## 2 Materials and Methods
### Histologic Analysis  
With the implants in place, the specimens were removed from the metal holders by cutting at a distance of 10 mm relative to the surface of the implants using the diamond band saw described above. Subsequently, the specimens were dehydrated in alcohol solutions of increasing concentrations, clarified in xylene and embedded in polymethylmethacrylate (Technovit 9100, Heraeus Kulzer, Hanau, Germany). One sagittal section (Figure 2) parallel to the long axis of the implant and corresponding to the center of the strain gauge was obtained per specimen by a cutting and grinding technique [16]. With the sections reduced to a thickness of 120 \(\upmu\)m, microradiographs (Faxitron X-ray, Lincolnshire, IL, USA; 14 kV, 0.3 mA, 2.5 min; Insight Dental Film, Carestream Health Inc., Rochester, NY, USA) were obtained for determining bone mineral density (BMD) in the surrounding of the implants (Figure 3). Following further reduction of the sections to a thickness of 30 \(\upmu\)m, bone to implant contact (BIC) and bone damage were quantified histomorphometrically using a microscope (LEICA DM4B, LEICA Mikrosysteme Vertrieb GmbH, Wetzlar, Germany) equipped with a color image analyzing system (LEICA Application Suite, LEICA Phase Expert, LEICA Mikrosysteme Vertrieb GmbH). All measurements were made on images gathered at 20\(\times\) magnification. Following the outlining of the implant surface (Figure 4a, yellow line) and the internal bony wall of the drill holes (Figure 4a, red line), BIC was defined as bone appearing within a radius of 500 \(\upmu\)m surrounding a specific point on the implant surface. The region of interest for evaluating bone damage was defined by circles with a radius of 300 \(\upmu\)m surrounding the bony walls at points best representing the outer geometry of the implants (Figure 4b, blue line). Bone damage, as indicated by crack formation or deformation of bone structure, was quantified with cracks exceeding  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Group Name** & **Straumann** & **Astra** \\ \hline \multirow{4}{*}{**Implant**} & Straumann Bone Level & OsseoSpeed TX 4.0 S \(\times\) 13 mm \\  & Tapered 4.1 \(\times\) 12 mm & (Astra Tech Implant System, \\  & (Institut Straumann AG, Basel, & Dentipsly Implants \\  & Switzerland) & Manufacturing GmbH, \\ \hline \multirow{4}{*}{**Drill sequence**} & Needle drill & Round bur \\  & 2.2 mm pilot drill & Twist drill 2.0 \\ \cline{1-1}  & 2.8 mm BLT drill & Twist drill 3.2 \\ \cline{1-1}  & 3.5 mm BLT drill & Twist drill 3.7 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Implant types and drill protocols.  
Figure 1: Insertion of an OsseoSpeed implant in bovine rib bone, which has been positioned in a metal holder and equipped with a strain gauge on the buccal surface. The sensing element of the strain gauge is positioned in the horizontal direction.  
100 \(\upmu\)m being classified as macro cracks, while cracks with a length shorter than 100 \(\upmu\)m were classified as microcracks.  
Figure 3: Microradiograph of an OsseoSpeed implant placed in bovine rib bone and sectioned in the bucco-lingual direction. The areas used for determining bone mineral density (BMD) in the cortical and trabecular parts are outlined in yellow and blue color respectively.  
Figure 2: Overview of a histologic section showing an OsseoSpeed (**a**) and a Straumann BLT (**b**) implant placed in bovine rib bone. The implant bone interface was analyzed in varying numbers of images at 20\(\times\) magnification.