Patent Application
20080096784
1. Field of the Invention
The invention relates to a composition for cleaning dental instruments, in particular to remove acid-base cement residues, and a corresponding process.
2. Description of the Related Art
In the dental practice, instruments and equipment, such as impression trays, forceps, pliers etc., required for examination and treatment must be cleaned to remove contamination adhering to the surface. In present-day dental treatment, an impression of the patient's dentition is taken with a view to providing prostheses from inlay work produced in the laboratory, such as crowns, bridges, inlays, partial crowns etc. For this, the patient must bite into a so-called “impression tray” (moulding tray) filled with a soft impression composition. The teeth of the dentition displace the impression composition, so that a negative mould results, which cures and can be pulled away from the patient's dentition. The negative mould can now be cast with filler compositions and a positive impression produced. In this context, an exact reproduction of the details to be reproduced is required.
When the impression composition is removed from the impression tray, as a rule some of the cured impression composition remains stuck to the tray. Cleaning of the impression tray is a difficult working operation because simple washing by hand using a brush is not sufficient. Due to the geometric design of the impression tray, the impression composition can stick in the grooves or openings thereof, so that removal of the material is even more difficult to achieve.
To avoid the difficulty of cleaning dental impression trays, disposable impression trays of plastic are marketed. After use, the contaminated tray is simply thrown away. However, the use of disposable impression trays of plastic is uneconomical for cost reasons and ecologically disadvantageous.
The most usual material for creating an anatomical impression of fully toothed, partly toothed and toothless jaws are alginates, the water-soluble salts of water-insoluble alginic acid. Alginic acid is a polyuronic acid and consists of 1,4-glycosidically linked D-mannuronic acid and L-guluronic acid having up to 750 units. It is obtained from red and brown algae and is converted into the corresponding salts. The principle of creating alginate impressions comprises conversion of the water-soluble sodium, potassium or ammonium salts into the water-insoluble calcium, lead or barium alginates by reaction of the water-soluble salts with calcium sulfate or suitable lead or barium salts. The setting process is started by dissolving a powder which contains a water-soluble salt of alginic acid and a suitable further salt, such as e.g. calcium sulfate, in water. A sol initially forms, which rapidly passes into the gel state, since the water-soluble salt of alginic acid reacts with the further salt and precipitates out irreversibly as a sparingly soluble alginate, e.g. calcium alginate. Chemically, the setting reaction is thus an ion exchange reaction in which the metal ions change places at positions where the carboxylate groups of the alginate can be satisfied coordinatively.
In the case of zinc phosphate and zinc polycarboxylate cements, a basic to amphoteric powder and an acidic aqueous solution form the starting components. In zinc phosphate cements, phosphoric acid is set with zinc oxide. The reaction between one part by weight of orthophosphoric acid and two parts by weight of zinc oxide thus leads to the crystalline reaction product hopeite, which is reached via intermediate phases of primary and secondary phosphates existing partly side by side. In practice, successful cleaning of dental instruments to remove contamination by zinc phosphate cements is particularly important. On the one hand zinc phosphate cement is a material which is employed very often, and on the other hand it is distinguished by a very high adhesiveness, which is why the removal of this material requires particular effort. In the case of zinc polycarboxylate cements, polyacrylic acid is set with zinc oxide. The dissolved zinc ions are complexed by the polyacrylic acid. The polymer chains are fixed electrostatically by incorporation of the zinc ions.
In the prior art of cleaning of dental instruments, cured residues of “acid-base” cements adhering firmly to the surface of the instruments are cleaned with effort with the aid of concentrated cleaning solutions or cleaning powders if disposable instruments are not used.
Several attempts have already been made to improve the cleaning of dental instruments, e.g. metallic impression trays, to remove “acid-base” cements. These proposals are often based on the attempt to cause the compounds formed in the setting reactions to undergo chemical degradation.
The document JP 07265335 discloses a steam treatment of an impression tray at 100° C. to 130° C. in order to clean the tray in this way to remove contaminating material within a short time. A disadvantage of this process, however, is obviously the high expenditure on apparatus.
The publication JP 08003588 describes a cleaning composition which is obtained by mixing a metal-chelating agent, such as EDTA, and an alkali metal salt of a diaminoethylglyerol derivative and which dissolves alginate without corroding the tray. JP 2003165997 describes a composition which comprises peroxyhydrates, such as sodium perborate and/or hydrogen peroxide, and an azole compound, such as benzothiazole. The tray-cleaning action is improved if at least one alkali metal salt chosen from the group consisting of carbonates, bicarbonates, phosphates, sulfates or hydrogen sulfates is added to the composition, such as e.g. sodium carbonate, sodium bicarbonate, sodium phosphate or sodium sulfate. The disadvantages associated with the use of hydrogen peroxide have already been mentioned above. In water, sodium perborate dissociates into hydrogen peroxide and sodium hydrogen borate. The latter compound passes through waste water treatment plants virtually unchanged and can thus enter the groundwater.
Reference may also be made to the following documents:
The object of the present invention is to remedy the disadvantages of the prior art which have been described and to render possible a cleaning of dental instruments to remove contamination originating in particular from zinc phosphate cements which is more effective compared with the prior art, in particular at neutral to weakly alkaline pH values of from approx. 7.0 to 9.5. The cleaning should preferably be easier and/or faster to carry out compared with the prior art. Preferably, a cleaning composition to be provided should be widely usable, which means on the one hand that preferably it should be possible to clean every type of dental instrument, in particular one of aluminium, with this composition without damage, and on the other hand that preferably it should be also possible to remove other “acid-base” cements effectively, in addition to zinc phosphate cements.
According to a first aspect of the present invention, this object is achieved by a composition for cleaning dental instruments, comprising or (preferably) consisting of:
Water is not included here in the additives of component (g) of the composition.
The use of amino acids or alpha-hydroxy acids or salts thereof as chelating agents is indeed already known from the prior art. The invention is now based, however, on the surprising knowledge that on combination of amino acids (or salts thereof) and alpha-hydroxy acids (or salts thereof), a synergistic increase can be achieved in the cleaning power, that is to say the combination of these constituents can have a cleaning action which goes beyond mere addition of the cleaning actions of the individual components. This surprisingly effective cleaning action is achieved in particular at only neutral or weakly basic pH values (pH 7.0 to 9.5) compared with the prior art. In this pH range, dental instruments, in particular those of aluminium, are not corroded by the cleaning solution.
The synergism effect on which the invention is based is not known from the prior art. The combination of amino acids (or salts thereof) and alpha-hydroxy acids (or salts thereof), in particular of nitrilotriacetate or nitrilotriacetic acid and citric acid or trisodium citrate, in a cleaning composition with which in particular dental instruments are to be freed from “acid-base” cement residues also is not known.
Precisely the use of amino acids, some of which have a very poor water-solubility, is not known in the connection according to the invention. Astonishingly, these compounds, which are poorly soluble in water, give very good results in respect of their rate of solution in water. Their rapid dissolution in water presumably takes place due to a neutralization of the acids by the metal carbonates and metal bicarbonates present in the mixture as component (c).
If (regularly sparingly soluble) amino acids are used, the storage stability of a corresponding composition according to the invention is comparatively high, presumably due to the lower hygroscopy of the amino acids in relation to the salts of the amino acids. In some preferred cases, component (a) comprises exclusively amino acids, that is to say no aminocarboxylates. In other cases, component (a) comprises exclusively aminocarboxylates.
WO 00/27438 A discloses certain compositions for removal of biofilms, but no compositions which comprise, in addition to comparatively large amounts of amino acid/carboxylate and alpha-hydroxy acid/salt, only 0-5 percent by weight of surfactants.
DE 196 03 977 teaches the use of a disinfection solution and a cleaning solution independent of this in a method for cleaning and disinfecting delicate medical equipment, in particular endoscopes. Since endoscopes are primarily contaminated with residues of human tissue and blood, the cleaning problem there is quite different to that of removal of “acid-base” cement residues from dental instruments. According to one embodiment, the disinfection solution disclosed comprises nitrilotriacetate and citric acid in equal contents by weight. A reason for the simultaneous use of the two substances is not given. In particular, no synergistic interaction is described. DE 196 03 977 discloses no composition having a pH in the range of from 7.0 to 9.5. The preferred pH ranges stated in this citation are below 7, in particular between 4.5 and 6.5. Since the pK value of the last protonation stage of citric acid is 6.4, the citric acid is present in monoprotonated form in a low pH range of this type, which is why it is to be expected that its chelating action would be impaired and there would no longer be a synergistic interaction with nitrilotriacetate in the removal of cement residues. The surprisingly high cleaning power of a composition according to the present invention allows the dental instruments to be cleaned at room temperature to remove “acid-base” cement residues, while DE 196 03 977 teaches a temperature range of from 55 to 65° C. for other contamination.
The patent specification DE 198 14 829 discloses a cleaning and disinfection composition for medical instruments, such as surgical instruments and anaesthesia material, in particular for endoscopy. It teaches the use of citric acid in an approximately three-fold weight excess over nitrilotriacetate. The role of the citric acid in adjusting the pH of the composition, which is between 1 and 5, is emphasized. No reason is given for the simultaneous use of citric acid and nitrilotriacetate. As already discussed above for DE 196 03 977, in the pH range and weight ratio of citric acid to nitrilotriacetate which are the teaching of DE 198 14 829, no synergistic intensification of the cleaning action of the two substances is to be expected if they were to be used on the unrelated cleaning problem of removal of cement residues from dental instruments. DE 198 14 829 moreover teaches working in the temperature range of from 50 to 70° C.
Compositions according to the first aspect of the present invention which are preferred are those in which the weight ratio of the total amount of amino acids and salts thereof to the total amount of alpha-hydroxy acids and salts thereof in the composition is greater than 1:1, preferably greater than 1.5:1, and in this context preferably less than 5:1, preferably less than 3:1. At these weight ratios, the synergistic intensification of the cleaning effect is surprisingly particularly high.
In preferred compositions according to the first aspect of the present invention, the amino acids of component (a) or salts thereof are chosen from the group consisting of nitrilotriacetate (NTA), ethylenediaminetetraacetate (EDTA), diethylenetriamine-pentaacetate, hydroxyethylethylenediaminetriacetate, methylglycine diacetate, acids thereof and the corresponding mixtures of acid(s) and/or salt(s). Nitrilotriacetate, nitrilotriacetic acid and mixtures thereof are particularly preferred.
Preferred compositions are furthermore those comprising alpha-hydroxy acids of component (b) and/or salts thereof which are chosen from the group consisting of glycolic acid (hydroxyacetic acid) and salts thereof (glycolates), lactic acid (2-hydroxypropanoic acid) and salts thereof (lactates), mandelic acid (hydroxyphenylacetic acid) and salts thereof (amygdalates), malic acid (hydroxysuccinic acid) and salts thereof (malates), tartaric acid (dihydroxysuccinic acid) and salts thereof (tartrates), citric acid (2-hydroxy-1,2,3-propanetricarboxylic acid) and salts thereof (citrates), and the corresponding mixtures of acid(s) and/or salt(s). Citric acid and/or salts thereof is particularly preferred.
As already mentioned, in the case of the joint use of amino acids and/or salts thereof, preferably nitrilotriacetic acid and/or nitrilotriacetate, and alpha-hydroxy acids and/or salts thereof, preferably citric acid and/or citrate, a surprisingly synergistically increased effectiveness can be achieved in the cleaning of dental instruments to remove “acid-base” cement residues.
A second aspect of the present invention therefore relates to a composition comprising or (preferably) consisting of
Water is not included here in the additives of component (g) of the composition.
DE 198 14 829 A1 discloses no composition having a components ratio according to the invention.
It has already been pointed out that a pH in the neutral to weakly alkaline range of from 7.0 to 9.5 is preferred for a composition with which in particular aluminium instruments can be cleaned without the danger of corrosion. Preferably, the pH of a solution prepared by mixing the composition according to the second aspect of the present invention with 4,000 parts by weight of water is therefore in the range of from 7.0 to 9.5, if amino acids are absent preferably in the range of from 7.5 to 9.5.
The compositions according to the first and second aspect of the present invention, in particular in their embodiments described above and in the following as preferred, preferably comprise components such as surfactants, tabletting auxiliaries, corrosion inhibitors and/or other additives. Examples of preferred other additives are (further) buffer substances for adjusting and stabilizing the pH and further chelating agents.
These and all the following parts by weight stated in the description are in each case to be understood with the proviso that components (a), (b), (c), (d), (e), (f) and (g) are present in total in an amount of 100 parts by weight.
The adjustment of the pH with the aid of buffer substances in the form of or in addition to components (a) and (b), which can themselves be described as buffer substances, is of particular importance. As stated above, on the one hand it is known that ion-complexing compounds, such as aminocarboxylates (e.g. EDTA, NTA), display their complexing action to the fullest extent at a pH of approx. 11 or above, since complete deprotonation cannot be achieved at lower pH values. On the other hand, dental instruments, in particular also impression trays, are made of the most diverse metals, such as steel, aluminium, copper, nickel and the corresponding alloys. It was therefore extremely surprising to find that the compositions according to the invention achieved very much higher cleaning actions than conventional cleaning agents for “acid-base” cements from the prior art at pH values of not more than 9.5 in the removal of “acid-base” cement residues. They therefore can be employed as universal cleaning compositions, suitable for cleaning any type of metallic dental instruments. It was surprising to find that at pH values of less than or equal to 9.5, at which NTA is not completely deprotonated, a good cleaning of “acid-base” cement residues can be achieved. At the same time, aluminium instruments advantageously are not attacked. In principle, all the buffer substances which are suitable for use in the cleaning of dental instruments can be employed in compositions according to the first or second aspect of the present invention. However, in the absence of amino acids, the presence of from 10 to 25 parts by weight of one or more alkali metal carbonates and/or bicarbonates as component (c) in the compositions according to the first or second aspect of the present invention is particularly preferred.
Dissolving of a composition according to the invention results in a complex buffer system due to the interaction of all the buffer substances it contains. For example: Carbon dioxide and alkali metal carboxylates are formed by reaction of one or more alkali metal carbonates and/or bicarbonates (e.g. sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate or mixtures thereof) with an alpha-hydroxy acid. The resulting pH depends on the stoichiometric conversion of the educts. The alkali metal carbonate and/or bicarbonate and alpha-hydroxy acid system is a buffer system wherein the ratio between carbonate (and/or bicarbonate) and acid determines the pH. In the case where the composition is in the form of a solid (in this context, see below), the amount of these components determines their rate of solution in an aqueous solution. The aminocarboxylates of component (a), the alkali metal salts of which react as bases, likewise act as a buffer substance. Further constituents optionally contained in a composition according to the invention, for example fatty alcohol ethoxylates as surfactants and alkali metal salts of benzotriazole as corrosion inhibitors (see above), can likewise act as buffer substances.
The alpha-hydroxy acids or salts thereof of component (b) serve several primary purposes in the compositions according to the first and second aspect of the present invention, namely both (i) complexing of metal ions and therefore cleaning, and (ii) adjustment of the pH and (iii) if alkali metal carbonates and/or bicarbonates of component (c) are present, optionally the dissolving process of the composition. The amino acids or aminocarboxylates of component (a) serve for both (i) stable complexing of metal ions which are liberated during dissolving of the “acid-base” cement residues, and therefore cleaning, and (ii) adjustment of the pH and (iii) if amino acids are used, the dissolving process of the composition. It goes without saying that these purposes and, which is particularly important, a synergistic interaction of components (a) and (b) are to be taken into account when composing a composition according to the invention. The use of an amount of alkali metal carbonates and/or bicarbonates which is sufficient to achieve a virtually complete deprotonation of the alpha-hydroxy acid(s) or the amino acid(s) is preferred.
The use of fizzy effervescent tablets for automatic cleaning of dental prostheses is known and is described, for example, in the patent specifications DE 695 32 420, DE 37 17 920, DE 38 88 503, DE 38 12 693, DE 100 54 693, DE 39 31 129, DE 42 00 002 and DE 39 34 390. The technical requirements of chemical/physical removal of contamination on dental prostheses based on plastic with the aid of a cleaning effervescent tablet or a cleaning effervescent powder are very different to those in the detachment of set residues of “acid-base” cement from dental instruments, such as metallic impression trays. While the compositions for cleaning dental prostheses primarily have to remove fatty residues of food and protein-containing and sparingly soluble mineral deposits from saliva from the prosthesis material of plastic, the active constituents of a composition for cleaning dental metallic instruments to remove solid “acid-base” cement residues must meet other requirements. In particular, the metal ions must be dissolved out of their complexes with the acids here, in order then to be able to break down the firm bond of the acids.
wherein the components are chosen such that the pH of a solution prepared by mixing the composition with 4,000 parts by weight of water is in the range of from 7.0 to 9.5, if nitrilotriacetic acid is absent preferably in the range of from 7.5 to 9.5.
Preferably, in this context the weight ratio of the total amount of nitrilotriacetic acid and nitrilotriacetate to the total amount of citric acid and its salts in the composition is less than 5:1, preferably less than 3:1.
It should be expressly pointed out once again that water is not included here in the additives of component (g) of the composition. However, in addition to components (a), (b), (c), (d), (e), (f) and (g), the composition can comprise further components, in particular water. In this case also, there is the proviso that the pH of a solution prepared by mixing such a composition with 4,000 parts by weight of water is in the range of from 7.0 to 9.5.
Particularly preferred compositions are the following compositions (A) and (B) in the form of tablets comprising or consisting of:
(A)
Mixtures of the abovementioned surfactants can also be used. The nonionic surfactants are preferably employed because of their low tendency towards foaming, which facilitates handling.
Apart from removal of “acid-base” cements, compositions according to the first or second aspect of the present invention are also suitable for removal of adhesive lacquer from dental instruments. A composition according to the invention is also particularly suitable for cleaning so-called joiner's trays. These trays are made of chromed zinc, which is brought into its shape by a pressure casting process. Such materials are often easily corroded, since microcracks can easily occur in the chromium layer applied. This is largely suppressed by the pH range of a cleaning liquid comprising a composition according to the invention and the corrosion inhibitors preferably used. Apart from cleaning of metallic dental instruments, the compositions according to the invention are of course also suitable for cleaning instruments of plastic.
It is moreover an advantage of the compositions according to the invention that they are biodegradable and are protective on materials according to OECD guidelines.
According to a third aspect, the present invention also relates to a process for the preparation of an aqueous cleaning liquid for dental instruments, comprising the following step:
An example of this is the dissolving of a composition according to the invention in the form of a tablet in water or an aqueous solution.
According to a fourth aspect, the present invention furthermore relates to an aqueous cleaning liquid for dental instruments, comprising
pt. by wt. = parts by weight
In each Example 1 to 16, the sum of the parts by weight (pt. by wt.) is 100.
The compositions were in each case in the form of a solid (powder).
Compositions A, B, C, D and E according to the following table were prepared and in each case dissolved in 4,000 parts by weight (pt. by wt.) of water at 20° C. The pH was then adjusted to in each case 8.5 with HCl or NaOH.
#pH adjusted with HCl or NaOH
pt. by wt. = parts by weight
The weight content of citric acid in the nitrilotriacetate/citric acid mixture is plotted on the x axis. 1 therefore means exclusively citric acid (corresponding to composition A), 0 means exclusively nitrilotriacetate (corresponding to composition E). The cleaning action standardized to the maximum value is plotted on the y axis. The synergistic intensification of the cleaning action is highest at a ratio of nitrilotriacetate:citric acid of 2:1.
The cleaning compositions of the prior art (I, II and III) had the following compositions according to our own analyses (comparison examples):
pt. by wt. = parts by weight
a) Conditions Corresponding to the Manufacturer's Instructions
A comparison of their cleaning action under these conditions with the cleaning action of the dissolved composition according to the invention produced the following result:
The cleaning actions of the cleaning compositions from the prior art under conditions corresponding to the manufacturer's instructions (pH, active substance concentrations in solution) were lower than that of the dissolved composition according to the invention.
b) Standardized Conditions
The products of the prior art (I and III) in the form of a solid were mixed with water in the same ratio as the composition according to the invention of Example 17 (in each case 100 pt. by wt. of product with 4,000 pt. by wt. of water). Product II, in the form of a solution, was employed in undiluted form and therefore contained a comparatively high concentration of EDTA. Solutions of products I and III were adjusted by addition of HCl to the same pH as the solution which results when the composition according to the invention is dissolved (pH 8.5).
The cleaning actions in this context are standardized to the cleaning action of the dissolved composition according to the invention (cleaning action 100).
| Number | Date | Country | Kind |
|---|---|---|---|
| 06 125 777.0 | Dec 2006 | EP | regional |
| 2,570,970 | Dec 2006 | CA | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2006/062315 | May 2006 | US |
| Child | 11866884 | Oct 2007 | US |
