Knoop Hardness Number Research Articles

Comparative Evaluation of Flexural Strength and Microhardness of Two Different Ceramic Reinforced 3-D Printed Resins with Cad-cam Milled and Conventional Tooth Coloured Heat Cured Polymethylmethacrylate Resins as Long-term Provisional Restorative Materials” – An in Vitro Study

Background: Long-term provisional restorations play a crucial role in complex clinical scenarios, Implant-supported prostheses, full-mouth rehabilitation cases & Maxillofacial Prosthodontics. Understanding the mechan-ical properties such as flexural strength and microhardness of newer commercially available provision-al restorative materials is necessary to select an optimum material for long-term provisional fixed den-tal prosthesis. This Research study was conducted to evaluate and compare the Flexural Strength and Microhardness of Two Different Ceramic-reinforced 3-D Printed Resins with CAD-CAM Milled and Conventional Tooth Coloured Heat Cured Polymethylmethacrylate Resins as Long-Term Provisional Restorative Materials. Methods: Twenty-one specimens of dimensions 25 mm × 2 mm × 2 mm (ADA-ANSI specification #27) were fabricated each using: Group A (Control group)-Conventional tooth colored heat cured polymethyl-methacrylate resin (DPI Heat cure tooth moulding powder), Group B-CAD-CAM milled resin, Group C- Ceramic reinforced polymer 3-D printed resin (Temporary CB resin) and Group D- Ceramic rein-forced polymer 3-D printed resin (Permanent CB resin). Flexural strength and microhardness were measured and the values obtained were evaluated. Results: The measured mean flexural strength values (Mega Pascals) were 39.41 (Group A), 153 (Group B), 124.91 (Group C), and 136.50 (Group D). The measured mean microhardness values (Knoop hardness number) were 37.9 (Group A), 40.5 (Group B), 34.67 (Group C), and 43.88 (Group D). The difference in flexural strength and microhardness values of the three groups was statistically significant according to the analysis of variance (ANOVA) as well as the intergroup comparison done using Tukey’s honest significant difference (HSD) Post Hoc test (P < 0.05). Conclusions: Flexural strength with higher values in Group B were noted and the Microhardness test showed higher values in Group D.

Influence of different curing modes on the bonding effectiveness of self-adhesive resin luting cements in combination with universal adhesives

ObjectivesThis study aimed to investigate the immediate dentin bond performance and bond durability of self-adhesive resin luting cements (RLCs) in combination with universal adhesives in different curing modes. MethodsTwo self-adhesive RLCs were used with universal adhesives as primers. They were also used alone as self-adhesive RLCs. Two multiple-step RLC systems were used as comparison materials. To measure the shear bond strength (SBS) in different curing modes, 12 specimens were prepared for each group. Stainless-steel rods were bonded to bovine dentin, and the bonded specimens were assigned to the baseline group (stored for 24 h) and artificially aged group (thermal cycling [TC], 10,000 cycles). After each storage period, the SBS of the bonded specimens was measured. The Knoop hardness number (KHN) of the cured RLCs was measured with or without primer application in different curing modes at 24 h and after 10,000 TC. The representative RLC/dentin interfaces were observed using scanning electron microscopy (SEM). ResultsDentin SBS was significantly influenced by the RLC system but not by the curing mode. Self-adhesive RLCs alone showed significantly lower SBS values than self-adhesive RLCs with primer regardless of the curing mode or storage period. The storage period, curing mode, and RLC system significantly influenced the KHN. SignificanceThe use of universal adhesives as a primer may help enhance the immediate dentin bond performance and bond durability of self-adhesive RLCs.

In vitro characterization of a novel resin-based restorative material containing alkaline fillers.

In this study, a comparative evaluation of the physicochemical properties of Cention N and other direct restorative materials was performed. Three restorative materials-a resin-modified glass ionomer (Fuji II LC), an alkasite-based resinous material (Cention N), and a resin composite (Tetric N Ceram)-were characterized in terms of degree of conversion, Knoop hardness number (KHN) ratio, flexural strength, elastic modulus, water sorption, water solubility, microshear bond strength to dentin, immediate microleakage, and radiopacity. The microshear bond strength to dentin and microleakage of Cention N were evaluated with and without the application of an adhesive system (Tetric N Bond Universal). A one-way ANOVA test was used to analyze the data in terms of degree of conversion, KHN ratio, water sorption, water solubility, microshear bond strength to dentin, and radiopacity. A two-way ANOVA test (carried out considering the material type and ethanol aging as factors) was used to analyze the data in terms of flexural strength and elastic modulus. The Kruskal-Wallis test was used to statistically analyze the data on microleakage. A significance level of α=0.05 was used for all tests. Fuji II LC was found to have the highest degree of conversion, water sorption, and microleakage, as well as the lowest flexural strength. Cention N had the highest solubility; when used with an adhesive system, it achieved bond strength and microleakage similar to those of the Tetric N Ceram composite. Tetric N Ceram had the highest degree of conversion, KHN ratio, and radiopacity. Conclusion: The properties of Cention N validate its efficacy as an alternative direct restorative material when used in conjunction with an adhesive system.

Development of whitening mouth rinses formulated with mushroom residues and their effect on enamel's physical properties.

This study aimed to develop whitening mouth rinses formulated with industrial mushrooms and compare them with over-the-counter whitening mouth rinses. Formulations with black shimeji mushrooms, mushroom substrates, and mushroom stalks were developed. Bovine enamel/dentin samples were divided into 7 groups (n = 10): Colgate Luminous White, Listerine Whitening Extreme (LWE), Listerine Cool Mint (LC), mushroom extract rinse (MEC), mushroom substrate rinse (MSB), mushroom stalk rinse (MTC), and artificial saliva. Samples were stained with black tea for 6 days, and then were immersed in 100 mL of each mouth rinse twice daily for 14 days. Color parameters (CIELAB [ΔE*], CIEDE2000 [ΔE00], whiteness index for dentistry [ΔWID]) and microhardness (Knoop hardness number [KHN]) were analyzed at T1 (initial), T2 (24 hours), and T3 (7 days). Mouth rinse pH was measured, and enamel was examined using a scanning electron microscope. Data were analyzed using generalized linear models, and KHN with the generalized linear mixed model for repeated measures (p ≤ 0.05). ΔE* was higher in LW and MSB groups. No significant differences were found for ΔE00 (p = 0.0982) and ΔWID (p = 0.2536). Experimental mouth rinses did not promote enamel whitening based on ΔE00 and ΔWID. LWE and LC reduced KHN and had a more acidic pH, while MEC had higher KHN at T2. MEC, MSB, and MTC had alkaline pH, not altering the tooth surface. Black shimeji mushrooms are promising for mouth rinse development due to their alkaline pH and non-altering effect on surface microhardness.

Remineralizing Potential of Bioactive Glass–Ceramic over White Spot Lesions

Abstract Objective This study evaluated the effect of incorporating biosilicate (Bio) particles into experimental toothpaste (ET) on their abrasiveness and remineralization capacity for white spot lesions (WSLs). Materials and Methods Thirty-two fragments of bovine teeth (6 × 6 × 2 mm) were obtained. Initial microhardness (Knoop hardness number [KHN], HMV Microhardness Meter, Shimadzu) and surface roughness (Rugosimeter Surfcorder SE 1700) readouts were performed. Fragments were submitted to a cariogenic challenge to simulate WSLs and then divided into four groups: Control, conventional toothpaste (Colgate Smiles, Colgate-Palmolive Company); ETF, ET with fluoride (carboxymethylcellulose + glycerol + thickening silica + fluoride); ETB, ET with Bio; BS, biosuspension (10 in weight% Bio). Toothpaste treatments were performed through simulated toothbrushing (Pepsodent, MAVTEC, 14,600 cycles). BS was applied by immersion for 8 hours followed by 16 hours in artificial saliva at 37°C for 60 days, totalizing 1,440 cycles. After treatments, final KHN and surface roughness readings were performed, and scanning electron microcopy (SEM) was conducted (Jeol JSM-6610LV) for morphological analysis. Data were analyzed with one-way analysis of variance, Tukey's test (p < 0.05). Results BS produced the least surface roughness change, different (p < 0.05) from all the other groups. ETB caused higher KHN than ETF (p < 0.05). SEM images revealed that ETB and BS resulted in abraded surfaces with deposition of particles. Conclusion ETB resulted in similar abrasiveness to the control group, and it caused higher microhardness than the ETF. Practical Implication Considering its higher KHN, ETB could be considered a proper alternative for the treatment of WSLs.

Randomized in situ evaluation of surface polishing protocols on the caries-protective effect of resin Infiltrant

The aim of this placebo-controlled randomized in situ study was to evaluate the effect of different surface polishing protocols on enamel roughness, bacterial adhesion and caries-protective effect of a resin infiltrant. Seventy-five bovine enamel samples having artificial caries lesions were treated with a resinous infiltrant and afterwards randomly dividided into five polishing protocols: aluminum oxide flexible disks (Al2O3-Disks), silicon carbide tips (SIC-Tips), silicon carbide brush (SIC-Brush), silicon carbide polyester strips (SIC-Strips) or no polishing [negative control (NC)]. Average surface roughness (Ra) was assessed by profilometry. Samples were mounted in palatal appliances under a mesh for biofilm accumulation. Fifteen volunteers wore the intraoral appliances (14-days) and cariogenic challenge was triggered by sucrose solutions. Biofilm formed was collected for microbiological analysis of caries-related bacteria (Streptococcus mutans, Lactobacillus acidophilus) and demineralization was assessed by cross-sectional microhardness. Mean Knoop hardness numbers (Kg/mm2) were plotted over lesion depth (µm) and area under the lesion curve was subtracted from sound enamel to determine demineralization (ΔS, Kg/mm2xµm). Data were analyzed by ANOVA and post-hoc comparisons (α = 0.05). NC resulted in significantly higher Ra means than Al2O3-Disks and SIC-Strips. Bacterial counts were not significantly different between the groups (p > 0.05). Regards ΔS means, however none of the groups were significantly different to NC (6983.3 kg/mm2xµm /CI 4246.1–9720.5, p > 0.05). Conclusions: Polishing protocols (Al2O3-Disks, SIC-Strips) significantly decreseased roughness of infiltrated-enamel, however none of the polishing protocols could signicantly decrease bacterial counts nor resulted in significant less demineralization.

Early Phase Enamel Bond Performance of a Two-step Adhesive Containing a Primer Derived from a Universal Adhesive.

To investigate the changes in the enamel bond performance of a two-step adhesive containing a primer derived from a universal adhesive in the early phase before 24 h and compare them to those of other adhesives. The Knoop hardness number (KHN) of the cured adhesive layers and resin composite was measured. A new two-step adhesive using universal adhesive technology, G2-Bond Universal, was tested. Two conventional two-step adhesives, Clearfil SE Bond 2 and OptiBond eXTRa, and an established universal adhesive, Scotchbond Universal Plus Adhesive, were used as comparison materials. Twelve specimens per group were used to measure the shear bond strength (SBS) to bovine enamel in different etching modes. The bonded specimens were stored in distilled water at 37°C for 5 min or 1, 6, 12, or 24 h before SBS testing. The KHN of the adhesive layer and resin composite was determined after the same storage periods as for SBS testing. All adhesives exhibited increased SBS with prolonged storage periods, irrespective of the etching mode. The KHN of the adhesive layer and resin composite increased over time. There were strong positive correlations between the SBS and KHN of the adhesive layer and resin composite. Phosphoric acid pre-etching of enamel effectively increases enamel bond performance. The two-step adhesive G2-Bond Universal demonstrated significantly higher bond strength in the early phase than the other adhesives in self-etch mode.

Influence of Novel Experimental Light-Cured Resin Cement on Microtensile Bond Strength.

The purpose of this study was to evaluate the microtensile bond strength (µTBS) and Knoop hardness number (KHN) of a novel experimental light-cured resin cement (HL). Eighteen flat dentin surfaces of human molars were polished using #600 SiC paper and bonded to CAD/CAM resin blocks with the respective resin cements and composites: HL, Panavia V5 (PV), and Clearfil AP-X (AP). All specimens were stored in distilled water at 37 °C for 24 h and 7 days. Scanning electron microscope (SEM) and energy dispersive X-ray (EDX) observations were performed to evaluate filler morphology and to detect the elements. The resin cements had a significant effect on the immediate µTBS (F = 22.59, p < 0.05) and after water storage µTBS (F = 22.83, p < 0.05). Significant differences (p < 0.05) in the KHN between the tested materials were observed, and HL indicated the highest KHN when compared with PV. HL showed a combination of the regular-shaped filler and spherical-shaped filler within the matrix. Silicon was detected in HL from the EDX evaluation. HL exhibited better bonding performance and polymerization, which may have contributed to the improvement of the adhesive strength.

Effectiveness of an actuator-driven pulsed water jet for removal of softened carious dentin.

The aim of this study was to assess the utility of an actuator-driven pulsed water jet (ADPJ) as a hardness-dependent carious dentin removal device by using different outputs. Thirty-six plane surface dental caries samples were treated with the ADPJ at 150, 200, and 250 voltage (12 teeth each). The Knoop hardness number (KHN) and Ca/P mass ratio were measured at 70 μm from the deepest point of the removing groove. Furthermore, three other teeth samples were manually treated with the ADPJ at the three above mentioned voltages (one tooth each) for 1 min. The KHN and Ca/P mass ratio were measured at 70 μm from the surface of the residual dentin part. In both the KHN and Ca/P mass ratio, higher residual dentin depended on the applied voltage of ADPJ. The ADPJ enabled the removal of softened carious dentin in an applied voltage-dependent manner.

Assessment of remineralisation potentials of bioactive dental composite using an in-vitro demineralised dentine model

ObjectiveMinimally invasive dentistry encourages conservative caries excavation and remineralisation of the remaining dental tissues. However, dentine remineralisation is more difficult than enamel remineralisation due to the differences in their composition. This study aims to assess the remineralisation potential of Activa BioActive-Restorative and Beautifil II restoration on demineralised dentine samples, and compares it with glass-ionomer (GIC) restoration using energy dispersive X-ray (EDX) and Knoop hardness number (KHN). MethodsNon-carious extracted molar teeth were used, a total number of ten teeth were sectioned into halves and partially demineralised using 37.0% phosphoric acid for 60 s. All samples are assessed using EDX and KHN prior to restorations. The samples are then subdivided into four groups (n = 5). Group 1 was restored with Activa BioActive-Restorative, Group 2 received Beautifil II, Group 3 was restored with GIC, and the last group was used as a negative control. After storage, the samples were analysed using EDX and KHN. ResultsThe demineralisation protocol with 37.0% phosphoric acid significantly decreased the calcium:phosphate (Ca:P) ratio and KHN. Remineralisation occurred in all groups, but the highest percentage change in Ca:P ratio and KHN was observed in the Activa BioActive-Restorative group (20.7%, 82.0%, respectively), followed by the Beautifil II group, glass ionomer group, and the control group, in that order. ConclusionActiva BioActive-Restorative restoration presents superior remineralisation compared to Beautifil II and glass-ionomer dental restorations.

Immediate bond performance of resin composite luting systems to saliva-contaminated enamel and dentin in different curing modes.

The purpose of this study was to evaluate the immediate shear bond strength of resin composite luting systems to tooth with or without saliva contamination in different curing modes. The Knoop hardness number of the resin composite luting agents was measured. Four combinations of resin composite luting systems were used. The shear bond strength to bovine teeth was measured with and without saliva contamination in different curing modes at different storage periods. The Knoop hardness number of the resin composite luting agents was also evaluated. Significantly lower enamel and dentin shear bond strengths and Knoop hardness number values were observed in all resin composite luting systems at 5min versus 24 h, regardless of the curing mode or saliva contamination. The influence of the curing mode of the resin composite luting systems on shear bond strengths and Knoop hardness number was dependent on material. For the saliva contamination conditions, only G-CEM ONE EM did not show any significant difference in shear bond strength among the groups with and without saliva contamination, regardless of curing mode, storage period, or tooth substrate. All the resin composite luting systems showed lower shear bond strengths and Knoop hardness number values immediately after setting.

Microhardness Indentation Studies of 2‐4‐6 Trinitrotoluene

AbstractThe microhardness of the {001} faces of 2‐4‐6 trinitrotoluene crystals has been investigated using both Vickers and Knoop indentation methods. The Vickers hardness number was found to be 22.5 kg mm−2 independent of crystal orientation and perfection. At ambient temperatures (∼20 °C) the Knoop hardness number varied between 20.5 kg mm−2 and 24.0 kg mm−2 with crystal orientation. At higher temperature (50 °C) the Knoop hardness anisotropy curve retained its shape, although the overall hardness decreased by 10 %. We interpret this change as reflecting a simple temperature dependant loosening of the crystal lattice rather than any change in deformation mechanism. No variation of Knoop hardness was evident with changing load. The hard direction was [010] and the soft [100]. The dominant operative slip system was defined to be {001}[010].

Influence of Different Application Methods on the Bonding Effectiveness of Universal Adhesives to Dentin in the Early Phase.

To investigate the changes in the dentin bond strengths of universal adhesives during the early phase and evaluate the effect of a double-layer adhesive application on the performance of the dentin bond. Three universal adhesives and a two-step self-etch adhesive were employed to ascertain the shear bond strengths (SBS) of specimens to bovine dentin with the use of the etch-and-rinse or self-etch mode. The specimens were further divided into two groups based on adhesive application in a single or a double layer. The bonded specimens were stored in distilled water at 37°C for 5 min or 1, 6, 12, or 24 h prior to SBS measurement and the adhesives' Knoop hardness number (KHN). All the adhesives showed increased SBS with prolonged storage periods regardless of the adhesive layer (single or double) or etching mode. Most universal adhesives in the double adhesive layer groups showed significantly higher SBS than single adhesive layer groups for the same storage period. All the adhesives also showed increased KHN with increased storage period. The SBS and KHN values of the adhesives increased with increasing storage duration over a 24-h period. Double adhesive layer application mediated increased dentin bond strength in the early phase.

Flexural properties and wear behavior of computer-aided design/computer-aided manufacturing resin blocks.

This study investigates the flexural properties, Knoop hardness number (KHN), and wear behavior of computer-aided design and computer-aided manufacturing (CAD/CAM) resin blocks and compares these values with those of conventional resin composites for direct restoration (RCDs). Four CAD/CAM resin blocks and two RCDs are compared. Ten specimens per material are used to obtain the flexural properties according to ISO 6872 specifications, and five specimens per material are used for KHN measurement. For sliding impact wear testing, twelve specimens are prepared. Confocal laser scanning microscopy (LSM) is used to determine maximum facet depth and volume loss. Polished material surfaces and worn surfaces after wear testing are observed using scanning electron microscopy and LSM. While measured flexural properties and KHN are found to be material-dependent, CAD/CAM resin blocks exhibit higher wear resistance than RCDs. CAD/CAM resin blocks polymerized at high-pressure and high-temperature are found to exhibit wear behaviors far superior to those of RCDs.

Handling properties and surface characteristics of universal resin composites

This study investigated the handling and surface characteristics of universal resin composites and determined the interrelations among the composites' handling, mechanical, and physical properties. Five recently introduced universal resin composites were tested. Twelve specimens per material were used to measure the stiffness and stickiness (handling properties) of the resin composite pastes. Additionally, surface properties (Knoop hardness number [KHN], surface roughness [Sa], surface gloss [SG], water contact angle [CA], and surface free energy [SFE]) of cured resin composites were determined in 12 specimens per material immediately after preparation (baseline) and after subjection to thermal cycles (TCs). Handling and surface properties of the resin composites were material dependent. All the resin composites showed significantly lower KHN in the post-TC subgroups than that in the baseline subgroups. However, the influence of TC on the other surface properties was dependent on the material used. Some resin composites did not indicate any significant differences in Sa, SG, or CA between the baseline and post-TC groups. Although the resin composites in the baseline groups presented with different handling and surface properties, the surface properties of most of the composites were significantly affected by TC. Extremely strong positive or negative correlations were observed between stiffness and stickiness, KHN and Sa, KHN and SG, Sa and SG, and CA and SFE. Most correlations between the handling and surface properties were weak. Therefore, the selection of resin composites in clinical situations should be based on comprehensive consideration of their properties.

Simulating Knoop hardness anisotropy of aluminum and β-HMX with a crystal plasticity finite element model

We report a crystal plasticity finite element model for simulating the variation of the Knoop hardness number with indenter orientation, i.e., the hardness anisotropy. We propose a modification to the Voce hardening law to include the effects of slip on multiple systems on the hardening rate. The model is validated using single crystal aluminum in a two-step procedure: (a) calibration of the material model with single crystal tension experiments, and (b) prediction of the hardness anisotropy of the {001}, {011} and {021} planes. The predicted hardness anisotropy follows experimental trends very well for the {001} and {021} planes, while for the {011} plane there is a deviation of the predictions from experiments at higher angles of the indenter. The model is then used to simulate the hardness anisotropy of the (010), (011) and (110) planes of β-HMX measured by Gallagher et al. (2015). Due to the lack of single crystal data, we were unable to calibrate the model prior to simulating the hardness anisotropy. Hence, we assumed unknown variables to make predictions for comparison to experiments, including the set of active slip systems and the hardening and twinning behavior. From simulations of the indentation of the (010) plane with the set of slip systems from Barton et al (2009) we found that the hardness anisotropy is inversely proportional to the activity of the slip system (101)[01¯0], and to a lesser extent the twin system. Suppressing the (101)[01¯0] slip system improved the predictions, suggesting that the viable set of slip systems for β-HMX need not include it. The predicted twinning activity did not match well with the observations from Gallagher et al. (2015). Suppressing the twinning resulted in a better prediction of the hardness anisotropy. Due to the simplicity of the twinning part of the model we do not make definite conclusions related to twinning. We report predictions for the hardness anisotropy of the (011) and (110) planes of β-HMX using parameters that maximized agreement between simulations and experimental indentation of (010) plane. These predictions are in reasonable agreement with experiments. In addition, we report the predictions of the hardness anisotropy using the sets of slip systems proposed by Pal and Picu (2018) and Zhou et al. (2012), which both gave inferior agreement with experiments.

In Vitro Enamel Remineralization Efficacy of Calcium Silicate-Sodium Phosphate-Fluoride Salts versus NovaMin Bioactive Glass, Following Tooth Whitening.

Objectives This study aimed to evaluate the effect of in-office bleaching on the enamel surface and the efficacy of calcium silicate-sodium phosphate-fluoride salt (CS) and NovaMin bioactive glass (NM) dentifrice in remineralizing bleached enamel. Materials and Methods Forty extracted premolars were sectioned mesio-distally, and the facial and lingual enamel were flattened and polished. The samples were equally divided into nonbleached and bleached with 38% hydrogen peroxide (HP). Each group was further divided according to the remineralization protocol ( n = 10); no remineralization treatment (nontreated), CS, or NM, applied for 3 minutes two times/day for 7 days, or CS combined with NR-5 boosting serum (CS+NR-5) applied for 3 minutes once/day for 3 days. The average Knoop hardness number (KHN) and surface roughness (utilizing atomic force microscopy) were measured. Surface topography/elemental analysis was analyzed by using scanning electron microscopy/energy dispersive X-ray analysis. All the tests were performed at baseline, after bleaching, and following each remineralization protocol. Data were statistically analyzed by two-way analysis of variance and Bonferroni post hoc multiple comparison tests (α = 0.05). Results HP significantly reduced KHN and increased roughness ( p < 0.05). All remineralization materials increased the hardness and reduced the surface roughness after bleaching except NM, which demonstrated significantly increased roughness ( p < 0.05). Ca/P ratio decreased after bleaching ( p < 0.05 ), and following treatment, CS and CS+NR-5 exhibited higher remineralization capacity in comparison to NM ( p < 0.05). Conclusion Although none of the material tested was able to reverse the negative effect of high-concentration in-office HP on enamel completely, the remineralization efficacy of CS and CS+NR-5 was superior to that of NM.

Surface properties of resin-modified glass-ionomers subjected to in-office bleaching agents

This study examined the influence of two in-office bleaching on surface roughness, topography and microhardness of RMGIs. Disc-shape samples of RMGIs (Ketac N100, Fuji II LC-Capsule, and Photac Fil Quick Aplicap) were prepared and polymerized by a LED light curing unit. Polished samples, were subjected to in-office bleaching agents, Opalescence Xtra Boost (OXB) and Pola Office (PO), for 3 consecutive applications of 15 min each. The surface roughness parameters (R a and R max, μm) and Knoop hardness number (KHN, kg/mm2) were measured using contact profilometer and microhardness tester, respectively. The surface topography of the bleached surfaces was evaluated by SEM. Two-way ANOVA demonstrated high significant differences between the KHN, R a and R max values among the RMGIs and the bleaching agents evaluated as well as their interactions (p < 0.05). Pearson’s correlation indicated mainly no significant correlation between KHN and R a surface finish at each in-office agent for each RMGI (p > 0.05). Low R a (0.193 µm) and high KHN (49.34) values were presented in N100, whereas high R a (0.916 µm) and low KHN (31.54) were found in PFQ and FII, respectively, after bleaching with OXB. Surface properties are affected by the differences in material’s composition, mainly fillers, and type of bleaching agent. High concentration of hydrogen peroxide from bleaching agent and type of RMGIs can influence the chemical softening of these restorations and their clinical durability.

Influence of one-step professional mechanical tooth cleaning pastes on surface roughness and morphological features of tooth substrates and restoratives.

This study investigated the influence of professional mechanical tooth cleaning (PMTC) pastes on the surface texture of different subject materials. Two one-step PMTC pastes, Clinpro Cleaning Paste for PMTC (CP) and PRG Pro-Care Gel (PG), and multiple-step PMTC pastes, Merssage Regular (MR), Merssagge Fine (MF), and Merssage Plus (MP), were used. For comparison, PMTC was performed using distilled water without paste (DW). The subjected materials used were bovine enamel (ENA) and dentin (DEN), a resin composite (FSU), and lithium disilicate (IEC). The prepared specimens were polished using a #2000-grit silicon carbide paper. PMTC was performed using a brush at 1,000 rpm for 15 s. The surface roughness (Ra) values of the specimens before and after PMTC were measured by laser scanning microscopy. The Knoop hardness number (KHN) of the subjected material was obtained. The types of PMTC pastes and subject materials had a significant influence on the Ra values and KHN. For the majority of subject materials, the descending order of Ra values after PMTC was MR > MF > CP > PG > MP > DW. The descending order of KHN of the materials was IEC > ENA > FSU > DEN. Although one-step PMTC pastes appeared to be effective, it is important to consider the subject material during PMTC.

Time-dependent Microhardness Gradients of Self-adhesive Resin Cements Under Dual- and Self-curing Modes.

Acid-functional monomers in self-adhesive resin cements may decrease their self-curing polymerization ability. Light irradiation optimizes polymerization performance. Purpose: The aim of this study was to investigate Knoop microhardness of self-adhesive resin cements under dual- and self-curing modes in simulated canals for describing the polymerization behavior.Methods and Materials: Slots in lightproof silicone cylinders with one open end were filled with the following eight materials: a traditional resin cement (Duolink), a core build-up resin material (MultiCore Flow), and six self-adhesive resin cements (RelyX Unicem 2, G-Cem Automix, Maxcem, Biscem, Multilink Speed, and PermaCem 2.0). The resins were exposed to light through the open end and then stored in a lightproof box. The Knoop hardness gradient for each resin was measured after 1 hour and 120 hours. Surface readings were obtained at 1-mm intervals from 1 mm to 10 mm away from the open ends. The data were analyzed by two-way analysis of variance and the Student-Newman-Keuls test (α=0.05).Results: All the resin materials had stable Knoop hardness numbers (KHNs) at a certain depth; their KHNs in the self-curing mode did not change (p>0.05). The region above this certain depth was regarded as having undergone the dual-curing mode, and the KHN decreased gradually with depth (p<0.05). Between 1 and 120 hours postexposure, the ratio of the KHN at a 5-mm depth (self-cured) to that at a 1-mm depth (dual-cured) increased in Duolink and MultiCore Flow. However, the ratios of the six adhesive resin cements varied.Conclusion: Without light, most self-adhesive resin cements differed from traditional dual-cured resin materials in terms of Knoop micro-hardness, and they had a lesser capacity for chemical-induced curing.