Streptococcus mutans and Streptococcus sobrinus biofilm formation and metabolic activity on dental materials

OBJECTIVES

To examine potential correlations between streptococcal biofilm formation and lactate production in streptococcal biofilms formed on the surface of dental materials with different surface characteristics.

MATERIALS AND METHODS

Samples of a glass-ionomer cement (Ketac Molar) and a ceramic (Empress 2) were incubated with whole saliva and suspensions of Streptococcus mutans ATCC 25175 or Streptococcus sobrinus ATCC 33478 for initiating single-species biofilm formation for either 4 or 24 h. The relative amount of adherent, viable cells was determined using a Resazurin and a MTT assay. Metabolic activity was assessed by quantifying lactate production with a modification of the commercial Clinpro Cario L-Pop kit.

RESULTS

Both assays identified similar S. sobrinus biofilm formation on the two substrata; for S. mutans, the MTT test showed significantly fewer streptococci on the glass-ionomer cement than on the ceramic. Concerning metabolic activity, for S. sobrinus, significantly higher lactate production was observed for biofilms formed on the glass-ionomer cement in comparison to the ceramic, whereas similar values were identified for S. mutans.

CONCLUSIONS

Within the limitations of the study, the results suggest that the pure amount of adherent streptococci does not a priori indicate the metabolic activity of the cariogenic bacteria organized in the respective biofilm. Thus, comparisons between the relative amount of adherent streptococci and their metabolic activity may allow for an improved understanding of the effect of dental material surfaces on the formation and metabolic activity of streptococcal biofilms.

Determination of caries risk at resin composite margins

PURPOSE

To design an artificial mouth in order to evaluate if a new diagnostic tool (Clinpro Cario Diagnosis) can be used for early detection of secondary caries at resin composite margins in vitro.

METHODS

32 intact human third molars received standardized Class-V resin composite restorations (Tetric Ceram bonded with Syntac SC). After storage for 4 weeks at 37 degrees C, teeth were subjected to 5,000 or 10,000 thermocycles (+/- 5 degrees C and +/- 55 degrees C) and polysiloxane impressions were taken. Streptococcus mutans 10449 (SM) was used in a nutrition medium to initiate a secondary caries process. Daily, the teeth were incubated for 2 x 2.5 hours in SM containing nutrition medium followed by 2 x 9.5 hours incubation in artificial saliva. Teeth were investigated after total incubation periods of 4, 6, and 8 weeks. After the different incubation protocols, the restoration margins were evaluated for infection and secondary caries processes in using Clinpro Cario Diagnosis which measures site-specifically the lactic acid production of SM in response to a sucrose challenge. The color signal was read 5 minutes after removal of the diagnostic impression. After thermocycling and biological load cycling, precision polysiloxane impressions were taken and replicas were investigated under a light microscope for gap widths at enamel and dentin margins. Demineralization was evaluated by fluorescence microscopy in using a special FITC filter. The demineralization depths at the cavity margin were calculated with Xpert for Windows using a pixel distance of 5 microm.

RESULTS

After the different thermocycling protocols, no differences in gap widths and demineralization depths were found (P > 0.05). After SM incubation, gap widths and demineralization depths were significantly dependent on SM incubation time and previous number of thermocycles (P < 0.05). Lactic acid formations of SM were detectable by Clinpro Cario Diagnosis at dentin cavosurface margins formed after 6 weeks of incubation with SM (P < 0.05).

Subgingival plaque removal in buccal and lingual sites using a novel low abrasive air-polishing powder

AIM OF THE STUDY

This study was aimed at assessing the efficacy of subgingival plaque removal in buccal and lingual sites during supportive periodontal therapy (SPT) using a novel low abrasive air-polishing powder.

MATERIAL AND METHODS

In 27 SPT patients, subgingival debridement was performed using the novel air-polishing powder (test) and hand instruments (positive control) in a randomized split mouth design. Before and immediately after treatment, subgingival plaque samples were taken from two teeth with pockets of 3-5 mm depth in both groups. To assess the influence of plaque sampling on the microflora, samples were also taken twice from two untreated teeth (negative control). The mean reduction in total colony forming units (CFU) was assessed by anaerobic culture. The patients' perception of treatment was assessed by a visual analog score (VAS). Therapy and plaque sampling were repeated after a 3-month interval.

RESULTS

Test treatment resulted in a significantly greater reduction in mean CFU than positive control treatment (log 1.7+/-0.98 and log 0.61+/-0.79 respectively; p<0.05). Following both treatments, the CFU reduction was significantly greater compared to negative control treatment (log 0.06+/-0.49; p<0.05). In addition, test treatment was perceived as significantly more pleasant than hand instrumentation (p<0.05).

CONCLUSION

The novel low abrasive air-polishing powder is superior to curettes in removing subgingival plaque from pockets of 3-5 mm depth in supportive periodontal therapy and offers greater patient comfort.

Subgingival plaque removal at interdental sites using a low-abrasive air polishing powder

BACKGROUND

The aim of the study was to test the efficacy of a novel low-abrasive air polishing powder in subgingival plaque removal at interdental sites during periodontal maintenance therapy (PMT).

METHODS

Using a split mouth design, subgingival plaque was removed in 23 PMT patients using a low abrasive powder using a standard air polishing unit (test) or curets (positive control). Before and immediately after treatment, subgingival plaque samples were taken from interdental sites with 3 to 5 mm probing depth (PD) at 2 test teeth and 2 positive control teeth. To evaluate the influence of sampling on the microflora, plaque samples were also taken twice at 2 teeth without therapy with PD of 3 to 5 mm (negative control). PMT treatment and plaque sampling were repeated 3 times at quarterly intervals. Anaerobe cultivation was utilized to assess the mean reduction of total colony forming units (CFU) immediately after treatment.

RESULTS

Test treatment resulted in a significantly greater reduction in subgingival bacterial counts (log 1.9 +/- 0.7) than positive control treatment (log 1.1 +/- 0.6) and subgingival plaque sampling alone (log 0.5 +/- 0.5; P < 0.05). Differences between positive and negative control were not significant (P < 0.05).

CONCLUSION

The novel low-abrasive air polishing powder is superior to curets in removing subgingival plaque at interdental sites with up to 5 mm probing depth in PMT.

In vitro evaluation of novel low abrasive air polishing powders

AIM OF THE STUDY

Though efficient in stain and plaque removal, air polishing is highly abrasive on root cementum or dentin even if working parameters are adjusted to minimize damage. As abrasiveness is also influenced by the physical properties of the powders used, the aim of the study was to evaluate the safety of novel low abrasive air polishing powders in vitro.

MATERIAL AND METHODS

Using four novel air polishing powders (A, B, C and D) and a standard sodium bicarbonate (NaHCO3) powder, roots of 126 extracted teeth were air polished under standardized conditions at various working parameter combinations (distance: 2 mm, 4 mm and 6 mm; powder and water setting: low, medium and high) at an angulation of 90 degrees for 20 s. Instrumentation was performed in triplicate; resulting root defects were quantified laser-optically.

RESULTS

Mean defect depths after application of powders A, B, C and D were significantly lower than with standard powder (A: 17.9 +/- 10.9 micro m, B: 48.2 +/- 32.7 micro m, C: 92.5 +/- 57.9 micro m, D: 33.9 +/- 19.6 micro m, NaHCO3: 163.1 +/- 71.1 micro m) (Kruskal-Wallis test). Among the experimental powders, D was transported most reliably in the air polishing unit and allowed complete removal of disclosed plaque as assessed on freshly extracted teeth.

CONCLUSION

The novel air polishing powder D is of low abrasiveness to root cementum and dentin while being effective in removing dental plaque. Thus, it may be useful for safe and efficient plaque removal on exposed root surfaces.

Sulfitolysis and thioredoxin-dependent reduction reveal the presence of a structural disulfide bridge in spinach chloroplast fructose-1,6-bisphosphatase

A significant difference between cytosolic and chloroplastic fructose-1,6-bisphosphatase (FbPase) is an extra peptide in the middle of chloroplast FbPase which contains three additional cysteine residues. Sit-directed mutagenesis experiments have shown that at least two of these cysteine residues are involved in forming the regulatory disulfide bridge [Jacquot, J.-P. et al., FEBS Lett. 401 (1997) 143-147] which is the presupposition for the thioredoxin-dependent control of chloroplast FbPase activity. Here we report that each subunit of the FbPase contains an additional structural disulfide bridge which has been observed by combined application of thioredoxins and sulfitolysis. Observation of the structural disulfide bridges by sulfitolysis was only possible when the FbPase was already specifically reduced by the homologous thioredoxin species TRm. and TRf from spinach chloroplasts. Interestingly, the accessibility of the structural disulfide bridge for sulfite ions depends on the thioredoxin species engaged in the thioredoxin/FbPase complex.

Dehydroascorbate and dehydroascorbate reductase are phantom indicators of oxidative stress in plants

In many physiological studies dehydroascorbate (DHA) reductase is regarded as one of the chloroplast enzymes involved in the protection against oxidative stress. Here, evidence is presented that plant cells do not possess a specific DHA reductase. The DHA reductase activities measured in plant extracts are due to side reactions of proteins containing redox-active dicysteine sites. Native gel electrophoresis combined with specific activity staining revealed three different proteins with DHA reductase activity in leaf and chloroplast extracts. These proteins have been identified as thioredoxins and trypsin inhibitors (Kunitz type) by Western blot analysis. The essential regulatory functions of thioredoxins in chloroplast metabolism are strongly inhibited in the presence of as little as 50 microM DHA. Thus, the intracellular DHA concentration should be kept below 50 microM but not all proteins with DHA reductase activity are effective enough for this purpose. A specific DHA reductase is frequently demanded as part of the enzymatic equipment to avoid oxidative stress. We argue that this is not necessary because in chloroplasts DHA does not accumulate to any significant extent due to the high activities of monodehydroascorbate reductase and of reduced ferredoxin.

Kinetic evidence for protein complexes between thioredoxin and NADP-malate dehydrogenase and presence of a thioredoxin binding site at the N-terminus of the enzyme

The kinetics of activation of NADP-malate dehydrogenase (MDH; EC 1.1.1.82) from soybean and spinach leaves by the chloroplast thioredoxins isolated from the same plants, by the corresponding storage forms of the soybean chloroplast thioredoxins from soybean seeds, and by the bacterial Escherichia coli thioredoxin have been studied. The Hill equation has been applied to evaluate the saturation kinetics. The observed variable thioredoxin saturation characteristics (Vmax 0.37-14.5 mumol NADPH min-1 mg enzyme-1; K0.5 0.15-1.33 microM; Hill coefficient h 0.90-3.04) indicate that the activation of NADP-MDH depends strongly on the individual thioredoxin used. Thus, thioredoxin action is not solely due to simple reductive activation of the NADP-MDH. Specific thioredoxin complex formation between thioredoxin and NADP-MDH must be included into the mechanism of the activation process. To study the regulatory consequences of the specific thioredoxin/NADP-MDH complexes we investigated the saturation kinetics of the substrates NADPH and oxaloacetate in presence of different concentrations of each individual thioredoxin species. The kinetic characteristics of the substrates (S0.5, Vmax, and Hill coefficients h) varied individually in response to the different thioredoxin species substantiating our model of thioredoxin/ NADP-MDH complex formation. Aminopeptidase-K-truncated pea NADP-MDH has been used to demonstrate that the N-terminal 37 amino residues are involved in providing a specific thioredoxin binding site. The fact that the versatile light-dependent regulation of numerous enzyme activities by only two thioredoxin species in chloroplasts cannot be accomplished without the formation of thioredoxin/target enzyme complexes is discussed in detail.

Completion of the thioredoxin reaction mechanism: kinetic evidence for protein complexes between thioredoxin and fructose 1,6-bisphosphatase

The activation of chloroplast fructose 1,6-bisphosphatase from spinach and soybean leaves by the two chloroplast thioredoxins isolated from the same plants has been studied. The thioredoxin saturation characteristics (Vmax: 0.15-103.2 mumol Pi/min per mg enzyme; K0.5: 0.0048-0.84 microM; Hill coefficient n: 1.02-3.80) indicate that in addition to the reductive activation by thioredoxin specific complex formation between thioredoxin and fructose 1,6-bisphosphatase is responsible for fine regulation of the enzyme activity. This complex formation has been inserted into the thioredoxin mechanism and the physiological consequences discussed. Obviously, physiologically relevant investigations of the thioredoxin-dependent regulation of fructose 1,6-bisphosphatase activity can only be performed in homologous enzyme-thioredoxin combinations. Dithiothreitol and E. coli thioredoxin are no complete substitutes in regulatory studies.

Identification and localization of the first glutaredoxin in leaves of a higher plant

Glutaredoxin(thioltransferase) has been identified and purified to homogeneity from spinach leaves. Its cytosolic localization was demonstrated by chromatographic and immunological analysis of extracts from isolated spinach chloroplasts and mitochondria, respectively. Spinach glutaredoxin shows a significant crossreactivity with antibodies raised against E. coli glutaredoxin and possesses a specific thioltransferase activity comparable to that of the E. coli protein. Minor thioltransferase activities (less than 10% of total leaf activity) have been observed in spinach chloroplasts which are probably due to the presence of trypsin inhibitor and thioredoxins (TRf and TRm).

A novel-dehydroascorbate reductase from spinach chloroplasts homologous to plant trypsin inhibitor

Dehydroascorbate reductase has been isolated from spinach chloroplasts and purified to apparent homogeneity. The N-terminal amino acid sequence of the enzyme is homologous to the Kunitz-type trypsin inhibitors from plant sources. It is shown that spinach DHA reductase and soybean trypsin inhibitor are both capable of reducing dehydroascorbate when in the reduced (thiol) form but acquire trypsin-inhibiting activity in the oxidized (disulfide) state. Reduced chloroplast thioredoxins also reduce dehydroascorbate.

Structure requirements for disulfide bridge sulfitolysis of oxidized Escherichia coli thioredoxin studied by fluorescence spectroscopy

Sulfitolysis of wild-type and four mutated Escherichia coli thioredoxins ([D26A]thioredoxin, [P34H]thioredoxin, [K36E]thioredoxin and endo-Arg33a-thioredoxin) has been investigated at millimolar concentrations of sulfite in the absence of protein-denaturing agents by fluorescence spectroscopy. Sulfitolysis of the single disulfide bridge of these proteins is associated with an increase in fluorescence emissions at 345 nm. Evaluation of the fluorescence emission spectra revealed that sulfitolysis of thioredoxins is a homogenous process. The reactivities of the thioredoxins are determined by negatively charged (Asp26) or positively charged (Lys36) amino acid residues near the active site disulfide bridge.

Facile sulfitolysis of the disulfide bonds in oxidized thioredoxin and glutaredoxin

Thioredoxins and glutaredoxins, in their oxidized form, possess a single disulfide bridge located on an edge of the small compact molecules. In contrast to most other disulfide-containing proteins, this S-S bridge is cleaved by millimolar concentrations of sulfite in the absence of protein denaturing agents at pH 7-8 and ambient temperature; however, the reaction is not quantitative. Sulfitolysis of Escherichia coli thioredoxin was found to be associated with an increase in fluorescence at 345 nm. A comparative study of sulfitolysis in 12 different thioredoxins and glutaredoxins of bacterial and plant origin has been made. Although they are all thought to be highly conserved in three-dimensional structure, their reactivities towards sulfite and the effects of 6 M guanidinium chloride (not affecting, or enhancing sulfitolysis) vary strongly in the series, with E. coli thioredoxin being less reactive and plant thioredoxins and E. coli glutaredoxin being more susceptible molecules. Contrary to expectation, reaction with sulfite is not generally correlated with the presence of negatively or positively charged amino acid residues near the disulfide loop but is determined by individual sequence and surface features in every single protein. These results confirm our hypothesis that thioredoxin sulfitolysis and inactivation [Würfel, M., Häberlein, I., Follmann, H. (1990) FEBS Lett. 268, 146-148] can occur in plant cells under physiological conditions and provide a biochemical rationale for the phytotoxicity of SO2.

Non-redox protein interactions in the thioredoxin activation of chloroplast enzymes

Thioredoxin derivatives lacking SH groups such as S,S'-dicarboxymethyl-, dicarboxamidomethyl-thioredoxin and cysteine----serine mutant protein are capable of activating chloroplast NADP malate dehydrogenase and fructose-bisphosphatase when added to enzyme assays together with suboptimal amounts of native thioredoxin. The modified thioredoxins alone are inactive. These findings indicate that protein-protein interactions play a significant role in addition to disulfide/thiol exchange reactions in the light-driven regulation of plant enzymes by the various plant thioredoxins.

Inactivation of thioredoxin by sulfite ions

Oxidized thioredoxin undergoes sulfitolysis of its single disulfide bond at low concentrations of sulfite ions and protein and in the absence of denaturing agents. The reaction, which has an optimum at pH 8, was studied using [35S]sulfite and E. coli thioredoxin as model. The product, thioredoxin-S-sulfonate, has a half-life of several hours in solution. It is unable to activate chloroplast NADP malate dehydrogenase. Thioredoxin sulfitolysis may therefore be a physiologically important factor in mediating the phytotoxic effects of sulfur dioxide in plants.

Unexpected specificity in the thioredoxin activation of fructose-bis-phosphatases from different plants

Green seedlings of soy bean and wheat contain, like the plant seeds, multiple thioredoxin proteins which possess all typical thioredoxin properties but are inactive in the stimulation assay with spinach fructose-bis-phosphatase. However the pure proteins do have thioredoxin f activity when tested with homologous enzymes isolated from soy bean or wheat leaves, respectively, in the presence of Mg++. This new type of species specificity, unknown in all other in vitro assays of reduced thioredoxins, has to be considered in characterizing complete thioredoxin profiles in plants.