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Biomedical subjects

D T Davy

Publications and source records attributed to D T Davy.

45 records · Page 3Linked to original sources
PubMed1984

A computational method for stress analysis of adaptive elastic materials with a view toward applications in strain-induced bone remodeling.

A computational method has been developed to obtain numerical results in the stress analysis of adaptive elastic materials. The method is based on a 3-dimensional finite element model that can change geometry and material properties based on the local strain. The solution procedure is iterative; the model is updated in time steps based on the current remodeling to provide incremental remodeling predictions. The method provides a vehicle for examination of different continuum models and their corresponding parameters for strain-induced remodeling in long bone. Use of the method with simple models of theoretical interest is presented. Results show agreement with available analytical results as well as the importance of coupled remodeling effects not previously examined.

Adaptation, Physiological↗
PubMed1984

Load-bearing capacity of the tibial component of the total condylar knee prosthesis. An in vitro study.

The load-bearing capability of the tibial component of total knee prostheses is affected by the coverage of the osteotomized tibial surface by the tibial component. An anthropometric study of the proximal tibia indicated that standard total condylar tibial knee components may significantly underutilize the available weight-bearing tibial surface. The unloaded area values ranged from 6% to 43% in males and from 1% to 25% in females. An experimental study of the load-bearing capability of both standard tibial components and tibial components custom-fitted to conform to the periphery of the upper tibial surface was performed. Improvement in single load to failure with the conforming prosthesis averaged 29% in females with stemless prosthesis, 21% in females with stemmed prostheses, 41% in males with stemless prostheses, and 89% in males with stemmed prostheses. Post-test examination of the failed tibiae with conforming implants indicated failure by major fragmenting of the proximal tibia rather than cancellous bone crushing, suggesting that the maximal load-bearing ability of the upper tibial surface was more nearly being achieved. The results demonstrate the benefit to be gained by fully utilizing the available tibial surface for load transmission across the joint and suggest that use of custom-fitted tibial components has considerable merit.

Anthropometry↗
PubMed1982

The biomechanical behavior of healing canine radii and ribs.

An experimental study and accompanying theoretical study of the biomechanics of healing canine ribs and radii have been conducted. Biomechanical behavior of the healing bones was determined experimentally by whole bone structural tests in four point bending. The experimental results indicated that the non-weight-bearing ribs regained bending stiffness more rapidly than bending stiffness, while the weight-bearing radii regained bending stiffness more rapidly than bending strength. These differences were not found to correlate with differences in overall callus biochemistry, but physical examinations of the bone suggested that differences in callus morphological details between the two bone types might offer an explanation. Utilizing a theoretical model, a parameter study of the influence of callus geometry and morphology on bending behavior was conducted. The results of the parameter study demonstrate that the experimentally observed variations in the amount and distribution of callus materials and in bone geometry can produce the qualitative biomechanical differences measured experimentally. The results of the parameter study also demonstrate that bending stiffness must be used with caution as a healing criterion since it does not necessarily reflect structural strength.

Animals↗
PubMed1981

Determination of stress patterns in root-filled teeth incorporating various dowel designs.

A theoretical investigation has utilized the finite element technique to analyze mechanical stress patterns in a reconstructed maxillary central incisor. A series of designs for endodontic dowel posts incorporated into prosthesis has been comparatively evaluated. For the load condition considered, the results show that minor changes in the stress patterns are produced by the post diameter, length, and taper variations considered. 1. In general, larger post diameters decrease the maximum stresses for both the cylindrical and tapered designs. Variation of diameters over a 15% range produced stress variations of about 8%. 2. The effect of post length on the highest stresses in bending was less than the diameter changes. The real effect of the length changes was to change the location of the stress concentrations that occurred at the post apex in all cases. 3. The effect of taper was found to be slight if the local tapered-post diameter was comparable to the cylindrical post diameter in the high-stress region. 4. For the load considered in this study, the tapered-post design experienced slightly higher tensile and slightly lower shear stresses than the cylindrical post. 5. Using the peak stresses in the dentin and at the dentin-post interface as a criterion, the cylindrical post with the largest diameter is the best design among those examined.

Crowns↗
PubMedDate not supplied

Anterior-inferior capsular shift of the shoulder: a biomechanical comparison of glenoid-based versus humeral-based shift strategies.

This study compared the biomechanical effects of an anterior-inferior capsular shift based at the humeral side with one on the glenoid side of the joint on resultant multidirectional glenohumeral translation and rotation. Nine matched pairs of fresh cadaveric shoulders were placed in a testing apparatus that constrained 3 rotations but allowed simultaneous free translation of the humeral head with respect to the glenoid. The right and left shoulders of each of the matched pairs were randomized to undergo either a glenoid-based or humeral-based anterior capsular shift. The shoulders were tested vented and following the capsular shift procedure. Translational testing was performed at 0 degrees, 45 degrees, and 90 degrees of glenohumeral elevation with the humerus in neutral rotation, 30 degrees internal rotation, and 30 degrees external rotation. Sequential loads of 30 N in anterior, posterior, and inferior directions were applied while maintaining a 22-N joint compressive load. The maximum arc of internal and external rotation after application of a 1-newton-meter moment was determined for the vented specimens and then after the capsular shift procedure. Both shift strategies resulted in significant limitation of anterior, posterior, and inferior translation in all of the tested positions. No significant differences were noted between the 2 shift strategies with respect to restriction of translation in the anterior or inferior directions. The glenoid-based shift caused a significantly greater decrease in posterior translation at 45 degrees and 90 degrees of abduction. With respect to rotation, the glenoid-based shift exerted significantly greater restriction on external rotation than the humeral-based shift. This study supports the use of either a humeral-based or glenoid-based shift to control multidirectional glenohumeral instability. Greater reduction in external rotation was demonstrated after the glenoid-based shift. Specific differences demonstrated in translation control for humeral-based versus glenoid-based capsular shift procedures may be useful in tailoring a procedure for specific instability patterns.

Aged↗
PubMedDate not supplied

Fate of vascularized and nonvascularized autografts.

Controlled laboratory data demonstrate biologic and mechanical characteristics of orthotopically placed canine ulnar autografts. The pattern of bone repair was similar in vascular and nonvascular ulnar grafts beginning with resorption followed by appositional reactive bone formation. The time intervals in the sequence were accelerated in the vascularized grafts. Both the strength and stiffness of the vascularized grafts were found to be significantly greater in Groups studied from six weeks to six months postoperation. There was no statistical difference between the grafts for mechanical testing performed on dogs either one week or one year postoperation. The vascularized ulnar bone grafts fared better than comparably sized nonvascularized grafts and were more rapidly repaired. The mechanical testing demonstrated superior strength and stiffness of the vascularized grafts throughout the repair process.

Animals↗