Deep bone defects are caused by the progression of periodontal disease, which breaks down bone and connective tissue that hold teeth in place. In this case, a 37-year-old male patient presented a deep bone defect with advanced periodontal disease around an upper canine. Medical-grade calcium sulfate was mixed with demineralized freeze-dried bone allograft and used to repair and regenerate the defect. Analysis of the radiographs at the 5-month time point showed the bone had completely regenerated.
A study was conducted to characterize the dissolution, morphology, and chemical composition of a calcium sulfate/poly (L-lactic acid) (CS/PLLA) composite material before and after immersion in simulated body fluid (SBF). Twelve groups of experimental samples were prepared by coating CS pellets 1, 2, 3, or 4 times with one of three concentrations of a PLLA solution and wrapping them in mesh; CS pellets for use as controls were similarly prepared but not coated. The PLLA coating added from 1 to 22% to the weight of experimental pellets; scanning electron microscopy revealed that the coating thickness ranged from 2 to 50 microm depending on the concentration of the coating solution and the number of coatings. All samples were immersed in SBF for up to 97 days. After immersion, the experimental coatings thinned out, small cracks and holes formed in the coating, and the coating became roughened. Mean dissolution rates for each of the 12 CS/PLLA groups were significantly lower than those of uncoated CS pellets; among CS/PLLA groups, dissolution rates varied according to concentration of the coating solution and number of coatings. The half-life of pure CS pellets was 19 days whereas the half-life of CS/PLLA composite pellets ranged from 30 to 70 days. X-ray microprobe analysis of experimental pellets after immersion in SBF revealed that mineralization occurred in the CS portion of these pellets as well as on the coating; most of the mineral was calcium phosphate, most of which was on the coating. Further studies will be required to confirm this composite's promise as a clinically effective osteoconductive material.
In vitro and in vivo testing and development of bone graft substitute materials requires detailed analysis of bone and soft tissue response to complex multiphasic biomaterials, as well as analysis of changes in the graft materials over time. This often requires high resolution imaging of the materials and their surrounding tissues as well as microanalysis of both tissue and graft materials. We are currently testing a series of alloplastic calcium sulfate (CS) based bone graft substitutes ranging from rapidly resorbing cements and particulates to longer lasting timed release CS particulates (CS-TR) that are either coated with or are a composite with poly-L-lactic acid (PLLA).Medical grade CS (plaster of paris) particles and cements, and two types of calcium sulfate/poly-llactic acid (PLLA) timed-release materials (CS-TR); calcium sulfate/ PLLA composite particles, and calcium sulfate particles coated with thin layers of PLLA, were examined in a series of in vitro and in vivo studies (rabbit femur and tibia defect models) at time periods from a few days up to sixteen weeks. Faxitron high resolution x-ray, micro computed tomography (MCT), undecalcified plastic embedded histology, scanning electron microscopy in secondary electron imaging (SEI) and backscattered electron imaging (BEI) modes, x-ray microprobe (XRM), and Fourier transformed infrared (FT-IR) analysis techniques have all been used to evaluate these materials and their tissue response.The CS materials were observed to dissolve rapidly in vitro and in vivo, from the outer surface inward at rates as high as 1mm per week. They were also observed to stimulate new bone formation although bone was not observed to come in direct contact with the CS. In most animal models they dissolve completely in as little as 4 weeks, leaving behind mineral deposits in the form of concentric rings in surrounding tissue. Histologically, these deposits stain like bone mineral and often show attachment of osteoid and new bone. They were observed to act as scaffolds for new bone formation. BEI, XRM, and FT-IR show that these deposits are not immature bone or residual calcium sulfate, but are calcium phosphate deposits (Figure 1) in the form of a precipitated carbonate apatite and are very similar to bone mineral in composition. These precipitates also form in vitro when CS materials are incubated in simulated body fluids without cells present. The CS-TR materials behave in a similar fashion, but the PLLA component was observed to delay dissolution for up to 16 weeks (Figure 2) depending on amounts of PLLA used and whether the PLLA was distributed throughout the particles (as in composites) or as coatings on the outsides of the CS pellets. The CS-TR materials showed excellent biocompatibility with bone, and in contrast with the basic CS materials, persisted within the matrix of newly forming trabecular bone, for more than 16 weeks, acting as a lattice for bone formation.
No abstract
A CS/PLLA composite (ratio, 96:4) is an excellent bone graft material.
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