US20050011885A1 - Hand-held microwave polymerization system for dentistry - Google Patents

Hand-held microwave polymerization system for dentistry Download PDF

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US20050011885A1
US20050011885A1 US10/822,548 US82254804A US2005011885A1 US 20050011885 A1 US20050011885 A1 US 20050011885A1 US 82254804 A US82254804 A US 82254804A US 2005011885 A1 US2005011885 A1 US 2005011885A1
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microwave
polymer
dental
filler
composition
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Marc Seghatol
Jean-Pierre Durand
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Seghatol Marc
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Marc Seghatol
Jean-Pierre Durand
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Priority to CA 2246663 priority Critical patent/CA2246663A1/en
Priority to CA2,246,663 priority
Priority to US09/399,580 priority patent/US6254389B1/en
Priority to US09/399,997 priority patent/US6441354B1/en
Priority to US09/897,317 priority patent/US7004755B2/en
Priority to US10/166,569 priority patent/US6737619B2/en
Application filed by Marc Seghatol, Jean-Pierre Durand filed Critical Marc Seghatol
Priority to US10/822,548 priority patent/US20050011885A1/en
Publication of US20050011885A1 publication Critical patent/US20050011885A1/en
Application status is Abandoned legal-status Critical

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    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61LMETHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION, OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS, OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS, OR SURGICAL ARTICLES
    • A61L2/00Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor
    • A61L2/02Methods or apparatus for disinfecting or sterilising materials or objects other than foodstuffs or contact lenses; Accessories therefor using physical phenomena
    • A61L2/08Radiation
    • A61L2/12Microwaves
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C13/00Dental prostheses; Making same
    • A61C13/20Methods or devices for soldering, casting, moulding or melting
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C5/00Filling or capping teeth
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C5/00Filling or capping teeth
    • A61C5/70Tooth crowns; Making thereof
    • A61C5/77Methods or devices for making crowns
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B6/00Heating by electric, magnetic, or electromagnetic fields
    • H05B6/64Heating using microwaves
    • H05B6/80Apparatus for specific applications
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C13/00Dental prostheses; Making same
    • A61C13/12Tools for fastening artificial teeth; Holders, clamps, or stands for artificial teeth
    • A61C13/16Curing flasks; Holders therefor
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C13/00Dental prostheses; Making same
    • A61C13/20Methods or devices for soldering, casting, moulding or melting
    • A61C13/203Methods or devices for soldering, casting, moulding or melting using microwave energy
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C13/00Dental prostheses; Making same
    • A61C13/20Methods or devices for soldering, casting, moulding or melting
    • A61C13/206Injection moulding
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B2206/00Aspects relating to heating by electric, magnetic, or electromagnetic fields covered by group H05B6/00
    • H05B2206/04Heating using microwaves
    • H05B2206/045Microwave disinfection, sterilization, destruction of waste...

Abstract

A hand-held microwave system for intra-oral dentistry utilizes microwave energy to cure polymer materials intra-orally so as to produce dental composites having improved physical characteristics, and also utilizes microwave energy to detect the presence of and to preferentially heat caries or cavities, thereby disinfecting and therapeutically treating the caries in a potentially non-invasive manner. The intra-oral polymerization process can be accomplished with less overall energy and with composite-matrices that maximally absorb the microwave energy so as to reduce heating of adjacent tissue. The antenna of a hand-held version of the intra-oral microwave system is also advantageously designed to detect the presence of and to preferentially heat caries or cavities, thereby disinfecting and therapeutically treating the caries in a potentially non-invasive manner. A method and product by process for the system are also disclosed.

Description

    RELATED APPLICATIONS
  • The present invention is a continuation of two co-pending applications, the first of which is U.S. patent application Ser. No. 10/166,569 entitled, “MICROWAVE POLYMERIZATION SYSTEM FOR DENTISTRY,” filed Jun. 10, 2002, which is a continuation of U.S. patent application Ser. No. 09/399,997, also entitled, “MICROWAVE POLYMERIZATION SYSTEM FOR DENTISTRY,” filed Sep. 20, 1999, and now issued as U.S. Pat. No. 6,441,354, which claims priority to PCT Application No. PCT/US99/20960, filed Sep. 17, 1999, which claims priority to Canadian Patent No. 2,246,663, filed Sep. 18, 1998, the second of which is U.S. patent application Ser. No. 09/897,317 entitled, “HAND-HELD MICROWAVE INTRA-ORAL DENTAL SYSTEM,” filed Jul. 2, 2001, which is a continuation of U.S. patent application Ser. No. 09/399,580, also entitled, “HAND-HELD MICROWAVE INTRA-ORAL DENTAL SYSTEM,” filed Sep. 20, 1999, and now issued as U.S. Pat. No. 6,254,389, the contents of all of which are hereby incorporated by reference.
  • FIELD OF THE INVENTION
  • The present invention relates generally to the field of dentistry. More specifically, the present invention relates to a hand-held microwave system for intra-oral dentistry that utilizes microwave energy to cure polymer materials intra-orally so as to produce dental composites having improved physical characteristics, and also utilizes microwave energy to detect the presence of and to preferentially heat caries or cavities, thereby disinfecting and therapeutically treating the caries in a potentially non-invasive manner.
  • BACKGROUND OF THE INVENTION
  • The use of polymer materials in the dental arts for the restoration of lost or damaged teeth is well known. Such uses fall into two general categories: (i) the use of polymer materials to produce dental prosthetics, such as dentures, bridges and crowns, that are either permanent or removable articles, and (ii) the use of polymer materials to create dental composites for fillings to repair teeth instead of using conventional amalgam fillings or as veneers to refinish tooth enamel surfaces. The first category of dental articles, dental prosthetics, are created outside of the patient (i.e., extra-oral), typically by making an impression of what the desired article should look like and then molding the article to match the impression. The second category of dental articles, dental composites, are created directly in the patient's mouth (i.e., intra-oral) as fillings or veneers to repair or resurface teeth. Regardless of which category is being considered, dental articles made of polymer materials must have adequate strength, durability, and dimensional stability and must also be biocompatible and chemically inert. It is also important to be able to process each type of dental article rapidly, conveniently, safely and economically.
  • An example of a dental prosthetic in the first category of dental articles that is created using polymer materials is a removable denture. Most commercial dentures are created using a paste or resin matrix formed of various polymers, co-polymers and monomers (typically methyl methacrylate), as well as certain cross-linking agents, initiators, accelerators and other additives. This resin matrix is formed into a plaster mold and is then hardened or cured by applying energy in the form of heat. Typically, the plaster mold containing the uncured denture is prepared in a dental laboratory based on an impression taken by the dentist. To cure the resin matrix, the plaster mold is placed into a flask that is then put in a thermal water-bath for up to 8 hours. This conventional process of curing a denture takes such a long time because both the plaster molds and the polymers in the resin matrix are relatively poor thermal conductors and are heated only from the outside via the thermal water-bath. The conventional process can also result in large numbers of voids and significant shrinkage during curing due to uneven thermal conduction and non-uniform polymerization of the resin matrix. These problems are discussed in Feilzer A. J. et al., “Curing contraction of composites and glass-ionomer cements,” Journal of Prosthetic Dentistry, Vol. 59, pp. 297-300 (1988); and Ferracane J. L. et al., “Wear and marginal breakdown of composite with various degrees of cure,” J Dent. Res., Vol. 76, No. 8, pp. 1508-16 (1997). The lack of completely uniform polymerization of the denture also leaves residual monomers that are toxic and can act as irritants to oral tissues and compromise the physical characteristics of the denture.
  • In an effort to overcome the long cure times associated with the conventional thermal water-bath technique, a technique of using commercial microwave ovens to heat and cure polymer resins to form dental prosthetics has been developed. In the conventional thermal curing method for polymer dental articles, a temperature differential is required to force heat by conduction from the surface of the flask and mold to the center of the article. Because the heat penetrates from the outside to the internal portions of the material by thermal conduction, overheating and degrading polymers can occur at the outer surface of the article. When microwaves are used to initiate the thermal curing processing, it is possible for the article to be heated uniformly as the electromagnetic radiation instantaneously penetrates deeply and heating occurs throughout all three dimensions of the irradiated article. The main advantages provided by microwave energy include a rapid internal heating independent of the heat flow through the surface, as well as minimal thermal lag and thermal gradients throughout the interior of the article, which results in a more homogeneous curing of the article with a higher degree of conversion of monomers into polymer chains.
  • Comparisons of these two techniques can be found in Hayden W. J., “Flexure strength of microwave-cured denture baseplates,” General Dentistry, Vol. 343, pp. 367 (1986); Al Doori D et al., “A comparison of denture base acrylic resins polymerized by microwave irradiation and by conventional water bath curing systems,” Dental Materials, Vol. 4, pp. 25-32 (1988); and Geerts G. et al., “A comparison of the bond strengths of microwave and water bath-cured denture materials,” The Journal of Prosthetic Dentistry, Vol. 66, No. 3, pp. 403-07 (September 1991). Various types of flasks and molding equipment that can be used in conjunction with a commercial microwave oven for processing and curing dental articles made of polymers have been developed as described, for example, in U.S. Pat. Nos. 4,971,735, 5,151,279, 5,324,186 and 5,510,411, European Patent No. 0 687 451 A2, and Japanese Patent No. JP7031632A. The repair of dentures and related articles using microwave processing is also described in Turck M. D. et al., “Microwave processing for dentures, relines, repairs and rebases,” The Journal of Prosthetic Dentistry, Vol. 69, No. 3, pp. 340-43 (1993). Generally, dentures cured by commercial microwave ovens have improved mechanical properties, and often have better adaptation than those cured by the water-bath method. The primary advantage of microwave curing, however, is the reduced processing times which can be shortened from 8 hours or more to as little as a few minutes.
  • While the use of commercial microwave ovens to cure dental prosthetics solves some of the problems of conventional thermal water-bath cured prosthetics, dental prosthetics processed in this manner can be less than satisfactory in terms of their physical and biocompatibility characteristics because varying degrees of cure, micro-shrinkage and porosities are still present. Any large degree of micro-shrinkage or porosities in the polymers of dental prosthetics cured using conventional microwave ovens will lead to fitting inaccuracy and unreliability. These problems are discussed in Wallace P. W. et al., “Dimensional accuracy of denture resin cured by microwave energy,” The Journal of Prosthetic Dentistry, Vol. 68, pp. 634-40 (1992); and Salim S. et al., “The dimensional accuracy of rectangular acrylic resin specimens cured by three denture base processing methods,” The Journal of Prosthetic Dentistry, Vol. 67, pp. 879-85 (1992).
  • It understood in the dental arts that micro-shrinkage is primarily due to the resin matrix. The physical and mechanical properties of a polymer material, such as hardness, stiffness and abrasion resistance and strength, are highly influenced by the arrangement of the resin matrix when the fillers and coupling agents are fixed during the curing process. Micro-shrinkage results from the shorter distance between atoms in the resin matrix after polymerization than before polymerization. The monomers in the resin matrix are located at Van der Waals distance, which change to a covalent bond distance once the resin matrix is polymerized. If all of the monomers in the resin matrix are not converted into polymer chains during the polymerization curing process, then this change in distance can induce mechanical stresses in the form of micro-shrinkage in those areas where there was not complete conversion of the monomers into polymers. Commercial resin matrices are found to undergo volume shrinkage of as much as 7% with most resin matrices shrinking 2-3%. This kind of micro-shrinkage causes volumetric dimensional change that can result in poor fitting of the dental prosthetic to oral tissues and can build up mechanical stress in the dental prosthetic that can lead to premature mechanical failure. A discussion of some of these issues can be found in D. Bogdal, “Application of Diol Dimethacrylates in Dental Composites and Their Influence on Polymerization Shrinkage,” J. Appl. Polym. Sci., Vol. 66, pp. 2333-2337 (1997), and D. Bogdal et al., “The Determination of Polymerization Shrinkage of Materials for Conservative Dentistry,” Polimery, Vol. 41, pp. 469 (1996).
  • Another problem caused by the residual monomers not being converted into polymer chains during the polymerization curing process is the leaching of any unbound monomers or additives out of the article. The leaching has an impact on both the structural stability and biocompatibility. The residual monomers can leach into salivary fluids which then irritates any mouth tissues in contact with these contaminated fluids; or the residual monomers can diffuse directly into the dentin and pulp of teeth adjacent to the dental prosthetic. These problems are described in Ferracane J. L., “Elution of leachable components from composites,” Journal of Oral Rehabilitation, Vol. 21, pp. 441-52 (1994); and Hume W. R. et al., “Bioavailability of components of resin-based materials which are applied to teeth,” Crit. Rev. Oral Biol. Med., Vol. 7, No. 2, pp. 172-79 (1996).
  • The primary solutions to these problems have focused on increasing the degree of polymerization and cross-linking of all of the monomers in the resin matrix by changing the formulation of the resin matrix. Improvements in resin formulation involve, for example, the introduction of spiro orthocarbonates and stereoisomers. U.S. Pat. No. 5,502,087 describes various polymer-based resins that are designed to improve the physical characteristics of thermal water-bath cured resin matrices or light-activated resin matrices. U.S. Pat. No. 5,147,903 describes polymer materials that exhibit desired degrees of swelling and cross-linking for light-activated resin matrices. Examples of polymer resin matrices that are specifically formulated to utilize microwave energy supplied by a commercial microwave oven for the thermal polymerization of the polymers into dental articles are shown in U.S. Pat. Nos. 4,873,269, and 5,218,070, and Canadian Patent No. 2,148,436. The impact of the role played by the polymer initiator in a microwave cured resin matrix has been evaluated by Urabe H. et al. in “Influence of polymerization initiator for base monomer on microwave curing of composite resin inlays,” Journal of Oral Rehabilitation, Vol. 26, pp. 442-46 (1999).
  • Another solution to these problems is also described in Canadian Patent No. 2,148,436 in which the resin matrix in the mold is compressed by a mechanical ram that injects additional uncured polymer components into the mold while the mold and flask are being cured inside a commercial microwave oven. The mechanical ram slowly forces some of the uncured polymer material contained in an injection cartridge through a passageway or sprue into the mold. The addition of polymer material applied under mechanical compression while it is still fluid is another way of reducing problems related to the polymerization shrinkage and porosity. U.S. Pat. Nos. 5,175,008 and 5,302,104 and Canadian Patent No. 2,120,880 describe various solutions for providing similar types of mechanical compression in the context of molding dental prosthetics without using microwave energy to cure the resin matrix.
  • There had been relatively little research, however, into the potential impact of the microwave energy itself on the polymerization process. The most common use of microwave energy to cure dental prosthetics actually involves a two-stage process where, as described in U.S. Pat. No. 4,971,735, the microwave energy first quickly heats water in or around the flask or humidity in a moist mold, with the superheated water vapor then thermally conducting the generated heat to the resin matrix. Due to the superheated nature of this process, cure times can be dramatically reduced. Moreover, because the microwave energy is primarily being absorbed by water as the intermediary thermal agent, this process lends itself very well to the use of commercial microwave ovens operating at full power settings where the primary objective is to heat the water, and not necessarily the resin matrix. This is advantageous because commercial microwave ovens are controlled by cycling the microwave generator, known as a magnetron, on and off to provide an average output power that corresponds to the percentage of the duty cycle. For example, a 50% duty cycle operates the magnetron on 50% of the time and produces a power output in terms of watts of energy produced by the oven that would be one-half of the maximum power output of the oven.
  • The other mechanism by which microwave energy can be used to cure dental prosthetics involves a single stage process where the microwave energy is directly absorbed by the molecules of the resin matrix without any substantial assistance of an intermediary thermal transfer agent, such as water vapor. In this case, the microwave energy essentially vibrates the resin molecules in a complicated process that is dependent upon the specific nature of the chemical composition of the resin matrix. It has been found that where water vapor in the form of humidity is present in the process, the actual polymerization of the resin matrix will occur as a result of a combination of thermal conduction from water vapor and internal microwave energy transfer.
  • Unfortunately, the high temperatures generated in the targeted article by microwave heating with available commercial microwave ovens set to manufacturers' recommendations (e.g., 3 minutes at 550 W at 100% duty cycle for a G.C. Acron dental microwave oven) tend to result in the thermal degradation of, and porosity formation in, many thermosetting polymer materials since high temperatures (above 150° C.) are often produced during these curing processes. In addition, hot and cold spots are often found within commercial microwave ovens that tend to create thermal gradients corresponding to these variations in microwave energy internal to the article being cured. The problems caused by these hot and cold spots can be compounded by the superheated nature of the water vapor, which effectively amplifies any uneven distribution of the thermal energy to the resin matrix.
  • What little research has been done on the effect of microwave energy on the polymerization process has generally focused on the duty cycle used for the microwave curing process. The impact on porosity of denture material cured using lower wattage, longer duration microwave cure times (i.e., a lower duty cycle for a longer time) versus higher wattage, shorter duration microwave cure times (i.e., a higher duty cycle for a shorter time) is compared in Alkhatib M. B., et al., “Comparison of microwave-polymerized denture base resins,” The International Journal of Prothodontics, Vol. 3, No. 2, pp. 249-55 (1990). European Patent No. 0 193 514 B1 describes a microwave processing system for dental prosthetics that has a magnetron, a waveguide, a surface radiating antenna, a flask, and a temperature sensor that is inserted in the flask and connected to a regulating processor. The regulating processor limits the temperature in the flask as measured by the temperature sensor by turning on and off the magnetron based on frequency modulation of the duty cycle. Although not used for polymerization of dental articles, U.S. Pat. No. 5,645,748 does describe a microwave system for sterilization that controls duty cycle of a microwave oven for the purpose of minimizing arcing caused by metallic surgical or dental instruments.
  • Any increase in the degree of conversion of monomers into polymer chains in the polymerization process will result in improved mechanical properties and biocompatibility of microwave cured dental prosthetics. While existing solutions utilizing improved resin compositions and mechanical compression during the curing process with a commercial microwave oven have resulted in many improvements over the conventional thermal water-bath method of producing dental prosthetics, it would be desirable to further improve the uniformity and the degree of conversion of monomers into polymer chains in the polymerization process and further compensate for volumetric shrinkage during the polymerization process in order to produce even better dental prosthetics.
  • With respect to the second category of dental articles created using polymer materials, dental composites formed of polymer matrix-composites are increasingly being used as an alternative to mercury-containing dental amalgam for aesthetic and restorative dental materials. These kinds of polymer matrix-composites are usually photo polymerizable in that they are cured using some kind of light instead of heat. Generally, the polymer matrix-composite is based on a photo polymerizable polyfunctional methacrylate compound that can be used alone or as mixture with monomethacrylates, light sensitive cure initiators pigments and fillers in a mixture with various comonomers such as triethyleneglycol dimethacrylate. Although the half-life of these polymer matrix-composites cured by light is on the order of 5-8 years and, therefore, they tend to wear out earlier than conventional dental amalgams, the enhanced biofunctionality and more pleasing aesthetic qualities of these polymer matrix-composites have gained favor over conventional dental amalgams.
  • The main deficiencies of polymer composite resins used as dental composites are surface degradation that leads to inadequate wear resistance, polymerization shrinkage and a lack of density. In addition to the problems previously described for dental prosthetics, micro-shrinkage of polymer dental composites produces interfacial gaps on the surface of the composites, which can results in microleakage through the dental composite. The long-term consequence of such microleakage can be bacterial penetration into the tooth that can cause a variety of adverse reactions in the tooth such as pulp damage, tooth sensitivity, possible pulpal death and loss of adhesion of the dental composite.
  • Just as with polymer dental prosthetics, improving the degree of polymerization of polymer matrix-composites is generally considered to be one way of improving their physical and biofunctionality characteristics of polymer dental composites as this would lead to stronger dental composites that are less susceptible to degradation, wear and fracture. It would also lead to improved biocompatibility, since there would be reduced amounts of uncured monomer that could act as a biohazard.
  • Unlike polymer dental prosthetics, however, the curing of polymer matrix-composites by application of thermal energy generally has not been used to date. Obviously, in the case of the conventional thermal water-bath process, it would be impractical to require a patient to remain at the dentist's office for up to 8 hours with their mouth open and with a tooth immersed in a hot water bath in order to set a thermally polymerizable matrix-composite. It is also not possible to place a patient's mouth into a commercial microwave oven to set a thermally polymerizable matrix-composite.
  • While there are numerous hand-held medical catheter devices that utilize radio frequency and microwave energy to perform ablations and similar heating operations, for example, in the vascular system of a patient, there have been relatively few uses of thermal or electrical energy applied to hand-held dental tools for intra-oral applications. There have been a few hand-held dental probes that utilize an electrically resistive heated tip for diagnosis of dental decay or for melting a sealing material in an intra-oral context as described, for example, in U.S. Pat. Nos. 4,527,560 and 5,893,713. U.S. Pat. No. 5,421,727 describes the use of radio frequency/microwave energy as part of a hand-held endodontic root canal device to raise the temperature of the adjacent tooth, thereby tending to disinfect the tooth during the root canal procedure as a result of the increased temperature.
  • The extra-oral use of microwave energy for the purpose of characterizing dental decay in extracted teeth has been described by N. Hoshi et al., in “Application of Microwaves and Millimeter Waves for the Characterization of Teeth for Dental Diagnosis and Treatment,” IEEE Transactions on Microwave Theory and Techniques, June 1998, Vol. 46, No. 6, pp. 834-38. This study confirmed the higher absorbency behavior of carious lesions in extracted teeth when irradiated by microwave energy as compared to the lower absorbency of such microwave energy by healthy enamel and dentin.
  • While existing photo polymerizable dental composites have enjoyed success as compared to conventional dental amalgams for dental fillings and veneers, it would be desirable to further improve the uniformity and degree of conversion of monomers into polymer chains in the polymerization process in order to produce even better dental composites. It would also be desirable to provide a dental tool that could take advantage of the use of microwave energy for purposes other than the polymerization of dental composites.
  • SUMMARY OF THE INVENTION
  • The present invention is a hand-held microwave system for intra-oral dentistry that utilizes microwave energy to cure polymer materials intra-orally so as to produce dental composites having improved physical characteristics, and also utilizes microwave energy to detect the presence of and to preferentially heat caries or cavities, thereby disinfecting and therapeutically treating the caries in a potentially non-invasive manner. The intra-oral polymerization process can be accomplished with less overall energy and with composite-matrices that maximally absorb the microwave energy so as to reduce heating of adjacent tissue. The antenna of a hand-held version of the intra-oral microwave system is also advantageously designed to detect the presence of and to preferentially heat caries or cavities, thereby disinfecting and therapeutically treating the caries in a potentially non-invasive manner.
  • The hand-held dental tool is designed to apply continuous microwave energy in accordance for use in creating dental composites directly in a patient's mouth. Microwave energy having a frequency of between 1 GHz to 50 GHz, and preferably between 14 GHz to 24 GHz, is applied by an antenna at the distal end of the hand-held tool which is connected via a conductor or wave guide to a microwave generator that supplies low power microwave energy in response to precisely controlled voltages. Preferably, the microwave energy power is less than about 10 W and ideally between 3 W and 5 W and the control voltages operate between 12 V and 65 V, depending upon the desired curing time and the particular composition of the resin matrix to be cured. Preferably, the antenna and distal end of the hand-held tool are structured to enable the operator to exert some degree of pressure on the composite resin-matrix in the mouth while it is being cured by the application of microwave energy. The low power microwave energy provided by the hand-held tool of this embodiment is safe for intermittent human exposure as the power and frequency ranges emitted by the antenna are similar to that emitted by cellular telephones.
  • One of the advantages of the hand-held dental tool is that it can also serve as a tool for non-invasively detecting and/or treating caries or cavities. Carious tooth tissue consists of demineralized and softened and moist tooth enamel or dentin, and contains micro-organisms. If the carious tooth tissue has not degraded to the point where the physical properties of the tooth are compromised, it is possible for the carious tooth tissue to recalcify and reharden if the micro-organisms causing the carious tooth tissue can be killed and the tooth can be kept under aseptic conditions. Infected tooth tissue which is not removed or not kept under aseptic conditions will remain as an active carious lesion, and will continue to cause progressive and destructive loss of tooth tissue. The use of the continuous microwave energy supplied by the hand-held dental tool embodiment of the present invention can eliminate or reduce the infection caused by the micro-organisms as the type of microwave energy is selected to preferentially heat and destroy the micro-organisms in the carious tooth tissue. In some cases, the hand-held dental tool can be used to kill the micro-organisms internal to the tooth tissue by the use of microwave energy and then a sealant can be applied to the exterior of the tooth which will be sufficient to keep an aseptic environment and promote the recalcification of the underlying tooth tissue. In other cases, portions of the carious tooth tissue may need to be removed and the hand-held tool can be used to kill the micro-organisms both internal to the tooth tissue and on the surface of the cavity. Once the micro-organisms have been destroyed, a polymer dental composite can be applied to the cavity. The polymer dental composite is preferably microwave cured using the hand-held dental tool to seal the treated tooth tissue and provide additional physical and structural support for the cavity.
  • The present invention is a microwave polymerization system for dentistry that utilizes specifically controlled microwave energy to cure polymer materials so as to produce dental prosthetics and dental composites. Unlike the microwave energy delivered by commercial microwave ovens which is controlled by pulsing a maximum output power on and off at a given duty cycle, the present invention utilizes metered and controlled microwave energy that is preferably continuous and voltage controlled, and regulates the application of this microwave energy by use of various feedback mechanisms. The metered and controlled microwave energy enables a higher degree of conversion and cross-linking of monomers into polymer chains in the polymerization process, thereby enhancing the physical and biocompatibility characteristics of both dental prosthetics and dental composites made in accordance with the present invention. In an extra-oral embodiment, gaseous pressure is applied to the resin matrix during the polymerization process to further enhance the polymerization process. In an intra-oral embodiment, the polymerization process can be accomplished with less overall energy and with composite-matrices that maximally absorb the microwave energy so as to reduce heating of adjacent tissue.
  • In one embodiment, a microwave oven is designed to apply continuous microwave energy in accordance with the extra-oral embodiment of the present invention for use in producing dental prosthetics at either a dental laboratory or a dental office. Microwave energy of between 1 GHz to 100 GHz, and preferably about 2.45 GHz, is continuously generated in the microwave oven in response to precisely controlled voltages of between 25 V and 110 V, depending upon the desired curing time and the particular composition of the resin matrix to be cured. A flask for use in the microwave oven is preferably provided with a mechanism to rotate the flask and with quick disconnect rotatable couplers for both liquid polymer insertion and gas pressurization while the article is rotating and undergoing the microwave curing process. The insertion of additional polymer and the gas pressurization system are utilized to maintain controlled gaseous pressure on the polymer material during the curing process to increase the density of the cured dental prosthetic and to compensate for micro-shrinkage that may occur during polymerization. Pressurization rates depend upon the strength characteristics of the polymer composition being used and preferably range between 10 psi to 125 psi with optimal ranges of between 12-35 psi. The flask may be equipped with an internal membrane to compress and adapt the pasty curable resin matrix onto the mold and with a vacuum forming system to draw the curable resin matrix into the mold and assist in maintaining the resin matrix in the mold during the curing process. In one embodiment, a cartridge is provided with quick disconnect couplers between the gas pressurization system and a sprue connected to the flask to permit filling of the mold with the curable resin matrix stored in the cartridge. Optionally, the microwave oven may be provided with features that also allow it to be used to sterilize dental prosthetics and other objects in a dental office or dental laboratory.
  • In another embodiment, a hand-held dental tool is designed to apply continuous microwave energy in accordance with the intra-oral embodiment of the present invention for use in creating dental composites directly in a patient's mouth. Microwave energy having a frequency of between 1 GHz to 50 GHz, and preferably between 14 GHz to 24 GHz, is applied by an antenna at the distal end of the hand-held tool which is connected via a conductor or wave guide to a microwave generator that supplies low power microwave energy in response to precisely controlled voltages. Preferably, the microwave energy power is less than about 10 W and ideally, between 3 W and 5 W, and the control voltages operate between 12 V and 65 V, depending upon the desired curing time and the particular composition of the resin matrix to be cured. Preferably, the antenna and distal end of the hand-held tool are structured to enable the operator to exert some degree of pressure on the composite resin-matrix in the mouth while it is being cured by the application of microwave energy. The low power microwave energy provided by the hand-held tool of this embodiment is safe for intermittent human exposure as the power and frequency ranges emitted by the antenna are similar to that emitted by cellular telephones.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is an isometric view of a microwave oven embodiment of the present invention.
  • FIG. 2 is an electrical schematic of the control circuitry for generating the microwave energy in the microwave oven embodiment shown in FIG. 1.
  • FIG. 3 is an exploded isometric view of a flask for use in the microwave oven embodiment shown in FIG. 1.
  • FIG. 4 is a cross-sectional side view of the flask shown in FIG. 3.
  • FIG. 5 is a top cut-away view of the flask shown in FIG. 3 showing a mold in position within the flask.
  • FIG. 6 is a partial cross-sectional side view of the flask of FIG. 3 in position in the microwave oven embodiment of FIG. 1.
  • FIG. 7 is a partial cross-sectional side view of the flask similar to FIG. 6 showing the details of a preferred embodiment of the air pressurization system.
  • FIG. 8 is a partial cross-sectional side view showing the details of a preferred embodiment of the polymer material injector system of the microwave oven embodiment of FIG. 1.
  • FIG. 9 is an isometric view of a hand-held dental tool embodiment of the present invention.
  • FIGS. 10-13 are various embodiments of antennas for the distal end of the hand-held dental tool embodiment of FIG. 9.
  • FIG. 14 is an electrical schematic of the control circuitry for generating the microwave energy in the hand-held dental tool embodiment shown in FIG. 9.
  • DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • Referring now to the various figures, a detailed description of the preferred embodiment of the present invention will be presented. Various complex dielectric permittivity, temperature and distribution pattern studies of microwave heated teeth and simulations of specific absorption rate distribution have been conducted as part of the research into the present invention. The complex permittivity was measured on differen