Papers by Author: Christine Knabe

Abstract: 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.

Abstract: The setting behaviour, the compressive strength and the porosity of four calcium alkali orthophosphate cements were examined under laboratory conditions (dry) and under conditions similar to those during clinical application (37°C, contact with body fluid). The results showed an increase of the setting times when specimens were covered with simulated body fluid. Especially, the final setting time (FHZ) was significantly higher for three of the four cements. Furthermore, when specimens were stored in SBF for 16h, an extensive decrease of the compressive strength was noted. The porosity was more than twice as high after 16h in SBF and this may be the cause for the great decrease of the compressive strength.

Abstract: Commercially available calcium phosphate cements set by precipitation of nanoapatite or brushite. The goal of this study was to elucidate the most suitable conditions for forming cements from calcium potassium sodium phosphate. Furthermore, the behaviour of these cements after immersion in SBF and/or TRIS solution was investigated. Using varying additives resulted in differences in solubility kinetics. The XRD spectra of all investigated cement compositions displayed Ca2KNa(PO4)2 after setting. However, the various cement compositions differed with respect to apatite formation when immersed in TRIS buffer in and/or SBF solution. Therefore, when investigating calcium phosphate cements we consider it necessary to clearly differentiate between the phases which form after completion of the final setting time when these materials set in air, and the phases which form in a time dependant manner after immersion in different biological fluids.