Explore the vast range of titles available.

Objective The objective of the study was to compare the retentive force and deformation of conventional casting and selective laser melting (SLM) cobalt-chromium (Co-Cr) clasps assembly of removable partial dentures (RPD) following recurrent insertion and removal forces. Materials and methods A total of 12 RPD samples were used in this study, which were divided equally into two groups: Group A (indirect digital conventional casting) and Group B (direct digital SLM) Co-Cr clasp assembly. The retention was measured using a universal testing machine after the recurrent removal and insertion of the RPD. Deformation was measured using Geomagic Control X professional metrology software. The retention and deformation data were compared between the two groups using an independent sample t-test. The association between the variables was studied using the Pearson correlation test. A statistical significance was established at P  < 0.05. Results A statistically significant difference in retention was observed between the two groups. Direct digital SLM Co-Cr clasp assembly showed higher retention and lower distortion compared to the indirect digital conventional casting Co-Cr clasp assembly. A significant negative correlation (correlation coefficient=-0.807, p-value = 0.004) between deformation and retention suggests that increased deformation reduces the retention. Conclusion The direct digital SLM Co-Cr clasp assembly in the RPD showed higher retentive force and lower deformation than the indirect digital conventional casting Co-Cr clasp assembly in the RPD.

Background: Polyetheretherketone (PEEK) has provided the option to fabricate RPDs with aesthetics unlike metal RPDs, but little attention has been paid to its suitability, especially towards the retentive forces and deformation of the clasp. This study aimed to examine the retentive forces and the fitting surface (inner surface) deformation of clasps made from PEEK and compare it with cobalt–chromium (Co-Cr) clasp. Methods: Forty-two circumferential clasps (14 Co-Cr and 28 PEEK) were fabricated and divided into two groups with clasp undercuts (0.25 mm and 0.5 mm) with thicknesses of 1 mm and 1.5 mm. Each was examined for retentive forces after cycle test on its abutment for 360 cycles. Initial and final retentive forces were recorded. The fitting surface deformation was determined using 3-Matic research analysis software. Results: The results revealed that highest mean initial retentive force was of Co-Cr clasps with 0.50 mm undercut 22.26 N (±10.15 N), and the lowest was the 1 mm PEEK clasps with 0.25 mm undercut 3.35 N (±0.72 N) and highest mean final retentive force was the Co-Cr clasps with 0.50 mm undercut 21.40 N (±9.66 N), and the lowest was the 1 mm PEEK clasps with 0.25 mm undercut 2.71 N (±0.47 N). PEEK clasps had a lower retentive force than Co-Cr clasps with 0.50 undercut. PEEK clasps (1.5 mm) at 0.25 mm undercut had the least deformation (35.3 µm). PEEK showed significantly less deformation (p ≤ 0.014) than Co-Cr. Conclusion: The deformation of PEEK clasps fitting surface was lower than Co-Cr clasps and retentive forces were close to the Co-Cr clasps, suggesting the use of PEEK as an aesthetic clasp option for RPD framework.

Objectives To examine the retention force of removable dental prosthesis (RDP) clasps made from polyetheretherketone (PEEK) and cobalt-chrome-molybdenum (CoCrMo, control group) after storage in water and artificial aging. Materials and methods For each material, 15 Bonwill clasps with retentive buccal and reciprocal lingual arms situated between the second pre- and first molar were manufactured by milling (Dentokeep [PEEKmilled1], NT digital implant technology; breCAM BioHPP Blank [PEEKmilled2], bredent), pressing (BioHPP Granulat for 2 press [PEEKpressed], bredent), or casting (remanium GM 800+ [CoCrMo], Dentaurum); N = 60, n = 15/subgroup. A total of 50 retention force measurements were performed for each specimen per aging level (initial; after storage [30 days, 37 °C] and 10,000 thermal cycles; after storage [60 days, 37 °C] and 20,000 thermal cycles) in a pull-off test. Data were statistically analyzed using one-way ANOVA, post hoc Scheffé and mixed models ( p < 0.05). Results Initial, PEEKpressed (80.2 ± 35.2) and PEEKmilled1 (98.9 ± 40.3) presented the lowest results, while PEEKmilled2 (170.2 ± 51.8) showed the highest values. After artificial aging, the highest retention force was observed for the control group (131.4 ± 56.8). The influence of artificial aging was significantly higher for PEEK-based materials. While PEEKmilled2 and PEEKpressed showed an initial decline in retention force, all other groups presented no impact or an increase in retention force over a repetitive insertion and removal of the clasps. Conclusions Within the tested PEEK materials, PEEKmilled2 presented superior results than PEEKpressed. Although CoCrMo showed higher values after artificial aging, all materials exhibited sufficient retention to recommend usage under clinical conditions. Clinical relevance As RDPs are still employed for a wide range of indications, esthetic alternatives to conventional CoCrMo clasps are sought.

Purpose: This study was aimed to evaluate the retentive forces and the clasp deformation of Bio-Hpp Aker's clasps and Cobalt-Chrome (Co-Cr) Aker's clasps constructed by CAD/CAM milling machine and by lost wax technique. Materials and Method: Twenty models were constructed by placing premolar tooth inside a rectangular stone block. Models were divided equally according to the clasp material into two groups. Group I for Bio-Hpp Aker's clasp and Group II for Cobalt-Chrome (Co-Cr) Aker's clasps, both groups I, II were subdivided according to method of clasp construction into group Ia for Bio-Hpp Aker's clasp constructed by CAD/CAM milling, group Ib for Bio-Hpp Aker's clasps constructed by lost wax technique (injection method (press)), group IIa for Cobalt-Chrome (Co-Cr) Aker's clasps constructed by CAD/ CAM milling, group IIb for Cobalt-Chrome (Co-Cr) Aker's clasps constructed lost wax technique. Each testing model and its clasp were mounted inside universal testing machine. Retention of each clasp was measured by applying withdrawal force to it using universal testing machine at pre-test (0 cycle) and after cycling intervals (360 cycles, 720 cycles, 1080 cycles and 1440 cycles) representing day of delivery, three, six, nine and twelve months follow up periods, deformation of the clasp after each cycle was recorded by measuring the distance (mm) between the clasp tips was conducted using a digital micrometer. The data were collected tabulated and statistically analyzed using 3-way-ANOVA test followed by pair-wise Tukey's post-hoc if showed significance. Results: Regarding retention: Retention mean values decreased significantly from baseline to 12 months evaluation time (p =< 0.0001 < 0.05) at both groups with loss of retentive forces in Co-Cr metal groups more than in Bio-Hpp groups. Both construction technique subgroups showed statistically significant decrease in retention mean values where loss of retention in lost wax subgroups was higher than milled subgroups. Regarding clasp deformation: Deformation was observed in both groups, however, Bio-Hpp milled group showed least deformation values followed by Bio-Hpp lost wax group, then Co-Cr milled and the highest deformation values was observed in the Co-Cr lost wax technique group. Clinical significance: Bio-HPP Akers' clasp material showed acceptable retention values with less deformation than Co-Cr clasp group CAD/CAM construction method is considered acceptable as an alternative to the traditional lost wax-technique.

Objectives To investigate the retention force of polyetheretherketone (PEEK) removable dental prosthesis clasps in comparison with a cobalt-chrome-molybdenum control group after storage in artificial saliva. Materials and Methods Clasps were milled (Dentokeep (PEEKmilled1), NT digital implant technology; breCAM BioHPP Blank (PEEKmilled2), bredent), pressed (BioHPP Granulat for 2 press (PEEKpressed), bredent), or cast (remanium GM 800+ (cobalt-chrome-molybdenum), Dentaurum); N = 60, n = 15/subgroup. Retention force was examined 50 times/specimen in a pull-off test using the universal testing machine (Zwick 1445), where pull-off force was applied with a crosshead speed of 5 mm/minute until the maximum force dropped by 10%, at different aging levels: (1) initial, after storage in artificial saliva for (2) 90 and (3) 180 days. Statistical analysis was performed using one-way ANOVA followed by post hoc Scheffé-test and mixed models ( p < 0.05). Results Cobalt-chrome-molybdenum presented the highest retention force. No differences were observed between polyetheretherketone materials. Cobalt-chrome-molybdenum showed a significant decrease of its values after artificial aging, while polyetheretherketone materials presented similar results over the course of aging. Regarding a repetitive insertion and removal, even though PEEKmilled2 and cobalt-chrome-molybdenum showed an initial increase, ultimately, a decrease in retention force was observed for all tested groups. Conclusions Although the control group showed significantly higher results, the retention force of polyetheretherketone materials indicate a potential clinical application. Neither the manufacturing process nor artificial aging showed an impact on the retention force of polyetheretherketone clasps. Clinical relevance Mechanical properties of novel removable dental prosthesis clasp materials devised to meet the growing esthetic demands of patients need to be investigated to ensure a successful long-term clinical application.

Integrity of the Golgi apparatus requires the microtubule (MT) network. A subset of MTs originates at the Golgi itself, which in this case functions as a MT-organizing center (MTOC). Golgi-derived MTs serve important roles in post-Golgi trafficking, maintenance of Golgi integrity, cell polarity and motility, as well as cell type-specific functions, including neurite outgrowth/branching. Here, we discuss possible models describing the formation and dynamics of Golgi-derived MTs. How Golgi-derived MTs are formed is not fully understood. A widely discussed model implicates that the critical step of the process is recruitment of molecular factors, which drive MT nucleation (γ-tubulin ring complex, or γ-TuRC), to the Golgi membrane via specific scaffolding interactions. Based on recent findings, we propose to introduce an additional level of regulation, whereby MT-binding proteins and/or local tubulin dimer concentration at the Golgi helps to overcome kinetic barriers at the initial nucleation step. According to our model, emerging MTs are subsequently stabilized by Golgi-associated MT-stabilizing proteins. We discuss molecular factors potentially involved in all three steps of MT formation. To preserve proper cell functioning, a balance must be maintained between MT subsets at the centrosome and the Golgi. Recent work has shown that certain centrosomal factors are important in maintaining this balance, suggesting a close connection between regulation of centrosomal and Golgi-derived MTs. Finally, we will discuss potential functions of Golgi-derived MTs based on their nucleation site location within a Golgi stack.

Kronheimer and Mrowka asked whether the difference between the four-dimensional clasp number and the slice genus can be arbitrarily large. This question is answered affirmatively by studying a knot invariant derived from equivariant singular instanton theory, and which is closely related to the Chern–Simons functional. This also answers a conjecture of Livingston about slicing numbers. Also studied is the singular instanton Frøyshov invariant of a knot. If defined with integer coefficients, this gives a lower bound for the unoriented slice genus, and is computed for quasialternating and torus knots. In contrast, for certain other coefficient rings, the invariant is identified with a multiple of the knot signature. This result is used to address a conjecture by Poudel and Saveliev about traceless SU(2) representations of torus knots. Further, for a concordance between knots with non-zero signature, it is shown that there is a traceless representation of the concordance complement which restricts to non-trivial representations of the knot groups. Finally, some evidence towards an extension of the slice-ribbon conjecture to torus knots is provided.

The purpose of this study was to evaluate the retentive forces over time of removable partial denture clasps fabricated by the digital method. Occlusal rest seats were fabricated on three premolar teeth fixed in acrylic blocks (9 × 20 × 40 mm). Digitization of the teeth was performed using a laboratory scanner (Zirkonzahn Scanner S600 GmbH, Gais, Italy). After the analysis and determination of the insertion axis, two types of clasps with mesial occlusal rests were designed per tooth: the back-action and the reverse back-action clasps, using the Partial Planner Zirkonzahn program. The file was sent for fabrication of six metal clasps from a cobalt-chromium SP2 alloy in the EOSINT M270 system by a direct laser sintering process. The Instron 5544 universal testing machine was used to perform 20,000 cycles of clasp insertion and removal in the corresponding tooth with a load cell of 100 N and a speed of 2.5 mm/s. The retentive force was recorded for each of the 1000 cycles, and the change in retention over time was calculated. Statistical analysis was performed using the nonparametric Mann–Whitney test and a significance level of 5%. At 16,000 cycles, a maximum change in retention of 3.74 N was recorded for the back-action clasps and a minimum of −24.28 N at 1000 cycles for the reverse back-action clasps. The reverse back-action clasps exhibited statistically significant lower change in retention than the reverse-action clasps at 4000 and 5000 cycles. No differences were observed in the remaining cycles. During the 20,000 cycles, the change in retention was low regardless of the type of clasp. For most cycles, there were no differences in the change in retention between the two types of clasps.

Purpose The retention force of a realistic clasp is influenced by multiple, interrelated factors, which complicates the identification of the fundamental relationship between clasp geometry and retention force. While realistic clasps exhibit various shapes, they share basic geometric elements such as length, diameter, and curvature. Simpler geometries are often more conducive to identifying the underlying issues. The aim is to investigate the relationship between clasp geometry and retention force using finite element analysis. Methods A three-dimensional clasp model was created in ANSYS 19.0 (ANSYS, USA). Two types of models were analyzed: rod-shaped clasps with varying lengths (1–15 mm) and diameters (0.6–1.6 mm), and bending clasps with different base widths (6–12 mm) and heights (0.5–5 mm), all made from cobalt-chromium alloys. For the rod models, stress and retention force were assessed by applying displacement loads and analyzing data with nonlinear regression. For the bending models, a similar analysis was conducted for varying base widths and heights. Results Maximum stress consistently concentrated at the clasp base. In rod models, retention force decreased with the third power of length and increased with the fourth power of diameter. For bent specimens, the retention force was approximately inversely proportional to the cube of the base width and inversely proportional to the first power of the height. Conclusions Finite element analysis revealed distinct functional relationships between clasp geometry and retention force. Further laboratory validation is required.

Clasp retainers made of metal alloys may be esthetically unappealing or cause allergic reactions. To investigate alternative materials, we used the nonfiller polyetheretherketone (PEEK) to fabricate the clasp retainer of a removable partial denture for the mandibular bilateral distal free-end abutment of an 84-year-old female. Two years later, few color and texture changes of PEEK were found macroscopically. The rest part and the clasp arm fitted well without any deformation. There were no particular occlusal or periodontal problems. Subjective satisfaction was expressed by both the practitioner and the patient.