## 2 Materials and Methods  
A homogeneous, 3 mm thick [30] sheet of medium density foam (Solid Rigid polyurethane foam 30 pcf, Sawbones Europe AB, Malmo, Sweden) was used for simulating the residual host bone underneath the sinus floor (Figure 2). Mimicking sinus lift situations with simultaneous implant placement, osteotomies were created using the drilling steps described in Table 1. Similarly, low density polyurethane foam material (Solid Rigid polyurethane foam 10 pcf, Sawbones Europe AB) was used as bone surrogate material [16; 35; 36] for simulating immediate implant placement. To this end, an extracted maxillary premolar was impressed into silicone material in order to achieve a negative form of its root portion which could subsequently be filled with casting wax. The wax pattern and a centrally positioned shaft were then cast in non-noble alloy (Heranium CE, Kulzer, Hanau, Germany). The root analog was pushed into the bone surrogate material using a surveyor thereby ensuring perpendicular alignment of the extraction sockets to the bone surface (Figure 3). Mimicking clinical practice, apical and palatal preparation of osteotomies was performed using the drilling steps described in Table 1.  
Figure 1: Bone level implant types used in this study comprising NobelActive 4.3 \(\times\) 10 mm (**a**) and AlfaGate 4.3 \(\times\) 10 mm (**b**).  
Figure 3: Simulation of immediate implant placement in an extraction site obtained through pressing a root analog (**a**) into polyurethane foam material to a depth of 10 mm (**b**) and following osteotomy preparation using a twist drill (**c**). Implant stability was assessed by means of resonance frequency analysis (**d**).  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Sinuslift** & **Extraction Site** \\ \hline \multirow{2}{*}{Implants} & NobelActive Internal RP 4.3 \(\times\) 10 mm & NobelActive Internal RP 5.0 \(\times\) 10 mm \\  & REF 34131 LOT 13125039 & REF 34137 LOT 12168347 \\ \cline{2-3}  & AlfaGate Novel Design 4.3 \(\times\) 10 mm & AlfaGate Novel Design 5.0 \(\times\) 10 mm \\ \hline \multirow{2}{*}{Drill sequence} & 2.0 & \multirow{2}{*}{Preformed Socket Depth: 10 mm} \\  & 2.4/2.8 & & 2.4/2.8 \\ \cline{2-3}  & 3.2/3.6 & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Description of the implant systems and drill sequences used in this study for creating osteectomies in simulated sinuslift situations and extraction sites. All implants were inserted with a surgical motor set at 25 rpm.  
Figure 2: Simulation of sinuslift procedure with simultaneous implant placement following osteotomy preparation with twist drills (**a**) and anchorage of implants in residual bone (**b**).  
In the control group, traditional tapered implants [33] with a cervical back taper (Figure 1a) were placed while in the test group the novel implant design (Figure 1b) described above was utilized. All implants (n = 10) were placed (Figure 2) with a surgical motor capable of recording actual torque over time [16] and which was set at 25 rpm (iChiropro, BienAir, Biel, Switzerland). Following implant placement, specific MuTiPegs (MuTiPeg #51 for AlfaGate, MuTiPeg #29 for NobelActive, Integration Diagnostics, Gothenburg, Sweden) were attached to the implants and resonance frequency analysis (RFA) was performed twice (Ossetll ISQ, Ossetll, Gothenburg, Sweden) [24].  
For statistical analysis, mean values of RFA measurements were calculated and mean maximum values were derived from the curves recorded for insertion torque [16]. Following Shapiro-Wilk-Tests on normality of distribution of measurement values, Welch two sample t tests were applied for comparisons between the two implant types with the level of significance set at \(\alpha\) = 0.05.