Testing Machine Research Articles

Acoustic emission noise reduction: A case of a uniaxial compression test of gypsum-like rock

In acoustic emission tests, the effective signal generated by crack initiation and propagation inside a sample is easily affected by the testing machine, earth vibration and other external noise, which increases the difficulty of data processing and analysis. To solve this problem, a gypsum sample under uniaxial compression is taken as an example to analyze and process the acoustic emission signal during the experiment. The test results show that these noises generally have the characteristics of acoustic sources far from the probe and signal types different from the effective signal. Therefore, a series of methods concerning the noise reduction of acoustic emission signals, including acoustic emission signal preprocessing, acoustic source distance denoising, and acoustic source type denoising, is proposed. Through three analyses and treatments of acoustic emission parameters, noise reduction was achieved with good results. According to the principles of these methods, some suggestions have been put forward for the position of probes in acoustic emission tests; that is, the connection of two probes should not be perpendicular to a weak plane (bedding, joints, etc.). These results could provide a theoretical reference for the postprocessing of acoustic emission signals in mechanical tests.

Evaluation of the Stability of Open-Tray Impression Coping Using Two Different Impression Materials at Three Different Subgingival Implant Placement Depths.

Objective To evaluate and compare the stability of the open trayimpression coping within the set impression while attaching the lab analog when polyether (PE) heavy body and polyvinyl siloxane (PVS) putty impression materials were used and the implant platform was placed sub-gingivally at three different depths. Methods Two impression materials, PE and PVS, and custom-made plexiglass models with embedded single implants to simulate implant positioning depths of 0 mm, 2 mm, and 4 mm, sub-gingivally, were used in the study. Open tray impressions were made after attaching impression coping to theimplant embedded in themodel. Implant lab analog was attached to the impression coping in the set impression, and its stability was measured using a universal testing machine. Forty-two open tray impressions were madein six groups, with seven impressions in each group. Descriptive statistics such as mean and standard deviation were calculated. A comparison of the meanstability between the two impression materials at each depth was done using an independent t-test.Comparison of the mean stability between the three different subgingival implant depths in each material was done by one-way ANOVA with the Scheffe multiple comparison test (post-hoc analysis). The level of significance was set at p<0.05. Results The stability of the impression coping was measured as the force in Newtons required for the displacement of the analog attached to the impression coping embedded in the set impression. PEwith the embedded impression coping at a depth of 0 mm gave the highest mean stability value (4.37+/-0.41), and the least mean stability was offered by PVS with the embedded impression coping at 4 mm depth (1.88+/-0.37). When an independent t-test was done to compare the mean stability values of PE and PVS,there was a statistically significant difference at0 mm, 2 mm, and 4 mm. On doing one-way ANOVA to compare the mean stability between the different depth groups, there was a statistically significant difference between the three depth groups in PE and PVS. Scheffe multiple comparison tests (post-hoc analysis) revealed a statistically significant difference between 0 mm, 2 mm, and 4 mm subgingival depths of the impression coping placement in bothPE and PVS. Conclusion The accuracy of the master cast is an important determinant for the precise fit and long life of the final prosthesis. In the case of maxillary anterior implant placements where deep subgingival placement of the implant platform is needed for aesthetic and functional reasons, the impression material should be selected carefully to ensure the stability of the impression coping. Among the materials included in the present study, the PE impression material offered the maximum stability for impression coping compared to PVS.

Comparative Assessment of the Shear Bond Strength of Ceramic Brackets Bonded to the Enamel Surface with a Self-adhesive System

Objectives: This study aimed to evaluate the shear bond strength of ceramic brackets bonded to the enamel surface using Vertise Flow, with or without the application of phosphoric acid. Materials and Methods: Forty-five extracted human premolar teeth were randomly assigned to three groups (N=15) based on the adhesive used for bonding: 1) Transbond XT, etch, and bond; 2) Vertise Flow; 3) Etch and Vertise Flow. After a 500-round thermocycling procedure, the shear bond strength was measured using a universal testing machine. The samples were then evaluated under a stereomicroscope to determine failure modes, and the Adhesive Remnant Index (ARI) was measured for each group. The data were analyzed with one-way ANOVA and post-hoc Tamhane at a significance level of P&lt;0.05. Results: The highest shear bond strength values were observed in the Transbond XT (13.5±5.38MPa), acid etch and Vertise Flow (11.2±2.89MPa), and Vertise Flow (6.2±3.16MPa) groups, respectively, in descending order. The Vertise Flow group exhibited a significantly lower shear bond strength value compared to the other two groups, with no significant difference between the latter two. Conclusion: While all three study groups demonstrated clinically acceptable shear bond strength values, Vertise Flow showed lower values compared to the other two adhesives. The Vertise Flow composite resin system, whether used alone or with acid etching, remains a suitable choice for bonding ceramic brackets, offering the advantage of a simplified bonding procedure.

Early‐age cracking due to restraint: Laboratory and field investigations on the predictive capacity of the simplified method in Annex D of the future EC2

AbstractThe Annex D of the future EC2 draft gives guidance on the evaluation of early‐age cracking of large structures due to restraint. In case of restrained conditions, compressive stresses are firstly generated in massive structures due to temperature increase, then tensile stresses are generated due to temperature decrease and shrinkage. Due to these tensile stresses, there is a risk of cracking which may be evaluated by the simplified method in Annex D. This method is currently verified against laboratory tests performed in the temperature‐stress testing machine and field cases on restrained concrete elements. The laboratory verification consisted of five approaches to consider different available input (modeled, assumed, or measured). The field investigation focused on the relation between the calculated cracking risk and the observed damage. The results show that the method has very good accuracy and captures with reasonable simplicity the mechanisms and the relations between the parameters involved.

Effect of three common hot beverages on the force decay of orthodontic elastomeric chain within a 28-day period: An in vitro study.

This study aimed to assess the effects of commonly consumed hot drinks on the force decay of orthodontic elastomeric chains. This in vitro experimental study evaluated 375 pieces of elastomeric chains with six rings placed on a jig. Four rings were stretched by 23.5 mm corresponding to the approximate distance between the canine and the second premolar. Fifteen pieces served as reference samples at time zero, and 360 pieces were randomized into four groups: control, hot water, hot tea, and hot coffee. Each group was further divided into six subgroups (n = 15) according to the different exposure periods. The specimens in the experimental groups were exposed to the respective solutions at 65.5°C four times per day for 90 seconds at 5-second intervals. The control group was exposed to artificial saliva at 37°C. The force decay of the samples was measured at 1, 2, 7, 14, 21, and 28 days using a universal testing machine. Data were analyzed using repeated-measures analysis of variance. Maximum force decay occurred on day 1 in all groups. The minimum force was recorded in the control group, followed by the tea, coffee, and hot water groups on day 1. At the other time points, the minimum force was observed in the tea group, followed by the control, coffee, and hot water groups. Patients can consume hot drinks without concern about any adverse effect on force decay of the orthodontic elastomeric chains.

Can a Novel Device with Pure Dry Air Increase the Shear Bond Strength of Dental Composites to Dentin? An Experimental Study.

Modern conservative dentistry is taking the lead in daily clinical practice and is relying on adhesion. Whether it is a simple composite, ceramic inlays, onlays, veneers or crowns, the common factor for a successful outcome is a good bonding of these elements to dental structures. Thus, the purpose of this study was to evaluate the bond strength of resin composite to dentin when using a new device, the DENTIPURE KM™ (KM, Beirut, Lebanon), which provides a pure air flow, free of any contaminants and without humidity, when compared to other dental equipment. One hundred and eighty extracted human molars were equally divided into three groups according to the device used, the DENTIPURE KM™ (KM, Beirut, Lebanon), the KAVO™ (ESTETICA E30/E70/E80 Vision, KAVO, Biberach, Germany), or the ADEC™ (A-dec Performer 200, Newberg, OR, USA). The shear bond strength (SBS) was evaluated after 24 h of storage in distilled water on a universal testing machine. Statistical analysis was set with a level of significance at p ≤ 0.05. The results revealed that significantly different bond strength was imparted by the DENTIPURE KM™ device and the ADEC™ dental unit (p = 0.042). In conclusion, while the DENTIPURE KM™ device shows promise in providing contaminant-free air during bonding, its impact on dentin bond strength compared to devices like the KAVO™ appears minimal. Further research is needed to fully assess its potential in enhancing dentinal adhesion procedures.

Influence of different endodontic irrigants on shear bond strength of composite resin to coronal dentin: An in vitro study

Objectives: Endodontic irrigants are critical in root canal treatments, but their influence on the coronal dentin bond strength of composite restorations is a key concern for a favorable clinical prognosis. The present in vitro study explores the effect of different endodontic irrigants on shear bond strength of composite resin. Material and Methods: Fifty permanent human mandibular molars were sectioned to expose coronal dentin and divided into five groups. Each group received a specific irrigant treatment before composite resin bonding. Shear bond strength was examined using Instron Universal testing machine, and statistical analysis was conducted using post hoc Tukey’s test and analysis of variance. Results: Group A (Saline) showed a mean shear bond strength of 18.5 Megapascal (MPa). Group B [sodium hypochlorite (NaOCl)] had mean shear bond strength of 15.2 MPa. Group C [Chlorhexidine (CHX) Gluconate] exhibited mean shear bond strength of 20.3 MPa. Group D ethylenediaminetetraacetic acid (EDTA) recorded mean shear bond strength of 14.8 MPa, while Group E [citric acid (CA)] had the highest mean shear bond strength at 22.7 MPa. Conclusion: The type of endodontic irrigant used significantly affected the shear bond strength of composite restorations to coronal dentin. CHX gluconate and CA displayed superior bond strengths compared to Saline, NaOCl, and EDTA. This underscores the importance of irrigant selection in achieving successful composite restorations in endodontically treated teeth.

Universal Inference Meets Random Projections: A Scalable Test for Log-Concavity

Shape constraints yield flexible middle grounds between fully nonparametric and fully parametric approaches to modeling distributions of data. The specific assumption of log-concavity is motivated by applications across economics, survival modeling, and reliability theory. However, there do not currently exist valid tests for whether the underlying density of given data is log-concave. The recent universal inference methodology provides a valid test. The universal test relies on maximum likelihood estimation (MLE), and efficient methods already exist for finding the log-concave MLE. This yields the first test of log-concavity that is provably valid in finite samples in any dimension, for which we also establish asymptotic consistency results. Empirically, we find that a random projections approach that converts the d-dimensional testing problem into many one-dimensional problems can yield high power, leading to a simple procedure that is statistically and computationally efficient.

All-suture anchor size and drill angle influence load to failure in a porcine model of subpectoral biceps tenodesis, a biomechanical study

BackgroundTenodesis of the long head of the biceps tendon is frequently performed in shoulder surgery, and all-suture anchors have become more popular as fixation methods. However, uncertainty still exists regarding the ultimate load to failure of all-suture anchors and the best insertion angle at a cortical humeral insertion point.PurposeThe purpose of this study was to compare the biomechanical characteristics of three types of all-suture anchors frequently used for biceps tenodesis. In addition, the influence of two different insertion angles was observed in a porcine humeri model.MethodsThe ultimate load to failure and failure mode of three types of all-suture anchors (1.6 FiberTak®, 1.9 FiberTak®, 2.6 FiberTak®, Arthrex®) applicable for subpectoral biceps tenodesis were evaluated at 90° and 45° insertion angles in 12 fresh-frozen porcine humeri. The anchors were inserted equally alternated in a randomized manner at three different insertion sites along the bicipital groove, and the suture tapes were knotted around a rod for pullout testing. In total, 36 anchors were evaluated in a universal testing machine (Zwick & Roell).ResultsThe 2.6 FiberTak® shows higher ultimate loads to failure with a 90° insertion angle (944.0 N ± 169.7 N; 537.0 N ± 308.8 N) compared to the 1.9 FiberTak® (677.8 N ± 57.7 N; 426.3 N ± 167.0 N, p-value: 0.0080) and 1.6 FiberTak® (733.0 N ± 67.6 N; 450.0 N ± 155.8 N, p-value: 0.0018). All anchor types show significantly higher ultimate loads to failure and smaller standard deviations at the 90° insertion angle than at the 45° insertion angle. The major failure mode was anchor pullout. Only the 2.6 FiberTak® anchors showed suture breakage as the major failure mode when placed with a 90° insertion angle.ConclusionsAll three all-suture anchors are suitable fixation methods for subpectoral biceps tenodesis. Regarding our data, we recommend 90° as the optimum insertion angle.Clinical relevanceThe influence of anchor size and insertion angle of an all-suture anchor should be known by the surgeon for optimizing ultimate loads to failure and for achieving a secure fixation.

Evaluation of fracture resistance of radicular dentin treated with nanochitosan-loaded calcium hydroxide and nanographene-loaded calcium hydroxide, when used as intracanal medicament: An in vitro study

ABSTRACT Aim: This study aimed to evaluate and compare the effect of using calcium hydroxide (CH) loaded with nanochitosan and nanographene on radicular dentin fracture resistance. Materials and Methods: A total of 40 mandibular premolar root canals were instrumented with the ProTaper rotary system. The fracture resistance of radicular dentin was measured with the universal testing machine, following which intracanal medicament was placed for 10 days. CH alone and CH mixed with nanoparticles of chitosan and graphene were used. Not using any intracanal medicament was used as the control. A one-way ANOVA, followed by the post hoc Tukey’s test, was used to compare the results of different groups. Results: The highest mean for the force at compressive stress was seen in the control group, and the least was recorded by CH. Intergroup comparison for Young’s modulus showed a statistically significant difference (P &lt; 0.05) between the control group and CH (P = 0.002); CH and chitosan + CH (P = 0.003) on post hoc analysis. Conclusion: Incorporation of chitosan and graphene nanoparticles in CH when used as intracanal medicament improves the modulus of elasticity and compressive strength of radicular dentin, which in turn improves dentin elasticity and fracture toughness when compared to CH alone.

Exploring the physicomechanical properties and biocompatibility traits of CuO Substituted 45S5 bioactive glass through in-vitro analysis

While clinically approved, 45S5 bioactive glass possesses limitations in terms of mechanical and biological properties for broader biomedical applications. To address this, we have synthesized 45S5 bioactive glass with partial substitution of CuO for CaO using the melt-quench technique. We conducted extensive characterization using XRD (X-Ray Diffraction), FTIR (Fourier Transform Infrared Spectroscopy), SEM (Scanning Electron Microscopy), and UTM (Universal Testing Machine), in-vitro simulated body fluid (SBF) studies, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide), antibacterial and hemolysis assays. Our results demonstrate that CuO-substituted glasses exhibit enhanced bioactivity, as evidenced by the formation of a hydroxyapatite layer on their surface after immersion in SBF, confirmed from XRD, FTIR and SEM. Additionally, MTT assay with MG-63 cells reveals improved cell proliferation, particularly with 1.5 mol% of CuO addition. Furthermore, Cu_2 to Cu_4 compositions demonstrate effective inhibition of E. coli (Escherichia coli) colonization. The substitution of CuO also leads to significant improvements in the mechanical properties of these bioactive glasses. The density of 45S5 glass increases from 2.72 to 2.86 g/cc, compressive strength from 53 to 64 MPa and young's modulus from 76.74 to 82.21 GPa after the substitution of copper from 0.0 to 2.5 mol%, respectively. Partial substitution of CuO for CaO in 45S5 bioactive glass significantly enhances its physicomechanical properties and biocompatibility compared to the original 45S5 bioactive glass that can be used as implant materials for various biomedical applications.

The Impact of Bonding Agents and Bone Defects on the Fracture Resistance of Reattached Vertically Root-Fractured Teeth

Many patients experience vertical root fractures, and clinicians often consider conservative treatment options like reattaching the fractured root segments. The study investigated the impact of different bonding agents on the fracture resistance of rebonded vertically fractured teeth with various alveolar bone defects. Human premolar teeth with a single root were sectioned and reattached using dual-cure resin cement (DCRC), resin-modified glass ionomer (RMGI), and cyanoacrylate. The reattached teeth were then restored with a resin fiber post, composite resin core, and full veneer metal copings. These teeth were embedded in acrylic blocks with angular, V-shaped, and step-shaped bone defects to simulate various alveolar bone conditions. After subjecting the samples to thermal cycling, the fracture resistance was evaluated using a universal testing machine. Teeth samples reattached with RMGI exhibited a higher average fracture resistance. The study also found that DCRC proved to be an effective bonding agent for VRF teeth. However, cyanoacrylate-rebonded teeth exhibited the lowest fracture resistance. The V-shaped defects had a significant impact on the fracture resistance of reattached VRF teeth, with largely unfavorable fractures observed in these cases. Predominantly favorable fractures were observed in the teeth treated with RMGI. The fracture loads in both RMGI and DCRC groups exceeded the expected masticatory load.

Cost-effectiveness of the McGill interactive pediatric oncogenetic guidelines in identifying Li-Fraumeni syndrome in female patients with osteosarcoma.

Li-Fraumeni syndrome (LFS) is a penetrant cancer predisposition syndrome (CPS) associated with the development of many tumor types in young people including osteosarcoma and breast cancer (BC). The McGill Interactive Pediatric OncoGenetic Guidelines (MIPOGG) decision-support tool provides a standardized approach to identify patients at risk of CPSs. We conducted a cost-utility analysis, from the healthcare payer perspective, to compare MIPOGG-guided, physician-guided, and universal genetic testing strategies to detect LFS in female patients diagnosed at an age of less than 18years with osteosarcoma. We developed a decision tree and discrete-event simulation model to simulate the clinical and cost outcomes of the three genetic referral strategies on a cohort of female children diagnosed with osteosarcoma, especially focused on BC as subsequent cancer. Outcomes included BC incidence, quality-adjusted life-years (QALYs), healthcare costs, and incremental cost-utility ratios (ICURs). We conducted probabilistic and scenario analyses to assess the uncertainty surrounding model parameters. Compared to the physician-guided testing, the MIPOGG-guided strategy was marginally more expensive by $105 (-$516; $743), but slightly more effective by 0.003 (-0.04; 0.045) QALYs. Compared to MIPOGG, the universal testing strategy was $1333 ($732; $1953) more costly and associated with 0.011 (-0.043; 0.064) additional QALYs. The ICUR for the MIPOGG strategy was $33,947/QALY when compared to the physician strategy; the ICUR for universal testing strategy was $118,631/QALY when compared to the MIPOGG strategy. This study provides evidence for clinical and policy decision-making on the cost-effectiveness of genetic referral strategies to identify LFS in the setting of osteosarcoma. MIPOGG-guided strategy was most likely to be cost-effective at a willingness-to-pay threshold value of $50,000/QALY.

A Baseline Drift-Elimination Algorithm for Strain Measurement-System Signals Based on the Transformer Model

Strain measurements are vital in engineering trials, testing, and scientific research. In the process of signal acquisition, baseline drift has a significant impact on the accuracy and validity of data. Traditional solutions, such as discrete wavelet transform and empirical mode decomposition, cannot be used in real-time systems. To solve this problem, this paper proposes a Transformer-based model to eliminate the drift in the signal. A self-attentive mechanism is utilized in the encoder of the model to learn the interrelationships between the components of the input signal, and captures the key features. Then, the decoder generates a corrected signal. Meanwhile, a high-precision strain acquisition system is constructed. The experiments tested the model’s ability to remove drift from simulated voltage signals with and without Gaussian noise. The results demonstrated that the transformer model excels at eliminating signal baseline drift. Additionally, the performance of the model was investigated under different temperature conditions and with different levels of force applied by the electronic universal testing machine to produce strain. The experimental results indicate that the Transformer model can largely eliminate drift in dynamic signals l and has great potential for practical applications.

Strain Virtual Sensing Applied to Industrial Presses for Fatigue Monitoring.

The techniques that allow one to estimate measurements at the unsensed points of a system are known as virtual sensing. These techniques are useful for the implementation of condition monitoring systems in industrial equipment subjected to high cyclic loads that can cause fatigue damage, such as industrial presses. In this article, three different virtual sensing algorithms for strain estimation are tested using real measurement data obtained from a scaled bed press prototype: two deterministic algorithms (Direct Strain Observer and Least-Squares Strain Estimation) and one stochastic algorithm (Static Strain Kalman Filter). The prototype is subjected to cyclic loads using a hydraulic fatigue testing machine and is sensorized with strain gauges. Results show that sufficiently accurate strain estimations can be obtained using virtual sensing algorithms and a reduced number of strain gauges as input sensors when the monitored structure is subjected to static and quasi-static loads. Results also show that is possible to estimate the initiation of fatigue cracks at critical points of a structural component using virtual strain sensors.

In-Vitro Investigation of the Shear Bond Strength of Different Orthodontic Adhesives to Enamel

ABSTRACT Background: The shear bond strength (SBS) of orthodontic adhesives to enamel is a critical factor in the success of orthodontic treatment. Various adhesives are available in the market, each with different trade names and claimed properties that could influence their bond strength. Understanding these differences is essential for clinical decision-making. Materials and Methods: In this in-vitro study, 60 freshly extracted human premolars were collected and randomly divided into four groups: Group A (Adhesive X—Trade Name: BondPlus), Group B (Adhesive Y—Trade Name: OrthoBond), Group C (Adhesive Z—Trade Name: PowerBond), and Group D (Control). The enamel surfaces were cleaned, polished, and etched following standard protocols. Orthodontic brackets were bonded to the teeth using the respective adhesives according to the manufacturer’s instructions. A universal testing machine was employed to measure the SBS, and the data were analyzed using ANOVA with post-hoc tests. Results: The mean SBS values (MPa) were as follows: Group A = 15.2, Group B = 14.8, Group C = 16.5, and Group D (Control) =10.3. Statistical analysis revealed significant differences among the groups (P &lt; 0.05). Post-hoc tests indicated that Group C exhibited significantly higher SBS compared to the other groups. Conclusion: Our findings suggest that among the orthodontic adhesives tested, PowerBond demonstrated superior shear bond strength to the enamel. However, further research is warranted to explore other aspects of adhesive performance and clinical implications.

Early-age thermal cracking performance of carbon nanotube modified face slab concrete

The thermal cracking of face slab concrete (FSC) seriously affects the durability of face rockfill dams. The mechanical properties of carbon nanotubes such as high strength, excellent thermal conductivity provide great potential to improve the temperature cracking of the FSC. In this paper, the effects of CNTs on the thermal cracking resistance of the FSC at early ages were investigated in terms of mixture workability, pore structure, tensile modulus, and temperature stress testing machine test. It was demonstrated that the incorporation of 0.1 wt% CNTs significantly improved the pore structure of FSC and increased the tensile modulus of FSC at early ages. Besides, a model for the coefficient of thermal expansion (CTE) of FSC at early ages was established based on the temperature stress testing machine test, and the cracking comprehensive index, the cracking core index, and the cracking refinement index were compared. The incorporation of CNTs effectively reduced the CTE and the cracking temperature of FSC at early ages, and improved the ability of FSC to resist cracking in harsh environments. Therefore, CNTs exhibited a great potential to enhance the early-age cracking resistance performance of FSC.

Study on the microstructure and properties of a laser cladding Fe–Ni–Al coating based on the invar effect

The purpose of this study was to investigate the effect of Al content on Fe–Ni–Al coatings. A Fe–Ni–Al coating was prepared using a semiconductor laser, and the influence of the Al content on the microstructure and properties of the coating was examined. The microstructure of the coating was characterized using scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The coefficient of thermal expansion of the coating was measured using a static thermomechanical analyzer. The microhardness and wear performance of the coating were analyzed using a microhardness tester and a wear testing machine. The results were as follows. The addition of Al to the Fe–Ni ferroalloy powder resulted in the in situ formation of an AlNi/Fe–Ni laser cladding layer. When the Al content was low, the coating mainly consisted of γ-[Fe,Ni] austenite. As the Al content increased, the matrix phase structure of the cladding layer transformed into the α phase. Consequently, the Invar effect was gradually compromised, leading to the generation of defects in the coating. When the Al content was 4%, the coating performance improved while maintaining a low coefficient of thermal expansion. At this point, there were relatively few cracks in the cladding layer, and it exhibited the best wear resistance.

Effect of cement spacer on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks

BackgroundCement spacer is essential for compensating deformation of zirconia restoration after sintering shrinkage, allowing proper seating and better fracture resistance of the restoration. Studies assessing the effect of cement spacer on fit accuracy and fracture strength of zirconia frameworks are missing in the literature. Therefore, the aim of this study was to evaluate the effect of different cement spacer settings on fit accuracy and fracture strength of 3-unit and 4-unit zirconia frameworks.MethodsSixty standardized stainless-steel master dies were manufactured with 2 prepared abutments for fabricating 3-unit and 4-unit zirconia frameworks. The frameworks were assigned into 6 groups (n = 10) according to cement spacer setting (30 μm, 50 μm, and 80 μm) as follows: 3-unit frameworks; 3u-30, 3u-50, 3u-80, and 4-unit frameworks; 4u-30, 4u-50, and 4u-80. The frameworks were assessed for fit accuracy with the replica method. The specimens were cemented to their corresponding dies, and the fracture strength was measured in a universal testing machine. The Weibull parameters were calculated for the study groups and fractured specimens were inspected for failure mode. Two-Way ANOVA followed by Tukey test for pairwise comparison between study groups (α = 0.05).ResultsThe cement spacer had a significant effect on both fit accuracy and fracture strength for 3-unit and 4-unit frameworks. The 50 μm spacer had significantly better fit accuracy followed by 80 μm, and 30 μm spacers. Both 50 μm and 80 μm spacers had similar fracture strength, and both had significantly better strength than 30 μm spacer.ConclusionsFor both 3-unit and 4-unit zirconia frameworks, 50 μm cement spacer can be recommended over 30 μm and 80 μm spacers for significantly better fit accuracy and adequate fracture strength.

Bioinspired poly-dopamine/nano-hydroxyapatite: an upgrading biocompatible coat for 3D-printed polylactic acid scaffold for bone regeneration.

Poly-lactic acid (PLA) has been proposed in dentistry for several regenerative procedures owing to its biocompatibility and biodegradability. However, the presence of methyl groups renders PLA hydrophobic, making the surface less ideal for cell attachment, and it does not promote tissue regeneration. Upgrading PLA with inductive biomaterial is a crucial step to increase the bioactivity of the PLA and allow cellular adhesion. Our purpose is to evaluate biocompatibility, bioactivity, cellular adhesion, and mechanical properties of 3D-printed PLA scaffold coated with poly-dopamine (PDA) and nano-hydroxyapatite (n-HA) versus PLA and PLA/n-HA scaffolds. The fused deposition modelling technique was used to print PLA, PLA with embedded n-HA particles, and PLA scaffold coated with PDA/n-HA by immersion. After matrices characterization for their chemical composition and surface properties, testing the compressive strength was pursued using a universal testing machine. The bioactivity of scaffolds was evaluated by monitoring the formation of calcium phosphate compounds after simulated body fluid immersion. The PLA/PDA/n-HA scaffold showed the highest compressive strength which was 29.11 ± 7.58 MPa with enhancing calcium phosphate crystals deposition with a specific calcium polyphosphate phase formed exclusively on PLA/PDA/n-HA. With cell viability assay, the PDA/n-HA-coated matrix was biocompatible with increase in the IC50, reaching ⁓176.8 at 72 without cytotoxic effect on the mesenchymal stem cells, promoting their adhesion and proliferation evaluated by confocal microscopy. The study explored the biocompatibility, bioactivity, and the cell adhesion ability of PDA/n-HA coat on a 3D-printed PLA scaffold that qualifies its use as a promising regenerative material.