Analysis of the Statistical Comparability of the Hardness and Wear of Polymeric Materials for Orthodontic Applications

Comparative Evaluation of the Tribological Properties of Polymer Materials with Similar Shore Hardness Working in Metal-Polymer Friction Systems

This article presents comparative tests of contact strength and tribological wear resistance of polymer sliding materials of the polyamide group. The aim of this work was to study Shore hardness, indentation hardness, modulus, creep, relaxation, Martens hardness and sliding wear resistance of two commercial materials. One of these materials was produced with the recycling process in mind. Abrasion tests were performed against a stainless-steel ball (100CRr6) on a normal load of 5 N for 23,830 friction cycles. The samples were tested under dry friction conditions and taking into account the hydrothermal factor, the presence of which was assumed in the anticipated operating conditions. It was distilled water at a temperature of 50 °C. The volumetric wear of the samples under various environmental conditions was assessed and related to the mechanical properties, in particular, Shore hardness. This mechanical size, which characterizes the surface, was considered the most frequently used by engineers selecting polymeric materials for tribological applications in industry. The Shore hardness of both materials was similar, which may indicate similar tribological performance properties. However, research and analysis indicate the need to use measures that directly correspond to tribological wear. The friction and wear of both materials varied. The coefficient of friction in hydrothermal conditions was lower and the wear was higher than in the dry friction test. It seems that it was not hardness that determined the suitability in the anticipated operating conditions, but the ability to form a sliding layer on the friction surface. The properties of the material that has been envisaged as a replacement may be appropriate for the intended uses.

Three-Dimensional-Printed Customized Orthodontic and Pedodontic Appliances: A Critical Review of a New Era for Treatment

Three-dimensional (3D) designing and manufacturing technology is a direct derivative of digital technology. Three-dimensional volume and surface acquisition, CAD software, and 3D manufacturing are major changes included in daily practice in many orthodontic and pedodontic offices. Customized appliances can be designed using dental CAD software or general-purpose CAD software in the office or a laboratory. Materials that can be used are resins, alloys, or zirconia. Methods: The search strategy of this critical review included keywords in combination with MeSH terms in Medline, Scopus, and Cochrane Library up to June 2022 in the English language without any limit to the publication period. Results: According to our search, 12 articles were selected for our study. All the articles were in vitro prospective studies. Conclusions: The results suggested that almost all the known appliances can be designed and printed in a tailor-made fashion in contrast to the traditional one-size-fits-all approach. Customized appliances should be manufactured according to the patient’s needs, and this is justified by the certainty that this approach will be beneficial for the patient’s treatment. There is a need for more research on all direct 3D-printed appliances.

Mechanical Properties of 3D Printed Orthodontic Retainers

Orthodontic retention is the final important stage of orthodontic treatment, the aim of which is to consolidate the functional and aesthetic position of teeth. Among adults, fixed retainers made of different types of wires are the most common. The aim of this study was to analyse the mechanical properties of a new generation of fixed orthodontic retainers-printed by 3D printers.

MATERIALS AND METHODS

The study was conducted using samples made of Nextdent MFH C&B N1 resin in the form of cuboid bars with nominal dimensions of width b = 3 mm, thickness d = 0.8 mm; 1 mm; 1.2 mm, length l = 30 mm for each type. The influence of the thickness of the retainers on their strength under loaded conditions was evaluated. Flexural strength, elastic properties, deflection, and creep were compared. The samples were aged in an artificial saliva bath at 37 ± 1 °C during the strength tests.

RESULTS

It was shown that differences in the thickness of the samples affected their elastic and strength properties. The highest average flexural modulus, the highest deflection, creep, and strength was characteristic of the samples with the highest thickness (1.2 mm). Samples with an average thickness of 1 mm had the lowest modulus of elasticity.

CONCLUSIONS

The mechanical properties of 3D printed retainers show that they can be an alternative to metal retainers and the procedure of making new retainers, especially when patients have aesthetic requirements or allergies to metals.

Emergence of Nano-Dentistry as a Reality of Contemporary Dentistry

(1) Background. Nanotechnology offers significant alternative ways to solve scientific, medical, and human health issues. Dental biomaterials were improved by nanotechnology. It manufactures better materials or improves the existing ones and forms the basis of novel methods for disease diagnosis and prevention. Modern nanotechnology makes oral health care services more acceptable for patients. Nanotechnology is now important area of research, covering a broad range of applications in dentistry. (2) Methods. Relevant literature from Scopus published in English was selected using the keywords “nanoparticle” and “dentistry”. To the selected articles we applied the inclusion and exclusion criteria to choose the relevant ones. (3) Results. Based on the relevant articles, a literature review was prepared. This review provides an insight into the applications of nanotechnology in various branches of dentistry. We applied several regression models to fit number of papers versus time and chose the best one. We used it to construct the forecast and its 95%-confidence interval for the number of publications in 2022–2026. (4) Conclusions. It shows that a significant rise in papers is expected. This review familiarizes dentists with properties and benefits of nanomaterials and nanotechnology. Additionally, it can help scientists to consider the direction of their research and to plan prospective research projects.

Assessment of Padding Elements Wear of Belt Conveyors Working in Combination of Rubber-Quartz-Metal Condition

Elements of belt conveyors, like other machine parts, are subject to wear processes. The conveyors transporting the spoil in the quartz sand mine are exposed to accelerated wear due to the effect of quartz on metal elements. Intensive wear of metal parts leads to downtime and the need to replace damage parts which generates additional costs. Therefore, it is important to perform surface treatment of metal elements, which will allow to extend the operation time of belt conveyors by reducing wear. The main objective of the article is to determine the impact of the pad welding process of the surface layer of metal elements on the abrasive wear of elements working in the metal–quartz sand–rubber conditions used in belt conveyors. In this research study, three different types of electrodes were used for pad welding the surface. The wear results obtained on the test stand were compared to wear of the basic element without surface treatment. The average wear value of the samples padded with electrode 3 was about 25% lower than the samples without surface treatment. The main mechanism of sample wear was the abrasion process due to the interaction between the steel surface and hard sand particles. The results presented in the article are important not only for belt conveyor elements but also for other machine parts where it is desirable to reduce abrasive wear.

Energy Structure and Luminescence of CeF3 Crystals

The results of the calculation of the energy band structure and luminescent research of CeF₃ crystals are presented. The existence of two 5d1 and 5d2 subbands of the conduction band genetically derived from 5d states of Ce³⁺ ions with different effective electron masses of 4.9 m_e and 0.9 m_e, respectively, is revealed. The large electron effective mass in the 5d1 subband facilitates the localization of electronic excitations forming the 4f-5d cerium Frenkel self-trapped excitons responsible for the CeF₃ luminescence. The structure of the excitation spectra of the exciton luminescence peaked at 290 nm, and the defect luminescence at 340 nm confirms the aforementioned calculated features of the conduction band of CeF₃ crystals. The peculiarities of the excitation spectra of the luminescence of CaF₂:Ce crystals dependent on the cerium concentration are considered with respect to the phase formation possibility of CeF₃.