Strain-Based Assessment to Evaluate Damage Caused by Deep Rolling.

The positive effects of deep rolling on fatigue strength-reduced surface roughness, work hardening and compressive residual stress-in the near-surface region are achieved by controlled high plasticisation of the treated material. However, excessive and/or repeated plasticising poses a risk of damage to the machined component. This paper investigates the damage caused by deep rolling of a railway axle. Two sections of the axle are experimentally deep rolled repeatedly at different feed rates until damage is detected. For comparative analysis, these experiments are numerically analysed and the damage is assessed using the strain-based damage calculation. The results are compared and a damage sum of ~120% is evaluated for both tests, thus developing a reliable and conservative assessment method. The single deep rolling treatment at a feed rate of 0.25 mm causes damage of 6.1%, and at a feed rate of 0.5 mm, damage of 4.7%. The developed and experimentally validated evaluation method allows for investigating the limits of applicability of different deep rolling parameters. The influence of the deep rolling force and feed rate and a proposed optimisation with multiple deep rolling with reduced deep rolling forces are investigated.

Shear Strength of Repaired 3D-Printed and Milled Provisional Materials Using Different Resin Materials with and without Chemical and Mechanical Surface Treatment.

The aim of this study was to assess the shear bond strength of 3D-printed and milled provisional restorations using various resin materials and surface finishes. There were 160 preliminary samples in all, and they were split into two groups: the milled group and the 3D-printed group. Based on the resin used for repair (composite or polymethylmethacrylate (PMMA)) and the type of surface treatment utilized (chemical or mechanical), each group was further divided into subgroups. The specimens were subjected to thermocycling from 5 °C to 55 °C for up to 5000 thermal cycles with a dwell time of 30 s. The mechanical qualities of the repaired material underwent testing for shear bond strength (SBS). To identify the significant differences between the groups and subgroups, a statistical analysis was carried out. Three-way ANOVA was used to analyze the effects of each independent component (the material and the bonding condition), as well as the interaction between the independent factors on shear bond strength. Tukey multiple post-hoc tests were used to compare the mean results for each material under various bonding circumstances. The shear bond strengths of the various groups and subgroups differed significantly (p < 0.05). When compared to the milled group, the 3D-printed group had a much greater mean shear bond strength. When compared to PMMA repair, the composite resin material showed a noticeably greater shear bond strength. In terms of surface treatments, the samples with mechanical and chemical surface treatments had stronger shear bonds than those that had not received any. The results of this study demonstrate the effect of the fabrication method, resin type, and surface treatment on the shear bond strength of restored provisional restorations. Particularly when made using composite material and given surface treatments, 3D-printed provisional restorations showed exceptional mechanical qualities. These results can help dentists choose the best fabrication methods, resin materials, and surface treatments through which to increase the durability and bond strength of temporary prosthesis.

Residual stress associated with crystalline phase transformation of 3-6 mol% yttria-stabilized zirconia ceramics induced by mechanical surface treatments.

Monolithic dental prostheses made of 3-6 mol% yttria-stabilized zirconia (3-6YSZ) have gained popularity owing to their improved material properties and semi-automated fabrication processes. In this study, we aimed to evaluate the influence of mechanical surface treatments, such as polishing, grinding, and sandblasting, on the residual stress of 3-6YSZ used for monolithic prostheses in association with crystalline phase transformation. Plate specimens were prepared from five dental zirconia blocks: Aadva Zirconia ST (3YSZ), Aadva Zirconia NT (6YSZ), Katana HT (4YSZ), Katana STML (5YSZ), and Katana UTML (6YSZ). The specimens were either polished using 1, 3, or 9 µm diamond suspensions, ground using 15, 35, or 55 µm diamond discs, or sandblasted at 0.2, 0.3, or 0.4 MPa. The residual stress, crystalline phase, and hardness were analyzed using the cosα method, X-ray diffraction (XRD), and Vickers hardness test, respectively. Additionally, we analyzed the residual stress on the surfaces of monolithic zirconia crowns (MZCs) made of 4YSZ, 5YSZ, and 6YSZ, which were processed using clinically relevant procedures, including manual grinding, followed by polishing using a dental electric motor on the external surface, and sandblasting on the internal surface. Residual stress analysis demonstrated that grinding and sandblasting, particularly the latter, resulted in the generation of compressive residual stress on the surfaces of the plate specimens. XRD revealed that the ground and sandblasted specimens contained a larger amount of the rhombohedral phase than that of the polished specimens, which may be a cause of the residual stress. Sandblasting significantly increased the Vickers hardness compared to polishing, which may possibly be due to the generation of compressive residual stress. In the case of MZCs, compressive residual stress was detected not only on the sandblasted surface, but also on the polished surface. The difference in the residual stress between the plate and crown specimens may be related to the force applied during the automated and manual grinding and polishing procedures. Further studies are required to elucidate the effects of the compressive residual stress on the clinical performance of MZCs.

The effect of chemical and mechanical treatment of the denture base resin surface on the shear bond strenght of denture / Efeito do tratamento químico e mecânico da superfície da resina de bases de dentaduras nas forças de cisalhamento em reparos de dentaduras

OBJECTIVE: This study was aimed to evaluate the effect of three surface treatment methods on the shearbond strength of denture repairs. MATERIAL AND METHOD: 40 specimens (15 x 15 x 7mm) were fabricated according to the manufacturers’ instructions from each of three denture base materials: a heat-cured acrylic resin (VeracrilTM), a rapid-setting heat-cured acrylic resin (QC-20TM), and a pourable resin (Selecta PlusTM). The samples of each material were divided into four groups of ten. One of the groups served as a control and underwent no surface treatment. The other groups received one of three surface treatments: air blasting with 50 ìm aluminum oxide particles at 0.5 MPa pressure for 5 seconds; immersion in methyl methacrylate (MMA) for 180 seconds or immersion in acetone for 3 seconds. An autopolymerizing repair resin (Rapid RepairTM) was applied to the bonding area (6 mm in diameter, 2 mm in height) and polymerized at a pressure of two bar for 30 minutes using a pressure pot. All specimens were subjected to 10,000 thermal cycles. The shear bond strength (MPa) of the specimens was measured in a universal testing machine at a 1 mm/min crosshead speed. The effect of the mechanical and chemical treatments on the surface of the base resins wasexamined using SEM. Statistical tests used were 2 way ANOVA and Kolmogorov-Smirnov. The level ofstatistical significance was established at (p<0.05). RESULTS: There were statistically significant differencesbetween bond strength in surface treatment levels across acryl level categories (p=0.042). The results also showed differences between treatment levels (p=0.0001).Abrasive blasting significantly increased the bond strength of the repair material, but there were no significant differences between the bond strengths of the control group and the experimental groups treated with MMA or acetone. Examination by SEM revealed that chemical treatment with MMA or acetone produced a smooth surface similar...

OBJETIVO: O presente estudo foi dirigido para avaliação do efeito de três métodos de tratamento de superfície na reparação de resinas-base de dentaduras. MATERIAL E MÉTODO: 40 espécimes (15 x 15 x 7 mm) foram fabricados de acordo com as instruçõesdos fabricantes de cada um de três materiais-base de dentaduras: uma resina termopolimerizada (VeracrilTM); uma resina de termopolimerização rápida (QC-20TM) e uma resina autopolimerizável (Selecta PlusTM). Cada material foi dividido em quatro grupos de dez corpos de prova. Um dos grupos serviu como controle, não recebendo tratamento de superfície. Os outros grupos receberam três tipos de tratamento de superfície: jato abrasivocom partículas de óxido alumínio (50) com pressão de 0,5 MPa durante cinco segundos; imersão em metil metacrilato (MMA) por 180 s; imersão em acetona por três segundos. Uma resina de reparo autopolimerizável (Rapid Repair TM) foi aplicada na área de adesão (6 x 2 mm) e polimerizada sob pressão de duas atmosferas por 30 minutos, utilizando um frasco de pressão. Todos os espécimes foram sujeitos a 10.000 ciclos térmicos. A resistência às forças de cisalhamento foi medida numa máquina universal de testes a uma velocidade de 1 mm/min. O efeito do tratamento químico e mecânico das superfícies da resina base foi avaliado usando SEM. Testes estatísticos utilizados foram ANOVA e Kolmogorov-Smirnov. O nível de significância estatística foi estabelecido a p<0.05. RESULTADOS: Houve diferenças estatisticamente significantes na resistência ao cisalhamento entre as categorias de tratamento de superfície (p=0,042). Os resultados também mostraram diferenças entreníveis de tratamento (p=0,0001). O jato abrasivo aumentou significativamente a resistênciaao cisalhamento do material de reparo, mas não houve diferenças significativas entre a resistência do grupo controle e dos grupos experimentais tratados com MMA ou acetona. O exame com microscopia eletrônica demonstrou que o tratamento químico com MMA...