Patent Application
20160113735
See Application Data Sheet.
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1. Field of the Invention
The invention relates to a root canal instrument for preparing a recess for a pivot inside the dental roots.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
The pulpless teeth often require the installation by sealing or screwing of a pivot for supporting a restoration of the crown. To this end, it is known to drill a space in the root canal by means of round drills the cutting of which occurs in rotation by means of contra-angles or handpieces. The preparation is thus round and is performed at the expense of the walls of the channel and does not respect the anatomy of the roots, in particular the flat or curved ones, since these drills are rigid and straight. The rotary implementation of these instruments may result into a weakening of the walls, especially the mesial walls or the distal walls, and may afterwards result into fractures or, during the preparation, into perforations compromising the future of the dental organ. The space created during the preparation of the root canal is then provided with a pivot with a circular cross-section, standardized to the dimensions of the drill, in particular to its round cross-section.
The invention provides a novel instrument, which does not have all or part of the drawbacks of the existing instruments. More specifically, the invention provides a novel root canal instrument characterized in that it includes a working portion extending along a longitudinal axis, a frustoconical casing of the working part having, in a cross-sectional view, a cross-section of the type comprising a front curve portion and a rear curve portion united by two side curve portions, a radius of curvature of the front portion being larger than or equal to a radius of curvature of the upper portion.
The novel instrument, with its cross-section that is no longer circular, but rather more or less flattened, permits to perform preparations in harmony with the root anatomy, in particular with that of the roots that have an ovoid or flattened cross-section and to avoid the weakening of the walls by performing a preparation directed to thicker safety areas of the root. Depending on the shape of the roots, the cross-section of the instrument will be chosen ovoid, elliptical, oblong, or more generally as defined above.
In the instrument according to the invention, the casing as a whole comprises a front face and a rear face united by two lateral faces, the front face and the rear face corresponding to the areas of the casing farthest away from each other; each face extending all along the casing and has, in a transverse plane, a cross-section having the shape of a curve portion, as the case may be, a front portion, a rear portion and side portions, respectively, as defined above.
Preferably, for example for roots having flat zones may be chosen an instrument according to the invention, the two side faces of which are planar.
The instrument according to the invention preferably includes, all along the working part, one or several blades permitting to cut the root canal walls during a reciprocating longitudinal movement of said instrument. Thus, the instrument cuts the dentin of the canal walls during reciprocating longitudinal movements and no longer as a cut by rotation of the instrument. This reciprocating longitudinal movement can be performed manually, the instrument being held between the fingers, or in an automated manner using a contra-angle imparting to the instrument a longitudinal reciprocating movement of variable amplitude as described by Levy in Patent FR 2563101 entitled “Driving head for instruments for endodontic interventions” and published on 1985-10-25. Preferably, the instrument according to the invention is provided with blades reproducing the characteristics of a K-type file, thus active longitudinally in both directions, or reproducing the characteristics of the Hedstroem limes.
The mesial and distal roots of the lower and upper molars have ovoid or flat channels on roots of the same shape with particularly thick buccal walls, slightly thinner lingual faces. We find this peculiarity on the lower and upper premolars or on the lower incisors and the canines. Thus, for making of space for a pivot in this type of root, it is preferable to provide for same at the expense of the thickest wall, i.e. the buccal wall and to a lesser extent at the expense of the lingual or palatal wall, finally to a limited extent at the expense of the mesial or distal walls, in order to prevent a perforation of the wall on the periodontium. To this end, an instrument according to the invention can have, in the working part, deeper and more active blades on the front face and the rear face relative to the blades present on the side faces. Thus, the cutting occurs preferentially on the buccal walls, to a lesser extent on the lingual or palatal wall and finally to a limited extent on the mesial and distal faces.
Longitudinally an instrument according to the invention has for example a 12 mm long active part, the tip being preferably made of foam and generally blunt. This total length of the working part may be more generally within the range from 10 to 16 millimeters, in order to meet uses of instruments on short or long roots.
According to a variant, the instrument comprises at least one helical blade extending from a heel (i.e. the gripping end or the end for connecting to a driving tool) to a tip (i.e. the free end) of the working part of the instrument. According to another variant, the instrument comprises a plurality of blades distributed along the working part, each blade extending in a plane no longer non-parallel to the longitudinal axis and preferably in a plane substantially perpendicular to the axis longitudinal.
Even more preferably, the blade or blades are less deep at the tip than at the heel of the working part. In other words, the depth of the blade or blades increases from the tip of the working part to the heel of the working part. This permits to start the widening of the channel with little active blades, then to increase the force exerted on the wall of the channel as the instrument penetrates into the channel.
Finally, the invention relates to a pivot standardized to the dimensions of the working part of an instrument according to the invention as described above, characterized in that it is accommodated very exactly in the space created in the roots by said instrument.
Such a pivot is preferably made of steel and titanium alloy, or of plastic material, of resin or burn-out material.
The invention will be better understood and further features and advantages of the invention will become clear from the following description of exemplary embodiments of an instrument according to the invention. These examples are given in a non-restrictive way. The description should be read with reference to the attached drawings.
a,
3
a,
4
a,
5
a show cross-sectional views of various examples of the instrument of
b,
3
b,
4
b,
5
b show cross-sectional views of different examples of the instrument of
According to the invention, a frustoconical casing of the working part has, in a cross-sectional view, a cross-section of the type comprising a front curve portion 20 and a rear curve portion 30 united by two side curve portions 40, a radius of curvature 2 of the front portion 20 being larger than or equal to a radius of curvature (3) of the upper portion 30.
The total casing of the working part comprises a front face and a rear face united by two side faces, the front face and the rear face corresponding to the areas of the casing farthest away from each other; each face extending all along the casing and has, in a transverse plane, a cross-section having the shape of a curve portion, as the case may be, a front portion 20, a rear portion 30 and side portions 40, respectively.
In the example of
In the working part of the instrument, blades are formed by machining a solid metal wire, for example of nickel-titanium, preferably with a helix angle of 45° and a positive cutting angle.
This machining may be circular, providing a central core 50 of 30/100th of a millimeter in diameter at the tip of the working part, which ensures deep and active blades on the rounded faces of the instrument and zero on part of the side and divergent faces. In the example of
Starting from the example of
For example, the portions of a circle 20, 30 of the instrument may have a diameter 2, 3 equal on their semi-circle, this provides parallel planar side curves 40 and a globally oblong cross-section of the instrument, as shown in
Or, the instrument may have a cross-section with an ovoid (
Also, the maximum widths (1 and 1′) at both ends of the working part (the tip and the heel) can vary. For example, with maximum widths of 120/100ths to 140/100ths of a millimeter for the heel (1′) and from 60 to 80/100ths of a millimeter for the second (1).
In the example of
As a variant,
The machining occurs by grinding on solid wires or rods made of special steels, based on stainless steel or on an alloy comprising titanium and nickel. For creating the blades, this machining may be circular, it may also be elliptical, which permits to adjust the depth of the blades around the instrument. Once the machining is completed, the instrument may be subjected to a bending of 10° relative to the main axis of the mesial side towards the distal side on its last working third (distal side of the blade), in order to prepare curved channels: this permits to close the cutting angle of the blades on the inner side of the curvature of the instrument and to open the cutting angle on the outer side of the curvature of the instrument; this makes the instrument less aggressive on its inner face and more aggressive on its outer face; this also avoids the rectification of the curvature, hence the root perforations.
According to the invention, a pivot standardized to the working part of the instrument is inserted into the gap left in the root, in order to be sealed therein. This pivot can be formed from materials of different natures: titanium, fiberglass, plastics, resins or burn-out materials. The pivot includes an intra-ductal part and an extra-ductal part. This extra-ductal part can strengthen the restoration of a crown. This extra-ductal part has different shapes and lengths and can be adjusted by grinding.
15 handle
b: cross-section at the heel:
| Number | Date | Country | Kind |
|---|---|---|---|
| 13 01230 | May 2013 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2014/051277 | 5/28/2014 | WO | 00 |
