Patent Application
20080248444
Not applicable.
This invention relates to endodontic instruments, and, in particular, to ultrasonic instruments for endodontic procedures.
A tooth contains one or more roots each having a canal. The canals connect to a pulp chamber and both the canals and the pulp chamber are filled with pulp. The pulp includes blood vessels, nerve tissue, and other cellular bodies. For various reasons, the pulp may become diseased. To eliminate pain, infection, and further degradation of the tooth, any diseased pulp must be removed from the tooth.
Typically, this diseased pulp is removed by an endodontic procedure, commonly known as a root canal. A root canal begins with the removal of a portion of the tooth's enamel and dentine to expose the pulp chamber. Next, the diseased pulp is removed from the pulp chamber and the root canals. Often, not only the soft pulp tissue, but also a portion of the adjacent harder dentine that defines the canal is removed to thoroughly clean the canals. While the controlled removal of some dentine may be necessary to fully clean the canals, the uncontrolled removal of dentine can excessively enlarge the canals and cause complications. Because the tooth canal is often curved, it is difficult to uniformly remove the diseased pulp and some of the surrounding dentine. Once the pulp is removed, the remaining void is filled with an inert biocompatible filling material. The removal and cleaning of the pulp from the canal walls is often performed using either an endodontic file or an ultrasonic endodontic tip. Although they may perform similar tasks, files and tips are different in structure as well as in the way they function.
An endodontic file is an instrument that is used to cut and enlarge the root canal. Endodontic files are tapered blanks of metal, typically stainless steel or nickel-titanium, that are either twisted or machined to form the clinical endodontic file. They are often straight and have surface features that perform the filing action. Although an endodontic file can be used as hand instrument, it is more commonly used in rotary devices.
The selection of a strong, stiff material such as titanium (modulus of elasticity of about 10 Msi) or stainless steel (modulus of elasticity of about 28 Msi) ensures that the file is sufficiently stiff to effectively remove all of the diseased pulp in the root canal. Moreover, the file needs to be strong enough that it is unlikely to fracture as it cleans the canal. Because the file will be under cyclic loading as the file bends and twists as it navigates the root canal, stronger and stiffer materials have been utilized to reduce the possibility of instrumentation fracture. When the file fractures during a root canal procedure, it is not a trivial task for the endodontist to remove the broken piece from the root canal. However, because the file is stiff, it can also have the undesirable effect of preferentially removing excess material, such as dentine, from the canal walls, particularly when the canal is curved. Since the root canal is curved and most files are straight, the file will often remove more tooth material from some areas of the curved root canal than others.
There are numerous patents that describe stiff, metallic endodontic files as meeting the currently perceived needs such as U.S. Pat. Nos. 4,299,571, 5,735,689, 5,882,198, and 5,980,250 by McSpadden, U.S. Pat. Nos. 4,536,159 and 4,611,508 by Roane, and U.S. Pat. No. 4,538,989 by Apairo and Heath. Other patents describe the use of tubular devices using stiff metals such as U.S. Pat. No. 4,135,302 by Kronman and Goldman and U.S. Pat. No. 4,505,676 by Groner. Some patents even describe the use of specific sets of stiff metal devices for cutting and widening the canal in each of the major sections of the canal, such as U.S. Pat. No. 6,558,163 to Riitano.
The prior art has recognized that plastic materials might be used in the construction of endodontic files and other types of dental instruments that are controlled by hand or a rotary device. In U.S. Pat. No. 6,981,869, a single piece, injection-molded brush is described that is capable of removing a smear layer or film in a tooth canal instead of a previously-used chemical surfactant. However, the '869 patent does not contemplate the removal of any of the relatively hard dentine material with the injection-molded brush. In U.S. Pat. No. 6,443,730 to Davidson, an endodontic file composed of a fiber-reinforced polymer is disclosed. However, each of the plastic instruments in these prior art patents are not subject to ultrasonic energy.
In contrast to endodontic files, an ultrasonic endodontic tip works under vibratory action. An ultrasonic endodontic tip is placed in an ultrasonic handpiece and vibrated at high frequencies. Often, the tip is composed of stainless steel and is coated with either diamond or zirconium nitride to improve the tip's cutting efficiency. If the tip makes contact with any tooth material, then the vibration causes the working area of the tip to abrade the tooth material. In the field of endodontics, an ultrasonic endodontic tip may be useful in locating canals, removing post material from previous endodontic operations, removing separated instruments, improving canal access, and preparing root ends for surgery.
Unlike rotary- or hand-controlled endodontic files, the use of a strong, stiff material, such as stainless steel or titanium, has been considered necessary for ultrasonic tips. This is particularly true for endodontic applications, where there is an increased risk of having a broken tip lodged in the tooth if the instrument fails. Because nodes form as the tip vibrates, and these nodes are the locations most susceptible to failure initiation, providing stronger materials throughout the tip has been considered crucial to reducing tip failure rates.
The use of plastic materials, particularly plastic materials having a low modulus of elasticity, in ultrasonic applications has not been recognized in the prior art suitable for use in root canal procedures. In U.S. Pat. No. 5,899,693, a modular ultrasonic scaler for the external cleaning of teeth is disclosed having plastic or metal elements. However, the '693 patent teaches that the plastic material must have a high hardness and high modulus of elasticity in order to properly transmit the ultrasonic energy (col. 5, lines 44-50 and col. 6, lines 60-68). U.S. Pat. No. 7,217,128 discloses an ultrasonic tool having exchangeable metal and plastic tips. The disclosed benefit of having exchangeable tips is that the metal tips can be used for heavy work such as scaling, cleaning, and the like, while the plastic tips can be used for delicate work such as work around the gum lines or around fragile dental work that would otherwise be damaged by metal tips (col. 3, lines 14-24).
Thus, the prior art has not suggested that that low-modulus materials could be used in conjunction with ultrasonic energy to perform the level of abrasive work necessary to perform root canals. It has been believed that low-modulus materials either were incapable of transmitting ultrasonic energy for heavy abrasion or that, if reinforced by fibers, the fibers would cause a degradation in the plastic matrix material and result in tip failure. Moreover, it was believed that the use of a low-modulus material would result in an unacceptable amount of tip failures.
Hence, it would be desirable to provide a dental tool that is capable of controlled cleaning of the root canals and other areas of teeth without the potential for damaging the tools or excessively enlarging the root canal.
The present invention provides an ultrasonically-driven endodontic tip that is composed of a material or materials having a low modulus of elasticity. The prior art had suggested that an ultrasonic endodontic tip must be made of a stiff material to effectively remove pulp and dentine in procedures such as root canals. It was believed that low-modulus materials could not effectively transmit sonic and ultrasonic frequencies, that they would be incapable of removing harder tooth material such as dentine, and that they would be prone to failure when in use or damage the teeth. However, the inventors have devised an ultrasonic endodontic tip from low-modulus materials that is capable of improved navigation of the root canals for the controlled removal of the dental pulp and the dentine surrounding the root canal. More specifically, the inventors of the present invention have determined that an ultrasonic endodontic tip having an elastic modulus less than 8.0 Msi (55 GPa) can be used advantageously in such applications.
In one form, the tip has a main body extending from a proximal end, configured for attachment to a device that provides ultrasonic energy to the tip, to a distal end. The main body has a working surface that can abrade a portion of the tooth upon contact. The ultrasonic endodontic tip can be driven at ultrasonic frequencies from 10 KHz to 150 KHz and, more specifically, at frequencies between 20 KHz and 40 KHz.
The main body of the tip can be composed of a metal, a polymer, ceramic, or a combination of two or more of these materials having an elastic modulus of less than 8.0 Msi. Metals can be selected from the group consisting of magnesium, lithium, selenium, tellurium, and the like, as well as their respective alloys. It is contemplated that if a polymeric material is selected that the modulus of elasticity of the ultrasonic endodontic tip could be less than 3.5 Msi.
When two or more materials are used, a composite material can be made having a matrix portion and a reinforcing portion. The reinforcing portion can be fiber, nanotube or particulate filler. If the selected material is a polymer, then it can be a fiber-reinforced polymer, such as polyphtalamide with 45% chopped glass fiber.
Additionally, at least a portion of the working surface can have an abrasive or a hardening surface treatment to enhance the abrasive action of the tip in the root canal. At least a portion of the tip can be covered with hard abrasive material such as diamond, silica, silicon carbide, aluminum oxide, zirconium oxide and oxides, nitrides, and borides. It is also contemplated that a hard surface coating or treatment may be used to differentiate the working surface from the bulk of the tip having the low modulus of elasticity.
The tip can be used to perform endodontic procedures involving the root canal. During the procedure, the ultrasonic endodontic tip will exert minimal radial force such that the tip is generally confined to removing tooth material in the intended work zone of the root canal. During the procedure, the ultrasonic endodontic tip is capable of removing the both dental pulp and dentine.
These and other features and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate one or more preferred embodiments of this invention.
Referring now to the drawings, an endodontic tip 10 is shown in
The main body 16 protrudes from the first circular face 22 of the connecting end 18. The main body 16 has a first curving portion 30 that extends away from axis A and the distal end 14 as it protrudes from the first circular face 22. The first curving portion 30 transitions into a second curving portion 32 that extends back towards axis A and the distal end 14. The second curving portion 32 transitions into a straight portion 34 that extends toward the distal end 14. The diameter of the first curving portion 30, the second curving portion 32, and the straight portion 34 does not need to be uniform, and, as shown, will narrow as they extends from the proximal end 12 to the distal end 14. There may be a transitional radius 36 between the first curving portion 30 and the first circular face 22. A water outlet 38 may be located at an intermediate location on the main body 16.
At the distal end 14 of the straight portion 34 there is a working tip 40 having a working surface 42. As shown in
The known ultrasonic endodontic tips have been composed of materials having elastic moduli greater than 8.0 Msi. For example, it is well known to fabricate ultrasonic endodontic tips from titanium and stainless steel. Titanium has an elastic modulus of about 16.5 Msi (115 GPa). Stainless steel has an elastic modulus of about 28 Msi (190 GPa). Even the known, and relatively new, endodontic tip manufactured from “memory metal” alloys such as nitinol (NiTi) and titanium-molybdenum alloys (TMA or TiMo) have elastic moduli above 9 Msi. Such relatively high-modulus materials have been considered essential to transmit the ultrasonic energy, to provide the necessary cutting action to clean the root canals, and to reduce the possibility of the tip fracturing.
However, in the present invention, the main body 16 is composed of a material having an elastic modulus less than 8.0 Msi (55 GPa). This material may be a metal, a polymer, ceramic or a combination of two or more of the materials to form a composite material. It is also contemplated that two low-modulus materials may be combined in a single embodiment. For example, a magnesium alloy core could be coated with a polymer having an abrasive. It is also contemplated that the working tip 40 could be a low modulus metal with the remainder of the endodontic tip 10 being composed of low modulus plastic or composite material.
Some metals that can be used in the present invention include magnesium (6.4 Msi, 44 GPa), lithium (2 Msi, 14 GPa), selenium (8 Msi, 55 GPa), tellurium (6 Msi, 42 GPa), and the like, as well as their respective alloys. Some of the alloying metals include, but are not limited to, aluminum, titanium, zirconium, copper, zinc, tin, silver and niobium. Although the list of alloying metals includes individual metals having elastic moduli greater than 8.0 Msi, the metal alloy that is used in the endodontic tip must have an elastic modulus less than 8 Msi.
It is also contemplated that if the material is a polymer, that it may have an elastic modulus of less than 3.5 Msi (24.2 GPa). For example, nylon has an elastic modulus of about 0.3 Msi (2.1 GPa), PET has an elastic modulus of about 0.32 Msi (2.2 GPa), polystyrene has an elastic modulus of about 0.45 Msi (3.2 GPa), and polyethylene has an elastic modulus of about 0.07 Msi (0.5 GPa). Both thermoplastics and thermosets are appropriate for this invention, and include, but are not limited to, epoxies, phenolics, methylmethacrylates, acrylics, phenolics, polyolefins, polysulphones, polyetherketones, nylons, polyesters, polyamides, combinations of different polymers, and the like.
Additionally, carbon nanotube or standard fiber reinforcement may be used to increase the strength and toughness of the material. For example, glass, carbon, Kevlar, and other ceramic fibers may be embedded into the low-modulus matrix material to enhance the overall material properties. For example, in one embodiment of the present invention, the endodontic tip is composed of a fiber-reinforced polymer containing polyphtalamide with 45% chopped glass fiber content. It is also contemplated that other fiber-reinforced polymers, such as polyamide-imide with 30% carbon fiber content could be used. In particular, composite materials that are fatigue resistant and that will not significantly degrade as the temperature of ultrasonic endodontic tip 10 increases due to frictional heating will be considered desirable for this invention.
At least a portion of the working surface 42 can be covered by a hard abrasive. The hard abrasive can include diamond, silica, silica carbide, aluminum oxide, zirconium oxide, and the like, as well as other oxides, nitrides and borides. Although it is not necessarily required that an abrasive be present, in the case where the main body 16 is a polymer, the presence of an abrasive can increase the level of effectiveness of the endodontic tip 10. The abrasive material and its grit size can be selected to provide a tip capable of providing the desired amount of abrasive machining for the procedure to be performed.
The abrasive material may be applied in a number of ways. The abrasive material can be applied to the portion of the working surface 42 using a process such as electroplating. Alternatively, the abrasive can be affixed to the portion of the working surface 42 using an adhesive or an epoxy. The abrasive material might also be mixed into the bulk of the material to form a composite material that provides the abrasive material on the surface of the tip.
It is also contemplated that in some situations, a hard abrasive might not be required or may be replaced with a hard surface coating such as chromium or the like. Additionally, it is contemplated that other means of hardening the surfaces may also provide a hard surface that is capable of abrading a tooth.
In the case where more than one material is used to form the main body 16, the first material may have an elastic modulus less than 8.0 Msi and the second material may also have an elastic modulus less that 8.0 Msi. Alternatively, the combined elastic modulus of the materials when combined can be less than 8.0 Msi overall, even though one or more of the constituent materials has an elastic modulus greater than 8.0 Msi.
It should be appreciated that the endodontic tip 10 described may include the described features, as well as those known to others in the art. For example, the embodiment shown in
The drive unit 50 can supply the energy in a variety of ways. For example, the sonic or ultrasonic energy can be supplied electromechanically, through the use of a piezoelectric material, or other types of transducers. The ultrasonic energy may also be coupled with reciprocating or rotary drives to enhance the cutting action as is known to those skilled in the art.
The frequency of the sonic or ultrasonic vibrations can be controlled using the dial 52. Generally, human hearing only extends to around 20 kilohertz. Any frequencies above that range will typically be inaudible and therefore defined as “ultrasonic.” In typical operation, the frequency of the supplied ultrasonic vibrations will be in the range of 20 kilohertz to 40 kilohertz. However, it is contemplated that frequencies in the range of 10 kilohertz to 150 kilohertz could be provided depending on the abrasive qualities of the endodontic tip being used or the endodontic tip's particular operation.
The sonic or ultrasonic energy driving the endodontic tip 10 cycles the endodontic tip 10 between multiple points very quickly. Although the endodontic tip 10 does not move very far, the high frequency at which the endodontic tip travels between the points means that any stationary surface that the endodontic tip encounters, such as a tooth, will likely be abraded by the tip assuming the tip has sufficient abrasive qualities. The abrasive material, its grit size, and the frequency at which the tip is driven will all effect the cutting action and rate of material removal of the endodontic tip.
It is also contemplated that rotational motion of the endodontic tip 10 can be beneficial to the cutting action. This is referred to those skilled in the art as rotary ultrasonic machining (RUM). It is contemplated that modifications may be may to the disclosed design to incorporate provide ultrasonic vibration simultaneously with rotational movement to the working tip 40 to improve the rate at which the tooth material is removed.
Turning now to
It should be appreciated that because the main body 16 of the endodontic tip 10 has a low modulus of elasticity, the endodontic tip 10 is capable of flexibly navigating the root canals 72 and 74 while the working tip 40 controllably removes some amount of dentine 58. Because the endodontic tip 10 is composed of a material having a low modulus of elasticity, the endodontic tip 10 exerts only minimal radial forces as it navigates the curves of the root canals 72 and 74. Thus, the endodontic tip 10 is less prone to preferentially remove dentine 58 along only certain portions of the root canals 72 and 74. If the main body 16 was sufficiently stiff, then the working tip 40 would be forced to remove material along a straight line. If the root canal of interest is curved and the main body 16 and working tip 40 was sufficiently stiff, then the working tip 40 might not uniformly and controllably remove the dentine 58 defining the root canal walls. This could result in damage to the roots 62 and 64 of the diseased tooth 54 if the working tip 40 came out the side of one of the roots 62 and 64 or otherwise initiate the fracture of a portion of one of the roots 62 and 64.
Referring now to
Although not shown, the invention could also include a working tip 40, that extends in a direction not parallel to the straight portion 34 of the main body 16. Because the working tip would be oriented at an angle relative to the straight portion 34, this particular embodiment may be preferred for operations in which the direction of cutting would require holding the handpiece 46 in a position that is difficult to achieve or where the handpiece 46 or the main body 16 of the endodontic tip 10 would interfere with the tooth or other part of the mouth of the individual being worked on.
Although not shown, it is also contemplated that the working tip 40 could have some amount of curvature to assist it in flexibly navigating of the root canals 72 and 74. Such a modification could be made only to the working tip 40, or could also be made structural modifications to the main body 16.
It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.
This patent application claims the benefit of U.S. Provisional Application No. 60/910,096, filed Apr. 4, 2007, and which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60910096 | Apr 2007 | US |
