The Impact of Simulated Bruxism Forces and Surface Aging Treatments on Two Dental Nano-Biocomposites-A Radiographic and Tomographic Analysis.

Background and Objectives: Nowadays, indication of composite materials for various clinical situations has increased significantly. However, in the oral environment, these biomaterials are subjected (abnormal occlusal forces, external bleaching, consumption of carbonated beverages, etc.) to changes in their functional and mechanical behavior when indicated primarily for patients with masticatory habits. The study aimed to recreate in our lab one of the most common situations nowadays-in-office activity of a young patient suffering from specific parafunctional occlusal stress (bruxism) who consumes acidic beverages and is using at-home dental bleaching. Materials and Methods: Sixty standardized class II cavities were restored with two nanohybrid biocomposite materials (Filtek Z550, 3M ESPE, and Evetric, Ivoclar Vivadent); the restored teeth were immersed in sports drinks and carbonated beverages and exposed to an at-home teeth bleaching agent. The samples were subjected to parafunctional mechanical loads using a dual-axis chewing simulator. A grading evaluation system was conducted to assess the defects of the restorations using different examination devices: a CBCT, a high-resolution digital camera, and periapical X-rays. Results: Before mechanical loading, the CBCT analysis revealed substantially fewer interfacial defects between the two resin-based composites (p > 0.05), whereas, after bruxism forces simulation, significantly more defects were identified (p < 0.05). Qualitative examination of the restorations showed more occlusal defects for the Evetric than the other nanohybrid composite. Conclusions: There were different behaviors observed regarding the studied nanocomposites when simulation of parafunctional masticatory forces was associated with aging treatments.

Neer Award 2017: wear rates of 32-mm and 40-mm glenospheres in a reverse total shoulder arthroplasty wear simulation model.

BACKGROUND: Larger glenosphere diameters have been used recently to increase prosthesis stability and impingement-free range of motion in reverse total shoulder arthroplasty. The goal of this study was to evaluate the rate of polyethylene wear for 32-mm and 40-mm glenospheres. METHODS: Glenospheres (32 mm and 40 mm, n = 6/group) and conventional polyethylene humeral liners underwent a 5-million cycle (MC) wear simulation protocol. Abduction-adduction and flexion-extension motion profiles were alternated every 250,000 cycles. At each interval, mass loss was determined and converted to volume loss and wear rate. At 0, 2.5 MC, and 5 MC, liners were imaged using micro-computed tomography to determine surface deviation. White light interferometry was performed on liners and glenospheres at 0 and 5 MC to quantify surface roughness. Wear particle morphology was characterized by environmental scanning electron microscopy. RESULTS: Total volume loss was significantly higher in 40-mm liners from 1.5 MC onward (P < .05). Overall, volumetric wear rate was significantly higher in 40-mm liners compared with 32-mm glenospheres (81.7 ± 23.9 mm3/MC vs. 68.0 ± 18.9 mm3/MC; P < .001). However, micro-computed tomography surface deviation results demonstrated increased linear penetration on 32-mm glenospheres compared with 40-mm glenospheres (0.36 ± 0.03 µm vs. 0.28 ± 0.01 µm; P = .002). Surface roughness measurements showed no difference for liners; however, increased roughness was noted for 40-mm glenospheres at 5 MC compared with 32 mm (P < .05). CONCLUSION: Larger glenospheres underwent significantly greater polyethylene volume loss and volumetric wear rates, whereas smaller glenospheres underwent greater polyethylene surface deviations. The enhanced stability provided by larger glenospheres must be weighed against the potential for increased polyethylene wear.

Wear rates of highly cross-linked polyethylene humeral liners subjected to alternating cycles of glenohumeral flexion and abduction.

BACKGROUND: Although short-term outcomes of reverse total shoulder arthroplasty have been promising, long-term success may be limited due to device-specific complications, including scapular notching. Scapular notching has been explained primarily as mechanical erosion; however, the generation of wear debris may lead to further biologic changes contributing to the severity of scapular notching. METHODS: A 12-station hip simulator was converted to a reverse total shoulder arthroplasty wear simulator subjecting conventional and highly cross-linked ultra-high-molecular-weight polyethylene humeral liners to 5 million cycles of alternating abduction-adduction and flexion-extension loading profiles. RESULTS: Highly cross-linked polyethylene liners (36.5 ± 10.0 mm(3)/million cycle) exhibited significantly lower volumetric wear rates compared with conventional polyethylene liners (83.6 ± 20.6 mm(3)/million cycle; P < .001). The flexion-extension loading profile exhibited significantly higher wear rates for conventional (P < .001) and highly cross-linked polyethylene (P < .001) compared with the abduction-adduction loading profile. Highly cross-linked wear particles had an equivalent circle diameter significantly smaller than wear particles from conventional polyethylene (P < .001). CONCLUSIONS: Highly cross-linked polyethylene liners significantly reduced polyethylene wear and subsequent particle generation. More favorable wear properties with the use of highly cross-linked polyethylene may lead to increased device longevity and fewer complications but must be weighed against the effect of reduced mechanical properties.

Wear rates of retentive versus nonretentive reverse total shoulder arthroplasty liners in an in vitro wear simulation.

BACKGROUND: Although short-term outcomes of reverse total shoulder arthroplasty (rTSA) remain promising, the most commonly cited complication remains prosthetic instability. A retentive rTSA liner is commonly used to increase system constraint; however, no studies have evaluated the rate of polyethylene wear. Our hypothesis was that more constrained retentive liners would have higher wear rates than nonretentive liners. METHODS: Six nonretentive and six retentive rTSA non-cross-linked polyethylene liners were subjected to 4.5 million cycles of alternating cycles of abduction-adduction and flexion-extension motion loading profiles. The rTSA liners were assessed for gravimetric wear loss, 3-dimensional volumetric loss by novel micro-computed tomography analysis, and particulate wear debris analysis. RESULTS: Volumetric wear rates were significant at 7 specific time points (1.0, 2.0, 2.5, 3.25, 3.75, 4.0, and 4.5 million cycles) throughout testing between nonretentive and retentive liners; however, overall mean volumetric wear rate was not statistically significant (P = .076). Total volume loss between liner test groups was found to be significant starting after 3.5 million cycles of testing. Maximum and mean surface deviations were found to be larger for retentive liners vs. nonretentive liners by micro-computed tomography analysis across the entire articulation surface. DISCUSSION AND CONCLUSION: Retentive liners undergo significantly greater volume loss and greater surface deviation compared with nonretentive liners, most notably at later time points representing extended implantation times. Additional stability afforded by retentive liners should be balanced against the potential for increased wear and potential for subsequent polyethylene wear-induced aseptic loosening.

Effect of Polyethylene Crosslinking and Bearing Design on Wear of Unicompartmental Arthroplasty.

Wear and polyethylene damage continue to be important factors affecting outcomes of unicompartmental knee arthroplasty. We compared two design rationales for unicompartmental arthroplasty: fully congruent mobile bearings; or moderately conforming fixed bearings using experimental and computational wear simulation. Experimental wear rates were 3.89 (±0.12) mg/million cycles for the highly crosslinked Triathlon PKR fixed bearing compared to 18.35 (±0.19) mg/million cycles for the low crosslinked Oxford mobile bearing. Finite element analysis was used to calculate the effect of crosslinking and backside wear. Increase in polyethylene crosslinking reduced wear by 68% while backside wear comprised 46% of the total wear in the mobile bearing. Increasing conformity may not be the sole predictor of wear performance and highly crosslinked fixed-bearing polyethylene insert can also provide high wear performance.

Efficient Wear Simulation Methodology for Predicting Nonlinear Wear Behavior of Tools in Sheet Metal Forming.

In conventional wear simulation, the geometry must be updated for succeeding iterations to predict the accumulated wear. However, repeating this procedure up to the desired iteration is rather time consuming. Thus, a wear simulation process capable of reasonable quantitative wear prediction in reduced computational time is needed. This study aimed to develop an efficient wear simulation method to predict quantitative wear reasonably in reduced computational time without updating the geometry for succeeding iterations. The wear resistance of a stamping tool was quantitatively evaluated for different punch shapes (R3.0 and R5.5) and coating conditions (physical vapor deposition of CrN and AlTiCrN coatings) by using a progressive die set. To capture the nonlinear wear behavior with respect to strokes, a nonlinear equation from a modified form of Archard's wear model was proposed. By utilizing the scale factor representing the changes in wear properties with respect to wear depth as input, the simulation can predict the behavior of rapidly increasing wear depth with respect to strokes after failure initiation. Furthermore, the proposed simulation method is efficient in terms of computational time because it does not need to perform geometry updates.

An efficient and robust simulator for wear of total knee replacements.

Wear on total knee replacements is an important criterion for their performance characteristics. Numerical simulations of such wear have seen increasing attention over the last years. They have the potential to be much faster and less expensive than the in vitro tests in use today. While it is unlikely that in silico tests will replace actual physical tests in the foreseeable future, a judicious combination of both approaches can help making both implant design and pre-clinical testing quicker and more cost-effective. The challenge today for the design of simulation methods is to obtain results that convey quantitative information and to do so quickly and reliably. This involves the choice of mathematical models as well as the numerical tools used to solve them. The correctness of the choice can only be validated by comparing with experimental results. In this article, we present finite element simulations of the wear in total knee replacements during the gait cycle standardized in the ISO 14243-1 document, used for compliance testing in several countries. As the ISO 14243-1 standard is precisely defined and publicly available, it can serve as an excellent benchmark for comparison of wear simulation methods. We use comparatively simple wear and material models, but we solve them using a new wear algorithm that combines extrapolation of the geometry changes with a contact algorithm based on nonsmooth multigrid ideas. The contact algorithm works without Lagrange multipliers and penalty parameters, achieving unparalleled stability and efficiency. We compare our simulation results with the experimental data from physical tests using two different actual total knee replacements. Even though the model is simple, we can predict the total mass loss due to wear after 5-million gait cycles, and we observe a good match between the wear patterns seen in experiments and our simulation results. When compared with a state-of-the-art penalty-based solver for the same model, we measure a roughly fivefold increase of execution speed.

Two-body wear test of enamel against laboratory polished and clinically adjusted zirconia.

AIM: A two-body wear test experiment was performed on human enamel, in simulated chewing motion, against non-veneered zirconia ceramic. Aim-1 was to ascertain the effect of zirconia roughness on enamel wear. Aim-2 was to ascertain the relative enamel wear between enamel-zirconia wear pair and enamel-enamel control pair. MATERIALS: Six molar and premolar human enamel cusps per group were used for a dental wear test against laboratory polished (LP) zirconia and laboratory polished and clinically adjusted (LP + CA) zirconia. Enamel antagonists were tested against incisor teeth as a control group to demonstrate laboratory enamel wear. METHODOLOGY: Two-body wear tests were conducted in a dual-axis biomimetic dental wear simulator. 49N loading force was used for 120,000 cycles with 1 mm lateral movement of the test specimen at 1.6Hz frequency, under constant ambient temperature water flow. Surface roughness before testing was determined using 3D profilometry. Loss of enamel height and volume i.e. vertical wear and volumetric wear respectively, were measured by superimposition of before and after testing scans by 3D laser scanning. Scanning electron microscopy was used for surface morphology assessment. One-way ANOVA and Post Hoc Multiple Comparisons with Bonferroni corrections were used at the 5% significance level to determine whether surface finish affected volumetric and vertical enamel loss. The relationship between volumetric and vertical loss of enamel was assessed using Pearson's correlation test. RESULTS: No significant difference was found between LP and LP + CA zirconia in vertical and volumetric enamel wear results. Control enamel had significantly higher vertical and volumetric enamel wear than LP and LP + CA zirconia. Pearson correlation revealed a strong relationship between vertical wear and volumetric wear of enamel. CONCLUSION: Within the constraints of the test method in this experiment, zirconia irrespective of surface preparation, was found to cause less vertical and volumetric enamel wear compared to control enamel. No statistically significant difference was seen between LP zirconia and LP + CA zirconia.

In Vitro Simulation and In Vivo Assessment of Tooth Wear: A Meta-Analysis of In Vitro and Clinical Research.

Tooth wear may be described as a side-effect of occlusal forces that may be further induced by the common use of contemporary prosthetic materials in practice. The purpose of this systematic review was to appraise existing evidence on enamel wear from both in vitro and clinical research and explore whether evidence from these study designs lies on the same direction. Five databases of published and unpublished research were searched without limitations in August 2019 and study selection criteria included in vitro and clinical research on enamel tooth wear. Study selection, data extraction, and risk of bias assessment were done independently and in duplicate. Random effects meta-analyses of standardized mean differences (SMDs) or weighted mean differences (WMDs) with 95% confidence intervals (CIs) were conducted while a Monte Carlo permutation test for meta-regression on the exploration of the effect of the study design on the reported outcomes was planned. A total of 27 studies (23 in vitro and 4 clinical) were eligible while 12 contributed to meta-analyses. Overall, some concerns were raised for the quality of the existing evidence and the potential for risk of bias. Enamel wear (mm) of antagonist teeth was more pronounced when opposed to conventional porcelain compared to machinable ceramics (SMD = 2.18; 95%CIs: 1.34, 3.02; p < 0.001). Polished zirconia resulted in decreased volumetric enamel wear (mm3) of opposing teeth compared to pure natural enamel (SMD = -1.06; 95%CIs: -1.73, -0.39; p = 0.002). Monolithic zirconia showed evidence of enhanced potential for antagonist wear (µm) compared to natural teeth (WMD = 107.38; 95%CIs: 30.46, 184.30; p = 0.01). Study design did not reveal an effect on the tooth wear outcome for the latter comparison when both clinical and in vitro studies were considered (three studies; Monte Carlo test, p = 0.66). In conclusion, there is an overriding need for additional evidence from clinical research to substantiate the findings from the already existing laboratory simulation studies.

Wear of different materials for total hip replacement under adverse stop-dwell-start in vitro wear simulation conditions.

Hip simulation is a common technique for pre-clinical evaluation of wear performance of total hip arthroplasty. Standard techniques replicate kinematics of walking patterns of a typical patient. Attention has focussed in developing simulations of other typical patient daily activities to improve accuracy of wear predictions. A method for simulating stop-dwell-start motion during patient walking and the effect on 36-mm metal-on-metal total hip arthroplasty was previously presented by the authors. This study sought to extend the previous work to look at the effect of these conditions on ceramic-on-ceramic, metal-on-polyethylene and ceramic-on-polyethylene bearings. Two stop-dwell-start protocols were used: one reproducing average patient movement patterns and one examining more severe conditions. For all materials tested, no significant increase in wear was observed under average stop-dwell-start conditions, suggesting the bearing types tested are robust to this type of activity. A significant increase in wear was observed for metal-on-metal, metal-on-polyethylene and ceramic-on-polyethylene bearings under severe stop-dwell-start conditions, this was attributed to depletion of lubricant in the bearing during the dwell period. A greater relative increase in wear was observed for metal-on-metal bearings compared with metal-on-polyethylene and ceramic-on-polyethylene bearings. This may be explained by the contributions of the different lubrication mechanisms in each bearing type. Wear of ceramic-on-ceramic was very low in all tests, suggesting normal measurement variation was masking any effect of the adverse conditions. It was not possible to determine any effect of the different activities. These results emphasise the importance of exploring adverse patient activity simulations. The increase in wear rate associated with an adverse activity such as seen in stop-dwell-start motion, has to be considered in the context of the frequency of the adverse activity cycle relative to other activities such as standard continuous walking, to determine the impact on the total wear in a given time period.

Metal ion release barrier function and biotribological evaluation of a zirconium nitride multilayer coated knee implant under highly demanding activities wear simulation.

Total knee arthroplasty is a well established treatment for degenerative joint disease, which is also performed as a treatment in younger and middle-aged patients who have a significant physical activity and high life expectancy. However, complications may occur due to biological responses to wear particles, as well as local and systemic hypersensitivity reactions triggered by metal ions and particles such as cobalt, chromium and molybdenum. The purpose of the study was to perform a highly demanding activities (HDA) knee wear simulation in order to compare the wear characteristics and metal ion release barrier function of a zirconium nitride (ZrN) coated knee implant, designed for patients with suspected metal ion hypersensitivity, against an uncoated knee implant made out of CoCrMo. The load profiles were applied for 5 million HDA cycles, which represent 15-30 years of in vivo service depending on the activity level of the patient. Results showed a significant wear rate reduction for the coated group (1.01 ±â€¯0.29 mg/million cycles) in comparison with the uncoated group (2.89 ±â€¯1.04 mg/million cycles). The zirconium nitride coating showed no sign of scratches nor delamination during the wear simulation, whereas the uncoated femurs showed characteristic wear scratches in the articulation areas. Furthermore, the metal ion release from the coated implants was reduced up to three orders of magnitude in comparison with the uncoated implants. These results demonstrate the efficiency of zirconium nitride coated knee implants to reduce wear as well as to substantially reduce metal ion release in the knee joint.

Vitamin E stabilised polyethylene for total knee arthroplasty evaluated under highly demanding activities wear simulation.

As total knee arthroplasty (TKA) patients are getting more active, heavier and younger and structural material fatigue and delamination of tibial inserts becomes more likely in the second decade of good clinical performance it appears desirable to establish advanced pre-clinical test methods better characterizing the longterm clinical material behaviour. The questions of our study were 1) Is it possible to induce subsurface delamination and striated pattern wear on standard polyethylene TKA gliding surfaces? 2) Can we distinguish between γ-inert standard polyethylene (PEstand.30kGy) as clinical reference and vitamin E stabilised materials (PEVit.E30kGy & PEVit.E50kGy)? 3) Is there an influence of the irradiation dose (30vs 50kGy) on oxidation and wear behaviour? Clinical relevant artificial ageing (ASTM F2003; 2weeks) of polyethylene CR fixed TKA inserts and oxidation index measurements were performed by Fourier transform infrared spectroscopy prior testing. The oxidation index was calculated in accordance with ISO 5834-4:2005 from the area ratio of the carbonyl peak (between 1650 and 1850cm-1) to the reference peak for polyethylene (1370cm-1). Highly demanding patient activities (HDA) measured in vivo were applied for 5million knee wear cycles in a combination of 40% stairs up, 40% stairs down, 10% level walking, 8% chair raising and 2% deep squatting with up to 100° flexion. After 3.0mc all standard polyethylene gliding surfaces developed noticeable areas of progressive delamination. Cumulative gravimetric wear was 355.9mg for PEstand.30kGy, 28.7mg for PEVit.E30kGy and 26.5mg for PEVit.E50kGy in HDA knee wear simulation. Wear rates were 12.4mg/mc for PEstand.30kGy in the linear portion (0-2mc), 5.6mg/mc for PEVit.E30kGy and 5.3mg/mc for PEVit.E50kGy. In conclusion, artificial ageing of standard polyethylene to an oxidation index of 0.7-0.95 in combination with HDA knee wear simulation, is able to create subsurface delamination, structural material fatigue in vitro, whereas for the vitamin-E-blended materials no evidence of progressive wear, fatigue or delamination was found. STATEMENT OF SIGNIFICANCE: As total knee arthroplasty patients are getting more active, heavier and younger and structural material fatigue and delamination of polyethylene tibial inserts becomes more likely in the second decade of good clinical performance, it appears desirable to establish advanced pre-clinical test methods better characterizing the longterm clinical material behaviour. Various studies reported in literature attempted to artificially create delamination during in vitro knee wear simulation. We combined artificial ageing to clinically observed oxidation of gamma inert and vitamin E stabilised polyethylene inserts and highly demanding patient activities knee wear simulation based on in vivo load data. With this new method we were able to create clinically relevant subsurface delamination and structural material fatigue on standard polyethylene inserts in vitro.

Cycle-dependent in vitro wear performance of dental ceramics after clinical surface treatments.

AIM: To investigate the two-body wear performance of dental ceramics after different clinical surface treatments as a function of number of wear cycles. MATERIAL AND METHODS: Standardized specimens (n=72/material) were prepared from two different zirconia ceramics, a veneering porcelain, and a lithiumdisilicate glass ceramic. Specimens were progressively glazed, ground, and polished. After each treatment step 24 specimens per material were kept at the obtained surface state. Steatite and human enamel specimens served as reference materials. Two-body wear tests were performed with steatite spheres as antagonists in a pin-on-block design (50N, 1.6 Hz, lateral movement: 1mm, mouth opening: 2mm) under simultaneous thermal cycling (5/55 °C, 2 min/cycle). For investigating the dynamic evolution of the wear process, 9 groups per material (n=8/group) were defined, differing in surface state (glazed, ground, and polished) and number of chewing cycles (40T, 80T, and 120T; T: ×1000): glazed 40T, glazed 80T, glazed 120T, ground 40T, ground 80T, ground 120T, polished 40T, polished 80T, polished 120T. Surface roughness, wear depth of the specimens and relative wear area of the steatite antagonists were determined using an optical 3D laser scanning microscope. SEM evaluation was done. Mean values and standard deviations were calculated and statistically analyzed (one-way ANOVA, post-hoc Bonferroni, α=0.05). RESULTS: Veneering and lithiumdisilicate ceramics showed higher wear depths than zirconia ceramics (p<0.05). Wear of veneering and lithiumdisilicate ceramics and their antagonists increased with wear cycles but was only marginally influenced by the initial surface state. Wear of zirconia was not influenced by wear cycles but antagonists of zirconia showed a cycle-dependent wear increase. Polished zirconia surfaces showed lowest wear for material and antagonist. Wear mechanism of common ceramics was characterized by abrasive wear. Zirconia in contrast showed a superficial cyclic shifting of worn material of the antagonist. CONCLUSIONS: Wear of zirconia and standard ceramics showed different wear performances, strongly influenced by surface treatments as well as number of wear cycles.

Comparison of wear behaviors for an artificial cervical disc under flexion/extension and axial rotation motions.

The wear behaviors of a ball-on-socket (UHMWPE-on-Ti6Al4V) artificial cervical disc were studied with 1.5 MC (million cycles) wear simulation under single flexion/extension and axial rotation motion and their composite motion. The wear rates, wear traces, and contact stress were analyzed and contrasted based on mass loss, optical microscopy and SEM as well as 3D profilometer, and ANSYS software, respectively. A much higher wear rate and more severe wear scars appeared under multi-directional motion. Flexion/extension motion of 7.5° lead to more severe wear than that under axial rotation motion of 4°. The above results were closely related to the contact compression stress and shear stress. The wear surface in FE motion showed typical linear wear scratches while revealing obvious arc-shaped wear tracks in AR motion. However, the central zone of both ball and socket components revealed more severe wear tracks than that in the edge zone under these two different motions. The dominant wear mechanism was plowing/scratching and abrasive wear as well as a little oxidation wear for the titanium socket while it was scratching damage with adhesive wear and fatigue wear due to plastic deformation under cyclic load and motion profiles for the UHMWPE ball.

Force-controlled dynamic wear testing of total ankle replacements.

Currently, our knowledge of wear performance in total ankle replacements is limited. The aim of this study is to develop a scenario for force-controlled testing and wear testing of total ankle replacements. A force-controlled wear test was developed: based on cadaver measurements, the passive stabilization (ligaments and soft tissue) of the ankle joint was characterized and a restraint model for ankle stabilization was developed. Kinematics and kinetics acting at the replaced ankle joint were defined based on literature data and gait analysis. Afterwards, force-controlled wear testing was carried out on a mobile, three-component, total ankle replacement design. Wear was assessed gravimetrically and wear particles were analyzed. Wear testing resulted in a mean wear rate of 18.2±1.4mm(3)/10(6) cycles. Wear particles showed a mean size of 0.23µm with an aspect ratio of 1.61±0.96 and a roundness of 0.62±0.14. Wear testing of total ankle replacement shows that a relevant wear mass is generated with wear particles in a biologically relevant size range. The developed wear test provides a basis for future wear testing of total ankle replacements.

Wear testing of total hip replacements under severe conditions.

Controlled wear testing of total hip replacements in hip joint simulators is a well-established and powerful method, giving an extensive prediction of the long-term clinical performance. To understand the wear behavior of a bearing and its limits under in vivo conditions, testing scenarios should be designed as physiologically as possible. Currently, the ISO standard protocol 14242 is the most common preclinical testing procedure for total hip replacements, based on a simplified gait cycle for normal walking conditions. However, in recent years, wear patterns have increasingly been observed on retrievals that cannot be replicated by the current standard. The purpose of this study is to review the severe testing conditions that enable the generation of clinically relevant wear rates and phenomena. These conditions include changes in loading and activity, third-body wear, surface topography, edge wear and the role of aging of the bearing materials.

The High performance of nanocrystalline CVD diamond coated hip joints in wear simulator test.

The superior biotribological performance of nanocrystalline diamond (NCD) coatings grown by a chemical vapor deposition (CVD) method was already shown to demonstrate high wear resistance in ball on plate experiments under physiological liquid lubrication. However, tests with a close-to-real approach were missing and this constitutes the aim of the present work. Hip joint wear simulator tests were performed with cups and heads made of silicon nitride coated with NCD of ~10 µm in thickness. Five million testing cycles (Mc) were run, which represent nearly five years of hip joint implant activity in a patient. For the wear analysis, gravimetry, profilometry, scanning electron microscopy and Raman spectroscopy techniques were used. After 0.5 Mc of wear test, truncation of the protruded regions of the NCD film happened as a result of a fine-scale abrasive wear mechanism, evolving to extensive plateau regions and highly polished surface condition (Ra<10nm). Such surface modification took place without any catastrophic features as cracking, grain pullouts or delamination of the coatings. A steady state volumetric wear rate of 0.02 mm(3)/Mc, equivalent to a linear wear of 0.27 µm/Mc favorably compares with the best performance reported in the literature for the fourth generation alumina ceramic (0.05 mm(3)/Mc). Also, squeaking, quite common phenomenon in hard-on-hard systems, was absent in the present all-NCD system.

Wear assessments of a new cervical spinal disk prosthesis: Influence of loading and kinematic patterns during in vitro wear simulation.

Surgical treatment is one of the effective methods of treatment in cervical spondylosis. The traditional method of operation is decompression fusion; however, this surgery results in restricted movement of cervical vertebra and adjacent segment degeneration. Due to the deficiency of traditional surgery, scholars have widely carried out artificial cervical disk replacement surgery and have achieved good clinical effects. Comparing to the characteristics of the common artificial cervical disk which is used frequently, we developed a new artificial cervical intervertebral disk prosthesis. The purpose of this study was to determine the wear behavior in a cervical total disk replacement system. The total disk replacement system tested consists of a ultra-high-molecular-weight polyethylene inlay articulating between a Ti6Al4V alloy superior plate and an inferior plate, using a spine wear simulator, per the ISO 18192-1:2011 standard test methods. Three rotations and axial force were applied on each station. The specimens were removed at 5 × 10(5) and 10(6) cycles and at intervals of 10(6) cycles thereafter to determine the actual mass loss. The serum was replaced every 5 × 10(5) cycles. The specimens were changed periodically among the different stations. A mean ultrahigh molecular weight polyethylene inlay wear rate of 0.53 mg per million cycles (standard = 0.13 mg per 10(6) cycles) was found after 10(7) cycles. All inferior plates showed slight scratching after 10(7) cycles. The impingement wear simulation introduced here proved to be suitable to predict in vivo impingement behavior in regard to the contact pattern seen on retrieved devices of the Pretic-I disk arthroplasty design in a preclinical test.

Wear behavior of monolithic zirconia against natural teeth in comparison to two glass ceramics with two surface finishing protocols: an in-vitro study / Comportamento do desgaste da zircônia monolítica frente a dentes naturais em comparação com duas cerâmicas de vidro com diferentes protocolos de acabamento superficial: um estudo in vitro

Objective: To evaluate and compare the wear behavior of three different ceramic systems; monolithic zirconia, lithium di-silicate and nano-fluorapatite glass ceramic with two finishing procedures polishing and glazing, and their effect on the wear of natural tooth antagonists. Material and Methods: Forty two ceramic disc specimens (10mm x3mm) and forty two natural tooth antagonists were used. Samples were divided according to ceramic materials into 3 groups (n = 14). Group I: nano-fluorapatite glass ceramic (FLU) (IPS e.max Ceram), Group II: lithium disilicate (LD) (IPS e.max CAD) and group III: monolithic zirconia (ZIR) (ZirkoZahn Prettau). Each group was further subdivided into two subgroups (n = 7), according to the surface finish: Polishing (P) and glazing (G). Specimens were subjected to a custom designed two-body wear simulator. Quantitative wear assessment was carried out using weight loss measurements. Scanning electron microscope was used for characterization of wear patterns. Kruscal Wallis and Dunn's tests were used to compare between weight loss of the three ceramic materials. Whitney U test was used to compare the weight loss between the two surface finish protocols. Wilcoxon Signed rank test was used to compare the weight loss between ceramic specimens and antagonist teeth (p ≤ 0.05). Paired t-test was used to compare weight loss before and after wear test. Results: After wear, LD and FLU had the highest weight loss values compared to ZIR (p < 0.05). For teeth, there was no significant difference between the weight loss values with the three materials (p > 0.05). P and G specimens showed no significant difference in weight loss values. SEM images of the wear patterns verified the previous analysis. Conclusion: ZIR is more wear resistant than LD and FLU. However, the surface treatment had no impact on the wear behavior. (AU)

Objetivo: Avaliar e comparar o comportamento ao desgaste de três diferentes sistemas cerâmicos; zircônia monolítica, di-silicato de lítio e vitrocerâmica de nano-fluorapatita com dois procedimentos de polimento e glaze, e seu efeito no desgaste de dentes naturais antagonistas. Material e Métodos: Foram utilizadas quarenta e duas amostras de discos cerâmicos (10 mm x 3 mm) e quarenta e dois dentes naturais como antagonistas. As amostras foram divididas de acordo com o material cerâmico em 3 grupos (n = 14). Grupo I: vitrocerâmica nano-fluorapatita (FLU) (IPS e.max Ceram), Grupo II: dissilicato de lítio (LD) (IPS e.max CAD) e grupo III: zircônia monolítica (ZIR) (ZirkoZahn Prettau). Cada grupo foi subdividido em dois subgrupos (n = 7), de acordo com o acabamento da superfície: Polimento (P) e Glaze (G). As amostras foram submetidas a um simulador de desgaste de dois corpos projetado. A avaliação quantitativa do desgaste foi realizada usando medidas de perda de massa. Microscópio eletrônico de varredura foi utilizado para caracterização de padrões de desgaste. Os testes de Kruscal Wallis e Dunn foram usados para comparar a perda de massa dos três materiais cerâmicos. O teste U de Whitney foi utilizado para comparar a perda de massa entre os dois protocolos de acabamento superficial. O teste de Wilcoxon Signed Rank foi utilizado para comparar a perda de massa entre amostras de cerâmica e os dentes antagonistas (p ≤ 0,05). O teste t pareado foi utilizado para comparar a perda de massa antes e depois do teste de desgaste. Resultados: Após o desgaste, LD e FLU apresentaram os maiores valores de perda de massa em comparação ao ZIR (p < 0,05). Para os dentes, não houve diferença significativa entre os valores de perda de massa com os três materiais (p > 0,05). As amostras de P e G não mostraram diferença significativa nos valores de perda de massa. Imagens SEM dos padrões de desgaste confirmaram a análise anterior. Conclusão: O ZIR é mais resistente ao desgaste do que LD e FLU. No entanto, o tratamento de superfície não teve impacto no comportamento do desgaste. (AU)

Reinforced glass-ceramics: parametric inspection of three-dimensional wear and volumetric loss after chewing simulation

Abstract The aim of this study was to investigate the three-dimensional wear, volumetric loss and surface roughness after chewing simulation of two glass ceramics. Lithium disilicate (LD, Emax CAD, Ivoclar) and Zirconia reinforced lithium silicate (ZLS, Vita Suprinity, Vita Zhanfabrick) discs (n=20/g) were scanned to obtain stereolithography (STL) files for each sample. All discs were submitted to chewing simulation with sliding configuration (30 N, 300,000 cycles, 6 mm and 1.7 Hz) with steatite as antagonist. The samples were then scanned again and the volume loss and the deepest defect depth was measured using the superimposed file from the baseline using three-dimensional digital parametric inspection software (GOM Inspect, Braunschweig, Germany). Surface roughness (Ra and Rz) was analyzed with a contact profilometer. Data were analyzed by one-way ANOVA and Tukey test (α=0.5%). ANOVA showed significant differences among the groups. Considering the ceramic volume loss, wear depth defect length and Rz roughness, LD (-22.09±5.57%; 0.80±0.06 µm; 3.08±1.02 µm) showed higher mean values than ZLS (-15.67±4.51%; 0.56±0.09 µm; 1.51±0.90 µm). Ra mean values were similar for both materials (p=0.064). All discs exhibited slight surface scratches along with the sliding direction with pitted wear patterns, while large cracks were observed on wear traces. These same areas can be identified in blue, overlapping the STL files before and after chewing simulation in inspection software. The linear reduction generated by sliding contact shows a graph with a similar wear pattern shape. ZLS was more resistant to wear than LD, with less volume loss and shallower surface defects.

Resumo O objetivo deste estudo foi investigar o desgaste tridimensional, perda volumétrica e rugosidade após a simulação de mastigação de dois materiais vitro-cerâmicos. Discos de dissilicato de lítio (LD, Emax CAD, Ivoclar) e silicato de lítio reforçado com zircônia (ZLS, Vita Suprinity, Vita Zhanfabrick) (n=20/g) foram confeccionados e digitalizados para obtenção de arquivos de estereolitografia (STL) de cada amostra. Todos os discos foram submetidos à simulação de mastigação com configuração deslizante (30 N, 300.000 ciclos, 6 mm e 1,7 Hz) com esteatita como antagonista. As amostras foram escaneadas novamente e a perda de volume e o defeito mais profundo foram medidos usando o arquivo sobreposto da linha de base através de um software de inspeção paramétrica digital e tridimensional (GOM Inspect, Braunschweig, Alemanha). A rugosidade superficial (Ra e Rz) foi avaliada através de rugosímetro de contato. Os resultados foram analisados por ANOVA 1-fator e teste Tukey (α=0,5%). ANOVA mostrou diferenças significantes entre os grupos. Considerando a perda de volume cerâmico, comprimento do defeito e rugosidade Rz, LD (-22,09±5,57%; 0,80±0,06 µm; 3,08±1.02 µm) apresentou valores médios superiores a ZLS (-15,67±4,51%; 0,56±0,09 µm; 1.51±0.90 µm). Todos os discos exibiram pequenos arranhões na superfície conforme a direção de deslizamento com padrões de desgaste, enquanto grandes ranhuras foram observadas nos traços de desgaste. Essas mesmas áreas podem ser identificadas em azul, sobrepondo os arquivos STL antes e depois da simulação de mastigação no software de inspeção. A redução linear gerada pelo contato deslizante mostra um gráfico com uma forma de padrão de desgaste semelhante. ZLS foi mais resistente ao desgaste do que LD, com menor perda de volume e menores defeitos superficiais.