Tooth Root Research Articles

Nanosecond infrared laser (NIRL) for cutting roots of human teeth: thermal effects and quality of cutting edges

A nanosecond infrared laser (NIRL) was investigated in cutting dental roots. The focus of the investigation was defining the preparation accuracy and registration of thermal effects during laser application. Ten teeth were processed in the root area using a NIRL in several horizontal, parallel incisions to achieve tooth root ablation as in an apicoectomy. Temperature change was monitored during ablation and the quality of the cutting edges in the roots were studied by means of micro-CT, optical coherence tomography, and histology of decalcified and undecalcified specimens. NIRL produced clearly defined cut surfaces in dental hard tissues. The automated guidance of the laser beam created regular, narrow dentin defects that tapered in a V-shape towards the ablation plane. A biologically significant increase in the temperature of the object and its surroundings did not occur during the laser application. Thermal dentin damage was not detected in histological preparations of treated teeth. Defined areas of the tooth root may be ablated using a NIRL. For clinical translation of NIRL in apicoectomy, it would be necessary to increase energy delivered to hard tissue and develop beam application facilitating beam steering for oral treatment.

Lateral Alveolar Ridge Augmentation with Autogenous Tooth Roots and Staged Implant Placement-5-Year Follow-Up Case Series.

Background/Objectives: Alveolar bone augmentation before implant placement is a safe and effective treatment option for the reconstruction of a deficient alveolar ridge. According to recent research, permanent teeth have been used as bone graft materials, with studies confirming their clinical and histological results. This study aimed to evaluate the efficacy of alveolar ridge augmentation with autogenous tooth roots and staged implant placement, and peri-implant tissue stability in augmented sites. Methods: A total of 20 augmentations with autogenous tooth roots on mandibular alveolar ridges in 15 patients were performed. After 6 months, the ridge width (RWa) and ridge width gain (RWg) were measured. Titanium dental implants were placed in grafted sites and loaded 10 weeks after placement. Clinical parameters (bleeding on probing-BOP; probing depth-PD; mucosal recession-MR; and clinical attachment level-CAL) were assessed 2 months (T1), 3 years (T2), and 5 years (T3) after implant loading. Results: The mean RWa was 6.71 ± 0.74 mm, and the RWg was 3.15 ± 0.54 mm, respectively. No statistically significant differences were observed for clinical parameters (BOP, PD, MR, and CAL) among different time points (p > 0.05). Conclusions: Autogenous tooth roots represent a viable solution for alveolar ridge augmentation and implant placement, providing a stable environment for peri implant tissues.

Computer Numerical Control Machining Simulations and Experimental Analysis of a Novel C-Gear

C-gear is a novel gear transmission system, with no existing special machining and cutting tools to realize its construction. In this study, we employed a 5-axis computer numerical control (CNC) machining center to construct a C-gear, while solving the prototype manufacturing problem at the experimental research stage. We deduced the C-gear mathematical model and studied the three-dimensional (3D) modeling methods based on the analysis of its generation principle. The C-gear processing technique using the 5-axis CNC machining center and the tool path designs were established using the VERICUT and MASTERCAM softwares, and the C-gears were experimentally constructed. The maximum overcut and residual of the gear positioning hole surface were both found to be 0.094 mm. Moreover, the maximum overcut on the tooth surface and root were 0.02 and 0.03 mm, respectively, and the maximum residual on both the tooth surface and root was 0.03 mm. The machining overcuts and residual amounts of the proposed method were better than those of reference [14]. The existing overcut and residual errors included the errors generated by surface fitting during the 3D modeling of the gears. Therefore, the machining errors of the physically constructed tooth surface are expected to be smaller than the theoretical value, suggesting a high feasibility of the proposed method to realize the machining of C-gears.

Are different screw lengths associated with osteosynthesis quality in the region of the mental foramen?

AbstractIntroductionThe use of two monocortical malleable 04‐hole miniplates, placed above and below the mental foramen, has been indicated to prevent the adverse effects of tension and torsion forces on fracture healing. To obtain good fixation in the mandible's outer cortex screws, 5–8 mm long have been recommended. However, studies have shown thicknesses in the mental foramen region of up to 3 mm, meaning the length of the screw could be a risk to nerve or tooth root damage. The purpose of this study is to identify the influence of screw length on osteosynthesis quality in the region of the mental foramen.Materials and Methods10 synthetic polyurethane human lower jaw replicas were subjected to a linear loading test to evaluate fixation techniques with 5 and 10 mm of displacement. In the photoelastic analysis, 02 lower jaw models were made of photoelastic resin and subjected to linear loading in the fixation technique with 10 mm of displacement. Two 04‐hole miniplates in the region of the mental foramen either fixed completely with 4 mm screws (group 1) or with 5 mm screws in the tension zone and 8 mm screws in the compression zone (group 2). The variables were registered for peak load and peak displacement, and final load and final displacement. One‐way analysis of variance (ANOVA) was applied, followed by the Tukey test, with a significance of 5% (p = 0.05) for the comparisons between the means.ResultsConsidering 95% confidence intervals, the mechanical test showed no statistical differences in peak load between the fixations groups. In the photoelastic analysis, the fringes were concentrated on the distal segment of the fracture in both groups.ConclusionDue to the lack of statistical difference in the biomechanical and photoelastic tests, considering the methodologic limitation, our study indicates a tendency of advantage toward the treatment of fractures with two 04‐hole plates, fixed with 4 mm screws, to minimize complications like tooth or nerve damage. In vivo studies are needed to verify the convergence of the results of in vitro studies to evaluate the resistance and stability in real masticatory forces.

Deficiency of Trps1 in Cementoblasts Impairs Cementogenesis and Tooth Root Formation

Cementum is the least studied of all mineralized tissues and little is known about mechanisms regulating its formation. Therefore, the goal of this study was to provide new insights into the transcriptional regulation of cementum formation by determining the consequences of the deficiency of the Trps1 transcription factor in cementoblasts. We used Trps1Col1a1 cKO (2.3Co1a1-CreERT2;Trps1fl/fl) mice, in which Trps1 is deleted in cementoblasts. Micro-computed tomography analyses of molars of 4-week-old males and females demonstrated significantly shorter roots with thinner mineralized tissues (root dentin and cementum) in Trps1Col1a1 cKO compared to WT mice. Semi-quantitative histological analyses revealed a significantly reduced area of cellular cementum and localized deficiencies of acellular cementum in Trps1Col1a1 cKO mice. Immunohistochemical analyses revealed clustering of cementoblasts at the apex of roots, and intermittent absence of cementoblasts on Trps1Col1a1 cKO cementum surfaces. Fewer Osterix-positive cells adjacent to cellular cementum were also detected in Trps1Col1a1 cKO compared to WT mice. Decreased levels of tissue-nonspecific alkaline phosphatase (TNAP), an enzyme required for proper cementogenesis, were apparent in cementum, periodontal ligament, and alveolar bone of Trps1Col1a1 cKO. There were no apparent differences in levels of bone sialoprotein (Bsp) in cementum. Quantitative analyses of picrosirius red-stained periodontal ligament revealed shorter and disorganized collagen fibers in Trps1Col1a1 cKO mice demonstrating impaired periodontal structure. In conclusion, this study has identified Trps1 transcription factor as one of the important regulators of cellular and acellular cementum formation. Furthermore, this study suggests that Trps1 supports the function of cementoblasts by upregulating expression of the major proteins required for cementogenesis, such as Osterix and TNAP.

Enhancing Root Canal Therapy with NIR-II Semiconducting Polymer AIEgen and Low-Concentration Sodium Hypochlorite Synergy.

Despite significant efforts to eliminate bacterial biofilm within root canals, achieving effective disinfection remains challenging due to the complex anatomy and limitations of disinfectants. In this study, a second near-infrared (NIR-II) semiconducting polymer with aggregation-induced emission (AIE) properties, named PIDT-TBT, is deliberately designed and synthesized. This proposes an AIE luminogen-based sterilization strategy in synergy with a low concentration of sodium hypochlorite (NaClO). Water-dispersible PIDT-TBT nanoparticles (NPs) are prepared, demonstrating good biocompatibility, as well as photothermal and photodynamic properties. Subsequent antibacterial tests show that PIDT-TBT NPs exhibit excellent bactericidal effects against three bacterial strains: Staphylococcus aureus, Streptococcus mutans, and Enterococcus faecalis, upon 808nm laser irradiation. In synergy with a low concentration of NaClO (0.5%) solution, PIDT-TBT NPs significantly improves the outcome of root canal treatment under 808nm laser irradiation in a human extracted tooth root canal infection model. Additionally, it is found that PIDT-TBT NPs combine with a low concentration of NaClO solution could safely dissolve dentin debris and further increase the efficiency of root canal preparation by altering the elemental composition of the inner root canal wall.

Position and frequency of lateral canals in carnassial teeth of dogs

Carnassial teeth, as one of the most important teeth in dogs, are commonly affected by different types of injuries and pathological disorders, which require endodontic treatment. Lateral canals, which leave the main root canal, and apical deltas are present in the root canal system of dogs. These canals represent small branches that leave the main root canal at a sharp angle and terminate in a region of the periodontal ligament on the external root surface. In this study, 200 teeth were included, of which 100 were superior fourth premolars and 100 were inferior first molars. Lateral canals were present in a total of 30 roots of superior fourth premolar teeth, whereas in inferior first molars, these canals were found in 3% of roots. In superior fourth premolars, lateral canals were mostly present in the apical third, 86%, while 14% were present in the middle third of the root. In inferior first molars, lateral canals were found in 3% of the roots, 2% in the apical third and 1% in the middle third of the roots. The knowledge of the complex root canal morphology is essential for any endodontic treatment. Due to the presence and frequency of lateral canals, it is imperative to perform more thorough cleaning and instrumentation while performing endodontic treatment on superior fourth premolars compared to inferior first molars.

Active contour-based tooth segmentation in radiographs using fuzzy logic and CNN

Radiographic imaging is a crucial tool frequently employed by dentists for initial diagnosis and treatment planning. However, these images often suffer from distortion or inaccuracies due to incorrect exposure settings, making it challenging to identify critical regions such as tooth roots and margins. This study addresses these issues by presenting two innovative methods for tooth segmentation from radiographs, aimed at isolating the tooth regions for better analysis. The first method utilizes fuzzy logic rules to detect edges within the radiographic images. These detected edges are then used as a mask for the Active Contour Method (ACM) to segment the teeth accurately. The second method involves the creation of a Convolutional Neural Network (CNN) for tooth segmentation. The segmentation performance of the CNN is further refined using the ACM, leveraging the initial segmentation as a mask. Both methods demonstrated notable results with varying performance metrics. Specifically, the Fuzzy-Based Active Contour Method achieved precision, recall, and F1 score values of 0.6246, 0.4169, and 0.50, respectively. In contrast, the CNN-Based Active Contour Method calculated accuracy and specificity values of 0.9706 and 0.9872, respectively. These findings indicate that both approaches have distinct strengths in different performance aspects. Our study suggests that these advanced segmentation techniques can significantly enhance the diagnostic capabilities of dental professionals by providing clearer images of tooth structures, aiding in the detection of issues such as root problems, fractures, and wear patterns. Implementing these methods either independently or in combination could lead to more accurate diagnoses and better patient outcomes. Future work could explore the integration of these techniques to leverage their complementary strengths, potentially leading to even greater segmentation accuracy and reliability.

Efficacy of the CALM® Algorithm in Reducing Motion-Induced Artifacts in CBCT Imaging: A Fractal Dimension Analysis of Trabecular Bone.

The primary goal of this investigation was to ascertain the efficacy of the CALM® motion artifact reduction algorithm in diminishing motion-induced blurriness in Cone Beam Computed Tomography [CBCT] images. The assessment was conducted through Fractal Dimension [FD] analysis of the trabecular bone. A desiccated human mandible was subjected to Planmeca ProMax 3D® scanning under eight distinct protocols, marked by variations in motion presence [at 5, 10, and 15 degrees] and the deployment of CALM®. In every scan, five distinct regions of interest [ROIs] were designated for FD analysis, meticulously avoiding tooth roots or cortical bone. The FD was computed employing the box-counting method with Image-J 1.53 software. Our findings reveal that a 5-degree motion does not significantly disrupt FD analysis, while a 10-degree motion and beyond exhibit statistical differences and volatility among the sites and groups. A decreased FD value, signifying a less intricate or "rough" bone structure, correlated with amplified motion blurriness. The utilization of CALM® software seemed to counteract this effect in some instances, reconciling FD values to those akin to the control groups. Nonetheless, CALM®'s efficacy differed across sites and motion degrees. Interestingly, at one site, CALM® application in the absence of motion resulted in FD values considerably higher than all other groups. The study indicates that motion, particularly at 10 degrees or more, can considerably impact the FD analysis of trabecular bone in CBCT images. In some situations, the CALM® motion artifact reduction algorithm can alleviate this impact, though its effectiveness fluctuates depending on the site and degree of motion. This underscores the necessity of factoring in motion and the employment of artifact reduction algorithms during the interpretation of FD analysis outcomes in CBCT imaging. More research is necessary to refine the application of such algorithms and to comprehend their influence on different sites under varying motion degrees.

Investigation of periodontal tissue regeneration using octacalcium phosphate and collagen composite

ObjectiveThis study aimed to investigate periodontal tissue regenerative potential of octacalcium phosphate (OCP) and collagen composite (OCPcol), recognized as excellent bone-regenerative materials, in artificial bone defect models using beagle dogs. This study specifically assessed the efficacy of OCPcol in periodontal soft-tissue regeneration. MethodsOCPcol was implanted in bone defects adjacent to the roots of the left mandibular third and fourth premolars in six beagle dogs (OCP group), while five dogs did not receive OCPcol (control group). The dogs were observed for 3 months. The specimens were evaluated radiologically and histologically. ResultsMicrocomputed tomography revealed bone regeneration originating from the lateral cortical bone surface adjacent to the created defect. The superficial layer of the regenerated bone was cortical bone-like and continuous with the upper and lower alveolar bone. The bone was regenerated by maintaining a continuous void in the periodontal ligament space above and below the dentinal defect. Dental defects of roots were not regenerated. The control group did not exhibit sufficient bone regeneration. Histologically, in the OCP group, formation of new cementum was observed on the outer surface of the root dentin, with connective tissue attachment and an oblique-running periodontal ligament in the space between the new bone and dentin. However, the dentinal defects were not regenerated． ConclusionsAlveolar bone and periodontal ligament regenerated when OCPcol was implanted into a bone and dentinal defect created around a natural tooth root. These results suggest that OCPcol effectively regenerates periodontal tissue, without ankylosis.

How accurate is predicted root movement achieved in four first-premolar extraction cases with Invisalign?

This study aims to compare the achieved and predicted root movements in adults after four first-premolar extractions and Invisalign treatment. Thirty-three consecutive adults (22 Class I, 9 Cusp-to-cusp Class II and 2 Cusp-to-cusp Class III) from a single clinical division who completed the first series of aligners after premolar extractions were included in this retrospective study. A pretreatment cone-beam computed tomography model was registered onto the pretreatment surface-scanned dental model (SSDM) to locate the pretreatment root apices of the whole dentition. These were copied and transferred to the predicted and achieved post-treatment SSDMs to acquire the locations of the predicted and achieved post-treatment root apices. The differences between predicted and achieved root movements (DPARMs) were tested using the paired t-test or Wilcoxon signed rank test. In the anteroposterior direction, posterior root movements of maxillary and mandibular anterior teeth were poorly achieved (3.24-5.74 mm DPARMs, p < .05). In the vertical direction, roots of maxillary anterior teeth achieved greater intrusion (0.70-0.93 mm DPARMs, p < .05), while those of mandibular incisors achieved less intrusion (0.57-0.65 mm DPARMs, p < .05) than predicted. In the mediolateral direction, lateral incisor roots did not move distally (-0.65 to -0.96 mm DPARMs, p < .05), while those of canines did not move buccally, compared with the prediction (-0.75 mm DPARMs, p < .05). In the four first-premolar extraction treatments with Invisalign, root movements were not achieved as predicted, particularly for anterior teeth in the anteroposterior direction.

Effects of isotretinoin on tooth movement, orthodontically induced and non-orthodontic root resorption: A micro-CT study.

This study aims to investigate whether cumulative dose-dependent isotretinoin (Roaccutane®) could affect orthodontic tooth movement (OTM) and root resorption. Ninety male Wistar Albino rats were divided into 4 groups. While, the control (SALINE), solvent (SOYBEAN) and orthodontic drug (ISOTM) groups underwent orthodontic force, the non-orthodontic drug group (ISO) did not. The rats were administrated saline, soybean oil (SBO) and isotretinoin diluted in SBO (ISOTM, ISO) for 30 days, respectively. Six rats were euthanized in each orthodontic group. Fifty grams of orthodontic force was applied to the remaining rats' first molars using the incisors as anchorage. Six more rats in each group were euthanized on the 7th, 14th and 21st days of the force application. In the ISO group, six rats were euthanized on the 37th, 44th and 51st days of administration. Six rats that were euthanized for ISOTM on the 30th day were also used for ISO to reduce the number of rats used. Micro-computed tomography (micro-CT) and histological analysis were performed. Independent of orthodontic force, isotretinoin caused root resorption in the apical region. However, there was no statistically significant influence of isotretinoin on OTM and orthodontically induced root resorption (OIRR). Despite the lack of strong evidence supporting the orthodontically induced resorptive effect of isotretinoin, this study provided findings regarding the resorptive effects of isotretinoin on non-orthodontic root resorption. Therefore, the present results underscore the importance of close monitoring during orthodontic treatment to mitigate potential root resorption in patients who use isotretinoin because of acne complaints.

An innovative method for three-dimensional bone reconstruction of the anterior mandible with preserved dentition using an allogeneic bone block: A 6-month follow-up.

Bone defects around the teeth affect a large portion of the population. Bone regeneration in the area of existing teeth is completely different from that in an edentulous area. To date, no method has been developed for three-dimensional (3D) bone reconstruction in regions with preserved teeth. This study aimed to radiologically evaluate the results of the new method of 3D mandibular bone reconstruction in preserved dentition using a custom-made allogeneic bone block with a 6-month follow-up. Alveolar ridge dimensions were radiographically assessed before and 6 months after reconstruction using cone beam computed tomography (CBCT) scans in 32 patients (192 teeth). Reconstruction used a bone block that had been previously planned and prepared using CAD/CAM technology. The observed changes in alveolar bone dimensions were highly significant in most cases (p < 0.001). The closer to the tooth root apex, the lower the bone growth in the sagittal dimension (average of the mean values for each tooth examined in the measured heights): CEJ2: 2.9 mm, ½ CEJ2: 2.7 mm, ¼ CEJ2: 1.9 mm, and API: 1.4 mm. The maximum bone growth in the vertical dimension was observed on tooth 43 (9.9 mm), followed by 32 (9.8 mm), 33 (8.5 mm), 31 (8.4 mm), 42 (8 mm), and 41 (7 mm). The degree of decrease in vestibular dehiscence of the bone was greater the closer the tooth was to the midline (average of -3.8 mm and -3.4 mm for the central incisors; average of -2.8 mm and -2.6 mm for the lateral incisors; average of -2.6 mm and -2.5 mm for the canines). The results prove that it is possible to prevent bone dehiscence in patients undergoing orthodontic treatment, increasing the ability and effectiveness of covering recessions and improving the morphology of the lower part of the face.

Planetary gearbox fault classification based on tooth root strain and GAF pseudo images

Traditional signal processing methods based on acceleration signals can determine whether a fault has occurred in a planetary gearbox. However, acceleration signals are severely affected by interference, causing difficulties in fault identification. This study proposes a gear fault classification method based on root strain and pseudo images. Firstly, fiber optic sensors are employed to directly acquire strain data from the ring gear root. Next, the strain signals are preprocessed using resampling and a time-domain synchronous averaging algorithm. The processed signals are encoded into two-dimensional images using Gramian Angular Fields (GAF). Then, CN-EfficientNet with contrast learning is proposed to analyze and extract deeper fault features from the image texture features. In the classification experiments for different types of faults, the accuracy reached 96.84%. The results indicate that the method can effectively accomplish the task of fault classification in planetary gearboxes. Comparative experiments with other common classification models further indicate the superior performance of the proposed learning model. Visualization based on Grad-CAM provides interpretability for the fault recognition network’s results and reveals the underlying mechanism for its excellent classification performance.

Effect of hydrogen peroxide versus charcoal-based whitening mouthwashes on color, surface roughness, and color stability of enamel

BackgroundPatients tend to favor the whitening mouthwashes as they are easily applied and affordable. This study aimed to evaluate the effect of hydrogen peroxide versus charcoal-based whitening mouthwashes on color, surface roughness, and color stability of enamel. In the current study, the whitening mouthwashes used have the ability to stop future stains due to their white seal technology.MethodsA total of 21 permanent central incisor teeth extracted for periodontal reasons were used in the present study. Teeth roots were sectioned and crowns were mounted in self-cured acrylic resin blocks. The specimens were randomly divided into three groups (n = 7) according to the tested whitening mouthwash: Control group ‟ DW” (Distilled water), ‟OW” group: Peroxide-based mouthwash (Colgate Optic White) and ‟CP” group: Charcoal-based mouthwash (Colgate® Plax Charcoal). Regarding ‟OW” and ‟CP” groups, the specimens were immersed in 20 ml of the tested mouthwash in each corresponding group for 1 min twice daily (morning and evening) for a total of 12 uninterrupted weeks. Color change was assessed using VITA Easyshade spectrophotometer and surface roughness (Ra) was measured using a white light interferometer. The specimens were stained using black tea solution and color was measured after 24 h of immersion for assessment of color stability.ResultsColor change results revealed that both whitening mouthwashes were able to restore color comparable to the control group with no significant difference between them. Regarding surface roughness, the control group showed the highest mean Ra value, followed by ‟OW” group while ‟CP” group showed the lowest mean Ra value. While color stability after staining, the control group showed a significantly higher value than the ‟CP” and ‟OW” groups.ConclusionHydrogen peroxide and charcoal-based whitening mouthwashes improve the color of enamel with no adverse effect on the surface roughness. Both whitening mouthwashes were beneficial to maintain the color after staining and prevent future enamel stains.

Applications of Micro-CT Imaging in Age-At-Death Estimates of Maya Dogs

ABSTRACT While there are many techniques for estimating age-at-death in archaeological dogs, the pulp cavity/tooth width ratio is considered one of the most accurate methods. This study adapts this technique for application to MicroCT imaging, a non-destructive methodology that is rapidly gaining ground in faunal analysis. Mandibular first molar and upper and lower canine teeth recovered from two Late Classic-Early Postclassic period sites in the Maya highlands, Moxviquil and Tenam Puente, were imaged using a SCANCO μCT35 MicroCT scanner. The widths of tooth roots, pulp cavities, cuspal enamel thicknesses, and enamel attrition measurements were then taken using both the scanner’s post-processing system and 3D Slicer, an open-access programme designed for imaging biomedical scans and other 3D files, and pulp cavity infilling ratios were calculated to obtain an age-at-death estimates in months for each specimen. Based on these, this study presents preliminary interpretations of canid age-at-death patterns at Moxviquil and Tenam Puente, including a range of juvenile specimens from a funerary cave context at Moxviquil.

The DTR Technique-Drilling through the Roots of Posterior Teeth for Anatomically Guided Immediate Implant Placement: A Cohort Study.

The present study clinically analyzes implant survival of immediate implant placement cases using the drilling through roots (DTR) technique for anatomically-guided implant site preparation, as an aid to placing immediate dental implants in multi-radicular teeth. This clinical analysis utilized patients' electronic dental records who underwent immediate implant surgery using the DTR technique. All immediately placed implants were followed up regularly every year, after restoration. Implant survival was assessed with the Albrektsson et al. criteria. Inferential statistics was performed using SPSS v 21(IBM Corp., Armonk, NY) software. The Kaplan-Meier survival analysis was done to assess the implant survival probability. A total of 250 records of dental implants placed in 227 subjects using the DTR technique were considered. Results showed that the mean survival duration of implants was found 63.29 months and the median survival duration to be 55 months. A 100% success rate was seen in implant fixed bridge cases, and about 97.6% success was seen in single crown cases. No significant difference was seen in the survival rates during the follow-up period when compared according to the quadrants/site of implant placement. The findings concluded that tooth-guided rapid implant placement is a unique strategy for convenient and safe insertion, providing accurate three-dimensional positioning. The DTR method is a novel approach that facilitates accurate positioning and angulation of the implant bed preparation by stabilizing and guiding the osteotomy drills using the retained root. As a result, it enables optimal implant positioning at multirooted extraction sites. How to cite this article: Mahesh L, Miselli A, Bhasin MT, et al. The DTR Technique-Drilling through the Roots of Posterior Teeth for Anatomically Guided Immediate Implant Placement: A Cohort Study. J Contemp Dent Pract 2024;25(5):432-439.

Experimental analysis of failure modes depending on different loading conditions applied on cylindrical polyamide 66 gears

Abstract Engineering plastics are increasingly used for gearing systems, such as in the automotive sector, e-mobility sector, and household appliances. The basic task of the gearing system is to efficiently transfer power from the source to the application user. The use of engineering plastics for gearing applications is conditioned by the lack of tribological characteristics of material pairs which influence on fatigue and wear behaviour of the whole gearing system. The paper presents testing of the steel/Polyamide 66-gear by determining fatigue life in an infinite area, considering high precision optical measurements in the range of micro-meter accuracy of abrasion flank wear together with surface temperature in contact, providing an important database for engineers about material suitability for appropriate mechanical systems. Observing the results, gear flank wear of PA66 HT is directly proportional to the meshing temperature and torque. Thermal melting is a characteristic failure mode of the polymer gears which are exposed to higher load levels. In the middle torques, the dominant failure mode is flank fracture known as pitch point fracture. The greater impact of the gear wear mechanism occurs at lower torques where initial crack propagation starts at the pitch point and ends in the tooth root area.

Herpes Simplex Virus Type 1 Infection of Human Periodontal Ligament.

The periodontal ligament (PDL) is a complex connective tissue that connects the tooth root to the dental alveolar bone and plays crucial mechanical roles. PDL also exhibits regenerative roles and regulatory functions to maintain periodontium integrity and homeostasis. While PDL exposure to oral microbial pathogens is common, virtually nothing is known regarding viral infections of PDL. In particular, human herpes simplex virus type 1 (HSV-1) persistently infects the oral cavity through infections of the oral epithelium, connective tissue and neurons. While the oral spread of HSV-1 is generally asymptomatic, this virus has also been implicated in various oral pathologies. In this study, using a primary cell model derived from PDL (PDL cells), and whole surgical fragments of PDL, we provide evidence supporting the efficient infection of PDL by HSV-1 and the promotion of cytopathic effects. Infection of PDL by HSV-1 was also associated with an acute innate inflammatory response, as illustrated by the production of antiviral interferons and pro-inflammatory cytokines. Furthermore, this inflammatory response to HSV-1 was exacerbated in the presence of bacterial-derived products, such as peptidoglycans. This work therefore highlights the ability of HSV-1 to infect mesenchymal cells from PDL, suggesting that PDL may serve as a viral reservoir for the periodontal spread of HSV-1. Moreover, this raises questions about HSV-1 oral pathogenesis, as HSV-1-associated cytopathic and inflammatory effects may contribute to profound alterations of PDL integrity and functioning.

Elastohydrodynamic lubrication analysis and temperature field simulation of gear system

Abstract The gearbox is one of the key components in the aero engine. In the process of high-speed operation, the internal temperature of the gearbox rises significantly, which seriously affects the service performance of transmission equipment. Based on the meshing principle and Herz contact theory, the basic meshing parameters are analyzed, and the comprehensive friction coefficient and heat flux are solved. According to the principle of convective heat transfer in a rotating disc and the frictional heat diffusion model, the CHTC (convective heat transfer coefficient) is analyzed. The FE model of the gear system is built based on ANSYS software, and the temperature distribution is analyzed by loading thermal boundary conditions with the APDL program. The calculation results indicate that the middle of the tooth tip or root of the gear has the maximum temperature. The research provides some reference values for the calculation method of the temperature field of the gear system under elastohydrodynamic lubrication.