BIOMECHANICS APPLIED TO IMPLANTOLOGY

 

It is unthinkable to speak about the different types of implants and their relative techniques without making a reference to Biomechanics.

I don't believe that up to now the different kinds of implants have gone through some biomechanical tests nor that the tools used for the different kinds of implants can exclude any damages caused by their use.

It's necessary to think that every tool we use must be studied in order to have such characteristics nor to provoke any damages and to get the prearranged result.

When we try to face the problem we must remember that the bone is a living tissue which has its own characteristics of liveliness, elasticity and memory. It's a complex of more or less condensed cells into a liquid maintaining everything in a movement which makes it reactive to the trauma, both during the immediacy of the surgical phase and during the function of support it is submitted to by an implant ( remodel ).

All the tools must be sharp in order to avoid any type of lacerated and contused wound.

Let's examine which could be the most reliable and the less traumatic tools we should use.

A Maillefer drill. A very sharp tool, after hardening, which has the characteristic of incising first and then to make a way by means of a chirurgical action on the walls, all that without making any lacerated and contused wounds.

 

Hand Graduated drill with the diameter of the screw shaft whose characteristics must avoid any damages by working in depth with a lack of penetration: in fact on the contrary of the drill it has the sinistrorsal unloading.

Let's have a look now to avoid the negative use of the screw tap used by everybody even if the implant is named " self tapping". This instrument conceived in such a way is not certainly appropriate to obtain a female thread. The bone, I repeat, is not a piece of wood. The insertion of the screw rarely can follow the female threads made by the screw tap and so there will be a braking of the walls with an easily understandable result. ( especially whit a machine screw).

The absolute respect of the compact superficial occlusion layer, possibly without opening, with the help of the integrity of the periosteum are factors which can help very much, especially to avoid the famous periimplant damage.

Now let's speak about the immediate mechanical fixation. This is the phase regarded very attentively by implantologists because it is the first and the most important action and conjecture to bring about the recovery of the tissue.There have been numerous remedies to obtain the immediate mechanical fixation, and the negative results have been numerous, too.

For this purpose I don't think it's useful to divide our cranium in sections following the consistence of the tissue in which we think to put our implant. Of course we can't compare it to the different kinds of woods to express the consistence, nor put a clear limit between the different sectors. Our body isn't composed by drawers. I think that the method of the sounding by means of a properly used drill, could give more warranties of reliability.

Now let's consider everything in a contest of surgical intervention in which the most salient event is the creation of a pseudo-fracture and consequently we must operate with an like orthopaedic treatment.

Let's operate a pseudo-plaster cast by means of which you can obtain the immobilization of the two heads. In other words, we look for the support on the opposite cortical, ignoring the classification which could create many unnecessary problems.

Let's accept the idea of "bicorticalism"!

Let's examine now an important factor which happens when the intervention is executed: the flexibility of elements.

Our bones are flexible, our teeth are inserted in an articular context called "gonfosi": now we can't subvert what mother nature has taught us.

The perfect osteointegration of the handmade isn't certainly the ideal solution, it would be like accepting an anchylosis.

So we need a certain elasticity in supporting the charge, and a handmade as elastic as to support the micro-traumas during the physiological phase of the mastication.

Certainly it isn't an element like the root-form which can solve this problem: but an implant with an elastic module given by the shaft-type and by the metal-type.

In this picture we can see an example:

It's an implant which has been working for more than 25 years. If the photo was enlarged, the spaces created by the flexibility of the shaft would be noticed.

 

This x-ray shows a tooth before extraction: the bony tissue around the tooth is completely destroyed and, of course, the anterior wall is missing, too.

 

This image shows the implant inserted.

 

This is a rare x-ray, taken few seconds after the insertion of the implant, which we have just seen. As the anterior wall is missing, the hinder pointed out, since in these cases I palatalize by using the hard "lamina" as a support in order to obtain a kind of bicorticalism, as shown in this image:

I have been polarized by these incisions; I couldn't explain how and why they had stressed so much, and why not in other cases, until I decided to enlarge the x-ray and all in a sudden I was struck by some other details.

Examining the x-ray carefully you can see the difference between the two incisions: the one marked number 1 is in a cancellous-bone tissue formed by living and vital cells which respond to the trauma in an elastic way, almost gummy ( don't forget that the bone isn't a piece of wood! ) that's why the incision immediately reduces after the passage of the thread.

The incision marked number 2 has instead maintained a sharper print, the characteristic of the thread and this is because in this point the screw exploits as bicorticalisms the hard "lamina" which isn't as elastic as the cancellous tissue.

This justifies what I have previously asserted and then explains the reason for which some changes have been made: these changes have given good in reducing the few failures.

In fact during all my life I have never tried to subvert the world, but my purpose has always been to reduce, even if slightly, the number of the failures.

The careful examination of this x-ray lead to the change of some details of the screw, to reduce those who were already the slightest trauma and facilitate the process of recovery of the tissue concerned by the implant.

          

There are some rounding supposed to be very important for the recovery of the bone connected with numbers 4 and 5.

In surgery all the interventions which can produce an angulations must be avoided, because these zones can meet necrosis because of lack of blood contribution.

The round zone at the level of the insertion of the thread with the shaft permits the screw to increase its strength in the point where a fracture may happen more easily.

At point 5 you can see that the point is slightly round in order to facilitate the removal of the bone tissue, avoiding the jamming which easily happens with a very sharp blade-shape point.

Point 3 shows that a small angle ("spoglia") has been removed in order to avoid useless scarification during the relieving manoeuvre and, as I previously said, since the bone behaves in an elastic way, to facilitate the removal of the tissue in the following phase of the scalpel, without any jamming.