Polyurethane Block Research Articles

Modular baseplate augmentation: a simple and effective method for addressing eccentric glenoid wear

BackgroundAugmented baseplates can be effective at addressing eccentric glenoid wear in reverse total shoulder arthroplasty (rTSA). However, these implants often come in a limited number of predetermined shapes that require additional reaming to ensure adequate glenoid seating. This typically involves complex instrumentation and can have a negative impact on implant stability. Modular baseplate augmentation based on intra-operative measurements may allow for more precise defect filling while preserving glenoid bone. The purpose of this investigation was to assess the stability of a novel ringed baseplate with modular augmentation in comparison to non-augmented standard and ringed baseplate designs. MethodsIn this biomechanical study, baseplate micromotion was tested for three constructs according to American Society for Testing and Materials (ASTM) guidelines. The constructs included a non-augmented curved baseplate, a non-augmented ringed baseplate and ringed baseplate with an 8 mm locking modular augmentation peg. The non-augmented constructs were mounted flush onto polyurethane (PU) foam blocks, while the augmented baseplate was mounted on a PU block with a simulated defect. Baseplate displacement was measured prior to and after 100,000 cycles of cyclic loading. ResultsPrior to cyclic loading, the non-augmented and augmented ringed baseplates both demonstrated significantly less micromotion than the non-augmented curved baseplate design (81.1 μm vs 97.2 μm vs 152.7 μm; p=0.009). After cyclic loading, both ringed constructs continued to have significantly less micromotion compared to the curved design (105.5 μm vs 103.2 μm vs 136.6 μm; p<0.001). The micromotion for both ringed constructs remained below the minimum threshold required for bony ingrowth (150 μm) at all time points. ConclusionIn the setting of a simulated glenoid defect, locked modular augmentation of a ringed baseplate does not result in increased baseplate micromotion when compared to full contact, non-augmented baseplates. This design offers a simple method for tailored baseplate augmentation that can match specific variations in glenoid anatomy, limiting the need for excessive reaming and ultimately optimizing the environment for long term implant stability. Level of EvidenceBasic Science Study; Biomechanics

Primary stability evaluation of different morse cone implants in low-density artificial bone blocks: A comparison between high-and low-speed drilling

This study aimed to evaluate various biomechanical parameters associated with the primary stability of Maestro and Due Cone implants placed in low-density artificial bones, prepared using high-speed drilling with irrigation and low-speed drilling without irrigation. The insertion torque (IT), removal torque (RT), and implant stability quotient (ISQ) values were recorded for Maestro and Due Cone implants placed in low-density polyurethane blocks (10 and 20 pounds per cubic foot (PCF) with and without a cortical layer) prepared using high-speed and low-speed with or without irrigation using a saline solution, respectively. A three-way ANOVA model and Tukey's post-hoc test were conducted, presenting data as means and standard deviations. P-values equal to or less than 0.05 were considered statistically significant. No statistically significant differences in IT, RT, and ISQ between drilling speeds were observed. However, Maestro implants exhibited lower IT and RT values after high- and low-speed drilling across almost all polyurethane blocks, significantly evident in the 20 PCF density block for IT and in the 20 PCF density block with the cortical layer for the RT with low-speed drilling (IT: 47.33 ± 10.02 Ncm and 16.00 ± 12.49 Ncm for Due Cone and Maestro implants, respectively, with p < 0.01; RT: 44.67 ± 22.81 Ncm and 20.01 ± 4.36 Ncm for Due Cone and Maestro implants, respectively, with p < 0.05) and among the same implant types inserted in different bone densities. Additionally, the study found that for all bone densities and drilling speeds, both implants registered ISQ values exceeding 60, except for the lowest-density polyurethane block. Overall, it can be inferred that low-speed drilling without irrigation achieved biomechanical parameters similar to conventional drilling with both implant types, even with lower IT values in the case of Maestro implants. These findings suggest a promising potential use of low-speed drilling without irrigation in specific clinical scenarios, particularly when focusing on preparation depth or when ensuring proper irrigation is challenging.

Comparison of Four Different Dental Implant Removal Techniques in Terms of the Weight and Volume of Bone Loss.

Several approaches have been suggested for implant removal. However, further research is necessary to review data regarding the amount of bone removed and the duration of removal time for different procedures. This study evaluates and compares various implant removal techniques. Materials and methods: A polyurethane block was scanned to create an implant surgical guide. Afterward, implant-guided surgery was performed on 60 simulated bone blocks. The implants were then separated into four groups and removed utilizing the counter-torque ratchet, trephine drills, burs, and piezosurgery. For the weight of bone loss, there were significant differences in the median between the counter-torque ratchet technique (CTRT) and trephine (p < 0.01), CTRT and bur (p < 0.01), trephine and piezo (p < 0.01), and bur and piezo (p = 0.04). All groups, except CTRT and the piezo group, demonstrated a statistically significant difference (p < 0.01) in the procedure durations. Regarding the volume of bone loss, a statistically significant difference (p < 0.01) was found between each group. Conclusions: CTRT showed the least amount of bone loss. On the other hand, the trephine technique was demonstrated to be the fastest. It is essential to consider the limitations and risks when choosing the approach for implant removal.

Molecular design and hygrothermal resistance of high‐toughness polysiloxane–polyurethane block copolymer composite adhesives

AbstractWith the development of new energy sources, the demand for aluminum composite films for power batteries is expanding; at the same time, higher requirements have been put forward for aluminum composite films and adhesives. Polyurethane, as the binder of aluminum composite films, strongly affects the performance of aluminum composite films when exposed to moisture and high temperature and can lead to delamination. This thesis prepares a polyurethane and silicone block copolymer composite adhesive by adjusting the ratio of hard and soft polyurethane segments to obtain polyurethane (PU) with excellent flexibility. On the basis of block copolymerization with bis‐amino‐terminated organosiloxane (ATPS), obtained excellent flexibility, high peel strength, moisture resistance, and heat resistance from a polysiloxane‐based polyurethane composite adhesive (PUSR). The properties are also tested using tensile tests and peel strength tests. The test results show that by adjusting the ATPS content, the flexibility and hydrophobicity of the PUSR composite adhesive further improved, with a tensile strength of 36 MPa, an elongation at break of 757%, and bonding performance of 11 N/15 mm. Additionally, the damp heat resistance of 6 N/15 mm, exceeding the international standard of 3 N/15 mm, in the power battery soft package aluminum–plastic film has potential application prospects.

Boosting Energy Return Using 3D Printed Midsoles Designed With Compliant Constant Force Mechanisms

Abstract The enhancement of midsole compressive energy return is associated with improved running economy. Traditional midsole materials such as ethylene vinyl acetate (EVA), thermoplastic polyurethane (TPU), and polyether block amide (PEBA) foams typically exhibit hardening force–displacement characteristics. On the other hand, a midsole with softening properties, which can be achieved through compliant constant force mechanisms (CFMs), can provide significant benefits in terms of energy storage and return. This study presents the development of such a midsole, incorporating 3D printed TPU CFM designs derived through structural optimization. The mechanical properties under cyclic loading were evaluated and compared with those of commercially available running shoes with state-of-the-art PEBA foam midsoles, specifically the Nike ZoomX Vaporfly Next% 2 (NVP). Our custom midsole demonstrated promising mechanical performance. At similar deformation levels, the new design increased energy storage by 58.1% and energy return by 47.0%, while reducing the peak compressive force by 24.3%. As per our understanding, this is the first study to prove that the inclusion of CFMs in the structural design of 3D printed midsoles can significantly enhance energy return.

Use of a Novel Artificial Intelligence Tool for Evaluating Primary Stability and Immediate Loading Suitability of Dental Implants: An In Vitro Pilot Study.

To evaluate the correspondence between output from a new artificial intelligence tool (AIT) and clinician evaluation regarding the immediate loading suitability of dental implants based on insertion torque curves recorded during implant placement in an in vitro test. The secondary aim was to analyze peak insertion torque (PIT) and variable torque work (VTW) values of the implants. The study was performed with four different densities of artificial bone blocks of solid rigid polyurethane without a cortical layer. Five types of implants with different macrogeometries were used. A total of 140 implants (7 implants of each type in the four polyurethane blocks) were inserted. Immediately after implant placement, the insertion torque curves were classified by the operator as suitable (S) or nonsuitable (NS) for immediate loading. The same curves were then analyzed by the new AIT, which classified them as belonging to the 'YES' or 'NO' class. For each implant, PIT and VTW values were also recorded. The correspondence between clinician and AIT evaluation was 99.3%, with only one false negative reported by the algorithm analysis. The AIT was found to have a sensitivity of 98.95%, specificity of 100%, positive predictive value of 100%, and negative predictive value of 97.8%. Mean PIT of the whole sample was 34.19 ± 19.43 Ncm, while mean VTW was 2,266.89 ± 1,993.73 Ncm. Statistically significant differences were found between implant systems in the whole sample and according to density of the polyurethane block. The AIT showed a high level of accuracy in the prediction of immediate loading suitability of dental implants based on the provided insertion torque curves. All the implants used in the in vitro test achieved good levels of primary stability, except when inserted in the least-dense polyurethane block. Clinical studies conducted with larger samples and more clinicians are necessary to confirm these results.

Analysis of the Mechanical Behavior of Porcine Graft Fixation in a Polyurethane Block Using a 3D-printed PLA Interference Screw.

Objective The interest in using 3D printing in the healthcare field has grown over the years, given its advantages and potential in the rapid manufacturing of personalized devices and implants with complex geometries. Thus, the aim of the present study was to compare the mechanical fixation behavior of a 3D-printed interference screw, produced by fused deposition modeling of polylactic acid (PLA) filament, with that of a titanium interference screw. Methods Eight deep flexor porcine tendons, approximately 8 mm wide and 9 cm long, were used as graft and fixed to a 40 pounds-per-cubic-foot (PCF) polyurethane block at each of its extremities. One group was fixed only with titanium interference screws (group 1) and the other only with 3D-printed PLA screws (BR 20 2021 018283-6 U2) (group 2). The tests were conducted using an EMIC DL 10000 electromechanical universal testing machine in axial traction mode. Results Group 1 (titanium) obtained peak force of 200 ± 7 N, with mean graft deformation of 8 ± 2 mm, and group 2 (PLA) obtained peak force of 300 ± 30 N, and mean graft deformation of 7 ± 3 mm. Both the titanium and PLA screws provided good graft fixation in the polyurethane block, with no slippage or apparent deformation. In all the samples, the test culminated in graft rupture, with around 20 mm of deformation in relation to the initial length. Conclusion The 3D-printed PLA screw provided good fixation, similar to that of its titanium counterpart, producing satisfactory and promising results.

In vitro evaluation of blood plasma coagulation responses to four medical-grade polyurethane polymers.

Segmented polyurethane (PU) block copolymers are widely used in implantable cardiovascular medical devices due to their good biocompatibility and excellent mechanical properties. More specifically, PU Biospan MS/0.4 was used in ventricular assist devices over the past decades. However, this product is being discontinued and it has become necessary to find an alternative PU biomaterial for application in cardiovascular devices. One important criterion for assessing cardiac biomaterials is blood compatibility. In this study, we characterized the surface properties of four medical-grade PU biomaterials: Biospan MS/0.4, BioSpan S, BioSpan 2F, and CarboSil 20 80A, including surface chemistry, topography, microphase separation structure and wettability, and then measured the blood plasma coagulation responses using bovine and human blood plasma. Results showed that BioSpan 2F contains high amounts of fluorine and has the lowest surface free energy while the other materials have surfaces with silicone present. An in vitro coagulation assay shows that these materials demonstrated improved blood coagulation responses compared to the polystyrene control and there were no significant differences in coagulation time among all PU biomaterials. The chromogenic assay showed all PU materials led to low FXII contact activation, and there were no significant differences in FXII contact activation, consistent with plasma coagulation responses.

Influence of Restorative Material on the Distribution of Loads to the Bone in Hybrid Abutment Crowns-In Vitro Study.

Background: The objective of this study was to evaluate the load transmitted to the peri-implant bone by seven different restorative materials in single-unit rehabilitations with morse taper implants using a strain gauge. Materials: In a polyurethane block that simulated type III bone, a morse taper platform implant was installed (3.5 × 11 mm) in the center and 1 mm below the test base surface, and four strain gauges were installed around the implant, simulating the mesial, distal, buccal and lingual positions. Seven similar hybrid abutment crowns were crafted to simulate a lower premolar using different materials: 1-PMMA; 2-glass ceramic over resin matrix; 3-PEEK + lithium disilicate; 4-metal-ceramic; 5-lithium disilicate; 6-zirconia + feldspathic; 7-monolithic zirconia. All groups underwent axial and oblique loads (45 degrees) of 150 N from a universal testing machine. Five measurements (n = 5) were performed with each material and for each load type; the microdeformation data underwent statistical analysis. The data were obtained in microdeformation (με), and the significance level was set at p ≤ 0.05. Results: There was no statistically significant difference in the evaluation among the materials under either the axial load or the oblique load at 45 degrees. In turn, in the comparison between axial load and oblique load, there was a difference in load for all materials. Conclusion: The restorative material did not influence the load transmitted to the bone. Furthermore, the load transmitted to the bone was greater when it occurred obliquely at 45° regardless of the material used. In conclusion, it appeared that the different elastic modulus of each material did not influence the load transmission to the peri-implant bone.

Primary Stability Assessment of Conical Implants in Under-Prepared Sites: An In Vitro Study in Low-Density Polyurethane Foams

Bone characteristics, the implant macrogeometry, and the drilling technique are considered the main important factors to obtain a good implant primary stability (PS). Indeed, although it is known that implant placement in poor bone sites increases the possibility of implant failure, several surgical procedures have been proposed to improve PS, such as site under-preparation. Hence, this in vitro study aimed to evaluate the insertion torque (IT), removal torque (RT), and resonance frequency analysis (RFA) of conical implants (3.3 and 4 × 13 mm) placed in under-prepared sites on 10 and 20 pounds per cubic foot (PCF) density polyurethane sheets (simulating a D3 and D2 bone, respectively) with and without a cortical sheet of 30 PCF in density (corresponding to a D1 bone). After using ANOVA or Kolmogorov–Smirnov test to elaborate data, the resulting IT and RT values were directly proportional to the polyurethane block densities (e.g., the lowest and highest IT values were 8.36 ± 0.52 Ncm in the 10 PCF density sheet and 46.21 ± 0.79 Ncm in the 20 PCF density sheet + cortical for 4 × 13 mm implants) and increased with the increasing amount of site under-preparation (the highest results for both implants were found with a 2.2 mm under-preparation, showing a significantly higher IT with a p &lt; 0.05 compared with others, especially in the highest-density sheets). Both implants inserted in the 20 PCF density block + cortical with all under-preparation protocols exhibited significantly higher RFA values (p &lt; 0.05–0.0001) compared with the corresponding ones in the 10 PCF block. Moreover, 3.3 × 13 mm implants showed the same results comparing the 20 PCF block and the 10 PCF block + cortical. In conclusion, in this in vitro study using low-density polyurethane blocks, the under-preparation of the implant insertion sites was shown to be effective in increasing implants’ PS.

A Novel NQO1 Enzyme-Responsive Polyurethane Nanocarrier for Redox-Triggered Intracellular Drug Release.

The design of nano-drug delivery vehicles responsive to tumor microenvironment stimuli has become a crucial aspect in developing cancer therapy in recent years. Among them, the enzyme-responsive nano-drug delivery system is particularly effective, as it utilizes tumor-specific and highly expressed enzymes as precise targets, leading to increased drug release at the target sites, reduced nonspecific release, and improved efficacy while minimizing toxic side effects on normal tissues. NAD(P)H:quinone oxidoreductase 1 (NQO1) is an important reductase associated with cancer and is overexpressed in some cancer cells, particularly in lung and breast cancer. Thus, the design of nanocarriers with high selectivity and responsiveness to NQO1 is of great significance for tumor diagnosis and treatment. It has been reported that under physiological conditions, NQO1 can specifically reduce the trimethyl-locked benzoquinone structure through a two-electron reduction, resulting in rapid lactonization via an enzymatic reaction. Based on this, a novel reduction-sensitive polyurethane (PEG-PTU-PEG) block copolymer was designed and synthesized by copolymerizing diisocyanate, a reduction-sensitive monomer (TMBQ), and poly(ethylene glycol). The successful synthesis of monomers and polymers was verified by nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). Then, the PEG-PTU-PEG micelles were successfully prepared by self-assembly, and their reductive dissociation behavior in the presence of Na2S2O4 was verified by dynamic light scattering (DLS), 1H NMR, and GPC. Next, the model drug doxorubicin (DOX) was encapsulated into the hydrophobic core of this polyurethane micelles by microemulsion method. It was observed that the drug-loaded micelles could also achieve a redox response and rapidly release the encapsulated substances. In vitro cell experiments demonstrated that PEG-PTU-PEG micelles had good biocompatibility and a low hemolysis rate (<5%). Furthermore, in the presence of an NQO1 enzyme inhibitor (dicoumarol), lower drug release from micelles was observed in A549 and 4T1 cells by both fluorescence microscopy and flow cytometry assays, but not in NIH-3T3 control cells. Predictably, DOX-loaded micelles also showed lower cytotoxicity in 4T1 cells in the presence of NQO1 enzyme inhibitors. These results indicate that drug-loaded polyurethane micelles could accomplish specific drug release in the reducing environment in the presence of NQO1 enzymes. Therefore, this study provides a new option for the construction of polyurethane nanocarriers for precise targeting and reductive release, which could benefit the intracellular drug-specific release and precision therapy of tumors.

PEO-PU block copolymer membrane for air dehumidification

Membrane separation was an efficient process for air dehumidification. In this study, an environmentally friendly and low-cost polyethylene oxide (PEO)-polyurethane (PU) block copolymer (Permax232) membrane was prepared successfully using water as solvent. An aqueous polycarbondiimide (PCD) crosslinking agent was added into the membrane to improve its water stability property. The physicochemical properties and the crosslinking mechanism of the membrane were investigated using various analytical methods. Compared with the Permax232 membrane, the cross-linked Permax232 membrane exhibited improved water stability and mechanical properties. The surface roughness of the cross-linked membrane increased, and the intensity of the crystalline peak decreased. The crosslink density increased with the PCD content based on the water swelling method. The modified Flory-Huggins model showed excellent agreement between the crosslink density and water vapor sorption. When the appropriate amount of PCD was added, the Permax232 membrane exhibited a high water vapor permeability of 1.45 × 105 Barrer and a water vapor/N2 selectivity of 8.2 × 104. In addition, the water vapor permeability of the cross-linked Permax232 membrane did not change significantly with increasing temperature at the same humidity.

Biomechanical comparison of lag screw and non-spiral blade fixation of a novel femoral trochanteric nail in an osteoporotic bone model

There is no consensus regarding the advantages of the lag screw type over the blade type for treating femoral trochanteric fractures. We aimed to investigate whether non-spiral blade (Conventional-Blade, Fid-Blade) nails provide better biomechanical fixation than lag screws in a severe osteoporotic bone model. Different severities of osteoporotic cancellous bone were modelled using polyurethane foam blocks of three densities (0.24, 0.16, and 0.08 g/cm3). Three torsional tests were performed using each component for each density of the polyurethane block, and the maximum torque was recorded; subsequently, the energy required to achieve 30° rotation was calculated. Using a push-in test, the maximum force was recorded, and the energy required to achieve 4-mm displacement was calculated. For 0.08-g/cm3 density, the peak torques to achieve 30° rotation, energy required to achieve 30° rotation, peak force to achieve 4-mm displacement, and energy required to achieve 4-mm displacement were significantly greater for Conventional-Blade and Fid-Blade than those for Lag Screw. The fixation stability of the blade-type Magnum nail component is better than that of the lag screw type under any test condition. The blade-type nail component may have better fixation stability than the lag screw type in a severe osteoporotic bone model.

Wear Resistance Improvement of Linear Block-Polyurethanes Under Conditions of Liquid Friction

Abstract A significant disadvantage of parts made of linear block polyurethanes under conditions of friction contact in the presence of an aqueous medium is the intensification of hydrolysis processes and decrease in volume strength. It was proposed to slow down the hydrolysis of polyurethanes in three ways: by directed changes in chemical structure, by electromagnetic radiation of different intensities and by creation of composite materials, based on the principle of additional intermolecular crosslinking at the manufacturing and hot processing stages. The conditions for the formation of a smooth wear-resistant surface that protects the material from rapid destruction are revealed.

PH-Responsive and degradable polyurethane film with good tensile properties for drug delivery in vitro

In this paper, we synthesized a new type of pH-responsive block polyurethane (PMCU) through the condensation polymerization of N-methyldiethanolamine (MDEA), poly(ε-caprolactone) and 4,4′-dicyclohexylmethane diisocyanate. The chemical structure of the PMCU were characterized, and the influence of MDEA content on the physicochemical properties of the casted PMCU films were studied detailly. The tensile test demonstrated the good tensile properties of the PMCU films with the breaking strain of 983–425% and the ultimate strength of 11.7–31.2 MPa. The tertiary amine groups and polyester segments endowed the material with pH sensitivity and hydrolytic degradability, respectively. The pH responsiveness of the films was confirmed from the enhanced equilibrium swelling ratio (ESR) with decreasing pH value of the medium, and the ESR in acidic condition (pH 1.5) was much higher than that in neutral (pH 7.0) and basic (pH 12.0) conditions. The studies of drug sustained-release in vitro at different pH indicated a pH-dependent release efficiency, which was closely related with the ESR and almost unaffected by the slow hydrolytic degradation. In addition, the cytotoxicity assay showed that the PMCU had good cytocompatibility to L929 cells. This study showed that pH-responsive promising platform for targeted drug delivery in the biomedical areas.

Development of a Screw-Crane System for Pre-Lifting the Sternal Depression in Pectus Excavatum Repair: A Test of Mechanical Properties for the Feasibility of a New Concept.

BackgroundPre-lifting of the sternum marked a major turning point in pectus excavatum repair. The author developed the crane technique in 2002 and successfully applied it to more than 2,000 cases using sternal wire stitching. However, blind sternal suturing limited the use of the wire-stitch crane. We propose a novel screw for sternal lifting as a new tool for the crane technique.MethodsWe developed a screw system strong enough to withstand the pressure needed for sternum lifting. The screw was designed to have a broader thread to hold the bony tissue securely. The screw’s sustaining power was tested using the torsion, driving torque, and axial pull-out tests in a polyurethane block and ex-vivo porcine sternum.ResultsThe screws were easily driven into the sternum, and the head of the screw was connectable to the table-mounted retractor. In the torsion test, the 2° offset torsional yield was 4.53 N·m (reference value, 1 N·m). In the polyurethane block driving torque test, the maximum torque was 0.98 N·m (reference value, 0.70 N·m). The axial pull-out test was 446 N (reference value, 100 N). The maximum pull-out resistance in the ex-vivo porcine sternum model was 1,516 N.ConclusionThe screw crane was strong enough to sustain the chest wall weight to be lifted. Thus, the screws could effectively replace the sternal wire stitching in crane pre-lifting of the sternum. We expect that application of the screw-crane will be easy and that it will improve the safety and success rate of pectus repair surgery.

The Effect of Threads Geometry on Insertion Torque (IT) and Periotest Implant Primary Stability: A High-Density Polyurethane Simulation for the Anterior Mandible

The implant geometry provides a key role in the osseointegration process and is able to improve the mechanical interaction and primary stability into the bone tissue. The aim of the present investigation was to compare different implant profiles to evaluate their influence on the primary stability on high-density polyurethane block. Methods: A total of 100 implants were used on 20 pcf polyurethane density in the present investigation, i.e., 20 implants for each of 5 groups (A, B, C, D, and E), characterized by different thread pitch and geometry. The insertion torque (IT), and Periotest mean values were recorded during the implant positioning. Results: Mean values for insertion torque values were higher for the group C and group E implant profiles when compared to all other groups (p &lt; 0.01). No significant differences were detected between these two groups (p &lt; 0.05). Lower IT (&lt;20 Ncm2) were presented by groups A, B, and D (p &lt; 0.05). All groups showed negative Periotest values. Group C implants showed the lowest level of Periotest values (p &lt; 0.05). No significant Periotest differences were found between group B and group D and between group A and group E (p &gt; 0.05). Conclusions: Implants with a wider and V-thread profile and a round apex showed a higher stability in a standardized polyurethane foam. Their use could be suggested in high-density bone in clinical practice.

Molecular dynamics simulation, synthesis and characterization of polyurethane block polymers containing PTHF/PCL mixture as a soft segment

To understand the role of mixed soft segments (PCL/PTHF) on the microphase separation of TPUs, thermodynamic calculations, molecular dynamics (MD) simulation and experimental approaches were used. With the use of three-component Flory–Huggins model, interaction parameter and solubility parameters, the free energy of mixing of soft segments and hard segment was investigated. MD simulation was also used to evaluate different types of hydrogen bonding and segmental interactions at atomic levels. To this end, the extent of microphase separation (αsep), state of hydrogen bonding, segment melting enthalpies, crystallization process time and temperature, morphology of soft and hard phases and mechanical properties were fully characterized by ATR-FTIR, DSC, TEM, RMS and tensile techniques. Isothermal and non-isothermal examinations have shown that using mixed soft segments accelerates the microphase separation process comparing samples containing one type of polyols. Mechanical properties data showed that using mixed soft segments disallowed early failure and TPU with extreme enhanced elongation at break and toughness could be obtained.

Biomechanics effect of two implant system with different bone height under axial and non–axial loading conditions

The objective of this current in silico study was to evaluate the influence of axial and non-axial loads on unitary implant-supported implants, with external hexagon or Morse-taper connection in two different bone level, using finite element analysis. Two implant models with the same length (13 x 3.75 mm) were analyzed according to the prosthetic connection (external hexagon or morse Taper) and bone height (bone level or 5 mm of bone loss). Both implant systems received screw-retained metallic crowns in chromium-cobalt. The peri-implant tissue was simulated as an isotropic material (polyurethane resin). The polyurethane block has been fixed and a load of 300 N was applied on the occlusal surface in two different directions (Axial or Non-axial) for each implant model and bone condition. The results were analyzed in terms of von-Mises stress and bone microstrain. The materials were considered isotropic, homogeneous, linear and elastic. The results showed that there is no difference regarding the prosthetic connection for the generated stress and strain under the same load incidence. However, bone loss and non-axial loadings increased the stress and strain magnitude regardless the prosthetic connections. In conclusion, the load incidence is more prone to modify the implant stress and bone microstrain than the prosthethic connection. In addition, the higher the bone loss the higher the stress and strain magnitude generated, regardless the loading condition.

Influence of the dental implant macrogeometry and threads design on primary stability: an in vitro simulation on artificial bone blocks

The implant macrogeometry and thread profile represent one of the most important factors for a successful achievement of primary stability during the positioning procedure. The aim of the present investigation was to evaluate the insertion torque (IT), removal torque (RT) and Implant stability Quotient (ISQ) of two different implant macrogeometry and thread profile on solid rigid polyurethane model. Two different implants macrogeometries were tested: K2 (Group I) with 11° angle, 1.17 mm pitch and self-cutting V thread profile and K3 (Group II) implants with 30° angle, 0.71 mm pitch and spyral thread profile. A total of 120 specimens (n = 60 for each group) were positioned into different conditions of solid rigid polyurethane blocks. The insertion torque (IT), removal torque (RT) and ISQ were measured for each specimen. All specimens achieved the positioning into solid rigid polyurethane blocks for both of groups with no loss of stability. A significantly higher IT, RT and ISQ were detected in Group II (p < 0.05). In both groups the mean values for IT, RT and ISQ appeared promising from a clinical point of view. In spite of different macrogeometry and thread profile, both implant types achieved high primary stability on solid rigid polyurethane block to support the functional loading for a clinical application.