1. Field of the Invention
This invention relates to compositions and methods for the treatment of pain and discomfort associated with sensitive teeth. More particularly, this invention relates to oral compositions that relieve the pain and discomfort associated with sensitive teeth.
2. Description of Related Art
Dentin is a portion of the tooth internal to the enamel and cementum that has a radially striated appearance owing to a large number of fine canals or tubules known as the dentinal tubules. Tubules run from the pulp cavity to the periphery of the dentin and are generally about two microns in diameter at their base and somewhat narrower at their periphery. Tubules are not usually exposed to the environment in the oral cavity, as they are usually covered by enamel or cementum. The cementum in turn is often covered by the gums.
While not wishing to be bound by theory, it appears that exposed tubules can lead to tooth sensitivity, an irritating and painful condition. In this theory, recession of the gum lime exposes cementum to erosion. The eroded cementum in turn exposes the hollow dentinal tubules. The exposed tubules cause nerves within the tooth to be affected excessively by external oral stimuli because material and energy transfer between the exterior and interior of the tooth is accelerated through the tubules. Common environmental stimuli, such as heat, cold, chemicals and physical and mechanical pressure or stimuli, such as brushing, are able to irritate the nerve through the open dentin tubules and thereby create pain. The pain of sensitive teeth appears to result from these stimuli, which apparently cause fluid movements in the dentinal tubules that activate pulpal nerve endings. Such pain certainly does not encourage daily oral care and treatment and so as a result those plagued with sensitive teeth do not brush as often as they should nor can they always enjoy certain foods and beverages.
Various attempts have been made in the art to cure or treat sensitive teeth so as to relieve the associated pain. One approach to relieving the pain of sensitive teeth is to reduce the excitability of the nerve in a sensitive tooth. This technique interferes with the ordinary triggering process of the nerve by altering the chemical environment of the nerve. The most well known agent for this purpose is potassium nitrate, used in commercial dentifrices for sensitive teeth and discussed in U.S. Pat. No. 3,863,006 to Hodosh, issued Jan, 28, 1975. U.S. Pat. Nos. 4,631,185 and 4,751,072 both to Kim disclose the desensitization of teeth using oral compositions comprising potassium salts such as potassium bicarbonate and potassium chloride, while U.S. Pat. No. 4,990,327 to Neirinchx describes the desensitization of teeth with strontium and fluoride ions. Other prior art methods disclose the treatment of sensitive teeth using zinc and strontium ions (U.S. Pat. No. 3,888,976 to Mlkvey et al.), and a specific blend of chloride salts (U.S. Pat. No. 3,689,686 to Svajada) Although these chemical methods of treatment provide relief in varying degrees, they are not always immediately effective.
Another approach to treating sensitivity has been to block the dentinal tubules wholly or partially with "tubule blocking agents." Tubule blocking agents can block the tubules for varying amounts of time and with varying degrees of success. The use of particulate materials as tubule blocking agents, is set forth in U.S. Pat. No. 5,718,885 to Gingold et al. for cationic alumina, U.S. Pat. No. 5,589,159 to Markowitz et al. for Laponite.RTM. clay and other hectorite clays, and in U.S. Pat. No. 4,992,258 to Mason, for montmorillonite clay. Thus prediction of beneficial tubule blocking agents is not a trivial exercise.
The use of water-soluble or water-swellable polyelectrolytes or the salts thereof as tubule blocking agents is also known. In addition, maleic acid copolymers are known to reduce the deposition of dental plaque onto teeth, with varying degrees of success, as shown in U.S. Pat. No. 4,362,713 to Buck, issued Dec. 7, 1982.
U.S. Pat. No. 4,057,021 to Pashley et al. uses oxalate salts applied to the surface of the tooth to alleviate sensitivity. Other proposed agents include various polymer systems for delivery of active agents to the teeth and gums including apatite particles (U.S. Pat. Nos. 4,634,589 and 4,710,372 to Scheller).
Along a similar vein, U.S. Pat. Nos. 5,300,290 and 5,320,842 both to Spencer disclose the use of solid polymeric particles such as polystyrene, polymethyl methacrylate, and polyvinyltoluene, among others, that have an ionically charged outer surface to which an oppositely charged antimicrobial agent such as chlorhexidine is adsorbed. The composition is used for antimicrobial action in the oral cavity in general, however, not in the treatment of sensitive teeth.
Two related patents disclose the use of similar microparticles for desensitizing teeth. U.S. Pat. No. 5,250,288, issued Oct. 5, 1993, and U.S. Pat. No. 5,211,939, issued May 18, 1993 both to Turesky et al. disclose a dentifrice comprising positively charged polystyrene particles which, it is postulated, desensitize the tooth by clinging to the surface of the teeth. The particles are intended to block the dentin tubules, thereby protecting the nerve from exposure to outside stimuli. The particles are generally from about 0.01 to 3.0 microns in diameter and may have an antimicrobial, analgesic or other therapeutic substance absorbed therein absorb thereon.
U.S. Pat. No. 5,374,417 to Norfleet et al., issued Dec. 20, 1994, discloses a dentifrice for the cleaning and desensitization of sensitive teeth consisting of a standard toothpaste base or carrier containing the potassium salt of a synthetic anionic polycarboxylate polymer as the desensitizing agent. The polycarboxylate polymer particles apparently enter the dentinal tubules during brushing, and their penetration blocks the tubules and prevents physical, chemical and/or osmotic stimulation of the nerves.
U.S. Pat. No. 5,188,818 to Merianos et al., issued Feb. 23, 1993, discloses a dentifrice comprising about 0.1% to 20% of a strontium salt of a maleic anhydride/methyl vinyl ether copolymer as a desensitizer. The carrier base consists of the standard surfactants, humectants, thickeners, anti-caries agents and flavors as is known in the art.
U.S. Pat. No. 5,270,031 to Lim et al., issued Dec. 14, 1993, discloses oral compositions for relieving the pain and discomfort of sensitive teeth, consisting of water-soluble or water-swellable polyelectrolyte salts. The polyelectrolyte salts can comprise the anionic, cationic or amphoteric forms of methyl vinyl ether and maleic anhydride copolymers or polyacrylic acid polymers with sodium, calcium, potassium, ammonium, zinc and other similar metals.
Dentin sensitivity is, of course, not the only problem that can arise in the mouth, and polymers have long been known for various dental applications. U.S. Pat. No. 4,685,883 to Jernberg discloses the use of biodegradable microspheres to deliver chemotherapeutic agents to treat periodontal disease. U.S. Pat. No. 3,956,480 to Dichter et al., issued May 11, 1976, describes and claims the treatment of teeth with anionic polymers that are complexed with a cationic antimicrobial agent such as chlorhexidine.
However, in order for any of the aforementioned compositions to be effective as a tubule blocker, thereby reducing the pain and discomfort of sensitive teeth, they must not only be able to block the tubule once inside the tubule, but they must also be able to enter the tubule in the first place. Tubules of sensitive human dentin may contain organic material that prevents the bulk movement of certain materials into the tubules. Additionally, evidence has shown a continuous outward flow of fluid when vital dentin is exposed and the dentinal smear layer is removed. This outward fluid flow from the tubules could counteract the ability of any desensitizing materials to enter the tubules for blockage of fluid movement. The mere application of such materials with a toothbrush (as a paste) or in solution (as a mouthwash) would not necessarily generate sufficient force to drive the desensitizing materials into the tubules of live, sensitive dentin. Hence, the need exists for desensitizing compositions that have an affinity for the tubule interior and the outer regions of the tubule so as to insure a desensitizing effect.