REINFORCED GINGIVAL RETRACTION CORD

Abstract

A dental retraction elongated member, for example, a retraction cord, for placement between a tooth and its adjacent gum tissue during dental impression taking and restorative procedures includes a core coated with a thermoplastic material so that the retraction cord is resistant to shredding, tearing, and sticking to dental restorative and impression taking materials.

Claims

1. A flexible dental retraction elongated member placeable between a tooth and adjacent gum tissue to retract the gum tissue from the tooth, comprising: a core comprising a single strand of metal wire or a braided metal wire; and a thermoplastic which coats the core, wherein the core reinforces the thermoplastic; wherein: the dental retraction elongated member is bendable, the dental retraction elongated member remains bent after being placed between the tooth and the adjacent gum tissue, the dental retraction elongated member is not chemically impregnated, a ratio of a diameter of the dental retraction elongated member to a diameter of the core is from 7:6 to 10:1, the diameter of the dental retraction elongated member is at most 10% of a length of the dental retraction elongated member, and with the proviso that the metal is at least one selected from the group consisting of silver, aluminum, and steel.

2. The dental retraction elongated member of claim 1, wherein the diameter of the dental retraction elongated member is from 0.5 to 3.0 mm.

3. The dental retraction elongated member of claim 1 which has a circular cross-section or an oval cross-section.

4. The dental retraction elongated member of claim 3, which has a circular cross-section.

5. The dental retraction elongated member of claim 1, wherein the thermoplastic is irreversibly attached to the core.

6. The dental retraction elongated member of claim 1, wherein the thermoplastic is polytetrafluoroethylene, polyester, or nylon.

7. The dental retraction elongated member of claim 1, wherein the thermoplastic comprises a photo-activated shape-memory polymer.

8. The dental retraction elongated member of claim 1, wherein the thermoplastic comprises a polymer which swells upon contact with a liquid.

9. The dental retraction elongated member of claim 2, wherein the diameter of the core is from 0.25 to 2.1 mm.

10-11. (canceled)

12. The dental retraction elongated member of claim 1, wherein the core is a single strand of metal wire.

13. The dental retraction elongated member of claim 1, wherein the polymer is present, and the polymer is rubber, poly(methyl methacrylate), polyvinyl chloride, or mixtures thereof.

14. The dental retraction elongated member of claim 13, wherein the polymer is rubber.

15. (canceled)

16. The dental retraction elongated member of claim 15, wherein a diameter of the strands is from 0.05 to 0.15 mm.

17. A dental kit, comprising: the dental retraction elongated member of claim 1, and a retraction cord packer.

18. The dental retraction elongated member of claim 1, which has a Young's modulus of from 1 to 100 GPa.

19-20. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a cross-sectional view of an embodiment of a dental retraction elongated member.

[0039] FIG. 2 is a side view illustrating the elongated body of an embodiment of a dental retraction elongated member.

[0040] FIG. 3 is a front view of a tooth and its adjacent gum tissue, where an embodiment of a dental retraction elongated member is disposed in the periodontal sulcus to retract the gum tissue from the tooth surface.

[0041] FIG. 4 is a cross-sectional side view of the dental retraction elongated member according to embodiment in FIG. 3, where the dental retraction elongated member is positioned in the periodontal sulcus between a tooth and its adjacent gum tissue so as to reflect or retract the gum tissue from the tooth surface.

[0042] FIG. 5 is a cross-sectional side view of a tooth and its adjacent gum in a non-retracted state.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0043] Embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the disclosure are shown.

[0044] As used herein, the term dental retraction elongated member (e.g., retraction device) refers to a retraction cord 100, which is shown for example in FIGS. 1-5. The retraction cord 100 comprises a central core 101 with an outer surface coated with a thermoplastic 102, e.g., a thermoplastic coating. The core 101 reinforces the thermoplastic 102. As used herein, the term reinforce refers to the presence of the core 101 to increase the stiffness of the retraction device relative to the thermoplastic 102 alone. As used herein, the term stiffness refers to the rigidity of an object and the extent to which it resists deformation in response to an applied force. The Young's modulus, a measure of stiffness, of the retraction cord 100 may range from 1-100 GPa, preferably 5-50 GPa, more preferably 5-20 GPa.

[0045] In one embodiment, the thermoplastic 102 is attached to the core 101 with one or more adhesives such as a collagen-based adhesive (e.g. an adhesive comprising porcine collagen, poly(L-glutamic), and water-soluble carbodiimides), a plant-based adhesive (e.g. gum Arabic, Canada balsam, latex, and starch), a silicone (e.g. polydimethylsiloxane and decamethyl cyclopentasiloxane), and an epoxy (e.g. bisphenol A epoxy, bisphenol F epoxy, glycidylamine epoxy, and novolac epoxy resin). The adhesive may be applied onto the outer surface of the core 101 before coating the thermoplastic 102. In one embodiment, the thermoplastic 102 is irreversibly attached to the core 101 with the use of the aforementioned adhesives. For example, there is cross-linking between the core 101 and the thermoplastic 102. As used herein, the term irreversibly attached means the thermoplastic 102 cannot be peeled/stripped from the core without damaging the thermoplastic 102, the core 101, or both.

[0046] The provision of the thermoplastic 102 results in the retraction cord 100 having a smooth outer or contacting surface. The average surface roughness (R.sub.a) of the retraction cord 100 is in a range of 0.01-10 m, preferably 0.01-5 m, more preferably 0.01-2 m, and R.sub.z of the retraction cord 100 is in a range of 0.05-40 m, preferably 0.05-20 m, more preferably 0.05-8 m. As used herein, the term R.sub.z refers to the average distance between the highest peak and the lowest valley in a sampling length according to American Society of Mechanical Engineers (ASME) Y14.36M -1996 Surface Texture Symbols (incorporated herein by reference in its entirety). The smooth outer surface is an improvement over the non-smooth outer surfaces of knitted or braided cords (e.g. made from cotton) which are subject to tearing and shredding during its insertion and removal from periodontal sulcus 304. Therefore, the disclosed retraction cord 100 reduces tissue trauma, bleeding, and post-operative patient discomfort. Compared to knitted or braided cords, the disclosed retraction cord 100 is easier to place because it does not unravel or fray and the core 101 helps the retraction cord 100 retain the deformations imparted to it by the packing tool so that it stays in the sulcus 304. In addition, the presence of the thermoplastic 102 allows the retraction cord 100 to be made without the presence of chemically impregnated additives such as a hemostatic agent. In one embodiment, the retraction cord 100 consists of the core 101 and the thermoplastic 102. As used herein, the term chemically impregnated refers to the penetration of the aforementioned additives into the core 101, thermoplastic 102, or both. Exemplary hemostatic agents include, without limitation, aluminum potassium sulfate, aluminum sulfate, aluminum chloride, ferric sulfate, inorganic salts of organic vasoconstrictors such as epinephrine (R or S enantiomers or racemic mixtures thereof) and pseudoephedrine, and Visine. Thus, the retraction cord 100 may be used on chemically sensitive patients and their previously experienced adverse chemical side effects caused by chemically impregnated cords can be avoided. The thermoplastic 102 coats at least 70%, preferably at least 80%, more preferably at least 99% of the outer surface and both ends of the core 101.

[0047] A shape of the cross-section of each of the core 101 and the thermoplastic 102 may independently be circular, polygonal (e.g. rectangular, triangular, hexagonal), elliptical, or oval, preferably circular (FIG. 1). A length of the retraction cord 100 is unlimited and may be determined in accordance with packing and winding requirements or restrictions, and the intended use of the cord 100. A diameter of the retraction cord 100 may be in a range of 0.5-3.0 mm, preferably 0.5-2.5 mm, more preferably 1.0-2.0 mm. As used herein, the term diameter refers to the longest distance measured between two points on the perimeter of the cross-section of the retraction cord 100 (or the core 101). A diameter of the core 101 may be in a range of 0.25-2.1 mm, preferably 0.25-1.5 mm, more preferably 0.5-0.75 mm. A ratio of the diameter of the retraction cord 100 the diameter of the core 101 is in a range of 7:6 to 10:1, preferably 2:1 to 7:1, more preferably 2:1 to 4:1. A weight of the core 101 is 10-90 wt % of the retraction cord 100, preferably 40-90 wt %, more preferably 50-80 wt %, based on a total weight of the retraction cord 100. A weight of the thermoplastic 102 is 10-90 wt % of the retraction cord 100, preferably 10-60 wt %, more preferably 20-50 wt %, based on the total weight of the retraction cord 100. The diameter of the retraction cord 100 is at most 10%, preferably at most 5%, more preferably in a range of 2-4% of a length of the retraction cord 100.

[0048] The core 101 comprises one or more of a metal, a polymer, or mixtures thereof. The metal may be silver, copper, aluminum, stainless steel, or mixtures thereof. Preferably, the metal is stainless steel and may comprise up to 50 wt % of silver/copper/aluminum, preferably up to 30 wt %, more preferably up to 10 wt %. In one embodiment, the metal does not contain copper. The core 101 may be a single strand of metal wire or a braided metal wire. Preferably, the core 101 is a single strand of metal wire. The polymer may be rubber, poly(methyl methacrylate), polyvinyl chloride, or mixtures thereof. Preferably, the polymer is rubber. Exemplary types of rubber include, without limitation, natural rubber and synthetic rubber (e.g. neoprene, ethylene propylene diene monomer (EPDM) rubber, silicone rubber, nitrile rubber, Viton, butyl rubber, and polyurethane rubber). In one embodiment, both the metal and the polymer are present in a weight ratio that is in a range of 1:99 to 99:1, preferably 1:99 to 80:20, more preferably 1:99 to 30:70. In one embodiment, the core 101 may comprise a plurality of strands of the metal, a plurality of strands of the polymer, or both, which are woven, braided, or twisted together. The core 101 may comprise a total of 4-40 strands, preferably 4-28 strands, more preferably 4-20 strands. For example, the core has 16 strands: four pairs of warp strands and four pairs of filling strands. In one embodiment, the core comprises a mixture of metal strands and polymer strands, and a ratio of the number of metal strands to polymer strands may be in a range of 1:19 to 10:10, preferably 1:19 to 5:10, more preferably 1:19 to 3:17. As is well known in the art, each pair of the filling strands successively passes over and then under adjacent pairs of warp strands, and each pair of warp strands successively passes over and then under adjacent pairs of filling strands. The metal strand may be braided/weaved/twisted with the polymer strand at the same time, or it could be threaded through the braided/weaved/twisted polymer strands with a sewing needle. In one embodiment, the core 101 is made of a braided or woven strands made of any conventional material such as cotton. For instance, the cotton strands may be woven or braided together and then be coated with the thermoplastic 102 by a conventional die/extruder device. A diameter of the strands is in a range of 0.05-0.15 mm, preferably 0.1-0.15 mm, more preferably 0.1-0.12 mm. In an alternate embodiment, a conventional knitted or braided retraction cord 100 may be impregnated with the thermoplastic 102 so as to make up a cord 100 which is smooth and resistant to tearing. This embodiment may comprise 5-60 wt % of the thermoplastic 102, preferably 10-40 wt %, more preferably 20-30 wt %, based on a total weight of the retraction cord 100.

[0049] The thermoplastic 102 is preferably a biocompatible, non-toxic polymer which causes no known clinical or scientific adverse medical reactions. Exemplary biocompatible, non-toxic polymers include, without limitation, polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (e-PTFE), polyester, nylon, or mixtures thereof. Preferably, the thermoplastic 102 is PTFE and/or e-PTFE because the non-stick property results in the cord 100 being resistant to sticking or adhering to dental materials (e.g. restorative and/or impression taking materials). P IFE materials are commercially available from, for example, DuPont. In one embodiment, the thermoplastic 102 is not liquid permeable. A thickness of the thermoplastic 102 may be in a range of 0.25-1.5 mm, preferably 0.25-1 mm, more preferably 0.5-1.25 mm. In one embodiment, the thermoplastic is not wax.

[0050] In one embodiment, the thermoplastic 102 comprises up to 80 wt % of a photo-activated shape-memory polymer, preferably up to 60 wt %, more preferably up to 50 wt %, based on the weight of the thermoplastic 102. The photo-activated shape-memory polymer switches between an elastomer and a rigid polymer by shining light of different wavelengths. This feature may allow the retraction cord 100 to retain the curvature around the tooth 301/teeth when an impression is taken. The photo-activated shape-memory polymer may be an acrylate-based polymer, such as polyacrylate, polymethacrylate, polyethylacrylate, polyurethane, a siloxane polymer, an epoxy polymer, an oxetane polymer or mixtures thereof. The photo-activated shape-memory polymer may contain a photo-reactive pendant group which forms cross-links between adjacent photo-activated shape-memory polymer chains and breaks the cross-links in response to light of different wavelengths. Hence, the restoration band 100 can be fixed into the curvature by shining ultraviolet-visible light (with a wavelength 260-700 nm) and then recover the original shape when exposed to light with a wavelength in the far-UV region (10-200 nm) to facilitate removal. Exemplary photo-reactive groups include, without limitation, cinnamic, coumarin, stilbene, vinylene, chalcone, thymine, and derivatives thereof. The photo-activated shape-memory polymer may be blended with the aforementioned thermoplastic 102 in an extruder (for example, in a compound extrusion process) thereby forming a polymer blend which then coats the core 101.

[0051] In another embodiment, the thermoplastic 102 comprises up to 80 wt % of a superabsorbent polymer, preferably up to 60 wt %, more preferably up to 50 wt %, based on the weight of the thermoplastic 102. The superabsorbent polymer may absorb and retain fluids (e.g. saliva, blood, water) present near the tooth 301 and then swell to open the sulcus 304 greater than the original diameter of the cord 100 so that the margin is visible for impression taking. The expanded retraction cord 100 may also compress the gum tissue 302 and stop any bleeding. The expanded diameter of the cord 100 may be in a range of 0.55-3.5 mm, more preferably from about 0.55-3.0 mm, and most preferably from about 1.05-2.5 mm. The superabsorbent polymer may comprise polyacrylate, polyacrylic, polyacrylamide, polyvinyl alcohol, polyacrylonitrile, polyethylene glycol, or mixtures thereof. In other embodiments, the superabsorbent polymer may be sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, ammonium polyacrylate, or mixtures thereof. The superabsorbent polymer may be blended with the aforementioned thermoplastic 102 in an extruder thereby forming a polymer blend which then coats the core 101.

[0052] Exemplary techniques to coat the core 101 with the thermoplastic 102 include, without limitation, extrusion coating, electrostatic spray, fluidized bed coating, and dip coating.

[0053] The retraction cord 100 may be utilized by practitioners (e.g. dentists) as illustrated in FIGS. 3 and 4 in both prosthetic and restorative dentistry. In restorative dentistry, for example, when restoration of dental caries at, near, or below the marginal attached gingiva (i.e. gum line) is required, it is necessary to distend and retract the adjacent gum tissue 302 in order to achieve adequate access to the carious lesion. Such access allows successful removal of caries and placement of fillings (e.g. VLC composite resins or amalgams).

[0054] The retraction cord 100 may also be used in prosthetic dentistry involving the construction of crowns, caps, bridge works, dentures, implants, and the like. In prosthetic dentistry, it is imperative that accurate impressions or molds of a tooth 301, teeth, or implant be obtained for which prosthetics will subsequently be fabricated at a dental laboratory. At the interface of the tooth surface and gum line, it is important that prior to impression taking that the gingival sulcus 304 be retracted so that an accurate impression of the prepared tooth structure can be made. Additionally, the limit line 303 must remain uncovered, accessible, and clear of fluid and humidity. FIG. 5 illustrates a tooth 301 in unretracted form with gum tissue 302.

[0055] In order to uncover preparation limit line 303, the flexible retraction cord 100 as shown in FIGS. 3 and 4 is pressed into the periodontal sulcus 304 surrounding tooth 301 prior to flowing the impression taking material onto the tooth 301 or teeth with conventional techniques and tools such as a cord packer. The disposition of the retraction cord 100 within the periodontal sulcus 304 retracts gum tissue 302 from the tooth structure to be worked on so as to ensure adequate visibility of and access to the surface of tooth 301 and allows limit line 303 to remain uncovered, accessible, and substantially free of body fluids.

[0056] Once the impression material hardens and is removed from the patient's mouth, the retraction cord 100 may be removed from the periodontal sulcus 304 by conventional methods known in the art and discarded.

[0057] For distributing purposes, the retraction cord 100 may be wound on a spool and packaged in a dispensing container. The retraction cord 100 may be cut into suitable lengths with an orthodontic wire cutter. Various retraction cords having the aforementioned diameters can also be assembled into kits that can be provided to dental practitioners. A kit comprising retraction cords in multiple sizes is useful because the sizes and shapes of teeth and gum lines can vary from patient to patient. By providing the kit with multiple embodiments of the retraction cord 100, a practitioner is able to selectively use the retraction cord 100 that is most appropriately configured in size to retract the gum from different tooth structures such as incisors, canine teeth, premolars, and molars. These kits may also comprise a cord packer.