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Fluoride in dental fillings
From an abstract of a paper by Willoughby Dayton MILLER, read at the World´s Columbian Dental Congress in 1893 (Dental Cosmos 35 (1893) 802), "Concerning various methods advocated for obviating the necessity of extracting devitalized tooth-pulps":
"The practice now in vogue among good practitioners, of thoroughly removing the pulp and filling the root canal to the apex is usually so easily carried out in the incisors and cuspids, and gives such sure results, that there is no probabillity that a better method will ever be found. But when we extend this treatment to the bicuspids and molars, the labor and expense put it beyond the reach of the great majority of the human race, and the method is not always successful. It will consequently be a great boon if some means or method can be devised which would render unnecessary the removing of the pulp and filling the root canals of molars.
While every dentist has now and then knowingly left remains of the pulp in narrow and tortuous canals, or in canals obstructed by calcific matter, and while many dentists in Europe have contented themselves with simply devitalizing the pulp, filling over it with amalgam and leaving the rest to nature, the first systematic attempt to do away entirely with the necessity of extracting the root portions of the pulp appears to have been made by Witzel, who in 1874 presented the view that arsenious acid carefully applied to the inflamed pulp devitalized only the diseased tissue, and that by amputating the coronal portion twenty-four hours later, the ends of the root stumps might be treated as healthy, freshly exposed pulps. ...
Perhaps the majority of dentists have also made more or less extensive use of the method recommended by Boedecker when they have left a portion or the whole of the pulp in the buccal roots of upper, or mesial root of lower molars, and filled directly over them, after thoroughly bathing with carbolic acid or some other antiseptic.
I have for a long time felt that the solution of the problem was to be sought for in the direction pointed out by Witzel, except that our efforts should be directed not to retaining the vitality of the root-stumps, but to preventing their subsequent decomposition by impreganting them with a suitable antiseptic. I am convinced that the success of the impregnation method depends to a very great extent upon the character of the antiseptic employed, and upon its chemical action upon the pulp apart from its antiseptic action.
The qualities desirable appear to me to be:
1. It must be a strong antiseptic.
2. It must be sufficiently soluble and diffusible to guarantee the impregnation of the whole pulp
3. It must not be so diffusible that it will be completely taken up by the surrounding tissue and finally disappear altogether, as is the case with applications of carbolic acid. It is my impression that there is greater danger in too great solubility than in insolubility.
4. A coagulating action upon the tissue of the pulp appears desirable, though not absolutely essential. A pulp which is coagulated into a hard, insoluble body, is less likely to furnish nourishment for bacteria and offer irritation to the periapical tissue than one in a soft or semi-liquid condition...
5. It is desirable that the substance employed have no irritating action upon the pericementum.
6. It should not discolor the tooth, although, as the treatment concerns chiefly molars, a slight discoloration need not be considered as a very serious matter.
7. Solid substances are better adapted to the purpose than liquids."
For Miller it was "difficult to find a substance which fulfills all the above mentioned conditions", but for anyone familiar with the properties of fluoride it is not too difficult to think of it as the ideal substance that would -in the above sense- allow a dentist to do a rather shoddy job. But what would it do to a pulp not devitalized, i.e. if there was still no need for root canal treatment?
That fluoride was indeed used by manufacturers as an addition to dental cements was at first unknown to many of the general practitioners: "Owing to the secrecy observed by the inventors and manufacturers of most of the dental silicate cements, it has proved almost impossible for the average dentist to obtain exact data regarding their chemistry and physical characteristics, except at considerable expense of time and money for the making of investigations - with the result that very little was written about them in this country during the first ten years after they came into widespread use that would shed much light on their composition and their value as filling materials. (Volker C.J.: "Dental silicate cements in theory and practice", Dental Cosmos 68 (1916) 1098).
In a discussion (Dental Cosmos 68 (1916) p. 1168) of Volker´s article, the famous Dr. W. D. Tracy, of New York, remarked: "In regard to the silicate cements, however, I believe that most of us have been using them simply as materials that were good substitutes for porcelain, not knowing -and many not caring- that the powder contained sodium silicate and basic beryllium nitrate, or that orthophosphoric acid was modified with the phosphate of aluminum or hydrofluosilicic acid. While the successful use of the material may not be dependent upon a thorough knowledge of its constituents, it is desirable that we should know and understand its composition. It is not so many years ago that these silicate cements were accused of being dangerous to use because of their large arsenic content, but, as shown in the paper just read, pulp devitalization occurring under silicate cement fillings is due to other definite and well-understood causes [Volker: "probably already affected by the progress of caries"], and not to the presence of arsenic. This incident is noted simply to show how easily the dentist may be misled when his use of a material is entirely empirical, and how he would have looked for other causes for his devitalized pulps had he had a definite knowledge of the chemistry of the material he was using."
After clinical observations and animal experimentation it became soon obvious "that silicate cements exert a harmful effect on the dental pulp. ... That this damage must be attributed to the irritating qualities of silicate cement and not to the operative procedures of cavity preparation is apparent because comparable cavities filled with zinc oxide - eugenol cement showed no pulpal damage. ... It is interesting to note that the histologic study supports the belief that there is an individual difference in the severity of the reaction experienced by the patients used in this study" (Zander H.A.: "The reaction of dental pulps to silicate cements", J. Am. Dent. Assoc. 33 (Oct. 1946) 1233). "Despite differences in the severity, the nature of the pulpal reaction was comparable in all sound teeth. The odontoblastic layer which corresponds to the tubules in contact with the cavity shows degeneration in most instances. Cellular infiltration ranging in severity from a mild reaction to abscess formation or pulp necrosis was a consistent finding. The picture of inflammation depends to some extent on the length of time that the silicate cement fillings had been in position. Polymorphonuclear leucocytes are numerous in the pulps of the teeth from patients 2, 3, and 7. In all other cases, monocytes and plasma cells dominate the picture. The pulp presents a non-specific acute to chronic type of inflammation."
"The depth of the cavity determines the degree of the damage; when the silicate cement lies within 0.5 mm of the pulp, progressive degeneration occurs" (Roydhouse R. H.: "Silicate cements and pulpal degeneration", J. Am. Dent. Assoc. 62 (June 1961) 470). Fluoride was detected as a component of the leach.
In a study by Helgeland and Leirskar, silicate cements showed also a cytotoxic effect in vitro which was traced to fluoride release and increased with acidity of the environment (as formation of HF increases the uptake of the fluoride) (Helegland K., Leirskar J.: "pH and the cytotoxicity of fluoride in an animal cell culture system", Scand. J. Dent. Res. 84 (1976) 37)
Is there a difference between dental cements and the newer filling materials? To quote from one of the patents on filling materials: "Studies ... comparing fluoride release by silicate cements and composite resins have shown that the overall release of fluoride from the two materials was comparable..."