Effect of Cross Section Shape of Metal Strengthener on Stress Distribution in Acrylic Denture Bases

Purpose : The purpose of this study was to investigate the influence of the cross section shape of a metal strengthener on stress distribution and deflection in acrylic denture bases under loading.Materials and Methods : Thirteen 3-D finite element models of acrylic palatal straps with embedded metal strengtheners of different section shapes (square, rectangle, inverted concave, concave, inverted convex, convex, inverted triangle, triangle, flat top half round, flat bottom half round, inverted horseshoe, horseshoe, and round) having an equal area size were created. The thickness and anterior-posterior width of each strap were 2 mm and 11.2 mm, respectively. One end of each strap was fixed on the ridge, and the median line on the deepest palatal vault of each model was fixed vertically. A vertical or 30 degree distally oblique force of 10 N was loaded on the other end of each strap.Results : The straps with the triangular and square cross section-shaped strengtheners had lower maximum stresses and deflections, while higher values were found in the straps with the round, half round and horseshoe section strengtheners. The straps with the round and half round section strengtheners demonstrated sharp stress concentrations at the interface between the metal and the acrylic denture base under oblique loads.Conclusion : The use of triangular or square section-shaped metal strengtheners effectively minimized both the maximum stress in the acrylic denture base and deflection of the saddle.