Assessment of the cariogenic potential of Streptococcus mutans strains and its relationship to in vivo caries experience

Changes in the oral environment after placement of lingual and labial orthodontic appliances

Background

This study compared the oral hygiene and caries risk of patients treated with labial and lingual orthodontic appliances throughout a prospective evaluation of the status of the oral environment before and after bracket placement.

Methods

A total of 20 orthodontic patients aged 19 to 23 years were included in the study and were divided into two groups: 10 patients wore Roth labial appliance (American Orthodontics, Sheboygan, WI, USA) and 10 patients wore STb lingual appliance (Ormco Corporation, Glendora, CA, USA). Plaque index (PI), gingival bleeding index (GBI), salivary flow rate, saliva buffer capacity, salivary pH, and Streptococcus mutans and Lactobacillus counts in saliva were determined at three time points: before orthodontic appliance placement (T0), 4 weeks after bonding (T1), and 8 weeks after bonding (T2). After appliance placement, all patients were periodically educated to the oral hygiene procedures. Wilcoxon rank and Mann-Whitney U tests were used to determine intragroup and intergroup differences as regards qualitative data. To compare quantitative data between the groups, chi-square and Fisher's exact tests were undertaken, while intragroup differences were tested with McNemar test. The level of statistical significance was set at p < 0.05.

Results

Statistical analysis of the data obtained revealed a statistically significant difference between the data of T0 and T1 and the data of T0 and T2 of the PI scores and between T0 and T2 of the GBI scores in the group treated with the lingual appliance. The GBI value increased significantly between T0 and T1 but decreased significantly between T1 and T2 (p < 0.01) in the group treated with labial appliance. S. mutans counts increased significantly between T0 and T2 in the saliva samples of patients treated with lingual appliance. No statistically significant differences were found between S. mutans and Lactobacillus counts at the three terms of saliva collection in patients treated with labial appliance. No statistically significant differences were found between the two groups at the three time points as regards the salivary flow rate and saliva buffer capacity.

Conclusions

Lingual and labial orthodontic appliances showed a different potential in modifying the investigated clinical parameters: patients wearing STb lingual orthodontic appliance had more plaque retention 4 and 8 weeks after bonding, while there were more gingival inflammation and more S. mutans counts 8 weeks after bonding. No differences were found between the two groups as regards the Lactobacillus counts, the salivary flow rate, and saliva buffer capacity.

Mechanisms of interaction between Candida albicans and Streptococcus mutans: an experimental and mathematical modelling study

OBJECTIVE

To evaluate the mechanisms of microbial interaction between the oral pathogens Candida albicans and Streptococcus mutans.

MATERIALS AND METHODS

Growth kinetics for the two micro-organisms, cultured individually or together, were followed experimentally for 36 h. The different growth curves were analysed by means of mathematical modelling.

RESULTS

Under the experimental conditions, S. mutans final concentration, when grown individually, was 5-times that of C. albicans. Contrarily, when both micro-organisms grew together, this ratio was inversed and C. albicans final concentration was even higher than that of S. mutans. When both micro-organisms share the niche, a model including linear competition among one another was best suited to reproduce the experimental observations. The results of this model show that the initial growth rates of both species are positively influenced by their mutual interaction. However, at longer incubation times, C. albicans prevents bacterial growth and achieves concentrations 4-times higher than when grown individually.

CONCLUSIONS

The results suggest that C. albicans biofilm formation could be potentiated by the presence of S. mutans by two mechanisms: synergically at short times and by competition at longer periods.

The influence of different types of fixed orthodontic appliance on the growth and adherence of microorganisms (in vitro study)

Orthodontic appliances serve as different impact zones and modify microbial adherence and colonization, acting as foreign reserves and possible sources of infection. This study was conducted to investigate the effect of different types of fixed orthodontic appliances on the growth and adherence of microorganisms in oral flora which are Streptococcus mutans (S. mutans) and Candida albicans. Sixty-four of four different fixed orthodontic appliance-samples were used, divided into four groups of sixteen. Type I: Sapphire brackets- Coated wires, type II: Sapphire brackets- Stainless steel wires, type III: Stainless steel brackets- Coated wires and type IV: Stainless steel brackets- Stainless steel wires. Oral strains of S. mutans and Candida albicans were studied in the present study using biochemical test then microbial suspensions were prepared to do the tests of each microorganism including the antimicrobial effects of different appliance-samples on the growth of microorganisms and their adhesion tests. The results showed significant differences between the different appliances in terms of inhibition zone formation (P<0.001). The adhesion test, which is classified into low, medium and high, showed the adhesion of S. mutans, is low with type I and II, medium with type III and high with type IV, whereas the adhesion of Candida albicans is medium with both type I and II and high with both type III and IV with high significant differences (P<0.001). Appliance with high esthetic appearance, sapphire brackets and coated arch wire, showed the least adherence of S. mutans and Candida albicans in comparison to other appliances with less esthetic and more metal components.

Key words:Orthodontic appliance, Adherence, Streptococcus mutans, Candida albicans.

Influence of Different Orthodontic Brackets on Adherence of Microorganisms In Vitro

OBJECTIVE

To define the capacity of different bracket materials to modify the growth and adherence of microorganisms.

METHODS

Three types of brackets from the right upper central incisor were used: metallic, ceramic, and composite. Streptococcus mutans and Candida albicans were studied. The association of both species was also evaluated. The brackets were placed in flat-bottomed vials containing basal medium with 20% sucrose added; the flasks were inoculated with each of the microbial suspensions. The samples were incubated at 37 degrees C for 48 hours, after which the brackets were removed. The supernatant was removed from the flasks, the cells adhering to the glass were counted, and the brackets were studied with electron microscopy.

RESULTS

The adherence of Streptococcus mutans was not modified by the different brackets. The adherence of Candida albicans was increased by the composite bracket, whereas the use of metallic brackets decreased the number of colony-forming units (CFUs). By electron microscopy we demonstrated that the adherence of Streptococcus mutans plus Candida albicans together varied according to the bracket materials with composite > ceramic > metallic.

CONCLUSIONS

Orthodontic appliances serve as different impact zones and modify microbial adherence and colonization, acting as foreign reserves and possible sources of infection.

[In vitro utilization of fructooligosaccharide by streptococci mutans]

Neosugar is the trade name of a fructooligosaccharide (FOS) whose utilization by oral bacteria is not well known yet. The aim of the present study was to evaluate in vitro the effect of this product on the growth, fermentation and production of plaque by mutans streptococci: S. mutans, serotypes c, e and f, S. sobrinus, serotype d, S. downei, serotype h, S. cricetus, serotype a and S. rattus, serotype b. The evaluation of growth was carried out in Brain Heart Infusion (BHI) broths containing or not sucrose and FOS and in buffered broths having glucose or FOS as carbon sources, through optical density reading in spectrophotometer after 24 hours of incubation at 37 degrees C. Thereafter the reading of pH was made in the same media. The plaque produced on glass sticks in BHI broths containing 5% sucrose or FOS was weighed and carbohydrates and proteins were assayed. The possible cariogenicity of Neosugar was confirmed, since it sustained the same growth and intensity of fermentation of sucrose in BHI broth for all streptococci and permitted in vitro production of plaque by some of them. The amount of plaque as well as its content of proteins and carbohydrates were smaller than those produced with sucrose, although the difference was statistically significant only for carbohydrates.

Does assessment of microbial composition of plaque/saliva allow for diagnosis of disease activity of individuals?

Microbiological tests are limited in their applicability in the assessment of caries activity and in caries prediction. They can be effective in group of persons with high or low caries experience. The reasons for the limitation of microbiological tests rests with unique characteristics of the microflora and local environments of the oral cavity, which will modify the cariogenicity of plaque in an individual. Thus, high numbers of S. mutans may be associated with the development of a lesion at a site, while a second susceptible site with high levels of this organism in the same subject will remain caries free. This paper identifies some aspects of oral bacteria which can contribute to the unique nature of the microflora associated with plaque in an individual. Firstly, the range of bacteria potentially involved in caries has widened and now includes, for example, 'low pH' non-mutans streptococci. The presence of such organisms in plaque in an individual may influence early enamel demineralization. Most significantly, Streptococcus mutans, Streptococcus mitis and Actinomyces naeslundii have been shown to be comprise many distinct clones, with different distribution among subjects. Little is known of the impact of clonal diversity on caries activity but in some bacterial diseases particular clones are associated with virulence. Therefore, possession of a particular clone or clones by an individual could be related to caries activity. Also, the extent of clonal diversity may reflect the nature of the oral environment. Recent studies suggest that cells are released from biofilms, during adherence and growth, i.e. the early phases of development. Thus, determination of the numbers of a given species in non-stimulated saliva may indicate whether it is actively growing in plaque. Microbiological tests on the oral flora should perhaps be used to monitor the status of the oral cavity, after establishing a norm for the individual patient. Research on species and clonal diversity of oral bacteria among human populations; diversity and its role in the caries process; and the liberation of biofilm cells could provide data to allow better appreciation and evaluation of the results of microbiological testing.

Microbial attachment on orthodontic appliances: I. Wettability and early pellicle formation on bracket materials

The objectives of this study were to investigate the wettability of orthodontic bracket material surfaces and the composition of salivary films adsorbed onto them after 30 and 60 minutes in vivo exposure. Specimens from stainless steel, fiber-reinforced polycarbonate, and polycrystalline alumina bracket manufacturing raw materials were subjected to (a) contact angle measurements with a homologous series of liquids, (b) micro multiple internal reflection Fourier transform infrared spectroscopy (microMIR FTIR) for the characterization of the molecular composition of the in vivo adsorbed groups, and (c) incident light optical microscopy of the acquired films. The highest critical surface tension was obtained from stainless steel (40.8 +/- 0.4 dynes/cm) followed by polycarbonate (32.8 +/- 1.3 dynes/cm) and alumina (29.0 +/- 0.9 dynes/cm), suggesting a higher potential for increased plaque-retaining capacity for the stainless steel brackets. Accordingly, the total work of adhesion and its polar and nonpolar components were consistent with the surface tension ranking. The nonpolar component of the work of adhesion was higher than its polar counterpart for all materials tested, implying a possible higher attachment prevalence for those microorganisms using dispersive forces, such as van der Waals forces, as the predominant attachment mechanism to surfaces. Qualitative and quantitative variations were observed in the adsorbed films after 30 and 60 minutes intraoral exposure that may reflect the influence of the surface properties of these substrates on the structure of the pellicle formed in vivo.

An in vitro investigation of the cariogenic potential of oral streptococci

Whilst the importance of the mutans streptococci in the aetiology of dental caries is clear, a number of studies have described caries development in their absence. This investigation aimed to assess the cariogenic potential of Streptococcus gordonii, Strep. sanguis, Strep. vestibularis and Enterococcus faecalis in comparison with Strep. mutans and Strep. sobrinus, using a recently described in vitro model. In the presence of a 146 mM sucrose solution and powdered hydroxyapatite, each species was incubated for 5 h, after which acid anion production, calcium release and change in pH were measured. It was possible to assign each species to one of three groups, with E. faecalis, Strep. gordonii, Strep. sanguis exhibiting low, Strep. vestibularis intermediate, and Strep. mutans and Strep. sobrinus high in vitro cariogenic potential. This assay could be used as a screening test to assess the potential cariogenicity of a range of bacterial species.