Search Results (185)

The 7075-T7451 aluminum alloy, widely used in aerospace, aviation, and automotive fields for critical load-bearing components due to its excellent mechanical properties, suffers from residual stresses induced by thermo-mechanical coupling during milling, which deteriorate workpiece performance. This study explores how key milling parameters—spindle speed *n_c*, feed per tooth *f_z*, cutting depth *a_p*, and cutting width *a_e*—affect surface residual stress and cutting force via orthogonal experiments and finite element analysis (FEA). Results show *a_e* is critical for X-direction residual stresses, while *f_z* dominates Y-direction ones. Cutting force increases with *f_z*, *a_p*, and *a_e* but decreases with higher *n_c*. Multivariate regression-based prediction models for residual stress and cutting force were established, which effectively characterize parameter–response relationships with maximum prediction errors of 18.69% (residual stress) and 12.27% (cutting force), showing good engineering applicability. The findings provide theoretical and experimental foundations for multi-parameter optimization in aluminum alloy milling and residual stress/cutting force control, with satisfactory practical effectiveness. Full article

This study evaluated the physicochemical and morphological properties of tooth enamel in patients with caries-predisposing SNPs (rs4694075 in AMBN and rs2337359 in TUFT1 genes), based on the DMFT index. We included 40 of 120 individuals (aged 19–43), collecting stimulated saliva and 58 healthy teeth extracted for orthodontic/surgical reasons. Saliva DNA was genotyped. Enamel properties were assessed using Vickers microhardness, deposition thickness, and calcium content. Genotype and allele frequencies aligned with the literature. The TUFT1C/C genotype subgroup showed a significantly higher DMFT index (p = 0.03) compared to the T/T genotype, while AMBN showed no such correlation. Calcium content, microhardness, and enamel thickness were similar across all polymorphic variants of both genes. A statistically significant correlation (p = 0.003) was found between reduced enamel calcium content and a higher DMFT index. Despite existing literature on the subject, the studied SNPs did not reflect any correlation with morphological or physicochemical changes in enamel. The above results suggest that genetic variability identifies patients classified by dentists as being at higher risk of caries, even though these patients follow a non-cariogenic diet and adhere to a hygiene regime. As no structural or physicochemical changes in the enamel of this group were observed, the potential cause may be disturbances in the remineralisation mechanisms or enamel surface properties that promote biofilm adhesion in polymorphic patients. Intensive tooth calcification control algorithms using LIF and RVG, as well as remineralisation cycles to increase hydroxyapatite saturation with calcium phosphates and bioadhesive fluoride delivery systems for long-term biofilm control, are used to more effectively prevent or slow down the progression of caries. Full article

Background: Attachments are essential components in clear aligner therapy, enhancing retention and improving the predictability of tooth movements. Mechanical and wear properties of the composite resins used for attachment reproduction are critical to maintaining their integrity and shape over time. This study aimed to evaluate and compare the mechanical properties, thermal behavior, and wear performance of the hybrid composite Aligner Connect (AC) and the flowable resin (Connect Flow, CF). Methods: Twenty samples (ten AC and ten CF) were reproduced. All specimens underwent differential scanning calorimetry (DSC), combustion analysis, flat instrumented indentation, compression stress relaxation tests, and tribological analysis. A 3D wear profile reconstruction was performed to assess wear surfaces. Results: DSC and combustion analyses revealed distinct thermal transitions, with CF showing significantly lower Tg values (103.8 °C/81.4 °C) than AC (110.8 °C/89.6 °C) and lower residual mass after combustion (23% vs. 61%), reflecting reduced filler content and greater polymer mobility. AC exhibited superior mechanical properties, with higher maximum load (585.9 ± 22.36 N) and elastic modulus (231.5 ± 9.1 MPa) than CF (290.2 ± 5.52 N; 156 ± 10.5 MPa). Stress relaxation decrease was less pronounced in AC (18 ± 4%) than in CF (20 ± 4%). AC also showed a significantly higher friction coefficient (0.62 ± 0.060) than CF (0.55 ± 0.095), along with greater wear volume (0.012 ± 0.0055 mm³ vs. 0.0070 ± 0.0083 mm³) and maximum depth (36.88 ± 3.642 µm vs. 17.91 ± 3.387 µm). Surface roughness before wear was higher for AC (Ra, 0.577 ± 0.035 µm; Rt, 4.369 ± 0.521 µm) than for CF (Ra, 0.337 ± 0.070 µm; Rt, 2.862 ± 0.549 µm). After wear tests, roughness values converged (Ra, 0.247 ± 0.036 µm for AC; Ra, 0.236 ± 0.019 µm for CF) indicating smoothened and similar surfaces for both composites. Conclusions: The hybrid nanocomposite demonstrated greater properties in terms of stiffness, load-bearing capacity, and structural integrity when compared with flowable resin. Its use may ensure more durable attachment integrity and improved aligner–tooth interface performance over time. Full article

Background: The rising demand for aesthetic dental treatments has spurred interest in peroxide-free color correctors as alternatives to traditional hydrogen peroxide formulations, which are associated with tooth sensitivity and potential enamel demineralization. This systematic review evaluates the whitening efficacy and safety profile of hydrogen peroxide-free color corrector (HPFCC) products, focusing on color change metrics, enamel and dentin integrity, and adverse effects. Methods: Following PRISMA guidelines, we searched PubMed, Scopus, and Web of Science throughout January 2025 for randomized controlled trials, observational studies, and in vitro experiments comparing HPFCC to placebo or peroxide-based agents. The data extraction covered study design, sample characteristics, intervention details, shade improvement (ΔE00 or CIE Lab), enamel/dentin mechanical properties (microhardness, roughness, elastic modulus), and incidence of sensitivity or tissue irritation. Risk of bias was assessed using the Cochrane tool for clinical studies and the QUIN tool for in vitro research. Results: Six studies (n = 20–80 samples or subjects) met the inclusion criteria. In vitro, HPFCC achieved mean ΔE00 values of 3.5 (bovine incisors; n = 80) and 2.8 (human molars; n = 20), versus up to 8.9 for carbamide peroxide (p < 0.01). Across studies, HPFCC achieved a mean ΔE00 of 2.8–3.5 surpassing the perceptibility threshold of 2.7 and approaching the clinical acceptability benchmark of 3.3. Surface microhardness increased by 12.9 ± 11.7 VHN with HPFCC (p < 0.001), and ultramicrohardness rose by 110 VHN over 56 days in prolonged use studies. No significant enamel erosion or dentin roughness changes were observed, and the sensitivity incidence remained below 3%. Conclusions: These findings derive from one clinical trial (n = 60) and five in vitro studies (n = 20–80), encompassing violet-pigment serums and gels with differing concentrations. Due to heterogeneity in designs, formulations, and outcome measures, we conducted a narrative synthesis rather than a meta-analysis. Although HPFCC ΔE00 values were lower than those of carbamide peroxide, they consistently exceeded perceptibility thresholds while maintaining enamel integrity and causing sensitivity in fewer than 3% of subjects, supporting HPFCCs as moderate but safe alternatives for young patients. Full article

An analysis of the working surfaces of cylindrical gears after scuffing shock tests allowed for the assessment of the effect of loading conditions on the form of damage to the tooth surfaces. Unlike the method of scuffing under severe conditions, where loading is applied gradually, the presented tests employed direct maximum loading—shock loading—without prior lapping of the gears under lower loads. This loading method significantly increases the vulnerability of the analyzed components to scuffing, enabling an evaluation of their limit in terms of operational properties. To identify the changes and the types of the teeth’s working surface damage, the following microscopy techniques were applied: scanning electron microscopy (FE-SEM) with EDS microanalyzer, optical interferential profilometry (WLI), atomic force microscope (AFM), and optical microscopy. The results allowed us to define the characteristic damage mechanisms and assess the efficiency of the applied DLC coatings when it comes to resistance to scuffing in shock scuffing conditions. Tribological tests were performed by means of an FZG T-12U gear test rig in a power circulating system to test cylindrical gear scuffing. The gears were made from 18CrNiMo7-6 steel and 35CrMnSiA nano-bainitic steel and coated with W-DLC/CrN. Full article

With engineering plastics increasingly replacing traditional materials in various drive and control gear systems across numerous industrial sectors, material selection for any gearwheel critically impacts its mechanical and thermal properties. This paper investigates the engagement of steel and Polyvinylidene Fluoride (PVDF) gear pairs tested under several load conditions to determine polymer gears’ characteristic service life and failure modes. Furthermore, recognizing that the application of polymer gears is limited by insufficient data on their temperature-dependent mechanical properties, this study establishes a correlation between the tribological contact, meshing temperatures, and wear coefficients of PVDF gears. The results demonstrate that the flank surface wear of the PVDF gears is directly proportional to the temperature and load level of the tested gears. Several distinct load-induced failure modes have been detected and categorized into three groups: abrasive wear resulting from the hardness disparity between the engaging surfaces, thermal failure caused by heat accumulation at higher load levels, and tooth fracture occurring due to stiffness changes induced by the compromised tooth cross-section after numerous operating cycles at a specific wear rate. Full article

Fixed orthodontic appliances, which are cemented to tooth surfaces, complicate the maintenance of oral hygiene and create a rough surface that is favorable for bacteria attachment. Additionally, the presence of orthodontic appliances may conceive a unique environment that interacts with cariogenic microorganisms, fostering a distinct microbial ecosystem compared to that of the patients without orthodontic appliances, thus increasing the vulnerability of tooth surfaces to demineralization and caries formation. Silver (Ag) has shown strong antimicrobial effects and has been extensively investigated in the medical field. Here, we aim to review the antibacterial properties and potential side effects of silver nanoparticles (AgNPs) when incorporated into orthodontic bonding reagents. This valuation could contribute to the development of novel bonding reagents designed to prevent the formation of white spot lesions and caries during orthodontic treatments. Full article

To address poor film pickup, incomplete soil–film separation, and high soil content in conventional residual film recovery machines, this study designed a belt-tooth type residual film recovery machine. Its core component integrates flexible belts with nail-teeth, providing both overload protection and efficient conveying. EDEM simulations compared film pickup performance across tooth profiles, identifying an optimal structure. Based on the kinematics and mechanical properties of residual film, a film removal mechanism and packing device were designed, incorporating partitioned packing belts to reduce soil content rate in the collected film. Using Box–Behnken experimental design, response surface methodology analyzed the effects of machine forward speed, film-lifting tooth penetration depth, and pickup belt inclination angle. Key findings show: forward speed, belt angle, and tooth depth (descending order) primarily influence recovery rate; while tooth depth, belt angle, and forward speed primarily affect soil content rate. Multi-objective optimization in Design-Expert determined optimal parameters: 5.2 km/h speed, 44 mm tooth depth, and 75° belt angle. Field validation achieved a 90.15% recovery rate and 5.86% soil content rate. Relative errors below 2.73% confirmed the regression model’s reliability. Compared with common models, the recovery rate has increased slightly, while the soil content rate has decreased by more than 4%, meeting the technical requirements for resource recovery of residual plastic film. Full article

Background: This study aimed to evaluate the effect of in-office bleaching with 38% hydrogen peroxide (HP) on the surface roughness of a nanohybrid composite resin by comparing two measurement techniques: Scanning Electron Microscopy (SEM) and profilometry. Methods: Sixty composite specimens of identical shade and thickness were prepared, light-cured, and polished following the manufacturer’s guidelines. These samples were divided into six groups based on the applied surface treatments: group 1: fresh composite (the control group), group 2: old composite, group 3: bleached fresh composite, group 4: bleached old composite, group 5: old repolished composite, and group 6: old repolished bleached composite. Surface roughness was measured using profilometry and SEM. Results: Pearson correlation analysis revealed a moderately significant linear relationship (r = 0.548, p < 0.001) between the surface roughness measurements obtained using SEM and the profilometer, indicating that both methods provide comparable results. A comparison of most groups showed significant differences (p < 0.001), highlighting the increased surface roughness observed after bleaching both fresh and aged composites. Conclusions: Bleaching increased the surface roughness of nanohybrid composites. It might be better to use SEM and a profilometer together to obtain a more comprehensive understanding of the surface characteristics. Full article

Maintaining the cleanliness of orthodontic aligners is crucial for oral hygiene and preserving the optical properties of aligners. In this randomized clinical trial, we compared the effectiveness of different cleaning methods for the maintenance of Invisalign clear aligners. Twelve adult patients received five aligners, each worn for 10 days. The aligners were divided based on the cleaning method: tooth brushing with whitening toothpaste, vinegar, Fittydent Super Cleansing Tablets, Invisalign cleaning crystals, and only water. Scanning electron microscopy (SEM) was used to detect surface morphology changes; color changes (ΔE) were evaluated using a spectrophotometer. Fourier transform infrared spectroscopy (FTIR) with a diamond hemisphere was used to study the aligners’ chemical compositions. Nanoindentation testing was used to assess changes in the elastic modulus. SEM confirmed the effectiveness of Invisalign cleaning crystals in maintaining cleanliness, revealing a surface similar to that of the control group with no adverse effects. Color stability analysis revealed significant ΔE value differences; whitening toothpaste had significantly lower ΔE values than water and Invisalign cleaning crystals. The elastic modulus and FTIR analyses indicated no significant differences between the cleaning methods. Therefore, Invisalign cleaning crystals and whitening toothpaste are safe for aligner maintenance, showing successful and aesthetically pleasing results. Full article

The color stability of dental ceramics in the oral cavity is influenced by multiple factors, including the patient’s dietary habits and oral hygiene practices, which can affect the optical and surface properties of resin-containing dental restorative materials. The purpose of this study was to evaluate the effects of surface finishing procedures and simulated tooth-brushing on the surface roughness, surface gloss, and color stability of resin matrix ceramics before and after coffee immersion. Forty specimens were prepared from a resin matrix ceramic and divided into four experimental groups according to surface finishing procedures, coffee immersion, and simulated tooth-brushing. The surface roughness, surface gloss, and color stability of the tested material were measured, and the data were statistically analyzed at a significance level of p < 0.05. The surface finishing procedures, measurement times, and application sequences affected surface roughness, surface gloss, and color stability. The most significant color differences occurred after coffee immersion; however, tooth-brushing had a more significant effect on the surface roughness and surface gloss. Coffee caused perceivable and clinically unacceptable color differences in the resin matrix ceramics. Tooth-brushing had a positive impact on the tested parameters. This study presents a novel approach by integrating both chemical (coffee immersion) and mechanical (tooth-brushing simulation) degradation processes to assess their combined and isolated effects on a resin matrix ceramic material. The findings provide clinically relevant insights into how finishing procedures and oral hygiene may influence the long-term esthetic performance of such restorative materials. Full article

Background/Objectives: In the oral environment, tooth-colored restorations are frequently exposed to staining agents, affecting their aesthetic and physical properties. This study assessed the impact of stains and bleaching agents on the surface roughness, microhardness, and color stability of four different composite materials (Omnichroma, Charisma, Z350, and TPH). Methods: Based on group distribution, the discs of all the composite material samples were prepared. All the ninety-six-disc specimens (n = 96) were then randomly divided into four different groups based on different composite resin groups. The samples were then immersed into four different immersing media [each group had twenty-four-disc samples (n = 24)]. Finally, all the samples then faced the challenge of a bleaching agent application. Measurements were taken at baseline, post-immersion, and post-bleaching stages. Results: Red wine caused increased roughness in Filtek™ Z350 and significant color change in Omnichroma, while coffee increased roughness in Omnichroma and altered the color of TPH spectra. Soda led to increased roughness and significant color change in TPH spectra. Additionally, Filtek™ Z350 experienced reduced microhardness across all solutions after bleaching. Conclusion: This study concluded that staining and bleaching adversely affected the tested composites, with increases in surface roughness, color change, and microhardness reduction observed. Overall, Charisma diamond demonstrated the greatest resilience to staining and bleaching challenges, whereas Filtek™ Z350 XT exhibited the most pronounced degradation, indicating that composite formulation critically governs both aesthetic and mechanical stability under clinically relevant conditions. Full article

The purpose of this study was to evaluate the gene expression pattern of the caries-inhibiting effect of Cudrania tricuspidata (C. tricuspidata) extract on cariogenic bacteria Streptococcus mutans (S. mutans). We examined bacterial growth, tooth surface attachment, biofilm formation, acid production, free calcium release, and toxicity gene expression. The major components of the extract were investigated by UPLC-Q-TOF-MS analysis. Exposure to C. tricuspidata inhibited bacterial growth and attachment at concentrations of ≥15 μg/mL. Inhibition effects on biofilm formation, acid production, and free calcium release due to acid production were observed at concentrations ≥ 30 μg/mL. S. mutans virulence gene expression analysis showed that it inhibited the expression of gbpB and spaP, which mediate bacterial attachment to the tooth surface, and that of genes contributing to biofilm formation (gtfB, gtfC, and gtfD) and acid resistance (brpA and relA), and regulation (vicR). Analysis using UPLC–Q–TOF–MS/MS showed that the main component was phenylpropanoids. These results suggest that C. tricuspidata may inhibit the cariogenic properties associated with the expression of caries-related genes in S. mutans. Full article

Background: The bonding protocol for lithium disilicate veneers in the esthetic zone plays a crucial role in modern dental restoration techniques, focusing on the replication of natural tooth properties and esthetics. This process involves several meticulous steps on both ceramic and tooth surfaces to optimize material performance and bond strength. Methods: The objective of this article is to provide an updated review of the literature on the clinical steps for bonding lithium disilicate veneers in the anterior dentition and to document a clinical case where these advanced restorative techniques were applied to treat a female patient seeking to improve her smile. A preliminary review was conducted on the existing literature regarding the clinical protocols for bonding lithium disilicate veneers in the esthetic zone. The main advantage of careful bonding procedures is that they maximize the full potential of the materials’ properties. Results: A review of the literature reveals some minor differences in cleaning the veneers prior to cementation and in the number of steps involved when combining certain materials in a single application process. However, well-executed bonding procedures, following the manufacturer’s recommendations, can maximize the adhesion between the ceramic and the tooth, allowing the restorations to meet the patient’s esthetic demands. Conclusions: Effective bonding of lithium disilicate veneers in the esthetic zone requires multiple treatments on both the ceramic and tooth surfaces. When procedures are followed carefully, long-term esthetic and functional outcomes can be achieved. It is essential that clinicians are familiar with these steps. Proper patient selection, thoughtful treatment planning, and methodical execution of the case can lead to highly esthetic results that satisfy the patient’s demands and ensure long-term success. Full article

Background: Lithium disilicate ceramic veneers are considered the gold standard in aesthetic dentistry due to their translucency, strength, and adhesive bonding properties. This clinical case report details the aesthetic rehabilitation of a patient through the use of pressed lithium disilicate veneers, highlighting the treatment workflow, material selection rationale, and the long-term functional and aesthetic outcomes achieved. Methods: A review was conducted to evaluate the long-term success of lithium disilicate. A case study is presented that involves a 32-year-old female patient with anterior tooth discoloration, minor morphological discrepancies, and a desire for smile enhancement. A conservative approach using pressed lithium disilicate was chosen to restore harmony and enhance natural aesthetics. The treatment involved minimally invasive tooth preparation, digital smile design, and adhesive cementation using a total-etch technique with light-cured resin cement. High-resolution intra-oral and extra-oral photographs documented the case, capturing the preoperative, preparation, and final restoration stages. These images highlight shade matching, margin adaptation, and smile transformation after veneering. Results: Postoperative evaluation showed excellent aesthetic outcomes, color integration, and marginal adaptation, with the patient expressing high satisfaction. The veneers exhibited optimal translucency and strength, ensuring long-term durability. A one-year follow-up revealed no debonding, marginal discoloration, or surface degradation, confirming the clinical reliability of lithium disilicate veneers. Conclusions: Lithium disilicate provides predictability, durability, and high aesthetic results, making it an ideal choice for minimally invasive smile enhancement. The use of photographic documentation emphasizes the importance of case planning, precise preparation, and adhesive bonding for successful outcomes. Future research should focus on long-term survival rates and complication prevention to further refine material selection and bonding protocols. Full article