l-Arginine Modifies the Exopolysaccharide Matrix and Thwarts Streptococcus mutans Outgrowth within Mixed-Species Oral Biofilms.

UNLABELLED: l-Arginine, a ubiquitous amino acid in human saliva, serves as a substrate for alkali production by arginolytic bacteria. Recently, exogenous l-arginine has been shown to enhance the alkalinogenic potential of oral biofilm and destabilize its microbial community, which might help control dental caries. However, l-arginine exposure may inflict additional changes in the biofilm milieu when bacteria are growing under cariogenic conditions. Here, we investigated how exogenous l-arginine modulates biofilm development using a mixed-species model containing both cariogenic (Streptococcus mutans) and arginolytic (Streptococcus gordonii) bacteria in the presence of sucrose. We observed that 1.5% (wt/vol) l-arginine (also a clinically effective concentration) exposure suppressed the outgrowth of S. mutans, favored S. gordonii dominance, and maintained Actinomyces naeslundii growth within biofilms (versus vehicle control). In parallel, topical l-arginine treatments substantially reduced the amounts of insoluble exopolysaccharides (EPS) by >3-fold, which significantly altered the three-dimensional (3D) architecture of the biofilm. Intriguingly, l-arginine repressed S. mutans genes associated with insoluble EPS (gtfB) and bacteriocin (SMU.150) production, while spxB expression (H2O2 production) by S. gordonii increased sharply during biofilm development, which resulted in higher H2O2 levels in arginine-treated biofilms. These modifications resulted in a markedly defective EPS matrix and areas devoid of any bacterial clusters (microcolonies) on the apatitic surface, while the in situ pH values at the biofilm-apatite interface were nearly one unit higher in arginine-treated biofilms (versus the vehicle control). Our data reveal new biological properties of l-arginine that impact biofilm matrix assembly and the dynamic microbial interactions associated with pathogenic biofilm development, indicating the multiaction potency of this promising biofilm disruptor. IMPORTANCE: Dental caries is one of the most prevalent and costly infectious diseases worldwide, caused by a biofilm formed on tooth surfaces. Novel strategies that compromise the ability of virulent species to assemble and maintain pathogenic biofilms could be an effective alternative to conventional antimicrobials that indiscriminately kill other oral species, including commensal bacteria. l-Arginine at 1.5% has been shown to be clinically effective in modulating cariogenic biofilms via alkali production by arginolytic bacteria. Using a mixed-species ecological model, we show new mechanisms by which l-arginine disrupts the process of biofilm matrix assembly and the dynamic microbial interactions that are associated with cariogenic biofilm development, without impacting the bacterial viability. These results may aid in the development of enhanced methods to control biofilms using l-arginine.

Clinical evaluation of the anti-plaque effect of a commercial chewing gum.

OBJECTIVE: The objective of this research was to evaluate the dental plaque control effect of a chewing gum versus brushing with a dentifrice via four clinical studies. METHODOLOGY: Study 1 compared a commercial chewing gum (Colgate Dental Gum, CDG) with a water control after 24 hours post-brushing; Studies 2 and 3 compared CDG to two different brands of commercially available fluoride dentifrices after 24 hours post-brushing; Study 4 examined the anti-plaque effect of CDG plus a regular fluoride dentifrice (Colgate Winterfresh Gel, CWG) versus brushing with CWG alone for five days. The 24-hour clinical tests employed the Modified Gingival Margin Plaque Index (MGMPI), while the Quigley-Hein Plaque Index (QHPI) was used for the five-day study. All studies utilized a randomized, crossover design with a one-week washout period, and were single-blinded to the clinical evaluator. RESULTS: In Study 1, the mean MGMPI score for CDG was significantly lower (p < 0.05) compared to the water control. In Studies 2 and 3, while brushing with regular fluoride dentifrices provided improved plaque control compared to CDG, the chewing gum alone with no tooth brushing delivered a plaque reduction 60% as effective as brushing with a fluoride dentifrice. In Study 4, the group using the combination of chewing with CDG and brushing with CWG provided a significantly lower (p < 0.05) mean QHPI score compared to the group using the dentifrice only, particularly on the hard-to-brush lingual surfaces. CONCLUSIONS: Four clinical studies demonstrated that CDG provides a plaque control benefit. The results suggest that chewing gum may serve as an effective oral hygiene device when brushing may not be possible and, additionally, that chewing gum may serve as an effective adjunct to brushing for enhanced oral health.

Safety profile of a new liquid whitening gel.

Colgate Simply White Clear Whitening Gel, an at-home tooth-whitening product purchased over the counter, contains 18% carbamide peroxide (equivalent to 6.5% hydrogen peroxide) as the active ingredient in a brush-applied liquid gel. The excipients include ingredients commonly used in dentifrices. The potential for effects on the tooth pulp, oral soft tissue irritation, enamel damage, and tooth sensitivity with this peroxide-containing product have been evaluated. An in vitro study demonstrated that pulpal chamber hydrogen peroxide levels are well below those considered to cause an effect on pulpal tissue. An exaggerated-use (4 applications per day for 3 weeks) clinical study showed that no oral irritation occurred during 3 weeks of use. A study measuring peroxide salivary concentration after use of Colgate Simply White Clear Whitening Gel showed that the concentration of peroxide in the saliva after use of the product was extremely low, further supporting the position that this product has a low potential for causing oral irritation. Additional studies demonstrate that Colgate Simply White Clear Whitening Gel does not harm the enamel surface or produce demineralization after exposure equivalent to 3 weeks of normal use and over 6 weeks of exaggerated use. Colgate Simply White Clear Whitening Gel has not produced oral irritation (hard and soft tissues) or tooth hypersensitivity in a clinical subject population of 141 individuals using varying treatment regimens. These studies prove that Colgate Simply White Clear Whitening Gel is safe for daily use as directed.

Clinical comparison of the stain-removal efficacy of a novel liquid whitening gel containing 18% carbamide peroxide and a commercially available whitening dentifrice.

The objective of this examiner-blind clinical study was to compare the extrinsic tooth-stain removal efficacy of a novel, nontray, "paint-on" liquid whitening gel containing 18% carbamide peroxide (Colgate Simply White Clear Whitening Gel) with a commercially available whitening dentifrice. After a baseline examination for extrinsic tooth stain, qualifying adult men and women from Canada were randomized into two treatment groups balanced for age, gender, and level of extrinsic tooth stain. Subjects were instructed to brush their teeth twice daily (morning and evening) for 1 minute with their assigned dentifrice (Group 1: nonwhitening dentifrice; Group 2: whitening dentifrice). The subjects in Group 1 also were instructed to use the paint-on whitening gel for 30 minutes twice daily. Examinations for extrinsic tooth stain were repeated after 2 and 3 weeks. Ninety-seven subjects complied with the protocol and completed the entire study. At both the 2- and 3-week examinations, subjects assigned to the liquid whitening gel-treatment group exhibited statistically significant reductions in extrinsic tooth stain (P < .05) with respect to stain area (22.7% reduction at 3 weeks), stain intensity (26.3% reduction at 3 weeks), and overall stain removal (32% reduction at 3 weeks) compared with the commercially available whitening dentifrice group. Thus, the results of the examiner-blind clinical study support the conclusion that Colgate Simply White Clear Whitening Gel provides a significantly greater level of extrinsic tooth-stain removal efficacy than a commercially available whitening dentifrice.