Dental sleeve and its use
BACKGROUND OF THE INVENTION 
     Various types of dental caps are known as a carrier or base on which porcelain veneer is applied, and therefore being a very important component of the finished dental crown. The crown retainer has predominantly been modelled in wax and cast in a fusing alloy. 
     In a new process according to European Patent Specification No. 104,320, round discs (FIG. 1) are cut out from a metal foil, prefabricated as star-shaped umbrellas (FIG. 2) and subsequently adapted manually to the tooth stump by means of special tools. 
     Furthermore, German Patent Specification No. 3,511,847 discloses a conical stove-pipe made of metal foil, in which several folded-out portions having a trapezoidal cross section are arranged over the periphery thereof; the stove-pipe, after being adapted to the tooth stump or model, has a three-layer outer surface at least in an edge region thereof, that is to say in the subsequent cervical region. 
     However, manual shaping is time-consuming, is subject to considerable fluctuations attributable to the individual performance thereof by the dental technician, and causes uneven folding leading to a large loss of mechanical strength. Random or angular folding results in stresses in the ceramic mass. In general, the production tolerance of the materials associated with manual shaping is very high because such must be manipulated by different dental technicians; material tests have shown that the laborious folding by hand of the umbrella or stove-pipe results in uneven inner faces which fail to form plane diffusion surfaces. The subsequent diffusion of the layer of pure gold by fusion to form a compact closed cap is often incomplete. The results are edge deformation, inaccuracy of fit and ceramic chipping. 
     According to German Offenlegungsschift No. 3,523,000, a metal foil which lays itself automatically against the tooth stump as soon as a force K is exerted on it from outside is used (FIG. 3). Under the effect of the above-mentioned force, the metal foil lays itself onto the surface of the tooth stump 1, linear vertical folds 2 being defined at equal distances from one another (FIG. 4). The number of loop-shaped folds and the interspaces are calculated so that, for example, a double folding strip 3 (FIG. 5) or a strip-like vertical strut 4 (FIG. 6) is obtained. 
     Accordingly, the tooth-crown retainer thereby formed consists of one or more metal layers, depending on the folding pattern and the arrangement in the pattern. Like the above-mentioned caps according to EP No. 104,320 and DE No. 3,511,847, at its lower edge or at the gingival margin, that is to say precisely where it is to provide a tight seal, it has a thickness which is irregular because of the folds, and this has a disruptive effect especially in the cervical and labial region and can lead to deformations in the subsequent dental crown and consequently to instability or only partial accuracy of the fit. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a new dental sleeve that does not have the disadvantages described above, to be used as a carrier for the porcelain veneer of a composite ceramic crown. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following the preferred embodiments of the invention will be described with reference to the accompanying drawings in which: 
     FIGS. 1-6 illustrate the prior art, 
     FIG. 7 illustrates a first type of a conventional tooth stump, 
     FIGS. 8a and 8b are a side view and a perspective view of a second type of a conventional tooth stump, 
     FIGS. 9a and 9b are a side and a front view of a third type of a conventional tooth stump, 
     FIG. 10 shows a first embodiment of the invention as applied to the tooth stump of FIG. 7, 
     FIG. 11 shows a second embodiment of the invention as applied to the tooth stump of FIGS. 8a/8b, 
     FIG. 12 shows a third embodiment of the invention as applied to the tooth stump of FIGS. 9a/9b, 
     FIG. 13 is a perspective view of a sleeve before it is assembled by spot welding, 
     FIG. 14 is a sectional view of a sleeve mounted on the corresponding tooth stump, 
     FIG. 15 is a sectional view of a further embodiment of the sleeve mounted on the tooth stump, 
     FIG. 16 is a side view of the sleeve for producing a composite ceramic crown, 
     FIGS. 17 to 21 are perspective views of other embodiments according to the present invention, 
     FIG. 22 shows four different successive steps in a method of using the sleeve, and 
     FIG. 23 shows a step of heating the sleeve for facilitating the diffusion of the gold layer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The new dental sleeve according to the present invention can be used directly on tooth stumps having conventional anatomical shapes (FIGS. 7, 8a, 8b, 9a and 9b). 
     The sleeve according to the invention consists of a composite foil having a cylindrical form (FIG. 10), a cylindrical bottom and lingually shaped conical top (FIG. 11), or a lingually and laterally conical shape (FIG. 12). In terms of material, it consists of at least two layers, the inner layer, and optionally also the outer layer when three or more layers are employed, consisting of fine gold or a gold alloy, while the other layer or layers consist of platinum, palladium, silver, indium or iridium or of an alloy or alloys comprising at least two of these metals or at least one of these metals and gold or of a slightly reduced fusing alloy. The above-mentioned shape of the sleeve is established by means of spot welds 5 on the inner fine-gold or gold-alloy layer on the two narrow sides of the composite foil, while the height and circumference of the sleeve are selected in conformity with those of the tooth stump or model to be enclosed. 
     However, until recently it has been virtually impossible to bond gold foils or metal foils coated with gold or with gold alloy to one another by means of spot welding. When conventional welding appliances having copper electrodes were used, a hole formed at too high a voltage, whereas welding did not take place at too low a voltage. Since, in the present dental sleeve, the spot welds of the precious-metal composite foil are a constructional requirement and the welding technique for this requirement had to be developed, the present invention could not be derived from the dental caps of the patent specifications mentioned in the introduction. 
     The invention is further described in detail below. 
     The composite foil advantageously has a total thickness of approximately 0.06 mm. It is a rolled sandwich foil, of which at least one layer (depending on the manufacturing company, i.e. gold and silver parting institutions) generally consists of an alloy comprising two or more of the metals platinum, palladium, silver, indium, iridium and gold or of a slightly reduced fusing alloy. A slightly reduced fusing alloy refers to an alloy comprising at least 50% of fine gold. In most cases, however, there are more than only one such layer, resulting in a laminate; the single layers, then, may consist of metals or alloys different than those mentioned above. One or both surfaces of the above-mentioned layer or laminate are covered with a fine gold layer or a gold-alloy layer; these can also be fine-gold granular layers. 
     The composite foil, for instance, may have in the following composition: 
     1st layer: fine gold 
     2nd layer: alloy of Au, Pt, Pd and Ag, e.g. Au 80%, Pt 10%, Pd 5% and Ag 5% 
     3rd layer: alloy of Pd, Ag and Au or Pd, Ag and Ir, e.g. Pd 55%, Ag 5% and Au 35% or Pd 80%, Ag 12% and Ir 8% 
     4th layer: same as the 2nd layer 
     5th layer: fine gold 
     To produce the dental sleeve, the foil is first cut into rectangular pieces, the width and length of which correspond to the height and circumference of the sleeve or the tooth stump or model to be enclosed, plus the weld segment 6. The cut pieces are then shaped into cylinders on specially adapted tools, the edges of the narrow sides not overlapping, but resting against one another at the outside (FIG. 13), so that the inner gold layer or gold-alloy layer on one narrow side and the same layer on the other narrow side rest on one another. The edges of the narrow sides, arranged in this way, are then joined to one another over the height of the cylinder by means of spot welding (FIG. 10). 
     The importance of the spot welding has already been stressed. It is advantageously carried out by means of spot-welding appliances designed specifically for welding these components by having wolfram (tungsten) electrodes. However, spot welding by the use of laser beams is also possible. In general, the welds are made and the welded segment 6 is disposed on the lingual side 7 of the tooth stump (FIG. 14). 
     To produce dental sleeves having the second shape mentioned above, that is to say cylindrical at the bottom and lingually conical at the top (FIG. 11), the spot welding is carried out in the lower part of the cylinder only, the cylinder is pressed, above the welded part, against the lingual side of the tooth stump or model so that the upper part of the cylinder acquires a conical shape, and the protruding edges are joined together in the upper unwelded part by spot welding along the incline surface defining the cone. 
     When dental sleeves having the third shape mentioned above, that is to say the lingually and laterally conical shape (FIG. 12), are to be produced, then, in addition to the steps mentioned above, one or two protruding folds 8 will be formed at one end or at both ends of the transverse axis by drawing in the upper part and pressing it together (FIG. 15), and the protruding fold or protruding folds will be cut off to make fusion diffusion easier in the production of the composite ceramic crown. 
     Thus, prefabricated dental sleeves are obtained, and have one of three above-mentioned shapes illustrated in FIGS. 10, 11 and 12, the height and circumference of which correspond to those of a particular tooth-stump size chosen and which can be fabricated in the form of models having a range of dimensions. The sleeves will fit flush around the cervical stump part (preparation limit), with an excess length in relation to the lowest cervical preparation point of 1.5 to 2.0 mm. 
     Each model within a range thus represents a standardized collar, the circumference of which will correspond to the cervical part of the particular tooth stump. The circumference of the cervical part can be measured by means of a dentimeter; the suitable model is then selected from the various models on the basis of the measurement obtained. 
     According to the invention, these dental sleeves are used for producing composite ceramic crowns, by carrying out an accurate matching of the dental sleeve to the dimensions of the tooth stump and at the same time bending the upper edges of the sleeve towards each other, so that the upper orifice is closed. For this purpose, cut-outs 9 are made in the upper marginal portion of the cylinder (FIGS. 16 and 17) and the remaining protruding portions 10 are bent against the center of the sleeve (FIG. 18). In the sleeve having the conical shape, the sides 11 of the sleeve are bent towards each other in the upper part (FIGS. 19 and 20) and the remaining opening is then closed according to a known procedure (FIG. 21). If the porcelain jacket provided on the sleeve is too thick in relation to the height of the tooth stump to ensure the satisfactory static behavior of the tooth crown, the upper edges can be drawn together into an incisal fold 12 (FIG. 22). If appropriate, the mesial and distal sides of the sleeve are also drawn together to form a fold (FIG. 15) or folds. If only the inner layer of the dental sleeve consists of fine gold or a gold alloy, in addition a corresponding outer layer is applied to the sleeve, advantageously by means of an appropriate paste. The dental sleeve matched in this way is then heated to a temperature of approximately 1030° to approximately 1080° C., preferably in a gas flame 13 (FIG. 23) or in an oven, for diffusion of the fine-gold layers or gold-alloy layers by fusion. An adhesion promotoer or a binder for the porcelain veneer is then coated on the dental sleeve and fused thereon, and the ceramic mass is applied to the dental sleeve and fused to it. 
     Before the dental sleeve is used, a precondition exists in which the model stump is to be trimmed and a groove is to be made exactly underneath the preparation limit, followed by subsequent cylindrical filling with a special blocking-out plastic (for example, Uniblock or Zappite). Any recesses in the tooth stump will also be filled. This preparation phase is well known to the dental technician. 
     It is preferable to proceed particularly in accordance with the following working steps. 
     (a) Adapting tihe sleeve, while at the same time allowing for an excess length of 2.0 to 3.0 mm, to the incisal tip 12 of the model stump (FIG. 22). 
     (b) Should further adaptation be necessary in the cervical peripheral region of the sleeve, an individual bracing fold 8 (FIG. 15) can be made on the mesial or distal side of the model stump, that is to say a sleeve selected with too large a circumference can thus be matched closely to and flush with the preparation limit. 
     (c) Accurate excision of the cervical edge seal part by means of micro-shears to a residual part of approximately 1.0 mm below the preparation edge. 
     (d) By the use of a conventional hammer press (swager) with a maleable base foil of approximately 0.015 to 0.020 mm, adaptation is carried out by means of 2 to 3 moderate hammer blows. 
     (e) Vertical diffusion by fusion in a Bunsen burner while held with a special wire holder 14 shown FIG. 23 or in an oven. 
     (f) Fine adjustment according to a process already known. 
     (g) Acid treatment or sand-blasting with aluminium oxide having very fine granules, degreasing. 
     (h) Fusing on of a conventional adhesion promoter (bonder, masking gold, bonding gold), fine-film baking (wash baking), first baking, dentine baking, etc; fusing on is carried out in the same way as with a cast cap. 
     The advantages arising from the invention can be summarized as follows: 
     Extremely efficient production, in terms of time, of a precious-metal carrier sleeve for carrying subsequently formed composite ceramic crown, doing away with the conventional cast cap. 
     A single uniform layer in the labial and cervical region and therefore a better cervical edge seal and a cosmetically perfect appearance. 
     The capability of the upper incisal part of the sleeve to be pressed into an incisal fold 12 (FIG. 22) thereby, according to the porcelain and manufacturer&#39;s recommendation, ensuring a static support of the porcelain veneer when the stump is too short in relation to the height of the tooth crown. 
     Economical consumption of precious metal because of exactly sized precut pieces for the particular stump size. 
     Cut pieces, the three above-mentiond basic of which are matched to the particular stump shapes.