Scaffolds play an important role in tissue engineering. However, little is known about the proliferation and differentiation of DFCs and dNC-PCs on different types of materials. As we have learned from previous studies mechanical properties such as surface stiffness are decisive for a successful osteogenic differentiation of dental stem cells [13,14]. Moreover, we showed that bone substitute materials such as β-tricalcium phosphate (TCP) supports the osteogenic differentiation [10]. Our study proposed therefore that bone-like materials such as commercially available bone substitutes are superior for dental tissue engineering. Therefore, bone substitute materials SB and AP were compared with soft or connective tissue like materials. SB is synthetic and consists of 60% HAP and 40% TCP. In contrast, AP is an allograft product, which was derived from human donor bone. For comparison, two different soft materials silicone or PA were used in our study. Whereas silicone is routinely applied in regenerative medicine, the self-made PA scaffold has been very often used in cell biology studies [15].

dNC-PCs and DFCs attached on SB, AP, and silicone, but not on PA unless it was untreated. A modification with the extracellular matrix protein collagen permitted the attachment of dental cells. Interestingly, cell proliferation on silicone was hampered, because dental cells grew in non-attached spheroid cell clusters. This formation of spheroid cell clusters reminds on the neurogenic differentiation of DFCs [16-18]. The proliferation of DFCs on SB and AP was better than that of dNC-PCs, because the attachment of DFCs on these materials was lower than that of dNC-PCs. However, we conclude that bone substitute materials are suitable for dental cell attachment and proliferation. Our results for bone substitute materials are comparable to that of previous studies with different dental cell types. Kasaj and co-workers showed that cell adherence and cell proliferation of PDL cells on nanostructured HAP bone replacement grafts in vitro [19]. In another study, PDL cells adhere and proliferate on chitosan or on a combination of chitosan and nanostructured HAP [20]. In this setting, the combination of chitosan and nanostructured HAP was even favored by PDL cells. The adhesion and proliferation of dental pulp derived cells on HAP was demonstrated by Abe et al. [21].