Artificial Onlay Tooth Crowns and Inlays

Europaisches Patentamt 0 389 461 J European Patent Office (jO Publication number: A1 Office europeen des brevets

EUROPEAN PATENT APPLICATION

@ Date of filing: 20.03.90

© Date of publication of application: S-811 81 Sandviken 1(SE) 26.09.90 Bulletin 90/39 Applicant: Nobelpharma AB © Designated Contracting States: Box 5190 AT CH DE DK ES FR GB IT LI SE S-402 26 Gdteborg(SE)

Artificial onlay tooth crowns and inlays.

@ The present invention relates to artificial onlay increase. tooth crowns or inlays composed of a prefabricated core designed for preparations for onlay tooth crowns or inlays in natural teeth. The core is preferably fabricated from a high strength densely sintered ceramic material by copy milling from a negative reproduction from the prepared cavity to a com- K pacted body or a presintered ceramic material. Dur- ing the copy milling the sintering shrinkage is con- *"sidered by enlargement of the copy milled com- ^pacted body or the presintered body corresponding ^to the sintering shrinkage. The onlay tooth crowns presintered body. After the final sintering the exter- material OOnal surface can be shaped before a veneer Fig.5 '"'is attached to the external surface of the core by e.g. O firing of dental porcelain. To manufacture onlay tooth the method of the ^ crowns or an inlay according to Uj invention decreases essentially the manufacturing time for onlay tooth crowns and inlays and at the same time the strength and the accuracy to shape

Xerox Copy Centre EP 0 389 461 A1

Artificial onlay tooth crowns and inlays

BACKGROUND OF THE INVENTION (porcelain, glass etc) in artificial tooth crowns is their brittleness, which often gives early fracture, This invention relates to accurately shaped ar- and these artificial crowns and inlays must be tificial all ceramic onlay tooth crowns and inlays as replaced more or less regularly. replacement for lost tooth structure. By starting from a negative reproduction of the prepared tooth and from this copy mill the surface which will fit OBJECTS AND SUMMARY OF THE INVENTION into the prepared cavity, a tooth crown or an inlay is obtained which is easier to produce and to lower One object of the present invention is to pro- cost. In addition, the onlay crown and inlay has w vide artificial tooth crowns and inlays, which are higher strength and a more accurate shape. Prefer- easier and accordingly cheaper to make and, in ably the coping is manufactured from a biocom- addition, have higher strength and accuracy to patible, high strength, ceramic material, which is shape. sintered to high density. Another purpose is to make an inlay or an Artificial tooth crowns and inlays made from a 75 onlay tooth crown by using densely sintered, high metal are today manufactured mainly in the follow- strength ceramic material, provided that the de- ing way: A dentist makes a preparation on a tooth, mand of high strength, accuracy to shape (that on which a dental construction is to be fixed in the means compensate for the shrinkage during sinter- mouth of a patient, an impression is made and with ing) can be combined with the demand on the this impression a copy of the preparation is made 20 application of porcelain concerning burning, adher- in gypsum. On this model a dental technician pre- ence, biocompatibility and esthetics. pares a crown in wax. The adjacent teeth must be considered, and the dental technician must have models from the two jaws. A sprue former in wax is BRIEF DESCRIPTION OF THE DRAWINGS fixed on one of the cusps of the wax crown. The 25 wax crown is loosened from the gypsum model. Fig 1 is a natural tooth with an artificial inlay The wax crown with the sprueformer are invested (dotted). This figure explains which cross sections in a metal ring with investment. The wax is burnt are shown by Fig.2 and Fig.3 out and a crown can be cast in a precious or non- Fig.2 is a cross section of a natural tooth precious metal. The cast crown can in certain 30 with an inlay cases be covered by a veneer made of porcelain in Fig.3 is a cross section of a root filled natural order to obtain a colour of the tooth crown similar tooth with an inlay. to the colour of natural teeth. Instead of porcelain Fig.4 is a natural tooth with an onlay tooth plastic material can be used. crown (dotted). This figure explains which cross The fabrication of tooth crowns in glass is very 35 sections are shown by Fig.5 and Fig 6. close to the technique described above with the Fig.5 is a cross section of anatural tooth with difference that after the casting a thin layer of an onlay tooth crown. porcelain is painted on the surface and fired, in Fig.6 is a cross section of a root filled order to give the tooth crown individual tooth col- tooth.with an onlay tooth crown. ours. 40 Tooth crowns fabricated mainly of porcelain DETAILED DESCRIPTION OF THE PREFERRED can be made with conventional dental porcelain EMBODIMENTS technique on a sheet made of a precious alloy. Porcelain crowns and inlays can also be made with Fig.1 shows an inlay in a tooth. In the figure conventional dental porcelain technique on a model 45 the border between the cavity and the inlay is of the abutment. The material in this model has no indicated as I, the axis of the tooth as X. changes in dimension on heating up to 1200° C. Fig.2 shows a cross section of an inlay in a natural When the tooth crown or the inlay is ready the tooth. In the figure.the veneer is indicated as A, the model of the abutment is removed by sand blast- core made from dense sintered ceramic as B, the ing. so cement as C, the copy milled surface of the core The above described complicated and time as D, the prepared surface of cavity as E, the pulp consuming methods are used to manufacture as F, and the natural tooth root as H. crowns and inlays, which will fit in individually Fig.3 shows a cross section of an alternative de- prepared cavities in natural teeth. sign for a root filled tooth, the same letters mean The problem with the material now used the same things as with Fig 2, while a root filling is EP 0 389 461 A1 indicated with G. tion. The contour outside the cavity is prepared Fig.5 shows a cross section of an onlay tooth manually with conventional dental technical ma- crown on a natural tooth, and chining practice. A negative reproduction can be Fig.6 shows a cross section of an alternative de- e.g. a Kerr impression, or a silicon impression. sign for an onlay tooth crown for a root filled tooth, 5 Preferably the core according to the invention the same letters mean the same things as with Fig is made from a biocompatible densely sintered, 2 and Fig.3. high strength ceramic material. On the core ob- In each of the Figures, the artificial onlay tooth tained the veneer is built up, so that the final crown or the inlay are the combination of the core product will be a tooth crown or an inlay fitting into B with the veneer A. They are fixed in the prepared w existing preparation and to the actual whole set of cavity E with cement C. teeth. According to the present invention, artificial on- As can be seen from Fig. 2 and Fig. 3 artificial lay tooth crowns and inlays are made in which the inlays are made as a core in densely sintered core is prefabricated from a biocompatible material ceramic (B) with veneer (A). They are fixed in the with part of the outer surface of the core D given 75 prepared cavity by e.g. cementing. The thin layer such dimensions as to fit into a preparation E, of cement (C) connects the prepared cavity walls which can be a preparation for an inlay or a prep- (E) with that part of the surface of the inlay or the aration for an onlay tooth crown or a preparation for onlay tooth crown, which has been made so that a tooth crown on a root canal pin. A biocompatible this surface (D) fits with great precision into the material for the core is a material which is not toxic 20 prepared cavity (E). The layer of cement can have and does not cause damage on oral tissues or a thickness < 200um preferably 25-75 urn. Artifi- does not give unwanted system effects. In addition cial onlay tooth crowns are made as a core in this material must not give any discolourations or densely sintered ceramic (B) with veneer (A). As otherwise give unwanted effects to the veneer ma- can be seen from Fig. 6 the preparation of a root terial. The onlay tooth crowns and the inlays are 25 filled tooth is extended down into the root canals in fixed by cementation in the cavities. order to have optimum retention of the tooth crown. The present invention allows a considerable The veneer (A) can be made from dental porcelain simplification of the handicraft of the dental techni- or plastic. The cementing of the constructions can cian. With the aid of gypsum models of the two be made with e.g. glassionomercement, jaws and with the prefabricated core placed on the 30 phosphatcement, or some resin can be used. In the model of the tooth preparation a dental technician last case it can be an advantage to silane treat the can make the final design of the onlay tooth crown surfaces (D) of the constructions which will be or inlay and at the same time control their function joined with the prepared surfaces of the tooth and size. In order to make the veneer, a porcelain structure. The enamel walls of the prepared cavity furnace or an apparatus for pressing of composite 35 can be etched and the dentin walls of the prepared veneer is needed. The method of making a tooth caviy can be treated with dentine adhesive (E) crown or an inlay to fit into an existing preparation before the above described restorations are ce- according to the present invention decreases es- mented with resin, which could comprise fillerpar- sentially the time of production for these construc- ticles of e.g.ceramic or polymer material. The prep- tions and at the same time the strength and preci- 40 aration of the cavity is made without undercut. sion regarding the accuracy to shape increase. Undercuts can be blocked with some cement e.g. Cores according to the invention can be made glassionomercement. several of metals or alloys by e.g. titanium or dental alloys, The ceramic powder can be made by plastic, porcelain, glass-ceramic or apatite ceramic well known methods. Traditional powder metallur- where the different by copy milling the negative reproduction from the 45 gical techniques can be used, prepared cavities (E). This copy milling gives the components are mixed and ground under dry or boundary surface of the onlay tooth crown or of the wet conditions with water or an inorganic solvent SOL- inlay to the cavity (D). A negative reproduction is (e.g.alcohols) as grinding liquid. So called made by making an impression of the prepared GEL technique can also be used where different tooth or a model from this tooth together with its 50 oxide materials are deposited together from a water adjacent teeth. The impression material fills up the solution or are co precipitated from metal alcoxides whole cavity and when the impression is removed in e.g. water free alcohol by controlled addition of from the teeth, this impression comprisess the sur- water. A combination of different techniques can face D and the contact points to the adjacent teeth. also be used by using SOL-GEL technique to de- From the impression material closest to surface D 55 posit a surface layer of desired metal oxide on a is adjusted in order to have this surface D within powder material. Lubricants or other organic bind- of method reach for copy milling. The contacts with the adja- ers depending on the choice forming cent teeth give the limitation in mesial distal direc- may be added to the ceramic powder when need- EP 0 389 461 A1 ed at suitable times in the process as is conven- atmosphere, which is an advantage when natural tionally known. Other preparation routes of the ce- teeth are to be imitated. Pure oxide material can be ramic material are also possible such as reaction sintered in air, but some composites have to be sintering where a suitable metal is oxidized, nitrid- sintered in inert or controlled atmosphere. The core ed etc. For example, aluminium can be oxidized 5 is given an external shape so that the building-up under carefully controlled processing to alumina. of the veneer is facilitated. The external shape can These methods allow preforming or reinforcement be such that it is roughly similar to natural teeth. by fibres, e.g., in a felt infiltrated with liquid metal. After the final sintering the surfaces of the core Many of the monolithic ceramics which are may need some grinding, especially the external biocompatible may have a brittle performance if w surfaces outside the prepared cavity. This grinding they are not sintered to nearly full density, more will be made with the inlay or the onlay crown on a than 98% and preferably > 99.5% of the theoretical model of the prepared tooth. If dental porcelain is density. However, these ceramics can be streng- used as the veneer with a coefficient of thermal thened by a number of toughening mechanisms. expansion adapted to the material of the core, the Finely dispersed particles, platelets, whiskers or 75 porcelain will adhere better. In the case of AI2O3 as fibers raise the fracture toughness of the compos- the core material there will be a "chemical bond" ite. Typical additives are the nitrides, carbides, between AI2O3 and porcelain. This means that the borides or mixtures thereof of the transition metal external surface of the core does not need any of group IV-VI or of the elements Al or Si. Tough- retention elements. When using other veneer ma- ening may also be achieved by so called trans- 20 terials e.g. plastic, mechanical retention elements formation toughening, i.e., additions of unstabilized can be needed e.g. grooves, pits or on the external ZrO2 or ZrO2 stabilized with Y2O3, MgO or GaO. surface sintered retention elements or a silane The additions of these latter oxides shall not ex- treatment of the surface. The core can also be ceed 25 wt%, but should be more than 2 wt%. The given such a shape that the ceramic inlay or onlay best performance is obtained with 3-12 wt% of the 25 tooth crown does not need any veneer material. ZrO2. The surfaces of the inlay or the onlay tooth crown The powder with lubricants and/or other or- which is a part of the external surfaces of the ganic binders is cold isostatically compacted , un- repaired tooth must in this case before the cement- iaxially pressed, slip cast, pressure cast, injection ing be ground and polished to a surface fineness of moulded or compacted in another suitable way. 30 0.5-5um preferably 0.5-1 urn. The compacted body has such dimensions that it The ceramic base material in the core com- comprises enough material for the copy milling of prises preferably one or several biocompatible ox- the outer shape of the core, which will fit into the ides (including phosphates, silicates and suifates), prepared cavity (E). During this copy milling the with the additives of carbides, silicides, nitrides or sintering shrinkage must be considered. Thus, the 35 borides with or without binder metal (preferably copy milled surface (D) must be enlarged so that iron-group metals) in addition to conventional sin- the compacted body has such dimensions that tering aids. The base material can also comprise after the shrinkage during the subsequent sintering other biocompatible high performance ceramics process to high density, has desired final geometri- such as nitrides, oxynitrides, carbides, etc. Exam- cal external shape. (D) which will fit into the pre- 40 pies of the two former materials are Si3N+, SJ2N2O, pared cavity (E) with great accuracy. sialon, AIN, AION, etc. Examples of biocompatible The ceramic body can also be presintered oxides, which can form base matrix for the ceramic before the copy milling of the surface (D) fitting to body, are AI2O3, TiO2, MgO, ZrO2, and ZrO2 - the prepared cavity (E). All the other surfaces are (partly or totally stabilized with amounts of up to 25 prepared near final shape before the final sintering. 45 weight% of Y2O3, MgO or GaO). It is important that the ceramic material is sintered Also, components such as SiC, TiN, TiC, TiB2, to closed porosity, which for an oxide material Si3N*, or other biocompatible carbides or nitrides means at least 95% of theoretical density, but in of group IV,V or VI can be present as particles with order to ensure good mechanical strength the ma- a size of <25um preferably <10um and/or as terial should preferably have a density over 98%, 50 whiskers (hair shaped single crystals) with a length while densities over 99.5% give the best strength. to diameter ratio >5, preferably >10 and/or fibers The sintering can take place in a vacuum or (polycrystalline) with a diameter >10um and/or as under hydrogen atmosphere, under normal atmo- single crystal platelets with an approximate diam- spheric pressure or under increased pressure in eter of 5-50 urn preferably 5-20 urn and a thick- connection with the overpressure sintering or hot 55 ness of 1-10um, preferably 1-4 u,m. The amount of isostatic compaction or alternatively by hot press- whiskers, fibers and/or platelets should not exceed ing. Highly pure AI2O3 becomes translucent during 60 volume%, preferably less than 40 volume %.. sintering to full density in vacuum or in hydrogen In a preferred embodiment the ceramic ma- EP 0 389 461 A1 terial comprises >50% preferably >85% by weight was fired at 1150° C during 10 minutes. During the of AI2O3 with additives of conventional sintering heating the furnace was under vacuum, but when aids. In order to increase the strength <25weight % the final firing temperature was reached the firing 3-12 % of ZrO2, and/or 5-40 was performed under atmospheric pressure. The preferably weight * weight % preferably 1 0-30 weight % of SiC whisk- 5 remainder of the crown was fired at 960 C. The ers can be added. In order to get a suitable colour, dental porcelain combined chemically with the alu- coloured components can be chosen. Additives e.g mina without any gap between the porcelain and 0.1-10 weight % preferably 0.5-5 weight %, of TiN the densely sintered core. The onlay crown fitted and/or ZrN will give AI2O3 based inlays and onlay perfectly on the model of the tooth and was ready crowns a faint yellow shade. io to be cemented with conventional methods in the The principles, preferred embodiments and tooth cavity in the mouth of a patient. modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, Claims however, is not to be constructed as limited to the 75 particular forms disclosed, since these are to be 1. Artificial onlay tooth crown or inlay compris- regarded as illustrative rather than restrictive. Vari- ing a core and a veneer characterized in that the ations and changes may be made by those skilled boundary surface of the core which will fit into a in the art without departing from the spirit of the prepared tooth cavity is made by copy milling a invention. 20 negative reproduction from the prepared cavity. The invention is additionally illustrated in con- 2. Artificial onlay tooth crown or inlay according nection with the following Example which is to be to claim 1 characterized in that the core is made considered as illustrative of the present invention. It of a biocompatible ceramic material with a relative should be understood, however that the invention is density of > 95%. not limited to the specific details of the example. 25 3. Artificial onlay tooth crown or inlay according to claim 2 characterized in that the ceramic material in the core is based on one or more of the EXAMPLE oxides AI2O3 ,TiO2, MgO, ZrO2 or ZrO2 with up to 10 mole% Y2O3 or MgO. A core to fit a prepared cavity in a molar 30 4. Artificial onlay tooth crown or inlay according according to Fig.5 was made from a powder with to any of claims 2, 3 or 4 characterized in that the the approximate composition 99.85 weight % of core also comprises whiskers and/or particles of AI2O3 and 0.15 weight % MgO. Blocks SiC, TiN, ZrO2 and/or ZrN. (15mmx15mmx30 mm) of the powder were uniax- 5. Artificial onlay tooth crown or inlay according ially compacted and presintered at 1200 C. An 35 to any of the previous claims characterized in that impression was made of the tooth with the pre- it is made by copy milling of a compacted body or pared cavity with a putymass of a silicon impres- a presintered body and the sintering shrinkage has sion material. This impression contained the nega- been considered by linear addition for the surface tive reproduction (D) of the prepared cavity walls (D) of the core after the sintering to final' density (E). With a scalpel the impression material outside 40 will fit into the prepared tooth cavity (E). the boundary (I) was carefully removed. From the impression with use of the presintered blocks the surface (D) was copy milled and at the same time enlarged to such a size that it allowed a shrinkage of 16.5% during the sintering. From the boundary 45 (I) the external surface of the core was milled and machined to a minimum thickness of the core of 1.2 mm in the direction of the axes through the tooth. The sintering was performed in air during 2 hours at 1600° C. After the sintering the core had a 50 relative density of 99.5% and a minimum thickness of 1 mm in the direction of the axes through the tooth. An ordinary impression was made from the whole jaw and from this impression a model of the jaw was made i gypsum. The core fitted perfectly 55 into the prepared cavity and commercially available dental porcelain was fired on the surface. The first layer porcelain compriseed about 50% AI2O3 and Fig.1

Fig.2

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Fig.3 EP 0 389 461 A1

Fig.6 European Patent Application Number J>) EUROPEAN SEARCH REPORT Office

EP 90 85 0107

DOCUMENTS CONSIDERED TO BE RELEVANT Category Citation of document with indication, where appropriate, Relevant CLASSIFICATION OF THE of relevant passages to claim APPLICATION Gnt. C1.5) EP-A-0 033 492 (BECKER) A 61 C 5/10 * Page 7, line 1 - page 8, line 9; figures 1-3 *

X DE-A-3 604 531 (KURT) 1 * Column 4, lines 30-62; figures 1,3 *

A DE-A-3 720 308 (HELLGE) 2 * Abstract; figure 1 *

A FR-A-2 490 950 (0RI0) 2,3 * Page 2, lines 28-35; page 5, lines 21-26 *

A FR-A-2 318 842 (SUMITOMO) 3 * Page 6, line 7 - page 7, line 10 *

A FR-A-2 558 717 (ANDERSSON) 1 * Page 6, line 8 - page 7, line 28; figures 1,2 * TECHNICAL FIELDS SEARCHED (Int. ci.5)

A 61 C

The present search report has been drawn up for all claims Place of search Date of completion of the search Examiner THE HAGUE 30-05-1990 KOUSOURETAS I.

CATEGORY OF CITED DOCUMENTS T : theory or principle underlying the invention E : earlier patent document, but published on, or X : particularly relevant if taken alone after the filing date Y : particularly relevant if combined with another D : document cited in the application I document of the same category L : document cited for other reasons A : technological background bo O : non-written disclosure & : member of the same patent family, corresponding O document b P : intermediate document