The Optimum Characteristics of Dental Floss for Personal Oral Hygiene* |
Another objection to waxed dental floss is the film of wax that is left on the surface of the tooth in using it to clean within the gingival crevice. The presence and accumulation of foreign material on the normal smooth enamel cuticle where the gingival epithelium rests against it initiates gingivitis, the earliest stage of periodontoclasia. Wax from dental floss applied daily to the cuticle in this same area, would have the same kind of foreign body effect, but probably not as great. Still another objection to waxed floss is the single cord effect, and the relatively unyielding shape, in cleaning the entire depth of the gingival crevice or sulcus (Fig. 1). Low twist floss, without wax or size, adjusts itself more or less to the very narrow space between the gum and tooth, whereas waxed floss does not spread and adjust, to the same extent.
CHOICE OF FILAMENT SIZE
High tenacity nylon yarn is made either "bright" or "semidull”. An inert delustrant is added to produce the latter type. Only bright nylon yarn should be used for dental floss. For trade purposes the manufacturer of nylon designates bright, high tenacity yarn, with no size or oil applied, as "Type 300." This type is the most suitable for dental floss. The relative merits of other types need not be taken up here. Type 300 nylon is made in different filament sizes ranging from 2 up to 6 denier per filament. The author has devoted much study and experimental work over a considerable period of time in an effort to ascertain the optimum size of filaments for the purpose. The size decided upon is 2 denier per filament. For the information of others who may wish to investigate the question, some of the considerations favoring selection of this size are given here. If floss made of 1 denier filaments (available in "normal" tenacity only) is drawn against rough surfaces between contacting teeth, although there may be only microscopic roughness, there is considerable breakage of the very fine delicate filaments. This is definitely objectionable. On the other extreme 6 denier filaments are stronger and break less under the same circumstances. However, floss made of this size does not pass with the same ease and smoothness as that made of smaller sizes. It seems that floss made of the larger size filaments cannot mold and adjust to the close space as well as floss made of smaller filaments. Actually it finally comes down to choosing between the 2 and 3 denier filaments. Micrometric determinations on 100 filaments of each of these two sizes gave an average diameter of .016 mm. for the 2 denier and .020 mm. For the 3. The average for 6 denier filaments is .028 mm. Thus it will be seen that the thickness of the 3 denier filament is only about 1/4 greater than the 2, whereas the 6 is nearly twice as thick. It requires definitely more force to separate teeth enough to pass a 6 denier filament, or a number of overlapping filaments of that size in dental floss, between contacting teeth, than for the 2 denier. The feel of coarseness of the 6 compared to the smooth and easy passage of the 2 denier floss is easily recognized. Two volunteer test subjects, while blindfolded, could differentiate between these sizes almost every time. In a number of blindfolded practical-use tests the author has been able ' to correctly differentiate, 8 out of 10 times, between floss of equal total denier made of 2 and of 3 denier filaments. Although the difference is very slight, it is to that extent in favor of the 2 denier size. In dental floss of a given total denier, the number of filaments is 50 per cent greater if it is made of 2 denier filament yarn than if made of 3 denier. In use each separate filament may serve to dislodge some small part of the microscopic particles present-bacteria and other. The advantage, in this respect, is definitely in favor of floss made of 2 denier filaments with the larger total number of separate filaments. An important function of dental floss is to take up and hold for removal, microscopic material, in the spaces between, and on the surface of, the filaments. Since these are considerably more numerous and greater respectively in floss made of 2 denier filaments than that made of 3 denier, there must be some advantage in this regard, of the smaller size. The author has not succeeded in setting a satisfactory experiment to prove the slightly greater effectiveness, in dislodging and removing bacterial material, of 2 denier over 3 denier filament floss. However, this is certainly theoretically true. A little breakage of filaments occurs when either 2 or 3 denier filament floss is drawn forcibly across rough surfaces, as in cleaning rough surfaces on some teeth. Although the difference is difficult to demonstrate with certainty, there must be some more breakage in the 2 than in the 3 denier filament floss. However, there is so little breakage in the 2 denier filament floss, when properly used, that this is negligible and unimportant. Whatever slight advantage there is, in this regard, of the 3 denier filament floss, it is far outweighed by the other advantages of the 2 denier filament floss indicated above.
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CONSTRUCTION, TWIST
The manufacturers of nylon supply 2 denier filament, Type 300 nylon yarn to manufacturers of floss in the form of 70 denier, 34 filament, Z twist, turn to the inch. The floss manufacturer* must twist together a sufficient number of threads to make the size or total denier of floss desired. The amount of twist is expressed as the number of turns per inch. The direction of twist is designated as S or Z.** Some twist is necessary to hold the filaments together during manipulation in cleaning the teeth. Floss with very low twist or with no twist at all passes through close spaces, as between contacting teeth, with the greatest ease. If it is held against the close space and drawn slightly back and forth lengthwise, the somewhat elastic filaments tend to pass a given point singly or in small numbers. On the other hand, hard twisted floss cannot mold or spread out in the same way. Therefore more force must be applied and the teeth must be spread farther apart for it to pass (usually with a snap). Flosses with 0, 1, 2 or 3 turns to the inch pass between teeth, each with about the same ease. Obviously the filaments of floss with 3 turns to the inch will hold together better, when it is being used and handled, than those of lower twists. Floss with 6 turns to the inch is much harder and more unyielding. In fact one can make out definite difference between 3 turns and 4 turns per inch floss in passing them between contacting teeth. The 4 is just a little harder-and therefore less suited to the purpose than 3. Soft low twist floss when passed into the proximal gingival crevice, and held or drawn against the tooth there, tends to spread out and flatten (Fig. 3) and to fit without harm into the very deepest part of the space. Round hard twisted floss does not yield so well, therefore, it is less well adapted for use in the gingival crevices. Soft low twist floss dislodges and holds between its filaments, more microscopic bacterial material than hard twisted floss. All evidence together tends to favor a twist of about 3 turns to the inch. The direction of the twist is of some importance. Most people are right handed. In cleaning the teeth one uses a piece of floss 2 to 3 feet long. One end is wound, with 2 or 3 turns, around the last phalanx of the right index finger, to facilitate holding and manipulating the string. The floss is passed between two teeth, the proximal surfaces down to the bottom of the gingival crevices (Fig. 3) of both of them are cleaned, the floss is withdrawn and then applied to succeeding teeth until all have been cleaned. As the floss is soiled by use, one should move along the string to a clean place from time to time, by taking another turn around the finger now and then. This manipulation tends to twist the string a little to the right. This untwists Z twist floss but holds or slightly increases S twist. While the direction of the twist is not of great importance, the S twist is preferable and should be specified. Twisted unsized nylon yarn or floss, when it is drawn off from the spool and allowed to go free, untwists, losing almost all of the twist that had been put into it. Therefore, for dental floss, the twist given must -be set so it will not untwist in usage. Exposure, for the proper length of time, to live steam is the most satisfactory method. It is especially important that the low twist dental floss here proposed be steam set. Manufacturers should give this matter the necessary attention. Information can be obtained direct from the manufacturers of nylon or from some of their publications.
TOTAL DENIER
The size or total denier of dental floss is important. In making the selection, proper consideration must be given to several different pertinent Factors. The bacterial film pack between two contacting teeth has more or less the form of an irregularly outlined biconcave disc, the thicker portion being at the periphery and the thinner portion at the center (Fig. 5). At the center corresponding to the contact point between the teeth, there is room for only very small amounts of bacterial material. If the margin of the gum has receded from the normal location, then the periphery of the disc is wider (and thicker) on its rootward side.
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The bacterial material between teeth is dislodged and removed by the proper use of the right kind of toothbrush as far as the bristles of the brush can be forced into the space. The optimum diameter of toothbrush bristles has been shown1 to be 007" (about .177 mm.) . The brush therefore cleans between teeth down to where the space is .177 mm. Wide. The remainder of the disc of bacterial material around the contact points must be dislodged and removed by the proper use of dental floss. Soft low twist floss molds and adjusts in shape to fit the space. when it is passed between contacting teeth. Therefore, the diameter of the string should be considerably greater than the .177 mm, to more effectively clean all of the area which cannot be cleaned by the bristles of the toothbrush. The size floss finally decided upon and advocated here is 350 denier, made by plying and twisting together 5 threads of 70 denier 34 filament yam. It has been arrived at after long and tedious experiments with many different sizes, ranging from 1050 denier, the size of the usual waxed nylon floss in dental supply and drug stores, down to 100 denier, which is entirely too small for satisfactory effective use (Fig. 6). The average of 50 separate micrometric determinations of the diameter of 350 denier floss was .267 mm. This is well above the .177 mm. Diameter of the toothbrush bristles (Fig. 7). Although considerable molding and flattening takes place when floss is passed between contacting teeth, it has been found that this 350 denier size effectively dislodges and removes the part of the bacterial film around the contact points which is not removed by the brush. The size passes between contacting teeth with practically as much ease as any smaller size. The greater bacterial film-dislodging and holding capacity favors it over smaller sizes. As the size of floss is increased above this 350 denier size it is found to be a little more difficult to pass between contacting teeth. The increased difficulty is so slight, however, with the near larger sizes, that it could be disregarded, if there were any real need for a larger size. But there is not. This 350 denier size, when properly used, is as effective as larger sizes in cleaning the proximal surfaces of teeth around the contact point and toward, the gingival margin. Another important use of dental floss is cleaning the surface of the tooth at the gingival margin and within the gingival crevice, down to the very bottom. Too large a string must be forced, to pass it into the narrow space between the tooth and the gum. Too small a string does not have as much dislodging and holding or removing capacity as larger sizes. What is needed is the largest size that can be used in the crevices without harmful forcing. It has been found that the 350 denier size can be used within the gingival crevice with as much ease and as much effectiveness as smaller sizes. It molds and flattens (Fig. 3.) when held against the tooth and passes with the greatest ease to the bottom of the crevice. Larger sizes are a little less satisfactory in this regard, therefore, are not as desirable.
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COMMENT
Every person, in any walk of life, who has teeth to save, and everyone who wishes to maintain a reasonable degree of oral cleanliness, must use the right kind of dental floss. Dental floss conforming to the specifications indicated in this paper is the most effective and appropriate for the purpose. Most people do not now know that it is necessary to use dental floss, or how to use it. They must be taught. Those who are interested in teaching personal oral hygiene, and in promoting dental health and personal oral cleanliness, must give proper consideration to dental floss. Manufacturers should be able to conform to the specifications here indicated, without difficulty, whenever the demand arises.
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SUMMARY
Information has been presented indicating the following optimum characteristics of dental floss for personal oral hygiene:
Material - high tenacity bright nylon yarn ("Type 300"), 2 denier per filament ; Construction - made by twisting together 5 threads of 70 denier, 34 filament yarn; Twist - 3S twist; steamset; Size - 350 total denier. Manufacturer's technical designation for this floss is: 70-34/5 S 3 Nylon 300, steamset.
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BIBLIOGRAPHY
1. Bass, Charles C.-The Optimum Characteristics of Toothbrushes for Personal Oral Hygiene. DENTAL ITEMS OF INTEREST, July 1948, pp. 697-718. 2. Bass, Charles C.-The Enamel Cuticle in Relation to the Early Stage of Caries. (To be published soon). 3. Stephan, R. M.-Changes in Hydrogen-Ion Concentration on Tooth Surfaces and in Carious Lesions. Jour. A. D. A, 27:718, 1940. 4. Stephan. R. M. - Intra-Oral Hvdrogen-Ion Concentrations Associated with Dental Caries Activity. Jour. Dent . Res., 25 :257, 1944. 5. Bass, Charles C.-The Enamel Cuticle in Relation to the Early Stage of Periodontoclasia. (To be published soon). 6. Bass, Charles C.-A Demonstrable Line on Extracted Teeth Indicating the Outer Border of the Epithelial Attachment. Jour. Dent. Res., 25 :401-415, 1946. 7. Tentative Recommended Practice for a Universal System of Yarn Numbering. A.S.T.M. Standards on Textile Materials. 34, October 1946, American Society for Testing Materials, Philadelphia. 8. Physical-Chemical Properties and Processing of Nylon Textiles. E. I. du Pont de Nemours & Co., Wilmington, Del.
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*Pg. 926 of the original - The denier designation will be used throughout this paper although the A.S.T.M. Committee D-13(7) has recommended the adoption of the grex system and the Society has accepted it, pending final adoption as standard. Those who wish to convert to grex only need to take the denier number x 1.1111. P930
**Pg. 930 of the original - The author wishes to thank Richard T. Kropf, Director of Research, Belding Heminway Corticelli. New York and Stefan L. Grapnel, Research Engineer. Belding Heminway Corticelli, Putnam, Connecticut, for much helpful technical information and for supplies, from Putnam, of many research samples, most of them specially manufactured to conform to specifications which, as our experiments progressed, seemed to be needed.
***Pg. 930 of the original - A yarn or cord has S twist if, when held in a vertical position, the spirals conform, in direction of slope, to the central portion of the capital letter S, and Z twist if the spirals conform in direction of slope to the central portion of the capital letter Z.
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