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Biomedical subjects

S D Cook

Publications and source records attributed to S D Cook.

At least 271 records · Page 15Linked to original sources
PubMed1982

A clinical comparison of LTI carbon, alumina, and carbon-coated alumina blade-type implants in baboons.

The clinical performance of LTI carbon, carbon-coated aluminum oxide, and uncoated aluminum oxide blade-type dental implants was studied in baboons. The objective of the study was to determine the effect that implant material elastic modulus and surface composition have on implant performance. Clinical parameters of mobility, sulcus depth, soft tissue characteristics, and radiographic appearance were used in the evaluation. The implants were placed in healed extraction sites in adult female baboons and were used as a distal abutment for a three-unit fixed gold prosthesis. The restorations were allowed to assume normal occlusal function and were left in situ for a period of two years. The radiographic and sulcus depth measurements appeared inferior for the LTI carbon implants and best for the carbon-coated aluminum oxide implants. No differences in mobility or soft tissue characteristics were noted for the three implant systems. Two implants both in the same animal--one LTI carbon and one uncoated aluminum oxide--were definite clinical failures. The results of the study indicate that an elastic modulus mismatch between implant and bone is not an a priori cause of implant failure and that the implant surface composition had little apparent effect on the clinical and radiographic performance of these implant materials.

Aluminum↗
PubMed1982

The influence of the bone-implant interface stiffness on stress profiles surrounding Al2O3 and carbon dental implants.

Dental implants have been used and studied for the replacement of missing teeth for many years. Finite element stress analysis (FESA) has previously been used in their evaluation to study the effect of various design parameters on induced stresses. A two-dimensional FESA was used to evaluate the effect that the implant-bone interface elastic modulus has on the stress distribution around LTI carbon and aluminum oxide dental implants. The results of this investigation indicate that a soft tissue interface between implants and bone negates the effect of implant elastic modulus and results in stress profiles that were almost identical for the LTI carbon and aluminum oxide implants.

Aluminum↗
PubMed1982

Serum immunoglobulins in Guillain-Barré syndrome.

Serum major class immunoglobulin concentrations were measured in 162 patients with Guillain-Barré Syndrome (GBS) and 85 normal controls. Significant elevations of IgM, A and G were found in the GBS group. Forty-four of 162 GBS patients (27%) had IgM concentrations greater than two standard deviations above the control mean. GBS patients with high serum IgM were young and 68% showed serologic evidence of recent infection with DNA core agents, cytomegalovirus, Epstein-Barr virus, or Mycoplasma pneumoniae. Longitudinal studies in seven patients with elevated serum IgM revealed that clinical improvement was accompanied by a marked decline in serum IgM. IgA and IgG changes were less consistent. Our findings indicate that the serum immunoglobulin response in GBS is polyclonal and follows the usual pattern seen in infections and other conditions with an immune component.

Adult↗
PubMed1982

A three-dimensional finite element analysis of a porous rooted Co-Cr-Mo alloy dental implant.

A three-dimensional finite element model was used to investigate the biomechanical response of a porous rooted Co-Cr-Mo alloy implant. The load displacement responses calculated from the finite element model were verified with experimentally-determined values for three-cylindrical, porous rooted Co-Cr-Mo alloy dental implants retrieved from canines after two years in function. Models were developed based on histological analyses of tissue surrounding the implants. The results of the study indicate that the assumption of a direct bone-to-implant interface (i.e., an ankylosed implant) may not be a good representation for a porous rooted implant retained by bone ingrowth.

Animals↗
PubMed1982

A model for the implant-bone interface characteristics of porous dental implants.

The use of computer-aided design techniques, such as finite element stress analysis, to evaluate implant designs requires that the mechanics at the interface between the implant and the bone be characterized. This problem is accentuated when implants designed to achieve stabilization by tissue growth into porous coatings are used. A model has been developed to represent the mechanical properties of the porous material-bone interface. The model, which accounts for the mechanics of bone tissue grown into a porous implant surface, was also developed so that it could be incorporated into a three-dimensional finite-element analysis. The analytical results from a three-dimensional finite-element model of a cylindrical porous rooted dental implant system incorporating the interface model were compared to the results of mechanical tests performed on similar implants which had resided in canines for two yr. The results from the finite element analysis using the interface model were found to be in better agreement with the experimental results than when a direct bone-to-porous-material interface was assumed.

Animals↗
PubMed1982

The effects of intramedullary implants on bone strains and remodeling in the femur.

Bone remodeling and strain distribution in the femur was studied after implantation of LTI pyrolytic carbon, bioglass coated Co-Cr-Mo alloy, and carbon coated porous Co-Cr-Mo alloy intramedullary plugs. Mechanical testing and finite element analysis has shown that the intramedullary stems significantly alter the strain pattern in the femur. However, no statistically significant differences were observed among the implant groups. The analytical and experimental results were found to be in good agreement. Radiographically, differences were observed in the bone remodeling around the carbon implant compared to either of the Co-Cr-Mo based implants. Both internal and external bone remodeling takes place when an intramedullary implant is present.

Animals↗
PubMed1982

Stress distribution in the proximal femur after surface replacement: effects of prosthesis and surgical techniques.

The increasing number of reported femoral neck fractures following surface replacement indicates a potentially serious problem in this procedure. A comparison of the stress levels in the proximal femur before and after hip surface replacement was made using the finite element technique. A proposed surgical bone graft procedure utilizing a strut of cortical bone placed through the femoral head into the neck to help support the surface replacement was also studied as an adjunct for use in avascular necrosis. The findings indicate that stress magnitudes and distributions in the proximal femur are markedly altered after surface replacement when compared to a femur without a prosthesis. Stress levels in the femoral head with surface replacement were found to be significantly lowered suggesting future problems with stress shielding. Lateral neck stresses were found to be equal to or greater than stress levels in the femur without a prosthesis. Stress orientation in the femoral neck is also markedly altered. Surface replacement design and recommended surgical positioning were important variables in determining stress levels. Femoral neck stresses were found to be significantly lowered for all designs of surface replacement when the bone graft modification was utilized. The results of this study explain the major mechanisms of failure of the femoral component. The proposed bone graft modification is demonstrated by the finite element model to decrease the possibility of femoral neck fracture.

Femur↗
PubMed1982

Retention characteristics of porous rooted Co-Cr-Mo alloy dental implants.

The interface characteristics of porous rooted cobalt-chromium-molybdenum alloy (Co-Cr-Mo) dental implants which had been in free standing function in canine mandibles for a period of two years were investigated. The displacement of the implants and of points on the adjacent mandibular cortex were determined by mechanical testing. Bone ingrowth was quantified, and the structure of the bone-implant interface and mandibular cortex were characterized using histologic and microradiographic analyses. Displacement characteristics were correlated with determinations of the tissue structure adjacent to and growth within the implant to provide information about the biological attachment. A correlation was found between the thickness of the buccal and lingual cortical plates and implant displacements; implants having the greatest displacement response were in mandibles with the thinnest cortical plates. A relationship could not be established between the implant displacement response and the quantitative tissue structure data. Differences observed in the displacement response of the implant by mechanical testing were not observed by clinical measurements of mobility. It was concluded that implant retention mechanical behavior results from both interfacial displacement and deflection of the adjacent mandibular structures.

Animals↗
PubMed1982

The mechanical behavior of normal and osteoporotic canine femora before and after hemiarthroplasty.

Nutritional secondary hyperparathyroidism (NSH) was induced in adult beagle dogs through nutritional control by feeding them a diet containing high phosphorus (1.2%) and low calcium (0.12%). A control group was fed a diet containing 0.42% phosphorus and 0.54% calcium. An osteoporotic condition was produced by NSH, which was verified with histologic, histomorphometric, and biochemical analyses. A significant increase in i-PTH level was measured at both ten and 20 weeks after initiation of the diet in experimental animals when compared with control animals. A 25% reduction in volume fraction cancellous bone and increased osteoclastic activity was found in histologic sections from the femoral heads of the NSH animals when compared with control animals. No abnormally large osteoid seam was found in the cancellous bone of the experimental animals. The results of energy dispersive radiographic analysis and bone ash analysis revealed no significant differences in calcium-to-phosphorus or mineral-to-matrix ratios between the two groups. The results of in vitro mechanical testing indicated significant differences in the strain state for the NSH and control animal femora, with the highest strains being observed in the calcar region of the NSH femora. The presence of a Co-Cr-Mo alloy femoral head prosthesis was found to alter the strain distribution significantly in both the control and NSH femora.

Animals↗
PubMed1981

Role of infection in Guillain-Barré syndrome: laboratory confirmation of herpesviruses in 41 cases.

Serological evidence of either acute cytomegalovirus (CMV) or Epstein-Barr virus (EBV) infection was sought in a large series of patients with Guillain-Barré syndrome (GBS) and control subjects. Using an indirect immunofluorescent technique, IgM antibody directed against CMV was found in the serum of 33 of 220 GBS patients. The CMV-positive patients were mainly young adults (average age, 25.6 years), previously healthy, and the most common prodromal illness was mild coryza. Alternations in serum CMV IgM antibody level closely paralleled the patients' clinical course. Persistently elevated titers were found in patients with severe and protracted paralysis, whereas rapid disappearance of virus-specific IgM characterized benign cases. Striking time clusters of CMV-seropositive patients were found during three periods between January, 1971, and October, 1973. In a parallel study, EBV-specific IgM was found in 8 of 100 GBS patients (8%). All 8 also had heterophil antibodies. Thus, EBV and CMV appear related to a substantial number of cases of this primary demyelinating disease and, to date, are the two most common agents we have been able to link with GBS.

Antibodies, Viral↗
PubMed1981

An evaluation of ion-textured aluminum oxide dental implants.

A study was undertaken to evaluate the ion-beam texturing of aluminum oxide as a means of providing a surface which will produce a biological prosthetic attachment. A wafflelike pattern of surface contours 150 x 75 x 35 microm deep was produced on cylindrical dental implants. The textured surfaces were compared to the as received surfaces in adult mongrel dogs. Implants were inserted into surgically modified healed extraction sites and were left in place for six months. Post-sacrifice mechanical testing was used to quantify the displacement response of the implants. The clinical, radiographic and mechanical testing evaluations did not reveal any statistically significant differences in the performance of the dental implants. However, it was observed that anatomical site and mandibular geometry with respect to implant size play a significant role in affecting implant retention.

Aluminum Oxide↗
PubMed1981

The influence of implant elastic modulus on the stress distribution around LTI carbon and aluminum oxide dental implants.

A three-dimensional finite element analysis (FEA) has been used to determine the effect of implant elastic modulus on stresses in tissues around LTI carbon and aluminum oxide dental implants. The finite element model was constructed to represent a baboon mandible containing a blade type dental implant. A three unit fixed bridge was modeled connecting the dental implant to a natural molar. The results of the study indicate that stress levels of approximately a factor of 3 lower in the crestal region can be expected for aluminum oxide implants when compared to the LTI carbon implants. It was also observed that the use of LTI carbon and aluminum oxide dental implants as an abutment in a fixed bridge results in a reduction of stresses in tissues around the natural tooth when compared to normal physiological stress levels.

Aluminum↗
PubMed1981

A radioimmunoassay search for measles and distemper antigens in subacute sclerosing panencephalitis and multiple sclerosis brain tissues.

Solid-phase direct sandwich radioimmunoassays have been developed which will detect measles antigen in as little as 20 microgram of SSPE brain, measles antigen in 5 x 10(4) pfu/ml of measles virus, and canine distemper antigen in 5 x 10(5) pfu/ml of this virus. Using these assays, a search was carried out for measles and distemper antigens in CNS autopsy tissue from 3 multiple sclerosis (MS) patients. Even in 1000-fol higher concentrations of MS brain (20 mg), antigens of neither virus were detected. Additional studies were carried out using similar radioimmunoassays but employing IgG from 2 MS patients as probe against MS brain specimens, including IgG and acute plaque material from the same individual. However, no reaction between MS IgG and MS brain was detected. Thus no evidence was found for foreign antigen in the MS brain nor for autoantibody which reacted with brain tissue antigens. It is concluded that either measles or distemper are not present in acute MS lesions, or that they are present in such small amounts that their detection will require techniques even more sensitive than those used in the present study.

Animals↗