Plaque-free Zone Research Articles

Revisiting “Plaque Free Zone”- Island of Peace in a Zone of Conflict: A stereomicroscopic study

Aim: This study was undertaken to find if Plaque Free Zone (PFZ) indeed was a ubiquitous entity observed both on healthy and diseased teeth and further to compare the width of PFZ in healthy and diseased teeth.
 Material & Methods: Out of total 31 teeth, 18 teeth extracted from patients with chronic periodontitis and 13 teeth extracted from healthy individuals were examined. The teeth were stained and measurements of width of PFZ were made. Photomicrographs were taken at 20X magnification using a stereomicroscope & measurements were made using Image J software. The data obtained was subjected to statistical analysis.
 Results: A significantly wider PFZ was found on the surfaces of teeth of healthy group as compared to diseased group.
 Conclusion: Wider PFZ zone in healthy teeth may have a protective role preventing direct contact of bacteria with underlying periodontal ligament. Invasion of this zone during mechanical instrumentation needs to be avoided.
 Clinical Significance: The existence of plaque free zone has clinical implications. Instrumentation beyond the base of the pocket during SRP may upset the delicate balance existing at tooth sulcus/pocket interface.

Chlorhexidine with or without alcohol against biofilm formation: efficacy, adverse events and taste preference.

In recent years, different chlorhexidine formulations have been tested, including an alcohol-free alternative, but the effect of this solution on early biofilm formation is not clear. A crossover, randomized, double-blind clinical trial was conducted to evaluate the effect of two chlorhexidine solutions against supra- and subgingival biofilm formation (NCT#02656251). Thirty-five participants were randomized and asked to rinse twice daily with 15 ml of an alcohol-containing 0.12% chlorhexidine solution, an alcohol-free 0.12% chlorhexidine solution, or placebo. The study was conducted in three experimental periods of 4 days each, with a 10-day washout between the periods. All the experimental periods followed the same protocol, except that the solutions were switched. Biofilm distribution was evaluated every 24 hours by the Plaque-Free Zone Index, during 96 hours. Adverse events were self-reported and sensory evaluation was performed using a hedonic scale. Compared to the placebo, the chlorhexidine solutions resulted in a significantly higher number of surfaces free of plaque over 96 hours (p < 0.01), and were able to prevent subgingival biofilm formation (p < 0.01). The alcohol-free chlorhexidine solution was associated with a lower incidence of adverse events, compared with alcohol-containing chlorhexidine (p < 0.05); it also received better sensory evaluation and acceptance by trial participants, compared with the alcohol-containing chlorhexidine (p = 0.007), and had a similar inhibitory effect on the formation of supra- and subgingival biofilms.

The characteristics of periodontal disease in respect to biofilm disease

The purpose of the present study was to examine whether bacterial biofilm concerned with bacterial colonization and growth of subgingival plaque. We observed subgingival plaque of 95 severe adult periodontitis-affected teeth by scanning electron microscope. In the coronal one-third zone of subgingival plaque, cocci, rods and others established biofilm by glycocalyx-like structure. In the middle one-third zone, several kinds of bacterial species were coaggregated. Film-like microcolonies were also observed in this zone. We detected filamentous microorganisms appeared to come out from the film-like colonies, and observed holes which microorganisms had been passed through the colonies. In the apical one-third zone, several kinds of bacterial species aggregated by glycocalyx-like structures, which comprised netlike and mucoidal structure. In the “plaque-free zone”, two types of bacterial colonization were observed : bacterial cell wall directly contacted with the root surface, and microorganisms adhered to the root surface mediated by glycocalyx netlike materials. In this zone, five periodontal disease-associated bacteria, including Porphyromonas gingivalis, were detected using back-scattered electron imaging modes. The results of the present study suggested that bacterial biofilms were partially related to colonization and growth of subgingival plaque.

Identification of periodontal disease-associated bacteria in the "plaque-free zone".

Subgingival plaque bacteria live within a biofilm covered with glycocalyx, and little is known of the bacterial species associated with biofilm formation at the bottom of human periodontal pockets, the so-called "plaque-free zone"(PFZ). Seventy-seven extracted teeth from 56 patients with severe advanced adult periodontitis were examined. Porphyromonas gingivalis, Campylobacter rectus, Fusobacterium nucleatum, Actinobacillus actinomycetemcomitans, Treponema denticola, Prevotella nigrescens, and Actinomyces viscosus were examined by scanning immunoelectron microscopic techniques, using both secondary and back-scattered imaging, with rabbit antibodies specific for each bacteria. Secondary electron images showed that rods, filaments, and spirochete-shaped bacteria formed small aggregates in the PFZ. Some of the bacteria were covered with an amorphous film-like structure. By back-scattered electron imaging, positive reactions with anti-P. gingivalis were found in 8 of 13 samples examined, and film-like structures coated several cells of 6 positive samples examined. Labeled cells with anti-C. rectus, anti-T. denticola and anti-P. nigrescens were detected in 3 of 11, 5 of 10, and 1 of 8 samples examined. A. viscosus were found in 6 of 11 of the samples. A. viscosus tended to overlay the amorphous capsula and aggregate. F. nucleatum and A. actinomycetemcomitans were not detected in any samples examined. These findings indicated that P. gingivalis, C. rectus, T. denticola, P. nigrescens, and A. viscosus were present in the PFZ, and that some specified bacteria were possibly related to plaque-biofilm formation of subgingival plaque.

The apical border plaque in severe periodontitis. An ultrastructural study.

This study concerns the apical border (AB) plaque in relation to severe forms of periodontitis (SP), including juvenile, post-juvenile, and rapidly progressing periodontitis. Twenty-four (24) teeth from 16 patients with SP were examined by transmission electron microscopy (TEM). The AB was not discrete, with islands of bacteria in the so-called plaque-free zone (PFZ). Coronal to the AB the established plaque consisted of a layer of Gram-positive cocci and ghost cells and a superficial layer mainly of Gram-negative morphotypes, including cocci, rods, filaments, fusiforms, and spirochetes. The most apical apparently intact organisms in the PFZ were in bacterial islands or in isolation and were predominantly Gram-negative cocci and rods, with ghost cells in abundance. Ruthenium red, alcian blue-lanthanum nitrate, and safranin O were used to label matrix polyanionic macromolecules, and periodic acid (thiosemicarbazide) silver proteinate for intracellular polysaccharide (IPS). The matrix components were mainly fibrillar. Many intact bacteria exhibited extracellular polysaccharides or glycocalyces associated with their cell wall, and cytoplasmic IPS granules. The latter varied in distribution and were evident even in the most apically advanced intact microorganisms. The results indicate that IPS and some matrix features of the apical border plaque in severe periodontitis in certain aspects resemble those of sub-contact area plaque on children's teeth, in health or associated with early chronic gingivitis, and with those in chronic adult periodontitis. They also suggest the establishment of acidic regions in the microniche at the bottom of the periodontal pocket in the various forms of periodontitis differing in rate of progression. It was concluded that there was a limited range of intact bacterial morphotypes in the apical border plaque in severe periodontitis, similar to those in chronic adult periodontitis.

Ultrastructure and Histochemistry of the Dental Cuticle in Adult Periodontitis

This study examined the dental cuticle (DC) at the interface with cementum surface, as well as its relationship to the overlying subgingival plaque (SP), the so-called plaque-free zone (PFZ), the junctional epithelium (JE), and the coronal fibers of the residual periodontal ligament (PL) by transmission electron microscopy (TEM) and histochemistry. Material comprised of 41 extracted, adult periodontitis-affected teeth (AP). Following extraction, 20 teeth were fixed in 3% glutaraldehyde in 0.1M sodium cacodylate, post-fixed in 1% osmium tetroxide, embedded in araldite, decalcified in EDTA, re-embedded in araldite, and sectioned. En bloc histochemistry was undertaken on the remaining 21 teeth, using ruthenium red, alcian blue-lanthanum nitrate, or safranin-O, and processed as above. Results show that the DC covered the cementum surface from the SP to the JE, and formed an interface with these structures. No DC was observed at the interface with PL. Morphological variations in DC surface were observed at the interface with the SP and at the so-called PFZ where bacteria were always in close contact with or surrounded by the DC. At the interface with JE, the DC appeared homogeneous, although layers varying in electron density were distinguishable. Teeth treated histochemically revealed a positive reaction of DC and bacteria to the three methods, suggesting the presence of anionic polymers including glycoproteins in the DC. It was concluded that on adult periodontitis affected teeth, the DC always covers exposed cementum and may mediate bacterial adhesion, and adsorb components from the periodontal pocket.

The apical border plaque in chronic adult periodontitis. An ultrastructural study. I. Morphology, structure, and cell content.

THIS STUDY CONCERNS THE APICAL BORDER (AB) plaque in relation to chronic adult periodontitis (AP). Fifty-six teeth from 24 patients with AP were examined by transmission electron microscopy (TEM). The AB was not discrete with islands of bacteria in the so-called plaque-free zone (PFZ). Coronal to the AB, the established plaque commonly consisted of three to four layers of Gram-positive and Gram-negative cocci, rods, filaments, and spirochetes and a superficial layer, mainly of spirochetes, but including filaments, "test tube brush," and "corn-cob" formations. The most apical apparently intact organisms in the PFZ were in bacterial islands or in isolation and were predominantly Gram-negative cocci and rods, with occasional other morphotypes. The most apical microorganisms were invariably ghost cells. A cuticle of varying thickness and structure was present at the plaque/tooth interface. It was concluded that there was a limited range of intact bacterial morphotypes in the apical border plaque in chronic periodontitis.

The width of plaque‐free zones on primary molars with attachment loss

The width of plaque-free zones on stained surfaces of extracted primary molars showing attachment loss was measured. The teeth were divided into 4 groups: maxillary first and second molars, mandibular first and second molars. 30 measurements were made under a stereomicroscope on each of the 4 surfaces in every group. The plaque-free zone had a mean width of 1.75 +/- 0.49 mm and a range of 1.0-4.3 mm. The plaque-free zone was significantly (P less than 0.001) wider on the proximal surfaces (1.94 +/- 0.56 mm) than on the combined buccal and lingual surfaces (1.56 +/- 0.32 mm). There was no difference between the 2 proximal surfaces while the lingual surfaces gave higher values than the buccal ones. On the second and on the lower primary molars, the plaque-free zones were wider than on the first and on the upper molars.

Scanning electron microscopy observations of initial clot formation on treated root surfaces.

This study presents the morphological sequence of events in initial blood clot formation on various root surfaces of freshly extracted human teeth. Four teeth with periodontal disease (PD) and three teeth without PD were extracted and the roots sectioned into halves. Those root surfaces with PD had four treatment areas: (1) intact periodontal ligament (PDL), (2) unplanned PD, (3) PD plus planed, (4) PD plus planed plus application of pH 1 citric acid (CA). The roots with no PD had three treatment areas: (1) intact PDL, (2) planed, (3) planed plus CA. Both root halves were reinserted together into the original extraction site. Each root half was then removed at either zero, one, two or four minutes and prepared for scanning electron microscope (SEM) evaluation. SEM observations suggested that plasma proteins were deposited initially on all root surfaces. Platelets and erythrocytes enmeshed in fibrin deposited most rapidly and consistently over the plasma protein layer where intact PDL was present. Similar observations were noted on the planed plus CA surfaces and appeared to occur at an earlier time than on the planed-only surfaces. A constant feature at all time periods was the absence of organized clot formation over the plaque-free zone of the PD root surfaces. By two minutes all surfaces, except the plaque-free zone of the PD area, appeared to have clot lysis occurring. While clot formation appeared to occur more rapidly over surfaces in the non-PD roots, no marked morphological differences in clot formation were observed between PD and non-PD teeth with similar root surface treatments.

Plaque-free zones on human teeth in periodontitis.

The surface morphology of the pocket area of extracted, periodontally involved, human teeth was studied with steromicroscope. A plaque-free zone was found to be present in all specimens. The width of the plaque-free zone was found to decrease as the pocket depth and loss of attachment increase.

Method for detecting antiviral agents on paper chromatograms.

SummaryA procedure has been developed whereby paper chromatograms of antiviral agents can be developed by applying them to virus infected, agar overlay, chick embryo cell tissue cultures. Plaque-free zones are produced, thus indicating the area on paper chromatogram where the active material can be located. Using antiviral substances antibiotic W-112 and isatin-monothiosemicarbazone, W. Nile and vaccinia viruses, and 4 chromato-graphic solvent systems, it was possible to localize the biological activity of these antiviral agents. As little as 1 μg of antibiotic W-112 produced large plaque-free zones when paper chromatogram was applied to the overlay culture 1 hr after virus infection. When 100 μg of same material was used, large plaque-free areas resulted even when the paper was applied 46 hr after virus infection. Isatin-monothiosemicarbazone at 50 μg level not only produced a plaque-free zone but also produced a yellow spot on paper chromatogram that coincided exactly with the zone of antiviral activity.

Agar diffusion method for detection and bioassay of antiviral antibiotics.

A procedure has been developed whereby agar diffusion technics used in bacteriology can be applied to antiviral agents. Chick embryo cell monolayers were grown in Pyrex baking dishes, infected with virus and overlaid with agar. Filter paper discs impregnated with the test materials were deposited on the hardened agar surface. After proper incubation the virus produced plaques in the cell sheet, except in the area around a disc containing an antiviral agent. Since size of the plaque-free zone was proportioned to concentration of the antiviral agent present in the disc, bioassays were simply performed in exactly the same manner as done with antibacterial antibiotics.