IMPROVEMENTS IN OR RELATING TO SUBSTRUCTURES FOR BONDING TO SUPPORT STRUCTURES

Abstract: A substructure (19) for a dental inlay, crown, bridge or the like having a roughened surface suitable for bonding to a surface of a support structure is formed by a method comprising bonding granules (20) to a moulding surface (22) of a dental investment model (23) of the appropriate part of the mouth. A mouldable material is applied to the moulding surface (22) so as to cover the granules (20), and the material is then allowed to at least partially set. Finally the material is removed from the moulding surface and the granules are removed from the material so as to leave a substructure having a roughened surface of the required form for bonding to the support structure surface. This technique is particularly applicable to production of roughened surfaces on substructures which cannot be easily etched. One such substructure is a glass-infiltrated alumina substructure such as In-Ceram.

Description: "Improvements in or relating to Substructures for Bonding to Support Structures" This invention relates to the production of substructures having roughened surfaces suitable for bonding to support structures, to substructures so formed and to kits for forming such substructures. In the dental field it is known to use glass- infiltrated alumina substrates, such as In-Ceram (Registered Trade Mark) substrates, to form substructures for dental crowns of exceptionally high strength. Such substructures are generally coated with porcelain to provide both biocompatibility and aesthetic matching with existing teeth. The completed crown may be cemented in position within the patient's mouth. However it is important that the crown is cemented in position as securely as possible as it is subject to high loads within the mouth and many dental problems are caused by dislodgement of such crowns. Whilst such bonding is considerably improved if the surface of the substructure to be bonded is roughened prior to cementing, it is difficult to produce such a roughened surface by conventional techniques, such as acid etching, in view of the hardness of the material from which the substructure is formed. For the same reason it has proved difficult to produce dental inlays or crowns in this manner. It is an object of the invention to provide a novel technique capable of applying to such substructures a roughened surface suitable for bonding to the required support structure. According to the present invention there is provided a method of producing a substructure having a roughened surface suitable for bonding to a surface of a support structure, which method comprises bonding granules to a moulding surface constituted by or corresponding to the support structure surface, applying mouldable material to the moulding surface so as to cover the granules and allowing the material to at least partially set, and removing both the material from the moulding surface and the granules from the material so as to leave a substructure having a roughened surface of the required form for bonding to the support structure surface. This technique is particularly applicable to production of roughened surfaces on substructures which cannot be easily etched. One such substructure is a glass-infiltrated alumina substructure such as In-Ceram. The moulding surface will generally be a model of the support surface to which the substructure is to be bonded, although it may in certain circumstances be the support surface itself. The model is preferably an investment model. The granules are preferably elongate retention chips of small size, that is with maximum dimensions which are in the range 0.05 to 0.80mm, and which are most preferably about 0.2mm, and are advantageously bonded to the moulding surface by a thin layer of adhesive, such as a mixture of polyvinyl acrylate and water, such that the granules project from the adhesive layer and provide a major portion of their surface area and/or a series of undercuts proud of the adhesive layer for coating by the mouldable material. Furthermore the granules are preferably removed from the material by heating so as to cause the granules to carbonize. The method has particular application to the production of substructures for dental inlays, crowns, bridges and the like in which case the granules are bonded to a moulding surface of a dental investment model of the appropriate part of the mouth. However the method may also be used in the repair of bone and other structures. The invention also provides a kit of parts for producing a substructure having a roughened surface suitable for bonding to a surface of a support structure, the kit comprising granules for bonding to a moulding surface constituted by or corresponding to the support structure surface, an adhesive for effecting such bonding, and a mouldable material for applying to the moulding surface so as to cover the granules prior to allowing the material to at least partially set, the granules being removable from the material and the material being removable from the moulding surface so as to leave a substructure having a roughened surface of the required form for bonding to the support structure surface. The mouldable material may be omitted from such a kit if the kit is to be supplied for use with a specified mouldable material. The invention further provides a substructure, such as a dental inlay, crown, bridge or the like, having a roughened surface suitable for bonding to a surface of a support structure, the substructure having been formed by the above-described method. In order that the invention may be more fully understood, several methods in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures 1 to 8 are explanatory diagrams illustrating a method of producing a dental inlay; Figure 9 is an explanatory diagram illustrating a method of producing a dental crown; Figures 10 and 11 are explanatory diagrams illustrating a method of producing a Maryland bridge; Figures 12 • and 13 are explanatory diagrams illustrating a method of producing an inlay-retained bridge; Figures 14 and 15 are explanatory diagrams illustrating two alternative methods of repairing a bone fracture; and Figure 16 is an explanatory diagram illustrating a method of repairing a jug. In order to extend the use of the In-Ceram system to Maryland bridges and porcelain inlays, experiments have been conducted with various means of etching to produce good positive retention when cemented within the mouth. However no satisfactory solution to the problem has been found until now as even hydrofluoric acid will not etch the structure. A consistent method of producing an In-Ceram inlay with good positive retention will now be described with reference to Figures 1 to 8. Figure 1 shows a section through a part 1 of a plaster cast 2 (see Figures 2 and 3) of the portion of a patient's mouth containing the cavity within which the inlay is to be fitted. The part 1 corresponds to the tooth containing the cavity and includes a corresponding cavity 3. In an initial preparation step a known die spacer material 4 is applied to the vertical internal walls 5 only of the cavity 3 in a layer which terminates about 1 mm short of the occlusal surface to provide an uncoated region 6. This allows space for the cement to be used in bonding the inlay in position in the mouth.' The base 7 of the cavity 3 is left uncoated. A duplicate is then taken of the relevant part of the cast 2 using conventional techniques involving application of a block 8 of plasticine containing a moulding material such as Dreve Dublisil A/hyrophill. Referring to Figure 4 two models are then cast from the Dublisil impression 9 so formed by pouring a moulding material 10 into the impression 9 to produce a model including a cavity 11 (see Figure 5) formed by a projecting part 12 of the impression 9 which has in turn been formed by the cavity 3 in the part 1 of the cast 2. The first model is produced using Vita In-Ceram Special Plaster as the moulding material which need only be poured into the preparation area. The second model is produced using Vitadurvest with sufficient coverage to ensure good bite registration. In both cases the models, when set, are removed from the impression 9 and cleaned prior to being worked on in a manner which will now be described. Figure 5 shows a section through a part 13 of the first, Inceramvest model which has been worked on by having a 0.5 mm layer 14 of wax applied to its vertical walls 15, and by having its base 16 coated with a very thin adhesive layer 17 of cyanoacrylate cement mixed with acetone in equal parts (or alternatively of polyvinylacetate and water mixed in proportions of 1:5), and a single layer 18 of irregularly-shaped retention chips, such as Bredent retention chips, sprinkled onto the adhesive layer 17 before it sets so that the chips are fixed to the base 16 by the adhesive layer 17 but are not coated by the adhesive layer other than at their lower ends. After this initial preparation, the In-Ceram core 19 has been formed by applying the moulding material to the cavity 11. As may be seen in the explanatory diagram of Figure 5A the retention chips 20 are retained by the very thin adhesive layer 17 so that they provide a series of undercuts 21 and a large uncoated surface area to be covered by the material of the In-Ceram core 19 to provide a good retention pattern. The In-Ceram core is then fired and glassed in the In-Ceramat furnace and blasted in convention manner, the firing having the effect of carbonising the retention chips and aiding removal of the core 19 from the model. Thus it will be appreciated that the In-Ceram core 19, when removed from the model, will have a roughened retention surface where the chips have been carbonised leaving pits as though the surface had been mechanically etched. The next stage of the process is then carried out using the second, Vitadurvest model. Figure 6 shows a section through a part 23 of the second model containing a cavity 24 corresponding to the cavity 11 which has been coated with a very thin layer 25 of Vita 725 glaze powder mixed with 30M liquid ensuring that the mixture does not pool in the corners of the cavity 24. This involves the standard pre-heating of the model as for the production of porcelain veneers, and subsequent firing to a glaze stage. The In-Ceram core 19 has subsequently been bonded to the glazed base 22 of the cavity 24 with a layer 26 of cyanoacrylate adhesive. The core 19 is a loose fit within the cavity 24 by virtue of the fact that the material from which the first model is made shrinks during firing, no such shrinkage occurring with the second model. Referring to Figure 7 Vitaduralpha porcelain is then applied to the cavity 24 to form the required porcelain coating 27 surrounding the core 19. The completed inlay 28, as shown in Figure 8, is then removed from the model 23 in conventional manner and blasted using 60 lbf/in 2 (4 Bar) pressure with 50 micron aluminium oxide blasting medium. The roughened retention surface 29 of the In-Ceram core 19 is blasted with a fine nozzle using 50 micron aluminium oxide at 80 lbf/in 2 , and the internal surfaces 30 of the porcelain coating 27 are etched with hydrofluoric acid or Vita Cerec etch. The inlay 28 is then ready for fitting into the cavity in the patient's mouth using a conventional cementation system, such as Kulzer denthesive with Kulzer twinlock enamel bond using silicoup silane coupling agent. A strong 11 m.p. bond to dentine can be achieved in view of the presence of the roughened retention surface 29 of the In-Ceram core 19 and the etching of the porcelain coating 27. A broadly similar technique may be used to produce shoulderless crowns or bridges which can be fitted using etching cements to ensure a positive bond. Figure 9 shows a crown 32 in the course of production fitted to a model 33 and consisting of a layer 34 of retention chips applied to the model 33 by a very thin layer of cyanoacrylate/acetone adhesive in the manner previously described, a layer 35 of In-Ceram, and a porcelain coating layer 36 (added, as before, after firing of the In-Ceram layer) . In this case only a single, Inceramvest model is required which is prepared by standard techniques except that the model is not coated with In-Ceram sealer. The crown is fired, glassed, blasted and finished in the normal way, and is thereby provided with a roughened retention surface due to carbonisation of the retention chips. A similar technique may be used in the manufacture of In-Ceram Maryland bridges. Referring to Figure 10 an Inceramvest model 40 is prepared with saw cuts 41 and bonded to a ceramic base 42 in conventional manner. The ears 43 and 44 of the bridge are then formed by applying a layer 45 of retention chips to the required areas of the parts 46 and 47 of the model 40 corresponding to the adjacent teeth to which the bridge is to be secured in the mouth, the chips being secured by a very thin layer of adhesive as previously described. Vita In-Ceram sealer is then applied to the pontic area 48 of the model avoiding the ears 43 and 44, and a layer 41 of wax is applied to the proximal sides only of the pontic area 48. An In-Ceram layer 49 is then applied to the ears 43 and 44 in conventional manner as well as to the pontic area (although the layer 49 is omitted in the pontic area in Figure 10 in order to make the figure easier to read) . Figure 11 is a labial view of the completed bridge 51 fitted in the patient's mouth showing the bridge finished in conventional manner with a porcelain coating 50 in the pontic area and the ears 43 and 44 secured by their roughened retention surfaces to the palatal surfaces of the retaining teeth. A technique based on that described with reference to Figures 1 to 8 may also be used for producing inlay-retained bridges, predominantly for fitting to back teeth. Figure 12 is a sectional view of such a bridge 64 taken along the line Y-Y in Figure 13 fitted between two retaining teeth 65 and 66 and Figure 13 is a sectional view taken along the line X-X in Figure 12. The bridge 64 has an In-Ceram core 67 and a porcelain outer layer 68, and each end of the bridge 64 is in the form of an inlay 69 within a cavity 70 in the associated retaining tooth 65 or 66 formed as previously described so as to have a roughened retention surface 71. Alternatively one of the retaining parts may be in the form of a crown and the other retaining part may be in the form of an inlay. The described technique can also be used in applications outside the dental field, for example for repair of bone fractures. Figure 14 shows two In-Ceram plates 52 and 53 applied to a bone 54 in the vicinity of a fracture 55. The plates 52 and 53 are formed with roughened retention surfaces 56 either according to a standard profile or using a model of the actual area of the fracture 55, the surfaces 56 having pits produced by carbonisation of retention chips as previously described. Alternatively, as shown in Figure 15, two cavities 57 each having an arcuate base and parallel sides are formed in the vicinity of the fracture 55, and two In-Ceram inlays 58 having arcuate roughened inner retention surfaces 59 are fitted within the cavities 57. The technique may also be used in a structure which is intended to provide resurfacing, reshaping or realignment of bone to which the structure is applied, by an osteointegration process in which the bone grows into cavities within the structure over the course of time in order to provide a permanent bond with the bone. A similar technique may be used for the production of osteointegrated dental implants. The technique may additionally be used in the mending of fractures in other objects. Figure 16 shows a jug 60 having a crack 61 which has been mended by the application of two In-Ceram substructures 62 and 63 to the inside surface of the jug in the vicinity of the crack 61. The substructures 62 and 63 are formed with roughened retention surfaces in the manner described using the inside surface of the jug itself as a model. Other materials, such as In-Ceram Spinel (Registered Trade Mark) , may be used for the substrate, in place of In-Ceram.

Claims: CLAIMS 1. A method of producing a substructure having a roughened surface suitable for bonding to a surface of a support structure, which method is characterised by the steps of bonding granules (20) to a moulding surface (22) constituted by or corresponding to the support structure surface, applying mouldable material to the moulding surface (22) so as to cover the granules (20) and allowing the material to at least partially set, and removing both the material from the moulding surface (22) and the granules (20) from the material so as to leave a substructure (10) having a roughened surface (29) of the required form for bonding to the support structure surface. 2. A method according to claim 1, wherein the substructure (10) is a glass-infiltrated alumina substructure. 3. A method according to claim 1 or 2, wherein the moulding surface (22) is a model of the support surface to which the substructure is to be bonded. 4. A method according to claim 3, wherein the model is an investment model. 5. A method according to any preceding claim, wherein the granules (20) are elongate retention chips having maximum dimensions which are in the range 0.05 to 0.80mm. 6. A method according to any preceding claim, wherein the granules (20) are bonded to the moulding the granules (20) project from the adhesive layer (17) and provide a surface area and/or a series of undercuts (21) proud of the adhesive layer (17) for coating by the mouldable material. 7. A method according to any preceding claim, wherein the granules (20) are removed from the material by heating so as to cause the granules (20) to carbonize. 8. A method according to any preceding claim, when applied to the production of substructures for dental inlays, crowns, bridges or the like. 9. A substructure, such as a dental inlay, crown, bridge or the like, having a roughened surface suitable for bonding to a surface of a support structure, the substructure having been formed by a method in accordance with any preceding claim. 10. A kit of parts for producing a substructure having a roughened Surface suitable for bonding to a surface of a support structure, the kit comprising granules (20) for bonding to a moulding surface (22) constituted by or corresponding to the support structure surface, an adhesive (17) for effecting such bonding, and a mouldable material for applying to the moulding surface (22) so as to cover the granules (20) prior to allowing the material to at least partially set, the granules (20) being removable from the material and the material being removable from the moulding surface so as to leave a substructure (19) having a roughened surface (29) of the required form for bonding to the support structure surface.

Inventors: BATEMAN RICHARD, BATEMAN, RICHARD
Applicants: BATEMAN RICHARD, BATEMAN, RICHARD
Application year: 1993
Main classification: A61C13
IPC codes: A61C13