The Merck Index, 1968, pp. 160, 178. .
"Accepted Dental Remedies," ADR, 1967, American Dental Assn. p. 138. .
Rose et al., "Condensed Chemical Dictionary," 7th Ed., Reinhold, (1969), N.Y., p. 131. .
Ashikari et al., Journal of Polymer Science, Vol. 31, 31 No. 122, (1959), pp. 249-251..
It has been known to use synthetic plastic materials for filling tooth cavities, in the form of mixtures of polymers in powder form and monomeric liquids, which contain various types of additives, in particular catalysts and/or accelerators for rapid curing at low temperatures. These filling materials have become widely used and have proved generally satisfactory because of their desirable properties, but do, however, frequently have disadvantages. When not expertly used, damage of the tooth pulp may occur during the introduction of the uncured mixtures into the cavity and during the curing of the mixtures. Such irritation of the pulp, which starts with damage to the odontoblasts, may cause death of the pulp. This irritation occurs primarily because an ineffective sub-filling is used, which fails to keep the toxic monomeric liquid out of contact with the viable pulp. Thus, with incorrect or inexpert subfilling the possibility is always present that the monomeric liquid will diffuse, together with the sometimes also toxic catalyst constituents, through the layer of dentine covering the pulp and lead to damage or death of the pulp, either immediately or maybe after the filling has cured.
This damage of the living tooth texture is believed not to be the result of acidity, as occurs with other tooth filling materials, but probably is the result of a protein precipitating effect by the strongly fat-dissolving monomer in the polymerizable liquid. Since the development of synthetic fillings in the dental field, there have been many experiments to protect the pulp from damage by the monomer liquid. It is known to cover the cavity with a synthetic film prior to inserting the filling material, which film is intended to prevent the monomer liquid from diffusing through into the living tooth pulp. However, these so-called cavity varnishes have not been able to give effective protection of the pulp, possibly because of the organic solvents introduced during application of these synthetic films causing the same texture damage also observed without the application of such a film.
Acrylic-based tooth restorations have been used for some time:
"The Science of Dental Materials;" Skinner and Phillips, W. B. Saunders Company, Philadelphia, Fifth Edition, page 200 et seq., Chapter 13, "Tooth Restorations with Acrylic Resins"
Clinical tests have shown that fast hardening acrylic-based filling materials show statistically a pulp necrosis rate greater than 4 percent:
1. "Auto-polymerizing Resin Fillings," Coy, Bear and Kreshover, Journal of the American Dental Association, Volume 44, No. 3, March 1952, page 255
2. Spreter von Kreudenstein Deutsche Zahnaerztliche Zeitschrift, 10, (1955), page 1619
3. "Pulp Reactions to Restorative Materials" Stanley, Swerdlow and Buonocore, Journal of the American Dental Association, Volume 75 (1967)
Some results of the case of filling material according to this invention are given in:
1. Fischer, Grosz and Masuhara Deutsche Zahnaerztliche Zeitschrift, 23 (1968), page 209 et seq.
2. Fischer, Knolle and Tan Das Deutsche Zahnaerzteblatt, 23 (1969), page 251 et seq.
It has now been found that this type of damage of the pulp can be prevented by using boric acid or, under the filling conditions compounds supplying boric acid, when working with the synthetic fillings.
This invention consists of the use of boric acid (or under the filling conditions of boron compounds supplying boric acid) in the application of known synthetic filling materials, particularly acrylic ones, which consist of a pulverulent polymer and a monomer liquid and contain catalysts and/or accelerators which provide for the fast hardening of the mixture at low temperatures. As is known, these mixtures of polymer powder and monomer liquid are usually based on compounds of the acrylic acid- and methacrylic acid series, especially on the acrylic acid- and methacrylic acid esters, homopolymers as well as copolymers being used. The monomer liquid does not have to be a single monomer, but may be a mixture of different monomers. But such monomer liquids are toxic to the tooth pulp, as are the numerous compounds that may be used as catalysts and accelerators. This has been known in the dental field for a long time, i.e., that such materials undesirably affect the pulp.
The boron compounds are preferably used in amounts of 0.01 to 5 percent by weight, advantageously 0.05 to 3 percent by weight, and in particular 0.1 to 1 percent by weight, based on the liquid constituents of the agent.
As well as boric acid itself, boron compounds, in particular borates, for example tributyl borate or trioctyl borate, have been proved to be effective boron compounds for protecting the pulp. These effective boron compounds can be used either directly in a suitable liquid, for example dissolved in water or an organic solvent, or can be dissolved in a monomeric polymerisable liquid for brushing out the tooth cavity before inserting the filling. They can be and preferably are added to the plastic mixture itself before it is introduced into the tooth cavity.
It is believed surprising that boron compounds introduced in a relatively small amount to the monomer liquid in accordance with this invention would hydrolize in the practically waterfree monomer liquid to any appreciable extent. This hydrolysiscan only take place at the interface between the filling and tooth substance, and it is considered particularly surprising that the protective effect would be exerted at such low boric acid concentrations as are present at the interface.
Examples 1 and 2
A plastic mixture suitable for the filling of tooth cavities consisted of a fill composition containing pulverulent methyl methacrylate polymer or copolymer, which was mixed with monomeric methyl methacrylate to form a pasty mixture and was cured under the influence of a Redox System as known per se after introduction into a tooth cavity to form a filling. The monomeric liquid contained 0.1 percent free boric acid. A filling material which was of similar composition but which contained 5 percent of tributyl borate in the monomeric liquid also formed a satisfactory filling. With both compositions it was impossible to determine any damage to the pulp by the plastic filling or by the constituents thereof, which are toxic in the uncured state.
Examples 3, 4 and 5
These filling materials are prepared in accordance with known methods whereby the pulverulent polymers and monomeric liquids are mixed in a suitable ratio and are brought into the tooth cavity wherein the mixture polymerizes or hardens into the filling in a few minutes under the influence of the catalysts and accelerators at mouth temperature. In general, there are mixed about two parts powder with one part liquid; however, these quantities can vary, depending on the portion of the filler.
3. Powder: A pearl polymer of 95 percent methacrylic acid methylester and 5 percent butylphthalylbutylglycolate (Santicizer B-16-Monsanto Chemical), particle size <50 μ is ground with 1 percent dibenzoylperoxide with small additions of inorganic pigments to give the mixture a tooth-like color.
Liquid: 92 percent methacrylic acid methyl ester, 4.5 percent glycol-dimethacrylate, 0.5 percent dimethyl-p-toluidine, 3 percent tributylborate.
4. Powder: This powder corresponds to that of Example 3, but contains in addition 0.6 percent di-p-toluene-sulfonylmethylmethylamine.
Liquid: 99 parts by weight methacrylic acid methylester, 0.5 parts by weight β-phenylethyldimethyl-carbethoxymethyl-ammoniumchloride, 0.03 parts by weight copperacetylacetonate. Directly prior to mixing, there are dissolved in the liquid 3 parts by weight of tri-n-butyl-boron.
5. Powder: First, 75 percent quartz flower having a particle size of <50 μ are mixed with 25 percent of a copolymer of 95 percent methacrylic acid methylester and 5 percent butylacrylate in pearl form having a particle size of <50 μ. To this mixture there is added, besides pigments, 1 percent dibenzoylperoxide and 2 percent boric acid. The liquid component corresponds to that of Example 3.