The Optimum Characteristics of Dental Floss for Personal Oral Hygiene*
by Charles C. Bass, M.D.** School of Medicine, Tulane University of Louisiana, New Orleans, La.
*Studies promoted by facilities to which the author has had access at the School of Medicine, Tulane University of Louisiana, and by aid for equipment and supplies provded by the University.
**School of Medicine, Tulane University of Louisiana, New Orleans, La.
Both caries and periodontoclasia, the two diseases from which almost all loss of teeth results, can be prevented by effective personal oral hygiene. Except for some advanced-stage lesions and some unusual conditions, control and prevention of further progress of these diseases, after they have started, can be secured in the same way. These two diseases cannot be thus prevented and controlled by any other practical method now known. Any person, to prevent the initiation and further progress of caries and periodontoclasia, must clean his teeth right, every night before retiring. If he also cleans them at other times, this contributes to greater personal oral cleanliness. The only way now known whereby one can clean his teeth well enough to prevent caries and periodontoclasia, and to maintain decent oral cleanliness, is by the proper use of the right kind of bothtoothbrush and dental floss. The functions of dental floss and the specifications of floss necessary for the best results, are presented here. In a companion paper1, the functions of the toothbrush and specifications for the most effective and most appropriate brush are presented.
FUNCTIONS OF DENTAL FLOSS
Proper use of dental floss is necessary to clean the considerable area on the proximal surfaces of teeth, which cannot be reached by the bristles of the toothbrush. Proximal caries occurs at and aroundthe contact point in these areas. In the early stage there is only partial decalcification, giving rise to the "white spot" which, at first, is microscopic in extent, but it gradually increases, if the etiological conditions are prolonged. As the lesion extends and enlarges, and as the decalcification process is continued, sooner or later the enamel breaks down and a cavity develops. This is the more advanced stage of caries. Substantiating similar observations of others, I have shown2 that the film of bacterial material beneath which caries begins and progresses consists principally of filamentous types of organisms. One end of the organism is attached to the enamel cuticle from which it extends outward toward the surface of the film. The deeper part of this bacterial film is a compact mass of more or less parallel microorganismal filaments radiating from the surface of the enamel. At the outer surface of the film there are the growing ends and fruiting heads of these filamentous organisms, among which there are numerous other organisms of many varieties from the oral cavity. The chewing and masticating process thoroughly and heavily inoculates food material with the great variety of bacteria in the saliva, which are derived from all of the different surfaces within the mouth. Such inoculated food material, when lodged and retained upon the continuously present filamentous bacterial pad, is rapidly decomposed, not only by the bacteria from the saliva which is mixed with the material, but also by the growing microorganisms at the surface of the pad. If favorable carbohydrates are present, acids are produced. It has been shown" that the application of sugar solutions to the bacterial pad ("material alba") is quickly followed by marked increase in acidity. Acids produced at the surface of the film are taken up and carried, as if by a sponge or wick, down to the surface of the tooth where they attack the enamel. Continuation and frequent renewal of these conditions, although microscopic and microchemical in nature, result in the early white spot stage of caries, and ultimately the later cavity stage. The purpose of the use of dental floss, so far as caries and personal oral cleanliness are concerned, is (a) to dislodge and remove any decomposing food material that has accumulated at the proximal surfaces since the previous cleaning and which cannot be reached and removed by the brush, (b) to dislodge and remove as much as possible of the growth of filamentous and other organisms that has accumulated in these protected caries susceptible areas, since the previous cleaning. The lesion of periodontoclasia begins at the gingival margin and is initiated by the irritation and inflammation (microscopic at first) of the marginal gingival tissue by compacted and encrusted bacterialmaterial on the enamel cuticle. Normally the marginal gingival tissue rests upon the soft, smooth,non-irritating enamel cuticle. When, however, any rough hard material is superimposed upon the cuticle, it acts as a-mechanical irritant like a foreign body. Once this hardened incrustation is established theresulting inflammation and exudation tend to promote its continuation and extension. Lime salts aredeposited. Gradually the calculus and the overlying bacterial film impinge more and more upon theinflamed gum which recedes as the disease progresses.
In the further advanced lesion, on one side there is an inflamed suppurating surface of epithelial tissue, extending from the gingival margin down to the very bottom of the lesion, where is located the outer border of the epithelial attachment and the zone of disintegrating epithelial attachment cuticle6. On the other side is the tooth on which there is more or less rough hard calculus to which is attached, and to the tooth around it, a pad of soft bacterial material consisting of a compact mass, of variable thickness, of stems and filaments extending outward toward the space (“pyorrhea pocket”) and downward toward the very bottom of the lesion (Fig 1). The outer portion of the pad attached to the tooth within the lesion, consists largely of radiating filaments which protrude at the surface as a thickset carpet-like pile of growing, branching and fruiting stems of leptotrichia, among which there are large numbers of other microorganisms. The purpose of the use of dental floss, so far as periodontoclasia and personal cleanliness in this location are concerned is, (a) to dislodge and remove any food material that has accumulated at the gingival margins, and in the gingival crevices between the teeth, since the previous cleaningand which is not removed by the brush, (b) to dislodge and remove as much as possible of the growth of bacterial material upon the tooth or the superimposed calculus, that has accumulated there since the previous cleaning. Keeping clearly in mind the functions for which dental floss is to be used relative to caries, periodontoclasia and personal cleanliness, we may proceed to consider the characteristics of floss that will be most effective for the purpose.
NYLON MOST FAVORABLE MATERIAL
Before the recent war the best material available, and the most widely used for dental floss, was silk. During the war silk became unavailable and synthetic substitutes were tried. All of these were quite unsatisfactory. Nylon was not available for this purpose during the war but it has been taken up by manufacturers since and is now quite generally used in place of silk. Nylon is so far superior to silk for dental floss for personal use that the latter is not likely ever to be used for this purpose in the future. There are several advantages of nylon over silk - nylon can be made of uniform high quality whereas there is considerable variation in the quality of different lots of silk through trade sources; the individual filaments of nylon are cylindrical, smooth and uniform in size (Fig.2) for the selected type, whereas those of silk are irregular in size and shape: nylon can be supplied with filaments of whatever size is found to be best for the purpose; the tensile strength of high tenacity nylon is somewhat greater than that of silk; the abrasion resistance of nylon, when drawn over rough surfaces, is considerably greater than that of silk; the elasticity of nylon is greater than that of silk, allowing it to pass through close places and over rough surfaces with less filament breakage.
The filaments in nylon yarn are continuous and free from loose ends whereas silk may have loose ends. This is especially objectionable in the low twist floss, without wax or size, which our studies have shown to be necessary for most effective use. The twist in the desirable low twist nylon floss can be set by steaming whereas objectionable size or wax would be required for silk. "The term 'nylon' refers to a 'family' of chemically related products and is a 'generic term' for any long-chain synthetic polymeric amide which has recurring amide groups as an integral part of the polymer chain.” There are two kinds of "66" nylon yarns made today-normal and high tenacity yarns. Only the high tenacity yarn should be considered for dental floss. It has higher tensile strength, greater abrasion resistance and adequate stretchability. High tenacity nylon yarns have a tenacity of 6 to 7 grams per denier* and an elongation, before break, of approximately 15 to 20 per cent.
*The author wishes to thank J. D. Zerbe, Jr., Technical Service, Nylon Division, E. I. du Pont de Nemours and Co., Wilmington, Del., for much helpful technical information and for generously supplying samples of nylon yarn.
OBJECTIONS TO WAX OR OTHER SIZE
A piece of nylon dental floss is composed of a large number of separate, very small, somewhat elastic filaments. When it is drawn over an object like the surface of a tooth, the position of the filaments, with relation to each other, is adjusted according to the force or pressure applied to the different filaments. The filaments spread out and the round string tends to flatten out and widen (Fig. 3). Such a flattened string composed of many loose nylon filaments, when drawn either crossways or obliquely against a surface covered with bacterial film or other microscopic material, dislodges and holds between the filaments, the maximum amount of such material. Each separate filament tends to scrape off or move some material. The spaces between the filaments receive and hold microscopic particles which are removed with the floss. If the filaments are held together by the usual waxing treatment, the spaces between them are filled by the wax. The floss has the effect, in this regard, of a single solid cord. Separate mechanical action of the many filaments is prevented and the purpose to hold and remove large numbers of microscopic particles between the filaments is defeated, by the presence of the wax. When an object is forced to pass between the contact points of two teeth in normal direct contact, either the teeth are forced apart sufficiently to permit the object to pass, or the object yields in shape, more or less, and separation of the teeth is required. For instance, a metal wire forced between two contacting teeth, forces them apart as much as the diameter of the wire; heavily waxed or sized nylon floss, under pressure, tends to yield somewhat in thickness, hence less separation of the teeth is produced when it is passed between contacting teeth; small low-twist nylon floss, not waxed, yields readily to pressure, tends to flatten and pass a given point in the close space, only one or a few of the elastic filaments at a time, hence, only negligible movement of the teeth is necessary to allow it to pass with ease. When a piece of the usual form of waxed dental floss is drawn over the surface of a tooth while it is held in the field of a dissecting microscope, it can be seen that a thin film of wax (Fig. 4) is left on the area against which the waxed floss was applied. Another satisfactory experiment is to draw waxed dental floss, back and forth, over the surface of a finger nail. The film of wax left on the nail can be seen with the unaided eye, and the waxy, sticky material can be recognized by feeling it with the finger. Similarly, when a piece of the same kind of waxed floss is drawn between two contacting teeth and then back out, as in cleaning the teeth, a thin film of wax is left on the contacting surfaces and also on the other surfaces against which it was pressed. This film of wax, although of microscopic thickness, between the contact points of persons who have full sets in normal contact, is sufficient to separate the teeth enough to cause more or less soreness of the sockets for a few hours. The author observed this often when he used to use waxed dental floss in cleaning his own teeth and has confirmed it experimentally several times since. Likewise it has been confirmed by the experience, of several volunteer subjects. It would be difficult to determine whether such temporary microscopic separation of the teeth daily, and the soreness of the sockets caused thereby, is harmful. At any rate it is not desirable. Although it is undoubtedly better than not to use any floss at all, the lessened effectiveness and possible harmfulness are valid, very definite, objections to waxed floss for personal oral hygiene.