US20030199605A1

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Publication number: US20030199605A1
Application number: US10/128,970
Authority: US
Inventors: Dan Fischer
Original assignee: Ultradent Products Inc
Current assignee: Ultradent Products Inc
Priority date: 2002-04-23
Filing date: 2002-04-23
Publication date: 2003-10-23
Also published as: US7780449B2; US20050196726A1

Abstract

Endodontic sealant compositions and methods for sealing a root canal using sealant or other filling materials. The compositions include one or more resins that promote adhesion to hydrophilic dental tissues. Examples include alkyl methacrylates and derivatives thereof, such as alkylamino acrylates and methacrylates, oxyphosphoro acrylates and methacrylates, and acrylates and methacrylates substituted with oxysulfur, borate, carboxylic acid, or cyano groups or derivatives. The compositions include a radio opacifying agent, so that they may be seen using X-rays, and one or more polymerization initiators to effect curing, at least one chemical initiator and, optionally, a photoinitiator, to yield a curable sealant composition. The compositions are introduced into the root canal using a narrow cannula coupled to a high pressure hydraulic delivery device. Additional pressure may be applied to the sealant compositions using a syringe-like plunger introduced within a cylindrical access hole drilled through the crown of the tooth. The chemical initiator causes the mixed composition to harden over time. Hardening of at least a portion of the composition can be accelerated by including a photoinitiator and irradiating the mixed composition with radiant energy (e.g., from a dental curing lamp).

Description

BACKGROUND OF THE INVENTION

1. The Field of the Invention[0001]

The invention is in the field of compositions and methods for sealing a root canal during an endodontic procedure. More particularly, the invention involves compositions having enhanced adhesion to hydrophilic dental tissues found within root canals which assists their ability to effectively seal and protect a newly cleaned root canal. Such compositions are preferably radiopaque and are cured more rapidly compared to conventional endodontic sealing compositions, thus allowing for quicker placement of a final filling or crown to complete the root canal procedure.[0002]

2. The Relevant Technology[0003]

Following an endodontic root canal procedure, in which the root canal is cleaned using special root canal tools and irrigation devices, it is important to fill and seal the evacuated root canal in order to preserve the dead tooth from further decay that might compromise the integrity of the tooth and cause infection. In a typical procedure, one or more soft, resilient, needle-like inserts known as “gutta percha” points are inserted in each root canal branch in order at least partially seal and fill the root canal.[0004]

The term “gutta percha” refers to a rubbery material derived from natural rubber, typically blended with zinc oxide. This particular rubbery material is preferred because it is compressible, flexible and relatively soft so that it can be used to fill voids within the exposed root canal. The gutta percha points are typically impregnated with other materials such as radiopaque solids, zinc oxide, for its medicinal properties, and other passive or active ingredients as desired. It is impossible, however, to completely seal a root canal from all ingress of fluids, which may be laden with bacteria, using gutta percha alone. Conventional techniques require multiple gutta percha cones per canal and laborious “later condensation” techniques. For some, it requires a heating the gutta percha in an attempt to make it flow into the lateral canals. However, this technique, coupled with the properties of gutta percha, make it hard to achieve fine adaptation to canal walls and flow into the dentinal tubules.[0005]

The filling and sealing of the root canal can be further enhanced by inserting flowable materials, such as antiseptic pastes and/or sealing resins along with the gutta percha points. Due to the high viscosity of typical antiseptic pastes, such as zinc oxide/eugenol, or sealing resins, which tend to be epoxy-based, such materials are first applied to the gutta percha and then inserted into the root canal along with each gutta percha point. Alternatively, they may be inserted using a lentalo applicator. In this manner, it is hoped that the remaining spaces between the gutta percha points and the root canal can be filled with the antiseptic paste or resin. In addition, it is hoped that the epoxy-based resin will help to seal the root canal.[0006]

One of the drawbacks of using conventional pastes or resins is that such materials tend to be hydrophobic. This renders such materials somewhat incompatible with dental tissues within the root canal, which are highly mineralized, somewhat moist and therefore extremely hydrophilic. The hydrophilic nature of the root canal environment inhibits wetting and adhesion of the root canal by hydrophobic materials. As a result, conventional antiseptic pastes and epoxy-based resins actually form a poor seal between the gutta percha points and the walls of the root canal, thus potentially providing access for microbes and infection.[0007]

A further problem of conventional antiseptic pastes and epoxy-based endodontic sealing resins are their inability to adequately penetrate into, wet and seal the lateral canals which extend laterally from the root canal into the root of the tooth. Occasionally, the inability to seal the lateral fissures using conventional pastes and/or epoxy-based resins creates one more place where microbes may establish a beach head and be capable of festering over time.[0008]

In addition to the inability of the antiseptic pastes or epoxy-based resins to adequately adhere to and seal the root canals and lateral fissures, another problem relates to the inability to evacuate all air bubbles or pockets from the root canal during placement of the gutta percha points and associated pastes or resins. As the gutta percha point coated with pastes or resins is packed into the root canal, or as sealers are worked in with a lentalo applicator, upper portions of the gutta percha or sealer can seal against the root canal wall, thus trapping air between the coronal portion and the root canal apex. Failure to remove such air pockets creates an area where subsequent infection can fester. Although gutta percha is highly radiopaque, even if the dentist can observe whether or not the root canal spaces have been adequately filled, the task of removing the packed materials and repeating the procedure is time consuming, expensive, and uncomfortable for the patient. Moreover, many sealer pastes are only moderately radiopaque and include silver powder, which makes the root canal too dark.[0009]

Lateral condensation using gutta percha is typically not sufficient to force the highly viscous pastes, gutta percha, or resins into the lateral canals. Merely pushing against the top portion of the gutta percha does not exert very much force on the flowable pastes or resins, since pressurized fluids can escape around the space between the gutta percha, lateral condensation instrument, and the root canal rather than being forced into the lateral canals or other areas occupied by air bubbles or pockets.[0010]

Finally, in the case where nonpolymerizable pastes, such as zinc oxide/eugenol are used, the chemistries of such materials can interfere with the ability of subsequently placed prosthetic filling materials to chemically bond or adhere to the tooth.[0011]

In short, it would be an improvement of the art of endodontic procedures to provide compositions and methods which improved the ability of an endodontic sealing material to penetrate, wet, adhere and seal to the dental tissues surrounding or defining the root canals.[0012]

It would be an additional improvement in the art to provide compositions and methods that provided for a more thorough evacuation of air bubbles or air pockets within the root canal, as well as including lateral spaces or canals connected to or in communication with the main root canal branches.[0013]

It would also be an improvement in the art to provide compositions and methods which yielded a filled root canal in which the sealing material did not interfere with the ability of a subsequently placed composite resin material to bond or adhere to the tooth.[0014]

It would be a further advancement in the art if such compositions and methods provided for the ability to allow for variable curing times such as faster or slower curing, to account for variations in difficulty and success that may be experienced by a dental practitioner.[0015]

It would yet be an improvement in the art if such compositions could also be light cured so as to reduce the time a patient must wait until the root canal sealing material was sufficiently cured to permit subsequent filling of the remainder of the tooth with a composite filling material.[0016]

Such compositions and methods for more effectively filling and sealing a root canal and providing a bonding surface are disclosed and claimed herein.[0017]

SUMMARY OF THE INVENTION

The present invention encompasses adhesive resins for use in filling and/or sealing a root canal during an endodontic procedure, as well as procedures that employ such compositions. The adhesive sealing and filling resins according to the present invention include a component that is compatible with a hydrophilic environment and that allows the resin to wet, penetrate and adhere to the dental tissue surrounding the root canal. In addition, such resins are better able to penetrate into and seal the lateral canals that often extend from the main root canal branches. In order to assist such sealing, improved methods for applying a pressure to the sealing and filling resins are also disclosed.[0018]

The adhesive sealing and filling compositions of the present invention include one or more polymerizable acrylate or methacrylate monomers, oligomers or other prepolymers, preferably substituted with a hydrophilic constituent for better adhesion, a radio opacifying agent, and one or more types of polymerization initiators. The composition may also include other additives such as diluent or complementary monomers, oligomers, or prepolymers, fillers, antimicrobial agents, plasticizers, solvents and the like.[0019]

An example of an adhesive methacrylate resin substituted with a hydrophilic group (e.g., an oxyphosphorus group) is bis-glycidyl dimethacrylate phosphate. In the alternative, the hydrophilic group may include one or more of an oxysulfur group, a borate group, a carboxyl group, a nitro group or a cyano group. An example of a radio opacifying agent according to the present invention is bismuth chloride. An example of a suitable diluent monomer is urethane dimethacrylate. Examples of polymerization initiators include chemical initiators, such as peroxides and amines, and photoinitiators, such as camphor quinone. Because it is typically impossible to completely cure a polymerizable resin using photo initiation as the sole means to initiate polymerization, particularly all the way down to the apex of the root canal, it will typically be advantageous to include a chemical initiator so as to ensure complete curing of the polymerizable resin(s) over time.[0020]

In a preferred embodiment, the chemical initiator will be selected and included in an amount so as to provide sufficient time for a dental practitioner to properly place the composition within the root canal and ensure good penetration into the lateral canals. In most cases, it will be advantageous to include a chemical curing agent that causes the polymerizable resin to cure within a time period of from about 2 minutes to about 2 hours, more preferably from about 5 minutes to about one hour, and most preferably from about 10 minutes to about 30 minutes.[0021]

In the event that the dentist determines that the endodontic sealing resin has been properly placed, the dentist can optionally rapidly cure the upper portion of the resin by means of the inclusion of a photoinitiator and the application of curing radiation, such as light generated by a conventional dental curing lamp. In this way, the dentist can cure the top few millimeters of endodontic sealing resin by means of the curing lamp so as to provide a hardened upper surface to which a composite filling material can be chemically bonded or adhered. This greatly speeds up the time in which a dentist can complete the endodontic procedure, although the procedure can be adequately performed using a chemical initiator alone without a photoinhibitor.[0022]

Embodiments that include “dual cure” compositions (i.e., compositions that are capable of both chemical and light cure) provide some advantage over single cure resins. The rate of chemical curing can be adjusted to provide an aforementioned window of time to account for variations in procedure difficulty and success, while the light cure properties provide for almost immediate curing of the top layer by photoinitiated curing once it has been determined that the sealing or filling material has been properly placed. This provides a tremendous advantage for both the dentist and the patient because it obviates the need for a patient to either sit in the dental chair wasting time while the resin cures or else having to make a return visit to receive the final filling material. Another advantage is that the duration of chemical curing is relatively short compared to conventional sealers, thus minimizing the tendency of the composition constituents to leach into the surrounding tissue.[0023]

In another aspect of the invention, the adhesive resins are placed within the root canal by means of a narrow cannula or syringe tip device attached to a high pressure hydraulic device or system. Due to the viscosity of the mixed polymerizable resins or non resinous pastes such as zinc oxide pastes, coupled with the small size of typical root canals, it is difficult to express sealing resins or pastes through cannulas or syringe tips capable of entering into a root canal. For this reason, the inventive methods according to the present invention contemplate the use of high pressure syringes or other hydraulic devices, such as those disclosed in copending U.S. application Ser. No. 09/467,419, filed Dec. 20, 1999, and presently assigned to Ultradent Products, Inc. For purposes of disclosure, the foregoing U.S. patent application is incorporated herein by specific reference.[0024]

In a preferred method for placing adhesive resins within a root canal, the apex of the root canal is first sealed using a gutta percha cone. In order to ensure that the apex has been adequately sealed, a “tug back” seal is formed. That is, the gutta percha cone is first inserted and then removed. If it can be removed with little or no force, the gutta percha point is trimmed to yield a larger diameter tip and reinserted into the apex. This process is repeated until there is “tug back,” thus indicating that the fit between the gutta percha point and the apex is sufficiently tight to adequately seal the apex and prevent flow of sealing or filling material therethrough into the surrounding bone tissue.[0025]

After sealing the apex, the sealing or filling resin is inserted into the root canal using a narrow cannula tip. The cannula tip is placed within the root canal near the apex and slowly raised as the root canal is filled with resin, thus minimizing or eliminating the formation of air pockets or bubbles as the sealing or filling resin is progressively placed within the root canal. This procedure greatly improves the ability of the resin to initially purge most or all of the air from within the root canal compared to simply dipping a gutta percha point in the resin and stuffing the point into the root canal, or spinning the material with lentalo applicators, as is typically done using conventional methods.[0026]

In order to further ensure that the endodontic sealing resin penetrates and seals every space, irregularity, or lateral canal of the root canal, it may be advantageous to apply pressure to the resin after it has been initially placed within the root canal. This may be accomplished, for example, by inserting a plunger of complimentary size into the hole previously bored through the crown of the tooth. The plunger will typically include a plunger rod and a resilient plunger plug, such as a plug made of gutta percha material. In a preferred method for forming a plunger, excess gutta percha material trimmed from a gutta percha cone used to fill a root canal is wrapped around the end of a stiff metallic wire or plunger rod. The wire and gutta percha are then placed through the hole of the tooth. The wire is heated, which momentarily causes the gutta percha to melt and coalesce together, thus forming a resilient plunger plug having a size complementary to the hole in the tooth.[0027]

Inward pressure of the plunger from the crown toward the apex of the root canal exerts pressure on the resinous sealing material, thus forcing the material into the cracks, crevices and lateral canals of the root canal. Because the resilient gutta percha plug seals against the walls defining the hole through the crown of the tooth, the resinous material is not able to squeeze out between the tooth and the gutta percha plug but is instead forced into the aforementioned spaces, crevices or canals. In this manner, the resinous sealing or filling material is able to substantially form a hermetic seal of the root canal.[0028]

Providing a more complete seal of the root canal greatly increases the ability of the sealed root canal to resist the ingress of fluids into the root canal. Such fluids, if allowed to enter a root canal, may introduce microbes capable of infecting the tooth and surrounding bone. In improving the ability of the resinous sealing material to actually seal the root canal, including lateral canals and other crevices typically hard to fill, the inventive compositions and methods provide a tremendous advantage over conventional compositions and methods in yielding a tooth that is more resistant to microbial leakage.[0029]

In view of the foregoing, one aspect of the invention is to provide compositions and methods which improve the ability of an endodontic sealing material to wet, adhere and seal to the dental tissue surrounding or defining the root canals.[0030]

Another aspect of the invention is to provide compositions and methods that provide for a more thorough evacuation of air bubbles or air pockets within the root canal, as well as lateral spaces or canals connected to, or in communication with, the main root canal branches.[0031]

A further aspect of the invention is to provide compositions and methods which yield a filled root canal having a material to which a subsequent composite resin material can chemically bond or adhere.[0032]

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.[0033]

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and other advantages and features of the invention can be obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:[0034]

FIG. 1 is a cross sectional view of a tooth showing a root canal with a gutta percha cone inserted into the apex so as to seal the apex and provide a fluid-tight seal;[0035]

FIG. 2 is a cross sectional view of the tooth of FIG. 1 in which a small diameter cannula device has been inserted within the root canal for the purpose of filling the root canal with an endodontic sealing or filling resin;[0036]

FIG. 3 is a cross sectional view of the tooth of FIGS. 1 and 2 after the root canal has been filled with an endodontic sealing or filling resin;[0037]

FIG. 4A is a cross sectional view of the tooth of FIG. 3 in which a portion of a gutta percha cone has been wrapped around the end of a wire preparatory to heating and melting the gutta percha to form a syringe-like plunger to be inserted into the tooth;[0038]

FIG. 4B is a cross section view of the tooth of FIG. 4A in which the gutta percha has been melted and conformed to the diameter of the opening in the tooth so as to form a plunger-like device used to exert pressure onto the endodontic sealing or filling resin to force the resin into the lateral microfissures in communication with the root canal; and[0039]

FIG. 5 is a cross section view of a tooth in which the endodontic sealing or filling resin within the root canal is being partially cured using a curing lamp preparatory to placing a final filling material and/or crown to seal the root canal.[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Introduction.[0041]

The present invention is directed to polymerizable resins used fill a root canal during endodontic procedures. The invention also related to improved procedures for placing the inventive sealing or filling resins, as well as conventional resins or pastes, within a root canal. To provide better compatibility with the hydrophilic environment within a tooth, the adhesive sealing or filling resins advantageously include a component that is compatible with hydrophilic and mineralized dental tissues. Increased hydrophilic compatibility facilitates wetting of the dental tissue, enables penetration of the sealing material within gaps, spaces and lateral canals associated with the root canal, and promotes penetration into the dentinal tubules and, hence, superior adhesion to the dental tissue surrounding the root canal.[0042]

Sealing or filling resins and other flowable sealing or filling materials may optionally be placed within a root canal by means of pressurized hydraulic systems or devices able to deliver viscous fluids through narrow cannulas placed within the root canal. Once placed, the sealing resins or other materials are advantageously forced under pressure into the lateral canals associated with the main root canal branches, thus providing a much better seal of the root canal. This may be accomplished by means of a mini syringe-like plunger or like device that works in conjunction with a customized bore through the crown of the tooth.[0043]

The adhesive sealing or filling resins within the scope present invention typically include one or more monomers, oligomers or other prepolymers that promote adhesion, such as acrylate or methacrylate monomers, oligomers, or prepolymers substituted with a hydrophilic constituent, a radio opacifying agent, and one or more types of polymerization initiators. The term “radiopaque” refers to materials that allow the composition to be more easily seen using an X-ray. The composition may also include other additives such as diluent monomers, oligomers, or other prepolymers, fillers, antimicrobial agents, plasticizers, solvents and the like.[0044]

The terms “alkyl acrylate” and “alkyl methacrylate”, unless otherwise specified, shall refer to monomers, oligomers, and other prepolymers thereof (e.g., copolymers).[0045]

The compositions and methods are effective in reliably sealing the root canal from the ingress of fluids and bacteria from the crown and/or periodontal tissue. This helps to ensure the mechanical integrity of the treated tooth. Equally or more important, it protects surrounding bone from being infected by bacteria that may have otherwise infected the treated tooth. In one embodiment, the sealing or filling resins may be dual curable, that is, curable both chemically and by irradiation with light energy. This gives the dentist greater control over the time it takes to provide sufficient curing of the sealing or filling resin to permit placement of a final filling material or prosthetic covering.[0046]

II. Endodontic Sealing or Filling Compositions.[0047]

A wide variety of polymerizable resins, radiopaque materials, initiators, and other components may be used within the inventive endodontic sealing or filling compositions within the scope of the invention, including those disclosed in U.S. Pat. No. 6,071,528 to Jensen and copending U.S. application Ser. No. 09/736,729, filed Dec. 14, 2000, both of which are assigned to Ultradent Products, Inc., South Jordan, Utah. For purposes of disclosure, the foregoing patent and application are incorporated by reference.[0048]

The compositions within the scope of the invention can be chemically curable, photo curable, or dual cure. In the case of chemical and dual cure sealing or filling compositions it will typically be necessary to provide a two-part (or multi-part) composition that is mixed by the dentist just prior to use. One part may advantageously include all the constituents of the resin sealing or filling together with one half of the chemical cure system (e.g., a peroxide compound), while another part will advantageously include all the constituents of the resin sealing with the other half of the chemical cure system (e.g., an amino compound). In the case of a photocured sealing or filling composition, the polymerizable resin will advantageously be stable in the presence of the photoinitiator absent the application of radiant energy.[0049]

In the case of chemically cured systems, the final endodontic sealing or filling composition, upon mixing the multiple parts together, will preferably cure within a time period of about 2 minutes to about 2 hours, more preferably in a range of about 5 minutes to about 1 hour, and most preferably in a range of about 10 minutes to about 30 minutes.[0050]

On the other hand, in the case of a photo cured system, including dual cure systems, irradiating the sealing or filling composition with radiant energy, such as from a ultraviolet curing lamp, can effect much more rapid curing than chemical cure alone. The upper 1-3 mm of sealing or filling material within the root canal can typically be photo cured in a period of time of from about 10 seconds to about one minute.[0051]

A. Polymerizable Adhesive and Diluent Resins.[0052]

The polymerizable sealing or filling compositions according to the invention include at least one polymerizable adhesive resin that is at least partially hydrophilic and/or includes constituents which make an otherwise hydrophobic resin more adhesive to dental tissue. The polymerizable adhesive resins within the scope of the invention may include any monomer, oligomer or prepolymer that yields a composition that is capable of wetting and penetrating into the dentinal tubules. General examples include a wide range of acrylates, methacrylates, alkylhydroxy methacrylates, alkylamino methacrylates, and derivatives thereof. More specific examples of polymerizable adhesive resins include glycidyl dimethacrylate, 2-hydroxy ethyl methacrylate, 3-hydroxy propyl methacrylate, 4-hydroxy butyl methacrylate, triethylene glycol dimethacrylate, and polyethylene glycol dimethacrylate.[0053]

In preferred embodiments, the adhesion monomer include one or more alkyl acrylates or alkyl methacrylates that have been substituted with at least one additional hydrophilic group in addition to the acrylate and/or methacrylate ester linkage. In a preferred embodiment, the additional hydrophilic group includes an oxyphosphorus group, such that preferred polymerizable adhesive resins include one or more of oxyphosphorus alkyl acrylates and oxyphosphorus alkyl methacrylates, an example of which is bis glycerol dimethacrylate phosphate. Examples of other oxyphosphorus alkyl methacrylates within the scope of the invention include bis 2-hydroxy ethyl methacrylate phosphate, phosphate ester of p-hydroxyphenyl methacrylamide, phosphate ester of 3-hydroxy propyl methacrylate, and phosphate ester of 4-hydroxy butyl methacrylate.[0054]

Notwithstanding the foregoing examples, the oxyphosphorus alkyl acrylates and alkyl methacrylates can be any alkyl acrylate or alkyl methacrylate having an oxyphosphorus group selected from the group consisting of:[0055]
wherein R comprises an alkyl or aryl radical.[0056]
The oxyphosphorus group not only tends to increase the adhesiveness of the resin compared to analogous compounds lacking this added constituent, but it also increases the water solubility and hydrophilicity, of the resulting resin. In an informal comparison of the relative water solubilities of glycidyl dimethacrylate and bis glycerol dimethacrylate phosphate, the latter was found to be considerably more water soluble compared to the former. On this basis, it was presumed that the addition of the oxyphosphorus group increased the hydrophilicity of the resulting compound compared to the original compound.[0057]
Examples of other hydrophilic groups include oxysulfur groups, boric acid derivatives, carboxylic acid and carboxylic acid derivatives, amino groups, nitro groups, and cyano groups. The term “oxysulfur” shall refer to hydrophilic groups containing sulfur that can be substituted on to alkyl acrylate and alkyl methacrylate resins, including sulfoxides, sulfonic acid, sulfonates, sulfinic acid, sulfinates, and sulphates. Oxysulfur groups (or radicals) generally have a formula selected from the group consisting of:[0058]
wherein R comprises a hydroxyl, alkyl, or alkoxy radical.[0059]
Boric acid derivatives (or borates) generally have the formula:[0060]
wherein R[0061]₁and R₂may variously comprises a hydrogen or alkyl radical.
Carboxylic acid and carboxylic acid derivatives (e g., esters and amides) (together “carboxyl radicals” or “groups”) generally have the formula:[0062]
wherein R comprises a hydroxyl, alkoxy, or amino radical.[0063]
Amino radicals generally have the formula:[0064]
wherein R[0065]₁and R₂may variously comprises a hydrogen or alkyl radical.
Nitro groups are generally designed as —NO[0066]₂.
Cyano groups include cyanide (—CN), isocyanide (—NC), cyanate (—CNO) and isocyanate (—NCO) radicals. Because the cyanide and isocyanide radicals in organo cyanide compounds (i.e , nitrites and isonitriles) are not nubile, such compounds do not possess the same level of toxicity as cyanide salts and hydrogen cyanide gas. Moreover, in light of the relatively fast curing times, there is little risk that dangerous monomers of any kind will diffuse into the body.[0067]
In addition to the adhesive resin, the compositions according to the invention may include one or more additional (or diluent) resins to achieve the desired properties of initial flowability, curability, and final cured strength and hardness. In the case where the adhesive resin includes an alkyl acrylate or alkyl methacrylate substituted with an additional hydrophilic group, the diluent resin may include one or more non substituted alkyl acrylate or alkyl methacrylates. In addition, resins that are more hydrophobic and yet are suitable as diluent resins include urethane dimethacrylate, p-hydroxyphenyl methacrylamide, butanediol dimethacrylate, and bisphenol-A-diglycidyl dimethacrylate (“Bis-GMA”).[0068]
The adhesion resins are preferably included in a concentration ranging from about 0.01% to about 90% by weight of the composition, more preferably from about 0.5% to about 30% by weight, and most preferably from about 1% to about 10% by weight of the composition.[0069]
The diluent resins may be included in amounts of up to about 95% by weight of the composition, preferably in a range from about 5% to about 80%, and more preferably in a range from about 10% to about 70% by weight of the composition.[0070]
B. Initiators.[0071]
Initiators are provided in the composition to induce polymerization of the monomer, oligomer, or other prepolymers within the sealing and filling compositions. The initiators or curing agents may include radiant energy polymerization initiators with or without an appropriate organic amine additive or a chemical initiator with an appropriate organic amine additive.[0072]
1. Photoinitiators.[0073]
Examples of photoinitiators within the scope of the invention include, but are not limited to, x-diketones, camphor quinone, benzoin methyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone, diphenyl 2,4,6-trimethylbenzoyl phosphine oxide, benzoin ethyl ether, benzophenone, 9,10-anthraquinone, and derivatives thereof. The photoinitiators can be used with or without tertiary amines. The photoinitiator provides for photo-initiated polymerization of at least about the upper 1-3 mm of the sealing and filling composition in a period of time about 10 seconds to about 1 minute.[0074]
Photoinitiators are preferably included in an amount in a range from about 0.05% to about 5% by weight of the composition, more preferably in a range from about 0.1% to about 2% by weight, and most preferably in a range from about 0.2% to about 1% by weight of the composition.[0075]
2. Chemical Initiators.[0076]
Examples of chemical initiators include a wide range of peroxides, other per components, and other free radical generators. A two-part chemical curing system typically includes a peroxide constituent in one part and an amino compound in another. Exemplary peroxides include, but are not limited to, benzoyl peroxide, 2-butanone peroxide, lauroyl peroxide, t-butyl peroxide, t-butyl peroctoate, potassium persulfate, sodium perborate, isopropyl percarbonate, cumene hydroperoxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, diisopropylbenzene monohydroperoxide, and ammonium persulfate.[0077]
Examples of amino compounds include, but are not limited to, dimethylamino ethylmethacrylate, triethylamine, 2-dimethylamino ethanol, diethylamino ethylmethacrylate, trihexylamine, N,N-dimethyl-p-toluidine, dimethyl-p-toluidine, N,N-dimethyl aniline, ferric ethylene dinitrilotetraacetate, polyethylene polyamines, N-methylethanolamine, 2,2′(p-tolyimino) diethanol, and derivatives thereof.[0078]
In a preferred embodiment, the chemical initiator will be selected and included in an amount so as to provide sufficient time to allow the dentist or dental practitioner to have sufficient time to place the resinous sealing or filling material into the root canal and cause it to flow into the lateral canals. In other words, once mixed, the curing time will be sufficiently long so as to allow the dentist to carry out a desired sealing and/or filling procedure. On the other hand, unlike conventional sealers, which often cure very slowly, sometimes over a period of one or more days, the sealing and filling materials of the invention are typically formulated so that they will cure more rapidly, typically in 2 hours or less in order to inhibit or avoid leaching of the polymerizable monomer into the surrounding dental tissue.[0079]
In most cases, it will be advantageous to include a chemical curing agent in order for the polymerizable resin to cure within a time period of about 2 minutes to about 2 hours, more preferably from about 5 minutes to about 1 hour, and most preferably from about 10 minutes to about 30 minutes. In some cases, it may be desirable to allow sufficient time to determine whether or not the sealing material has been properly placed. If not, the uncured resin can be removed and replaced with new resin in a follow-up procedure.[0080]
Chemical initiators are preferably included in an amount in a range from about 0.01% to about 5% by weight of the composition, more preferably in a range from about 0.05% to about 2% by weight, and most preferably in a range from about 0.1% to about 1% by weight of the composition.[0081]
C. Radiopaque Fillers.[0082]
Radiopaque fillers are advantageously included in order to provide the ability of the dentist to X-ray and determine how well the endodontic resin has penetrated into and filled the root canal, including the lateral canals. Examples of fillers that can provide increased radio opacity include bismuth salts such as bismuth chloride, silver and silver salts such as silver chloride, barium salts such as barium sulfate or barium chloride, tungsten salts, titanium dioxide, and strontium salts such as strontium sulfate and strontium chloride. These and other fillers such as silicon dioxide and calcium phosphate tribasic may also be used to minimize polymerization shrinkage and the total heat potential of polymerization.[0083]
It is within the scope of the invention to include fillers in an amount of up to about 85% by weight of the composition, more preferably in a range from about 2% to about 70% by weight, and most preferably in a range from about 5% to about 50% by weight of the composition.[0084]
D. Antimicrobial Agents.[0085]
The sealing or filling compositions may optionally include one or more antimicrobial agents to assist in cleansing and sterilizing the root canal and to prevent later infection. Examples of suitable antibacterial agents include organohalogens, antibiotics, alkali metal oxides, hydroxides and carbonates, and alkaline earth metal oxides, hydroxides and carbonates.[0086]
Examples of antibacterial organohalogens include 1,1′-hexamethylene bis(5(P-chlorophenyl)biguanide), cetyl pyridinium chloride, benzalkonium chloride, and cetyl pyridinium bromide.[0087]
Examples of suitable antibiotics include: 4′-sulfamoylsulfanilanilide, 3-amino-6-(2-(5-nitro-2-furyl)vinyl)pyridazine, trans-pseudomonic acid, xanthomycin, alpha-amino-p-toluene sulfonamide, alpha-azido benzyl penicillin, penicillin O, penicillin N, monopropionyl erthromycin, and erythromycin 9(O-((2-methoxy ethoxy)methyl) oxime.[0088]
Examples of suitable alkali metal hydroxides include sodium hydroxide and lithium hydroxide.[0089]
Examples of suitable alkaline earth metal oxides include calcium oxide, magnesium oxide, barium oxide, and strontium oxide.[0090]
Examples of suitable alkaline earth metal hydroxides include calcium hydroxide, magnesium hydroxide, barium hydroxide, and strontium hydroxide.[0091]
A more preferred antimicrobial agent is calcium hydroxide since calcium hydroxide not only kills microorganisms but is chemically compatible with dental tissue. The antimicrobial agent is preferably included in an amount in a range from about 0.001% to about 30% by weight of the composition, more preferably in a range from about 0.005% to about 10% by weight, and most preferably in a range from about 0.01% to about 5% by weight of the composition.[0092]
E. Other Additives.[0093]
It is certainly within the scope of the invention to include other additives or adjuvents as desired in order to impart a desired property, such as less or non radiopaque fillers, solvents, dyes or plasticizers. For example, silica may be included in order to impart hardness in the case where a sealing filler material is desired. Keeping the silica content low, however, improves the ability to later drill out a portion of the cured material if desired, such as to place a post during a crown restoration.[0094]
Polymerization inhibitors are often added to polymerizable resins at the time of manufacture to inhibit or prevent premature polymerization. If so, the raw polymerizable materials used in manufacturing dental bonding composition according to the invention may include one or more polymerization inhibitors. An example of a polymerization inhibitor is hydroquinone. Of course, it is also within the scope of the invention to deliberately add a polymerization inhibitor to the sealing and filling compositions according to the invention in order to prevent premature polymerization and curing.[0095]
III. Methods for Sealing Root Canal with Endodontic Resins.[0096]
An exemplary method for placing and then curing an endodontic sealing or filling resin within a root canal is illustrated in FIGS.[0097]1-5. FIG. 1 depicts atooth10 that has been subjected to a root canal procedure. Thetooth10 includes a pair ofroot canals12, each of which terminates at an apex14 that extends through the bottom of theroot16. Anopening18 through the crown of the tooth provides access to theroot canals12, thereby permitting endodontic tools (not shown) to be inserted into theroot canals12. A gutta perchacone20 has been inserted into each opening18 in order to seal the apex14 of eachroot canal12 to prevent flow of sealing material into the surrounding bone tissue.
In order to ensure that the gutta percha[0098]cone20 forms a reliable seal within the apex14, a procedure involving “tug back” is preferably performed. In this procedure, the gutta percha cone is inserted and removed, sometimes more than one time, to determine how much force is needed to remove the gutta percha cone. If it can be removed with little or no force, there is insufficient tug back, and the gutta percha point is trimmed to yield a larger diameter tip and reinserted into the apex. This process is repeated until there is sufficient tug back, or resistance, felt by the dentist or dental practitioner. One of ordinary skill in the art of endodontics will know when there is sufficient tug back to confirm an adequate seal of the apex14 by the gutta perchacone20. Sufficient tug back indicates that the fit between the gutta percha cone and the apex is sufficiently tight to adequately seal the apex and prevent flow of sealing or filling material therethrough into the surrounding bone tissue.
In addition to the[0099]root canals12,lateral canals22 extend from theroot canals12 and provide communication between theroot canals12 and the surrounding periodontal tissue of the lower portion of thetooth10. Thelateral canals22 are particularly difficult to seal using conventional compositions and methods. The inventive compositions and methods, however, facilitate penetration of resinous sealing or filling material into thelateral canals22.
In a preferred method for placing a resinous sealing or filling material within a root canal, FIG. 2 depicts a[0100]syringe tip24 having anarrow diameter cannula26 attached to anenlarged portion28 of thesyringe tip24 used to insert sealing or filling material into theroot canal12. Due to the narrow opening of thecannula26, and because typical sealing or filling materials often sufficiently viscous that they may not readily pass through thecannula26, it will generally be advantageous for thesyringe tip24 to be attached to a high pressure hydraulic injection system (not shown). An example of high pressure hydraulic syringes or systems are set forth in the aforementioned copending U.S. application Ser. No. 09/467,419, filed Dec. 20, 1999. Examples of narrow cannulas sized for entry into a root canal are set forth in U.S. Pat. No. 6,079,979, which is assigned to Ultradent Products, Inc. For purposes of disclosing hydraulic pressurizing systems and cannulas sized to fit within a root canal, the foregoing patent application and patent are incorporated herein by specific reference.
The tip of the[0101]cannula26 is initially placed within theroot canal12 near the apex14, and sealing or filling material (not shown) is expressed therefrom into theroot canal12. As the resinous material begins and continues to fill up theroot canal12, thecannula26 is slowly raised or withdrawn from theroot canal12. This manner of filling theroot canal12 with resinous material minimizes or eliminates the formation of air pockets or bubbles as the resin is progressively placed within theroot canal12. This procedure greatly improves the ability of the resin to initially purge most or all of the air from within theroot canal12 compared to simply dipping a gutta percha point in the resin and stuffing the point into a root canal, as is conventionally done.
FIG. 3 depicts a tooth into which a resinous sealing or filling[0102]material30 has been successfully placed within theroot canals12, with little or no formation of air pockets. Even so, initial placement of theresin30 in this manner does not typically result in complete filling of thelateral canals22. To ensure that the endodontic sealing or fillingmaterial30 has penetrated into and sealed every space, irregularity orlateral canal22 of theroot canal12, it may be advantageous to apply additional pressure to theresin30 after it has been initially placed within theroot canals12. In one embodiment, additional pressure may be applied by inserting a plunger-like device into ahole32 through thecrown33 of thetooth10 that is initially made to provide access to theroot canals12 during the root canal procedure. FIGS. 4A and 4B illustrate this optional procedure.
In order for the plunger-like device to work in applying sufficient pressure so that the filling or sealing[0103]resin30 is forced into thelateral canals22, it will be advantageous to provide a resilient plug-like material that is able to conform to and seal against theinner wall34 of thetooth10 defining thehole32. The resilient plug-like material will preferably have a diameter that is complementary to the diameter of thehole32. Although the plunger-like device may include any resilient plug-like material, in a presently preferred method, the resilient plug-like material is formed from excess gutta percha material that is trimmed off of the gutta perchacone20.
As more clearly depicted in FIG. 4A, a length of excess gutta percha is wrapped around a[0104]wire36 to form a gutta percha wrap or bundle38 to form aplunger40. Heat is then applied to thewire36 in order to cause the gutta percha wrap or bundle38 to melt slightly so that it coalesces together to form the resilient plug-like material. While the gutta perchabundle38 bundle is in a plastic state, theplunger40 is placed into thehole32 of thetooth10 in order to allow the gutta percha bundle to flow or otherwise conform to the size and shape of thehole32.
As shown in FIG. 4B, once the gutta percha[0105]bundle38 has coalesced together and conformed to the shape of thehole32, it yields aplunger40 having a gutta percha plug42 on the end thereof. The gutta perchaplug42 is allowed to cool and thereby adhere to thewire36. Thereafter, thewire36 and gutta percha plug42 yield aplunger40 that can be used to exert pressure on the resinous sealing or fillingmaterial30 in order to force it to flow into the cracks, crevices andlateral canals22 that may extend from theroot canal12. In addition, pressure applied by theplunger40 may also assist theresin30 to flow into the dentinal tubules in order to promote better adhesion between theresin30 and the dental tissue surrounding theroot canal12.
As depicted in FIG. 4B, force applied to the[0106]plunger40 in a direction from the crown of thetooth10 towards the apex14 of theroot canals12. Force may be applied to theplunger40 manually or by means of pliers or other gripping tools. Pressure is maintained on the resinous sealing or fillingmaterial30 because theelastomeric plug42 seals against theinner wall34 defining thehole32 through thecrown33 of thetooth10. Because of this, theresinous material30 is not able to squeeze out in appreciable amounts between thetooth wall34 and theresilient plug42. Instead, the pressure exerted onto theresinous material30 forces it into the aforementioned spaces, crevices or canals. In this manner, theresinous sealing material30 is able to form a substantially hermetic seal of theroot canals12.
Although FIGS. 4A and 4B depict a preferred method for forming a[0107]suitable plunger40 for use in applying pressure to the resinous sealing or fillingmaterial30, it should be understood that plunger-like devices or other pressurizing means would be within the scope of the invention. In view of the present disclosure, one of ordinary skill could design other pressuring means that would work to apply pressure to theresin30. For example, in place of gutta percha, theplunger42 may comprise any resilient or elastomeric material that can seal against the inner wall of thehole32 through the crown. Examples include other natural rubbers, silicone rubbers and other synthetic rubbers or elastomers.
Providing a more complete seal of the[0108]root canal12 greatly increases the ability of the sealedroot canals12 to resist the ingress of fluids therein. Such fluids may enter theroot canals12, for example, through fissures in the crown and/or periodontal tissue. Such fluids, if allowed to enter theroot canals12, may carry microbes capable of attacking and decaying the dental tissue surrounding theroot canals12, thus compromising the mechanical integrity of thedead tooth10 and, more importantly, potentially infecting surrounding teeth. In improving the ability of theresinous material30 to more effectively seal theroot canals12, including thelateral canals22 and other crevices that are typically hard to fill, the inventive compositions and methods provide a tremendous advantage over conventional compositions and methods in yielding a tooth that is more resistant to microbial attack.
As set forth above, the resinous sealing or filling materials may be chemically cured, photo cured or dual cured. In a preferred embodiment, the compositions will be dual cured. That is, they will preferably be cured both by means of a chemical curing agent and by the application of radiant energy. Because photo curing is only capable of curing the top layers of the resinous sealing or filling[0109]material30, but is incapable of sealing all the way down to the apex14 of theroot canal12, photo curing alone is typically insufficient to provide an adequately curedresinous material30 throughout the entire length of theroot canal12. For this reason, it will typically be necessary to provide chemical curing of theresinous material30 in order to ensure that resinous material cures completely throughout theentire root canal12 and associatelateral canals22, crevices and spaces.
Nevertheless, because chemically cured sealing or filling materials preferably cure slowly over time (e.g., between 20 minutes and 2 hours) so as to provide the dentist with adequate time to mix and then place the sealing or filling material, it may be desirable to speed up the curing process once proper placement of the resinous sealing material has been verified. Once a dentist or other dental practitioner is sufficiently confident that the resinous material has been adequately placed, it may be desirable to speed up the curing process, at least on the surface or[0110]upper portion44 of theresinous material30, in order to provide ahardened surface46 to which a composite material (not shown) can be bonded.
As depicted in FIG. 5, a curing[0111]lamp50 that emitsradiant energy52, such as ultraviolet radiation, can be used to cure the top orupper portion44 of a dual cure sealing or filling material. The photo curedportion44 will typically only extend partially down theroot canal12 while the remainingportion48 will extend all the way to the apex14 of the root canal. The hardenedupper portion44 of the resinous material provides ahardened surface46 to which a composite filling material (not shown) can immediately be chemically bonded or adhered. This allows the dentist to rapidly complete the endodontic process and eliminates the need for the patient to either sit in the dental chair while the resinous material chemically cures or make a appointment for a follow up visit to receive the final filling material.
It should be understood that the compositions and procedures according to the present invention may be used with or without gutta percha points. One advantage of using gutta percha points is that they can be used to seal the apex[0112]14 with eachroot canal12 prior to placing the resinous sealing material therein. This helps to prevent incursion of the sealing or filling material into the surround bone tissue. Another advantage of a gutta percha point is that it provides a path through which a hole can be drilled through the sealed root canal without compromising the surrounding cured sealing or filling material. Such holes are referred to as “channel holes” or “post channel holes”. Channel holes may be drilled, for example, in order to place reinforcing posts (not shown) down the root canal in the case of a relatively weak tooth. Posts are also used when attaching a prosthetic crown to a tooth.
On the other hand, the resinous sealing or filling materials according to the present invention will typically be softer than typical composite materials and may be easily drilled in many cases. Because of this, it may be unnecessary to utilize gutta percha points to facilitate the formation of channel holes through the root canal if needed.[0113]
Another advantage of the compositions and methods according to the present invention is that they provide a bonding surface to which a composite material, such as materials that include Bis-GMA, can form a chemical or adhesive bond. Prior art antiseptic pastes, such as zinc oxide/eugenol or calcium hydroxide mixed with iodoform, do not provide a bonding surface to which composites can bond. Such materials are generally inert and relatively soft, thus providing neither chemical nor mechanical bonding possibilities. Moreover, to the extent that such materials become interposed between the composite material and the tooth, they may inhibit bonding between the composite material and the tooth. In the case of amalgam, providing a hardened sealing or filling material, at least on the surface of the sealed root canal, will facilitate placement of the amalgam. Because of the soft nature of the prior antiseptic pastes, it was always necessary to utilize a post in order to provide a mechanical attachment surface to which a composite or amalgam filling material could attach. The photocurable sealing or filling materials according to the invention reduce or eliminate the need for such posts.[0114]
The resinous sealing or filling materials according to the present invention are also safer compared to prior art sealers, such as 26H or 26 Plus sold by Dentsply, which are known to leach formaldehyde into the surrounding dental tissue.[0115]
IV. Examples of the Preferred Embodiments[0116]
Several examples of the present invention are presented as merely illustrative of some embodiments of the present invention. These examples are not to be construed as limiting the spirit and scope of the invention. Examples written in past tense refer to actual compositions that have been made, while those in present tense are hypothetical in nature, though based on mix designs that have already been made.[0117]

Example 1

A dual cure dental composition suitable as an endodontic sealing or filling material was prepared in two parts, with each part having the following components in the stated amounts:[0118]



	Part 1
	Triethylene Glycol Dimethacrylate	16.8%
	Benzoyl Peroxide	0.2%
	Diurethane Dimethacrylate	30.0%
	Bis glycerol dimethacrylate phosphate	5.0%
	Bismuth Chloride Oxide	40.0%
	Calcium Lactate Pentahydrate	6.0%
	Silicon Dioxide	2.0%
	Total Part 1:	100%
	Part 2
	Triethylene Glycol Dimethacrylate	16.8%
	p-Tolyimino Diethanol	0.2%
	Phenyl bis(2,4,6-trimethyl benzoyl)	0.5%
	Phosphine Oxide
	Diurethane Dimethacrylate	30.0%
	Bis glycerol dimethacrylate phosphate	5.0%
	Bismuth Chloride Oxide	40.0%
	Calcium Lactate Pentahydrate	5.5%
	Silicon Dioxide	2.0%
	Total Part 2:	100%

The final composition was made by mixing equal amounts of Parts 1 and 2. Once mixed, the mixed composition was able to cure in less than 2 hours, thus preventing or inhibiting leaching of monomers and other materials from the root canal into the surrounding dental tissues. The mixed composition was also capable of accelerated curing as a result of irradiating the composition with radiant energy, such as by means of a dental curing lamp.[0119]

Example 2

The dental composition of Example 1 is reformulated so as to be only capable of chemical cure.[0120]

Example 3

An adhesive antimicrobial dental composition was formed having the following components and concentrations:[0121]



		Percent by Weight
	Component	of the Mixture

	calcium hydroxide	10.0%
	bis-glycerol methacrylate phosphate	5.0%
	urethane dimethacrylate	57.0%
	triethylene glycol dimethacrylate	6.0%
	titanium dioxide	1.0%
	calcium phosphate tribasic	10.0%
	dimethyl amino ethyl methacrylate	0.5%
	camphorquinone	0.2%
	barium sulfate	10.3%

Example 4

In this example, an adhesive antimicrobial dental composition is formed having the following composition:[0122]



		Percent by Weight
	Component	of the Mixture

	bis 2-hydroxy ethyl methacrylate	10.0%
	barium hydroxide	25.0%
	calcium phosphate tribasic	5.0%
	benzoin ethyl ether	0.4%
	N-methylethanol amine	0.5%
	glycerol dimethacrylate	59.1%

Example 5

In this example, an adhesive antimicrobial dental composition is formed having the following composition:[0123]



		Percent by Weight
	Component	of the Mixture

	strontium oxide	30.0%
	camphorquinone	0.5%
	diethyl amino ethyl methacrylate	0.5%
	bis glyceryl methacrylate phosphate	69.0%

Example 6

In this example, an adhesive antimicrobial dental composition is formed having the following composition:[0124]



	Percent by Weight
Component	of the Mixture

cetyl pyridinium chloride	4.0%
strontium chloride	10.0%
2-hydroxy-2-methyl-1-phenyl-1-propanone	0.5%
diphenyl 2,4,6-trimethylbenzoyl phosphine oxide	0.5%
xanthomycin	1.0%
phosphate ester of 4-hydroxy butyl methacrylate	29.0%
butane diol dimethacrylate	55.0%

Example 7

In this example, an adhesive antimicrobial dental composition is formed having the following composition:[0125]



		Percent by Weight
	Component	of the Mixture

	penicillin N	3.5%
	silicon dioxide fumed	16.0%
	bis-glyceryl methacrylate phosphate	3.0%
	benzophenone	1.0%
	tri hexyl amine	1.5%
	calcium phosphate tribasic	10.0%
	bis 2-hydroxy ethyl methacrylate	4.0%
	triethylene glycol dimethacrylate	61.0%

Example 8

In this example, an adhesive antimicrobial dental composition is formed having the following composition:[0126]



	Percent by Weight
Component	of the Mixture

4′-sulfamoylsulfanilanilide	1.0%
1,1′-hexamethylene bis(5(p-chlorophenyl)biguanide)	1.0%
phosphate ester of 3-hydroxy propyl methacrylate	5.0%
urethane dimethacrylate	92.0%
benzoin ethyl ether	1.0%
2-dimethylaminoethanol	1.0%

Example 9

In this example, an adhesive antimicrobial dental composition is formed having the following composition:[0127]



		Percent by Weight
	Component	of the Mixture

	magnesium oxide	15.0%
	barium chloride	40.0%
	9,10-anthraquinone	0.9%
	triethylamine	0.3%
	bis glyceryl methacrylate phosphate	43.8%

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrated and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.[0128]