The bone substitutes Maxgraft® (AP) and Maxresorb® (SB) were obtained from the company Botiss (botiss dental GmbH, Berlin, Germany). Maxgraft® is a sterile, high-safety allograft product (AP), derived from human donor bone. It is processed by an audited and certified bone bank (Cells⁺ Tissue Bank Austria, Berlin, Germany). In contrast, Maxresorb® is a fully synthetic bone graft substitute (SB) with controlled resorption properties. It is a homogenous composition of 60% hydroxyapatite and 40% beta-tri-calcium phosphate. SB maintains the volume and mechanical stability over a long time period. The osteoconductivity of SB is achieved by a matrix of interconnecting pores and a very high porosity of approximately 80%, as well as pore sizes from 200 to 800 μm (www.botiss.com). Experiments with AP and SB were done with solid blocks (10 × 10 × 20 mm cancellous block). PA was produced in our lab (see above), and silicone-based implant materials were obtained from Vivomed (Downpatrick, UK) as tubes. Silicone tubes were cut in pieces with a size which is similar to that of AP and SB.

Implant materials were washed with PBS or cell culture medium before use. DFCs and dNC-PCs were seeded onto materials for indicated periods of time. For the isolation of total RNA and the estimation of vital cell numbers, implant materials with cells were transferred to a fresh well with cell culture medium.

For the evaluation of apoptosis induction, cell culture eluates were produced by incubating 0.1 mL of bone substitutes or soft materials in 1-mL standard medium at 37°C for 24 h. This incubation step with the implant material was repeated twice with fresh cell culture media. Three eluates were pooled for cell culture experiments. DFCs were seeded onto cell culture plates and cultivated in standard cell culture media. After cell seeding (12 to 24 h), cell culture media were changed, and cells were cultivated in cell culture media with material eluates. After 24 h of cultivation, cells were harvested for flow cytometry analyses or protein isolation for Western blots (see below).