Method and apparatus for thermal polymerization of plastics for dental application.

The invention relates to a method and a device for the thermal polymerisation of plastic materials for dental purposes in a closed chamber of a pressure vessel in which a polymerization feed the ever-enclosing, heated medium is used at superatmospheric pressure.

The pressure-Polymerisation currently used in the dental laboratory in the manufacture of dental prostheses are only suitable for polymerizations take place in liquid medium, for example water or glycerol, which is for example is heated to a polymerization temperature of 120 ° C and at the same time under a pressure for example, 6 bar stands. It is usually filled in Wasserpolymerisation for each new polymerization the pressure vessel of the polymerization unit with fresh, cold water, in which the polymerization feed must be completely immersed. The polymers used there it comes to achieving good Polymerisationsergebnisses significantly on the exact observance of the polymerization and also to a uniform distribution of temperature in the cavity of the pressure vessel. These requirements can be met with water as a medium in which the polymerization takes place, light and easy to fulfill, because water is a good conductor of heat. On the other hand, the use of water as a polymerization medium the drawback that relatively much heat energy is required for its heating to a certain polymerization temperature. In addition, its handling is far complicated than it needs to be for each new polymerization newly introduced into the pressure vessel and then drained again. In addition, the use of water as a polymerization medium is expected to a pressure vessel, which is only accessible from above.

In order to achieve a slow heating and cooling of the plastic and thus avoid tensions in the provided with different wall thicknesses moldings, provides a known method (German Offenlegungsschrift 2021194) of the type mentioned before, that the shaped bodies having a surrounding Kontaktflüßigkeit in are contacted, as long as this has still lying below the polymerization temperature, that the shaped bodies are then heated together with the Kontaktflüßigkeit to polymerization temperature and finally cooled slowly. For this purpose, an additional container is provided, which is provided with a heat capacitor, which is arranged in an inflow channel to the interior space of this container or is designed as inflow duct to the interior of this vessel.

Apart from the fact that also in this case a liquid is used as the contact medium, which must be replaced more often, an additional container for receiving the Polymerisationsguts required by the more expensive and the device is cumbersome to use.

In another method of the polymerization, a predetermined amount of water is filled in a heatable pressure vessel with the polymerization feed and after closure of the pressure vessel is evaporated by heating. The result is thereby a mixture of hot air and water vapor. This method has proven itself not particularly because uneven cures with uneven hardness and uneven tones were observed. In addition, disturbances at the interface metal / plastic by formation of marginal gaps were observed in this process to an even greater extent than in the polymerization in a water bath. Obviously, the heat transfer from the heat source to the polymerization feed is insufficient in this method.

Recently, a device is in United States entered the market (Justi Pakto, HD Justi Company, Oxnad, CA) which is a kind of pressure cooker with the lid, is provided with which gas supply, pressure gauges, thermometers and pressure relief valve. The recoverable pressure range is 1.4 to 2.7 bar. Temperatures between 120 and 204 ° C and are generated by a built-in 5-stage Elektroheizplatte. Due to the low pressure can be used in this device only a single plastic material, namely 100% Polyglycoldimethacrylat. This material is high but not comparable to the commonly used today filled or unfilled plastics for dental purposes, which are optimized by appropriate admixtures in abrasion resistance, impact resistance, hardness, color, etc., and become very similar to the natural tooth. but they also require strict adherence to its polymerization.

The invention has for its object to provide a method and an apparatus for performing the method of the type mentioned by which overcomes these disadvantages, as well as shorter heating and lower energy consumption can be achieved.

This problem is solved procedurally in that air or an inert gas by forced convection in the closed space of the pressure vessel is passed to both a controlled heater as well as the polymerization feed as a heated medium.

For dental laboratories, this method, except that no more water is required, the advantage that the heating of the gaseous medium in the closed space of the pressure vessel substantially less thermal energy is needed, but that still required for carrying out the polymerization temperature sufficiently accurate and is also achieved sufficiently homogeneously in the interior of the pressure vessel and is available over the duration of the polymerization process, which may be several minutes. The heating of the medium to the desired polymerization can be effected in a substantially shorter period of time than as the polymerization is possible with the same heating capacity in the water.

The inert gas in particular is nitrogen and carbon dioxide in question. Prinzipell well as helium or argon can be used.

Particularly good results are obtained mainly in the dental field, when temperature of the mixture for less than 2 minutes, more preferably less than 1 minute.

After the heating, the temperature gradient should be within the space of the pressure vessel less than 5 ° C, preferably even less than 2 ° C.

For dental purposes the pressure at least 4 bar should, preferably 5 to 10 bar. Below these pressures may partially evaporate and form troublesome bubbles and foam conventional and suitable for the method, filled or unfilled plastics for dental purposes when heated to polymerization temperature between 90 ° and 140 ° C.

It is further object of the invention to provide an apparatus for performing the method according to claim 1, or of a tightly closable by a lid or a door pressure container with a built-in warming the medium and controllable by a temperature sensor heater, and with a compressed air compressed gas connection is provided pressure vessel consists, at which is guaranteed that which is achieved for starting up and maintaining the polymerization temperature required of the surrounding the polymerization feed gaseous medium as quickly as possible and maintained as closely as possible over the entire polymerization period of time in the interior of the pressure vessel and on the entire surface the polymerization material is uniformly available.

This object is achieved in that an electric motor-driven fan is disposed in the pressure vessel, which produces a directed through an arranged in a plane heater through the polymerization feed air or gas flow.

This arrangement not only a continuous and uniform circulation of the medium is ensured within the pressure vessel, but also ensures that there is always enough heat energy at the desired temperature is introduced to the polymerization feed during the entire polymerization process and to maintain the polymerization process during the intended polymerization available stands.

The embodiment of the invention of claim 5 is advantageous when the axial impeller is disposed within the pressure vessel where it less disruptive and where it also regarding the immediate pre-heat generated from the heater to the polymerization feed the best effect Has.

By configuring the invention of claim 6 is a considerable improvement of the heat distribution over the entire cross section of the pressure container inner space and at the same time homogenization of the air or gas flow generated by the impeller is achieved.

The measure of claim 7 the operation of the Axialgebläserades is improved.

The embodiment of the invention of claim 8 is advantageous when the there envisaged arrangement of the heater and the blower wheel is the least hindrance, easily mountable and spatially best unterbrinbar. For devices where the charging port is not on the top side, but arranged at the front, there is also the advantage that the floor space, on which the manager or object holder is parked with the polymerization feed, not prallel to the plane of the heating coil, but transversely thereto extends and thus the the impeller generated flow opposes the least resistance.

While the embodiment according to claim 9 to improve the flow conditions is within the closed polymerization space, further improvement of these flow conditions and at the same time an improved heat distribution throughout the polymerization space is achieved in the pressure vessel by the embodiment according to claim 10th

The arrangement of the temperature sensor according to claim 11 ensures not only accurate detection of the ruling in the entire polymerization space temperature but also a protection of the temperature sensor against external influences.

bwz The arrangement of the compressed air. Pressure gas terminal according to claim 12 it is ensured that the supplied pressure medium first conveyed to the heating coil, heated there and comes with the flow generated by the impeller of the distribution.

Another possibility for the arrangement of the impeller and the design of the pressure container is subject matter of claim 13, wherein it is possible to improve the homogeneous temperature distribution inside the pressure vessel through the embodiment according to claim fourteenth

Due to the configuration according to claim 15, the possibility is created to also perform Strahlungspolymerisationen in the same pressure vessel, wherein the radiation is reflected on the radiator facing away from surfaces of the polymerization material by the reflective coating of the blower wheel.

By maintaining a pre-heating temperature in the pressure vessel, which is made possible by the measure of claim 16, the heating time can be significantly shortened to the required polymerization temperature.

Reference to the drawing, the invention will be described in greater detail below. It shows:<ul><li>1 shows a pressure vessel of a polymerization unit in front view with the cover removed.</li><li>Figure 2 shows a section II-II of FIG. 1.</li><li>Figure 3 is a grid-like insert part in a top view.</li><li>Figure 4 shows another embodiment of the pressure vessel a curing light in a front view with removed closure part and without the grid-like insert part.</li><li>FIG. 5 is the same view as Fig. 4 with the inserted grid-like insert part and</li><li>Fig. 6 is a section VI-VI in FIG. 5.</li></ul>

The illustrated in FIGS. 1 and 2 pressure vessel 1 has a substantially circular, downwardly slightly conically narrowing cup-like shape. Its upper opening is closed by a cover 2, which is supported by a support shaft 3 pivotably mounted on the hinge pin 4 and 5. FIG. In its in Fig. 2 illustrated closed position of the cover 2 by means of a locking pin 6 which is inserted into the horizontal bore 7 of an upright fixed to one eyelet projection 9 locking bolt 8 can be locked . By a transverse pin 10 of the locking pin 6 is connected to a manually operable slide 11 in conjunction. The annular end face of the pressure vessel 1 is provided with an annular lip seal 12 which abuts sealingly against the underside of the cover. The pressure container as a whole is constructed as a diecast and is provided with a relatively thick wall 13 in which two diametrically opposed, recess-like enlargements are located 14 and 15 incorporated, whose width b corresponds approximately to half the average internal diameter of the pressure vessel first The significance of these extending over the entire height of the interior space 16, niche-like extensions 14 and 15 will be explained later.

Concentric with the vertical axis of symmetry 17 of the pressure container 1 is in its bottom wall 18 by means of a bearing bush 19 and disposed therein ball bearings 20, the shaft 21 of an axial fan wheel 22 rotatably driven by an electric motor 23, and thereby a in the center of the inner space 16 of bottom to top, and in the niche-like extensions produced from top downward flow. The electric motor 23 is fixed by means of a flange ring 40 and screws 41 to a base plate 42 which is in turn bolted to the bottom wall 48th Immediately above the axial Geläserad 22, a heater 24 is arranged in the form of an electrical heating element whose helical turns is arranged in a parallel to the rotation plane of the plane extending Axialgebläserades 22 with small radial winding distances. Here, the vertical or axial distance between the axial-fan wheel 22 from the inner surface of the bottom wall 18 is less than its distance from the heating device 24, but in any case so large that the axial impeller can exert its axial suction sufficiently.

Directly above the heater 24 is located on two ring-segment-like, both sides of the niche-like extensions 14 and 15 arranged lying in a plane parallel to bottom wall 18 extending plane bearing surfaces 25 and 26 a consists of a fine-mesh metal wire screen breaker plate 27 which covers the entire cross-sectional area of ​​the heating device 24th This baffle plate 27 is also provided with lateral, diametrically opposed, arc-shaped curved wall elements 28 and 29, which cover fit into the niche-like extensions 14 and 15 and these from the rest of the interior 16th Also these wall elements 28 and 29 consist of a fine metal wire mesh such as baffle plate 27 and are integrally formed on these. As 2 is seen from Fig., Rich these wall elements 28 and 29 in the axial direction not to the inner surface of the cover 2, but they end at a distance from the inner surface of the cover 2, the 14 or 15 corresponds approximately to the radial depth of the extensions, that the rebounding at this inner surface can flow each divided roughly equally freely enter the niche-like extensions 14 and 15 and continue downward therefrom. In the extension 14, a temperature sensor plate 30 is arranged approximately at half the height above the heating means 24, whose electrical connection lines are provided with a connection socket 31 in connection, which is sealingly screwed into the wall section 32 of the niche-like extension fourteenth This temperature sensor plate 30 is connected to an electrical temperature control and regulating device by means of which the desired polymerization can be adjusted and controlled. Such control devices are known per se and therefore require no further explanation here.

The resting on the shelves 25 and 26 baffle plate 27 also serves as a space for object holder 33 in which, for example, artificial teeth 34, dental crowns od. Like. May be attached. Usually such specimen holder made of perforated plates or wire loops, which are loosely fitted to the baffle plate 27 and designed the rest are such that they the heated by the heater 24 and the perforated, fine mesh baffle plate 27 penetrating air or gas flow as little as possible hinder.

In the thinner wall portion 35 of the niche-like extension 15 a pipe connection 36 is provided for the connection of a compressed gas or compressed air source in a plane below the axial-flow impeller 22 level. This arrangement of the pipe connecting branch 36 is taken to ensure that the introduced into the pressure vessel 1 through him cold compressed air or the cold compressed gas directly enters the intake region of the axial flow impeller 22 and is only heated before coming into contact with the polymerization feed 34th

The device described above, which is used to perform thermal polymerization, in particular for dental purposes, operates in the following manner:<ul><li>If after inserting the polymerization material, for example in the form of artificial teeth 34 or tooth crowns using the car parked on the baffle plate 27 Objekträgers 33 of the cover 2 is closed and locked, with the aid of the members of the other equipment of the polymerization unit electric control device the compressed air supply or pressurized gas supply and the heater 24 and the blower motor 23 turned on. If bar is reached in the pressure vessel 1 of the pre-adjustable pressure, for example 6, the further supply of compressed air or compressed gas supply is shut off while the heater 24 so long remains switched to the temperature probe 30 the preset polymerization temperature registered and accepts further control of the heater 24 so that the set temperature during the polymerization required to be copied exactly. Through the turned-on during the entire polymerization blower motor 23 driven by him axial fan 22 generates a largely extending in the direction of the shown in FIG. 2, arrow lines of air or gas circulation within the closed pressure vessel 1, wherein the gas or air stream from the fan generated 22 24 first reaches 27 through the turns of the heater to the acting as a throttle body and heat distributor baffle plate, where it further rises distributed through the fine-mesh perforation fairly evenly over the entire cross-section and the polymerization feed 34 flows around to thereafter bounce off the inside of the lid 2 or to be redirected. while receiving and in the niche-like extensions 14 and 15, the flow moving in the opposite direction and then finally back to get into the suction of the axial fan 22 and to begin the cycle anew. The baffle plate 27 and the laterally arranged thereon wall elements are 28 and 29 not only as flow but also as heat spreaders, and they contribute to that in the entire interior 16 and in the niche-like extensions 14 and 15 at any point in the same temperature and also the same pressure prevails, so that with a single temperature sensor 30 an exact temperature detection and a sufficiently accurate for a uniform temperature polymerization control is possible.</li></ul>

The embodiment illustrated in FIGS. 4 to 6 differing only with respect to its position of use from that of Fig. 1 and 2. While shown in FIGS. 1 and 2, pressure vessel 1 has a position of use in which its axis of symmetry 17 assumes a vertical position, the pressure vessel shown in FIGS. 4 to 6 1 'is designed so that its axis of symmetry 17 in the position of use is horizontal and 2, the cover is used in the manner of a flap. Instead, could also be provided for the hinge pins 4 and 5 with the propeller shaft 3 to be arranged such that the pivot axis is vertical and the cover 2 can be opened and closed like a door. In order to be used throughout the usage position can, including retaining housing, the pressure vessel 1 'in a further device components installed and / or, as shown in Figs. 4 to 6, be provided with support ledges 43 and legs 44th

Another difference from the embodiment of Figs. 1 and 2 is that the existing here, too, however, arranged in a vertical plane baffle plate 27 does not serve as a footprint, but that as a footprint, a horizontal, seated on support ribs 37 and 38 and thus transversely to the plane of the baffle plate 27 extending positioning plate 39 is provided, on which the specimen holder 33 as shown in FIG. 6 manner shown can be parked. This arrangement has the advantage that the object holder 33 the inflowing gas or the air flowing in a much less resistance than in the arrangement of Fig. 2 of the case.

All the other arrangements and functions are the same as in the embodiment of FIGS. 1 and 2, so that reference can be made to the corresponding description.

There is of course also possible to provide a container having a cylindrical or elliptical interior and those equipped in an analogous manner with an axial impeller. In this case, the fan may also be arranged so that the flow direction runs transversely to the cylinder axis or to the axis of symmetry of the elliptical cavity. It may also be expedient to arrange three-sided as flow and heat distribution in the interior perforated wall elements comprising from the sidewalls certain distance, so that the flow circuits may occur, which are favored by the arrangement of these wall elements.

It is also expedient to provide a Vorwärmthermostatschaltung, by means of which the internal temperature of the pressure vessel can be obtained at a constant preheat temperature of eg 80 ° C, so that the heating can be done in the higher lying polymerization of for example 120 ° in a shorter time.

It is also the possibility, for example, on the inside of the lid 2, facing the axial fan, an apparatus suitable for radiation polymerization radiation source, for. Example, to arrange a UV lamp and at the same time to mirror-coat the directed against the antenna element surfaces of the axial impeller so that the Polymerisationsstrahlung is reflected on the radiation source facing away from surfaces of the polymerization material.