Analytical electron microscopy of chlorhexidine-induced tooth stain in humans: direct evidence for metal-induced stain

STEM and HRTEM studies of accumulated deposits on human tooth surface

The aim of this study was to clarify the fine structure of accumulated deposits on the surface of teeth that are considered to affect the gloss of teeth. The study was carried out using, as specimens, human incisor teeth having gloss, which were extracted from teenage donors and those incapable of showing gloss even by brushing which were extracted from donors in their 50s. Thin longitudinal sections of tooth enamel with accumulated deposits on the surface were prepared by focused ion beam (FIB) milling, and the fine structure was analyzed using a scanning transmission electron microscope (STEM) and a high resolution transmission electron microscope (HRTEM). By FIB, thin longitudinal sections could be prepared from tooth enamel together with organic and inorganic substances accumulated on the surface without artifacts. The accumulated deposits on the surface of teeth having gloss were composed of organic substances. However, it was first revealed by STEM observation that the accumulated solid deposits on the surface of teeth having no gloss had a complicated structure wherein inorganic and organic substances coexisted. It is suggested that the organic substances contain proteins derived from saliva. The inorganic substances were spherical and needle-like hydroxyapatites (HAs). It is considered that amino acids constituting the proteins affected the nucleus formation and the crystal formation of HA. It is considered that the unevenness of the accumulated deposits existing on the surface of tooth enamel having no gloss causes the decrease in gloss of teeth due to diffuse reflection of light.

Mechanisms of Stain Formation on Teeth, in Particular Associated with Metal Ions and Antiseptics

Much has been written on the subject of extrinsic tooth discoloration, but, except when the pigment is intentionally applied, the etiologies and mechanisms are poorly understood. Extrinsic stains have been classified as non-metallic or metallic. The pigment usually lies not on or in the dental tissues, but in surface deposits, particularly the acquired pellicle layer and at sites receiving limited cleaning. Whether pigments absorb, adsorb, or chemically interact with dental surfaces is unclear. Some stains merely seem to reflect the color of the apparent source, whereas others have been ascribed to a secondary chemical alteration of a substance at the tooth or pellicle surface. Theories of chromogenic bacteria and formation of metal sulfides are frequently propounded but without clear supportive evidence. Staining by cationic antiseptics and, to a lesser extent, metal salts has attracted research interest. Chlorhexidine and other cationic antiseptics, it is hypothesized, may catalyze browning reactions or facilitate metal sulfide formation in pellicle. Controlled clinical studies have repeatedly shown that dental and mucosal staining associated with the use of chlorhexidine and some metal salts is dependent upon volunteers' imbibing reasonable quantities of chromogenic beverages, such as tea. However, it must be appreciated that cationic antiseptics and polyvalent metals can precipitate chromogenic material from a large range of dietary compounds. The control of dental staining, at least that associated with chlorhexidine, can be achieved both in vitro and in vivo by the use of oxidizing agents which appear to remove the stain physically from the surfaces.

The effect of an oxygenating agent on chlorhexidine-induced extrinsic tooth staining: a systematic review

BACKGROUND

Although chlorhexidine digluconate (CHX) is currently the most effective mouthwash for reducing plaque and gingivitis, one of its side effects is extrinsic tooth staining. Interestingly, oxygenating agents may reduce this staining.

OBJECTIVE

The aim of this review was to systematically search the literature for data concerning the inhibiting effect of an oxygenating agent (OA) on CHX-induced tooth staining.

METHODS

MEDLINE-PubMed, Cochrane-CENTRAL, EMBASE and other relevant electronic databases were searched for articles that were published up to November 2011. Articles were included if they were randomized controlled trials or controlled clinical trials conducted with healthy subjects ≥ 16 years of age that compared the effects of CHX mouthrinse combined with an OA with the effects of CHX alone.

RESULTS

An independent screening of 1183 titles and abstracts resulted in 4 publications that met the inclusion criteria. The extracted data allowed meta-analyses of intermediate length studies and showed that combining an OA with CHX mouthrinses led to a significant reduction in tooth staining (mean difference: 0.27; P = 0.02) and plaque scores (mean difference: 0.10; P = 0.003) when compared with CHX alone. One of the included studies reported a side effect for one participant. The present review was limited by the availability of data, and the included studies were methodologically and clinically heterogeneous, which affected the quality and interpretation of the evidence.

CONCLUSION

There is moderate evidence that a combination of CHX and an OA reduces tooth staining without interfering with plaque growth inhibition.

In vitro antimicrobial comparison of chlorhexidine, persica mouthwash and miswak extract

AIM

Herbal mouthwashes, such as persica (Salvadora persica, mint and yarrow extracts) and miswak extract have been shown to decrease gingival inflammation and plaque accumulation. The aim of this study was to compare the antimicrobial activities of persica and miswak extract with the conventional mouthwash chlorhexidine against Streptococcus salivarius, Streptococcus sanguis, Lactobacillus vulgaris and Candida albicans.

MATERIALS AND METHODS

In this in vitro study, blood-agar culture (Merk, Germany) was used to grow the streptococcus strains, saburd-dextrose culture (Merk, Germany) was used to grow C. albicans and MRS-agar was used to grow L. vulgaris. Various concentrations of these substances (0.1, 0.05 and 0.025% of miswak extract, 0.1, 0.05, 0.025 and 0.0125% of persica, 0.2, 0.1, 0.05 and 0.025% of chlorhexidine) were added to paper disks, separately, inserted into culture plates and transferred into the incubator. The inhibition zone around each disk was measured after 24 hours and the data was analyzed by the Kruskal-Wallis test.

RESULTS

Chlorhexidine possessed antibacterial activity at all concentrations tested. It was more effective than persica and miswak at all concentrations on S. salivarius (p = 0.022 for 0.1%, 0.009 for 0.05 and 0.025%). It had greater effect than the other two tested material on S.sanguis only at concentration 0.01%. Chlorhexidine was the most effective against S.salivarius; persica was the most effective against Lactobacillus (p = 0.005) and the least effective against S. salivarius; and miswak extract was the most effective against S. salivarius and S. sanguis at concentrations 0.1 and 0.05% (p = 0.005) and ineffective against L. vulgaris. None of these mouthwashes were effective against C. albicans.

CONCLUSION

This study revealed that chlorhexidine remains the gold standard as an antimicrobial agent, although herbal based mouthwashes do have marginal antimicrobial activities. It is necessary to conduct more clinical and microbiological studies focusing on periodontal pathogens and anaerobic microorganisms.

CLINICAL SIGNIFICANCE

Mechanical plaque control is the main way for periodontal disease prevention and mouthrinses are used to improve its efficacy. Based on the results of this study, chlorhexidine has the most antibacterial effect and although persica mouthwash and miswak are routinely used in some Asian countries their antibacterial efficacies are suspected.

Adsorption of chlorhexidine on synthetic hydroxyapatite and in vitro biological activity

The kinetic of chlorhexidine digluconate (CHXDG) uptake from aqueous solution by hydroxyapatite (HA) was investigated by ultraviolet (UV) analysis performed in HA powder (UV-solid) after the CHX adsorption. Adsorption isotherm of chlorhexidine (CHX) uptake was modeled by a combination of Languimir and Langmuir-Freundlich mechanisms. Strong molecule-molecule interactions and positive cooperativity predominated in the surface when CHX concentration was above 8.6 μg(CHX)/mg(HA). UV-solid spectra (shape, intensity and band position) of CHX bound to HA revealed that long-range molecular structures, such as aggregates or micelles, started to be formed at low CHX concentrations (1.52 μg(CHX)/mg(HA)) and predominated at high concentrations. Grazing-incidence X-ray diffraction (GIXRD) analysis from synchrotron radiation discarded the formation of crystalline structures on HA surface or precipitation of CHX crystalline salts, as suggested in previous works. The effect of the HA/CHX association on HA in vitro bioactivity, cytotoxicity and CHX antimicrobial activity was evaluated. It was shown that CHX did not inhibit the precipitation of a poorly crystalline apatite at HA/CHX surface after soaking in simulating body fluid (SBF). Cell viability studies after exposure to extracts of HA and HA/CHX showed that both biomaterials did not present significant in vitro toxicity. Moreover, HA/CHX inhibited Enterococcus faecalis growth for up to 6 days, revealing that binding to HA did not affect antimicrobial activity of CHX and reduced bacterial adhesion. These results suggested that HA/CHX association could result in a potential adjuvant antimicrobial system for clinical use.

New data on biological effects of chlorhexidine: Fe2+ induced lipid peroxidation and mitochondrial permeability transition

Chlorhexidine (CHX) is a bis-bis-guanide with anphipatic and antiseptic properties and is largely used in dentistry, mainly for management of periodontal problems and in oral pre-operatory procedures. The present study concerns the effect of CHX on lipid peroxidation, mitochondrial permeability transition (MPT), and the interaction of CHX with ferritin (HoSF). CHX (100 microM) increased iron release from HoSF by approximately 13-fold when compared to control values. CHX also increased iron-dependent lipid peroxidation. MPT induced by CHX was protected by ethylene glycol-bis(beta-aminoethyl-ether)-N,N,N',N'-tetraacetic acid (EGTA), dithiothreitol (DTT), and cyclosporin A (CsA), showing a Ca2+-dependent effect, in which oxidation of thiol groups is involved, as well as the involvement of the transmembrane proteinaceous pore. BHT, catalase or o-phenanthroline did not protect MPT induced by CHX. This suggests that a ROS-independent mechanism is involved in the induction of MPT.

Tooth discolouration and staining: a review of the literature

OBJECTIVE

To carry out an extensive review of the literature on tooth staining with particular regard to some of the more recent literature on the mechanisms of tooth staining involving mouthrinses.

DESIGN

Comprehensive review of the literature over four decades.

CONCLUSIONS

A knowledge of the aetiology of tooth staining is of importance to dental surgeons in order to enable a correct diagnosis to be made when examining a discoloured dentition and allows the dental practitioner to explain to the patient the exact nature of the condition. In some instances, the mechanism of staining may have an effect on the outcome of treatment and influence the treatment options the dentist will be able to offer to patients.

Reduced chlorhexidine tooth stain coverage by sequential administration of monoperoxyphthalic acid in the beagle dog

Extrinsic tooth stain is sometimes a side-effect observed with the chronic use of chlorhexidine-containing oral care products. This chlorhexidine (CHX)-induced tooth staining is observed both in humans as well as in experimental animals. The present study tested the hypothesis that the sequential administration of monoperoxyphthalic acid (MPA) will reduce the development of chlorhexidine-induced tooth stain coverage in a beagle dog. For this study, dogs were treated with 30 mL of mouthrinse b.i.d. for 28 days. The following treatment groups ( = 12 dogs/group) were tested: water (negative control), 1.0% MPA rinse, 0.12% CHX rinse, and 1.0% MPA rinse followed by 0.12% CHX rinse. The sequential dosing of 1.0% MPA followed by 0.12+ CHX resulted in significantly (p < or = 0.05) less tooth stain than when dogs were dosed with 0.12% CHX alone. Additionally, the sequential dosing of MPA followed by chlorhexidine resulted in a 75% reduction in plaque formation in this model, which was significantly different (p < or = 0.05) from results with either treatment alone. A further study demonstrated that similar results could be obtained when MPA plus CHX treatment alone. A further study demonstrated that similar results could be obtained when MPA plus CHX treatments were separated by approximately a five-hour period in an AM and PM schedule. We conclude that the oxidizer, MPA, can significantly reduce tooth stain induced by CHX while enhancing its antiplaque and antigingivitis activity.