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4MEDICAL SCIENCES
CHANGES OCCURRING IN THE BONE TISSUE OF A SINGLE IMPLANT
Musayev E..
Doctor of Philosophy in Medicine, Associate Professor Department of Orthopedic Dentistry Azerbaijan Medical University Baku, Azerbaijan Arkhmammadov A.. Doctor of Philosophy in Medicine, Associate Professor Department of Orthopedic Dentistry Azerbaijan Medical University Baku, Azerbaijan
Aliyev M.
Doctor of Philosophy in Medicine Department of Terapeutik Dentistry Assistant Azerbaijan Medical University Baku, Azerbaijan https://doi.org/10.5281/zenodo.7467637
Abstract
The bones of the skull, jaws and hard tissues of the teeth were formed under the influence of chewing load, which is a functional stimulus to maintain their physical properties. The availability of data on stresses and deformations in the bone structures of the jaws can improve the results of implant placement.
Keywords: stresses and strains, hard tissues, implants, jaw bone structures.
The life of bone tissue is largely determined by stresses and deformations. Stresses characterize the actions of internal forces, which, under physiological loads in the human musculoskeletal system, including chewing, are physiological stimuli that contribute to the action and maintenance of metabolic processes in bone tissue. In the area of application of the load—compression—negative potential is determined in the bone tissue, in the tension zone—positively charged ions, which determine the electrochemical nature of metabolic processes. In previous studies, we determined the magnitude of the stress that destroys a compact plate of bone tissue; it is in the range from 40 to 80 MPa; for cancellous bone, this value is 3-15 MPa; depends on the area of the bone tissue [1, 2], for a titanium implant - from 400 to 600 MPa. It has been clinically and experimentally shown that, despite such a 4-5-fold difference in the mechanical properties of the "implant-bone tissue" system, it functions quite well and for a long time. From the theory of strength of composite structures, it is known that structures made of different materials (in our case, the design of a dental prosthesis based on an implant or implants, which or which are in contact with compact and spongy bone tissue of the jaws) are characterized by different elastic moduli or breaking stresses[3]. At the boundary of dissimilar materials, additional stresses arise due to the different nature of stresses and strains[4.5]. Permanent additional stresses, summing up, form parasitic nodes or stress concentrators, which under certain conditions become destructive and subsequently lead to structural failure. This confirms the previously put forward position, despite the fact that the mechanical properties of implants and bone tissue differ, however, the elastic moduli of
the titanium implant, the internal cortical plate of the jaw and cancellous bone during their joint work are equal or close within chewing loads with stresses from 5 to 100 MPa and their joint functioning is carried out in the same conditions. Only in this case, the chewing load on the implant will be evenly perceived, redistributed and extinguished in the underlying and surrounding tissues. This prevents the formation of parasitic, and then destructive stresses and deformations at the boundaries between implants and other supporting structures. An analysis of stresses and strains that occur under a load of up to 100 N along the axis of a single implant, using mathematical models using the finite element method, showed that the main stresses are concentrated in the load application zone and reach 80 MPa. Stresses from the point of its application in a titanium implant gradually decrease along the entire length of the implant to 7-8 MPa in its apical part. At the point of contact between the implant and compact bone tissue, the stresses in the implant are up to 35 MPa, and in the bone tissue - up to 10 MPa; this indicates that the bone tissue actively compensates for stresses from the implant (breaking stresses for compact bone tissue are up to 80 MPa). The pattern of stresses in the bone tissue is represented by several zones: 1st - the smallest zone - the place of contact of the compact bone with the implant (with values up to 25 MPa); 2nd - goes from the 1st and occupies an area up to 2/3 of the size of the implant immersed in the bone with values from 20 to 5 MPa, and in a similar zone of a titanium implant these values are up to 10 MPa; 3rd - is projected onto the last apical third of the implant with values in the bone from 5 to 1 MPa, while in the implant itself in this zone the stresses are up to 7-8 MPa.
The analysis shows that, first of all, the stresses are compensated in the titanium implant itself, which has a high degree of elasticity due to its mechanical properties. The study showed that the stresses from the vertical load on the implant and bone tissue are fully compensated and fluctuate in the bone tissue from 1 to 35 MPa, while the destructive stresses of the bone tissue are within 80 MPa. The application of a load to the edge of the occlusal surface of the implant under vertical loading along its axis reveals significant splitting stresses along the vertical axis of the implant with values up to 60 MPa. The maximum stresses in the implant extend to the point of contact between the implant and the cortical plate on the load side, where they are concentrated and reach up to 40 MPa. On the opposite surface of the implant, stresses in the zone of its contact with bone tissue up to 10 MPa are determined. As the implant sinks into the bone tissue, the main stresses both in the implant and in the bone tissue are determined in the upper 2/3 of the implant and bone and are of a splitting nature, i.e. on the pressure side, the maximum stresses range from 0.5 to 7 MPa, and on the opposite side, a compression zone with stresses up to 10 MPa is formed reaching the top of the implant. Stresses are compensated, however, an unevenly acting at an angle load can form fatigue stress nodes in the area of contact between the implant and bone tissue from the pressure side, which can adversely affect the use of a denture on the implant. The study of stresses under load on an implant with a cantilevered support by 4 mm shows that the main stress concentrators are localized at the transition point of the cantilever to the implant with a stress of more than 120 MPa and, as in the previous case, are of a splitting nature. In the zone of contact of the compact plate with the implant on the pressure side, the stresses reach 25 MPa. On the opposite contact side, a pattern of much lower stresses is determined both in area and in their values from 1 to 10 MPa. The work of the implant in the bone tissue under cantilever loading will be dislocating, which is unfavorable for the bone and can lead to the loss of the implant. An analysis of stresses in the bone tissue at the junction
with the implant shows that the distribution of stresses is determined by the direction, magnitude, and point of application of the load. The study showed that the titanium implant, due to its elastic properties, most perceives and compensates for a significant part of the stresses from the denture. The optimal load for the implant is along its axis, however, other loads within the occlusal surface of the implant are compensated. In these cases, the stress at the point of contact with the bone tissue can reach up to 30-40 MPa with a small contact area (up to 3-5%). In the remaining bone tissue, these values reach 2-5 MPa, while the breaking stresses for bone tissue are up to 60 MPa. During the study, it was determined that, regardless of the load, the main stresses are fixed in the cervical part of the implant. In the apical, deepest part of the implant, the stresses are within 1 MPa and are completely compensated by the bone tissue. The main task of a denture fixed on an implant is to transfer the load from opposing teeth in a state of occlusion to the implant strictly along its vertical axis. During sagittal and transversal movements of the lower jaw, there should be no blocking moments on the antagonist teeth with the formation of loads acting at an angle or perpendicular to the vertical axis of the tooth and implant.
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