A ROOT CHANNEL PIN

Abstract: A root channel pin (3) is intended to be secured in a tooth in order, at its cervical end, to carry a column with a crown. The root channel pin (3) has a longitudinal and centrally disposed bore (11). The root channel pin (3) has a substantially cylindrical circumferential surface (10) and the bore is open at least towards the one end (12).

Description: A ROOT CHANNEL PIN TECHNICAL FIELD 5 The present invention relates to a root channel pin of the type which is intended to be secured in a tooth and carry, at its cervical end, a column with a crown. BACKGROUND ART 0 Root channel pins of the type intimated by way of introduction are previously known in the art. For example, such pins are sold in standardized sizes by Whaledent Scandinavia under the brand name Para Post. These root channel pins have a substantially cylindrical circumferential surface and are produced 1 5 from a suitable alloy in the form of a solid rod which is cemented in place in a tooth prepared for this purpose and which, at its cervical end, serves as a mounting for that column of metal on which the crown of the dental prosthesis is subsequently cemented in place. 20 The application of a root channel pin with column can be carried out in a reliable and efficient manner according to this prior art technique, but, nevertheless wishes for improvements have been expressed in the art. With the design and technique employed in the production of the column on 25 the root channel pin, the treating dental surgeon has no possibility to check afterwards how far the root channel pin extends into the column, for which reason the mechanical strength of the bond between the root channel pin and the column is unknown and, hence, may constitute a risk element. 30 While the working methodology according to this prior art technique is reliable and surgical failures are rare, there is, according to this prior art technique, in practice hardly any possibility of removing a root channel pin which has been V cemented in place, since this is considerably harder than the surrounding f dentin. Thus, it is as good as impossible to drill out a root channel pin without '* 35 causing such serious damage to the surrounding dentin that the mounting in place of a new root channel pin becomes impossible. PROBLEM STRUCTURE Thus, the present invention has for its object to devise the root channel pin intimated by way of introduction so that, with retained (or possibly even improved) mechanical strength, inspection may readily be effected of the penetration depth of the root channel pin into the column and, above all, so that a root channel pin cemented in place can be removed (drilled out) without manifest risk of damage to the surrounding dentin. SOLUTION The object forming the basis of the present invention will be attained if the root channel pin intimated by way of introduction is characterized in that it has a longitudinal bore. Hereby, the major advantage will be afforded that the penetration depth of the root channel pin into the column can readily be checked by insertion of a suitable probe into the bore of the root channel pin. Furthermore, this bore will function as an excellent guide if the need were to arise for drilling out the root channel pin from a tooth. If the bore is centrally placed, mechanical strength will not be impaired. Further advantages will be achieved according to the present invention if the root channel pin is also given one or more of the characterizing features as set forth in append Claims 2 to 6. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The present invention will now be described in greater detail hereinbelow, with particular reference to the accompanying Drawings. In the accompanying Drawings: Fig. 1 is a schematic cross section through a portion of a jawbone with a damaged tooth located therein, the tooth having been fitted with a dental prosthesis employing a root channel pin according to the present invention; and Fig. 2 is a longitudinal, diametric section through one embodiment of the root channel pin according to the present invention. DESCRIPTION OF PREFERRED EMBODIMENT In Fig. 1 , reference numeral 1 refers to a crown on a dental prosthesis, the crown being secured on a column 2 which, in its turn, is cast on a root channel pin 3. The root channel pin 3 is secured in the dental root 4 in a cylindrical bore therein by the employment of a suitable cement. It will further be apparent from the Drawing that the dental root 4 has a root filling 5 which may be effected in a conventional manner by the employment of gutta-percha as a filler material. In the Drawing, the jawbone surrounding the dental root 4 has been given reference numeral 6, and the gum reference numeral 7. It will further be apparent from Fig. 1 that a preparation has been carried out in the cervical region of the tooth, implying that the cylindrical bore intended for accommodating the root channel pin 3 has been given a gently arched and approximately funnel-shaped mouth portion 8 so that thereby the transition region between the column 2 and the root channel pin 3 proper may be made correspondingly gently arched so as to avoid indications of fracture. It will also be apparent from the Figure that the root channel pin extends into the column as intimated by broken lines 9. Fig. 2 shows a diametric longitudinal section through a root channel pin 3 as this may appear on delivery, i.e. before the column 2 has been made ready. It will be apparent from the Drawing that the root channel pin has a circumferential surface 10 which is substantially cylindrical but has, in relation to the size of the root channel pin 3, a rough surface structure such as a fluting, a gently profiled threading, a helical turn or the like. On manufacture of the root channel pin, it is vital for reasons of mechanical strength that the surface structure is not realized by cutting, since this would give rise to indications of fracture in the surface. Consequently, according to the present invention, the surface structure is realized by plastic processing, such as by pressing, rolling or blasting with non-edged or round grained blasting material. For example, a larger blank with a central channel can be rolled or drawn in a drawing die to the correct dimensions and correct surface structure. In the root channel pin 3, there is provided a longitudinal channel 11 in the form of a preferably centrally located circular bore which is open at least towards the one end 12 of the root channel pin. In the opposite end, the root channel pin may be provided with a head or a flattened portion 13 as intimated in the Figure. The purpose of this flattened portion is int. al. to create space for a dimensional marking of the pin. Possibly, the root channel pin may be manufactured in continuous lengths which are cut to intended dimensions, for example when being put to use. In the same way as mentioned above, it is a major advantage if the surface structure of the wall defining the channel 11 is not realized by cutting but by plastic processing, so that indications of fracture can be eliminated as far as possible. The importance in terms of mechanical strength of the surface structure of the channel surface is, however, less than for the outer surface, since the channel surface is located more proximal the neutral line on flexural loading than the outer surface. According to the present invention, it is an advantage if the channel 11 is a through channel, since it can then serve as evacuation route for excess cement on securing of the pin. Those diameter dimensions which, in practice, are used on the root channel pin according to the currently relevant type generally lie in the order of magnitude of between 1.5 and 1.75 mm, but may generally vary within the range of between 1.00 and 2.0 mm. In order that the channel 11 be capable of reliably functioning as a guide for a drill in the event that the root channel pin needs to be drilled out of a dental root (where the surrounding dentin is considerably softer than the material in the root channel pin), the channel 11 should have a diameter of the order of magnitude of between 0.25 and 0.5 mm, preferably about 0.3 mm. Possibly, slightly lower values can also be accepted, on condition that the drill employed on drilling out is of correspondingly suitable dimensioning and design. If the strength properties of the root channel pin or dental prosthesis are studied, it will be found that a small diameter (or transverse dimension) of the channel 11 can, in certain specific loadings, possibly improve the strength properties, but above all no quantifiable deterioration of mechanical strength will occur as compared with a solid root channel pin. However, according as the diameter of the bore is increased in relation to the diameter of the pin, a certain reduction in the level of strength begins to occur. If these strength properties are weighed together with the above-outlined aspects in respect of guiding properties of the bore 11 , it will be found that a suitable relationship between the outer diameter of the root channel pin 3 and the diameter (or cross section) of the bore 11 should be in the range of between 1 :2 and 1 :6. In most cases (depending slightly on the pertinent diameter of the root channel pin), a diameter relationship of between 1 :4 and 1.5 is, however, to be preferred. The construction of a prosthesis as shown in Fig. 1 proceeds largely in the following manner, the precondition being that the tooth has, for example, been broken off approximately flush with the arched mouth portion 8 shown on the Drawing. First, all soft tissue in the tooth is cleaned out, whereafter the nerve channel is filed and root filled with gutta-percha point. This is followed by root evacuation using cylindrical drills of gradually increasing diameter until a suitable diameter of the root channel is reached. As a criterion, it applies that the defining surfaces of the channel must be completely clad in dentin at the same time as the dental root 4 must not be weakened excessively. A diameter of 1.5 or 2.0 mm is often found to be just right. Thereafter, the arched cervical portion 8 is prepared, whereupon an impression pin, preferably of plastic, is passed down into the prepared root channel and an impression is taken of the fracture surface of the tooth and the arched mouth portion 8. On the basis of this impression, the column 2 is manufactured with the root channel pin 3 secured therein. When the unit comprising root channel pin 3 and column 2 has been obtained, the penetration length of the root channel pin 3 into the column 2 is suitably checked, for example by the employment of an appropriate measurement probe. When this check has been carried out and the penetration depth of the root channel pin 3 into the column 2 has been ascertained as being satisfactory, the root channel pin and the column are cemented in place in the dental root. Thereafter, the surfaces of the dental root are prepared about the periphery of the column 2 so that a gently arched contour is obtained. After this preparation, a new impression is taken of the end surface of the dental root 4 and the column 2 and, on the basis of this impression, the crown 1 is subsequently manufactured, whereafter this is cemented in place. If, during this working cycle, once the root channel pin 3 has been cemented in place, any mistake were to be made or if the results otherwise prove to be less satisfactory, the present invention affords a good possibility of repeating the operation without the dental root 4 needing to run the risk of being damaged. In order to remove the root channel pin, the crown and those parts of the column as required for exposing the the central bore 11 of the root channel pin 3 are ground or drilled away. Thereafter, the root channel pin may simply be drilled out of the dental root, employing the bore 11 as a guide during the drilling operation proper. That damage which may perchance occur in such instance to the dental root 4 is so insignificant that in all probability a new root channel pin of the same diameter can be used, but, as a rule there is also the possibility of somewhat increasing the diameter of the new root channel pin so that, for example, an increase may be effected of from 1.5 to 1.75 mm or possibly from 1,75 to 2 mm. Correspondingly, there is the possibility of replacing a dental prosthesis if this were to be damaged at a later date. DESCRIPTION OF ALTERNATIVE EMBODIMENTS In the foregoing, the root channel pin has been disclosed as designed with a substantially cylindrical circumferential surface with an uneven but smooth surface structure in relation to the dimensions of the root channel pin, i.e. a surface structure substantially without indications of fracture. However, according to the present invention there is nothing to prevent the root channel pin from having a slightly conical circumferential surface if desired. Furthermore, the root channel pin need not, naturally, be provided with the head or flattened portion 13 schematically illustrated in the Drawing, but the end located in this position may instead be of a design corresponding to the design of the end 12. Of course, the head 13 may also be in the form of a surrounding bead at the end of the pin. In order to permit a dimensional marking, the root channel pin may be provided, in its apical end, with a number of surrounding rings or beads with soft contours, the number of rings or beads indicating the relevant dimensions. Such rings or beads (possibly also grooves) may also be given the same function as or be included in the uneven surface structure. Further modifications of the root channel pin may be effected according to the present invention, without departing from the spirit and scope of the appended Claims.

Claims: CLAIMS 1. A root channel pin of the type which is intended to be secured in a tooth (4) and, at its cervical end, carry a column (2) with a crown (1), characterized in that it has a longitudinal bore (11). 2. The root channel pin as claimed in Claim 1 , characterized in that it is of the prefabricated type with a substantially cylindrical circumferential surface (10). 3. The root channel pin as claimed in Claim 1 or 2, characterized in that the bore (11) is disposed centrally in the root channel pin (3) and is open towards at least the one end (12). 4. The root channel pin as claimed in Claim 2 or 3, characterized in that the ratio between the outer diameter of the root channel pin (3) and the diameter of the bore (11) is in the range of between 1 :2 and 1 :6. 5. The root channel pin as claimed in any one of Claims 2 to 4, characterized in that the ratio between the outer diameter of the root channel pin (3) and the diameter of the bore (11) is in the range of between 1:4 and 1:5. 6. The root channel pin as claimed in any one of Claims 1 to 5 , characterized in that it has, on its circumferential surface (10) a substantially transverse fluting, thread or uneven surface structure in relation to the size of the root channel pin (3).

Inventors: HANSSON LARS, HANSSON, LARS
Applicants: HANSSON LARS, HANSSON, LARS
Application year: 1992
Main classification: A61C13
IPC codes: A61C5, A61C8, A61C13