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Biomedical subjects

J E Lemons

Publications and source records attributed to J E Lemons.

At least 73 records · Page 4Linked to original sources
PubMed1983

Histologic study of hydroxylapatite as an implant material for mandibular augmentation.

Dogs were used to compare supraperiosteal implantation of hydroxylapatite with subperiosteal implantation with and without partial decortication of the underlying bone. Whereas supraperiosteal implants were unstable, nine months of observation indicated that the subperiosteal implants developed a strong attachment and mechanical stabilization as a result of formation of investing fibrous and osseous tissues. These results provide a basis for a technique of alveolar augmentation and denture construction.

Alveolar Ridge Augmentation↗
PubMed1981

Investigations on the galvanic corrosion of multialloy total hip prostheses.

Total hip prostheses combining cobalt and titanium alloys in direct physical contact are currently being used. The purpose of this paper was to investigate the possibility of an accelerated corrosion occurring due to the coupling of these alloys. Electrochemical corrosion studies based on mixed potential and protection potential theories were used to study the in vitro effects of coupling the titanium and cobalt alloys. Verification of these studies was made by direct coupling experiments. Macroscopic examination of' surface features of four retrieved total hip prostheses ranging from 0-6 years implantation were conducted. The electrochemical studies predicted coupled corrosion potentials of -0.22 V and low coupled corrosion rates of 0.02 microA/cm2. Direct coupling experiments verified these results. Cobalt-titanium interfaces on the implants were macroscopically examined, and no instances of extensive corrosion were found. Overall, the in vitro corrosion studies and the examination of retrieved prostheses predicted no exaggerated in vivo corrosion due to the coupling of these cobalt and titanium alloys.

Alloys↗
PubMed1981

A comparison of three techniques for fabricating metal molds.

Investigation on the dimensional accuracy and techniques variability of metal molds and refractory casts for the construction of maxillofacial external prostheses have resulted in the following conclusions. 1. A relative comparison of the box-pour, open-cast, and wax-sprue techniques for constructing metal molds for external prostheses showed the open-cast technique to be the most accurate and easiest techniques. 2. The wax-sprue technique was the most complex and consumed maximum time and materials. This technique also offered the greatest possibility for introducing errors and obtaining inconsistent results because of multiple steps. 3. For all techniques the positive metal molds always demonstrated a poorer fit in comparison to the negative metal molds. The positive metal molds were larger castings. 4. Most metal molds were significantly larger than the standard brass die in length and width dimensions. 5. A direct comparison of a theoretic calculation and experimental measurements for dimensional accuracy shows the construction of metal molds to be very dependent on the manipulation of materials and reproducibility of methods.

Dental Casting Investment↗
PubMed1981

Suture techniques for atrioventricular valves: experimental study.

Repair of the complete atrioventricular canal defect is still complicated by dehiscence of sutured atrioventricular valves. An in vitro study of initial suture line strength during tensile loading was made using canine pericardial leaflets. Type of "non-pledgetted" stitch was not related to suture line strength. Closer spacing of non-pledgetted stitches (1 mm versus 2 mm) increased strength 29% (p less than 0.05). Pledgets increased strength 25% (p = 0.004). Greater depth (3 mm versus 1.5 mm) increased strength 32% (p less than 0.0001) in both pledgetted and non-pledgetted stitches. Larger suture size (4-0 versus 6-0) increased strength minimally. An in vivo study was performed to determine if the positive effect of pledgets on initial stitch strength would persist in a functioning mitral valve during healing. Four incisions were made at the base of the anterior mitral leaflet in dogs and were closed with one horizontal mattress stitch, with or without pledgets. After 1 to 7 days, none of the 16 pledget-supported stitches had disrupted whereas nine of the 16 stitches without pledgets had torn out of the leaflet (p = 0.001). Tensile testing indicated use of pledgets resulted in stronger stitches (p = 0.0005). Results indicate that in the repair of the complete atrioventricular canal defect, pledget-supported sutures should be used. If non-pledgetted stitches are necessary, bites should be deep and closely spaced.

Animals↗
PubMed1979

In vitro corrosion of Ti-6Al-4V and type 316L stainless steel when galvanically coupled with carbon.

In vitro corrosion experiments were conducted employing potentiostatic polarization techniques, a saline environment and candidate biomaterial alloy/carbon combinations. Corrosion currents and potentials of carbon/metal couples were predicted by mixed-potential theory utilizing the polarization curves generated. The alloys examined were annealed ELI grade Ti-6A1-4V and cold-worked 316L stainless steel while the types of carbon examined were LTI pyrolytic carbon and vapor-deposited carbon. It was determined that galvanic couples of carbon to cold-worked 316L stainless steel with carbon/metal area ratios of 10:1 to 100:1 produced coupled corrosion potentials in the range of the observed breakdown potential of the stainless steel. It was therefore predicted that localized corrosion in the form of pitting could occur on the cold-worked stainless steel when coupled to carbon with area ratios of 10:1 or greater. The titanium alloy did not exhibit a breakdown potential up to a potential of 1.2 V. Therefore, accelerated corrosion was not predicted for the titanium alloy to carbon galvanic couples under these experimental conditions. Direct carbon/alloy coupling experiments were conducted to verify the corrosion currents and potentials predicted from mixed-potential theory and polarization curve analysis. The experimental and theoretical values showed good agreement.

Alloys↗
PubMed1976

Biocompatibility studies on surgical-grade titanium-, cobalt-, and iron-base alloys.

An animal model system for the investigation of the influence of in vivo-produced metallic corrosion products upon tissues has been developed. Externally applied electrical stimulation produces the corrosion over a short period of time, and a poststimulation period is allowed for tissue stabilization. Tissue reaction adjacent to the metallic alloys shows fibrous tissue capsules and metallic corrosion product contamination. These preliminary studies show that this animal model and methodology may provide a technique for investigating long-term tissue biomaterial interactions and the influence of iron (316L), cobalt (Vitallium), and titanium (Tivanium) alloy corrosion products upon the susceptibility of tissues to various biocompatibility challenges.

Animals↗
PubMed1975

Biomaterials science protocols for clinical investigations on porous alumina ceramic and vitreous carbon implants.

A written protocol for the investigation of candidate surgical implant materials is quite important. Biomaterials science sections of clinical protocols have been developed for porous alumina ceramic and nonporous vitreous carbon biomaterials. Published data on the properties of the biomaterials were evaluated as related to bone replacement and augmentation. Where necessary, limited laboratory studies were conducted. If decisions could not be reached with respect to a given application, animal studies were initiated. The surgeons worked with biomaterials in the laboratory and the biomaterials scientist attended the experimental surgery procedures. Biomaterials Science Laboratory nondestructive investigations including stereomicroscopic and x-ray inspections were conducted on the vitreous carbon dental implant systems. The investigations elucidated a number of unexpected features for both implant biomaterials and the overall interaction between the different disciplines resulted in a more complete protocol for the study of these biomaterials at our Medical and Dental Center.

Aluminum↗
PubMedDate not supplied

Displacements of precious and nonprecious dental bridges utilizing endosseous implants as distal abutments.

An investigation was conducted to establish qualitative trends regarding to relative displacements exhibited by the distal and mesial abutments in a five-unit fixed dental bridge as a function of bridge material and implant design utilized in the distal abutment site. Both Au and Ni-based bridge systems utilizing double, natural-tooth mesial abutments and three types of distal abutments (natural second molar, blade dental implant, and hollow-basket implant) were tested on a dried human mandible and subjected to a controlled force applied distally. Dial gauges were positioned around each abutment site bilaterally to provide displacement data in the x(mesial/distal), y(buccal/lingual, and z(occlusal/gingival) directions. The results indicate some significant differences exist in the displacement profiles exhibited by the bridge systems as a function of both bridge material and abutment type.

Chromium Alloys↗