Dental Filling Materials

DENTAL FILLING MATERIALS, the name given in dentistry to substances used for filling carious cavities in teeth. Dental fillings were known very long ago. Thus, in Egypt, fillings were already known, as evidenced by fillings found in the teeth of mummies. Roman physicians also filled teeth, and for example, Celsus has indications for filling large carious cavities with canvas and lead. The oldest filling mass was invented by Nero's personal physician, Andromachus. The famous French surgeon and dentist Fauchard (17th century) developed a method for closing carious cavities with metal. At one time, cotton wool impregnated with mastic or sandarac (resin of the plant Callitris quadrivalvis, infused in alcohol) was also classified as dental filling materials. As is known, in the process of treating teeth, carious cavities are closed with cotton balls impregnated with these adhesive substances. However, they cannot be classified as dental filling materials; these are only materials for temporary sealing of carious cavities, and even for this purpose they are not entirely suitable: by the second day, the cotton becomes saturated with saliva, and the entire cavity becomes contaminated. Dental filling materials in the true sense of the word, i.e., preparations that fill defects in the hard tissues of teeth, must possess the following properties: 1) sufficient hardness so as not to change their shape or wear away during chewing; 2) stability and immutability under the influence of oral secretions and food taken; 3) absence of thermal conductivity to avoid irritation of the pulp in living teeth; 4) the ability to fit tightly against the walls of the carious cavity; 5) suitable color; 6) absolute harmlessness to the body and in particular to the tissues of the oral cavity; 7) absence of any difficulties in application, as well as comparative ease in their removal. It must be stated in advance that none of the existing dental filling materials meets all these requirements, and to this day there is still no ideal dental filling material. For the purposes of filling, the following materials are used: 1) gold, 2) amalgams, 3) tin-gold, 4) cements, 5) gutta-percha, 6) porcelain mass. Of these, amalgams, cements, and gutta-percha are plastic materials, as they are introduced into carious cavities in a soft, paste-like form and there already acquire a firm consistency. The oldest dental filling material is gold. It is used in the form of cylinders twisted from sheets of gold foil. One of the most important properties of gold, on which the method of filling with it is based, is its cohesiveness, i.e., the ability of one cylinder to adhere to another. Based on a series of experiments, it has been established that the cohesiveness of gold is significantly enhanced by the influence of calcining it over a flame. However, it must be emphasized that this somewhat reduces the strength of the gold. Moisture significantly reduces the cohesiveness of gold; even touching the filling gold with fingers deprives it of cohesiveness, and it must again be passed over an alcohol flame. There is also spongy or crystalline gold, which is prepared by treating it with iron sulfate or oxalic acid. This type of gold is rarely used for filling purposes, although it was previously indicated that crystalline gold is not only cohesive but also has the ability to adhere to the walls of the carious cavity. As a dental filling material, gold possesses sufficient hardness, does not change under the influence of chemical processes occurring in the oral cavity, and generally does not change in volume. However, it has significant thermal conductivity, unsuitable color, and working with it is extremely painstaking, difficult, and requires considerable skill and great technical proficiency. Relatively shallow cavities require from 1/4 to 1 1/2 hours for careful filling, and absolute dryness must be maintained in the carious cavity. In recent years, the use of gold for filling by the so-called cohesive method has been decreasing and is giving way to the use of cast inlays, for which ordinary high-grade gold is used. There were also indications of the antiseptic properties of gold. The indications for the use of gold fillings are limited mainly to small carious cavities with thick, completely stable, strong walls. Even in carious cavities of medium depth, it is better to place a fairly thick layer of cement on the bottom as an insulating medium against the thermal conductivity of gold. Gold as a dental filling material does not have wide application, especially in mass dentistry, which depends, on the one hand, on the difficulty of working with it, and on the other hand, on the high cost of the material itself. Tin-gold. For filling, tin foil (tinfoil) is used. Only high grades of soft and malleable tin foil are suitable for filling. Tin does not have cohesive properties and therefore is used for filling only in combination with gold. As Miller indicates, the advantage of this combination is that such a filling has very little thermal conductivity. Moreover, in the oral cavity, apparently under the influence of electrochemical processes, tin-gold fillings turn into dense compounds resembling amalgams. Tin-gold does not irritate the pulp and has some antiseptic properties. However, this preparation did not receive wide application for fillings and is used extremely rarely. Of the indications for use, only one can be mentioned: weakness of the walls of the carious cavity and proximity to the pulp. Amalgams (see). In dentistry, copper, silver, gold, and platinum amalgams are used. These amalgams must form completely plastic masses that do not harden too quickly, so that during work they can be well shaped and smoothed to the edges of the carious cavity. On the other hand, when amalgams harden, they must not shrink and must not become brittle, so that their thin edges and contour fillings in general do not break from pressure during the act of chewing. Especially important is the property of sealing the edges of the carious cavity (Kantenfestigkeit), as the open edge of enamel or dentin serves as a place for the recurrence of caries. According to some German authors (Miller, Fleischmann and others; 1900), gold amalgam has the greatest ability to seal the edges of carious cavities. The basis for all filling amalgams is usually tin and silver. Zinc, added to the amalgam in an amount not exceeding 2%, significantly reduces the compressibility of the filling and makes its color more stable. Palladium completely discolors the amalgam. Amalgams consist either of one metal with mercury—double, two metals with mercury—triple, etc.—Copper amalgam consists of one part of fine copper filings and two parts of mercury. Paschkis indicates the following method for manufacturing copper amalgams: copper is precipitated from a diluted solution of copper sulfate with the help of metallic zinc, which is washed in dilute sulfuric acid, and then in hot water. The precipitated copper is moistened with a small amount of mercuric nitrate, then triturated—or rather kneaded in a mortar with two parts of mercury, the excess of the latter is squeezed through cloth, and the amalgam is rolled into the form of roll-shaped pieces. After some time, this amalgam becomes completely hard. For filling, pieces of hard amalgam are heated over the flame of an alcohol lamp, during which droplets of mercury appear over the entire surface of the metal piece, and then they are triturated in a mortar with a pestle to the consistency of a plastic mass. To some types of copper amalgam, 2 1/2% of tin is also added (Lippold). For a time, copper amalgam was the most common dental filling material, especially in Germany. Miller indicates that in Germany, no dental filling material has saved as many teeth as copper amalgam. As is known, in the USA, copper amalgam never had such widespread use. For a time, attention was drawn to the remarkable property of copper amalgam to penetrate deeply into the substance of the tooth and preserve it for a long time; this property is manifested even after the removal of long-existing copper amalgams. Miller at one time showed that of all dental filling materials, only copper amalgam prevents the development of gelatin-splitting fungi in it, and on this basis he attributes antiseptic properties to this dental filling material. Therefore, until recently, copper amalgam was the most common material for filling milk teeth. However, a major negative property of copper amalgams is their darkening in the mouth and staining of the tooth; both the tooth and the filling often turn black. This limits their application. In general, if copper is added to other amalgams, this also gives them a black color. It must be emphasized that remnants of already used copper amalgam can be used again with the same success, since repeated use does not change its properties. Silver amalgam consists of silver filings (65%) and tin (35%) and has the appearance of a white, very plastic mass that hardens slowly and at the same time shrinks at the edges.

After some time following the filling, silver amalgama turns black (less so than copper amalgama) due to the formation of silver sulfide. Usually, various impurities are added to silver amalgamas to eliminate their negative properties. The best results are achieved with the addition of gold (7%). One can add during the mixing of silver filings with mercury 1-2 cylinders of gold filling material, which is quickly amalgamated and gives the amalgama a lighter appearance and considerable plasticity (Gofung). When kneading such a mixture with fingers, a metallic crunch is produced. To prepare the filings for such dental filling materials, silver and gold (and platinum) are melted together, while tin is melted separately, with the first alloy being poured into the tin and the entire mixture quickly poured into the appropriate mold. From the hardened ingot, filings-powder are prepared with large machine files, which is then combined with mercury to form a plastic mass ready for filling. As for the stability of form and volume, in this respect silver amalgama is inferior to copper amalgama: after just a few months it creates a gap between the filling and the cavity wall, which undoubtedly depends both on the property of the amalgama to shrink and on its tendency to assume a spherical shape upon hardening. This has been pointed out for a long time, although not everyone agrees with this. However, one can almost certainly say that amalgamas containing gold, or even better gold and platinum, suffer from this defect to the least extent. For example, Black (Blak) points out that amalgamas have the property of shrinking upon hardening, which leads to the formation of cracks along the edges of the cavity. Practice shows that silver amalgama is the best filling and can be confidently recommended for general dental practice. Due to the thermal conductivity of silver amalgama (though less than that of copper amalgama), preliminary measures (a cement lining) must be taken when there is a vital pulp. The indications for the use of amalgamas are very extensive: they are mainly used on the chewing surfaces of molars and premolars, as well as on the approximal (interdental) surfaces of teeth, where they very well preserve the interdental contact and preserve the teeth for a long time. A major negative property of amalgamas is their unsuitable color. The question of the harmful effect of amalgam fillings on the general state of health has been raised repeatedly (see Amalgamas). It became a program topic at the All-German Odontological Congress in September 1926. A number of experimental works presented at the congress revealed disagreements in this direction. Thus, Dieck showed that copper amalgama even two years old releases Hg, while silver amalgama, when properly prepared and appropriately placed in a carious cavity, stops releasing Hg after 24-48 hours. Schonebeck arrives at the same conclusions. Meyer indicated that copper amalgama releases Hg 3-4 times more than silver amalgama. Fleischmann found Hg in the urine, saliva, or feces in 81% of wearers of copper amalgam fillings. In the 37 cases studied, mercury was found in 30. Gofung repeated the simple experiments of Witzel. Extracted teeth were filled with copper and silver amalgama and placed at the bottom of a test tube, with the inner side of the stopper, which sealed the test tube, being covered with gold foil. The outside of the stopper at the edges of the test tube was sealed with paraffin. Both test tubes were placed in a thermostat at 37°. Daily checks during the first week showed no changes to the gold foil in either test tube. On the 10th day, it was already noticeable that the foil in the test tube with copper amalgama had a dull silvery tint in places; this was clearer and well established with the help of a magnifying glass. After a month, the gold foil on the stopper of this test tube was completely amalgamated, while in the second test tube, where a tooth filled with a silver filling lay, the foil remained completely unaffected by the mercury, and its entire surface was smooth and shiny. Two years after the experiment, the results of examining the gold foil in both test tubes are the same. Since there was no contact between the filling and the gold foil in these experiments, it is quite clear that the amalgamation of the gold foil was a consequence of the release of Hg and its deposition on the surface of the foil. It apparently also has great significance that old copper amalgamas, no matter how many years they have been in carious teeth, still release mercury after heating, while a freshly hardened silver amalgama does not have this ability. Based on all these data, one can conclude that copper amalgama indeed has the ability to release Hg vapor, and its complete cessation of use in dentistry should be recommended. As for individual cases of the effect of silver amalgama on the general state and on the oral mucosa, this is more likely to be attributed to the special sensitivity of these individuals to Hg. Such cases of idiosyncrasy have been described repeatedly. Dentists, constantly working with amalgamas, run the greatest risk of chronic poisoning. Therefore, preventive measures in this direction are particularly important; good ventilation of dental clinics and offices is important; it is good to place a zinc board near the dental chair (zinc easily combines with mercury, which due to its weight collects mainly on the floor, near dental chairs). In addition, dentists should not mix silver amalgama with their fingers on their palm. Although Miller denies the possibility of chronic Hg poisoning in dentists, it is still possible, and one must be very cautious when working with mercury. Cements-Dental filling materials, consisting of powder and liquid; after mixing in the appropriate proportion, they give a pasty sticky mass that hardens relatively quickly and acquires a consistency that is sufficiently dense and stable. The old cement, so-called Paris cement, proposed by Sorel (1858), consists of a powdered mixture of zinc oxide, ground glass, and a liquid-zinc chloride. This mixture hardens quickly and acquires a stone-like consistency, so that work on filling the carious cavity with it must be done extremely quickly. This cement, despite its rapid hardening, still releases zinc chloride, whose strongly caustic action causes irritation of the pulp. In addition, its resistance to oral secretions is insignificant. All these circumstances have made it little applicable for filling teeth, so that it is no longer manufactured today. At present, phosphate, silicate, and phosphate-silicate cements are widely used. Phosphate cement, or zinc phosphate, consists of zinc oxide powder and liquid orthophosphoric acid, with a certain amount of coloring substances (iron oxide, manganese, etc.) added to give it the proper color. Phosphate cement does not have the luster characteristic of tooth enamel and therefore differs from it. Its advantages lie in its excellent adhesion to dry cavity walls, its good appearance, and indeed its considerable chemical resistance. Zinc sulfate, or Fletcher cement, Artifical Dentine Fletcher, is a powder consisting of zinc oxide and calcined zinc sulfate. Its liquid consists of an aqueous solution of Gummi arabici with a small amount of glycerin, borax, traces of opium, and carbolic acid. It is used in dentistry as a temporary filling to isolate medicinal dressings from the external environment, as well as as an indifferent lining under amalgama or cement. For permanent fillings, it is not sufficiently stable and quickly deteriorates. Jenkins' porcelain mass. As early as 1887, Land proposed a porcelain mass for making fillings, individually measured for each case, but this mass was not adopted because, on one hand, it was very refractory, and on the other hand, it decreased significantly in volume after firing. After this, a number of authors also unsuccessfully proposed their porcelain preparations. Only in the early 20th century did Jenkins in Dresden succeed in combining such a porcelain mass that fully meets all requirements: it is easily fusible, shrinks little after firing, in color it completely merges with the tooth enamel, and is extremely resistant to chemical and mechanical influences. Jenkins' "Porcelain Enamel" consists of feldspar, silica, kaolin, glass, and coloring substances; according to some authors, this is more of a porcelain-like body, closer to porcelain than to glass. Jenkins' porcelain mass is in the form of a fine powder, available in 22 colors, and requires mixing individual powders to obtain particularly fine color shades. For use, it is mixed with alcohol to a sour cream-like consistency (see Fillings, to fill?). Gutta-percha.

Gutta-percha in its pure form began to be used for filling teeth as early as 1897, and soon after Hill released a gutta-percha filling material under the name "Hills-Stopping," consisting of gutta-percha, caustic lime, finely ground quartz, and feldspar. At present, there are many factory-made gutta-percha filling materials, with the main admixture being zinc oxide and silicic acid. Two types of gutta-percha are used: 1) White and red sticks - soft gutta-percha, which softens very quickly over an alcohol flame, becomes sticky and viscous, and hardens after a few minutes. 2) White and pink plates - hard gutta-percha; requires a stronger flame to soften and acquires considerable density upon cooling. The soft variety of gutta-percha is used only for temporary fillings and for sealing medicinal preparations into carious cavities. Hard gutta-percha is sometimes applicable as a permanent filling, for example, in isolated elderly teeth, as well as at the cervical margin. With prolonged stay in the mouth, soft varieties of gutta-percha lose their compactness and give off an unpleasant odor.

Root canal filling - materials for filling root canals in teeth that have lost their pulp. For this purpose, gutta-percha in the form of points is predominantly used, ¹ 520 "Guttapereha Points," which are inserted into the canal. Previously, gutta-percha points are coated with a liquid-mixed phosphate cement with the addition of iodoform or else with a chloro-percha solution - gutta-percha in chloroform. A number of disinfecting pastes are also used for filling canals - thymol, iodoform, tricresol-formaldehyde, and others, with which it is rarely possible to fill the entire root canal. Albrecht's root canal filling is composed of resorcinol (saturated solution 8:5), formalin, and 10% caustic soda. These three liquids, combined in equal parts, condense after 17-2 hours into a gelatinous mass, which has deeply diffusing properties and fills all the sinuosities and anastomoses of the root canals. Schreider's root canal filling "Radizan" is composed of two liquids: 1) tetramethyl ether of silicic acid and 2) shellac lacquer. It is introduced into the canals in liquid form. The tetramethyl ether, upon coming into contact with organic residues or acids in the canal, decomposes into methyl alcohol and a colloidal solution of silicic acid; the latter gradually thickens and turns into a glassy mass, which fills the canal. Bone filling. The idea of filling cavities that have formed in bones under the influence of various pathological processes has existed for a long time. A bone filling is understood as the filling of defects in bone tissue with a material that is foreign to the body and aseptic. For this purpose, various masses have been proposed at different times: metal powder, celluloid, glass, carbolic plaster, white lead, copper amalgam, gutta-percha, and others. Absorbable substances were also used, such as catgut. Fantino and Valan, based on a series of experiments, recommended filling bone defects with a mixture of bone ash, thymol, and iodoform. This mass acquires a stony consistency at body temperature, and is then gradually replaced by living tissue. Mosetig-Moorhof proposed his own mass for bone filling, which consists of 60 parts iodoform and 40 parts spermaceti and sesame oil. The bone defect is filled with this mass, which is first cleansed of all necrotic parts of the diseased bone and shaped with the help of circular saws and burs, driven by a dental engine or electricity. When the cavity is properly prepared and bleeding has stopped, the entire cavity is thoroughly dried, and the mass, liquefied by heating, is poured into it and immediately solidifies. The wound in the soft tissues over the filling can be completely closed with sutures. This filling is temporary; it is gradually destroyed by the granulations forming in the walls of the defect and replaced by living tissue. The main purpose of bone filling is to keep the existing defect in the bone completely filled aseptically until tissue regeneration occurs. Mosetig's filling found very wide application in surgery until recently.