The effect of sealing white spot lesions on lesion progression in vitro

The resistance of white spot lesions to acid demineralization when etched with phosphoric acid and sealed with a resin material was studied. Artificially created white spot lesions were sealed and re-exposed to an artificial caries medium along with unprotected white spot lesions. Examination with polarized light microscopy revealed continued progression of the unprotected white spot lesions, whereas no lesion progression was evident under the resin sealant. New lesions formed on unprotected sound enamel adjacent to the margin of the resin sealant over sound enamel tangent to the white spot lesions. The sealed sound enamel adjacent to the white spot lesions did not undergo demineralization indicating protection by the resin tags. Sealing white spot lesions following etching with a 37% phosphoric acid may be beneficial in inhibiting lesion progression.     

Orthodontic appliances and enamel demineralization. Part 1. Lesion development

A clinical trial was conducted to investigate carious lesion development associated with fixed orthodontic therapy. Specially designed orthodontic bands for plaque accumulation were attached to premolars scheduled to be extracted as part of an orthodontic treatment. Visible white spot lesions were seen within 4 weeks in the absence of any fluoride supplementation. Both microradiographic and SEM examinations showed surface softening of the enamel surface--that is, a surface layer was not seen in the lesions. The clinical significance of the present study is that enamel demineralization associated with fixed orthodontic therapy is an extremely rapid process caused by a high and continuous cariogenic challenge in the plaque developed around brackets and underneath ill-fitting bands. Careful inspection of the appliance at every visit and preventive fluoride programs are therefore required.     

A Monte Carlo simulation of the influence of sound enamel scattering coefficient on lesion visibility in light-induced fluorescence

Quantitative light-induced fluorescence (QLF) is based on the dark appearance of a white spot in otherwise highly fluorescent enamel. This can be explained by the increased scattering coefficient in the white spot compared with that of sound enamel. The aim of this study was to estimate the effect of different sound enamel scattering coefficients (s(SE)) and enamel thickness d, caused by developmental enamel differences, on the fluorescence appearance of white-spot lesions. We ran a Monte Carlo simulation of a 4 x 4 mm(2) illuminated enamel slab on a highly fluorescent background. The slab had a 0.7 x 0.7 mm(2), 100-microm-deep, white spot in the center. Fluorescent and back-scattered photons re-emitted from the central 2 x 2 mm(2) were recorded. We found that the fluorescence photon excitance from the white spot (F(WS)) was less than that of sound enamel (F(SE)), with an optimum difference for S(SE) between 20 and 80/mm. For s(SE) <20/mm, both F(SE) and F(WS) decreased with d. We found no relation with d for s(SE) >20/mm. The results indicate that for small s(SE), we are suffering from edge losses, which explains why the optimum for lesion visibility is not found at s(SE) = 0/mm, as would be expected.     

Ultrastructure of the intact surface zone of white spot and brown spot carious lesions in human enamel

Electron microscopy of the intact surface zone of white spot and brown spot carious lesions showed that in general their ultrastructure was similar. Their outermost crystalline surface consisted of small crystals similar to those in healthy enamel, crystals with central core dissolution, and rounded crystals. Below this, surface demineralization of enamel was observed as the enlargement of micropores, the central core dissolution of crystals, the formation of channels and the enlargement of spaces at prism boundaries. Remineralization of enamel was observed as the partial occlusion of voids, the rounding and enlargement of crystals, and some new needle-shaped crystals. Some other features indicated combined demineralization and remineralization. The occlusion of spaces at prism boundaries was a more common feature in brown spot lesions, whereas the pockets of rounded crystals were more common in white spot lesions. A relatively uniform distribution of needle-shaped crystals throughout the intact surface zone was a feature of some brown spot lesions only.     

Ultrastructure of the intact surface zone of white spot and brown spot carious lesions in human enamel

Electron microscopy of the intact surface zone of white spot and brown spot carious lesions showed that in general their ultrastructure was similar. Their outermost crystalline surface consisted of small crystals similar to those in healthy enamel, crystals with central core dissolution, and rounded crystals. Below this, surface demineralization of enamel was observed as the enlargement of micropores, the central core dissolution of crystals, the formation of channels and the enlargement of spaces at prism boundaries. Remineralization of enamel was observed as the partial occlusion of voids, the rounding and enlargement of crystals, and some new needle-shaped crystals. Some other features indicated combined demineralization and remineralization. The occlusion of spaces at prism boundaries was a more common feature in brown spot lesions, whereas the pockets of rounded crystals were more common in white spot lesions. A relatively uniform distribution of needle-shaped crystals throughout the intact surface zone was a feature of some brown spot lesions only.     

Detection of natural white spot caries lesions by an ultrasonic system

Ultrasound has been used in industrial business as one of the nondestructive measurement methods. It was hypothesized that nondestructiveness of the ultrasonics could be useful in determination of demineralization of noncavitated carious lesions on human enamel. This investigation was designed to determine the presence of natural carious lesions on proximal surfaces of human molar teeth using an ultrasonic system compared to radiography and histology as the gold standards. Measurements were made directly from proximal surfaces of 20 mandible molar teeth with white spot carious lesion by 2 examiners independently with the ultrasonic system. Ultrasonic evaluation of each natural white spot lesion had a sensitivity of 88%, specificity of 86%, positive predictive value of 88% and a negative predictive value of 86%, and the chance-corrected agreement was also satisfactory (kappa=0.74) compared to histology. The radiograph demonstrated chance-corrected agreement of 0.41:0.38 for the first and second examiners, respectively. Duncan test analysis of the numerical values was significantly different for the intact and the noncavitated carious surfaces (p<0.05). The results indicated that the ultrasonic evaluation is a sensitive method for the detection of the natural white spot carious lesions and can differentiate the changes in elastic properties of enamel numerically.     

In situ remineralization of early caries by a new high-fluoride dentifrice

The present study evaluated the ability of a high-fluoride dentifrice containing tricalcium phosphate to remineralize white spot lesions and inhibit lesion formation. Three demineralized enamel blocks and three healthy blocks (cut from a group of 30 molars), were exposed in pairs (one demineralized, one sound) via an appliance worn by 30 adults in a three-phase crossover study lasting 28 days per phase. The pairs were exposed to three dentifrices: one contained 5,000 ppm fluoride with tricalcium phosphate, one contained 5,000 ppm fluoride alone, and one contained no fluoride at all. Lesion status was analyzed using surface microhardness and transverse microradiography. Surface microhardness showed that the two dentifrices containing fluoride significantly inhibited enamel demineralization (p < 0.05) and significantly remineralized white spot lesions (p < 0.05), while the fluoride-free dentifrice did not. The results indicate that combining fluoride with tricalcium phosphate could provide more anti-caries benefits compared to using fluoride alone.     

In vitro interactions between the surfaces of enamel white spots and calcifying solutions.

The treatment of white spot enamel lesions with a saturated DCPD solution followed by a high fluoride topical application appeared to produce a surface coating consisting mainly of spherical particles that filled in the honeycombed-etched surface of the untreated enamel white spot. The conditions used in these pilot studies were not ideal to take advantage of the DCPD and fluoride reaction to form FAP. Additional study is warranted on the solution composition and application time along with identification of the reaction products formed.     

Enamel white spot lesions can remineralise using bio-active glass and polyacrylic acid-modified bio-active glass powders

Objective

To evaluate the potential of bio-active glass (BAG) powder and BAG containing polyacrylic acid (PAA-BAG) to remineralise enamel white spot lesions (WSL).

Methods

32 human enamel samples with artificial WSLs were assigned to 4 experimental groups (n = 8); (a) BAG slurry, (b) PAA-BAG slurry, (c) “standardised” remineralisation solution (positive control) and (d) de-ionised water (negative control). Mechanical properties of enamel were assessed using surface and cross-section Knoop microhardness. Micro-Raman spectroscopy in StreamLine™ scan mode was used to scan lesion cross-sections. The intensity of the Raman phosphate peak at 959 cm⁻¹ was fitted and measured producing depth profiles analysed using a double-step fitting function. A further 20 samples (n = 5) were used to obtain 3D images of surfaces using non-contact white light profilometry permitting measurement of lesion step height in relation to the sound enamel reference level, and to scan the lesion surface using scanning electron microscopy (SEM). Data were analysed statistically using one-way ANOVA with Tukey's HSD post-hoc tests.

Results

BAG, PAA-BAG and the remineralisation solution exhibited statistically significantly higher surface and cross-section Knoop microhardness compared to the negative control. Micro-Raman spectroscopy detected significantly higher phosphate content within the treated groups compared to the negative control group. Lesions’ depth was not significantly reduced. SEM images revealed mineral depositions, with different sizes and shapes, within BAG, PAA-BAG and the positive control groups.

Conclusion

BAG and PAA-BAG surface treatments enhance enamel WSL remineralisation, assessed by the resultant improved mechanical properties, higher phosphate content and morphological changes within the artificial lesions.     

Microstructural features of carious human enamel imaged with back-scattered electrons

We have used back-scattered electrons (BE) in the scanning electron microscope to produce mineral density images of enamel. Flat surfaces of artificially-carious enamel, softened in an intra-oral experiment, and naturally-carious (white spot) enamel were polished to a high gloss with diamond lapping compound, rendering them almost featureless by secondary electron scanning electron microscopy. They were then examined at 10 to 30 kV in a Philips 505 instrument fitted with a 4-quadrant BE detector. Study of surfaces prepared approximately parallel to the natural surface showed that mineral was lost from both prism core and the interprismatic region, leaving a thin mineral-rich rim at the prism periphery. The same lesions viewed longitudinally on a surface prepared perpendicular to the natural surface showed mineral-rich bands at the prism margins in the outer enamel. Near the advancing front of the lesion, the prism junctions were widened and the prism cores sometimes hypermineralized. Natural lesions sectioned in the prism long axis showed features previously seen with other techniques, e.g., cross-striations and striae of Retzius, but in much greater detail. Mineral enrichment at the prism periphery in the lesion body and a widening of the prism junction at the advancing fronts of lesions in permanent teeth were most obvious. Calculations showed that with an accelerating voltage of 30 kV, the images reflected mineral density up to 4 microns beneath the surface. BE microscopy produces a high-resolution image of mineral loss or gain in carious enamel, with relatively easy sample preparation.     

In vitro effect of a resin infiltrant on different artificial caries-like enamel lesions

ObjectivesA resin infiltrant was employed for the treatment of active white spot lesions due to its ability to penetrate into the enamel pores and prevent the progression of the lesion. However, limited information is available about its mechanical effect on different artificial enamel lesions as well as on its resistance to further demineralization. Therefore, this study aimed to evaluate the effects of the Icon® infiltrant on different artificial caries-like enamel lesions and its resistance to new acid challenges.DesignArtificial lesions were produced in bovine enamel using three different protocols (demineralization/remineralization cycling, DE-RE; 8% methylcellulose gel, MC; and methyl ethyl diphosphonate solution, MHDP; n = 13). The specimens were treated with Icon® and subjected to a new acid challenge using DE-RE cycling. The surface and cross-sectional hardness were evaluated in sound, demineralized, treated and further demineralized enamel areas. Data were statistically analyzed using ANOVA and Tukey’s test (p < 0.05).ResultsAll of the demineralizing protocols produced subsurface artificial caries lesions. The infiltrant was able to partially recover the surface hardness and prevent further surface hardness loss in enamel previously demineralized using the DE-RE and MHDP protocols. In regard to cross-sectional hardness, no positive effect was found.ConclusionsThe effect of the infiltrant depends on the type of lesion created in vitro, and its action is limited to the lesion surface.     

A scanning electron microscopic study of bacterial penetration of human enamel in incipient caries

In 23 human teeth, cracked enamel under white spot lesions without any visible loss of tooth substance was examined. Bacterial contamination from the enamel surface was prevented by brushing and consequent fixing of the remaining surface coatings before the enamel was fractured. In 7 of 23 specimens, bacterial colonies were observed under the enamel surface, sometimes as deep as the enamel-dentine junction and the dentine. In most samples the subsurface enamel appeared to be partly disintegrated. Bacteria can thus be found under surface enamel at an early stage of caries while the surface is still intact.     

Surface layer erosion of natural caries lesions with phosphoric and hydrochloric acid gels in preparation for resin infiltration

The infiltration of proximal enamel lesions with low-viscosity light curing resins could be a viable approach to stop lesion progression. However, penetration of sealant might be hampered by the comparatively highly mineralized surface layers of natural lesions. Therefore, the aim of this study was to compare the efficacy of three different etching gels in removing the surface layer in various etching times. Extracted human molars and premolars showing proximal white spot lesions were cut across the demineralized areas. Ninety-six lesions expected from visual examination to be confined to the outer enamel (C1) were selected. The cut surface and half of each lesion were varnished, thus serving as control. Subsequently, the lesions were etched with either phosphoric (37%) or hydrochloric (5 or 15%) acid gel for 30-120 s (n = 8/group). Specimens were examined using confocal microscopy and transversal microradiography. Surface layer reduction was significantly increased in lesions etched with 15% HCl gel for 90 and 120 s compared to those etched with H(3)PO(4) gel for 30-120 s (p < 0.05). No significant differences regarding the depths of erosion in the lesions compared to sound enamel could be observed (p > 0.05). An effective reduction in the surface layer of natural enamel caries can be achieved by etching with 15% hydrochloric acid gel for 90-120 s.     

The efficacy of a fluoride varnish in reducing enamel demineralization adjacent to orthodontic brackets: an in vitro study

OBJECTIVES: To test the hypothesis that fluoride varnish is effective in reducing demineralization (white spot) lesions adjacent to bonded orthodontic brackets. DESIGN: Two similar samples of extracted bovine incisors, with bonded orthodontic brackets, were separated into an experimental group (fluoride varnish was applied) and control group (no fluoride varnish) to examine the preventive effects of fluoride varnish. SETTING AND SAMPLE POPULATION: The dental clinic of the State University of Maringá--UEM (Maringá, Paraná, Brazil). Thirty-eight extracted bovine incisors with bonded orthodontic brackets. EXPERIMENTAL VARIABLE: Fluoride varnish was applied topically to half of the sample of extracted bovine teeth. No varnish was applied to the other half. OUTCOME MEASURE: The depths of enamel demineralization (white spot) lesions were measured from polarized light microscopy images using image analysis software. RESULTS: The teeth in both the experimental and control groups had been exposed to a cariogenic environment twice a day for 35 days. Those teeth that had been treated with two applications of fluoride varnish (one at the outset and another 15 days later) demonstrated about 38% less mean lesion depth than teeth where no varnish had been applied. CONCLUSION: Orthodontists may wish to consider the application of fluoride varnish during fixed orthodontic therapy to help reduce the development of enamel white spot lesions.     

Crystallographic and structural alterations in the mineral phase of human enamel with carious attacks

The present study aims to obtain further information about the crystallographic and structural alterations in the mineral phase of enamel with the onset of caries. For this purpose, X-ray microbeam diffraction analysis was carried out on ground sections prepared from natural white spot lesions. Electron spin resonance (ESR) analysis was also performed on block samples cut from white spot lesions and from undamaged enamel of the same teeth. The results of crystallinity measurements showed that enamel apatite in demineralized lesions was lower in crystallinity than the apatite in the surface layer and surrounding sound enamel. This X-ray diffraction study also revealed the presence of two non-apatitic minerals in the demineralized lesions. One type of the mineral is whitlockite, giving spotty rings. The nature of the other mineral, giving a single ring-like reflection, remains to be elucidated. A comparison of ESR spectra taken from the caries-attacked and undamaged enamel provided evidence that the former samples have a lower degree of alignment of apatite microcrystals. The occurrence of non-apatitic mineral phases and the observed difference in microcrystalline alignment may be the results of a remineralization process.     

Modified composite or conventional glass ionomer for band cementation? A comparative clinical trial.

The time to first failure, the position of band failure at deband, and the change in enamel white spot lesions of teeth bonded with a modified composite or a conventional glass ionomer were compared in a randomized half-mouth trial over the full course of orthodontic treatment. One hundred forty band pairs were cemented in 98 subjects. Overall band failure rates of 5% and 2.8% were recorded for the modified composite and the conventional glass ionomer, respectively, with no significant difference found between their times to first band failure. At the end-of-treatment deband, the position of band failure was predominantly at the enamel-cement interface for the modified composite and at the band-cement interface for the conventional glass ionomer (P <.001). A comparison of changes in mean enamel white spot lesion scores during treatment did not reveal significant differences between the cement groups (P =.16).     

渗透树脂在自然形成的早期龋损中渗透能力的研究

目的比较渗透树脂和粘接剂在自然形成的早期龋损中的渗透能力。方法选取36颗邻面有白垩色早期龋损的离体恒磨牙和前磨牙,垂直于龋损表面将牙齿一切为二。两半病损用15%的盐酸酸蚀2 min,随后一半病损用渗透树脂处理,另一半病损用粘接剂处理。用激光扫描共聚焦显微镜（CLSM）在双荧光模式下进行观察,测量树脂的渗透深度（PD）和病损深度（LD）,并且计算渗透百分数（PP）。结果在相同的病损组织学分级中渗透树脂组和粘接剂组间LD的差异无统计学意义（P＞0.05）,但是两组PD和PP间差异有统计学意义（P＜0.01）, 渗透树脂组明显高于粘接剂组。结论粘接剂和渗透树脂对早期龋损均有渗透作用,但是渗透树脂渗透更深,甚至能完全地渗入到病损内。     

Effects of acid-dissolution on thin ground sections of enamel caries studied by microradiography and X-ray microbeam diffraction

In order to obtain information about the chemical reactivity of localized areas within natural enamel caries, thin ground sections prepared from white spot lesions were subjected to MCI solutions with 0.01, 0.05, and 0.1 N concentrations. Microradiographic examination combined by densitometric analysis demonstrated that the surface layer covering demineralized lesions remained relatively stable against acid attacks and that, despite the original lower degree of mineralization, its microradiographic density became higher than that of the underlying normal enamel during acid-dissolution. Another interesting finding was that in the experiment using the most diluted HCI solution, a radiopaque zone became noticeable at the advancing front of the lesions in the course of dissolution. X-ray microbeam diffraction analysis of these sections showed that no apparent alterations occurred in mineral structure of enamel with acid dissolution, except for the decrease in crystallinity of enamel apatite. Based on the results obtained here, one can expect that the surface layer and the interior part of natural carious lesions possess a high degree of resistance to acid attacks, relative to the underlying normal enamel.     

Inhibition of enamel demineralization by a bioerodible fluoridated resin

PURPOSE: To investigate the efficacy of a bioerodible fluoridated resin on inhibition of enamel demineralization. METHODS: Eighteen extracted permanent molars were sectioned mesiodistally to obtain 36 caries-free enamel surfaces. Each sample was prepared by painting an acid-protective varnish, excluding a 2 x 8 mm window on either the buccal or lingual surface. The windows of exposed enamel were randomly divided into three separate groups (n = 12). Group 1 received an application of a 5% (by weight) sodium fluoride varnish. Group 2 had an experimental 5% sodium fluoride bioerodible resin applied to the window. Group 3 was left untreated and acted as a control. The samples were then exposed to an artificial caries challenge for 17 days, until a visible white spot lesion had been created on the control group. The samples were brushed for 1 minute daily. Following the acid challenge, the teeth were sectioned longitudinally to obtain 100 microm sections. Sections were then photographed under polarized light. Quantitatively the areas of the lesions were measured by utilizing a computerized imaging system. Finally, a comparison was made between mean lesion sizes of the sample groups in order to determine their respective efficacy of enamel demineralization inhibition. RESULTS: The mean areas (microm)2 of the artificial lesions (+/- SD) were: bioerodible fluoridated resin 3,785 +/- 1,794; fluoride varnish 7,362 +/- 2,853, and control 11,398 +/- 4,238. ANOVA was performed and identified a significant variance (P < 0.001). Tukey's multiple comparison test demonstrated that bioerodible fluoridated resin had significantly less enamel demineralization than the fluoride varnish and control groups (P < 0.05). The fluoride varnish group demonstrated significantly less enamel demineralization than the control group (P < 0.05).     

Effects of acid-dissolution on thin ground sections of enamel caries studied by microradiography and x-ray microbeam diffraction

In order to obtain information about the chemical reactivity of localized areas within natural enamel caries, thin ground sections prepared from white spot lesions were subjected to HCl solutions with 0.01, 0.05, and 0.1 N concentrations. Microradiographic examination combined by densitometric analysis demonstrated that the surface layer covering demineralized lesions remained relatively stable against acid attacks and that, despite the original lower degree of mineralization, its microradiographic density became higher than that of the underlying normal enamel during acid-dissolution. Another interesting finding was that in the experiment using the most diluted HCl solution, a radiopaque zone became noticeable at the advancing front of the lesions in the course of dissolution. X-ray microbeam diffraction analysis of these sections showed that no apparent alterations occurred in mineral structure of enamel with acid dissolution, except for the decrease in crystallinity of enamel apatite. Based on the results obtained here, one can expect that the surface layer and the interior part of natural carious lesions possess a high degree of resistance to acid attacks, relative to the underlying normal enamel.