Synergistic inhibitory effect of zinc and hexetidine on in vitro growth and acid production of Streptococcus mutans

Mineralising and antibacterial effects of modified calcium phosphate treatment on human root cementum

Background

Aging population will lead to the increase of incidence of root caries globally. The clinical management of root caries is challenging due to the difficulty in moisture isolation. The root caries is caused by the release of organic acids from cariogenic bacteria which results in the dissolution of cementum and dentin of the root. The purpose of this study is to study the efficacy of modified saturated calcium phosphate solution (CaP) supplement with zinc (Zn²⁺) and/or fluoride (F^-) in providing root cementum surfaces less susceptible to acid dissolution and bacterial colonization.

Methods

Human root cementum sections from extracted premolars were treated with three modified calcium phosphate solutions (M/A-CaPs) respectively: (A) CaP-F/Zn, supplemented with F^- and Zn²⁺; (B) CaP-F, supplemented with F^- only; (C) CaP-Zn, supplemented with Zn²⁺ only. The surface characteristics of treated cementum sections were investigated using scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FT-IR). Following the acid attack and Streptococcus mutans challenge, M/A-CaPs treated cementum surfaces were analysed using inductive coupled plasma (ICP) and SEM respectively.

Results

Compared with the control group, M/A-CaPs treated cementum presented significant improvements in resistance to acid dissolution and bacterial colonization. Among M/A-CaPs, the CaP-F/Zn treated cementum surfaces released the lowest amount of Ca²⁺ ions (2.11 ± 0.51 ppm) upon acid challenge (n = 3, p < 0.01) and also presented the most significant inhibiting effect against the colonization of S. mutans (n = 180, p < 0.05).

Conclusions

Saturated calcium phosphate solution CaP supplemented with both F^- and Zn²⁺ could be applied as an effective coating material providing acid resistance and antibacterial property on cementum surfaces. The modified calcium phosphate-based solution could be a new treatment strategy to prevent the development of root caries and arrest the further progression of root caries.

Antimicrobial efficiency of mouthrinses versus and in combination with different photodynamic therapies on periodontal pathogens in an experimental study

BACKGROUND AND OBJECTIVE

In the therapy of destructive periodontal disease, chemical antimicrobial agents and increasingly photodynamic therapy (PDT) play an important adjunctive role to standard mechanical anti-infective treatment procedures. However, both antiseptic methods have their shortcomings in terms of eliminating periodontal pathogens. The aim of the study was to compare the antibacterial efficacy of different antiseptic mouthrinses, of a conventional and a new, modified PDT^plus as well as of the different antiseptic mouthrinses combined with either the conventional or the modified PDT^plus against periopathogens.

MATERIAL AND METHODS

Six representative periodontitis-associated bacterial strains were grown for 24 h under anaerobic conditions. After mixing the individual cell pellets they were exposed to 10 different antiseptic mouthrinse formulations: chlorhexidine (0.2%, 0.06%, CHX); CHX + cetylpyridinium chloride (each 0.05%); sodium hypochlorite (0.05%); polyhexanide (0.04%, PHMB1; 0.1%, PHMB2); octenidine dihydrochloride (0.1%); fluoride (250 ppm); essential oils; povidone iodine (10%); and saline (0.9%, NaCl) as control. Furthermore, the bacteria were treated with conventional PDT based on light-emitting diodes and a new modified photodisinfection combining photosensitizer with hydrogen peroxide to PDT^plus also based on light-emitting diodes. In addition to the single treatments, a combined application of antiseptic exposure followed by use of PDT or PDT^plus was performed. The microbial viability was characterized by analyzing colony growth and fluorescence-based vitality proportions.

RESULTS

Nearly all mouthrinses caused a statistically significant growth inhibition. The most effective antiseptics, CHX (0.2%), CHX/cetylpyridinium chloride and octenidine dihydrochloride, inhibited bacterial growth completely. Conventional PDT resulted in moderate reduction of colony growth. The modified PDT^plus achieved maximum antimicrobial effect. The combination of antiseptic exposure and PDT against periopathogens predominantly increased antibacterial efficacy compared to the single applications. The mouthrinse containing essential oil seemed to interfere with PDT.

CONCLUSION

A combination therapy of preceding chemotherapeutical exposure and subsequent photodisinfection may be a more effective and promising antibacterial treatment than single applications of the antiseptic methods. The modified PDT^plus using oxygen-enriched toluidine showed a superior antibacterial effect on periodontal pathogens to conventional PDT and to the majority of the investigated mouthrinses.

Synthesis and characterization of new copper(II) complex compounds with chlorhexidine. Part I

Three new copper(II) complex compounds with chlorhexidine diacetate as a ligand have been prepared and characterized by elemental and thermogravimetrical analyses, molar conductances, magnetic susceptibility measurements, infrared, electronic and EPR spectra. The complexes correspond to the formulas: [Cu2(CHX)Cl4]·2C2H5OH, [Cu2(CHX)Br4]·2C2H5OH and [Cu2(CHX)(CH3COO)2] (CH3COO)2·2C2H5OH, where CHX = chlorhexidine, their composition and stereochemistry depending on the reaction conditions and the metal salt used. Chlorhexidine acts as neutral tetradentate NNNN donor, coordinating through the four imine nitrogen atoms. Investigations on antimicrobial activity in vitro show that all the complexes are active against the tested microorganisms, the complex with chloride being more active against Gram negative bacteria than chlorhexidine diacetate..

Fractional inhibitory concentration index of combinations of antibacterial agents against cariogenic organisms

OBJECTIVES

To examine the inhibitory effects between paired combinations of four antibacterial agents that have been investigated in dentistry against six bacteria associated with dentinal caries.

METHODS

The antibacterial agents tested were: chlorhexidine dihydrochloride, benzalkonium chloride, cetrimide and cetylpyridinium chloride. Two organisms each belonging to Streptococcus, Lactobacillus and Actinomyces species were evaluated against these agents. A checkerboard microtitration method was used to determine the minimum inhibitory concentration and fractionary inhibitory concentration (FIC) and summation operator FIC index of the paired combinations of antibacterial agents against the six species of bacteria. Appropriate controls were included. The summation operator FIC index was then used to determine if synergy, antagonism, or indifference occurred as a result of interactions between the antibacterial agents and the test organisms.

RESULTS

The data from a total of 295 test results were evaluated. Using summation operator FIC values for synergy as < or = 0.5 and antagonism as > 4.0 as recommended by The American Society for Microbiology, no significant synergistic or antagonistic interactions were observed between the paired antibacterial agents when tested against selected organisms. However, a tendency for an additive antibacterial effect was observed with approximately a third of the test results. Nonetheless, no combination of antibacterial agents appeared to be superior to any other.

CONCLUSIONS

According to these in vitro results, there appears to be no beneficial effect of combining the antibacterial agents against the individual cariogenic micro-organisms selected. However, it may be beneficial to use combined antibacterial agents that have a broader range of activity against an ecosystem of bacteria than using individual agents.

Combined effects of Zn(2+)-chlorhexidine and Zn(2+)-cetylpyridinium chloride on caries incidence in partially desalivated rats

The effects of Zn2+ combined with either chlorhexidine or cetylpyridinium chloride (CPC) on caries incidence in partially desalivated rats were investigated. Seven groups of 12 animals each received topical applications for 20 s with a saturated swab (0.2 ml) of the following aqueous solutions twice daily on weekdays (10 a.m. and 3 p.m.) and once daily during weekends (12 a.m.) for 5 wk: deionized water (placebo); 40 mM zinc acetate; 2.2 mM chlorhexidine diacetate; 4.4 mM CPC; 40 mM zinc acetate and 2.2 mM chlorhexidine diacetate; 40 mM zinc acetate and 4.4 mM CPC; and 20 mM NaF (positive control). Coronal caries was scored by the method of Keyes. All treatments except CPC alone resulted in significantly (P less than 0.05, ANOVA) less smooth-surface caries than did the placebo. NaF treatment resulted in significantly less smooth-surface caries than did Zn2+, chlorhexidine, CPC, and Zn(2+)-CPC. The inclusion of zinc ions did not significantly increase the caries-inhibitory efficacy of chlorhexidine (CH). The combination of Zn(2+)-CPC decreased smooth-surface scores significantly more than did CPC alone. Significant differences in sulcal-surface caries were not observed among the groups. Zn(2+)-CPC suppressed the Streptococcus sobrinus counts significantly more than did the separate agents. Animals treated with Zn(2+)-CH harbored the lowest populations of S. sobrinus.

Synergistic antibacterial effects of copper and hexetidine against Streptococcus sobrinus and Streptococcus sanguis

The aim of this study was to determine whether a combination of copper and hexetidine had a synergistic antibacterial effect against Streptococcus sobrinus OMZ 176 and S. sanguis 10556. Concentration ranges of the test agents alone and in combination were prepared by serial dilutions in microtiter trays with brain-heart infusion (BHI) broth as the bacterial growth medium. After incubation at 37 degrees C for 24 h, the minimum inhibitory concentration (MIC), corresponding to the lowest concentration showing no visible growth, was determined. Evaluated by the fractional inhibitory concentration index, a strong synergistic effect ranging from 0.39 to 0.40 was observed. A similar effect was also demonstrated by growth curves, which were constructed on the basis of growth in BHI broth with addition of MIC/4 of each agent alone or MIC/8 of each agent in combination. A probable explanation for these findings is that the surface-active hexetidine molecule alters the bacterial cell surfaces and thereby enables an increased amount of copper to be transported into the cell.

The effect of a combination of copper and hexetidine on plaque formation and the amount of copper retained by dental plaque bacteria

Zn++ in combination with hexetidine exerts a synergistic plaque inhibition. Studies in our laboratory on the mechanism of this effect suggested that Cu++ and hexetidine may have a similar combination effect. This hypothesis was tested in vivo on a human test panel in a double-blind crossover study. The amount of Cu++ retained by plaque bacteria in vitro was also evaluated. Seven volunteers rinsed with the solutions for 1 min twice daily for 5 days. The test solutions were H2O, 1.0 mM CuSO4, 2.0 mM hexetidine, and the last two in combination. During the test period no oral hygiene was allowed, and sucrose-containing chewing gum was used to enhance plaque formation. The plaque index scores after rinsing with the combination were significantly (p less than 0.05) lower than those of the other solutions. The effect of hexetidine on Cu++ retention in plaque bacteria was evaluated in plaque samples (n = 3) grown anaerobically overnight in PPLO medium. The bacteria were washed five times, digested in concentrated HNO3, and Cu++ determined by atomic absorption. The presence of hexetidine resulted in a significantly greater amount of Cu++ retained by bacteria at all CuSO4 concentrations. It is suggested that the nonpolar nature of the hexetidine molecule enables Cu++ bound to hexetidine to pass into the bacterial cell. Within the cell, Cu++ can interfere with bacterial metabolism, giving a reduction in plaque growth.

The effect on early plaque formation, gingivitis and salivary bacterial counts of mouthwashes containing hexetidine/zinc, aminefluoride/tin or chlorhexidine

This study was designed to investigate the effectiveness of mouthwashes containing hexetidine/zinc (HZA) or tin (ASF) in inhibiting plaque formation and gingivitis in humans. 24 dental students and assistants participated in the study (latin square design) with 7-day test periods. They rinsed twice daily for 1 min with one of the following formulations: HZA = 750 ppm hexetidine/750 ppm zinc acetate, ASF = 100 ppm aminefluorid/310 ppm stannous fluoride, CHX = 0.1% chlorhexidine and M = negative control. Plaque accumulation was determined planimetrically and gravimetrically. Gingivitis was evaluated with the papillary bleeding index. Total colony forming units and S. mutans counts were estimated from saliva samples. The results showed that HZA and CHX almost completely inhibited plaque accumulation and gingivitis. ASF was less effective than HZA and CHX but still reduced plaque significantly compared to the negative control. Furthermore, CHX reduced salivary S. mutans counts.

Plaque inhibition by hexetidine and zinc

Rinsing experiments with mouthwashes containing zinc ions, hexetidine and a combination of hexetidine and zinc ions were performed with a group of 10 volunteers. The amount of plaque was assessed after rinsing with the test solutions for 4 days during which mechanical toothcleaning was discontinued. Significantly improved inhibition was observed by the combination of hexetidine and zinc ions compared with the two agents used separately. In vitro bacteriological tests showed that hexetidine and zinc ions had a synergistic inhibitory effect on the growth of Streptococcus mutans.

Dentine hypersensitivity: effect of interactions between metal salts, fluoride and chlorhexidine on the uptake by dentine

A large number of compounds may be applied to the teeth for preventive or therapeutic purposes, most notably in dentine hypersensitivity. The uptake of any one compound by tooth substances may clearly be affected by another to produce synergistic, additive or antagonistic effects. This study determined whether uptake interactions occurred between fluoride, chlorhexidine, strontium, tin and zinc. All compounds, in particular tin, showed considerable affinity for dentine. Fluoride reduced the uptake of zinc but not tin, strontium or chlorhexidine. Chlorhexidine increased the uptake of zinc, but not tin, strontium or fluoride. Zinc and tin decreased fluoride uptake but strontium had no such effect. Finally, chlorhexidine uptake was increased by zinc and tin but not by fluoride or strontium. Based on the theories proposed for the reaction of these various compounds with calcified tissues, explanations for the interactions can be made. The results appear relevant to some reported clinical effects of combinations of these compounds and indicate that such interactions may have advantageous or disadvantageous consequences depending on the basis for treatment.