## 2 Material and Methods  
In this study, a total of 81 dental implant sites were made. For this purpose, nine fresh swine ribs were obtained from the Polish Large White (PLW) swine breed. The method of sample collection did not require permission from the ethical committee. The size (length, width, and thickness) of all samples were comparable, with the mean values of 146.2 mm \(\times\) 24.6 mm \(\times\) 21.3 mm, respectively. Implant sites were prepared using the following dental systems (Table 1):  
1. BEGO Semados(r) RS (BEGO Implant Systems GmbH & Co., Bremen, Germany)--drills: pilot, \(\phi\)2.5, and final, \(\phi\)3.0;
2. BIOMET 3(r) T3 (Biomet 3i LLC, Palm Beach Gardens, FL, USA)--drills: pilot, \(\phi\)2.3, and final, \(\phi\)2.75); and
3. NEO BIOTECH(r) IS-III Active (Neo Biotech Co., Ltd., Seoul, Korea)--drills: pilot, \(\phi\)2.2, and final, \(\phi\)2.9. Each of the drills was tested with different cooling methods and drill rotation speed. A cooling system was supplied with:  
1. 0.9% NaCl solution (temperature approx. 20 \({}^{\circ}\)C);
2. 0.9% NaCl solution (temperature approx. 3 \({}^{\circ}\)C); and
3. without any cooling liquid supplementation. Drilling was carried out with the following speeds (by the same person):1. 800 rpm;
2. 1200 rpm; and
3. 1500 rpm. In order to prepare the implant sites, the NeoSurge implant micromotor was set at a contra angle with a 32:1 gear reduction. In all caused, the pilot drilling was used before the final drilling, not only because of dental systems requirements, but also to evaluate the drill diameter as an injury factor acting in bone model. Each of the drills were used only once at each drilling speed (800, 1200, and 1500 rpm) to avoid it becoming blunt. This may in turn generate additional heat during this procedure. All the implant sites were made on the anterior side of the swine ribs, reaching the depth of 10 mm. The same trained surgeon prepared each of the dental implants maintaining the optimal drilling force. Additionally, the ribs were fixed to the table mount to ensure the stability and repeatability. Drilling was done with an infrared thermographic camera ThermaCAM P640 [14] that registered the heat produced. The samples were fixed in a 4% formaldehyde solution of pH 7.2 for two days and were rinsed under running water. Subsequently, the ribs were cut using a low-speed, water cooled diamond saw to obtain an opened implant site with the biggest possible diameter. The obtained material was rinsed in a shaker at 25 \({}^{\circ}\)C for 10 min. A 0.9% sodium chloride solution was used to extract clear bone tissue. The material was examined under a fluorescent microscope Nikon Eclipse 801 using UV-2A (EX:330-380, DM:400, BA:420) and B-2A (EX: 450-490, DM:505, BA:520) filters with a magnification of 40\(\times\) and 100\(\times\). Then, the rib was observed directly under fluorescence microscope and pictures were taken. Thanks to this method, we avoided a number of potential unwanted changes in the tissue adjacent to the drill hole. Moreover, it allowed almost direct observation of the borehole after the experiment. The morphometric analysis was carried out using NIS Elements AR software. Additionally, the performed measurements were done in a closed room under the same conditions, maintaining the temperature and humidity, without additional air flow. All data were subjected to statistical analysis using GraphPad Prism 5.0 (GraphPad Software, La Jolla, CA, USA) software. The D'Agostino and Pearson normality test were used to determine the normality of the data. Based on the data distribution, either a one-way ANOVA with the Bonferroni post-hoc test or the Kruskal-Wallis with the post-hoc Durns test were used to compare more than two groups of data. Correlations between the groups were determined using the Spearman correlation coefficient. \(p<0.05\) was considered statistically significant.