Preliminary evaluation of hydroxyapatite cement as an augmentation device in the edentulous atrophic canine mandible.

OBJECTIVE: The purpose of this study was to answer the following two questions: (1) Can hydroxyapatite cement in combination with demineralized freeze dried bone feasibly augment the dimension of an atrophic edentulous canine mandible? (2) What is the histologic fate of an augmentation graft composed of hydroxyapatite cement and demineralized freeze dried bone placed on the surface of an atrophic edentulous canine mandible? STUDY DESIGN: Each of four mixed-breed canines (weighing 50 to 60 pounds) underwent bilateral mandibular dental extraction (canine to second molar) and radical alveolectomy. After 4 months of healing, a bilateral subperiosteal mandibular augmentation graft was put into place, with hydroxyapatite cement/demineralized freeze dried bone on the surface of one hemimandible and porous granular hydroxyapatite and demineralized freeze dried bone on the surface of the other hemimandible. The animals were killed after functioning on a soft diet for 9 months, and the grafted hemimandibles were harvested. RESULTS: Both hydroxyapatite cement and granular hydroxyapatite grafts appeared to augment the edentulous atrophic canine mandible. On histologic exam, the hydroxyapatite cement grafts showed osteoconduction and subperiosteal and endosteal osteonal bone formation, whereas the granular hydroxyapatite grafts showed only osteoconduction. Neither graft material showed chronic or acute inflammation. CONCLUSION: Hydroxyapatite cement can function feasibly as a mandibular augmentation device. The histologic fate of hydroxyapatite cement is different from that of granular hydroxyapatite. It has a fate comparable to autograft or allograft cortical bone grafts.

Preserving the posterior superior synovial recess during allograft TMJ diskal condylar transplantation in the adult goat.

OBJECTIVE: The purpose of the study was to test the hypothesis that sparing the posterior superior synovial recess during the resection of temporomandibular joint condyle and disk would maintain a critical mass of synovium necessary to predictably achieve a successful allograft joint reconstruction. STUDY DESIGN: A group of 15 adult goats underwent unilateral resection of their temporomandibular condyle and meniscus. The fossa and posterior superior synovial recess were left intact. They were immediately reconstructed with cryogenically preserved allograft mandibular condyles and temporomandibular joint disk harvested from 15 adult donor goats. The animals were evaluated clinically and radiographically at 6 and 12 months and histologically at 12 months. RESULTS: Of the 15 animals, 13 met all the criteria to be declared a success and retained the posterior superior synovial recess. CONCLUSION: Immediate joint reconstruction using cryogenically preserved mandibular condyles and temporomandibular joint disk can have a high rate of success if the native posterior superior synovial recess remains intact.

Total reconstruction of the temporomandibular joint with cryogenically preserved allograft mandibular condyle, meniscus, and fossa in the adult goat.

OBJECTIVE: The purpose of this study was to determine the feasibility of total temporomandibular joint reconstruction with the use of cryogenically preserved allograft mandibular condyle, disk, and fossa in the adult goat. STUDY DESIGN: This study consisted of an experimental group of 10 adult goats that underwent total resection of their temporomandibular joints. These animals were immediately reconstructed with cryogenically preserved mandibular condyles, disks, and fossa. These allograft were harvested from 10 donor animals matched to the recipient animal with respect to age, sex, and head dimensions. These grafts were harvested and stored at -185 degrees C for several months before implantation. At 2 years after surgery, the animals were killed. They were evaluated, clinically, radiographically, and histologically. RESULTS: Fifty percent of the eight surviving animals had a normal clinically functional joint with an intact superior joint space and viable articular surfaces. CONCLUSION: The authors conclude that this temporomandibular joint reconstruction technique is feasible in the adult goat model and is deserving of further research.

Distribution of metals in mechanical fractions of soils from a lake catchment in Venezuela.

Soil samples were collected from both the surface and at depth from the lowlands around Lake Valencia and from the adjacent mountains. This paper reports results for Al, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb and Zn in mechanical fractions of the soils. Lowland soils, developed on lacustrine sediments, show a predominance of medium- to fine-grain size fractions whereas the shallow mountain soils show the highest percentage of particles in the coarse to medium fractions. Concentrations of most of the elements investigated increased toward finer particle sizes. The generally higher metal concentrations in lowland soils compared with mountain soils are consistent with release by weathering in the uplands and accumulation in the lowlands. The presence of carbonates derived from ubiquitous shelly material in the lowland soils may explain increases of Ca and Mg in labile fractions. In the lowland area, there is little evidence for the translocation of metals in the soil profiles, despite the high rainfall of a tropical climate, and the calcareous nature of these soils could account for the immobility of metals.

Metallic contaminant profiles in sediment cores from Lake Valencia, Venezuela.

Total extractable concentrations of AI, Fe, Mn, Pb, Cu, Zn, Hg and organic carbon (Corg) were determined along four sediment cores from Lake Valencia. In one selected core, the percentage labile fractions were determined in order to establish anthropic enrichment factors, the depth reached by the contaminants and their mobilities. The distribution patterns of concentration versus depth reflect the original concentrations of the settling sediments. Only Mn seems to show diagenetic cycling. No enrichment of Fe and Mn occurs in the upper part of the cores, in spite of good water circulation and aeration of bottom lake waters during five months of the year. This immobility can be attributed to the high pH of water (7.6 - 8.9). Pb, Zn, Cu and Hg are enriched in the upper part of the cores, probably reflecting the input of contaminants. These elements show enrichment factors of up to 3.0. Background concentrations of the studied metals are reached below a depth of 30 cm.

A comparison of the form and function of the human, monkey, and goat temporomandibular joint.

The anatomic form and function of the human temporomandibular joint is compared with the monkey (Macaca and Papio) and goat joint. The findings indicate that the joint of the goat seems to be superior to the joint of Macaca and Papio as a research model.

Cryogenically preserved adult and juvenile goat mandibular condylar transplantation.

Loss of a functional temporomandibular joint (TMJ) has long been a clinical challenge in both children and adults. Although reconstruction to date has been performed with various prosthetic devices or autogenous costochondral grafts, these procedures have a potential for complications and morbidity. Our studies were performed to determine the feasibility of healing, growth, and long-term function of TMJ reconstruction techniques with cryogenically preserved mandibular allografts in the goat model. This species was chosen because the surgical anatomy and biomechanics of the goat TMJ are very similar to those of the human TMJ. The positive results of the studies and their relevance will be described.

Heavy metals and organic carbon in sediments from the Tuy River basin, Venezuela.

The Tuy River basin, located in north-central Venezuela with an annual average temperature of 27°C and precipitation of 140 cm, was selected to conduct a geochemical study of bottom sediments, with the object of establishing the natural and human influences in the abundance and distribution of Fe, Mn, Cr, Co, Cu, Ni, Pb, Zn and organic carbon. The basin is lithologically divided into two sub-basins, north and south. The north sub-basin drains a iow-grade metasedimentary terrain with a population density of 800 persons km(-2) and approximateiy 600 industrial sites, while the south sub-basin in underlain by metavolcanic and ultramafic rocks, with a population density of less than 10 persons km(-2).Stream bottom sediment samples (150) were collected during the years of 1979-1986 in 16 unpolluted sites and 13 polluted sites. The sediments were air dried at room temperature and sieved through a 120 stainless steel mesh (125 µm). Samples of grain size smaller than 125 µm were analysed, the heavy metals being determined by atomic absorption spectrometry and the organic carbon (Corg) by dry combustion.The higher concentrations of heavy metals and organic carbon found in the pristine areas were in the south sub-basin, especially in those areas with higher annual precipitation and tropical forest. This indicated that the metavolcanic and ultramafic rocks yield higher concentrations of heavy metals than the metasedimentary rocks. It was also noted that the higher concentrations of Cr and Ni are associated with the ultramafic rocks. The results obtained from the sediment samples collected in the polluted sites showed that the elements Pb, Zn and Corg are enriched up to 4 times as a result of ail the human activities taking place in the basin. Organic carbon is an excellent indicator of domestic wastewater, Pb and Zn are good indicators of the automotive traffic and industrial effluents. The concentrations of each heavy metal did not show any significant correlation with grain size fractions; however, the concentration of organic carbon did show a negative correlation with grain size. The lithological, climatic and vegetation influence in the abundance of heavy metals and organic carbon in stream sediments clearly indicates the necessity of establishing background levels for the area under study when carrying out studies in environmental geochemistry.

Transplantation of cryogenically preserved mandibular condyles in the adult and juvenile goat.

Loss of a functional temporomandibular joint (TMJ), due to various causes including tumor resection, joint disease such as osteonecrosis, and injury or trauma, has long been a clinical challenge in both children and adults. It may be a significant problem facing physicians during another war. While reconstruction to date has been performed with various prosthetic devices or autogenous costochondral grafts, these procedures have a potential for complications and morbidity. This procedure could adversely delay the return of military members to a combat unit, or affect their ability to serve as functional members of society. Our studies were performed to determine the feasibility of TMJ reconstruction techniques, healing, and long-term function and growth using cryogenically preserved mandibular allografts in the goat. This species was chosen because the surgical anatomy and biomechanics of the goat TMJ are very similar to that of the human. The positive results of the studies and their relevance to future military medical readiness and civilian medicine will be described.

Pb, Cd, Mn y Fe en las particulas respirables del centro de Caracas. / Pb, Cd, Mn and Fe in inhalable particles of downtown Caracas

En el presente trabajo se determino la fraccion de Pb, Cd, Mn y Fe en las particulas respirables del Centro de Caracas.Las muestras recolectadas con un equipo de alto volumen, equipado con un impactador en cascada, fueron digeridas y luego analizadas por absorcion atomica. Ademas de las muestras del Centro de Caracas, se analizaron las particulas recolectadas a la salida de un tunel con alta densidad de trafico. Basandose en los resultados del tunel (representativo de las emisiones de los vehiculos automotores), los factores de enriquecimiento con respecto a la corteza terrestre, la distribucion de tamano (D.M.M.) y los resultados reportados en la literatura se concluye que: I) en Caracas las particulas inhalables capaces de penetrar hasta los pulmones se encuentran muy contaminadas en Pb. II) los niveles de Cd son superiores a los naturales y el enriquecimiento es atribuible a las emisiones de los incineradores. III) el Mn y el Fe se encuentran asociados a particulas grandes y la fuente mas probable es la recirculacion del polvo del suelo