BICORTICAL SCREW GARBACCIO

After many years experience of using this screw I have taken into consideration the general characteristics which could adapt themselves to other methodologies.

The histological exams carried out on a monkey by Professor Sarnachiaro at the University of Buenos Aires in 1985 and those of Professor Donath of University of Hamburg on a human lower jaw of six bicortical screws in 1991, ten years after their implant (exams carried out, obviously, post mortem) confirm the validity. Even at the outset of my implantation work my thoughts have always been drawn towards the study of instruments and methodologies that would improve healing time, lessen pain and above all guarantee functionality and longevity. A light hand which has a greater sensibility avoiding, sometimes, irreparable damage, cutting instruments which do not crush the tissues, do not cause cells burning or provoke ischemia and a biocompatible product are all factors to be included for an optimum result. The cells that surround the implant must, as far as possible, maintain their vitality so as to secure healing, as the primary healing of the wound induced avoiding a long process which normally follows in the majority of cases, due to osteolysis which the absorption of bone on the new formation with the inevitable presence of connective tissue.

Given these premises, I have devised a screw based essentially on the principle of bicortical stabilization with consequent protection of the healing processes.

From the biomechanical point of view the permanent stabilization of the endosseus artefacts should benefit from the compact support structure situated on the external surface of human bones. The mandible and the maxilla are no exception. The central spongy bone tissue has less retention and stabilizing capacity as it is formed of few trabeculas, poorly mineralized, immersed in abundant medullar spaces. In 1972 Pasqualini had already proved that the majority of the implantological failures "at unknown aetiology" where it had been possible to exclude surgical error and risk, the serious general illnesses and occlusal imbalance were due to poor retention power of the medullar tissue, both during the healing period and the successive period of implant function in time duration (fig. 1).

This screw, for its own morphology, has remarkable stability capacity because it is formed of successive level supports (the threads) orthogonal to the occlusion load. Furthermore, given its length, it opposes naturally a greater resistance to the lateral mechanical stress. It exploits constantly the principle of the bicortical support using both the resistance of the compact superficial occlusion layer and the resistance of the opposite compact layer: the sinus plate or the compact plate of the palatine bone in the upper jaw, or the compact shell of the lower jaw (fig. 2).

The bicortical support obtained as such is not accidental as sometimes happens during the introduction of some implants, but definite and constant with a practically inexistent negative percentage. This stabilization which, in effect, blocks the screw on two compact cortical situated on both sides, favours the definite consolidation of osteogenesis protected by the "tranquil state" in which healing occurs.

In few cases when it is impossible to reach the opposite cortical, you can have a good result, because the biggest screw surface is 263 square millimetres, and the surface of biggest root of toot is 350 square millimetres.

On these bases, it is obvious that we can load immediately the implant.

INSTRUMENTS

1) The drills Torpan Maillefer, whit mm. 1,2 of diameter and the length of 18 and 25 mm.

2) The Hand Graduated Drill to perfection the hole made by the drill.

3) The Screwing Instruments.

4) The screws have a length of 30 mm., a shaft diameter of 2,25, and are furnished with 3-4-5 threads, with a diameter of 3,5 or 4,5 mm., and are chosen on the basis of the situation and bone consistency.

The screws for the lower distal area have a lengthened tip with a diameter of 1,2 mm. to facilitate the passage in the slender space between the cortical wall and the mandible channel, and avoid the possibility to damage the nerve by the threads.

The screws for the "tuber" area as an elongated tip which extends to a length of 35 mm. and has threads with a 5,5 mm. The helical blade which form the threads presents some scalpel fixtures which, when making a surgical bone incision, remove small fragments without compression and, in particular, permit the creation of a female screw eliminating a screw tap, necessary for every other type of screw (fig. 3).

The tiny particles created during the insertion of the screw are deposited in the free spaces, facilitating "neoformation" of the bone. Furthermore, these cuttings favour after recovery, the blocking of the screw in a rotary direction. The cylindrical shaft ends in a square head where the screwing instruments are lodged, these have different shapes suitable for every situation.

SURGICAL TECHNIQUES

The obvious premise is that, before proceeding, specific exams must be carried out, and the patient must be informed precisely and correctly regarding the manner of the operation to which will be subjected to, and, above all, the importance of his collaboration during and after such.

My experience has taught me that a panoramic x-ray is sufficient to give an exact indication of the available space and most suitable area for intervention, bearing in mind the proportional disparity between the overall and real anatomy (which is confirmed by the probe drill).

Local anaesthetic (only in the part where the drill is to be inserted), is very important for the outcome of the implant and to avoid eventual inconvenience. Any type of pain felt by the patient is useful to distinguish the point reached during the operation: the impact of the hand graduated drill on a cortical wall provokes less violent pain and disappears when the movement stops, while the nearness to the mandibular channel causes more violent and persistent pain.

Given the insertion simplicity, the operation can be effected either without cutting the "mucosa" or not, the choice is based on the anatomic situation. In fact, when the bone crest is held between the fingers, to evaluate the form and consistency the drill tip is sufficient after this has surpassed the "mucosa". The use of the drill to start with is, incredibly, the most important factor at the lowest speed possible, to avoid overheating damage, it perforates the cortical occlusion at the established point, and at the moment it exceeds the same it gives the impression of free falling. In fact, we are in the spongy area. The disparity of the drill diameter 1,2 mm., in respect to the shaft of the screw which is 2,25 mm., is intentional: in fact, from now on we must proceed with very slow movements for the widening without sidetracking, taking surgical advantage of the instrument's sharpness (fig. 4)

After we can proceed whit the whit the and graduated drill until we reach the opposite cortical (fig 5)

The benefits which derive from this mode of procedure are numerous: avoidance of damaging the cells which surround this tunnel and alternating movement continuance consent the particles produced to exit liberally in the blood, permitting the cooling of the bone more than any direct water spray or miraculous perforated cutting burr.

The hand graduated drill widening and proceeding slowly, without wall friction, will give all the indications necessary to evaluate the real resistance encountered. One can then understand the effective consistency of the cancellus bone and the bone shape, indispensable data in order to choose the type of screw to be used, both for its diameter and number of threads. At this point, the drill (or the hand graduated drill) extracted full of blood will give a perfect evaluation of the depth reached which will be compared to the screw shaft (fig. 6).

At the beginning it is better to use the reduced round finger key which, given its conformation will be indispensable for positioning the screw and give the first turns even where the space is really small, because apart from its dimension it has the characteristics to hold the screw. It is opportune to remember that at the beginning the screw requires a light push rotary wise to engage and become self-sufficient. The instruments for continuation will be chosen according to necessity.

The insertion technique of this screw is very important and necessitates well determined movements to exploit in full the incisiveness of the scalpel like blades which create the feminine screw, one must therefore proceed effecting a half turn forward followed by a quarter of a turn backwards to lighten it.

On reaching the opposite cortical wall it is necessary to avoid excessive closure returning backwards a quarter of a turn. The x-ray must confirm the right position.

The patient, at the end of operation, he must feel all right without any kind off pain.

The versatility of this implant is schematized in fig. 7

And insertion is possible even in the thinnest crest (fig. 8).

 

PARTICULAR SITUATION

In the face of a missing tooth an implant is without doubt the most valid solution, either immediately after an extraction or a trauma, in the “agenesis” that one finds particularly in the young people, where often the space is very reduced and it is not easy to have at one’s disposition a suitable implant which avoids damage to the imminent teeth.

In the post-extraction implant it is not always possible, nor indicated, to follow the alveolar socket, especially in the maxillary, insofar as the apex in an unsuitable area due to the presence of damaged tissue and, furthermore, in this direction there is hardly ever enough bone tissue to support an implant. To obviate this situation, the insertion must take place at about three quarters from the gingival rim with a palatal direction avoiding the apex area (fig. 9).

fig. 9

One must remember that if the bone is too compact and doesn’t bleed, any type of implant will give a failure.

In the face of a partial failure, namely, a slight movement which could bring about expulsion, one must not try to substitute the screw with another of a larger dimension, because we would fall back into the previous situation.

Sometimes, one can find oneself in the situation in which, after having reached the cortical wall at a certain depth with the hand graduated drill, one cannot follow the same path with the screw. This is due to excessive hand graduated drill nearness to one of the cortical walls, therefore, not having taken into account the presence of the threads, which have impacted against the cortical wall. In this case, if the depth reached is sufficient, one can stop having however obtained the bicortical support. Otherwise, one must retrace one’s steps and try another way, avoiding putting another screw in the same place because one would do nothing but damage the interested tissue.

In the case where during insertion the screw opposes resistance to the point of seeming blocked, take a control X-ray, to avoid that unusual impact has produced a torsion, even if only the tip with possible consequent breakage.

It is important to now, having overcome the compact wall and entered into the spongy area, if one proceeds with caution, without using force, it is impossible to cause damage.

INFERIOR DISTAL AREA

Numerous are the patients that present a form without teeth in the inferior distal areas, for which resorting to prothesism through implant would resolve a very uncomfortable situation, but the presence of the mandibular nerve poses a few problems. Various are the solutions with which one can obtain good results. I have made recourse to my screws making opportune modifications, namely, lengthening the tip and reducing the diameter down to 1,2 mm., to facilitate the passage in the slender space between the cortical wall and the mandible channel, and avoid the possibility to damage the nerve by the threads (fig. 10).

Naturally, in these cases, radiological exams must be carried out to localize the course of the mandibular channel, and to obtain more precise indications regarding the direction to give the implant.

Having overcome the cortical wall, as customary, one proceeds in the most appropriate direction, leaning the hand graduated drill towards the cortical wall farthest from the channel, slowly and with great caution, stopping before impacting the cortical wall.

The input of the screw cannot cause damage given the slenderness of the tip and its length which does not permit the threads to reach the nerve.

TUBER

In this area the anatomic situation is certainly unfavourable for an implant. Even with the most different systems results have not always been brilliant

To obtain some good results one must not wait for the various cortical walls to already be collapsed, but intervene when the tuberosity presents its proper form once again.

Even the most sophisticated exams cannot always give us the certainty that the implant can be carried out.

Sometimes, even simple devices are enough to obtain good results. With the usual drill technique and after having overcome the cortical wall by about half a centimetre, proceeding stopping the rotation, without forcing, pushing the drill until it encounters resistance, it has penetrated completely. At this point, inserting the screw one realizes that penetrates in such a way that the threads pass the cortical wall, after which, bearing in mind the poor bone mineralization, it will be necessary to push, rotating, until the screw engages in the passage formed by the three cortical walls. The screw, carrying on, is guided by the tip which touching tangentially the walls will lead it to the right position. After insertion, given the anatomic situation, this is the only implant which I leave in place without loading for at least two months, in fact, its position causes the patient no discomfort.

PARALLELISM

Upon reaching the ideal position, not being able to evaluate precisely the length of the screw to insert, one can obtain the exact height of the post, reducing it with a cutter cooled with a water jet. One must prepare the implant to the prothesis bearing in mind that an imprecise parallelism can create problems to the prothesis and to success of the implant itself. Sometimes one can parallel an implant straight away at the end of insertion, by bending, using the stump bender, because during this phase the ischemia produced in the bone part gives a few seconds duration, without provoking damage. In the case of non elimination of the square of the screw, remember to reduce, with a steel bur, the angle necessary to permit the insertion of the stump bender (fig. 11).

Only whit a perfect instrument we can obtain a right angle (fig. 12),

Naturally, everything must be done using one’s common sense according to the case. Naturally, the most perfect parallelism is that carried out first in the laboratory and then in the mouth. The imprint must be taken with an imprint holder and the transfers must be inserted in the model in the correct position. The laboratory will make an acrylic crown fitting the stump perfectly. The modifications for the parallelism will be done on the stump with the acrylic capsule in position. The acrylic crown-cap, now repositioned in the mouth, with relative modifications will act as a guide in order to obtain the same correction as that of the laboratory, using the correct bur with a water jet. It will be necessary for the technician to mark the crown so that the dentist can reposition it exactly in the mouth and copy the corrections made in the laboratory to the chalk stump model.

PROSTHESIS

The implant can be loaded immediately with a provisional prosthesis which must be disarticulated for a long or short period of time according to the situation, informing the patient that he should avoid excessive masticator loading. Personally, I prefer to prosthesis definitively, especially in the aesthetic areas, placing the crown adequately on the labial mucosa, without compressing, leaving the lingual part hygienically to rinse. In this way I have never had to intervene either to substitute the prosthesis (there being no retraction).Some time, for immediate immobilization of the implants, we can use the welding intraoral machine with a little bar can be definitive or provisory (removed before the definitive prosthesis). Important fallow the rules for make a hygienic prosthesis.