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The Influence of Toothbrush Wear on the Variables of Plaque and Gingivitis in Clinical Trials.


Worn toothbrushes may be defined as those toothbrushes displaying splaying or bending of the filaments. Wide variations in toothbrush wear have been observed in groups of research subjects, and more than 73% of such subjects have been shown to use their toothbrushes for periods exceeding three months.[1] An American Dental Association (ADA) study established that 56% of toothbrushes used by the public were excessively worn.[2] Although no correlations have been found between the ability of toothbrushes showing different degrees of wear to remove artificial dental plaque in laboratory models,[3] it has been shown that worn toothbrushes are significantly less effective in plaque removal in vivo.[4]

In a study of human subjects, Daly et al.[5] found no significant differences in plaque scores achieved by those subjects with the highest toothbrush wear, in comparison to those subjects with the lowest toothbrush wear. This research group concluded that toothbrush wear did not result in reduced plaque removal and therefore concluded that the wear status of toothbrushes was not critical in ensuring optimal plaque removal. Previously, few studies have been published on the subject of toothbrush wear and its effect on clinical variables like dental plaque and gingivitis. The very few studies that have been published on this subject have reported contradictory results.


The aim of this study was to observe the rate of toothbrush wear in a group of subjects, and to determine the effects of toothbrush wear on the clinical variables of dental plaque and gingivitis.

Methods and Materials

There were 107 adult Caucasian subjects who participated in this trial. Subjects were selected from individuals seeking treatment at a dental hygiene school for initial therapy prior to periodontal treatment. The average age of the group was 30.4 years (range 19-52) and comprised of 28 males and 79 females. All of the subjects were medically healthy, and were not taking any medication.

After being accepted for participation in this study, plaque scores (using the Turesky Index[6]), and gingivitis levels (using the Loe and Silness Gingivitis Index[7]) were recorded. The subjects then received a thorough professional prophylaxis after which no further professional debridement was conducted for the duration of this study. Subjects were each given a new toothbrush and a tube of toothpaste with standardized instructions in their use. The manual toothbrush used in this study was a standard, flat profile with soft and end rounded filament. It conformed to the ADA guidelines for clinical trials. No other oral hygiene aids were used for the duration of the study. The subjects were assessed at baseline, and weeks 2, 4, 12, and 24. The indices of plaque and gingivitis were recorded immediately after tooth brushing which was performed for a standardized period of time at the dental clinic at each appointment. All clinical data were taken by the same investigator.

Prior to the start of the trial, the investigator was calibrated and found to have a percentage reproducibility in excess of 90%. At each appointment, subjects were required to bring the toothbrushes that had been issued to them at the initial appointment. After the toothbrushes were examined by the clinical investigator, those that showed signs of wear were replaced. Toothbrush wear was determined by observing the brushes visually for distortion or damage to the filaments that was greater than 1 mm from the vertical. At baseline, each subject was given four toothbrushes and instructed to replace each toothbrush once it showed signs of wear. The toothbrush assessment and the issuance of replacement toothbrushes at each review appointment was done by another person in a separate room so that the clinical investigator was effectively blinded as to this aspect of the study. Instructions to return the toothbrush for assessment and replacement prior to their actual appointments were given to those subjects whose brushes were wearing rapidly.

The data derived from the clinical variables of plaque and gingivitis were reduced to whole mouth subject mean scores for statistical analysis. At each appointment, the number of subjects receiving a replacement brush was annotated, and subjects were then classified according to the rate at which their toothbrushes required replacement during the trial period. As a result, two groups were identified and termed "rapid wearers" and "slow wearers." The "rapid wearers" were defined as those subjects who used more than three replacement toothbrushes during the six-month study period, and the "slow wearers" were defined as those subjects who used fewer than three replacement brushes throughout the study. The plaque and gingivitis scores of the two groups were then analyzed using the student "t" test to establish whether significant differences existed in the clinical variables between these two groups.


Of the 107 subjects in the study, 102 were found to have complete sets of data suitable for analysis. Of these, 59 (58%) were in the "rapid wearer" group, and 43 (42%) were in the "slow wearer" group. Table I illustrates both the number of subjects who used more than one toothbrush, and the week at which the first replacement toothbrush was issued. It can be seen that 18.6% of the subjects required replacement toothbrushes by week two, and 46% of subjects required replacement toothbrushes by week four. After this initial period, the number of replacement toothbrushes reduced to 21.5% and 4.9% at the three-month and six-month appointments, respectively. This implies that most of the toothbrush wear occurred in the initial phases of the study and reduced with time.
Table I. Frequency of replacement of
toothbrushes during the trial

                         Week 2    Week 4    Week 12   Week 24

Number of subjects who     19        47        22         5
received at least 1      (18.6%)   (46.0%)   (21.5%)   (4.9%)
extra brush

The week in which the      19        33         6         0
first extra brush was    (18.6%)   (32.3%)    (5.8%)   (0.0%)

It can also be seen in Table I that the majority of individuals who required replacement toothbrushes required them at the fourth week of the study (32.3%), and 50.9% of the replacement toothbrushes were issued in the early part of the study at weeks two or four.

Table II lists the number of replacement toothbrushes issued in the first and second three-months of the trial. From this table, it can be seen that 41 subjects used only one toothbrush in the first 12 weeks of the study, 35 subjects used two toothbrushes, while one subject used as many as six toothbrushes during this period. Nevertheless, 41 subjects could be considered as "slow wearers" as they only used one toothbrush during this period. During the second 12 weeks of the study, 19 subjects used only one toothbrush, 34 subjects used two, and one subject used as many as six replacement toothbrushes. When the overall results of toothbrush replacement are considered, it can be seen that over the six months, 15 individuals used only two toothbrushes whereas 22 individuals used three toothbrushes. Two subjects also used as many as 10 toothbrushes.
Table II. Number of toothbrushes issued during the
clinical trial

                    Number of replacement

                     1    2    3    4    5

Weeks 1-12
(First 3 Months)    41   35   11    7    3

Weeks 12-24
(Second 3 Months)   19   34   33    4    0

Overall             --   15   22   20   16

                    Number of replacement

                     6    7    8    9   10

Weeks 1-12
(First 3 Months)     1   --   --   --   --

Weeks 12-24
(Second 3 Months)    1   --   --   --   --

Overall              6    7    2    1    2

In Table III, the plaque scores for the "slow wearer" and "rapid wearer" groups can be seen at each time point during the study. At baseline the plaque levels for the "rapid" and "slow wearers" were similar with no significant differences between the two groups. Each time thereafter, the "slow wearers" had lower plaque scores than the "rapid wearers." The differences between the two groups were significant at 4 and 12 weeks, with the disparity between the two groups being just below the significant level at week two. By week 24, there was no significant difference between the two groups.
Table III. Comparison of mean plaque scores of rapid wearers and
slow wearers throughout the study

                pre-brushing     Baseline         Week 2
                               post-brushing   post-brushing
                values (SD)           Mean Values (SE)

Slow wearers        3.01           2.28            2.12
                   (0.44)         (0.06)          (0.06)

Rapid wearers       3.05           2.40            2.30
                   (0.32)         (0.06)          (0.06)

Significance                                      p=0.05

                   Week 4          Week 12         Week 24
                post-brushing   post-brushing   post-brushing

                               Mean Values (SE)

Slow wearers        2.41            2.53            2.72
                   (0.05)          (0.06)          (0.05)

Rapid wearers       2.56            2.72            2.78
                   (0.05)          (0.04)          (0.04)

Significance       p=0.04          p=0.01            N/S

The differences in gingivitis levels attained by the two groups are compared in Table IV. It can be seen that initially no significant differences in gingivitis levels were evident between the "slow" and the "rapid" wearers. At weeks two and four, however, significant differences in gingivitis levels were evident between the two groups. After week four, significant differences between the two groups were lost. Nevertheless the "rapid wearer" group showed consistently lower gingivitis scores than the "slow wearer" group throughout the duration of this study.
Table IV. Comparison of mean gingivitis scores of rapid
wearers and slow wearers throughout the study

                             Week 2    Week 4   Week 12   Week 24
                values(SD)          Mean values (SE)

Slow wearers       1.03       0.48      0.34     0.16      0.11
                  (0.34)     (0.03)    (0.02)   (0.02)    (0.01)

Rapid wearers      1.00       0.41      0.27     0.13      0.08
(0.27)            (0.27)     (0.27)    (0.02)   (0.02)

Significance      p=N/S      p=0.046   p=0.01   p=0.07    p=0.08


Most of the toothbrush wear occurred in the early phases of the study. A possible explanation for this observation may be that during the initial phases of the study, subjects were over-enthusiastic and highly motivated. This resulted in considerable toothbrush wear, even two weeks after the start of the study, with the rate of wear lessening with time as subjects became less enthusiastic.

It was also noted that the majority of toothbrushes required replacement for the first time by four weeks after the start of the study. This amounted to approximately 51% of the replacements required, probably for the reasons of early motivation described above. In total, 56% of the subjects required replacement toothbrushes at some time during the study. Therefore, just under half of the subjects did not require a replacement brush at any time throughout the six-month duration of the study. It might then be concluded that the frequency of the need for replacement toothbrushes is highly variable between individuals. Alternatively, this result could be interpreted as a "Hawthorne effect" in which subjects in a clinical trial are shown to display significantly better performance purely because they are more highly motivated because they are participating in a clinical trial.

Other plaque control studies have also highlighted the unexpected improvement in plaque scores observed in subjects participating in clinical trials, and have attributed the enhanced results to these motivational effects and to anticipation of frequent oral examination and recording of plaque scores.[5] Although this might somewhat explain the need for toothbrush replacement early in the study, it cannot account for the totality of this observation. Whether or not a Hawthorne effect might be a factor in this observation, the need for replacement toothbrushes for individuals who are "heavy wearers" as early as two to four weeks after the beginning of a clinical trial should be taken into account when designing clinical trials of tooth brushing efficacy. It could also be argued that in designing clinical trials in which tooth brushing is part of treatment, "rapid wearers" should be identified and considered for possible exclusion from the trial.

A great variation in toothbrush replacement requirements was highlighted. Throughout the course of this study, two individuals required as many as 10 replacement toothbrushes, whereas 15 individuals required only two brushes. Dean et al. reported that 49% of their subjects replaced their toothbrushes more frequently than three every month.[1] The decision to replace toothbrushes was a result of a subjective assessment of wear by the subjects. In addition, an objective wear index was derived and when this was compared with the subjective assessment of individual's decisions to change their toothbrushes, no significant differences were found between subjective assessment and the objective wear index. It may be concluded, then, that a substantial percentage of individuals in a clinical trial (approximately 59% of subjects in the current study) may be classified as "heavy wearers." These individuals may require replacement of their toothbrushes more frequently than three times every month to ensure that the toothbrushes remain at their optimum efficacy during the trial period.

Considerable variation in toothbrush wear was also observed.

Thus the simple classification of "rapid wearers" and "slow wearers" used in this study may not adequately reflect the effect of toothbrush wear. It may be necessary to classify individuals into further subclassifications of "very heavy wearers," "heavy wearers," "moderate wearers," "slow wearers," and "very slow wearers," or to utilize a scale that is even more finely graduated in order to take this factor into account for clinical trials of this nature.

When toothbrush wear is compared to plaque scores achieved, significant differences between "slow" and "rapid wearers" were evident during the course of the trial; although the level of significance was lost at the end of the trial. Therefore, in clinical trials it is important to take this factor into account. The "rapid wearers" demonstrated consistently poorer plaque scores than the "slow wearers." Even though by six months the differences between the two groups had become negligible, in the early stages of the trial these differences became progressively more significant.

It is interesting to observe that after the first assessment period at week two, plaque scores in both groups slowly rose with time. This seems to confirm the Hawthorne effect. It is also well known that motivation of individuals to maintain plaque control regimens assiduously for periods in excess of three months is limited. The reason why "slow wearers" and "rapid wearers" showed no significant difference by the six-month period may also relate to the fact that the toothbrushes used by the "slow wearers" had worn to a state in which they were similar to those of the "rapid wearers."

This study is not in agreement with the results of other studies, however. Daly et al. found no significant differences between those who had the highest and those who had the lowest degrees of toothbrush wear.[5] The Daly et al. study was short-term (nine weeks), and subjects received a professional prophylaxis at each assessment period.[5] Assessments were carried out at three, six, and nine weeks, so that each assessment period represented the effects of only the previous three weeks. Therefore this study can be seen as three consecutive three-week studies rather than a nine-week study. For this study, professional prophylaxis was only given at the initial appointment. This is also a six-month study, so assessments of variables took place over a much longer period of time.

It should be noted that the differences between the two groups in this study were not significant at baseline, and only became significant after 4 weeks, with greater significance at 12 weeks. Therefore the differences between the groups became more significant with time. It is therefore not surprising that significance was not established in the Daly et al. study at the three-week assessment intervals.[5] The two studies are therefore broadly in agreement in that, in shorter periods of time (i.e., two to three weeks), significant differences between "rapid" and "slow wearers" were insignificant. Significance only occurred with time and this could not be ascertained by the Daly et al. study.[5]

Other studies have demonstrated reduced plaque removal with progressively worn toothbrushes and this study tends to agree with such observations.[4] This implies that plaque removal is significantly reduced in those individuals who can be classified as "rapid toothbrush wearers," and as these individuals perform consistently poorer in clinical trials of this nature, it may be wise to consider excluding them from clinical trials where this may be a factor.

Lower levels of gingivitis were evident throughout this study in the "rapid wearer" group, and these were significantly better than the "slow wearer" group at weeks two and four. Although previous observations in this study have demonstrated poorer plaque reduction by the "rapid wearer" group, less gingival inflammation was present in this group. The greatest disparity in plaque removal between the two groups was seen in the early part of the study, and this disparity is reproduced in the assessment of gingival inflammation. This observation has to be taken at face value, as it seems to be contradictory to previous observations in this paper. Also, the generally accepted view is that better gingival health is directly related to better plaque removal. Although it has been shown in any number of studies that accumulation of dental plaque results in gingival inflammation, while re-institution of plaque control results in a reduction in gingival inflammation,[8] this contradicts the observation made in this study. It may be accepted that this observation is incorrect, but since it was reproduced at both the two-week and four-week assessment appointments and maintained at a level that was close to significance throughout the rest of the study, this is unlikely.

Alternatively this observation may simply be a unique observation pertaining to this group. If this result could be reproduced in similar studies in other groups, a reevaluation of the effects of tooth brushing on gingival health may be necessary. It may be that, although removal of dental plaque is essential in order to obtain gingival health, additional secondary effects of massaging or stimulating the gingival tissues during the physical brushing action might provide additional benefits.

Other studies have observed that increased toothbrush wear might be related to longer periods of tooth brushing,[9] the force with which the toothbrush was applied to the tissues[10] and the quality of the toothbrush filaments.[11] Increased tooth brushing activity and/or increased force applied during brushing may therefore have beneficial effects on gingival health, notwithstanding the reduced plaque removal and possibly more tooth abrasion. However, this study was not designed to interpret this unexpected observation, and further study clearly needs to be undertaken in order to determine whether this is a repeatable observation in other groups of subjects, and whether the hypothesis described above is valid.


The need for replacement toothbrushes due to wear is highly variable and ranged from two weekly to more than six a month. A small number of individuals required as many as six replacement toothbrushes during a three-month trial period to ensure that the toothbrushes in the trial remained at their optimal level of efficacy. Also, "rapid toothbrush wearers" had significantly higher mean plaque scores throughout the early part of the study. At the 24-week assessment, statistical significance was lost, indicating poorer plaque control by those individuals.

The differences in plaque removal between "rapid" and "slow wearers" were also significant at both one month and three months. These significant differences in performance groups could be expected to affect the outcome of a clinical trial. As the "rapid wearers" performed consistently worse than the "slow wearers," there may well be an argument for excluding "rapid wearers" from clinical trials of toothbrush efficacy or plaque control. However, gingivitis levels seemed to be affected beneficially in "rapid toothbrush wearers."


[1.] Dean DH, Beeson LD, Cannon DF, Plunket CB: Condition of toothbrushing in use: Correlation with behavioral and socio-economic factors. Clin Prev Dent 1992;14(1):14-18.

[2.] American Dental Association: Survey of family tooth brushing practices. J Amer Dent Assoc 1966;72:1489-1491.

[3.] Dean DH: Toothbrushes with graduated wear: Correlation with in vitro cleansing performance. Clin Prev Dent 1991;13(4):25-30.

[4.] Glaze PM, Wade AB: Toothbrush age and wear as it relates to plaque control. J Clin Periodontol 1986;13:52-56.

[5.] Daly CG, Chapple CC, Cameron AC: Effect of toothbrush wear on plaque control. J Clin Periodontol 1996;23(1):45-49.

[6.] Turesky S, Gilmore ND, Glickman J: Reduced plaque formation by the chloromethyl analogue of victamine C. J Periodontol 1970;41:41-43.

[7.] Loe H, Silness J: Periodontal disease in pregnancy. 1. Prevalence and severity. ACTA Odontol Scand 1966;21:533-551.

[8.] Loe H, Theilade E, Jensen B: Experimental gingivitis in man. J Periodontol 1965;36:177-187.

[9.] Kreifeldt S, Hill P, Calisti L: A systematic study of plaque removing efficacy of worn toothbrushes. J Dent Res 1980;59:2047-2055.

[10.] Fraleigh C, McElhaney J, Heiser R: Tooth brushing force study. J Dent Res 1967;46:209-214.

[11.] Rawls HR, Casella R, Melway-Tullock NJ: An in vitro and in vivo study of toothbrush bristle splaying. J Dent Res 1993;72(5):947-952.

Peter N. Galgut, MPhil, MSc, BDS, MRDRCS, DGDP (U.K.), LDSRCS is senior research fellow in the Eastman Dental Institute, University College, London, England.
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Author:Galgut, Peter N.
Publication:Journal of Dental Hygiene
Geographic Code:1USA
Date:Mar 22, 2001
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