Issue 67

T. Diburov et alii, Frattura ed Integrità Strutturale, 67 (2024) 259-279; DOI: 10.3221/IGF-ESIS.67.19

128 MPa

(c) Figure 6: The distributions of equivalent stresses (a, c) and strains (b) at the installation of the Oncology implant in the lower left position; (a) general view; (c) stresses in bone tissue. As a preliminary conclusion, two key identified results should be noted: 1) At concentrated loading of the implant, the distribution of stresses (and, accordingly, strains) was primarily determined by the implant length (through the arm size), as well as by the applied F (1) load of 50 N. After the multiple increase in the F (1) load up to 100 and 150 MPa, both stress and strain levels had to increase proportionally. Thus, if the fracture criterion was satisfied already at the minimum load, failure would inevitably occur at its average and maximum values. 2) The redistributions of both the patterns and the maximum stress levels depended on the macrostructure of the zygomatic bone (due to the resection of a fragment of bone tissue and fixation of the implant in its hole) and the mechanical properties. Since the “improved” digital model wad applied (as close as possible to the real structure), this fact enabled to explicitly consider the anatomical features of the structure of the zygomatic bones of the particular patient. For this reason, the results of such trial calculations may be the basis for changing the attachment locations or the standard size of installed zygomatic implants (at the discretion of the maxillofacial surgeon). In addition, the CT data accuracy in terms of reproducing the structure of the zygomatic bone could be determined the effectiveness of the proposed approach for calculating the SSS and, accordingly, treatment tactics (including prosthetics). Calculated SSS for installed all zygomatic implants and denture base Since the ultimate goal of installing the implants was to attach the dentoalveolar prosthesis Fig. 1, c), the SSS calculations were carried out for the case of attachment the denture base (Fig. 1, d). For this purpose, the implant abutments were immovably fixed in the polymer denture base. In order to reduce the number of calculation elements, computer simulation was performed by alternating impact on the denture base segments (Fig. 2, c). It was divided into eight sequentially loaded segments (numbered from right to left, according to Fig. 2, c). Boundary conditions (4) and (6) were preset. The F (2) load was applied alternately to the segments in the direction orthogonal to the surface (Fig. 2, c). In this way, the biting off process was simulated. Three load levels of 50, 100 and 150 N were assumed. The load of 100 N corresponds to average mastication force, while the load of 150 N was employed to estimate the systems’ performance under the overloading conditions. The SSS was assessed for the entire structure, including the zygomatic bones, the implants and the denture base. Tab. 4 presents the maximum values of equivalent von Mises stresses and strains for the entire (structure) system and separately for the zygomatic bones under different loading conditions. The calculated data are indicated for the most loaded both implants and areas of the zygomatic bones adjacent to the corresponding one. Through a slash, the values are given that were obtained by the calculation at the lower adhesion level (in contrast to the above data for ideal adhesion). This option could correspond to attachment of the implants to bone tissue with lower strength properties, for example. In most cases, a decrease in adhesion was accompanied by lowering the maximum local stresses. Nevertheless, other results were also observed when the location of the concentrator area changed, or the maximum stress level was higher than that for ideal adhesion. Let us summarize, that two sets of computational experiments were carried out. The first one assumes low adhesion between the implants and bone tissue. In doing so, the area of rigid contact was incomplete being realized between the thread and cylindrical shape hole only. The boundary conditions at other contact sites of the zigomatic implant with the bone tissue

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