Biomedical subjects

T R Katona

Publications and source records attributed to T R Katona.

At least 19 recordsLinked to original sources

PubMed2001

The influence of PDL principal fibers in a 3-dimensional analysis of orthodontic tooth movement.

The effects of mechanical loads on the tooth-alveolus complex are of particular concern in orthodontics. The concepts of center of resistance (CRes) and center of rotation (CRot) are used to characterize tooth responses to orthodontic loads. The mechanical environment (stresses and strains) associated with orthodontic tooth movement is a unique model in bone adaptation physiology. Numerous finite element models of varying complexity have been developed to calculate tooth movements and stress distributions within the alveolar bone and the periodontal ligament (PDL). In general, the PDL has been idealized as a homogeneous isotropic material. For this project, a 3-dimensional tooth/PDL/mandible/finite element model was developed in which, for the first time in such an analysis, the PDL's principal-fiber structure was also incorporated. Parametric analyses showed that the fiber orientation and the mechanical properties do not exert much influence on the locations of the CRes and the CRot and on the stress patterns within the bone and the PDL matrix. However, the absence of principal fibers produces not only different stress magnitudes, but also differences in stress patterns. Furthermore, the no-fiber-associated CRes and CRot are considerably separated from the cluster of fiber-influenced centers. It was concluded that it may be more realistic to incorporate "generic" principal fibers into finite element models than not to include them at all, despite the lack of reliable information about fibers.

Alveolar Process↗

PubMed2001

A mechanism of noncontinuous supraosseous tooth eruption.

Numerous theories have been propounded to explain the various aspects of tooth eruption, but no general consensus exists about some of the underlying mechanisms that govern these aspects. An important unresolved issue is the source of the motive forces that displace teeth. We proposed that supraosseous eruptive forces are generated by tooth socket distortions caused by functional jaw deformations. Previous studies used basic equations of static equilibrium to demonstrate that the concomitant stretching of the oblique periodontal ligament (PDL) fibers give rise to forces that may cause supraosseous tooth eruption. For a more rigorous and expanded analysis, we applied the finite element method (FEM). Three functional loads were considered, but the FEM calculations strongly suggested that all jaw deformations contribute to tooth extrusion. It was also demonstrated that the PDL fiber disruptions that are likely to occur with increased stretching can provide a mechanism to stabilize the erupted position.

Computer Simulation↗

PubMed2001

A mathematical analysis of the role of friction in occlusal trauma.

STATEMENT OF PROBLEM: It is recognized that high or misdirected forces can cause occlusal trauma. It is also known that the coefficient of friction between contacting teeth depends on (salivary) lubrication and on the material surfaces in contact. Friction changes the directions and magnitudes of contact forces, but the exact influence of friction on occlusal trauma is unknown. PURPOSE: The purpose of this mathematical study was to ascertain the influence of changed friction (as a result of xerostomia or a restoration) on the forces experienced by contacting teeth and the temporomandibular joint (TMJ). MATERIAL AND METHODS: Equations were derived for the forces on teeth and the TMJ. To assess the effects of friction on these forces, a parametric analysis was performed in which the coefficient of friction between teeth was set to 0.0 (idealized frictionless contact), 0.2 (salivary lubrication), 0.4 (xerostomia), or 1.0 (some artificial saliva lubrication). RESULTS: The computations indicated that a change in friction influences the directions and magnitudes of the forces experienced by teeth and the TMJ. The effect can be subtle or profound depending on the cusp angle and the direction of impending motion. CONCLUSION: Within the limitations of this study, the results suggest that change in friction between teeth, for any reason, should be considered a possible cause of occlusal trauma.

Dental Amalgam↗

PubMed2000

Experimental validation of a finite element model of light-activated polymerization shrinkage.

An important consideration in improving the longevity of dental resin composite restorations is how to minimize the stresses that develop between resin composites and the wall of the preparation as the resin shrinks during polymerization. If the stress is too great, failure of the bonded interface occurs and microleakage results, with possible margin failure, staining, and secondary caries. This present project was performed to validate a previously developed FEM approach for investigating polymerization shrinkage. Light-cured resin composite was condensed into a cylindrical cavity preparation, which contained a centrally located wire. A profilometer stylus was positioned on the end of the wire to detect the initial surface displacement as the wire moved with the superficial layer of composite resin. The plots of the experimentally derived data were compared to the data plot from the FEM. The initial segments of the experimental plots matched the calculated plot very closely in shape, thus validating the FEM approach.

Dental Materials↗

PubMed2000

Effects of T-loop geometry on its forces and moments.

The moments and forces produced by various orthodontic T-loop spring designs were measured. The effects of dimension changes (within clinically used ranges) and the addition of gable bends with heat treatment were assessed. Increasing the vertical or horizontal dimension reduced the spring's load-deflection rate and its moment-to-force ratio. Gable preactivation with heat treatment had the opposite effects.

Analysis of Variance↗

PubMed1999

Microdamage adjacent to endosseous implants.

Intense remodeling occurs in lamellar bone adjacent to osseointegrated endosseous implants. The purpose of this study was to compare microdamage accumulation subsequent to ex vivo fatigue loading of bone that surrounds an endosseous implant, (a) immediately after placement (nonadapted bone) and (b) following a 12 week healing period after placement (adapted bone). We hypothesize that there is less microdamage in the more compliant adapted bone than in the older nonadapted bone. Nonthreaded titanium plasma sprayed (TPS)-coated endosseous implants were placed into dog mid-femoral diaphyses and allowed to heal for 12 weeks. Block sections of bone, each containing one implant, were cut anteroposteriorly, resulting in an implant containing lateral cortex, and a medial cortex that was used for testing the nonadapted specimens. Control specimens (n = 14 each for adapted and nonadapted) were loaded at 0 N. Experimental specimens (n = 13, adapted; n = 14, nonadapted) were loaded at 100 N in cantilever bending for 150,000 cycles at 2 Hz, at 37 degrees C on a Bionix 858 testing machine. Specimens were bulk stained with basic fuchsin and 120-140 microm sections were obtained. Crack numerical density (Cr.Dn = Cr.N/ B.Ar, #/mm2), crack surface density (Cr.S.Dn = Tt.Cr.Le/ B.Ar, mm/mm2), and percent damage area (Dm.Ar = Cr.Ar x 100/B.Ar, mm2/mm2) were measured at x 250. Statistically significant differences (p < 0.0001) were seen for Cr.Dn, Cr.S.Dn, and Dm.Ar on the compressed cortices suggesting that adapted bone near the implant accumulated significantly less microdamage than nonadapted bone. Also, the adapted nonloaded control specimens had approximately 20-fold less damage than the respective nonadapted specimens. This study suggests that the compliant adapted bone adjacent to endosseous implants is relatively resistant to fatigue loads. The high success rates of endosseous implants may be due to the presence of a rapidly remodeling region that maintains tissue compliance and limits microdamage initiation.

Animals↗

PubMed1999

The limitations of the instantaneous centre of rotation in joint research.

The limitations on the use of the instantaneous centre of rotation (ICR), as calculated from discrete displacement data, are often not fully appreciated. As a consequence, the concept of the ICR has been improperly applied in some instances. In this paper, the procedures used to compute the ICR are developed in detail, and the factors that affect the computed results are identified. With an example, it is shown that in addition to being path dependent, ICR location is also sampling increment size dependent. Therefore, it is not appropriate to consider the ICR as a rotation centre if the body is undergoing general planar (combined translation and rotation) motion because it does not uniquely characterize the movement.

Humans↗

PubMed1998

Microhardness and anisotropy of the vital osseous interface and endosseous implant supporting bone.

Limited information is available on the mechanical properties of the rapidly remodeling bone that surrounds endosseous implants. Fifteen implant-bone blocks were obtained from the mid-femoral diaphyses of three mature male hounds 12 weeks after placement of the implants. To evaluate the microhardness and cortical anisotropy of bone, the implants were sectioned along their long axes. In this process, the femurs were sectioned transversely. Knoop microhardness measurements (HK) were made with a 50 g force on cortical bone and a 25 g force on periosteal callus, endocortical callus, and circumferential lamellar bone. The long diagonal of the indenter was placed parallel to the implant (in the radial bone direction). Measurements were made in cortical bone at 200, 400, 600, 800, 1,000, 1,500, 2,000, and 2,500 microm from both sides of the implant. To detect cortical anisotropy in the radial compared with the tangential direction, a second set of indentations was made perpendicular to the first. Microhardness of periosteal callus and endocortical callus and anisotropy of circumferential lamellar bone near the endocortical surfaces of the femur were also evaluated. Repeated measures analysis of variance showed significantly (p < 0.05) lower microhardness values (30.6 +/- 0.8 HK [mean +/- SEM]) for cortical bone at 200 microm than at any other location (range: 40.3-46.6 HK). Microhardness anisotropy was not detected in cortical bone. Furthermore, within 200 microm of the implant surface, the Knoop microhardness values were significantly lower for periosteal and endocortical calluses than for cortical bone. These data provide information about the mechanical properties of bone adjacent to endosseous implants at a microstructural level. The results are consistent with the high rate of remodeling seen adjacent to endosseous implants at 12 weeks after implantation.

Animals↗

PubMed1997

A comparison of the stresses developed in tension, shear peel, and torsion strength testing of direct bonded orthodontic brackets.

Strength testing of direct bonded orthodontic bracket systems is commonly performed with tension, shear peel, or torsion loads. In general, the results of these tests are reported as an average stress that is computed by dividing the experimentally measured force at failure by the area of the bracket base. The average value, obtained in this manner, implies an evenly distributed stress field. In this project, finite element model (FEM) calculations were used to determine the more realistic stress distributions generated within the cement. The results indicate that the three loading modes produce very different non-uniform stress field patterns. Furthermore, the calculated stress peaks and the stress component proportions depend on the loading method. It was therefore concluded that the manner of loading affects the strength measurements and that the average stress does not adequately characterize bond strength.

Dental Bonding↗

PubMed1997

Angiogenesis and osteogenesis in an orthopedically expanded suture.

The purpose of this study was to examine the angiogenic and the subsequent osteogenic responses during a 96-hour time-course after sutural expansion. Fifty rats were divided into: (1) a control group that received only angiogenic induction through injection of 5 ng/gm recombinant human endothelial cell growth factor (rhECGF); (2) an experimental group that received orthopedic expansion and rhECGF; (3) a sham group that received expansion and sodium chloride (NaCl) injection; and (4) a baseline group that received no expansion or injection. All rats were injected with 3H-thymidine (1.0 microCi/gm) 1 hour before death to label the DNA of S-phase cells. Demineralized sections (4 microm thick) were stained with hematoxylin and eosin. Angiogenesis and cell migration were analyzed with a previously established cell kinetics model. Analysis of variance was used to test the hypothesis that enhancement of angiogenesis stimulates reestablishment of osteogenic capability. Blood vessel number, area, and endothelial cell-labeled index significantly increased in experimental groups, but no difference was found between control and baseline groups. Labeled-pericyte index and activated pericyte numbers in the experimental group were also higher than in the sham groups. These results show that supplemental rhECGF enhances angiogenesis in expanded sutures but not in nonexpanded sutures. Data also suggest that pericytes are the source of osteoblasts in an orthopedically expanded suture.

Analysis of Variance↗

PubMed1997

Stresses developed during clinical debonding of stainless steel orthodontic brackets.

The purpose of this project was to use finite element modeling to calculate and compare the peak stresses generated during clinical debonding of resin bonded brackets. Five debonding techniques were considered: tension, shear-peel, torsion loads on the bracket, wedging of the cement margin, and bracket temperature increase. The data is presented in terms of the relative potentials of the methods for causing enamel fracture. That is, in this idealized model, it was assumed that enamel failures were governed by maximum principal or shear stress. Therefore, all debonding loads and calculated stresses were scaled to correspond to unit peak principal stress or unit peak shear stress in enamel. Furthermore, it was assumed that cement cohesive failure was also governed by maximum principal or maximum shear stress and that adhesive failures were caused by interface normal or shear stress. Thus, for example, it was found that for 1.0 MPa of peak shear stress in enamel, tension and shear-peel debonding generate, respectively, 1.34 and 0.96 MPa of peak normal (tensile) stress in the cement at the enamel-cement interface. The interpretation of this information is that tension debonding is less likely to cause enamel damage than shear-peel loading if it is assumed that (1) the enamel would fail due to the high shear stress, and (2) the joint would fail at the enamel-cement interface because its normal stress limit has been exceeded.

Adhesives↗

PubMed1997

Non-linear large deformation FE analysis of orthodontic springs.

Large deformation non-linear finite element models of T, V, L and B (Baldwin) orthodontic springs were developed and experimentally validated. Spring stiffnesses and moment/force ratios were computed. Compared to the T loop, under horizontal activation, the V loop was half as stiff, the L loop was equal, and the B spring was 10% as stiff. The moment/force ratio was 30% higher in the V configuration, while the B spring was less by 95%. The asymmetric L loop exerted a moment/force ratio that was 30% on the one side, but 180% in the opposite direction on the other side. With vertical activation, also compared to the T spring, the horizontal stiffnesses were 500% (V), 150% (L), and 30% (B). The concomitant vertical stiffnesses were 100%, 50% and 25%. The vertically activated moment/force ratios were nearly equal in the four springs. Experiments validated these FEM calculations.

Algorithms↗

PubMed1996

Stress analysis of a bulk-filled Class-V chemical-cured dental composite restoration.

Clinical problems associated with the polymerization shrinkage of dental composite restorations include tooth sensitivity, crown fracture, discoloration, recurrent decay, and loss of restoration. Our goal was to determine whether these complications could be attributed to the transient stresses developed during contraction. Thus, a finite element model was used to calculate the transitory deformations and composite-tooth interface stresses produced during the shrinkage of a chemical-cured ideal Class-V composite restoration. It was found that the interface stress peaks moved with the polymerization front, and that in some instances, their intermediate magnitudes were higher than the final, fully cured, values. Therefore, the results indicate that clinical failure may be related to these transitory changes during the polymerization process.

Dental Materials↗

PubMed1996

Angiogenic induction and cell migration in an orthopaedically expanded maxillary suture in the rat.

The purpose was to examine the effect of an angiogenic factor on cell migration patterns and osteoblast histogenesis during the 96 h following orthopaedic expansion of the anterior maxillary suture. Fifty rats were divided into four groups: (1) a control group that received only angiogenic induction via injection of 5 ng/g body wt recombinant human endothelial-cell growth factor; (2) an experimental group that received orthopaedic expansion and angiogenic induction; (3) a sham group that received orthopaedic expansion and normal saline injection; and (4) a baseline group that received no expansion or injection. The experimental and sham groups were subdivided to conduct experiments over 1, 2, 3 or 4 days. The anterior portion of each maxilla was dissected free and demineralized. Sections (4 microns thick) were cut from every block and stained with Mayer's haematoxylin and eosin. Cell migration was analysed using a previously established cell-kinetics model. The osteoprogenitor cells were divided into four categories according to nuclear volume: A cells (40-79 microns3), B cells (80-119 microns3), C cells (120-169 microns3) and D cells (> or = 169 microns3 A' cells are the portion of the A cell population that responds to osteogenic stimulus. As previously defined in periodontal ligament, the reciprocal association of a decreasing number of less differentiated (A + A) cells and an increasing number of C + D cells, as a function of distance from the nearest major blood vessel, was consistently found in all groups. This suggests a vascularly oriented gradient of progressively more differentiated osteoprogenitor cells. Also, A + A' cells were predominately located within 20 microns of the nearest major blood vessel whereas the C + D cells were found at a distance > 30 microns from the nearest major blood vessel. These results suggest that the A'-->C shift occurs 20-30 microns from the nearest major blood vessel. In the angiogenic induction groups, the numbers of committed osteoprogenitors (A + A') were significantly higher than in the sham group at day 1. At day 3, the numbers of preosteoblasts (C + D) in angiogenic sutures were significantly higher than in the sham groups. This enhancement of preosteoblast population strongly suggests the possible role of activated pericytes in expanded sutures as a source of osteoprogenitor cells.

Analysis of Variance↗

PubMed1996

A comparative biomechanical analysis of resorbable rigid fixation versus titanium rigid fixation of metacarpal fractures.

Linear (two-dimensional) and three-dimensional (3D) plating systems (Poly-Medics) composed of the resorbable copolymer of polyglycolic acid (PGA) and poly-l-lactic acid (PLLA) (Lactosorb) were studied in vitro. The plates were applied to osteotomized fresh frozen human cadaveric metacarpal bones that were then tested for torsional rigidity and three-point bending strength and rigidity. The results were compared to those from another study of two low-profile titanium plating systems (Leibinger and Synthes). Analysis of variance revealed that the linear-flat Lactosorb plate and screws had apex dorsal rigidity and force-to-displacement measurements equal to all but two of the titanium plates (3D). The 3D-flat Lactosorb plate had the highest torsional rigidity of the resorbable system, but it was only moderately rigid compared to the titanium plating systems. This in vitro biomechanical study of the copolymer PGA-PLLA plating system indicates that, in clinical applications, it may be better suited for metacarpal fractures rather than proximal phalangeal fractures due to the lower demands of torsional loading compared to apex bending.

Biomechanical Phenomena↗

PubMed1996

Finite element stress analysis of three filling techniques for class V light-cured composite restorations.

An important disadvantage of current dental resin composites is polymerization shrinkage. This shrinkage has clinical repercussions such as sensitivity, marginal discoloration, and secondary caries. The objective of this study was to compare three filling techniques in terms of the transient stresses induced at the resin composite/tooth interface during polymerization. The techniques were: bulk filling (B), three horizontal increments (HI), and three wedge increments (WI). A simple Class V cavity preparation was modeled in finite element analysis. Polymerization shrinkage was simulated by a thermal stress analogy, thereby causing 1% shrinkage due to an arbitrary coefficient of thermal expansion. Interface normal and shear stresses were calculated at nine steps during polymerization, proceeding from 0% to 100% volume of cured resin. The importance of the interface transient stresses was revealed by the finding that, in most cases, their peak values exceeded the final or residual stress. Also, the WI and B techniques consistently exhibited the highest and lowest maximum transient stresses, respectively. These results from the simple model of a Class V restoration suggest that bulk filling of light-cured resin composites should be used in restorations which are sufficiently shallow to be cured to their full depth.

Chemical Phenomena↗

PubMed1995

Stress analysis of bone modeling response to rat molar orthodontics.

The purpose of this project was to determine if alveolar bone modeling could be associated with altered mechanical environment. Finite element stress analysis of an orthodontically tipped rat molar periodontium was performed. The distributions of mechanical components within the periodontal ligament and cortical bone were compared to the well-documented bone formation and resorption patterns in the alveolus of the tooth. It was concluded that in orthodontically induced bone modeling activity, locations of osteogenesis uniquely coincided with increased tension within the periodontal ligament, while bone resorption areas could be associated with increases in other components (minimum principal and maximum shear stresses, strain energy density, and von Mises) within the bone itself.

Alveolar Process↗

PubMed1994

Engineering and experimental analyses of the tensile loads applied during strength testing of direct bonded orthodontic brackets.

The stress levels within the cement layer (hence, the apparent strength) of a direct bonded orthodontic bracket depends, to a large extent, on the alignment of the tensile loads that are applied to the specimen. The purpose of this analysis was to determine how the construction of a ligature wire harness affects the alignment of the applied loads. Tensile tests conducted on a modified bracket/cement system showed large variations in the force-elongation curve profiles. An engineering model was developed to explain these deviations. The results indicate that it is virtually impossible to evenly apply tensile loads to the bracket. It was also proposed that long harnesses constructed with thin ligature wire, prestressing the harness, and lubrication may reduce some of the effects of unavoidable load-bracket misalignment.

Biomedical Engineering↗