Hardness Of Dentin Research Articles

Polyphenols Can Improve Resin-Dentin Bond Durability by Promoting Amorphous Calcium Phosphate Nanoparticles to Backfill the Dentin Matrix.

To investigate the effects of proanthocyanidins (PA), myricetin, resveratrol, and kaempferol on the modification of dentin collagen and the inhibition of matrix metalloproteinase (MMP) activity, and to evaluate their contributions to the biomimetic remineralization and resin-dentin bonding performance. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and in situ zymography were applied to verify the collagen modification and MMP activity inhibition induced by these four polyphenols. Scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) analysis, X-ray diffraction (XRD), ATR-FTIR, Vickers hardness numbers (VHN), and micro-computed tomography (micro-CT) were performed to characterize the remineralized dentin. Microtensile bond strength (μTBS) and nanoleakage were investigated to evaluate the effects of the four polyphenols on resin-dentin bonding durability. ATR-FTIR and in situ zymography confirmed that these four polyphenols could modify dentin collagen and inhibit MMP activity, respectively. Chemoanalytic characterization exhibited the efficacies of the four polyphenols in promoting dentin biomimetic remineralization. The surface hardness of PA-pretreated dentin was the greatest. Micro-CT results demonstrated that the PAs group possessed the highest amount of dentin surface minerals and the lowest amount of deep-layer minerals. The surface and deep-layer mineral contents of the Myr group were higher than Res and Kae groups. Treatment with these four polyphenols significantly increased the initial μTBS compared with the control group without primer conditioning. μTBS decreased significantly during aging, and the decrease was more severe in the PAs and Kae groups than in the Myr and Res groups. With or without aging, the polyphenol groups exhibited relatively less fluorescence. However, the Myr and Res groups showed less serious nanoleakage after aging. PA, myricetin, resveratrol, and kaempferol can modify dentin collagen, inhibit MMP activity, promote biomimetic remineralization, and improve resin-dentin bond durability. Compared with PA and kaempferol, myricetin and resveratrol are more effective in improving resin-dentin bonding.

Silver Nanoparticles and Their Therapeutic Applications in Endodontics: A Narrative Review.

The efficient elimination of microorganisms and their byproducts from infected root canals is compromised by the limitations in conventional root canal disinfection strategies and antimicrobials. Silver nanoparticles (AgNPs) are advantageous for root canal disinfection, mainly due to their wide-spectrum anti-microbial activity. Compared to other commonly used nanoparticulate antibacterials, AgNPs have acceptable antibacterial properties and relatively low cytotoxicity. Owing to their nano-scale, AgNPs penetrate deeper into the complexities of the root canal systems and dentinal tubules, as well as enhancing the antibacterial properties of endodontic irrigants and sealers. AgNPs gradually increase the dentin hardness in endodontically treated teeth and promote antibacterial properties when used as a carrier for intracanal medication. The unique properties of AgNPs make them an ideal additive for different endodontic biomaterials. However, the possible side effects of AgNPs, such as cytotoxicity and tooth discoloration potential, merits further research.

Application of Scanning Acoustic Microscopy for Detection of Dental Caries Lesion

Introduction: A scanning acoustic microscope (SAM) is an apparatus for imaging acoustic properties. This apparatus can non-invasively and rapidly evaluate the hardness of materials in the elastic region. This device shows great potential for the diagnosis of dental caries in the clinical setting. However, since the tissue elastic modulus measured using a SAM is a property of the elastic region and the Knoop hardness is a property of the plastic region, the hardness properties differ completely. Therefore, we investigated whether the acoustic impedance measured using a SAM is related to the Knoop hardness, which is used as the standard for removal of carious dentin. Method: Polished sections were prepared from 20 extracted carious wisdom teeth. The acoustic impedance and Knoop hardness were measured for each section. In addition to comparing carious and healthy dentin in SAM images, we evaluated the difference between the carious and healthy dentin in terms of the acoustic impedance and Knoop hardness. We also evaluated the correlation between the Knoop hardness and acoustic impedance. Results: The SAM images were visualized as two-dimensional color images based on the acoustic impedance values. The mean acoustic impedance of carious dentin was significantly lower than that of healthy dentin, showing a similar trend as Knoop hardness. A strong correlation was observed between the two. Discussion: The acoustic impedance values obtained through acoustic microscopy differed significantly between carious and sound dentin. Both types of dentins were visualized using two-dimensional color images. A strong correlation was observed between the acoustic impedance value, which indicates the hardness of the elastic region, and the Knoop hardness, which indicates the hardness of the plastic region. The results of the present study indicate that acoustic impedance accurately reflects the hardness of dentin.

Hardness and indentation modulus of human enamel and dentin

Information on mechanical properties of human enamel and dentin and effect of load on their deformation and damage tolerance is very important in the development of successful dental materials. In this study, the hardness, indentation modulus and deformation characteristics of tooth have been investigated across the lingual–buccal enamel and dentin cross‐section by instrumented indentation up to 1500‐nm indentation depth. We realized and examined the distribution of hardness and modulus at different areas of enamel and dentin with the aim to understand deformation behaviour at these different locations. Scanning electron microscopy was used for the microstructure characterization of the enamel and dentin and their deformation behaviour. Raman spectroscopy analyses were carried out for determination of the enamel and dentin composition as well. The average values of hardness and modulus for enamel in the occlusal area are 5.35 ± 0.19 and 98.1 ± 1.5 GPa, in the inner area 3.68 ± 0.5 and 81.8 ± 5 GPa and in the area close to the dentin–enamel junction 2.83 ± 0.27 and 71.4 ± 4.1 GPa, respectively. The average values of hardness and modulus of dentin in the area close to the dentin–enamel junction are 0.71 ± 0.05 and 21.27 ± 0.76 GPa and in the inner area 0.65 ± 0.06 and 19.79 ± 0.93 GPa, respectively. The effect of the indentation location on deformation and mechanical properties was clarified.

Effect of caries excavation by Carisolv and SmartPrep burs on dentin hardness — An in vitro study

Objective: The purpose of this study was to comparatively evaluate two caries excavation methods-Smartprep(SS White) burs and Carisolv (Carisolv™) by measuring the Vickers hardness of prepared cavity. Materials and Methods: 40 extracted human molars with moderate occlusal caries were used in this study. Teeth with moderate caries extending till dentin without pulp involvement were selected. RVG was used to assess the depth of the cavity. The samples were divided into 2 groups, Group I by Smart prep burs and Group II using Carisolv. Each groups were subjected to morphological analysis under scanning electron microscope. Results: The samples prepared with Carisolv showed least difference in hardness values between the prepared surface and surrounding dentin compared to Smartprep burs. SEM analysis with Smartprep burs revealed surface covered with debris and smear layer while Carisolv showed rough and scaly surface with large areas with open dentinal tubules. Conclusion: Removal of infected carious dentin was superior when Carisolv was employed as compared to SmartPrep burs. The results concluded that smear layer removal of Carisolv was superior when compared to SmartPrep burs.

Demonstration of an optical dentin hardness measuring device using bovine dentin with different demineralization times.

.SignificanceThe increase in root caries is a serious problem as society ages. Root caries is diagnosed by inspection and palpation, which are qualitative. A method to objectively and quantitatively evaluate the progress of root caries in a clinical setting is strongly desired. The root caries could be diagnosed by measuring hardness because dentin becomes softer as the caries progresses. Vickers hardness has been customarily used as an indicator of tooth hardness. However, this method cannot be used to in vivo teeth because the teeth must be dried prior to measurement to make the indentation. A hardness meter using an indenter with light for tooth monitoring (HAMILTOM) is proposed as an optical device. HAMILTOM could measure hardness of teeth in wet condition as a dark area while applying a load to dentins without drying. Therefore, HAMILTOM may realize hardness measurements of in vivo teeth in a clinical setting quantitatively.AimThe aim of our study is to demonstrate the optical dentin hardness measuring device HAMILTOM using bovine dentin with different demineralization times and to evaluate the correlation between the dark areas measured by HAMILTOM and the Vickers hardness measured by the Vickers hardness tester.ApproachThe samples were 20 bovine dentins. They were demineralized by a lactic acid solution with different times and divided into groups 1 and 2 of 10 samples each. In both groups, the dark areas and Vickers hardness were measured for each sample. Group 1 was used to obtain a calibration curve to calculate Vickers hardness from the dark area. Group 2 was used to validate the calibration curve obtained from the dentin samples of group 1.ResultsThe areas appearing black without a total internal reflection of the indenter measured by HAMILTOM increased as the demineralization time increased. Additionally, the Vickers hardness of group 2 calculated by the dark areas of group 2 and the calibration curve obtained in group 1 and the Vickers hardness of group 2 measured by the Vickers hardness tester were strongly correlated with a determination coefficient of 0.99.ConclusionsThe results demonstrate that HAMILTOM may be a suitable alternative to the conventional method. Unlike the conventional method, which cannot be used for in vivo teeth, HAMILTOM holds potential to quantitatively evaluate the progress of caries in in vivo teeth.

The multi-scale meso-mechanics model of viscoelastic dentin

Human dentin is a hierarchical material with multi-level micro-/nano-structures, consisting of tubule, perti-tubular dentin (PTD) and intertubular dentin (ITD) as the major constituents at microscale; and the PTD and ITD are further composed of collagen and hydroxyapatite (HAp) crystals with different volume fractions at nanoscale. In most cases, the HAp is considered as elastic while the collagen as viscoelastic material. It is of great significance to study the hierarchical structure and viscoelasticity of human dentin to understand the mechanical properties of dentin for further development of restorative materials. Based on this, this paper focuses on multiscale modeling of the elastic properties and dynamic viscoelastic response of dentin and establishes a bottom-up micromechanics model from nano-to macro-scale. In order to study the nanostructural effect on the viscoelastic behavior of hierarchical structures, the homogenization theories of random platelets composites (HTRPC) and the locally-exact homogenization theory (LEHT) are introduced for the homogenization of heterogeneous materials of microstructures at different levels. The HTRPC, based on Eshelby Inclusion theory, is used to predict the effective modulus of PTD and ITD. The LEHT is a method for homogenizing multiphase dentin characterized by repeated unit cells (RUCs). The resulting predictions are in very good agreement with several experimental data from the literature. In addition, the results of nanostructrual effect on dentin show that the viscoelasticity of dentin is majorly contributed by collagen and the HAp greatly provide the strength and hardness of dentin. Furthermore, the ageing effect on dentin's viscoelasticity is considered from the proposed multiscale micromechanics model. It is demonstrated that the ageing effect is much more influential in affecting the loss moduli of dentin than the storage.

Nanoindentation and Atomic Force Microscopy Derived Mechanical and Microgeometrical Properties of Tooth Root Cementum

In the present research, nanoindentation, atomic-force microscopy and optical microscopy were used to study the mechanical and microgeometrical parameters of tooth tissues. A nanoindentation test unit equipped with Berkovich indenter was used to determine the values of the reduced Young’s modulus and indentation hardness and both nanoindentation and atomic force microscopy using a diamond probe on a silicon cantilever were used to study microgeometrical parameters of human tooth root cementum. Three areas of cementum were studied: the cervical region near the dentine–enamel junction, the second third of the tooth root, and the apex of the tooth root. The interpretation of the results was carried out using the Oliver–Pharr method. It was established, that the mechanical properties of cementum increase from the cervical region to the central part of the root, then decrease again towards the apex of the tooth root. On the contrary, the microgeometrical characteristics of cementum practically do not demonstrate any change in the same direction. A decrease in the roughness parameters in the direction from cellular cementum to dentine was observed. Additionally, a decrease in the reduced Young’s modulus and indentation hardness of dentine in the cervical area compared to dentine in the crown part of the tooth was found using nanoindentation. The investigation of the dentine–cementum junction with high resolution revealed the interspaced collagen fiber bridges and epithelial rests of Malassez, whose sizes were studied. The parameters of the topographic features of the cementum in the vicinity of the lacunae of cementocytes were also established.

Comparison Of An Experimental Root Canal Irrigant (Sapindus Mukorossi) And Ethylenediaminetetraacetic Acid On Microhardness Of Human Dentin.

The treatment of infected root canals is one of the most essential areas in dentistry. The endodontic therapy comprises of a sequence of steps that includes the purging of disease and infectious tissues from the root canal system. The objective of the study is to compare the effect of an experimental herbal root canal irrigant (Sapindus mukorossi) and Ethylenediaminetetraacetic acid, on the micro hardness of human dentin. Ninety single rooted teeth were collected displayed intact external morphology the selected teeth were than divided randomly into 3 groups (n=30); 1 control and 2 experimental groups: Group A consisted of specimen treated with Ethanolic extract of Sapindus mukorossi. Group B consisted of specimen treated with 17% Ethylenediaminetetraacetic acid and Group C (control group) consisted of specimen of roots were sectioned immersed in distilled water. After the removal of crowns, the roots were sectioned embedded in the polymer resin leaving the root dentine exposed, the micro hardness was determined. Then, the samples from each group were treated with respective irrigant solution for 15 minutes and then observation regarding the micro hardness were noted again by using Vickers micro hardness tester. Analysis of data were obtained by application of Wilcoxon signed rank test. The study revealed that there was no significant difference noted in dentin microhardness of group "A" sample after dipping in experimental irrigant solution (Sapindus mukorossi). However, the study found significant difference in context of decrease in dentin microhardness after dipping a sample in a group "B" irrigant solution (17% Ethylenediaminetetraacetic acid). In order to preserve the strength of dentin that will ultimately be beneficial for increase in survival of teeth in function, probably the herbal extract of Sapindus mukorossi would be better candidate for future endeavour and presented as an economic and effective alternative amongst root canal irrigants.

Hardness and Compressive Strength Evaluation of Dental Composites Containing Biosilica-Encapsulated Healing Liquid

Tooth cavity is one of the most common dental health problems in Indonesia that can be treated by applying dental fillings. However, dental fillings often experience microcrack and secondary caries. Self-Healing Dental Materials (SHDM) which use microencapsulation technique as healing system, are developed to solve this problem. In this work, we employed mesoporous biosilica from Cyclotella striata TBI as microcapsule to entrap healing liquid contains polyacrylic acid and polybasic carboxylic acid. SHDM was prepared by mixing Filtek Z350XT flowable composite with fluoroaluminosilicate healing powder and healing liquid encapsulated in biosilica. We also added silica containing cetyltrimethyl ammonium bromide (CTAB@PSN) filler as antibacterial agent. Six groups of tested samples were prepared with various composition of biosilica and CTAB@PSN. Filtek composite was used as a control. We studied the entrapment of helaing liquid in biosilica and effect of biosilica addition towards mechanical properties of the resulting SHDM. The statistical analysis was determined using ANOVA. Scanning Electron Microscopy and Fourier Transform Infra-Red showed that the microencapsulation of healing liquid in biosilica was successful with immersion method without stirring. Addition of biosilica and CTAB@PSN fillers into the Filtek composites resulted in the decrease of the mechanical properties. The hardness values of the resulting composites were in the range 44.33–53.25 VHN. Nevertheless, the hardness values were still comparable to the hardness of dentin. Addition of filler decreased the compressive strength, but statistically insignificant, from 268.68 MPa to 228.53–252.04 MPa. To conclude, healing liquid can be entrapped in porous biosilica. Adding healing agent affects SHDM composite’s hardness but not its compressive strength.

Impact of deproteinization methods on the physical and mechanical properties of dentin

This study was performed to evaluate the effects of thermal and chemical deproteinization methods on the microhardness and mineral phases of human dentin. Forty extracted non-carious human premolars were cut from below the cementoenamel junction to prepare 5 mm-thick dentin slices, and then randomly divided into four groups of 10 in each according to the treatments. Group A: thermal treatment (300 °C, rate of 30 °C /min for 10 min); Group B: 50 ml of 1N NaOH; Group C: 50 ml of 30% H2O2, at 37 °C for 7 days; Group D: control. Dry ash was obtained to measure the mass loss of organic content. The microhardness value (MHV) of the exposed root dentin was tested with a Vickers microhardness tester. The structure of the residual dentin mineral was examined using a SEM. Crystallinity was assessed by X-ray diffraction spectroscopy. Data were analyzed with one-way ANOVA and Post Hoc Tukey tests. In the comparison of microhardness values between heat, NaOH, H2O2, and control groups, significant differences were noticed between groups (P < 0.05). Since the organic component was largely removed, it can be seen that the main influence on the hardness of dentin could be the inorganic component rather than the protein content. Thermal treatment was able to completely deproteinize human dentin without significant effects on its physical and mechanical properties, while chemical deproteinization significantly changed the mechanical properties and crystallography of human dentin (P < 0.05).

Promotion Effect of Carboxymethyl Chitosan on Dental Caries via Intrafibrillar Mineralization of Collagen and Dentin Remineralization.

Objective: To observe ultrastructural changes during the process of carboxymethyl chitosan (CMC)-mediated intrafibrillar mineralization, we evaluated the biomimetic remineralization potential of CMC in type-I collagen fibrils and membranes, and further explored the bond strength as well as the bond interfacial integrity of the biomimetic remineralized artificial caries-affected dentin (ACAD). Methods: A mineralized solution containing 200 μg/mL CMC was used to induce type-I collagen biomimetic remineralization in ACAD, while traditional mineralization without CMC was used as a control. The process and pattern of mineralization were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) as well as structured illumination microscopy (SIM). The Vickers hardness test was used to quantify the dentin hardness, while the microtensile bond strength (µTBS) test was used to assess the bond strength and durability. The bond interfacial integrity was evaluated by a confocal laser scanning microscope (CLSM). Results: TEM, SEM, and SIM images showed that CMC had a positive effect on stabilizing amorphous calcium phosphate (ACP) and promoting intrafibrillar mineralization, while extrafibrillar mineralization was formed without CMC. Furthermore, hardness evaluation and µTBS proved that CMC significantly increased dentin hardness and bond strength. CLSM indicated that CMC could create a significantly better bond interfacial integrity with less of a micro-gap in ACAD. Significance: CMC possessed the ability to promote intrafibrillar mineralization and remineralization in demineralized caries dentin lesions, as well as improve bond performance, which implied its potential in carious dentin demineralization or dentin hypersensitivity and possibly even as a possible material for indirect pulp-capping, to deal with deep caries. Highlights: CMC possessed the ability to induce intrafibrillar mineralization effectively; the bond strength and bond durability of demineralized caries dentin were improved via CMC-induced remineralization; the CMC-induced remineralization complex is a potential material for indirect pulp-capping, to deal with deep caries.

Effect of the thicknesses of bulk-fill composites on bonding strength.

This work evaluated the effects of thickness on resin bonding strength. We set the two bulk-fill composites Filtek Bulk Fill Posterior (FBF) and Tetric N-Ceram Bulk Fill (TBF) as the experimental groups and the two conventional composites Filtek Z100 (Z100) and Spectrum TPH (ST) as the control groups. The translucency parameter (TP), color difference, Vickers hardness (HV), and microtensile bond strength (μTBS) of dentine and the resin composites were measured at different depths. In each group, TP and HV decreased with the increase in thickness. At the same depth, the TP of the bulk-fill composites was higher than that of the conventional composites. At the same depth, the HV of the four different resin composites followed the order of Z100>FBF>TBF>ST (except for the upper surface). Except for FBF at 3 and 4 mm, all of the other groups showed no visible color change at all the tested thicknesses. Although the μTBS values of the four different composites obtained through the bulk-fill technique were lower than those of composites obtained through the incremental fill technique, the μTBS of the bulk-fill composites obtained through the bulk-filling technique can reach 30 MPa. Bulk-fill composites applied in single 4 mm increments can meet the requirements of clinical application. However, the color stability of some bulk-fill composites cannot be maintained.

Effect of Preirradiation Fluoride Treatment on the Physical Properties of Dentin.

Objective To determine the effects of preirradiation fluoride treatments on the Knoop hardness of dentin. Materials and Methods Human posterior teeth mounted into acrylic resin molds were polished with silicon carbide (SiC) abrasives and 3-micron diamond paste. The Knoop hardness of dentin was measured with a Leco hardness instrument. The teeth were divided into groups of ten teeth per group as follows: no treatment (control), treatment with silver diamine fluoride (SDF), MI varnish (MI), and cavity shield (CS). The teeth were exposed to 2 Gy of daily radiation for six weeks using an X-Rad 320ix biological irradiator. Hardness was measured weekly, before, during, and after irradiation. The teeth were stored in artificial saliva at 37oC between radiation treatments. Results In preirradiation dentin, a Knoop hardness value of 58.8 (14.1) KHN was obtained. Treatment with SDF significantly increased KHN before irradiation. Immediately after radiation treatment, hardness was significantly reduced in all experimental groups. Postirradiation fluoride treatments increased the hardness of dentin to varying degrees. Conclusions Preirradiation fluoride treatment does not provide protection from decreases in the hardness of dentin. Treatment of teeth with fluoride formulations after radiation progressively restores the hardness of dentin to different degrees.

Dentin hardness differences across various mammalian taxa.

Differences in dentin microstructure have been used as a tool for dietary reconstruction; however, the extent that diet is associated with this aspect of dental morphology has yet to be empirically tested. We conducted microhardness tests of mammalian dentin sections, hypothesizing that species with adaptations to particularly hard diets would have softer dentin, owing to a higher proportion of soft intertubular dentin. Species adapted to abrasive diets, in contrast, should have harder dentin, resulting from a higher proportion of hypermineralized peritubular dentin. We examined molar dentin hardness in ten mammalian taxa with durophagous diets, abrasive diets, and a comparative "control" group of mechanical generalists. Samples included six primate taxa and four non-primate species representing various dietary regimes. Our results reveal significant variation among taxa in overall hardness, but the data do not distinguish between hard and abrasive diets. Several taxa with generalized (i.e., mechanically diverse) diets resemble each other in exhibiting large variance in hardness measurements and comparably soft dentin. The high variation in these species appears to be either a functional signal supporting the niche variation hypothesis or indicate the absence of sustained unidirectional selective pressure. A possible phylogenetic signal of dentin hardness in the data also holds promise for future systematic investigations.

Microstructure, elemental composition and mechanical properties of enamel and dentine in the polar bear Ursus maritimus

ObjectiveTo investigate the microstructure, elemental composition and mechanical properties of polar bear teeth. DesignIncisors, canines and fourth premolar teeth of two subadult male museum specimens were analysed. Teeth were measured, photographed, embedded in Epoxy resin, sectioned, polished and etched for scanning electron microscope (SEM) imaging, elemental composition and nanomechanical testing analyses. ResultsThe thickness of enamel ranged from 350-430 µm in canines, 220–330 µm in incisors and 320–510 µm in premolars. SEM images showed distinct transversely-oriented undulating Hunter Schreger bands from the enamel-dentine junction (EDJ) to the outer enamel surface. Enamel prisms had a hexagonal shape, with open prism sheaths. Prisms measured 6–8 µm in diameter. The EDJ was straight with no evidence of scalloping. Larger tubules adjacent to the EDJ were observed in the mantle dentine zone. Enamel Hardness and Elastic modulus values were higher in premolars (6.9 GPa and 269 GPa), followed by canines (6.5 GPa and 230 GPa) and incisors (4.9 GPa and 187 GPa). Dentine Hardness and Elastic modulus values were higher in canines. CaO and P2O5 were the components with higher oxide weight percentage in both enamel and dentine. ConclusionsUnderstanding the microstructure, elemental composition and mechanical properties of polar bear teeth can help elucidate the biology and functional morphology of this globally threatened species and could be used as a proxy for studies with fossil ursids.

Application of Er,Cr:YSGG laser versus photopolymerization after silver diamine fluoride in primary teeth

Examine the effect of dental curing light and laser treatments applied after Silver Diamine Fluoride (SDF) on dentin hardness in carious primary molars. This in-vitro study consisted of 30 extracted primary molars with caries extending into dentin without pulpal involvement. The collected teeth were randomly divided into three groups: group 1: received SDF then Sub-ablative low-energy of Er,Cr:YSGG laser, group 2: received SDF followed by application of curing light for 40 s, group 3: had SDF treatment only. In all groups, 38% Ag (NH3)2F SDF was used. Vickers hardness test was performed on sound dentin below carious lesion. Kruskal–Wallis Test was used to determine the mean difference in dentin hardness of the groups at 5% Significance level using SPSS software. Surface hardness of sound dentin below the carious lesion was statistically significantly higher in the laser + SDF group (891.24 ± 37.33 kgf/mm2) versus the two other groups (Light cure + SDF = 266.65 ± 90.81 kgf/mm2 and SDF only = 117.91 ± 19.19 kgf/mm2) with p-value ≤ 0.001. Although Photopolymerization of SDF increases the surface hardness of sound dentin below the carious lesion, applying laser after SDF has the highest surface hardness due to the laser’s sub-ablation of dentin.

Hardness Development in Resin Composite Core Materials.

To investigate the hardness characteristics of 13 contemporary resin core materials. Specimens (n = 12) were fabricated using stainless steel molds with top surfaces of dual-cure products photopolymerized while additional groups were allowed to self-cure. Twelve Knoop hardness indentations 500 microns apart were obtained of photopolymerized top and bottom sample surfaces as well as the self-cured sample surface with the mean recorded as the representative sample hardness. Testing was completed at 10 minutes, 1 hour, and 24 hours. In addition, hardness values were compared to that obtained from polished coronal dentin samples. Mean data between groups were analyzed with Kruskal-Wallis/Dunn's, within groups with repeated measures ANOVA/Tukey's. Hardness results were material dependent. All but two products demonstrated a 0.8 bottom/top Knoop hardness ratio at 10 minutes. Product's self-cure cure reaction did not attain hardness similarity with any photopolymerized top surfaces and while some materials were found to have similar dentin hardness to resin top surface ratio similarity, only one product had hardness equal to or greater than that of dentin during any time period. Under this study's conditions, hardness development was material dependent and all but two products demonstrated adequate hardness-derived degree of cure assessment at 10 minutes after preparation. Self-cured samples demonstrated hardness increase; however, no self-cured material achieved hardness similarity to photopolymerized top surfaces. None of the materials achieved hardness similarity to dentin and only one product demonstrated hardness greater than that of dentin.

Adjunctive procedure with solvent mixtures in non-surgical endodontic retreatment: does it affect root dentin hardness?

The aim of this study was to compare the effects of new irrigation solvent mixtures with Methyl ethyl ketone (MEK)/Tetrachloroethylene (TCE) and MEK/Orange oil (OOil), and different agitation techniques on dentin hardness. One hundred forty-four mandibular teeth were prepared and standardized, with each root's middle part transversely sectioned. Initial hardness was measured using a Vickers microhardness tester. Specimens were divided into four groups of agitation techniques (n = 36): no agitation; EndoActivator; IrriSafe; and XP-endo Finisher R. Each group was subdivided into six subgroups of irrigation protocols (n = 6): saline solution; NaOCl + EDTA; NaOCl + EDTA + MEK/TCE; MEK/TCE; NaOCl + EDTA + MEK/OOil; MEK/OOil. Final hardness was measured. The irrigation protocols NaOCl + EDTA, NaOCl + EDTA + MEK/TCE, and NaOCl + EDTA + MEK/OOil significantly decreased dentin hardness, while MEK/OOil increased it (p < 0.05). Comparing to NaOCl + EDTA sequence, dentin hardness increased significantly with the additional exposure to MEK/TCE (3%NaOCl + 17%EDTA + MEK/TCE) or MEK/OOil (3%NaOCl + 17%EDTA + MEK/OOil) (p < 0.05). There were no significant differences regarding agitation effects on dentin hardness decrease. The irrigation protocols affected dentin hardness significantly. However, the additional solvent proposals do not seem to address further concerns on dentin's mechanical properties. Agitation did not show any influence on dentin's hardness reduction.

Evaluation of tooth demineralization and interfacial bacterial penetration around resin composites containing surface pre-reacted glass-ionomer (S-PRG) filler

ObjectiveTo evaluate preventive effects of S-PRG-filled resin-composites on surrounding tooth demineralization and interfacial bacterial penetration. MethodsCavities were prepared on enamel or dentin blocks and treated by BeautiBond Universal (Shofu) and filled by resin-composites containing S-PRG filler (Shofu) at 0 wt% (P0, control), 10 wt% (P10), 30 wt% (P30), 50 wt% (P50) or 70 wt% (P70). The specimens were demineralized by Streptococcus mutans biofilms for 12 days. Wall lesion depth (WL-depth) and outer lesion depth (OL-depth) were measured from fluorescence microscopy. Interfacial bacterial penetration area (BPA) was evaluated from confocal laser scanning microscopy. Wall lesion hardness (WL-hardness) and outer lesion hardness (OL-hardness) were measured with a Vickers microhardness tester. Elemental analysis of resins and surrounding lesions was conducted by scanning electron microscopy and energy dispersive X-ray spectrometry. ResultsResin-composites in P70 contained significantly more F, Na and Al than that in P0 and P10. P70, P50 and P30 showed significantly lower WL-depth than P0. P70 showed significantly lower OL-depth, fewer Ca and P loss in lesions than P0. P70 showed significantly higher WL-hardness and OL-hardness in dentin specimens than P0. Enamel margins had a higher gap frequency than dentin margins. However, BPA did not show significant differences among the groups. SignificanceResin-composites containing S-PRG fillers at ≥30 wt% can inhibit wall lesions and that at 70 wt% can further decrease outer lesions, reduce Ca and P loss in lesions and increase surrounding dentin hardness. However, S-PRG-filled resin-composites does not inhibit interfacial biofilm penetration after a short-term demineralization period.