Removable partial denture design: A photoelastic study

Abstract

Quantifiable frozen-stress photoelastic techniques were used to analyze stresses induced in mandibular models by a conventional free-end saddle removable partial denture. Four quasi-anatomical mandibular models were constructed for processing, together with their respective calibration specimens, through identical time/temperature stress-freezing cycles. After processing and slicing, an unloaded control model demonstrated some low-order fringes adjacent to the coronal third of the abutment tooth roots, but was otherwise stress free. A lower bilateral free-end saddle partial denture was constructed and fitted in turn to each of the remaining three models. Each denture/model combination was then loaded and processed through a stress-freezing cycle. After processing, 6-mm slices were cut from selected regions for analysis for the presence of stresses. Using a polariscope with circular polarized, monochromatic light, values for maximum shear stress were calculated at selected points in the slices taken from the three loaded models. Variations up to 28% of the mean were obtained for the three experimental models as compared with the consistent results for the material fringe values obtained from the calibration specimens. The study pointed out the problems involved in using photoelastic stress analysis on complicated anatomical models. The interpretation of the results from such studies should be approached with caution.

RGB photoelastic method based on gradient-square inversion correction

“…For the orthogonal circularly polarized field under monochromatic light, the corresponding isochromatic fringe intensity normalization equation is [1]:…”

“…The principle of the RGB photoelasticity method is to establish an objective function to evaluate the similarity between the RGB value of the target test point and the LUT. The formula is [1] 𝑒 𝑖 = (𝑅 𝑖 − 𝑅 𝑡 ) 2 + (𝐺 𝑖 − 𝐺 𝑡 ) 2 + (𝐵 𝑖 − 𝐵 𝑡 ) 2 (2) Where Ri, Gi, Bi are the standard RGB values in the LUT, Rt, Gt, Bt are the RGB values at the measurement point of the test piece, and ei is the sum of the squares of the differences. By comparing the difference between the RGB value at the target measurement point and all points in the LUT to find the minimum ei value, the fringe orders N corresponding to the point in the LUT can be obtained.…”

“…( 1) to reconstruct the photoelastic fringes Ig(fi, ɑi). The objective evaluation function between the establishment Ig and the experimental photoelastic fringe Io within the disk range is as follows [1]:…”

“…As a full-field stress analysis method, the photoelastic method has been widely used in mechanical experiments and engineering measurements [1]. The principal stress difference and principal stress direction of the material can be obtained by analyzing the isochromatic and isoclines.…”

Photoelastic Measurements of Polymer Insert Stress in the Knee Prostheses Designed for High/Deep Flexion

“…After stress freezing, the model is sectioned into slices without disturbing the stress field, and then the stress in each slice is analysed using two-dimensional methods. For the analyses of the frozen-stress fringe pattern, it is necessary to know the material fringe value of the model material at the stress-freezing temperature (Stewart and Edwards 1984).…”