Double Tooth Research Articles

Modeling and dynamics analyzing of a torsional-bending-pendular face-gear drive system considering multi-state engagements

A face-gear drive system has been extensively used in important transmission devices with strict requirements for size and weight such as helicopter reducer and so on. Its dynamic characteristics directly affect the stability and reliability of the equipment. A piecewise torsional-bending-pendular nonlinear dynamics model of the face-gear drive system is established to study its nonlinear dynamics and dynamic characteristics. The multi-state engagements including drive-side teeth engaging, teeth disengagement, back-side teeth engaging, and alternate engaging between single-teeth pair and double-teeth pairs caused by the couple of the backlash and the contact ratio being greater than 1.0 is considered. The change of the dynamic engaging force and load distribution ratio for the system is analyzed by numerical results under three different states engagement. The effects of the load coefficient, meshing frequency and the comprehensive transmission error on the dynamic characteristics and nonlinear dynamics of the system are studied based on three different Poincaré mappings defined by bifurcation diagrams, top Lyapunov exponent diagrams, phase portraits and variation curve of the dynamic engaging force. Results show that the complex phenomena such as teeth disengagement, drive-side and back-side impact occur with alternating meshing of the single and double pair teeth via the change of studied parameters. The research is helpful for the optimization of the face-gear drives.

Sociodemographic and behavioral factors associated with developmental dental hard-tissue anomalies in children with primary dentition

Introduction: Developmental dental hard-tissue anomalies include anomalies of number, size, shape, and structure of the teeth. Anomalies in primary dentition are associated with anomalies in the permanent dentition. The present study identified the sociodemographic and behavioral factors associated with developmental dental hard-tissue anomalies in primary dentition. Materials and Methods: This was a cross-sectional study of 433 preschool children aged 5 years and below in Enugu East Local Government Area, Enugu, Nigeria. Data on sociodemographic profile were collected, and clinical examination was conducted on the children to record the presence of double tooth, hypodontia, hyperdontia (supernumerary), microdontia, talons cusp, hypoplasia, and Hutchinson's incisors. Results: The prevalence of developmental dental hard-tissue anomalies was 14 (3.2%). Five-year-old children (28.6%), male children (57.1%), and children belonging to high socioeconomic status (50.0%) had developmental dental hard-tissue anomalies, and there was a statistically significant association between past dental visit (P

Daimi Dentisyonda Füzyon ve Geminasyonun Dağılımı ve Sıklığı: Klinik ve Radyolojik Çalışma

Objective: Fusion and gemination are developmental dental anomalies. The aim of this study was to determine the prevalence, localization, distribution according to age and gender of double teeth (fusion and gemination) in permanent dentition. Material and Methods: The presence of a fusion and/or gemination in patients admitted to the Department of Oral and Maxillofacial Radiology for dental examination was investigated. Diagnoses of fusion and gemination were done by clinic and radiographic examination. The incidence, age, gender and upper and lower jaw localization were examined. Results: A total of 32 double teeth were detected in 30 patients after clinical and radiological examination, and the prevalence was found as 0.47%. Fusion was found in 22 patients, gemination was in 8 patients. Fusion was seen in two patients bilaterally. Fourteen (43.8%) cases were in the upper jaws and 18 (56.2%) cases were in the lower jaws. Mandibular and maxillary molars were the most commonly affected teeth (n:21, 65.6%). Conclusion: Fusion and gemination are uncommon dental anomalies. A careful clinical and radiological examination is important in the diagnosis of double teeth. Early diagnosis of these teeth is important to prevent possible complications. It will also facilitate treatment procedures such as endodontic, orthodontic or surgery to be performed by the dentist.

Uticaj parametara projektovanja na raspodelu magnetnog fluksa kod reluktantnog aktuatora

The paper presents an analysis of reluctance actuator for speckle reducing in laser based projectors, head-up displays, metrology and 3D scanning units to improve the quality of the generated images by a moving diffuser. Design concepts for one-dimensional laser speckle reducer actuator are analyzed through different designs structures. There are two resonant structures with three spring lengths, and two actuation structures with single tooth and double teeth. Reluctance actuator is evaluated in details, taking into account simple design and functional requirements of the laser speckle reducer (generated force and maximum displacement). The resonate frequency and influence of geometrical parameters are determined with the use of COMSOL Multiphysics. The forces developed through the actuating structures are obtained from the simulated material magnetic flux distribution, saturation. Evaluation suggests the next steps in the actuating structure optimization from which better performance of the device could be obtained.

An Unusual Case of Double Mandibular Parapremolars: A Cone Beam Computed Tomography Assessed Case Report

Background: Extra teeth number in the patient’s mouth is scientifically known as supernumerary teeth. Multiple supernumerary teeth are frequently seen in patients with developmental disorders. Cone-Beam Computed Tomography (CBCT) is a three-dimensional imaging tool that can provide a precise case planning. The purpose of this paper is to present a rare case of double parapremolars in on single quadrant and investigate these teeth by using Cone-Beam Computed Tomography (CBCT). Case Description: A 28-year-old, Filipino female patient came to PNU dental clinics. She was medically fit, not on medications and no allergies were detected. Intraoral examination revealed presence of two supernumerary teeth at the area between #35 and #36. The Parapremolars located in quadrant three, both are with normal shape and color. Regarding the position, the first supernumerary has erupted lingually, the second is in the arch line but slightly tilted to the lingually. As a result of the extra teeth number, moderate crowding found in the area. The patient denied any family history of similar findings. Discussion: Extraction of the first supernumerary tooth was carried out after radiographic analysis using CBCT, to facilitate proper oral hygiene, to prevent food impaction, and to eliminate its possible effects on the adjacent teeth. Extraction was performed cautiously without causing any damage to the anatomical structures. Regarding the anatomical position of the tooth, we prepared splint for teeth stabilization in case of adjacent teeth mobility. Extraction was done under local anesthesia. The patient was followed up after the extraction, no complications were reported. Conclusion: Double parapremolar teeth were found in a non-syndromic patient. CBCT precisely locate malposed supernumerary teeth and help in getting proper treatment plan without complications.

Fusion of a supernumerary tooth with primary central incisor

Fusion is a relatively rare developmental anomaly of the shape of the tooth characterized by union of two adjacent teeth. This can be seen in both deciduous and permanent dentition. Depending on the stage of development of teeth at the time of union, fusion may be either complete or incomplete. The prevalence of tooth fusion in the primary dentition is 0.5%–2.5% and 0.1% in permanent dentition. The exact etiology is not known, but it is thought that some physical forces or pressures cause the contact of developing teeth. The fused teeth can lead to various problems. Here, we discuss a case of a fusion in primary central incisor with supernumerary tooth in a 7-year-old male child.

Prevalence and Distribution of Dental Anomalies among Orthodontic Patients of Kathmandu, Nepal

Introduction: Dental anomalies are commonly seen during regular dental check-up. It occurs due to abnormal morphodifferentiation of teeth during different stages of tooth development. The purpose of this study was to find out the of dental anomalies among orthodontic patients of Kathmandu, Nepal.
 Materials & Method: A total of 601 patients (242 males and 359 females) of aged 10 to 35 years (mean age= 16.42±3.42 years) who require orthodontic treatment were selected. The patients were assessed clinically and dental panoramic radiographs were evaluated for disturbance in number and other anomalies. A chi-square test was used to determine the difference in the prevalence of dental anomalies between genders and among different classes of malocclusion.
 Result: The prevalence of dental anomalies was 15.3% that is 92 participants were exhibited at least one dental anomaly among 601 orthodontic patients. Among dental anomalies, hypodontia was the most prevalent (7.48%) followed by hyperdontia (2.99%), microdontia (2.16%), macrodontia (0.66%), transposition (0.66%), taurodontism (0.49%), double teeth (0.33%), amelogenesis imperfecta (0.33%) and dentinogenesis imperfecta (0.16%). The prevalence of oligodontia was 0.33%. There were no statistically significant difference in prevalence of anomalies in between gender and among different classes of malocclusion.
 Conclusion: Prevalence and distribution of some dental anomalies in orthodontic patients of Kathmandu differed from other studies. Maxillary lateral incisor was the most commonly missing and microdontic tooth. Orthodontists have the responsibility to observe each patient carefully for dental anomalies to correct or improvise this condition without any complications.

КОНСТРУКЦИЯ ЧЕРНОВОЙ ЧЕРВЯЧНОЙ ФРЕЗЫ ДЛЯ ОБРАБОТКИ ЗУБЧАТОГО КОЛЕСА КРУПНОГО МОДУЛЯ

For today cog-wheels are widespread parts in mechanical engineering. Hobbing cutters are to machine such parts with an efficient gear-cutting tool. For the preliminary machining of cog-wheel teeth of diesel locomotive wheel-pair m=10mm with the allowance for grinding there are used rough hobbing cutters. At that for the improvement of grinding conditions an allowance must be uneven: larger at the tooth top and less at the dedendum. Therefore special milling cutters are needed for machining cogwheels with the allowance for grinding. The existing solutions are not urgent in the field of limited and small-batch production in connection with high cost and large laboriousness in manufacturing such milling cutters. 
 The paper reports the analysis of existing designs of rough hobbing cutters and also there is investigated and developed a design and methodology of rough hobbing cutter profiling for the preliminary teeth machining of a cog-wheel m=10mm of a diesel locomotive wheel pair. The most efficient solution is development of a solid rough double tooth hobbing cutter. This solution has a number of both design and engineering advantages. 
 The modeling of a cutting process allowed offering an efficient circuit of allowance cutting. The analysis carried out has shown that such a design has a number of advantages including economic ones and it may be recommended for practical application.

Secondary dentition characteristics in an ethnic Chinese orthodontic population: A retrospective cross-sectional study.

To determine the prevalence of dental anomalies and its association with gender. This retrospective cross-sectional study was conducted using radiographs, photographs and clinical records of patients who attended the Department of Orthodontics at the National Dental Centre Singapore. Records of 2508 ethnic Chinese orthodontic patients aged 14-25years were examined for the prevalence of dental anomalies in the permanent dentition, excluding third molars. Statistical analyses were performed using SAS version 9.4 (SAS Institute Inc.). Logistic regression was used to determine the association between gender and the occurrence of various dental anomalies. Kappa coefficients were calculated to test for intra-examiner reproducibility. Statistical significance was set at P<0.05. Prevalence of dental anomalies was 5.7% hyperdontia, 11.1% hypodontia, 5.5% peg-shaped upper lateral incisors, 21.9% impacted teeth, 1.3% transposition and 0.4% double teeth. There was no significant gender difference in the occurrence of the anomalies except hyperdontia, with males having significantly higher odds of hyperdontia compared with females (odds ratio, 1.488; 95% confidence interval, 1.062-2.085; P=0.021). Occurrence of hyperdontia is greater in males than females, while no significant gender differences were noted for hypodontia, peg-shaped upper lateral incisors, impacted teeth, transposition and double teeth.

Double-arc harmonic gear profile design and meshing analysis for multi-section conjugation

Harmonic gear with double-circular-arc tooth profile has great advantage in the meshing performance. However, only the single cross section meshing or the adjustment of the flexible gear structure is considered to design the conjugate profile in the current research, which leads to the increase of the machining difficulty and is not consistent with the actual working condition of the harmonic gear transmission. Considering the cone deformation of the flexible gear shell, in the direction perpendicular to the axis, the conjugate of the flexible gear teeth is different from that of the rigid gear. Therefore, based on the envelope theory, a double circular arc tooth profile of rigid gear can be designed to achieve multi-section conjugation. Then MATLAB programming is used to simulate the flexible teeth in multi-section. At the same time, according to the assembly simulation, it is shown that the different parts of the flexible gear are engaged with the rigid gear continuously in the meshing process. The results show that on the premise of not adjusting the structure of the gear, this method is more consistent with the actual working condition of the harmonic gear compared with the method of only designing the tooth profile of the middle section conjugate. During the meshing process, there is a double conjugate phenomenon in some regions. By means of parameter adjustment, effective conjugation can be realized in a wider range. When the wave generator cam rotates 67.13°, the tooth profile of the middle section is separated from the rigid gear, and the pairs of meshing teeth are increased and the load capacity is strong. Through the finite element analysis, the dynamic characteristics of the harmonic gear device under normal working conditions are studied, and it is proved that the design parameters of the device can fully meet the strength requirements. A prototype of the double circular arc harmonic gear reducer is manufactured. And by means of assembly and dynamic performance test, the accuracy error of return is 105.2 s. The continuous conjugate meshing with multiple sections can improve the stability and bearing capacity of the transmission and is suitable for actual production and processing. The continuous conjugate meshing with multiple sections can improve the stability and bearing capacity of the transmission, and this is suitable for actual production and processing of rigid gear.

Metoda optymalizacji niezawodności przekładni stożkowej z zastosowaniem algorytmu genetycznego i elementów dyskretnych

Gear transmission is the most basic transmission component in mechanical transmission system. Many scholars have done a lot of research on gear reliability. When the variation coefficient is used to calculate and optimize the reliability of bevel gear, in order to calculate the reliability of bevel gear, it is often assumed that the gear works under constant torque, that is, the coefficient of variation (COV) is zero, but this is not the case in practice. In this paper, a gear reliability method based on discrete element simulation is proposed. The purpose of this method is to simulate the actual working conditions of gears, calculate more accurate coefficient of variation in the real world, and improve the accuracy of gear reliability design. Firstly, the real working conditions of the bevel gear transmission are simulated by discrete element method (DEM), and in the transmission system, the tangential force COV of the bevel gear is proved to be equal to the torque COV of the crusher central shaft. Secondly, the multi-objective function model of the gear transmission system is established based on the double tooth roll crusher (DTRC). The optimal volume and reliability of the bevel gear transmission are taken as the objective function, and the teeth number, module and face width factor of basic parameters of gear are optimized by genetic algorithm (GA). Finally, the accuracy of the optimization results is verified by Monte Carlo method. The main purpose of the manuscript is to analyse the effect of actual conditions (DEM simulation) on the optimization results. The results show that the COV of nominal tangential load of bevel gear is about 0.65 under actual working conditions, so in order to guarantee the same reliability, total volume need to be increased by 34.4%. This method is similar to the selection of gear safety factor. In practical production, the selection of safety factor is often based on experience. This paper provides a new method to optimize the reliability of bevel gear, combining with DEM simulation, which provides theoretical guidance for optimal design of bevel gear

Unerupted permanent incisors and associated dental anomalies.

The aim of the present study was to investigate the association between unerupted permanent incisors and dental anomalies among children and adolescents. The clinical records of patients between January 2005 and December 2014 were retrieved to identify those with unerupted permanent incisors. A retrospective audit on the presence or absence of any dental anomalies was done from all available records of the included patients. A total of 266 patients with 320 unerupted permanent incisors were identified from the 15987 patients in the study. Among the unerupted permanent incisors, 222 (69.4%) were associated with dental anomalies, which was significantly higher than those showing an absence of dental anomalies (N=98, 30.6%, P<0.001). For the unerupted maxillary central incisors, a significantly higher proportion was associated with supernumerary teeth (P<0.001). For the unerupted maxillary lateral incisors, a significantly higher proportion was associated with the ectopic eruption of permanent canines when compared with other dental anomalies (P<0.001). The presence of the ectopic eruption of permanent canine, double teeth, and hyperdontia was significantly higher among male patients with unerupted permanent incisors. Unerupted permanent incisors were associated with supernumerary teeth and ectopic eruption of permanent canines. Specifically, a higher proportion of unerupted maxillary central incisors was associated with the presence of supernumerary teeth, whereas a higher percentage of unerupted maxillary lateral incisors was associated with the ectopic eruption of permanent canines.

Gemination mandibular third molar – A rare case with use of CBCT in diagnosis and treatment planning

It is not uncommon to find dental anomalies in routine practice. Developmental dental anomalies may be seen in tooth number, size, shape, and structure. Gemination and fusion are anomalies of shape with close similarity but with different etiology. Differential diagnosis is difficult and so the term “double teeth” is often used. The incidence of double teeth is less than 1% and even more so in permanent dentition. Here, we present a unique case of gemination in mandibular third molar diagnosed effectively with the help of three-dimensional imaging and managed with the surgical technique.

Prevalence of Dental Anomalies in Deciduous Teeth and their Correlation with the Permanent Dentition: Double Teeth, Hypodontia and Hyperdontia

Prevalence of Dental Anomalies in Deciduous Teeth and their Correlation with the Permanent Dentition: Double Teeth, Hypodontia and Hyperdontia

Comparison of breakage behavior between the sieving crusher and ordinary teeth roll crushers

ABSTRACTComparison of breakage behavior of coals is conducted between the industrial sieving crusher (SC) and ordinary teeth roll crushers in different breakage flow sheets. Two types of coals, about 10 tons, are used for each comparison, and consumed energy and size distribution of products are analyzed. Due to differences in roll rotation rate and teeth distribution on roll, breakage product of SC shows the lower yield of +50 mm particles and −6 mm fines, and the higher content of −50 + 6 mm progenies. SC also indicates the advantage of saving energy if compared with that of single tooth roll crusher and double teeth roll crusher (DTRC). On the other hand, the combined flow sheet of classification and breakage is compared with the single utilization of a SC. The −50 mm particles in the feed are removed by hand sieving and +50 mm particles are broken by DTRC. As a comparison, raw coal without any pretreatment is fed to a SC. Results indicate that the decrease of coal mass to DTRC can reduce the consumed breakage time and energy, but products of SC have a higher yield of −50 + 6 mm particles. Parallel tests show the small standard deviations. In summary, experimental results of this paper are reliable, and SC shows advantages in breakage efficiency and saving energy, which is a benefit for the breakage of coarse particles.

A Case of Familial Focal Dermal Hypoplasia: A Report of 3 Cases in Consecutive Generations

Focal dermal hypoplasia (FDH), or Goltz syndrome, is a rare multisystem disorder affecting mesodermal and ectodermal structures, with the skin, eyes, teeth, and musculoskeletal systems most commonly affected. FDH results from mutations in the PORCN gene. Ninety-five percent of cases arise from novo mutations, whereas 5% are hereditary with an X-linked dominant inheritance pattern. Here, we describe an uncommon presentation of FDH in three consecutive generations. Patient 1 is an 8-month-old female born of non-consanguineous marriage who presented with diffuse alopecia of the scalp, linear hypopigmented, atrophic papules, and plaques with peripheral hyperpigmentation on the left hemiabdomen and right lateral leg along Blaschko's lines as well as syndactyly of the right second and third toes. Skin biopsy from the abdomen showed a thin epidermis with flattened rete ridges and massive dermal edema within collagen fibers and reactive capillaries. Family history was significant for similar skin lesions and bone deformities in her mother and similar skin lesions in her grandmother. Patient 2 (patient 1’s mother) is a 17-year-old female with similar linear hypopigmented, atrophic plaques with peripheral hyperpigmentation on the abdomen and right axilla, syndactyly of the right hand, patchy alopecia of the scalp, microdontia, teeth fusion, enamel defects, verrucous papillomas in the axillae and onycholysis. Patient 3 (patient 1’s grandmother), presented with similar hypopigmented, atrophic plaques on the abdomen and left arm.

Premolar Double Teeth in a Group of Irish Orthodontic Referrals

This is a report of gemination type premolar double teeth in patients who were referred for orthodontic consultation in the Eastern Health Board, Ireland. Prevalence was low (0.06%) with just three patients presenting with this dental anomaly. The premolar double teeth involving two maxillary and one mandibular premolar are illustrated.

Research on composite bending stress of asymmetric gear in consideration of friction

Compared with the conventional gear, the asymmetric gear has better root bending stress and tooth contact stress. Taking a pair of asymmetric involute spur gears as the research object, a model of asymmetric gear considering the influence of friction and shear stress on root bending stress is established. Take the upper boundary point of single tooth meshing area as example, the formula for calculating root bending stress of asymmetric gear is deduced under friction, get the rule of root bending stress without neglecting the friction force and the shear stress by MATLAB. At the same time, we design the plane finite element model of conventional gear (20°/20°) and asymmetric gear (20°/35°) by using APDL. The upper and lower boundary points of the double tooth meshing area, the upper and lower boundary points of the single tooth meshing area, the meshing node are systematically studied, get the change rules of root bending stress in the meshing process under the condition that the friction force cannot be ignored.

Improved analytical models for mesh stiffness and load sharing ratio of spur gears considering structure coupling effect

Abstract Due to the lack of efficient formulas, fillet foundation stiffness under double tooth engagement has long been a challenging problem for mesh stiffness calculation of spur gears by analytical method. Direct summation of the mesh stiffness of each meshing tooth pair overestimates the total mesh stiffness, which may lead to a large calculation error. An improved fillet foundation stiffness calculation method is proposed considering the structure coupling effect, namely, one gear body is shared by two meshing teeth simultaneously. On the basis of the proposed method, a mesh stiffness model and a load sharing model are analytically established. In the mesh stiffness model, fillet foundation stiffness correction factor is introduced to improve the calculation accuracy. Based on the minimum potential energy principle (MPEP), the load sharing ratio is determined by the proposed load sharing model. The accuracy of the proposed models is validated by comparing with finite element method (FEM).

A case of dental fusion in primary dentition from late bronze age Greece

Background/Aim: Dental fusion is a developmental abnormality that can occur in primary and/or permanent dentition. Case report: A case of double primary teeth from a Late Bronze Age cemetery in Greece is presented. Age estimation of the skeleton was based on dental eruption and development as well as on fusion of primary ossification centres of the cranial and post-cranial skeleton. Analysis of double teeth used morphology, anatomy, location, tooth count and radiological examination. Results showed a 18 month infant. Primary lower right central and lateral incisors were joined by the dentin, and they had distinct crowns and separated pulp chambers; each tooth maintained its own root canal and resembled a normal primary central and lateral incisor shape respectively. Diagnosis showed that double teeth were the result of partial fusion rather than gemination. No other dental abnormalities or lesions were recorded and subsequent teeth were not affected. Conclusions: This is the first example of double teeth in primary dentition reported in the literature from archaeological assemblages in Greece. Being one of the rare examples of dental fusion in the bioarchaeological record, this report adds further to the mapping of dental anomalies in past populations.