Greater Bending Strength Research Articles

Structural and biomechanical basis of sexual dimorphism in femoral neck fragility has its origins in growth and aging.

The structural basis for sex differences in femoral neck (FN) fragility was studied in 1196 subjects and 307 patients with hip fracture. The absolute and relative patterns of modeling and remodeling on the periosteal and endocortical envelopes during growth and aging produce changes in FN geometry and structure that results in FN fragility in both sexes and sexual dimorphism in hip fracture risk in old age. Femoral neck (FN) fragility in old age is usually attributed to age-related bone loss, while the sex differences in hip fracture rate are attributed to less bone loss in men than in women. The purpose of this study was to define the structural and biomechanical basis underlying the increase in FN fragility in elderly men and women and the structural basis of sex differences in hip fracture incidence in old age. We measured FN dimensions and areal bone mineral density in 1196 healthy subjects (801 females) 18-92 years of age and 307 patients (180 females) with hip fracture using DXA. We then used the DXA-derived FN areal bone mineral density (BMD) and measured periosteal diameter to estimate endocortical diameter, cortical thickness, section modulus (a measure of bending strength), and buckling ratio (indices for structural stability). Neither FN cortical thickness nor volumetric density differed in young adult women and men after height and weight adjustment. The sex differences in geometry were confined to the further displacement of the cortex from the FN neutral axis in young men, which produced 13.4% greater bending strength than in young women. Aging amplified this geometric difference; widening of the periosteal and endocortical diameters continued in both sexes but was greater in men, shifting the cortex even further from the neutral axis maintaining bending strength in men, not in women. In both sexes, less age-related periosteal than endocortical widening produced cortical thinning increasing the risk for structural failure by local buckling of the enlarged thin walled FN. Relative to age-matched controls, women and men with hip fractures had reduced cortical thickness, but FN periosteal diameter was increased in women and reduced in men, differences are likely to be originated in growth. The absolute and relative patterns of modeling and remodeling on the periosteal and endocortical envelopes during growth and aging produce changes in FN diameters, cortical thickness, and geometry that results in FN fragility in both sexes and sexual dimorphism in hip fracture risk in old age.

粉液型光重合リライニングレジンの曲げ強さに関する実験的研究

The purpose of this study was to investigate the effect on the bending strength of denture base resin relined with REBARON LC and to compare it with other direct relining materials.The following experiments were performed as follows.Experiment 1: The bending strength of denture base resin (ACRON) relined with four hard direct relining resins was tested in the three-point flexure test.The immersion time and the thickness of relining resins were varied in this test.Experiment 2: The bending strength of four denture base resins relined with REBARON LC was tested in the three-point flexure test.The following results were obtained:1. TOKUSO REBASE showed the greatest bending strength and deformation of all relining materials, but there was no significant difference.REBARON LC showed a similar bending strength to other relining materials.2. As the immersion time increased, the bending strength of REBARON LC, TOKUSO REBASE and EPOREX decreased and the bending deformation of Rebaron, TOKUSO REBASE and EPOREX increased.3. Regarding the influence of relining resin thickness on the bending strength, the 1.0 mm thickness of REBARON LC had the greatest bending strength followed by 0.5 mm and 1.5 mm.4. ACRON had the greatest bending strength when relined with REBARON LC, followed by ACRON MC, Palapress and METADENT.

Canine Osteotomy Healing when Stabilized with Decreasingly Rigid Fixation Compared to Constantly Rigid Fixation

SummaryThis study investigated the effect of destabilizing initially rigid external fixation of transverse canine tibial osteotomies, compared to contralateral osteotomies continuously stabilized, with rigid fixators. Destabilization, by conversion of a type III configuration fixator to a type I configuration, after one to four weeks resulted in increased periosteal callus formation but decreased mechanical strength and histologically a preponderance of fibrous and cartilaginous tissues in the osteotomy when studied after nine weeks. Destabilization at six weeks did not result in an increase in periosteal callus formation, nor greater bending strength. Histologically there was a combination of woven and lamellar bone, with the appearance of more active remodelling of primary bone healing. Destabilization at 12 weeks did not result in any effect, when studied after 15 weeks. These findings suggest that increasing weight-bearing loading of a fracture, at the proper time, may enhance the remodelling and hypertrophy of primary bone healing. However, inappropriate timing of destabilization may not have any or even a deleterious effect.Effects of reducing initially rigid fixation of canine tibial osteotomies, after various periods of time, were studied. Destabilization after one to four weeks caused increased periosteal callus formation but decreased mechanical strength. Destabilization after six weeks resulted in increased mechanical strength but no increase in periosteal callus, and destabilization after 12 weeks had no effect compared to osteotomies continuously stabilized with rigid fixation.