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Biomedical subjects

Jack E Lemons

Publications and source records attributed to Jack E Lemons.

17 recordsLinked to original sources
PubMed2007

Surface analysis and biocorrosion properties of nanostructured surface sol-gel coatings on Ti6Al4V titanium alloy implants.

Surfaces of biocompatible alloys used as implants play a significant role in their osseointegration. Surface sol-gel processing (SSP), a variant of the bulk sol-gel technique, is a relatively new process to prepare bioreactive nanostructured titanium oxide for thin film coatings. The surface topography, roughness, and composition of sol-gel processed Ti6Al4V titanium alloy coatings was investigated by atomic force microscopy (AFM) and X-ray electron spectroscopy (XPS). This was correlated with corrosion properties, adhesive strength, and bioreactivity in simulated body fluids (SBF). Electroimpedance spectroscopy (EIS) and polarization studies indicated similar advantageous corrosion properties between sol-gel coated and uncoated Ti6Al4V, which was attributed to the stable TiO2 composition, topography, and adhesive strength of the sol-gel coating. In addition, inductive coupled plasma (ICP) and scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) analysis of substrates immersed in SBF revealed higher deposition of calcium and phosphate and low release rates of alloying elements from the sol-gel modified alloys. The equivalent corrosion behavior and the definite increase in nucleation of calcium apatite indicate the potential of the sol-gel coating for enhanced bioimplant applications.

Alloys↗
PubMed2007

Accelerating aging of zirconia femoral head implants: change of surface structure and mechanical properties.

Recently, alternations of zirconia ceramic femoral heads of total hip prostheses during in vivo conditions have caused concern in the medical disciplines regarding phase transformation of zirconia prosthetic components. In this paper, we have investigated the mechanical and structural properties of different laboratory aged zirconia femoral heads and correlated changes in mechanical properties with the phase compositions of the sample. From laser microscope observation, cross-sectional Scanning electron microscopy imaging, and X-ray diffraction analysis on the surface of the zirconia femoral heads, we found monoclinic to tetragonal phase transformation in zirconia prostheses over time during the aging process in the laboratory. Mechanical properties, mainly hardness (H) and Young's modulus (E) values, were measured by nanoindentation technique on the surface of these implants. The results showed that both H and E values decreased with increased monoclinic phase in zirconia, thus confirming a phase transformation over time during aging.

Biocompatible Materials↗
PubMed2006

Bone associated with implants in diabetic and insulin-treated rats.

OBJECTIVES: Diabetes is an increasingly prevalent disease with oral health manifestations. While diabetes clearly has an affect on bone, its impact on the healing of bone associated with dental implants is not completely understood. The purpose of this study was to measure bone response to implants in uncontrolled and insulin-controlled diabetic rats. MATERIAL AND METHODS: One hundred and fifty-two rats were divided into control, diabetic, and insulin groups. Rats received streptozotocin (65 mg/kg) to induce diabetes; animals in the insulin group also received a subcutaneous slow-release insulin implant. Titanium alloy implants (1.5 x 8 mm) were placed in the proximal tibiae of animals. Implants were harvested at 2, 7, 14, and 24 days and examined histologically. Bone or bone-like tissue adjacent to implants was quantified as a percent. Data were compared using a two-way analysis is variance (ANOVA) with time and treatment as primary independent factors. RESULTS: Time and treatment were significant factors in predicting bone response to implants (P<0.0001). Mean bone volume peaked at day 7 and decreased over time to day 24. Mean bone volume percent at 2, 7, 14, and 24 days (+/-SD) was 8.2 (+/-8), 22.9 (+/-8), 18.8 (+/-10), and 14.9 (+/-9), respectively. Mean total bone volume percent (adjusted for day) for control, diabetic, and insulin groups (+/-SD) was 12.4 (+/-9), 22.6 (+/-10), and 17 (+/-7), respectively. Bone volume adjacent to implants in diabetic rats was significantly greater than controls (P<0.05). Diabetic animals treated with insulin were not statistically different from controls. CONCLUSIONS: Induction of diabetes with STZ is associated with increased bone response compared with controls. This response was mediated by treatment with insulin.

Animals↗
PubMed2005

Osteoblast adhesion and matrix mineralization on sol-gel-derived titanium oxide.

The biological events occurring at the bone-implant interface are influenced by the topography, chemistry and wettability of the implant surface. The surface properties of titanium alloy prepared by either surface sol-gel processing (SSP), or by passivation with nitric acid, were investigated systematically using X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy and contact angle metrology. The bioreactivity of the substrates was assessed by evaluating MC3T3-E1 osteoblastic cell adhesion, as well as by in vitro formation of mineralized matrix. Surface analysis of sol-gel-derived oxide on Ti6Al4V substrates showed a predominantly titanium dioxide (TiO(2)) composition with abundant hydroxyl groups. The surface was highly wettable, rougher and more porous compared to that of the passivated substrate. Significantly more cells adhered to the sol-gel-coated surface, as compared with passivated surfaces, at 1 and 24h following cell seeding, and a markedly greater number of mineralized nodules were observed on sol-gel coatings. Collectively our results show that the surface properties of titanium alloy can be modified by SSP to enhance the bioreactivity of this biomaterial.

3T3 Cells↗
PubMed2005

Biologic mechanical advantages of 3 different cranial bone grafting techniques for implant reconstruction of the atrophic maxilla.

PURPOSE: The purpose of this study was to test the mechanical capacities of 3 different bone grafting techniques in the atrophic maxilla when co-stabilized with dental implants. Reconstruction of the atrophic maxilla is a difficult clinical challenge and implants cannot be placed without adequate bone. METHODS: The biomechanical performance of 3 different grafting techniques was evaluated in vitro using a maxillary model, cadaveric cranial bone blocks, and dental implants. A maxillary model fabricated from polyurethane (sawbone) was selected as a substrate for this study because of consistency in shape, size, and mechanical properties. This anatomic model was more consistent than different cadaveric maxilla, where significant variation was found to exist among atrophic specimens. Cadaveric cranial bone graft blocks were secured to the model maxilla (sandwich, ridge only, and sinus inlay) with a dental implant. The strength of the implant/bone graft complex was tested to failure in an Instron machine (Instron Inc, Canton, MA). RESULTS: The 3 bone grafting methods showed significantly different deformation and strength characteristics. The sandwich technique enhanced resistance to deformation under higher imposed loads. The location of the graft influenced the overall mechanical performance (eg, the ridge onlay) and showed a significantly higher resistance to compressive loads applied toward the alveolar ridge (mastication force). CONCLUSION: The ridge onlay grafting procedures created a higher biomechanical tolerance to imposed load than the sinus grafting (sinus inlay). Sinus grafting, although successful, was not the most ideal location for immediate mechanical loading resistance when compared with ridge augmentation in this in vitro model.

Alveolar Bone Loss↗
PubMed2005

A comparison of torque required to fracture rotary files with tips bound in simulated curved canal.

The purpose of this study was to compare torque force and rotation needed to fracture three types of nickel titanium alloy rotary instruments in a simulated curved root canal space that were bound at the file tip. Files of similar size tips were studied. The files studied were ProFiles with 0.04 taper diameters of 15, 20, 25, 30, 35, 40, 45; 0.04 ProFile GT sizes 20, 30, 40; and ProTaper files sizes S1, S2, F1, F2, and F3. All files were 25 mm in length. Unwinding was defined as the rotation in degrees it took for a file to fracture after the first evidence of permanent deformation. All files exhibited permanent deformation before breaking, with the ProFile GT files demonstrating the greatest unwinding. The #45 0.04 ProFile withstood the most force while the #20 ProFile GT required the least amount of force before beginning to exhibit permanent deformation. The S1 and S2 ProTaper files fractured with so little rotation that no extended data were recorded. Generally, as the file diameter increased, the force needed to begin unwinding also increased. Also, as the file diameter increased, the force needed to fracture also increased.

Analysis of Variance↗
PubMed2004

Biomaterials, biomechanics, tissue healing, and immediate-function dental implants.

Selected factors and opinions are reviewed specific to immediate function of dental implants in terms of biomaterial and biomechanical properties and how they might influence postsurgical tissue healing. Comparisons are made among plate, rod, and screw vs plateau, finn, and porous geometry endosteal dental-implant designs with and without alterations in device body-surface microchemistry and microtopography. Available information introduces more questions than answers, and recommendations are made for ongoing studies of bone responses specific to the implant fit and fill parameters focused on the kinetics of postsurgical osteotomy healing and applied loading. The clinical literature supports opportunities for immediate function; however, proposals about pathways for bone healing need further investigation. The current trends within the discipline of implant dentistry offer opportunities to reevaluate current vs previous immediate-function systems.

Biocompatible Materials↗
PubMed2003

Prosthetic implant associated sarcomas: a case report emphasizing surface evaluation and spectroscopic trace metal analysis.

Advances with implantation of synthetic biomaterials in the setting of orthopedic surgery have clearly resulted in improvements in patient outcomes. However, all implants have been shown to have associated risks. For example, ionic and particulate debris from implants have been shown to engage in biological interactions with the native tissue, and have been associated with a wide range of metabolic, bacteriologic, immunologic, and oncogenic effects. The propensity of synthetic biomaterials to undergo degradation, producing an inflammatory reaction or other sequelae, has been well recognized. The use of porous implants, which allow for a greater interface area between native tissue and the prosthesis, may magnify the interaction between biologically active tissue and synthetic devices in some situations, giving rise to new and intriguing issues concerning biocorrosion and biocompatibility. In this article, we report the case of a high-grade conventional osteosarcoma occurring at the site of a modular porous-surfaced titanium and cobalt alloy total hip prosthesis 3 years after device implantation. Detailed spectroscopic trace metal analysis was performed and elevated levels of both vanadium and chromium, but not aluminum, nickel, or titanium were identified in the tumor.

Alloys↗
PubMed2003

A comparison of torque required to fracture three different nickel-titanium rotary instruments around curves of the same angle but of different radius when bound at the tip.

Instrument fracture is an unfortunate but possible sequela of instrumentation of canals, especially when the instrument is bound at the tip. The purpose of this study was to compare the torque required to fracture three file sizes of three different rotary file types around two simulated canal curvatures, gradual or acute, when the tip of the working end of the file was bound. Profile Series 29 0.04 and 0.06 taper and Profile 0.06 ISO rotary files were placed passively into simulated canal curvatures of the same angle but of different radii. The file tips were bound 2 mm from the working end and a measurable torque was applied until fracture. ANOVA with Tamhane post-hoc comparison showed that the 0.06 Series 29 did not differ from the ISO 0.06 taper or the 0.04 Series 29 but there was statistical difference (p < 0.01) showing that the 0.04 Series 29 broke with less force than did the 0.06 ISO files. Statistical tests (p < 0.01) also showed smaller files failed with less torque, as did files in more acute canal curvatures.

Analysis of Variance↗
PubMed2003

A modified test for patellar instability: the biomechanical basis.

OBJECTIVE: (1) Determine if displacement of the patella in a distal lateral direction results in a more sensitive method to show deficiency of the medial patellofemoral ligament (MPFL), the primary restraint to lateral patellar dislocation, than the traditional patellar apprehension test in a direct lateral direction. (2) Determine objective criteria for defining a positive patellar instability test rather than subjective evaluation of apprehension. DESIGN: In vitro biomechanical study. SPECIMENS: Ten above-the-knee amputation specimens. MAIN OUTCOME MEASURES: Force-displacement curves with direct lateral patellar displacement were compared with curves with distal lateral patellar displacement before and after sectioning the MPFL. RESULTS: After dividing the MPFL, average terminal restraining force to distal lateral patellar displacement declined by 53% (P=0.024), but force declined only by 30% (P=0.09) with lateral displacement. The greatest difference in terminal slope (eg, end point) was with the MPFL intact with lateral displacement compared with distal lateral displacement with the ligament divided (P=8.67x10(-5)). The terminal slope declined after ligament division with lateral (P=0.07) and distal lateral patellar displacement (P=0.09). CONCLUSION: Displacement of the patella in a distal lateral direction is a more sensitive maneuver to detect disruption of the MPFL, the primary soft tissue restraint, than with traditional lateral displacement. With the knee flexed 30 degrees and patella displaced 2 cm, objective criteria for a positive patellar instability test include greater ease of patellar translation and a softer end point compared with a normal, contralateral knee.

Adult↗
PubMed2002

Gamma irradiation alters fatigue-crack behavior and fracture toughness in 1900H and GUR 1050 UHMWPE.

Pitting and delamination remain causative factors of polyethylene failure in total knee replacement. Gamma irradiation induces cross linking in ultra-high-molecular-weight polyethylene, which has been shown to improve wear resistance. Irradiation may reduce fracture toughness and fatigue strength, however, and the effects of irradiation are dependent upon the resin, processing technique, and radiation dose. The effects of varying levels of gamma irradiation (0, 33, 66, and 100 kGy) on the fracture toughness and fatigue-crack resistance of UHMWPE, isostatically molded from 1900H and GUR 1050 resins, were examined. Paris law regressions were performed to quantify fatigue-crack propagation rates as functions of change in stress intensity, and J-integral methods were used to quantify the elastic-plastic fracture toughness. The results indicated that gamma irradiation reduced the resistance of both materials to fatigue-crack growth, and that the reductions were radiation dosage and resin dependent. Irradiation at any level was detrimental to the fracture toughness of the 1900H specimens. Irradiation at 33 kGy increased fracture toughness for the GUR 1050 specimens, and substantial reductions were observed only at the highest irradiation level. Scanning electron microscopy of the fracture surface revealed diamond-like fracture patterns of the nonirradiated specimens indicative of ductile, multilevel fracture. Pronounced striations were apparent on these fracture surfaces, oriented perpendicular to the direction of crack growth. The striations appeared as folds in surface layers of the GUR 1050 specimens. At the highest irradiation levels, the striations were nearly eliminated on the fracture surfaces of the 1900H specimens, and were markedly less severe for the GUR 1050. These results demonstrated that at higher irradiation levels the materials became more brittle in fatigue, with less ductile folding and tearing of the fracture surfaces.

Arthroplasty, Replacement, Knee↗
PubMed2002

Failure characteristics of multiple-component fibrin-based adhesives.

A series of analyses were performed on fibrin-based adhesives to describe their failure characteristics. Two test methods were used: uniaxial, monotonic tensile testing of the bulk material, and blister testing using fresh porcine-source skin graft as the adherend. Two fibrin concentrations, high (HFC), and low (LFC), were used to investigate the effects of the gel matrix density upon mechanical properties. In tensile tests, fibrin gels strain hardened, as functions of percent strain and of strain rate. An increase in modulus of elasticity (E) was seen with increasing strain and strain rate at both tested fibrin concentrations. Mode I failure mechanisms were predominant. Both adhesives appeared to fracture from the outer edge to the interior of the specimen at slower strain rate tests. This trend reversed as strain rate increased, becoming a classic "cup and cone" ductile fracture. Syneresis occurred at both concentrations at lower strain rates, but was more pronounced for the LFC. Ultimate tensile strength and E were greater for the HFC than for the LFC at all strain rates, decreasing with increasing strain rate. In the blister test, the failure locus changed from cohesive to adhesive as the strain rate was increased for the HFC. Failure of fibrin gels likely occurs by percolation of the pressurized saline, displacing the entrapped liquid phase of the gel in regions of relatively low moduli and strength, leading to fracture of the matrix. For LFC, the overall fracture locus remained predominantly cohesive regardless of strain rate. Burst strength and failure energy were higher for HFC than for LFC. It would appear that fibrin acts more as a viscous liquid than a rubberlike/elastic material at lower concentrations because adhesive failures had a higher burst strength and fracture energy (Gc) than did cohesive failures.

Animals↗
PubMed2002

Quasi-linear viscoelastic behavior of the human periodontal ligament.

Previous studies have not produced a comprehensive mathematical description of the nonlinear viscoelastic stress-strain behavior of the periodontal ligament (PDL). In the present study, the quasi-linear viscoelastic (QLV) model was applied to mechanical tests of the human PDL. Transverse sections of cadaveric premolars were subjected to relaxation tests and loading to failure perpendicular to the plane of section. Distinct and repeatable toe and linear regions of stress-strain behavior were observed. The amount of strain associated with the toe region differed as a function of anatomical location along the tooth root. Stress relaxation behavior was comparable for different anatomical locations. Model predicted peak tissue stresses for cyclic loading were within 11% of experimental values, demonstrating that the QLV approach provided an improved, accurate quantification of PDL mechanical response. The success of the QLV approach supports its usefulness in future efforts of experimental characterization of PDL mechanical behavior.

Aged↗
PubMed2002

Histomorphological evaluation of loaded plate-form and root-form implants in Macaca mulatta monkeys.

As part of a long-term evaluation of endosteal dental implants in primates, this paper describes the histological response to plate-form and root-form implants. Thirty-six primates received 48 mandibular distal abutment implants. After healing, the implants were restored with fixed partial dentures, which remained in function for two years. A subset of the group was ligated at the gingival sulcus to biologically stress tissues supporting the implants. Crestal bone height around implants was quantified using digital subtraction radiographic techniques. The ligated implants lost more crestal bone than non-ligated implants, as shown by ANOVA (P < 0.05). After retrieval, implants were embedded and sectioned for histomorphometric analysis including measurement of per cent osseointegration. Both plate-form and root-form non-ligated implants demonstrated about 60% osseointegration. When ligated, plate-form implants dropped to an average integration of only 34%, while root-form implants maintained 62% integration, a significant difference. These data show that in this primate model, plate-form and root-form implants maintained integration while in function for two years. When stressed with ligation, root-form implants maintained relative amounts of osseointegration, while per cent osseointegration of plate-form implants decreased.

Alveolar Bone Loss↗
PubMed2002

Nonlinear stress-strain behavior of periodontal ligament under orthodontic loading.

Previous studies of the periodontal ligament (PDL) have applied high forces to the dental units to examine the stress-strain behavior of this soft tissue. In this study, cadaveric specimens of mandibular premolars from 2 young adult and 2 elderly adult donors were tested to determine the biomechanical behavior of the PDL over an orthodontic force range. Transverse specimens were prepared from 9 premolars and subjected to loading in intrusion and extrusion. Stress-strain curves for both loading directions had distinct toe and linear regions, demonstrating nonlinear behavior of the PDL. The average linear shear modulus was higher for intrusion than for extrusion. The toe extrusive modulus was higher for the young group, and extrusive toe size was larger for the elderly group. In extrusion, the average modulus was higher for the cervical margin and the apex regions than for the midroot regions. The size of the toe region was smaller for intrusion than extrusion. The results indicate age-dependent, location-dependent, and load-direction-dependent nonlinear properties of the human PDL and suggest that analytical computer simulations of orthodontic tooth movements might benefit from incorporating the nonlinear material properties of the PDL.

Adult↗
PubMedDate not supplied

Nanostructured ceramics for biomedical implants.

Recent progress in the synthesis, characterization, and biological compatibility of nanostructured ceramics for biomedical implants is reviewed. A major goal is to develop ceramic coating technology that can reduce the friction and wear in mating total joint replacement components, thus contributing to their significantly improved function and longer life span. Particular attention is focused on the enhancement of mechanical properties such as hardness, toughness, and friction coefficient and on the bioactivity as they pertain to the nanostructure of the material. The development of three nanostructured implant coatings is discussed: diamond, hydroxyapatite, and functionally graded metalloceramics based on the Cr-Ti-N ternary system. Nanostructured diamond produced by chemical vapor deposition (CVD) techniques and composed of nano-size diamond grains have particular promise because of the combination of ultrahigh hardness, improved toughness over conventional microcrystalline diamond, low friction, and good adhesion to titanium alloys. Nanostructured processing applied to hydroxyapatite coatings is used to achieve the desired mechanical characteristics and enhanced surface reactivity and has been found to increase osteoblast adhesion, proliferation, and mineralization. Finally, nanostructured metalloceramic coatings provide continuous variation from a nanocrystalline metallic bond at the interface to the hard ceramic bond on the surface and have the ability to overcome adhesion problems associated with ceramic hard coatings on metallic substrates.

Animals↗