Tension gripper for ondotological use

Abstract: In a tensioning gripper (1) with ring (2) and coaxially arranged rotary pin (3), both being provided with a slot (5, 4) suitable for receiving the matrix (6) to be tensioned, the slot (4) of the rotary pin (3) has a symmetry plane (γ) parallel to the longitudinal axis (h) of the rotary pin (3). The sides of the slot are composed by two angled portions (4', 4''), said sides being arranged mirror-like on both sides of said symmetry plane (γ) and both portions (4', 4'') are converging towards said longitudinal axis (h) of said rotary pin (3), the two vertices (B, C) of the portions (4', 4'') being opposite and adjacent one to the other. Such a slot allows an easy introduction and gripping of the matrix until, by rotating the pin, the matrix is held and tensioned.

Description: The present invention relates to a tensioning gripper for gripping and tensioning a matrix used for dental reconstruction in odontology, in particular of the type suitable for being actuated by means of a tensioning device similar, e.g., to the device disclosed by the same Applicant in prior patent application PCT/EP93/02940 or US-A-4 396 374, which forms the basis for the preamble of claim 1. Such a type of tensioning gripper consists of an external ring of relatively rigid material coupled to a coaxial rotary pin. Both the ring and the pin are provided with one or more slots which are suitable to receive the matrix to be tensioned, which is driven by the rotary pin, winding it and remaining fastened to it. Due to the small size of the tensioning gripper on which the operator must work, sometimes introducing the matrix into the slot of the rotary pin results to be difficult, and it is still more difficult to keep said matrix fastened to its interior in a reliable enough way in order that it may be driven by the rotary pin without slipping out or getting disengaged, thus obliging the operator to repeat the whole procedure. It is the object of the present invention to present a tensioning gripper with which it is easy for the operator to introduce the matrix to be tensioned and which secures the matrix until it is winded up for tensioning. This object is attained with a tensioning gripper according to claim 1. The functional features of the tensioning gripper according to the present invention and the advantages which can be obtained by means of it are disclosed hereinafter in greater detail by referring to the accompanying drawings. Figure 1 shows a perspective view of the rotary pin of a preferred embodiment of the tensioning gripper according to the present invention, Figure 2 shows a perspective view of the ring of the same embodiment of Figure 1, Figure 3 shows a perspective view of the whole tensioning gripper according to the present invention, with a matrix entered in it, and Figure 4 shows a partial plan view of the tensioning gripper with the ends of the matrix following the rotation of the rotary pin. The above Figures only represent a preferred embodiment which shall not be construed as being binding or limitative relatively to other embodiments in which the several components have different shapes or sizes. In Figure 1 is shown a rotary pin 3 of an exemplary tensioning gripper according to the present invention which is similar to the rotary pins known from the prior art as regards both its outer shape and the small crown gear 9 suitable for getting coupled with an appropriate tensioning apparatus. The throughgoing slot 4 of the pin 3, on the contrary, is different, and, as one will observe on considering Figure 1 together with Figure 3, the slot 4 is symmetrical relative to a plane γ passing through, resp. being arranged parallel to the longitudinal axis "h" of the pin 3 and is composed of two sides having each two angled portions 4', 4'' and being arranged substantially mirror-like. The portions 4', 4'' converge towards longitudinal axis h of the pin, with each pair of adjacent portions generating a vertex B, resp. C. The gap between the two vertices B and C is smaller than the double thickness of the matrix for being able to clamp the ends of the matrix, whereby the sides are slightly resilient. According to the preferred embodiment as displayed in the accompanying Figures, the angle α formed by two mutually opposite convergent portions of the sides is approximately 30°, see Fig. 4. By suitably dimensioning slot 4 the introduction of the matrix 6 is made easier thanks to said sides diverging outwards, and furthermore the result is obtained that the matrix 6, after having been pushed beyond the longitudinal axis h of pin 3, remains gripped in this position by the effect of the pressure applied by the sides at the vertices B and C. All the above allows the process of matrix 6 winding and thus tensioning to be started more reliably and rapidly. In order to further increase the retaining engagement of the matrix 6 on the rotary pin 3, the inner surface of the ring 2 of the tensioning gripper 1 can be provided with a groove 7, facing the rotary pin 3 (Figures 3 and 4). By providing such a groove 7 in a diametrically opposite position relatively to the position of slot 5, which is one of the plurality of slots provided through the ring 2 for the matrix to enter (in the embodiment displayed herein, only one slot is present). If the matrix 6 is introduced until it comes to rest against the concave portion of groove 7, the result will be obtained that, after even a limited initial rotation of the rotary pin 3 took place, for example in the direction of arrows A, the end portions of the matrix 6 which initially protruded into groove 7 are so bent during the rotation (Fig. 4), as to come to lay inside the gap existing between the inner wall of the ring 2 and the outer surface of the pin 3, thus forming an edge 6' which prevents the matrix 6 from slipping in opposite direction to its entering direction in the tensioning gripper 1. By operating in that way the matrix 6 can be provided with an effective mechanical retaining means, more reliable than as offered by simple friction, or equivalent means. By providing a tensioning gripper 1 in which both the groove 7 on the ring 2 and the particularly shaped slot 4 of the rotary pin 3 are provided, an advantageous result is obtained as regards the rapidity and reliability of the whole matrix tensioning procedure. In a further improvement there is provided for an elastic, limitedly forced coupling between the ring 2 and the rotary pin 3. Instead of producing such a coupling by means of expensive precise dimensions during the moulding step of above said components, which is difficult to control precisely, the inner surface of ring 2 is provided with a plurality of peripherally arranged protrusions 8i (Figure 2). These protusions are plastically deformable to a prefixed extent when, between them, the rotary pin 3 having an outer diameter which is slightly greater than the diameter of the externally tangent circumference of said protrusions 8i is introduced. As a consequence of that, said protusions 8i are slightly deformed by compression and act as support means for the rotary pin 3. As already briefly mentioned, it is evident that one skilled of the art can envisage other embodiments which are different from those disclosed and represented up to here.

Claims: Tensioning gripper for a matrix tensioning apparatus for odontological use, comprising a ring (2) and a rotary pin (3) coaxially arranged inside said ring, with both said pin and said ring being provided with at least one slot (4, 5) suitable for receiving the ends of the matrix (6) to be tensioned, wherein the slot (4) through the rotary pin (3) has a symmetry plane (γ) parallel to the longitudinal axis (h) of said rotary pin (3), characterized in that each side of the slot (4) is composed of two angled portions (4', 4''), said sides being arranged mirror-like on both sides of said symmetry plane (γ) and both portions (4', 4'') converging towards said longitudinal axis (h) of said rotary pin (3), the vertices (B, C) of the portions (4', 4'') being opposite and adjacent one to the other. Tensioning gripper according to claim 1, in which the corresponding convergent portions (4'; resp. 4'') of the sides of said slot (4) form, between them, an angle (α) of approximately 30°. Tensioning gripper (1) according to claim 1 or 2, characterized in that said ring (2) is provided, on its inner surface facing said rotary pin (3) and in a diametrically opposite position to the position of a slot (5) provided in the ring, with a groove (7) at least extending throughout the height of that portion of ring (2) which is frontally opposite to one of said portions (4', 4'') which constitute said slot (4) of the rotary pin (3). Tensioning gripper (1) according to any of claims 1 to 3, characterized in that the inner surface of the ring (2) to be coupled with the rotary pin (3) is peripherally provided with a plurality of protrusions (8i) which are plastically deformable to a prefixed extent when said rotary pin (3) is introduced between them.

Inventors: WEISSENFLUH BEAT A V, WEISSENFLUH HANS V, WEISSENFLUH, BEAT A. V., WEISSENFLUH, HANS V.
Applicants: WEISSENFLUH HAWE NEOS, HAWE NEOS DENTAL DR. H. V. WEISSENFLUH AG
Application year: 1995
Main classification: A61C5
IPC codes: A61C5