WO1999032046A1

WO1999032046A1 - Coating of ptfe dental floss

Info

Publication number: WO1999032046A1
Application number: PCT/GB1998/003762
Authority: WO
Inventors: Jacob Moses Blass; Dennis Aston
Original assignee: Westone Products Limited
Priority date: 1997-12-19
Filing date: 1998-12-15
Publication date: 1999-07-01
Also published as: AU1570899A; GB9726909D0

Abstract

A dental floss in the form of an elongate article comprising at least one elongate PTFE element providing the tensile strength of the floss has on the PTFE element a coating of a coating material which (i) is not a wax, (ii) is solid at room temperature (25 °C), (iii) is water-insoluble, (iv) has a narrow melting temperature range (e.g. less than 10 °C), (v) is non-toxic. The coating material may be at least 90 % by weight of at least one compound selected from mono, di- and tri-glycerides of fatty acids having 14 to 20 carbon atoms, C14-C20 aliphatic alcohols and C14-C20 aliphatic acids. It may contain an additive having flavouring or medicinal effect.

Description

COATING OF PTFE DENTAL FLOSS

FIELD OF THE INVENTION

The invention relates to a dental floss comprising one or more elongate PTFE elements and a coating applied to increase the coefficient of friction to improve grip properties of the PTFE material. The term "dental floss" here includes dental tape . BACKGROUND OF THE INVENTION Dental flosses have been used for many years to clean interdental spaces and spaces under the gum margin. A variety of flosses include adjuvants including medicinal compounds e.g. fluoride and bactericidal compounds to increase the effectiveness of the floss in inhibiting dental caries and flavourings to improve taste during flossing. In general these adjuvants are applied in a coating or as a coating on the floss. However, although flossing has been shown to be beneficial to oral health, inhibiting dental caries and gum problems, dental floss is considered by many consumers to be uncomfortable to use.

The problems in consumer acceptance of dental floss relate to its high coefficient of friction. When pulling dental floss between teeth, substantial force may need to be applied. This often results in the floss impacting on the gums, the resulting irritation of the gums often causing bleeding.

There have been many developments in dental floss manufacture to attempt to solve some of these problems and encourage the use of floss. In recent years, PTFE dental floss has been successfully marketed. PTFE has a lower coefficient of friction than prior conventional floss materials such as polyamide . Published patent documents include EP-A-335466 and WO92/10978 (US patent 5220932), which describe dental flosses made of sintered PTFE which are coated with wax. The improvement of the strength properties of PTFE in the form of sheet, tape or rod by processes involving heating and stretching is well known. Particularly important has been the development of the process of "expansion" of PTFE by W L Gore & Associates, Inc. (Gore), which involves stretching an unsintered PTFE article at a high rate of stretch at an elevated temperature, to cause expansion (i.e. density reduction, with increase of porosity) of the PTFE. The isothermal expansion stage is followed by increase of temperature, with the material retained in its expanded state, to at least 327 °C which effects the phenomenon known as amorphous locking or node-locking, by the formation of amorphous regions in the PTFE which appear to lock together fibrils of PTFE. This process is described for example in Gore's US Patents 3953566 and 3962153. WO96/10478 (US patents 5657779 and 5806539) describes manufacture of a new form of PTFE which is suitable for use as a dental floss, either coated with wax or in uncoated form, by reason of its surface properties. EP 335466 and WO92/10978 both also propose that additives, such as dentifrices and components having a pharmaceutical or other beneficial effect when released in the mouth, are incorporated in the dental floss. This might be done either in the wax or as a substrate coating on the PTFE before the wax is applied.

WO97/24078 (US patent 5800823) discloses a method of incorporating additive in the PTFE material of the floss . Although PTFE has a lower coefficient of friction than conventional materials used to make floss materials, the floss is still effective in cleaning tooth surfaces. The reduced friction of coefficient of floss enables the user to insert the floss between tight interdental spaces more easily with reduced propensity for the floss to cause bleeding of the gums . However the extremely low coefficient of friction of PTFE floss makes the floss difficult to handle. As a result wax has been proposed to increase the coefficient of friction of the floss to enable easier grip during use. In use, the wax coating provides an increased coefficient of friction for handling. When the floss is inserted between the teeth the wax coating tends to be stripped off, exposing the PTFE which, with its lower coefficient of friction, glides more easily between tight interdental spaces. Wax has also been coated on non-PTFE dental floss, e.g. polyamide flosses, and therefore was readily acceptable when coated on PTFE floss. The use of waxes to coat PTFE floss in order to increase ease of handling has some disadvantages. In use, wax coated PTFE dental floss leaves a sticky residue on fingers used to grip it and a residue on the teeth. The present invention aims to provide a coating for PTFE floss which results in improved properties and avoids the disadvantage of the sticky feeling of wax on the fingers of the user.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a coated PTFE dental floss which is improved in handling.

According to the invention there is provided a dental floss in the form of an elongate article comprising one or more elongate PTFE elements providing the tensile strength of the floss. On the PTFE element or elements a coating of a coating material which (i) is not a wax

(ii) is solid at room temperature (25 °C) (iii) is water-insoluble (iv) has a narrow melting temperature range (v) is non-toxic.

The present inventors have investigated the possibility of coating of PTFE dental floss using various food quality materials such as mono-, di- and tri- glycerides of stearates and palmitates, and the acids and alcohols of C₁₄ to C₂₀ long chain aliphatic compounds. It has surprisingly been found that a class of water- insoluble materials can adhere satisfactorily to the PTFE without impairing the behaviour of the PTFE as a floss and that the coating improves grippability of the product by a user without leaving a sticky residue on the fingers. The coating weight can be very small, yet provide a desired coefficient of friction. Moreover the coating can satisfactorily hold additives such as medicaments and flavourings provided in or on the PTFE or in the coating, while permitting release of the additive in use . The dental floss of the invention typically has, to provide its tensile strength, one or more strands which are integral, unitary PTFE elements. The term PTFE is here used, as is usual, to describe a range of polymers based on polytetrafluoroethylene . For example, as is conventional, small amounts of co-monomers may be included, such as ethylene, chlorotrifluoroethylene or hexafluoropropylene, provided that the properties of the product are satisfactory. Conventionally, PTFE is extruded with a lubricant, which is subsequently removed, for example, by heat cleaning or solvent extraction. The PTFE may, as is conventional, include one or more fillers and/or pigments. For dental floss, unfilled PTFE is preferred.

In the preferred embodiment PTFE has been expanded by stretching in at least one direction, typically at an elevated temperature, so as to increase in porosity. The resulting PTFE has a porous structure. Suitable PTFE materials are described in WO96/10478 (US patents 5657779 and 5806539) . Preferably a porous PTFE material is used, with a density of not more than 1.5g/cm³.

In a dental floss of the invention, preferably the tensile strength of the PTFE is at least 100 MPa, e.g. in the range 200 - 600 MPa. Preferably the PTFE is a monofilament ribbon, and preferably the width of the ribbon is in the range 0.5 - 4mm, more preferably 1 - 3mm, most preferably 1.2 - 2.4mm. The thickness is preferably in the range 20 - 120μm, more preferably 20 - lOOμm and most preferably 40 - lOOμm. The ribbon may be twisted.

The floss has typically a density of about 0.9g/cm³ with typical pore size of approximately lOμm.

The melting point of the coating material should preferably be above normal blood temperature to avoid melting on finger contact, i.e. at least 38^βC, more preferably at least 40 °C, and preferably is in the range 42 to 62°C.

Preferably according to the invention the PTFE element or elements are coated with coating material which (excluding any additive material which may be included as described below) is at least 90% by weight of at least one compound selected from mono-, di- and tri- glycerides of fatty acids having 14 to 20 carbon atoms, ^C ₁₄-C₂₀ aliphatic alcohols and C₁₄-C₂₀ aliphatic acids. More preferably, the coating material (excluding any additive material) is at least 90% by weight of one or more compounds selected from mono-, di- and tri-glycerides of stearic, oleic and palmitic acids, stearic acid, stearyl alcohol, and cetyl alcohol .

The coating may consist substantially wholly of such materials (apart from any additive included) .

Such coatings to be used in the invention share the following common features; they are not waxes (i.e. they do not have wax characteristics, such as wide melting point range, do not exhibit softening prior to melting when heated to melting and on the floss do not have a waxy feel) ; they have relatively low melting points; the melting temperature range is narrow, e.g. not more than 10 °C, particularly not more than 6°C, preferably not more than 4°C, more preferably not more than 2'C; they are insoluble in water, they are non-toxic and preferably of food quality. The narrow melting temperature range is advantageous in manufacture of the floss, because the coating when applied as a liquid just above its melting temperature can be quickly solidified, giving an even and uniform coating.

Examples of coatings which may be used include, but are not limited to, stearic acid, palmitic acid, glyceryl monostearate, stearyl alcohol, cetyl alcohol and hydrogenated castor oil.

The coating may be on one or both sides of the PTFE ribbon-shaped element. The amount of the coating is preferably in the range 0.2 to 10% by weight of the dental floss, more preferably 0.2 to 5%, e.g. 1 to 5%. The dental floss may include a water-soluble or water- insoluble additive material adapted to be released in the mouth in use of the floss to provide a medicinal, diagnostic, cosmetic or flavouring effect, said adjuvant material being located within the PTFE material of the PTFE element or elements and/or on the surface of said PTFE element or elements under the coating, or in the coating. A suitable method of incorporating such adjuvants in the PTFE is described in WO97/24078 (US patent 5800823) . If the adjuvant is in the coating, it can be released by the mechanical disruption of the coating in use. Herein, melting point means the temperature of first appearance of liquid on heating. The melting temperature range is the temperature range from first appearance of liquid (solidus) to disappearance of all solid (liquidus) . DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be illustrated by non- limitative examples. EXAMPLE 1

Glyceryl monostearate is a known pharmaceutical excipient and is composed of a mixture of mono-, di-, and tri-glycerides of primarily stearic and palmitic acids. Some oleate radicals may be present . It contains not less than 90% of total fatty acid glycerides, of which at least 35% are the stearic acid monoglyceride . The glyceryl monostearate used in this example had a melting point of 58 °C and a melting temperature range of about 2'C (i.e. 58 - 60"C) . In this embodiment of the present invention, the glyceryl monostearate is heated to melting point and then held at about 60 °C whilst a lick roller is partially immersed in the molten mass. The lick roller is driven so as to pick up a thin film of the glyceryl monostearate which is then transferred onto essentially one side only of a tape-shaped PTFE filament of dental floss dimensions which is pulled over the exposed surface of the roller. After the coating has cooled and then solidified on-line, the filament is wound onto bobbins for packaging in dispensers. The PTFE filament was one made in accordance with WO 96/10478.

Glyceryl monostearate is thus applied in a suitable amount to provide the desired handling properties in use. Excessive coating may make the floss hard and brittle in use . The amount of glyceryl monostearate in the coated floss is approximately 0.2 - 10% w/w, preferably 0.5 - 5% w/w (weight of glyceryl monostearate/weight of floss) . EXAMPLE 2

The PTFE filament, which is the same as used in Example 1, is treated to incorporate a flavouring by immersion batchwise in an alcohol solution of dental mint flavour. The immersion may be done in a continuous process with the coating, but in either case the alcohol is allowed to evaporate before coating. The flavour may also be incorporated into the filament without the use of alcohol. The level of flavouring is 1 - 50%, preferably 3 - 10%, in the filament. The PTFE fibre is then coated with glyceryl monostearate in the same manner as in Example 1. The filament is coated with glyceryl monostearate at 0.5 - 5% w/w. The glyceryl monostearate used has a narrow melting temperature range of about 2°C. The product exhibits only a small amount of odour in comparison to the quantity of flavour added but, on use in the mouth, the flavour is intensified. This indicates that the flavour is essentially present in the pores of the PTFE filament and is shielded by the coating on one side. As the coating is insoluble in water this suggests that the coating is being mechanically removed from the surface of the PTFE floss during use. It may be that the flavour is released by the external force applied to the floss during use, compression of the floss forcing the flavour to migrate to the surface. Two-sided coating may be employed to give better shielding of the flavour in the PTFE.

Although in this example, the incorporation of a flavouring into the floss is described, other active components may be incorporated, e.g. active components incorporated during manufacture of the PTFE element or incorporated in the coating. These additives may include, but are not limited to, fluoride-containing compounds, plaque control agents, tartar control agents, teeth whitening and bleaching agents, antibacterial agents, antifungal agents, vitamins, minerals, cooling agents e.g. menthol, colourant agents or dyes to identify plaque deposits, pharmacologically active compounds such as antibiotics, antigens, anti-inflammatory agents, analgesic agents, and haemostatic agents. When a solid additive is in the coating, there is a matrix of the coating material with the solid additive dispersed through it .

As the following Examples show, a water-soluble additive is released from the coating in useful amounts on contact with water, e.g. on contact with saliva in the mouth. This effect is not so readily obtained with wax coatings . EXAMPLE 3 Example 1 is repeated with incorporation of sodium fluoride in the coating. Sodium fluoride is added to the coating material in the coating bath at a level of 9% w/w. Since the sodium fluoride is not dissolved in the coating and remains suspended as discrete particles, the melting point of the coating is unaffected. The amount of coating material in the coated floss is approximately 0.5 - 5% w/w. The coated PTFE has been shown to release about 30% of the sodium fluoride present in the coating into water at 37 ^*C, thus indicating useful release into the mouth in use of the floss. EXAMPLE 4

The PTFE filament, which is the same as that used in Example 1, is treated in the same manner with a coating comprising a mixture of glyceryl monostearate, stearyl alcohol and sodium fluoride in the ratios 10:1:1 by weight . The sodium fluoride is not dissolved in the coating. The melting point of this mixture is about 58 'C. The PTFE is coated with the mixture at 0.5 - 5% w/w. The coated PTFE has been shown to release approximately 50% of the sodium fluoride in the coating into water at 37 ° C . EXAMPLE 5 The PTFE filament, which is the same as that used in Example 1, is given a coating as described in Example

4 but with the addition of 10% cetylpyridinium chloride (CPC) . CPC and sodium fluoride are not dissolved in the coating and the melting point of the mixture is about 58 ^*C. The PTFE is coated with the mixture at 0.5 - 5% w/w. The coated PTFE has been shown to release approximately 50% of the sodium fluoride into water at 37°C. EXAMPLE 6 The PTFE filament, which is the same as that used in Example 1, is given a coating as described in Example

5 but with the addition of 10% triclosan in addition to the CPC and sodium fluoride. Triclosan, CPC and sodium fluoride are not dissolved in the coating, and the melting point of the coating mixture is about 58 'C. The PTFE is coated at 0.5 - 5% w/w. The coated PTFE has been shown to release approximately 50% of the sodium fluoride into water at 37'C. Triclosan is a water-insoluble additive but does show antibacterial action when released from the coating when the coating is mechanically removed from the filament . EXAMPLE 7 The PTFE filament, which is the same as that used in Example 1, is treated in the same manner to apply a coating of stearyl alcohol containing sodium fluoride at a level of 9% w/w. Stearyl alcohol has a melting point of about 58 "C and a melting point range of approximately 58 - 60^* C. The PTFE is coated with the mixture at a level of 0.5 - 5% w/w. Sodium fluoride is released into water at a level of approximately 50% at 37°C. EXAMPLE 8

The PTFE filament is coated in the same manner with stearyl alcohol containing 5% sodium bicarbonate and 5% sodium fluoride. The PTFE is coated with the mixture at 0.5 - 5% w/w. The coated PTFE has been shown to release approximately 70-80% of the sodium fluoride into water at 37 'C. The same effect was obtained when silica was used instead of sodium bicarbonate. EXAMPLE 9

The PTFE filament is coated with the mixture described in Example 8 but containing 5% CPC. The PTFE is coated with the mixture at 0.5 - 5% w/w. The coated PTFE has been shown to release approximately 70-80% of the sodium fluoride into water at 37"C. CPC is released into water similarly. EXAMPLE 10

The PTFE filament is coated with the mixture described in Example 8 but containing 5% triclosan. The coated PTFE has been shown to release approximately 70- 80% of the sodium fluoride into water at 37 °C. EXAMPLE 11

The PTFE filament is treated to incorporate dental mint flavour by the processes described in Example 2. The PTFE filament is then coated with stearyl alcohol which has a melting point of about 58 °C and a melting point range of 58 - 60 ° C approximately. The filament is coated with stearyl alcohol at 0.5 - 5% w/w and displays properties similar to those of the product of Example 2.

The products of these Examples had excellent handling characteristics when used in the mouth. The users can comfortably and securely grip the floss, and do not have a residue left on their hands. The coated filament feels dry and non-tacky. The beneficial character of the PTFE floss in the mouth is retained. The dental floss, consisting of or comprising the PTFE tape described above, can be packaged in a conventional manner, for example in a container such as a plastics material box, with an outlet aperture through which the tape can be pulled. The tape can be packed loosely in the box, or wound on a spool in the box. As is normal, the box may have a cutting means for assisting the breaking of the floss, and this may be a notch. Alternatively, the PTFE tape can be used as a floss element in a flossing device, e.g. of the type where the floss element extends between two holding arms of a frame. When wound on polypropylene or polystyrene cores, the preferred dimensions of the bobbins containing the coated PTFE tape used as dental floss are: product contents 45m, diameter up to 26mm and depth up to 10mm.

While the invention has been illustrated herein by embodiments, it is not limited to those embodiments, and modifications and variations may be made within the scope and concept of the invention herein disclosed.

Claims

CLAIMS :

1. A dental floss in the form of an elongate article comprising one or more elongate PTFE elements providing the tensile strength of the floss, and on said PTFE element or elements a coating of a coating material which (i) is not a wax

(ii) is solid at room temperature (25 ┬░C) (iii) is water-insoluble (iv) has a narrow melting temperature range

(v) is non-toxic.

2. A dental floss according to claim 1, wherein said coating material is safely edible by humans.

3. A dental floss according to claim 1 or 2 , wherein said coating material has a melting temperature range of not more than 10 'C.

4. A dental floss according to claim 3, wherein said melting temperature range is not more than 4'C.

5. A dental floss according to any one of claims 1 to 4, wherein said coating material has a melting point above 38 ┬░ C .

6. A dental floss according to claim 5, wherein the melting point is not lower than 42 ┬░C and not higher than 62^╬▓C.

7. A dental floss according to any one of claims 1 to 6, wherein said coating material is at least 90% by weight of at least one compound selected from mono-, di- and tri-glycerides of fatty acids having 14 to 20 carbon atoms, C₁₄-C₂₀ aliphatic alcohols and C₁₄-C₂₀ aliphatic acids .

8. A dental floss according to claim 7, wherein said coating material is at least 90% by weight of one or more compounds selected from mono-, di- and tri-glycerides of stearic, oleic and palmitic acids, stearic acid, stearyl alcohol, and cetyl alcohol.

9. A dental floss according to claim 8, wherein said coating material is at least 90% by weight of glyceryl monostearate .

10. A dental floss according to any one of claims 1 to 9, wherein the amount of said coating material is in the range 0.2 to 10% by weight of the dental floss.

11. A dental floss according to any one of claims 1 to

10, wherein said PTFE element or elements are made of PTFE having a density of not more than 1.5g/cm³.

12. A dental floss according to any one of claims 1 to

11, wherein said PTFE element or elements are made of a PTFE which has been expanded by stretching in at least one direction so as to decrease its density.

13. A dental floss according to any one of claims 1 to 12, having a water-soluble or water-insoluble additive material adapted to be released in the mouth in use of the floss to provide a medicinal, diagnostic, cosmetic or flavouring effect, said additive material being located within the PTFE material of said PTFE element or elements and/or on the surface of said PTFE element or elements under said coating and/or in the coating.