Polishing Discs Research Articles

A Comparative Analysis of Enamel Surface Roughness Following Various Interproximal Reduction Techniques: An Examination Using Scanning Electron Microscopy and Atomic Force Microscopy.

Interproximal enamel reduction (IER) is a minimally invasive therapeutic procedure commonly used in orthodontics to address both functional and aesthetic issues. Its mechanical effects on enamel surfaces induce the formation of grooves, furrows, scratches, depressions, and valleys. The aim of this study was to assess the enamel surface roughness resulting after the application of currently available methods for interproximal reduction. Ninety freshly extracted human teeth were divided into six groups and subjected to the stripping procedure, using a different method for each group (diamond burs, abrasive strips of 90 μm, 60 μm, 40 μm, 15 μm, and abrasive discs). A single individual performed stripping according to the manufacturer's recommendations, involving interproximal reduction on one tooth's proximal face and leaving the other side untreated. Qualitative and quantitative assessment of the enamel surfaces was carried out using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), obtaining 2D and volumetric 3D images of the enamel surface microstructure and nanostructure. The study found that diamond burs and abrasive strips of 60 μm and 90 μm increased enamel roughness due to intense de-structuring effects, while the 40 μm polisher had a gentler effect and 15 μm abrasive strips and polishing discs preserved enamel surface quality and removed natural wear traces.

Influence of Low pH on the Microhardness and Roughness Surface of Dental Composite-A Preliminary Study.

Dental composites are gaining great popularity in restorative dentistry because of their aesthetic appeal and capacity to replicate the natural color of teeth. Nevertheless, their lifespan and durability rely on various factors, such as the polishing technique and the environmental conditions they are exposed to. The study aimed to assess the influence of the method of final polishing of dental composite on the surface roughness and microhardness of materials also considering the environment of different pHs. Disc-shaped samples (5 mm diameter and 2 mm thickness) have been prepared for microhardness and roughness tests from two dental composites: A2 Clearfil Majesty ES 2 Classic and A2D Clearfil Majesty Premium. One-third of samples were polished with polishing discs, OptiDisc, another one-third of samples were polished with Eve Diacomp Twist rubbers and polishing brush with diamond particles, and rest of the samples were stored without any polishing (the control group). Tested materials were incubated in distilled water or acidic buffer (pH = 2) for 3 weeks at a temperature of 37 °C. No statistically significant differences were found for roughness for the two materials tested after incubation in liquids. A decrease in Vicker microhardness was found for Clearfil Majesty ES 2 Classic after soaking in a low pH liquid, and no such relationship was found for Clearfil Majesty Premium. The improved resistance of these materials to the negative oral environment may result in the longer survival of composite restorations in patients with poor diet or diseases, causing a decrease in oral pH.

Color Stability and Surface Roughness of Different Composite Resins after Using Different Polishing Systems.

Background and objectives: To evaluate and compare the color stability and surface roughness of different composite resins after using different polishing systems and then submitting to accelerating artificial aging (AAA) and staining by black tea. Method: Twenty disk-shaped specimens (were compacted into the custom-made cylindrical plastic mold that had an internal diameter of 10 mm and a depth of 2 mm) were prepared for each composite resin type (3M Z350, Tokoyama palfique and shofu Beautifil II) for a total of 60 specimens, each composite group was divided into two subgroups according to the polishing system (n=10) (Shofu super-snap polishing disks and Eve Diacomp Plus Twist wheel). Color parameters (L*, a*, and b*) and surface roughness were measured before and after accelerating artificial aging (2000-4000 thermal cycle) and staining. Results: It was observed that all resin-based materials showed an increase in color change value and surface roughness values after 2000 thermal cycles. while after 4000 thermal cycles only the surface roughness value decreased in all resin-based materials. Conclusion: all resin-based materials showed clinically acceptable color stability and surface roughness >0.2 µm) after (2000 thermal cycle) and staining. Keywords: color stability, surface roughness, thermal cycle, staining.

Effect of rotation frequency of polishing discs on the surface roughness of resin composite material.

The aim of this study was to evaluate the effect of rotation frequency (rpm) of different polishing discs on the surface roughness of a nanohybrid resin composite material. 126 specimens were prepared in metal molds of 10 mm diameter and 2 mm depth using a nanohybrid resin composite material. The prepared specimens were kept in distilled water for 24 hours. Polishing treatments at 5k, 10k, 15k, and 20k rpm were applied to the nanohybrid resin composite material by grouping different brand polishing discs: Sof-Lex Contouring and Polishing Discs (3M Espe, USA) (3M Group), Optidisc (Kerr Corporation, USA) (Kerr Group), Super-Snap Rainbow Technique Kit (Shofu Dental, Japan) (Shofu Group), Finishing Disc (Bisco Dental, USA) (Bisco Group). The surface roughness was evaluated at three different points by atomic force microscopy for all specimens and scanning electron microscopy was used for visual assessment. Data were evaluated by Two Way ANOVA and Tukey's HSD Test. The mean surface roughness (Ra, μm) of all prepared samples showed significant differences (α = 0.05). According to Two-Way ANOVA, there is a statistically significant relationship between the rpm values and the discs. The 3M group showed the highest roughness value at all rpm speeds. Shofu group at 15k, 20k rpm, Bisco group at 10k, 15k, 20k rpm, the Kerr group at 15k, 20k rpm showed the lowest roughness value and had roughness close to the surfaces finished with a mylar strip. The smoothest surfaces were obtained at 15k rpm, even though polishing discs from different brands were used. It was also observed that 5k and 20k rpm polishing speeds can increase the surface roughness of the nanohybrid resin composite material.

Fabrication and Polishing Performance of Diamond Self-Sharpening Gel Polishing Disk.

A diamond gel polishing disk with self-sharpening ability is proposed to solve the problem of glazing phenomenon in the gel polishing disks. Aluminum nitride (AlN) powder with silica sol film coating (A/S powder) is added to the polishing disk, and a specific solution is used to dissolve the A/S powder during polishing, forming a pore structure on the polishing disk. To realize the self-sharpening process, the dissolution property of the A/S powder is analyzed. The effect of A/S powder content on the friction and wear performance and the polishing performance of 4H-SiC wafers are investigated. Results showed that the friction coefficient of the polishing disk with 9 wt% A/S powder content is the most stable. The surface roughness Ra of 2.25 nm can be achieved, and there is no obvious glazing phenomenon on the polishing disk after polishing. The surface roughness of the 4H-SiC wafer is reduced by 38.8% compared with that of the polishing disk with no A/S powder addition after rough polishing, and the 4H-SiC wafer then obtained a damage-free surface with a Ra less than 0.4 nm after fine polishing by chemical mechanical polishing (CMP).

The Effect of Usage of Antiasthmatic Inhalers on Color Stability and Surface Roughness of Dental Restorative Materials: An In Vitro Study.

Increased demand for esthetics by parents and children has resulted in the use of tooth-colored restorative materials. Children with chronic respiratory conditions like asthma use inhalers which have shown to affect the surface of restorative materials. Hence, the aim of the present study was to evaluate the effect of antiasthmatic inhalers on color stability and surface roughness of three restorative materials. Forty samples each of three dental restorative materials: group A: glass ionomer cement (GIC), group B: alkasite restorative material, and group C: composite resins were prepared. Each group was further divided into two subgroups of 20 samples each according to the inhaler used. All the specimens were polished using polishing discs and stored in artificial saliva in order to simulate the oral environment. The baseline color value and surface roughness of all the samples were measured using a spectrophotometer and a profilometer, respectively. Group 1 and group 2 were exposed to 0.31 mg of salbutamol sulfate and 20 mg formoterol fumarate in combination with budesonide, respectively, for every 12 hours, for a period of 15 days following which the samples were evaluated for color changes and surface roughness. The data obtained was subjected to statistical analysis and level of significance was set at p < 0.05. Exposure to both the inhalers caused a change in color and surface roughness in all three restorative materials. There was a significant change in the color of GIC and composite resin (ΔE > 3.3), following exposure to both the inhalers (p < 0.05). The change in color of alkasite restorative material was not significant. A significant increase in the surface roughness of composite resin from 0.56 ± 0.14 to 0.67 ± 0.19 was seen following 15 days' exposure to formoterol in combination with budesonide inhaler (p < 0.05). Following exposure, both the inhalers had an equal effect on color and surface roughness of all three restorative materials. Alkasite restorative material showed greater resistance to change in color and surface roughness when exposed to antiasthmatic inhalers, compared to GIC and composite resin. Thus, children who use inhalers and nebulizers should be advised to implement more precautionary oral hygiene measures and periodic dental visits.

AL-ProMP: Force-relevant skills learning and generalization method for robotic polishing

Skill learning in robot polishing is gaining attention and becoming a hot issue. Current studies on skill learning in robot polishing are mainly about trajectory skills, and force-relevant skills learning models are less studied. A skill learning method with good generalization and robustness is one of the elements worth investigating. In this study, a force-relevant skills learning method called arc-length probabilistic movement primitives (AL-ProMP) is proposed to improve the efficiency of robot polishing force planning. AL-ProMP learns the mapping between the contact force and polishing trajectory, and the temporal scaling factor and force scaling factor in AL-ProMP enable better robustness of force planning in speed scaling tasks and polishing tasks in different scenarios. Speed scaling is an important property for adaptation of the polishing policy. For the generalization of polishing skills to different polishing tools in robotics disc polishing tasks of unknown geometric model workpieces, a novel force scaling factor for different polishing discs is proposed according to the contact force model. In addition, polishing contact position learning provides the basis for polishing trajectory generalization. Finally, it is experimentally verified that the proposed method is effective in learning and generalizing the demonstrated skills and improving the polishing surface quality of the workpiece with unknown geometric model.

Analysis of nano grinding removal mechanism of 3C-SiC material under the coupling action of double abrasive grains

In order to study the influence mechanism of coupling effect on 3C-SiC material removal process under nanometer conditions, the repeated scratches of different abrasive grains, machined surface morphology, dislocation distribution, grinding force and abrasive wear were analyzed by molecular dynamics method, and the geometric characteristics and damage distribution of machined surface under the coupling effect of dual abrasive grains, as well as the influence rule of coupling effect on surface/subsurface characteristics were obtained. This study is of great significance to understand the mechanism of 3C-SiC removal in nano-scale grinding process, and is helpful to guide the preparation of fixed abrasive polishing discs.

Unilateral peg-shaped mandibular central incisor and direct composite resin treatment: A case report

Aim: This case report describes the restorative treatment process of a non-syndromic unilateral peg-shaped left mandibular central incisor. Case presentation: A 23-year-old female patient was admitted for aesthetic concerns related to the appearance of the anterior mandible and a peg-shaped incisor. The color selection was done on clean, hydrated teeth. The teeth were roughened with a minimal red belt bur, a 37% phosphoric acid gel was applied to the enamel for 30 seconds, and the teeth were washed with water for 30 seconds to remove the acid agent. Following the application of a universal adhesive to the surface according to the manufacturer’s instructions, the palatal and proximal walls were formed using a mylar strip and an A2B-colored resin composite. Then, polymerization of the restoration was completed using an incremental layering technique. After the removal of any excess restoration, low-speed finishing and polishing were done using aluminum oxide and flexible rubber polishing disks containing diamond particles. After the resin application, the treatment was completed. Conclusion: To achieve optimal results in the treatment of patients, restorative treatment can be recommended, considering the position and condition of the tooth. When choosing the most appropriate treatment for a patient, the advantages and limitations of each technique should be carefully explained, and the most conservative treatment should be recommended. How to cite this article: Fidan M. Unilateral peg-shaped mandibular central incisor and direct composite resin treatment: A case report. Int Dent Res 2023;13(1):44-47. https://doi.org/10.5577/idr.2023.vol13.no1.7 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Assessment of color stability of shade less composite resin: an in-vitro study

Objective: This study aimed to assess the color stability of omnichroma composite resin after immersion in coffee, cola and iced tea. Methods: A total of 30-disc shape specimens of omnichroma, 10mm diameter and 2mm thickness, were made in a Teflon mold. The samples were washed and stored in artificial saliva for 24 hours in a 37&amp;#xb0;C incubator. The top surfaces of specimens were polished with polishing disks (Sof-lex; 3M ESPE). Samples were divided randomly into 3 groups, and each group contained 10 discs. Groups were immersed in 15 ml of 3 different storage media (cola, iced tea and black coffee). Immersion groups were stored in an incubator at 37 &amp;#xb0;C. Color assessment was carried out by VITA Easy shade 2.0 spectrophotometer color assessment device according to the CIE L*a*b*system, against a gray background to measure baseline records for the samples. After 4 weeks, a second record was taken for the samples after they were gently rinsed with distilled water and dried. The experimental data were statistically evaluated using the Wilcoxon sign rank test with a significance level &amp;lt; 0.05%. Results: The highest color change was reported with coffee (ΔE=20.16) followed by cola (ΔE=19.6) and iced tea (ΔE=4.75). Conclusion: All assessed drinks resulted in discoloration of the shade less composite resin material above the clinically acceptable level (ΔE&amp;gt;3.3) after 30 days of immersion. Coffee has the highest staining among the three drinks, followed by cola, and then iced tea.

Investigation of the coloring effects of different ground-based coffee types on composite resin materials

Aim: The aim of this study is to investigate the effect of different ground-based coffee types on the color change of nanohybrid and bulk-fill composites. Methodology: A total of 80 disk-shaped samples were made using Teflon molds (5 mm in diameter and 8 mm thick) and two types of A2 resin with nanohybrid (Tetric N Ceram Ivoclar Vivadent, Schaan, Liechtenstein) and bulk-fill (Filtek Bulk-Fill, 3M ESPE, St. Paul, MN, USA) structures. All samples were finished and polished with four-stage (thick, medium, fine, and superfine) polishing disks (Sof-lex, 3M ESPE, St. Paul, MN, USA) and kept at 37°C for 24 hours. Color measurements of the samples were performed using a spectrophotometer (Vita Easy Shade, Vita ZahnFabrik, Bad Sackingen, Germany) and were divided into subgroups: the control group, filter coffee, Turkish coffee, espresso, and Mırra (n = 8). Distilled water was used as a control. Prepared coffees were added to the microcentrifuge tubes and refreshed daily during the 14-day exposure period. ΔE values were calculated for each material. Statistical analyses were performed using one-way variance analysis and Tukey multiple comparisons (p = 0.05). Results: There was no significant color change for either the nano-fill or bulk-fill composite groups in the control group samples (p&gt;0.05). Filter coffee was found to be the most effective colorant coffee type for both composites (p &lt; 0.05). Among the coffee types, Mırra caused the least coloration for both composites. Conclusion: The consumption of two or more cups of coffee per day, especially filter coffee, can cause color changes in both conventional and bulk-fill composites, and it should be considered an important factor in aesthetic problems with dental restorations. How to cite this article: Erdoğdu M, Tunçdemir MT, Güntekin N. Investigation of the coloring effects of different ground-based coffee types on composite resin materials. Int Dent Res 2022;12(Suppl.1):16-21. https://doi.org/10.5577/intdentres.448 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

The effect of different herbal teas on the color stability of nanohybrid and bulk-fill composites

Aim: The aim of this study is to investigate the effects of green tea and rosehip tea, on the color stability of nanohybrid and bulk-fill composite resins. Methodology: A total of 60 disc-shaped samples were made from two types of A2 resin with nanohybrid (Tetric N Ceram, Ivoclar Vivadent, Schaan, Liechtenstein) and bulk-fill (Filtek Bulk-Fill, 3M ESPE, MN, USA) structure with the help of 10 mm diameter and 2 mm thick Teflon molds in this study. All samples were finished and polished with 4-stage (thick, medium, fine, superfine) polishing discs (Sof-lex, 3M ESPE, MN, USA) and kept in an oven at 37 °C for 24 hours. The samples, whose initial color measurements were made by spectrophotometer, were divided into subgroups for the control group and two different herbal teas (Green tea, Rosehip) (n=10). Color measurements were repeated, and ΔE values were calculated. Wilcoxon, Kruskal-Wallis, and Bonferroni tests were used to analyze the data (p &lt; 0.05). Results: There was no statistically significant difference in color change between the composite resins (p &gt; 0.05). No significant color change was found for either the Tetric N-Ceram or Filtek Bulk-Fill composite resin samples immersed in distilled water (p &gt; 0.05, ΔE&lt;3.3). Conclusion: Rosehip and green tea affect the color stability of composite resin restorations. Whereas the color change caused by green tea is at a clinically acceptable level, that stemming from rosehip tea falls within clinically unacceptable levels. How to cite this article: Tunçdemir MT, Dereli Z, Bahar A. The effect of different herbal teas on the color stability of nanohybrid and bulk-fill composites. Int Dent Res 2022;12(Suppl.1):103-7. https://doi.org/10.5577/intdentres.445 Linguistic Revision: The English in this manuscript has been checked by at least two professional editors, both native speakers of English.

Effect of Different Surface Finishing Procedures on Color Stability of Leucite-reinforced Feldspathic CAD-CAM Ceramic

Statement of the problem: The color stability of newly introduced leucite- reinforced feldspathic CAD-CAM ceramic with different surface treatments remains unclear. Objective: This in-vitro study aimed to examine the effect of different surface finishing procedures on the color stability of leucite-reinforced feldspathic CAD-CAM ceramic. Materials &amp; Methods: Twenty-four monochromatic, leucite-reinforced, A2-shaded feldspathic ceramic specimens prepared in 1 mm thickness. The specimens were randomly divided into 3 groups according to their surface finishing methods (n=8): a control group without surface finishing (Group C), surface finishing with polishing discs (Sof-Lex, 3M ESPE), and surface finishing with glaze (Group G). All the specimens were immersed in a coffee solution and kept in an incubator at 37 °C for 14 days. Initial color measurements were made with a digital spectrophotometer and the Commission Internationale de l'Eclairage (CIE) L*a*b* values were recorded. The color measurements were repeated at the ends of the 1st, 3rd, 7th, and 14th days with the spectrophotometer under the same conditions. The color change of the specimens was calculated with the CIEDE2000 (ΔE00) formula. Statistical analysis of the data was performed with a two-way mixed ANOVA and Bonferroni post-hoc tests (α=0.05). Results: Time and surface finishing procedures caused statistically significant color changes in the specimens (P&lt;0.05). However, the interaction of time and surface finishing was not statistically significant (P&gt;0.05). The lowest mean ΔE00 value was observed in Group G on day 14 (0.93 ± 0.74); the highest mean ΔE00 value was found in Group P on the 3rd and 14th days (2.16 ± 0.72). While the C and G groups exhibited similar color change values, Group P caused higher ΔE00 values compared to the glaze application (P&lt;0.05). Conclusions: Based on the findings of this study, glaze application led to less color change compared with disk polishing. Glazing can be preferred to polishing to ensure long-term color stability in leucite-reinforced feldspathic ceramics.

Influence of the Scalpel Finishing Technique on Marginal Gap Formation in Class II Resin Composite Restorations.

Modern adhesives and composites allow the restoration of deep defects. In such cases, the matrix technique is particularly challenging, and excess composite is a common problem. Removing such overhangs with a scalpel has already been described as a substance preserving or selective finishing technique. Clinically, restoration margins may appear as a white line after scalpel finishing, and it is unclear whether this line represents a marginal gap and/or whether scalpel finishing promotes marginal gap formation. Therefore, the aim of this study was to investigate the influence of scalpel finishing of deep Class II composite restorations on marginal gap formation. Standardized mesioocclusal-distal (MOD) cavities were prepared and restored in 60 human molars randomly divided into six finishing protocol groups: G1, scalpels (SC); G2, oscillating files (OF); G3, finishing strips (FS); G4, scalpels and finishing strips (SC+FS); G5, scalpels and polishing discs (SC+PD); G6, polishing discs alone (PD, controls). The groups were additionally assigned to finishing and polishing in a phantom head (groups 1-4) or hand-held setting (groups 5-6) to simulate clinical and in-vitro research conditions, respectively. After restoration, artificial aging was performed by thermocycling (5-55°C, 2500 cycles) and mechanical loading (50 newtons (N) with 500,000 cycles) prior to scanning electron microscopy analysis of proximal restoration margin quality on the mesial and distal surfaces (n=120) of each tooth. Outcomes (perfect margin, marginal gap, overhang, marginal fracture) were statistically analyzed by t-test, Mann-Whitney U test, single-factor analysis of variance, post-hoc t-test, Kruskal-Wallis test and Dunn-Bonferroni correction for multiple group comparisons. Cohen's effect size d(Cohen) was calculated to show the strength of the relationship between variables. Overall, marginal quality was significantly better in the hand-held setting (SC+PD and PD) than the phantom head setting (SC, OF, FS, SC+FS). The best marginal quality was achieved with oscillating files in the phantom head setting and with scalpels plus polishing discs in the hand-held setting. Marginal gaps occurred significantly more often with scalpels, but the proportion of gaps was very low and clinically insignificant. Finishing strips were the least effective instruments for removing overhangs but performed better in combination with scalpels. Scalpel finishing can effectively and gently remove overhangs from enamel. However, blades should be used with caution as they can cut the dentin and cementum. Scalpel finishing does not lead to a clinically relevant increase in marginal gaps, but should be followed by polishing, whenever possible, to eliminate any marginal fractures that might be present.

Chemical mechanical polishing exploiting metal electrochemical corrosion of single-crystal SiC

A chemical mechanical polishing (CMP) method of single-crystal SiC is proposed based on metal electrochemical corrosion. The oxidation mechanism of SiC by electrochemical corrosion of metals and the mechanism of surface material removal are revealed by corrosion and polishing experiments. The metallic aluminum sheet that is in contact with single-crystal SiC was immersed in sodium sulfate (Na2SO4) electrolyte solution, and the morphological and elemental changes of single-crystal SiC surface were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Then, polishing experiments were conducted on single-crystal SiC using different metal polishing discs and different polishing solutions. The XPS and EDS results show that single-crystal SiC can electrochemically corrode to generate a silica reaction layer. The use of metal polishing discs in CMP significantly improved the material removal rate (MRR) of SiC, with the highest MRR of 1011.43 nm/h for aluminum polishing discs, followed by that for iron polishing discs, and the lowest MRR for copper and alumina ceramic polishing discs. When metal polishing discs were used, the addition of electrolyte solution significantly improved the MRR and reduced the surface roughness of the SiC surface. Polishing with Na2SO4 solution when the polishing disc was aluminum disc, the MRR was higher than that for using deionized water by 105%, and the surface roughness Ra decreased by 37.8% to 2.8 nm. The metal electrochemical corrosion reaction can promote the oxidation of single-crystal SiC and generate a soft SiO2 reaction layer on the SiC surface, thereby improving the polishing efficiency of single-crystal SiC.

Simulation and experimental research on magnetorheological finishing under dynamic pressure with a gap-varying

Magnetorheological finishing (MRF) is a novel machining method used to obtain ultra-smooth and even surfaces. To improve the material removal rate (MRR) while attaining smooth and undamaged surfaces, an MRF method with a varying machining gap between the polishing disks and workpieces is proposed to increase the polishing efficiency and improve the surface quality. According to the computational fluid dynamics (CFD) method, the behaviors of MRF fluids under the effect of magnetic fields are measured using a rheometer. Furthermore, a simulation model for fluids based on the gap-varying MRF is established to evaluate the influence of the varying machining gap on the behaviors of the flow field of MRF fluids. The results show that the flow field formed during gap-varying MRF presents a periodic dynamic change and formation of turbulence. Both the fluid pressure and velocity on the workpiece surface show a periodic change and the maximum fluid velocity on the workpiece surface in the x-direction is much greater than that in the z-direction; the transverse shear velocity contributes to the material removal and abrasive update. Under the same polishing time and rotational speed, the surface roughness is reduced from Ra 6.36 nm to Ra 0.155 nm after MRF without varying gaps for 5 h; in contrast, the surface roughness decreases from Ra 6.44 nm to Ra 0.104 nm after MRF with a varying gap, attaining an atomic step-structure. Properly increasing the frequency and amplitude of gap variations is conducive to achieving a better polishing effect. By conducting real-time force measurement and establishing a material removal function, it is shown that the simulation results match the test results. MRF with a varying gap can increase the polishing efficiency and surface quality by changing the behaviors of the flow field.

The Effect of Different Abrasives on the Shear Bond Strength of Adhesive Resin Cements to Dentin

Aim: The aim of this study was to evaluate the influence of dentin surface preparation with coarse diamond, extra-fine diamond, and polishing discs on the shear bond strength (SBS) of two resin cements (RCs) to dentin. Materials and Methods: Sixty-six recently extracted human mandibular third molar teeth that were free of cracks, caries, or restorations were collected. Sixty teeth were used for the SBS test. The occlusal part of the crowns was cut to expose mid-coronal dentin. The teeth were divided into three dentin preparation groups: coarse diamond (Meisinger, Germany), extra-fine diamond, and polishing discs (SofLex, 3MESPE, USA), and further conventional RC combined with a self-etch adhesive (Panavia F2.0/ED Primer II, Kuraray, Japan) or self-adhesive RC (Maxcem Elite, Kerr, USA) subgroups ( n = 10). Sixty composite resin blocks were prepared (diameter: 3 mm, height: 4 mm) and bonded to the teeth according to the groups. The SBS test was performed with a universal testing device. Six teeth were used for the observation of prepared dentin surfaces and the resin–cement dentin interfaces using field emission scanning electron microscopy (Mira 3 XMU, Tescan). Statistical analyses were performed using the Mann–Whitney U and Kruskal–Wallis tests ( P &lt; .05). Results: Panavia F2.0/ED Primer II exhibited significantly higher SBS values for coarse and extra-fine diamond than for the polishing discs ( P &lt;.05). Regarding Maxcem Elite, no significant difference was observed for the preparation methods ( P &gt; .05). Panavia F2.0/ED Primer II had higher bond strength than Maxcem Elite for the dentin surface prepared with the coarse diamond ( P &lt;.05). The differences were not significant for the extra-fine diamond and the polishing disc groups ( P &gt; .05). Conclusion: The use of polishing discs did not increase the SBS of the RCs to the dentin.

FINISHING OF COMPOSITE RESTORATIONS OF TEETH. COMPARATIVE CHARACTERISTICS OF POLISHING SYSTEMS

Abstract. As you know, one of the most important stages in the aesthetic restoration of teeth is its finishing, which means grinding and polishing to a “dry shine”. When carrying out restoration work by a dentist, light-curing composite filling materials are used. However, the fact that different materials at the final stage are completely polished differently is rarely taken into account. The aim of the study is to achieve a “dry gloss” of restorations from the most popular composite materials with prepolymerized inclusions from the composite itself, as well as a subsequent comparative analysis of the results. A laboratory study was carried out aimed at determining the polishing properties of composite materials, and a technique for evaluating the polishing of composite materials with prepolymerized inclusions was also developed for subsequent comparison. Polishing discs, polishing rubber heads, brushes with polishing paste were used. First, the sample of the composite material was polished with all polishing discs in the manner prescribed by the manufacturer. If a “dry sheen” was achieved as a result of polishing, then the polishing was considered successful. If this effect was not achieved, the following polishing agent was used. The steps were repeated until the desired result was achieved. A microscopic examination of four composite materials before and after polishing was carried out to compare the results. The data obtained are summarized in a single table. It has been found that different composite materials are polished in one step or in multiple steps to achieve a "dry sheen". Each composite material requires different forces and the use of different systems and tools, which is important for timing when taking a patient.

Effect of surface sealants on color stability of different resin composites

The aim was to assess the effect of surface sealants on the color stability of different composite materials. 120 samples were prepared using Filtek Ultimate (3M, USA), Charisma Topaz (Kulzer, Germany), and Clearfil Majesty Es-2 Premium (Kuraray Noritake, Japan) composites. The samples were polished with polishing discs and divided by test groups (n=10 for each), regarding the sealant used; Permaseal (Ultradent Products, USA), Biscover LV (Bisco, USA), Optiglaze Clear (GC Corp., Japan) and control. The samples were discolored for 144 hours in coffee solution at constant 37ºC, renewing daily. Color measurements were performed at the baseline, following the sealant application, and after discoloration procedure, using a spectrophotometer (EasyShade 5, Vita-Zahnfabrik, Germany). The collected L*C*h* coordinates were converted to corresponding L*a*b* coordinates and the color changes (ΔE) were calculated. All the sealants presented perceptible (>1.2) and unacceptable (>2.7) color changes. Biscover LV presented the lowest ΔE among all sealants (p<0.001). The highest ΔE was observed for Permaseal (p<0.001). Color changes for Optiglaze and control groups were similar (p≥0.05). Filtek Ultimate presented the highest color stability (p<0.001), followed by Charisma Topaz and Clearfil Majesty. The combination of Filtek Ultimate with Biscover LV was considered to have the highest color stability, whereas the combination of Clearfil Majesty with Permaseal was considered the lowest, among all. Experimented sealants were considered relatively effective on color stability of resin composites depending on the type of the sealant and the composite material. However, the use of surface sealants may not be advantageous every time. Biscover LV have inhibited the level of discoloration, whereas Permaseal had an increasing effect generally.

An ultra-smooth planarization method for controlling fluid behavior in cluster magnetorheological finishing based on computational fluid dynamics

The machining method for controlling the behavior of Bingham fluids in cluster magnetorheological finishing (MRF) is a novel ultra-smooth planarization method. It is necessary to simulate cluster MRF fluid state during machining to optimize the surface microstructures on the polishing disk. The behavior of MRF fluids in a magnetic field is determined by using a rheometer. On this basis, a simulation model is established for fluids during the machining for controlling the behavior of Bingham fluids in cluster MRF pads using the computational fluid dynamics (CFD). The influences of different surface microstructures on polishing disks on the magnetic flux density modulus, size of polishing pads, fluid velocity, and fluid pressure are studied. Surface microstructures on the polishing disk can increase the magnetic flux density modulus, decrease fluid velocity, and increase fluid pressure, and can enhance the polishing effect of soft abrasives. In addition, these surface microstructures reduce slip between the polishing pads and the polishing disk, thus slowing the wear of the polishing disk. Simulation results show that the polishing disk with micro-holes demonstrates the largest magnetic flux density modulus and forms the most extensive polishing pressure. Polishing tests are conducted using sapphire wafers with a diameter of two inches (50 mm) as workpieces. Compared with using a smooth polishing disk, the material removal rate (MRR) is 68.4% higher, while the roughness Ra and peak-to-valley (PV) values are decreased by 34.1% and 75% when using the polishing disk with micro-holes. The test results match the simulation results arising from the use of the model.