Tooth Failure Research Articles

On the morphology and failure of worn human molar cusps

ObjectivesEnamel wear is a common occurrence that may lead to tooth failure. Beyond reducing enamel thickness, wear exposes different regions of enamel microstructure to various types of stresses. This work was aimed at elucidating the effect of enamel wear on enamel morphology and tooth resilience in human molar teeth undergoing large-scale contact. MethodsIntact/polished molar cusps were indented with a hard disk/ball. The unloaded specimens were sectioned longitudinally or transversely, and the damage examined by optical and scanning electron microscopy. The onset of cracks at the dentin horn apex was determined by a FEM stress analysis that modeled a cusp as truncated, conical enamel shell supported by dentin. ResultsThe damage consisted of radial and cylindrical cracks growing under the contact, sparsely distributed radial cracks in the enamel shell region, and cracking from tufts at the dentin horn apex (TA cracks). The damage under the contact circle exhibited shear deformation zones. These zones helped relieve contact stresses, absorb energy, contain damage, and solicit cylindrical cracks in order to avoid growth of wear-sensitive cone cracks. Enamel tufts provided stress shielding while Hunter-Schreger Bands helped maintain this benefit by enforcing a collaborative cracking. The TA cracks were deemed a primary cause for tooth failure. The FEA predicted well the onset of these cracks. Making use of in vivo enamel wear data, the analysis showed that cusp failure might routinely occur at old age. SignificanceThe results provided new information on the response of the interior part of enamel to contact loading. This included the resistant effects of the waviness of enamel rods, interrods and tufts. The unique microstructure of enamel gave rise to shear bands under the contact circle that helped relieve contact stresses, absorb energy and contain damage. Enamel interrods solicited cylindrical cracking in order to avoid the wear-sensitive cone cracks. The onset of cracks at the dentin horn apex (TA cracks) was deemed critical to a tooth survival. The FEA showed that this cracking mode might routinely occur at old age due to natural enamel wear. Finally, the occlusal force needed to initiate the TA cracks in intact cusps can help explain the natural design logic involving the maximum bite force of hominid species.

Effect of interference magnitude on ultimate strength and failure analysis of aluminium-drill-pipe-body-tool-joint-assemblies with Johnson-Cook model

In this paper, a three-dimensional non-linear finite element model of aluminium drill pipe body and tool joint assemblies is established to analyze the effect of interference on ultimate strength and failure modes. Johnson-Cook model is selected to describe the plastic behavior and failure phenomena. For quickly meshing thread connection into hexahedron grids, grid parametric modeling program is written by Matlab software. The interference assembly is carried out by coupling the temperature field with the stress field. The accuracy of the model is verified by experiments, and the error is less than 6%. The ultimate torsional strength, ultimate tensile strength, ultimate torque under different tension, failure modes and anti-loosing ability are obtained for different interference values. The result shows that interference values have little impact on ultimate tensile strength but have positive effect on torsional strength. For the coupling action of tension and torque, the ultimate strength for larger interference value is greater than smaller interference value. Besides, critical values for failure mode transition are found under different interference values. When tension exceeds the critical value, the failure modes changes from thread body fracture to thread teeth failure. The anti-loosing ability increases with the increase of the interference, however, for the interference being greater than a critical value, the influence of the interference will be almost unchanged. The present results can help to determine the safe range of working parameters for aluminium drill pipe in practical engineering, and provide theoretical support for the optimization of interference in the production of aluminium drill pipe.

Gearbox Fault Diagnosis Based on Improved Variational Mode Extraction.

Gearboxes are widely used in drive systems of rotating machinery. The health status of gearboxes considerably influences the normal and reliable operation of rotating machinery. When a gearbox experiences tooth failure, a vibration signal with impulse features is excited. However, these impulse features tend to be relatively weak and difficult to extract. To solve this problem, a novel approach for gearbox fault feature extraction and fault diagnosis based on improved variational mode extraction (VME) is proposed. Since the initial value of the desired mode center frequency and the value of the penalty parameter in VME must be assigned, a short-time Fourier transform (STFT) was performed, and a new index, the standard deviation of differential values of envelope maxima positions (SDE), is proposed. The feasibility and effectiveness of the proposed approach was verified by a simulation signal and two datasets associated with a gearbox test bench. The results demonstrate that the VME-based approach outperforms the variational mode decomposition (VMD) approach.

Nonlinear analysis of cylindrical gear dynamics under varying tooth breakage

Linear and nonlinear analyses served to detect the degree of tooth damage in a cylindrical gear. The gear in question is widely used in industrial applications and is often subject to gear tooth damage. Multiple-sourced vibrations affecting the test stand may distort or conceal the vibration components responsible for tooth failure. Given its construction, the test stand offers low stiffness, and additional control and measurement equipment further contribute to overall vibrations. Therefore, the vibration signal is likely to contain various disturbances, which further hinder correct diagnosis. Basic vibroacoustic signal analysis methods, which were employed at a preliminary stage, failed to produce unambiguous and satisfactory results. Hence, nonlinear recurrence analysis of gear operation dynamics was applied. It is assumed that the occurrence of damage to the gear will impede the regularity of drive transmission. The adopted research method addresses the limitations of a two-state diagnosis of gear condition (no damage/damage) by allowing the extent of gear tooth damage to be specified.

Radiographic diagnosis and surgical management of compound composite odontome with supernumerary tooth and impacted central incisor – A rare case report

Odontomas are the most frequent hamartomatous developmental abnormality. The condition is frequently associated with one or more unerupted teeth and is often detected through the failure of teeth to erupt at the expected time. Although most cases are found impacted within the jaw, there are instances where odontomas have erupted into the oral cavity. Majority of the odontomas are asymptomatic nonetheless these anomalies can cause delayed eruption, impaction, or even result in retention of primary teeth. Odontomas are atypical calcified conglomeration of dental tissues such as enamel, dentin, pulp, and cementum and emerge from odontogenic epithelium thus, they are mixed odontogenic tumor. According to the literature, its origin can be local trauma, infection, or genetic mutations, however, the exact cause is unknown. This case report presents a compound composite odontome in a 25-year-old patient along with its related clinical and radiological manifestations and the surgical management and emphasis on the early diagnosis and treatment planning.

Fiberglass versus cast metal posts: a practical review based on mechanical properties

The current review aimed to compare the mechanical properties and clinical behavior of fiberglass and cast metalposts. It included in-vitro studies, finite element analysis, clinical studies, and systematic reviews that evaluatedfiberglass and metal posts with reliable methodologies. The reports in the literature diverge on tooth failure modesand stress distributions in the root according to different posts. Investigations suggest that fiberglass posts arepreferable because their elastic modulus is similar to dentin. Other studies mention that the flexibility of fiber postsmay damage the interface. The fracture load values of different studies could not be compared. The presence of aferrule seems beneficial. Cast metal posts provide higher characteristic strength to the set but with more unfavorablefailures. Intraradicular posts with a lower elastic modulus produce more stress between the cement layer and dentin.In conclusion, fiberglass and cast metal posts can be used with a ferrule. Cast metal posts seem more appropriatefor weakened teeth. The presence of a ferrule benefits the system. Weakened teeth tolerate higher loads whenrestored with cast metal posts, but when these posts fail, the only solution is tooth extraction. Clinical follow-upscannot yet detect differences between the survival rates of intraradicular fiberglass and cast metal posts. KEYWORDSFiberglass; Post and core technique; Dental prosthesis; Mechanical tests; Finite element analysis.

Study on fracture behavior of molars based on three-dimensional high-precision computerized tomography scanning and numerical simulation.

A series of three-dimensional (3D) numerical simulations are conducted to investigate the gradual failure process of molars in this study. The real morphology and internal mesoscopic structure of a whole tooth are implemented into the numerical simulations through computerized tomography scanning, digital image processing, and 3D matrix mapping. The failure process of the whole tooth subject to compressions including crack initiation, crack propagation, and final failure pattern is reproduced using 3D realistic failure process analysis (RFPA3D) method. It is concluded that a series of microcracks are gradually initiated, nucleated, and subsequently interconnect to form macroscopic cracks when the teeth are under over-compressions. The propagation of the macroscopic cracks results in the formation of fracture surfaces and penetrating cracks, which are essential signs and manifestations of the tooth failure. Moreover, the simulations reveal that, the material heterogeneity is a critical factor that affects the mechanical properties and fracture modes of the teeth, which vary from crown fractures to crown-root fractures and root fractures depending on different homogeneity indices.

Tooth Failure Post-Radiotherapy in Head and Neck Cancer: Primary Report of the Clinical Registry of Dental Outcomes in Head and Neck Cancer Patients (OraRad) Study

To elucidate long-term sequelae of radiation therapy (RT) in head and neck cancer (HNC) patients, a multicenter, prospective study, Clinical Registry of Dental Outcomes in Head and Neck Cancer Patients (OraRad), was established with tooth failure as its primary outcome. We report tooth failure and associated risk factors. Demographics and cancer and dental disease characteristics were documented in 572 HNC patients at baseline and 6, 12, 18, and 24 months after RT. Eligible patients were aged 18 or older, diagnosed with HNC, and receiving RT to treat HNC. Tooth failure during follow-up was defined as losing a tooth or having a tooth deemed hopeless. Analyses of time to first tooth-failure event and number of teeth that failed used Kaplan-Meier estimators, Cox regression, and generalized linear models. At 2 years, the estimated fraction of tooth failure was 17.8% (95% confidence interval, 14.3%-21.3%). The number of teeth that failed was higher for those with fewer teeth at baseline (P < .0001), greater reduction in salivary flow rate (P=.013), and noncompliance with daily oral hygiene (P=.03). Patients with dental caries at baseline had a higher risk of tooth failure with decreased salivary flow. Patients who were oral-hygiene noncompliant at baseline but compliant at all follow-up visits had the fewest teeth that failed; greatest tooth failure occurred in participants who were noncompliant at baseline and follow-up. Despite pre-RT dental management, substantial tooth failure occurs within 2 years after RT for HNC. Identified factors may help to predict or reduce risk of post-RT tooth failure.

Gear root bending strength: statistical treatment of Single Tooth Bending Fatigue tests results

Gear tooth failure due to tooth root bending fatigue is one of the most dangerous failure modes in gears. Therefore, the precise definition of gear bending fatigue strength is a key aspect. Furthermore, in order to calculate the service life of a gear component, an accurate estimation of the S‑N curve is required. This curve must properly account for the slope of the fatigue strength region, the slope of the region ahead the fatigue knee, as well as the position of the knee itself. Hence, in order obtain a curve at different reliability levels, a proper estimation of the dispersion associated with the experimental points is required. Usually, Single Tooth Bending Fatigue (STBF) tests are used to investigate the gear load carrying capacity with respect to the bending failure mode. Then, starting from the gear specimen test data, the S‑N curve that has to be used in the rating method has to be determined. Maximum Likelihood Estimation (MLE), a statistical tool capable of considering also interrupted tests (e.g. runouts) has been used to estimate, in the most reliable way, the S‑N curve from experimental points. Furthermore, if the STBF test is performed in a symmetrical configuration, i.e. two teeth loaded at the same time, also the survival of one of the two teeth represents an information that can be taken into account thanks to MLE.Moreover, additional effects must be considered to obtain the S‑N curve of a real component starting from STBF tests. In reality, the load history and the statistical behaviour are different, since in a meshing gear the strength is determined by its weakest tooth, while in a STBF test the failing tooth is predetermined. The latter effect is considered by means of the statistic of extremes, which enables the estimation of the strength of the weakest tooth and therefore of the gear. This paper describes in detail the proposed calculation method and explains its application to determine the S‑N curve in practical cases.

Mechanical failure of posterior teeth due to caries and occlusal wear- A modelling study

ObjectivesThe purpose of the present work is to explore the effect of occlusal wear and different types and degrees of caries on the mechanical performance and structural integrity of posterior teeth. MethodsThree-dimensional (3D) computational models with different combinations of caries parameters (caries location, caries size and caries induced pulp shrinkage) and occlusal wear factors (enamel thickness, marginal ridge height and cuspal slope) were developed and analyzed using the extended finite element method (XFEM) to identify the stress distribution, crack initiation load and ultimate fracture load values. The effect of a non-drilling conservative treatment using resin infiltration on the recovery of mechanical properties of carious molar teeth was also investigated. ResultsPresence of fissural caries, worn proximal marginal ridge and decreased enamel thickness due to occlusal wear, imparted a significant negative effect on the crack initiation load value of the lower molar models. Accordingly, models with intact and strong proximal marginal ridge, generally exhibited higher crack initiation loading, regardless of caries size and location. Presence of fissure caries drastically decreased (55%–70%) the crack initiation load compared to sound teeth. The depth of the fissural lesion and the presence of proximal caries did not have a major effect on crack initiation load values. However, increasing the caries size resulted in lower final fracture load values in most of the cases. Accordingly, the groups with combined and connected large fissural and proximal lesions experienced the largest drop in the fracture load values compared to sound tooth models. The worst condition consisted of two connected large proximal and fissural caries with no proximal marginal ridge, in which the fracture load dramatically decreased to only 25% of that for sound teeth with intact marginal ridge. On the other hand, decreased cuspal slope due to occlusal wear and shrinkage of the pulp due to caries appeared to have a protective role and a direct relation with the fracture resistance of the tooth. Following the application of resin infiltration on the carious models, the crack initiation load and the fracture load could recover up to 75% and 90% of the values for the corresponding sound tooth models, respectively. SignificancePresence of fissural caries, if not treated (either with remineralization, resin infiltration or restoration), can be a major risk factor in the initiation of tooth fracture. When combined with decreased enamel thickness and loss of proximal marginal ridge due to mechanical or chemical wear, the weakening effect of the caries will be amplified specially in teeth with steep cuspal slopes. The application of a conservative treatment with resin infiltration can be an effective approach in prevention of further mechanical failure of demineralized enamel. The findings of this study emphasize the importance of early interventions in the management of caries for the prevention of future cuspal or tooth fracture especially in subjects with higher risk factors for tooth fracture such as caries, wear and bruxism.

Comparative Analysis of the Wear Performance of Spindle Hook Teeth During Fieldwork

Abstract The wear performance of the spindle hook teeth during fieldwork was compared, and the causes of the wear failure of the spindle hook teeth were analyzed. Samples of three kinds of spindle were obtained from the fixed installation position under continuous field operation conditions. The hardness, phase structure, elemental composition, and micromorphology of the spindle hook teeth were characterized using microhardness, X-ray diffractometer (XRD), energy spectrum analyzer (EDS), and scanning electron microscope (SEM) after cutting of the spindles. Results show that the coating hardness and element penetration zone of No.3 spindle hook tooth are the largest, and the surface coating phase structure of the three kinds of the spindle is mainly a body-centered cubic structure of Cr (211). Micro-crack and hole defects exist in the coating of all three kinds of the spindle. The thicknesses of the coating of No.1, No.2, and No.3 spindles are 74, 100, and 130 µm, respectively. During the field operation, the wear of the spindle hook tooth coating is caused by abrasive wear and fatigue wear, while the wear of the substrate is the result of the combined effect of abrasive wear and oxidation wear. Extracting the wear area and width of spindle hook teeth shows that the wear area of all three kinds of spindle hook teeth increases exponentially and the wear width changes linearly with the increase in the field operation area.

Alternative conservative approach for tooth build-up in patients with special healthcare needs

Purpose: The success of an artificial crown mainly depends on the biomechanical factors such as bonding capacity of cement between the crown and abutment tooth, and root strength of the abutment tooth. In this case series, we aim to provide insight on the potential use of the cast metal post and cost for patients with intellectual disabilities and severely compromised tooth structure. Material and methods: The first patient was a 41-year old male with the chief complaint of a dislodged porcelain fused metal (PFM) crown of tooth #20 (mandibular left second bicuspid). The patient was informed about the advantages, disadvantages, and risks of each option. After further consideration and discussion with the parents and the patient, we decided to rebuild the coronal tooth structure with the cast metal post and core and prosthetic restoration with the same crown. Patient satisfaction was measured on the visual analog scale as 10/10. The second case involves a 26-year old female, who presented with a chief complaint of chronic lingering pain on tooth #9. The tooth structure was extensively damaged and un-supportive of the ferrule, therefore, it was decided to build a metal post and core instead of a fiber post. The prosthetic restoration was made with a monolithic zirconia crown and the patient was followed up twice in 6 months and graded the satisfaction as 10/10 on a visual analog scale. Results: The most common type of posts used in dentistry has been cast post and cores in the last decade which generally includes an additional laboratory stage where a custom post is prepared according to the impression taken from the prepared post space. Conclusions: Both the presented cases explain an interesting advantage of restoring a root canal treated tooth with a metal post and core system which implies that in a prefabricated post and core restored tooth failure, a metal post, and core can potentially be the treatment of choice instead of extracting the tooth. Keywords: post and core; special needs; cast metal post.

Alternative Conservative Approach for Tooth Build-Up in Patients with Special Healthcare Needs

Purpose: The success of an artificial crown mainly depends on the biomechanical factors such as bonding capacity of cement between the crown and abutment tooth, and root strength of the abutment tooth. In this case series, we aim to provide insight on the potential use of the cast metal post and cost for patients with intellectual disabilities and severely compromised tooth structure. Material and Methods: The first patient was a 41-year old male with the chief complaint of a dislodged porcelain fused metal (PFM) crown of tooth #20 (mandibular left second bicuspid). The patient was informed about the advantages, disadvantages, and risks of each option. After further consideration and discussion with the parents and the patient, we decided to rebuild the coronal tooth structure with the cast metal post and core and prosthetic restoration with the same crown. Patient satisfaction was measured on the visual analog scale as 10/10. The second case involves a 26-year old female, who presented with a chief complaint of chronic lingering pain on tooth #9. The tooth structure was extensively damaged and un-supportive of the ferrule, therefore, it was decided to build a metal post and core instead of a fiber post. The prosthetic restoration was made with a monolithic zirconia crown and the patient was followed up twice in 6 months and graded the satisfaction as 10/10 on a visual analog scale. Results: The most common type of posts used in dentistry has been cast post and cores in the last decade which generally includes an additional laboratory stage where a custom post is prepared according to the impression taken from the prepared post space. Conclusions: Both the presented cases explain an interesting advantage of restoring a root canal treated tooth with a metal post and core system which implies that in a prefabricated post and core restored tooth failure, a metal post, and core can potentially be the treatment of choice instead of extracting the tooth.

Classification of gear faults in internal combustion (IC) engine gearbox using discrete wavelet transform features and K star algorithm

Vibration-based fault diagnosis is one of the widely used techniques for condition monitoring of the machines equipped with a gearbox. Severe operating conditions of gearbox result in gear tooth failure. To develop an effective fault diagnosis technique for the mechanical system, a machine learning approach is highly necessary and plays a vital role in the area of condition monitoring. This paper presents the vibration-based fault diagnosis of IC engine gearbox operating under actual running condition. An Eddy current dynamometer is used to apply the external load on the output shaft of the engine. Driving gear with healthy condition and progressive tooth defect conditions are considered for the analysis. The vibration signals of engine gearbox under various gear tooth conditions are measured. Discrete wavelet transform features are extracted from the vibration signals and more contributing features for classification are selected using decision tree algorithm. The Lazy based classifiers viz, k-nearest neighbour algorithm, K-star algorithm and locally weighted learning algorithm are used for classification. A comparative study of these classifiers is made using percentage of classification accuracy. The maximum classification accuracy of about 97.5% is achieved by the K-star algorithm. Based on the experimental results, K-star algorithm and discrete wavelet transform technique can be used for diagnosing the gear faults in IC engine gearbox using vibration signals.

Collective effect of damage prevention in taenioglossan radular teeth is related to the ecological niche in Paludomidae (Gastropoda: Cerithioidea)

The molluscan radula, a thin membrane with embedded rows of teeth, is the structure for food processing and gathering. For proper functioning, radular failures must be either avoided or reduced when interacting with the preferred food, as this might be of high significance for the individual fitness. Thus, the analysis of structural failure in radular teeth could be included in studies on trophic specializations. Here, we tested the failure of non-mineralized, chitinous radular teeth from taxa, belonging to an African paludomid species flock from Lake Tanganyika and surrounding river systems. These species are of high interest for evolutionary biologists since they represent a potential result of an adaptive radiation including trophic specialisations to distinct substrates, the food is attached to. In a biomechanical experiment a shear load was applied to tooth cusps with a force transducer connected to a motorized stage until structural failure occurred. Subsequently broken areas were measured and breaking stress was calculated. As the experiments were carried out under dry and wet conditions, the high influence of the water content on the forces, teeth were capable to resist, could be documented. Wet teeth were able to resist higher forces, because of their increased flexibility and the flexibility of the embedding membrane, which enabled them either to slip away or to gain support from adjacent teeth. This mechanism can be understood as collective effect reducing structural failure without the mineralisation with wear-minimizing elements, as described for Polyplacophora and Patellogastropoda. Since the documented mechanical behaviour of radular teeth and the maximal forces, teeth resist, can directly be related to the gastropod ecological niche, both are here identified as an adaptation to preferred feeding substrates. Statement of significanceThe radula, a chitinous membrane with teeth, is the molluscan feeding structure. Here we add onto existing knowledge about the relationship between tooth's mechanical properties and species’ ecology by determining the tooth failure resistance. Six paludomid species (Gastropoda) of a prominent species flock from Lake Tanganyika, foraging on distinct feeding substrates, were tested. With a force transducer wet and dry teeth were broken, revealing the high influence of water content on mechanical behaviour and force resistance of teeth. Higher forces were needed to break wet radulae due to an increased flexibility of teeth and membrane, which resulted in an interlocking or twisting of teeth. Mechanical behaviour and force resistance were both identified as trophic adaptations to feeding substrate.

A CURIOUS CASE OF THE GIRL WITH THE MISSING TEETH

Case Report A 3-year-old girl presented to the maxillofacial clinic with an asymptomatic large lump on the left side of the mandible with failure of teeth to erupt in the area. She presented with a firm, nontender swelling of the lower left canine region exhibiting no signs of infection. Furthermore, her lower left deciduous canine was missing despite normal dental development elsewhere in the mouth. Computed tomography scan of the mandible revealed an expansile, cystic lesion closely associated with an unerupted mandibular deciduous canine. Odontogenic tumors with analogous clinical and radiographical presentations as described include keratocysts, ameloblastomas and odontogenic myxomas. An incisional biopsy was performed to determine a definitive diagnosis where histology revealed a central odontogenic fibroma (COF). In particular, the nest of odontogenic epithelium in between the fibroblastic stroma was pathognomonic for COF. Subsequently, she underwent complete enucleation of the mass, curettage of the residual bone, and extraction of the enveloped deciduous tooth. Clinical Relevance COFs are an extremely rare group of benign neoplasms accounting for <1.5% of all odontogenic tumors. Such distinctions between the differential diagnoses are vital because several of the aforementioned tumors have high recurrence rates, whereas COF classically does not. Furthermore, the age of the patient here is remarkable because the literature describes the mean age of presentation as 31 years old. Conclusions This atypical case of COF highlights the importance of accurate histologic findings, which are pertinent to its diagnosis. It also incorporates several specialties and emphasizes the importance of early detection, diagnosis, and treatment. A 3-year-old girl presented to the maxillofacial clinic with an asymptomatic large lump on the left side of the mandible with failure of teeth to erupt in the area. She presented with a firm, nontender swelling of the lower left canine region exhibiting no signs of infection. Furthermore, her lower left deciduous canine was missing despite normal dental development elsewhere in the mouth. Computed tomography scan of the mandible revealed an expansile, cystic lesion closely associated with an unerupted mandibular deciduous canine. Odontogenic tumors with analogous clinical and radiographical presentations as described include keratocysts, ameloblastomas and odontogenic myxomas. An incisional biopsy was performed to determine a definitive diagnosis where histology revealed a central odontogenic fibroma (COF). In particular, the nest of odontogenic epithelium in between the fibroblastic stroma was pathognomonic for COF. Subsequently, she underwent complete enucleation of the mass, curettage of the residual bone, and extraction of the enveloped deciduous tooth. COFs are an extremely rare group of benign neoplasms accounting for <1.5% of all odontogenic tumors. Such distinctions between the differential diagnoses are vital because several of the aforementioned tumors have high recurrence rates, whereas COF classically does not. Furthermore, the age of the patient here is remarkable because the literature describes the mean age of presentation as 31 years old. This atypical case of COF highlights the importance of accurate histologic findings, which are pertinent to its diagnosis. It also incorporates several specialties and emphasizes the importance of early detection, diagnosis, and treatment.

Clinical outcomes and complications of posterior three-unit porcelain-fused-to-metal restoration combined with tooth-implant-supported prosthesis: A meta-analysis

Background/purposeThe three-unit bridge that combines a natural tooth and an implant provides extended treatment possibilities for partially edentulous patients. We conducted a systematic review and meta-analysis of clinical trials to evaluate three-unit porcelain-fused-to-metal (PFM) tooth-implant-supported prosthesis (TISP) compared with implant-supported-prosthesis (ISP) reconstruction outcomes and complications. Materials and methodsThe PubMed, Embase, and Cochrane library databases were searched for articles published before February 2021. The meta-analysis used a random-effects model to calculate overall effect size. The study was registered with PROSPERO (number: CRD 42021232606). ResultsSeven articles published between 2004 and 2015, with sample sizes ranging from 10 to 250 patients were included. No significant difference in the prosthesis failure rate, implant failure rate, prosthesis technical complication rate, implant technical complication rate, and marginal bone level change was observed between the TISP group and the ISP group. In TISP group, natural tooth failure rate was reported to range from 0% to 4.3%, biological complication related to the natural tooth was reported to range from 0% to 26.9%, and no trial reported natural tooth intrusion. ConclusionThe three-unit short-span TISP is a potentially reliable treatment option for patients with missing posterior teeth.

Pain, New Caries and Failure of Carious Primary Teeth after Application of Silver Diamine Fluoride Versus Sodium Fluoride Varnish: A Randomized Clinical Trial

Background: The aim of this study was assessment of the pain, new caries and failure of carious primary teeth after application of silver diamine fluoride versus sodium fluoride varnish immediately after application and after 3,6,9,12, months. Methods: This study was performed on 62 children with 255 carious primary teeth. After proper selection according to eligibility criteria and proper diagnosis. They were randomly allocated (1:1) into two groups. Group I (SDF): 38% Silver Diamine Fluoride and group II (NAF): 5% Sodium Fluoride Varnish. Assessment of postoperative pain, new caries,and failure at baseline, after 3,6,9,12, months. Results: Independent t-test was performed to compare between both groups and revealed that group II was significantly higher than group I after 9 and 12 months regarding postoperative pain, new caries, and failure.Also, strong positive significant correlation between failure and pain, and between failure and new caries was found using Spearman`s correlation coefficient test. Conclusions: SDF application isa successful alternative conservative treatment which eliminate the need to general anesthesia. Also, it is inexpensive, fast, and pain-free procedure but it causes discoloration. It`s successful results regardingstopping progression of new caries compensate its drawbacks such as discoloration.

Experimental Wear Behavior Analysis of Coated Spindle Hook Teeth under Real Harvesting Work Conditions.

This study aimed to investigate the wear failure changes of spindle hook teeth and the reasons for such failure during field work. Spindle samples were obtained from a fixed position of the spindle bar under different field picking area conditions and combined with the spatial distribution characteristics of cotton bolls in Xinjiang. After cutting a spindle sample, a scanning electron microscope and an energy spectrum analyzer were used to characterize the micromorphology and element composition of the hook tooth surface and cross section under different working area conditions. The wear parameters of the hook teeth were then extracted. The results showed that the thickness of the coating on the surface of the hook tooth used in this study was between 66.1 µm and 74.4 µm. The major chemical element was chromium, with a small amount of nickel. During the field picking process, failure of the coating on the surface of the hook teeth initially appeared on the tooth tip and tooth edge, and then spread to the entire hook tooth surface. The wear failure of the hook teeth resulted from abrasive wear, oxidative wear, and fatigue peeling. As the picking area increased, the wear area of the hook teeth increased exponentially, while the wear width increased linearly. When the field picking area reached 533.33 ha, the maximum change rate of the wear area was 2.33 × 103 µm2/ha, and the wear width was 1.84 µm/ha. During field work, the thickness of the coating decreased from the cutting surface to the tooth edge, and the wear rate gradually increased. The wear rate at Position 1 was the slowest, at 0.01 µm/ha, and the wear rate at Position 5 was the fastest, at 0.25 µm/ha.

Fuzzy diagnostics for gearbox failures based on induction motor current and wavelet entropy

In this work, a strategy is proposed for the automatic diagnosis of failures in gearboxes using current signals from an induction motor. The stator currents were represented by the extended Park vector approach technique and decomposed by the wavelet packet transform. The calculation of the wavelet packet entropy promoted the distinction between broken tooth failures and the levels of severity of surface wear. The entropies of two wavelet details were used as inputs for a fuzzy inference for automatic classification of the gearbox condition. The experimental results presented a high rate of correctness in the fuzzy diagnosis, confirming the efficiency of the strategy for high rotation (60 Hz) and low rotation (20 Hz). The strategy presents simplicities related to the practical implementation and reduction of the amount of data analyzed.