Biomedical subjects

J E Lemons

Publications and source records attributed to J E Lemons.

At least 19 recordsLinked to original sources

PubMed1996

Interfacial shear strength and histology of plasma sprayed and sintered hydroxyapatite implants in vivo.

The interfaces of bone with sintered hydroxyapatite (SHA) and plasma sprayed hydroxyapatite-coated (HAC) implants in the femora of six dogs were examined by light microscopy, scanning electron microscopy, energy dispersive X-ray analysis, and push-out tests. The results demonstrated that there was no significant difference at 12 and 24 weeks after insertion between the interfacial shear strengths with bone for the two types of implants, however, the histological characteristics of the bone around the plasma sprayed HA could be distinguished from that of the sintered HA. The HAC implants showed an early surface biodegradation as compared with the SHA implants. The observed differences in the interfacial zones may be attributed to different bone cell activities and variations in the dynamics of bone formation, possibly resulting from a higher level of dissolution/reprecipitation along the plasma sprayed HA surface.

Animals↗

PubMed1996

Ceramics: past, present, and future.

The selection and application of synthetic materials for surgical implants has been directly dependent upon the biocompatibility profiles of specific prosthetic devices. The early rationale for ceramic biomaterials was based upon the chemical and biochemical inertness (minimal bioreactivity) of elemental compounds constituted into structural forms (materials). Subsequently, mildly reactive (bioactive), and partially and fully degradable ceramics were identified for clinical uses. Structural forms have included bulk solids or particulates with and without porosities for tissue ingrowth, and more recently, coatings onto other types of biomaterial substrates. The physical shapes selected were application dependent, with advantages and disadvantages determined by: (1) the basic material and design properties of the device construct; and (2) the patient-based functional considerations. Most of the ceramics (bioceramics) selected in the 1960s and 1970s have continued over the long-term, and the science and technology for thick and thin coatings have evolved significantly over the past decade. Applications of ceramic biomaterials range from bulk (100%) ceramic structures as joint and bone replacements to fully or partially biodegradable substrates for the controlled delivery of pharmaceutical drugs, growth factors, and morphogenetically inductive substances. Because of the relatively unique properties of bioceramics, expanded uses as structural composites with other biomaterials and macromolecular biologically-derived substances are anticipated in the future.

Ceramics↗

PubMed1996

Analysis of consecutively placed loaded root-form and plate-form implants in adult Macaca mulatta monkeys.

The present paper describes 36 consecutively treated non-human primates (Macaca mulatta) as part of a balanced block design study to examine osseointegration in root- and plate-form implants prepared by atraumatic preparation of bone. Clinical measurements around selected teeth and digital radiology were utilized to monitor periodontal disease and bone loss around root- and plate-form implants which were loaded with a fixed prosthesis. Results indicate that once monthly regimen of scaling and root planing can prevent attachment loss in natural teeth, serving as abutments of loaded bridges. Root-form implants exhibited a significant loss of crestal bone height during the first year (P < 0.03) while plate-form implants showed less loss in bone height. There was an increase in bone mass over time for root-form or plate-form implants. Both root-form and plate-form implants provided radiographic evidence of osseointegration in loaded bridges.

Alveolar Bone Loss↗

PubMed1994

Surface energy characterization of unalloyed titanium implants.

Osteointegration is dependent on a variety of biomechanical and biochemical factors. One factor is the wettability of an implant surface that is directly influenced by its surface energy. This investigation used the Zisman plot to determine critical surface tension as one representative measurement of surface energy. The effects of surface treatment, bulk grain size, and surface roughness on the critical surface tension of unalloyed titanium (Ti) were examined. Radio frequency glow discharge-treated Ti had the highest critical surface tension, followed by the passivated and heat-sterilized conditions. Titanium with no surface treatment had the lowest critical surface tension. The surface energy of Ti with an average grain size of 23 microns was not significantly different from that with a grain size of 70 microns. Surface roughness was shown to cause significant difference in measurements and definitely should be considered in studies of this kind.

Prostheses and Implants↗

PubMed1994

Evaluation of consecutively placed unloaded root-form and plate-form implants in adult Macaca mulatta monkeys.

The present paper describes 18 consecutively-treated non-human primates (Macaca mulatta) as part of a balanced block design study of 36 animals to examine osseointegration in root- and plate-form implants prepared by atraumatic preparation of bone. Clinical measurements around selected teeth and digital radiology were utilized to monitor periodontal disease and bone deposition around the unloaded implants. Once a month scaling procedures were utilized as a means of preventing further advance of periodontal disease. Results indicate that once-monthly regimen of scaling and root planing can prevent attachment loss of natural teeth and will not interfere with the healing of either type of implant; once-monthly scalings produce significant reduction in redness (P < .05) and reduced probing depths (P = .01). A second finding is that both root and blade implants show radiographic evidence of osseointegration in this primate model. The quantitative analysis demonstrates bone gain is not stabilized until 6 months after healing. The data may indicate that occlusal loading of mandibular implants at 3 months may be premature.

Alveolar Bone Loss↗

PubMed1993

Arthroscopy training using a "black box" technique.

In orthopaedic surgery residency, arthroscopic training is an essential component and one of the educational program requirements. A system using standard arthroscopy instrumentation and a "black box" has been developed for the purpose of teaching basic arthroscopic surgical skills in a laboratory setting. The black box component can be used as a dry or wet model, permitting a variety of arthroscopic techniques to be mastered under controlled circumstances. This unit has provided excellent feedback from residents and staff, and is cost effective. The basic principles of the orthopedic black box can be adapted for the development of basic skills in other specialties.

Arthroscopy↗

PubMed1993

Evaluation of the medial soft-tissue restraints of the extensor mechanism of the knee.

We performed an anatomical dissection of the medial soft-tissue retinacular fibers that restrain lateral patellar displacement and found that the medial patellofemoral ligament inserts not only on the patella but also on the undersurface of the distal aspect of the quadriceps mechanism. The deep capsular layer contained substantial retinacular fibers that were associated with the medial patellomeniscal ligament. Functional studies of the relative contributions of the medial soft-tissue restraints in the prevention of lateral patellar displacement were also performed. Twenty-five fresh-frozen specimens of the knee, obtained after amputations (nineteen specimens) or from cadavera (six specimens) were tested biomechanically on a universal testing instrument. We ranked the soft-tissue restraints, in order of their relative contributions to the restraining force, on the basis of the percentage of force provided by the retinacular and ligamentous tissue that resisted the lateral displacement of the patella. The medial patellofemoral ligament, although varying in size and importance, was found to be the major medial soft-tissue restraint that prevented lateral displacement of the distal knee-extensor mechanism, contributing an average of 53 per cent of the total force. The patellomeniscal ligament and associated retinacular fibers in the deep capsular layer of the knee, which were previously thought to be functionally unimportant in the stabilization of the patella, contributed an average of 22 per cent of the total force. The previously described retinacular fibers (the patellotibial band) were functionally unimportant in the prevention of lateral displacement.

Adult↗

PubMed1992

In vitro strength analysis of sagittal split osteotomy fixation: noncompression monocortical plates versus bicortical position screws.

An in vitro study using bovine ribs was performed to compare the strength of monocortical plates with bicortical position screws. An osteotomy was created to simulate a sagittal split and a 5-mm bone gap was produced. Four study groups were created: screw nongap, screw with gap, plate nongap, and plate with gap. Parameters of strength were analyzed by elastic deformation, stiffness ratio, permanent deformation, and breaking load. The results showed that monocortical plate fixation in bovine ribs provides less rigidity and is more susceptible to deformation than is bicortical position screw fixation.

Alloys↗

PubMed1992

Intraoral corrosion resulting from coupling dental implants and restorative metallic systems.

Materials used for the construction of dental restorations and implants include a wide range of metals and alloys, ceramics and carbons, and polymers. When metals and alloys are placed in direct contact in the oral cavity, a galvanic cell can be formed that may compromise the longevity of one or more of the materials in the couple. In vitro electrochemical corrosion analyses have proven to be a valuable tool for providing guidance on the selection of metallic materials. These analyses can provide basic data on electrochemical potentials, current rates, and the evaluation of galvanic corrosion conditions. This article seeks to provide the clinician with information that can be valuable in the selection of metallic materials that may be placed in direct contact with one another in the oral cavity.

Copper↗

PubMed1992

Biodegradation of restorative metallic systems.

Metallic materials utilized for the construction of intra-oral and implant dental restorations include a wide range of relatively pure metals and multicomponent alloys. Basic corrosion and biodegradation properties of these alloys have been studied by both in vitro and in vivo techniques. These property characteristics have been shown to be dependent on composition and metallurgical state, combinations within a construct, surface conditions, mechanical aspects of function, and the local and systemic host environment. The susceptibility of these metallic materials to various forms of biodegradation will be presented, with emphasis on corrosion.

Biodegradation, Environmental↗

PubMed1992

Retrieval analyses of a blade implant after 231 months of clinical function.

A blade implant that was retrieved in 1990 after 231 months of clinical function (since 1971) was analyzed with respect to clinical, histological, and biomechanical characteristics. The implant clinical records demonstrated no abnormalities or pathological lesions over the tenure of treatment. The bone to implant interface showed a mixture of interfacial tissue components and conditions with adequate direct bone contact (46.4 to 82.3 percent) for classification as osseointegrated. The abutment fracture leading to removal was characterized as a cyclic fatigue mechanism and the distribution of tissue components along the interface could not be correlated with specific biomechanical loading directions. This report considers the clinical and biomechanical records as they relate to the detailed histological investigation.

Blade Implantation↗

PubMed1991

The influence of radiation therapy on subperiosteal hydroxyapatite implants in rabbits.

Granular hydroxyapatite (HA) was implanted into subperiosteal pockets along both the right and left proximal tibias of 12 adult New Zealand white rabbits. The left extremities of 10 rabbits served as controls, whereas the right sides were irradiated with 2,250 rad in three doses over 5 days. The animals were killed at 1-week intervals starting at 2 weeks postirradiation. One half of each site was evaluated using standard histologic techniques while the other half was examined as a nondecalcified section. The quantity and the quality of new bone formation was determined using a rating scale and histomorphometric digitization. The results of this 4-month study showed that the amount of new bone formation around the HA granules was significantly greater in the irradiated sites. The irradiation produced no deleterious effects on the implant or the surrounding tissue areas.

Animals↗

PubMed1991

In vitro vs in vivo corrosion analyses of two alloys.

The in vitro and in vivo corrosion characteristics of two alloys, cast Co-Cr-Mo (ASTM F75) and wrought Ni-Cr-Mo, were evaluated using electro-chemical corrosion analysis. Two in vitro electrolytic solutions were utilized, an isotonic saline solution consisting of 0.9 w/o NaCl in distilled water and an isotonic saline solution with 10 v/o sterile calf serum. The in vivo environment was created by implanting cylindrically shaped specimens of each alloy into the back muscles of New Zealand white rabbits. Cyclic anodic and cathodic polarization curves were generated for the three test conditions and subsequently were compared. Anodic curves conducted using the isotonic saline and isotonic saline plus serum electrolyte solutions were very similar to the anodic curves generated for the implanted alloy specimens for both alloys. The corrosion rates predicted from the in vitro and in vivo cathodic polarization curves were not statistically different for the three test conditions. Overall, the corrosion data generated using the in vitro environmental conditions adequately predicted the in vivo corrosion behavior of the cast Co-Cr-Mo and wrought Ni-Cr-Mo alloys.

Animals↗

PubMed1991

Evaluation of cryopreserved bone and synthetic biomaterials in promoting spinal fusion.

The purpose of the study was to evaluate the use of cryopreserved allograft bone and tricalcium phosphate in promoting spinal fusion. Nine 20-30 lb swine underwent posterior spinal fusion at T5-T6, T13-T14, and L2-L3. Autogenous bone, cryopreserved allograft bone, or equal parts of allograft bone and tricalcium phosphate were added to the decorticated posterior elements. A total of 27 sites were prepared for fusion. The spines were retrieved at 6 months and evaluated for integrity and stability of the fusion sites by clinical examination, three-point bending tests, multiplanar radiographs, and undecalcified tetracycline-labeled and decalcified histologic sections. The nine sites that received autogenous bone were solidly fused. There were one clinical and two radiographic nonunions in the nine sites that received cryopreserved allograft bone. Sites that received a mixture of allograft bone and tricalcium phosphate demonstrated slight motion at two locations and radiographic evidence of fusion at all levels. The extent and degree of fusion was not site-specific. Three-point bending analysis did not demonstrate a significant trend as to site or materials specificity. No adverse histologic response was noted. Histologic sections and tetracycline labels confirmed abundant new bone formation at all sites at 6 months. Although autogenous bone remains the gold standard for use in spinal arthrodesis, this study demonstrates the value of cryopreserved allograft bone alone and in combination with tricalcium phosphate in promoting spinal fusion.

Animals↗

PubMed1990

Multiaxis cyclic biomechanical testing of Harrington, Luque, and Drummond implants.

The performance characteristics of Harrington-Moe distraction rods, paired wired Luque rods and Drummond's system were evaluated and compared when subjected to nondestructive cyclic, multidirectional biomechanical testing. Twelve fresh, frozen swine spines with intact facet joints and anterior and posterior ligamentous complexes were instrumented and tested in a specially designed pneumatic testing machine. The instrumented spines were subjected to 207 kN/m2 compression and 49 N-m torsion. Each spine was cycled 28,000 times at 1 cycle per second. Linear and angular displacements were determined by digitizing photographs and video tapes made during testing. A computer program developed and refined for the project was used to complete the data analysis. Approximately 540 items of angular and linear displacement data were collected for each spine. Inspection of the spines after cyclic, multidirectional testing revealed no change in their osteoligamentous integrity compared with pre-testing. Pre- and post-testing radiographs showed no evidence of osseous failure, hook dislodgement or wire breakage. Erosion of laminal bone at the Harrington hook attachment sites was observed. Displacement of the Harrington hooks was seen during off-axis compression-torsion testing. Fretting and deposit of metal wear debris occurred between the sublaminal wires and "L" rods. There was no evidence of loosening of either the Drummond or Luque implants or fatigue failure of any component. Analysis of the linear and angular displacement data showed that the Luque and Drummond instrumented spines displaced less in axial compression, off-axis compression and off-axis compression-torsion than the single Harrington-Moe distraction rod.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Dental implant biomaterials.

Synthetic materials for surgical implant devices have evolved from the early metallic systems to a variety of material combinations and composites. Current biomaterial and biomechanical properties provide relatively optimal stable bone and soft tissue interfaces and simplified restorative treatments. Further improvements in existing systems require a continuation of the multidisciplinary approach to laboratory, experimental animal, and human clinical research.

Biocompatible Materials↗

PubMed1990

Histologic response after implantation of porous hydroxylapatite ceramic in humans.

After periods of observation from 3 to 36 months, biopsies were obtained from 22 patients in whom porous block and particulate hydroxylapatite ceramic (Interpore 200) had been used for augmentation procedures and in two patients in whom nonporous particulate hydroxylapatite (Calcitite) had been used. Histologic examination of serial sections of decalcified specimens revealed vital bone formation in relation to the blocks, whereas the particulate was encapsulated in fibrous tissue. The differences in biological behavior are discussed.

Adult↗

PubMed1990

Clinical longevities of ramus frame implants.

A variety of ramus frame dental implant designs is indicated for endosseous restoration to retain lower dentures, and the different designs utilize various alloys. The objective of this study was to present an analysis of the clinical applications for ramus frame dental implants with emphasis on the statistics of clinical longevities. The investigation involved an extensive statistical evaluation and, when possible, metallographic, scanning electron microscopic, histological, mechanical, and stereomicroscopic surface evaluations. The statistical analysis presents averages and percentages of devices in place vs. devices removed. Analyses of survival probability were also determined by means of the Kaplan-Meier statistical methods. A comparison of these results with the general criteria listed in the Harvard Conference shows that more than 75% of the implant devices were in place after five years.

Dental Alloys↗