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Use of bioactive glass

Use of bioactive glass description/claims

The present invention relates to the use of bioactive glasses as abrasive agents in the management of dental pain.

Dental pain is a common problem affecting 17% of the population at any one time and increases in frequency with age. (Litkowski L J., Hack G D., Sheaffer H B., Greenspan D C., 1997, Occlusion of dentine tubules by 45S5 Bioglass®, Bioceramics 10 Procs 10th Int., Symposium on ceramics in Medicine pp 411-414, Ed. Sedel L & Rey C. Elsevier Science Ltd). The principle causes of this dental discomfort arise from both abrasion and acid erosion of external root dentine, which has either been revealed after gingival recession (due to periodontal disease or as a feature of maintaining teeth further into old age) or bas developed due to dental caries i.e. the acid dissolution of dental tissues resulting from bacterial plaque metabolic activity.

One of the currently accepted causes of dental pain is the hydrodynamic theory (Litkowski, et al 1997) whereby movement of fluid through the dentine tubule tracts excites either the odontoblasts, whose processes (once) occupied the tubules, or adjacent nerve fibres directly. In the normal healthy state, these tubules are closed off by the overlying enamel crown or cementum of the root. When dentine is exposed either by the ravages of periodontal disease (gingival recession) or by dental treatment eg acid etching after cutting a restoration cavity, the tubules are lain open, allowing large fluid movements and consequential dental pain.

Regardless of its similarities, toothache resulting from cavity formation relates to a different problem area to hypersensitive dentine. Sensitivity associated with caries, and pain caused by irritation is usually treated by removal of decay and restoration by filling. At the bottom of the prepared cavity, a commercially available preparation is placed against the pulp, the biologically active component of such preparation is usually calcium hydroxide. At the cell level, the strongly alkaline calcium hydroxide first induces irritation, which leads to the necrotisation of the tissue. Over a longer time span, however, it promotes the healing process. The result of the treatment is the formation of reparative secondary dentine. The formed tissue layer separates the pulp from the damaged area or the filling, but its effect on the mineralization of dentine tubules is minimal.

During filling, the dentinal tubules can also be closed by glass ionomer cement, or with different preparations based on polymer chemistry (binder plastics, resins, and dentine adhesives). These substances close dentinal tubules mechanically and improve the retention of the filling being prepared.

The epidemiological data describing the extent of the problem caused by hypersensitive dentine and the need for its treatment is limited. However, it is widely accepted that tubule occlusion by varnishes, resins or crystal precipitation will reduce or eliminate dentine sensitivity (Litkowski, et al 1997). The duration of the relief equates to the service lifetime of the occluding material (Litkowski, et al 1997), which can be all too brief e.g. if applied to a root surface continually abraded by a toothbrush.

Recently, in connection with tooth hypersensitivity, Litkowski, et al 1997 has shown in vitro that bioactive glasses can occlude exposed tubules and encourage re-mineralisation of the tooth surface.

U.S. Pat. No. 5,891,233 discloses preparations containing bioactive glass which act to induce mineralisation in exposed dentine and their use in the treatment of pulpal irritation i.e. tooth hypersensitivity and/or tooth strengthening. The bioactive glass demonstrated must be applied and maintained in moist form to encourage chemical interaction between the glass phase and the dentine.

Thus, in U.S. Pat. No. 5,891,233 the bioactive glass preparations are presented in the form of solutions, suspensions and pastes. In use, the bioactive glass preparation is placed in direct contact with the area of the tooth to be treated. For example, the paste or solution is placed in a periodontal pocket, in a drilled cavity or spread onto a polished surface or otherwise exposed dentinal surface. The bioactive preparation is then covered with protective packing or cementum to prevent displacement of the preparation.

However such methods suffer from the disadvantage that the area to be treated must first be prepared using conventional dental techniques. For example, in the case of cavity formation, the caries must first be removed with a drill or the like before the bioactive paste can be applied. Moreover, as mentioned above, when applied as a paste the bioactive preparation must be retained in place with protective packing for an extended period. In use such packing is prone to becoming detached and the paste then simply washes away. Moreover, when used to treat hypersensitivity the packing is often visible during the period of treatment. Such unsightly packing can lead to premature removal of the packing by the patient and thus failure of the treatment.

U.S. Pat. No. 5,735,942 discloses a novel silica based bioactive glass composition having a particle size range <90 μm for use in conjunction with a delivery agent such as a toothpaste, and the use of such compositions in treating dentine hypersensitivity.

U.S. Pat. No. 6,086,374 reports that the compositions of U.S. Pat. No. 5,735,942 may be used to remineralise enamel and prevent tooth decay.

Air abrasion as a means of cutting or preparing tooth substrate surfaces by harnessing the transferred kinetic energy of alumina particles accelerated in a controlled compressed gas stream has been known since the 1950s. The abrasive stream cuts (abrades) through the target substrate by repeated localised impacts serially removing material from the point of aim. More recently, dental “air polishing” employing bicarbonate of soda as an abrasive for tartar removal has gained acceptance.

The use of other gases as a propellant (eg CO2 or N2) is included in the definition of “air abrasion” and the use of water or other fluids to act as dust suppression agents (regardless of potential contribution to the overall cutting effect) are also included, however delivered—either included in the gas stream or entrained around it (e.g. The Aquacut air abrasive machine—Medivance Instruments Ltd, Harlesden, London).

We have now found that by using bioactive glass as an abrasive agent (cutting and/or surface peening agent) in a conventional air abrasion system, benefits are observed in the cutting of both tooth enamel and dentine and in the delivery of the bioactive glass.

Accordingly the present invention provides a method of treatment for and/or prophylaxis of a person suffering from or susceptible to dental hard tissue and pulpal disorders, defined herein to include dental caries, pain, tooth wear, discoluration, dentine hyper-sensitivity and dental tissue congenital malformations, which method comprises contacting the affected area with bioactive glass using an air abrasion system.

Alternatively the present invention provides the use of a bioactive glass in the manufacture of an air abrasive agent for use in the treatment of dental disorders.

Thus the present invention is based upon the observation that when applied through a conventional air abrasion system the bioactive glass particles and fragments thereof become embedded in the surface of the treated area providing long term effect and minimising the amount of glass lost by erosion. The embedded bioactive glass provides long term effect, encouraging rapid re-mineralisation of the affected area, accelerating surface healing and reducing the patient's dental pain.

The fact that particles of bioactive glass are actually embedded in the surface of the treated area obviates the need for protective packing to prevent their displacement, thereby reducing the risk that the preparation will be washed away and increasing the success rate of the treatment.

Moreover, bioactive glass may be used as an abrasive agent in the air abrasive system to cut and abrade enamel and cariously damaged surfaces (i.e. de-mineralised enamel & dentine). Therefore the present invention obviates the need for a separate preparation step as required when using bioactive glass pastes and solutions to treat dental pain associated with caries.

Further advantages arise by carefully controlling the hardness and/or shape of the bioactive glass to be used, different types of dental material may be cut and/or abraded. Thereby giving rise to differential cutting and minimising the possibility of cutting too far.

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