GB2289421A - Coated P.T.F.E. dental floss - Google Patents

Abstract

The floss comprises expanded PTFE coated with e.g. microcrystalline wax, which may be applied by immersion of the PTFE strand(s) in the molten or dispersed wax, to increase the coefficient of friction of the floss and, thereby, its ease of handling. Alternatively, the coating may be of polyvinyl alcohol and/or polyethylene oxide. The floss has a tensile strength of at least c. 10,000 p.s.i., a weight of 500-1500 denier and a friction coefficient when coated of 0.08-0.25. It may comprise a single strand or multiple strands and may contain dentifrice or pharmaceutical for delivery to the teeth and gums during use.

Description

DENTAL FLOSS The present invention relates to dental flosses produced from expanded polytetrafluoroethylene (PTFE) having a friction coating to increase the friction coefficient of the floss and to enhance handling characteristics of the floss. More particularly the invention is directed to single stranded expanded polytetrafluoroethylene dental flosses and multi-stranded expanded polytetrafluoroethylene dental flosses.

Dental flosses have long been used effectively to clean the spaces between the teeth and under the gum margin. One example of a dental floss is disclosed in US-A-3800812. To increase the effectiveness of the floss, some flosses have included certain medicinal ingredients such as fluoride compounds to protect the tooth enamel from acid attack. Bactericides have also been used in connection with dental floss to inhibit periodontal disease. The medicinal components have typically been applied as a coating to the preformed dental floss.

When used properly, dental floss has been found to be effective in inhibiting tooth decay and gum disease and is recommended by dentists in the daily dental hygiene program. Dental floss often has the disadvantage of causing the gums to bleed, which discourages its use by some people. Bleeding of the gums may be caused by the friction of the floss against the gum surface and by the rough texture of the floss.

There have been numerous attempts in the art to produce a superior dental floss that is convenient to use and is less prone to cause bleeding of the gums. Other dental flosses have been provided with a dentifrice component. For example, US-A-3830246, US-A-3897795, US- A-4215478 and US-A-3771536 disclose dental flosses which are impregnated with a fluoride compound to aid delivery of the fluoride to the tooth surface between adjacent teeth. US-A-4033365 discloses a floss designed to retain flavourants over a long period of time through the use of non-wax polymeric coatings containing spray-dried flavour particles.

US-A-3943949 discloses a dental floss-like material in the form of a bundle of natural or synthetic fibres, such as nylon. The floss is coated with various waxes, including microcrystalline wax, to reduce the friction of the floss against the tooth surface. The wax coating is disclosed as containing a spray-dried flavourant to be dispersed during use.

As exemplified by these patents, flossing is an extremely important adjunct to proper dental hygiene.

Many of the dental flosses presently on the market have received limited consumer acceptance. The lack of consumer acceptance of any single dental floss on the market is due in part to the propensity of dental floss to cause gingival bleeding. In addition, dental floss is generally considered difficult and uncomfortable to use.

The consumer dissatisfaction with some dental flosses is caused by the relatively high coefficient of friction (COF) of the floss.

Since prior art flosses have such high friction coefficients, the user must apply substantial downward force to pull the floss between the contact points of the teeth. Unfortunately, the typical user will pull downward with sufficient force to allow the floss to pass between the teeth and snap against the gum surface, causing irritation and possible bleeding of the gum tissue. Some of the difficulty in pulling the floss between the teeth is the result of the thickness of the floss compared to the spaces between the teeth. In order to reduce the risk of gum injury, many manufacturers have coated the floss with wax or other lubricant to reduce the friction coefficient and increase the ease with which it can be inserted between the teeth.

The present invention is directed to dental flosses having a friction coefficient that is less than conventional dental flosses that may enable the user to insert the floss between tight spaces between the teeth with reduced risk of injury to the user. Although the dental floss has a reduced friction coefficient, the floss can be effective in cleaning the tooth surfaces above and below the gum line.

The dental (e.g. cleaning) floss of the invention is preferably produced from polytetrafluoroethylene, suitably in the form of a strand. In a preferred embodiment, the floss is expanded (or stretched) polytetrafluoroethylene (e.g. PTFE that has been expanded at an elevated temperature). The floss may comprise a single strand, or a plurality of strands in which case the strands may form a thread. The PTFE is preferably expanded PTFE and/or has a porous structure (for example, this may comprise a series of nodes interconnected by fibrils). The extremely low friction coefficient of polytetrafluoroethylene, however, can make it difficult to handle by the user. In order to increase the ease of handling, a coating of a composition capable of increasing the coefficient of friction may be applied to the floss which can result in an increase in the friction coefficient of the floss.Thus, the coating preferably comprises a material having a higher COF than PTFE. In a preferred form of the invention, the coating comprises a wax, and in particular a wax coating comprising a microcrystalline wax. The wax is preferably of a low to medium molecular weight.

The floss can be produced from polytetrafluoroethylene that has been stretched at an elevated temperature. The resulting polytetrafluoroethylene usually has a highly porous structure consisting of nodes interconnected by very small fibrils. The size of the floss as it is to be used may range from about 200 or 500 denier to about 1500 denier and, preferably, about 600 denier to about 1200 denier. The floss suitably has a tensile strength greater than about 10,000 psi (6.90 x 107 N/m2 or Pa), and/or a polymeric matrix strength of at least about 100,000 psi (6.90 x 108 Pa).

The or each individual polytetrafluoroethylene strand can be of a denier of about 100 denier to about 1500 denier. When the strand denier is less than about 600 denier, the floss will usually be a multi-stranded floss. That is say about 2 to 12 strands of the floss will preferably be used, usually in a lightly twisted condition in order to form the strands into a cohesive single thread. In multi-stranded polytetrafluoroethylene flosses the wax may serve two purposes. One purpose is to maintain the individual strands in the twisted single thread shape. A second is to increase the coefficient of friction to about 0.08 to 0.25.

In a preferred embodiment, a strand of the expanded polytetrafluoroethylene is immersed in a bath of a microcrystalline wax either in a molten state or dispersed in an organic solvent or carrier. The strand is removed from the bath, and when a solvent is used, dried to remove the solvent. In use, the wax coating may provide a sufficient friction coefficient to be easily handled by the user. It may also hold multi-stranded flosses in a single thread form. When the coated floss is inserted between the teeth, the wax coating tends to be removed as the floss is pulled between the contact points of adjacent teeth to expose the polytetrafluoroethylene and allow ease of insertion between the teeth. A thinner floss of 600 or 800 denier is particularly easy to use and provides sufficient tensile strength to resist breakage.

In another preferred embodiment multiple strands of the expanded polytetrafluoroethylene are immersed in the molten or emulsion wax bath. Either just prior to, within, or just after the wax bath the strands can be lightly twisted to form a single thread. The twisted strands are then cooled to maintain the strands in a twisted state.

In a further preferred embodiment, the floss is coated or impregnated with a bioactive component. The dentifrice or bioactive component may be applied to the floss before coating with the wax and/or may be dispersed in the wax and applied simultaneously.

Many of the disadvantages and limitations of the previous dental floss materials can be overcome by the present invention while producing a dental floss that is convenient to use. The dental floss of the present invention may be sufficiently strong to be used without breakage and has a friction coefficient substantially less than conventional dental floss.

The dental floss of the invention can be produced from polytetrafluoroethylene to provide a floss with a low friction coefficient. Conventionally produced polytetrafluoroethylene has a low tensile strength, a tendency to readily stretch under tension, and is generally not suitable as a dental floss. It has been found that dental floss of sufficient strength can be produced from expanded polytetrafluoroethylene. The polytetrafluoroethylene in a preferred embodiment can be produced according to one of the methods disclosed in US A-3953566 and/or US-A-3962153 (W.L. Gore & Associates).

Here, the floss strands are produced by paste-forming techniques where the polymer is converted to a paste and shaped into a strip which is then expanded by stretching in one or more directions. While it is held in the stretched condition, it is heated to at least 3270C, after which it is cooled. This strip is then cut to form different denier floss strands.

The sheet or tape from which the floss strands are produced can be produced by various techniques.

Extrusions of various cross-sectional shapes such as tubes, rods and tapes are comronly obtained from a variety of polytetrafluoroethylene resins. Paste-forming operations, such as calendaring and moulding, are also practised commercially to obtain the desired shapes.

Paste-forming processes often include mixing the resin with a lubricant such as an odourless mineral spirit, and carrying out forming methods in which the resin is subjected to shear, thus making the shaped articles cohesive. The lubricant can then be removed from the extruded shape, usually by drying. If this unsintered product is heated above the polymer's melting point, generally about 3270C, it will sinter or coalesce into an essentially impermeable structure and not be effective to make a floss.

Instead the paste-formed, dried unsintered shapes should be expanded by stretching them in one or more directions under certain conditions so that they become substantially much more porous and stronger. This phenomenon of expansion with a resulting increase in strength occurs with certain preferred polytetrafluoroethylene resins and within preferred ranges of rate of stretching and preferred temperature ranges. The preferred temperature range is from 350C to 327 cm. At lower temperatures within this range it has been found that there is a maximum rate of expansion beyond which fracture occurs, as well as a lower limit beneath which fracture also occurs or where weak materials are obtained. The lower limit is of much more practical significance. At high temperatures within this range, only a lower limit of the expansion rate has been detected.The lower limit of expansion rates interact with temperature in a roughly logarithmic fashion, being much higher at higher temperatures. Most, but not all, of the desirable products are obtained when expansion is carried out at the higher temperatures within the range of 35"C to 327"C.

The balance of orientation in the extruded shape also affects the relationship between the proper range of expansion rates and temperature. It has been found that some resins are much more suitable for the expansion process than others, since they can be processed over a wider range of rate and temperature and still produce useful products. The primary requisite of a suitable resin is a very high degree of crystallinity, preferably in the range of 98% or above, and a correspondingly low amorphous content. It has been found that techniques for increasing the crystallinity, such as annealing at high temperatures just below the melt point, improve the performance of the resin in the expansion process.

Copolymers of polytetrafluoroethylene, which have defects in the crystalline structure that introduce a higher amorphous content, do not work as well as homopolymers.

However, it has been found, for example, that resins which contain less than 0.2% of hexafluoropropylene as a comonomer can be made to work in this invention by using very high rates of expansion at high temperatures just below the melting point.

The porous microstructure of the expanded material is affected by the temperature and the rate at which it is expanded. The structure usually consists of nodes interconnected by very small fibrils. In the case of uniaxial expansion the nodes are elongated, the longer axis of a node being oriented perpendicular to the direction of expansion. The fibrils which interconnect the nodes are oriented parallel to the direction of expansion. These fibrils appear to be characteristically wide and thin in cross-section, the maximum width being about 0.1 micron (1000 angstroms), which is the diameter of the crystalline particles. The minimum width may be 1 or 2 molecular diameters or in the range of from 5 to 10 angstroms. The nodes may vary in size from about 400 microns to less than a micron, depending on the conditions used in the expansion.Products which have been expanded at high temperatures and high rates have a more homogeneous structure, i.e. they have smaller, more closely spaced nodes and these nodes are interconnected with a greater number of fibrils. These products are also found to have much greater strength. The expansion process results in a tremendous increase in the tensile strength of the polytetrafluoroethylene and an increase in the porosity.

The increase in strength of the polymer matrix is dependent upon the strength of the extruded material before expansion, the degree of crystallinity of the polymer, the rate and temperature at which the expansion is performed, and amorphous locking. When all these factors are employed to maximize the strength of the material, tensile strength of 10,000 psi and above with porosity of 90% or more are obtained. In these cases the polymeric matrix has strengths in excess of 100,000 psi.

In contrast, the maximum tensile strength of conventional extruded or moulded polytetrafluoroethylene after sintering is generally considered to be about 3,000 psi (2.07 x 107 Pa), and for conventional extruded and calendared polytetrafluoroethylene tape which has been inserted the maximum is about 5,000 psi (3.52 x 107 Pa).

Porous polytetrafluoroethylene shaped articles have been produced by stretching to lengths exceeding 1500 times the original sample length. Useful products have been produced by stretching samples in the range of a few hundred percent to greater than 50 times the original sample length.

By definition, the tensile strength of a material is the maximum tensile stress, expressed in force per unit cross-sectional area of the specimen, which the specimen will withstand without breaking (see, for example, The American Society for Testing and Materials, "1970 Annual Book of ASTM Standards - Part 24", at p.41). For porous materials, the cross-sectional area of solid polymer within the polymeric matrix is not the cross-sectional area of the porous specimen, but is equivalent to the cross-sectional area of the porous specimen multiplied by the fraction of solid polymer within that cross-section.

This fraction of solid polymer within the cross-section is equivalent to the ratio of the specific gravity of the porous specimen itself divided by the specific gravity of the solid polymeric material which makes up the porous matrix. Thus, to compute matrix tensile strength of a porous specimen, one divides the maximum force required to break the sample by the cross-sectional area of the porous sample, and then multiplies this quantity by the ratio of the specific gravity of the solid polymer divided by the specific gravity of the porous specimen.

Equivalently, the matrix tensile strength is obtained by multiplying the tensile strength computed according to the above definition by the ratio of the specific gravities of the solid polymer to the porous product.

The expanded polytetrafluoroethylene generally has a coefficient of friction of less than about 0.08.

Conventional dental flosses produced from nylon have a coefficient of friction of about 0.2. The uncoated, expanded polytetrafluoroethylene has been found to be effective as a dental floss and may easily slide through close spaces between the teeth. The low coefficient of friction of polytetrafluoroethylene reduces injury and trauma to the gum tissue even at thickness of as low as 500 denier. The uncoated polytetrafluoroethylene floss has, however, been found to be difficult to handle due to the extremely low coefficient of friction of the polytetrafluoroethylene. It has been found that the polytetrafluoroethylene floss can be coated or otherwise treated with a friction coating, such as a wax, to increase the coefficient of friction to a level where the floss is easier to handle and does not slip through the fingers of the user as easily as the untreated floss.It has further been found that the thinner polytetrafluoroethylene flosses of 600 to 800 denier that are coated with a friction enhancing coating can be easy to handle and comfortable to use. The 600 to 800 denier flosses are particularly suitable for users having closely spaced teeth. Although the polytetrafluoroethylene has a very low coefficient of friction, it has been found that waxes and some other coating materials will adhere to the floss sufficiently to increase the coefficient of friction of the floss. It is believed that the ability of the friction coating to adhere to the floss is due in part to the porous nature of the expanded polytetrafluoroethylene.

The friction coating can comprise any substance (e.g. a wax) that will adhere to the surface of the expanded polytetrafluoroethylene and which will increase the coefficient of friction of the expanded polytetrafluoroethylene surface to 0.08 or greater.

Waxes will usually adhere to the surface of expanded polytetrafluoroethylene to a high degree. Polyvinylalcohol will also adhere to the surface of expanded polytetrafluoroethylene. If the substance itself will not sufficiently raise the coefficient of friction, it can carry an additive which will increase the coefficient of friction. The objective is to adhere a material to the expanded polytetrafluoroethylene surface so that the coefficient of friction can be increased to a desired level to improve the handling characteristics.

In this regard waxes are effective. A variety of waxes can be used. This includes naturally occurring and synthetic waxes. Petroleum derived waxes, such as paraffin and microcrystalline waxes, can be used. A suitable wax should have a melting point of greater than about 500C and/or should be plastic and pliable at room temperature. The wax is preferably not brittle at room temperature. These latter requirements can negate the use of some waxes. Waxes that melt at less than about 500C can become molten during product storage and cause the wax on the floss strands to flow. This could result in problems in dispensing the floss from the rolls.

Also, if the melting point of the wax is around 40"C, the coating could end up being a lubricant at room and body temperatures if it becomes a liquid. This would then lower the coefficient of friction of the strand during usage rather than raise the coefficient of friction. In addition, if the wax is brittle the wax may crack and become removed from the floss during processing and packaging, and later during dispensing and handling prior to usage. Thus, essentially any wax can be used as long as it has a melting point greater than about 500C and the wax is not brittle at room temperature, i.e. about 250C.

It also should not be tacky at room temperature.

In preferred embodiments of the invention, the friction coating comprises a microcrystalline wax.

Microcrystalline waxes are well known in the art.

Preferred microcrystalline waxes have a molecular weight of from about 500 g/mole to about 900 g/mole, optimally from about 600 g/mole to about 800 g/mole. Such microcrystalline waxes may have a melting point of from about 500C to about 1000C and preferably from about 600C to about 800C. Alternative coating materials may include, for example, a water soluble coating, such as polyvinyl alcohol or polyethyleneoxide. These can also be used in addition to a wax coating. The friction enhancing coating may comprise any coating material that is able to adhere to the polytetrafluoroethylene floss to increase the coefficient of friction. Preferably the coating material is sufficiently soft so that the coating can be easily scraped off during the initial use of the floss to expose the polytetrafluoroethylene.

Microcrystalline waxes which can be used in the present invention include those sold under the trademarks Ultraflex (mp 65.60C), Victory (mp 78.9"C), Be Square 175 (mp 83.90C), Starwax (mp 85.60C), Be Square 185 (mp 87.80C), Be Square 195 (mp 92.2"C), Petrolite C-700 (mp 92.20C) and Petrolite C-1035 (mp 93.3"C) from Petrolite Corporation of Tulsa, Oklahoma.Other microcrystalline waxes which may be used include, for example, those sold by Boler Petroleum Company of Wayne, Pennsylvania under the trademark Bowax 1018 (mp 68.30C), Mekon White (mp 93.30C) and Fortex (mp 96.l"c). The preferred micro crystalline waxes are sold by Petrolite Corp. under the trademark Victory and by Witco under the trademark Witco 445, having a melting point of 78.90C and an average molecular weight of about 650 g/mole.

The molecular weights of waxes are calculated as the average of the molecular weights of their hydrocarbon constituents. Paraffin waxes are mainly composed of normal acyclic hydrocarbons and can frequently be characterised by their average molecular weights. It is more difficult to determine the molecular weight of the microcrystalline waxes which typically contain substantial amounts of secondary and tertiary acyclic hydrocarbon isomers and/or cyclic hydrocarbons. There is not necessarily a direct correlation between melting point and molecular weight of the microcrystalline waxes.

Nevertheless, lower melting microcrystalline waxes generally have lower molecular weights.

The dental flosses can be prepared from expanded polytetrafluoroethylene having a weight of from about 100 denier to about 1500 denier. In one preferred form of the invention, the expanded polytetrafluoroethylene has a weight of from about 600 denier to about 800 denier.

As used herein, denier is intended to refer to the weight in grams of the strand per 9,000 metres. The weight of the strand in denier is thus proportional to the diameter of the strand and the extent of the expansion process.

The flosses prepared from 600 denier to 800 denier strand are especially effective as flosses. In another preferred embodiment multiple strands of polytetrafluoroethylene of a denier of from about 100 to 600 are formed into a single thread floss. This will consist of about 2 to 12 strands of expanded polytetrafluoroethylene, depending on the denier. The strands are suitably lightly twisted to produce a single thread. This may then consist of about 1 to 5 twists per inch (or per 2.54 cm). In this case the friction-increasing coating will preferably be a wax that will perform the function of binding the strands into a thread and also increase the coefficient of friction of the expanded polytetrafluoroethylene. The objective is a floss that has a multiple number of strands, but yet a lower coefficient of friction than conventional nylon flosses.The resulting thread suitably has a denier of from about 200, or 500, to about 1500, and preferably from about 600 denier to about 1200 denier.

The tensile strength of the expanded polytetrafluoroethylene is generally at least about 10,000 psi (6.90 x 107 Pa). The polymeric matrix strength of the polytetrafluoroethylene is suitably at least about 100,000 psi (6.90 x 108 Pa). It has been found that the relationship of the tensile strength of the expanded polytetrafluoroethylene and the weight in denier is not linear. Although the tensile strength decreases as the denier decreases, the expanded polytetrafluoroethylene at 500 to 600 denier has sufficient tensile strength to be used as a dental floss without breaking. The low coefficient of friction of the polytetrafluoroethylene minimizes the trauma and irritation of the floss against the gum tissue at a low floss weight.The low coefficient of friction of the polytetrafluoroethylene may result in reduced friction against the tooth surface thereby allowing a thin floss of 600 or 800 denier to be used without breakage of the floss.

The wax or other friction coating may be applied to the expanded polytetrafluoroethylene floss by conventional techniques including, for example, spraying, padding and immersing in a molten or emulsion bath. In one embodiment of the invention, the wax is dispersed in a solvent or carrier as a bath. The strand is passed through the bath and dried to remove the solvent. The dried floss is then wound on a spool and packaged according to conventional procedures. In another embodiment the strand is passed through a molten wax bath. The strand picks up wax and exits the bath. On cooling there is produced an effective coating of the wax on the strand.

The wax or other friction coating applied to a multi-strand material may likewise be applied from either an emulsion or molten bath or wax. The multiple strand material can be passed through this bath with an (e.g.

light) twisting either before passing into the bath, while in the bath, or after exiting the bath. A light twisting is about 1 to 5 twists per inch (per 2.54 cm).

The friction coating is suitably applied to the expanded polytetrafluoroethylene floss at a coat weight to result in a floss having a friction coefficient of from about 0.08 to about 0.25, preferably from about 0.08 or 0.12 to about 0.20 or 0.22. The friction coating may contain suitable known additives to adjust the friction coefficient. It has been found that the expanded polytetrafluoroethylene coated with a wax to have a friction coefficient of 0.08 to 0.25 can be handled easily by the user and can slide easily between the teeth without injury to the gums. It is believed that, during use, as the floss is passed through the tight spaces between the teeth, some of the friction increasing material (e.g. wax coating) is removed, such as scraped, from the floss to expose the polytetrafluoroethylene.The exposed polytetrafluoroethylene may have a sufficiently low friction coefficient to inhibit injury to the gum tissue during use of the floss.

In a preferred form of the invention, the floss is provided with an active component such as, for example, a dentifrice or pharmacological compound. The component may be dispersed in the friction coating, applied as a substrate coating before the friction coating, or as an outer coating over the friction coating. In a preferred embodiment, the active component is dispersed in a solvent or carrier with the friction coating and applied to the floss in a single coating step. Alternatively the active component can be impregnated into the porous structure of the floEs whereby the active component is released during use.

The dentifrice is preferably a fluoride or fluoridecontaining compound such as sodium fluoride, potassium fluoride, ammonium fluoride, sodium silicofluoride, zinc fluoride, and stannous fluoride. Other dentifrices include, for example, ureases, acid phosphates, calcium carbonate and magnesium carbonate. Examples of the acid phosphates which may be used include, for example, orthophosphoric acid, monosodium phosphate, monopotassium phosphate, disodium phosphate, dipotassium phosphate, monoammonium phosphate, hemisodium phosphate and sodium hexametaphosphate salts. If present, the dentifrice is preferably included in the floss in an amount sufficient to provide a topical concentration of from about 5 to about 1000 ppm at the tooth surface.

Other active components which may be incorporated within the floss include peroxides, e.g. hydrogen peroxide, or peroxide producing components such as PVP H2O2 or Carbamide H202 Fluoride, tooth acidulating agents such as buffered or acidulated phosphofluoride, sodium monofluorophosphate, plaque control agents, tartar control agents, antibiotics to treat pyorrhea and gingivitis, teeth whitening and bleaching agents, pH buffering agents, antifungal agents, remineralising agents, hemostatic agents, immunological agents and nonionic and cationic antibacterials such as benzothonium chloride, acetyl trimethyl ammonium bromide, sanguinaria, triclosan (nonionic), tetracycline, cetyl pyridinium chloride, and benzothonium chloride. When triclosan or a similar agent is used, preferably a Gantrez resin is also present.Gantrez resins are a product of GAF Corporation.

Additional active components include vitamins, such as Vitamin A, surfactants and flavours including anise, peppermint, wintergreen, spearmint, fruit flavours and the like.

Among the pharmacological active agents which may be included are, for example, anti-cancer agents, stimulants, bone growth agents, antigens, hormones, steroids, anti-inflammatory agents and analgesic agents.

In a further embodiment, the active agent may be a coagulant to inhibit any bleeding which may be produced by flossing. Although the flosses of the present invention are less prone to cause bleeding than the conventional dental flosses, some bleeding may nevertheless occur in some circumstances, for example if the user has sensitive gingival tissue. Preferably, the coagulant is mixed in the (e.g. wax) coating so as to directly contact the gum tissue. The coagulants may include vitamin K, calcium ions in the form of watersoluble calcium salts, aluminium ions and blood factors or other substances, especially proteins, that may initiate the coagulation cascade. It is possible to incorporate other coagulants from solution in finely dispersed form in the wax coating medium.Alternatively, the coagulants may be solubilized in non-toxic (usually organic) solvents, such as ethanol, polyethylene terephthalate, or diethyl ether. A preferred carrier for this purpose is a water-soluble type of resin, such as polyethylene glycol having an average molecular weight from about 4000 to about 6000 g/mole. The coagulating agents may be applied to the (e.g. wax) coating during or after the initial wax coating has dried. Additional active agents may include, for example, aminocaproic acid, tranexamic acid, adrenaline, alum, noradrenaline, iron salts, zinc salts and calcium alginate.

In further embodiments, dentally acceptable agents such as a cooling agent, for example, menthol and derivatives or analogues thereof such as N-ether-pmethane-3-carboxamide may be incorporated with the coated floss to help the patient to detect where the treatment has been applied. The floss may further incorporate colouring agents and/or a fluorescent dye to identify residual plaque deposits, such as, for example, FD & Red 3 and FD & Red 4. Polishing agents such as hydrated amorphous silica, hydrated alumina, and calcium carbonate may be applied to the expanded polytetrafluoroethylene floss after the strand is formed.

The generally low coefficient of friction of the (e.g. wax) coated expanded polytetrafluoroethylene flosses of this invention may give them a significantly enhanced ability to glide easily between tight interproximal contact point areas. The low coefficient of friction of the polytetrafluoroethylene means that it may be less abrasive on the gingival tissue, enamel, dentin and/or cementum than most currently available dental floss. The (e.g. wax) coating generally appears to be easily removed from the floss as it passes between the interproximal dental contact points so that the remaining exposed expanded polytetrafluoroethylene floss slides without tending to cause substantial gingival bleeding. Moreover, the expanded polytetrafluoroethylene can be about as strong as conventional flosses, but it may be significantly more resistant to shredding and breaking.

The following examples demonstrate the ability of a wax coating on the expanded polytetrafluoroethylene to increase the coefficient of friction to a desirable level whereby the floss may be easily handled by a user.

Unless otherwise indicated, the coefficient of friction is measured by the technique described by Scott & BR< Robbins, J. Soc. Cosmet. Chem., 31: 179-200 (July/August, 1980). This technique, described for measuring friction of reference surfaces by particularly passing hair fibres through an immersed combing device and measuring the COF with Instron (TM) Tensile Tester, is suitable for COF measurement of dental floss with interstitial dental surfaces replacing the combing device.

The invention will now be described, by way of example, with reference to the following Examples which are provided for the purpose of illustration and are not be construed as being limiting.

COMPARATIVE EXAMPLES 1 to 8 and EXAMPLES 9 to 13 These Examples consider the ability to coat an expanded polytetrafluoroethylene fibre with a microcrystalline wax and its effect on the coefficient of friction. For comparative purposes, four commercially available nylon dental flosses (identified as Examples 1, 2, 3 and 4) were tested to determine the coefficient of friction. Four test samples of expanded polytetrafluoroethylene were obtained from W.L. Gore & Associates, Inc.

The comparative test samples were about 1100 denier.

Comparative sample 5 contained no particulate filler material. Comparative sample 6 contained 2.0% Ti02, while comparative sample 7 contained 8.0% Tit2. Additional samples of the expanded polytetraflucroethylene were coated with a microcrystalline wax sold under the trademark Victory by Petrolite Corp. The expanded strands were coated by immersing the strands in a bath and drying the impregnated strands. The coefficient of friction for each sample is recorded in Table I.

TABLE I Coefficient Example ComDosition of Friction 1 Waxed nylon (I) 0.22930 2 Unwaxed nylon 0.21294 3 Nylon (extra fine) 0.20098 4 Waxed nylon (II) 0.15820 5 Expanded PTFE 0.06886 6 Expanded PTFE with 2.0% Tio2 0.07152 7 Expanded PTFE with 8.0% Tio2 0.07926 8 Expanded PTFE with anti-tartar agent 0.07455 9 Waxed expanded PTFE with 8.0% TiO2 and white oil 0.08970 10 Waxed expanded PTFE with flavouring agent 0.09148 11 Waxed expanded PTFE 0.10352 12 Waxed expanded PTFE with flavouring agent 0.18080 13 Waxed expanded PTFE with anti-tartar agent 0.21605 The data in Table I demonstrates that the commercial nylon flosses have a friction coefficient significantly higher than the expanded coated or uncoated PTFE. The expanded PTFE which was coated with the microcrystalline wax has a higher friction coefficient than the uncoated PTFE and is still lower than the conventional nylon floss of Comparative Example 1.

EXAMPLES 14 to 17 and COMPARATIVE EXAMPLE 18 A selection of four single strand expanded polytetrafluoroethylene flosses according to the invention (Examples 14 to 17) were consumer tested along with a commercially available multi-filament waxed nylon floss (Comparative Example 18) obtainable from Johnson & BR< Johnson. The test was a four week, blind, crossover study. The test panelists were all floss users and used floss at least three times per week. During the study the test floss had to be used at least three times per week. The correlations of the test panel data is set out in Tables II and III. The flosses were rated by the panelists according to their overall preference.

TABLE II 600 D 800 D 1200 D Nylon Floss* Like better than 13 17 17 9 Like the same as 16 20 21 18 Like less than 15 6 6 19 their regular floss *Johnson & Johnson Co.

TABLE III 600 D 800 D 1200 D Nylon Floss* Like a lot 10 15 17 7 Like somewhat 11 13 18 11 Neither like nor 10 12 5 9 dislike Dislike somewhat 13 4 5 10 Dislike a lot 1 1 1 6 *Johnson & Johnson Co.

The data illustrates that 600 denier, 800 denier and 1200 denier expanded polytetrafluoroethylene single strand floss was preferred as compared to a conventional nylon multi-filament floss. Of the expanded polytetrafluoroethylene flosses, the 800 denier and 1200 denier flosses were preferred.

Claims (21)

1. A dental floss comprising one or more expanded polytetrafluoroethylene (PTFE) strands, at least part of the floss having a coating comprising at least one material adapted to increase the coefficient of friction of the floss, the floss having a denier of from 200 to 1500 and a coefficient of friction (COF) of from 0.08 to 0.25.

2. A dental floss according to claim 1 which comprises a plurality of polytetrafluoroethylene strands.

3. A dental floss according to claim 2 wherein each strand has a denier of from 100 to 600.

4. A dental floss according to claim 1 which comprises a single polytetrafluoroethylene strand of from 600 denier to 1200 denier.

5. A dental floss according to any of claims 1 to 4 wherein the coating comprises a wax.

6. A dental floss according to claim 5 wherein the wax has a melting point of at least 50"C and is not brittle at 250C.

7. A dental floss according to claim 5 or 6 wherein the coating comprises microcrystalline wax, polyvinyl alcohol and/or polyethyleneoxide.

8. A dental floss according to any of claims 1 to 7 wherein the floss has a coefficient of friction of from 0.15 to 0.20.

9. A dental floss according to any of claims 1 to 8 wherein at least one polytetrafluoroethylene strand comprises at least one active material which is a remineralizing agent, whitening agent, antibiotic, antifungal agent, immunological agent, anti-tartar agent, anti-caries agent, anti-plaque agent, lysozyme, antibacterial agent, anti-inflammatory agent, hemostatic agent, analgesic and/or a mixture thereof.

10. A dental floss according to claim 9 wherein the active agent is sodium fluoride, zinc chloride, tetrasodium pyrophosphate, sodium acid pyrophosphate, tetrapotassium pyrophosphate, Vitamin K, a water soluble calcium salt, blood factor that initiates the coagulation cascade, aminocaproic acid, tranexamic acid, adrenaline, alum, noradrenaline, iron salt, calcium alginate, sodium monofluorophosphate, stannous fluoride, chlorhexidine, hexachlorophene, cetyl pyridinium chloride, benzethonium chloride, ureases, calcium carbonate, magnesium carbonate, orthophosphoric acid, monosodium phosphate, monopotassium phosphate, disodium phosphate, dipotassium phosphate, hemisodium phosphate, benzothonium chloride, acetyl trimethyl ammonium bromide, sanguinaria, triclosan, tetracycline, cetyl pyridinium chloride or benzothonium chloride and/or a mixture thereof.

11. A dental floss according to any of claims 4 to 9 wherein the wax is a microcrystalline wax having a melting point of from 60"C to 800C.

12. A dental floss according to any of claims 1 to 11 wherein the polytetrafluoroethylene strands are twisted to form a thread.

13. A dental floss according to claim 12 wherein the floss comprises a thread formed from two to twelve polytetrafluoroethylene strands which are twisted to from one to five turns per inch.

14. A dental floss according to claim 12 or 13 wherein the material capable of increasing the coefficient of friction comprises wax, polyvinyl alcohol and/or polyethylene oxide.

15. A dental floss according to claim 14 wherein the wax comprises microcrystalline wax and/or has a melting point of at least 500C.

16. A dental floss according to any of claims 1 to 15 wherein the or each strand has a tensile strength of at least 1 to 10,000 psi (6.90 x 107 Pa).

17. A dental floss according to any of claims 1 to 16 wherein the floss includes at least one bioactive component.

18. A dental floss according to any preceding claim wherein the polytetrafluoroethylene has been expanded by stretching at an elevated temperature.

19. A dental floss according to any preceding claim wherein the material has a COF greater than PTFE.

20. A dental floss according to any preceding claim wherein the coating is adapted to be removed, during use, to expose the PTFE.

21. A dental floss substantially as herein described with reference to any of Examples 9 to 13 and 14 to 17.