Peritubular Dentin Research Articles

Radiotherapy Reduces Microhardness and Mineral and Organic Composition, and Changes the Morphology of Primary Teeth: An in vitro Study

Objective: We aimed to evaluate whether radiotherapy causes changes in the mineral composition, hardness, and morphology of enamel and dentin of primary teeth. Materials and Methods: Thirty specimens of primary teeth were subjected to radiotherapy. At baseline and after 1,080, 2,160, and 3,060 cGy, the specimens were subjected to microhardness, FT-Raman spectroscopy, and scanning electron microscopy (SEM) analysis. The pH of artificial saliva was determined, as were the calcium and phosphate concentrations. The data were subjected to the Shapiro-Wilk normality test, showed a nonnormal distribution, and were compared by the Kruskal-Wallis test. Results: The results showed that the microhardness of the enamel surface decreased after 2,160 cGy (281.5 ± 58 kgf/mm²) when compared to baseline (323.6 ± 59.5 kgf/mm²) (p = 0.045). For dentin, the surface hardness decreased after 1,080 cGy (34.9 ± 11.4 kgf/mm²) and 2,160 cGy (26 ± 3.5 kgf/mm²) when compared to baseline (56.5 ± 7.7 kgf/mm²) (p < 0.0001). The mineral and organic contents of phosphate (p < 0.0001), carbonate (p < 0.0001), amide (p = 0.0002), and hydrocarbons (p = 0.0031) of enamel decreased after 3,060 cGy (5,178 ± 1,082, 3,868 ± 524, 999 ± 180, and 959 ± 168 kgf/mm², respectively). For dentin, we noticed a growing increase in phosphate v2, amide, and hydrocarbon content after 1,080 cGy (8,210 ± 2,599, 5,730 ± 1,818, and 6,118 ± 1,807 kgf/mm², respectively) and 2,160 cGy (1,0071 ± 2,547, 7,746 ± 1,916, and 8,280 ± 2,079 kgf/mm², respectively) and a reduction after 3,060 cGy (6,782 ± 2,175, 3,558 ± 1,884, and 3,565 ± 1,867 kgf/mm², respectively) (p < 0.0001). SEM images showed cracks on enamel and degradation of peritubular dentin. Conclusion: We concluded that radiotherapy caused a reduction in surface hardness, changed mineral and organic composition, and promoted morphological changes on the enamel and dentin of primary teeth.

Micron-scale crack propagation in laser-irradiated enamel and dentine studied with nano-CT

ObjectivesThe aim of this study was to see the effect of Er:YAG laser irradiation in dentine and compare this with its effect in enamel. The mechanism of crack propagation in dentine was emphasised and its clinical implications were discussed.Materials and methodsCoronal sections of sound enamel and dentine were machined to 50-μm thickness using a FEI-Helios Plasma (FIB). The specimen was irradiated for 30 s with 2.94-μm Er:YAG laser radiation in a moist environment, using a sapphire dental probe tip, with the tip positioned 2 mm away from the sample surface. One of the sections was analysed as a control and not irradiated. Samples were analysed using the Zeiss Xradia 810 Ultra, which allows high spatial resolution, nanoscale 3D imaging using X-ray computed tomography (CT).ResultsDentine: In the peritubular dentine, micro-cracks ran parallel to the tubules whereas in the inter-tubular region, the cracks ran orthogonal to the dentinal tubules. These cracks extended to a mean depth of approximately 10 μm below the surface. On the dentine surface, there was preferential ablation of the less mineralised intertubular dentine, and this resulted in an irregular topography associated with tubules.Enamel: The irradiated enamel surface showed a characteristic ‘rough’ morphology suggesting some preferential ablation along certain microstructure directions. There appears to be very little subsurface damage, with the prismatic structure remaining intact.ConclusionsA possible mechanism is that laser radiation is transmitted down the dentinal tubules causing micro-cracks to form in the dentinal tubule walls that tend to be limited to this region.Clinical relevanceCrack might be a source of fracture as it represents a weak point and subsequently might lead to a failure in restorative dentistry.

Structure-Function Correlative Microscopy of Peritubular and Intertubular Dentine.

Peritubular dentine (PTD) and intertubular dentine (ITD) were investigated by 3D correlative Focused Ion Beam (FIB)-Scanning Electron Microscopy (SEM)-Energy Dispersive Spectroscopy (EDS) tomography, tapping mode Atomic Force Microscopy (AFM) and scattering-type Scanning Near-Field Optical Microscopy (s-SNOM) mapping. The brighter appearance of PTD in 3D SEM-Backscattered-Electron (BSE) imaging mode and the corresponding higher grey value indicate a greater mineral concentration in PTD (~160) compared to ITD (~152). However, the 3D FIB-SEM-EDS reconstruction and high resolution, quantitative 2D map of the Ca/P ratio (~1.8) fail to distinguish between PTD and ITD. This has been further confirmed using nanoscale 2D AFM map, which clearly visualised biopolymers and hydroxyapatite (HAp) crystallites with larger mean crystallite size in ITD (32 ± 8 nm) than that in PTD (22 ± 3 nm). Correlative microscopy reveals that the principal difference between PTD and ITD arises primarily from the nanoscale packing density of the crystallites bonded together by thin biopolymer, with moderate contribution from the chemical composition difference. The structural difference results in the mechanical properties variation that is described by the parabolic stiffness-volume fraction correlation function introduced here. The obtained results benefit a microstructure-based mechano-chemical model to simulate the chemical etching process that can occur in human dental caries and some of its treatments.

Zn-containing polymer nanogels promote cervical dentin remineralization.

Nanogels designing for effective treatment of eroded cervical dentin lesions. Polymethylmetacrylate-based nanoparticles (NPs) were doxycycline (D), calcium, or zinc loaded. They were applied on eroded cervical dentin. Treated surfaces were characterized morphologically by atomic force and scanning electron microscopy, mechanically probed by a nanoindenter to test nanohardness and Young's modulus, and chemically analyzed by Raman spectroscopy at 24h and 7days of storage. Data were submitted to ANOVA and Student-Newman-Keuls multiple comparisons tests. Dentin treated with Zn-NPs attained the highest nanomechanical properties, mineralization, and crystallinity among groups. Nanoroughness was lower in Zn-treated surfaces in comparison to dentin treated with undoped gels. Dentin treated with Ca-NPs created the minimal calcification at the surface and showed the lowest Young's modulus at peritubular dentin. Intertubular dentin appeared remineralized. Dentinal tubules were empty in samples treated with D-NPs, partially occluded in cervical dentin treated with undoped NPs and Ca-NPs, and mineral covered when specimens were treated with Zn-NPs. Zn-loaded NPs permit functional remineralization of eroded cervical dentin. Based on the tested nanomechanical and chemical properties, Zn-based nanogels are suitable for dentin remineralization. The ability of zinc-loaded nanogels to promote dentin mineralization may offer new strategies for regeneration of eroded cervical dentin and effective treatment of dentin hypersensitivity.

Improved reactive nanoparticles to treat dentin hypersensitivity

The aim of this study was to evaluate the effectiveness of different nanoparticles-based solutions for dentin permeability reduction and to determine the viscoelastic performance of cervical dentin after their application. Four experimental nanoparticle solutions based on zinc, calcium or doxycycline-loaded polymeric nanoparticles (NPs) were applied on citric acid etched dentin, to facilitate the occlusion and the reduction of the fluid flow at the dentinal tubules. After 24 h and 7 d of storage, cervical dentin was evaluated for fluid filtration. Field emission scanning electron microscopy, energy dispersive analysis, AFM and Nano-DMA analysis were also performed. Complex, storage, loss modulus and tan delta (δ) were assessed. Doxycycline-loaded NPs impaired tubule occlusion and fluid flow reduction trough dentin. Tubules were 100% occluded in dentin treated with calcium-loaded NPs or zinc-loaded NPs, analyzed at 7 d. Dentin treated with both zinc-NPs and calcium-NPs attained the highest reduction of dentinal fluid flow. Moreover, when treating dentin with zinc-NPs, complex modulus values attained at intertubular and peritubular dentin were higher than those obtained after applying calcium-NPs. Zinc-NPs are then supposed to fasten active dentin remodeling, with increased maturity and high mechanical properties. Zinc-based nanoparticles are then proposed for effective dentin remineralization and tubular occlusion. Further research to finally prove for clinical benefits in patients with dentin hypersensitivity using Zn-doped nanoparticles is encouraged. Statement of SignificanceErosion from acids provokes dentin hypersensitivity (DH) which presents with intense pain of short duration. Open dentinal tubules and demineralization favor DH. Nanogels based on Ca-nanoparticles and Zn-nanoparticles produced an efficient reduction of fluid flow. Dentinal tubules were filled by precipitation of induced calcium-phosphate deposits. When treating dentin with Zn-nanoparticles, complex modulus values attained at intertubular and peritubular dentin were higher than those obtained after applying Ca-nanoparticles. Zn-nanoparticles are then supposed to fasten active dentin remodeling, with increased maturity and high mechanical properties. Zinc-based nanogels are, therefore, proposed for effective dentin remineralization and tubular occlusion. Further research to finally prove for clinical benefits in patients with dentin hypersensitivity using Zn-doped nanogels is encouraged.

An analysis of crack growth in dentin at the microstructural scale.

Dentin is a biocomposite possessing complex hierarchical structure, which endows this hard tissue with excellent damage tolerance. In this study, crack growth in dentin at the microstructural scale is investigated and the synergistic effects of plastic deformation of intertubular dentin (ITD), elasticity and fracture properties of peritubular dentin (PTD), and fracture properties of PTD/ITD interface on the fracture of dentin are explored. A micromechanical model is developed, which captures the experimentally observed fracture process of dentin, i.e. occurrence of microcracking of PTD ahead of the main crack. It is found through numerical simulations that high relative stiffness and low cohesive strength of PTD increase the propensity of microcracking of PTD, whereas reduce the plastic dissipation and toughness of the microstructure of dentin. The microcracking of PTD can be also promoted by low toughness of PTD. The large friction angle and weak strain hardening of ITD could promote the microcracking of PTD, and simultaneously enhance the toughness of the microstructure of dentin. In addition, it is identified that the cohesive strength of the PTD/ITD interface plays a crucial role in dominating fracture mechanisms; low cohesive strength leads to fracture of interface and suppresses microcracking of PTD, which provides an explanation for the crack deflection along interface observed in experiments. Nevertheless, the toughness of interface has a negligible influence on the fracture of dentin.

A zinc-doped endodontic cement facilitates functional mineralization and stress dissipation at the dentin surface.

BackgroundThe purpose of this study was to evaluate nanohardness and viscoelastic behavior of dentin surfaces treated with two canal sealer cements for dentin remineralization.Material and MethodsDentin surfaces were subjected to: i) 37% phosphoric acid (PA) or ii) 0.5 M ethylenediaminetetraacetic acid (EDTA) conditioning prior to the application of two experimental hydroxyapatite-based cements, containing sodium hydroxide (calcypatite) or zinc oxide (oxipatite), respectively. Samples were stored in simulated body fluid during 24 h or 21 d. The intertubular and peritubular dentin were evaluated using a nanoindenter to assess nanohardness (Hi). The load/displacement responses were used for the nano-dynamic mechanical analysis to estimate complex modulus (E*) and tan delta (δ). The modulus mapping was obtained by imposing a quasistatic force setpoint to which a sinusoidal force was superimposed. AFM imaging and FESEM analysis were performed.ResultsAfter 21 d of storage, dentin surfaces treated with EDTA+calcypatite, PA+calcypatite and EDTA+oxipatite showed viscoelastic discrepancies between peritubular and intertubular dentin, meaning a risk for cracking and breakdown of the surface. At both 24 h and 21 d, tan δ values at intertubular dentin treated with the four treatments performed similar. At 21 d time point, intertubular dentin treated with PA+oxipatite achieved the highest complex modulus and nanohardness, i.e., highest resistance to deformation and functional mineralization, among groups.ConclusionsIntertubular and peritubular dentin treated with PA+oxipatite showed similar values of tan δ after 21 d of storage. This produced a favorable dissipation of energy with minimal energy concentration, preserving the structural integrity at the dentin surface. Key words:Dentin, fracture, hydroxyapatite, remineralization, viscoelastic, zinc.

Bonding Performance of Universal Adhesives to Eroded Dentin.

To evaluate the microtensile bond strength (µTBS) and nanoleakage (NL) of several universal adhesives to eroded dentin (ED), using etch-and-rinse (ER) or self-etch (SE) strategies, and to characterize the surface using two pH cycling models to erode dentin (citric acid and a soft drink). Molars were eroded either by soft-drink or citric acid cycling, or were left untreated as control (SD). For each surface, the following adhesives were applied: 1. All-Bond Universal; 2. Ambar Universal; 3. Clearfil Universal; 4. Futurabond U; 5. One Coat 7 Universal; 6. Peak Universal Bond; 7. Prime&Bond Elect; 8. Scotchbond Universal; 9. Tetric n-bond Universal, and 10. Xeno Select. After application of the composite, specimens were sectioned into composite-dentin sticks and tested under tension (0.5 mm/min). Selected sticks from each tooth were used to assess NL. The occlusal dentin surfaces after erosive cycling were examined using SEM. Data were analyzed by three-way ANOVA and Tukey's post-hoc test (a = 0.05). In ED, there was no difference in μTBS and NL between ER and SE strategies (p > 0.61). Most μTBS and NL values obtained for ED were, respectively, lower and higher than those for SD (p < 0.01), being worse for citric acid ED (p < 0.001). Citric-acid-eroded dentin showed more enlarged tubules, with partial loss of peritubular dentin when compared to soft-drink eroded dentin. The different pH cycling models reduced μTBS and increased NL of the composite/eroded-dentin interface; however, in ED, the performance of the universal adhesives did not depend on the adhesive strategy used.

The variation in surface morphology and hardness of human deciduous teeth samples after laser irradiation

The variation in surface morphology and hardness of human deciduous teeth samples has been investigated after laser irradiation at different wavelengths and energies. Nd:YAG was employed as a source of irradiation for IR (1064 nm) and visible (532 nm) radiation, whereas an excimer laser was used as the source of UV (248 nm) radiation. Scanning electron microscope (SEM) analysis was carried out to reveal the surface morphological evolution of teeth samples. Vickers microhardness tester was employed to investigate the modifications in the hardness of the laser-treated samples. It is observed from SEM analysis that IR wavelength is responsible for ablation of collagen matrix and intertubular dentine. For visible radiation, the ablation of collagen along with hydroxypatite is observed. With UV radiation, the ablation of peritubular dentine is dominant and is responsible for the sealing of tubules. The decrease in hardness at lower energy for both wavelengths is due to the evaporation of carbon content. With increasing energy, evaporation of water along with carbon content, and resolidification and re-organization of inorganic content causes the increase in hardness of the treated dentine. SEM as well as microhardness analyses reveal that laser wavelengths and energy of laser radiation significantly influence the surface morphology and hardness of samples.

The effect of microcracking in the peritubular dentin on the fracture of dentin

Dentin is a biocomposite possessing elegant hierarchical structure, which allows it to resist fracture effectively. Despite the considerable efforts to unravel the peculiar fracture behavior of dentin, the effect of microstructural features on the fracture process is largely unknown. In this study, we explore the interaction between the primary crack with crack tip located in intertubular dentin (ITD) and microcracking of peritubular dentin (PTD) ahead of the primary crack. A micromechanical model accounting for the unique composite structure of dentin is developed, and computational simulations are performed. It is found that the microcracking of PTD located in the crack plane in front of the primary crack tip can promote the propagation of the primary crack, increasing the propensity of coalescence of primary crack and microcracks nucleating in PTD. We show that the two-layer microstructure of dentin enables reduction in driving force of primary crack, potentially enhancing fracture toughness. The high stiffness of PTD plays a critical role in reducing the driving force of primary crack and activating microcracking of PTD. It is further identified that the microcracking of PTD arranged parallel to the crack plane with an offset could contribute to the shielding of primary crack.

The peritubular reinforcement effect of porous dentine microstructure.

In the current study, we evaluate the equivalent stiffness of peritubular reinforcement effect (PRE) of porous dentine optimized by the thickness of peritubular dentine (PTD). Few studies to date have evaluated or quantitated the effect of PRE on composite dentine. The miscrostructure of porous dentine is captured by scanning electron microscope images, and then finite element modeling is used to quantitate the deformation and stiffness of the porous dentine structure. By optimizing the radius of PTD and dentine tubule (DT), the proposed FE model is able to demonstrate the effect of peritubular reinforcement on porous dentine stiffness. It is concluded that the dentinal equivalent stiffness is reduced and degraded with the increase of the radius of DT (i.e., porosity) in the certain ratio value of Ep/Ei and certain radius of PTD, where Ep is the PTD modulus and Ei is the intertubular dentine modulus. So in order to ensure the whole dentinal equivalent stiffness is not loss, the porosity should get some value while the Ep/Ei is certain. Thus, PTD prevents the stress concentration around DTs and reduces the risk of DTs failure. Mechanically, the overall role of PTD appears to enhance the stiffness of the dentine composite structure. These results provide some new and significant insights into the biological evolution of the optimal design for the porous dentine microstructure. These findings on the biological microstructure design of dentine materials are applicable to other engineering structural designs aimed at increasing the overall structural strength.

Analysis of crack interacting with the composite microstructure of dentin

Abstract Dentin possesses strong fracture resistance, which is attributed to various toughening mechanisms associated with its unique hierarchical structure. In this study, the effects of microstructural features on crack growth in dentin are analyzed. A plasticity model incorporating a local fracture criterion is used to model the mechanical behavior of intertubular dentin (ITD), and a brittle cracking model is used for the peritubular dentin (PTD). Computational simulations of fracture behavior of microstructured dentin are performed, showing that crack growth in microstructured dentin is accompanied by microcracking of PTD ahead of the primary crack, and that fracture of dentin is caused by the merging of the primary crack and microcracks nucleating in PTD. It is identified that the decrease in tubule radius and PTD thickness can lead to the development of a significant degree of microcracking in PTD, thereby enhancing toughness. We further reveal that the toughness of microstructured dentin is dependent on tubule density. The transition in fracture mechanism from multiple void interactions to crack-void interaction occurs as the tubule density decreases, which promotes toughness of dentin. In addition, the effect of the arrangement of dentin tubules is also discussed. The findings of this study provide a mechanistic insight into the region dependent fracture behavior of dentin.

Mechanical loading influences the viscoelastic performance of the resin-carious dentin complex

The aim of this study was to evaluate the changes in the mechanical behavior and bonding capability of Zn-doped resin-infiltrated caries-affected dentin interfaces. Dentin surfaces were treated with 37% phosphoric acid (PA) followed by application of a dentin adhesive, single bond (SB) (PA+SB) or by 0.5 M ethylenediaminetetraacetic acid (EDTA) followed by SB (EDTA+SB). ZnO microparticles of 10 wt. % or 2 wt. % ZnCl2 was added into SB, resulting in the following groups: PA+SB, PA+SB-ZnO, PA+SB-ZnCl2, EDTA+SB, EDTA+SB-ZnO, EDTA+SB-ZnCl2. Bonded interfaces were stored for 24 h, and tested or submitted to mechanical loading. Microtensile bond strength was assessed. Debonded surfaces were evaluated by scanning electron microscopy and elemental analysis. The hybrid layer, bottom of the hybrid layer, and peritubular and intertubular dentin were evaluated using a nanoindenter. The load/displacement responses were used for the nanodynamic mechanical analysis III to estimate complex modulus, tan delta, loss modulus, and storage modulus. The modulus mapping was obtained by imposing a quasistatic force setpoint to which a sinusoidal force was superimposed. Atomic force microscopy imaging was performed. Load cycling decreased the tan delta at the PA+SB-ZnCl2 and EDTA+SB-ZnO interfaces. Tan delta was also diminished at peritubular dentin when PA+SB-ZnO was used, hindering the dissipation of energy throughout these structures. Tan delta increased at the interface after using EDTA+SB-ZnCl2, lowering the energy for recoil or failure. After load cycling, loss moduli at the interface decreased when using ZnCl2 as doping agent, increasing the risk of fracture; but when using ZnO, loss moduli was dissimilarly affected if dentin was EDTA-treated. The border between intertubular and peritubular dentin attained the highest discrepancy in values of viscoelastic properties, meaning a risk for cracking and breakdown of the resin-dentin interface. PA used on dentin provoked differences in complex and storage modulus values at the intertubular and peritubular structures, and these differences were higher than when EDTA was employed. In these cases, the long-term performance of the restorative interface will be impaired.

Crack initiation and propagation in composite microstructure of dentin

Dentin possesses unique hierarchical structure through long-term natural selection, which imparts exceptional mechanical properties to this hard tissue. In this study, the combined effects of ductile fracture of intertubular dentin (ITD) and brittle cracking of peritubular dentin (PTD) on the crack initiation and propagation in the composite microstructure of dentin are explored. A micromechanical model accounting for the unique two-layer microstructure of dentin is developed and numerical simulations of fracture of microstructured dentin are performed. It is found that microcracking of PTD prior to the penetration of main crack into PTD and crack deflection along the interface between PTD and ITD are two major mechanisms involved in the fracture of microstructured dentin, which is in a good agreement with experimental observations. The competition between the two mechanisms is governed by PTD strength. Furthermore, we reveal that the elastic and fracture properties of PTD and strain hardening of ITD greatly affect the fracture behavior of dentin. The decrease in elastic modulus and increase in tensile strength of PTD elevate the notch tip plasticity, increasing the propensity of crack initiation at notch tip. Whereas such variations in elastic modulus and tensile strength of PTD can lead to the transition of fracture mechanism from multiple void interactions to crack-void interaction, thereby enhancing toughness of dentin. Increasing the strain hardening exponent of ITD can also give rise to the amplified toughness.

Ions-modified nanoparticles affect functional remineralization and energy dissipation through the resin-dentin interface

The aim of this study was to evaluate changes in the mechanical and chemical behavior, and bonding ability at dentin interfaces infiltrated with polymeric nanoparticlesstandard deviations and modes of failure are (NPs) prior to resin application. Dentin surfaces were treated with 37% phosphoric acid followed by application of an ethanol suspension of NPs, Zn-NPs or Ca-NPs followed by the application of an adhesive, Single Bond (SB). Bonded interfaces were stored for 24h, submitted to microtensile bond strength test, and evaluated by scanning electron microscopy. After 24h and 21 d of storage, the whole resin-dentin interface adhesive was evaluated using a Nano-DMA. Complex modulus, storage modulus and tan delta (δ) were assessed. AFM imaging and Raman analysis were performed. Bond strength was not affected by NPs infiltration. After 21 d of storage, tan δ generally decreased at Zn-NPs/resin-dentin interface, and augmented when Ca-NPs or non-doped NPs were used. When both Zn-NPs and Ca-NPs were employed, the storage modulus and complex modulus decreased, though both moduli increased at the adhesive and at peritubular dentin after Zn-NPs infiltration. The phosphate and the carbonate peaks, and carbonate substitution, augmented more at interfaces promoted with Ca-NPs than with Zn-NPs after 21 d of storage, but crystallinity did not differ at created interfaces with both ions-doped NPs. Crosslinking of collagen and the secondary structure of collagen improved with Zn-NPs resin-dentin infiltration. Ca-NPs-resin dentin infiltration produced a favorable dissipation of energy with minimal stress concentration trough the crystalline remineralized resin-dentin interface, causing minor damage at this structure.

Mesoscale porosity at the dentin-enamel junction could affect the biomechanical properties of teeth.

In this paper, the 3D-morphology of the porosity in dentin is investigated within the first 350μm from the dentin-enamel junction (DEJ) by fluorescence confocal laser scanning microscopy (CLSM). We found that the porous microstructure exhibits a much more complex geometry than classically described, which may impact our fundamental understanding of the mechanical behavior of teeth and could have practical consequences for dental surgery. Our 3D observations reveal numerous fine branches stemming from the tubules which may play a role in cellular communication or mechanosensing during the early stages of dentinogenesis. The effect of this highly branched microstructure on the local mechanical properties is investigated by means of numerical simulations. Under simplified assumptions on the surrounding tissue characteristics, we find that the presence of fine branches negatively affects the mechanical properties by creating local stress concentrations. However, this effect is reduced by the presence of peritubular dentin surrounding the tubules. The porosity was also quantified using the CSLM data and compared to this derived from SEM imaging. A bimodal distribution of channel diameters was found near the DEJ with a mean value of 1.5-2μm for the tubules and 0.3-0.5μm for the fine branches which contribute to 30% of the total porosity (∼1.2%). A gradient in the branching density was observed from the DEJ towards the pulp, independently of the anatomical location. Our work constitutes an incentive towards more elaborate multiscale studies of dentin microstructure to better assess the effect of aging and for the design of biomaterials used in dentistry, e.g. to ensure more efficient bonding to dentin. Finally, our analysis of the tubular network structure provides valuable data to improve current numerical models.

Decreased dentin tubules density and reduced thickness of peritubular dentin in hyperbilirubinemia-related green teeth.

BackgroundIt is stated anecdotally that patients with liver diseases in childhood who develop green teeth have increased risk for rampant caries, which may be secondary to changes in dental structure. The aim of this study was to test the hypothesis that hyperbilirubinemia affects the dentin morphology of green teeth.Material and MethodsSixteen primary teeth were prepared and divided into two groups (green teeth, n = 8 and control, n = 8), which were transversely fractured across the cervical third of the dental crowns; dentin was prepared and sputter-coated with gold, and examined under a scanning electron microscope. The mean density and mean diameter of dentin tubules, as well as the thickness of peritubular dentin, were compared.ResultsHyperbilirubinemia was associated with a decrease in the density of the dentin tubules (p< .01) and the thickness of peritubular dentin of green teeth (p< .01).ConclusionsThere was a correlation between childhood hyperbilirubinemia and changes in the dentin morphology, including a decrease in the density of the dentin tubules and a reduction in the thickness of peritubular dentin in green teeth. Key words:Hyperbilirubinemia, liver disease, childhood, dentin tubules, human teeth, scanning electron microscopy.

Final irrigation protocols may affect intraradicular dentin ultrastructure.

The aim of this study was to evaluate the effect of different irrigation protocols on the root dentin structure using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thirty-nine lower bovine incisors were hemisected longitudinally and randomly divided into 13 groups (n=3). After the root halves were reassembled, it was applied a specific irrigation protocol for each group, as following: G1, distilled water (control); G2, 0.9% saline; G3, saline+17% EDTA; G4, saline+PUI; G5, saline+PUI+EDTA; G6 to G9 received the same protocol as above replacing 0.9% saline by 2.5% NaOCl; and G10 to G13 by 2% CHX. One-half of each sample was prepared and evaluated using SEM and the other one by TEM observations. TEM descriptive analysis showed modifications in dentin organic ultrastructure, characterized by the thinning of dentin collagen fibrils, caused by NaOCl, enhanced by EDTA and/or PUI. SEM analysis showed that NaOCl with PUI caused significantly larger erosion of the peritubular dentin than in all the other groups (P<0.05), followed by NaOCl+EDTA and NaOCl+EDTA+PUI. NaOCl caused ultrastructural alterations in the dentin collagen, and enhanced by EDTA and/or PUI, promoted peritubular and intertubular erosion. The effect of irrigating solutions on dentin ultrastructure was still unclear. The acknowledgment about the kind of solution, concentrations, application time, and sequence of use was important to achieve the right sanitization without jeopardizing the dentin ultrastructure quality.

Observation and analysis of microstructure of dentin caries lesions through 3D laser scanning microscope

Microstructural changes in dentin carious lesions were investigated using a 3D laser scanning microscope, which has a morphological theoretical foundation in the further study of clinical caries disease prevention and treatments. Six fresh extracted caries molars were prepared into cross-section specimens. The sections were examined by 3D and laser measuring morphology. Zones were identified in the lesions on the basis of their optical appearance. Two zones were identified in the lesions on the basis of their laser appearance. The microstructure showed that the tubular was partly closed in transparent dentin; peritubular and intertubular dentin were reduced in the zone of demineralization; peritubular and intertubular dentin were damaged and fused; a beaded sample and oval lesions formed in the zone of bacterial invasion; and abnormal dentin structure was present in the zone of destruction on the basis of their laser appearance. Four zones were iden-tified in the lesions according to their colors, as determined from their 3D appearance. 3D laser scanning micros-cope may be a powerful, accessible, and non-destructive technique, as it identified the lesion and tubular zones, as well as peritubular and intertubular dentin in the four zones' lesions. The microstructure of dentin caries lesions may have significant merit in the evaluation of clinical prevention and treatment.

In vitro effects of acid challenge on incisal/occlusal cupping/cratering

Statement of problemThe cause of occlusal/incisal cupping/cratering (depressed dentin surrounded by elevated rims of enamel) has been postulated to be primarily the effect of acid on exposed dentin. It is hypothesized that abrasion, bruxism, attrition, and stress-corrosion may play a secondary role in lesion formation. The primary cause and sequence of occlusal/incisal cupping/cratering remain scientifically controversial. PurposeThe purpose of this in vitro study was to determine the effects of acid on human enamel, mantle dentin, and peritubular dentin in the creation of incisal/occlusal cupping/cratering. This study was designed to visually illustrate the role of acid in the formation of cupping/cratering. Material and methodsA soft compact toothbrush was tested using both high relative dentin abrasivity (RDA)- and low-RDA dentifrices and water only (nonabrasive) on extracted human teeth. Seventeen specimens of 4 teeth each (68 teeth) were subjected to horizontal brushing with a 1:1 dentifrice-to-water slurry or water only. Twelve of these 17 specimens, a total of 48 teeth, were subjected to acid challenge. Each of these 12 specimens were brushed for 500 strokes after each acid challenge for a total of 150000 strokes and 300 acid immersions. Half the specimens were acid challenged for 5 minutes and the other half for 10 minutes between brushings. ResultsNo visible loss of tooth structure was noted in the control specimens brushed in water only. The control specimens brushed in a 1:1 slurry of toothpaste/water demonstrated incisal/occlusal cupping/cratering. The acid-challenged specimens brushed in water only demonstrated enamel and peritubular dentin loss with elevated rims and/or plateaus of mantle dentin, the opposite of occlusal/incisal cupping/cratering. All specimens brushed with the higher abrasive dentifrice demonstrated visible wear of enamel, mantle, and peritubular dentin, culminating in occlusal/incisal cupping/cratering. Surprisingly, those acid-challenged specimens brushed with the lower abrasive toothpaste demonstrated visible wear of the enamel and peritubular dentin, resulting in elevated rims and/or plateaus of mantle dentin. ConclusionsAcid affects both the enamel and the mineralized component of dentin. This study demonstrated that incisal/occlusal cupping/cratering occurring in worn dentition can be caused by the use of dentifrice alone. Acid challenge affects the inorganic components of tooth structure but not the organic components and so does not cause the dentinal cupping/cratering of the incisal/occlusal surfaces of the human dentition.