Medium chain triglyceride oils are interesterified with long chain domestic oils in order to form interesterified structured lipids. These structured lipids find special application in pan release cooking compositions and methods. The products have a relatively low viscosity of between about 20 and about 52 centipoise while having a smoke point which is especially suitable for cooking applications.

1. Field of the Invention
This invention generally relates to structured lipids which are especially suitable for use as edible oil components having a relatively low viscosity. More particularly, the invention relates to structured lipids for use as pan release components or in pan release products, especially such components or products which are applied by spraying onto a cooking surface and which have a smoke point which is suitable for cooking applications.
2. Description of Related Art
Vegetable-based edible oil compositions long have been used in cooking applications. Edible oil products provide taste, nutrition and anti-stick properties for any number of pan cooking, baking or similar types of uses and applications. Edible oil products of this general type include margarines, whipped spreads, tub margarines, shortenings, oils and sprayable compositions. Room temperature viscosities of these products vary depending upon the composition and the intended end use. Some such end uses require a viscosity low enough to permit propelling of the composition by an aerosol unit, a pump assembly, or other means for dispensing in a spray or mist pattern, whether for use in home kitchens, commercial kitchens, or on industrial cooking or baking lines. Products which are dispensable in these manners are referred to herein as pan release products or pan release compositions.
In the pan release art, references such as Rubin et al. U.S. Pat. No. 3,661,605 teach a surface release product in the form of an aerosol composition which is dispensed onto a cooking surface intended to be heated for food cooking purposes. This so-called pan release composition contains lecithin in a water dispersion, together with an aerosol propellant and a preservative which can be a vegetable oil and a fatty acid ester in relatively low quantities. When a typical product of this type is sprayed onto a cooking surface, the objective is to have a non-stick film of hydroxylated lecithin formed on the cooking surface. While products of this type have proven to be successful, improvements have been sought in these types of products, and this invention provides means for improving pan release products.
The present invention provides a novel type of pan release component or product which incorporates interesterification technology to provide pan release products that have multiple advantageous properties which are desired for pan release applications. These include a smoke point which is adequate to perform properly in various types of cooking applications. It is often difficult to obtain an adequately high smoke point in a product which must be thin enough to be sprayable. It is also important that pan release products exhibit a lightness in color so as to not detract from the appetizing appearance of the food or the like being cooked or baked with the pan release product.
Medium chain triglyceride (MCT) edible oils are known in the art including Seiden U.S. Pat. No. 5,288,512, Bertoli et al. U.S. Pat. No. 5,395,629, Hidaka U.S. Pat. No. 5,503,855 Takeuchi U.S. Patent Publication No. 2002/0001660, and Heydinger and Nakhasi, xe2x80x9cMedium Chain Triacylglycerols, Journal of Food Lipids, 3, pages 251-257 (1996). Each of the publications and patents noted throughout herein are incorporated by reference hereinto.
Publications such as these define these medium chain triglyceride or medium chain triacylglycerol (MCT) compounds as being a class of lipids of glycerol ester fatty acids. MCTs are esters of glycerol with medium chain fatty acids of 6 to 12 carbon chain lengths. Sources typically are lauric oils. Coconut and palm kernel oils contain significant quantities of C8 (caprylic) and C10 (capric) chains. Often, isolated fractions of C8 and C10 acids contain small amounts of C6 and C12 acids as well. Generally, MCT esters are unsaturated. Accordingly, the primary components of MCT edible oils have C8:0 and C10:0 fatty acid chains.
Interesterification is a known reaction of triacylglycerol structures whereby individual positions of interesterified fatty acids are interchanged on the glycerol moiety. This is at times referred to or recognized as a randomization wherein fatty acid moieties from one glycerol component are exchanged with those of another glycerol component. The result is glycerol moieties which have interchanged fatty acid moieties which vary from glycerol structure to glycerol structure. Art in this area includes Pelloso et al. U.S. Pat. No. 5,434,278, Doucet U.S. Pat. No. 5,908,655, Cherwin et al. U.S. Pat. No. 6,124,486 and Liu et al. U.S. Pat. No. 6,238,926.
The art of interesterification has developed to provide, for example, triglyceride compositions which provide certain melt profiles which can be of interest in certain applications. Generally these are recognized as structured lipids in order to help distinguish the interesterified products from physical blends of the same components which have not been subjected to interesterification.
Heretofore, it has not been appreciated that the combination of interesterification technology and MCT technology would be especially advantageously applied to the task of improving pan release compositions. An especially important problem in this regard, which is addressed by interesterified components according to the invention, is to provide a composition that has a water-like viscosity to enable even aerosol spraying while simultaneously having a smoke point high enough to provide excellent pan cooking or baking characteristics.
In accordance with the present invention, products are provided which have viscosities that are advantageously low and smoke points that are high in order to satisfy in an exceptional manner the needs of pan release cooking products. These products have as a principal component a structured lipid which is a product of the interesterification of an edible domestic oil and a medium chain triglyceride. These structured lipids can be formulated in conjunction with components of a type typically included within pan release compositions, such as propellants, lecithin, and other suitable components in this regard. The structured lipids have a relatively low viscosity of between about 20 at about 52 centipoise, together with a smoke point of between at least about 195xc2x0 C. and about 221xc2x0 C. (at least about 383xc2x0 F. and about 430xc2x0 F.).
A general object of the present invention is to provide low viscosity structured lipids which have a viscosity suitable for dispensing in a spray pattern and which have a smoke point suitable for cooking.
An aspect or object of the present invention is that it provides medium chain triglycerides which have been modified by longer chain edible oils, which has been found to reduce viscosity and enhance smoke points when compared with blends of the same MCT and longer chain components.
Another aspect of this invention is that it provides structured lipids displaying a solids fat content which is substantially liquid at 10xc2x0 C., which solids fat content is very appropriate for pan release cooking uses.
Another aspect of the present invention is providing an interesterification process for accomplishing randomized interesterification of medium chain edible oils with long chain edible oils and the use of the resulting product in pan release contexts.
Other aspects, objects and advantageous of the present invention will be understood from the following description according to the preferred embodiments of the present invention.
The present invention is directed toward structured lipids produced from medium chain triglycerides. Medium chain triglycerides usually are produced commercially by splitting and distilling fatty acids from coconut or palm kernel oils. Production includes esterification with glycerin to form a triglyceride having fatty acid chain lengths of from C6 to C12. These known edible oils typically contain 50 to 80 weight percent of C8 caprylic fatty acids and between about 20 and about 50 weight percent of C10 capric fatty acids. Minor levels, typically between about 1 and about 2 weight percent, of either or both of C6 caproic fatty acids and C12 lauric fatty acids can be present in some such products.
Known MCT products include some NEOBEE(copyright) products such as NEOBEE(copyright) M-5 (trademark and product of Stepan Company), CAPTEX(copyright) 300 (trademark and product of Abitec Corp.), and MIGLYOL(copyright) 812 (trademark and product of Clionova, Inc.). Traul et al., xe2x80x9cReview Of The Toxicologic Properties Of Medium-Chain Triglyceridexe2x80x9d, Food and Chemical Toxicology, 38, pages 79-98 (2000) indicate that MCTs are essentially non-toxic in acute toxicity tests conducted in several species of animals. This article also indicates that MCTs exhibit virtually no ocular or dermal irritant potential, even with prolonged eye or skin exposure. This article also indicates that MCTs exhibit no capacity for hypersensitivity induction. According to this publication, the safety of MCTs in human dietary consumption has been indicated up to levels of 1 g/kg.
Another publication indicates that MCTs result in lower fat deposition when compared with long chain triglycerides. This is noted in Ingale et al., xe2x80x9cDietary Energy Value of Medium-Chain Triglyceridesxe2x80x9d, Journal of Food Science, Volume 64, No. 6, pages 960-963 (1999). Conclusions reached in this article state that differences in energy utilization show that increments of heat associated with the metabolism of MCTs appears to be about 16% higher as compared to long chain triglycerides. With this in mind, the calculated mean net caloric energy value for MCTs used in diets is on the order or 6.8 kcal/g. This is lower than typical LCTs. According to the publication, substituting MCTs for LCTs as the source of fat in diets show reduced weight gain and reduced fat deposition in laboratory animals and humans. This is said to be due to the lower gross energy density of an efficient utilization of energy from MCTs.
From this information, medium chain triglycerides are indicated as having dietary advantages at least from the point of view of fat deposition. Medium chain triglycerides also are indicated by art such as this as being suitable for use in the context of human food applications. MCTs however have relatively high viscosities and low smoke points, making them less than satisfactory for pan release uses.
Interesterification of these MCTs according to the invention includes charging them to an interesterification location or vessel as part of the charge for forming the structured lipid. Typically, MCTs comprise between about 25 and about 75 weight percent of the structured lipid charge. Generally, the charged quantities of interesterification reactants correspond closely to the respective weight percents in the interesterified structured lipid. Preferably, the quantity of MCTs is between about 30 at about 60 weight percent, most preferably between about 35 and about 55 weight percent.
Also part of the charge for forming the structured lipids are so-called domestic oils. Domestic oils for the interesterification according to the invention include soybean oil, corn oil, cottonseed oil, canola oil, safflower oil, sunflower oil, peanut oil, olive oil, oil from grain plants, and identity preserved oils such as identity preserved canola oil and the like. Whichever edible oil is chosen, it will be a liquid oil. Hydrogenation typically need not be carried out. Oils of these types are well recognized as so-called long chain lipids. Chain lengths of these oils generally lie between C16 and C22, as will be generally appreciated in the art.
The charge of such domestic oil to the interesterification location or vessel comprises between about 75 and about 25 weight percent of the charge, and substantially the same level of long chain component is in the interesterified structured lipid. Preferably, this amount is between about 70 and about 40 weight percent, most preferably between about 65 and about 45 weight percent, based upon the weight of the charge or interesterified structured lipid.
With further reference to the domestic oils having chain lengths longer than the MCT reactant, advantageously they are preferably substantially unsaturated oils such as soybean, corn, cottonseed and canola, which are well known in the art as liquid oil commodities. Certain specialty oils also are encompassed within the preferred domestic oils. These include identity preserved canola oils and refined, bleached and deodorized high stable oils. Included is naturally high stable canola oil such as NATREON oil (trademark, available from Dow Agro Sciences, Canbra Foods), which is naturally higher in monounsatarated fats and in oleic fatty acid and lower in linolenic fatty acid. In this regard, Sornyk et al U.S. Pat. No. 5,965,755 and Lanuza et al. U.S. Pat. No. 6,169,190 are noted.
The chemical interesterification used in making the structured lipids of the invention involves charging the reactants into an interesterification reactor vessel. Such vessels have means for heating the reactants during agitation and under reduced pressure or vacuum conditions. The reaction is carried out in the presence of a suitable interesterification catalyst and typically proceeds rapidly to completion or substantial completion. Typically, the interesterification is a reaction to or toward complete randomization, which would equate to a degree of interesterification of 100% of the fatty acyl chains.
Interesterification catalysts include metal alkoxides, alkali metals, alkali metal alloys, and metal hydroxides. Alkoxides include alkali metal alkoxides, such as sodium methoxide, sodium ethoxide, potassium methoxide and potassium ethoxide. Alkali metals include sodium. Alkali metal alloys include sodium/potassium alloy, and metal hydroxides include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.
Once the interesterification has proceeded to form the desired structured lipid, steps can be taken to modify the conditions away from reaction conditions. This can include inactivating the catalyst, reducing the temperature, reducing the vacuum applied, ceasing agitation, or any combination of these changes. Means for accomplishing these changes will be appreciated by those skilled in the art.
Reaction temperatures range between about 80xc2x0 C. and about 100xc2x0 C. (about 160xc2x0 F. to about 212xc2x0 F.). A most suitable temperature at which to carry out the interesterification within the reaction vessel is approximately midway within this range. Vacuum conditions within the vessel range between about 5 mbar and about 100 mbar (between about 4 mm Hg and about 75 mm Hg). Preferably, the level is within the lower portion of this range, or less than about 40 mbar (about 30 mm Hg), most preferably at or below about 26.7 mbar (about 20 mm Hg).
Reaction time will range between about 30 minutes and about 2 hours. An especially suitable reaction time is about 45 minutes. This reaction time can be controlled, for example, by timed neutralization of the catalyst. Neutralization for a catalyst such as sodium methoxide can be accomplished with 0.7 weight percent of citric acid solution of 42% strength.
The interesterified structured lipid can be treated to remove any residual soaps and/or to remove all the color bodies if needed. These include filter aids and silica sources such as TRISYL(copyright) S-615 (trademark, available from W. R. Grace and Co.) used for the refining of vegetable oil. Color removal can be with a bleaching earth or the like. The structured lipid also typically will be subjected to deodorization in accordance with approaches generally known in the art.
In preparing the pan release products, the interesterification structured lipid typically is combined with other components which will be generally appreciated by those skilled in the art. In those situations where pan release spraying is by aerosol means, a propellant is included in the pan release composition. Other components which typically are included within aerosol spray formulation are short chain alcohols, most typically ethyl alcohol, food grade surfactants and emulsifiers such as a lecithin. Other additives can include phospholated mono and diglycerides (PMDs), which are suitable for cooking under rugged conditions such as barbeque grilling. Water can also be a component of these sprayable formulations.
One or more of these components can be present in spray formulations which are not of the aerosol type, for example pump sprayers, squeeze-activated sprayers, or industrial sprayers for large-scale food manufacturing. It will be appreciated that the structured lipids are very advantageously incorporated into aerosol formulations which must exhibit low viscosity and contain relatively high melting edible oils.
The interesterified structured lipid according to the invention is combined with components such as these, as may be necessary, in order to assist in propelling action characteristic of sprayed components. The structured lipid is the component which provides the primary pan release functions in such compositions. This lessens the importance of other typical components such as those noted above. The structured lipid provides the smoke point levels needed for a pan release product. The structured lipid also has the advantageous low viscosity needed for a composition to be delivered by some form of spraying. Higher viscosities would cause clogging of spray nozzles or other outlets.
Pan release compositions according to the invention include the structured lipid at levels between about 60 and about 100 weight percent, based upon the total weight of the pan release product. Typically the structured lipid will be present at between about 80 and about 95 weight percent.
With further reference to components in addition to the interesterified structured lipid according to the invention, specific details concerning other components for pan release compositions can be found in U.S. Pat. Nos. 3,928,056, 4,108,678, 4,371,451, 5,370,732, 5,374,434, 5,503,866, 5,662,956 and 6,210,743. As noted previously, each of these patents is incorporated by reference hereinto.
Especially in those products which are intended for aerosol delivery, one or more propellants will be included. These are generally categorized as pressurized gas, liquefied gas, soluble gas dissolved in the liquid of the product, and other propellant types. Perhaps the currently most common propellant is nitrous oxide. Another is carbon dioxide. Dimethyl ether also is a known propellant. Generally, conventional hydrocarbon propellants can be less than totally desirable for food uses. Fluorocarbons, which are normally gaseous, tend to be disfavored for environmental reasons and to governmental regulations. Depending upon the particular pan release composition being formulated, propellants can be at levels as high as 75% or above and as low as about 10% by weight, based upon the total weight of the product.
If lecithin is included, it typically would be present at a level lower than lecithin in pan release compositions in which lecithin is the primary anti-stick component. Lecithin products can vary somewhat in their make-up, depending upon their source and/or supplier. For example, soybean lecithin is obtained as a byproduct in the manufacture of soybean oil. Phosphatide or solids content varies within lecithin products. Generally, such phosphatide or solids content or contents are important to any lecithin function in a pan release composition. With these variables in mind, when lecithin is included in the present products, same will be at a level of between about 0.5 and about 15 percent by weight, based upon the total weight of the product.
Humectants are included in possible components of typical pan release compositions. Usually these will be at levels of about 4 percent or less by weight, based upon the total weight of the product. Examples include polyhydric alcohols such as glycerol, sorbitol, propylene glycol, and the like.
At times, a suspending agent can be included in the pan release product at relatively low levels. For example, stearates, silicates and the like can be included at levels on the order of about 0.5 to about 2 percent by weight, based upon the total weight of the pan release product.
Modifying agents also can be included in order to prepare a pan release product having certain sensory properties or shelf stability properties. These include flavorants, colorants, antioxidants, preservatives, inhibitors, and the like. Levels of use will depend upon the result desired and will be generally appreciated by those skilled in the art.
Some pan release compositions rely upon water as an inexpensive solvent which readily evaporates upon contact with a hot surface. At times, water can also perform the function of a carrier and/or as a component of an emulsion system. For example, when a lecithin component is included, water will be useful in partially hydrating the phosphatide portion of the lecithin material. Water also can serve as a humectant. Because of these wide variations in the function of water within a pan release composition and the manner by which the pan release composition is delivered, either on a consumer level or within an industrial food preparation operation, water amounts can very considerably. Some formulations will include water at a level approaching 75% by weight, based upon the total weight of the product composition. In other formulations, the amount can be on the order of 50% by weight or less. A somewhat general range is between about 0.2 and about 22 percent by weight, based upon the total weight of the product composition. When water is used purely as a humectant, it typically would be at a level of 1.5% or less by weight, based upon the total weight of the product.
Brookfield viscosity measurements for the compositions should be between about 20 and about 52 centipoise when measured at 20xc2x0 C. with a No. 4 spindle at 50 rpm. Preferably, the range is between about 30 and about 50 centipoise, most preferably between about 35 and about 48 centipoise.
Examples now are provided in order to illustrate the concepts of the invention with a certain degree of specificity.

Low viscosity structured lipid pan release compositions and methods


A method for restoring immunoreactivity of a tissue, particularly decalcified tissue, fixed width an aldehyde fixative agent and embedded in an embedding medium, usually comprising celloidin, the method comprising the steps of contacting the tissue with an aldehyde releasing reagent solution comprising a solvent and an aldehyde releasing reagent and removing aldehyde released by the aldehyde releasing reagent from contact with the tissue by reacting the aldehyde in a substantially irreversible manner to form a non-aldehyde derivative, and removing excess base from the tissue. A preferred solution for celloidin-embedded decalcified tissue comprises methanolic sodium hydroxide at about one-third saturation.

Tissue sections obtained from clinical specimens or animal experimentation frequently are fixed, embedded, and stored in a form suitable for later examination by light microscopy. Immunological reagents, especially monoclonal antibody reagents, currently permit examination of at least certain of these fixed tissue samples for the presence of particular antigenic compounds. Antigens of interest may be associated with a disease process or pathology, or may identify a particular type or tissue. In the case of recently prepared biopsy and autopsy samples, such immunohistochemical analyses are of immediate diagnostic value.
However, immunohistochemical analyses of tissue specimens have been hampered because of antigenic loss during specimen fixation. Traditional fixation methods frequently have employed aldehyde fixatives, which fix the tissue by causing cross-linking reactions within and between tissue proteins.
Two types of cross-linking reactions have been recognized. The first is a Schiff's base-type polymerization: formaldehyde condenses with the amino groups of the protein, resulting in the Schiff's base intermediate, which is capable of undergoing rapid polymerization leading to cross-linking of the proteins.
In the second type of reaction, called the Mannich reaction, the formaldehyde can react with both an amino group and an active hydrogen group, resulting in the formation of a Mannich base. Polymerization of the Mannich bases results in protein cross-linking.
Cross-links preserve tissue morphology and integrity, harden the tissue for slicing, and inhibit microbial attack. Unfortunately, the cross-linking process also causes loss of tissue antigenicity, a result which impedes the usefulness of immunological reagents on tissues fixed with aldehyde reagents such as formaldehyde. The chemistry of the cross-linking of amino acids and proteins by formaldehyde is described in Harlan and Feairheller, "Chemistry of the Cross-Linking of Collagen During Tanning," and Kelly, et al. "Cross-Linking of Amino Acids by Formaldehyde," (1976). The role of Mannich-type reactions in cross-linking of protein amino groups and aromatic amino acids with formaldehyde is discussed in Fraenkel-Conrat, et al., J. Biol. Chem. (1947) 168:99-118, and Fraenkel-Conrat and Olcott, J. Biol. Chem. (1948) 174:827-843. Further discussions of aldehyde cross-linking reactions are found in Fox. J. Histochem. Cytochem. (1985) 33:845-855; Jones, "Reactions of aldehyde with unsaturated fatty acids during histological fixation," in Fixation in Histochemistry, P. J. Stoward, ed. (1973); and Kunkel et al., Mol. Cell. Biochem. (1981) 34:3. Mannich type reactions are described in general in March, "Advanced Organic Chemistry," particularly at 333,424, 670-672 (1968).
In an attempt to circumvent the disadvantages of aldehyde fixation, alternative fixation methods have been developed, such as microwave heating (Mayers, J. Clin. Pathol. (1970) 28:273; Hopwood et al., Histochem. J. (1984) 16:1171) and alcohol immersion (Battiform and Kopinski, J. Histochem. Cytochem. (1986) 34:1095). Despite some advantages of alternative fixation methods, they have not displaced aldehyde fixation in general use. Their limited acceptance may reflect drawbacks present in these alternative methods. For example, microwave heating lyses red cells and disrupts membrane lipids. Although ethanol fixation is reported to produce improved antigenicity of tissue samples, ethanol causes increased cellular shrinkage (Battiform and Kopinski, id.) Consequently methods for restoring antigenicity to aldehyde fixed tissues continue to be useful for specimens generated by current clinical practices.
In addition, methods for restoring antigenicity are useful because of the vast number of aldehyde fixed tissue samples already in collections. These stored tissue samples provide a rich reservoir of material for retrospective immunohistochemical examination. If a suitable method of subsequent immunohistochemical staining were available, newly generated immunohistochemical data could be combined with existing diagnostic results obtained from traditional investigations on the same tissues. Often clinical samples are saved for decades, so that the critical outcome of the patient's underlying pathological process already is known. In the case of experimental tissues, such as those obtained from animals in toxicology testing, other measurements of pathology and toxicity in general already will have been performed and documented. In both cases, immunological analyses of the affected tissues could add important correlative information.
Because of the development of immunological reagents over the past decades, immunohistochemical analyses can now be performed that were impossible at the time many tissues were originally stored. In addition, new knowledge or hypotheses concerning the disease process may prompt reexamination of stored tissues. Immunohistochemical studies on stored tissue samples provide a relatively time- and cost-effective means for performing a clinical study on a statistically large sample population. Therefore the application of immunohistochemical analyses to routine clinically or experimentally derived embedded tissue sections is a matter of considerable interest.
Antigenic loss during aldehyde tissue fixation is due to chemical modification of the protein (not to physical removal of the antigen). Loss of immunoreactivity is believed to occur by two mechanisms. In the first mechanism, the fixative agent chemically modifies the reactive epitope, rendering it incapable of binding antibody. In the second mechanism the fixative agent causes chemical cross-linking of the antigenic protein at sites outside the targeted epitope. Such cross-linking may be intramolecular or intermolecular, i.e., with involvement of nearby proteins. This cross-linking sterically hinders access of the antibody reagent to the reactive epitope.
The second mechanism, steric hindrance due to intraprotein or interprotein cross-linking outside the epitope of interest, has been reversed by protease digestion of formalin fixed tissues in order to remove the interfering cross-linked portions of proteins. This approach has been shown to improve immunostaining of keratins in formaldehyde fixed tissues (Battifora and Kopinski, J. Histochem. Cytochem. (1986) 34:1095-1100). However, protease treatment actually degraded the staining of tissues fixed in alcohol, a fixative solution which does not cause protein cross-linking. Some improvement in immunostaining by proteolysis of formaldehyde fixed tissues for limited time periods has been shown for other antigens (Huang, et al., J. Lab Invest. (1976) 35:383-390.) In a study of immunostaining of 23 antigens of pathological interest, prior trypsinization was shown to give no improvement in immunostaining of formaldehyde fixed tissues except in the case of cytokeratins and desmin. For many antigens, enzyme digestion actually diminished antigen staining. (Leong, et al., J. Pathology (1988) 156:275-282.) These results support the hypothesis that aldehyde fixative-induced cross-linking of proteins diminishes immunostaining both by chemical modification of epitopes and by steric hindrance mediated by cross-linking. The mixed results obtained from treating fixed tissues with proteolytic enzymes are readily rationalized: although partial proteolysis decreases cross-linking and reduces steric hindrance, proteolysis also may cleave and remove the epitopes of interest. Moreover, proteolysis cannot reverse antigenic masking due to chemical modification of the epitope. By contrast, a procedure which could reverse the chemical cross-linking reaction produced by aldehyde fixatives has the potential to unmask antigens previously hidden by either mechanism.
A procedure for restoring antigenicity of formalin-fixed, paraffin embedded tissue sections by heating the tissue in a microwave in a heavy metal solution has been described in Shi, et al. J. Histochemistry and Cytochemistry 39(b): 741-48 (1991). This procedure provides enhanced immunostaining in approximately three-fourths of the samples tested. The described methods is part of a process that involves the steps of tissue section deparaffinization and rehydration, brief treatment with aqueous peroxide to block endogenous peroxidase, washing of the slides with distilled water, coveting the slides with distilled water or a heavy metal solution, and brief microwave heating for several minutes. Following this procedure, slides are cooled, rinsed, and immunostained in a conventional fashion.
This method for restoring antigenicity is subject to certain limitations. First, it requires the use of a microwave oven to heat the tissue samples. Many laboratories may not be equipped with a microwave oven, and some tissue samples may not be suited to microwave heating. A need exists for an antigen retrieval method that can be used at room temperature, without any external heat source. In addition, the previously described procedure is especially suitable for tissues embedded in a hydrocarbon medium such as paraffin. It is not well suited for tissue sections embedded in celloidin, a preferred embedding medium for bony tissues. A need also exists for a method which is suitable for use with celloidin embedded tissues. Moreover, a need particularly exists for a method which may be used with decalcified bony tissue samples, since decalcified tissues are often refractory to the previously described method.
Methods and compositions are provided for restoring antigenicity for immunohistochemical analysis of aldehyde fixed tissue. The methods and compositions are especially useful with celloidin embedded tissue and with decalcified bony tissue. The method involves treating aldehyde fixed tissue with a chemical agent or agents that catalyze an essentially irreversible Mannich/Schiff's Base reaction which converts the aldehyde released thereby into a nonreactive form, i.e., into a non-aldehyde derivative. In this application such chemical agent or agents will be termed an "aldehyde releasing agent." In one aspect, the aldehyde releasing reagent comprises a nucleophilic reagent solution and the method involves. (1) treating aldehyde fixed tissue with the nucleophilic reagent solution, optionally containing a chaotropic agent, (2) removing excess nucleophile by neutralizing or rinsing the tissue sample, and (3) reacting the tissue with an immunoreactive agent. In another aspect, the aldehyde releasing reagent comprises an oxidizing agent and the method involves (1) treating aldehyde fixed tissue with the oxidizing agent, (2) removing excess agent and (3) reacting the tissue with an immunoreactive reagent. In a third aspect, the aldehyde releasing reagent comprises an organic acid/base pair and the method in step (1) involves treatment with the organic acid/base pair. Exemplary organic acids are set forth below. Exemplary bases are sodium hydroxide and potassium hydroxide. Also provided is a kit for immunostaining of aldehyde fixed tissue. The kit minimally comprises a solution for restoring antigenicity comprising a solvent and an aldehyde releasing reagent. Optionally, the kit can also comprise a solution to remove excess aldehyde releasing reagent or a reagent immunostaining reagent.
The invention provides a method for restoring immuoreactivity of a tissue fixed with an aldehyde fixative agent and embedded in an embedding medium, the method comprising the initial step of contacting the tissue with an solution for restoring antigenicity comprising a solvent and an aldehyde releasing reagent. The aldehyde releasing reagent catalyzes reversal of the reaction between the aldehyde and biological components in the tissue, such as by catalyzing a reverse Mannich or a reverse Schiff base reaction. The released aldehyde reacts in a substantially irreversible manner to form a non-aldehyde derivative. Alternatively, the initial step can be broken down into two steps by adding the components of the antigenicity restoring solution separately: fist adding solvent to remove at least part of the embedding medium, followed by adding an aldehyde releasing reagent, usually in the same or a different solvent. The initial step is followed by removing excess aldehyde releasing reagent from the tissue prior to immunostaining. Preferred embodiments of the invention provide a method for restoring immunoreactivity of a decalcified tissue fixed with an aldehyde fixative agent and embedded in an embedding medium comprising celloidin. Specific embodiments are described in complete detail below. A general theory of how the invention operates is set forth immediately below, along with a brief discussion of the physical and chemical processes that are believed to take place during the initial fixation process and the antigenicity restoring process of the invention. It must be understood that these are merely theories, and the invention can be fully practiced simply by reference to the descriptions of specific operations (and variations thereof) to be carried out by the practitioner.
The aldehyde fixation of tissue is believed to produce cross-linked proteins. This cross-linking is mediated by the reaction of aldehyde groups in the fixative with amino groups on amino acid residues of tissue proteins, such as lysine and the N-terminal a-amino acid group. The initial product of this interaction is an amino-aldehyde conjugate, either an imino Schiff base (CHR1═NR2R3) or an aminomethylo (CHR1OHNR2R3) intermediate. The intermediate may then undergo nucleophilic attack by susceptible neighboring amino acid groups, such as α-carbonyl methylene carbons having an acidic proton, nucleophilic heteroatoms, or electron rich aromatic rings. Prime nucleophiles include aromatic rings such as the ortho-position of the phenol ring of tyrosine, the C-2 position of the indole ring of tryptophan, and the imidazole ring of histidine; the a-carons adjacent to the side chain carboxylic acid groups of glutamate and asparatate; basic heteroatoms such as lysyl ε-amino groups; and neutral nitrogen atoms such as asparaginyl and glutaminyl amide groups and the indole ring nitrogen of tryptophan. Formally, all such reactions are types of or at least similar to Mannich reactions, at least inasmuch as the reactive electrophile is the intermediate amino-aldehyde conjugate species. These reactions result in a covalent bond between the electrophilic aldehyde carbon and a nucleophilic carbon or heteroatom.
The resulting cross-linking fixes proteins in a particular conformation and fixes the entire tissue by forming covalent bonds among adjacent proteins. The cross-linked proteins resist penetration by macromolecules such as antibodies. In addition, chemical modification or epitopes (which contain amine, amide, or aromatic amino acid residues) produces an altered structure unrecognizable to an antibody against that epitope.
The commonest aldehyde fixative is formaldehyde, which is unifunctional and produces cross-linking by direct contact between methylol-amino groups of lysine and adjacent susceptible amino acid target residues. However, other difunctional or polyfunctional cross-linking aldehydes are known. Of these the commonest is glutaraldehyde, a five carbon chain with aldehyde at both termini. This difunctional reagent provides additional opportunities for cross-linking, since the alkyl chain of the reagent functions as a spacer. The mechanism of reaction is believed similar, regardless of the particular aldehyde reagent used for fixation.
The method of the present invention provides a means for reversing or breaking at least some of these cross-linkages, thereby restoring the antigenicity of previously fixed proteins. The method involves treating the previously aldehyde-fixed tissue with a solution containing an aldehyde releasing reagent, which is believed to promote reversal of the Mannich-type reaction and other reactions between formaldehyde and tissue components. Antigenic restoration also may proceed as a result of limited proteolysis. In order to effectively restore antigenicity, the reagent need not reverse or break all aldehyde induced linkages. Partial breakage of cross-linkings loosens the fixed proteins sufficiently to permit penetration by antibodies. Particularly susceptible linkages are believed to be those produced between aminomethylol reactants and heteroatoms, such as amines and amides, or alpha-carbonyl methylene groups.
Most effective aldehyde releasing reagents for the practice of the invention are nucleophiles, preferably basic nucleophiles. An especially preferred nucleophile is hydroxide anion, which is conveniently supplied as an alkali metal hydroxide such as sodium or potassium hydroxide. Other convenient nucleophiles include primary, secondary, or tertiary amines, especially those with minimal steric hindrance to attack, such as piperidine or morpholine. Hydroxylamine and glycine are preferred. Other nucleophiles include thiols such as mercaptoethanol. Yet another nucleophile of interest is azide, e.g. sodium azide (NaN3). In general, any nucleophile capable of promoting a reverse Mannich reaction will be capable of cleaving at last some protein cross-linkings, as such reagents will also catalyze reversal of other types of reactions caused by formaldehyde. The concentration of the nucleophile may vary widely, with more concentrated solutions acting more quickly. For short exposures, nucleophile concentrations of 0.5M or greater are usually preferred. In the case of NaOH in methanol, concentration of one-tenth to one-half of saturation (approximately 0.6 to 3M) are preferred in most circumstances. For hydroxylamine, for example in the form of hydroxylamine hydrochloride, or for glycine, a 10% aqueous solution is preferred. Additional nucleophiles include hydrazine hydrate. And for hydrazine hydrate, an aqueous (v/v) solution in the range of about 2.0% to about 5.0% preferably 5.0%, is suitable.
Other effective aldehyde releasing reagents for the practice of the invention are oxidizing agents. Preferred oxidizing agents are hydrochlorites and periodates, especially sodium hydrochlorite or sodium periodate. Concentration of the oxidizing agent will vary with the reagent. For example, for sodium hypochlorite, an aqueous (v/v) solution in the range of about 0.01% to about 0.005%, preferably 0.005%, is suitable. For sodium periodate, an aqueous (v/v) solution in the range of about 0.1% to about 1.0%, preferably 0.1%, is suitable. Treating the sample with the oxidizing agent is believed to break the cross-linkages between the aldehyde and tissue components and converts the released aldehyde into a non-reactive form, for example by converting formaldehyde to formic acid.
We have found that certain acid/base pairs will function as an aldehyde releasing releasing agent within the confines of this invention. The following pairs are exemplary:
Organic Acid/Base PairConcentration(Acid/Base)(Acid/Base)MinutesTrichloroacetic10% aqueous/10% NaOH in10/20Acid/NaOHmethanolToluene Sulfonic5% aqueous/40% aqueous30/30Acid/NaOHCitric Acid/NaOH10% aqueous/40% aqueous30/30Oxalic Acid/NaOH20% aqueous/40% aqueous30/30Tartaric acid/NaOH10% aqueous/40% aqueous30/30
The solvent for the aldehyde releasing reagent solution may be any solvent compatible with and capable of dissolving the aldehyde releasing reagent. Aqueous solutions are possible; and preferable where the aldehyde releasing reagent is an oxidizing agent or an organic acid/base pair. Organic solutions are preferable where the aldehyde releasing reagent is a nucleophile because they promote better penetration of the embedding medium. In addition, proteolytic fragments are insoluble in most organic solvents and therefore tend to remain in place on the slide.
A preferred solvent for use with celloidin embedded tissue sections is a polar organic solvent. Alcoholic solutions are preferred because they promote good penetration of the celloidin embedding medium and are good solvents for nucleophiles of interest, especially alkaline metal hydroxides. Lower alcohols are preferred, such is methanol, ethanol, propanol, and butanol; methanol is especially preferred. Polyols such as ethylene glycol and glycerol are also useful; they have the advantages of low volatility and greater viscosity, which permit them to remain on the slide for an extended period without evaporating or running off. Polar aprotic solvents such as dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) also may be used with appropriate nucleophiles. Furthermore, mixed solvent solutions are acceptable, provided the component solvents are compatible with the reagents and each other.
Two solvents may be used consecutively under some circumstances. For example, a celloidin embedded slide may be treated initially with methanol to solubilized the embedding medium, then treated with an aldehyde releasing reagent solution such as KOH in glycerol.
Nonpolar organic solvents are useful with tissues embedded in nonpolar media such as paraffin. In the case of a nonpolar solvent such as toluene, a quaternary base is desirable since it is soluble in nonpolar solvents. Examples include tetraalkylammonium hydroxide (e.g. tetraethylammonium hydroxide) or a quaternary phosphonium salt. A nonpolar solvent and quaternary base may be combined with an immiscible polar aqueous phase in a phase-transfer reaction. The two phases may be applied to the tissue simultaneously, or the nonpolar phase may be applied first in order to facilitate solubilization of the paraffin embedding medium.
Additives may be included to enhance the desirable properties of the solution. Chaotropic agents, such as sodium thiocyanate, are preferred additives.
The embedded and fixed tissue sections are immersed in or covered by the aldehyde releasing reagent solution for periods ranging from several minutes to several hours. The optimal treatment period will vary depending concentration of aldehyde releasing reagents, type of solvent (if any), degree of penetration of the embedding medium by the solution, extent of tissue fixation, and temperature. For a particular combination of variables, an optimum time of treatment may be readily determined by treating tissue samples for different increments of time and measuring the extent of immunostaining. For a solution comprising methanolic sodium hydroxide at 25% saturation, a period of treatment of about 30 minutes is adequate for most tissue sections. Little improvement is seen for times less than about 5 minutes. At periods of contact longer than about 2 hours, the tissue may tend to detach from the slide; this is especially pronounced with 20 mm celloidin sections.
The treatment temperature affects reaction rate in the typical predictable pattern for chemical reactions, with elevated temperatures producing more rapid results. The method may be practiced conveniently at room temperature, and temperature control is not normally practiced.
After the treatment period with the aldehyde releasing reagent solution, excess reagent is removed from the tissue sample prior to immunostaining. This may be accomplished most conveniently by rinsing the tissue with solvent or solution which is free of the reagent. Multiple changes of rinsing solution are preferred. For greater preservation of tissue hydration and morphology characteristics, at least one of the rinsing solution preferably will contain a mixture of the solvent used in the aldehyde releasing reagent solution and aqueous buffer. This facilitates re-equilibration of tissue with buffer. Preferably one or more washes with aqueous buffer will be performed prior to immunostaining. A preferred rinsing procedure uses at least one wash with buffer containing a detergent follows by one or more rinses with buffer containing a detergent followed by one or more rinses with buffer without detergent. The detergent may be any tissue compatible detergent, either ionic or non-ionic, although non-ionic detergents such as Triton X-100 are preferred.
As an alternative to the rinsing step, excess reagent may be neutralized with acid or a buffer. This alternative is most feasible when the solvent is similar or identical in composition to the solution to be used for the immunostaining. In general, immunostaining solutions are themselves aqueous buffers. For most applications, removal of excess base by rinsing will be preferable.
After removal of excess reagent, the tissue is immunostained by any conventional technique. A great variety of immunostaining procedures, reagents, and antibodies are known, many of which are commercially available. The procedures for restoring antigenicity described above leaves the tissue in a condition compatible with most immunostaining procedures. Typically, the tissue is incubated with a primary antibody against the antigen of interest, followed by treatment with a detectable label. The detectable label often includes a second antibody against the primary antibody; in turn, the second antibody may have the capacity to bind with a third species which is actually detected. These multiple levels of binding provide a means for amplifying the intensity of the detectable signal. In general, the antigen retrieval method described above does not interfere with the detection procedure.
The present method for restoring antigenicity using aldehyde releasing reagents may be used with essentially any embedding medium, including hydrocarbons, such as paraffin, and synthetic resins. However, it is particularly useful with celloidin, which is a traditional embedding medium for bony tissues. Celloidin is a pure form of pyroxylin, the low-nitrogen form of nitrocellulose. Celloidin is available from various commercial sources.
The described method preferably is performed with solution which either solubilizes or swells and softens the embedding medium. Most embedding media are supplied as solutions. Hence an appropriate solvent for the solution may be inferred based upon the solvation characteristics (e.g. hydrophobicity, polarity, hydrogen bond donor/acceptor potential) of the solvent supplied for the embedding medium. The solution need not employ a solvent identical to that used for the embedding medium. However, the identity of suitable embedding medium solvents provides a guideline to the appropriate characteristics for the aldehyde releasing solvent.
In the case of celloidin, the embedding medium is soluble in ether-alcohol mixtures, clove oil (comprising aromatic terpenes), alcohols, and acetone. Methanol is a suitable solvent, since it also solubilizes basic nucleophiles, and is a preferred solvent for use with celloidin embedded tissues.
Bony tissues in the past have presented particular problems, at least in part because of the decalcification treatment to which bone often is exposed during fixation. Conventional decalcification is performed with an acid such as trichloroacetic acid (Cl3CCOOH). At present, immunohistochemical staining is not widely in diagnostic and investigative pathology for routinely processed formaldehyde fixed, decalcified, and celloidin embedded bony tissues, as for example temporal bone sections. Several reported attempts to immunostain temporal bone sections focus on modified fixation, decalcification, and embedding protocols (Veldman et al., Advances in oto-immunology. New trends in functional pathology of the temporal bone, Laryngoscop (1987) 97:413; Huizing et al., Progress in temporal bone histopathology. I. Semithin 3-5 um sectioning of undecalcified human temporal bone after plastic embedding, Acta Otolaryngol (Stockh) (1985) Suppl 423:24; Veldman et al., Progress in temporal bone histopathology, II. Immuno-technology applied to the temporal bond, Acta Otolaryngol (Stockh) (1985) Suppl 423:29; Arnold, W., Immunohistochemical investigation of the human inner ear, Acta Otolaryngol (Stockh) (1988) 105:392; and Bauwens et al., Progress in temporal bone histopathology. III. An improved technique for immunohistochemical investigation of the adult human inner ear, Acta Otolaryngol (Stockh) (1990) Suppl 470:34).
The disclosed method simultaneously neutralizes any residual acidity from decalcification, which might impede restoration of antigenicity using water or other solvent by itself with bony specimens. As the accompanying experimental results demonstrate, the disclosed method permits effective immunostaining of temporal bone sections which have been routinely processed and embedded. This is significant because human temporal bone collection amounting to 8,000 and 13,000 specimens exist in Europe and the United States, respectively (Schuknecht, Ann. Otol. Rhinol. Laryngol, (1987) 96 (Suppl. 130):1). These collections provide an excellent research base for understanding otopathology by light microscopy.
A kit for use in immunostaining of a tissue can be provided to simplify practice of the method described above. The kit will minimally contain a receptacle adapted to hold one or more individual reagent containers and at least a first container containing (1) an aldehyde releasing reagent solution comprises a solvent and an aldehyde releasing reagent or (2) the aldehyde releasing reagent in an amount appropriate to make up the desired concentration when solvent from another container is used to fill the aldehyde releasing reagent container to a predetermined level. In most cases, the kit will also contain a second container containing (1) an immunostaining reagent or (2) a wash solution for removing excess aldehyde releasing reagent solution, or containers with both such material. Wash solutions are typically buffered solutions that do not further dissolve or swell the embedding medium, such as aqueous buffered solutions. The solvent in the wash solution will be capable of dissolving the solvent and aldehyde releasing reagent used in the antigen retrieval alcohol. The immunostaining reagent generally comprises an antibody and staining moiety. Such reagents are well known in the art and require no further description here. Specific examples are given in the general examples of the invention set out below. Appropriate instructions for carrying out the method of the invention will also be included in the kit.
The invention now being generally described, the same will be better understood by reference to the following detailed examples which are provided for illustration and are not to be considered as limiting the invention unless so specified.

Enhancement of immunochemical staining in aldehyde-fixed tissue


A fastening system comprises a screw including a thread formed on a shank and configured to form a threaded bore in a plug made of a plastic material, and at least one notch formed in the shank between at least two adjacent turns of the thread. The system also comprises a clip including first and second clip bows connected at joined portions thereof. The first and second clip bows further have firs and second through apertures in their central portions which are aligned and sized to define a channel for allowing the shank of the screw to pass through. At least one of the first and second through apertures has an internal thread matching with the thread of the screw. The clip has at least one resilient lug adapted to engage with the at least one notch when the screw is fastened into the internal thread.

This invention relates to a fastening system. It serves for attaching a structural component to a carrier material.
It is been known already to insert a plug into a bore of a carrier material and to locate it therein by friction or securing it in place. In such a case, the plug has a bore into which a screw is rotated in order to fasten the structural component to the carrier material. The plug may then be located in the carrier material by forcing it in or latching it in by hinged feet or widening it by means of the screw. In known plastic plugs, threads are formed in the bore by rotating the screw in, e.g. by thread-molding or thread-cutting. For this purpose, the screw has a flank angle, which is comparatively acute as compared to screws for metal sheeting or metric-thread screws and typically is 30xc2x0. In addition, such screws have a pitch which is large as compared to screws for metal sheeting or metric-thread screws and may be 2.24 mm, for example.
The aforementioned fastening may be employed particularly for flat carrier materials which have a through-bore to receive a plug. Such a fastening is used especially in automobile manufacture, e.g. for attaching guide strips or panelings to the body.
In addition, fastenings for structural components to flat carrier materials are known already, which include a metallic screw and a metallic clip. The metallic screw typically has a relatively large flank angle of about 60xc2x0 and a relatively small pitch of 1.6 mm, for example. The metallic clip has a through-bore which traverses either clip bow. One clip bow has formed in it a thread. The metallic clip is slid onto the edge of a carrier material so that its through-bore is aligned with a through-bore of the carrier material. The metallic screw is then rotated into the flush through-bores with its thread interacting with the thread of the metallic clip until the metallic screw is secured in place with the metallic clip and the carrier structural component which is received thereby. The structural component is secured on a through-bore between the screw head and the metallic clip. The threaded joint is self-locking.
Fastenings of this type are also employed specifically in automobile manufacture when structural components require to be attached in the marginal area of metal sheetings, e.g. panelings to wheel housings or safety bumpers to the body.
A drawback is that, apart from the plastic plug and the metallic clip, different screws need to be manufactured, kept in stock, and handled for these different fastenings which are employed in the same areas.
Based on this fact, it is an object of the invention to provide a less expensive fastening, system for fixing structural components to carrier materials.
The inventive fastening system includes
a screw which comprises a screw head and on a screw shank a thread which with respect to the pitch and the flank angle is matched to the formation of a thread in a bore of a plastic material, and at least one axially extending deepening on the thread root, and
a plastic material with a bore into which the screw may be threaded whilst forming a thread and/or
clip with two clip bows and a clip back which connects these and which comprises a through-bore traversing the clip bows, with a thread for rotating in the screw and at least one resilient lug aligned radially to the axis of the through-bore for latching into the at least one deepening of the screw when this is rotated into the through-bore of the clip.
The fastening system comprises a xe2x80x9cplastic-tailoredxe2x80x9d screw. This means that the screw is configured as to its pitch and flank angle in such a way that it is capable of forming an appropriate thread in a bore of a plastic material. At this point, the pitch must not be dimensioned so small and the flank angle must not be dimensioned so large that the formation of a thread in the bore can no longer be achieved at an acceptable expenditure and the load-carrying ability of the threaded joint is too low. On the other hand, the pitch must not be chosen so large to prevent the engaging threads from being self-locking and the flank angle chosen must not be chosen so small that the load-carrying ability of the thread flank becomes insufficient.
Preferably, the thread of the screw has a flank angle of about 20 to 40xc2x0, especially about 30xc2x0. Preferably, the thread of the screw further has a pitch of from 1.5 to 3.5 mm, specifically 2.2 mm (cf. the embodiment), which particularly depends on the measure of the outside diameter.
However, the ranges given may be exceeded or remain below the mark because shaping a plastic-tailored thread may be dependent on influencing parameters such as the surface finish of the screw and the substance of the plastic material, the dimensions of the screw and the bore, and the speed of the screw-driver for rotating in the screw, which may vary very much from one case to another.
The design of the screw ensures that structural components can be fixed to plastic materials. This may concern, in particular, a plug made of plastic or carrier materials in plastic or plastic portions of carrier materials thereof. In particular, it may concern a plastic dome of a carrier material which may be of a different material. The carrier materials may be both thick and flat.
Furthermore, it is possible to fix a structural component to a flat carrier material or a flat portion of a carrier material by means of a clip. It has a thread which is matched to the thread of the plastic-tailored screw, i.e. it has a pitch larger than that of a conventional metallic clip. This screwed joint has less self-locking properties. However, it is ensured that the clip be locked by the fact that the clip latches its at least one resilient lug into the at least one axially extending deepening of the screw when this one has been rotated into the clip. It is understood here that the at least one lug may be latched several times into the at least one deepening while the screw is rotated in, and may be unlatched again therefrom. Preferably, there are several deepenings to make arresting possible in various angular positions of the screw. Also, several lugs may be uniformly spaced around the through-bore of the clip in order to uniformly load the screw at the circumference.
The deepening extends in the axial direction of the screw, which deepening may also run in a helical shape. What is essential is that it has a pitch which at least differs from that of the screw thread. Preferably, however, the at least one deepening extends parallel to the screw shank. Since the screw thread has a relatively large pitch it may have a thread root which may be relatively wide and on which at least one deepening may be accommodated.
The at least one deepening may be of a symmetrical (e.g. a U or V-shaped) or an asymmetrical (e.g. a saw-tooth shaped) cross-section. The latter offers a possibility, while the screw is rotated into the thread of the clip, to make it easier for the lug to exit from the deepening by appropriately inclining one flank thereof and, if there is a load in the opposed direction, to make it more difficult for the lug to exit from the deepening by causing the lug to abut against a correspondingly steep flank.
The clip preferably is designed as a spring clip where a spring bow may have an angled tab to make it easier to slide the spring clip onto a flat material. In addition, the clip may have one or more barbs at the inside to secure the clip to a structural component in a pre-assembled position.
The at least one lug may have an end portion tapering towards the free end, which makes it more convenient to rotate in the screw and to precisely lock it in a determined position. Preferably, the at least one lug is bent out of the flat material of the clip. Although the material of the clip may be a metal, particularly a metal sheeting, a plastic may be considered as well.


Orthodontic treatment is achieved using a series of successive, removable repositioning appliances, such as thin polymeric shell appliances referred to as aligners. A set of aligners is originally provided to the patient. If the patient""s treatment goes off course using the original set of aligners, further aligners are designed and fabricated to move the deviant tooth arrangement back to a target tooth arrangement which was part of the original treatment program.

1. Field of the Invention
This invention relates in general to a method of repositioning teeth for use in orthodontic treatment. Particularly, this invention relates to the use of orthodontic appliances for producing tooth movements. More particularly, this invention relates to the use of a plurality of elastic repositioning appliances for producing such tooth movements.
Orthodontic treatments involve repositioning misaligned teeth and improving bite configurations for improved cosmetic appearance and dental function. Repositioning teeth is accomplished by applying controlled forces to the teeth over an extended period of time. This is conventionally accomplished by wearing what are commonly referred to as xe2x80x9cbraces.xe2x80x9d Braces comprise a variety of appliances such as brackets, bands, archwires, ligatures, and O-rings. After they are bonded to the teeth, periodic meetings with the orthodontist are required to adjust the braces. This involves installing different archwires having different force-inducing properties or by replacing or tightening existing ligatures. Between meetings, the patient may be required to wear supplementary appliances, such as elastic bands or headgear, to supply additional or extraoral forces.
Although conventional braces are effective, they are often a tedious and time consuming process requiring many visits to the orthodontists office. Moreover, from a patient""s perspective, they are unsightly and uncomfortable. Consequently, alternative orthodontic treatments have developed. A particularly promising approach relies on the use of elastic positioning appliances for realigning teeth. Such appliances may comprise a thin shell of elastic material, referred to as an xe2x80x9calignerxe2x80x9d, that generally conforms to a patient""s teeth but is slightly out of alignment with the initial tooth configuration. Placement of an aligner over the teeth applies controlled forces in specific locations to gradually move the teeth into the new configuration. Repetition of this process with successive appliances comprising new configurations eventually move the teeth through a series of intermediate arrangements to a final desired arrangement. A full description of an exemplary elastic polymeric positioning appliance is described in U.S. Pat. No. 5,975,893, and in published PCT application WO 98/58596 which designates the United States and which is assigned to the assignee of the present invention. Both documents are incorporated by reference for all purposes.
Systems of preformed aligners employing technology described in U.S. Pat. No. 5,975,893, are commercially available from Align Technology, Inc., Santa Clara, Calif., under the tradename Invisalign(copyright) System. Align Technology, Inc., is the assignee of the present application. The Invisalign(copyright) System relies on designing and fabricating at least most of the aligners to be worn by the patient at the outset of treatment. The design of the aligners relies on computer modeling of a series of successive tooth arrangements, and the individual aligners are designed to be worn over the teeth and to elastically reposition the teeth to each of said tooth arrangements. Usually, the set of aligners which is designed and fabricated at the outset of the treatment is able to successfully reposition the teeth to a final desired arrangement. In some cases, however, the treatment deviates from the planned movement stages making continued treatment with the previously provided set of aligners difficult or impossible. Such deviations can arise from biological variations in the individual patient, poor patient compliance, or other factors. The deviations will usually become apparent when the next aligner to be worn in the set of successive aligners does not fit. A poor fit indicates that the tooth arrangement has not progressed to the desired intermediate stage and that the teeth are not ready for the next aligner.
When such deviations occur, the response has usually been to start over with whatever actual tooth arrangement that has been received being the starting point. Aligners are then planned and fabricated to bring the teeth from the actual intermediate arrangement to the desired final arrangement, which is usually the same final arrangement as was the target of the original set of aligners. Starting over, however, can be inefficient and wasteful. Relatively large numbers of aligners can be required, and the remaining aligners in the original set will usually be wasted.
For these reasons, it would be desirable to provide alternative and/or improved methods for making mid-course corrections in orthodontic treatment utilizing sets of aligners or other repositioning appliances which are removable and successively worn by a patient to effect a course of orthodontic treatment. It would be particularly desirable if such methods did not require disposal of all or some of the aligners from the original set and were relatively easy to implement with minimum patient inconvenience. At least some of these objectives will be met by the inventions described hereinafter.
2. Description of the Background Art
U.S. Pat. No. 5,975,893, and published PCT application WO98/58596, have been described above. Co-pending application Ser. No. 09/616,830, relates to the fabrication of orthodontic aligners having varying elastic moduluses. The full disclosures of each of these patents and pending applications are incorporated herein by reference.
According to the present invention, an improved method for repositioning teeth is provided. The method for repositioning generally relies on use of an original set of removable positioning appliances, typically aligners as described in U.S. Pat. No. 5,975,893, the full disclosure of which has been previously incorporated herein by reference. The aligners or other appliances are shaped to move teeth through a plurality of predetermined successive arrangements corresponding to the shape of each appliance. That is, the appliances will be configured to apply repositioning forces to the teeth so that the teeth are moved to an arrangement which closely conforms to the unstressed geometry of the aligner. Thus, after a patient has completed wearing any individual aligner or other appliance, it will be expected that the tooth arrangement will match the shape of the aligner or appliance and that the teeth will be ready to receive a next successive aligner or other appliance. The next successive aligner will be shaped slightly differently from the immediately prior aligner, and it is this difference in shape that will move the teeth still further to their next arrangement. Wearing of successive aligners or other appliances thus can effect an entire course of orthodontic treatment as the teeth are moved through a series of predetermined successive arrangements.
In the case of the Invisalign(copyright) System, an original set of aligners will be designed and fabricated at the outset of treatment. The individual aligners will then be available to the patient and/or treating professional so that the aligners may be worn and exchanged as the teeth progress through the expected successive arrangements. Usually, each individual aligner is worn for about two weeks corresponding to one stage of treatment. This period, of course, can vary from several days to several weeks or longer, depending on the individual treatment plan selected for the patient.
The present invention is concerned with those patients who do not progress through treatment as expected and planned. In some cases, an actual tooth arrangement achieved by a patient will differ from the expected tooth arrangement corresponding to the shape of a particular appliance. Such deviation from the expected treatment will usually become apparent when the patient tries to wear the next aligner in a series. If the actual tooth arrangement differs to any significant degree from that which was expected, the next aligner in series will typically not be able to seat properly over the teeth. Such inability to fit or seat on the teeth provides an indication that the actual tooth arrangement which has been achieved at that point in treatment differs from the expected tooth arrangement which should have been achieved after treatment with the immediately prior appliance.
The present invention provides methods for correcting such deviations in the planned and expected treatment path by providing at least one additional removable appliance which has a shape or a compliance selected to move the teeth from the actual (but deviant) tooth arrangement back to one of the predetermined successive tooth arrangements. The tooth arrangement to which the teeth are reconfigured will often be the arrangement to which they should have been at the end of the just completed stage. Alternatively, the arrangement could be any one of the successive stages, usually five stages or fewer beyond the just completed stage, more usually four stages or fewer, and typically no more than three stages beyond the just completed stage.
For the most minor deviations, it will be often be sufficient to provide an aligner or other tooth positioning appliance which has the same geometry as an aligner from the original set, usually as the next aligner in the series. While the aligner will have the same shape, it will be more compliant or elastic so that it can fit and seat over the teeth, even though the shape is further from the geometry of the actual tooth configuration than had been originally intended. The more compliant aligner can then bring the teeth back toward the target configuration for that stage of treatment. Optionally, two or more compliant aligners having the same geometry could be employed, where successive ones of the new aligners will be incrementally stiffer or more rigid to continue to move the teeth toward the target configuration.
The use of additional aligners having the same shape as an original aligner, but which are more compliant, is particularly advantageous since it simplifies design and fabrication of these aligners. The shape or geometry of the aligner would already have been planned during the initial treatment planning process (as described in detail in prior patent U.S. Pat. No. 5,975,893, which has been incorporated herein by reference), and it is necessary only to mold or otherwise fabricate the aligner out of materials having different elasticities. The ability to form aligners having different elasticities is described in detail in co-pending application No. 09/616,830, the full disclosure which has previously been incorporated herein by reference.
In some instances, however, it may not be possible and/or desirable to use aligners having the same geometry as an original aligner to bring the teeth back on to the intended treatment path. In such cases, it will be necessary to design one or more aligners having different shapes in order to move the teeth back from their actual configuration to a tooth arrangement corresponding to one of the appliances from the original set of appliances. Such treatment planning can be performed, for example, by the methods used for the original treatment planning as described in U.S. Pat. No. 5,975,893, the full disclosure of which has been incorporated herein by reference. That is, the actual tooth arrangement, i.e., the tooth arrangement which has been actually achieved in the treatment thus far, will be digitally modeled. Based on the digital model of the actual tooth configuration as a starting point, and a selected one of the target intermediate stages as an ending point, a series of one, two, three, four, or five, or more, new aligners or other positioning appliances can be designed using the computer-aided design protocols described in the patent. Once the new aligner designs are finalized, the digital models of the aligners can be used to fabricate actual aligners using the previously described methods.
For both compliant aligners and differently shaped aligners, the patient will wear the corrective aligners until the teeth have returned to an arrangement which allows an aligner from the original set of aligners to be worn and to move teeth to the next successive arrangement. Depending on the degree of deviation, it may take one, two, three, four, five, or even more, additional aligners or other positioning appliances to provide the desired correction. The corrective aligners or other appliances might be worn from several days to several weeks, or more, until the desired correction is achieved.

Methods for correcting deviations in preplanned tooth rearrangements


An electrical cover plate includes a base having a planar member. A first set of removable tabs is connected to the base so that removal of the first set of removable tabs forms a first set aperture, and a second set of removable tabs is connected to the base so that removal of the second set of removable tabs forms a second set aperture. The first set aperture and the second set aperture may each be bounded by an aperture periphery line so that the aperture periphery lines intersect. Also, the first tab set and the second tab set may have at least one tab in common, and each tab set may be bounded by a tab set periphery line so that the tab set periphery lines intersect. The tabs may be connected to the base by grooved connectors, connecting tabs, or other connections that removably connect the tabs to the base. The apertures may be shaped and positioned to receive a variety of specified electrical devices, such as round electrical sockets, duplex outlet sockets, ground-fault circuit interrupt sockets, or light switches.

1. Technical Field
This invention relates generally to a cover plate for electrical outlets, and more particularly to a universal cover plate that can be converted into a desired specific cover plate by detaching removable tabs.
2. Background Art
Cover plates enclose outlets behind a wall, thereby preventing inadvertent access to the electrically conductive elements of the outlets and hiding the unattractive wiring. The electrical devices attached at the outlet vary, and consequently cover plates of many varieties are known. For example, electric sockets, both standard and ground fault current interrupts; light switches, both toggle and rocker plates; and cable television or telephone ports may be wired at a given outlet. The outlets may be used for indoor or outdoor weatherproof wiring, or may require a locked cover.
Each type of outlet has a different type of cover plate configured for it. To install or service the outlets, an electrician must carry several types of cover plates to each site, necessitating the ordering and inventorying of many types of cover plates. This is time-consuming, expensive and inefficient. It is desirable, therefore, to have a universal cover plate to accommodate most commonly-encountered outlets.
To this end, a partial solution to the problem is known in the art including a three-piece cover plate with interchangeable parts. The base of this device has two pieces, a frame having a rectangular aperture and an insert that fills the aperture. Several versions of inserts are available, depending on the type of device to be wired. For example, one insert accommodates a duplex electrical socket and a separate insert accommodates a ground-fault circuit interrupt. The base is hinged at one end to receive a mated lid, thereby creating a hinged enclosure. The desired insert is chosen, inserted into the aperture of the frame, the lid attached, and the cover plate attached to the wall. To use this device for various types of outlets multiple parts must be carried by the electrician, including multiple inserts, bases, and lids. The prior art therefore does not solve the problem of having to order, stock and carry many different parts. Furthermore, the variety of cover plates is limited to the number of inserts, and only a single-axis hinged lid is known, and the base-lid pair does not allow for a base without a lid.
U.S. Pat. No. 5,763,831 to Shotey, which issued on Jun. 9, 1998, (the ""831 patent) is incorporated herein by reference for its supportive teachings. The ""831 patent is a significant advancement toward a practical cover plate that is convertible between different specific cover plate configurations. Shotey discloses a cover plate having tabs that can be removed to convert the cover plate to different specific cover plate configurations. However, the embodiments disclosed in the ""831 patent are each able to be converted to only a limited number of specific cover plate configurations.
Therefore, there existed a need to provide a practical cover plate that is convertible between several different specific configurations. The present invention provides such a cover plate that is convertible between several different configurations without the need for an excessive number of parts.
According to the present invention, an electrical cover plate includes a base having a planar member. A first set of removable tabs is connected to the base so that removal of the first set of removable tabs forms a first set aperture, and a second set of removable tabs is connected to the base so that removal of the second set of removable tabs forms a second set aperture. The first set aperture and the second set aperture may each be bounded by an aperture periphery line so that the aperture periphery lines intersect. Also, the first tab set and the second tab set may have at least one tab in common, and each tab set may be bounded by a tab set periphery line so that the tab set periphery lines intersect. The tabs may be connected to the base by grooved connectors, connecting tabs, or other connections that removably connect the tabs to the base. The intersecting aperture periphery lines and tab set periphery lines and the corresponding overlapping areas of adjacent potential apertures allows the base to be converted to a much larger variety of configurations without requiring additional parts.
The base plate can include more than two tab sets that can be removed to form even more varieties of apertures. The apertures may be shaped and positioned to receive a variety of specified electrical devices, such as round electrical sockets, duplex outlet sockets, ground-fault circuit interrupt sockets, or light switches. The base may include removable hinge members on multiple substantially non-parallel sides that are adapted to mate with removable hinge members of a cover. Also, the base may define a head aperture that is shaped and positioned to receive the head of a fastener and a shank aperture that is shaped and positioned to receive the shank of the fastener, but not the head of the fastener.


The invention relates to the representation, independent of access type, of ISDN accesses (PRA, BRA) in the central core (cVst) of a packet-oriented exchange (P-Vst). By adapting the signaling information transmitted by ISDN accesses in a peripheral unit (PE) it is possible to handle different ISDN access types as a uniform access type in the central core (cVst) of the packet-oriented exchange (P-Vst). The adaptation can be performed for example with the aid of a conversion table for the user data references and call references contained in signaling messages. The invention has the advantage of providing a simple, low-cost, low-overhead representation of ISDN data in the central core of the packet-oriented exchange (P-Vst). Changes such as e.g. a concentration of the user data channels can be carried out easily and flexibly by the network management (NetMg).

The convergence or merging of time division multiplex-based networks—also called TDM (time division multiplexing) networks—and packet-based networks leads to new call processing requirements in terms of the conversion of signaling and user data.
In the course of the coordination of time division multiplex-based and packet-based networks with one another—the term "interworking" is also often used here—adaptations are necessary on both the subscriber side and the switching node side.
A TDM-based exchange or TDM-based switching node initiates the call control and the termination or through-connection of the user information channels. On the other hand, the range of tasks of an exchange for data transmission in the packet network—referred to in the following as a packet-oriented exchange—includes, in addition to the conventional call control, the control of the associated user information channels, which are generally routed outside the packet-based exchange, via external devices (e.g. gateways, resource servers, . . . ) which provide suitable interfaces for user data streams (e.g. using the RTP (Real Time Protocol)) and control (e.g. using one of the following protocols: MGCP (Media Gateway Control Protocol), H.248, H.323).
For the terminal device side, as well as the classical analog and ISDN terminals and private branch exchanges there are also terminals which are suitable for the packet network and permit broadband data access, but which in addition are also capable (e.g. using the H.323 protocol or the SIP (Session Initiation Protocol) protocol) of supporting the basic service features known from public telephone networks. Subscriber lines operated by means of suitable xDSL techniques (DSL: Digital Subscriber Line) or cable networks are frequently used as a broadband access medium or access network to the subscriber.
The interface between access network and transmission network, e.g. packet-based IP (Internet Protocol) network, is typically formed by means of subscriber-side adaptation facilities. The term "peripheral adapter" is also frequently used for subscriber-side adaptation facilities. Examples of subscriber-side adaptation facilities are IADs (Integrated Access Devices) for terminating a xDSL link and MTAs (Multimedia Terminal Adapters) on or in the cable modem, which terminate the access network on the transmission network side. The connection of broadband terminal equipment (e.g. PC with Internet access, television set, videophone), as well as that of traditional subscriber terminals, e.g. analog telephone, ISDN telephone, and also analog and ISDN private branch exchanges, is then possible via subscriber-side adaptation facilities and access networks.
Packet-oriented exchanges should, wherever possible, provide all the service features known from line-connected connection technology for traditional terminal devices, i.e. telephones and private branch exchanges, so that the integration of packet-oriented networks does not lead to a restriction of the range of service features offered. At the same time the non-availability of hardware and software resources and the non-accessibility of terminal devices must be detected and where applicable an alert signaled to the operator. Structures of the intermediate access networks are usually not known to the packet-oriented switching node, however. For example, failure situations affecting components and network shares which relate to the signaling path between packet-oriented switching node and subscriber terminal equipment are disclosed to the switching node only indirectly, i.e. via detection of the non-accessibility of subscribers and private branch exchanges.
Traditional analog and ISDN subscribers accessible via a packet network are identified for administrative purposes in a particular way in the packet-based switching node to distinguish them from purely packet-based subscribers (SIP, H.323) and traditional, line-connected analog and ISDN subscribers (e.g. connections via the interfaces V5.1 and V5.2). The peripheral, subscriber-side adaptation facilities possess special functions (e.g. telephony client in IADs and MTAs) which enable the transmission of the signaling information between terminal device and packet-based exchange via intermediate access networks and packet-based transmission networks or wide area networks (WANs). The packet-based switching systems and clients in the peripheral adaptation facilities (IAD, MTA) can be appropriately configured for this purpose by the network management function. From the point of view of the switching system, a distinction is made between analog and ISDN interfaces with regard to the provision of functions in the subscriber-side adaptation facilities for the transmission of the signaling information. A further differentiating feature from the viewpoint of the packet-based switching system is the assignment of service features of a main access line or a private branch exchange line. From the viewpoint of the subscriber, either an analog or ISDN terminal device operated as a main access line is then connected to the peripheral adapter (IAD, MTA), or an analog or ISDN private branch exchange (PBX) is connected in the same way.
With regard to ISDN interfaces, e.g. on the peripheral adaptation facility, a distinction is made between two different access types or interfaces.
With the basic access, also referred to as BRA (Basic Rate Access), one or two user information channels are present. Often there are two user information channels (B channels), each operating at 64 kbit/s (56 kbit/s in the USA), and a signaling channel (D channel) operating at 16 kbit/s.
The second access type, also referred to as PRA (Primary Rate Access), is the primary rate TDM access, usually consisting of 30 B channels (on account of the PCM30 system), a synchronization channel, and a signaling channel (D channel). In accordance with standardization, up to 4 PCM30 systems with a single D channel can likewise be combined into a PRA.
Contrary to the case of a packet-based exchange, the status (Layer 1, Layer 2, blocking state) of the ISDN access (BRA, PRA) is known to a traditional local exchange of a TDM network owing to physical line termination or the interface protocols to subscriber concentrators and access networks.
Small ISDN private branch exchanges must also be connectable for packet networks via a BRA or a plurality of BRAs by means of peripheral adapters; large ISDN private branch exchanges must be connectable via one or more PRAs, whereby it must also be possible to support mixes of BRAs and PRAs with regard to a given ISDN private branch exchange. In this case BRA and PRA are possibly connected and physically terminated via a standardized peripheral adapter or via specific peripheral adapters. The ISDN signaling can then be exchanged between peripheral adapter and packet-oriented exchange using packet-based means (e.g. by means of ISDN User Adaptation IUA and SCTP). This typically takes place by means of the DSS1 (Digital Signaling System No. 1) protocol, details of which are specified in the ITU-T Q.931 standard (ISDN user-network interface layer 3 specification for basic call control).
The object of the invention is to ensure flexible and efficient handling of different ISDN access types by a packet-oriented exchange.
The object is achieved by a method, a peripheral device and a packet-oriented exchange according to the independent claims.
In general, an exchange comprises peripheral units, e.g. access units for subscribers or lines, as well as central units or a central component or core which includes, for example, a central computer platform, a message buffer, a switching matrix, protocol termination facilities, background memory, etc. With regard to a packet-based exchange the existence of a switching network is optical in this arrangement. According to the invention an adaptation is performed in a peripheral unit, by means of which adaptation the different ISDN accesses can be represented and controlled in the central core of the packet-oriented exchange in the same uniform manner. A peripheral unit in which the adaptation according to the invention can be performed is the packet control unit of a packet-oriented exchange which controls the user data transmission over the packet network.
In the context of the method according to the invention, signaling information is exchanged between an ISDN access, for example an ISDN BRA or ISND PRA access, and the central core of a packet-oriented exchange via a peripheral unit of the packet-oriented exchange. An ISDN terminal device or an ISDN private branch exchange, for example, can be connected to the ISDN access. The handling or processing of the signaling information transmitted by the ISDN access takes place in the central core of the packet-based exchange independently of the type of the ISDN access. For example, no distinction is made between ISDN BRA and ISDN PRA accesses in the packet-based exchange. For the purpose of ISDN access type-independent handling of signaling information by the central core of the packet-oriented exchange, signaling information transmitted from the ISDN access to the exchange is adapted in suitable peripheral units of the exchange. Similarly, signaling information transmitted by the central core of the packet-oriented exchange in the direction of the ISDN access is adapted in suitable peripheral units of the exchange in accordance with the ISDN access type. In this way different ISDN accesses can be represented by a single access type in the central core of the packet-oriented exchange. Different ISDN access types generally comprise a different number of user data channels. Thus, the PRA access generally has 30 user data channels and one signaling channel. The BRA access or basic rate access, on the other hand, comprises one or two user data channels and one signaling channel. In the inventive adaptation of signaling information in the peripheral unit, the different user data channels can be mapped onto one another for different access types. In this case user data channels or logical ports in the packet network can be distinguished by the addressing of the packets or the addresses of the packets. In the context of user data transmission in the TDM and in the packet network, the term "bearer" is also often used instead of the term "user data channel". According to the invention, an assignment then exists between logical port or user data channel (bearer( and the provisioning of resources in packet-oriented switching systems. For example, a call processing program can be executed in the packet-oriented switching system in accordance with the logical port or the user data channel. On the ISDN access side, physical ports are provided and also user data channels which are assigned to fixed time slots during the transmission via a TDM network. The signaling information relating to the ISDN access and transmitted to the packet-oriented exchange is often adapted in a peripheral adapter (e.g. IAD or MTA) for transmission to the packet-oriented exchange via a packet network. The signaling information arriving at the peripheral unit is adapted for example with the aid of a table for ISDN access type-independent processing by the central core of the packet-oriented exchange. Such a table can be set up in the peripheral unit by the network management. This is conditional upon the network management knowing the hardware interfaces or the physical ports of the ISDN access in order to be able to set up the table. In contrast to the network management, the details regarding the ISDN access are transparent to the central core of the packet-oriented exchange. The provision of the means for adaptive signaling information transmitted from an ISDN access to the central core of the packet-oriented exchange for the purpose of ISDN access type-independent processing and handling of the signaling information by the central core of the packet-based exchange in a peripheral unit is flexible with regard to changes and configurations. A costly and complex implementation of means for differentiating different ISDN access types in the central core of the packet-oriented exchange is avoided, i.e. the implementation overhead is reduced. This also simplifies the expansion of traditional exchanges by control functions for voice connections routed via a packet network. The inventive adaptation in the peripheral unit also permits a concentration of user data channels. For example, the 30 user data channels of a private branch exchange with PRA access can be mapped to fewer than 15 BRA accesses in the packet-oriented exchange. In this case it is assumed that the previously mentioned logical port type of the packet-based exchange coincides with the ISDN BRA with up to two bearer channels. This is an economical solution when there is only low utilization of the user data channels of the ISDN access. By configuration of the peripheral unit the concentration of the user data channels can be flexibly adjusted as necessary to a change in the utilization of the user data channels of the ISDN access. The inclusion of PRA with more than 30 user information channels is likewise possible in this case.
When there are differences between the logical ISDN accesses in the packet-oriented exchange and the subscriber-side physical ISDN accesses, in addition to a mapping of the user data channel references, e.g. channel numbers, the call ID often has to be adapted also. In this context the call ID denotes the identification information referred to as the "Call Reference" in ITU-T Q.931, ISDN user-network interface layer 3 specification for basic call control. This call reference serves to distinguish calls. In contrast to the call number for a subscriber, the call reference for a connection can assume different values on disjunct line sections. Call references are assigned to connections. After the end of a connection the associated call reference is free again and can be reassigned. Finally, a call reference is only unique within a signaling channel. The latter attribute means that it is necessary for the call reference to be converted in many cases. For example, logical BRA ISDN accesses are used on the exchange side, each of which comprises two basic channels and a signaling channel. A number of these logical BRA ISDN accesses are then mapped to one PRA ISDN access with thirty user data channels and one signaling channel. Consequently, multiple signaling channels are mapped to one signaling channel; in other words, without the call references being adapted, the uniqueness of the call references would be open to question.
Signaling information sent from the ISDN access to the packet-oriented exchange can be transmitted via a peripheral adaptation function in the packet control unit of the packet-based exchange, said function being responsible for adaptations for transmission of the signaling information via a packet network. The D channel protocol DSS1 (Digital Subscriber Signaling System No. 1) is used, for example, for the signaling between ISDN access and peripheral adaptation function of the packet control unit. In this case the packet control unit is a special peripheral unit of the packet-based exchange.

Efficient handling of ISDN connections by a packet-oriented exchange