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Biomedical subjects

J C Keller

Publications and source records attributed to J C Keller.

17 recordsLinked to original sources
PubMed1992

Optimization of surface micromorphology for enhanced osteoblast responses in vitro.

In vitro cellular responses of osteoblast-like cells were studied on titanium surfaces with different surface morphologies. Surface profilometry was used to determine whether rough or smooth surfaces with regular or irregular morphologies can be produced by conventional fabrication techniques. Significantly higher levels of cellular attachment were found using rough, sandblasted surfaces with irregular morphologies. These results correlate with recent in vivo findings and suggest that implants should be prepared with roughened surfaces at bony contact areas.

Analysis of Variance↗
PubMed1992

Short-term plasma-cleaning treatments enhance in vitro osteoblast attachment to titanium.

The purpose of this research was to characterize the in vitro cellular behavior of osteoblast-like cells on titanium surfaces prepared with argon plasma-cleaning (PC) treatments for various lengths of time. The highest levels of cell attachment were observed for surfaces which had been plasma-treated for one min. Surface analyses indicated that although PC treatments dramatically improved surface wettability, the presence of inorganic contaminants was observed with longer treatment times and may have interfered with cell attachment. Further work is suggested to investigate the longer-term phenotypic expression of osteoblasts when grown on implant surfaces.

Analysis of Variance↗
PubMed1992

Comparison of stress transmission in the IMZ implant system with polyoxymethylene or titanium intramobile element: a finite element stress analysis.

Using the finite element method, this study modeled a 4.0 x 13.0-mm IMZ implant, restored with a cast gold crown, to examine the influence of the polyoxymethylene (POM) intramobile element (IME) on the transmission of vertical and oblique forces. Stress concentrations in the bone and in components of the implant system were much greater under a 30-degree load than under an equal vertical load. Stress transmission to bone occurred chiefly in the crestal region, and these stresses were not reduced when the IME was modeled in POM rather than in titanium. Maximum stress concentrations occurred in the fastening screw.

Alveolar Process↗
PubMed1991

Bond strength and failure analysis of light-cured denture resins bonded to denture teeth.

This study examined the tensile bond strength and failure sites of one heat-cured (Microlon) and two visible light-cured (Triad and Extoral) denture resins to two types of denture teeth. The resins were processed into cylinders against denture teeth milled to the same size. Half of the specimens were thermocycled. After tensile testing, statistical analysis (p 0.05) showed that the strongest bond was achieved with the heat-cured resin Microlon, whereas Triad resin displayed the stronger bond between the two light-cured resins. Scanning electron microscopic analysis showed that the nature and location of the fracture sites was different among the three resins tested.

Acrylic Resins↗
PubMed1991

The concept of osseointegration and bone matrix expression.

Osseointegration has been defined as the direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant. To date, this concept has been described by descriptive histological and ultrastructural criteria but not by biochemical means. This review evaluates the basic science work performed on this concept and then applies the concept to the principle of osseous healing. Specific studies are cited where alterations in the healing response are due to clinical management of implant placement and how studies of surface properties may lead to further insights on implant design and prognosis. In addition, a review of bone expression as a function of in vitro stress applications is given. This is followed by an indepth review of the collagens and noncollagenous proteins, described to date, within isolated bone matrix. It is this collagenous matrix (especially type I) that is described as being close to and oriented with a glycoprotein component next to the implant surface. In turn, the large family of noncollagenous proteins are important in mediating bone proliferation, matrix accumulation, orientation, mineralization, and turnover. This section is followed by a discussion of specific growth factors as they may relate to osseous healing around an implant.

Animals↗
PubMed1991

In vitro periodontal ligament fibroblast attachment to plasma-cleaned titanium surfaces.

The objective of this research was to characterize the in vitro cellular behavior of fibroblast-like cells derived from rat periodontal ligament on commercially pure titanium surfaces which were sterilized by a variety of treatments. Following standard surface preparation protocols, the Ti specimens were sterilized by either steam autoclaving, exposure to ethylene oxide gas, exposure to ultraviolet light, or plasma-cleaning in argon for either one min or five min. Fibroblast-like cells in serum-supplemented media were incubated on the various Ti specimens for up to two h. In general, the levels of cell attachment for plasma-cleaned surfaces were significantly higher than those for steam-sterilized surfaces, but were significantly lower than the attachment levels for both the ultraviolet-treated surfaces and the tissue culture plastic control. The duration of plasma cleaning itself did not have a significant effect on the percentage of cell attachment at any time period. SEM evaluations indicated that by two h, the cellular morphology was different on the variously treated specimens. These studies indicate that the method of sterilization following implant surface preparation can affect the initial in vitro biological events of cell attachment and spreading.

Animals↗
PubMed1990

Characterization of sterilized CP titanium implant surfaces.

Surface analysis techniques and in vitro biologic assays were used to characterize sterilized commercially pure titanium surfaces. Significant surface alterations were observed following sterilization treatments. These alterations led to decreased fibroblast cell attachment and altered cellular spreading phenomena compared to nonsterilized control surfaces.

Cell Adhesion↗
PubMed1989

Effects of indomethacin on bone ingrowth.

The effects of indomethacin, a nonsteroidal antiinflammatory agent, on bone ingrowth were studied using a rabbit animal model and a porous cylindrical implant system. Bone ingrowth was found to be independent of pore size in the range tested (0.6-1.0 mm). In the control (placebo-treated) group, there was a significant increase in bone ingrowth between the 2- and 8-week groups of animals. However, in the indomethacin-treated group, there was no increase in bone ingrowth with time.

Animals↗
PubMed1989

Interaction of dental cements with the complement system.

The relative complement-activating properties of several dental cements were investigated. After the cements were incubated with fresh human serum as a source of complement, the percent of the electrophoretic conversion was assessed by means of the C3 crossed-immunoelectrophoresis technique. It was determined that the ZnO-containing cements--which include zinc phosphate, zinc polycarboxylate, zinc oxide eugenol, and zinc hexyl vanillate--each caused C3 conversion, indicative of complement activation. Glass-ionomer cement, which does not contain ZnO, did not activate the complement system. In dose-response studies, ZnO at relatively low concentrations was effective in causing C3 conversion, while at higher concentrations ZnO appeared to block C3 conversion. Supernatants from ZnO suspensions also caused C3 conversion. Cement particle size, as well as soluble degradative products containing ZnO or Zn++, were suggested as possible factors contributing to the differential effects of the dental cements on complement activation and/or function.

Complement Activation↗
PubMed1987

Quantitative bone remodelling resulting from the use of porous dental implants.

Histomorphometric analyses were used to quantitatively determine the patterns of bony ingrowth which resulted from the placement of porous-surfaced dental implants into the mandibles of Rhesus monkeys for up to 74 months utilizing a two-stage approach. Quantitative histopathologic evaluations were made using ground section microscopy. Implant stability resulting from bone remodelling and ingrowth occurred to varying degrees with all implants. Bone ingrowth occurred from medullary trabeculae and contact with the adjacent cortical plates. Quantitative histomorphometric analyses revealed that in only one case was the bone ingrowth into the available internal pores less than 45%. Minimal fibrous connective tissue ingrowth was observed in the implant crypts and was not thought to be due to micro-motion. The observed bone remodelling indicated a favorable prognosis for long-term implant performance.

Animals↗
PubMed1985

Porosity reduction and its associated effect on the diametral tensile strength of activated acrylic resins.

Each acrylic resin tested is basic to the armamentarium of the clinical dentist. From this study it is apparent that there exist several possible mechanisms that will aid in the reduction of porosity and subsequently enhance the tensile strength properties of chemically activated acrylic resins. With the manufacturer's recommended powder to liquid ratio mixtures, indications are that only small increases in curing pressure (approximately 0.68 MPa) are required to substantially enhance strength levels of the test materials. Therefore, when cured under conditions that avoid residual stress buildup, the small increases in pressure attainable by modified pressurization devices may indeed be of benefit in reducing porosity and enhancing the tensile strength of the acrylic resins. Similar increases in strength appear possible with various combinations of powder particle sizes and powder/liquid ratios used in an effort to reduce the monomer concentration in clinically desirable acrylic mixtures. It is important to realize that alteration of powder/liquid ratio and powder particle size mixtures offers a method of reducing porosity without the addition of external pressure. However, at this time it is not recommended that these sophisticated alterations of the basic resin components be performed by the clinician.

Acrylic Resins↗
PubMed1985

Preliminary studies of the histopathological responses to Ti-13% Cu casting alloys.

A preliminary study of some of the biological properties of a new dental casting alloy (Ti-13% Cu) was undertaken by employing the skeletal muscle implantation test in rabbits. Routine histopathological and chemical analysis techniques were utilized to study in vivo tissue reactions of skeletal muscle to this alloy. A moderately thick, somewhat cellular fibrous connective tissue capsule surrounded the implants after 2 wk. Remodelling of the fibrous tissue into a thin acellular tissue capsule occurred at 52 wk after implantation. Chemical analyses failed to detect deposition of either Ti or Cu corrosion products at the implant sites or within major organs.

Animals↗
PubMedDate not supplied

Load-extension-time behavior of orthodontic Alastiks.

Typical elastomeric behavior displayed by Alastik orthodontic bands resulted in load-extension curves that depended on the rate of extension as well as the amount of extension. Initially, the modules tested at the faster speeds had higher moduli and were stronger; but as extension continued, the trend reversed, and at breakage the more slowly stretched modules were the strongest. Therefore, although the Alastiks appear to be uniformly produced, the clinician still needs to know his rate of deformation and degree of stretching to accurately assess the module force. In addition, the module, once in position, will not maintain a constant force but will experience a decrease in applied load with time kept at a constant extension. Because the initial load decay is more rapid for both faster extension and higher load, it seems reasonable to suggest that care be taken by the clinican to stretch the module more slowly into place. This should result in a higher load level for a longer period of time. Although the measured changes in loads are not necessarily of sufficient magnitude to seriously influence the clinical result, a clearer understanding of the module behavior, such as currently presented, will hopefully assist in more comprehensive clinical evaluations.

Dental Stress Analysis↗