In many countries, caries prevalence has considerably declined in several age groups during the past 40 years. However, there is little evidence that oral hygiene per se has remarkably contributed to this oral health improvement.1 This raises the question whether techniques and means usually recommended for daily oral hygiene are appropriate and validated by the best available evidence. The present chapter will restrict this question to manual toothbrushes and techniques and scrutinize the design of manual toothbrushes and usual oral hygiene procedures.
Until a few years ago, there was a generally accepted idea of what a “good” manual toothbrush would look like. It should have a short head, a flat bristle field with many bristle tufts (multitufted) arranged in parallel, and end-rounded nylon bristles (Fig 8-1). However, this toothbrush shape did not originate from scientific evidence, but from tradition and as a result of the available manufacturing techniques. Basically, a toothbrush in its development is nothing more than a small broom used to clean small things, namely the teeth. Looking at a broom or even a clothes brush, they have essentially the same shape as the toothbrush described above: parallel bristles, many tufts, and a flat bristle field (Fig 8-2). However, a broom has been designed to clean even surfaces, such as floors. In contrast, when looking at a dental arch, it becomes clear that such a broom is basically unsuitable for cleaning the convex surfaces of teeth with fissures, interproximal spaces, and the gingival sulcus (Fig 8-3).
Developments in production technology today enable the manufacture of differently designed toothbrushes. This in particular relates to the bristle field. Although toothbrushes with V-shaped bristle field were also produced earlier, with the technique available at that time, it was not possible to round off the bristle ends that stood in the “valleys” of the bristle field. Therefore, the so-called V-toothbrushes were rejected at that time. For several years, however, the toothbrush industry has been able to round off the bristle ends in the “valleys.” In addition, it is now possible to round the bristle ends first and then attach them in the brush head. Various methods are available for this: In the injection molding process, the bristles are first brought into the correct position and then the brush head is sprayed around the bristles. In the insertion process, the bristles are pressed into the heated and thus soft material of the brush head. When the brush head has cooled, the bristles are firmly and substantially bonded to it, in the same way as by injection molding. In the welding process, bristles and brush head, which must then consist of the same material, are welded together by simultaneous heating. These new joining techniques not only allow new designs of bristle fields, but also a virtually gap-free fastening of the bristles in the brush head (Fig 8-4). This is important in view of the recurring discussion of the toothbrush as a germ reservoir. In the conventional method, the bristle tufts are anchored in the brush head with the aid of metal staples, which is not possible without a gap.
In this section, the classic criteria of manual toothbrush design are questioned and, if justified by evidence, replaced by new ones.
Rounded nylon bristles
Although there is no scientific research, it is now agreed that the bristles of a toothbrush should be made of nylon or a similar plastic. Natural bristles are rejected for hygienic reasons (bacterial colonization of the marrow channels of the bristle hairs) and because they splice quickly. Many descriptive in vitro studies have been done with respect to the end-rounding quality of toothbrush bristles. However, there is little evidence of the importance of bristle end-rounding with respect to the prevention of soft-tissue trauma. Only one study showed that the extent of gingival lesions was by 30% greater when not-end-rounded bristles were used.2 In conclusion, end-rounded nylon bristles are recommended even if scientific evidence is low because there is no convincing alternative (Fig 8-5).
Flat multitufted bristle field
The flat bristle field of a toothbrush, which has long been regarded as ideal, generally seems less suitable for cleaning teeth. Since a tooth surface has no flat, but only convex surfaces and the optimum cleaning is achieved by maximum contact between the brush and the tooth, a good toothbrush should rather have a concave bristle field, ie, a form matching to the dental arch. One possibility to achieve this is that the outer bristles are longer than the inner ones (Fig 8-6). The present author’s investigations have also shown that using a toothbrush with a dense, flat bristle field makes it difficult to clean the fissures. When the toothbrush is placed on the chewing surface of the tooth, a wedging effect occurs which prevents the bristles from penetrating deeper into the fissure (Fig 8-7). If the bristles are packed less densely, this works much better (Fig 8-8), even if the bristles of a toothbrush hardly succeed in reaching the fundus of a fissure perfectly. The same applies to the likewise very narrow interdental spaces and the gingival sulcus, a critical area especially with regard to the development of gingivitis and periodontitis. A toothbrush that has compact shorter bristles with more protruding less dense thin bristles has also been shown to clean these hard-to-reach areas better than a conventional brush (Fig 8-9).3,4
These are only two examples of modern hand toothbrushes with improved cleaning effect. Another aspect that is becoming important in the development of new toothbrushes is that it is increasingly clear that good oral hygiene can also have side effects: hypersensitive teeth, visible hard tissue defects, and trauma to the gingiva and mucosa are increasing. This is largely due to false and with-too-much-force-applied tooth brushing techniques. First and foremost, therefore, the user must be trained in the most careful but also gentle care technology possible. The toothbrush industry can also help tackle this problem by providing a range of toothbrushes with different properties. Here arises, for example, the question about bristle stiffness, eg, whether a toothbrush should have rather hard or soft bristles.
In former times, hard toothbrushes in particular were preferred and then a change to the medium-hard variant took place. Increasingly, soft toothbrushes were recommended in the recent past under the impression of a more intensive mechanical oral hygiene and associated side effects. In fact, some of these toothbrushes have been shown to clean as well as the compared medium-hard toothbrushes with less gum trauma.5,6 Since these comparisons of toothbrushes differed not only in bristle stiffness but also in the shape of the bristle field, the equally good cleaning effectiveness could not be unequivocally justified by the degree of hardness of the toothbrushes. For this reason, the present author evaluated similar toothbrushes with different degrees of hardness (hard, medium, soft) in vivo in terms of cleaning effectiveness and gingival trauma. The result was unambiguous. Toothbrushes with hard bristles caused more gingiva injuries, but they also showed a much better cleaning effect. Toothbrushes with medium-hard bristles were in the middle for both parameters.7 A recent in vitro study by the present author’s working group has also shown that soft toothbrushes lead to more abrasion of dentin than hard or medium-hard toothbrushes.8 This sounds surprising at first, but is due to the fact that the bristles of the soft toothbrush bend at the ends and thereby lead to a more flat surface contact with the tooth surface than is the case with hard bristles. Due to the surface contact with the tooth surface, the toothpaste, which is indeed the abrasive, is brought more intensively into surface contact with the dental hard tissue and thus is more abrasive. This observation was confirmed by a study by Wiegand et al.9
Size of the brush head
One of the key requirements for the design of a manual toothbrush used to be a short brush head. That sounds reasonable, because the oral cavity is a narrow space with hard-to-reach areas, where it is easier to maneuver with a small brush head than with a large one. On the other hand, it is obvious that a larger broom can clean a larger area at the same time. Since the time spent for brushing teeth is one of the most crucial factors and is usually not long enough,10,11 it seems questionable whether a small toothbrush head really is an advantage. In a clinical study over 8 weeks, the present author examined two toothbrushes that differed only in the size of their brush head with respect to biofilm removal and improvement of gingivitis (Fig 8-10). For biofilm removal, there was a tendency for superiority of the toothbrush with the larger head after 8 weeks, but this was not statistically significant. However, with regard to the reduction of gingivitis as measured by the Papillary Bleeding Index (PBI), the larger toothbrush was significantly superior. There was an improvement of 0.426 in relation to 0.178, which is also a clinically significant difference.12
From the findings presented so far, the following desired design features for a manual toothbrush can be derived:
- A toothbrush should have end-rounded nylon bristles to prevent gingival injury.
- A toothbrush should have a bristle field that is adapted to the shape of the tooth and the dental arch for optimal cleaning (shape congruence). Single bristle tufts and a less densely packed bristle field improve the biofilm removal in hard-to-reach areas.
- Patients with poor oral hygiene who do not show soft tissue injuries should use a hard toothbrush.
- Patients with good oral hygiene and existing soft tissue injuries should use a soft toothbrush.
- Patients with brushing abrasions on dental hard tissue should use low abrasive toothpaste, preferably in combination with a hard toothbrush (unless they have soft tissue defects at the same time). In addition, it is of course particularly important to establish a gentle brushing technique with not too much contact pressure.
- A slightly larger brush head seems to clinically improve cleaning performance.