John P. Schmitz

Reconstruction of bone using calcium phosphate bone cements: a critical review.

The calcium phosphate cements (CPCs) are rapidly emerging as a new technology in craniofacial surgery and will soon impact many areas of orthopedic and maxillofacial reconstructive surgery as well. These materials are, in many ways, substantially different from the previously marketed dense, crystalline, hydroxyapatite (HA) ceramic materials of the 1980s. The CPCs are blends of amorphous and crystalline calcium phosphate compounds and set to produce HA. These materials 1) have x-ray diffraction spectra similar to the mineral phase of bone, 2) set endothermically at body temperature, 3) are capable of being injected into fractures or bone defects, 4) have compressive strengths equal to or greater than bone, 5) form chemical bonds to the host bone, and 6) may exhibit osteoconductive properties. This review provides an overall commentary on the different types of CPCs, emphasizing those materials currently on the market or soon to emerge in the marketplace.

Oxidative stress and degenerative temporomandibular joint disease : A proposed hypothesis

The molecular events that underlie degenerative temporomandibular joint diseases are poorly understood. Recent studies have provided evidence that a variety of molecular species, including cytokines, matrix degrading enzymes, neuropeptides, and arachidonic acid catabolites may be involved. This paper advances the theory that mechanical stresses lead to the accumulation of damaging free radicals in affected articular tissues of susceptible individuals. This condition is called oxidative stress. The authors postulate mechanisms that may be involved in the production of free radicals in the temporomandibular joint and in the subsequent induction of molecular events that may amplify damage of articular tissues initiated by free radicals. If the proposed model is correct, then future therapeutic strategies directed at the control of oxidative stress could be effective in the management of degenerative temporomandibular joint diseases.

Molecular biology of temporomandibular joint disorders: Proposed mechanisms of disease☆

PURPOSE The biologic processes of temporomandibular joint adaptation and disease are poorly understood. However, recent technologic advances have provided methods that allow sophisticated studies of the molecular mechanisms that are relevant to the pathophysiology of degenerative temporomandibular joint diseases. This review examines current models of the molecular events that may underlie both adaptive and pathologic responses of the articular tissues of the temporomandibular joint to mechanical stress. It is hoped that an increased understanding of these complex biologic processes will lead to improved diagnostic and therapeutic approaches directed to the management of temporomandibular disorders.

Demineralized bone matrix in bone repair: history and use.

Abstract Demineralized bone matrix (DBM) is an osteoconductive and osteoinductive commercial biomaterial and approved medical device used in bone defects with a long track record of clinical use in diverse forms. True to its name and as an acid-extracted organic matrix from human bone sources, DBM retains much of the proteinaceous components native to bone, with small amounts of calcium-based solids, inorganic phosphates and some trace cell debris. Many of DBMs proteinaceous components (e.g., growth factors) are known to be potent osteogenic agents. Commercially sourced as putty, paste, sheets and flexible pieces, DBM provides a degradable matrix facilitating endogenous release of these compounds to the bone wound sites where it is surgically placed to fill bone defects, inducing new bone formation and accelerating healing. Given DBMs long clinical track record and commercial accessibility in standard forms and sources, opportunities to further develop and validate DBM as a versatile bone biomaterial in orthopedic repair and regenerative medicine contexts are attractive.

Characterization of rat calvarial nonunion defects

This study examined the healing of nonunions by describing the histology and ultrastructural appearance of craniotomy defects as a model. Bone defects (3, 4 and 8 mm) were created in the calvaria of adult rats. Central and peripheral specimens of 8-mm defects were retrieved at 1, 3, 7, 10, 14, 21, 28 and 42 days and examined using both light and transmission electron microscopy. Specimens from the 3- and 4-mm defects were retrieved at 28 days and examined using light microscopy. In all sizes of defects, bony repair was consistently localized to the dural side of the defect. The 3- and 4 mm defects demonstrated the greatest degree of osseous bridging and evidence of normal osseous repair throughout the defect. The 8-mm defects repaired in general with the formation of nonunions which contained a small amount of bone at the periphery and fibrous connective tissue. Bone formation was evident at 10 days in the peripheral regions of the 8-mm defects and exhibited bony peninsulas with normal primary calcification fronts. Matrix vesicles containing hydroxyapatite-like crystals were present. In contrast, the central regions of the 8-mm defects were characterized by several islands of cartilage-like cells which stained metachromatically with toluidine blue. Transmission electron microscopy of this region at 14 days demonstrated a dense, collagenous extracellular matrix with matrix vesicles infiltrating the collagen bundles. There was no evidence of crystal formation in the matrix vesicles nor of calcification in the collagenous matrix. At 21 days, both the central and peripheral regions of the 8-mm calvarial nonunions were characterized by dense fibrous connective tissue repair and inactive fibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin D regulation of metalloproteinase activity in matrix vesicles.

Matrix vesicles (MVs) are enriched in matrix metalloproteinases (MMPs) capable of degrading proteoglycans. The aim of the present study was to identify which MMPs are present in MVs and determine whether these MMPs are regulated by 1,25-(OH)2D3 [1,25] and 24,25-(OH)2D3 [24,25]. To do this, growth zone (GC) and resting zone (RC) chondrocytes were isolated from rate costochondral cartilage and placed into culture. At confluence, GCs were treated with 1,25 and RCs with 24,25 for 24 hours. MVs, plasma membranes (PMs), and conditioned media were then collected from the cultures. RTPCR demonstrated the presence of mRNA for stromelysin-1 and 72 kDa gelatinase in both RCs and GCs, Casein zymography revealed activity at M(r) 48 and 28 kDa in MV, but not PM or conditioned media; Western analysis confirmed that this activity was stromelysin-1. Gelatinolytic activity, at low levels, was also found in MVs, but not PMs or conditioned media. When enzyme activity was measured using a proteoglycan bead assay, it was found that both GCs and RCs produced MVs and PMs containing neutral metalloproteinase. Both cells also produced MVs and PMs containing plasminogen activator. The addition of 1,25 to GCs caused a significant 4- to 5-fold increase in metalloproteinase activity in MVs, but not PMs. In contrast, MVs from cultures of RCs treated with 24,25 contained decreased metalloproteinase activity; enzyme activity in PMs was unaffected by 24,25. Plasminogen activator in MVs from RC was increased by treatment with 24,25, while MV enzyme activity was decreased after treatment of GC cultures with 1,25. This study shows that both RCs and GCs produce stromelysin-1 and 72 kDa gelatinase and that these enzymes are preferentially localized in MVs. Further, MMP and plasminogen activator activities in MVs and PMs are regulated by vitamin D metabolites.

Chondrocyte cultures express matrix metalloproteinase mRNA and immunoreactive protein; stromelysin-1 and 72 kDa gelatinase are localized in extracellular matrix vesicles.

Previous studies have shown that costochondral cartilage cell cultures produce extracellular matrix vesicles which contain metalloproteinase activity. In the present study, we examined whether two matrix metalloproteinases (MMPs) known to be present in cartilage, stromelysin‐1 and 72 kDa gelatinase, are expressed by fourth passage resting zone and growth zone costochondral chondrocytes and whether they are specifically incorporated into matrix vesicles produced by the cells. We also examined whether the cells synthesize tissue inhibitor of metalloproteinase‐1 and ‐2 (TIMP‐1 and TIMP‐2). Oligonucleotide primers for stromelysin‐1, 72 kDa gelatinase, tissue inhibitor of metalloproteinases‐1 and ‐2 (TIMP‐1 and TIMP‐2), and GAPDH were synthesized and optimized for use in the reverse transcription‐polymerase chain reaction (RT‐PCR). It was found that both resting zone and growth zone chondrocytes produced mRNA for both MMPs and the two TIMPs. Further, immunostaining of cell layers with antibodies to 72 kDa gelatinase and stromelysin‐1 showed that both cell types produced these MMPs in culture. Substrate gel electrophoresis and Western analysis were used to characterize MMP activity in matrix vesicles, media vesicles, or plasma membranes as well as in conditioned media produced by the chondrocyte cultures. It was found that matrix vesicles but not plasma membranes or media vesicles were selectively enriched in stromelysin‐1. Also, 72 kDA gelatinase was found in matrix vesicles, but to a lesser extent than seen in media vesicles. The relative activity of each enzyme detected was cell maturation‐dependent. No MMP activity was detected in conditioned media produced by either cell type. The results of this study show that MMPs are expressed by resting zone and growth zone chondrocytes in culture and differentially distributed among three different membrane compartments. This suggests that, in addition to the well‐known activators and inhibitors of MMP activity in the matrix, differential membrane distribution may enable more precise control over the site, rate, and extent of matrix degradation by the cell.

Elution of proteins by continuous temporomandibular joint arthrocentesis

PURPOSE The purpose of this study was to determine whether specific proteins recovered from human temporomandibular joints (TMJs) by superior space arthrocentesis are eluted at different outflow volumes. MATERIALS AND METHODS Twenty subjects with unilateral TMJ pain and restricted mandibular range of motion underwent superior space arthrocentesis of the affected TMJ. Sixteen serial fractions of the arthrocentesis outflow volume were collected for analysis. The protein content of each fraction was determined by a BCA protein assay and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). In addition, samples from each collected fraction were assayed for protease activity. RESULTS The average amount of protein recovered in the total 32 mL of collected arthrocentesis fluid was 1.5 mg (0.72 to 2.1 mg). Significant differences (P = .03) in total protein recovered from arthrocentesis fluid were observed between males (0.824 +/- 0.43 mg/20 mL) and females (1.389 +/- 0.54 mg/20 mL). In general, protein concentration declined serially in collected TMJ lavage fluid fractions. Specific proteins and proteases detected in the lavage fluid were eluted at different outflow volumes. CONCLUSIONS Although specific proteins are eluted from the TMJ at different outflow volumes during arthrocentesis, the procedure effectively reduces the protein concentration of the lavage fluid in a volume-dependent manner. Based on empirical assumptions, it is estimated that approximately 100 mL of total arthrocentesis volume is sufficient for a therapeutic lavage of the superior joint space of the human TMJ.

A Preliminary Study of the Osteogenic Potential of a Biodegradable Alloplastic-Osteoinductive Alloimplant

A biodegradable copolymer of polylactide-polyglycolide was combined with allogeneic demineralized freeze-dried bone (DFDB) and implanted into 15-mm diameter defects in the calvaria of 26 New Zealand White rabbits. Similar defects were created in the calvaria of another 26 rabbits. These animals served as controls and did not receive copolymer implants. Upon sacrifice, both the implants and the controls were evaluated clinically, roentgenographically, and histomorphometrically using a Zeiss Image Analysis System (Videoplan, version 4.1). Both controls and implants were evaluated in groups at four, eight, 12, 16, 20, and 24 weeks. When compared with the control defects, the copolymer-DFDB implants displayed a significantly greater volume of trabecular bone. Three of the 15-mm diameter defects displayed evidence of complete osseous bridging at eight weeks. No adverse host-tissue responses were observed histologically in any of the implant specimens.

The Future of Biodegradable Osteosyntheses

In the last 3 decades, much progress has been made in the development of biodegradable osteosyntheses. Despite this progress, these materials are still only used in small numbers, and the scope of their application has been limited. The limitations of biodegradable osteosyntheses mainly are related to problems with their mechanical properties and, in particular, biocompatibility. These problems need to be solved so that biodegradable osteosyntheses can perform up to their full potential and thus, eventually, make their general clinical application routine. This paper presents a historical perspective on the development of biodegradable osteosyntheses, discusses the successful developmental achievements and the still-existing problems, and gives a perspective on their future development.