While bone substitute materials are routinely used, especially vertical bone, augmentation of the jaws is still a problematic step. Dental stem cells in combination with bone substitute materials may accelerate the augmentation of alveolar bone and perhaps, stem cell-based therapies can become an alternative to autologous, allogenic, or synthetic bone transplants and substitutes. However, scaffolds are required for cell delivery, and here, commercially available bone substitute materials could be an excellent source for dental tissue engineering.

For more than 10 years, human dental stem cell research has focused on the identification and characterization of human stem/progenitor cell populations, which can be isolated, for example, from retained third molars of juvenile patients. One example for such type of dental stem cells are undifferentiated cells from the dental follicle (DFCs). These highly proliferative cells can be differentiated in vitro into periodontal ligament (PDL) cells, cementoblasts and osteoblasts, and into PDL-like cells in vivo. Preliminary results from animal studies suggested that DFCs have also a good osteogenic differentiation potential and could be an excellent source for the regeneration of craniofacial bone. Another excellent source for cellular therapies of mineralized tissues is progenitor cells from the dental apical papilla of retained third molar tooth (dNC-PCs). These dental cells differentiate into osteoblast-like cells after the induction with osteogenic differentiation medium under in vitro conditions and under in vivo conditions in immunocompromised mice.

For the osteogenic differentiation under in vivo conditions, stem cells are combined actually with hydroxyl-apatite (HAP) or β tricalcium phosphate (TCP) scaffolds. Although this is routinely applied, we know only little about the adherence and the viability of dental progenitor cells on these implant materials. Conversely, an optimal bone substitute material has not been identified so far for different dental stem cell types. In a recent study, we investigated, therefore, cell survival/proliferation and cell differentiation of DFCs in combination with a commercially available TCP. Here, DFCs attached on TCP and cell numbers increased after 6 days of cultivation. We showed that DFCs had a typical flattened-shaped morphology with close contacts to the bone substitute material. Interestingly, the gene expression of osteogenic markers such as osteopontin or RUNX2 was increased, and the alkaline phosphatase (ALP) activity was induced on TCP in differentiated DFCs. All these data support the assumption that TCP could be the optimal scaffold for a successful differentiation protocol of DFC.

Unfortunately, an additional study showed that TCP induced apoptosis in DFCs. However, the induction of apoptosis exposed a risk for cellular therapies. We decided therefore to evaluate additional implant materials for the identification of a suitable scaffold for dental stem cells. Soft materials such as silicone are successfully used in regenerative medicine, and they are suitable for tissue engineering, but, however, we propose that rigid and bone-like materials are superior for dental tissue engineering than soft implant materials. Therefore, this study evaluated and compared solid bone substitute materials with elastic materials such as silicone or polyacrylamide (PA). This study investigated the proliferation, the induction of apoptosis, and the osteogenic differentiation of DFCs and dNC-PCs after the attachment on implant-materials.