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
2) The Hand
Graduated Drill to perfection the hole made by the drill.
3) The Screwing
Instruments.
4) The screws have a length of
The screws for the lower distal area
have a lengthened tip with a diameter of
The screws for the "tuber"
area as an elongated tip which extends to a length of
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
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).
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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
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.