Components Of Dentin Research Articles

Nanostructure of healthy and caries-affected human teeth

Spatially resolved small-angle x-ray scattering based on synchrotron radiation combines the quantitative assessment of nanometer-sized components using scattering with the real-space imaging by means of scanning. The method enables us to study the effect of caries-induced damages on the inorganic and organic nanoscopic components in human teeth. We demonstrate for several 200- to 500-μm-thin tooth slices that the bacterial processes dissolve the ceramic components in enamel and dentin, but the dentinal collagen network remains practically unaffected with respect to its abundance and orientation in early stages of caries and in parts of extended carious lesions. Consequently, we speculate that future caries treatments can be developed reversing the effect of bacterial attacks by means of suitable remineralization of the dentin. From the Clinical EditorIn this groundbreaking study of caries pathology using synchrotron-based X-ray scattering, the authors demonstrated that while bacterial processes do dissolve the ceramic components in enamel and dentin; however, the dentinal collagen network remains unaffected, enabling the development of future caries treatments that re-mineralize the dentin.

Dentin Matrix Protein 1 (DMP1) Signals via Cell Surface Integrin

Dentin matrix phosphoprotein 1 (DMP1) is a non-collagenous, acidic extracellular matrix protein expressed chiefly in bone and dentin. We examined the DMP1 ability to engage cell-surface receptors and subsequently activate intracellular signaling pathways. Our data indeed show that the presence of extracellular DMP1 triggers focal adhesion point formation in human mesenchymal stem cells and osteoblast-like cells. We determine that DMP1 acts via interaction with αvβ3 integrin and stimulates phosphorylation of focal adhesion kinase. Further biochemical characterization confirms the activation of downstream effectors of the MAPK pathways, namely ERK and JNK, after DMP1 treatment. This activation is specifically inhibitable and can also be blocked by the addition of anti-αvβ3 integrin antibody. Furthermore, we show that extracellular treatment with DMP1 stimulates the translocation of phosphorylated JNK to the nucleus and a concomitant up-regulation of transcriptional activation by phosphorylated c-Jun. The evidence presented here indicates that DMP1 is specifically involved in signaling via extracellular matrix-cell surface interaction. Combined with the published DMP1-null data (Feng, J. Q., Ward, L. M., Liu, S., Lu, Y., Xie, Y., Yuan, B., Yu, X., Rauch, F., Davis, S. I., Zhang, S., Rios, H., Drezner, M. K., Quarles, L. D., Bonewald, L. F., and White, K. E. (2006) Nat. Genet. 38, 1310-1315) it can be hypothesized that DMP1 could be a key effector of ECM-osteocyte signaling.

Effects of N‐acetylcysteine on TEGDMA‐ and HEMA‐induced suppression of osteogenic differentiation of human osteosarcoma MG63 cells

Triethyleneglycol dimethacrylate (TEGDMA) and 2-hydroxyethyl methacrylate (HEMA) are major resinous components of dental restorative materials and dentin bonding adhesives. Resin monomers are known to cause cytotoxicity in mammalian cells via oxidative stress and inhibit differentiation of dental pulp cells and osteoblasts. This study was aimed to investigate whether oxidative stress was involved in the inhibition of TEGDMA- and HEMA-induced differentiation. TEGDMA and HEMA reduced alkaline phosphatase (ALP) activity and the mRNA expression of the osteopontin (OPN) gene in MG63 cells at noncytotoxic concentrations. On the other hand, N-acetylcysteine (NAC) did not affect ALP activity at concentrations below 10 mM. Reduced ALP activity and OPN mRNA expression by TEGDMA were partially recovered via cotreatment with NAC. However, NAC did not exhibit significant effects in HEMA-treated cells. Glutathione (GSH) levels were also down-regulated by both TEGDMA and HEMA. The addition of NAC induced the partial recovery of GSH in cells treated with 0.5 mM TEGDMA. On the other hand, the levels of GSH in HEMA-treated cells were not affected by NAC. These results suggest that oxidative stress is involved in the suppression of differentiation by TEGDMA. Translocation of Nrf2 from the cytoplasm to the nucleus has been known to play a role in the suppression of osteogenic differentiation by oxidative stress. However, Nrf2 did not move into the nucleus in resin monomer-treated MG63 cells, suggesting the contribution of other signaling pathways to the suppressive effects of resin monomers.

In Vitro Cytocompatibility of N-acetylcysteine–supplemented Dentin Bonding Agents

Introduction Cytotoxic resin components of dentin bonding agents are known to cause oxidative damage and suppress odontogenic differentiation of dental pulp cells. Because antioxidants were found to protect cells from cytotoxicity of resin monomers in previous studies, we investigated the effect of N-acetylcysteine (NAC) on cytotoxicity and anti-differentiation activity of bonding agents. Methods Human dental pulp cells were treated with the extracts of dentin bonding agents (Prime & Bond NT, Adper Single Bond, and Dentin Cement), and then cell viability, alkaline phosphatase (ALP) activity, and matrix mineralization were observed. To assess the effects of NAC, NAC was directly added into culture media or mixed with bonding agents before extraction. Release of NAC from bonding agents was also observed by high-performance liquid chromatography. Results NAC enhanced ALP activity and mRNA expression of dentin sialophosphoprotein gene, whereas extracts of dentin bonding agents inhibited the induction of ALP activity. When the cells were treated with extracts of the bonding agents, the NAC in the culture media reduced the cytotoxicity of the bonding agents. When NAC was incorporated into bonding agents, a protective effect was only seen for Prime & Bond NT containing more than 1% NAC. The disruption of ALP activity and matrix mineralization in pulp cells was partially reversed by NAC only in Prime & Bond NT–treated cells. High-performance liquid chromatography analysis of NAC showed that the amount of NAC effluxed from Prime & Bond NT was not greater than that effluxed from Adper Single Bond. Conclusions NAC was useful for reversing cytotoxicity and anti-differentiation effects of Prime & Bond NT on human dental pulp cells.

Effects of heating by steam autoclaving and Er:YAG laser etching on dentin components

The simultaneous need for infection-control protocols in sample preparations and for safe laser irradiation parameters prompted this study about the effects of heat produced by both sample sterilization and laser etching on dentin components. The dentin was exposed on 30 bovine incisors, and then divided into two main groups: autoclaved (group A) or thymol treatment (group B). The surface of the dentin was schematically divided into four areas, with each one corresponding to a treatment subgroup. The specimens were either etched with phosphoric acid (control-CG) or irradiated with Er:YAG laser (subgroups: I-80 mJ, II-120 mJ, and III-180 mJ). Elemental distribution maps were done by energy-dispersive X-ray fluorescence (μ-EDXRF) on each treatment area. The dentin surface in depth was exposed and line-scan maps were performed. The B_CG treatment produced the best distribution of calcium (Ca) and phosphorus (P) content throughout the dentin surface. Er:YAG laser etching produced irregular patterns of elemental distribution in the dentin. Laser energies of 120 and 180 mJ produced the highest maximum calcium values. The Er:YAG laser energy of 180 mJ produced a localized increase in Ca and P content on the superficial layer of the dentin (∼ 0-0.10 mm). The autoclaving treatment of samples in experiments is not recommended since it produced damaging effects on dentin components. Er:YAG laser irradiation produced a heterogeneous Ca and P distribution throughout the dentin surface with areas of increased Ca concentration, and this may affect clinically the permeability, solubility, or adhesive characteristics of dental hard tissues with restorative procedures.

Dentin wetting by three adhesive systems: Influence of etching time, temperature and relative humidity

Objectives The purpose of this study was to investigate the wetting properties of three adhesives systems on etched dentin surfaces submitted to a brief air-drying procedure, as in clinical conditions. The influence of two clinical parameters (surface temperature and surrounding hygrometry) on wetting was investigated. Methods Two total-etch adhesives (Excite™ Vivapen and Adper™ Scothbond 1XT) and one self-etching adhesive (GC-G Bond™) were used. Superficial and deep dentin slice were obtained from six caries-free extracted third molars. Before the adhesive deposition, the dentin samples were etched with 37% phosphoric acid for different time durations. The surface topography was characterised by atomic force microscopy (AFM) observations and the wetting properties of dentin were studied by contact angle measurements. Results Unlike clinical expectations, the contact angles increased with the acid exposure time, and consequently with both surface roughness and the organic–mineral ratio of the dentin components. The wetting properties were clearly more sensitive to the surrounding relative humidity than the temperature. The contact angles values were reduced by about 50% when the relative humidity increased from 37% to 80% and by about 15% when the temperature was raised from 25 °C to 37 °C. Conclusion Acid-etched dentin exposed to a brief air-drying appears as the key parameter to control the wetting properties of total-etch adhesive–dentin systems. The experimental results seem to be well described by the Cassie–Baxter approach, and suggest that dentinal tubules through an adhesive repellent contribution should account for the observed wettability decreases.

Nano-Mechanical and -Electromechanical Heterogeneity in Single Collagen Fibrils

Type I collagen, as the most abundant protein in mammals, is the main organic component of bone, tendon, dentine, and cornea. Functioning in such diverse tissues shows the multifunctional capability of collagen fibrils. The gap and overlap regions in axial direction of a fibril with a characteristic period of ∼67 nm is believed to be an important factor in microstructure of the fibrils enabling its multifunctionality. For example, in bone mineral nano-crystals are deposited specifically in the gap region. In this study, we focus on studying mechanical and electromechanical properties at different scale levels, ranging from subfibrillar microstructure of single collagen fibrils ∼100 nm in diameter up to bone samples.In terms of mechanical (elastic and viscoelastic) properties, implementing near-surface static and dynamic nanoindentation technique with AFM, we show that the gap and overlap regions in single collagen fibril have significantly different elastic and energy dissipation properties, correlating the significantly different molecular structures in these two regions. We further show that such subfibrillar heterogeneity holds in collagen fibrils inside bone and might be related to the excellent energy dissipation performance of bone.It is known that bone and tendon are piezoelectric, and it is believed that the piezoelectric charges produced under mechanical deformation in these tissues have a potential role in mechanoelectric transduction leading to their growth and remodeling. With high resolution PFM we probe piezoelectric properties in bone and show that single collagen fibrils are responsible for piezoelectric behavior of bone and behave predominantly as shear piezoelectric materials. Furthermore, we show that there is an intrinsic electromechanical heterogeneity in axial direction of individual fibrils that holds even for the collagen fibrils embedded in bone matrix. Such heterogeneity may have implications in regulating the ionic environment in bone responsible for bone remodeling.

Compositional Changes of Enamel and Dentine after Er:YAG Laser Irradiation

The aim of the present study was to investigate the organic and inorganic compositions of enamel and dentine after Er:YAG laser irradiation using Fourier-transform Raman spectroscopy (FT-Raman). The enamel and dentine of extracted human teeth were irradiated by Er:YAG laser at an energy density of 29.7 J/cm2. The organic and inorganic components were evaluated from Raman spectra of untreated and laser-treated of extracted human teeth. The results showed that the Raman intensity ratio of the carbonate peak (1067 cm-1) to the phosphate peak (957 cm-1) and the organic peak (2940 cm-1) to the phosphate peak of enamel and dentine decreased after laser irradiation. Therefore, laser treatment can reduce the organic and inorganic components of human enamel and dentine.

High-resolution X-ray microdiffraction analysis of NaOH-treated dentin

Various kinds of basic chemicals interact with dentin directly in different clinical conditions. However, owing to the lack of appropriate models and technology, it is still not known how the mineral components of dentin react to these chemicals. The technology of high-resolution X-ray microdiffraction, in combination with scanning electron microscopy, has been applied to study the microstructure and minor crystallographic changes in a longitudinal dentin section before and after chemical treatment. Phase analysis was performed; the crystal sizes at two dentin sections were calculated from the reflections (002) and (211), and the crystal orientations of reflections (222), (213) and (002) were compared before and after treatment. The results show an inhomogeneity of the microstructure in dentin between the coronal and the root regions and that they react differently to basic treatment. In particular, NaOH treatment causes a change in crystal sizes and disorder.

Dentinal tubules driven wetting of dentin: Cassie-Baxter modelling

We investigate the wetting properties of dentin surfaces submitted to a phosphoric acid etching followed by an air drying procedure, as in clinical situations of adhesive dentistry. The surface topography of the etched surfaces was characterized by AFM, and the wetting properties of water on these rough and heterogeneous surfaces were studied, by contact angle measurements. We showed that the contact angle increases with the acid exposure time and consequently with both surface roughness and the organicmineral ratio of the dentin components. From the whole results, obtained on dentin and also on synthesized hydroxyapatites samples, we inferred a water contact angle of ~133° on the dentinal tubule. These experimental results may be described by the Cassie-Baxter approach, and it is suggested that small air pockets could be formed inside the dentinal tubules.

Effects of Er:YAG laser irradiation and manipulation treatments on dentin components, part 1: Fourier transform-Raman study

The effects of laser etching, decontamination, and storage treatments on dentin components were studied using Fourier transform (FT)-Raman spectroscopy. Thirty bovine incisors were prepared to expose the dentin surface and then divided in two main groups based upon the decontamination process and storage procedure: autoclaved (group A, n=15) or stored in thymol aqueous solution (group B, n=15). The surfaces of the dentin slices were schematically divided into four areas, with each one corresponding to a treatment subgroup. The specimens were either etched with phosphoric acid (control subgroup) or irradiated with erbium-doped yttrium-aluminum-garnet (Er:YAG) laser (subgroups: I-80 mJ, II-120 mJ, and III-180 mJ, and total energy of 12 J). Samples were analyzed by FT-Raman spectroscopy; we collected three spectra for each area (before and after treatment). The integrated areas of five Raman peaks were calculated to yield average spectra. The areas of the peaks associated with phosphate content (P<0.001), type I collagen, and organic C-H bonds (P<0.05) were reduced significantly in group A (control). Analyses of samples irradiated with reduced laser energies did not show significant changes in the dentin components. These results suggest that thymol storage treatment is advised for in vitro study; furthermore, 12 J of Er:YAG laser energy does not affect dentin components.

Effects of Er:YAG laser irradiation and manipulation treatments on dentin components, part 2: energy-dispersive X-ray fluorescence spectrometry study

The effects of laser etching, decontamination, and storage treatments on dentin components were studied by energy-dispersive X-ray fluorescence spectrometry (EDXRF). Thirty bovine incisors were prepared to expose the dentin surface and then divided into two main groups based upon the decontamination process and storage procedure: autoclaved (group A, n=15) or stored in aqueous thymol solution (group B, n=15). The surfaces of the dentin slices were schematically divided into four areas, with each one corresponding to a treatment subgroup. The specimens were either etched with phosphoric acid (control subgroup) or irradiated with erbium-doped yttrium-aluminum-garnet (Er:YAG) laser (subgroups: I-80 mJ, II-120 mJ, and III-180 mJ). Samples were analyzed by micro-EDXRF, yielding three spectra for each area (before and after treatment). Surface mappings covering an area of 80x60 points with steps of 20 mum were also performed on selected specimens. The amount of Ca and P in group A specimens decreased significantly (P<0.05) after the acid etching and the CaP ratio increased (P<0.001). Er:YAG laser-etching using lower laser energies did not produce significant changes in dentin components. The mapping data support the hypothesis that acid etching on dentin produced a more chemically homogeneous surface and thus a more favorable surface for the diffusion of adhesive monomers.

Anticariogenicity of Casein Phosphopeptide-amorphous Calcium Phosphate: A Review of the Literature

This review of the literature examines the role of the natural components of saliva in maintaining tooth mineralization and the role of different casein phosphopeptide amorphous calcium phosphate-based (CPP-ACP) compounds in controlling demineralization/remineralization and their clinical applications. A group of peptides, known as CPP, have been shown to stabilize calcium and phosphate preserving them in an amorphous or soluble form known as amorphous calcium phosphate (ACP). Calcium and phosphate are essential components of enamel and dentine and form highly insoluble complexes, but in the presence of CPP they remain soluble and biologically available. This CPP-ACP complex applied to teeth by means of chewing-gum, toothpaste, lozenges, mouth rinses, or sprays is able to adhere to the dental biofilm and enamel hydroxyapatite providing bioavailable calcium and phosphate ions. Significantly high levels of calcium and phosphate have been found in both biofilm and subsurface incipient caries lesions and in lower level demineralization of enamel or dentine surfaces previously treated with CPP-ACP based compounds. When placed on the surface of a tooth with early carious lesions, pastes with CPP-ACP complexes can prevent tooth demineralization and improve enamel remineralization and enhance fluoride activity. Remineralization of white spot lesions has been achieved clinically by applying pastes based on these compounds, and a similar effect to self-applied fluorides has been observed in reducing the appearance of new caries lesions in patients with xerostomia. Use of CPP-ACP based compounds offers a potential for use in the prevention of dental caries.

Focused ion beam milling and ultramicrotomy of mineralised ivory dentine for analytical transmission electron microscopy

The use of focused ion beam (FIB) milling for preparation of sections of mineralised ivory dentine for transmission electron microscopy (TEM) is investigated. Ivory dentine is essentially composed of fibrillar type-I collagen and apatite crystals. The aim of this project is to gain a clearer understanding of the relationship between the organic and inorganic components of ivory dentine using analytical TEM, in order to utilise these analytical techniques in the context of common skeletal diseases such as osteoporosis and arthritis. TEM sections were prepared in both single and dual beam FIB instruments, using two standard lift-out techniques, in situ and ex situ. The FIB sections were systematically compared with sections prepared by ultramicrotomy, the traditional preparation route in biological systems, in terms of structural and chemical differences. A clear advantage of FIB milling over ultramicrotomy is that dehydration, embedding and section flotation can be eliminated, so that partial mineral loss due to dissolution is avoided. The characteristic banding of collagen fibrils was clearly seen in FIB milled sections without the need for any chemical staining, as is commonly employed in ultramicrotomy. The FIB milling technique was able to produce high-quality TEM sections of ivory dentine, which are suitable for further investigation using electron energy-loss spectroscopy (EELS) and energy-filtering TEM (EFTEM) to probe the collagen/apatite interface.

Infantile Cortical Hyperostosis (Caffey Disease): A Review

Face swelling in infants may have several causes including infantile cortical hyperostosis (Caffey disease), an inflammatory process with swelling of soft tissues and periosteal hyperostosis of some bones. New insights show that this self-limited condition is collagen I-related. Collagen I is the most important component of bone and dentine. We reviewed literature to lighten this new collagenopathy, the first one with a self-regressive course. After describing a typical case and the clinical and radiologic features of the disease, we discuss the pathogenic pathways and management care for oral professionals. Oral practitioners could be asked for differential diagnosis. Surgeons could be queried for surgical correction of the bony deformity, especially of facial and mandibular asymmetry.

Heat Treatment Strengthens Human Dentin

The flexural strength of Type I collagen, the major organic component of human dentin, increases with heat. We hypothesized that human dentin can be strengthened by heating, which may help prevent fracture of non-vital teeth after restoration. Beam-shaped dentin specimens were obtained from the crowns of human third molars. The dentinal tubular orientations were arranged to run parallel or perpendicular to loading surfaces. The flexural and microtensile strengths of dentin in the parallel specimens were 2- to 2.4-fold greater after being heated between 110 degrees C and 140 degrees C for 1 hr. The stress intensity factors at fracture also increased after specimens were heated. The x-ray diffraction analyses suggested that shrinking of the lateral packing of the collagen triple-helices from 14 A to 11 A was the probable cause of the strengthening of heated dentin. We conclude that heat treatment strengthens human dentin.

Tensile strength of dentin after bleaching treatment

The mechanical properties of dentin are changed after bleaching, although the effects of the bleaching conditions on the tensile strength of dentin have not been determined. In the current study, a tensile test of bovine dentin was conducted after bleaching and the effects of the bleaching conditions were investigated, including the number of bleaching times, the location where the bleaching agent was applied, and the kind of illumination. The weight of organic content in dentin before and after application of the agent was also measured. The results showed that the tensile strengths did not change after three times office bleaching procedure, and the location where the bleaching agent was applied, the kind of bleaching agent and the kind of illumination did not have influence on the tensile strength. On the other hand, organic component in dentin significantly decreased after application of the agent (p<0.05). Since the bleaching agent would potentially affect tensile strength with deterioration of collagen matrix, the frequency of bleaching treatment should be minimized in clinical use.

Effects of Hydrogen Peroxide on Human Dentin Structure

It has been hypothesized that hydrogen peroxide (H(2)O(2)) bleaching may cause destruction of dentin by a mechanism of protein oxidation. However, to our knowledge, there has been no direct chemical evidence to validate this viewpoint. To investigate the effects of H(2)O(2) on the structure of human dentin, we used Fourier transform infrared spectroscopy (FTIR) and attenuated total reflection (ATR) spectroscopy. Human intact dentin specimens were treated either with 30% H(2)O(2) or Hanks' balanced salt solution (HBSS). Significant differences were observed in ATR spectra parameters. Additionally, demineralized dentin specimens were also tested. They were completely dissolved in the H(2)O(2), but remained intact in the 0.1 N HCl and HBSS. The results suggested that H(2)O(2) attacked both the organic and mineral components of dentin. Destruction of the organic components was mainly because of the oxidizing ability of H(2)O(2), while changes in the mineral components were probably due to its acidity.

Effect of sodium hypochlorite on human root dentine – mechanical, chemical and structural evaluation

To investigate the mechanical, chemical and structural alterations of human root dentine following exposure to ascending sodium hypochlorite concentrations. Three-point bending tests were carried out on standardized root dentine bars (n = 8 per group, sectioned from sound extracted human third molar teeth) to evaluate their flexural strength and modulus of elasticity after immersion in 5 mL of water (control), 1% NaOCl, 5% NaOCl or 9% NaOCl at 37 degrees C for 1 h. Additional dentine specimens were studied using microelemental analysis, light microscopy following bulk staining with basic fuchsin, and scanning electron microscopy (SEM). Numerical data were compared using one-way ANOVA. Bonferroni's correction was applied for multiple testing. Immersion in 1% NaOCl did not cause a significant drop in elastic modulus or flexural strength values in comparison to water, whilst immersion in 5% and 9% hypochlorite reduced these values by half (P < 0.05). Both, carbon and nitrogen contents of the specimens were significantly (P < 0.05) reduced by 5% and 9% NaOCl, whilst 1% NaOCl had no such effect. Exposure to 5% NaOCl rendered the superficial 80-100 mum of the intertubular dentine permeable to basic fuchsin. Three-dimensional SEM reconstructions of partly demineralized specimens showed NaOCl concentration-dependent matrix deterioration. Backscattered electron micrographs revealed that hypochlorite at any of the tested concentrations left the inorganic dentine components intact. The current data link the concentration-dependent hypochlorite effect on the mechanical dentine properties with the dissolution of organic dentine components.

Double-quantum filtered heteronuclear correlation spectroscopy under magic angle spinning

We present a simple experimental method to extract the van Vleck second moment of a multiple-spin system under high-resolution condition. The idea is to incorporate a double-quantum (DQ) filter into the pulse sequence of heteronuclear correlation spectroscopy so that a DQ excitation profile can be obtained by measuring a series of 2D spectra. The effects of spinning frequency and proton decoupling are demonstrated on the measurements of two model compounds, viz. hydroxyapatite and brushite. Based on the results obtained for the model compounds, the P-31 homonuclear second moment of the apatite component in rat dentin is characterized. The method is generally suited for the study of bone, enamel and dentin.