Zinc Incorporation Improves Biological Activity of Beta-tricalcium Silicate Resin–based Cement

Introduction

Matrix metalloproteinase (MMP) inhibition may improve endodontic treatment prognosis. The purpose of this study was to determine if zinc incorporation into experimental resin cements containing bioactive fillers may modulate MMP-mediated collagen degradation of dentin.

Methods

Human dentin samples untreated and demineralized using 10% phosphoric acid or 0.5 mol/L EDTA were infiltrated with the following experimental resins: (1) unfilled resin, (2) resin with Bioglass 45S5 particles (OSspray, London, UK), (3) resin with beta-tricalcium silicate particles (βTCS), (4) resin with zinc-doped Bioglass 45S5, and (5) resin with zinc-doped βTCS particles. The specimens were stored in artificial saliva (for 24 hours, 1 week, and 4 weeks) and submitted to radioimmunoassay to quantify C-terminal telopeptide. Scanning electron microscopy analysis was also undertaken on dentin samples after 4 weeks of storage.

Results

Collagen degradation was prominent both in phosphoric acid and EDTA-treated dentin. Resin infiltration strongly reduced MMP activity in demineralized dentin. Resin containing Bioglass 45S5 particles exerted higher and stable protection of collagen. The presence of zinc in βTCS particles increases MMP inhibition. Different mineral precipitation was attained in dentin infiltrated with the resin cements containing bioactive fillers.

Conclusions

MMP degradation of dentin collagen is strongly reduced after resin infiltration of dentin. Zinc incorporation in βTCS particles exerted an additional protection against MMP-mediated collagen degradation. However, it did not occur in resin containing Bioglass 45S5 particles, probably because of the formation of phosphate-zinc compounds.     

Biomimetic remineralization of dentin

Objectives

Remineralization of demineralized dentin is important for improving dentin bonding stability and controlling primary and secondary caries. Nevertheless, conventional dentin remineralization strategy is not suitable for remineralizing completely demineralized dentin within hybrid layers created by etch-and-rinse and moderately aggressive self-etch adhesive systems, or the superficial part of a caries-affected dentin lesion left behind after minimally invasive caries removal. Biomimetic remineralization represents a different approach to this problem by attempting to backfill the demineralized dentin collagen with liquid-like amorphous calcium phosphate nanoprecursor particles that are stabilized by biomimetic analogs of noncollagenous proteins.

Methods

This paper reviewed the changing concepts in calcium phosphate mineralization of fibrillar collagen, including the recently discovered, non-classical particle-based crystallization concept, formation of polymer-induced liquid-precursors (PILP), experimental collagen models for mineralization, and the need for using phosphate-containing biomimetic analogs for biomimetic mineralization of collagen. Published work on the remineralization of resin–dentin bonds and artificial caries-like lesions by various research groups was then reviewed. Finally, the problems and progress associated with the translation of a scientifically sound concept into a clinically applicable approach are discussed.

Results and significance

The particle-based biomimetic remineralization strategy based on the PILP process demonstrates great potential in remineralizing faulty hybrid layers or caries-like dentin. Based on this concept, research in the development of more clinically feasible dentin remineralization strategy, such as incorporating poly(anionic) acid-stabilized amorphous calcium phosphate nanoprecursor-containing mesoporous silica nanofillers in dentin adhesives, may provide a promising strategy for increasing of the durability of resin–dentin bonding and remineralizing caries-affected dentin.     

Hardness,elasticity and ultrastructure of primary tooth dentin bonded with a self-reinforcing one-step self-etch adhesive

Objective

This study evaluated the interfacial quality of sound and caries-affected primary tooth dentin bonded with a self-reinforcing one-step self-etch adhesive.

Methods

Non-carious, sound dentin was prepared with water-cooled high-speed diamond burs. Caries-infected dentin was removed with water-cooled low-speed round steel burs and hand instrument. Dentin was bonded with Bond Force (Tokuyama Dental). A nano-indentation tester was employed for determination of hardness (H) and Young's modulus (Y) of resin–dentin interface. Similar resin–dentin interfaces were examined with a SEM/EDX, and with a TEM using ammoniacal silver nitrate tracer for nanoleakage.

Results

In the comparison of the H and Y values between the interfacial dentin and the underlying mineralized dentin, no significant difference was seen in caries-affected dentin, however, the values of the interfacial dentin were significantly lower in sound dentin. The H value of the interfacial dentin of sound dentin was significantly lower than that of caries-affected dentin with significantly higher Ca content. No significant difference was observed in the Y values of the interfacial dentin of the two substrates. For both sound and caries-affected dentin, TEM revealed silver deposits in the interfacial dentin and adhesive layer, and smear layer remained within the resin–dentin interface. However, Ca and P contents of the adhesive layer at 10 μm above the dentin surface were the same as those present in the interfacial dentin.

Conclusions

Both for sound teeth and caries teeth, Bond Force does not prevent the nanoleakage along the resin–dentin interface.     

Near-infrared hyperspectral imaging of water evaporation dynamics for early detection of incipient caries

Objectives

Incipient caries is characterized as demineralization of the tooth enamel reflecting in increased porosity of enamel structure. As a result, the demineralized enamel may contain increased amount of water, and exhibit different water evaporation dynamics than the sound enamel. The objective of this paper is to assess the applicability of water evaporation dynamics of sound and demineralized enamel for detection and quantification of incipient caries using near-infrared hyperspectral imaging.

Methods

The time lapse of water evaporation from enamel samples with artificial and natural caries lesions of different stages was imaged by a near-infrared hyperspectral imaging system. Partial least squares regression was used to predict the water content from the acquired spectra. The water evaporation dynamics was characterized by a first order logarithmic drying model. The calculated time constants of the logarithmic drying model were used as the discriminative feature.

Results

The conducted measurements showed that demineralized enamel contains more water and exhibits significantly faster water evaporation than the sound enamel. By appropriate modelling of the water evaporation process from the enamel surface, the contrast between the sound and demineralized enamel observed in the individual near infrared spectral images can be substantially enhanced.

Conclusions

The presented results indicate that near-infrared based prediction of water content combined with an appropriate drying model presents a strong foundation for development of novel diagnostic tools for incipient caries detection.

Clinical Significance

The results of the study enhance the understanding of the water evaporation process from the sound and demineralized enamel and have significant implications for the detection of incipient caries by near-infrared hyperspectral imaging.     

Abrasion of eroded dentin caused by toothpaste slurries of different abrasivity and toothbrushes of different filament diameter

Objective

This study aimed to evaluate the impact of toothpaste slurry abrasivity and toothbrush filament diameter on abrasion of eroded dentin in vitro.

Methods

Eroded dentin samples (hydrochloric acid, pH 2.6, 15 s) were brushed with 40 strokes in an automatic brushing machine using manual toothbrushes with different filament diameter (0.15, 0.20 or 0.25 mm). The toothbrushes were applied with a control slurry free of abrasive particles (RDA-value 10) or toothpastes slurries with different abrasivity (RDA-values 20, 50 or 100). Each erosive–abrasive cycle was followed by storage of the dentin samples in artificial saliva for 3 h. After each 4 cycles, the samples were stored in artificial saliva for 15 h. After 60 cycles, dentin loss was measured by profilometry and statistically analysed by ANOVA and linear regression analysis.

Results

Dentin loss increased along with the RDA-value of the toothpaste slurries. The impact of the filament diameter on dentin loss was less evident compared to the RDA-value. However, toothbrushes with smaller filament stiffness caused higher dentin wear in all toothpaste slurry groups (RDA 20, 50 and 100) except for the paste-free control group (RDA 10).

Conclusion

Abrasion of eroded dentin increased along with the RDA-value of the toothpaste slurry and with decreasing filament diameter of the toothbrush.     

Nano-structural and compositional basis of devitalized tooth fragility

Objective

Increased tooth fragility after devitalization is commonly observed but there is no definite mechanistic explanation for such phenomenon. Therefore, it is important to analyze more profoundly structural and compositional properties of this altered form of dentin. The present study investigates the differences between normal and devitalized dentin using advanced techniques.

Methods

Atomic force microscopic imaging (AFM), energy dispersive X-ray analysis (EDX) and micro-Raman spectroscopy were performed on 16 dentin specimens, eight vital and eight that underwent root-canal treatment at least two years before extraction and had no infection in root canals before or after devitalization.

Results

The mean size of mineral crystals showed by AFM was larger in devitalized than in healthy dentin in the same age category. AFM phase shifts in devitalized cases revealed altered mechanical characteristics and suggested differences in composition of material between devitalized teeth and healthy controls. No significant difference in Ca/P ratio between vital and devitalized teeth was found using EDX. However, micro-Raman analyses showed that in devitalized teeth, apart from hydroxyapatite, dentin contained significant amounts of apatite phases with lower calcium content: octacalcium phosphate, dicalcium phosphate dihydrate and tricalcium phosphate.

Significance

Differences between vital and devitalized dentin bring new insights into the basis of devitalized tooth fragility. Larger mineral crystals could account for decreased mechanical strength in devitalized teeth. Moreover, calcium–phosphate phases with lower Ca content have lower material strength, and the presence of these phases in devitalized teeth may explain their increased fragility.     

Quality of the interface of primary tooth dentin bonded with antibacterial fluoride-releasing adhesive

Objective

Limited information is available on the physical properties and ultrastructure of resin–dentin interfaces created in primary teeth. The interfacial quality of sound and caries-affected primary tooth dentin bonded with an antibacterial fluoride-releasing self-etch adhesive was examined in the present study.

Methods

Primary molars were bonded with Clearfil Protect Bond (Kuraray Medical). A nano-indentation tester was employed for creating indentations vertically across resin–dentin interfaces of the bonded sound and caries-affected primary dentin for determination of hardness (H) and Young's modulus (Y). Statistical analysis were performed using one-way and two-way ANOVA and Fisher's PLSD test at p < 0.05. Similar resin–dentin interfaces were examined with SEM/EDX, and with TEM using ammoniacal silver nitrate tracer for nanoleakage.

Results

In both sound and caries-affected dentin, compared to the underlying dentin, significantly lower values were seen in the H and Y values of the interfacial dentin except for the H in caries-affected dentin. No significant difference between the interfacial dentin and the underlying dentin was observed in the H of caries-affected dentin and the Ca and P contents in both sound and caries-affected dentin. TEM revealed extensive interfacial nanoleakage in bonded sound dentin, while no silver deposit in bonded caries-affected dentin. However, silver deposits were observed in the porous caries-affected dentin beneath the interface.

Conclusion

Within the limitation of this study, Clearfil Protect Bond cannot demonstrate evidence of remineralization, does not increase the hardness and elasticity of the interfacial dentin, and does not prevent nanoleakage along the resin–dentin interface.     

Probing nano-scale adhesion force between AFM and acid demineralized intertubular dentin: Moist versus dry dentin

Objective

The aim of this study was to investigate the effect of dentin dryness on the variation in the probed nano-scale adhesion force between an AFM silicon nitride tip and demineralized intertubular dentin collagen fibrils network surface.

Methods

Dentin specimens were etched with 37% phosphoric acid for 15 s and then divided into three groups. Specimens of the first two groups were air-dried for 5 or 10 s (DH5s and DH10s), respectively, whereas specimens of the third group were left in the hydrated condition (H). For each group, Force curves were characterized by contact-mode AFM and the adhesion force (Fad) was calculated. The structure of the demineralized collagen fibrils network was characterized by tapping mode AFM. The tensile bond strength (TBS) to dentin was evaluated using one alcohol-based dentin self-priming adhesive. The dentin/resin interface was investigated by SEM.

Results

Dentin specimens in the wet-hydrated condition (H) showed significantly higher adhesion force and TBS values than dry-dehydrated specimens (DH5s and DH10s). AFM images showed open collagen fibrils network structure in wet-hydrated specimens (H), while the dry-dehydrated specimens (DH5s and DH10s) showed a collapsed appearance to varying degrees. SEM images revealed minimum resin infiltration in dry-dehydrated specimens.

Significance

The nano-scale adhesion force between the AFM probe and demineralized intertubular dentin surface was shown to be sensitive to surface air-drying. The decrease in the nano-scale adhesion force with the increase in the time of air-dryness is related to dehydration of the demineralized collagen fibrils network surface.     

Stabilization of dentin matrix after cross-linking treatments,in vitro

Objectives

To evaluate the effect of EDC on elastic modulus (E), MMPs activity, hydroxyproline (HYP) release and thermal denaturation temperature of demineralized dentin collagen.

Methods

Dentin beams were obtained from human molars and completely demineralized in 10 wt% H₃PO₄ for 18 h. The initial E and MMP activity were determined with three-point bending and microcolorimetric assay, respectively. Extra demineralized beams were dehydrated and the initial dry mass (DM) was determined. All the beams were distributed into groups (n = 10) and treated for 30 s or 60 s with: water, 0.5 M, 1 M or 2 M EDC or 10% glutaraldehyde (GA). After treatment, the new E and MMP activity were redetermined. The beams submitted to DM measurements were storage for 1 week in artificial saliva, after that the mass loss and HYP release were evaluated. The collagen thermal denaturation temperature (TDT) was determined by DSC analysis. Data for E, MMP activity and HYP release were submitted to Wilcoxon and Kruskal–Wallis or Mann–Whitney tests. Mass loss and TDT data were submitted to ANOVA and Tukey tests at the 5% of significance.

Results

EDC was able to significantly increase collagen stiffness in 60 s. 10% GA groups obtained the highest E values after both 30 and 60 s. All cross-linking agents decreased MMP activity and HYP release and increased TDT temperature. Significant differences were identified among EDC groups after 30 or 60 s of cross-linking, 1 M or 2 M EDC showed the lowest MMP activity.

Significance

Cross-linking agents are capable of preventing dentin collagen degradation. EDC treatment may be clinically useful to increase resin-dentin stability.     

Mineral distribution and CLSM analysis of secondary caries inhibition by fluoride/MDPB-containing adhesive system after cariogenic challenges

Objective

To evaluate the inhibition zone formation (IZ) and mineral distribution along the interface of adhesive systems either containing fluoride and antibacterial primer or not, after chemical and biological artificial caries challenges.

Methods

Forty-eight third molars were used. Artificial caries was developed with S. mutans in a 4 mm × 4 mm area of occlusal dentin surface. Carious dentin was removed and cavities were restored with Adper Scotchbond Multi-Purpose (SBM) and Clearfil Protect Bond (CPB) (n = 24). Samples were submitted to secondary caries development by chemical (C) (acidic gel) or biological (B) (S. mutans culture) methods for 5 days. Four groups were tested (n = 12): (1) SC (SBM + C); (2) SB (SBM + B); (3) CC (CPB + C); (4) CB (CPB + B). The IZ and outer lesion (OL) formations were analyzed by confocal laser scanning microscopy (CLSM). The distribution of calcium (Ca) and phosphorus (P) content along the interface was analyzed by micro X-ray fluorescence spectrometer by energy-dispersive (μEDX).

Results

The frequency of IZ formation and mean values of IZ thickness differed among the groups. The CC group presented the lowest OL depth. μEDX analysis showed that CPB had the highest mineral loss by the biological method, but the lowest mineral loss by the chemical method. SC and SB groups showed intermediate values of mineral loss.

Conclusion

The mineral loss along the dentin/restoration interface was affected by the artificial caries method, and hybrid layer formation by adhesive systems used. The adhesive system containing fluoride and antibacterial primer did not prevent secondary caries formation.     

Biomimetic remineralization of human dentin using promising innovative calcium-silicate hybrid “smart” materials

Introduction

The hypothesis was that experimental ion-leaching bioactive composites enhance remineralization of apatite-depleted dentin.

Materials and methods

Calcium-aluminosilicate (wTC-Ba) or fluoride-containing calcium-aluminosilicate (FTC-Ba) Portland-derived mineral powders were mixed with HTP-M methacrylate HEMA/TEGDMA/PAA-based resin to prepare experimental composites. Controls were Vitrebond and Gradia Direct LoFlo.Calcium- and fluoride-release, pH of soaking water, solubility and water uptake were evaluated in deionized water using material disks (8 mm diameter and 1.6 mm thick).The apatite-formation ability (bioactivity) and the ability to remineralize previously demineralized dentin were assessed by ESEM-EDX and FTIR after soaking in a phosphate-containing solution.Human dentin slices (0.8 mm thickness) were demineralized in EDTA 17% for 2 h, placed in close contact with the material disks and immersed in a phosphate-containing solution (Dulbecco's Phosphate Buffered Saline, DPBS) to assess the ability of the materials to remineralize apatite-depleted dentin.

Results

Only the experimental materials released calcium and basified the soaking water (released hydroxyl ions). A correlation between calcium release and solubility was observed. FTC-Ba composite released more fluoride than Vitrebond and formed calcium fluoride (fluorite) precipitates. Polyacrylate calcium complexes (between COO⁻ groups of polyacrylate and released calcium ions) formed at high pH.The formation of apatite was noticed only on the experimental materials, due to the combination of calcium ions provided by the materials and phosphate from the DPBS. Apatite deposits (spherulites showing Ca and P EDX peaks and IR bands due to phosphate stretching and bending) were detected early on the experimental material disks after only 24 h of soaking in DPBS.Only the experimental composites proved to have the ability to remineralize apatite-depleted dentin surfaces. After 7 days in DPBS, only the demineralized dentin treated with the experimental materials showed the appearance of carbonated apatite (IR bands at about 1400, 1020, 600 cm⁻¹). EDX compositional depth profile through the fractured demineralized dentin slices showed the reappearance of Ca and P peaks (remineralization of dentin surface) to 30-50 μm depth.

Conclusions

The ion-leachable experimental composites remineralized the human apatite-depleted dentin. Ion release promotes the formation of a bone-like carbonated-apatite on demineralized dentin within 7 days of immersion in DPBS.The use of bioactive “smart” composites containing reactive calcium-silicate Portland-derived mineral powder as tailored filler may be an innovative method for the biomimetic remineralization of apatite-depleted dentin surfaces and to prevent the demineralization of hypomineralized/carious dentin, with potentially great advantage in clinical applications.     

Effect of desensitising toothpastes on dentinal tubule occlusion: A dentine permeability measurement and SEM in vitro study

Objectives

The purpose of this study was to evaluate the in vitro effectiveness of a new bioglass-containing and two commercial desensitising toothpastes on dentinal tubule occlusion after citric acid challenge or artificial saliva (AS) immersion.

Methods

One hundred dentin discs from human third molars were used. Specimens were randomly divided into five groups (n = 20), Group 1: EDTA-treated dentin; Group 2: brushing with distilled water; Group 3: brushing with Novamin; Group 4: brushing with Sensodyne Freshmint; Group 5: brushing with Colgate Sensitive. In each group, samples were then equally split into two subgroups (n = 10) to test two post-treatments: 6% citric acid challenge or 24 h immersion in artificial saliva. Dentine permeability of each specimen was measured before and after each treatment using a hydrostatic device working at 20 cm H₂O pressure. Data were analysed by two-way repeated measures ANOVA to determine if there were any significant differences within or between groups. Dentine morphology and surface deposits were observed by SEM.

Results

All three desensitising toothpastes significantly reduced dentine permeability and created precipitates on the treated dentine surfaces. Moreover, the reductions in dentine permeability showed partial recovery after a citric acid and artificial saliva immersion. Sensodyne showed significant resistant to acid attack and Novamin exhibited the lowest permeability after artificial saliva immersion for 24 h.

Conclusions

The application of the three toothpastes resulted in effective dentinal tubule occlusion. However, the new bioglass-containing toothpaste (Novamin) represented excellent occlusion effects after brushing treatment and AS immersion, while Sensodyne demonstrated more reduction in permeability when citric acid challenged.     

In vitro evaluation of plant-derived agents to preserve dentin collagen

Objective

Biomodification of dentin by a natural crosslinker has been recommended to improve a mechanical property of demineralized dentin. This study investigated the effect of various plant-derived agents (hesperidin, proanthocyanidin, epigallocatechin gallate and genipin) on the stability of dentin collagen matrix to resist collagenase degradation.

Methods

The dentin specimens were treated with glutaraldehyde (0.5% and 5.0%) and each plant-derived test solution (0.5%). They were subjected to ultimate tensile strength (UTS) and swelling ratio measurements. Demineralized human dentin powder was incubated with 0.02%, 0.1% and 0.5% of each test agent and followed by bacterial collagenase digestion. The extent of collagen degradation was investigated using hydroxyproline assay.

Results

The UTS and swelling ratio measurements revealed that the mechanical property of dentin was improved by the use of these natural agents. The greatest reduction in collagen degradation was shown following the use of hesperidin, proanthocyanidin, and epigallocatechin gallate at 0.5%.

Significance

The use of hesperidin, proanthocyanidin, and epigallocatechin gallate could improve the mechanical properties of collagen and resist enzymatic degradation, leading to functional repair of pathological dentin lesion.     

Solubility study of phytochemical cross-linking agents on dentin stiffness

Objectives

The effects of interactions between cross-linking proanthocyanidins (PA) in polar solvents and type-I collagen of demineralized dentin were investigated.

Methods

Three PA-rich extracts, two from grape seed (GSEP and GSES) and one from cocoa (COE), were dissolved (water, ethanol:water and acetone:water) and analyzed for their ability to increase the modulus of elasticity of demineralized dentin. Sound dentin beams (0.5 mm × 1.7 mm × 7 mm) were fully demineralized and divided into 12 groups according to the type of cross-linking agent and solvents used. Specimens were immersed in the respective solutions and tested at baseline, 10, 30, 60, 120 and 240 min.

Results

The elastic modulus (EM) of dentin was significantly increased by the PA treatment regardless of time (p < 0.05 for all times). The extracts showed different solubility in different solvents. GSEP showed the highest increase in EM when diluted in distilled water and acetone at all exposure times. Both GSEs showed superior results when diluted in distilled water and after 4 h of treatment, while COE produced strongest enhancement when dissolved in ethanol:water.

Conclusions

The results indicates that herbal extraction process and other pharmacognostic parameters have an important influence on extract solubility as well as constitution and, consequently, on the PA–dentin matrix interaction.     

HEMA reactivity with demineralized dentin

Objectives

2-Hydroxyethylmethacrylate (HEMA) was compared to its epoxy analogue, glycidoxypropylmethacrylate (GMA), for reactivity with 2,6-diaminohexanoic acid (Lysine), an amino acid present in collagen possessing a reactive amino side chain. The aim was to verify whether HEMA could chemically react with collagen fibers.

Methods

Capillary electrophoresis was used to analyse reaction products together with computer aided chemistry. Retention of HEMA in demineralized dentine particles was investigated by infrared spectroscopy.

Results

It was found by that HEMA does not form any new molecular species when contacted with lysine whereas GMA completely reacts to form the expected addition product. Computer aided chemistry confirmed this finding. Infrared spectroscopy showed that demineralized dentin has strong affinity for HEMA and retains this monomer despite extensive water washing.

Conclusions

We interpret this behavior as demonstrating solvation of HEMA in the collagen polymer network.     

Effect of saliva contamination on bond strength of resin luting cements to dentin

Objectives

This study examined the effect of saliva contamination on the microtensile bond strength (μTBS) of resin luting cements to dentin.

Methods

For RelyX ARC (ARC, 3M ESPE), dentin surfaces were etched with 32% phosphoric acid. The subgroups were: ARC-control (uncontaminated), ARC-I (saliva contamination, blot-dried), ARC-II (saliva contamination, rinse, blot-dried) and ARC-III (saliva contamination, rinse, re-etch, rinse, blot-dried). For Panavia F 2.0 (PF, Kuraray), the subgroups were: PF-control (uncontaminated), PF-I (saliva contamination, dried), PF-II (saliva contamination, rinse, dried), PF-III (primer, saliva contamination, dried), PF-IV (primer, saliva contamination, dried, primer re-applied) and PF-V (primer, saliva contamination, rinse, dried, primer re-applied). Composite blocks were luted onto dentin using the two cements. Bonded specimens were sectioned into 0.9 mm × 0.9 mm beams for μTBS testing. Representative fractured beams were prepared for fractographic analysis.

Results

For ARC, salivary contamination of etched dentin (ARC-I) significantly lowered bond strength (p = 0.001). Rinsing saliva off with water (ARC-II) restored bond strength to control level. Re-etching dentin surface after rinsing (ARC-III) resulted in the lowest bond strength (p < 0.001). For PF, salivary contamination of dentin before (PF-I) and after application of primer (PF-III and PF-IV) significantly lowered bond strength (p < 0.001). Rinsing saliva off with water and re-application of primer (PF-II and PF-V) improved bond strength.

Conclusion

Saliva contamination during luting deteriorated the bond quality of resin cements. Decontamination by rinsing with water was most effective in restoring the bond strength of RelyX ARC. Decontamination by water-rinsing and primer re-application after rinsing improved the bond strength of Panavia F 2.0.     

Long-term protective effect of surface sealants against erosive wear by intrinsic and extrinsic acids

Objective

To test sealants to prevent erosive tooth wear caused by extrinsic and intrinsic acids under long-term exposition.

Methods

144 bovine enamel samples were randomly allocated to twelve groups (1–12). Samples of groups 1, 5 and 9 remained unsealed (positive controls), 2, 6 and 10 were sealed with Silicon Seal Nano Mix and 3, 7 and 11 with Seal&;Protect. Groups 4, 8 and 12 were sealed with flowable composite (negative controls).Groups 1–4 were immersed in artificial saliva, 5–8 in hydrochloric acid and groups 9–12 in citric acid for 28 days, respectively. After 1, 2, 4, 7, 11, 14, 21 and 28 days, solutions were renewed and enamel wear was quantified by assignation of ³²P in the solutions.

Results

In all immersion solutions, lowest mineral loss was observed for the negative controls whilst highest loss was observed for unsealed positive controls.In artificial saliva and citric acid, the loss from samples sealed with Seal&;Protect was not significantly different compared with negative controls whilst loss in groups sealed with Silicon Seal Nano Mix was significantly higher.In hydrochloric acid, loss from samples sealed with Seal&;Protect was not different compared with that of negative controls up to 4 days. Except day 1, the mineral loss in the Seal&;Protect group was significantly lower compared with that of the Silicon Seal Nano Mix group.

Conclusion

The tested resin based surface sealant is able to significantly reduce the erosive demineralisation of enamel caused by hydrochloric and citric acid even under long-term exposition.     

Interplay between fluoride and abrasivity of dentifrices on dental erosion–abrasion

Objectives

Eroded teeth are more susceptible to toothbrushing wear than sound teeth. We tested the hypothesis that fluoride and abrasivity of dentifrices can interact, modulating the development of erosive–abrasive lesions.

Methods

Human enamel and root dentin specimens were submitted to cycles of demineralization, remineralization and toothbrushing using six dentifrices formulated with three different abrasivity levels: low (L), medium (M) and high (H); with (+F) and without (−F) fluoride. Surface loss was quantified by optical profilometry and compared among groups (α = 0.05).

Results

In dentin, it was ranked: L < M < H, for both +F and −F dentifrices. In enamel, +F dentifrices had similar results; however for −F formulations, M and H did not differ. Fluoride reduced surface loss in enamel, at all abrasive levels. In dentin, the same fluoride effect was observed but only for the low abrasive formulation.

Conclusions

Both fluoride and abrasivity were important modulators of enamel surface loss, while abrasivity had a higher impact than fluoride on dentin.     

Effects of different amine fluoride concentrations on enamel remineralization

Objectives

The aim of this study was to investigate the effects of decreasing fluoride concentrations on repeated demineralizing challenges on human enamel.

Materials and methods

In 24 teeth, 3 mm × 3 mm windows were prepared on the buccal and lingual sides and treated in a cycling demineralization–remineralization model. Remineralization was achieved with 100, 10 and 0.1 ppm fluoride from anime fluoride. Coronal sections were cut through the artificial lesions, and three sections per tooth were investigated using polarized light microscopy and scanning electron microscopy with quantitative element analysis.

Results

The morphology of the lesions was studied, and the extensions of the superficial layer and the body of the lesion were measured. Using element analysis, the Ca, P and F content were determined. The body of the lesion appeared remineralized after application of 100 ppm fluoride, while remineralization of the lesion was less successful after application of 10 and 0.1 ppm fluoride. The thickness of the superficial layer increased with decreasing fluoride concentrations, and also the extension of the body of the lesion increased. Ca and P content increased with increasing fluoride concentrations.

Conclusions

The effectiveness of fluoride in enamel remineralization increased with increasing fluoride concentration.

Clinical relevance

A consistently higher level of fluoride in saliva should be a goal in caries prevention.     

Effect of a new liner/base on human dentin permeability

Objectives

Resin-modified glass ionomers (RMGI) have demonstrated clinical success in their ability to minimize post-operative sensitivity of restorations. RMGIs have been recently introduced as paste-liquid systems for convenience of clinical usage. The objective of this study was to measure the ability of a new paste-liquid RMGI liner/base to reduce fluid flow through human dentin.

Methods

Dentin permeability was measured on human crown sections on etched dentin, using etched dentin as a model for the exposed tubules typical of root sensitivity, and permitting measurement of the maximum permeability. In the one group, the etched dentin was coated with the RMGI, and pre- and post-treatment permeability was measured on the coated dentin. In the second group, a smear layer was created on the dentin with sandpaper, then the samples were coated with the RMGI; permeability was measured on the smeared and coated dentin. Samples from each group were sectioned and examined via scanning electron microscopy (SEM).

Results

The new paste-liquid RMGI liner/base significantly reduced fluid flow through dentin, and exhibited excellent seal on dentin with either a smear layer or open tubules. SEM images show evidence that the RMGI infiltrated the smear layer with resin during placement, penetrated dentin tubules, and formed resin tags in acid-etched dentin.

Conclusions

Based on these results, combined with previous research on adhesion and microleakage, it is concluded that the new RMGI liner/base should minimize post-operative sensitivity in restorations.