Holder

A holding device allows for tightening of a screw joint in a bone-anchored dental implant without imposing stress upon the tissue surrounding the implant. The device includes a first part which is rotationally locked in relation to the implant and a second part in the form of an arm which is rigidly connected to the first part, extends substantially perpendicularly thereto and is provided with a holding portion which interacts with the stationary part of the tightening tool to prevent undesirable rotary movements.

FIELD OF THE INVENTION 
The present invention relates to an apparatus adapted for tightening of a 
screw joint in a bone-anchored dental implant without imposing on the 
tissue surrounding the implant. 
BACKGROUND ART 
It is already known to anchor permanently a dental prosthesis in the jaw 
with the aid of screws made of titanium implanted in the jawbone. The 
screws are anchored in holes in the bone so that the upper part of the 
screw is situated on a level with or immediately below the upper surface 
of the jaw bone. The screw is then covered over with a mucous membrane 
flap and is left unstressed for a rest period of 3-6 months in order that 
the bone grows onto and form a unit with the implanted screw. After the 
rest period, the screw is uncovered and a distance element, also 
preferably made of titanium, is arranged on the screw, whereupon a dental 
prosthesis is anchored on the distance element. 
As a result of the high oral stresses during biting and chewing, dental 
prostheses have in general been anchored by means of a bridge construction 
with the aid of a number of fixtures, for example six pieces. If any of 
the screws comes loose, those remaining then ensure that the secure 
anchoring is still maintained. 
In recent years, however, efforts have been made to provide secure 
anchoring of individual teeth. In the case of such a single-tooth 
replacement, one single screw is to be able to absorb all arising oral 
stresses such as torsion, stretching and pressure forces. Especially 
important in this respect is the torsional load which tends to loosen the 
screw joint between distance screw and screw (fixture). For single-tooth 
replacements which are subjected the high oral stresses, it is of course 
important that the design and anchoring of the screw and the distance 
element are the best possible in order to prevent the screw joint from 
being loosened. In the Swedish Patent 87 01949-3, a screw joint anchoring 
is described which affords an increased anchoring stability compared with 
previously known dental prostheses of this type. The screw joint anchoring 
is designed in such a manner that the dental prosthesis is unlikely loosen 
and has great capacity for transmitting stresses. 
It is, however, not only important for the design of the screw and the 
distance element to be the best possible. The operational technique and 
the mounting of screw and distance element are also to be optimal. As a 
result of the torsional load, it is important for the distance screw to be 
tightened firmly. In this connection, the entire tightening torque comes 
to stress the screw which then risks loosening if special measures are not 
taken. According to the abovementioned Swedish Patent 87.01949-3, the 
distance element is provided with an inward, internal holder, in which 
fits one part of a double screwdriver adapted for the purpose fits. The 
other part of the double screwdriver is designed as a conventional 
screwdriver and fits the screwdriver slot in the head of the distance 
screw. 
The distance element is arranged on the firmly rooted screw (the fixture) 
in such a manner that first the spacer is locked firmly against the 
fixture with the aid of the distance screw which is screwed down into a 
bore in the fixture with the aid of the double screwdriver, in doing which 
it is ensured that the legs of the tubular part engage with recesses in 
the spacer and the other part of the screwdriver is passed through the 
tubular part so that it engages in the screwdriver slot in the screw head 
of the distance screw. Upon mounting, it is endeavoured to apply to the 
screwdriver parts torques of the same size but in opposite directions. 
This can, however, be difficult to achieve in practice, especially in the 
case of high tightening torques. 
The double screwdriver described above is of course applicable only in the 
case of manual tightening of the screw joint. There is, however, a desire 
to be able to carry out the tightening mechanically, that is to say with 
the drilling equipment available at the time of the dental operation. This 
facilitates the mounting for the dentist and also has the advantage that 
the tightening torque can be controlled. 
SUMMARY OF THE INVENTION 
The aim of this invention is to provide an apparatus which makes possible a 
mechanically controlled tightening of the screw joint of a dental implant 
without any torque being absorbed by the bone, so that the screw (the 
fixture) remains unstressed during mounting itself. 
A preferred embodiment of the invention is shown schematically in the 
attached drawings in which

FIG. 1 shows the hand-piece 1 of a drill of a known type which is used in 
connection with dental implant operations. The drill is used both for 
drilling of holes in the jawbone and for tightening of screw joints in the 
implant system. In this case, the drill is provided with a screwdriver 2 
which is intended to interact with the screwdriver slot in the distance 
screw 3 which firmly locks the distance element against the upper part of 
the screw (the fixture), see also FIG. 3. In FIG. 1, the threaded part 4, 
which is intended to engage with an internally threaded recess in the 
upper part of the fixture for locking the distance element against the 
fixture, protrudes from the distance screw. 
FIG. 1 also shows an apparatus 5 which interacts both with the distance 
element and with the hand-piece of the drill. The apparatus consists of a 
first, tubular part 6, the base of which connects to the distance element 
and through which the movable part of the drill, the screw-driver, runs, 
and a second, fork-shaped part 7 which interacts with the stationary part 
of the drill, the hand-piece 1. 
As more clearly seen from FIG. 3, the apparatus 5 functions as a holder at 
the time of tightening of the screw joint. The tightening torque does not 
come to stress the bone via the fixture since the fork-shaped part 
interacts with the hand-piece. An undesirable rotation of spacer and 
fixture is prevented by the legs of the fork-shaped part. 
In FIG. 2, a first embodiment of the apparatus 5 is shown. It comprises a 
first, tubular part 6, the base part of which is provided with an internal 
space 8 adapted to the spacer of the distance element in such a manner 
that the spacer is locked and cannot rotate in relation to the tubular 
part 6. The internal hole 9 has such a diameter that the screwdriver tool 
of the drill can rotate freely in this space. 
The tubular part 6 is provided with a fork 7, the base 7' of which extends 
essentially perpendicularly to the center line 9' of the tubular part, and 
the legs 10 of which are essentially parallel to the center line 9'. The 
fork is U-shaped and its bottom 11 forms a support for the hand-piece of 
the drill, and the legs 10, 10' are of such a length that they exceed the 
diameter of the hand-piece, see FIG. 2a and FIG. 1. 
In FIG. 3, a second embodiment of the apparatus 5 according to the 
invention is shown. In this case is shown how the device 5 interacts, on 
the one hand, with the screwdriver tool 2 of the drill and, on the other 
hand, with the distance element of the dental implant, in the form of a 
spacer 12 and a distance screw 3. The end surface 13 of the tubular part 6 
bears against the shoulder located on the spacer 12 and the recess 8 
corresponds to the cylindrical, hexagonal upper part of the spacer so that 
a rotation of the spacer in relation to the tubular part 6 is prevented. 
The distance screw 3 is provided in a known manner with a lower threaded 
part 4 intended to engage with an internally threaded recess in the upper 
part of the fixture for locking of the spacer against the fixture 14 which 
has been marked with broken lines in the Figure. The distance screw also 
has a waist 15 and a screw head 16 with screwdriver slot 17, in which the 
screwdriver tool 2 of the drill engages. As mentioned above, the 
tightening torque does not impose stress the spacer 12, and consequently 
the fixture, since this torque is absorbed by the legs 10 of the fork. 
The torque arising upon tightening, the screw tightening torque, gives rise 
to a reaction torque which in the case of normal tightening, tightening 
without holder, has to be conveyed via the hand. This torque then stresses 
the bone via the implant. With the present invention, the reaction torque 
does not have to be absorbed with the hand, but the hand-piece bears 
against one leg of the fork. In this manner, the reaction torque is 
transmitted from the hand-piece to the implant. As the tightening torque 
and the reaction torque are always of identical size but in opposite 
directions, this leads to the tissue surrounding the implant remaining 
unstressed. 
The present invention is not limited to the embodiments which are shown in 
FIGS. 2 and 3. The important aspect is that the device is rotationally 
locked against the stationary part of the tightening tool (the drill). A 
fork with two legs is preferable for this locking since rotational locking 
in both directions can then be achieved and moreover provides a support 
and guide for the tightening tool. In certain cases, however, a single arm 
which extends from the tubular part and interacts with the tightening tool 
can be sufficient.