An ultrastructural quantitative study of the significance of microbial multiplication during early dental plaque growth

Influence of the incorporation of triclosan methacrylate on the physical properties and antibacterial activity of resin composite

The incorporation of antimicrobials in the composites as an attempt to reduce bacterial adhesion without jeopardizing mechanical properties is a challenge for Dentistry. OBJECTIVE To evaluate the bacterial adhesion and physical properties of a composite containing the methacrylate triclosan- derivative monomer (TM). METHODOLOGY TM was synthesized and added to an experimental composite. Samples were divided into two groups: Control and TM (13.4 wt%). Antibacterial Activity: Three specimens of each material were prepared and placed on bacterial suspensions of Streptococcus mutans for 1, 5 and 10 days. After these periods the counting of the colonies (log10) was performed. Assays was performed in triplicate. Physical Properties: Three-body Abrasion (TBA): Ten specimens of each material were prepared and stored at 37°C/24 h. The surface roughness (Ra) and hardness (KHN) were analyzed. Next, the specimens were submitted to abrasive wear (30,000 cycles) and re-evaluated for Ra and KHN; Sorption/solubility (SS): cylindrical specimens (n=10) were prepared and weighted. The specimens were immersed in deionized water for 7 days at 37°C and then their weight was verified again. SS were calculated using accepted formulas; Diametral tensile strength (DTS): specimens (n=10) underwent test performed in an Instron universal testing machine at a crosshead speed of 1 mm/min. Data were submitted to appropriate statistical tests according to data distribution and assay (p<0.05). RESULTS Bacterial Adhesion: TM showed a significant reduction on biofilm accumulation in the evaluated periods: 1 day (1.537±0.146); 5 days (2.183±0.138) and 10 days (4.469±0.155) when compared with Control: 1 day (4.954±0.249); 5 days (5.498±0.257) and 10 days (6.306±0.287). Physical Properties: For TBA, SS and DTS no significant difference was found between groups Control and TM. The incorporation of methacrylate triclosan-based monomer in the experimental composite reduce bacterial adhesion of S. mutans and did not affect important polymer properties.

Differential Utilization of Basic Proline-Rich Glycoproteins during Growth of Oral Bacteria in Saliva

Although saliva is widely recognized as a primary source of carbon and nitrogen for growth of the dental plaque biofilm community, little is known about how different oral bacteria utilize specific salivary components. To address this question, 32 strains representing 16 genera commonly isolated from early plaque biofilms were compared for growth over two transfers in stimulated (by chewing Parafilm) whole saliva that was stabilized by heat treatment and dialysis. The cell densities, measured by quantitative PCR (qPCR), ranged from ∼1 × 10(6) to 1 × 10(7)/ml for strains of Streptococcus gordonii, Streptococcus oralis, and Streptococcus mitis and one strain of Streptococcus sanguinis Strains of Streptococcus mutans, Gemella haemolysans, and Granulicatella adiacens reached ∼1 × 10(5) to 1 × 10(6)/ml. In contrast, little or no growth was noted for three other strains of S. sanguinis, as well as for strains of Streptococcus parasanguinis, Streptococcus salivarius, Streptococcus vestibularis, Streptococcus sobrinus, Actinomyces spp., Abiotrophia defectiva, and Rothia dentocariosa SDS-PAGE, lectin blotting, and two-dimensional gel electrophoresis of saliva from cultures of S. gordonii, S. oralis, and S. mitis revealed species-specific differences in the degradation of basic proline-rich glycoproteins (PRG). In contrast, saliva from cultures of other bacteria was indistinguishable from control saliva. Species-dependent differences in the utilization of individual host sugars were minor. Thus, differences in salivary glycan foraging between oral species may be important to cross-feeding and cooperation between organisms in dental plaque biofilm development.

IMPORTANCE

Bacteria in the mouth use saliva for nutrition. How each of the many types of bacteria uses saliva is not clear. We show that a major protein in saliva, called PRG, is an important nutrition source for certain bacteria but not for others. PRG has many sugar molecules linked in chains, but the sugar is not available for bacteria until the chains are degraded. The bacteria that can grow by digesting this protein break the sugar chains into parts which not only support their own growth but could also be available to support the growth of those bacteria that cannot use the intact protein.

Prevalence of cariogenic streptococci on incisor brackets detected by polymerase chain reaction

INTRODUCTION

Streptococcus mutans and Streptococcus sobrinus are the main causative organisms for enamel demineralization during orthodontic treatment. In this study, we analyzed the prevalence of cariogenic streptococci adhering to incisor brackets.

METHODS

Four incisor brackets from both the maxilla and the mandible were collected from 80 patients at debonding, immediately after the visible plaque index and the gingival bleeding index were measured from the incisors. The genomic DNA of adhered cariogenic streptococci was extracted and amplified by using polymerase chain reaction, and the prevalence of cariogenic streptococci was determined and compared with oral hygiene indexes in the incisor area.

RESULTS

The results showed that the prevalence of S mutans on incisor brackets was higher than that of S sobrinus, and the maxillary incisor brackets were colonized by both cariogenic streptococci to a somewhat higher degree than were the mandibular brackets. The prevalence of S mutans was 50.0% on the maxillary incisor brackets and 33.8% on the mandibular incisor brackets, but that of S sobrinus was 17.5% and 15.0%, respectively. At least 1 species of cariogenic streptococci was detected on the incisor brackets of 51 subjects (63.7%). However, the prevalence of cariogenic streptococci was not significantly associated with the oral hygiene indexes at debonding.

CONCLUSIONS

Cariogenic streptococci can adhere to orthodontic brackets. Careful hygiene control around orthodontic brackets is important.

Evaluation of surface characteristics of Ti-6Al-4V and Tilite alloys used for implant abutments

The aim of this study was to evaluate surface free energy (SFE), surface roughness (SR) and surface hardness (SH) of two commercially available materials for fabricating dental implant abutments. In addition, the specimens were investigated by scanning electron microscopy (SEM) to determine the surface morphology. Twenty five discs (5 x 2 mm) of Ti-6Al-4V and Tilite (Ni-Cr-Ti) alloys were used in this study. Surface free energy was determined by the contact angle formed between a drop of distilled, deionized water and the surface of the specimen of each material. The surface roughness was measured with a mechanical profilometer and the surface hardness was evaluated by means of the Vickers hardness micro indentation test. SFE, SR and SH data were analyzed using one-way ANOVA (p < 0.05). Statistical differences (p < 0.05) were found between Ti-6Al-4V (36.2 erg.cm-2; 0.2 µm) and Tilite (30.9 erg.cm-2; 0.16 µm) for SFE and SR. However, the differences between the surface hardness values of Ti-6Al-4V (325.0 kg/mm²) and Tilite (324.3 kg/mm²) were not statistically significant (p > 0.05). Evaluations by SEM revealed different surface morphology. Within the limits of this study, it can be concluded that the Ti-6Al-4V and Tilite alloys showed differences in surface properties, except for surface hardness, suggesting that both alloys may be considered appropriate for producing abutments. Further studies are, however, necessary to elucidate the biological responses to implant abutments made with these alloys.

How to select the right mouthrinses in periodontal prevention and therapy. Part II. Clinical use and recommendations

Based on scientific proof, only few mouthrinse solutions can be recommended. However, it is impossible to construct an extended table that would provide precise recommendations or advices for mouthrinse utilisation related to any possible discomfort or diseases. Only reliable information on the drugs available against periodontal disease can be offered to the therapist. By evaluation of her or his individual experiences, she or he has to judge all the armamentarium she or he possesses to react in the best possible way in each specific situation.

Plaque as a biofilm: pharmacological principles of drug delivery and action in the sub- and supragingival environment

Dental plaque is the diverse microbial community, embedded in a matrix of host and bacterial polymers, growing on teeth as a biofilm. Dental plaque develops naturally, and contributes to the host defences by preventing colonization by exogenous species. The composition of dental plaque varies at distinct surfaces as a result of the inherent biological and physical properties at these sites; the balance of the predominant bacterial populations shifts in disease. Plaque has an open architecture, with channels traversing from the biofilm surface through to the enamel. This structure affects the movement of molecules within plaque, and gradients in key determinants develop. Bacteria growing on a surface display a novel phenotype; one consequence of which is an increased resistance to antimicrobial agents. Resistance can result from restricted inhibitor penetration (diffusion-reaction theory), slower bacterial growth rates, transfer of resistance genes, suboptimal environmental conditions for inhibitor activity, and the expression of a resistant phenotype. Such biofilm-associated traits, coupled with the pharmacokinetic profile of orally delivered antimicrobial agents (high concentrations for short periods/lower concentrations for longer periods), affect the mode of action and efficacy of antimicrobials. Agents with a broad spectrum of activity in laboratory studies may display a far narrower inhibitory profile under the conditions prevailing in the mouth. This may result in a selective inhibition of species implicated in disease, or reduced production of virulence factors, while preserving the benefits associated with a resident oral microflora.

Permeability of Streptococcus mutans and Actinobacillus actinomycetemcomitans Through guided tissue regeneration membranes and their effects on attachment of periodontal ligament cells

BACKGROUND

Microbial colonization on barrier materials used in guided tissue regeneration (GTR) may adversely affect treatment outcomes. The purposes of this study were: 1) to compare the invasion of Streptococcus mutans and Actinobacillus actinomycetemcomitans through 3 GTR membranes, composed of expanded polytetrafluoroethylene (ePTFE; non-resorbable), a glycolide fiber composite, and type I collagen (both bioabsorbable), and 2) to explore the effects of bacteria on the attachment of periodontal ligament (PDL) fibroblasts onto these membranes.

METHODS

Bacterial permeability was analyzed using a tube capped with a GTR membrane as a septum and filled with media. The tube was then placed in a bigger tube inoculated with S. mutans or A. actinomycetemcomitans. The passage of bacteria through the membranes into the inner tube was monitored. For cellular attachment experiments, primary human PDL cells were placed onto the GTR membranes with or without bacteria. Attached cells were analyzed by scanning electron microscopy (SEM) analysis.

RESULTS

The ePTFE membrane had the best barrier effects followed by the collagen membrane and then the glycolide fiber composite membrane. Moreover, S. mutans passed through these membranes faster than A. actinomycetemcomitans. The attachment of PDL cells on the 3 membranes was also varied. The ePTFE membrane was the worst substrate for PDL fibroblast attachment. Moreover, both bacteria influenced the cellular attachment on the GTR membranes.

CONCLUSIONS

Differences in the behavior of 3 GTR membranes penetrated by S. mutans and A. actinomycetemcomitans were demonstrated. The results suggest that attachment of PDL cells was affected on bacterial-contaminated GTR membranes, which may alter healing following membrane exposure.

Root surface roughness following Er:YAG laser irradiation at different radiation energies and working tip angulations

OBJECTIVES

The determination of roughness of root surfaces following treatment with 2.94 micro m Er:YAG laser radiation at different radiation energies and working tip angulations.

MATERIALS AND METHODS

The study sample comprised 85 extracted human molars, premolars, canines and incisors (n = 85). The source of laser radiation was an Er:YAG laser device (KAVO-Key II, System Aesculap Meditec) emitting pulsed infrared radiation at a wavelength of 2.94 micro m, with a pulse duration of 250 micro s, and a pulse repetition rate of 10 pps. The samples were randomly divided into three experimental units, for treatment with a constant amount of 380 laser pulses at a radiation energy of 60 mJ, 100 mJ, and 180 mJ. Each experimental unit was divided into five subgroups of five samples, which were irradiated at a working tip angulations of 15 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees. Five samples were treated mechanically using curettes. Five samples were left untreated as control. The mean (Ra) and maximum (Rmax) surface roughness of each sample was measured using a profilometer. The statistical analysis was undertaken using anova and Scheffé-test at a level of significance of 5% (p < 0.05).

RESULTS

Er:YAG laser radiation led to an Ra which ranged from 0.52 micro m (+/- 0.10) to 0.81 micro m (+/- 0.26) and to an Rmax between 3.4 micro m (+/- 0.48) and 9.26 micro m (+/- 3.08). The Ra and Rmax for samples treated with curettes was 0.51 micro m (+/- 0.11) and 5.08 micro m (+/- 4.98), respectively. That for the untreated control samples were 0.53 micro m (+/- 0.15) and 7.07 micro m (+/- 5.48), respectively.

CONCLUSIONS

The mean and maximum surface roughness of root surfaces following irradiation with Er:YAG laser was not significantly different to that obtained on samples treated with conventional hand instruments or left untreated. Furthermore, the surface roughness does not depend on the radiation energy and the angulation of the working tip.

Roles of salivary proteins in the adherence of oral streptococci to various orthodontic brackets

Knowledge of salivary pellicles on orthodontic brackets provides a better understanding of microbial adherence. The aim of this study was to analyze the effects of bracket pellicles on the adherence of Streptococcus gordonii and Streptococcus mutans. Bracket pellicles were formed by the incubation of 4 kinds of orthodontic brackets with unstimulated whole saliva for 2 hrs, and analyzed by electrophoresis, immunodetection, and amino acid analysis. Binding assays were then performed by the incubation of tritium-labeled streptococci with the pellicle-transfer blots and orthodontic brackets. The results showed that low-molecular-weight mucin, alpha-amylase, secretory IgA, acidic proline-rich proteins, and cystatins adhered to all kinds of brackets, though the amino acid composition of pellicles differed between bracket types. Some of these proteins increased the binding of S. gordonii to saliva-coated brackets. However, salivary pellicles decreased the binding of S. mutans. Collectively, salivary pellicles were found to play a significant role in the initial adhesion of oral streptococci to orthodontic brackets.

Effect of carbon starvation and proteolytic activity on stationary-phase acid tolerance of Streptococcus mutans

Previous research with Streptococcus mutans and other oral streptococci has demonstrated that the acid shock of exponential-phase cells (pH 7.5 to 5.5) resulted in the induction of an acid tolerance response (ATR) increasing survival at low pH (3.5-3.0). The current study was designed to determine whether two fresh isolates, H7 and BM71, and two laboratory strains, Ingbritt and LT11, were capable of a stationary-phase ATR as estimated by a survival test at pH 3.5 for 3 h. All four strains were unable to generate a stationary-phase ATR under control conditions at pH 7.5, with the exception of a burst of survivors in the transition between the exponential and stationary phases when the carbon source (glucose) was depleted. Adaptation at pH 5.5 resulted in the expected pH-dependent exponential-phase ATR, but only the fresh isolates exhibited a stationary-phase ATR at this pH. Glucose starvation of cells in complex medium was shown to enhance acid tolerance for the fresh isolates, but not the laboratory strains. This tolerance was, however, greatly diminished for all strains in a defined medium with a low concentration of amino acids. Growth of strain H7 in complex medium resulted in the formation of at least 56 extracellular proteins, nine of which were degraded in the early stationary phase following the induction of proteolytic activity during the transition period. No proteolytic activity was observed with strain LT11 and only 19 extracellular proteins/peptides were apparent in the medium with only one being degraded in the early stationary phase. Strain H7 was also shown to have two- to fourfold higher levels of intracellular glycogen in the stationary phase than strain LT11. These results suggest that S. mutans H7 possessed the required endogenous metabolism to support amino acid/peptide uptake in the early-stationary phase, which resulted in the formation of basic end products that, in turn, contributed to enhanced intracellular pH homeostasis.

Inhibitory effects of resin composite containing bactericide-immobilized filler on plaque accumulation

OBJECTIVE

Previously, we have reported that incorporation of the antibacterial monomer 12-methacryloyloxydodecylpyridinium bromide (MDPB) was effective in immobilizing bactericide in the resin matrix, and an antibacterial composite without release of the agent could be achieved. In this study, an attempt was made to increase the density of bactericide immobilized in composite, and the inhibitory effects of this modified antibacterial composite on plaque accumulation were determined, focusing on the reliability of the effects and the mechanisms to affect the plaque formation.

METHODS

An experimental composite containing immobilized bactericide at 2.83% was prepared by the incorporation of MDPB into a prepolymerized resin filler of control composite, and elution of antibacterial components and inhibition of in vitro plaque accumulation by Streptococcus mutans were determined. The inhibitory effects of the experimental composite on the attachment, glucan synthesis and growth of S. mutans on the surface were also examined in addition to the comparison of surface roughness and hydrophobicity with controls. The results were analyzed using the Student's t-test.

RESULTS

The experimental composite had reproducible inhibitory effects against plaque accumulation compared with control (p<0.05), although it showed no elution of unpolymerized MDPB. The plaque-inhibitory effect of the experimental composite was found to depend upon the ability to inhibit the attachment, glucan synthesis, and growth of bacteria on its surface as no significant differences in the surface characteristics were obtained between control and experimental composites (p>0.05).

SIGNIFICANCE

It was indicated that the experimental composite containing bactericide-immobilized filler has the possibility to be used clinically with an effective anti-plaque property.

Poly(L-lactide)acid/alginate composite membranes for guided tissue regeneration

The barrier membranes for guided tissue regeneration (GTR) to treat bone defects have to satisfy the criteria of biocompatibility, cell-occlusiveness, space-making, tissue integration and clinical manageability. In this study a system constituted of a poly(L-lactide) acid (PLLA) asymmetric membrane combined with an alginate film was prepared. The PLLA membrane functions to both support the alginate film and separate the soft tissue; the alginate film is intended to act as potential vehicle for the growth factors to promote osteogenesis. The structural, morphological, and mechanical properties of the bilamellar membrane and its stability in culture medium were evaluated. Moreover, the feasibility of using the alginate membranes as controlled-release delivery vehicles of TGF-beta was monitored. Finally, the bacterial adhesion and permeability of Streptococcus mutans, selected for the high adhesive affinity, were monitored. The results showed that the surfaces of the alginate side, to be used in contact with the bone defect, were rougher than PLLA ones. When in contact with complete culture medium, the PLLA-alginate membrane retained its mechanical and structural properties for more than 100 days. Then, the degradation processes occurred but the membrane continued to be stable and manageable for 6 months. Growth factors such as TGF-beta can be incorporated into alginate membranes functioning as drug delivery vehicle, and retain the biological activity when tested in an in vitro model system. The obtained membrane acted as a barrier to the passage of S. mutans bacteria and showed to promote a lower bacterial adhesion with respect to commercial GTR membranes.

The effects of surface roughness and type of denture acrylic on biofilm formation by Streptococcus oralis in a constant depth film fermentor

AIMS

To investigate the effects of surface roughness and type of denture acrylic on the early development of a Streptococcus oralis biofilm in a constant depth film fermentor (CDFF).

METHODS AND RESULTS

Streptococcus oralis was incubated with acrylic of known surface roughness in the CDFF. Adherent Strep. oralis were enumerated by viable counting. Cold-cure acrylic was rougher (P < 0.01) than heat-cure acrylic after polishing with abrasive paper of any given grit-grade. Heat-cure acrylic was colonized by fewer (P < 0.001) bacteria than cold-cure acrylic at any given surface roughness. The number of bacteria adhering to heat-cure and cold-cure acrylic increased linearly with mean surface roughness after 2 h incubation, the increase being greater (P < 0.001) for the cold-cure compared with the heat-cure acrylic. However, after 4 h incubation, surface roughness appeared to have no effect on the number of adherent bacteria.

CONCLUSION

The type of acrylic used, and its roughness, affect the early stages of biofilm formation by Strep. oralis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Choosing an appropriate type of smooth acrylic could lead to reduced biofilm formation in vivo.

Spatial distribution of vital and dead microorganisms in dental biofilms

To examine the spatial structure of dental biofilms a vital fluorescence technique was combined with optical analysis of sections in a confocal laser scanning microscope (CLSM). Enamel slaps were worn in intraoral splints by three volunteers for five days to accumulate smooth-surface plaque. After vital staining with fluorescein diacetate and ethidium bromide the specimens were processed for CLSM examination. Optical sections 1 microm apart were analysed in the z-axis of these dental biofilms. One of the films was 15 microm high, sparse and showed low vitality, i.e. <16%, while the others were taller (25 and 31 microm) and more vital, i.e. up to 30 and 69%, respectively. In all instances the bacterial vitality increased from the enamel surface to the central part of the plaque and decreased again in the outer parts of the biofilm. The spatial arrangement of the microorganisms in the biofilm showed voids outlined by layers of vital bacteria, which themselves were packed in layers of dead material.

Defects in D-alanyl-lipoteichoic acid synthesis in Streptococcus mutans results in acid sensitivity

In the cariogenic organism, Streptococcus mutans, low pH induces an acid tolerance response (ATR). To identify acid-regulated proteins comprising the ATR, transposon mutagenesis with the thermosensitive plasmid pGh9:ISS1 was used to produce clones that were able to grow at neutral pH, but not in medium at pH 5.0. Sequence analysis of one mutant (IS1A) indicated that transposition had created a 6.3-kb deletion, one end of which was in dltB of the dlt operon encoding four proteins (DltA-DltD) involved in the synthesis of D-alanyl-lipoteichoic acid. Inactivation of the dltC gene, encoding the D-alanyl carrier protein (Dcp), resulted in the generation of the acid-sensitive mutant, BH97LC. Compared to the wild-type strain, LT11, the mutant exhibited a threefold-longer doubling time and a 33% lower growth yield. In addition, it was unable to initiate growth below pH 6.5 and unadapted cells were unable to survive a 3-h exposure in medium buffered at pH 3.5, while a pH of 3.0 was required to kill the wild type in the same time period. Also, induction of the ATR in BH97LC, as measured by the number of survivors at a pH killing unadapted cells, was 3 to 4 orders of magnitude lower than that exhibited by the wild type. While the LTA of both strains contained a similar average number of glycerolphosphate residues, permeabilized cells of BH97LC did not incorporate D-[(14)C]alanine into this amphiphile. This defect was correlated with the deficiency of Dcp. Chemical analysis of the LTA purified from the mutant confirmed the absence of D-alanine-esters. Electron micrographs showed that BH97LC is characterized by unequal polar caps and is devoid of a fibrous extracellular matrix present on the surface of the wild-type cells. Proton permeability assays revealed that the mutant was more permeable to protons than the wild type. This observation suggests a mechanism for the loss of the characteristic acid tolerance response in S. mutans.

Deposition and retention of vital and dead Streptococcus sanguinis cells on glass surfaces in a flow-chamber system

The proportion of vital as compared with dead Streptococcus sanguinis cells attached to glass surfaces was monitored and related to varying proportions of planktonic vital as compared with dead Strep. sanguinis cells. In a flow chamber with six parallel-mounted glass plates, Strep. sanguinis was suspended in pretreated sterile human saliva. Deposition of Strep. sanguinis took place, with a proportion of vital sanguinis streptococci in saliva (%VSs) of 90%, 45% or 22.5%. After exposure times of 30, 60, 90, 120 and 240 min, adherent microorganisms were labelled with two fluorescence stains to differentiate between vital and dead bacteria. Proportions of vital attached streptococci (%VSa) were determined microscopically. Dead bacteria were detected on all glass plates. The %VSa at 30 min and 60 min was significantly lower than the baseline %VSs. During the course of a single run the %VSa frequently increased after either 30, 60 or 90 min without exceeding the %VSs at 4 h. %VSs was the only variable exerting a significant effect on %VSa at 30 and 60 min. It is suggested that during the initial events of microbial attachment the dead rather than vital Strep. sanguinis cells attach preferably to solid surfaces.

An approach to differentiate between antibacterial and antiadhesive effects of mouthrinses in vivo

An experimental set-up allowing differentiation in vivo between antibacterial and antiadhesive properties of mouthrinses is described. The percentage of vital bacteria (= microbial vitality) and the bacterial counts were microscopically evaluated in saliva and in supragingival dental plaque both collected simultaneously at various times during de novo plaque formation. In a cross-over design, 12 healthy participants refrained from all oral hygiene for four separate periods of 2 x 4 h and 2 x 72 h after having rinsed with either an amine fluoride/stannous fluoride solution (Meridol) or 0.9% NaCl (placebo). Stimulated whole saliva was collected before and after the rinse. Together with whole-saliva samples, representative 4, 24 and 72-h-old plaque samples were separately taken from defined vestibular tooth surfaces that had been either exposed to the mouthrinse (unprotected sites) or temporarily covered with inert plastic films (protected sites) during rinsing. The pooled plaque and saliva were stained with fluorescent dyes to differentiate vital from dead micro-organisms which permitted the estimation of the percentages of vital bacteria. The total bacterial counts were quantified under the darkfield microscope. The Wilcoxon test was used for selected pairwise comparisons (alpha = 0.05). The percentage of vital bacteria in saliva fell significantly from 80-95% to about 50-60% as a result of the antibacterial activity of the test solution. These baseline values and those found in the presence of 4 and 24-h-old plaque were frequently lower than those recorded after the placebo rinse. In comparison to the placebo, microbial vitality was significantly reduced in early supragingival plaque formed on unprotected sites after applying the test solution. The similar total bacterial counts in 4-h-old plaque recorded after the use of the test solution on the unprotected and the protected areas did not point to an antiadhesive effect of the agent. It is concluded that this new experimental set-up allows decoding of the mode of action of a mouthrinse.

Survival of oral bacteria

The global distribution of individual species of oral bacteria demonstrates their ability to survive among their human hosts. Such an ubiquitous existence is the result of efficient transmission of strains and their persistence in the oral environment. Genetic analysis has identified specific clones of pathogenic bacteria causing infection. Presumably, these express virulence-associated characteristics enhancing colonization and survival in their hosts. A similar situation may occur with the oral resident flora, where genetic variants may express specific phenotypic characteristics related to survival. Survival in the mouth is enhanced by dental plaque formation, where persistence is associated with the bacteria's capacity not only to adhere and grow, but also to withstand oxygen, wide fluctuations in pH and carbohydrate concentration, and a diverse array of microbial interactions. Streptococcus mutans has been discussed as a 'model' organism possessing the biochemical flexibility that permits it to persist and dominate the indigenous microflora under conditions of stress.

The effect of a 1-stage full-mouth disinfection on oral malodor and microbial colonization of the tongue in periodontitis. A pilot study

Oral malodor affects a large proportion of the population and may be the cause of a significant social and psychological handicap. This pilot study aimed to examine whether a 1-stage full-mouth disinfection in periodontitis patients (scaling and root planing of all pockets within 24 hours together with the application of chlorhexidine to all intra-oral niches followed by chlorhexidine mouth rinsing for 2 months) resulted in a significant improvement in malodor when compared to a fractionated periodontal therapy (consecutive root planings per quadrant, at a 1 to 2 week interval). The baseline and outcome data concerning oral malodor were linked to the presence of tongue coating and to its roughness (fissures). Twenty-four patients with severe periodontitis were randomly allocated to test and control groups. At baseline and after 1 and 2 months, the concentration of volatile sulfur compounds (VSC) in the mouth was measured and organoleptic ratings (expired air and total mouth air) were given. Plaque samples were collected from the dorsum of the tongue to calculate the number of colony forming units (CFU) per ml (anaerobic culturing) as well as the number of pigmented CFU/ml. Both the baseline organoleptic ratings and the VSC scores correlated well with the presence of tongue coating but not with the tongue roughness. Because a correlation between tongue coating and its microbial load could not be detected, it was hypothesized that the tongue coating per se, and not the bacteria, might be responsible for the malodor. The 1-stage full-mouth disinfection resulted in a faster and additional reduction in the organoleptic ratings of the oral malodor, even after 2 months. This might be explained by the improved periodontal outcome and/or the more significant reduction in the CFU/ml of pigmented species. In contrast to the organoleptic ratings, which were significantly reduced in both treatment groups (when compared to baseline), the VSC levels remained unchanged. This pilot study indicates that a 1-stage full-mouth disinfection has, in comparison to a standard periodontal therapy, additional beneficial effects in the treatment of oral malodor.

Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: a review of the literature

OBJECTIVES

The roughness of intraoral hard surfaces can influence bacterial plague retention. The present review evaluates the initial surface roughness of several intraoral hard materials, as well as changes in this surface roughness as a consequence of different treatment modalities.

METHODS

Articles found through Medline searches were included in this review if they met the following criteria: 1) stated threshold surface roughness values and reputed change in surface roughness due to different manipulation techniques; or 2) included standardized surface conditions that could be compared to the treated surface.

RESULTS

Recently, some in vivo studies suggested a threshold surface roughness for bacterial retention (Ra = 0.2 micron) below which no further reduction in bacterial accumulation could be expected. An increase in surface roughness above this threshold roughness, however, resulted in a simultaneous increase in plaque accumulation, thereby increasing the risk for both caries and periodontal inflammation. The initial surface roughness of different dental materials (e.g., teeth, abutments, gold, amalgam, acrylic resin, resin composite, glass ionomer or compomer and ceramics) and the effect of different treatment modalities (e.g., polishing, scaling, brushing, condensing, glazing or finishing) on this initial surface roughness were analyzed and compared to the threshold surface roughness of 0.2 micron. The microbiological effects of these treatment modalities, if reported, are also discussed and compared to recent in vivo data.

SIGNIFICANCE

Based on this review, the range in surface roughness of different intraoral hard surfaces was found to be wide, and the impact of dental treatments on the surface roughness is material-dependent. Some clinical techniques result in a very smooth surface (compressing of composites against matrices), whereas others made the surface rather rough (application of hand instruments on gold). These findings indicated that every dental material needs its own treatment modality in order to obtain and maintain a surface as smooth as possible.

In vitro permeability evaluation and colonization of membranes for periodontal regeneration by Porphyromonas gingivalis

The use of membranes for periodontal regeneration is well established. In clinical use, the exposure of membranes to the oral microflora may result in a pathway for periodontal infections. An important role in this process is played by Porphyromonas gingivalis. The purpose of the present study was to examine the colonization of 6 different bioresorbable and nonresorbable membranes for periodontal regeneration by the strain DSM 20709 of P. gingivalis and to determine the time needed by this microorganism to pass through the membranes. A device consisting of a tube sealed with the membranes and filled with a medium suitable for the growth of P. gingivalis was incubated in a bigger tube containing the same medium to study the process of colonization and the crossing of membranes. The outer tube was inoculated with 10(4) cells of P. gingivalis DSM 20709. The passage of bacteria through the membranes was monitored at 6, 24, and 48 hours by counting the number of cells in the inner tube. The colonized membranes were observed using a scanning electron microscope. Differences in the behavior of the 6 membranes analyzed were demonstrated.

Effect of localized experimental gingivitis on early supragingival plaque accumulation

Previous investigations have reported increased plaque formation in the presence of gingival inflammation as compared with gingival health. In these investigations, experimental gingivitis has been induced by total abolition of oral hygiene such that increased levels of salivary bacteria could contribute to the increased plaque formation. In the present study, experimental gingivitis was localized to 2 selected teeth whilst maintaining normal oral hygiene measures in the rest of the mouth. The aim of this study was to investigate whether the mass of plaque accumulating in a 3-day period is influenced by the inflammatory status of the adjacent gingival margins. Following scaling, prophylaxis and a period of optimal hygiene to establish gingival health, "plaque-guards" were worn during routine oral hygiene performance to prevent any cleaning on the buccal surfaces of teeth 14 and 15 from days 0 to 3. On day 3, accumulated plaque was removed from a 1.5 mm zone on the buccal surfaces of 14 and 15 adjacent to the gingival margins and weighed immediately. Subjects continued to wear their plaque-guards during oral hygiene until day 14 to induce experimental gingivitis around the experimental teeth. At day 14, all plaque was cleaned from the buccal surfaces of the experimental teeth and the mass of plaque accumulating over the next 3 days weighed on day 17. Comparison of plaque weights showed that the wet-weight of 3 day-old plaque was higher in the presence of experimental gingivitis than in the presence of gingival health (p = 0.02). This observation suggests that the inflammatory status of the marginal gingiva has an important effect on early, supragingival plaque accumulation.

Influence of tooth instrumentation roughness on gingival tissue reactions

Histological studies have demonstrated a relationship between the amount of subgingival plaque and the magnitude and extension of gingival tissue reactions. The objective of the present study was to evaluate inflammatory reactions in the gingival tissues facing plaque accumulation at a diamond and curet-instrumented root surfaces. Experimental, deep periodontal defects were established at buccal surfaces of mandibular and maxillary canine teeth in 5 beagle dogs. The root surfaces were instrumented by a flame-shaped, fine-grained. rotating diamond point, or by a sharp curet. Next, the dogs were fed a plaque-inducing diet for 70 days. The animals were then sacrificed, and tissue blocks of the experimental sites including teeth, alveolar bone, and gingival tissues were secured. The gingival soft tissue was processed for histomorphometric analyses at 3 levels. Epithelium and connective tissue area measurements showed no differences between the two instrumentations. Junctional epithelium (JE) cell point counts exhibited a higher proportion of inflammatory cells (IC)in specimens facing diamond compared to curet-instrumented defects. A higher proportion of IC was present within the coronal compared to the apical aspect of the JE for both instrumentations (P < 0.05). A significant difference in IC density between instrumentations was detected for non-infiltrated (P < 0.05), as well as for infiltrated (P < 0.01) connective tissue. The infiltrated connective tissue (ICT) inflammatory cell density was significantly (P < 0.01) and positively correlated to the JE inflammatory cell density (r = 0.75), and to area measurements of ICT (r = 0.55). The overall results demonstrate that the character of subgingival root instrumentations significantly affects gingival inflammatory reactions, most likely by influencing subgingival plaque formation.

Patterns and rates of growth of microcosm dental plaque biofilms

Rates of growth in wet weight and changes in them over time were established for microcosm dental plaques cultured from the mixed salivary bacteria in an artificial mouth. Standardized conditions included a continuous supply of medium containing 0.25% mucin and 1.5 ml of 5% w/v sucrose in 6 min every 8 h. Plaques were weighed daily. Plaque wet weight and total protein were highly correlated. Plaque doubling times were 3-7 h over day 1 and 9-21 h over day 2, which is similar to in vivo plaques. Subsequently, growth curves were either linear or between a linear and exponential increase. Evidence was obtained for plaque blooms. Methyl paraben (0.2%) applied for 15 min (3.75 ml) 6 times daily inhibited growth but only for 3 days, after which the rate was similar to control plaques, indicating that selection for resistance had occurred. It was concluded that the regulation of plaque growth rates is complex and does not conform to simple growth pattern models. Detailed studies of plaque growth and the effects of antiplaque agents can be carried out using this experimental system.

Microbial generation time during the early phases of supragingival dental plaque formation

The objective of this investigation was to determine the microbial generation time during early human supragingival plaque formation. On 2 occasions, 13 participants refrained from all oral hygiene measures for periods of 1, 2, 4, 8, 24 and 72 h. Plaque was sampled from defined areas of the teeth 13, 14, 15, 23, 24 and 25. Two independent methods were used to estimate the total number of viable cells: colony-forming units BCVF, total bacterial counts (BC) as enumerated by microscopic examination, and the percentage of vital bacteria using a vital fluorescence technique (VF) were recorded. The total number of vital microorganisms was calculated by BCVF (= BC x VF). The generation time based on either colony-forming units or BCVF increased significantly with plaque age. During the first interval (1-4 h), the microbial multiplication took slightly less than 1 h. After the establishment of a more mature plaque (24-72 h), the replicating time was between 12.5 h (BCVF) and 14.8 h (colony-forming units). It was concluded that the microbial generation time recorded at the initial stages of plaque formation is considerably lower than that found in older plaque.

The influence of surface roughness and surface-free energy on supra- and subgingival plaque formation in man. A review of the literature

In the oral cavity, an open growth system, bacterial adhesion to the non-shedding surfaces is for most bacteria the only way to survive. This adhesion occurs in 4 phases: the transport of the bacterium to the surface, the initial adhesion with a reversible and irreversible stage, the attachment by specific interactions, and finally the colonization in order to form a biofilm. Different hard surfaces are available in the oral cavity (teeth, filling materials, dental implants, or prostheses), all with different surface characteristics. In a healthy situation, a dynamic equilibrium exists on these surfaces between the forces of retention and those of removal. However, an increased bacterial accumulation often results in a shift toward disease. 2 mechanisms favour the retention of dental plaque: adhesion and stagnation. The aim of this review is to examine the influence of the surface roughness and the surface free energy in the adhesion process. Both in vitro and in vivo studies underline the importance of both variables in supragingival plaque formation. Rough surfaces will promote plaque formation and maturation, and high-energy surfaces are known to collect more plaque, to bind the plaque more strongly and to select specific bacteria. Although both variables interact with each other, the influence of surface roughness overrules that of the surface free energy. For the subgingival environment, with more facilities for microorganisms to survive, the importance of surface characteristics dramatically decreases. However, the influence of surface roughness and surface-free energy on supragingival plaque justifies the demand for smooth surfaces with a low surface-free energy in order to minimise plaque formation, thereby reducing the occurrence of caries and periodontitis.

Mechanisms of dental plaque formation

Much effort has been placed on elucidating the diverse mechanisms of microbial adhesion to tooth surfaces. Both specific and non-specific types of adhesion have been envisaged. Pioneer colonizers represent a selected part of the oral microflora, and it has been assumed that specific adhesin-receptor interactions between the microbial surface and the pellicle account for this specificity. Whereas microbial adhesion to tooth surfaces is a general prerequisite for initiation of plaque formation, microbial multiplication is probably the dominant feature in the build-up of dental plaque. Local environmental factors which influence the establishment and composition of the ultimate plaque community are therefore of greater importance than initial adhesion per se. The highly individual and site-related characteristics of the plaque flora illustrate the selective power of the environment. Environmental conditions are not uniform. Thus, each site represents its own conditions are not uniform. Thus, each site represents its own distinct ecosystem, and the microbial composition at the site depends on the outcome of a variety of host-microbial and microbial-microbial interactions. The relative in vivo significance of these interactions is difficult to assess.

Evaluation of a new toothbrush concept with regard to bacterial elimination. Imprint study using scanning electron microscopy

The efficacy of a new toothbrush filament layout concept (Topix, Peridental, France) was compared to that of a standard vertical-tuft toothbrush. Bacterial and exogenous deposit elimination were used as parameters of efficacy. 30 dental surgery students took part in the study. Plaque index scores were calculated according to a pre-defined protocol. Imprints of the 6 anterior teeth were taken before and after brushing with the 2 types of brushes, without toothpaste or rinsing. Imprints were examined by scanning electron microscopy (SEM). 12 h after brushing, imprint examination revealed bacterial flora polymorphism and the amount of dental plaque accumulated at the cervical third zone of teeth. Automated quantification in this zone of exogenous bodies showed that after brushing with vertical-tuft and cross-tuft brushes, there remained 1.26 mm2 and 0.83 mm2 of dental plaque, squamae, and blood residues, respectively. The plaque index values correlated to scanning electron microscopic observations. There was no significant difference in terms of efficacy between the cross-tuft and vertical-tuft toothbrushes.

Adherence of oral microorganisms to guided tissue membranes: an in vitro study

Microorganisms can adhere and colonize on an exposed guided tissue regeneration (GTR) membrane thus developing a nidus of infection. The purpose of this study was to compare early bacterial adhesion to three different GTR membranes. Expanded polytetrafluoroethylene, polyglactin 910, and collagen were used as the test membranes. In part I of this study 15 different oral microbes were used to compare their relative ability to adhere to the membranes. Six of the most strongly adherent bacteria (Actinomyces viscosus, Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Streptococcus mutans, Fusobacterium nucleatum, and Selenomonas sputigena) were selected for part II of this study. The membranes were placed in tubes containing broth cultures containing identical concentrations (1 x 10(8) cells/ml) of these bacteria at 37 degrees C. Membranes were placed in tubes of media without bacteria as controls. At 4, 6, 12, and 24 hours, the bacterial cultures were decanted and the membranes in the tubes were agitated gently in reduced transfer fluid (RTF) 4 times to remove non-adherent bacteria. Each tube was then sonicated for 30 seconds in 10 ml RTF to detach adherent bacteria. The detached adherent bacteria were counted using a Petroff-Hausser chamber. Data were analyzed by using the SAS program. Analysis of variance was used to test for differences between multiple means. Results showed S. mutans had the strongest attachment to the collagen membrane at 4 and 6 hours. Selenomonas sputigena had the lowest adherence capability to all test membranes. Polyglactin 910 had significantly (P < 0.05) lower S. mutants adherence than either the ePTFE or the collagen membrane at 4 and 6 hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of accumulation of oral gram-positive bacteria on mucin-conditioned glass surfaces in a model system

Strains of Streptococcus, Actinomyces and Lactobacillus were grown on glass surfaces in semi-defined medium (pH 7.0) with mucin, at a dilution rate of D = 0.1 h-1, in a modified chemostat. The accumulation of cells followed four phases. In phase 1 (0-1 h), cells did not divide on the surfaces and adhesion accounted for rapid accumulation. Phase 2 (1-4 h) comprised adhesion and cell division, and accumulation slowed, cell number doubling times (Cdt) Streptococcus, 2.7 h to 8.6 h, Actinomyces, 2.3 h to 7.5 h and Lactobacillus, 3.6 h to 3.8 h. Cell division on surfaces accounted for accumulation in phase 3 (4 h to 12 h): Cdt Streptococcus, 1.7 h to 5.2 h, Actinomyces, 2.4 h to 7.5 h and Lactobacillus, 2.2 h to 7.2 h. The biofilm stabilized in Phase 4, Cdt 18.5 h to 90.2 h. The numbers (10(6) colony-forming units per cm2) of cells in stable biofilms were Streptococcus, 4.02 to 5.12, Actinomyces, 12.5 and 34.0 and Lactobacillus, 2.77. Accumulation increased (Cdt 0.9 h-2.7 h) when cells were exposed to glucose excess or high dilution rates and phase 2 of accumulation did not occur.

Copper plate replica SEM of developing dental plaque in monkeys (Macaca fascicularis)

The aim of the study was to examine the development of dental plaque in macaque monkeys (Macaca fascicularis). Copper plate replicas were constructed from impressions of the labial surface of one of the upper central incisor teeth after tooth cleaning and when plaque had accumulated for 12, 24 and 48 h in each of five animals. Scanning electron microscope examination of the replicas showed that bacteria were present on the tooth surface as scattered individual cells, which after 24 h had formed a continuous layer. Both coccoid and filamentous bacteria were visible in 48-hour-old plaque. Such a rapid accumulation of potentially periodontopathic dental plaque emphasizes the importance of regular and meticulous oral hygiene.

Relationship between bacterial counts, microbial vitality and the accumulation of supragingival dental plaque in humans

Comparisons between plaque index (PlI) and bacterial counts have been made already; however, these did not take into account the area used for plaque sampling. The objective of the present study was to determine the correlation between the PlI score, the number of bacteria and the bacterial plaque vitality when dental plaque was repeatedly sampled from the same area in each subject during early plaque accumulation. Between intervals of optimal oral hygiene, 10 participants refrained from all oral hygiene measures for periods of 1, 2, 3, 4 and 5 days. The PlI was recorded on the vestibular surface of all first premolars as local PlI:LS. For statistical reasons, the scores of the independent variable LS were added for each subject giving LS* values ranging from 0 to 8. The plaque sampled from this specific surface was circumscribed by the marginal gingiva and an acrylic splint, giving reproducible areas for plaque collection. Total microscopic bacterial counts (BC), colony forming units of anaerobes (CFUan) and aerobes (CFUae), and proportions of vital bacteria (VF) were compared with LS* values. BC and LS* values were strongly correlated. CFUan and CFUae increased significantly with LS*, but this increase was higher for LS* 0 to 4 than for LS* 4 to 8. The ratio between vital and dead microorganisms, assessed by two different methods, was low when an LS* of 0 was recorded, with higher ratios registered for LS* values 4 and 8.

Development of dental plaque on the incisor teeth of monkeys (Macaca fascicularis)

Bacterial plaque which had accumulated for 0.5, 1, 2, 4, 7, 14 and 28 days was cultured from the labial surface of one of the central incisor teeth in 15 monkeys (Macaca fascicularis). Each sampling area was defined by a metal well contained within a custom-made removable acrylic block. The number (log10) of the total colony forming units (c.f.u.) increased significantly from 3.40 to 6.02 between 0.5 and 28 days. Similarly the number of streptococci increased from 2.80 to 4.79 during the same period, although when expressed as a percentage of the total c.f.u., the proportions decreased from 34.9 per cent at 1 day to 6.9 per cent at 7 days and then remained at that level. The number of micro-aerophilic actinomyces increased throughout the period of plaque accumulation and comprised 15.3 per cent of the total c.f.u. at 28 days. Neisseriae were infrequently isolated from 0.5- and 1-day-old plaque and were not recovered at more than 1 per cent of the total c.f.u. during any period of plaque accumulation. The fastest doubling time (median) of the total c.f.u. was 1.9 h (range 1.3-18.5 h). The rapid development of dental plaque after tooth cleaning emphasizes the importance of regular and meticulous oral hygiene to control the accumulation of potentially periodontopathic and cariogenic bacteria.

The influence of surface free energy and surface roughness on early plaque formation. An in vivo study in man

Previous in vivo studies suggested that a high substratum surface free energy (s.f.e.) and an increased surface roughness facilitate the supragingival plaque accumulation. It is the aim of this clinical trial to explore the "relative" effect of a combination of these surface characteristics on plaque growth. 2 strips, one made of fluorethylenepropylene (FEP) and the other made of cellulose acetate (CA) (polymers with surface free energies of 20 and 58 erg/cm2, respectively) were stuck to the labial surface of the central incisors of 16 volunteers. Half the surface of each strip was smooth (Ra +/- 0.1 microns) and the other half was rough (Ra +/- 2.2 microns). The undisturbed plaque formation on these strips was followed over a period of 6 days. The plaque extension at day 3 and 6 was scored planimetrically from color slides. Finally, of 6 subjects samples were taken from the strips as well as from a neighbouring smooth tooth surface (s.f.e. 88 erg/cm2; Ra +/- 0.14 microns). These samples were analysed with a light microscope to score the proportion of coccoid cells, and small, medium, and large rods or fusiform bacteria. At day 3, a significant difference in plaque accumulation was only obtained when a rough surface was compared with a smooth surface. However, at day 6, significantly less plaque was recorded on FEP smooth (19.4%) when compared with CA smooth (39.5%). Between FEP rough (96.8%) and CA rough (98.2%), no significant difference appeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Is early plaque growth rate constant with time?

Early plaque growth and plaque topography were studied in 15 young adults with a healthy periodontium during a 4-day period of no oral hygiene. After perfect tooth-cleaning, the recolonisation of the buccal surfaces of 48 teeth (front teeth and premolars) was recorded at the start and after 6, 12, 24, 30, 36, 48, 54, 60, 72, 84 and 96 h. At each visit, reproducible colour slides of the buccal tooth surfaces were taken after plaque disclosure. Plaque extension was calculated planimetrically as a % of the total surface area of the tooth. At the end of the experimental period, an average of 27.7% of the surface area was covered by plaque. The early plaque growth followed an exponential curve with a slight tendency for saturation at 96 h. During the night, the plaque growth rate decreased by up to 50%. Clear differences in plaque growth rate were observed between types of teeth, and the plaque growth pattern seemed to be closely correlated to irregularities of the tooth surface. The discontinuity in plaque growth and the influence from the tooth surface roughness have important implications for oral hygiene planning.

The early bacterial colonization of acrylic palates in man

Adhesive tape applied to the fitting surface was used to study the early colonization of acrylic palates in six subjects. Streptococci were major constituents of the plaque accumulated on the tape over the first 3 days. Bacterial colonization of the tape discs was selective in that dextran-producing streptococci constituted a greater proportion of the total streptococcal count after 15 min compared with that of the initial sample and saliva, while the converse was true for Streptococcus salivarius. Scanning electron microscopy showed that denture plaque development started in grooves and depressions on the surface of the tape, and became more extensive with time. Comparison of the colonization of tape and acrylic discs in one individual demonstrated that the tape was a suitable model for in vivo colonization of dentures or orthodontic appliances.