SE409649B - PROCEDURE FOR MANUFACTURE OF DENTAL PROSTHES AND APPARATUS THEREFORE - Google Patents

Description

HsO3369-7 10 15 20 I 25 30 35 of the obtained dough.

There are devices by which shrinkage compensation is accomplished by post-pressing the mixture of polymer and monomer from a storage vessel during the polymerization. Such a device is described in Ullmann's Bnzyklopädie der Technisohen Chemie, volume 5, p. 719 and 720. In this device, however, there is a risk that the mixture hardens prematurely in the compression duct and can no longer be pressed into the polymerization mold. A similar device is known from the Journal of the American Dental Association 1960, 413-43. In this device, for the production of dental prostheses, polymerizable material is pressed in from above from a storage in a polymerization form, which is heated from below by means of a hot plate. The material is polymerized under the influence of heat and pressure, whereby the metal parts of the polymerization mold consist of alloys with different thermal conductivity. These metal parts are arranged so that the polymerization sets in at the tissue side of the negative shape of the prosthesis, i.e. the plane of the prosthesis is parallel to the plane of the heating plate. Due to the use of alloys with different thermal conductivity, a small temperature difference arises between the polymerization form and the storage. In the applied device of the negative shape of the prosthesis, however, the polymerization reaches the indentation channel very quickly, so that it is blocked by polymer, before the prosthesis is completely polymerized. This causes errors in the prosthesis, since the shrinkage cannot be compensated with post-pressed material.

U.S. Pat. No. 2,806,253 discloses an apparatus for making plastic dental prostheses, in which polymerizable material is pressed into a polymerization mold which is heated from below by means of a hot plate or a hot bath. At all other surfaces, the polymerization form is heat-insulated and possibly also cooled, so that a temperature difference from below and upwards is generated. The negative shape of the prosthesis is arranged so that the polymerizable material is first polymerized at the gum side lying closest to the heat source. With this device it is intended to prevent the polymerization from starting at the thicker edge parts, where the teeth are attached. However, when the polymerization front has reached these edge portions, it has also reached the indentation channel, so that the material contained therein hardens by polymerization and can no longer be post-pressed to the higher edge regions to compensate for the shrinkage.

German patent specification 879 901 describes a device for producing dentures from polymerizable plastic material with post-pressing. The device is characterized by means for cooling the plastic storage used for shrinkage compensation during the polymerization. There is no information on the nature of the polymerization form. In particular, nothing is said about how the polymerization form is isolated, where the polymerization begins or how the polymerization proceeds. The fact that the plastic storage must be kept in a liquid state does not give any indication of its ability to flow to the places in the polymerization form where it is needed. Possibility of flow within the mold to the places where material is needed to compensate for the shrinkage can be obtained only by a special insulation of the polymerization mold and the pressing channel and by a special arrangement of the prosthesis and the injection channel together with a versatile heat supply.

The object of the invention is to produce dental prostheses of plastic by a method in which the post-pressing of polymerizable material to compensate for the shrinkage avoids premature polymerization of this material in the storage vessel or the pressing channel, so that satisfactory polymerization always takes place even in the negative edge regions.

An interference-free post-pressing is also possible when using a polymerizable material with a high monomer content, e.g. over 50%, which gives high detail accuracy, but also high volume contraction.

The invention relates to a method for producing a plastic dental prosthesis, in which polymerizable material from a storage is pressed into a polymerization mold and polymerized therein, whereby a temperature difference is maintained between the mold space and the storage and post-polymerizable for compensation of The method is characterized in that the mold space is arranged in a special way, as further specified in claim 1.

The apparatus for applying this method comprises a polymerization mold with a mold space for receiving the polymerizable material, which is connected via a press-w ... n .., 'zunzsæ-v 1oi 15 20 25 30 35 4 channel with a supply of the polymerizable material, and a device for pressing the polymerizable material into the polymerization mold. The apparatus is characterized in that the mold is thermally insulated in a special manner and arranged with the mold space in a special orientation, as further specified in claim 5.

With the specified measures, it is achieved that the polymerizable material can flow unhindered to the prosthesis mold space until the end of the polymerization, especially also to the places where the shrinkage has already begun. Thus, neither in the storage nor in the indentation duct does premature hardening of the polymerizable material occur. However, after completion of the polymerization, the material can be easily separated from the prosthesis.

The prosthesis mold space with its longest dimension is arranged in the direction of the largest temperature difference and its smallest dimension approximately perpendicular to the vertically extending indentation channel. Thereby the polymerization is controlled so that it begins at the edge furthest from the indentation channel and then concentrically progresses from the bottom upwards, so that at the end of the polymerization the supply of polymerizable material is still soft. In this way, polymerization shrinkages of 10 - 20% can be compensated without difficulty.

The slow progress of the polymerization from the bottom up can be made visible in the form of isotherms by experiments, in which the polymerization is stopped after equal time intervals.

As the polymerizable material, a mixture of at least one momomer and at least one polymeric ester of acrylic or methacrylic acid is preferably used. However, it is also possible to start from a pure monomer and irradiate it with light or other rays until the desired viscosity has been reached. This material is then introduced into the storage container and pressed into the polymerization mold.

It is also possible to use the hitherto common doughy mixtures of finely divided bead polymer and monomer in a volume ratio of 3: 1. By means of the invention, however, it is also possible to use mixtures with a higher monomer content than hitherto, whereby a higher level of detail is achieved. For example, a monomeric ester of acrylic or methacrylic acid may be used in a proportion of about 50-95% by weight, preferably about 50-75% by weight.

The residue preferably consists of the corresponding polymeric ester, in particular a bead polymer, which is dissolved in the monomeric ester.

Such a polymerizable material provides moldings with significantly improved impact strength, and it provides significantly better bonding of the plastic teeth to the base material than a polymerizable material with a higher polymer content.

Although alkyl, aryl and alkaryl esters of acrylic or methacrylic acid give the best results, other polymerizable double bond monomers can also be used, e.g. vinyl acetate, styrene or epoxy compounds, and corresponding polymers of these compounds.

If a polymerizable material with a syrupy consistency is used, this mass can be prepared before the start of the polymerization by simple mixing. Preferably, however, homogenization of polymer and monomer is carried out for a short time by vibration in a suitable mixer. Particularly suitable for this purpose is a mixer with two chambers, in which the components are stored separately until the mixture. Such mixers are described in German Pat. No. 2,009 HO3.

The polymerization of the polymerizable material can be initiated in a known manner by adding catalysts, e.g. peroxides or other radical-forming compounds, such as azodiisobutyric acid nitrile. Furthermore, color pigments, ultraviolet light stabilizers, fillers, crosslinking agents, fluorescent agents and / or stabilizers can be added to the polymerizable material. As crosslinking agents, di- or polyfunctional crosslinking agents are used, e.g. ethylene glycol dimethacrylate.

The stabilizers must prevent premature polymerization of the polymerizable material. For this purpose, e.g. radical-forming compounds, such as hydroquinone.

In carrying out the polymerization under the influence of heat, a heat bath is preferably used as the heat source, the temperature of which is preferably maintained at approximately 70-100 ° C and in each case at most 150 ° C. As a heating bath you can use e.g. a water bath, oil bath or glycerol bath, which is suitably provided with a level regulator. Preferably, the polymerization mold dips down only to the top edge of the side insulation guards. The polymerizable material is fully polymerized in less than an hour.

An apparatus for applying the method is described below in connection with the accompanying drawings.

Fig. 1 shows the whole apparatus in section.

Pig. 2 is a partial sectional view (at 900 angles to Figure 1) of the housing in which the polymerization mold is clamped, together with a sleeve in which a storage container for the polymerizable material is inserted.

Pig. 3 shows the sleeve from below on a larger scale.

Figures 1 and 2 show two frame-like housing parts 1 and 1 ', which fit against each other with their flat edges and are cast from a metal alloy, preferably an aluminum alloy. The two housing parts each have approximately the shape of a circle segment and each has a neck part 2, 2 'at the top. At the bottom, one housing part has a groove 3 (Fig. 2) and the other housing part a spring 4 (Fig. 1) for assembling the two housing parts. The housing parts provided with recesses on the right and left side can be closed by means of protection 5 and 5 'with low thermal conductivity. For this purpose, plastic lids, preferably of polyoxymethylene or a polyamide, can be used.

Under the neck part 2 at the two shoulders of the housing parts 1 and 1 '(Fig. 2) there is on the inside a recess, in which two halves 6 and 6' of a non-shaped insulating part are inserted. This insulating part preferably consists of. a plastic with low thermal conductivity. The insulating part 6, 6 'has a central injection opening 8, which narrows in the direction of a polymerization form 12, fi2' described below. Through the injection opening 8, the polymerizable material is pressed into the polymerization mold.

In the neck parts 2, 2 'a sleeve 9 of material with low thermal conductivity is inserted. This material may be the same as the material in the insulating part 6, 6 ', i.e. preferably a plastic with low thermal conductivity. The upwardly open sleeve 9 has at the top a flange 10 with numerous openings (Fig. 3), which engages in a corresponding groove in the neck parts 2, 2 '. At the bottom, the sleeve 9 is enlarged with a lower flange 11, which only partially abuts against the neck parts 2, 2 'of the housing parts 1, 1'. This is achieved by means of alternating recesses.

In this way, an annular air gap 7 is formed between the sleeve 9 and the neck parts 2, 2 ', so that the sleeve 9 and thus also a supply of polymerizable material in a storage container 20 is thermally insulated from neck parts 2, 2 '. The recesses on the lower flange 11 also reduce the heat transfer from the neck parts 2, 2 'to the sleeve 9. The seat of the sleeve 9 in the neck parts 2, 2' is provided only by the flange 10.

In the two housing parts 1, 1 'there is the two-part 12, 12' form of a suitable embedding material, e.g. hard gypsum, which over a long injection channel 8 'milled into the gypsum communicates with the supply 19. For joining the two housing parts, a clamping frame 13 is used, which preferably has the shape of a trough open at the bottom. It can consist of any casting material, e.g. aluminum castings. It should be noted that the edges of the two housings 1, 1 'do not lie close to each other. at the joint, but at a small distance from each other, while the surfaces of the two mold parts 12, 12 'must be close to each other. The opposite surfaces of the mold parts are locked to each other in a known manner.

In order for the two mold parts to lie close to each other, they must be compressed together with the two housing parts 1,1 'in the clamping frame. This can be done by means of a pressure piston 1H, which over the left cover 5 'presses against the left housing part 1'.

The piston 14 can be operated by means of a simple spindle press or hydraulic press (not shown), which acts on a spring housing 15 and a set of disc springs 16. Usually the press pressure is approximately 3 tons. Vid den i fíg. 1, the press pressure exerted by the hydraulic press can be maintained even after the device has been taken out of the hydraulic press by turning wedge-shaped rack 18 relative to a rack 17 and then locking the rings so that the device can be placed in the heating bath. and the polymerization is carried out with compressed housing parts.

The supply 19 of polymerizable material is contained in a storage container 20, which is inserted into the sleeve 9. The storage container 20 is provided at the bottom with a nozzle-shaped extension, which goes into the indentation channel 8. As material for the storage container 20, a metal cylinder open at the top or a rigid plastic container, e.g. polypropylene or polyamide. Preferably, a multi-chamber mixer is used as the storage container, as described in German Patent Specification 10 15 20 25 30 35 '7-'1403369-7 2 009 403. This mixer contains a downwardly displaceable bucket-shaped insert 21, in which the liquid monomer the blend component is present prior to the preparation of the polymerizable mixture. The liquid component is transferred by breaking the insert 21 along a guide line to the space 19, where the pulverulent polymeric component is located. The storage container 20 is then still closed in its nozzle-shaped extension by means of a pin. After the liquid component has been introduced into the space 19, the polymerizable mixture is formed by mixing in a swing mixer.

When using this mixer as a storage container 20 in Fig. 1, the bucket-shaped insert 21, on which the crack formed along the guide line has been closed again, protects the piston 22 from being contaminated by the polymerizable material, since the piston 22 does not come into direct contact with it. polymerizable material.

The piston 22 serves to press the polymerizable material from the supply 19 into the cavity 23 in the negative mold 12, 12 ', which corresponds to a flat-shaped dental prosthesis. The cavity is arranged so that the direction of the prosthesis height is approximately perpendicular to the vertical channel 8. In this way it is achieved that the polymerization first takes place at the edges which are furthest from the indentation channel, where the temperature is highest. Fig. 1 shows a tooth 2H, e.g. a plastic tooth, which has been inserted into the mold before the pressing of the polymer-moldable material. The material in the plastic tooth 2D is firmly combined with the polymerizable material.

The piston 22 is operated by means of a pressure device 25, which may be provided with a pressure gauge 26 and is connected to a pressure line 27. At the connection to the pressure line, a non-return valve (not shown) can be provided. This non-return valve makes it possible to catch a possible pressure drop in the pressure line.

The pressure should be above one atmosphere and preferably about 5 - 6 atmospheres. The pressure device 25 is detachably mounted on the neck parts 2, 2 'by means of a gripper 28. The gripper 28 can be fixed to the neck parts 2, 2 'by means of a clamping bracket 29. In the pressure device 25 there is a piston 30, which transmits the pressure by means of a piston rod 31 to the piston 22 in the storage container 20.

In the heating bath, depending on the size, up to about 10 pressure polymerization devices can be heated simultaneously.

The production of dental prostheses is shown in the examples below.

First, in the polymerization form 12, 12 '(dental technically called "cuvette"), a wax model of a prosthesis with inserted teeth is embedded in gypsum in a known manner, the wax is melted off and the gypsum surfaces are insulated.

The extended indentation channel 8 'with a diameter of approximately 3 mm is then milled out or scraped off as a connection to the storage container 20. Then the two mold parts 12 and 12' are joined together and inserted into the clamping frame 13, whereupon a pressure of 3000 kp is exerted on the piston. 14 in a hydraulic press. After the lever on the adjusting ring 18 has been folded over, the clamping frame is locked and taken out of the press.

Meanwhile, a mixer container is prepared which contains the components of the polymerization material, i.e. polymer and monomer. The mixing container contains 36 g of ordinary methyl methacrylate monomer stabilized with 60 parts per million of hydroquinone and Døethylene glycol dimethacrylate and 14 g of ordinary tooth% crosslinked with 4 polymers in the form of a methyl methacrylate bead polymer supplemented with 2 benzoyl peroxide.

After the two components have been joined, they are shaken for 5 minutes in an automatic mixer, after which the mixer container is inserted into the sleeve 9. Then the pressure device 25 is applied and a compressed air line with 6 atm pressure is connected. After 5 minutes under pressure, the polymerization mold and the clamping frame are applied in a heating bath with boiling water. The water level reaches just up to the upper edge of the plastic side lid 5, 5 'of the polymerization mold.

After 35 minutes, the entire polymerization apparatus, still under pressure, is placed for 10 minutes in a cold water bath for cooling. After the pressure has been relieved, the polymerization mold is taken out of the clamping frame 13 and the prosthesis is removed in a known manner.

The following are some mechanical properties of the polymethyl methacrylate plastic polymerized under pressure according to the invention in comparison with the same plastic which has been hot polymerized under normal conditions. The specimens were prepared according to ADA (American Dental Association) specification No. 12 and were tested for impact strength and the adhesion of the plastic teeth to the backing material. vuoszsa-7 10 Weight-to-liquid powder Polymerization temp., OC Polymerization time, min impact strength, kpcm / cm? Adhesion of plastic teeth, kp Conventional Polymerization polymerization according to invent. 2 1 1: 2 70 100 60 35 ll, 5 _-_ r_0,6 6,6¿0,8 6 - 18 20 - 38 _. If _ _

Claims (9)

-1 7403369-7 11 PATENT CLAIMS A method of manufacturing a plastic dental prosthesis, wherein polymerizable material from a storage is pressed through a pressure channel in a prosthesis mold space in a polymerization mold heatable by a heat source and polymerized therein by the action of heat and pressure under heat supply in such a manner. , that during the polymerization a temperature difference is maintained between the mold space and the storage with a temperature decreasing from the mold space through the pressing channel to the storage, and to compensate for the shrinkage occurring during the polymerization, polymerizable material is pressed from the storage to the mold space, characterized in that the prosthesis mold space is arranged with its greatest extent lying substantially in the direction of the largest temperature difference and with its height lying substantially at right angles to the indentation duct, 'to thermally insulate the polymerization mold at its surfaces surrounding the indentation duct and at the adjacent adjoining, substantially parallel to the largest extent of the mold space, but not insulating surfaces running along the smallest width of the mold space, and to produce a polymerization which proceeds from the mold space edges located furthest from the indentation channel through the mold cavity and mainly radially towards the pressing point. Process according to Claim 1, characterized in that a mixture of at least one monomeric acrylic or methacrylic acid ester and at least one polymeric acrylic or methacrylic acid ester is used as the polymerizable material, in which the proportion of monomeric ester is approximately 50 95% by weight, preferably 50 - 70% by weight. Process according to Claim 1 or 2, characterized in that polymerization catalysts, pigments, stabilizers for ultraviolet radiation, fillers, crosslinking agents, fluorescents and / or stabilizers are added to the polymerizable material. .-. ~, ._ ,. . . .? asssss ~? 12 R. A process according to any one of claims 1 to 3, characterized in that the polymerization form is introduced into a bath, the temperature of which is not more than 150 ° C, preferably 7 DEG-100 DEG C., and that the polymerizable material is polymerized for a shorter time. than an hour. Apparatus for carrying out the method according to claim 1, comprising a polymerization mold (ï2, 12 ') heatable by means of a hot bath with a prosthesis mold space for receiving a polymerizable material, which is connected via a pressing channel (8) to a supply (20) of the polymerizable material, and a device (22) for pressing the polymerizable material into the polymerization mold, characterized in that the polymerization mold (12, 12 ') is heat-insulated against the storage at its pressing channel (8) limiting surfaces by means of an insulating part (6, 6 ') and against the heat source at adjacent surfaces by means of protection (5, 5') lying parallel to the greatest extent of the mold space with low thermal conductivity, but is free from thermal insulation at surfaces which run along the smallest width of the mold space, and that the mold pump (23) is arranged with its height lying substantially at an angle to the direction of the indentation channel (8) and with its largest width in direction for the largest temperature difference, which is formed between the mold space and the storage when heating the polymerization mold in the heating bath. Apparatus according to claim 5, characterized in that the polymerization form consists of two parts (12, 12 '), which are compressed by means of two housing parts (1, 1') with a neck part (2, 2 *) g in which a sleeve (9) of a material with low thermal conductivity for receiving an insertable storage container (20) is arranged with an annular air gap (7) between the neck part and the sleeve. Apparatus according to claim 6, characterized in that the sleeve (9) is extended at the upper and the lower edge with flanges, of which the upper flange (10) is provided with openings and the lower flange (11) abuts only within sub-areas towards the neck part (2). 7403369-'7 13 Apparatus according to claim 6 or 7, characterized in that the storage container (20) consists of a mixing container with a squeezing opening and a bucket-shaped insert (21) displaceable therein. Apparatus according to one of Claims 5 to 8, characterized in that the supply (19) is connected to a piston (22) in a pressure device (25) which is detachably connected by means of a gripper (28). with the neck part (2). STATED PUBLICATIONS: Germany 824 838 (30 b: 16/02) US 2,806,253 (18-33) Other publications: Journat of the American dental association. 61 (1960), pp. 413-430.