Stress distribution in anchoring regions of posts cooperating with overdentures

The paper presents the results of model research of mechanical compatibility of selected overdenture structures. The tests based on finite elements method were conducted on flat models reflecting the areas of posts anchoring in a sagittal plane. The reference point was the structure of a prosthesis seated on ball-and-socket joints secured in tooth roots. As alternative solutions, dentures placed on two cylindrical implants supporting ball-and-socket joints were compared with a denture attached to a joint which consisted of a straight axis bar and an elastic clip as well as with a denture supported by a joint of elevated retention, built of a doubly bent axis bar and three elastic bar clips. Taking advantage of the MES Algor program functions, the diverse material structures of the systems investigated were modelled. Next, the reduced stresses σ_red and principal maximum stresses σ₁ generated in osseous tissues, in the implants anchoring area, were determined. The value of the mechanical stimulator decisive to the osseous tissue remodelling was assumed as an evaluation criterion. It was assumed that making use of patient's own tooth roots to attach implants is an optimal solution which, in terms of mechanics, is practically identical to the alveolodental ligament of a healthy tooth. The application of the other methods of implanted prosthesis attachment always creates a risk of undesirable changes, mostly in the upper area of post insertion into the osseous tissue. The least favourably, in the light of stresses comparison, looks the joint of a doubly refracted axis, where the probability of adverse changes of the osseous tissue in a short time is high. This indicates the necessity to carry on works in order to improve this solution characterized by good retention.