EXPERIMENTAL INJURY OF DOG GUMS
An experiment was undertaken to try to learn something of the damaging effect upon the gums of dogs, of brushes with different size bristles such as are available on the market and represent what the average person would be likely to get (Figs. 5 and 6). Brushes of four different widely advertised makes were purchased from the open market, each having bristles of either .014", .013", or .012" nylon. It was intended to compare the damaging effect of vigorous use of the different makes of brushes and size bristles upon the gums of the animals. This experiment was abandoned because it was found that there was so much damage produced by each of these brushes until no satisfactory comparison could be made between them. Also there would not seem to be any useful purpose in comparing implements, all of which are so damaging as to condemn their use. Under the dissecting microscope one could observe that the gums were badly traumatized, much of the outer epithelial layer was torn away, microscopic bleeding was considerable and the traumatic inflammatory reaction, hyperemia, swelling and weeping which followed were noticeable.
Another attempt was made, using brushes with bristles ranging down by .001" from .014" to 006".* These were all straight trimmed to approximately 7/16" length and an attempt was made by the manufacturer to round the ends of the bristles. Due to limitations in the equipment available at the time, this was only partially successful. There were many side ground, chisel or other sharp shaped bristles, and imperfect rounding of the ends of many of them. However the sharp points and edges were more or less smoothed and the traumatizing effect greatly reduced thereby.
*Large numbers of brushes have been supplied by the Prophylactic Brush Co., Florence, Mass., and made to conform to special specifications which were required as our experiments progressed. Cooperation and technical information were received from ]. R Brown, Jr., their Director of Chemical Research.
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There are four areas in the dog's mouth, all over the maxilla, which seem to be more accessible and better suited for testing the traumatizing effect of brushes, viz., an area on either side extending from the cuspid mesially over the two incisors and an area on either side extending distally from the cuspid over one or two teeth. Here again, in many tests the injury produced by vigorous brushing was greater than anticipated but it was so much less, as the smaller size bristle brushes were used, that the difference was very striking. It was possible to severely injure the gums with the coarser bristle brushes. Visible injury consisting of scratches and hemorrhage could be produced with all sizes down to .009" bristle brushes and sometimes with the .008" size. No visible injury could be produced by either the .006" or the .007" bristles, except occasional hemorrhage from the gingival border where there was more or less gingivitis present.
Lack of any exact control of the amount and force of the brushing, plus the weaknesses of personal observations, limit the usefulness of the conclusions drawn from this experience largely to the individual observer. The author concludes from his observations that the gums of dogs can be injured by brushing them with toothbrushes with bristles larger than .007", and that little or no injury can be produced by bristles of this size or smaller. There may be question as to how far this observation on dogs, for whatever it is worth, is applicable to the human.
SCRATCHING HUMAN GUMS
The author maintains his own teeth and gums free from active disease. No hemorrhage (even microscopic) occurs from his gums. The high state of health is maintained by the proper use of a toothbrush with round end .007" bristles, such as is specified herein, and 350 denier nylon dental floss as specified in the companion paper.1 Although such an experiment would seem superfluous, the damaging or scratching effect of a .012" bristle brush on normally tough and resistant gums was tested as follows:
The teeth and alveolar ridge gingiva on the labial and buccal surfaces of all four quadrants were brushed with the .007" round end bristle brush. Long cross strokes were used and an effort was made to apply the brush to the gums as vigorously as would be done by the average individual in brushing his teeth improperly, as most people do. Washings were collected from the brushed gums by taking normal (85 per cent) saline into the mouth and moving it about gently over the teeth (but not forcing it between them) and gums. This was repeated ten times during a period of fifteen minutes. The washings were collected in a beaker together with washings of the brush and this was brought up to a total of 100 cc by the addition of saline. This was strained through a pad of several thicknesses of surgical gauze to remove bubbles, transferred to large centrifuge tubes and centrifuged at 2300 r.p.m. so as to collect all cellular material. The clear supernatant fluid was poured off, the sediment was resuspended in saline, shaken thoroughly and then centrifuged again. The clear supernatant fluid was poured off, the sediment in the bottom was mixed by shaking and jarring the tube sideways. This concentrated suspension of the sediment was transferred to a slide, covered with a coverglass and examined for red blood cells. None was found present. This indicates that the friction on the gums with this .007" bristle brush did not damage the gums enough to cause escape of even microscopic amounts of blood cells, and also that the brushing did not cause the escape of any blood cells from periodontoclasia lesions between the teeth (there is none present as a result of the proper use of the right kind of dental floss). Similar tests to this have been run previously, from time to time, repeatedly confirming the fact that this .007” round end bristle brush does not injure the gums sufficiently to cause even minute bleeding.
Thirty-five minutes after the above brushing the same areas were again brushed in the same way with a widely advertised brush which had .012” bristles, serrated trim, not rounded. There were many of the usual pointed, chisel shaped and rough ended bristles present (Figs. 7 and 8). Looking at this brush under the microscope one would believe it capable of tearing up almost any tissue except the toughest. However, the alveolar ridge of the gum is one of the most resistant mucous membrane surfaces to abrasion or trauma.
Washings were collected in exactly the same way as previously, so far as possible. The material was prepared by centrifuging and the sediment was prepared for examination as before. There were many blood cells present. These can be differentiated readily from all other cellular and other material. There are an abundance of epithelial cells derived from the surfaces of the mouth and tongue which are constantly shedding hornified pavement cells, in addition to cells torn, by the bristles of the brush, from deeper layers of gum tissue. Although there was an abundance of red cells present, they were not as numerous as would be expected from the force applied and the apparent potential traumatic capacity of the weapon used.
Three or four weeks later, on May 3, the above experiment was repeated, using this time a currently popular so-called "professional" two row brush, serrated trim, .014", unrounded bristles. The preliminary brushing with the .007" round end bristle brush was carried out as described above. No blood cells were found present in the washings. Two hours afterward the teeth and gums were brushed vigorously with the stiff brush. The fact that the gums were being torn up and injured could be felt. Washings were collected over a period of thirty minutes, centrifuged and prepared as before. This time there were many red blood cells present.
The implications of these two experiments have to be accepted by others with reservations on account of the personal factor involved and the lack of absolute controls and quantitative determinations. They prove satisfactorily to the author that sufficient damage to the tissues is done by vigorous brushing with these brushes to permit escape of blood cells through the gums. Greater significance attaches to this observation in consideration of the structure of the gum tissue. There are no blood vessels in the epithelium. The connective tissue papillae which project into the epithelial tissue contain a network of capillaries. To cause even minute bleeding, it is necessary for the injury to extend through the epithelium to the underlying tips at least, of some of the papillae, and for some of the capillaries there to be broken. In this case the rough, sharp pointed, stiff bristles tear through the epithelial tissue and into some of the papillae, opening some of the capillaries. The .007" bristles, having only 1/16 the scratching strength of the .014" bristles, do not appreciably injure the thick tough gingival epithelial tissue in the same way (see Table 2 ).
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PUNCTURING STRENGTH OF BRISTLES
Obviously the ability of a sharp pointed bristle to puncture a tissue depends upon its stiffness which, in turn, is governed by size - all other things being equal. A sharp pointed object, when forced against a tissue, either penetrates the tissue or it bends. The values in Table 1 indicate that the .007" bristle would withstand only 1/16 as much force before bending* as the .014" size. In the same way as we have arbitrarily interpreted this information as indicating the different size bristles, we may also interpret it as indicating their "puncturing strength." The relative “puncturing strength” of the .014" bristles is therefore about 16 times that of the .007” size (see Table 2).
Numerous experiments have been carried out in an effort to ascertain the ability of sharp pointed toothbrush bristles to puncture the gums. The most satisfactory and conclusive evidence was obtained by tattooing the gums of dogs with brushes dipped in tattoo ink (powdered graphite from an ordinary indelible lead pencil was used) and applied vigorously so as to press the sharp pointed bristles firmly against the gums.
Permanent tattooing of skin or mucous membrane requires that the pigment be carried to, and in fact through, the basal layer of epithelial cells. Thus, the points carrying the pigment must penetrate to this depth. The epithelial tissue of the alveolar ridge gingiva is many cells thick and the tips of the papillae, where the basal layer lies nearest to the surface, are relatively deep. To permanently tattoo this part of the gum requires deep penetration by the points. It was found that the gums could be tattooed heavily, showing that the points of the bristles do penetrate the epithelial tissue. However, the pigment gradually faded (probably grew out) and usually disappeared within from a few days to about three weeks. This is interpreted as indicating that the points of the bristles do not penetrate the basal epithelial layer.
It was quite different when the thinner mucous membrane over the maxilla within the buccal or labial sulci and just above the alveolar ridge gingiva, was tattooed. Not only was it easy to tattoo but the pigment was permanently retained in the tissue. These results have been obtained repeatedly using .014" sharp pointed bristles (Figs. 5, 6 and 7), On the other hand it has not been possible to tattoo dog gums in the same way with the .007" bristles. In addition to the rough cut bristles similar to those of commercial toothbrushes, bristles of this same .007" size were ground on an abrasive belt in a way to produce long keen sharp points (Fig. 9). In repeated tests it was not possible to tattoo the dog's gums with these sharpened .007" bristles. When pressed against the gums these sharpened bristles bend before they penetrate enough to tattoo even superficially and temporarily. We can conclude that the "puncturing strength" of the .007" bristles is not sufficient to permit harmful puncture damage to the gums.
*McFarlane9 has shown that the force required to bend or buckle a filament varies inversely with the square of the length, instead of the cube, as in deflection.
TRIM
Years ago many of the toothbrushes were straight trimmed, making all bristles about the same length. Later serrated trim became more and more popular until now practically all brushes are trimmed in this way (Figs. 5 and 6). The outside bristles of each tuft are trimmed considerably shorter than those in the center. This gives more or less of an angular cut to nearly all of the bristles. Many of them have sharp pin- or chisel-shaped points (Fig. 7). These are the points which puncture the tissue when used with sufficient force against the mucous membrane. They also scratch and tear the gum when used vigorously with long strokes.
The idea is well founded that the serrated trim, with bristles in the center of each tuft considerably longer than those around the periphery, permits the longest bristles of current coarse bristle brushes to enter deeper into pits, grooves, depressions and narrow spaces on and between the teeth. These are the most important areas to be cleaned by the toothbrush. However, in the case of the usual size stiff bristles, the relatively small number of long bristles hold off and prevent effective application of the shorter bristles, thus greatly reducing the number of potentially effective bristles in the brush.
On the other hand when a straight trimmed brush, wherein all bristles are of about equal length (Fig. 10), is applied properly, every bristle is potentially effective in cleaning any area to which they are applied, provided the bristles are small enough .007”. Pressed against the irregular surfaces of the teeth, bristles that come, for the moment, against high places are deflected or bent allowing others to enter the depressions. This can be observed most satisfactorily by pressing and manipulating the brush against the occlusal surface of extracted molar teeth held in the field of a dissecting microscope and under incident light. With the proper short back and forth "vibratory" movement of the brush held firmly against the surface being cleaned, many bristles are applied effectively to the most important areas. This is made possible by the low bending resistance of the .007” bristle. Therefore, it is apparent that the total number of potentially effective bristles in a straight trim .007” bristle brush is several times greater than the number in a serrated trim coarse bristle brush.
SIZE OF BRISTLE IN RELATION TO THE SPACES TO BE CLEANED
The dimensions of pits, grooves and spaces on or about teeth vary greatly. However, the smaller the diameter of the bristle the smaller spaces it can enter. A .007" bristle can enter a space which is only one-half the width that can be entered by a .014” bristle (Fig. 4), Likewise the smaller size bristle can go deeper into a cone or wedge shaped space, such as the pits and fissures on teeth and sulci between them.
The smaller size .007" bristle is of still greater importance in cleaning the teeth at the gingival crevice. This size bristle not only is applicable to the tooth at the exposed gingival margin but it also enters the crevice (Fig. 3) to considerable depth, thus mechanically dislodging, and promoting removal of bacterial and other soft material on the tooth within the crevice. Ideally, we would like to clean the tooth down to the zdeac. This line is at the inner border of the bacterial film pad and the concretion on the surface of the tooth within the gingival crevice. The depth to which this material on the tooth extends within the crevice varies greatly on different teeth and at different locations around a given tooth.
When the brush is properly manipulated so as to direct and apply the ends of the bristles to the entrance to the gingival crevice, some of the small .007” bristles enter the crevice and go as far as they may, until they meet with sufficient resistance to deflect or bend them. Bristles of this size bend without injuring the tissues of the gingival crevice. However, they do have enough strength, before bending, to break up and dislodge much of the soft material there.
There is usually some hemorrhage from gingival crevices brushed in this way for the first time due to the presence of more of less gingivitis. Subsidence of the inflammation and healing of the tissue within the crevice is often so rapid, following brushing with this size bristles (and cleaning the interproximal crevices with the right kind of dental floss) at night before retiring, until little or no bleeding occurs at the next cleaning, or subsequently. Only where there are deep, extensive periodontoclasia lesions and under especially unfavorable conditions may bleeding occur again, indicating active disease at the particular location where effective cleaning had not been accomplished.
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NUMBER OF BRISTLES PER TUFT
The total number of bristles in each tuft may vary slightly. About 80 to 86 of the .007" bristles per tuft make them of proper size and allow sufficient space between the bristles of different tufts to favor effective application in cleaning the teeth. This much spacing also favors cleaning and drying of the brush after it has been used.
LENGTH OF BRISTLES
Considerable experimenting with bristles of different lengths has been carried out. The length finally decided upon for brushes for use by adults is 13/32". The author has found that this is the right length of .007" bristles for the most effective use in cleaning the most important locations on the teeth which can be cleaned with the brush. Bristles longer than this tend to bend easier and are less effective and less applicable to some of the areas of the teeth which we desire to clean with the brush. Shorter bristles tend to be less effective in penetrating spaces on and between the teeth, and those within gingival crevices. The 13/32" bristle brush is manipulated with greater ease within the mouth in brushing the teeth than brushes with either longer or shorter bristles.
ROUNDING THE ENDS OF THE BRISTLES
It is only necessary to see the ends of bristles of current types of toothbrushes under the microscope (Figs. 4, 5 and 6) and to recall the damage that almost all who have used them consistently have sustained, to realize that there is urgent need for improvement in this regard. The sharp pointed, chisel shaped, rough ended (Fig. 11) bristles must be corrected. This can be accomplished readily by grinding and finishing the ends of the bristles so as to eliminate all sharp, rough-cut points and edges, and to make the ends smooth and as nearly hemispherical in shape as possible (Fig. 12).
Since the "scratching strength" and the "puncturing strength" of the .007" bristles is so much less than that of coarser bristles, it is obvious that the need for rounding and smoothing them, to prevent injury to the gums, is very much less (Fig. 13). However, the rounded and smooth end bristles are also more appropriate for entrance and penetration of narrow spaces, such as gingival crevices, and for effective application within the crevices. Also the total potential area of such a bristle for dislodging and removing soft bacterial material there is much greater than that of a sharp pointed and rough cut bristle (Fig. 14).
The rounding and finishing* of the bristles can be accomplished by holding and revolving the brush endwise against a rapidly moving abrasive surface such as the flat side of a grinding wheel or a "sander belt". By regulating the pressure and the duration of the grinding, it is possible to finish the ends of the bristles so that most of them are almost perfect hemispheres (Figs. 10, 15). There is usually more or less angular grinding of some of the outside bristles due to the flexibility of the .007" size, but all objectionable sharp edges and points are eliminated from them.
Holding and manipulating the brush by hand against the grinding surface, the author has been able to round and finish the bristles entirely satisfactorily When the demand justifies, it can be done better and on a large scale by mechanical means. But this is a simple problem for the manufacturer to work out and need not be discussed here.
REDUCED SIZE BRUSH FOR CHILDREN
There is need for a similar brush of reduced size for the use of young children before they are old and large enough to use the regular size. Although the author's most intensive and thorough studies and experiments have applied especially to the diseases and conditions to be met in older people, he has carried out sufficient additional studies and tests relative to the problem in young children to permit laying down specifications for the most suitable toothbrush for their use.
The child's brush should correspond to the regular brush in every way except it should be of a reduced size. It should conform approximately to the following dimensions:
Over-all length 5", width 6/16"; bristles .005" high quality nylon straight trim, finished to 11/32" length, ends smooth and rounded. (For stiffness and relative scratching and puncturing strength of this size bristles see Tables 1 and 2).
*One manufacturer claims a patent on rounding the ends of the bristles on serrated trim brushes. The process as I understand it, is not intended for, or adapted to, rounding and finishing the bristles of straight trim brushes. It probably can be modified for this purpose.
COMMENT
Every person who has teeth to save and who wishes to maintain oral cleanliness must have the right kind of toothbrush and must know how to use it correctly. The brush herein specified meets the needs adequately for all purposes and should replace current inappropriate and harmful makes.
The manufacturer should be able to supply brushes conforming to the requirements indicated, whenever there is demand for them. Teaching effective use of the toothbrush should be done by dentists, dental hygienists, public health nurses, parents, teachers and others who are interested in promoting oral health.
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SUMMARY
The following optimum characteristics for toothbrushes for personal oral hygiene, and reasons therefore have been presented:
1. Plain straight-handle design; over-all length about 6", width about 7/16"; 3 rows of bristles, 6 tufts to the row, evenly spaced.
2. High quality nylon bristles, about 80 per tuft, .007" diameter, straight trim, finished to 13/32” length.
3. Ends of bristles ground and finished to hemispherical shape or at least enough to eliminate all sharp points and rough edges.
4. A similar brush of reduced size for the use of young children should have an over-all length of about 5", .005" bristles, finished to 11/32" length.
REFERENCES
1. Bass, C. C.-The Optimum Characteristics of Dental Floss for Personal Oral Hygiene. (To appear in DENTAL ITEMS OF INTEREST.)
2. Bass, C. C.-The Enamel Cuticle in Relation to the Early Stage of Caries. To be published soon.
3. Stephan, R. M. - Intra-Oral Hydrogen-ion Concentration Associated with Dental Caries Activity. J. D. Res., 23 :257, 1944.
4. Bass, C. C. - The Enamel Cuticle in Relation to the Early Stage of Periodontoclasia; (To be published soon).
5. Riggs, J. W. - Suppurating Inflammation of the Gums and Alveolar Process. Penn. J. D. Sci. 3 :99, 1876.
6. Bass, C. C.-The Habitat of Endamoeba Buccalis' in 'the Lesions of Periodontoclasia. Proc. Soc. Exp. Biol. and Med., 66: 1947.
7. Bass, C. C. - A Demonstrable Line on Extracted Teeth Indicating the Location of the Outer Border of the Epithelial Attachment: 1. D. Res., 25 :301, 1946.
8. Kitchin, P. C. - The Prevalence of Tooth Root Exposure and the Relation of the Extent of such Exposure to the Degree of Abrasion in Different Age Classes. J. D. Res., 20 :565, 1941.
Macfarlane. D. W. - The Stiffness of Toothbrushes. Brit. D. J., 79 :187, 1945.
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Erratum from the original
P. 704 "During recent yars,"
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