Color Alterations, Flexural Strength, and Microhardness of 3DPrinted Resins Treated in Different Coloring Agents.

Purpose This study evaluated the color alterations, flexural strength and microhardness properties of two different 3D-printed permanent crown resins. Materials and Methods Samples were produced from two different 3D Print permanent crown resins: Group 1 (Saremco Crowntec; Saremco, Switzerland), Group 2 (P-crown Version 2; Senertek, Turkey). Color changes (ΔE values), flexural strenght and vickers hardness number of the samples were calculated. Data were analyzed with Shapiro-Wilk normality test, Independent-t test, and Mann Whitney-U tests. Significance level was accepted as P<0.05. Results ΔE values for red wine were found to be significantly higher in Group 1 (6.43Å}2.26; P<0.001). The flexural strength values (MPa) of Group 1 were significantly higher than Group 2 in all three solutions (P<0.001). There was no significant difference between the VHN values of the samples kept in wine and coffee solutions (P= 0.271; 0.827). Conclusion 3D printing resins are affected at different levels by coloring solutions. Microhardness and flexural strength of 3D print samples kept in different coloring agents are different.In the use of 3D printing resins, product selection should be made by taking into account the individual factors such as the eating and drinking habits of the patients and the physical properties expected from the sample.

Erosion protective properties of the enamel pellicle in-situ.

OBJECTIVES: Previous studies on short- and long-term pellicles showed that the enamel pellicle provides partial protection against erosion. The aim of the present study was to investigate the protective properties of clinically relevant pellicles formed within 2 to 24 h. The hypothesis was that factors such as pellicle formation time, intraoral location, and acidic challenge severity would not influence the erosion-protective properties of the pellicle. METHODS: Six subjects participated in the study. Bovine enamel specimens were prepared and intraorally exposed at buccal or palatal sites for 2, 6, 12, and 24 h to allow pellicle formation, followed by erosion using 0.1 % or 1 % citric acid. Calcium release and surface microhardness were measured, and specimens were analysed using scanning and transmission electron microscopy. Quantitative data were statistically analysed with three-way ANOVA and Tuckey's multiple comparison test (p = 0.05). RESULTS: Pellicle formation time and intraoral location did not significantly influence the erosion-protective properties of the pellicle, while citric acid concentration significantly affected enamel erosion. The pellicle thickness increased with longer formation times and on buccal sites, but decreased or was entirely removed following treatment with 0.1 % or 1 % citric acid, respectively. The enamel surface exhibited a characteristic erosion pattern. CONCLUSIONS: This study underscores the importance of investigating pellicle properties within the critical 2- to 24-h timeframe and highlights the significance of pellicle thickness in acid resistance. CLINICAL SIGNIFICANCE: These findings provide valuable insights into the factors influencing the protective properties of enamel pellicles and could guide preventive measures in dental practice.

Mathematical-Physical description of the oxygen-inhibited layer (OIL) in nanofilled dental polymers / Descripción físico-matemática de la capa inhibida por oxígeno en polímeros dentales nano rellenados

Abstract This research evaluates the presence of the oxygen-inhibited layer (OIL) on the top surface of a photopolymerized dental composite resin protected with a glycerin layer. This evaluation was conducted using physical and mathematical methods. Polymerized discs were fabricated to evaluate Vickers microhardness (VHN), and pre-and post-polymerized samples were used for the calculation of C-O/C-H ratios through Fourier Transform Infrared Spectroscopy (FTIR) (n=10), using two types of glycerin, one for medical use (MG) and another for dental use (DG). Surface hardness decreased from MG to DG to CO, and the increase in C-O/C-H ratios decreased in the same order (p<0.05). Samples protected with medical and dental glycerin layers are harder and exhibit lower C-O/C-H bond ratios than the control group.

Resumen La presente investigación evalúa la presencia de la capa inhibida por oxígeno OIL en la última superficie fotocurada de una resina compuesta de uso odontológica que fue protegida con una capa de glicerina. Esta evaluación se hizo a partir de métodos físicos y matemáticos. Se fabricaron discos polimerizados para evaluar la microdureza Vickers (VHN) y pre y post polimerizados para el cálculo de tasas C-O/C-H por medio de Espectroscopía Infrarroja Transformada de Fourier (FTIR) (n=10) usando dos tipos de glicerina, una de uso médico (MG) y otra de uso dental (DG). La dureza superficial disminuyó de MG a DG a CO y el aumento de tasas C-O/C-H disminuyó en ese mismo orden (p<0,05). Las muestras protegidas con capas de glicerina médica y odontológica son más duras y presentan menos cantidad tasas de enlaces C-O/C-H que el grupo control.

Impact of calcium hydroxide and 2-hydroxyisocaproic acid on the microhardness of root dentine: an in vitro study.

To evaluate and compare the effect of calcium hydroxide [Ca(OH)2] and 2-hydroxyisocaproic acid (HICA) on the microhardness of root dentine. Fifty-one matured maxillary central incisors with straight root and type I canal configuration were decoronated to a standardized length of 16 mm. The root canals were cleaned and shaped using rotary instruments up to size F5. The tooth samples were then randomly assigned into three groups (n = 17) based on the intracanal medicament placed. Group A: control group with no intracanal medicament, Group B: root canals placed with Ca(OH)2, and Group C: root canals placed with HICA. After 1 week, the intracanal medicaments placed within the root canals were removed and the canals were dried. Subsequently, the specimens were split longitudinally into two halves and subjected to the Vickers microhardness test with indentations made at the coronal, middle, and apical-third root regions. The data were analyzed using one-way ANOVA and Tukey's post hoc tests. The control group showed significantly highest microhardness value (P < 0.001), followed by HICA and finally, Ca(OH)2 at the coronal, middle, and apical-third root regions, respectively. Nonetheless, there were no statistically significant differences in microhardness values across different root regions within each group. HICA was found to have a significantly lesser reduction in root dentine microhardness which could be a potential alternative to Ca(OH)2. Nevertheless, future studies are warranted to verify the present outcomes in the clinical setting.

Analysis of the Mechanical Properties of 3D-Printed Plastic Samples Subjected to Selected Degradation Effects.

The Fused Filament Fabrication (FFF) method is an additive technology that is used for the creation of prototypes within Rapid Prototyping (RP) as well as for the creation of final components in piece or small-series production. The possibility of using FFF technology in the creation of final products requires knowledge of the properties of the material and, at the same time, how these properties change due to degradation effects. In this study, the mechanical properties of the selected materials (PLA, PETG, ABS, and ASA) were tested in their non-degenerate state and after exposure of the samples to the selected degradation factors. For the analysis, which was carried out by the tensile test and the Shore D hardness test, samples of normalized shape were prepared. The effects of UV radiation, high temperature environments, high humidity environments, temperature cycles, and exposure to weather conditions were monitored. The parameters obtained from the tests (tensile strength and Shore D hardness) were statistically evaluated, and the influence of degradation factors on the properties of individual materials was assessed. The results showed that even between individual manufacturers of the same filament there are differences, both in the mechanical properties and in the behavior of the material after exposure to degradation effects.

Excellent performance of hybrid model manufactured via additive manufacturing process reinforced with GFRP for sport climbing equipment.

The figure eight model was successfully manufactured, analyzed, and characterized in the present study. The model was manufactured via 3D printing fused deposition modelling (FDM) and then reinforced with glass fiber-reinforced polymers (GFRP). There are three different designs in figure eight that are examined, and each design is made using 3D printing FDM and coated with GFRP, a hybrid material, as shown. Specimens that have been made from each design are then evaluated by tensile test, hardness test, surface roughness test, and density test. The results showed that the hybrid figure eight lamination with polylactic acid (PLA) and GFRP material could increase the tensile strength by more than two times higher. The highest tensile strength lies in design 1 with 4977, 3 N. Moreover, the highest hardness value occurred for design two at 75.1 Shore D, and the highest average density lies in design three at 1.2 g/mm3. The study also showed that the lowest cost occurred in hybrid design three at $ 1.2 per item. Based on the present study, the GFRP reinforcement can extend the model's performance with affordable cost and retain figure eight from the failure.

Surface Microhardness Of Microhybrid And Nanocomposite After Storage In Mouth Washes.

BACKGROUND: Dental composites are aesthetic direct restorative material. However, the effect of mouthwashes on the durability of the material is controversial. This study evaluated and compared the influence of mouthwash composition on the surface hardness of nanofilled (Z350XT) and microhybrid (P60) resin composites. METHODS: Comparative in-vitro study was conducted over 6 months at Multan Medical & Dental College. Sixty-four disc-shape specimens of each {nanofilled (Z350XT) and microhybrid (P60)} resin composite were prepared and stored in distilled water at 37°C for 24 hours. The baseline microhardness reading (To) was recorded by Vickers micro-hardness tester. Samples were then randomly divided into four groups (n=16) and stored in Listerine Cool Mint, Colgate Plax, Clinica and distilled water (control). The hardness test was repeated after 12 hours and 24 hours of storage. RESULTS: Nanocomposite (Z350XT) had statistically (p<0.01) higher surface hardness. A significant reduction (p≤0.05) in microhardness was observed after immersion of samples in mouthwashes. The reduction in surface hardness was dependent on the immersion time and composition of mouthwashes. Listerine Cool Mint (alcohol-based mouthwash) had greatest degradation effect. CONCLUSIONS: Mouth rinses negatively impacted the surface microhardness of the tested resin-based materials. Alcohol-based mouthwashes had greater potential for reducing microhardness. Microhybrid composite appears to be a more suitable material for restoring teeth in patients accustomed to using regular mouthwashes.

Comparison of the methods of disinfection/sterilization of extracted human roots for research purposes.

BACKGROUND: Extracted human teeth are used to simulate dental procedures and are essential for practical education and research studies. OBJECTIVES: The aim of this study was to evaluate the efficacy of different sterilization methods for extracted human roots and to assess the effects of these methods on dentin microhardness. MATERIAL AND METHODS: The crowns of 40 mandibular incisors were removed. The roots were sectioned at 10 mm and divided into 4 groups (n = 10 per group): G1 - no sterilization (control); G2 - microwave radiation (650 W, 5 min); G3 - ethylene oxide (288°C, 3 h); and G4 - autoclave (121°C, 15 min). The roots were immersed in brain heart infusion (BHI) and incubated at 37°C in variable oxygen atmospheres. After 14 days, the samples were assessed for turbidity. Three slices were obtained from each root, and indentations were made at 30, 60 and 120 µm from the root canal lumen. The microbiological data was analyzed with the Kruskal-Wallis test and Dunn's post-hoc test. Microhardness was evaluated by means of the twoway analysis of variance (ANOVA) and Tukey's test (p < 0.05). RESULTS: The roots submitted to autoclaving were 100% sterile, which differed from the other methods (p < 0.05); the control specimens had 0% sterility. For microhardness, significant differences were found between the methods, particularly for the apical third (68.06 ±12.50) (p < 0.05). CONCLUSIONS: Although all the evaluated techniques reduced dentin microhardness, autoclaving should be used as the most reliable method of sterilization of extracted dental roots.

Mechanical characterization of aesthetic orthodontic brackets by the dynamic indentation method.

The objective of this study is to investigate the mechanical properties, such as the dynamic hardness and indentation elastic modulus, of commercially available aesthetic orthodontic brackets, such as ceramic and plastic brackets, by the dynamic micro-indentation method. Five ceramic brackets, which were made of alumina (both monocrystalline and polycrystalline forms) or zirconia, and two plastic brackets, which were made of glass fiber-reinforced polycarbonate or polyamide, were tested. There were significant differences in the mechanical properties of the monocrystalline and polycrystalline alumina brackets. The mechanical properties of the glass fiber-reinforced plastic bracket were significantly superior to these of the non-glass-fiber-reinforced plastic bracket. The differences in the crystal structures of the ceramic brackets surface affected the dynamic hardness and indentation elastic modulus. Furthermore, the short glass fibers contained in the plastic bracket might contribute to the improvement of the mechanical properties.

Influência do clareamento dentário de consultório na dureza superficial de resinas compostas: um estudo in vitro / Influence of in-office tooth whitening on the surface hardness of composite resins: An In Vitro Study

O estudo objetivou avaliar a dureza superficial de três resinas compostas (Filtek Z350 - 3M ESPE, Zirconfil - TECHNEW, Vitra ­ FGM), após processo de clareamento dental de consultório a base de peróxido de Hidrogênio a 40%. Foram confeccionados 60 corpos de prova, com espessuras de 6,0 x 2,0 mm, sendo 20 corpos de cada material restaurador (n=20). Após processo de acabamento e polimento, os espécimes foram divididos aleatoriamente em dois grupos para cada material restaurador (n=10), onde o grupo controle G1-C, foi mantido em saliva artificial e o grupo experimental G2-E, foi submetido ao gel clareador de consultório a base de peróxido de hidrogênio a 40% de acordo com a indicação do fabricante. O teste de dureza utilizado foi o de Vickers. Para cada corpo de prova, foram realizadas quatro leituras consecutivas e equidistantes, com uma carga de 300g de força durante 15s. Os valores de dureza para resinas testadas foram estatisticamente mais elevadas no grupo controle, do que no grupo teste. Sendo que a maior diferença nos valores das médias entre os grupos ocorreu na resina Z350XT e para a margem de erro fixada (5%) se comprova diferença significativa (p < 0,05) entre os grupos teste e controle para cada resina. O uso do peróxido de hidrogênio 40% pela técnica de consultório, promoveu mudanças significativas na dureza superficial das resinas testadas. Além disso, a resina Z350XT apresentou dureza superior as demais resinas, porém foi a mais afetada pelo agente clareador (AU).

The study aimed to evaluate the surface hardness of three composite resins (Filtek Z350 - 3M ESPE, Zirconfil - TECHNEW, Vitra - FGM), after an in-office tooth whitening process using 40% hydrogen peroxide. Sixty specimens were made, with thicknesses of 6.0 x 2.0 mm, with 20 specimens of each restorative material (n=20). After finishing and polishing, the specimens were randomly divided into two groups for each restorative material (n=10), where the control group G1-C was maintained in artificial saliva and the experimental group G2-E was subjected to gel in-office bleaching agent based on 40% hydrogen peroxide, according to the manufacturer's instructions. The hardness test used was the Vickers hardness test and for each specimen, four consecutive and equidistant readings were performed, with a load of 300g of force for 15s. Hardness values for tested resins were statistically higher in the control group than in the test group. The greatest difference in mean values between the groups occurred in the Z350XT resin and for the fixed margin of error (5%) there is a significant difference (p < 0.05) between the test and control groups for each resin. The use of 40% hydrogen peroxide by the in-office technique promoted significant changes in the surface hardness of the tested resins. In addition, the Z350XT resin presented higher hardness than the other resins, but was the most affected by the bleaching agent (AU).

Evaluation of Remineralizing Potential of CPP-ACP, CPP-ACP + F and ß TCP + F and Their Effect on Microhardness of Enamel Using Vickers Microhardness Test: An In Vitro Study.

Context: The change in understanding of dental caries which is now believed to be a reversible lesion has led to the change in its management. Aim: To evaluate the remineralizing potential of three remineralizing agents [casein phosphopeptide (CPP)-amorphous calcium phosphate (ACP), CPP-ACP + F, and beta-tricalcium phosphate (ß TCP) + F] and their effect on microhardness of enamel using Vickers microhardness test. Materials and method: Forty freshly extracted premolars, extracted for orthodontic purpose were collected and specimen prepared. The specimens were equally divided into four groups. Baseline surface microhardness measurement was taken for the specimens. Demineralization of enamel was carried out by keeping the specimens in 20 mL of demineralizing solution for 72 hours, and microhardness was evaluated. Remineralizing agents CPP-ACP, CPP-ACP + F, and ß TCP + F was applied to Group A, Group B, and Group C, respectively for 28 days and microhardness was evaluated again. Group D was kept as control group. Statistical analysis was done by One-way ANOVA test. Percentage microhardness recovery was calculated to evaluate the regain in microhardness after remineralization and thus assess the remineralizing efficacy of the agents. Results: After demineralization surface microhardness of enamel decreased to the range of Vickers hardness number (VHN) 155-167 but after application of remineralizing agents surface microhardness for Group B was found to be highest, in other words, VHN 240.78 followed by Group C, in other words, VHN 214.29 and Group A the least VHN 197.90. Conclusion: The result of this study concludes that surface microhardness of enamel decreased after demineralization procedure and increased after application of all the remineralizing agents. The highest increase was seen in group tested with CPP-ACP + F followed by ß TCP and least for CPP-ACP. The values for all the three groups were higher than the control so we can conclude that all the agents can be used as remineralizing agent with CPP-ACP + F being the best among the three. How to cite this article: Bhat DV, Awchat KL, Singh P, et al. Evaluation of Remineralizing Potential of CPP-ACP, CPP-ACP + F and ß TCP + F and Their Effect on Microhardness of Enamel Using Vickers Microhardness Test: An In Vitro Study. Int J Clin Pediatr Dent 2022;15(S-2):S221-S225.

Determination of microhardness of bulk-fill resins at different depths.

The aim of this study was to determine Vickers microhardness (HV) in bulk fill resins at different depths. Test specimens were prepared with different bulk fill resins: Filtek Bulk-Fill (3M ESPE) [FBF], Surefill SDR flow (Dentsply) [SDR], Fill-UP (COLTENE) [FU] and Surefill (Dentsply) [SF]. Semi-cylindrical test specimens were prepared in a mold 6 mm in diameter and 4 mm thick (n=5). A 1000 mW/cm2 light curing unit was applied (Coltolux LED - Coltene) for 20 seconds. HV was determined with three indentations (Vickers Future Tech FM300, 300 g, 8 s) at four depths: 1, 2, 3 and 4 mm from the top surface to the interior. Data were recorded immediately (t0) and 24 hours later (t24). Results were analyzed with two-way ANOVA (p<0.05), and multiple comparisons were performed using Tukey's test. Mean and SD of HV at t0 for each mm were: [FBF] t0: 49.23(4.65) / 48.32(3.36) / 44.38(2.06) / 40.59(2.58); [FBF] t24: 61.37(3.47) / 62.63(3.03) / 57.27(5.22) / 56.37(5.88);[SDR]t0:27.81(3.13) / 28.07(2.4) / 27.24(2.94) / 25.71(3.0); [SDR] t24: 35.11(2.16) / 35.17(1.96) / 35.53(1.81) / 33.18(2.08); [FU] t0: 41.43(1.41) / 39.87(0.88) / 38.11(1.81) / 39.09(1.92); [FU] t24: 49.27(1.54) / 48.77(1.77) / 48.65(1.88) / 46.76(4.93); [SF] t0: 71.35(7.09) / 67.39(9.76) / 68.95(6.21) / 64.1(8.35); [SF] t24: 76.06(6.61) / 75.31(9.37) / 75.2(11.57) / 69.81(12.14). ANOVA showed significant effect of material, depth and recording time (p<0.05), and Tukey's test showed that recording sites (depths) differed significantly, giving four homogeneous groups. Under the conditions of this study, it can be concluded that microhardness of bulk-fill resins can be affected by depth and post-curing time.

El objetivo del presente estudio fue determinar la microdureza Vickers (HV) en resinas bulk-fill a diferentes profundidades. Se confeccionaron probetas semicilíndricas de 6 mm de diámetro y 4 mm de profundidad con diferentes composites de aplicación en bloque (Bulk-fill): Filtek Bulk-Fill (3M ESPE) [FBF], Surefill SDR flow (Dentsply) [SDR], Fill-UP (COLTENE) [FU] y Surefill (Dentsply) [SF]. Se polimerizaron con Coltolux LED (Coltene) con 1000 mW/cm2 durante 20s. La HV se determinó realizando 3 indentaciones con 300 g durante 8 s a 1,2 3 y 4 mm desde la superficie de la probeta hacia el interior inmediatamente después de curada y a las 24 h. Se utilizó un microdurómetro Vickers Future Tech FM300. Los resultados se analizaron estadísticamente mediante ANOVA de dos vías y Prueba de Tukey. La media y DS de HV fueron: [FBF] t0: 49,23(4,65) / 48,32(3,36) / 44,38(2,06) / 40,59(2,58); [FBF] t24: 61,37(3,47) / 62,63(3,03) / 57,27(5,22) / 56,37(5,88);[SDR]t0: 27,81(3,13) /28,07(2,4) / 27,24(2,94) / 25,71(3,0); [SDR] t24: 35,11(2,16) / 35,17(1,96) / 35,53(1,81) / 33,18(2,08); [FU] t0: 41,43(1,41) / 39,87(0,88) / 38,11(1,81) / 39,09(1,92); [FU] t24: 49,27(1,54) / 48,77(1,77) / 48,65(1,88) / 46,76(4,93); [SF] t0: 71,35(7,09) / 67,39(9,76) / 68,95(6,21) / 64,1(8,35); [SF] t24: 76,06(6,61) / 75,31(9,37) / 75,2(11,57) / 69,81(12,14). La evaluación con análisis de varianza mostró el efecto significativo de las variables material, profundidad y momento del registro (p<0,05) y la prueba de Tukey mostró que los sitios de registro (profundidad) fueron estadísticamente significativos, dando cuatro grupos homogéneos. Bajo las condiciones de este estudio podemos concluir que la microdureza de las resinas de inserción en bloque se ve afectada por el nivel de profundidad y el tiempo pos curado.

The effect of therapeutic radiation on dental enamel and dentin: A systematic review.

OBJECTIVES: The conventional radiotherapy protocol to treat head-and-neck cancer is usually followed by tooth-decay onset. Radiation impact on mineralized tooth structures is not well-understood. This systematic review aimed to collect the recorded effects of therapeutic radiation on tooth chemical, structural and mechanical properties, in relation with their means of investigation. DATA: Systematic search (January 01 2012 - September 30 2021) terms were "Radiotherapy", "Radiation effects", "Dental enamel", "Dentin", "Human" and "Radiotherapy" NOT "Laser". SOURCES: PubMed, DOSS and Embase databases were searched. STUDY SELECTION: Selected studies compared dental enamel, coronal and root dentin properties before and after in vitro or in vivo irradiation up to 80 Gy. RESULTS: The systematic search identified 353 different articles, with 28 satisfying inclusion criteria. Their reference lists provided two more. Twenty-two studies evaluated dental enamel evolution, nine assessed coronal dentin and eight concerned root dentin. Coronal and root dentin results indicate a major impact of the radiation on their organic matrix. Dental enamel's chemical properties are less modified. Enamel and root dentin's hardness are decreased by therapeutic radiation, but no consensus arises for coronal dentin. CONCLUSIONS: Our findings revealed some interesting information about enzymatic degradation mechanisms of dentin organic matrix and highlighted that dental hard-tissue characterization requires highly specific expertise in materials science. That scientific knowledge is necessary to design suitable protocols, adequately analyze the obtained data, and, thus, provide relevant conclusions. CLINICAL SIGNIFICANCE STATEMENT: Better knowledge and understanding of the mechanisms involved in the degradation of enamel and dentin would enable development of new preventive and therapeutic methods for improved medical care of patients undergoing radiotherapy.

Determination of microhardness of bulk-fill resins at different depths / Determinación de microdureza de resinas bulk-fill en diferentes profundidades

ABSTRACT The aim of this study was to determine Vickers microhardness (HV) in bulk fill resins at different depths. Test specimens were prepared with different bulk fill resins: Filtek Bulk-Fill (3M ESPE) [FBF], Surefill SDR flow (Dentsply) [SDR], Fill-UP (COLTENE) [FU] and Surefill (Dentsply) [SF]. Semi-cylindrical test specimens were prepared in a mold 6 mm in diameter and 4 mm thick (n=5). A 1000 mW/cm2 light curing unit was applied (Coltolux LED - Coltene) for 20 seconds. HV was determined with three indentations (Vickers Future Tech FM300, 300 g, 8 s) at four depths: 1, 2, 3 and 4 mm from the top surface to the interior. Data were recorded immediately (t0) and 24 hours later (t24). Results were analyzed with two-way ANOVA (p<0.05), and multiple comparisons were performed using Tukey's test. Mean and SD of HV at t0 for each mm were: [FBF] t0: 49.23(4.65) / 48.32(3.36) / 44.38(2.06) / 40.59(2.58); [FBF] t24: 61.37(3.47) / 62.63(3.03) / 57.27(5.22) / 56.37(5.88); [SDR] t0: 27.81(3.13) / 28.07(2.4) / 27.24(2.94) / 25.71(3.0); [SDR] t24: 35.11(2.16) / 35.17(1.96) / 35.53(1.81) / 33.18(2.08); [FU] t0: 41.43(1.41) / 39.87(0.88) / 38.11(1.81) / 39.09(1.92); [FU] t24: 49.27(1.54) / 48.77(1.77) / 48.65(1.88) / 46.76(4.93); [SF] t0: 71.35(7.09) / 67.39(9.76) / 68.95(6.21) / 64.1(8.35); [SF] t24: 76.06(6.61) / 75.31(9.37) / 75.2(11.57) / 69.81(12.14). ANOVA showed significant effect of material, depth and recording time (p<0.05), and Tukey's test showed that recording sites (depths) differed significantly, giving four homogeneous groups. Under the conditions of this study, it can be concluded that microhardness of bulk-fill resins can be affected by depth and post-curing time.

RESUMEN El objetivo del presente estudio fue determinar la microdureza Vickers (HV) en resinas bulk-fill a diferentes profundidades. Se confeccionaron probetas semicilíndricas de 6 mm de diámetro y 4 mm de profundidad con diferentes composites de aplicación en bloque (Bulk-fill): Filtek Bulk-Fill (3M ESPE) [FBF], Surefill SDR flow (Dentsply) [SDR], Fill-UP (COLTENE) [FU] y Surefill (Dentsply) [SF]. Se polimerizaron con Coltolux LED (Coltene) con 1000 mW/cm2 durante 20s. La HV se determinó realizando 3 indentaciones con 300 g durante 8 s a 1,2 3 y 4 mm desde la superficie de la probeta hacia el interior inmediatamente después de curada y a las 24 h. Se utilizó un microdurómetro Vickers Future Tech FM300. Los resultados se analizaron estadísticamente mediante ANOVA de dos vías y Prueba de Tukey. La media y DS de HV fueron: [FBF] t0: 49,23(4,65) / 48,32(3,36) / 44,38(2,06) / 40,59(2,58); [FBF] t24: 61,37(3,47) / 62,63(3,03) / 57,27(5,22) / 56,37(5,88); [SDR] t0: 27,81(3,13) / 28,07(2,4) / 27,24(2,94) / 25,71(3,0); [SDR] t24: 35,11(2,16) / 35,17(1,96) / 35,53(1,81) / 33,18(2,08); [FU] t0: 41,43(1,41) / 39,87(0,88) / 38,11(1,81) / 39,09(1,92); [FU] t24: 49,27(1,54) / 48,77(1,77) / 48,65(1,88) / 46,76(4,93); [SF] t0: 71,35(7,09) / 67,39(9,76) / 68,95(6,21) / 64,1(8,35); [SF] t24: 76,06(6,61) / 75,31(9,37) / 75,2(11,57) / 69,81(12,14). La evaluación con análisis de varianza mostró el efecto significativo de las variables material, profundidad y momento del registro (p<0,05) y la prueba de Tukey mostró que los sitios de registro (profundidad) fueron estadísticamente significativos, dando cuatro grupos homogéneos. Bajo las condiciones de este estudio podemos concluir que la microdureza de las resinas de inserción en bloque se ve afectada por el nivel de profundidad y el tiempo pos curado.

Evaluation of the mechanical behavior of bulk-fill and conventional flowable resin composites using dynamic micro-indentation.

The purpose of this research was to investigate the mechanical behavior of commercially available bulk-fill and conventional flowable resin composites using the dynamic micro-indentation method. The effect of inorganic filler content on mechanical properties was also assessed. Weight percentages of the inorganic filler in the resin composite were measured using the ashing technique. The results showed that dynamic hardness and elastic modulus tended to increase with inorganic filler content. Furthermore, the differences in mechanical properties between top and bottom surfaces were less pronounced in bulk-fill flowable resin composites compared with conventional flowable resin composites. In conclusion, the mechanical properties of bulk-fill flowable resin composites are affected by filler content. Moreover, bulk-fill flowable resin composites have a higher polymerization depth than conventional flowable resin composites when sample thickness is 4 mm.

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.

Indentation Modulus, Indentation Work and Creep of Metals and Alloys at the Macro-Scale Level: Experimental Insights into the Use of a Primary Vickers Hardness Standard Machine.

In this work, the experimental method and the calculation model for the determination of indentation moduli, indentation work, and indentation creep of metallic materials, by means of macroscale-level forces provided by a primary hardness standard machine at the National Institute of Metrological Research (INRIM) at the at room temperature were described. Indentation moduli were accurately determined from measurements of indentation load, displacement, contact stiffness and hardness indentation imaging and from the slope of the indentation unloading curve by applying the Doerner-Nix linear model; indentation work, representing the mechanical work spent during the force application of the indentation procedure, was determined by calculating the areas under the loading-unloading indentation curve, through fitting experimental data with a polynomial law. Measurements were performed with a pyramidal indenter (Vickers test). The applied force was provided by a deadweight machine, and the related displacement was measured by a laser interferometric system. Applied forces and the occurring indentation depths were simultaneously measured: the resulting loading-unloading indentation curve was achieved. Illustrative tests were performed on metals and alloy samples. Discussion and comments on the suitability of the proposed method and analysis were reported.

Effect of different irrigation protocols for applications in regenerative endodontics on mechanical properties of root dentin.

The objective of this study was to evaluate the effect of different concentrations of NaOCl with and without passive ultrasonic irrigation (PUI) on mechanical properties of human dentin for applications in regenerative endodontics (RE). Sixty single-rooted teeth were sectioned into 2 halves (n = 120). Dentin bars were produced from one half for flexural strength and the other half was used for microhardness. Specimens were randomly assigned into 10 groups: G1 and G2 (control): distilled water for 30 and 60 min, respectively; G3: 1.5%NaOCl for 30 min; G4:1.5%NaOCl for 60 min; G5: 1.5%NaOCl + PUI for 30 min; G6: 1.5%NaOCl + PUI for 60 min; G7: 5.25%NaOCl for 30 min; G8: 5.25%NaOCl for 60 min; G9: 5.25%NaOCl + PUI for 30 min; G10: 5.25%NaOCl + PUI for 60 min. An increase in NaOCl concentration showed highly significant reduction in mechanical properties. There was no significant difference between 1.5% NaOCl and control group except for specimens treated with PUI for 60 min. NaOCl in concentrations recommended for RE did not have a significant effect on mechanical properties of dentin. However, PUI with increased irrigation time might have an effect even with low NaOCl concentration.

Influence of Alternative Restoration Technique with Different Composite Resins for Flared Root Reinforcement.

PURPOSE: To evaluate the influence of type and viscosity of composite resins used for root reinforcement in the adhesion of glass-fiber posts to flared root canals. MATERIALS AND METHODS: The crowns of 78 uniradicular permanent teeth were removed and the teeth were endodontically treated. After one week, the roots were prepared for root reinforcement and randomly divided into 6 groups (n = 13): positive control group ([PCG] the root canals were not enlarged), negative control group ([NCG] root canals were enlarged, no reinforcement), and in the remaining 4 groups, root canals were enlarged to receive root reinforcement according to a combination of the factors composite resin type (bulk-fill or conventional) and viscosity (flowable or regular). After fiber post cementation, six slices were obtained from each root (2 each from the cervical, middle, and apical thirds). For each group, 7 teeth underwent push-out bond strength testing, and 6 teeth were evaluated for nanoleakage and Vickers microhardness. Bond strength and nanoleakage data were submitted to two-way ANOVA and Tukey's test (α = 0.05), and microhardness data to one-way ANOVA and Tukey's test (α = 0.05). RESULTS: The root reinforcement groups with regular and flowable bulk-fill composite resins showed statistically superior adhesion results (higher bond strength and less nanoleakage) compared to the negative control in all root regions. Microhardness values were higher in the cervical third followed by the middle third. CONCLUSION: Regular or flowable bulk-fill composite resins should be chosen for root reinforcement of flared root canals prior to fiber post cementation.

Low Temperature Nanoindentation: Development and Applications.

Nanoindentation technique at low temperatures have developed from initial micro-hardness driving method at a single temperature to modern depth-sensing indentation (DSI) method with variable temperatures over the last three decades. The technique and implementation of representative cooling systems adopted on the indentation apparatuses are discussed in detail here, with particular emphasis on pros and cons of combination with indentation technique. To obtain accurate nanoindentation curves and calculated results of material properties, several influence factors have been carefully considered and eliminated, including thermal drift and temperature induced influence on indenter and specimen. Finally, we further show some applications on typical materials and discuss the perspectives related to low temperature nanoindentation technique.