The Discussion

The Clinical Effect of Dentifrices Containing Stabilized Stannous Fluoride on Plaque Formation and Gingivitis - A Six-Month Study with Ad libitum Brushing⁴

Discussion A six-month, double-blind clinical study was conducted to evaluate the effect on gingivitis, relative to a sodium fluoride control, of two dentifrices containing 0.454% SnF2 stabilized with different levels of sodium gluconate. To be eligible for the study, subjects had to have a minimum of five sites which bled (individual sites with a score of 2 or 3) during the Gingival Index examination. This restriction was intended to enable recruitment of a clinical population which exhibited mild to moderate levels of gingivitis. As can be seen from the baseline data, the gingivitis and gingival bleeding scores for the treatment groups at the start of the trial were approximately 0.7 and 18, respectively. This confirms that qualifying criteria of five bleeding sites were successful in selecting a clinical population with the targeted level of gingivitis. For perspective, subjects in the present study had approximately 10% of their gingival sites bleed upon probing, whereas in a recent survey of oral health in employed U.S. adults, it was observed that about 6% of gingival sites bled upon probing.¹⁹

At the start of, and throughout the course of the study, groups were well-balanced with respect to all clinical parameters and demographic characteristics. Review of the results show that the gingivitis scores of the stannous fluoride groups were significantly lower than the control group at both the three-and six-month examinations. However, there were no significant differences between the two stannous fluoride dentifrices with respect to gingivitis. This suggests that both stabilization systems were equally effective at delivering therapeutic levels of stannous fluoride during tooth brushing.

There was a clear trend toward reduced gingival bleeding for both the lowGluc and highGluc stabilized stannous fluoride dentifrices relative to the control group. This trend was strongest for the lowGluc stabilized stannous fluoride dentifrices where a statistically nonsignificant 30.5% reduction in gingival bleeding was seen. It should be noted that while this study was designed to have adequate statistical power for detecting significant differences between treatment groups with respect to gingivitis, it was not sized to demonstrate that differences of a similar magnitude in gingival bleeding were statistically significant.

The significant reductions in gingivitis seen in this study for the stannous fluoride groups were not accompanied by corresponding decreases in plaque scores. There are a number of possible explanations for this observation. One possibility is that clinical assessments of plaque coverage may be affected by artifacts associated with stannous fluoride use. Tinanoff and Weeks²⁰ and Rykke et al.²¹ have observed an increased deposition of the pellicle protein layer as a result of topical stannous fluoride use. Several authors have speculated that this "thickened" pellicle layer could complicate plaque area measurements.^3,9,22 It is possible that relative to other, non-stabilized stannous fluoride products, the increased bioavailability associated with the stabilized stannous fluoride dentifrices might confound plaque measurements to an even greater extent.

Another possible explanation for not observing plaque reductions is that stannous fluoride, through its inhibition of bacterial metabolism, improves gingival health by reducing plaque virulence.^3,6,23 Such a qualitative effect would not necessarily be expected to lead to a corresponding quantitative decrease in plaque.

As would be expected, the extended use of stannous fluoride dentifrices resulted in more extrinsic dental stain than the control group. To investigate whether tooth staining might result in examiner bias, subjects wore pre-fabricated, custom-made tooth covers at the six-month but not three-month examination. This allowed for a comparison of the observed stannous fluoride effects with and without the use of the covers. As can be seen from the three- and six-month efficacy results (Table III), the measured effectiveness for the stannous fluoride dentifrices were unaffected by the presence or absence of tooth covers. This indicates that during the assessment of gingivitis in this study, the presence of stain did not bias the gingivitis examiner. The results from this trial are in agreement with a previously published study where tooth covers were employed during the gingivitis examination to mask antimicrobial stain.²⁴ The outcome of this trial suggested that well-trained examiners were capable of focusing on the criteria of the Gingival Index and not be influenced by the presence of stain.

In order to assess the possible impact of this increased staining on dental prophylaxes, the time and effort that was required for dental hygienists to complete each prophylaxis, as well as their assessment of the amount of stain present, was determined. Interestingly, the increased tooth staining associated with the use of the stannous fluoride dentifrices did not appear to translate into increased prophylaxis efforts on the part of the dental hygienists. This can be seen when the total prophylaxis times for the control and stabilized stannous fluoride groups are considered. It was found that mean prophylaxis times were increased by less than five minutes for subjects in the stannous fluoride groups. This increase was not statistically significant and was of a small enough magnitude to be considered relatively unimportant. Further illustrating the minor impact of the stain were the results from the dental hygienist questionnaires assessing both the coverage and difficulty in removing stain. When asked to rate the difficulty of removing stain (1 = easy, 2 = moderately easy, 3 = average, 4 = moderately difficult, 5 = difficult) hygienists reported their efforts in the "moderately easy" range for the control (1.78), lowGluc (2.16), and highGluc (2.38) stabilized stannous fluoride groups. Consistent with the clinical assessment, hygienists also reported observing increased stain for the stabilized stannous fluoride groups relative to the control group. However, to put this in perspective, it should be noted that when asked to estimate how much stain was present (0 = none, 2 = slight, 4 = moderate, 6 = severe), hygienists reported only a "slight" amount visible on the teeth of subjects in the stannous fluoride groups. As a whole, these results indicate that from a professional standpoint, the increase in tooth stain associated with the use of stannous fluoride can be easily managed by employing standard oral prophylaxis techniques and effort.

Objective and subjective safety parameters assessed throughout this six-month study indicate that the stannous fluoride dentifrices were safe. No serious, or potentially serious, adverse effects were observed during the oral soft tissue examinations. Further, of the many minor, routine soft tissue conditions seen, the frequencies and nature of the observations were similar for all treatment groups.

In an effort to more closely approximate habitual brushing patterns, subjects entering the clinical trial were instructed to brush with their assigned dentifrice as they normally would. In addition, subjects were not given new toothbrushes at the start of the study and were instructed to replace their brushes from commercial sources at their own discretion. Subject interactions with the clinical site were kept to a minimum and restricted to their examinations and the reporting of any adverse events. As a result of this approach, the test dentifrices were used under conditions resembling conventional oral hygiene practices. Therefore, the gingival health improvements observed for the stannous fluoride dentifrices are likely directly representative of the benefits that would be seen for people in the general population who brushed with these dentifrices.