Search Results (323)

As a core component of industrial robots, the transmission accuracy life (TAL) of rotary vector (RV) reducers constitutes a primary factor determining the high-precision operation of robotic systems. However, current life evaluation methods for RV reducers predominantly rely on conventional bearing strength life calculations, while neglecting its transmission accuracy degradation during operation. To address this limitation, a static analysis model of RV reducers is established, through which a calculation method for transmission accuracy and TAL is presented. Simultaneously, tooth surface and bearing wear models are developed based on Archard’s wear theory. Through coupled analysis of the aforementioned models, the transmission accuracy degradation law of RV reducers is revealed. The results show that during the operation of the RV reducer, the transmission error (TE) maintains relative stability over time, whereas the lost motion (LM) exhibits a continuous increase. Based on this observation, LM is defined as the evaluation metric for TAL, and a novel TAL estimation model is proposed. The feasibility of the developed TAL estimation model is ultimately validated through accelerated transmission accuracy degradation tests on RV reducers. The error between the predicted and experimental results is 11.06%. The proposed TAL estimation model refines the life evaluation methodology for RV reducers, establishing a solid foundation for real-time transmission accuracy compensation in reducer operation. Full article

Background/Objectives: To compare the marginal integrity of sectional non-invasive laminate veneers versus sectional minimally invasive laminate veneers. Methods: A total of eighty (80) intact maxillary and mandibular frontal teeth (central incisors) were randomly divided into four groups (n = 20). Two groups received non-invasive veneers made of feldspathic porcelain (Feldspathic Non-Invasive—FNI) and lithium disilicate (Lithium Disilicate Non-Invasive—LNI) accordingly. Groups FP and LP received minimally invasive veneers manufactured by feldspathic porcelain and lithium disilicate, respectively. Following cementation, three grooves with mesio-distal orientation on the labial surface of teeth of each sample, at the incisal, middle, and cervical third, were made. Before and after artificial aging, the mesio-distal distance between the end of the groove on the tooth and the edge of each veneer was measured in micrometers (μm) employing an SEM immediately after cementation (T₀), after simulated artificial aging equivalent to four months of everyday brushing (T₁), and after twelve months of everyday brushing (2 times per day) (T₂) to identify the wear of veneers. In the same manner, the horizontal dimension of the cement layer extending from its edge till the margin of the veneer was measured for all the groups at T₀, T₁, and T₂, respectively. The statistical analysis was performed employing non-parametric Kruskal–Wallis ANOVA and Dunn’s test. Results: No significant differences from T₀ to T₁ and from T₁ to T₂, as well as from T₀ to T₂, were identified for all the groups tested. No significant differences were allocated among all groups for the dimensional changes in the cement. Conclusions: All the groups responded similarly to aging factors, regardless of the non-invasive or minimally invasive approach, or the material used to fabricate the veneers. Full article

Background: Attachments are essential components in clear aligner therapy, enhancing retention and improving the predictability of tooth movements. Mechanical and wear properties of the composite resins used for attachment reproduction are critical to maintaining their integrity and shape over time. This study aimed to evaluate and compare the mechanical properties, thermal behavior, and wear performance of the hybrid composite Aligner Connect (AC) and the flowable resin (Connect Flow, CF). Methods: Twenty samples (ten AC and ten CF) were reproduced. All specimens underwent differential scanning calorimetry (DSC), combustion analysis, flat instrumented indentation, compression stress relaxation tests, and tribological analysis. A 3D wear profile reconstruction was performed to assess wear surfaces. Results: DSC and combustion analyses revealed distinct thermal transitions, with CF showing significantly lower Tg values (103.8 °C/81.4 °C) than AC (110.8 °C/89.6 °C) and lower residual mass after combustion (23% vs. 61%), reflecting reduced filler content and greater polymer mobility. AC exhibited superior mechanical properties, with higher maximum load (585.9 ± 22.36 N) and elastic modulus (231.5 ± 9.1 MPa) than CF (290.2 ± 5.52 N; 156 ± 10.5 MPa). Stress relaxation decrease was less pronounced in AC (18 ± 4%) than in CF (20 ± 4%). AC also showed a significantly higher friction coefficient (0.62 ± 0.060) than CF (0.55 ± 0.095), along with greater wear volume (0.012 ± 0.0055 mm³ vs. 0.0070 ± 0.0083 mm³) and maximum depth (36.88 ± 3.642 µm vs. 17.91 ± 3.387 µm). Surface roughness before wear was higher for AC (Ra, 0.577 ± 0.035 µm; Rt, 4.369 ± 0.521 µm) than for CF (Ra, 0.337 ± 0.070 µm; Rt, 2.862 ± 0.549 µm). After wear tests, roughness values converged (Ra, 0.247 ± 0.036 µm for AC; Ra, 0.236 ± 0.019 µm for CF) indicating smoothened and similar surfaces for both composites. Conclusions: The hybrid nanocomposite demonstrated greater properties in terms of stiffness, load-bearing capacity, and structural integrity when compared with flowable resin. Its use may ensure more durable attachment integrity and improved aligner–tooth interface performance over time. Full article

Pressures applied to horses via nosebands are of growing concern. The current study applied noseband pressure to the head of a dead horse. Pressure sensors were placed on the left nasal bone to record pressures as the noseband was progressively tightened. Tightness increased as predicated by holes in the strap of the noseband (as supplied) through eight steps from two fingers’ space, assessed using the standard International Society for Equitation Science Taper Gauge through to zero space. Sensors were also placed at the midline frontal plane and intra-orally at the level of the second premolar tooth. A strain gauge integrated into the noseband recorded tensions within the noseband at each tightness level, and a digital taper gauge under the noseband recorded forces on the face. Pressures at the left nasal bone rose to 403 kPa, while those at the frontal nasal plane reached 185 kPa. Pressures rose rapidly once the noseband was tightened at the equivalent of 1.4 fingers’ space under the noseband. These findings may help to explain cases of bone and skin damage at the noseband location and indicate the need to ensure that nosebands can accommodate more than the equivalent of 1.4 fingers beneath them in the nasal midline. Given that pressures are expected to rise from those reported here when horses wear bits, locomote, and when the reins are under tension, we conclude that the traditional provision of two fingers’ space should be retained. Full article

The continuous need for simplified, minimally invasive restorative procedures with a high precision has led to the advancement of highly filled flowable resin-based materials. These materials present excellent initial outcomes in various clinical applications, including the injection molding technique. Given that several clinical reports present signs of wear and staining, this systematic review aims to investigate the mechanical and optical properties of highly filled flowable composite resins. A comprehensive literature research was conducted to identify relevant studies from the PubMed, the Cochrane Library, and Scopus databases. Data extraction and screening was performed by two independent evaluators. Both in vitro studies and clinical trials were included. A total of thirty-one studies were included in this review. A total of 27 in vitro studies investigated highly filled flowable composite resins independently, or in comparison with conventional composite resins, traditional flowable composites, bulk-fill flowable composites, glass ionomer cements, and compomers. Additionally, four randomized controlled clinical trials (RCTs) compared highly filled flowable composite resins with their conventional counterparts. Highly filled flowable composite resins exhibit adequate optical properties. Despite their significant improvements, their mechanical properties remain inferior to those of medium-viscosity composite resins. These materials demonstrate a favorable initial performance in the injection molding technique. Based on a limited number of RCTs, these materials demonstrate an adequate performance in class I and II restorations; however these findings should be interpreted with caution. The reported drawbacks in laboratory studies may contraindicate their clinical application in extensive cavities, load-bearing areas, and in cases of excessive tooth wear and parafunctional activity. A careful clinical case selection is strongly recommended. Full article

Background: Artificial tooth wear impacts prosthesis durability and function; understanding material–antagonist interactions guides clinical choices. Aim: This in-vitro study aimed to assess the wear behavior of isosit and nanohybrid composite resin artificial teeth when opposed to various antagonist materials using 3D volumetric wear analysis. Materials and Methods: Sixty specimens (n = 10 per group) were prepared from two artificial tooth materials and assigned to six antagonist combinations: isosit–isosit, isosit–nanohybrid composite, isosit–porcelain, nanohybrid composite–isosit, nanohybrid composite–nanohybrid composite, and nanohybrid composite–porcelain. Specimens were scanned before and after 600,000 chewing cycles using a structured-light 3D scanner. Volumetric wear was calculated by superimposing pre- and post-test scans. Data were analyzed using two-way ANOVA and Tukey’s HSD test (α = 0.05). Results: Porcelain antagonists produced the highest wear values (p < 0.05). No significant difference was found between isosit and nanohybrid antagonists (p > 0.05). Identical material pairings showed less wear, though differences were not statistically significant. Conclusions: Porcelain as an antagonist increased wear risk. Using identical materials bilaterally, such as isosit–isosit or nanohybrid–nanohybrid, may help reduce artificial tooth wear in removable prostheses. Full article

With engineering plastics increasingly replacing traditional materials in various drive and control gear systems across numerous industrial sectors, material selection for any gearwheel critically impacts its mechanical and thermal properties. This paper investigates the engagement of steel and Polyvinylidene Fluoride (PVDF) gear pairs tested under several load conditions to determine polymer gears’ characteristic service life and failure modes. Furthermore, recognizing that the application of polymer gears is limited by insufficient data on their temperature-dependent mechanical properties, this study establishes a correlation between the tribological contact, meshing temperatures, and wear coefficients of PVDF gears. The results demonstrate that the flank surface wear of the PVDF gears is directly proportional to the temperature and load level of the tested gears. Several distinct load-induced failure modes have been detected and categorized into three groups: abrasive wear resulting from the hardness disparity between the engaging surfaces, thermal failure caused by heat accumulation at higher load levels, and tooth fracture occurring due to stiffness changes induced by the compromised tooth cross-section after numerous operating cycles at a specific wear rate. Full article

Tooth wear is a growing oral health concern with implications for function, esthetics, and psychological well-being, ultimately affecting oral health-related quality of life (OHRQoL). While clinical indices assess tooth wear severity, they fail to capture patient-reported outcomes (PROs) and patient-reported outcome measures (PROMs). This narrative review aims to identify and synthesize the use of PROs and PROMs used in adults with tooth wear and to map their assessed domains against the Wilson and Cleary model of health outcomes, highlighting gaps and guiding the development of condition-specific instruments. A comprehensive search of the literature was conducted across PubMed, MEDLINE, and Embase. Studies involving PROMs in adults with tooth wear were included. Extracted data encompassed psychometric properties and domains assessed. PROMs such as the OHIP, OES, OIDP, and QMFQ have been frequently used, focusing on functional limitation, esthetic perception, and psychological distress. However, no single instrument comprehensively addresses all relevant domains of the Wilson and Cleary model. Moreover, variation in tools and constructs limits comparability across studies and clinical settings. Existing PROMs capture only partial aspects of the patient experience related to tooth wear. When mapping these instruments to a validated theoretical model, significant gaps become evident, especially in terms of general health perceptions and overall quality of life metrics. To improve the evaluation and management of tooth wear in clinical settings, it is essential to create a condition-specific PROM based on a solid conceptual framework. Full article

Background: Dental erosion is the irreversible loss of tooth structure from acid exposure. Its prevalence is rising globally, making it an important oral health concern. However, longitudinal data from Eastern Europe are scarce, especially in Romania. This pilot study aimed to assess the 10-year incidence of dental erosion in Romanian young adults and to compare clinical index scoring with digital scanning. Methods: A 10-year prospective study followed 540 Romanian adults (aged 18–30) selected with no erosive lesions at baseline (Basic Erosive Wear Examination BEWE = 0). Erosive wear was assessed at the 10-year follow-up using BEWE, with 40 participants also undergoing digital intraoral scanning to measure enamel loss (μm). Gender differences were analyzed. Chi-square tests, relative risk, and correlation analyses were performed. Results: After 10 years, 23.2% of participants developed dental erosion. Males exhibited a higher incidence than females (29.9% vs. 17.2%; RR = 1.74, p < 0.001). Among the scanned subset (n = 40), the mean enamel loss was 137 ± 79 µm, with greater wear on palatal vs. buccal surfaces (p = 0.002). BEWE scores were moderately correlated with digital enamel loss (r = 0.58, p < 0.001). Conclusions: Erosion progressed over time in this cohort, with males at higher risk. Digital scanning detected subtle enamel loss not captured by BEWE, indicating greater sensitivity to early changes. BEWE and digital methods provided complementary information; their combined use offers a more comprehensive assessment. Full article

Deep hole trepanning of large-diameter titanium alloy rods presents several challenges, including chip breaking, chip clogging, tool wear, and chipping. To address these issues, an optimized multi-tooth trepanning design was developed. An L9 orthogonal experimental array was employed to assess the influence of cutting speed, feed rate, and cutting fluid pressure on the chip volume ratio and to determine optimal process parameters. Results indicate that the impact of process parameters on the chip volume ratio of the first and third cutting teeth follows the order of cutting speed, feed rate, and cutting fluid pressure. Optimal chip morphology for internal chip removal is achieved with a cutting speed of 63.3 m·min⁻¹, a feed rate of 0.18 mm·r⁻¹, and a cutting fluid pressure of 4 MPa. Conversely, improper parameter matching can result in numerous long spiral chips, causing adhesive wear, diffusion wear of the multi-tooth drill, and severe chipping of the cutting edge. Full article

Background and Objectives: Conventional methods for removing cemented fixed prosthetic restorations (FPRs) are unreliable and lead to unsatisfactory outcomes. At their best, they allow the tooth to be saved at the expense of a laborious process that also wears down rotating tools and handpieces and occasionally results in abutment fractures. Restorations are nearly never reusable in any of these situations. Erbium-doped yttrium-aluminum-garnet (Er:YAG) and erbium-chromium yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers casafely and effectively remove FPRs, according to scientific studiesre. This study sets out to examine the impact of Er:YAG laser radiation on the debonding of different ceramic restorations, comparing the behavior of various ceramic prosthetic restoration types under laser radiation action and evaluating the integrity of prosthetic restorations and dental surfaces exposed to laser radiation. Materials and Methods: The study included a total of 16 removed teeth, each prepared on opposite surfaces as abutments.y. Based on the previously defined groups, four types of ceramic restorations were included in the study: feldspathic (F), lithium disilicates (LD), layered zirconia (LZ), and monolithic zirconia (MZ). The thickness of the prosthetic restorations was measured at three points, and two different materials were used for cementation. The Er:YAG Fotona StarWalker MaQX laser was used to debond the ceramic FPR at a distance of 10 mm using an R14 sapphire tip with 275 mJ, 20 Hz, 5.5 W, with air cooling (setting 1 of 9) and water. After debonding, the debonded surface was visualized under electron microscopy. Results: A total of 23 ceramic FPRs were debonded, of which 12 were intact and the others fractured into two or three pieces. The electron microscopy images showed that debonding took place without causing any harm to the tooth structure. The various restoration types had the following success rates: 100% for the LZ and F groups, 87% for the LD group, and 0% for the MZ group. In terms of cement type, debonding ceramic FPRs cemented with RELYX was successful 75% of the time, compared to Variolink DC’s 69% success rate. Conclusions: In summary, the majority of ceramic prosthetic restorations can be successfully and conservatively debonded with Er:YAG radiation. Full article

To address the limitations in time–frequency feature representation of shearer arm gear faults and the issues of parameter redundancy and low training efficiency in standard convolutional neural networks (CNNs), this study proposes a diagnostic method based on an improved S-transform and a Depthwise Separable Convolutional Neural Network (DSCNN). First, the improved S-transform is employed to perform time–frequency analysis on the vibration signals, converting the original one-dimensional signals into two-dimensional time–frequency images to fully preserve the fault characteristics of the gear. Then, a neural network model combining standard convolution and depthwise separable convolution is constructed for fault identification. The experimental dataset includes five gear conditions: tooth deficiency, tooth breakage, tooth wear, tooth crack, and normal. The performance of various frequency-domain and time-frequency methods—Wavelet Transform, Fourier Transform, S-transform, and Gramian Angular Field (GAF)—is compared using the same network model. Furthermore, Grad-CAM is applied to visualize the responses of key convolutional layers, highlighting the regions of interest related to gear fault features. Finally, four typical CNN architectures are analyzed and compared: Deep Convolutional Neural Network (DCNN), InceptionV3, Residual Network (ResNet), and Pyramid Convolutional Neural Network (PCNN). Experimental results demonstrate that frequency–domain representations consistently outperform raw time-domain signals in fault diagnosis tasks. Grad-CAM effectively verifies the model’s accurate focus on critical fault features. Moreover, the proposed method achieves high classification accuracy while reducing both training time and the number of model parameters. Full article

This paper presents an analysis of the abrasive wear influence on the tooth flank geometry of plastic gear wheels, emphasizing the contribution of tooth stiffness to the observed changes. The study examined gear wheels made from polylactic acid (PLA) with wall thicknesses of 0.6 mm, 1.0 mm and 2.4 mm, manufactured using FDM technology. A standard layer height of 0.2 mm was chosen as it offers a balance between good precision and reasonable printing times. The PLA gear wheels were tested for wear in a meshing configuration with a metallic reference gear. The results indicate that wear intensity increases as tooth stiffness decreases, suggesting an inverse proportionality between abrasive wear and tooth stiffness. In all tested cases, the tooth tip was more affected by abrasive wear compared to the rest of the profile. The analysis establishes that sliding velocity has the greatest influence on the abrasive wear characteristics of the evaluated gears. Based on experimental findings, a mathematical model was developed for simulating abrasive wear in plastic gears, with scalability across various manufacturing technologies. For PLA gears, both experimental and simulated data confirm that full tooth infill is essential for functional durability. Full article

Background: In recent years, thanks to the improvement of adhesive techniques, patients affected by tooth wear, related to erosion and/or parafunctional habits, can undergo restoration by adding only what has been lost of their dentition (additive approach). However, since not all clinicians are convinced that dental rehabilitation should be proposed in the early stages of exposed dentin, several treatments are often postponed. It is important to emphasize that, in the early stages, the clinical approach should remain conservative, focusing on dietary counseling, the modification of harmful habits, fluoride application, and risk factor management. Only when these preventive and non-invasive strategies prove insufficient, and the condition continues to progress, should invasive restorative treatments be considered. Unfortunately, epidemiological studies are reporting an increase in the number of young patients affected by erosive tooth wear, and not intercepting these cases earlier could lead to a severe degradation of the affected dentition. In addition, parafunctional habits are also becoming more frequent among patients. The combination of erosion and attrition can be very destructive, and may progress rapidly once dentin is exposed and the risk factors remain unaddressed. The aim of this report was to present a conservative full-mouth rehabilitation approach for severe erosive lesions and to provide a 10-year follow-up assessing the biological, functional, and esthetic outcomes. Methods: In this article, the postponed restorative treatment of a patient, suffering from severe tooth wear, is illustrated. The patient had sought dental treatment in the past; however, due to the already very compromised dentition, a conventional but very aggressive treatment was proposed and refused. Four years later, when the patient finally accepted an alternative conservative therapy, the tooth degradation was very severe, especially at the level of the maxillary anterior teeth. The combination of three different approaches, Speed-Up Therapy, BOPT (Biologically-Oriented Preparation Technique), and the 3 Step Technique, however, improved the capacity to successfully complete the difficult therapeutic task. Results: The biological goals (maintenance of the pulp vitality of all of the teeth and the minimal removal of healthy tooth structure) were accomplished, relying only on adhesive techniques. Conclusions: The overall treatment was very comfortable for the patient and less complicated for the clinician. At 10-year follow-up, biological, functional, and esthetic success was still confirmed. Full article

Labyrinth seals, extensively used in aerospace and turbomachinery as non-contact sealing devices, undergo accelerated wear and enhanced leakage due to repeated rub-impact between rotating shafts and sealing rings. To address the problem of increased leakage under rub-impact conditions, this research integrates experimental and numerical methods to investigate the deformation mechanisms and leakage characteristics of thermoplastic labyrinth seals. A custom designed rub-impact test rig was constructed to measure dynamic forces and validate finite element analysis (FEA) models with an error of 5.1% in predicting tooth height under mild interference (0.25 mm). Computational fluid dynamics (CFD) simulations further demonstrated that thermoplastic materials, such as PAI and PEEK, displayed superior resilience (with rebound ratios of 57% and 70.3%, respectively). Their post-impact clearances were 4.8–18.3% smaller than those of PTFE and F500. Leakage rates were predominantly correlated with interference, causing a substantial increase compared to the original state; at 0.25 mm interference (reverse flow), increases ranged from 151% (PAI) to 217% (PTFE), highlighting material-dependent performance degradation. Meanwhile, tooth orientation modulated leakage by 0.5–3% through the vena contracta effect. Based on these insights, two optimized inclined-tooth geometries were designed, reducing leakage by 28.2% (Opt1) and 28.1% (Opt2) under rub-impact. These findings contribute to the development of high-performance labyrinth seals suitable for extreme operational environments. Full article