Sequencing platinum foil matrix removal in postceramic soldering of the collarless veneered retainer.

Postceramic soldering of collarless veneered retainers in which the porcelain margins were formed with a platinum foil matrix technique was investigated. The purpose of the study was to determine if removing the platinum foil matrix before or after indexing and soldering procedures would affect the porcelain margin integrity in fixed partial dentures. Prostheses were fabricated on a nickel-chromium laboratory model using both sequences. Six test cycles were performed. Each cycle included one soldering with matrix support and one without the matrix, for a total of 12 solderings. The fixed partial dentures were compared for degree of marginal seating with a measuring microscope and for configuration changes at the porcelain margins with scanning electron micrographs. In the microscopic analysis of marginal closure, soldering without foil matrix was statistically equal to soldering with foil in place. Removal of the platinum foil matrices prior to indexing provided for no further seating of the metal ceramic retainers. Evaluation by scanning electron microscopy demonstrated distinct configuration changes in the porcelain margins for the specimens soldered without matrix support.

Cranial, iliac, and demineralized freeze-dried bone grafts of the mandible in dogs.

Both autogenous bone grafts and demineralized freeze-dried allogeneic bone implants were evaluated for mandibular reconstruction. Four-centimeter segmental defects of the midbody of the edentulous mandible were reconstructed in 36 dogs, with specimens recovered at 3 and 6 months and quantitatively compared for total and new bone by histomorphometric analysis. Autogenous grafts consisted of corticocancellous cranial block (CB), corticocancellous iliac block (IB), and particulate cancellous iliac marrow (PM). The allogeneic bone was demineralized and freeze-dried, and consisted of particulate cortical endochondral bone (FP), cranial cortical block (FCB), and iliac cortical block (FIB). Clinically and histomorphometrically, results appeared to indicate that (1) CB compared favorably with IB at 3 and 6 months for total bone, but IB showed a trend for more new bone formation at 6 months, a trend that may be due to the thicker cortical component of CB, which requires longer time periods to remodel than the cancellous rich IB; (2) FP failed to achieve bony union at 3 months, with inadequate rates of new bone formation; and (3) FCB and FIB compared favorably for total bone with CB and IB at 6 months, although new bone for autogenous CB and IB was 26.9% and 45.4%, while new bone for allogeneic FCB and FIB represented only 7.9% and 17.4%.

A scanning electron microscopic study of in vitro toxicity of ethylene-oxide-sterilized bone repair materials.

Polylactic acid (PLA) and polyglycolic acid (PGA) have been under investigation for use in the management of hard- and soft-tissue wounds. Current research has included the incorporation of osteo-inductive substances into a PLA-PGA copolymer alloplastic implant material for enhancement of the healing of osseous defects. Conventional methods of sterilization--such as dry heat, steam heat, or 60Co--tend either to destroy or attenuate osteo-inductive activity and alter polymer biodegradation. Ethylene oxide (EO) gas sterilization is currently being tested as an alternate method. This study examined the relationship of EO-induced cytotoxicity to the length of time of polymer aeration following EO sterilization. Three groups of copolymer implant discs were studied: (1) 50:50 PLA-PGA copolymer, (2) PLA-PGA polymer with hydroxyapatite (HA), and (3) PLA-PGA with autolyzed, antigen-extracted (AA) bone particles. Polymer discs, as well as particulate HA and AA bone controls, were sterilized with EO for 12 hours. Following periods of two weeks, one week, one day, or no subsequent vacuum aeration, samples were placed into 24-well culture plates. A suspension of human fibroblasts was added to each well. Cell growth and attachment were permitted for 24 hours. Medium was then removed, and solutions for cell fixation, buffer washing, and dehydration were added to each well. SEM examination revealed changes in cell growth with increasing periods of aeration suggestive of increasing cell vitality. Cells growing on discs having no aeration were small, round, and lobulated, whereas those of seven to 14 days' aeration were more numerous, and flattened with many microvilli, pseudopodia, and dendritic processes, features consistent with normal cell morphology. These results suggest that EO-sterilized polymer implants should be aerated for least seven to 14 days prior to surgical use.

Scanning electron microscopic study of cell attachment to biodegradable polymer implants.

The biodegradable polymers--polylactic acid (PLA) and polyglycolic acid (PGA)--are currently being studied as carriers for bioactive bone regeneration compounds. The inclusion of osteo-inductive substances in poly-(DL, lactide-co-glycolide) copolymer alloplastic implants has been shown to enhance the repair of osseous defects. The purpose of this study was to examine, by SEM, the attachment relationship of biodegradable polymer implants to cells and tissue matrix. Three groups of copolymer implants were studied: (1) plain 50:50 PLA-PGA copolymer, (2) PLA-PGA copolymer with hydroxyapatite (HA), and (3) PLA-PGA copolymer with autolyzed, antigen-extracted (AA) bone particles. Polymer discs were surgically implanted into the pectoralis muscles of rats. At seven, 14, and 21 days post-implantation, the baskets were removed and the contents prepared for SEM. Results showed that at one week, implants were coated primarily with red and white blood cells in a fibrinoid clot. Degradation of the polymers was evidenced by irregular enlarging of polymer surface pores. At two and three weeks, polymers became lobular and then fibrinoid as degradation progressed. Inflammatory cell and red blood cell adhesions were increasingly replaced by fibroblasts and collagen matrix deposition. As polymer degradation progressed, AA and HA particles were exposed; however, the lack of cell or tissue adhesion in these areas suggests that degradation may be more influenced by the fluid environment than by direct cell attachment. Furthermore, degradation may inhibit direct cell attachment.

Differential expression of phenotype by resting zone and growth region costochondral chondrocytes in vitro.

This study establishes an in vitro model for examining endochondral cartilage cell metabolism. Chondrocytes derived from the resting cell zone and adjacent growth zone of rat costochondral cartilage were compared for retention of phenotype in culture. At third passage confluence, two cell populations differ morphologically and biochemically. Resting zone cells are fibroblast-like, with smooth cell membranes and little rough endoplasmic reticulum. Growth zone cells are more polygonal, smaller in diameter, with numerous cytoplasmic extensions of the plasma membranes and abundant rough endoplasmic reticulum. Both cell populations produce matrix vesicles that are comparable morphologically to matrix vesicles isolated enzymatically from epiphyseal cartilage. While membrane vesicles are released into the media by cells derived from the resting zone as well as from the growth cartilage, alkaline phosphatase activity is enriched in media vesicles produced by growth cartilage cells. Alkaline phosphatase enriched vesicles appear to be preferentially incorporated into the extracellular matrix. Both the plasma membrane marker enzyme activity and the membrane phospholipid composition are differentially expressed in matrix vesicles and plasma membranes and are cell specific. Matrix vesicles produced by resting zone cells are enriched in alkaline phosphatase, 5'-nucleotidase, ouabain sensitive Na+/K+ ATPase and cardiolipin when compared to the cell membrane. In addition, the plasma membranes of these cells contain more phosphatidylcholine plus sphingomyelin than do growth cartilage plasma membranes. Resting zone cell matrix vesicles have less phosphatidylethanolamine than do vesicles from growth cartilage cultures. Matrix vesicles produced by growth cartilage cells contain one proteolipid at 43,000 Mr which comigrates with plasma membrane proteolipid and an additional proteolipid at approximately 3,000 Mr. These data indicate that both cells retain differential expression of phenotype in culture and that one expression of this phenotype is production of specific extracellular matrix vesicles.

A study of the odontoblast process with transmission electron microscopy.

Freshly extracted human third molars with completely formed roots were sectioned and placed in Karnovsky's fixative. The specimens were decalcified in ethylenediaminetetraacetic acid (EDTA) for 91 days, followed by digestion in collagenase. They were then fixed in a solution of buffered osmium tetroxide or ruthenium red and buffered osmium tetroxide, embedded in Spurr's plastic mixture, and sectioned for transmission electron microscopy. Each section was stained with uranyl acetate and lead citrate and viewed with a transmission electron microscope. No odontoblast processes could be identified at the cemental third of the dentin with the described technique.

The effect of alternatives to formocresol on antigenicity of proteins.

As part of an overall evaluation of possible substitutes for the pulpotomy agent formocresol, this study was initiated to compare the antigenicity of the reaction products of protein with formaldehyde, glutaraldehyde, or dimethylsuberimidate (DMS). Rabbits were injected with rabbit serum albumin (RSA) which had been treated with one of the following solutions: phosphate-buffered saline, 2% glutaraldehyde, 4% formaldehyde, or 2% DMS. The antisera from the rabbits were analyzed for elicited antibodies by the enzyme-linked immunosorbent assay (ELISA) and in a horseradish peroxidase (HRP) assay using a spot technique on nitrocellulose paper. These assays demonstrated that DMS-treated RSA was the most antigenic of the reaction products tested. The least provocative was the glutaraldehyde-treated RSA; the reaction product of formaldehyde was intermediate. Our findings suggest that if non-immunogenicity of a pulpotomy agent is a desirable property, then DMS does not meet the criteria of an alternative pulp fixative. In contrast, the relatively low antigenicity of glutaraldehyde reinforces other favorable findings which support its use clinically.