Demineralization and Remineralization of Root Surface Caries

Although enamel, cementum and dentin all develop carious lesions in roughly the same manner there are significant differences between enamel and the other two tissues. While early enamel lesions are white, root surface lesions in cementum or dentin are light brown or yellow. The color probably arises from extrinsic stain materials, and it is possible that very early, actively forming lesions are colorless. Cementum and dentin often acquire a hypermineralized surface when first exposed to the oral environment. When caries begins to form, this layer can enlarge or disappear. Therefore, it is possible to have lesions with hypermineralized surface layers, hypomineralized surface layers, or no surface layer. Hypermineralization can also occur deeply within a lesion, probably as a result of remineralization. When this occurs the lumen of the tubules fill with mineral and the crystals within the lesion body become larger. Fluoride is readily taken up by carious root tissues and contributes to remineralization. Remineralization of artificial root surfaces after treatment with monofluorophosphate has been shown. In these lesions much of the newly acquired mineral was found near the surface but some was also found in the lesion body.     

Methodological Issues Relative to the Quantification of Root Surface Caries1

The purpose of this study was to assess the effect upon the quantification of root surface caries (RSC) of (1) the separation of the disease into its discrete clinical phases, (2) the confounding caused by the presence of restored abraded surfaces, and (3) the decision rule formulated for dealing with lesions and restorations which involve both crown and root. It was found that the apparent prevalence of RSC varied widely depending upon arbitrary decisions as to what stages of the disease were included in the measurement scheme. The addition of restorations (confined to the root) greatly enlarged the various disease measures, but probably also introduced some degree of error since there are several indications from the data and the clinical patterns of affected surfaces which suggest that some of the restored surfaces were formerly abraded rather than carious. The inclusion of lesions and restorations involving both root and crown produced another conspicuous increment in all disease measures, which is a cause for concern given that these components are included in some studies and ignored in others. These findings serve as the basis for several recommendations for future prevalence and incidence studies of RSC.     

The Clinical Profiles of Individuals With and Without Root Surface Caries1

As part of a collaborative multidisciplinary investigation of root surface caries (RSC), 273 subjects (median age = 57) were clinically evaluated for coronal caries, debris, calculus, gingivitis, periodontal pocketing, recession, abrasion, as well as RSC. The entire study group was divided into three subgroups: (1) subjects whose exposed root surface were without lesions or restorations (non-diseased individuals, n= 43); (2) subjects whose exposed root surfaces had one or more lesions and may or may not have had restorations (diseased individuals, n= 110); (3) subjects with one or more restorations but no lesions, since it was not known whether these restorations were preceded by RSC or abrasion the disease status of these individuals was unclear (n= 120). A comparison of Subgroup 1 (unequivocally non-diseased) and Subgroup 2 (unequivocally diseased) revealed that subjects without RSC had more teeth, less coronal caries, less recession, less debris, less calculus, less gingivitis, and more abrasion. We infer that the common factor underlying most if not all of the subgroup differences is oral hygiene which must therefore be a major disease determinant.     

Prevention of Root Caries1

Primary prevention of root caries should focus on preventing periodontitis and the concomitant loss of gingival attachment. This requires a regimen of plaque control consisting of scrupulous oral hygiene, supplemented, if necessary, by antimicrobial agents. Once gingival recession has occurred, available data from human and animal studies indicate that to prevent root caries, patients should limit their dietary sucrose intake both in amount and frequency. The cornerstone of any preventive regimen for patients at high risk for caries is some mode of topical fluoride therapy. No controlled clinical data exist that show one agent (sodium fluoride versus stannous fluoride) or one vehicle (gel versus rinse) as more effective than another. When used daily at home, these topical fluoride agents reduce caries in patients with xerostomia. Some reports claiming efficacy are anecdotal, but ethical considerations preclude the use of an untreated control group. As no studies exist documenting an effect of topical fluoride in controlling root caries per se, current recommendations are based on extrapolation from studies of these xerostomic patients. Limited studies, both in humans and animals, indicate that drinking fluoridated water helps in reducing root caries. Progression of early root caries lesions can be arrested by a combination of mechanical/chemical therapy, recontouring and smoothing the roots, and applying topical fluoride to these surfaces.     

Epidemiology of Root Caries1

Over a dozen studies have been conducted on the prevalence of and factors associated with root caries, yet our knowledge of this disease process remains limited. This is due, in large part, to a lack of consistency of reporting among the studies undertaken and the wide spectrum of population groups investigated. Nevertheless, the occurrence of root caries is between 20 and 40 percent in healthy, urban adults. Certain population groups such as the institutionalized elderly and patients with periodontal disease tend to exhibit much larger prevalence rates. New root caries develops slowly and tends to be concentrated in a few individuals, usually on the buccal and proximal surfaces of teeth. It is generally accepted that only roots with gingival recession are susceptible to root caries and that age, sex, oral hygiene, diet, saliva, systemic fluoride and previous carious experience have been shown to be associated factors. The next wave of investigations of root canes should focus on testing hypotheses relating to causation so that efficacious preventive and treatment procedures can be developed.     

The Diagnosis of Root Caries – A Review

Interest in root caries has grown among dental caries research workers over the past 20 years. However, many studies, either in the fields of microbiology, pathology, epidemiology or clinical trials, have used differing definitions in their diagnosis of root caries. These differences mean that comparison between studies is difficult, if not impossible. Most of the criteria currently in use are neither sufficiently specific to allow the identification of the initial root caries lesion, not detailed enough to assess the progression of lesions. Furthermore, most definitions provide no information on treatment need within the populations studied. In this paper, the criteria which have been used to diagnose root caries, and their individual components – texture, cavitation, position, size, colour and radiolucency – are reviewed. It is concluded that there is a need to standardise terminology and definitions used for the diagnosis of root caries.     

Extensive Description and Comparison of Human Supra-Gingival Microbiome in Root Caries and Health

Knowledge of the polymicrobial etiology of root caries is limited. To conduct a comprehensive research study on root caries, we utilized 454-pyrosequencing of 16S rRNA gene libraries and quantitative PCR to compare supra-gingival bacterial communities from healthy sites and carious sites of 21 patients with root caries (Patient-controls and Patient-cases) and the sites of 21 healthy individuals (Healthy-controls) from two nursing homes. Healthy-controls and Patient-cases showed no significant differences in terms of biomass, species richness, and species diversity. However, as for beta diversity based on either community membership metric (unweighted UniFrac) or community structure metric (weighted UniFrac), Healthy-controls and Patient-cases were clearly distinguished from each other, appearing more variable in the community membership and structure in root caries microbiome but relatively conserved in the health microbiome. The Patient-controls group was at an intermediate stage between Healthy-controls and Patient-cases, but was more inclined to the former. Demonstrated in both relative abundance and prevalence of species in health and root caries, Propionibacterium acidifaciens, Streptococcus mutans, Olsenella profusa, Prevotella multisaccharivorax, and Lactobacillus crispatus were found to be most associated with root caries, whereas Delftia acidovorans, Bacteroidetes[G-2] sp., Lachnospiraceae[G-3] sp., and Prevotella intermedia are most associated with health. Our study provides a basis for further elucidating the microbial etiology of root caries in the elderly.     

Effect of Root Agglutinin on Microbial Activities in the Rhizosphere

A total of 220 bacterial isolates were obtained from pea rhizosphere and nonrhizosphere samples. Of these samples, 100 isolates were chosen randomly to test for their agglutinative reaction against pea root exudate. The percentage of positive agglutination of bacteria isolated from the nonrhizosphere sample was significantly lower than that of bacteria isolated from the rhizosphere sample. Moreover, this agglutinative reaction could not be blocked either by treating the bacterial cells or root exudate with different carbohydrates before they were mixed or by boiling the root exudate first. Bacteria that could be agglutinated by pea root exudate followed the downward growth of the pea root through the soil profile. The greater abilities of such bacteria to colonize the pea rhizosphere were indicated by their higher rhizosphere-colonizing (rhizosphere/nonrhizosphere) ratios, whether the bacteria were added alone or together with nonagglutinating bacteria. However, bacteria did show different agglutinative reactions toward root exudates obtained from different plants.     

Specific Microbial Attachment to Root Knot Nematodes in Suppressive Soil

Understanding the interactions of plant-parasitic nematodes with antagonistic soil microbes could provide opportunities for novel crop protection strategies. Three arable soils were investigated for their suppressiveness against the root knot nematode Meloidogyne hapla. For all three soils, M. hapla developed significantly fewer galls, egg masses, and eggs on tomato plants in unsterilized than in sterilized infested soil. Egg numbers were reduced by up to 93%. This suggested suppression by soil microbial communities. The soils significantly differed in the composition of microbial communities and in the suppressiveness to M. hapla. To identify microorganisms interacting with M. hapla in soil, second-stage juveniles (J2) baited in the test soil were cultivation independently analyzed for attached microbes. PCR-denaturing gradient gel electrophoresis of fungal ITS or 16S rRNA genes of bacteria and bacterial groups from nematode and soil samples was performed, and DNA sequences from J2-associated bands were determined. The fingerprints showed many species that were abundant on J2 but not in the surrounding soil, especially in fungal profiles. Fungi associated with J2 from all three soils were related to the genera Davidiella and Rhizophydium, while the genera Eurotium, Ganoderma, and Cylindrocarpon were specific for the most suppressive soil. Among the 20 highly abundant operational taxonomic units of bacteria specific for J2 in suppressive soil, six were closely related to infectious species such as Shigella spp., whereas the most abundant were Malikia spinosa and Rothia amarae, as determined by 16S rRNA amplicon pyrosequencing. In conclusion, a diverse microflora specifically adhered to J2 of M. hapla in soil and presumably affected female fecundity.     

Effect of a 0.05% Neutral NaF Mouthrinse on Coronal and Root Caries of Adults1

Three-year coronal and root caries increments were compared in adults rinsing with either a 0.05% neutral NaF mouthrinse or a placebo mouthrinse. 1006 subjects, initially 20–65 years old (mean age: 39.9 yrs). who resided in fluoride deficient communities used a fluoride or placebo mouthrinse daily in their homes and brushed with an A.D.A. accepted fluoride dentifrice provided by the study. After three years, 731 subjects remained. Compliance was good. There were no significant differences (t-test, p≤ 0.05) in coronal DMFT, coronal DMFS, root DFT and root DFS between the two groups. In subjects exhibiting root caries at the final examination, the DF root surface increment was 25.1% less in the fluoride mouthrinse users compared to those using the placebo rinse, but this difference was not statistically significant. The only significant difference in the caries increment between the two study groups was found for the mesio-distal root surfaces of 45–65 year old participants.     

Microbial and Root Components of Respiration of Sod-Podzolic Soils in Boreal Forest

The microbial contribution to the respiration of sod-podzolic soils has been estimated during two seasons (2012–2013) in boreal forest (Valdai district in Novgorod oblast, Russia) by a combination of methods of substrate induced respiration (SIR) and integration of components (IC). Despite the higher accuracy of SIR in estimating soil microbial respiration (R_mic), it is found that the combined application of these two methods results in a better correspondence of field experiments to the published data based on laboratory experiments. The contribution of microbial respiration differs between wooded and degraded sites. Hence, these sites should be investigated separately in upscaling studies of microbial respiration in soils of a boreal forest. The underestimation of microbial respiration should also be noted when using the IC method in field experiments. Among the main controls of R_mic are abiotic ones (soil temperature at a depth of 10 cm; month of the vegetation season), as well as the type of the mesohabitat. The seasonal dynamics of microbial respiration was related to the Selyaninov hydrothermal factor. Despite seasonal and cross-habitat differences in R_mic, it was specific for the particular type of soil and ecosystem.     

Wavelike Distributions of Microbial Populations along an Artificial Root Moving through Soil

Abstract In a previous paper, we described wavelike distributions of bacterial populations along roots of wheat, and hypothesized that one mechanism underlying these distributions might be growth and death cycles of microorganisms in response to a moving nutrient source, the root tip. Similar wavelike distributions in microbial biomass were obtained using a simulation model for growth and death of bacteria in relation to their substrate (BACWAVE). The model was parameterized with data from one experiment on rhizosphere bacterial populations along wheat roots, and compared against a similar but independent experiment. In experiments described in this paper, similar wavelike distributions in bacterial populations were observed in response to a single artificial exudate moving linearly through a soil that had been air-dry for almost 2 years. The period of the spatial waves was longer when the tip of the artificial exudate moved at a speed of 4.2 cm/day compared to a tip moving at 1.1 cm/day, but after transformation into the temporal domain, the periods of the waves were similar for both moving speeds. The observed distributions were simulated using the BACWAVE model with similar parameter values as derived from the experiment with wheat roots mentioned above. The results presented in this paper confirm our hypothesis that wavelike distributions of bacterial population along plant roots can arise from ``exudates' released primarily from the root tip, without the need for additional exudation points. Received: 12 October 1999; Accepted: 9 March 2000; Online Publication: 28 August 2000     

Microbial Transformation of Nitroaromatics in Surface Soils and Aquifer Materials

Microorganisms indigenous to surface soils and aquifer materials collected at a munitions-contaminated site transformed 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT), and 2,6-dinitrotoluene (2,6-DNT) to amino-nitro intermediates within 20 to 70 days. Carbon mineralization studies with both unlabeled (TNT, 2,4-DNT, and 2,6-DNT) and radiolabeled ([¹⁴C]TNT) substrates indicated that a significant fraction of these source compounds was degraded to CO₂.     

The Effect of Pseudomonas putida Colonization on Root Surface Peroxidase

Increased activities of peroxidase and indole 3-acetic acid (IAA) oxidase were detected on root surfaces of bean (Phaseolus vulgaris) seedlings colonized with a soil saprophytic bacterium, Pseudomonas putida. IAA oxidase activity increased over 250-fold and peroxidase 8-fold. Enhancement was greater for 6-day-old than for 4- or 8-day-old inoculated plants No IAA oxidase or peroxidase activities were associated with the bacterial cells. Native polyacrylamide gel electrophoresis demonstrated that washes of P. putida-inoculated roots contained two zones of peroxidase activity. Only the more anodic bands were detected in washes from noninoculated roots. Ion exchange and molecular sizing gel chromatography of washes from P. putida-colonized roots separated two fractions of peroxidase activity. One fraction corresponded to the anodic bands detected in washes of P. putida inoculated and in noninoculated roots. A second fraction corresponded to the less anodic zone of peroxidase, which was characteristic of P. putida-inoculated plants. This peroxidase had a higher IAA oxidase to peroxidase ratio than the more anodic, common enzyme. The changes in root surface peroxidases caused by colonization by a saprophytic bacterium are discussed with reference to plant-pathogen interactions.