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Although autogenous bone grafts are currently the standard of care for bone reconstruction in implant dentistry, bone substitute materials are extensively studied in order to avoid harvesting autogenous bone. Recently, the use of tricalcium phosphate (TCP) and bioactive glass 45S5 particles as alloplastic bone graft materials for alveolar ridge augmentation and sinus floor elevation procedures has received increasing attention in implant dentistry. However, given the clinical findings with these current bone substitute materials there continues to be interest in bone substitute materials which degrade more rapidly, but still stimulate osteogenesis at the same time. As a result considerable efforts have been undertaken to produce rapidly resorbable bone substitute materials, which exhibit good bone bonding behaviour by stimulating enhanced bone formation at the interface in combination with a high degradation rate. This has led to the synthesis of a new series of bioactive, rapidly resorbable calcium alkali phosphate materials. These are glassy crystalline calcium alkali orthophosphates, which exhibit stable crystalline Ca2KNa(PO4)2 phases. These materials have a higher solubility than TCP and therefore they are designed to exhibit a higher degree of biodegradability than TCP. On this basis, they are considered as excellent alloplastic materials for alveolar ridge augmentation. In order to evaluate the osteogenic potential in vitro, we first examined the effect of various rapidly resorbable calcium alkali orthophosphate bone grafting materials on the expression of osteogenic markers characteristic of the osteoblastic phenotype in vitro and compared this behaviour to that of the currently clinically used materials β-tricalcium phosphate (TCP) and bioactive glass 45S5. These studies showed that several calcium alkali orthophosphate materials supported osteoblast differentiation to a greater extent than TCP.