Silicon Carbide Paper Research Articles

In-lab simulation of CAD/CAM milling of lithium disilicate glass-ceramic specimens: Effect on the fatigue behavior of the bonded ceramic

The aim of this study was to evaluate the effect of in-lab simulation procedures performed on a lithium disilicate ceramic luted to a dentin-analogue material regarding the fatigue performance and topographic changes. Lithium disilicate ceramic (IPS e.max CAD) discs (Ø = 13.5 mm and 1.5 mm of thickness) were produced in different ways: milled in a CAD/CAM system (CAD/CAM – control group); mirror-polished (POL group); produced in-lab and ground with #60 silicon carbide paper (SiC group); with #60 wood sandpaper (WS group); with a fine diamond bur (DB group); or with a CAD/CAM bur adapted in a handpiece with a custom mandrel (MANDREL group). The ceramic discs were adhesively luted (Multilink N) onto dentin analogue discs (Ø = 12 mm and 2 mm of thickness) and fatigue testing (n = 19 discs) was performed by step-stress methodology (initial load of 200 N; step-size of 50 N; 10,000 cycles per step; 20 Hz). Surface roughness and contact angle analysis were also performed. According to Kaplan-Meier and post-hoc Mantel-Cox (log-rank), distinct fabrication methods affected the fatigue performance of bonded glass-ceramic discs (p< 0.001). The CAD/CAM group presented the lowest fatigue failure loads (1250 N) and number of cycles for failure (185,000), while the POL groups obtained the highest results (1752 N; 284,444 cycles). The in-lab groups had intermediate values (1355 – 1526 N; 206,052 – 238,684 cycles). Polished specimens presented the lowest roughness values (Ra = 0.041 μm), while the SiC (1.604 μm), WS (1.701 μm), and MANDREL (1.867 μm) groups showed statistically similar roughness values to the CAD/CAM group (1.738 μm). Despite differences before etching, the contact angle was similar among the milled and simulated groups after etching, except for the polished group. Even with some topographic similarities, the tested in-lab simulation methods were not able to mimic the milled specimens in terms of fatigue findings, leading to distinct magnitude of overestimations of the results.

A study on corrosion resistance of ISO 5832-1 austenitic stainless steel used as orthopedic implant

The ISO 5832-1 austenitic stainless steel used as biomaterial is largely applied in the area of orthopedics, especially in the manufacture of implants, such as temporary or permanent replacement of bone structures. The objective of this study was to evaluate the localized corrosion resistance of the ISO 5832-1 stainless steel used in orthopedic implants by electrochemical tests in two different solutions. The results of this study are of great interest to evaluate the corrosion of metallic implants that can result in the release of corrosion products into bodily fluids causing possible adverse biological reactions. The determination of the chemical elements in the composition of the ISO 5832-1 stainless steel was performed by neutron activation analysis (NAA). The samples for electrochemical tests were grinded with silicon carbide paper up to #4000 finishing, followed by mechanical polishing with diamond paste. The open circuit potential measurements and anodic polarization curves were obtained in solution of 0.90 wt. % of NaCl and of simulated body fluid (SBF). The results indicated that the ISO 5832-1 stainless steel presented a high resistance to crevice corrosion in simulated body fluid solution but high susceptibility to this form of corrosion in the chloride solution.&#x0D;

Influence of direct current (DC) on mild steel coating stainless steel rods via TIG welding: A model for the rehabilitation of steel components

In this paper, the influence of varying DC current on microstructures of mild steel substrates coated with stainless steel using TIG welding technique was investigated. To achieve the desired results, mild steel substrates of sizes 40 mm × 10 mm × 1.5 mm were used. The mild steel substrates were ground using Silicon Carbide (SiC) papers to achieve smooth surfaces and to remove oxides that might be present on their surfaces. Then the substrates were coated using stainless-steel rods on TIG 2200i AC/DC machine as a welding power source. The process was undertaken under six varying currents of 40 A, 50 A, 55 A, 60 A, 65 A and 70 A. For purpose of characterization, microstructures of the coated samples were studied using optical microscopy and quantitative image analyses. The depth of penetration of the melt pool below the substrates and the coating thickness were measured for all the samples. Based on the optical microscopy, four zones were identified on the TIG coated samples; the heat-affected zone (HAZ), fusion, coating and a skirt (the region that formed between the substrates and the coatings). Minute porosities were also observed in the coated samples. It was observed that the maximum coating thickness was 5.345 mm and the highest average coating thickness was 3.522 mm, which both occurred at 40 A. The maximum length of penetration was 3.864 mm and was observed when 60 A DC was used. Similarly, the highest average depth of penetration was 2.422 mm and occurred at 65 A. The results of this study showed that for direct current, as the current increased from 40 A to 50 A, the porosities in the coated samples increased. However, at 55 A, the number of porosities decreased, but continued to increase from 60 A to 65 A, but the porosities decreased again at 70 A.

Surface roughness and gloss of polished nanofilled and nanohybrid resin composites

Background/purposeThere is limited literature on the polishability of new launched nanofilled and nanohybrid. The aim of this study is to evaluate the polishability of nanofilled and nanohybrid composites by measuring surface roughness and gloss values and explore the surface qualities of composite before and after polishing in vitro.Materials and methodsOne nanofilled resin composite, two nanohybrid resin composites and one microhybrid resin composite were selected. All specimens were light cured against celluloid matrix strips. Then surface roughness(Ra) and gloss(GU) values were tested as negative control. Specimens were roughened with a 600-grit silicon carbide paper for 30 s to serve as positive control and then polished with Sof-Lex polishing disk system. Mean Ra and GU values of each step were measured with a profilometer and a small-area glossmeter. The surface qualities were observed by scanning electron microscope.ResultsRa values of polished surfaces were significantly higher than negative control and lower than positive control(P < 0.05). All materials showed no significant difference on Ra values after polishing(P > 0.05). GU values of polished surfaces were significantly lower than negative control and higher than positive control(P < 0.05). After polishing the microhybrid resin composite showed lower GU values than nanofilled and nanohybrid resin composite groups. The SEM images showed surface textures and irregularities were corresponded to the results of surface roughness and gloss.ConclusionNo significant differences were noted on surface roughness among nanofilled, nanohybrid, and microhybrid composites after polishing with Sof-Lex disc system. Microhybrid composite presented lower gloss values than nanofilled and nanohybrid resin composites.

The measurement threshold and limitations of an intra-oral scanner on polished human enamel

ObjectiveTo investigate the measurement threshold of an intra-oral scanner (IOS) on polished human enamel. MethodsThe optical performance of an IOS was compared to a gold-standard non contacting laser profilometer (NCLP), on a painted microscope slide, compared to increasing particle size of silicon-carbide papers (21.8–269.0 μm) and separately on polished human enamel with increasing step-heights. The enamel samples were randomised (n = 80) and scanned using the IOS and NCLP at increasing step-height depths (μm) (1.87–86.46 μm) and quantified according to ISO:5436-1. The measurement threshold of the IOS was determined using a custom designed automated lesion localisation algorithm, corroborated by Gaussian skewness (Ssk) and kurtosis (Sku) analysis, to assess the minimum step-height measured on each enamel sample. ResultsThe NCLP showed statistically increased Sq surface roughness for all silicon carbide particle sizes compared to the microscope slide, whereas, the IOS Sq roughness discriminated silicon-carbide particles above 68.0 μm compared to the glass slide (p ≤ 0.02). On polished enamel, the automated minimum detectable step-height measurable on each sample was 44 μm. No statistically significantly different step-height enamel lesion measurements were observed between NCLP and IOS above this threshold (p > 0.05). SignificanceThis study revealed the fundamental optical metrological parameters for the IOS, was step-heights above 44 μm and this reflects the data acquisition of the system. These results highlight the limitations of IOS used in this study, mandating further research to optimise the performance of other IOS systems, for measuring wear of materials or tooth wear on human unpolished natural enamel surfaces.

Visually acceptable gloss threshold for resin composite and polishing systems

BackgroundThe objective of this study was to compare dentists’ perceptions of gloss values of composite specimens with increased levels and to identify the gloss value considered to be clinically acceptable. MethodsDisk-shaped composite specimens were finished and polished 3 ways: metallurgically using silicon carbide papers and alumina paste, manually using Enhance finisher and PoGo polisher (EP) (Dentsply Sirona), and manually using Sof-Lex (SLex) disks (3M). Specimens were produced with surface gloss ranging from 0 through 100 gloss units (GU) in increments of approximately 10 GU as measured with a glossmeter. A GU of 0 was nonglossy, and a GU of 100 was perfectly glossy. Ten dentists evaluated the specimens, ranking them in order from low to high gloss and in 4 groups: low (dull or rough), medium (moderate gloss, clinically unacceptable), high (glossy, clinically acceptable), and superior gloss. The authors performed Spearman correlation analysis (α = 0.05). ResultsFor each finish and polish method, there was an excellent correlation between the machine-measured (actual) gloss ranks and the clinician-evaluated gloss ranks (r2 ≥ 0.95). There was no difference in perception of surface gloss of the composite when metallurgically polished (with silicon carbide papers and alumina paste) or polished with EP to the same GU. There was a slight difference in gloss perception when comparing the 2 different commercial polishing systems. ConclusionsTen dentists consistently perceived gloss of 40 through 50 GU as clinically acceptable. However, the composite was considered clinically acceptable at a lower gloss (40 GU) when polished with SLex disks than when polished with EP or metallurgically (50 GU). Practical ImplicationsGloss values of 40 through 50 GU are considered to be clinically acceptable for resin composites.

On the tribological properties of extremely different wood materials

Three different woods (lignum vitae; black fiber palm; spruce) were investigated regarding their friction and wear properties under abrasion and sliding. For the abrasive wear against silicon carbide paper, the palm wood gave the lowest removal of material, especially under an orientation of the black fibers normal to the contact region (on R–T-plane in R-direction). At the same time, this material had the highest anisotropy. Slightly less abrasion resistant was lignum vitae, whereas spruce was most easily abraded. This can be considered as an indication that spruce can easily be machined. Under sliding conditions against smooth steel, a similar tendency, but at much lower wear rates compared to abrasion, was found. The relatively high coefficient of friction under dry sliding allows the use of these woods as friction materials, for example in brakes. Additional lubrication of the two best woods, lignum vitae and black fiber palm, by soaked sunflower oil brought the coefficient of friction to a much lower level, so that the use of these woods as bearing materials in various applications is promising.

Peels as an alternative to ground sections - An in vitro microscopic study.

Background:The routine approach to delve into the organization of mineralized and nonmineralized structures of teeth is by studying whole tooth or slices of it by making thin section which requires laborious grinding or employing specialized equipment and also leads to specimen wastage. Peels hitherto utilized for fossil studies hold promise in overcoming the aforesaid shortcomings. Although the acetate peel technique has been modified for the study of tooth structure, the field remains largely unexplored.Aim:The current study was taken up to explore the usefulness of cellulose acetate peels in reproducing microscopic structures of teeth as seen in routine ground sections and further if they could supplement or replace the same.Materials and Methods:Extracted human teeth were embedded in plaster blocks in longitudinal and transverse orientation, ground and polished with silicon carbide paper. Following etching, washing and drying, the polished surface was wet with acetone and precut cellulose acetate film was placed over it and allowed to dry. As the acetate polymer dissolved in acetone and subsequently re-polymerized after setting into the micro reliefs produced by tooth etching, it registered the microscopic tooth details on its surface. The peels were mounted and secured on a glass slide and subjected to routine light and phase contrast microscopy for observing captured details of the tooth structure.Results and Conclusion:Acetate peels successfully reproduced most of the microscopic tooth details which were better than those observed in ground tooth sections. Hence, this technique could be considered as a quick, durable and inexpensive alternative or supplement to routine thin ground sections of dental hard tissues.

Effect of chelating agents on shear bond strength of EpoSeal Plus™ sealer to root canal dentin: In vitro study

Introduction: The aim of the study was to evaluate the effect of 17% ethylenediaminetetraacetic acid (EDTA) and 7% maleic acid (MA) on shear bond strength of EpoSeal Plus sealer to root canal dentin. Materials and Methods: Twenty-one decoronated maxillary central incisors were longitudinally split into two halves, and each half of the root was further split into three sections, coronal, middle, and apical thirds, respectively, and embedded in dental stone block and abraded with silicon carbide paper to create smear layer. Random division of samples was done into Group 1 (n = 12): 0.9% of saline (5 mL/min), Group 2 (n = 15): 17% EDTA (5 mL/min), and Group 3 (n = 15): 7% MA (5 mL/min). After drying the specimens using paper points, polyethylene tubes were placed on the center of the root canal dentin, and EpoSeal Plus sealer was placed into the tubes, followed by which testing of shear bond strength using a universal testing machine was done. One-way ANOVA and Tukey's honestly significant difference post hoc test was done with a significance level (P = 0.05). Results: The results demonstrated significantly more shear bond strength in MA than EDTA in the middle and apical thirds (P Conclusion: The shear bond strength of EpoSeal Plus was found to be the maximum at all thirds of root canal dentin when irrigated with 7% MA.

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.

Adhesive bonding of noble metals with a thiohydantoin primer

ObjectiveThe purpose of this study was to assess the effects of an experimental primer containing acetone solution and a sulfur-containing functional monomer, 10-methacryloyloxydecyl-(2-thiohydantoin-4-yl)propionate (MDTHP), on the bonds between noble metals and acrylic resin. MethodsThe experimental primer used as the control for comparison consisted of 6-(4-vinylbenzyl-n-propyl)amino-1,3,5-triazine-2,4-dithione (VBATDT) in acetone. These primers were prepared as equimolar functional monomers (0.1 mol%). A self-polymerizing acrylic resin initiated with tri-n-butylborane (TBB) was used as the luting agent. Four elemental metal disks (silver, copper, palladium, and gold) were used as adherend specimens. All the disks were wet-ground with silicon carbide paper (#1500). Bonding reactions were performed on 12 combinations of the four metals, and the disks were either primed with MDTHP or VBATDT or were unprimed (control). Shear bond strengths were determined pre- and post-thermocycling (5–55 °C, dwell time 60 s, 20,000 cycles). The results were statistically analyzed via a non-parametric test (α = 0.05). ResultsThe post-thermocycling shear bond strengths of the MDTHP primer were as follows (median, n = 11): 13.2 MPa on silver, 25.9 MPa on copper, 4.1 MPa on palladium, and 11.3 MPa on gold. The MDTHP primer showed higher post-thermocycling shear bond strength on all the four metals. Additionally, on silver and copper, the MDTHP bond strengths were higher than on the other metals. SignificanceWithin the limitation of current of experimental setting, the MDTHP compound may be applicable as a functional monomer for bonding noble metal alloys.

Repairability of a 3D printed denture base polymer: Effects of surface treatment and artificial aging on the shear bond strength

ObjectivesThe present study aimed to evaluate the repairability of a 3D printed denture base material. The effects of surface treatments and artificial aging on the shear bond strength (SBS) were investigated. MethodsA total of 224 specimens were printed by digital light processing technology (Rapid Shape D30II) using a 3D printing denture base material (FREEPRINT denture). To evaluate the repairability, the SBS and failure modes were measured after surface treatment and artificial aging. Specifically, half of the specimens were further performed with thermocycling (5–55 °C, 5000 cycles) for artificial aging. The aged and non-aged specimens were further divided into four subgroups (n = 28) to simulate a denture base repair with one of the following treatments: control (without surface treatment), monomer (applying methylmethacrylate for 120 s), P600 (grinding with P600 silicon carbide paper) and sandblasting (blasted with 125 μm aluminum oxide with 2 bar), respectively. Surface roughness was measured (n = 6) and surface topography was observed by scanning electron microscopy (n = 2). A test rod was built on the sample surface using the same 3D printing material. Afterward, all specimens further underwent thermocycling (5–55 °C, 10,000 cycles). ResultsFor non-aged groups, no significant differences in SBS could be found (p < 0.05), and bondings failed cohesively in the denture base material. Regarding the aged control and monomer group, adhesive failures at the interface were primarily observed, and SBS values were statistically lower than those of the other groups (p < 0.05). ConclusionsThe 3D printed denture base material exhibited favorable repairability. For the realignment surface, the SBS at the bonding interface is satisfying and additional surface treatments could be not necessary. In contrast, the aged surface could significantly decrease the SBS; hence subtractive surface treatments are highly recommended.

COMPARATIVE EVALUATION OF THE SHEAR BOND STRENGTH OF THREE SELF-ETCH DENTIN BONDING AGENTS TO DENTIN: AN IN-VITRO STUDY

Background:Dentin bonding is an ever-evolving field in adhesive dentistry. With the introduction of newer systems into the market, there is a crucial need to test their efficiency in terms of bond strength. Dual-cured adhesives in theory may provide for a better degree of conversion as compared to conventional light-cured adhesives .Thus, the aim of this study was to compare the shear bond strength of three different self-etch adhesives namely ClearfilSE bond (Kuraray), Tetric N Bond Universal (IvoclarVivadent) and Futura Bond DC (Voco) to dentin. Materials &amp; Methods: Ninety extracted non-carious, intact human mandibular molar teeth were selected for this study. Each tooth was decoronated using a double-sided diamond disc with water coolant to a depth of 2mm from the cusp tip .The cut dentin surface was then abraded against 600-grit wet silicon carbide papers for 60 seconds to produce a uniform smear layer. The root portion of each tooth was mounted on a plastic ring using cold cure acrylic resin. Specimens were then divided into three adhesive groups of 30 teeth each, Group A: ClearfilSE Bond (Kuraray), Group B: Tetric N Bond Universal (IvoclarVivadent), Group C :Futura Bond DC (Voco). All bonding agents were used according to the manufacturers’ instructions, in combination with the resin composite Tetric N Ceram (IvoclarVivadent). The samples were thermocycled, followed by shear bond strength testing using a Universal testing machine (Hounsfield). Data were subjected to statistical analysis using one-way analysis of variance (ANOVA) (P&lt;0.05) and Post hoc Tukey’s test for inter- and intra- group analysis respectively. Results: Clearfil SE Bond yielded the highest shear bond strength values (30.9 ±4.66 MPa) which were statistically significant, followed byTetric N Bond Universal group (29.8 ±4.34) and the lowest shear bond strength values were recorded for Futura Bond DC (18.2 ±3.13). Conclusion: Clearfil SE bond and Tetric N bond Universal can be considered as better options than Futura Bond DC.

A study on corrosion resistance of ISO 5832-1 austenitic stainless steel used as orthopedic implant

The ISO 5832-1 austenitic stainless steel used as biomaterial is largely applied in the area of orthopedics, especially in the manufacture of implants, such as temporary or permanent replacement of bone structures. The objective of this study was to evaluate the localized corrosion resistance of the ISO 5832-1 stainless steel used in orthopedic implants by electrochemical tests in two different solutions. The results of this study are of great interest to evaluate the corrosion of metallic implants that can result in the release of corrosion products into bodily fluids causing possible adverse biological reactions. The determination of the chemical elements in the composition of the ISO 5832-1 stainless steel was performed by neutron activation analysis (NAA). The samples for electrochemical tests were grinded with silicon carbide paper up to #4000 finishing, followed by mechanical polishing with diamond paste. The open circuit potential measurements and anodic polarization curves were obtained in solution of 0.90 wt. % of NaCl and of simulated body fluid (SBF). The results indicated that the ISO 5832-1 stainless steel presented a high resistance to crevice corrosion in simulated body fluid solution but high susceptibility to this form of corrosion in the chloride solution.&#x0D;

Isothermal Oxidation Behavior of Fe-33Ni-18Cr Alloy in Different Heat Treatment Temperature

This research study describes the influence of different heat treatment temperature on isothermal oxidation of Fe-33Ni-18Cr alloy. The Fe-33Ni-18Cr alloy was undergone heat treatment at three different temperatures, namely 1000 °C, 1100 °C and 1200 °C for 3h soaking time followed by water quench to vary the grain size of the alloy. This alloy was ground by using several grit of silicon carbide papers as well as weighed by using analytical balance and measured by using Vernier caliper before oxidation test. The heat-treated Fe-33Ni-18Cr alloy was isothermally oxidized at 800 °C for 150h. The characterization of oxidized samples was carried out using optical microscope, scanning electron microscope equipped with energy dispersive x-ray (SEM-EDX) and x-ray diffraction (XRD). The results showed that, increasing the heat treatment temperature was increased the average grain size. The kinetics of oxidation followed the parabolic rate law which represents diffusion-controlled oxide growth rate. Fine grain structure of 1000 °C sample shows minimum weight gain and lower oxidation rate compared to samples of 1100 °C and 1200 °C that indicated oxide spallation and porous structure. Besides, phase analysis showed that the oxidized sample formed several oxide phases.

Effect of Heat Treatment on Isothermal Oxidation of Fe-33Ni-18Cr Alloy at 1000°C

This research study was focused on the effect of heat treatment on the isothermal oxidation of Fe-33Ni-18Cr alloy at 1000 °C. The Fe-33Ni-18Cr alloy was undergone heat treatment at three different temperatures, namely 1000 °C, 1100 °C and 1200 °C for 3 hours soaking time followed by water quench to vary the grain size of the alloy. The heat-treated alloys was prepared for further isothermal oxidation test. The heat-treated alloys was ground by using several grit of silicon carbide papers as well as weighed by using analytical balance and measured by using Vernier caliper before the oxidation test. The heat-treated Fe-33Ni-18Cr alloys was isothermally oxidized at 1000 °C for 150 hours exposure time. The characterization of the oxidized samples was carried out using optical microscope and scanning electron microscope (SEM). The heat treatment result shows that, increasing the heat treatment temperature was increased the average grain size of the alloy. The kinetics of oxidation was followed the parabolic rate law which represent the diffusion-controlled oxide growth rate. Fine grain structure of 1000i-1000 sample shows minimum weight gain and lower oxidation rate compared to samples of 1000i-1100 and 1000i-1200. On the other hand, 1000i-1100 and 1000i-1200 samples indicate the formation of oxide spallation and crack propagation on the oxidized surface, respectively.

Mechanical and abrasive wear response of PTFE coated glass fabric composites

The present study evaluates the influence of hybridization on the interlaminar shear and abrasive wear properties of composites manufactured with polytetrafluoroethylene (PTFE) coated glass fabrics. Homogeneous composites were manufactured using two dimensional plain woven (2D), three dimensional knitted (3D) and satin weave (SW) fabrics. Hybrid composites were manufactured with the same fabrics and a steel metal mesh (MM) stacked on the top and bottom of the laminates. The interfacial property was obtained through interlaminar shear strength (ILSS) tests. Abrasive wear tests were performed against a silicon carbide (SiC) paper of grit size 120 μm using a plate on plate apparatus. Loads ranging from 10 N to 50 N were applied at an interval of 10 N with a speed of 10 rad/s. Incorporation of MM influenced the physical properties like thickness, density and void content. Hybridization of homogeneous composites with MM improved the ILSS by 56%, 10% and 18% for 2D, 3D and SW composites, respectively. All the hybrid composites showed better wear performance in terms of coefficient of friction (COF) and specific wear rate (K0). SW and SW-MM composites exhibited better wear performance in all the wear properties as compared to the 2D, 2D-MM, 3D and 3D-MM composites. Scanning electron microscopy (SEM) revealed that the bonding between fibre and matrix could be improved in the case of 2D and 2D-MM composites.

Influence of Surface Finish on Small Punch Testing of 9Cr Eurofer-97 Steel

Abstract This study investigated the effect of surface finish on the deformation behavior of Eurofer-97 steel during room-temperature small punch testing. The surface finish of specimens was varied from coarse to fine (ranging from P240-grit silicon carbide paper to a polished finish using 0.06-μm colloidal silica). Testing was conducted on 8-mm diameter by 0.5-mm-thick disks using a 1-mm-radius punch head. No significant change was observed in the elastic-plastic transition load, maximum load, displacement at maximum load, or displacement at failure. Similarly, in all cases, failure occurred in a ductile manner, yielding a dimpled fracture surface. Although friction and surface defects may influence the output of small punch tests, the effect of altering the specimen surface finish alone was negligible in this case, indicating this is not a dominant factor in small punch testing.

Physical Properties of Nanohybrid and Microhybrid Resin Composites Subjected to an Acidic Environment: A Laboratory Study.

This study investigated the hardness and color stability of five resin composites subjected to different polishing methods following immersion in distilled water or lactic acid for up to three months. Three nanohybrid, Paradigm (3M ESPE), Estelite Sigma Quick (Tokuyama), Ice (SDI), and two microhybrid, Filtek P60 and Filtek Z250, composites were examined. Disc-shaped specimens (10×1.5 mm) were prepared and immersed in distilled water for 24 hours then polished using either silicon carbide paper, the Shofu polishing system or were left unpolished (control). The CIE values and microhardness were determined using a spectrophotometer and digital Vickers hardness tester, respectively (n=10) after one, 45, and 90 days of storage in distilled water or lactic acid. Data were analyzed using analysis of variance, Tukey test, and Pearson correlation coefficient. Ice exhibited the greatest color change, yet Paradigm and Filtek P60 demonstrated the least. Overall, discoloration of tested materials was multifactorial and the effect of storage media depended on the material, polishing method and time interval. The greatest hardness was obtained for Paradigm and the lowest for Estelite. Hardness was found to be significantly higher in lactic acid after 45 days (p=0.014) and even higher after 90 days (p<0.001) compared with distilled water. An acidic environment did not adversely affect color stability or microhardness of the resin composites. There was a significantly mild reverse correlation between hardness and color change in both storage media.

Effect of an Optical Whitening Toothpaste on Color Stability of Tooth-Colored Restorative Materials.

Objectives This study aimed to assess the effect of an optical whitening toothpaste on color stability of microhybrid, nanofilled, and microfilled composite resins and resin-modified glass ionomer (RMGI) cement in comparison of two other toothpastes. Materials and Methods In this experimental study, disc-shaped composite samples were fabricated. The samples were then polished using silicon carbide papers. Twenty-seven samples of each material were fabricated and subjected to colorimetry using a spectrophotometer. Each group of material was then divided into three subgroups for the application of conventional whitening and whitening containing blue covarine toothpastes. One operator brushed the samples with an electric soft toothbrush with circular motion twice a day, each time for 30 seconds. Colorimetry was performed at 0, 1, 7, 30, and 90 days. Statistical Analysis Two-way analysis of variance (ANOVA), one-way ANOVA, and Tukey’s honestly significant difference (HSD) test were used for statistical analysis. Results The interaction effect of type of restorative material and time on ∆E was not significant at baseline or 1 day ( p > 0.05). The effect of type of toothpaste on ∆E was not significant at baseline or 1 day ( p = 0.78) but the effect of type of material was significant ( p < 0.05). The toothpastes had significantly different effects on ∆E of Z250 at all time points ( p < 0.05) except for ∆E0–30 ( p = 0.106). The toothpastes had significantly different effects on ∆E of Z350 and Gradia at all time points ( p < 0.05). The same was true for RMGI except for ∆E0–7 ( p = 0.43) and ∆E0–90 ( p = 0.52). The majority of color changes caused by toothpastes were not clinically perceivable (∆E < 3.3), except for ∆E0–90 by the whitening toothpaste (∆E = 9), ∆E0–90 by the conventional toothpaste for Z350 (∆E = 3.9), and ∆E0–1 by the whitening toothpaste for RMGI (∆E = 3.7). Conclusion The color change of all composite samples was not clinically perceivable (<3.3) at all time points, which shows that the tested toothpastes do not cause a significant change in color of composite materials.