University of Texas System

About: University of Texas System is a education organization based out in Austin, Texas, United States. It is known for research contribution in the topics: Cancer & Population. The organization has 13901 authors who have published 10925 publications receiving 319328 citations. The organization is also known as: UT System.

Effect of abutment angulation on the strain on the bone around an implant in the anterior maxilla: a finite element study.

Abstract: Statement of problem Angled abutments are often used to restore dental implants placed in the anterior maxilla due to esthetic or spatial needs. The effect of abutment angulation on bone strain is unknown. Purpose The purpose of the current study was to measure and compare the strain distribution on the bone around an implant in the anterior maxilla using 2 different abutments by means of finite element analysis. Material and methods Two-dimensional finite element models were designed using software (ANSYS) for 2 situations: (1) an implant with a straight abutment in the anterior maxilla, and (2) an implant with an angled abutment in the anterior maxilla. The implant used was 4 × 13 mm (MicroThread). The maxillary bone was modeled as type 3 bone with a cortical layer thickness of 0.5 mm. Oblique loads of 178 N were applied on the cingulum area of both models. Seven consecutive iterations of mesh refinement were performed in each model to observe the convergence of the results. Results The greatest strain was found on the cancellous bone, adjacent to the 3 most apical microthreads on the palatal side of the implant where tensile forces were created. The same strain distribution was observed around both the straight and angled abutments. After several iterations, the results converged to a value for the maximum first principal strain on the bone of both models, which was independent of element size. Most of the deformation occurred in the cancellous bone and ranged between 1000 and 3500 microstrain. Small areas of cancellous bone experienced strain above the physiologic limit (4000 microstrain). Conclusions The model predicted a 15% higher maximum bone strain for the straight abutment compared with the angled abutment. The results converged after several iterations of mesh refinement, which confirmed the lack of dependence of the maximum strain at the implant-bone interface on mesh density. Most of the strain produced on the cancellous and cortical bone was within the range that has been reported to increase bone mass and mineralization.

Bone mineral content in patients with calcium urolithiasis

Abstract: 125I-photon absorptiometry was used to determine bone density (bone mineral content/bone width) in the distal third of the radius in 117 patients with absorptive hypercalciuria, 44 with renal hypercalciuria, 53 with primary hyperparathyroidism, and 69 patients with osteoporosis. Observed bone density in each patient was compared to the mean bone density for age- and sex-matched control subjects; the magnitude of the fractional change from control mean bone density was determined for each of the groups listed. In absorptive hypercalciuria, with normal or suppressed parathyroid function, the mean fractional change in bone density of −0.0010 was virtually identical to and not significantly different from the control mean (or zero). In renal hypercalciuria with secondary hyperparathyroidism, the mean fractional change in bone density of −0.0746 was significantly lower than the control mean (p < 0.001 by one-sample t-test; 95% confidence interval on mean fractional change ranges from −0.0970 to −0.0530). Similarly, the fractional change in bone density was significantly reduced (p < 0.001) in primary hyperparathyroidism and in osteoporosis (mean changes of −0.1275 and −0.1516, respectively). Individual value for bone density was below the lower limit of the 95% prediction interval for observations from control subjects in only one of 117 patients with absorptive hypercalciuria; it was low in 5 of 44 patients with renal hypercalciuria. These findings provide an additional support for the validity of separation of absorptive hypercalciuria from renal hypercalciuria.

The kinetics of recovery in irradiated colonic mucosa of the mouse.

Abstract: There is an increasing interest in radiotherapy as a pre or postoperative adjuvant to surgery in the curative treatment of rectosigmoid cancer. This is a concept completely unrelated to palliative treatment, and therefore we need to understand the response of incidentally irradiated intestine in order that maximally curative doses of radiotherapy may be used safely. There are two aspects of radiation injury: early mucosal injury and late fibrosis. We have studied the acute response of colonic mucosa of the mouse to single and multiple doses of gamma rays. The radiosensitivity of colonic mucosal cells is similar to that of other cells of epithelial origin, both normal and neoplastic. Two factors predominate in the response of colonic mucosa to multifraction irradiation: A) the ability of cells to repair non‐lethal radiation damage between dose‐fractions; and B) the regenerative capacity of surviving cells. We have studied these two aspects of the response of colonic mucosa and other cell renewal systems and shall discuss our results. Briefly, the capacity of colonic mucosa to repair nonlethal damage is similar to that of other epithelial cells. Although we do not have direct proof, it is likely from available radiobiology studies that neoplastic cells and normal cells are equally capable of this repair. However, the normal mucosa possesses a great capacity for regeneration, and this is probably the mechanism that provides the radiotherapist with a margin of safety in the postoperative treatment of residual small deposits of rectosigmoid cancer.