In a previous study, we showed that TCP induced the programmed cell death (apoptosis) in DFCs. Our new study investigated therefore the induction of apoptosis in dental cells. While SB and soft materials did not induce apoptosis or cell death, AP induced obviously cell death and apoptosis in dental cells. Here, the results for dNC-PCs and DFCs were almost the same. Interestingly, neither silicone nor PA induced the apoptosis in dental cells but did not also sustain the osteogenic differentiation of dental cells. Here, the ALP activity was strongly inhibited. Although no explanation for the induction of apoptosis by AP is available, the induction of apoptosis by AP does not correlate with the induction of the osteogenic differentiation. Both bone substitute materials sustained the differentiation, but only AP induced the expression of typical osteogenic differentiation markers. The induction of both osteogenic markers and apoptosis is very similar to that of our previous studies with TCP. Interestingly, a study with pre-differentiated human cord blood stem cells showed also very similar effects on TCP. They discovered a reduced number of pre-differentiated stem cells after long term cultures on TCP. But although cell numbers decreased between days 1 and 7, the gene expression of osteogenic cell differentiation markers was increased. In contrast, Marino et al. demonstrated that TCP scaffolds promoted both cell proliferation and osteogenic differentiation of human adipose stem cells. However, additional studies are required to disclose the molecular relationship between apoptosis and the osteogenic differentiation.

Finally, we could show that surface modifications are important for the attachment and cell proliferation of dental cells (Figure 6). Our results are in accordance to the results obtained in previous studies. For example, modifications such as fibronectin coating of TCP or composites with a combination of polymer of poly glycolic-lactic acid (PGLA) with TCP may also influence cell attachment and proliferation of seeded cells. Moreover, Seebach et al. showed that TCP products from different suppliers differ substantially in their morphology and that surface or porous structure seems to be of importance for the cell seeding and proliferation. Unfortunately, a modification of PA with collagen did not improve the osteogenic differentiation of dental stem cells.

In conclusion, our work supports our hypothesis that soft implant materials are not suitable for dental tissue engineering. Moreover, our study also supports the results of our previous studies with DFCs and TCP that induction of apoptosis did not impair the proliferation and the differentiation in dental stem cells.