Edward Korostoff

The Influence of Functional Use of Endosseous Dental Implants on the Tissue-implant Interface. I. Histological Aspects

Functional and non-functional endosseous dental implants were clinically compared in beagle mandibles for up to one year post-operatively. Differing biomechanical conditions led to clinical differences between functional and non-functional implants. Typical clinical tests, however, did not always reveal detailed histological differences between implant-tissue interfaces of functional and non-functional implants.

Electric currents, bone remodeling, and orthodontic tooth movement: II. Increase in rate of tooth movement and periodontal cyclic nucleotide levels by combined force and electric current☆

Piezoelectric currents in mechanically stressed bone were implicated in the activation of bone cells. The objectives of this experiment were to determine the usefulness of exogenous electric currents in accelerating orthodontic tooth movement and to study the effect of electric-orthodontic treatment on periodontal cyclic nucleotides. Maxillary canines were tipped in five cats by 80 g force. Two groups of five cats each were treated by an electric-orthodontic procedure to one maxillary canine for 7 and 14 days, respectively. Teeth treated by force and electricity moved significantly faster than those treated by force alone. Enhanced bone resorption was observed near the anode (PDL compression site), while bone formation was pronounced near the cathode (PDL tension site). Staining for cyclic nucleotides was increased when electric stimulation was added to the mechanical force. These results suggest that orthodontic tooth movement may be accelerated by the use of locally applied electric currents.

Electric currents, bone remodeling, and orthodontic tooth movement

Piezoelectric currents in mechanically stressed bone were implicated in the activation of bone cells. The objectives of this experiment were to determine the usefulness of exogenous electric currents in accelerating orthodontic tooth movement and to study the effect of electric-orthodontic treatment on periodontal cyclic nucleotides. Maxillary canines were tipped in five cats by 80 g force. Two groups of five cats each were treated by an electric-orthodontic procedure to one maxillary canine for 7 and 14 days, respectively. Teeth treated by force and electricity moved significantly faster than those treated by force alone. Enhanced bone resorption was observed near the anode (PDL compression site), while bone formation was pronounced near the cathode (PDL tension site). Staining for cyclic nucleotides was increased when electric stimulation was added to the mechanical force. These results suggest that orthodontic tooth movement may be accelerated by the use of locally applied electric currents.Osteogenesis has been found to occur in response to the application of electric currents to bone. The objective of this experiment was to study the effects of D.C. electric currents on periodontal tissues in cats. Cyclic nucleotides, compounds known to be involved in cellular activation, were studied by immunohistochemistry in the involved tissues. Three groups of three young adult cats each were treated for 1, 3, and 7 days, respectively, by a device delivering 15 microamperes of direct current to bone osteoblasts and PDL cells stained intensely for cAMP and cGMP were observed adjacent to the cathode and anode, and bone apposition was found near the cathode. These results suggest that electric stimulation enhances cellular enzymatic phosphorylation activities in periodontal tissues and may be a potent tool in accelerating alveolar bone turnover.

Biochemical mediators of the effects of mechanical forces and electric currents on mineralized tissues

SummaryCyclic nucleotides (cAMP and cGMP) and prostaglandin E (PGE) have been implicated as possible mediators of the effects of external stimuli on bone cells. The objective of this study was to determine changes in relative levels of these substances in mineralized tissue cells in response to mechanical and electrical stimuli, by the use of a combined immunohistochemical-microphotometric procedure. Canine teeth of eight 10–12 month-old female cats were tipped distally with 80 g force for either 1 h or 14 days. After 1 h, a slight elevation of staining intensity in alveolar bone osteoblasts and periodontal ligament (PDL) cells was observed at sites of tension and compression. After 14 days of treatment, this effect was markedly increased. Fifteen female cats, 10–12 months old, received electric stimulation (20 µ amperes d.c.) to the gingiva of 1 maxillary canine for 1, 5, 15, 30, or 60 min. At the cathode, significant increases of staining intensity in periosteal osteoblasts for cAMP, cGMP, and PGE were found at 15 and 60 min. At the anode, a significant rise in the staining intensity of these cells for PGE was seen at 15 min; at 60 min, cGMP and PGE, but not cAMP, were elevated. These results demonstrate the usefulness of the immunohistochemical technique in detecting relative changes in mineralized tissue cell content of cyclic nucleotides and prostaglandins in response to local application of physical stimuli of short and long duration.

Oscillatory and step response electromechanical phenomena in human and bovine bone

Bone generates electrical potentials or strain-related potentials when mechanically deformed. These electrical potentials may be partially responsible for the remodeling process which bone experiences in response to mechanical loads. A large body of evidence suggests that streaming potentials are the dominant mechanism responsible for strain-related potential generation in fluid saturated bone. Recently, biphasic poroelastic theory has been coupled to electrokinetic theory in an attempt to further elucidate this mechanism. The work reported here expands the experimental evidence in support of this theory. Experimental results which characterize electrical and mechanical phenomena in both wide frequency oscillatory and step response testing of 47 human and bovine bone specimens are reported. These results also include data from experiments in which the viscosity and conductivity of the solutions permeating 10 human and bovine bone specimens were varied. A specially designed mechanical testing of bone specimens. Testing procedures, which were optimized for strain-related potential measurement, were developed. These included procedures for varying testing solution viscosity and conductivity. The experimental data was analyzed using descriptive and inferential statistical techniques and linear and nonlinear regression methods. The following objectives were established for the work reported here: (1) to confirm the existing experimental results; (2) to attempt to obtain a successful correlation between theoretically predicted and experimentally observed mechanical phenomena; (3) to extend the experimental results over the wider frequency range of 0.05-100 Hz; (4) to test the theory in the time domain; (5) to test the theory for changes in viscosity and conductivity of the permeating fluid; and (6) to extend the experimental testing to include human bone specimens. All of these objectives were met except that a highly variable correlation between the theoretically predicted and experimentally observed mechanical phenomena was obtained. Patterns in these data are explored and the possible causes of the highly variable correlation are discussed. The results strongly suggest an electrokinetic origin for the observed electrical potentials. The microporosity of bone appears to be the location in which this mechanism operates.

Compressive Viscoelastic Properties of Human Dentin : I. Stress-Relaxation Behavior

Stress-relaxation measurements were performed on specimens of radicular human dentin. The relaxation modulus showed a linear dependence on the logarithm of time and the approximation to the logarithmic distribution function of relaxation times was used to predict the behavior of other viscoelastic properties. This experimental technique provides significant criteria for the design of polymeric restorative and prosthetic materials.

A linear piezoelectric model for characterizing stress generated potentials in bone.

Abstract A comprehensive model is presented for the characterization of stress generated potentials (SGP) in bone, based entirely upon the linear piezoelectricity (PZE) of single crystal collagen. The model calls for a theoretical antiparallel polarization configuration in adjacent lamellae that yields to parallel polarization for minimization of free energy. The direction of reorientation is guided by a stress-gradient-induced trigger polarization that specifically determines the polarity in bending and artifactually determines polarity under normal stress. It describes a decoupling of the signs of the PZE tensor of single crystal collagen from the coordinates of the bone: hence, no assumption of the validity of a PZE matrix applied directly to bone can lead to correct results. The model is consistent with all major experimental SGP observations and provides a fresh viewpoint for externally applied electricity for bone stimulation.

Stress generated potentials in bone: Relationship to piezoelectricity of collagen

Abstract A parametric matrix is derived to characterize stress generated electric potentials (SGP) in Haversian bone. It substantially agrees with experiment, whereas the commonly accepted C6 hexagonal piezoelectric matrix does not. We show the specific dependence of SGP on microstructure, and hence the limited usefulness of any conventional piezoelectric matrix for bone.

Deformation potentials in whole bone

Abstract When freshly excised whole bone specimens were subjected to mechanical deformation or strain, electrical potentials were consistently generated. Compressed areas were electronegative with respect to areas under tension. Potentials reached a maximum of 2.7 mV in normal bones. Peak voltage increased as both deformation and rate of deformation increased, but the relationships were nonlinear. So long as deformation was maintained, a uniform steady-state potential persisted. This steady-state potential was directly proportional to the deformation but was independent of the rate of deformation. Although these studies were not specifically designed to determine the origins of the deformation potentials, they seem to indicate that these potentials do not arise through a single mechanism alone. The biological significance of these deformation potentials remains unknown, but it has been postulated that they may play a vital role in fracture healing, bone remodelling, growth and development, and the prevention of osteoporosis.

Stress-Induced Potentials in Moist Bone in Vitro

Moist bovine cortical bone specimens were milled to exact dimensions and subjected to bending stress under carefully controlled conditions. The surface under compression was consistently electronegative with respect to that under tension, and potentials up to 7.6 millivolts were recorded. With loads above one kilogram the relationship of peak voltage to load was nearly linear while the relationship of voltage to rate of load was non-linear, the increments in voltage being small beyond a certain rate. Under constant load there was a steady-state potential that was directly proportional to the load but not dependent on the rate of loading. A mathematical equation was derived relating voltage to time, load, and load rate. Although the potentials were clearly stress-induced, and perhaps more accurately strain-related, their origin could not be determined from these studies.