ΔT > 13 ◦C

The average exposure time under ΔT >13 ◦C for ceramic implants was 25.10 s in group 1, 16.93 s in group 2, and 10.19 s in group 3. Three machined implants (group 1: 42.2, 36.1, and 32.1 s) and two sandblasted implants (group 2: 34.6 and 33.2 s) experienced more than 30 s temperature increase of over 13 ◦C. No sandblasted and acid-etched implants (group 3) experienced such a temperature change for longer than 30 s.

The average exposure time under ΔT >13 ◦C for titanium implants was 19.03 s at 3 of 15 implants in group 4 (group 4: 19.8, 21.8, and 15.6 s). Two machined implants experienced more than 13 ◦C temperature increase (group 5: 13.9 and 17.4 s) No sandblasted and acid-etched implants (group 6) experienced a temperature increase of 13 ◦C or more.

#### ΔT > 18 ◦C

The average exposure time under ΔT > 18 ◦C for ceramic implants was 11.36 s at 5 of 8 implants in group 1, 7.98 s at 6 of 11 implants in group 2, and 0.43 s at 3 of 11 implants in group 3. Two machined ceramic implants (group 1: 25.4 and 14.2 s) and two sandblasted ceramic implants (group 2: 19.0 and 16.7 s) experienced a temperature increase of more than 18 ◦C for more than 14 s. No sandblasted and acid-etched implants (group 3) experienced a temperature change greater than 18 ◦C for more than 14 s.

Only one titanium implant (group 4) exceeded 18.70 ◦C and had an exposure time of 20.40 s for ΔT > 18 ◦C.

#### 3.3.2. Bone Window 2

In bone window 2, the temperature increase never exceeded values > 10 ◦C.

#### *3.4. Material-Dependent Thermal Energy Propagation*

Figure 7 shows the image captured by the infrared camera during the process of inserting titanium and ceramic implants, both with sandblasted and acid-etched surfaces. Prior to the insertion process—meaning the implants were completely outside of the bone cavity—there was very little temperature difference between the titanium implant (33.2 ◦C) and the ceramic implant (31.2 ◦C). Bone window 1 shows the nearly regulated temperature of the thermo box (Figure 3) encapsulating the in vitro setup (37.5 ◦C; 37.2 ◦C).

**Figure 7.** Material-dependent heat dissipation. (**a**) ceramic implant before insertion; (**b**) ceramic implant during insertion; (**c**) titanium implant before insertion; (**d**) titanium implant during insertion.

At the moment of maximum temperature development during implant insertion, the ceramic implant was heated to 48.7 ◦C below the cortical bone (bone window 1) and to 33.6 ◦C outside the bone. In contrast, the titanium implant showed 42.9 ◦C within bone window 1 and 38.0 ◦C outside the bone. Thus, at the same distance, the titanium implant had a 3 times lower temperature gradient than the ceramic implant during the insertion process (ΔTceramic = 15.1 ◦C vs. ΔTtitanium = 4.9 ◦C).

The summary of all results is shown in Table 1.

#### **4. Discussion**

The aim of the in vitro study was to dynamically detect heat development at the bone–implant interface during the entire process of inserting a cylindrical screw implant into bone. For this purpose, an in vitro setup was developed, which achieves the highest possible quality of simulation of the clinical conditions and uses of test specimens, which differ in only one parameter, as far as possible.

#### *4.1. Identical Specimen*

It was important for good reproducibility of the temperature values at the implant surface that the implant specimens had an identical endosteal macrodesign and were identically manufactured (Figures 1 and 2). The measured surface roughness (Figure 5b) did not differ significantly between the ceramic (ZrO2) and titanium implant materials in the sandblasted and sandblasted-etched surfaces. Only on the machined implants was the titanium surface statistically significantly smoother.

Repetition of the test series with the same implants after each additional surface treatment allowed for a nearly identical macrodesign with a different microdesign. Only removal of material by subtractive surface treatment caused a reduction in implant diameter. However, this was recorded by measurement and taken into account in the osteotomy protocol. In other words, the last cutter for bone preparation was also correspondingly smaller in diameter.
