Finite element analysis of the transfer of sound in the myringosclerotic ear.

This work presents a biomechanical study of myringosclerosis (MS), an abnormal condition of the ear that produces calcification of the lamina propria of the eardrum. The study researched the transfer of sound to the stapes depending on the localization, dimension and calcification degree of the MS plaques. Results were obtained using a validated finite element model of the ear. The mechanical properties of the lamina propria were modified, in order to model MS plaques, using the rule of mixtures for particle composites considering that the plaques are made of hydroxyapatite particles in a matrix of connective tissue. Results show that the localization and dimension of the plaques are a factor of higher importance than calcification for loss of hearing through MS. The mobility of the stapes decreased with the presence of larger plaques and also when the tympanic annulus and the area of the handle of the malleus were involved.

Finite element stress analysis and fatigue behavior of cast circumferential clasps.

STATEMENT OF PROBLEM: Deformation and fracture of cast circumferential clasps may be a result of stresses induced during mastication. Most biomechanical clasp studies have been performed only under static conditions. There is little information regarding behavior of clasps over time. PURPOSE: The purpose of this study was to evaluate stress distribution on cast circumferential clasps, and the displacements or deformations, depending on the load placement and range. Fatigue analysis was then conducted to evaluate the behavior of clasps over time. MATERIAL AND METHODS: Static stress values and distribution induced in cast circumferential clasps were calculated and studied using 3-dimensional finite element experimental models for Co-Cr cast circumferential clasps. Average loads between 20 and 35 N were applied vertically along the clasp components to simulate static stress distribution during translation and rotation of the denture. After determination of stress concentration areas, the fatigue behavior of clasps was studied using finite element analysis during simulated cyclic masticatory loads (loads between 0 and 20 N included in 4500 masticatory cycles over 24 hours). RESULTS: For the translation simulation, the maximum stress was 310.27 MPa, located near the lower margin of the retentive arm, and for the rotation simulation, the maximum stress was 310.31 MPa, located near the upper margin of the same arm. Under simulated static load, the magnitude of stresses found in the clasps was under the reported yield strength (640 MPa) of the Co-Cr alloy. The maximum stresses indicated the area of highest fracture risk, but fractures occurred only under a simulated cyclic mastication load representing 5.5 years of service. CONCLUSION: Within the limitations of the simulation study, static stress analysis of cast circumferential clasps indicated the location of greatest fracture risk to be at the junction of the clasp arm with the body, for all situations. In addition, fatigue analysis estimated clasp degradation over time and the survival rate of the same clasps, which was found to be 5.5 years, on average.