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ABSTRACT Objective Material and Methods Results Conclusion To investigate the pull‐off forces on implant‐supported restorations caused by sticky food, to understand how much retention force cemented restorations must have to withstand chewing forces without unintentional retention loss. The influence of food type, restoration design, and surface treatment were investigated.Monolithic implant‐supported CAD/CAM zirconia crowns were fabricated and divided into groups according to their design: no (NC), flat (FC) and high cusps (HC) and subdivided according to surface roughness: rough (r) and smooth (s) (n = 10/group). NC represented the control group. The crowns were fixed in a universal testing machine opposite to each other. Four sticky foods (caramel, fruit jelly, candy strips and licorice) and a resin crown remover were tested. These were heated (36.4°C), placed between the crowns and compressed, then tensile strength tests were performed. The maximum pull‐off force was recorded (Newton [N]). Statistical analysis was performed using 3‐way ANOVA.The highest mean pull‐off force among food samples was with caramel_HC_r (12.09 ± 1.26 N), whereas the lowest was with licorice_FC_s (3.21 ± 0.15 N). For the resin crown remover, a mean pull‐off force of 55.41 ± 3.87 N was measured in the HC_r group. Both food type and crown design showed a significant influence on pull‐off force (p < 0.001), whereas no significant effect was reported with different surface roughnesses (p = 0.344).This study reported pull‐off forces of up to 20 N between all‐ceramic restorations caused by sticky food. The clinical implication of these findings is that a cemented implant‐restoration must have a minimum retention force of 20 N to withstand unintentional displacement during function. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study was to evaluate the effect of sterilization on the retention forces of lithium disilicate (LD) and polymer‐infiltrated ceramic network (PICN) crowns bonded to titanium base (Ti‐base) abutments. Materials and methods: Forty LD and 40 PICN crowns were milled and then bonded to 80 Ti‐bases with two resin composite cements: Multilink Hybrid Abutment (mh) and Panavia V5 (pv) for a total of 8 groups (n = 10). Half of the specimens (test) underwent an autoclaving protocol (pressure 1.1 bar, 121°C, 20.5 min) and the other half not (control). Restorations were screw‐retained to implants, and retention forces (N) were measured with a pull‐off testing machine. The surfaces of the Ti‐bases and the crowns were inspected for the analysis of the integrity of the marginal bonding interface and failure mode. Student's t‐test, chi‐square test, and univariate linear regression model were performed to analyze the data (α = 0.05). Results: The mean pull‐off retention forces ranged from 487.7 ± 73.4 N to 742.2 ± 150.3 N. Sterilized groups showed statistically significant overall higher maximum retention forces (p <.05), except for one combination (LD + mh). Sterilization led to an increased presence of marginal gaps and deformities compared to no‐sterilization (p <.001), while no statistically significant relationship was found between failure mode and sterilization (p >.05). Conclusions: Sterilization may have a beneficial effect on the retention forces of LD and PICN crowns bonded to titanium base abutments, although it may negatively influence the integrity of the marginal bonding interface. [ABSTRACT FROM AUTHOR]

Purpose This study aimed to evaluate the retentive force between stud and resilient telescopic crown attachments for implant‑retained mandibular overdenture. Patients and methods A total of 20 male patients were selected from the Clinic of Removable Prosthodontics Department. Faculty of Dentistry, Sinai University (Kantara). Patients were divided into two equal groups. Group I (control group): patients were treated with two implants of 3.7 mm diameter and 13 mm length (in the canine regions), retaining mandibular overdentures with ball abutments, and by conventional maxillary complete dentures. Group II: patients were treated with two implants of 3.7 mm diameter and 13 mm length (in the canine regions), retaining mandibular overdentures with conical abutments with a 6° taper, and by conventional maxillary complete dentures. Retention force was recorded at the time of insertion (T0), 6 months (T6), and 12 months (T12) later. Results One‑way anova revealed significant differences between the two groups in initial retention forces (T0). However, no significant difference was observed between the two groups at T6 and T12. Group II (telescopic attachment) was associated with significantly higher retention losses than Group I (ball attachment). In comparing the mean retention loss values for the two groups at different follow‑up periods, significant differences were observed for both groups. Conclusion Within the limitations of this study, it can be concluded that: telescopic attachment with taper 6° can provide acceptable retention compared to ball and socket attachment during 12 months of overdenture use. [ABSTRACT FROM AUTHOR]

Today, dental implantology represents a reliable technique for treating both partial and total edentulism. The fixation of dentures on dental implants can be achieved using various techniques, where the choice of a specific technique depends on the patient's individual needs, the jawbone's condition, and the prosthesis design. Currently, the two most common types of prosthetic abutment connections are cemented and screwed, each with its own set of advantages and disadvantages. This study aimed to analyze a novel Morse cone connection system between the prosthesis and implant using finite element analysis (FEA). The analysis of connection retention was conducted using three different approaches: analytical, in vitro, and FEA. Three-dimensional models were created for systems comprising an abutment, healing cap, and crown under three inclination conditions: 0°, 15°, and 30°. Using Ansys finite element software (R1 2023), the impact of the tilt on the system retention was examined. The FEA showed results comparable with the in vitro studies regarding the retention strength for an abutment cap system with a 4° taper, obtaining 66.6 N compared with the 68 N calculated in our in vitro study. The inclination of the abutment affected the system retention due to the hole made in the abutment's surface, decreasing the contact area between components. The Morse cone prosthesis–implant connection system was found to be the most stable and efficient compared with threaded or cemented systems. The retention was influenced by factors such as the abutment conicity, insertion strength, and the contact surface between components. [ABSTRACT FROM AUTHOR]

Objectives: The aim of the current study is to investigate the influence of mechanical stress as well as cleaning agents on the performance of various polyether ether ketone (PEEK) inserts for implant‐retained overdentures (IOD). Materials and Methods: Three different standard PEEK inserts were subjected to rapid artificial aging through storage in chemical denture cleaning agents (acetic acid, sodium hypochlorite, or sparkling denture cleaner) as well as demineralized water. The pre‐aged PEEK inserts were then placed in unilateral IOD and subjected to 200,000 chewing loads (5 kg ~ 50 N), with 5000 thermal cycles (5/55°C), and 1100 removal/insertion cycles (vertical movement 2 mm). Results: For all the PEEK inserts, the retention forces decreased significantly with an increasing number of mechanical load cycles and after exposure to all the cleaning agents. PEEK inserts aged by exposure to chemical cleaning agents showed a significantly higher decline in retention force than the inserts stored in water. Confocal laser scanning microscopy indicated that the decline in retention force might be caused by wear on the internal insert surface in contact with the patrix. Conclusions: Within the limitations of this study, it can be concluded that the application of chemical cleaning agents accelerates the decline in the retention forces of PEEK retentive inserts in IODs. [ABSTRACT FROM AUTHOR]

Inspired by the water-repellent and self-cleaning properties of the lotus leaf in the natural world, artificial superhydrophobic surfaces have attracted extensive interest in academia and industry. Static and dynamic hydrophobicities are very important phenomena in our daily life as well as in many industrial processes. However, the difference between these two phenomena has not been well understood. The objective of this study was to investigate and predict the sliding behavior of water droplets on silicone sheet surfaces with uniaxial groove structures. The groove structures were fabricated on silicone sheet surfaces by a molding process using three different molds with different groove widths. Increasing the groove width decreased the sliding angle. The sliding angle could be reduced to a greater extent than that of previously reported fluorinated hydrophobic surfaces, which exhibited sliding angles of less than 2°. The retention force between the water droplet and the silicone sheet surface was proportional to the contact ratio. It was found that the retention force was proportional to the shape of the water droplet on the surface at the sliding angle, especially the product of the contact angle hysteresis and the width of the contact line. [ABSTRACT FROM AUTHOR]

The objective of this study is to compare retention capacity of mandibular implant-supported overdenture with all zirconia, zirconia–PEEK, and all PEEK telescopic attachments. Sixty acrylic resin models of mandible were used. Telescopic attachment system was made up of all zirconia, all PEEK, and zirconia–PEEK. Evaluation of retention force was done using universal testing machine. Obtained data were statistically evaluated. Highest initial force value was obtained with zirconia–PEEK group. All PEEK and zirconia–PEEK groups showed significantly decreased final retention values in comparison to their initial values. Zirconia can be regarded as the material of choice for telescopic crown, whereas polyetheretherketone and zirconia–PEEK telescopic crowns showed retention loss over a period of time.

In combined prosthetics, the retention is performed by friction between the parts of the complex attachments. The appropriate selection of a profile configuration of the two parts is a necessary condition for good retention. The aim of this study is to examine and compare the retention force of telescopic crowns fabricated with different designs and technologies. Chrome-cobalt alloy telescopic crowns were fabricated on tooth 26 (Frasaco Typodont A3) by 3D printing (EOS M 100) with a different design (primary telescope height and taper angle), arranged in four groups (1st gr. - classical method, 2nd gr. - FGP methodology, 3rd gr. - USIG-folie system, 4th gr. - method created by the team). Each group included 10 specimens. For all test specimens (n=70), the virtual prototype of the primary and secondary telescope was made on a software program (3-Shape). The specimens from the four groups were subjected to 6,000 cycles of mechanical loading (50N) in artificial saliva. To determine the retention forces, they were subjected to a tensile test on the LMT 100 (LAM Technologies, Italy) apparatus every 500 cycles. For the study, the specialized statistical software IBM SPSS Statistics v.26 was used. The results of the comparison of the four groups of specimens show a statistically significant difference in retention between the groups. This is due both to the groups' different design and the systems used. The retention force was highest in subgroup "d" of the fourth group, with a taper angle of 0° and a telescope height of 5 mm. The weakest retention force was exhibited by subgroup "a" of the fourth group, as well as by the third group (USIG-Folie). According to this laboratory study, the group with 0° taper angle and 5mm height of the telescopic crown showed the highest retention force values, indicating that for some methods for producing telescopic crowns - the lower the taper angle, the higher the retention force is. [ABSTRACT FROM AUTHOR]

The objective of this study is to compare retention capacity of mandibular implant-supported overdenture with all zirconia, zirconia--PEEK, and all PEEK telescopic attachments. Sixty acrylic resin models of mandible were used. Telescopic attachment system was made up of all zirconia, all PEEK, and zirconia--PEEK. Evaluation of retention force was done using universal testing machine. Obtained data were statistically evaluated. Highest initial force value was obtained with zirconia--PEEK group. All PEEK and zirconia--PEEK groups showed significantly decreased final retention values in comparison to their initial values. Zirconia can be regarded as the material of choice for telescopic crown, whereas polyetheretherketone and zirconia--PEEK telescopic crowns showed retention loss over a period of time. [ABSTRACT FROM AUTHOR]

Droplet retention during pesticide application is a serious problem because run-off droplets flow out of the target area and pose a hazard to human health and the environment. The present study was conducted with the aim to measure the droplet retention of sprayed droplets on crop leaves in vivo using a constructed test system. In the measurement, three crop species with different surface properties (tomato, chili pepper, and winter wheat) were selected for droplet retention determination, and the variations in the time intervals of maximum retention and stable retention were determined. Contact angle and surface roughness ( R a ), which are the most important surface properties of crop leaves, were used as independent variables. The R a values of tomato, pepper, and winter wheat were 24.73 μ m , 5.28 μ m , and 17.59 μ m , respectively, while the contact angles of tomato, pepper, and winter wheat were 97.67°, 70.07° and 131.98°, respectively. The results showed that the curves of droplet retention on sprayed tomato and wheat leaves had similar patterns over time and could be divided into four periods (rapidly increasing period, slowly increasing period, collapsing period, and stable period). The maximum droplet retention on tomato leaf surface was R m a x = 0.169 g ⋅ cm − 2 , and the stable retention was R s t = 0.134 g ⋅ cm − 2 . The maximum droplet retention on the surface of winter wheat leaf was R m a x = 0.244 g ⋅ cm − 2 , and the stable retention was R s t = 0.093 g ⋅ cm − 2 . However, droplet retention on pepper leaves was different from that on tomato and wheat leaves. The curve pattern of droplet retention on pepper leaves over time showed two peaks and two valleys. Moreover, the maximum retention, R m a x , was in the range of 0.149~0.151 g ⋅ cm − 2 , and the stable retention was R s t = 0.077 g ⋅ cm − 2 . It is expected that the obtained results can be used to characterize the properties of crop leaves and that this study can contribute to the improvement of droplet retention for effective chemical application and the reduction in the environmental pollution caused by agricultural pesticides. [ABSTRACT FROM AUTHOR]

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Objectives: To analyze the retention forces between primary and secondary telescopic crowns milled from various materials and to compare them with the retention forces between cast telescopic crowns made of precious metal alloys. Materials and methods: Primary and secondary crowns (N = 60; n = 10 per group) were fabricated using various material combinations (1: zirconia [ZIR]/polyether ether ketone [PEEK]; 2: titanium grade IV [TI]/PEEK; 3: PEEK/PEEK; 4: non-precious alloy [NPA]/PEEK; 5:NPA/NPA), while precious alloy (PA) was used for the control group (6: PA/PA). The retention forces at 10, 1000, 5000, and 10,000 connection and disconnection cycles and the relative weights were analyzed, applying nonparametric repeated measures ANOVA and post hoc Mann–Whitney and Wilcoxon signed-rank tests (α < 0.05). Results: Globally, significant differences in the retention forces among the materials (p < 0.0001), time points (p < 0.0001), and wear resistance for the various materials (p < 0.0001) were observed. No significant changes in retention forces compared to baseline were observed in groups 2, 4, 5, and 6. A significantly higher weight loss for both primary and secondary crowns was observed in groups 4 and 6. Conclusions: The material combination in telescopic attachments influences retention forces and wear. Interactions between materials and time were evident, indicating that the change in retention forces differs among the materials. The combinations of milled TI/PEEK and NPA/NPA qualify for further preclinical testing in a more clinically realistic setup, determining a material-specific double-crown design. Clinical relevance: The design of precious alloy telescopic crowns cannot be directly transferred to other milled material combinations due to different retention behaviors. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effects of fiber orientation, silane treatment, and thermal cycling on the retention force of fiber-reinforced composite resin (FRC) posts on resin composite. Two types of FRC posts (linear and woven) were prepared with and without silane treatment. Pull-out test specimens were made of FRC posts and resin composite for core buildup. Specimens were either incubated in distilled water for 24 h or subjected to 10,000 thermal cycles. The maximum fracture load obtained by a pullout test was defined as the retention force. Fracture modes were observed after the test. Fiber orientation and thermal cycling did not affect the retention force on resin composite, and the retention force was improved by silane treatment. Whereas, fiber orientation affected the fracture mode. The result showed woven fiber orientation could contribute to the mechanically interlocking with the resin composite. [ABSTRACT FROM AUTHOR]

Droplet retention during pesticide application is a serious problem because run-off droplets flow out of the target area and pose a hazard to human health and the environment. The present study was conducted with the aim to measure the droplet retention of sprayed droplets on crop leaves in vivo using a constructed test system. In the measurement, three crop species with different surface properties (tomato, chili pepper, and winter wheat) were selected for droplet retention determination, and the variations in the time intervals of maximum retention and stable retention were determined. Contact angle and surface roughness (Ra), which are the most important surface properties of crop leaves, were used as independent variables. The Ra values of tomato, pepper, and winter wheat were 24.73 μm, 5.28 μm, and 17.59 μm, respectively, while the contact angles of tomato, pepper, and winter wheat were 97.67°, 70.07° and 131.98°, respectively. The results showed that the curves of droplet retention on sprayed tomato and wheat leaves had similar patterns over time and could be divided into four periods (rapidly increasing period, slowly increasing period, collapsing period, and stable period). The maximum droplet retention on tomato leaf surface was Rmax = 0.169 g⋅cm−2, and the stable retention was Rst = 0.134 g⋅cm−2. The maximum droplet retention on the surface of winter wheat leaf was Rmax = 0.244 g⋅cm−2, and the stable retention was Rst = 0.093 g⋅cm−2. However, droplet retention on pepper leaves was different from that on tomato and wheat leaves. The curve pattern of droplet retention on pepper leaves over time showed two peaks and two valleys. Moreover, the maximum retention, Rmax, was in the range of 0.149~0.151 g⋅cm−2, and the stable retention was Rst = 0.077 g⋅cm−2. It is expected that the obtained results can be used to characterize the properties of crop leaves and that this study can contribute to the improvement of droplet retention for effective chemical application and the reduction in the environmental pollution caused by agricultural pesticides.

Purpose: This in vitro study aimed at ascertaining the retention forces for telescopic crowns fabricated with Selective Laser Manufacturing (SLM) and Selective Laser Sintering (SLS) additive technologies, and Computer Aided Design - Computer Aided Manufacturing (CAD-CAM) subtractive technology, by using suitable materials for each. Materials and Methods: Full-factorial design was employed for experimental testing, considering the following three factors: (a) inner crown material technology (zirconia CAD-CAM; metal-alloy SLS; metal-alloy SLM); (b) tooth type (canine or molar); (c) wet vs. dry conditions (i.e. either with or without artificial saliva). The roughness of the inner crowns was analyzed through atomic force microscopy. Three-way analysis of variance (ANOVA) was applied for statistical analysis, followed by Tukey's post-hoc comparisons between the crown types. Results: The retention force mean values were between 3.8 N (dry, SLM) and 14.8 N (artificial saliva, SLS), with statistically significant (p<0.001) differences between the three types of inner crowns and interaction with the tooth type. No significant interaction was found between crown or tooth types and the wet vs. dry testing conditions. The zirconia crowns' retention force was significantly (p<0.001) higher compared to similar SLM crowns, with 95% CI (3.62; 5.55) N for the differences. Zirconia was significantly (p<0.001) less retentive compared to similar SLS crowns, with 95% CI (-5.99; -4.06) N for the differences. The roughness decrease and subsequent loss of retention force was the largest in zirconia. Conclusions: The SLS inner crowns showed the best retention, followed by zirconia and SLM inner crows. [ABSTRACT FROM AUTHOR]

Clasps of removable partial dentures (RPDs) often suffer from fatigue stress that leads to plastic deformation, loss of retention, and RPD failure. Recently, computer-based technologies were proposed to optimize clasp geometry design. The objective of this study was to create an analytic model of I-bar clasps for computer-aided design (CAD)-RPD. The analytical model based on mechanical laws was established to simulate I-bar clasp retention, and optimize its design. The model considered the lengths of the vertical (L 1) and horizontal (L 2) arms of the I-bar as well as the radius (r) of its half-round cross-section. The analytical model was validated with mechanical experiments evaluating the retention of cobalt–chromium (Co–Cr) clasps in vitro and compared with finite element analysis (FEA). The analytical model was in good agreement with the mechanical experiments and FEA, and showed that I-bar clasp design could provide optimal mechanical performance as long as the length of arms (L 1 and L 2) do not exceed 6 mm. Clasps with L 1 > 8 mm and L 2 > 9 mm presented stress values exceeding the fatigue limit of Co–Cr. The proposed solution was to increase the radius of I-bar to conserve the initial mechanical performance of Co–Cr. Co–Cr I-bar clasps perform best on teeth with reduced mesiodistal dimensions (canine and premolar), and their designs could be optimized to prevent stress from reaching the yield strength and the fatigue failure limit. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In recent years, robots are increasingly used for rescue activities and inspections at disaster sites. However, many robots have limited adaptive environment, and there are still problems in actual use. We are studying vacuum suction, which is considered to be able to adsorb to various objects among suction components. There were many problems with conventional suction component. For example, suction part using a flexible material is weak to the load from the shear direction of the suction surface. In this paper, the suction force generated from the suction surface is divided into the suction force and the retention force by the suction area. By separating the suction force and the retention force, the retention force almost holds the suction surface, but the suction force holds a part of it. As a result, a large load can be held in the rigid part, and the durability is improved. By separating the suction mechanism and the retention mechanism with bellows, it is possible to correct the difference between the coordinates of the suction pad and the coordinates of the hand of the robot, and there is also an advantage when mounting the suction component on the robot. When the impact load falls on the robot, the bellows can recover the suction state in the time it takes to extend due to the bellows. Also, conventional suction components were limited of suction surface. Therefore, we develop composite sealing material to adsorb more variable surface. We show the improvement of adaptability to granite, concrete blocks, tile with grooves, and so on by applying this material. We report on useful findings from the results and discussion.

Attachment systems (AS) enhance retention and stability by anchoring the overdentures to implants. Since 2002, the McGill consensus statement recommends the 2-implant-retained overdentures as the standard choice for edentulous mandible (2-IRMO). Considering the large number of AS available, it remains difficult for a practitioner to make a reasoned choice. A systematic review was conducted in PubMed/Medline and carried out independently by three authors, on retention, wear, and maintenance of AS used clinically or in vitro specifically for 1- or 2-IRMO. The 45 selected studies include 14 clinical and 31 in vitro studies. The risk of bias was evaluated according to the revised Cochrane risk of bias tool for randomized trials (RoB 2). The initial retention force of the cylindrical system is higher than the ball system. The retention loss, related to the wear of the retention device, is responsible for the most common need of maintenance, requiring activation or replacement. Plastic retention devices wear out faster and more significantly than metal ones, implying a worse time behavior of cylindrical systems, but their maintenance rate is similar. Neither system appears categorically superior. Cylindrical systems provide higher initial retention than ball ones; this advantage reduces over time with wear without affecting their need for maintenance.

Aim: The aim was to evaluate and compare retention forces of all-zirconia (ZrO2), all-polyetheretherketone (PEEK), and ZrO2-PEEK Computer-Aided-Designing computer-Aided -Manufacturing (CAD-CAM) telescopic attachments for two implant-retained mandibular overdentures. Materials and Methods: Fifteen identical acrylic resin models of the edentulous mandibular arch without alveolar undercuts were fabricated. Two implants were inserted in the canine region of each model. According to the material of telescopic attachment, models were divided into three groups: all ZrO2 (ZZ): primary and secondary crowns were made of ZrO2, all PEEK (PP): primary and secondary crowns were made of PEEK, and ZrO2-PEEK (ZP): primary crowns were made of ZrO2 and secondary ones were made of PEEK. Identical experimental overdentures were constructed for all models. For measuring the retention force, a universal testing machine was used to apply a pull-off test in presence of artificial saliva between the crowns. The achieved maximum values of retention force were recorded at the beginning of the study (initial retention) and after 540 cycles of insertion and removal simulating 6 months of the clinical service (final retention). Results were statistically analyzed, analysis of variance (P < 0.05). Results: ZP group reported the highest initial force values for all groups. The final retention values of PP and ZP groups were significantly decreased than initial values, while the insignificant loss of retention was observed with ZZ group (P = 0.06). Independent samples test showed a significant difference in both initial and final retentions between each two groups. Conclusion: Within the limitations of this study, ZrO2 is more preferred as a secondary telescopic crown against a primary ZrO2 one. Despite the loss of retention by time, PEEK can still be used as a secondary telescopic crown against ZrO2 or PEEK primary crowns regarding the acceptable initial and final retention values. [ABSTRACT FROM AUTHOR]

The stud-shaped attachment systems (AS) with different shape designs (ball, cylindrical, conical) and materials (metallic, plastic, or a combination of both) are commonly used to provide better retention and stability in implant-retained mandibular overdentures (IRMO). The purpose of the present study was to evaluate and compare the retention loss and the wear (patterns, location, material loss) of three resilient unsplinted AS: a well-established ball attachment system (BAS) and two more recent cylindrical attachment systems (CAS), Locator R-Tx® and Novaloc®. The implants, their corresponding abutments, the color-coded or position-coded retention devices (RD), the matrix metal housing were incorporated within CAD/CAM resin blocks and cyclically loaded with 19.6 N along the implant axis in a chewing machine to simulate 10,000 insertion-removal cycles (IRC). At cycle 10, 100, 1,000, 5,000, and 10,000, the retention force was measured using a universal testing machine. The wear was qualitatively examined using a binocular magnifier for both systems, and quantitatively assessed from micro-computed tomography acquisitions for CAS. Material loss exceeding 50 μm was considered significant. The three AS showed different retentive behavior along time. All the Locator R-Tx® RD lost more than 50 % of their retention after 10,000 IRC. The retention of the Ball System slightly varied over time, the final retention loss in B med and B max groups being lower than 25 % of the initial retention. Wear was located at the tip of their gold RD and at the equator area of their ball abutment. For Locator R-Tx®, the more retentive the plastic RD, the greater its wear and retention loss. Only Novaloc® maintained a stable retention with even a slight tendency to increase and showed a negligible wear. Implant abutments of the CAS showed no significant wear. After 10,000 IRC, corresponding to approximately 5-years clinical use, almost all RD provided retention force over 5 N, which could be sufficient to maintain satisfaction in most of the patients. The retention loss observed most prominently for the Locator R-Tx®, then for the Ball System, seemed to correlate with the wear observed on their RD. The practitioner may expect less RD maintenance with the Novaloc® stable retention overtime. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this in vitro study was to evaluate the influence of cement type and application technique on seating discrepancies and retention forces of noble alloy castings cemented on titanium abutments. Materials and Methods: Eugenol-free zinc oxide (Freegenol), zinc phosphate (Harvard), glass ionomer (KetacCem), polycarboxylate (Durelon), and self-adhesive resin (RelyX Unicem) cements were used. The inner surfaces of the castings were either completely coated or half-coated with cement. Abutments were used as delivered with a machined surface for the first part of the study. Groups of 8 castings were cemented in both ways. For the second part of the study, the abutments were air-abraded (aluminum oxide, 50 μm particle size), and groups of 8 completely coated castings were cemented with all cements. Marginal discrepancies were measured before and immediately after cementation. Tensile tests were conducted to measure the retention forces. Statistical analysis was performed with pair-wise comparison using the Wilcoxon rank sum test modified by Bonferroni-Holm. Results: Change in seating discrepancies did not differ significantly among the different application techniques. The median retention forces for completely-coated castings were 177 N for eugenol-free zinc oxide, 346 N for zinc phosphate, 469 N for glass ionomer, 813 N for polycarboxylate, and 653 N for self-adhesive resin. With respect to retention force, 3 significantly different groups (P ≤ .05) were identified: (1) zinc oxide, (2) zinc phosphate/glass ionomer, and (3) polycarboxylate/self-adhesive resin. No differences in retention between the 2 coating techniques were found for any cement. However, air abrading the abutments resulted in increased retention of the castings for some of the cements. Conclusions: Half-coating of the restorations with cements did not result in reduced retention values compared to the complete coating technique, but air abrasion resulted in increased retention with some cements. [ABSTRACT FROM AUTHOR]

The retention force of electronic connectors, in general one of the essential specification requirements, is defined as a maximum force of metallic terminals withdrawn out of the corresponding plastic housing. Accurate prediction of the retention force is an important issue in the connector design stage; however, it is not an easy task to accurately assess the retention force based on the authors’ knowledge. A finite element analysis is performed in conjunction with a self-coded user subroutine accounting for relaxation/creep behaviors of semi-crystalline thermoplastic polymers under various loading conditions in order to appraise the mechanical performance of the plastic base structure. Material parameters adopted in the constitutive model are evaluated by utilizing the automated design exploration and optimization commercial software. Applications of the developed subroutine with several damage criteria to assess retention forces of two electronic connectors were conducted. Retention forces predicted by utilizing the current constitutive model agreed fairly well with the associated experimental measurements. A dramatic improvement of the underestimation of the retention force based on the approach commonly adopted in the industry is also demonstrated here.

The aim of this study was to investigate the effects of saliva contamination and the cleaning of the bond surface of titanium base (ti-base) abutments on the bonding stability and retention force values. The bond surface of the ti-base abutments was treated with airborne-particle abrasion. After contamination, the ti-base abutments underwent different cleaning protocols: water spray (H2O); alcohol (ALC); suspension of zirconium particles (SZP); reapplied airborne-particle abrasion (APA); and a control condition without contamination and cleaning (CTR). All lithium disilicate crowns were bonded to the ti-base abutments using a primer and a self-curing composite. Bonded specimens underwent thermo-mechanical aging. Bond failure analysis and pull-off testing were performed. Bond failure occurred more frequently in groups H2O, ALC, SZP, and APA (p < 0.05). Significant differences in retention force values were only found between CTR and ALC (p < 0.05). Specimens which did not show bond failure after ageing had higher retention force values than the specimens that showed bond failure (p < 0.05). Saliva contamination with cleaning can degrade the bonding properties to titanium. For the retention force values, only the protocol with alcohol after contamination could not restore the values.

Aim: The aim of this study is to compare the retention force of three different types of overdenture attachment systems used in implant-retained mandibular complete overdentures. Materials and Methods: Twenty-one similar acrylic resin blocks were prepared and divided into three study groups: Group A (snap attachment) - 10 specimens, Group B (locator attachment) - 1 specimen, and Group C (syncone attachment) - 10 specimens. A single rectangular heat cure acrylic resin block with two implant analogs 22 mm apart was used with all specimens. Each specimen was subjected to 5500 cycles of insertion and removal in the presence of artificial saliva, representing 5 years of usage. Retention was measured three times for each specimen using universal testing machine. Data were analyzed using one-way and two-way analysis of variance at 95% level of confidence. Results: Locator attachment group (Group B) showed the greatest retention level throughout the study, followed by snap attachment (Group A), and syncone attachment (Group C) showed the lowest retention level. Conclusion: Regardless of the initial retention level of overdenture attachment, gradual loss of retention values is inevitable. However, the rate of retention loss in overdenture attachments is higher in types which comprised plastic parts within their components, rather than those totally made up of noble metals.

Removable implant-anchored dentures have become an established treatment concept especially for older, multimorbid patients. This study investigates the retention force (RF) of two different attachment systems. A total of 96 specimens (n = 8 for each condition) were fabricated and RF was measured under different conditions: fatigue (10,000 cycles dislodging), thermal undulation (5/55 °C, 5000 cycles) and implant-angulation (0°, 5°, 10°, 15°, 20°). The Novaloc system ((N), 0° and 15° abutments, yellow matrix (Y)) was compared to the Locator system ((L), pink (P) and orange (O)). Initial RFs (8.57 ± 0.99 N (NY), 19.39 ± 8.10 N (LP), 8.8 ± 5.28 N (LO)) were reduced by ageing simulation (26% (NY), 66% (LP), 89% (LO); p < 0.001). After thermocycling, Novaloc’s RFs decreased by 33% (p < 0.001) while the Locators’ RFs increased by 34% (LP: p = 0.002, LO: p = 0.148). In contrast to LP, the RFs of Novaloc abutments and LOs predominantly showed no clinically relevant dependence on implant angulation. Ageing processes tended to result in lower RFs at higher implant angulation. Thus, the Novaloc attachment system offers an alternative to Locator attachments. It is characterized by a comparatively continuous RF-curve over the entire wearing period. Future clinical studies have to be conducted to verify the in vitro demonstrated advantages of the Novaloc system.

The aim of this study was to compare the retention forces after artificial aging of telescopic crowns fabricated either by a conventional lost-wax technique or by computer-aided design/computer-aided manufacturing (CAD-CAM) technology. Two types of telescopic crowns (0°) were fabricated conventionally using high-noble (group A) and non-precious metal (group B). CAD-CAM fabricated telescopic crowns (0°) were made of non-precious metal (group C). Retention forces were assessed before and after artificial aging and after axial and non-axial loading. Initially [I.] and after artificial aging [IV.], specimens of group C (I. 16.2 N; IV. 13.6 N) exhibited the highest retention forces. The retention forces in groups B (I. 12.5 N; IV. 4.6 N) and A (I. 9.6 N; IV. 2.9 N) were found to be lower than those of group C. The retention force differences between the groups were statistically significant (p < 0.001) at all measurement times [I. vs. IV.]. Different fabricated telescopic crowns with approximately identical designs and materials exhibited different retention forces and different long-term retentive behavior. An optimized CAD-CAM process with individually defined design parameters ensured telescopic crowns with a better fit. These findings might influence prospective clinical decision-making.

Abstract This in vitro study evaluated the effects of different abutment axial heights on the retentiveness of adhesively and self-adhesively luted zirconia copings. Ankylos implants were embedded in resin blocks. Two groups of titanium abutments (“long”, height: 6.79 mm, taper: 4.8°; “short”, height: 4.31 mm, taper: 4.8°; Compartis-ISUS, DeguDent) were used for the luting of CAD/CAM-fabricated zirconia copings (Compartis, DeguDent) with an adhesive (Multilink Automix; Ivoclar Vivadent) and a self-adhesive (RelyX Unicem; 3M ESPE) composite. After water storage and 5000 thermocycles (5 °C/55 °C), retention forces were evaluated using a universal testing machine (Zwick). Significant differences were determined via two-way ANOVA and t -tests with Bonferroni-Holm correction. Significant interactions between abutment geometry and luting agents were observed. RelyX Unicem showed the highest levels of retentiveness, irrespective of the varying abutment geometries (mean values long/short: 487.7 N/447.9 N). When Multilink Automix was used, removal forces were significantly lower (311.7 N/101.1 N) and negatively affected by the use of the shorter abutments. Customized long abutments supported better retention forces than customized short abutments for both luting agents. [ABSTRACT FROM AUTHOR]

Highlights • A model for rational design of laser-sintered circumferential clasps is proposed. • The model adjusts for tooth type, stress, alloy properties, undercut and retention. • The model helps to avoid plastic deformation and fatigue failure in clasps. • Laser-sintered Co–Cr circumferential clasps are vulnerable to failure in premolars. Abstract Objective Clasps of removable partial dentures (RPDs) often suffer from plastic deformation and failure by fatigue; a common complication of RPDs. A new technology for processing metal frameworks for dental prostheses based on laser-sintering, which allows for precise fabrication of clasp geometry, has been recently developed. This study sought to propose a novel method for designing circumferential clasps for laser-sintered RPDs to avoid plastic deformation or fatigue failure. Methods An analytical model for designing clasps with semicircular cross-sections was derived based on mechanics. The Euler–Bernoulli elastic curved beam theory and Castigliano’s energy method were used to relate the stress and undercut with the clasp length, cross-sectional radius, alloy properties, tooth type, and retention force. Finite element analysis (FEA) was conducted on a case study and the resultant tensile stress and undercut were compared with the analytical model predictions. Pull-out experiments were conducted on laser-sintered cobalt–chromium (Co–Cr) dental prostheses to validate the analytical model results. Results The proposed circumferential clasp design model yields results in good agreement with FEA and experiments. The results indicate that Co–Cr circumferential clasps in molars that are 13 mm long engaging undercuts of 0.25 mm should have a cross-section radius of 1.2 mm to provide a retention of 10 N and to avoid plastic deformation or fatigue failure. However, shorter circumferential clasps such as those in premolars present high stresses and cannot avoid plastic deformation or fatigue failure. Significance Laser-sintered Co–Cr circumferential clasps in molars are safe, whereas they are susceptible to failure in premolars. [ABSTRACT FROM AUTHOR]

Despite the extensive study of wetting in literature, there are still many unresolved issues regarding forced wetting . One of them refers to the effect of the initial droplet shape on the force required for spreading and sliding along a solid surface; an effect that has not ever been explicitly reported. Previous experimental works, in general, assume initially axisymmetric droplet shapes. In this study, experiments are performed with an innovative device, Kerberos, capable of subjecting sessile droplets at different tilting angles to varying centrifugal forces in order to explore the spreading/sliding behavior of droplets of different volumes and different initial shapes (including non-axisymmetric). A broad validation of the technique is achieved by the repeatability and consistency of measurements. Results for initially axisymmetric and non-axisymmetric droplets concerning contact angles, droplet length, droplet shape and velocity are presented and discussed. Furthermore, detailed results for the critical tangential accelerations required for the inception of spreading and sliding are presented showing the different sensitivity of these parameters on the droplet initial shape. Experimental results are employed to test the applicability of the well-known Furmidge equation for the retention force in the case of initially non-axisymmetric droplets. On this account, the initial length of droplets is found to be a more appropriate length scale in the Furmidge equation than the initial droplet width. [ABSTRACT FROM AUTHOR]

Objectives: The aim of the study was to compare the retentive behaviors of double crowns with different designs and material compositions before and after artificial aging.Materials and methods: Six pairs of double crowns were fabricated: telescopic crowns 0° made of high-noble metal (group A) or non-precious metal (group B), telescopic zirconia copings with secondary crowns made of electroplated gold 2° (group C), crowns with friction pins 2° made of non-precious metal (group D) or zirconia (group E), and conical crowns 6° made of high-noble metal (group F). Retention forces were assessed before and after artificial aging, and after axial and non-axial loading.Results: Initially, specimens in group D (13.9 N), B (12.5 N), and E (12.2 N) exhibited the highest retention forces. Retention forces in groups A (9.6 N), C (7.4 N), and F (6.0 N) were statistically significantly lower than those of the other groups (p < 0.05). After artificial aging, double crowns with additional retention elements exhibited the highest retention forces. The largest retention force losses were evident in groups A (70%), B (64%), C (39%), and F (47%).Conclusions: Double crowns with different designs and made of different materials exhibited different retention forces and different long-term retentive behavior. The highest retention force losses were evident in double crowns with more extended surface contact, such as telescopic crowns.Clinical significance: Telescopic crowns with additional retention elements were more resistant to wearing than double crowns without additional retention elements. An additional clinical benefit might be the quick and easy possibility of enhancing retention. [ABSTRACT FROM AUTHOR]

Press‐fit technology is a well‐known process in electrical joining and connecting. This process is combined with a subsequent ultrasonic excitation of the printed circuit board (PCB) to enhance the retention force. No additional temperature treatment is necessary because the holding force increases directly after the process. It is discussed how the amplitude and the duration of ultrasonic excitation determine the resulting retention force. A suitable set of parameters is found to increase the retention force. The materials details of the bonds are analyzed. Two models are created to explain the results. These models can be used to predict the retention force for further investigations with changed geometries or materials. [ABSTRACT FROM AUTHOR]

Mandarin thinning is done by hand, increasing labor costs and raising total crop production costs. Mechanical thinning has been tested in peaches and other fruits. To achieve the maximum efficiency thinning has to be applied at a specific stage of vegetative development. In this research study, the mechanical thinning of ‘Clemenrubi’ mandarin branches during the different fruit development stages have been assessed using a vibratory laboratory device (amplitudes 0.015 and 0.030 m and frequencies 34.8 and 37.8 Hz). Branches with flower buds, flowers, small green fruits, and medium green fruits were tested for 12 weeks, in two different seasons. It was possible to mechanically detach flower buds, flowers, and green fruits using different combinations of amplitudes and frequencies. Removal percentage decreased when increasing retention traction force, according to a logarithmic regression model. A significant increment in equatorial diameter and retention traction force was registered when the fruit setting was finishing, while mass had a similar development with a week delay. During fruit setting (weeks 5, 6, and 7) removal percentage was higher, while the retention force was very low. The first weeks just after the natural thinning could be considered the adequate time for a mechanical thinning operation.

PURPOSE. The purpose of this study was to analyze the retention force changes and wear behaviours of doublecrown systems over long-term use. MATERIALS AND METHODS. Ten groups, each consisting of six samples, were evaluated. Specifically, casting gold alloy primary crown - casting gold alloy secondary crown (AA), laser sintering primary crown - laser sintering secondary crown (LL), casting Cr alloy primary crown - casting Cr alloy secondary crown, (CC) zirconia primary crown - electroformed secondary crown (ZA), and CAD/CAM titanium alloy primary crown - CAD/CAM titanium alloy secondary crown (TT) groups were evaluated at cone angles of 4° and 6°. The samples were subjected to 5,000 insertion-separation cycles in artificial saliva, and the retention forces were measured every 500 cycles. The wear levels were analyzed via SEM at the beginning and end of the 5,000 cycles. RESULTS. In all samples, the retention forces increased when the conus angle decreased. The highest initial and final retention force values were found in the LL-4° group (32.89 N-32.65 N), and the lowest retention force values were found in the ZA6° group (5.41 N-6.27 N). The ZA groups' samples showed the least change in the retention force, and no wear was observed. In the other groups, wear was observed mostly in the primary crowns. CONCLUSION. More predictable, clinically relevant, and less excursive retention forces can be observed in the ZA groups. The retention force values of the LL groups were statically similar to those of the other groups, except the ZA groups. [ABSTRACT FROM AUTHOR]

Introduction. Double telescopic crowns are connecting elements of partial dentures and are considered to be prosthetic devices of high aesthetic and biological value. Their basic drawback is the assessment of retention force value which has to be strong enough to balance the opposite forces but, nevertheless, must not result in harming the periodontal tissue of retention teeth while taking the denture off. The retention force is the highest immediately after the denture's construction and is progressively declining until the end of the 'settling in phase', i.e. until the retention force value becomes well-established. Aim of the study was the measurement of the overall retention force of completed telescopic dentures and a survey of 'settling in phase' duration. Methods. The measuring was conducted on 20 telescopic dentures consisting of 2, 3 or 4 telescopic crowns made of gold alloy type IV and executed by dynamometer. Results. An optimal retention force was detected in only 37% of telescopic dentures. An insufficient retention force was observed in 16%, while in the remaining 47% an excessive force was detected. In the largest number of dentures (35%) the settling in phase began after 33 cycles, which shows that this phase takes on average 10,6 days. Conclusion. The 'settling in phase', during which retention force becomes stabilized, is completed in the first ten days after the delivery of the completed telescopic denture.

Oral appliance (OA) therapy with a mandibular advancement device (OAm) is a non-invasive, alternative approach to maintaining upper airway patency. The main requirement for an OAm to be effective is the adequate retention on the teeth while the patient is asleep. We evaluated the retentive forces of a new low-cost, customizable, titratable, thermoplastic OAm (BluePro ®; BlueSom, France). Dental impressions and casts were made for one patient with complete upper and lower dental arches including the third molars and class II bite proportions. A setup based on Frasaco ANA-4 models was also used. Two protrusive positions of the mandible were investigated: 3 mm and 8 mm, representing respectively 25% and 65% of the maximal protrusion. The forces required to remove the BluePro ® device from the carriers were recorded continuously over 730 cycles (=365 days, twice a day) to simulate 1 year of clinical use. At 8 mm protrusion the BluePro ® device showed retentive forces of ~27N. There was a slight but non-significant decrease in retentive forces in the tests on the epoxified carriers which was not found on the ANA-4 carriers. There were no significant differences between the carriers as a function of protrusion. The BluePro ® device tested in the present study possesses sufficient retention forces to resist initial jaw opening forces and full mouth opening forces estimated to be ~20N. It could therefore broaden the indications for use of thermoplastic OAms. It could provide a temporary OAm while a custom-made OAm is being manufactured or repaired. Patients could be provided with a low-cost try-out device capable of reliable titration, providing an indication of effectiveness and of patient acceptance of an OAm, although the effect of device shape and size on therapeutic outcome is not yet known. Finally it could provide an affordable OAm solution in resource-restricted healthcare settings.

The retention force of cemented crowns on implant abutments with various luting materials was evaluated. Cobalt–chromium crowns were cemented onto tapered titanium abutments (Camlog) with eugenol-free temporary cement (RelyX TempBond NE), composite-based temporary cement (Bifix Temp), zinc phosphate cement (Harvard Cement), glass-ionomer cements (Meron, Fuji I), and resin-modified glass-ionomer cements (Fuji II, Fuji Plus, Ketac Cem Plus). Specimen aging via hydrostress was performed in artificial saliva at 37 °C for 14 days (S1), followed by hydrothermal stress with thermocycling (S2). The crowns were removed, and the force was recorded (T1). Subsequently, the crowns were recemented, aged, and removed, and the force was recorded (T2, T3). The retention forces differences were statistically significant according to the storage conditions at T1 (p = 0.002) and T3 (p = 0.0002). After aging (S1), Ketac Cem Plus had the highest retention force median value difference (T3 versus T1) (−773 N), whereas RelyX TempBond NE had the lowest (−146 N). After aging (S2), Meron had the highest retention force median value difference (−783 N), whereas RelyX TempBond NE had the lowest (−168 N). Recementation decreased the retention force of the implant-supported cobalt–chromium crowns cemented and recemented with the same luting materials. Luting materials (at T1) and aging conditions significantly impacted the retention force.

Aim: The aim of this study is to compare the retention force of three different types of overdenture attachment systems used in implant-retained mandibular complete overdentures. Materials and Methods: Twenty-one similar acrylic resin blocks were prepared and divided into three study groups: Group A (snap attachment) -10 specimens, Group B (locator attachment) -1 specimen, and Group C (syncone attachment) -10 specimens. A single rectangular heat cure acrylic resin block with two implant analogs 22 mm apart was used with all specimens. Each specimen was subjected to 5500 cycles of insertion and removal in the presence of artificial saliva, representing 5 years of usage. Retention was measured three times for each specimen using universal testing machine. Data were analyzed using one-way and two-way analysis of variance at 95% level of confidence. Results: Locator attachment group (Group B) showed the greatest retention level throughout the study, followed by snap attachment (Group A), and syncone attachment (Group C) showed the lowest retention level. Conclusion: Regardless of the initial retention level of overdenture attachment, gradual loss of retention values is inevitable. However, the rate of retention loss in overdenture attachments is higher in types which comprised plastic parts within their components, rather than those totally made up of noble metals. [ABSTRACT FROM AUTHOR]

To assess the retention force between primary and secondary PEEK crowns made by different fabrication methods. Primary crowns with different tapers (0°, 1°, and 2°) were fabricated and secondary crowns that were either milled from breCam BioHPP blanks, pressed from pellets (BioHPP Pellet) or granules (BioHPP Granulat) were produced. Each specimen was measured 20 times in a pulloff- test and results were analyzed using 2-/1-way ANOVA and linear regression analyses (p<0.05). Within 0° tapered crowns milled secondary crowns showed lower retention forces compared to pressed pellet crowns. Crowns with a 1° taper, however, showed no impact of the fabrication method on retention force. At a 2° taper, granular pressed crowns displayed lower values than their milled counterparts. Within the milled group, a 0° taper showed lower retention values than the higher tapers, whereas in the pressed groups, no impact of taper angle on retention force was found. [ABSTRACT FROM AUTHOR]

In prosthetic dentistry, double crown systems have proved their suitability as retainers for removable partial dentures. However, investigations in this context, regarding polyetheretherketone, are scarce. Therefore, the aim of this study was to test the retention force (RF) between polyetheretherketone (PEEK) primary and cobalt-chromium (CoCr), zirconia (ZrO2) and galvanic (GAL) secondary crowns with three different tapers. Primary PEEK-crowns were milled with the tapers 0°, 1°, and 2° (n = 10/taper, respectively). Afterwards, 90 secondary crowns were fabricated: (i) 30 CoCr-crowns milled from Ceramill Sintron (AmannGirrbach, Koblach, Austria) (n = 10/taper), (ii) 30 ZrO2-crowns milled from Ceramill ZI (AmannGirrbach, Koblach, Austria) (n = 10/taper), and (iii) 30 GAL-crowns made using electroforming (n = 10/taper). RF was measured in a pull-off test (20 pull-offs/specimen) and data were analyzed using 2-/1-way Analysis of Variance (ANOVA) followed by the Tukey-Honestly Significant Difference (HSD) post hoc test and linear regression analyses (p < 0.05). The measured mean RF values ranged between 9.6 and 38.2 N. With regard to the 0°, 1°, and 2° tapered crowns, no statistically significant differences between CoCr and ZrO2 were observed (p > 0.141). At 0° taper, no differences in retention forces between GAL, CrCr, and ZrO2 crowns were found (p = 0.075). However, at 1° and 2° taper, lower RF for GAL-crowns were observed (p < 0.009, p < 0.001, respectively). According to this laboratory study, PEEK might be a suitable material for primary crowns, regardless of the taper and the material of secondary crown. Long-term results, however, are still necessary. [ABSTRACT FROM AUTHOR]

OBJECTIVE: The aim of this study is to compare the retention forces of three nylon males of Locator attachments i.e. clear or white, pink and blue. METHODOLOGY: A two implant retained overedenture model used to simulate the patient. Three pairs of each male attachment were subjected to vertical dislodgement forces using the Instron testing machine. RESULTS: The white attachment showed the highest retention force with a peak load-to-dislodgement of 35.49+-3.24 Nfollowed by the blue (19.02 ± 5.32 N) and then the pink male attachment (15.5 ± 2.52 N). CONCLUSION: The results of this study are in agreement of other studies in regard to the values of the retention forces of the white and pink male attachments. However, it is in disagreement of the claim that the blue male attachment has the least retention forces. [ABSTRACT FROM AUTHOR]

In prosthetic dentistry, double crown systems have proved their suitability as retainers for removable partial dentures. However, investigations in this context, regarding polyetheretherketone, are scarce. Therefore, the aim of this study was to test the retention force (RF) between polyetheretherketone (PEEK) primary and cobalt-chromium (CoCr), zirconia (ZrO2) and galvanic (GAL) secondary crowns with three different tapers. Primary PEEK-crowns were milled with the tapers 0°, 1°, and 2° (n = 10/taper, respectively). Afterwards, 90 secondary crowns were fabricated: (i) 30 CoCr-crowns milled from Ceramill Sintron (AmannGirrbach, Koblach, Austria) (n = 10/taper), (ii) 30 ZrO2-crowns milled from Ceramill ZI (AmannGirrbach, Koblach, Austria) (n = 10/taper), and (iii) 30 GAL-crowns made using electroforming (n = 10/taper). RF was measured in a pull-off test (20 pull-offs/specimen) and data were analyzed using 2-/1-way Analysis of Variance (ANOVA) followed by the Tukey-Honestly Significant Difference (HSD) post hoc test and linear regression analyses (p < 0.05). The measured mean RF values ranged between 9.6 and 38.2 N. With regard to the 0°, 1°, and 2° tapered crowns, no statistically significant differences between CoCr and ZrO2 were observed (p > 0.141). At 0° taper, no differences in retention forces between GAL, CrCr, and ZrO2 crowns were found (p = 0.075). However, at 1° and 2° taper, lower RF for GAL-crowns were observed (p < 0.009, p < 0.001, respectively). According to this laboratory study, PEEK might be a suitable material for primary crowns, regardless of the taper and the material of secondary crown. Long-term results, however, are still necessary.

Objectives: To evaluate zirconia as a substitute for gold alloy in primary crowns facing secondary crowns manufactured with different materials, in terms of long-term retention force changes, wear, and phase transformation was aimed. Materials and Methods: A total of 12 groups, each containing six samples, consisting of gold alloy primary crown-electroformed gold secondary crowns (AA), zirconia primary crown-electroformed gold secondary crowns (ZA) and zirconia primary crown-casted non-precious alloy secondary crowns (ZC) with conus angles of 0°, 2°, 4°, and 6° were evaluated. Samples were subjected to 10,000 insertion-separation cycles in artificial saliva and retention force was measured. X-ray diffraction and scanning electron microscope analysis were performed on the sample surfaces. Results: The highest retention forces were obtained from ZC-0° group (72.09-71.26 N) and the lowest were obtained from ZA-4° (12.73-19.44 N) and ZA-6° (5.36-19.73 N) groups in the beginning and after 10,000 cycles, respectively. Retention force increased as the conus angle decreased. The monoclinic phase ratio of the zirconia primary crowns decreased after the experiments. No wear was observed in zirconia primary crowns except for the ZC-0° and ZC-2° groups. The use of zirconia primary crowns resulted in a less excursive retention force. Conclusions: A more predictable and less excursive retention force can be obtained using a hard and rigid primary crown material like zirconia. Clinical Relevance: Despite a lack of knowledge about the aging of zirconia without a veneer layer in the oral environment, zirconia primary crowns are more advantageous in terms of retention force development and wear. [ABSTRACT FROM AUTHOR]

Objective The cost-effectiveness of cast nonprecious frameworks has increased their prevalence in cemented implant crowns. The purpose of this study was to assess the effect of the design and height of the retentive component of a standard titanium implant abutment on the fit, possible horizontal rotation and retention forces of cast nonprecious alloy crowns prior to cementation. Materials and Methods Two abutment designs were examined: Type A with a 6° taper and 8 antirotation planes ( Straumann Tissue- Level RN) and Type B with a 7.5° taper and 1 antirotation plane ( SICace implant). Both types were analyzed using 60 crowns: 20 with a full abutment height (6 mm), 20 with a medium abutment height (4 mm), and 20 with a minimal (2.5 mm) abutment height. The marginal and internal fit and the degree of possible rotation were evaluated by using polyvinylsiloxane impressions under a light microscope (magnification of ×50). To measure the retention force, a custom force-measuring device was employed. Statistical analysis: one-sided Wilcoxon rank-sum tests with Bonferroni- Holm corrections, Fisher′s exact tests, and Spearman's rank correlation coefficient. Results Type A exhibited increased marginal gaps (primary end-point: 55 ± 20 μm vs. 138 ± 59 μm, P < 0.001) but less rotation ( P < 0.001) than Type B. The internal fit was also better for Type A than for Type B ( P < 0.001). The retention force of Type A (2.49 ± 3.2 N) was higher ( P = 0.019) than that of Type B (1.27 ± 0.84 N). Reduction in abutment height did not affect the variables observed. Conclusion Less-tapered abutments with more antirotation planes provide an increase in the retention force, which confines the horizontal rotation but widens the marginal gaps of the crowns. Thus, casting of nonprecious crowns with Type A abutments may result in clinically unfavorable marginal gaps. [ABSTRACT FROM AUTHOR]

Attachment systems (AS) enhance retention and stability by anchoring the overdentures to implants. Since 2002, the McGill consensus statement recommends the 2-implant-retained overdentures as the standard choice for edentulous mandible (2-IRMO). Considering the large number of AS available, it remains difficult for a practitioner to make a reasoned choice. A systematic review was conducted in PubMed/Medline and carried out independently by three authors, on retention, wear, and maintenance of AS used clinically or in vitro specifically for 1- or 2-IRMO. The 45 selected studies include 14 clinical and 31 in vitro studies. The risk of bias was evaluated according to the revised Cochrane risk of bias tool for randomized trials (RoB 2). The initial retention force of the cylindrical system is higher than the ball system. The retention loss, related to the wear of the retention device, is responsible for the most common need of maintenance, requiring activation or replacement. Plastic retention devices wear out faster and more significantly than metal ones, implying a worse time behavior of cylindrical systems, but their maintenance rate is similar. Neither system appears categorically superior. Cylindrical systems provide higher initial retention than ball ones; this advantage reduces over time with wear without affecting their need for maintenance. [ABSTRACT FROM AUTHOR]

The aims of this study were to investigate the retention force changes of different attachment systems after 10,000 insertion-separation cycles and the difference in retention force between precious and non-precious materials of the same attachment system. Four types of attachments (Ball, Rod, M3 stud, andAP-Piccolino), produced using both precious and non-precious metal alloys, were tested (re=6). Data were analyzed using analysis of variance (ANOVA), Tukey's multiple comparison test, and J-test at a significance level of p⩽0.05. Retention forces of all attachment types were significantly decreased after 10,000 insertion-separation cycles (p<0.05). Rod and M3 attachment systems showed an initial increase in retention force, then an eventual decrease. At the end of the test, precious types of M3 and AP-Piccolino attachments had significantly higher retention force values than their non-precious ones (p⩽0.05). Friction between non-precious attachment parts resulted in a higher retention loss than precious metal alloys. [ABSTRACT FROM AUTHOR]

The puprose of this study was to evaluate retention force of conical double crowns in two material connections: gold casting alloy/gold casting alloy and gold casting alloy/gold electroforming alloy. 12 crown pairs of both material connections with the cone angles of 2°, 4° and 6° were made. Experiment of 10.000 in-and-out cycles was performed using a new device which allows the retentive force to be measured in continuous way without necessity of moving the samples to another device. It has been found that the higher the retentive force values, the lower the cone angle. Dispersion of the retention value was similar in both groups, but when cone angle was 2° or 4°, stability of retention force with the passage of time was higher in combinations with electroformed copings. The optimum solution was the cast alloy/cast alloy connection but only with cone angle 6°. However, retentive values seem to be too low to achieve proper retention of dentures. [ABSTRACT FROM AUTHOR]

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Gerodontology 2010; doi: 10.1111/j.1741-2358.2009.00352.x Influence of the lubricant and the alloy on the wear behaviour of attachments Objectives: Wear of attachments leads to a loss of retention and reduces the function of overdentures. This study evaluated the retention force changes of an attachment system for overdentures. The influence of the lubricant and the alloy on wear constancy was examined. Methods: Cylindrical anchors of the Dalbo®-Z system were tested (Cendres+Métaux SA). Three groups of alloy-lubricant combinations were generated 1.Elitor®/NaCl-solution (EN) 2.Elitor®/Glandosane®aquadest. (EG) and 3.Valor®/Glandosane®/aquadest. (VG). Ten samples of each group were subjected to 10 000 insertion-separation cycles. Results: For the EN-group, this led to a large increase in retention force. The EG- and VG-group showed a constant decrease after an initial increase in retention force at the beginning of the wear simulation. The change of the alloy caused no statistically significant differences. The use of a more viscous lubricant reduced the retention force increase significantly. Conclusions: The use of a lubricant which simulates clinical conditions is an absolute need for wear simulation because the retention force changes are influenced enormously. The change of the alloy at the Dalbo®-Z system did not influence the wear behaviour. As a slight decrease in retention force was recorded, it is useful for an attachment system to allow compensation with an adjustable matrix. [ABSTRACT FROM AUTHOR]