Retention Force Research Articles

Performance of Graphene-Based and Polyether-Ether-Ketone Polymers as Removable Partial Denture Esthetic Clasp Materials after Cyclic Fatigue.

The esthetic clasp material is a clinical demand for a satisfactory removable partial denture. The purpose of this study is to assess the mechanical performance of graphene-based polymer (GBP) and polyether-ether-ketone (PEEK) materials as clasp materials. Thirty-two clasps were fabricated by CAD-CAM from two materials, GBP and PEEK. All clasps were tested for retention force after 10,000 cycles of insertion and removal and thermocycling. The clasp arms’ deformation was measured, and areas of stress–strain concentration were explored. The Mann–Whitney U test was used to compare the retentive force of the studied groups, while the independent sample t-test was applied to check the difference in clasp arm deformation at α = 0.5. The results showed a significantly higher retentive force (2.248 ± 0.315 N) in PEEK clasps, at p < 0.001. The deformation of the clasp arm of the GBP clasps was significantly higher than PEEK clasps. Areas of stress–strain concentration were seen at the junction of the retentive arm to the minor connector and at the retentive arm terminal. It could be concluded that PEEK polymer had a better mechanical performance as an esthetic clasp material than the GBP. An optimization study for GBP might be required to check the validity of such an application.

Effect of traction direction and pressure load on the palatal plate on retentive force

BackgroundRecently, a denture adhesive that is easy to clean and contain moisturizing ingredients have been developed for patients with dry mouth. Although the retentive force produced by conventional denture adhesives and oral moisturizers have been compared on models, no study has reported their comparison in the oral cavity. In this study, we aimed to clarify the effects of different directions of traction and loads at the time of pressure contact on the retentive force on a palatal plate made from a dentulous jaw model.MethodsA palatal plate was fabricated with thermoplastic resin on a dentulous jaw model, and a loop-shaped traction device was attached to the centre of the palate. The test samples were a cream-type denture adhesive, a denture adhesive for dry mouth, an oral moisturizer, and a denture moisturizer. The specimens were applied to the inner surface of the plate, which was then mounted under vertical pressure. Then, the retentive force was measured, using a digital force gauge, while the plate was pulled in different directions and with different loads.ResultsNo significant difference in retentive force was observed in any of the test samples when the direction of traction was between 45° and 60°. The retentive force of the denture adhesive for dry mouth was significantly higher with a direction of traction of 90° than that of 45° or 60°. The retentive force when oral moisturizer was used was significantly higher in the 90° traction direction than in the 45° direction. There was no significant difference between a force of 4.0 kgf or 5.5 kgf when using a denture adhesive for dry mouth. Comparing the four load size conditions, the larger the load, the higher was the retentive force. Similar results were obtained for the cream-type denture adhesive and denture moisturizer. Significantly higher retentive force was observed for larger loads when oral moisturizer was used.ConclusionsThe results suggest that the direction of traction and the pressure load affect the retentive force on a palatal plate.

Career satisfaction among working age individuals with multiple sclerosis or spinal cord injury

BACKGROUND: Joint studies of multiple sclerosis (MS) and spinal cord injury (SCI), both types of spinal cord dysfunction, have identified barriers and facilitators to employment and key outcomes including earnings and job benefits. However, there has been an absence of research on satisfaction with employment over one’s career. Such knowledge would help to establish the foundation for targeted vocational rehabilitation interventions. as well as differences in quality of employment outcomes, establishing the foundation for targeted vocational rehabilitation interventions. OBJECTIVE: Identify and quantify demographic, educational, vocational, and functional characteristics associated with career satisfaction, a quality employment outcome, among people with MS and SCI. METHODS: There were a total of 3,371 participants, 1,229 with MS and 2,142 with SCI, all of whom were in the traditional working age range (&lt; 65 years old). Participants were identified from the Southeastern and Midwestern regions of the USA and data were collected, processed, and analyzed at a medical university in the Southeastern USA. Econometric modeling identified factors associated with career satisfaction, as defined by a five-item composite scale that was converted to Z-scores, integrating analysis using both diagnostic groups. RESULTS: Participants who were gainfully employed and those who had left the labor force (unemployed with no hopes to return to work), reported higher career satisfaction than those who were unemployed and hoping to return to work. Higher career satisfaction scores were associated with more formal education and having worked in management/professional, natural resources, or service occupations. Higher scores were also observed among those older, not single, and who had fewer functional deficits. No differences were identified as a function of diagnosis, race-ethnicity, sex, or time since injury/diagnosis. CONCLUSION: Career satisfaction was more strongly related to educational attainment, vocational history, and labor force participation, than to demographic and disability factors. Vocational counselors should target those still in the labor force for skills development, job retention, and reacquisition to promote career satisfaction.

Evaluation of retention and wear of a titanium-formed stud overdenture attachment with different interimplant angulations after simulated clinical use: An in vitro study

Statement of problemHow implant alignment impacts stud attachment retention and wear-induced alterations, notably when the attachment exhibits metal-to-metal frictional interlocking, is unclear. PurposeThe purpose of this in vitro study was to evaluate the effect of the interimplant angulation on retention forces and wear changes before and after 2 years of simulated clinical use of implant overdentures retained by titanium stud overdenture attachments. Material and methodsThe canine regions of 3 identical edentulous mandibular models were used to receive 2 dental implants analogs with TiTach attachments (Dental Evolutions, Inc) at interimplant angulations of 0, 30, and 60 degrees. Six identical overdentures were constructed over each model (n=6). A universal testing machine was used to determine overdenture retention forces at 0, after 1440, and after 2880 insertion and removal cycles to simulate the average insertion and removal cycles in 12 and 24 months. A stereomicroscope, a laser microscope, and a scanning electron microscope were used to evaluate the wear in the attachments. A linear regression model, ANOVA, and the Kruskal-Wallis tests were used to analyze the data (α=.05). ResultsAll groups demonstrated reduced retention over the study duration (P<.001). The retention forces of the 0- and 30-degree groups were not significantly different after 2880 insertion and removal cycles, but both were significantly higher than those of the 60-degree group (P=.002). Within each group, the wear pattern of the matrix cap was more noticeable than that of the patrix abutment, with increased wear changes as interimplant angulation increased (P<.001). ConclusionsTiTach attachments could retain overdentures on parallel and divergent implants with a 30-degree angle of interimplant angulation. However, at a 60-degree angle of interimplant angulation, considerable reduction in retention forces and increased wear changes were observed after 2 years of simulated clinical use.

Retentive force of conical crowns combining zirconia and fiber-reinforced composite

PurposeThis study investigated the retentive force of conical crowns combining zirconia primary and fiber-reinforced composite (FRC) secondary crowns and their changes due to aging. MethodsZirconia primary crowns were produced with a convergence angle of 3°. Thirty-two secondary crowns were milled from FRC and divided into two groups (n = 16/group) based on the polishing method of the secondary crown inner surfaces: diamond paste (Group 1) and silicone points (Group 2). After fitting the secondary crowns with different fitting forces (F), loosening forces (L) were determined. Tests were repeated after an occlusal stop (OS) was added to the secondary crown and artificial aging (10,000 insertion/removal cycles). Data were compared using the Wilcoxon and Mann–Whitney U tests. ResultsCrowns without an OS showed L/F ratios of 0.4586 (Group 1) and 0.4104 (Group 2). With an OS, maximum retention was not significantly affected by the polishing method and could be limited to Lmax = 19.31±7.77 N (Group 1) and Lmax = 16.12±5.92 N (Group 2). ConclusionsThese findings suggest that the combination of conical zirconia primary and FRC secondary crowns can obtain acceptable retentive forces that are not affected by aging if the inner surfaces are polished with diamond paste. OS generation could limit maximum retention, but should be adjusted if the target value of 10 N is not to be exceeded. With a change of the convergence angle to 4°, L/F values for crowns without an OS would be close to 1/3, which is considered ideal for conical crowns. Clinical significanceThe combination of zirconia primary crowns and FRC secondary crowns was found feasible to ensure the required retention for clinical use over a long time span. Furthermore, it offers an alternative to metal-based restorations while ensuring high levels of biocompatibility and esthetics.

Operationalizing the definition of “Commercial Space”

This paper operationalizes (i.e., collects data to test the validity of) propositions based on the evolution change motor applied to market level organizations. At these inter-organizational levels of analysis, Space Race Era activities are characterized as teleologically driven (directed by a centralized agent) and more recent space activities (such as suborbital tourism) as evolution driven (subject to forces of variation, selection, and retention). This definition assumes a continuous (non-dichotomous) definition along three dimensions, depicted as a Cartesian coordinate system, with each orthogonal axis corresponding to the three evolution motor forces. Force components include levels (total amounts from all contributing actors) and robustness (sensitivity to increase or decrease in number of contributing actors) of each. Proxies for the three forces include number and amounts of innovation (for the variation force), funding (for the selection force), and demand (for the retention force). A causal diagram shows the relationship of the proxy variables to market “commercialness” based on two extreme samples cases.

Axial and Non-axial Retention Forces of Milled Titanium Bar Versus Locator-Milled Titanium Bar Attachments in Implant-Supported Maxillary Overdenture: An In Vitro Study

Axial and Non-axial Retention Forces of Milled Titanium Bar Versus Locator-Milled Titanium Bar Attachments in Implant-Supported Maxillary Overdenture: An In Vitro Study

Effect of Indented Structures on the Retention of Cement-Retained Implant-Supported Crowns by Provisional Cement

Purpose: The objective of this study was to investigate the effect of indented structures, such as dimples and retention groove formations, on the retention of titanium abutment walls when cementing cobalt-chromium (Co-Cr) alloy crowns with zinc oxide-eugenol cement. Materials and Methods: Forty-eight titanium abutments (n = 6) were prepared, of which 24 abutments were 4.0 mm and the other 24 were 6.0 mm in height. These 4.0 mm and 6.0 mm abutments were organized into eight groups: no-dimple, 2-dimple, 4-dimple, and axial retention groove groups. The position and dimensions of the dimples and axial retention grooves were the same for all prepared abutments. Laser-sintered cobalt-chromium (Co-Cr) alloy crowns were cemented using a provisional cement. After thermocycling, a retention test was performed using a universal testing machine. Statistical analysis was performed using the nonparametric Kruskal–Wallis test and post-hoc Mann–Whitney U test (𝛼= .05) to compare the mean retentive force. Results: The lowest retentive force recorded was from the 4.0 mm no-dimple group (112.03 ± 20.30). Forming dimples and retention grooves increased the retentive force for the 4.0 mm groups, but the difference was not statistically significant (p > .05). A statistically significant difference was displayed by the 6.0 mm abutment with the 4-dimple group compared to the 6.0 mm no-dimple group (p < .05). Conclusion: Within the limitations of this in vitro study, the mean retentive force was higher with dimples and axial retention grooves for 4.0 mm titanium abutments but was statistically insignificant (p > .05). An increase in abutment height was statistically correlated with an increase in retentive force within the same number of dimple-groups (p < .05).

Effect of Various Retentive Element Materials on Retention of Mandibular Implant-Retained Overdentures.

This study aimed to examine the retentive characteristics of each retentive element material and the effects from thermocycling using the two implant-retained mandibular overdenture model. Two stud abutments and three retentive element materials; nylon, polyetheretherketone (PEEK) and polyvinylsiloxane (PVS) were used in this study. Four tested groups, with a total of 40 overdentures, were fabricated, including a Locator® abutment with nylon retention insert (NY), Novaloc® abutment with PEEK retention insert (PK), Locator® abutment with PVS retention insert (RL), and Novaloc® abutment with PVS retention insert (RN). The retentive force (N) was measured before thermocycling, and at 2500, 5000, and 10,000 cycles after thermocycling. Significant changes in the percentage of retention loss were found in the NY and PK groups (p < 0.05) at 6 and 12 months for the RL group (p < 0.05) after artificial aging. The RN group exhibited a constant retentive force (p > 0.05). The tendency of the percentage of retention loss significantly increased for PEEK, nylon, and PVS silicone over time. The results of the present study implied that retentive element materials tend to lose their retentive capability as a result of thermal undulation and water dispersion. Nylon and PEEK, comprising strong polar groups in polymer chains, showed a higher rate of retention loss than polyvinylsiloxane.

Factors Affecting the Attractive Force of Dental Magnetic Attachment: A Literature Review for Guiding Dentists in Clinical Application.

Aim The aim of this review is to get a comprehensive description of the factors that may influence the attractive force of the dental magnetic attachment. Background Dental magnetic attachment is a term for a magnet used as an overdenture retainer. Magnets that are widely used are permanent magnets such as neodymium iron boron (NdFeB) and samarium cobalt (SmCo). Theoretically, the magnetic attractive force in a permanent magnet has a constant retentive force, and the magnitude of the force will not decrease over time. However, several studies revealed that the magnetic attractive force can be decreased, resulting in the failure of overdenture retention. Some of the factors of reduced magnetic attraction that have been studied are corrosion and temperature. There are no articles that specifically review the factors that can influence magnetic attraction. Review Results. A total of 25,880 articles were obtained during a search on 3 journal databases: PubMed (2,647), ScienceDirect (23,184), and Scopus (229). From those publications, 15 articles reported relevant outcome data that were then extracted. Magnetic attractive force can be influenced by temperature, corrosion, keeper surface morphology, type of magnet, keeper-assembly size combination, inclination, insertion-removal cycle, gliding/loading cycle, number of magnets, crosshead speed, and force direction. Conclusion Many factors can affect the magnetic attraction force of the dental magnetic attachment. Corrosion is the most likely factor to occur because the dental magnetic attachment is always in the oral environment which contains corrosive saliva and is susceptible to damage due to mastication forces.

Pork longissimus dorsi marinated with edible mushroom powders: Evaluation of quality traits, microstructure, and protein degradation

In this study, we examined the effects of marination with five edible mushroom powders (3%, m/m) on the quality attributes and protein changes of pork longissimus dorsi compared to meat marinated with 0.2% papain and distilled water (control group). The results indicated that pork samples marinated with edible mushrooms displayed better water retention and lower shear force, especially in the 3% Hypsizygus marmoreus (HM) group (12.50 ± 0.73 N). Ultrastructural observation results showed that the Z-disk and M-line of the pork samples marinated with edible mushrooms were fractured and weakened. Furthermore, the degradation extent of desmin in the HM-marinated pork samples was obviously increased (43%) in comparison to the papain group (only 15%), which was further confirmed by the results of the myofibril fragmentation index. Overall, the pork samples marinated with 3% HM exhibited better quality traits among all groups and might be a potential strategy to improve tenderness.

Comparison between Two Different Attachment Caps Used in Comparison between Two Different Attachment Caps Used in Locator Attachments of Implant supported Overdentures (In-Vitro Locator Attachments of Implant supported Overdentures (In-Vitro Study)

Purpose: To compare different retentive cap material used in LOCATOR attachments, namely the nylon retentive cap versus PEEK retentive caps, and measure the loss of retention over a period of two years, through 2880 cycles of insertion and removal. Materials and methods: Two implants 3.8mm x 10.5mm were inserted into a clear epoxy resin cast, through a surgical guide, with the implants being 23mm apart. Two LOCATOR attachments with 5 mm gingival height were screwed to the implants, custom made nylon caps were fabricated as an exact replica of the PEEK retentive caps, then two dentures were constructed and pick up were done with both retentive cap materials. A hook was attached to the geometric center of both dentures, and measurement of the retentive forces was accomplished with a universal testing machine, and the data was recorded and analyzed. Results: The amount of retention achieved from PEEK retentive caps was twice that of the nylon retentive caps, indicating high statistical significance (p &lt; 0.001) of the effect of the material and remained so throughout the repeated cycles with (p &lt; 0.001), however both caps showed similar rate of retention loss throughout the study, but the amount of wear was statistically higher in the PEEK group throughout the cycles, except after 2880 cycles. Conclusion: PEEK showed higher retentive properties throughout the cycles, but both materials showed similar rate of retention loss

Fitness accuracy and retentive forces of milled titanium clasp.

Since cast titanium prostheses have many drawbacks, multi-directionally forged titanium grade 2 (MDF) was developed, and the application of the milling process was proposed for improving the titanium clasp. This in vitro study evaluated milled titanium clasps, including MDF titanium. Milling clasps were manufactured with commercially pure (CP) titanium grade 2 (CP 2), grade 4 (CP 4), Ti-6-Al-4V, and MDF. As a control, a CP 2 cast titanium clasp was fabricated in the conventional manner. No porosities and catastrophic failures were observed in the four milled titanium clasps. Fitness accuracy and retentive forces of milled CP 2 and CP 4 tended to be worse, and the milled MDF showed the higher retentive forces (12.45 N) than did cast and milled CP 2 clasps (9.32 N and 4.42 N). Milled titanium clasps can be recommended for longer-term clinical use as compared to cast clasps.

Femtosecond Laser for Cavity Preparation in Enamel and Dentin: Axial Wall Taper Related Factors.

Background and objective: Femtosecond laser (fs-laser) is a novel tooth preparation tool. After cavities were prepared by fs-laser, their axial-wall taper is closely related to the retention force and success of restorations, while the taper after preparation by fs-laser is not clear yet. This study aimed to explore the value of the taper after fs-laser tooth preparation and the effect of laser fluence, scanning line spacing, and scanning layers on taper. Materials and methods: Twenty cavities with a width of 0.5 mm were prepared by an fs-laser both in enamel and dentin to obtain the axial-wall taper (No. PKUSSIRB-201949124). To study the effects of three parameters of fs-laser, five different laser fluence were set as 1.56, 3.13, 4.69, 6.25, and 7.81 J/cm2 of five cavities. Scanning line spacing was set as 6, 12, 25, 30, 40, and 50 μm of six cavities and the scanning layers were 5, 10, 25, 50, 75, 100, 200, 300, and 400, respectively, of nine cavities. Laser pulses irradiated perpendicular to the tooth and the scanning path was controlled via a vibratory mirror. The taper was measured with a laser confocal microscope. Curves of the taper versus different parameters were drawn. Results: There was a significant difference in taper between enamel and dentin. Overall, the taper decreased gradually with the increase of laser fluence. The optimal taper obtained was 20.53° ± 0.28° in dentin and 38.71° ± 0.46° in enamel when the corresponding fluence was 6.25 J/cm2. In comparison, the scanning line spacing has little effect on the taper. The scanning layers significantly affect the taper, which decreased dramatically as scanning layers increased within 75 layers and does not change considerably as it was beyond 100 layers. Conclusions: Reasonable selection of laser fluence, scanning line spacing, and the number of scanning layers can optimize the cavity taper by fs-laser.

The Mechanical Behavior of a Screwless Morse Taper Implant-Abutment Connection: An In Vitro Study.

The use of screwless Morse taper implant–abutment connections (IAC) might facilitate the clinician’s work by eliminating the mechanical complications associated with the retention screw. The aim of this study is to evaluate the effect of artificial chewing on the long-term stability of screwless Morse taper IACs. Thirty-two implant abutments restored with an upper central incisor zirconia crown were used and divided into four groups according to the implant–abutment assembling manner (C1,H: screw retained (20 Ncm); C2: tapped; or C3: torqued (20 Ncm; the screws were removed before the dynamic loading)). All specimens were subjected to a cyclic loading (98 N) for 10 million chewing cycles. The survived samples were exposed to a pull-off force until failure/disassembling of the connection. All the samples revealed a 100% survival. Regarding the pull-off test, the screw-retained internal hexagonal IAC revealed significantly higher resistance to failure/disassembling (769.6 N) than screwless conical IACs (171.6 N–246 N) (p < 0.0001). The retention forces in the Morse taper groups were not significantly different (p > 0.05). The screw-retained hexagonal IAC showed the highest retention stability. The screw preload/retention in the conical IAC was lost over time in the group where the screws were kept in place during loading. Nevertheless, the screwless Morse taper IACs were stable for an extended service time and might represent a valid form of treatment for single-tooth replacement.

Additive manufacturing of post-process thermoformed wood-plastic composite cladding

To offer extruded Wood-Plastic Composite (WPC) cladding more design options, they could be thermally reshaped in an industrial post-process. However, there is little knowledge about how temperature, heating time, bending radius and fibre content impact mechanical properties and memory behaviour after thermoforming. Therefore, two compound formulations with different wood contents were investigated. While higher heat facilitates forming with smaller radii, strength significantly decreases, especially for thicker samples. In contrast, stiffness is less affected. Retention forces increase with narrow curving, but lower fibre contents counteract this. In contrast to heating duration, temperature tends to produce compound-independent reactions during conditioning, and among geometric parameters, the shaping radius exerts universal responses, more than the material thickness. The fibre content, as a compound-specific factor, affects the material behaviour entirely. For implementation on industrial scale, rupture modulus and retention force should be used for development and process control, whereas research should aim at compound optimisation.

Effect of adhesive system, resin cement, heat-pressing technique, and thermomechanical aging on the adhesion between titanium base and a high-performance polymer

Statement of problemEven though polyetheretherketone (PEEK) has become popular for various prosthetic indications, a standard adhesive protocol to bond the PEEK to titanium bases has not been yet established. How the heat-pressing technique performs in this respect is also not clear. PurposeThe purpose of this in vitro study was to investigate the effect of an adhesive system-cement combination, the heat-pressing technique, and thermomechanical aging on the retention force between titanium bases and PEEK specimens. Material and MethodsSixty 9×11×20-mm PEEK specimens with a titanium base slot integrated into the design were milled to simulate an implant-supported PEEK framework for a cantilevered fixed prosthesis. The specimens were assigned to 8 groups (n=10) according to the titanium base primer (MKZ or Monobond) and resin cement (DTK or Multilink hybrid) used and with or without thermomechanical aging. Twenty PEEK specimens were directly heat-pressed on titanium bases, and half of the specimens were not subjected to thermomechanical aging (n=10). For nonaged groups, the PEEK specimen complex was tightened to an implant analog and secured on a custom-made pull-off device. Retention forces were measured by using the pull-off tensile test in a universal testing machine, and the maximum tensile bond strength (MPa) was calculated. The aged groups were subjected to 5000 cycles of thermal aging (5 °C to 55 °C), and the specimens were clamped to load the extension (cantilever) for 1 200 000 cycles with 120 N and 200 N at 1.5-Hz frequency. After aging, the pull-off test was performed for those specimens that survived thermomechanical aging. A nonparametric Kruskal-Wallis test was used to determine whether there was a difference among the groups, followed by pairwise Wilcoxon rank tests with Bonferroni correction. The Wilcoxon rank test was used to analyze the effect of thermomechanical aging in each adhesive system-cement or heat-press group (α=.05 for all tests). ResultsNone of the specimens failed during cyclic loading. According to the Kruskal-Wallis test, the effect of the PEEK-Ti base bonding technique on the retention force in the nonaged (P=.019) and thermomechanically aged groups was significant (P=.010). In the nonaged groups, the heat-pressing technique resulted in a higher retention force than when the specimens were bonded by using the Monobond-Multilink hybrid combination (P=.031). Thermomechanical aging did not significantly affect the results (P>.241). All failures were adhesive, with cement remaining only on the Ti-bases. ConclusionsAll bonding protocols tested resulted in a stable bond between PEEK and Ti-bases, as all specimens survived thermomechanical aging. The heat-pressing technique resulted in mean bond strength values similar to those obtained with the tested adhesive system-cement combinations with 1 exception; the nonaged heat-pressed groups presented higher bond strength than the Monobond-Multilink hybrid combination. Failure types indicated that the weaker bond was between the PEEK and the cements tested rather than between the titanium base and the cements, regardless of the adhesive system-cement combination.

Novel Magnetic Attachment System Manufactured Using High-Frequency Heat Treatment and Stamp Technique: Introduction and Basic Performance

Recently, a novel magnetic attachment with extremely low cost and high performance was developed. This article aims to introduce a novel magnetic attachment and to evaluate its basic eligibility for denture retention in clinical practice. The novel magnetic attachment system used in this study was the direct-bonding root-keeper-type Magteeth™ MT800 (MagneDesign, Nagoya, Japan). The retentive force without displacement (position 0) and after horizontal displacement to positions 0.5, 1, 1.5, 2, 2.5, and 3 mm were measured. The values relative to the retentive force without displacement were gradually decreased to 82.7 ± 16.3%, 68.8 ± 17.1%, 62.4 ± 15%, 47.2 ± 13.1%, 35.7 ± 9.9%, and 20.7 ± 6.5%, respectively. The retentive force and magnetic field strength did not change significantly after the load test (100 N load, 10,000 times). No new gap between the metal and resin was found in the root keeper- and magnet assembly-embedded blocks after the load test. Some scratches on magnetic assembly and root keeper surface, while no change in the resin texture after the load test were observed. Based on the findings of this preliminary study, this novel low-cost magnetic attachment exhibited favorable retention, strength, and durability for clinical use.

Evaluation of the Effects of Repeated Insertion-Removal Cycles on the Retention of an Indexed Conometric Connection.

The objectives of this in vitro study were to evaluate changes in the retention force of the indexed conometric system subjected to repeated insertion-removal cycles and to examine the elements (matrix and patrix) that cause retention changes in the system as a result of repeated cycles. Monolithic zirconia crowns were cemented on 24 matrixes and 24 patrixes fixed on the implant analog. The pull-out test was performed with 12 matrixes and 12 patrixes attached, and the initial retention forces were recorded. Six of them were subjected to five insertion-removal cycles (5-cycle group), and the other six samples to 15 cycles (15-cycle group), and the final retention forces were calculated. Then, in both groups, an element of each pair exposed to the cycle was matched by an exchanging with new pieces: 5 cycles of matrix-new patrix (5M/0P), 5 cycles of patrix-new matrix (5P/0M), 15 cycles of matrix-new patrix (15M/0P), and 15 cycles of patrix-new matrix (15P/0M); thus, subgroups were created. A pull-out test was applied to these subgroups, and retention forces were recorded. Data were subjected to a paired-samples t test (α = .05). Two specimens from the 15-cycle group were randomly selected and analyzed by scanning electron microscopy. In the 5-cycle group, the mean initial retention force was 153.13 ± 7.08 N, and the mean final retention force was 111.59 ± 18.30 N. In the 15-cycle group, the mean initial retention force was 143.30 ± 15.46 N, and the mean final retention force was 78.55 ± 17.03 N. There was a statistically significant loss of retention in both groups (P < .05). The change in retention in the 5P/0M and 15P/0M subgroups was not statistically significant (P > .05). However, significant loss of retention was found in the 5M/0P and 15M/0P subgroups (P < .05). There was a significant loss of the retention force after insertion-removal cycles. The increase in these cycles caused a further decrease in retention force. The decrease in the retention force of this system mainly resulted from the changes in the surface characteristic of the frictional surfaces of the matrix.

In Vitro Evaluation of the Retentive Effectiveness of Axial Attachments Used in Implant-Retained Overdentures After 1 Year of Function.

The aim of this study was to measure and compare the retention degrees of different attachment systems before and after 1 year of mastication and removal/insertion simulations. A 4 × 10-mm implant embedded in self-curing acrylic resin was placed inside a rectangular metal frame installed in a plastic container with artificial saliva at 37°C. Three different attachment systems were connected to the implants: Dalbo Classic, Locator (with blue, pink, and clear inserts), and Klockner Rotula. A loading test at 100 N and 1.25 Hz frequency was repeated 10 times for each attachment (changing the matrix component or plastic insert) until a total of 300,000 cycles and 1,095 removal/ insertion sequences. The retention force was assessed at baseline until the end of the test (1 year) after 3-month intervals of simulation. One-way analysis of variance (ANOVA) and post hoc Tukey test (P < .05) were performed for statistical analyses. Klockner Rotula showed the highest retention values at the beginning (69.6 ± 9.2 N; 7.1 ± 0.9 kg) and the end of the test (51.4 ± 5.4 N; 5.2 ± 0.6 kg), while Dalbo Classic showed the lowest values both at the beginning (13.1 ± 1.7 N; 1.3 ± 0.2 kg) and the end of the test (6.7 ± 1.6 N; 0.7 ± 0.2 kg). Locator with clear insert exhibited the lowest retention loss ratio (20.4%), while Locator with blue insert showed the highest (50.8%). At the end of the test, all attachment systems showed a significant decrease in retention force in comparison with the initial retention (P < .001). Locator attachments with clear and pink inserts and the Klockner Rotula attachment system showed retention forces > 20 N (2 kg) after 1 year of mastication and prosthesis insertion/removal simulation. All attachment systems showed a progressive loss of retention, which was higher for Locator attachments with blue and pink inserts and Dalbo Classic. The Klockner Rotula attachment system showed the highest retention values both at the beginning and the end of the test.