Mouldable support article and method of making it

Abstract: An article made from a thermoplastic composition such as customizable mouldable parts of articles such as dental plates or hand grips or sports equipment which composition is set below 37°C and is conformably mouldable between about 50°C and 95°C. Such a composition includes a methacrylate polymer which may soften or become liquid in the range of 50°C to 95°C and may be mixed with another such polymer which is set at that temperature range so that a mouldable mass is formed, for example by warming in warm water. The invention includes a method of forming the composition.

Description: The invention relates to a method of making a thermoplastic composition to form a mouldable, settable article, which after setting is hard at body temperature, which method comprises mixing a liquid mixture comprising methyl methacrylate monomer and a plasticizer with a polyacrylic powder. Support devices, particularly orthopaedic supports are required in numerous circumstances. For example, supports may be required for any portions of the body, for disabled persons. Insoles may be required for shoes, to provide support for the feet. Joint supports may be required for various joints of the body which may have become injured or defective for any reason. A support may be required for the head or neck, or back. A seat may be required conforming to the shape of an individual. In addition, in very many cases supports are required for the hand or hands of a person suffering from some kind of disability. A person with no disability at all, may require to have a handle on an article which conforms precisely to the shape of his or her hand. Persons requiring such hand supports may simply require a shaped grip, which conforms precisely to the shape of their hand. Such persons may be craftsman, or it may be professionals such as surgeons, or may be sportsmen such as players of various games such as racquet sports and golf or other sportsmen such as fishermen and hunters any of whom may require an article such as the handle of a golf club, fishing rod, or the stock of a weapon, to be shaped to particularly conform to the hand. In most cases such a person will not be suffering from any disability, but will merely require a precise match between the shape of the hand grip and their hand. Conversely, persons suffering for example from arthritis of the fingers or other joints may require a hand grip of a peculiar shape, to conform to the somewhat deformed shape of their hand resulting from such a disability. In the case of certain other sports, shoe, or boot liners may be required to conform precisely to the shape of the foot. This is particularly required for example in the sport of skiing where the boot is required to fit snugly under the instep and all over the foot. Conformable support devices may also be required in many other cases other than orthopaedic situations. Such cases may arise in the case of packaging or containing of precision or scientific instruments, to prevent damage. Other cases may involve the provision of a shaped work support for holding a particular work piece, such as, an item of jewellery for example, while it is being worked upon. In the past, various different systems have been proposed of more or less considerable complexity and expense. Orthopaedic supports requiring special forming and moulding techniques are of course well known and are manufactured routinely from fast setting plaster materials. In other cases, supports have been shaped from bendable metal sections. In other cases, a complex multi-stage formation process is involved including the steps of making a "plug" in the shape of a limb, or portion of the body or an article, and them forming a support of glass fibre reinforced resin material, with or without padding. In other cases supports such as for example gun stocks are actually carved by hand out of wood, in an effort to as far as possible conform to the hand and body of the user. Clearly, where such a conformable support device is required, it is desirable if it can be manufactured in a simple one step technique out of low cost materials. Preferably it will be made by direct contact with the portion of the body, or the article, which it is intended to support. In this way any loss of accuracy due to the making of intermediate articles such as plugs, moulds and the like is avoided. In the particular field of dentistry, it has been known to utilize settable materials for obtaining a form from the mouth or teeth. These settable materials are then used in a multi-stage process for making dentures, or denture supports, or for example making caps for teeth. Such settable materials are of such a nature that generally speaking they do not set completely hard, and are relatively easily distorted out of shape. Consequently, once the form has been taken from the mouth, the materials must then be treated with considerable care. In the manufacture of dentures, it is customary for example that some parts of the denture shall be shaped so that supprort portions of the denture will actually fit on ridges formed by the gums, and thus be retained in position in the mouth. It is however well known that in these cases the retention formations on the dentures must be made with great care. If they conform precisely to the shape of the ridges and grooves in the gums, then the insertion and removal of the dentures may cause considerable discomfort. On the other hand, if there is any substantial degree of clearance or play, than they may easily become displaced. The use of denture retention materials only partially overcomes this problem. US-A-4.247.287 disloses a prosthetic denture fixture containing a rigid frame made from a first composition and an adjustable portion formed by an article as described above in the first paragraph. The liquid mixture of the article comprises exclusively an acrylic monomer, preferably methyl methacrylate monomer and a plasticizer, while the polyacrylic powder is methyl methacrylate or a mixture of methyl methacrylate and a copolymer of it. However, the adjustable portion or article, when cured becomes rigid but not completely polymerized and therefore deformable and capable of being shaped with finger pressure one or a limited number of times. In fact only fully denture are produced in large runs. The dentist softens the adjustable portion by immersion in hot water and remold it by finger pressure after inspection the oral cavity to determine the amount of adjustement required. After cooling, the dentist fits the remolded denture into the patient's mouth. If a second adjustement is necessary, the process is repeated to obtain a closer adjusted fit. This is only possible as long as the final setting is not reached. A remolding as often as required is not possible. Also the final fitting is impossible to obtain and a liner is needed for such final fitting. US-A-4.248.807 also discloses a similar prosthetic denture device having an adjustable portion having the same characteristics and method of use as describe herebefore. The liquid mixture comprises ethyl methacrylate and isobutyl acrylate and a plasticizer, while the polyacrylic powder is a mixture comprising polyvinyl acetate-based polymer, a homopolymer of ethyl methacrylate and a peroxide catalyst. When cured this adjustable portion becomes rigid but not completely polymerized and therefore capable of being remolded when elevated in temperature. Also a liner is needed for final fitting. US-A-4.361.528 discloses a method of making a dental impression tray which is used to hold impression material. This tray is made by heating under pressure a mixture of, on the one hand, a mixture of a liquid methyl methacrylate momomer and a plasticizer, and, on the other hand, a methyl methacrylate polymer powder. It is an object of the invention to provide for a method of making a thermoplastic composition of the above mentioned kind which permits to obtain a composition which is readily and easily be softened and reshaped from time to time as often as is required, so to ensure complete comfort for the wearer at all times. According to the invention, this object is accomplished by a method of the above kind, in which 27.8 to 76.75 parts of liquid methyl methacrylate monomer, 2.5 to 8 parts of liquid butyl methacrylate monomer and 20 to 64 parts of plasticizer mixture, said parts being per hundred of said liquid mixture, are mixed together and said mixture is mixed with powdered polyethyl methacrylate polymer being at least substantially set at temperatures below 95°C, together with a polymerization initiator, the powdered polyethyl methacrylate and the liquid mixture being mixed in a ratio by weight between 1/1 and 3/1, said liquid mixture and powdered polyethyl methacrylate polymer in said composition being polymerized, the composition being capable of being repeatedly rendered substantially manually re-moldable at temperatures between 50°C and 95°C for repeated customization to the shape of a portion of a person. The invention also relates to a dental article forming part of a dental fixture, said article comprising a thermoplastic composition which, after setting, is hard at body temperature, said thermoplastic composition consisting of a liquid mixture comprising a quantity of liquid methylmethacrylate monomer and a quantity of a plasticiser and a polyacrylic powder mixed with said liquid mixture. The invention seeks to incorporate in a denture or denture plate a mouldable and settable portion, such that it could be inserted into the mouth and then shaped to precisely fit the ridges an grooves in the gums, or fit the tongue to provide a secure retention of the denture plate within the mouth, and also to the floor of the mouth and to the bottom of the tongue, and furthermore that it could readily and easily be softened and reshaped from time to time as often as is required, so to ensure complete comfort for the wearer at all times. According to the invention, this object is accomplished by a dental article forming part of a dental fixture, of the above kind, in which the thermoplastic composition is made in accordance with the method of the invention, whereby the polymerized composition remains set after polymerization at temperatures in the region up to about 37°C, the article being located on the exterior of said fixture for contact with the person. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective illustration of a typical lower denture, showing the mouldable and conformable sublingual support devices formed of a material according to the invention attached to the inner walls of the denture; Figure 2 is a top view of an upper denture plate and shows the area where a thermoplastic postdam formed of a material according to the invention would serve to seal the back edge of the plate, from air entering underneath the plate; Figure 3 shows a denture base made of a uniform thin layer of thermosetting acrylic plastics material and a layer of soft thermoplastic reline material according to the invention inside the denture; Figures 4 shows how the thermoplastic denture wall formed of a material according to the invention on a lower denture can be made to conform into the undercuts at the back of the lower gums; Figure 5 shows an example of a partial denture, attaching artificial teeth to natural teeth, by means of a thermoplastic clasp formed of a material according to the invention; Figure 6 shows six front teeth of a denture fixed into a layer of thermoplastic material according to the invention, to be moveable and adjustable when heated; Figure 7 illustrates the handle of an article, in this case a bat for playing table tennis, showing a conformable and mouldable body in accordance with the invention thereon; Figure 8 shows a section of the handle, along line 8-8 of Figure 7 surrounded by a resilient flexible material, completely wrapped into a layer of thermoplastic material; Figure 9 illustrates the handle of the article of Figure 7, after being heated and moulded to fit the form of a hand; Figure 10 shows an insole for a shoe according to the invention; and Figure 11 shows a protective helmet according to the invention, partially in section. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As explained above, while the invention is of wide application to many fields, it is explained here principally in the field of its orthopaedic use, and in particular, in the field of dentistry. As is well known, the fitting of dentures and denture plates is a tiresome task both for the dentist and the patient. Moulds are taken by the dentist, in order for him to as far as possible build a denture or denture plate which is shaped to conform to the mouth. Retention devices are often incorporated in dentures and denture plates to retain them in position. In some cases wire loops or hooks are incorporated in denture plates to engage either the teeth, or to lie under the tongue. The fitting and bending and setting of these retention devices requires great care and skill. During actual use, the dentures are taken out at night and replaced in the morning, and must be fully cleansed. It is not unusual for dentures to become damaged, and in particular for the wire retention devices to become deformed. This then means that the denture must be returned to the dentist for refitting. Even when fitted with great care, it is well known that denture plates often cause discomfort and become loose. Denture retention materials, which are essentially formed of adhesive or mastic materials are well known, but are distasteful to use and are often only partially effective and are only deemed to be a temporary measure. Clearly therefore the provision of retention devices on a denture plate which are essentially self fitting, so that the actual wearer can shape them and fit them to suit the wearer, and can repeat the fitting and moulding operations as many times as is required. This will offer numerous advantages, and will substantially reduce the end cost of the dentures to the wearer. In accordance with the invention as illustrated in Figures 1 to 6, a denture supports of various types are illustrated, each having a plurality of teeth secured thereto. Such denture supports, also known as denture plates, are made in a variety of shapes, depending upon the number of false teeth that it is desired to support within a person's mouth, and their location. Typical denture plates have the generally U shaped configuration as shown, to conform to the gums of the upper or lower jaw. In other cases, full denture plates, extending across the mouth from side to side are provided, where greatest support is required. As is well known, the fitting of such denture supports to the gums and flesh of the interior of the mouth requires considerable time and skill. As mentioned above, such a fitting operation can never make a perfect fit to any individual. This is because a variety of reasons, including the difficulty of taking an accurate mould of the shape of a persons gums, the changes which take place in the shape of a persons gums from time to time, but most of all, from the fact that if an absolutely perfect fit is achieved, then inserting and removing the denture support may be extremely difficult if not impossible. Accordingly, it is customary for wearers of dentures to retain the denture support in the mouth with some form of mastic or adhesive-like material. This is messy and distasteful, and is also known to be somewhat ineffective in many cases. Figure 1 shows a lower denture 10 formed of conventional material but having teeth 12 and two mouldable conformable sublingual wings 14A, 14B. The sublingual wings are located to lie beneath the tongue of a wearer, and are illustrated as each having a U-shape, the legs of the U being short and the web being long in comparison to the legs. Such sublingual wings may be secured by means of a suitable permanent adhesive, or by thermoplastic material, or by thermosetting material. Whatever the material used, the ends of the legs 14a-14b define abutments of the material, embedded in holes, grooves or slots in the denture. The conformable sublingual wings 14A, 14B are formed of a material according to the invention of a type to be described below. The material is such that at normal ambient and body temperatures it is substantially hard and rigid. At somewhat elevated temperatures over 50°C, and usually between 50°C and 95°C, the material becomes soft and mouldable. If the user wishes to adjust the moulding of the sublingual devices 14A, and 14B, he may dip them in a cup of hot water to soften the material. The dentures may then be placed in the mouth while the sublingual devices are still soft, and the moulding may be adjusted by manipulating the sublingual devices with the fingers and/or with the tongue and/or the muscle on the bottom of the mouth. The sublingual devices can be moulded to conform precisely to the interior shape of the mouth as suggested in phantom in Figure 1. Figure 2 illustrates an upper denture support having teeth 20 and a postdam 22. Conventionally a postdam is constructed by scoring the stone model constructed from the impression moulds, at the palatal periphery, by hand with a sharp instrument or by drill more or less guessing at the depth and length of the postdam. The present invention allows the provision of a postdam region which is fully customizable to the patient's requirements. Simply by immersing the denture in warm water for a minute, the dentist can now adjust the postdam in any way required. At body temperature the material will regain rigidity. The postdam can even be shortened if required, simply by cutting the material while still warm, with sharp scissors. Figure 3 illustrates a denture 30 having a lining 32 of a material according to the invention. Such lining may be warmed in warm water and then conformed with the ridges and shape of the patients lower jaw. An upper denture may have a similar lining. In the construction of conventional lower dentures, when the lower ridges are badly shrunk, often it is not possible to give the patient a stable prosthesis. Up to now the large undercuts, always existing near the back of the lingual aspect of the mandible, could not be utilized to stabilize the lower denture. The "undercuts" are, however, particularly suitable for receiving the mouldable lingual aspects of a lower denture (Figure 4). When the dentures 40 (or at least the rear lingual aspects 42 of a lower denture) are formed of material according to the invention, the mouldable lingual aspects may be moulded into these undercuts, to hook into them. A different position of one the lingual aspects 42 is shown in phantom lines. Thus the mouldable lingual aspects may be bent in either direction of the arrow to hook into the undercuts or to disengage from them. The mouth may be rinsed with cold water to accelerate cooling and setting. Lingual aspects 42 may then remain substantially hard and rigid and retain the denture in position as long as the wearer wishes it to remain. In order to remove the denture, all that the wearer has to do is to rinse the mouth with hot water. The heat will tend to soften the lingual aspects 42. This will then permit the wearer of the denture to simply grasp the denture with a finger and thumb and withdraw it from the mouth. In accordance with the formulations of the invention described below, this operation may be carried out if desired on a daily basis. Figure 5 illustrates part of a denture 50 including a clasp 52 for attaching artificial teeth 54 of the denture 50 to natural teeth 56 in the patient's gum 58. The clasp 52 is made of material according to the invention and may be attached in position very easily. The dentures with the clasp material is immersed in warm water and inserted into the mouth while still warm. The clasp 52 is moulded firmly around the tooth 56 to which it is to be joined. A mouthful of cold water accelerates setting. Figure 6 illustrates the use of thermoplastic material according to the invention in the front aspect 62 of an upper denture 60. Again a firm bond, customized to the patient's mouth is easily achievable. Figures 7, 8, and 9 illustrate the use of material according to the invention for a non-dental application, i.e. for custom moulding the hand grip of a piece of sports equipment. Numerous such applications, such as helmets and other protective sportswear, splints, seating, shoe inserts and other foot wear and packing material are also possible. It will be appreciated that the general principal may be applied to any or all of these items as will be readily understood from the following description which is specific to the moulding of a table tennis bat handle. A table tennis bat 70 has a handle 72. The handle 72 comprises a central longitudinal core 74 optionally covered by a layer of compressible flexible material 76 such as foamed material. Over the layer of foamed material 76 or, if such material is not present, directly over the core 74 is a conformable article or an outer layer 78 of material according to the invention. The bat handle 72, before customization, may be roughly contoured to the shape of a hand gripping it or it may be substantially noncontoured. To customize the handle it is dipped in warm water and gripped by the user. The warm water softens the conformable outer layer 78 to make it conformably mouldable. The grip of the user, thereafter, moulds the layer 78 as shown i.e. by moulded handle 73 in Figure 9 to his particular grip. Setting may be hastened by dipping the moulded handle in cold water. When warm water is referred to herein, it is meant that the temperature of the water is sufficient to make the material according to the invention become conformably mouldable. This temperature is usually from 50°C to 95°C. From the possible range of uses of the material it will be appreciated that the set hardness will not necessarily be the same for all and uses. For example, a postdam region of a dental plate will generally be harder than a mouth guard or a table tennis bat handle. Figure 10 shows an insole for a shoe having a lower layer 82 formed of conventional insole material such as foam rubber. The insole also includes an upper layer 84 formed of the mouldable, conformable composition of the invention. When the insole is heated to a temperature between about 50°C and 95°C the upper layer 84 becomes mouldable. At a temperature within this range comfortable to the user the upper layer may be moulded to fit the shape of the foot. Thereafter, at body temperature, the shape is retained. Figure 11 shows a protective helmet for example a hockey helmet, in general outline. A section of the helmet is cut away to show the outer shell, and foam padding 92. An upper portion of padding 92 is provided with an inwardly directed layer 94 of thermoplastic material according to the invention which is conformably mouldable between 50°C and 95°C. Such a hockey helmet may have the layer moulded to conform to the head contours of a user by heating the helmet to a temperature within the range of about 50°C to 95°C. At a temperature comfortable to the user but within this range, the layer may be moulded to the shape of the user's head. Thereafter, at body temperature the layer will retain its moulded shape. various materials according to the invention and their method of preparation will now be described by way of example. Examples 1-6 Conformably mouldable compositions were prepared as follows: Six mixtures were prepared according to the ingredients and proportions set out in Table I. A polymer powder mixture was prepared comprising 99 parts by weight of solid polyethylmethacrylate and one part by weight benzoyl peroxide which is a polymerization initiator. The powder mixture was then used to prepare 6 different compositions set out below in Table 1, with different proportions of monomer mixtures. MONOMER LIQUID MIX 1 MIX 2 MIX 3 MIX 4 MIX 5 MIX 6 1. Methyl methacrylate (inhibited with hydroquinone 50 ppm) 54.5 27.8 76.75 63.4 58.95 72.3 2. Butyl methacrylate 5 8 2.5 4 4.5 3 3. Dibutyl phthalate 22 35.2 11 17.6 19.8 13.2 4. Dioctyl phthalate 18 28.8 9 14.4 16.2 10.8 5. Ethylene glycol dimethacrylate 0.5 0.2 0.75 0.6 0.55 0.7 (All figures are in parts per hundred) The compositions of liquid mixtures 1-6 were each mixed with the polymer powder mixture in a ratio of one part liquid mixture to two parts polymer powder mixture. Each of the resulting liquid monomer/powder polymer mixtures was held at 100°C in boiling water for a period of 30 minutes to polymerize the monomer, to result in six thermoplastic polymer compositions A-F (see below). Each polymer composition was used to mould various articles at between 50°C and 95°C and each was found to be especially appropriate for the uses as set out in Table II. Thermoplastic material Mixture used Ratio by weight of liquid mixture: polymer powder Use A 1 1:2 Mouthguards TMJ Appliances. B 2 1:2 Gasket clasps. C 3 1:2 Postdam regions of dental plates, hand grips, sports equipment, splints D 4 1:2 Dental clasps E 5 1:2 Sublingual wings F 6 1:2 Rear lingual aspect of lower dental plate It will be appreciated that the hardness or softness of the resulting product is dependent upon the proportion of methacrylate monomer used in the liquid monomer mixture B. It is possible to vary the ratio of liquid monomer mixture to polymer powder within a range of, for example, 1:1 to 1:3 by weight. Other polymerization inhibitors are, of course possible but should only be present in an amount to inhibit premature polymerization of the monomer prior to mixing with polymer. Many other variations and modifications are possible within the scope of the invention. The foregoing is a description of a preferred embodiment of the invention which is given here by way of example only. The invention is not to be taken as limited to any of the specific features as described, but comprehends all such variations thereof as come within the scope of the appended claims.

Claims: A method of making a thermoplastic composition to form a mouldable, settable article, which after setting is hard at body temperature, which method comprises mixing a liquid mixture comprising methyl methacrylate monomer and a plasticizer with a polyacrylic powder, characterized in that 27.8 to 76.75 parts of liquid methyl methacrylate monomer, 2.5 to 8 parts of liquid butyl methacrylate monomer and 20 to 64 parts of plasticizer mixture, said parts being per hundred of said liquid mixture, are mixed together and said mixture is mixed with powdered polyethyl methacrylate polymer being at least substantially set at temperatures below 95°C, together with a polymerization initiator, the powdered polyethyl methacrylate and the liquid mixture being mixed in a ratio by weight between 1/1 and 3/1, said liquid mixture and powdered polyethyl methacrylate polymer in said composition being polymerized, the composition being capable of being repeatedly rendered substantially re-moldable at temperatures between 50°C and 95°C for repeated customization to the shape of a portion of a person. A method according to claim 1, characterised in that the plasticizer mixture comprises a mixture of dibutyl phtalate and dioctyl phtalate. A method according to claim 1 or 2, characterised in that the ratio by weight between the powdered polyethyl methacrylate and the liquid mixture is between 1/1 and 2/1. A method according to any one of claims 1 to 3, characterised in that the liquid mixture includes ethylene glycol dimethacrylate as a cross-linking agent. A dental article forming part of a dental fixture, characterised in that said article comprises a thermoplastic composition made in accordance with the method of claim 1 whereby the polymerized composition remains set after polymerization at temperatures in the region up to about 37°C, the article being located on the exterior of said fixture for contact with the person. An article according to claim 5, characterised in that the plasticizer mixture comprises a mixture of dibutyl phtalate and dioctyl phtalate. An article according to claim 5 or 6, characterised in that the ratio by weight between the powdered polyethyl methacrylate and the liquid mixture is between 1/1 and about 2/1. An article according any one of claims 5 to 7, characterised in that the liquid mixture includes ethylene glycol dimethacrylate as a cross-linking agent.

Inventors: HUYBRECHTS ROBERT, HUYBRECHTS, ROBERT
Applicants: HUYBRECHTS ROBERT, HUYBRECHTS, ROBERT
Application year: 1993
Main classification: C08F265
IPC codes: A61C13, A63B59, C08F265, A42B3