Method of injection-molding slow release fluoride and a human dentition appliance formed thereby

SLOW-RELEASE FLUORANE INJECTION MOLDING PROCESS AND APPARATUS FOR HUMAN DENTITION RELATING TO IT.

The invention relates to oral appliances including apparatus for correcting human dentition, and more particularly relates to a method of injection molding chemicals based on fluoride, tin and other slow release preventive agents in an injection molding process. dental appliance for humans or animals to protect teeth and strengthen tissues through their fluoridation and bacteriostatic action, and incorporating these chemicals into hot-molded plastics, which in turn can be used in vacuum forming devices and by incorporating the chemicals into any flexible or rigid plastics or catouchoucs used for the manufacture of positioning devices and other devices manufactured by vacuum forming and / or by the heat or injection molding or other molding processes such as rotational molding and extrusion blow molding.

The World Health Organization recommends a fluoride ion level of 1.3 mg per day based on the exchange of fluoride by internal metabolism. Fluoride has heretofore been introduced into toothpaste, tooth fillers and even spray self-hardening acrylics for straightening appliances. Other materials such as dye and fragrances such as peppermint and other fragrances have been injection molded into orthodontic appliances.

The present invention contemplates fluoride injection molding in a human dental appliance by providing a charge of molding material or base material and mixing with the base material, by agitation, a charge of a mixture, comprising a fluoridating material and a high temperature solvent to form a pre-fluorinated mixture.

The pre-fluorinated mixture is then melted at softening temperatures, below the upper temperature limit of the high temperature solvent, to form a melt. The melt is injected into a relatively cold mold, it is shaped to form a molding in the configuration of a dental appliance for humans. It is also possible to form a dental appliance from sheets of a material which is heated and which is shaped on a model of the teeth. The dental appliance could also be formed by any molding process, such as, for example, rotational molding and extrusion blow molding. The mold is then cooled sufficiently below its softening temperature for the dental appliance to retain its shape when ejected.

The problems inherent in the methods of molding a slow release fluoride in a human plastic dental appliance are overcome by adding a high temperature solvent to the fluoridating material.

For example, a problem inherent in the above process is that the combination of moisture present in the plastic or on the injection molding machine with the fluoridating material produces hydrofluoric acid. Hydrofluoric acid is the most toxic acid known to exist. In addition, hydrofluoric acid can corrode the screw and barrel of the injection molding machine. By pre-mixing the fluoridating material with a solvent at high temperature, the fluoride will be distributed more evenly throughout the mass of the dental appliance, thus removing pockets of concentrated fluoride in and on the appliance, which can produce acid. hydrofluoric when mixed with saliva, which acid can burn tissue and stain teeth. Likewise, by premixing the fluoridating material with a solvent at high temperature, the problem of the retention of fluoride powder in the screw of the injection molding machine, forming pockets of concentrated fluoride which produce acid. hydrofluoric when mixed with moisture, is removed.

Another problem inherent in the process is the formation of stains in the molded plastic dental appliance by the fluoridating material resulting from heating the fluoridating material above its upper temperature limit. This problem is eliminated by premixing the fluoridating material with a solvent at high temperature.

When a fluoridated material such as slow release fluoride forms part of the apparatus since it has been injection molded directly into the material or absorbed by or formed into plastic, rubber, etc. Here, fluoride is brought into direct contact with the tooth surfaces most in need of decay prevention. The liberated fluoride mixes with saliva and remains in contact with the surfaces of the teeth, and in particular it can be introduced into the contact surface of adjacent teeth, to be absorbed by the regions of the teeth which decay the most frequently.

Although such a dental appliance has very wide applications, it would be particularly advantageous for children from remote regions of Third World countries who would use the appliance made according to the method of the invention, since these children frequently lack the necessary skills. fluoridated water, or any other means of obtaining fluoridation protection at an early age.

On the drawings:

Figure 1 is a perspective view of a preformed and / or custom fabricated appliance for human dentition made in accordance with the principles of the present invention;

Figure 2 is a top view of the apparatus of Figure 1;

Figure 3 is a view taken along the line III-III of Figure 2, partially in section and in elevation, showing further details of the embodiment of the apparatus;

Figure 4 is a partial cross-sectional view of the appliance of Figures 1 to 3, and showing how the appliance surrounds the user's teeth;

Figure 5 is a fairly schematic illustration of a screw-piston injection molding machine which can be used to carry out the steps of the process of the invention described herein.

Although the principles of the present invention are applicable to all oral appliances for humans, including preformed and / or custom-made dental appliances, it should be noted that the Applicant includes in the term oral appliances anti- devices. thumb sucking and pacifier type devices. The invention particularly relates to dental appliances which are injection molded from thermoplastic material rather than from sprayed self-hardening acrylic resin. Thus, the dental appliance shown in Figures 1 to 4 is an appliance made by injection molding or thermal shaping of a sheet from a thermoplastic material which includes silicone resins, polyurethane resins, polyvinyl chloride, rubber latex, waterborne polyvinyl chloride, polypropylene resins, polyethylene resins, polycarbonates and polyamides, and other thermoplastics which can be softened at temperatures below the upper temperature limit of the high temperature solvent.

For example, the mixture of the fluoridating material and the high temperature solvent should be compatible with and soluble in high temperature molded plastics such as PVC (177 ° C), polycarbonates (218 ° C) and polyamides (260 ° C). The best high temperature solvent to achieve the desired compatibility and solubility in high temperature molded plastics is a vegetable oil based solvent. It is also envisioned to use other molding methods using thermoplastic materials, such as rotational molding and extrusion blow molding.

The apparatus shown to illustrate the principles of the present invention is generally designated 20 and is U-shaped in plan to conform to the typical configuration of the human mouth, and is generally H-shaped in cross section, with a cavity 22 receiving the upper tooth and a cavity 24 receiving the lower tooth. The sides of the cavities 22 and 24 are linked by a lingual wing 26 which covers the rear of the teeth of the upper and lower arches and by a labial and buccal wing 28 which covers the front of the teeth of the two arches.

Note that the positioning apparatus 20 may have only an upper cavity 22 or a lower cavity 24. It is further noted that either or both of the cavities 22 and 24 may be provided with several depressions or alveoli receiving the teeth such as those represented in FIG. 2 at 22a, 22b, 22c, 22d, 22e, 22f, 22g and 22h.

The upper part of the lingual wing 26 immobilizes the regions of the lingual cingulum of the anterosuperior teeth and the lingual surfaces of the lingual cusps of the posterosuperior teeth, and it covers part of the upper gingival lingual surface. The lower portion of the lingual wing 26 generally conforms to the surface of the cingulum of the anteroinferior teeth and the lingual surface of the lingal cusps of the posterior inferior teeth and also extends over a portion of the lower gingival lingual tissue.

The lower labial and buccal wing 28 covers the labial and buccal surfaces of the antero and posterior inferior teeth and it also extends over part of the lower gingival labial and buccal tissue while the upper part of the labial and buccal wing 28 covers the entire labial and buccal surfaces of the antero and postero-superior teeth and it also follows a small part of the superior gingival tissue.

The various cavities such as 22a to 22h of the device are made so that the teeth are well fitted. An isthmus 30 joins the lingual and buccal or labial halves of the appliance and is generally shaped to resemble the normally relaxed space between the teeth, thus allowing all occlusal and incisor surfaces of the teeth to contact the tooth. device at all times when occlusal pressure is applied.

The variations in shape and thickness of isthmus 30 and pockets 22a to 22h inclusive are illustrated by comparing the cross-sectional portions of Figures 3 and 4.

The present invention relates in particular to an injection molding process. Generally speaking, injection molding is a process that transforms small granules of thermoplastic resins called molding powders into shaped articles, in this case a dental appliance designed for use with lacteal dentition or mixed dentition or dentition. pemanente. As indicated, it would also be possible to process the thermoplastic resins into sheets which can then be reshaped on tooth models.

Since most injection machines are made to work with molds that share in a single plane when opened, the items are designed to be conveniently ejected from these molds.

Although also applicable to the custom manufacturing or vacuum forming process, the injection molding process follows the following main steps: the feed granules or powders to be molded are chosen so that they can be melted. Further, as is envisioned in most injection molding processes, the melt is injected into a relatively cold mold and the molded product is cooled sufficiently below its softening range to retain its shape when. 'he is ejected. For many years, resin was melted in injection machines by being pushed by a piston through a heated cylinder with a metal core called a torpedo. Sometimes it has been realized that this conduction heating is not only slow but also burns plastic material. As a result, many injection molding machines today use the principle of screw plasticization borrowed from the extruder technique and adapted to injection molding. By way of illustration, one of these machines is shown in figure 5. It can be seen that it comprises a hydraulic motor 40 which turns a screw 41 by means of a splined shaft 42. A hopper 43 sends the material into a melting chamber 44. A non-return valve is shown at 46, and the accumulated melt is received in a compartment 47 having at its end a die 48. An injection piston 49 can move axially on the splined shaft 42. In this machine, the screw 44 rotates rapidly during part of the molding cycle as the melt which has just been injected into the cooled mold cools and solidifies, and the part is ejected. The mold is shown at 50, and it will be appreciated that the mold halves have a configuration such that they form the orthodontic appliance or human dental appliance 20.

When the mold closes, the rotation of the screw ceases and a hydraulic piston abruptly pushes the screw forward to inject the melt collected in the standby mold. When this happens, the machine die makes high pressure contact with the mold sprue nozzle, sealing the connection.

The injection molding machine of Figure 5 is similar to the machine illustrated and described by way of example in the Modern Plastics Encyclopedia 1988 pages 7 and 8.

In accordance with the principles of the present invention, it is contemplated to charge a thermoplastic resin base material into the hopper 43, however, prior to performing this loading, a charge of a mixture containing a material is mixed with the base material. fluoridating agent and a solvent at high temperature, to form a pre-fluorinated mixture.

Typical fluoridating materials are sodium fluoride, stannous fluoride, sodium monofluorophosphate, acidulated fluoride phosphate, aminofluoride, stannous chlorofluoride, potassium fluoride, magnesium fluoride, potassium trifluorostannite, hexafluorozirconate stannous, titanium fluoride, ammonium fluoride, fluoride glass ionomer or calcium fluoride, or any other source of fluoride and / or tin. The fluoridating material is mixed with a solvent at high temperature to form a mixture which is then mixed by stirring with the base material at concentrations varying from 0.01 mg to 200 mg per ml, or 0.01% to 70% in weight (0.02 to 10% F ion). The high temperature solvent is preferably a vegetable oil based solvent.

The most typical heat-resistant fluoride is sodium fluoride, although calcium fluoride is generally recognized as slower to release fluoride ions.

Any form of plastic or rubber used in the mouth and moldable by injection molding or heating / vacuuming processes at temperatures remaining below the upper limit of the high temperature solvent would be suitable as the base material. Thus, the beads or small granules of thermoplastic resin known under the name of molding powders could comprise any thermoplastic material chosen from silicone resins, polyurethane resins, polyvinyl chloride, rubber latex, polychloride. water-based vinyl, polypropylene resins, polyethylene resins, polycarbonates, polyamides and any other plastic resins which are injection moldable to form human dental appliances compatible with the human oral cavity.

After mixing the base material with a charge of the mixture indicated above to form a pre-fluorinated mixture, the pre-fluorinated mixture is melted at softening temperatures within a range having an upper limit not exceeding the stability limits of the solvent. at high temperature and a lower limit sufficient to soften and plasticize the base material to form a melt. As shown in Figure 5, the pre-fluorinated mixture is shown at 60 in the hopper and is melted in the chamber 44 of the injection molding apparatus. In accordance with the operation of the machine, the melt is accumulated in the melt chamber 47. '

In actual operation, sodium fluoride was found to be stable and retain its stability at temperatures below 177 ° C. In addition, most of the thermoplastic base materials listed above suitable for making orthodontic appliances plasticize or melt at temperatures above 93 ° C. For example, the melting point of PVC and polypropylenes is 177 ° C. In addition, the melting point of polycarbonates is 218 ° C while that of polyamides is 260 ° C. Under these conditions, it will be appreciated that the step of melting the pre-fluorinated mixture can be carried out in accordance with the invention at temperatures in the range of 93 ° C to 260 ° C.

The melt accumulated in chamber 47 is then injected into the relatively cool mold 50 which has molding recesses shaped to form a molding in the configuration of the human orthodontic appliance or dental appliance 20 illustrated and described in connection with Figures 1 through. 4. The molding is then cooled sufficiently below its softening range so that the apparatus retains its shape when ejected from the mold 50.

Since children are often required to wear dental braces which are made of flexible elastic plastic for one to several hours a day, or possibly overnight, while they are asleep, the present invention advantageously achieves a slow release of. fluoride that is extracted from the device when worn. The fluoridating material is heat stable so that when the child or user wears the device, fluoride will extract from the device and mix with fluids in the mouth, especially in the area between. dental apparatus and tooth surfaces.

Known oral, labial, lingual and occlusal surfaces of the teeth come in direct contact with the appliance and the fluids of the mouth and remain for 20 minutes to several hours every day, without being washed away with saliva, the environment is ideal for preventively fluoridating teeth when the appliance is in use, especially since the appliance is adjacent to the surfaces of the teeth.

The principles of the present invention are particularly applicable to devices or anti-sucking devices of the thumb, and of the pacifier type, intended for use by children in remote areas of Third World countries which frequently use these. devices but do not have fluoridated water or any other way of obtaining fluoridation protection at an early age. Stannous compounds (of tin), especially with fluorides, are also bacteriostatic in nature and reduce periodontal problems and plaque formation around the teeth, and as they are pressed into and around the gums. , they will prevent periodontitis and the problems it poses, especially by the slow release and long contact of fluoride and tin with the areas of the teeth and gums.

Fluoride and tin refill may be periodically performed on the apparatus, or it may be another method of dipping the apparatus into the fluoride (and stannous) compound. Certain regions of the appliance can also be submerged, for example only around the regions of the teeth, by placing the chemicals in the alveoli and allowing the chemicals to penetrate by absorption into the soluble type plastic. In this way, the fluoride based chemicals are mostly present on the surface of the teeth and not on the surface of the cheeks, so that irritation of the cheeks is avoided. After several hours of immersion, the device is rinsed and dried, and it is ready to be used in the mouth. The absorption of fluoride ion can be accelerated by giving the device a positive electric charge when submerged and, when placed in the mouth, the device can be inverted and receive a negative charge then that the body can receive a positive charge from simple accumulators.

Numerous modifications can be made to the invention by a person skilled in the art without departing from the scope of

The invention.