Micromorphological and micronanalytical characterization of stagnating and progressing root caries lesions

Root caries is the predominant disease of the tooth tissues in the elderly population and differs in progression and micromorphology from coronal dentin caries. Therefore, different clinical concepts are needed for the treatment of these progressing and arrested lesions. It was the aim of this study to investigate the three-dimensional structure and volume of stagnating and progressing root caries lesions and to determine the mineral composition of the different lesion zones to achieve a better understanding of the natural history of root caries lesion formation. Of 21 extracted human teeth of patients between 42 and 77 years of age with stagnating and progressing root caries lesions serial sections were cut and investigated with polarized light and scanning electron microscopy. From the polarized light micrographs 3D reconstructions were made to determine the volumes of the lesion zones and their relations expressed in a demineralization index (DI). With increasing size of the demineralizing zone the DI increased indicating an increase in the size of the translucent zone. The 3D reconstructions showed distinct differences between stagnating and progressing root caries lesions. In the hypermineralized translucent dentin not all dentin tubules were obliterated by intratubular dentin and within the translucent dentin scattered dead tracts were found. Electron dispersive X-ray (EDX) analysis showed that the intertubular dentin of the translucent dentin was also demineralized to a certain extent. The results indicate distinct morphological differences between progressing and stagnating root caries lesions which may have consequences for treatment strategies.

Development of an in situ root caries model. A. In vitro investigations

OBJECTIVES

The paper describes preliminary in vitro investigations, the objectives of which were to examine the influence of certain experimental parameters on artificial carious lesion formation in root hard tissues, and their remineralisation. These experiments formed part of a wider study that aimed to develop an in situ model of root caries, based on the existing coronal caries model used in Liverpool. The present studies examined the effects (a) of the anatomical origin of the dentine, the presence or absence of cementum, the exposure time and the type of demineralising system, on lesion development, and (b) of baseline lesion size on the extent and location of mineral re-precipitation.

METHODS

Mineral content parameters in plano-parallel sections taken from dentine lesions were determined by computer-controlled transverse microradiography.

RESULTS

The importance of the anatomical origin of the dentine on lesion formation was investigated by comparing in vitro lesion formation in premolar and molar dentine, and in dentine from apical, middle and coronal thirds of the root: no difference was observed between these sites. Lesions formed more rapidly in acid buffer solutions than in acid gel systems, and were more reliably produced when cementum was removed. The effect of baseline lesion size on subsequent in vitro remineralisation demonstrated that a small baseline mineral content was associated with a larger percentage mineral gain. The location of mineral deposition throughout the lesion was also influenced by baseline mineral content parameters.

CONCLUSIONS

The results form a basis for the further development of an in situ dentinal caries model, providing data to suggest that manipulation of parameters involved in the preparation of artificial carious lesions has a significant effect on the behaviour of the lesion, particularly the phenomenon of remineralisation. Further work is needed to investigate the behaviour of the model in situ.

Development of an in situ root caries model B. In situ investigations

OBJECTIVES

The aims of this pilot study were to assess the suitability of an in situ model for root caries studies, and to investigate the effect of sub-surface lesion mineral content and ultrastructural organisation on remineralisation.

METHODS

Subjects were selected by criteria generally used for coronal caries models. Plaque pH responses and salivary flow rates were determined by standard methods. The chosen substrate was human dentine with artificially induced caries-like demineralisation and sterilised by gamma-irradiation (4100 Gy). Two levels of baseline demineralisation were induced by exposure to an acid buffer for 2 or 5 days. Mineral content was measured by computer-controlled quantitative microradiography.

RESULTS

Remineralisation in situ was greater in smaller lesions with lower surface mineral content than in larger lesions in which the surface mineral content was high.

CONCLUSIONS

The model is suitable for further development for investigating dentinal caries. More work is needed to validate the model by means of a fluoride dose-response study.

Effect of Saliva Composition on Experimental Root Caries

The aim of this study was to determine the effect of saliva composition on caries lesion development independently of the flow rate of unstimulated whole saliva (UWS) and other caries-related variables such as lesion progression time, oral hygiene level, and fluoride exposure. We hypothesized that this could be done by developing experimental root caries under carefully controlled conditions in situ in test subjects with UWS flow rates within a narrow window of normalcy. Fifteen female and 5 male subjects (66 +/- 6 years) were selected for the study according to their UWS flow rates between 0.2 and 0.4 ml/min. All subjects developed experimental root caries lesions during a 62-day period in which UWS as well as stimulated whole saliva (SWS) were repeatedly collected and analysed for flow rate, pH, buffer capacity, inorganic, and organic composition. Caries lesion development was determined by quantitative microradiography. The mean UWS flow rate was 0.30 +/- 0.05 ml/min. Significant negative correlations were obtained between UWS total phosphate concentration and mineral loss (DeltaZ; r(s) = -0.72, p < 0.001) and UWS total protein concentration and DeltaZ (r(s) = -0.70, p < 0.01). SWS and its constituents had only limited or no effect on DeltaZ. Qualitative UWS protein analysis (SDS-PAGE) revealed that subjects with low DeltaZ values had broader and more stained amylase bands than subjects with high DeltaZ values. These findings were confirmed quantitatively by HPLC. We conclude that, within a group of subjects with normal UWS flow rates, the UWS composition was more important for caries lesion development than the SWS composition. Furthermore, high UWS concentrations of phosphate, protein, and amylase were caries-protective.

Influence of the mineral content and morphological pattern of artificial root caries lesion on composite resin bond strength

Dentine substrates with different mineral contents and morphological patterns were created by submitting root slabs to the following treatments: (A) immersion in artificial saliva during the experimental period (control), (B) demineralization for 32 h to induce caries lesion (demineralized group), and (C) demineralization for 32 h followed by remineralization for 8 d (remineralized group). The slabs were longitudinally sectioned, the mineral content was determined by cross-sectional microhardness, and the bond strength of an adhesive system/composite resin was assessed using a microtensile bond strength test. The dentine morphology after the treatments as well as the failure pattern of the debonded specimens was examined by scanning electron microscopy. Statistically significant differences were found in mineral content. Morphological analysis showed marked differences between the patterns of demineralized and remineralized substrates. The bond strength mean value of the control A did not differ from the group B, but was statistically higher than the group C. Since no linear relationship was found between dentine mineral content and bond strength values, it could be suggested that the morphological pattern may be more relevant than the mineral content to explain the bond strength of composite resin to dentine.

Penetration of an antibacterial dentine-bonding system into demineralized human root dentine in vitro

In this study, the penetration of three proprietary dentine-bonding agents (Prime & Bond 2.1, Single Bond, Liner Bond 2) and experimental dentine-bonding systems incorporating an antibacterial monomer, 12-methacryloyloxydodecylpyridinium bromide (MDPB), into artificial root caries lesions was evaluated, and the bactericidal activity of each material against Streptococcus mutans or Lactobacillus casei impregnated into demineralized dentine blocks was assessed. All of the commercial dentine-bonding agents were capable of penetrating into the artificial carious lesions to more than 150 microm. The depth of penetration of the experimental systems, which were based on Liner Bond 2, was not significantly different from that of their parent product. Liner Bond 2 primer exhibited the greatest bactericidal effects among the three proprietary dentine-bonding agents tested. Bactericidal activities of experimental primers containing MDPB were greater than those of any other products, and the application of 4% MDPB-containing primer resulted in complete killing of bacteria in demineralized dentine. The results indicate that the penetration of dentine-bonding agents into extensively demineralized root dentine is possible in vitro, and the experimental dentine-bonding systems containing the antibacterial monomer MDPB are capable of killing bacteria within demineralized dentine. This could be of benefit when managing root caries lesions.

Fluoride distribution in sound and carious root tissues of human teeth

Proton probe analysis has been used to provide for the first time quantitative F concentration data in carious root tissues from subjects consuming water containing 1 ppm F. In small lesions at the neck of the tooth with minimal tissue loss the F concentration was significantly higher at the outer lesion edge than at the outer edge of adjacent sound root tissue. In one sample with high F values the lesion edge had 19,000 ppm F and the adjacent sound root surface 5,400 ppm F microg F/g apatite). In large lesions with extensive cavitation F was again concentrated in the outer edge of the lesion and was significantly higher (1,800-4,100 ppm) than in adjacent sound inner dentine (190-290 ppm). Fluoride concentrations varied markedly along the outer edge of both normal and carious root tissues. Fluoride increase at the lesion edge is not an effect of tissue shrinkage but probably a result of remineralisation events during caries. This additional F may be expected to increase tissue resistance to further acid attacks.

Studies of dental root surface caries. 2: The role of cementum in root surface caries

Artificial caries lesions were produced in roots of teeth using an acetate buffer system, when the layer of cementum was either normal in thickness, excessively thickened by hypercementosis, or had been removed completely. The rates of lesion progression were measured in each case using polarized light microscopy to measure lesion depth. Analysis of calcium (Ca) and phosphorus (P) loss during the demineralizing process was carried out. The removal of cementum was found to significantly increase the initial rate of penetration of the lesion into the root, although this rate progressively reduced to a level consistent with that found in normal roots after seven days of demineralization. The overall depth remained consistently greater than that observed in normal roots, or when lesions were produced entirely within hyperplastic cementum. Chemical analysis also showed removal of cementum resulted in an initial doubling of the Ca and P lost from the root surface. Prior direct exposure of segments of normal roots to the oral environment was found not to significantly alter the rate of artificial lesion progression, in comparison with that in the originally protected segment of the root surface. It was concluded that an intact cementum layer has the intrinsic ability to protect the underlying dentine of exposed tooth roots against acidic demineralization and that prior exposure to the oral environment does not significantly alter this ability.

Studies of dental root surface caries. 1: Comparison of natural and artificial root caries lesions

Qualitative polarized light microscopy and cross-sectional microhardness testing profiles were used to compare artificial root caries lesions with those naturally present in extracted human teeth. The artificial lesions were produced by immersion of roots with exposed windows in chemical buffers of acetate and lactate with no added enzymes or bacteria. The three buffer systems used produced lesions with the range of histological characteristics of natural lesions. These included a 'body' or 'surface' zone of the lesion when viewed in water, and a 'frontal' zone of reverse birefringence when viewed in quinoline. The 'frontal' zone was noted to first develop after three days of immersion in acetate buffer. Advanced natural lesions exhibited a wide, diffuse, advancing front, which was similar to that produced by 28-60 day lesions in acetate. Microhardness profiles of natural lesions could all be matched by one or more of the artificial lesions. The demineralizing process was seen to reduce mineral content across the lesion from 45 per cent in normal dentine to between 15 and 25 per cent.

[The dynamics of pH, free calcium and total proteins in root plaque fluid and their relationships to the cariogenic potential]

OBJECTIVE

To enhance knowledge of root caries by analysis of the dynamics of dental plaque fluids on root surface and their relationships with the caries history.

METHODS

The pH, free calcium and total proteins of dental plaque fluids on sound root surfaces were analyzed before and after the sucrose challenge. Subjects were either root caries-free (RCF) or caries-positive (RCP).

RESULTS

After a sucrose challenge, the pH of plaque fluids dropped significantly and the concentration of free calcium increased significantly. There were no statistical differences in pH (RCF group 6.24 +/- 0.74, RCP group 5.96 +/- 0.70) and free calcium [RCF group (0.60 +/- 0.46) mmol/L, RCP group (0.89 +/- 0.54) mmol/L] between RCF and RCP group before sucrose challenge. Following sucrose exposure, pH (5.14 +/- 0.19) and free calcium [(1.73 +/- 0.74) mmol/L] in RCP group were significantly lower than RCP group [(pH 5.28 +/- 0.16), free calcium (2.73 +/- 1.25) mmol/L]. No interrelationship has been found between the amount of total proteins and free calcium. Components (contents, change trend) in root plaque were strongly related to that in coronal plaque.

CONCLUSIONS

The process of root caries may be consistent to coronal caries regarding to the acid production of bacteria after a sucrose challenge. Plaque compositions show a stronger cariogenic potential in RCP group.

1H-NMR analysis of microbial-derived organic acids in primary root carious lesions and saliva

In addition to lowered pH values, the molecular profile and concentrations of microbial-derived organic acids in carious dentin are important demineralization parameters involved in the induction, development and progression of dental caries. High-resolution proton ((1)H) NMR spectroscopy was employed to examine the organic acid status of primary root carious lesions. (1)H-NMR analysis of post-neutralized perchloric acid extracts of active carious lesions revealed that at an operating frequency of 600 MHz, the (1)H-NMR-detectable organic acid composition of carious dentin samples (mean molecular percentage content +/- standard error; the mean molecular percentage content is defined here as the mean of the concentration of each (1)H-NMR-visible organic acid/anion expressed as a percentage of total (1)H-NMR-detectable organic acid/anion level in each sample) was acetate 51 +/- 2%, formate 37 +/- 2%, lactate 5 +/- 1%, propionate 3 +/- 0.8%, pyruvate 2.4 +/- 0.3%, n-butyrate 1.2 +/- 0.2%; succinate 0.1 +/- 0.1%; iso-butyrate, n- and iso-valerate, and n- and iso-caproate (total) <0.2%. Further components detectable included alanine, glycine, choline, phosphorylcholine, trimethylamine oxide, methanol, glycolate and assorted saccharides. In view of their high dissociation constants (K(a)), our results demonstrate that formic and pyruvic acids (K(a) = 1.77 x 10(-4) and 3.20 x 10(-3) mol/dm(3), respectively) contribute substantially to the decreased pH values associated with active caries lesions (cf. lactate K(a) = 1.40 x 10(-4) mol/dm(3)), and hence the pathogenesis of primary root caries.

Visualization of root caries lesions by means of a diazonium dye

A diazonium dye was used to visualize caries lesions in root tissue. Root caries lesions were created in vitro according to a variety of protocols based on methylcellulose gel (6% w/v) and/or lactic acid buffer (0.05 M, pH 4.5). Teeth containing lesions were soaked overnight in an alkaline solution of 2% (w/v) 2-naphthol or resorcinol, rinsed with distilled water, and immersed in a diazonium solution (prepared by titration of aniline with sodium nitrite in 1 M HCl at 5 degrees C) for up to 10 min, prior to being thoroughly rinsed with distilled water. The area of the caries lesion on the anatomical surface was clearly marked with a red/orange color following 5 minutes' incubation in the diazonium solution. The diazonium complex formed with 2-naphthol was found to be more resistant to leaching during rinsing and sectioning than that formed with resorcinol. Microscopic examination of sections taken in the apicalcoronal plane showed that the depth of area of the lesion was also marked by the red/orange coloration. Chemical changes in root mineral monitored during lesion formation showed some degree of correlation between lesion area and mineral dissolution. Visualization of coronal caries by this technique is currently under investigation. The visualization technique provides a simple means of determining the extent and severity of root caries lesions and may be a useful first step in their classification.

A computer-assisted videodensitometric method to visualize mineral distributions in in vitro and in vivo formed root caries lesions

A computer-assisted videodensitometry (CAV) method is presented for the microradiographical mineral determination and mineral visualization of in vitro and in vivo formed dentin lesions. The method employs as essential steps (1) image digitizing by a CCD camera, (2) conversion of gray values to equivalent aluminium thicknesses and (3) conversion of aluminium thickness to vol% of mineral. Procedure and accuracy are described. The CAV method is illustrated for dentin lesions formed in vitro as well as for clinical root caries lesions. The CAV method is especially advantageous for clinical lesions because it can be employed for very complex mineral distributions and irregular lesion outlines. In given areas of interest, the mineral distribution (in vol%) can be plotted in 3D form in pseudo-colors. Conventional microradiographical profiles can be obtained directly from the CAV images. For in vitro lesions, the mineral distribution parameters, lesion depth, mineral loss, and mineral acquisition values can be generated from CAV images with a reproducibility of better than 7%. The CAV method is a valuable tool in quantitative mineral studies of clinical lesions in extracted teeth as well as in in situ lesion investigations.

Effect of a two-solution fluoride mouth rinse on deposition of loosely bound fluoride on sound root tissue and remineralization of root lesions in vitro

A constant-composition fluoride (F) titration method was used to measure the amount of leachable F deposited on root surfaces in vitro by a 1-min rinse with a 12 mmol/l sodium fluoride (228 micrograms/g F) solution or a two-solution rinse that contained 2 mmol/l sodium fluorosilicate (228 micrograms/g total F ) and 10 mmol/l calcium chloride. The mean +/- standard deviations (n = 3) F uptake from the two rinse treatments were 0.70 +/- 0.24 micrograms/cm2 and 3.25 +/- 0.74 micrograms/cm2, respectively. In a separate experiment, the effects of sodium fluoride and the two-solution rinses on remineralization of root lesions were evaluated in an in vitro pH cycling model. The results showed that the average decrease in mineral loss (delta Z) in the two-solution rinse group (60%) was significantly greater than that obtained in the NaF rinse (41%) or the control (9%) group.

Penetration of varnishes into demineralized root dentine in vitro

In this paper the penetration of three different varnishes employed in caries prevention (Duraphat, Fluor Protector and Cervitec) into demineralized dentine is quantified using confocal laser scanning microscopy. The results show that the varnish penetration into lesions about 85 microns in depth if for Cervitec about 35 microns and considerably less for Duraphat and Fluor Protector. The penetration is into the dentinal tubules and is influenced by dentinal tubule direction. The drying procedure--pretreatment of the dentine--influences the penetration, though sizeably only for Cervitec applications. This paper shows that varnish penetration into the tissue and presumably 'sealing' tubules completely or partly is valuable with respect to root caries prevention and hypersensitivity.

Remineralization of root lesions with concentrated calcium and phosphate solutions

Remineralization of enamel lesions in vitro by use of sequential treatments with an alkaline (pH 9) phosphate (1 mol/L) solution and slightly acidic (pH 6) calcium (1 mol/L) solution was reported to be relatively ineffective. An analysis of the diffusion processes that may occur during the remineralization treatments suggested that the driving force for diffusion of Ca into the lesion can be increased by making the calcium solution more alkaline than the phosphate solution. In the present study this modified treatment procedure was evaluated for remineralizing root lesions in vitro. Results show that (1) in the control group there was a slight increase in mineral density in the surface region of the lesion, (2) in the experimental group there were significant (p < 0.05) increase in mineral content in the outer 40 microns of the lesion, and (3) in contrast to the finding reported previously, thick mineral deposits on the surface of the root were not observed.

Root caries histopathology and chemistry

This paper reviews the histopathology of root surface caries, and the effect of fluoride on the root caries process. The root caries process may be defined as a dynamic equilibrium similar to enamel caries. The caries process produced acid demineralization in exposed root surfaces and resulted in a lesion body when viewed in the light microscope. A relatively intact surface layer was not always present unless root caries was observed. In the absence of fluoride, a significant surface layer was left devoid of mineral but with intact collagen. Fluoride helped to prevent lesion formation and produced radiodense banding within the lesions in in vitro models. Remineralization occurred on the remaining mineral and not on the collagen matrix devoid of mineral. The conversion of active to inactive root caries requires the formation of a mineralized layer and implies the loss of surface tissues and contour in the clinical situation.

The influence of the organic matrix on demineralization of bovine root dentin in vitro

The effect of matrix degradation on the rate of demineralization of dentin lesions was investigated. It was hypothesized that the demineralized matrix would inhibit the demineralization of the underlying mineralized dentin. Bovine root dentin specimens were alternately demineralized and incubated with either a bacterial collagenase or buffer (control). The demineralization was carried out under various conditions: Acetic acid solutions were used to form incipient and advanced erosive lesions, and lactic acid solutions containing a bisphosphonate were used to form incipient subsurface lesions. Under all conditions, the demineralization was found to be accelerated when the matrix was degraded by collagenase. This increase was more pronounced in advanced erosive lesions than in incipient lesions. Microscopic examination of collagenase-treated specimens revealed that the matrix of erosive lesions contained several layers of differently affected matrices, whereas the matrix of subsurface lesions appeared to be equally affected throughout the lesion. In conclusion, the matrix degradation was different in erosive and subsurface lesions but promoted the demineralization in both types of lesions.

In situ remineralization of root surface lesions using a fluoride chewing gum or fluoride-releasing device

The in situ remineralization of early root surface lesions was studied using a fluoride-releasing device (FRD) or a fluoride chewing gum. Root specimens with subsurface lesions were mounted in removable lower appliances in 6 adult subjects. Test groups chewed five sticks/day (0.1 mg F/stick) or one FRD (0.5 mg F/day release rate) was mounted in the midline of the appliance. A fluoride-free dentifrice was used three times/day for each 21-day control and the two test regimens. Separate root lesions were used to measure fluoride uptake or changes in mineral content by quantitative microradiography. Comparable values for percent remineralization for both FRDs and F gum were higher than controls, and the F uptake for FRDs exceeded both the F gum and controls (p = 0.05).

An in vitro model for studying the efficacy of fluoride dentifrices in preventing root caries

This investigation tested and validated an in vitro model for studying the effects of fluoride on human dentin mineral content and fluoride uptake. Four studies examined the effects of different concentrations of fluoride, established dose-response profiles with NaF and Na2PO3F, and tested commercial dentifrices. A 7- or 14-day cyclic treatment regimen involved four 1-min exposures of sound human dentin specimens to the treatment agents, a 4-hour acid challenge period, and 20 h in human saliva daily. Mineral content was analyzed by image analysis microradiography and fluoride assays were performed using a microdrill biopsy technique. Data from these studies established the ability of the in vitro model to provide reproducible results, to demonstrate significant dose-related differences in the effects of both NaF- and Na2PO3F-containing treatments on dentin fluoride uptake and demineralization, and to detect a fluoride-induced reduction in dentin caries, relative to a nonfluoride control, similar to results established in a clinical trial.