ToF-SIMS Analysis of Demineralized Dentin Biomodified with Calcium Phosphate and Collagen Crosslinking: Effect on Marginal Adaptation of Class V Adhesive Restorations

This study aimed to assess the effect of biomodification before adhesive procedures on the tooth-restoration interface of class V restorations located in caries-simulated vs. sound dentin, and the quality of dentin surface by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Class V cavities located on cervical dentin were prepared on the buccal surfaces of extracted human molars under the simulation of intratubular fluid flow. Two dentin types, i.e., sound and demineralized by formic-acid, were biomodified with 1% riboflavin and calcium phosphate (CaP) prior to the application of a universal adhesive (Clearfil Universal Bond) in etch and rinse or self-etch mode, and a conventional micro hybrid composite (Clearfil APX). Restorations were subjected to thermo mechanical fatigue test and percentages of continuous margins (% CM) before/after fatigue were compared. Bio modification of dentin surfaces at the molecular level was analyzed by Time-of-Flight Secondary Mass Spectometry (ToF-SIMS). % CM were still significantly higher in tooth-restoration interfaces on sound dentin. Meanwhile, biomodification with riboflavin and CaP had no detrimental effect on adhesion and in carious dentin, it improved the % CM both before and after loading. Etching carious dentin with phosphoric acid provided with the lowest results, leading even to restoration loss. The presence of molecule fragments of riboflavin and CaP were detected by ToF-SIMS, evidencing dentin biomodification. The adhesive interface involving carious dentin could be improved by the use of a collagen crosslinker and CaP prior to adhesive procedures.

Microhardness and Penetration of Artificial White Spot Lesions Treated with Resin or Colloidal Silica Infiltration

INTRODUCTION

Infiltration of early enamel lesions by materials having remineralizing capacity seems to improve aesthetics and arrests caries progression.

AIM

To evaluate and compare the surface microhardness and penetration depth of a low viscosity resin and colloidal silica nanoparticle infiltrates into artificially created white spot lesions.

MATERIALS AND METHODS

Forty extracted human central incisors were embedded in acrylic resin blocks exposing the labial surfaces of the crowns. The specimens were immersed in demineralizing solution for 96 hours to create white spot lesions on labial surfaces. The samples were then divided into two groups (n=20 each), where in Group 1-resin infiltration (ICON DMG, Hamburg, Germany) and Group 2-colloidal silica infiltration (Arrow Fine chemicals, Rajkot, Gujarat, India) was done. Samples were subjected to vicker's microhardness testing at baseline, after demineralization and after treatment with resin or colloidal silica infiltrates. Then, the crowns were sectioned longitudinally and penetration depth of the infiltrants was measured using confocal laser scanning microscope and compared the readings to lesion depth. All the collected data was subjected to statistical analysis using t-test.

RESULTS

Resin infiltration group showed significantly greater increase in microhardness compared to colloidal silica infiltration (p=0.001). The percentage of penetration of the resin group was 67.14% and that of colloidal silica group was 54.53% indicating significant difference between the two.

CONCLUSION

Resin infiltrates performed better in regaining the baseline microhardness and penetrating deep into the porous white spot lesions, when compared to colloidal silica infiltrates.

Lysyl oxidase like-2 reinforces unsatisfactory ossification induced by bone morphogenetic protein-2: relating nanomechanical properties and molecular changes

Bone morphogenetic protein-2 (BMP2) is among the most popular anabolic agents and substantially increase bone volume related to enhanced osteoblast differentiation. Here we demonstrate a remarkable deterioration in the nanomechanical properties of mineralized tissue induced from osteoblasts solely by the function of BMP2. Mineralized tissue of primary osteoblasts cultured with BMP2 shows molecular features of both bone and cartilage, but depletion of lysyl oxidase family members leads to poor nanomechanical properties of the mineralized tissue. Lysyl oxidase like-2 supplementation reinforces the inferior mineralized tissue induced from osteoblasts by BMP2 through intermolecular cross-linking of type II or type X collagen-rich extracellular matrix. This may also mimic a consolidation of bone fracture gaps, despite the fact that the distribution of the bone properties in such microenvironments has been poorly elucidated. These findings confirm the importance of testing newly induced bone down to the microscale and nanoscale in bone tissue engineering.

FROM THE CLINICAL EDITOR

Bone morphogenetic protein-2 is known to substantially increase bone volume related to enhanced osteoblast differentiation; however, this team of investigators report a remarkable deterioration in the nanomechanical properties of mineralized tissue induced from osteoblasts solely by the function of BMP2.

Experimental resin cements containing bioactive fillers reduce matrix metalloproteinase-mediated dentin collagen degradation

INTRODUCTION

Collagen dentin matrix may represent a suitable scaffold to be remineralized in the presence of bioactive materials. The purpose of this study was to determine if experimental resin cements containing bioactive fillers may modulate matrix metalloproteinase-mediated collagen degradation of etched dentin.

METHODS

Human dentin beams 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 (Sylc; OSspray Ltd, London, UK), and (3) resin with β-tricalcium phosphate-modified calcium silicate cement (HCAT-β) particles. The filler/resin ratio was 40/60 wt%. The specimens were stored in artificial saliva, and the determination of C-terminal telopeptide (ICTP) was performed by radioimmunoassay after 24 hours, 1 week, and 4 weeks. Scanning electron microscopic analysis of dentin surfaces after 4 weeks of storage was also executed.

RESULTS

Collagen degradation was prominent both in phosphoric acid and EDTA-treated dentin. Resin infiltration strongly reduced the MMP activity in demineralized dentin. Resin-containing Bioglass 45S5 particles exerted higher and more stable protection of collagen at all tested dentin states and time points. HCAT-β induced collagen protection from MMPs only in EDTA-treated specimens. Dentin remineralization was achieved when dentin was infiltrated with the resin cements containing bioactive fillers.

CONCLUSIONS

MMP degradation of dentin collagen is strongly reduced in resin-infiltrated dentin. The inclusion of Bioglass 45S5 particles exerted an additional protection of collagen during dentin remineralization.

Remineralization of partially demineralized dentine substrate based on a biomimetic strategy

Dentine remineralization is clinically significant for prevention and treatment of dentine caries, root caries, and dentine hypersensitivity. However, dentine remineralization is more difficult than enamel remineralization due to the abundant presence of organic matrix in dentine. The objective of this study was to develop a biomimetic method to facilitate remineralization of demineralized dentine through phosphorylation of type I collagen in demineralized dentine using sodium trimetaphosphate. The experimental results indicated that the effect of fluoride on remineralizing dentine was limited when residual mineral crystals were lacking on the surface of demineralized dentine, whereas the phosphorylation and Ca(OH)(2) pretreatment enhanced surface remineralization of the partially demineralized dentine. This biomimetic methodology resulted in favorable surface properties (i.e. highly negative charge and low interfacial free energy between substrate and aqueous medium) for crystal nucleation, and thus could be a promising method to remineralize superficially demineralized dentine lesions.

Antioxidant and osteogenic properties of anodically oxidized titanium

Cells adhering onto implant surfaces are subjected to oxidative stress during wound healing processes. Although titanium and its alloys are among the most frequently used biomaterials in orthopedic and dental implants, titanium surfaces do not have antioxidant properties, and cells grown on these surfaces can show permanent oxidative stress. The present study assessed the antioxidant property and osteogenic properties of titanium samples with or without oxidation treatments. A thick rutile TiO₂ film was observed on thermally oxidized titanium surfaces, while amorphous anatase TiO₂ formed on anodically oxidized titanium surfaces prepared by discharging in 1 M Na₂HPO₄. A resistance to the depletion of reduced glutathione in adherent osteoblasts, which correlates with antioxidant behavior, occurred on anodically oxidized titanium. Enhanced osteogenic gene expressions and nano-biomechanical properties of mineralized tissue were achieved on anodically oxidized titanium, in comparison with thermally oxidized or untreated titanium. Thus, anodic oxidation by discharging in electrolyte is expected to be a useful surface modification for titanium implants.

A novel polymer infiltrated ceramic for dental simulation

Simulation of tooth preparation using rotary cutting instruments is viewed as beneficial and essential in dental training. Various types of materials have been used for simulation systems in dental preclinical training. However, the phantom tooth materials used for simulation have not changed significantly for decades and they are acknowledged to be different from natural teeth. This study investigated the mechanical properties and microstructure of a widely used phantom tooth material and compared them with a novel, polymer infiltrated, ceramic. It was concluded that the polymer infiltrated ceramic has mechanical properties more similar to natural teeth than current phantom tooth materials, suggesting that it might be a good candidate material for phantom teeth for trainees to acquire initial tactile sense for tooth preparation.

Development of fluorapatite cement for dental enamel defects repair

In order to restore the badly carious lesion of human dental enamel, a crystalline paste of fluoride substituted apatite cement was synthesized by using the mixture of tetracalcium phosphate (TTCP), dicalcium phosphate anhydrous (DCPA) and ammonium fluoride. The apatite cement paste could be directly filled into the enamel defects (cavities) to repair damaged dental enamel. The results indicated that the hardened cement was fluorapatite [Ca(10)(PO(4))(6)F(2), FA] with calcium to phosphorus atom molar ratio (Ca/P) of 1.67 and Ca/F ratio of 5. The solubility of FA cement in Tris-HCl solution (pH = 5) was slightly lower than the natural enamel, indicating the FA cement was much insensitive to the weakly acidic solutions. The FA cement was tightly combined with the enamel surface, and there was no obvious difference of the hardness between the FA cement and natural enamel. The extracts of FA cement caused no cytotoxicity on L929 cells, which satisfied the relevant criterion on dental biomaterials, revealing good cytocompatibility. In addition, the results showed that the FA cement had good mechanical strength, hydrophilicity, and anti-bacterial adhesion properties. The study suggested that using FA cement was simple and promising approach to effectively and conveniently restore enamel defects.

Mechanical recovery of dentin following remineralization in vitro--an indentation study

This study sought to gain insights into the steps leading to remineralization and mechanical recovery of hydrated dentin. Mechanical recovery in water was hypothesized to result from effective mineral matrix binding and to occur from the innermost regions outwards due to an increase in the number of nucleation sites. Partially demineralized (0.05 M acetate, pH=5.0, 8h) dentin was remineralized using calcium and phosphate solutions of 10.1 or 9.8 degree of saturation (DS) for hydroxyapatite (pH=7.4) for 4, 8 or 24h. Remineralization used a constant solution composition approach, which allowed for a continuous mineral growth with relatively constant thermodynamic driving forces. Crystal growth rates (R) were calculated using concentrations of calcium and phosphate. Before and after de- and re-mineralization, specimens had their surface and cross-section elastic moduli measured using AFM-nanoindentation in water. DS=10.1 provided higher R and higher mechanical recovery at the surface (p<0.0001). Cross-sectional measurements showed that subsurface mechanical recovery occurred from the innermost demineralized areas gradually outwards for both groups with no statistical differences at different DS, thus suggesting that remineralization is driven by mineral growth within nucleation sites with preserved collagen fibrils. Further, mechanical recovery appeared to initially obey a heterogeneous pattern, which vanished with time. This study provides evidence of mechanical recovery of hydrated dentin after remineralization and novel insights into the steps leading to mechanical recovery of carious dentin.

Evaluation of surface structural and mechanical changes following remineralization of dentin

This study sought to gain insights into the surface structural and mechanical changes leading to remineralization of dentin. Remineralization was compared between a continuous remineralization approach and a nonbuffered static approach using solutions of the same initial composition. Artificial carious lesions were treated for 5 days and analyzed every 24 h using nanoindentation in water, SEM, and AFM. The continuous approach yielded a recovery of mechanical properties of up to 60% of normal dentin, whereas the static approach led to recovery of only 10%. Image analysis revealed that the static approach yielded the formation of areas suggestive of an apatite precipitate on the surface of the dentin matrix. In contrast, surface precipitate was absent using the continuous approach, suggesting that mineral formed within the lesion and re-associated with the collagenous matrix. This study provided evidence that mechanical recovery of dentin in near physiological conditions is attainable through the continuous delivery of calcium and phosphate ions.

Nanomaterials in preventive dentistry

The prevention of tooth decay and the treatment of lesions and cavities are ongoing challenges in dentistry. In recent years, biomimetic approaches have been used to develop nanomaterials for inclusion in a variety of oral health-care products. Examples include liquids and pastes that contain nano-apatites for biofilm management at the tooth surface, and products that contain nanomaterials for the remineralization of early submicrometre-sized enamel lesions. However, the treatment of larger visible cavities with nanomaterials is still at the research stage. Here, we review progress in the development of nanomaterials for different applications in preventive dentistry and research, including clinical trials.

Differential expression of matrix metalloproteinase-2 in human coronal and radicular sound and carious dentine

OBJECTIVE

To examine the differential expression of matrix metalloproteinase-2 (MMP-2) in human coronal and radicular sound and carious dentine using combined trichrome staining technique and immunofluorescence approach.

METHODS

Freshly extracted human premolars were fixed with formaldehyde, demineralised with 10% EDTA (pH 7.4), dehydrated and sectioned for light and immunofluorescence microscopy. Half of the sections were stained with Masson's trichrome and examined with light microscopy to identify regions in the coronal and radicular parts of the teeth that contained sound, caries-affected and caries-infected dentine. The rest of the sections were hybridized with anti-mouse MMP-2 primary antibody and FITC-conjugated secondary antibody. Immunofluorescence of the FITC that was indicative of the distribution of the MMP-2 in coronal and radicular dentine was analysed by fluorescence light microscopy.

RESULTS

Trichrome staining revealed a green zone of unaffected sound dentin, red irregular regions of caries-infected dentine and pink regions of caries-affected dentine. Immunofluorescence signals that were indicative of MMP expression were the lowest in sound dentine and most intense in the caries-infected dentine. Caries-affected dentine showed intermediate immunoreactivity. The variations in the intensities of immunofluorescence corresponded well with the distribution of caries-infected and caries-affected dentine in the trichrome-stained sections, for both coronal and radicular dentine.

CONCLUSION

Caries stimulates MMP-2 expression, resulting in the differential expression of this protease in sound, caries-affected and caries-infected dentine. The more intense MMP-2 expression in caries-affected dentine compared with sound dentine may imply more rapid hybrid layer degradation when caries-affected dentine is employed as the substrate for bonded restorations.

Biomechanical perspective on the remineralization of dentin

The objective of this article is to critically evaluate the methods that are used to assess outcomes of remineralization of dentin. Currently, the most used assessment methods fall either into quantitative analysis of the mineral content of the remineralized structures or dry measurements of their mechanical properties. Properties obtained from the dehydrated organic dentin matrix may not reflect the true mechanical behavior of the remineralized tissue under physiological and hydrated conditions. Here we seek to clarify the biomechanical aspects of remineralization of dentin, pointing out the effects of hydration and dehydration on the mechanical properties of treated tissues. We also emphasize that a more appropriate endpoint to evaluate the effectiveness of remineralization in dentin should be associated with the recovery of the mechanical properties of the hydrated tissue, which is presumed to correlate well with its overall functionality.