The prosthetic system under the action of masticatory forces is subject to the Law of Ante
As we have said, the prosthetic elements have their mechanical characteristics given by the elastic modulus and the geometry that interact in a strict sense with the distance between the pillar elements. So we can determine the bending of a bridge girder.
From all this follows the need to follow the concept of Isotopia (number of implant elements tending to the number of teeth to be replaced) Only in this way is it possible to reduce the interaxis between the abutments benefiting from the reduction of the flexion with function that varies in the cube. Therefore, rehabilitations with a small number of implants should be avoided.
Otherwise the typical pericervical re-absorption will occur earlier. This is the natural expression of the stresses transmitted to the bone by the implant that contracts a joint reaction defined as a joint.
The joint reacts by transferring vertical, horizontal and bending moment stresses to the supporting structures (bone) (force x arm). The latter is the result of the deformation induced by the acting forces that must be considered in their vector components.
The bone is generally subjected to a balance between deposition and structural resorption processes. This remodeling certainly occurs as a function of mechanical stresses both in terms of entity and direction. Any change in occlusal or postural relationships causes both macro and microscopic structural changes. In fact, trabeculation, an expression of opposition to the vectorial direction of forces, changes as a function of the variation of the same.
In conclusion, when an endo-osseous implant is inserted and loaded, a change is made in the direction of the loads and of the tensions that lead to a new and uneven distribution of mechanical stresses. The extent of the biological response that occurs around the plant depends on the quality and quantity of the bone itself. The greater the interface surfaces, the lower the load and deformation values of the peri-implant bone (Tab 2 -1).
Oral implantology involves not only axial transmission of masticatory forces, but also lateral transmission (shear forces) that can be exacerbated in the case of a non-axial positioning. This situation is completely bypassed with the introduction of immediate solidarity at the time of the intervention. The welder allows a truly non-deformable constraint in contrast to other systems that use components with different mechanical characteristics and with the inherent possibility of fatigue failure of the connection elements.
We now remember the table of loads according to the literature:
These loads compared to the support section of the cylindrical implants lead us to consider the amount of loads per cm² that can reach very high values according to the formula 2 – 3 in certain conditions.
Let us now see a comparison between the various finned implants and those of cylindrical shape.
With the same load (80 Kg) a type L screw with a diameter of 6 mm and a working length of 13 mm produces a load of 13.3 kg / cm² obtained from the formula
In the same loading conditions a cylindrical plant with a diameter of 3 mm gives a result of 114 kg / cm² based on the formula
After all, cylinder systems, even if rounded, induce excessive axial efforts at the apex of the system, determining what is defined as NAIL EFFECT.
Now consider the table of mechanical characteristics of bone
It is clear that the only structure capable of conveniently tolerating mechanical stresses is the cortical structure. The values tolerated both in compression and in traction are very high.
This fact is at the base of the whole orthopedics which considers this fabric to be the only one worthy of being considered as a support. The spongy as it appears has no relevance as an element of mechanical support.
Osteointegration is in fact considered, once obtained, as a peri-implant corticalization with a supporting function.
The immediately loaded biphasic plant has a very limited load bearing capacity mainly entrusted to the friction that occurs at the level of the intracortical passage section. Hence the complete function prohibition to the operated patients who are obliged for months to runny diets. We will see the study carried out later on.