance is less than 0.5 mm was impossible because the drilling destroyed the thin bone layer between the thermocouple and the drill. Here, we evaluated the temperature of the drill using a rotating thermocouple in direct contact. Importantly, we observed that the heat measured using the previous methods that measured the direct drilling temperature without the rotating slip ring on a thermosensor was much higher than our methods equipped with the rotating slip ring on a thermocouple [14]. This higher drill temperature is attributed to the frictional heat generated between the stationary thermocouple used in the previous works.