Islamov A.R.

Bashkir State Medical University, Ufa, Russia.

INFLUENCE OF THE INCREASED LOAD ON THE INCONSISTENCY OF ORTHOPEDIC CONSTRUCTIONS WITH THE SUPPORT ON THE DENTAL IMPLANTS

Intensive development of dentistry opens up new opportunities in the treatment of patients by implantation [2, 13]. The number of patients with dentures supported by implants is increasing [5]. The urgent problem of implantology is the complications that shorten the period of implant function , prevention and treatment, which devoted a lot of work [1, 3, 11, 13]. Their frequency varies from 0.55% in the early period to 0.8% in the late period after implantation [4, 5]. An important place in this series is the inconsistency of orthopedic structures with the support of implants due to stress factors of increased load [1, 12]. As the functional load affects the implant, the bone can react to stress and increase its density and strength, especially in the cervical part of the implant body during the first 6 months - 1 year of the load [14]. The strength of the alveolar bone can increase depending on the functional load. In other words, the area around the implant may be in the zone of pathological overload during the first year after installation, because in this area the stresses are the highest. But a voltage of less than the level of the cortical bone, can still be physiological, allowing the bone to be remodeled, becoming dense and firm. [10]

If the bone tissue is denser, then there is less bone loss. The maxillary arch often exhibits greater bone loss than the mandibular. Stress is greatest at the edge of the crest compared to other areas around the body of the implant. A very soft bone allows stress to spread further along the implant. Therefore, weak bone can affect loss a large area around the implant body and is often accompanied by a complete implant failure [2, 5, 11]. Progressive bone load changes the volume and density of the "bone-implant" contact. The bone has some time to respond to a gradual increase in the occlusal load [9]. Thus, stresses at the edge of the bone can cause a micro-fracture or an overload during the first year, but a change in bone strength due to the current load and its mineralization completely changes the stress-strain relationship and reduces the risk of micro-fracture over the next years [1]. Concentration of stress can also prevent the flow of blood into this area. Reducing the capacity of blood vessels can contribute to loss of bone and make the surrounding environment more susceptible to anaerobic bacteria. What leads to the risk of complications such as peri-implantitis. [4, 5, 6]. Occlusion loads on the implant can create a bending force moment that increases the level of stress acting on the bone. It is noted that these loads can cause a fracture of the implant body. There was an increase in the loss of the alveolar bone, when consoles were used to restore lost teeth. The length of the console also influenced the increase in the number of unrestrained restorations, fractures of prosthetic components and fractures of implant bodies [2, 7]. Treatment plans should include methods to reduce stress and minimize initial and long-term complications. One of the biomechanical methods of reducing stress is to increase the surface area. [16] Another method is the reduction of strength. The force can decrease by: 1) magnitude; 2) duration; 3) type; 4) direction; 5) factors that enhance it.

The overall stress on the system can be reduced by increasing the area to which the force is applied. The most effective method of increasing the surface area of implant support is to increase the number of implants. [5] Consequently, the number of intermediate parts of the prosthesis should be reduced, and the number of implant abutments should be increased. The location of the implants is also important in the distribution of the occlusal load. It is desirable to form a biomechanical triangle, i.e. indirect line. The proposal is that several elements are placed so as to create a three-sided deviation of the abutment position from the buccal side of the straight line (tripod effect). Increasing the length of the implant usually has very little effect on the level of stress in the transossal region around the implant at the edge of the bone ridge during the occlusal load. Thus, increasing the length of the implant is not an effective method of reducing stress in the presence of force factors. Width is more important than the length of the implant. Macrodesign of implant can affect the surface area even more than increasing the width. The cylindrical implant is characterized by a 30% smaller surface area than a conventional screw implant of the same size. A screw implant with 10 turns of thread for 10 mm has a larger surface area than that with 5 turns. The thread depth of 0.2 mm provides a smaller surface area than 0.4 mm. Thus, design can be the easiest way to significantly increase the surface area and reduce the overall risk for the contact area of the implant with bone tissue [5]. Loss of the cortical bone, unstable abutments and stress fractures of implants / prostheses due to material fatigue are more likely to result from parafunctional conditions (bruxism) [8]. Understanding the etiology of early loss of peri-implant bone, loss of retention by restorations and fractures of components of implantation systems enables the doctor to develop a treatment plan that will help reduce the impact of force factors. The treatment plan is changing to reduce its negative impact on the implant, bone and final restoration. Under these conditions, the solution is to increase the area of contact "bone-implant". Installing additional implants with adequate design is the method of choice for reducing stress, as well as increasing the width or height of the implant to reduce the number of intermediate parts and more efficient dissipation of stress on the bone structure, especially on the edge of the alveolar bone.

List of used literature:

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