Pairs Of Teeth Research Articles

New Suctobelbidae (Acari, Oribatida) from Mexico

ABSTRACT Two new suctobelbid mite species (Oribatida, Suctobelbidae), Suctobelbella (Flagrosuctobelba) crassisetosa sp. nov. and Suctobelbila tetrasetosa sp. nov. are described based on adults collected from leaf litter in secondary semi-evergreen tropical forest in Mexico. Suctobelbella (F.) crassisetosa sp. nov. is similar to S. (F.) muronokiensis and S. (F.) plumosa in having thick notogastral setae and numerous lateral teeth on the rostrum, but differs from both by the number of genital setae, and the morphology and length of some notogastral setae. Suctobelbila tetrasetosa sp. nov. is similar to S-bila dentata in having one pair of notogastral tubercles, three pairs of simple lateral teeth on the rostrum and short notogastral setae, but differs from the later by the number of genital setae and the presence of long notogastral cristae.

DETERMINATION OF POWER LOSSES DUE TO PERIODIC COMPRESSION-EXPANSION OF THE OIL-AIR MIXTURE BETWEEN THE TEETH OF GEARS. PART 1. MATHEMATICAL MODEL

The simultaneous contact of two pairs of teeth between their active profiles creates a closed volume of the oil-air mixture. Reducing this volume leads to the occurrence of such a negative phenomenon as periodic compression and expansion of the oil-air mixture in volume. At high gear rotation speeds, a significant increase in the pressure of the oil-air mixture is observed and, as a result, additional vibration of the gearing occurs. The oil-air mixture outflow rate can reach the speed of sound, which causes additional noise during gear operation, and at high rotational speeds, a hydraulic shock occurs in the space closed between the pinion and gear teeth, resulting in cavitation. By representing the helical gear as a set of spur gears displaced relative to each other in the tangential direction, it simplified the mathematical model to describe thermodynamic processes in a series of isolated cavities. The following variants are considered: a) the first cavity in the direction of engagement is connected to the environment on one side and to the next second cavity on the other side; b) some i-th cavity is connected to the cavities i - 1 and i + 1, respectively; c) the edge cavity N is connected to the previous cavity N - 1 and the environment. Thus, a mathematical model of the periodic compression-expansion of the oil-air mixture in the space closed between the teeth is presented, which considers the cross-sectional areas of the axial and radial flows of the oil-air mixture, the ambient pressure of the space closed between the teeth, the velocity of the radial flow of the oil-air mixture, the instantaneous volume of the elementary cavity closed between the teeth, and the current pressure in the cavity. Keywords: power losses, oil-air mixture, periodic compression-expansion, toothed gears, mathematical model, hydrodynamic model

Features of diagnosis and treatment of patients with unilateral retention of the second premolar

Treatment of patients with dental retention is an urgent task of orthodontics.
 Aim: Determine the features of the etiology, diagnosis and treatment of patients with unilateral retention of the second premolar due to premature removal of milk molars.
 Material and methods: 19 patients aged 14 to 19 years were examined and treated with unilateral retention of the second premolars after obtaining informed consent approved by the Ethics Committee. Methods of clinical examination generally accepted in dentistry with the analysis of anamnestic, radiological, biometric data were carried out. Biometrics of plaster models with asymmetrical arc shape was carried out on scaled (1:1) photographs with the application of the main landmarks on them.
 Results: Unilateral retention of the second premolar, due to premature removal of the second milk molar, as a rule, contributes to the formation of asymmetric dental arches with a deviation of their main parameters from the individual norm. The change in diagonal dimensions is due to the displacement of the canines and the first molars towards the defect. At the same time, on the side of the impacted tooth, there is a violation of the closure of pairs of antagonist teeth and a shift in the line of the aesthetic center by an average of (2.38 0.61) mm. The stages of treatment include, firstly, the creation of conditions for the eruption of the impacted tooth with the subsequent restoration of occlusive balance.
 Conclusion: Thus, the results of the study give us the basis for choosing methods for the diagnosis and treatment of asymmetric forms of dental arches caused by the retention of second premolars, which can be used in clinical orthodontics.

СВЯЗЬ ПАРАМЕТРОВ СТАТОРА И РОТОРА В ЭЛЕКТРИЧЕСКИХ МАШИНАХ МЕХАТРОННЫХ СИСТЕМ С СОСРЕДОТОЧЕННЫМИ ОБМОТКАМИ СТАТОРА И ВОЗБУЖДЕНИЕМ НА РОТОРЕ

The issues of choosing design relationships when designing electrical machines with single-tooth windings are considered.
 Based on the property of symmetry of the m-phase system of an electric machine, relationships are derived that connect the number of pairs of rotor poles and stator teeth in single-tooth machines, taking into account the number of phases and the number of teeth in a phase group.
 The relations derived in the work, in comparison with the previously known ones, allow us to consider a larger number of working options, among which there may be more rational ones, in addition, the proposed relations are easier to use for the developer, since they determine the nomenclature of phases and the direction of winding in both the case of even and and an odd number of phases.
 Structural dependencies allow the developer to design a wide range of devices, such as engines, generators and synchronous tachometers with excitation from the rotor side, including from permanent magnets, which can be used in the development of electric machines built into the design of mechatronic modules. In this way, a base of options is created for further in-depth design using finite element modeling and other design tools.
 The proposed approach is compared with known and previously used relationships. Using the example of an electric machine with one pair of poles, it is shown that by expanding the options under consideration, more rational implementation options can be obtained.

Relating metric crown dimensions to underlying internal daily secretion rates in antimeric premolars

ObjectivesThe underlying cause for metric differences in antimeric tooth pairs is an important question for understanding dental variation. We hypothesize that localized variation in crown dimensions will be reflected in localized variation in daily enamel secretion rate. DesignCasts of pairs of human premolars from a tissue bank were 3D scanned using an optical scanning system (n = 32). Histological slides were created, and daily secretion rates (DSRs) were recorded in two areas of enamel that corresponded to scanner measurements. Antimeres were compared for both metric measurements and DSRs. Outliers for scanner measures were compared to significant differences in DSRs measurements in right and left teeth in corresponding areas. ResultsThirteen of the 16 individuals differed significantly in antimeric metric measurements, but only ten of those also differed in the underlying DSR. Fifteen of the 16 total individuals differed significantly in at least one DSR area. DiscussionWhile some individuals were outliers for metric measurements and had multiple areas of DSR differences, the majority of individuals had antimeric DSR differences regardless of metric differences. While there was no conclusive correlation between 3D metric analysis and underlying DSR differences, the most important result of this study is that DSR differences between antimeres are common.

Efficacy of two different pulpotomy agents in primary molars in a tertiary care hospital, Multan: A randomized control trial.

Objective: Multifactorial chronic dental infection and degenerative condition, the dental caries is a major health issue. Initially formocresol was the gold standard treatment for the primary teeth pulpotomy but now multiple sealing agents are used. Study Design: Prospective Interventional study. Setting: Multan Medical and Dental College/Ibn-e-Sina Hospital. Period: 15th February to 15th August 2022 and follow up 15th August to 15th November 2022. Material & Methods: After informed consent, cavities in two primary teeth of equal size after clinical and radiological examination requiring pulpotomies were selected and a total of 40 pulpotomies were done. Results: Among 15 pairs of contralateral teeth, 9 pairs were clinically as well as radiographically successful for both MTA and CH pulpotomy during the follow up appointments at 0, 1 and 3 months appointment. One pair showed failure for both MTA and CH pulpotomy. Five pairs showed success with MTA pulpotomy but failure in CH pulpotomy cases. Conclusion: It can be concluded from the study that MTA is superior and more effective than CH in primary teeth pulpotomies.

Intracanal removal and apical extrusion of filling material after retreatment using rotary or reciprocating instruments: A new approach using human cadavers.

This study compared intracanal removal of filling as well as the frequency and volume of extruded material after retreatment with either HyFlex or Reciproc instruments in mandibular teeth from cadavers. The root canals of 14 pairs of contralateral single-rooted teeth in mandibles of cadavers were instrumented with Reciproc R40 and filled using lateral compaction. The mandibles were scanned in a micro-computed tomographic (micro-CT) device before and after retreatment procedures. The contralateral teeth were assigned to two groups (n = 14) according to the retreatment protocol using either HyFlex or Reciproc instrument systems. In the HyFlex group, the HyFlex Remover instrument was worked 3 mm short of the working length (WL), followed by HyFlex CM 40.04 and 50.04 at the WL. In the Reciproc group, the R50 instrument was worked up at the coronal two thirds, followed by two more cycles until the WL was reached. Pre- and post-operative micro-CT images were analysed for extrusion and intracanal removal of filling material. After retreatment, extrusion of filling material occurred in 11 (78%) and 14 (100%) teeth from HyFlex and Reciproc groups respectively (p > .05). A similar volume of extruded material was observed after retreatment with both systems (p > .05). A significant decrease in the intracanal filling volume was verified after retreatment with both tested systems (p < .05). However, residual filling material was found in all root canals, regardless of the system. The amount of filling material removed (HyFlex = 80.8%; Reciproc = 65.9%) and the operation time was similar between systems (p > .05). A high frequency of filling material extrusion was observed after retreatment with the two systems in a cadaver model, with no significant difference between them. Both protocols obtained similar efficacy in filling material removal procedures, although none completely cleaned the canals.

Illuminant metamerism between natural teeth and zirconia restorations evaluated with a chromatic adaptation transform

Little is known about the effect of illuminant metamerism between natural teeth and zirconia restorations, despite their increasing clinical popularity. The purpose of this in vitro study was to compare illuminant metamerism between pairs of natural teeth and layered zirconia restorations and pairs of natural teeth and monolithic zirconia restorations under 10 different illuminants and analyze their metameric potential. Spectral reflectance factors were obtained from 10 pairs of extracted natural teeth and layered zirconia restorations and 28 pairs of extracted natural teeth and monolithic multilayer zirconia restorations. Each pair showed a color match that was within the visual threshold for clinical acceptability (CIEDE2000≤1.8). A special index of metamerism for the change of illuminant (Milm) was calculated from the CIEDE2000 color difference equation. Descriptive statistics and the one-sample t test were used to analyze the results for the Milm and for both groups of layered and monolithic zirconia restorations (α=.05). Layered zirconia restorations reached a mean ±standard deviation value for Milm=0.3 ±0.2 and Milm=0.5 ±0.4 for monolithic zirconia restorations (P<.01). The effect of illuminant metamerism between natural teeth and zirconia crowns was weak and generally within the clinical acceptability limit.

Gear mesh stiffness and dynamics: Influence of tooth pair structural stiffness asymmetry

There are certainly a lot of different gear mesh stiffness models in the literature, nonetheless, it is not possible to find comprehensive and in-depth gear parametric studies that sweep the gear geometrical domain. To do so, it is required to have a fast and accurate gear mesh stiffness model, which is precisely one of the main developments of this work. By taking advantage of this new model, a parametric study on the influence of tooth pair structural stiffness asymmetry is conducted. This investigation evaluates how the referred stiffness asymmetry affects the gear mesh stiffness, dynamic displacements and load distribution by performing an extensive number of simulations that cover the entire selected gear geometry spectrum — two randomly generated populations of gears, one for spur and another for helical, are tested with and without the tooth pair structural stiffness asymmetry. It is concluded that tooth pair structural stiffness asymmetry cannot be neglected since it can lead to significant modifications on the frequency content of the gear mesh stiffness signal as well as the dynamic behavior of the geared system.

Exploration of trade-offs between NVH and efficiency in bevel gear design

Minimizing NVH and friction-induced power losses is becoming paramount in the design of geared transmissions. The aim of this paper is to present an automatic methodology to explore Pareto-optimal designs of bevel gears when minimization of noise and frictional losses is essential. In the first part, a semi-empirical model to estimate frictional power losses under elasto-hydrodynamic lubrication is described. The model has been validated against experimental data available in the literature in previous works by the authors. The efficiency calculation is coupled with a state-of-the-art loaded tooth contact analysis (LTCA) tool to obtain accurate predictions of the instantaneous load shared by the mating tooth pairs during the meshing cycle. In the second part, an automatic framework based on multi-objective optimization (MOO) is presented where the tooth micro-geometry is systematically designed. The design variables are represented by few coefficients of a polynomial basis that embodies the tooth flank ease-off topography. To ensure manufacturability, the polynomial modifications are projected onto the feasible set of the machine-tool envelopes. This step is achieved through a state-of-the-art identification algorithm that the authors have developed in previous work. Frictional losses are estimated with the aforementioned model, whereas the NVH level is measured by the loaded transmission error (LTE), directly available from the simulation tool. The maximum contact pressures are limited by the material properties, thus proper nonlinear constraints are prescribed. Application to a test case involving the design of a spiral bevel gearset reveals that the methodology presented allows the designer to obtain Pareto-optimal solutions in a systematic and automatic manner.

Calculation of tooth pair stiffness by finite element analysis for the multibody simulation of flexible gear pairs with helical teeth and flank modifications

Calculation of tooth pair stiffness by finite element analysis for the multibody simulation of flexible gear pairs with helical teeth and flank modifications

Tribological characteristics evaluation of a helical gear pair based on the tribo‐dynamic model

AbstractIn this paper, a tribo‐dynamic model of a helical gear is established. For the lubrication sub‐model, a finite line thermal elastohydrodynamic lubrication model of helical gear is adopted. The lateral vibration, axial vibration of gear and torsional vibration of the gear shaft are considered in the dynamic sub‐model. Results show that the tribological parameters of helical gear under the tribo‐dynamic model deviate significantly from that of the quasi‐static model, especially in the engaging‐in region of tooth pair. The friction excitation mainly affects the vibration along the off‐line‐of‐action direction of the gears. The influence of operating conditions on the tribological and dynamic properties of a helical gear pair is significant, especially in the case related to the characteristic frequency of gears.

Crowned spur gears for constant mesh stiffness: A conceptual approach

Flank line crowning is a gear surface geometry modification that can be applied as a measure to accommodate contact imperfections along the gear teeth facewidth, that are a consequence of misalignment from either geometric defects or elastic deflection. Due to flank line crowning, the contact stiffness between the teeth of an ideal spur gear changes, thus modifying the gear mesh stiffness. Gear mesh stiffness fluctuations are one of the main driving factors behind gear performance, such as transmission error, dynamic overload and overall system vibration. Regardless of manufacturing feasibility, a set of analytical equations, derived from the classical elliptical contact theory is presented aiming to find the flank line crowning values along the path of contact that eliminate gear mesh stiffness fluctuations. This is achieved by transforming the shape of single teeth pair mesh stiffness through the contact stiffness, making it similar to the shape of the load sharing. A direct method to find the load sharing of spur gears with flank line crowning is also presented.

Dynamic characteristics of the rack and pinion lift mechanism of the combined command cabin

This paper presents a novel approach to accurately simulate the dynamic characteristics of a rack and pinion lifting mechanism while accounting for the coupling effect of meshing tooth pair stiffness and grease characteristics in real-world environments. A structure-grease coupling meshing stiffness model is established based on the deformation coordination conditions of the tooth pair meshing. The model incorporates the effect of the grease stiffness term on the time-varying meshing stiffness of the rack and pinion. By analyzing the dynamic characteristics of the combined command cabin lifting mechanism using this model, we find that the total meshing stiffness of the gear teeth is lower when the transient thermoelastic flow effect of the grease is considered. Furthermore, the total stiffness value decreases as the normal meshing force at the meshing point decreases. This research reveals that the worst lubrication conditions are typically found on the gear wheel teeth near the base circle, where the grease film temperature rise is highest, the grease film pressure is highest, and the grease film thickness is thinnest.

Calculation methods of load distribution ratio for spiral bevel gear

The tooth strength of spiral bevel gear is compromised with decreased tooth thickness along the cone distance to transfer power between intersected axes. Its stress condition and transmission performance are generally studied by approximating the meshing process as an equivalent spur gear pair. This paper developed a mathematical model to bridge the meshing characteristics of spiral bevel gear and its basic parameters with no approximate simplification in the derivation process. It is constituted with the equations for the calculation of contact ratio, determining the track of contact areas, and describe the primary geometric parameters. The meshing model indicates that the contact profile of the teeth pair is determined by its spiral angle in certain working conditions. The multi-state meshing characteristic and stress condition of spiral bevel gear are analysed by dividing the tooth surface into different meshing regions. A calculation method of load distribution ratio for spiral bevel gear is proposed while two methods are developed for comparative analysis based on the length of the contact line and the potential energy principle, respectively. They are suitable for different working conditions. The results show that the stability of the spiral bevel gear drive is sensitive to the alternating of the meshing state, which is generally believed only appear in the gear drives with straight teeth. Additionally, an excitation source from the varying length of the contact line has been unveiled exists in the spiral bevel gear drive. The two types of excitations will occur simultaneously in some cases and become apparent with the increase of the meshing stiffness. The distribution law of the load is obtained and illustrated on the tooth surface. It provides a theoretical basis for the dynamic analysis and optimal designs of spiral bevel gear.

MACHINING OF TOOTH PROFILES ON CNC MACHINES

Conventional methods of tooth machining using worm modular milling cutters, gear wheels and gear combs have common disadvantages - they require specialized equipment, are characterized by complex readjustment and relatively low productivity, which are eliminated in skiving. This paper views the possibilities for machining tooth profiles by means of skiving on CNC turning and milling machines. A new version of the kinematics of the process upon cutting inclined teeth has been implemented, where the feed is in the direction of the tooth, no correction in the angular speed is required and a skiving tool profiled according to the profile of the machined surface is used. Meshing of a tooth pair with crossed axes is reproduced. As a result of the crossing, slipping of the profiles occurs, which is the main cutting motion. The cutting speed, as a determining mode factor, can vary widely and depends on a number of design and technological parameters. Single-factor experiments have been conducted to determine the influence of the conditions of the implementation of the skiving process (the crossing angle of the tool axes and the workpiece, determining the magnitude of the cutting speed, and feed rate) on the quality parameters of the machined surfaces (tooth profile deviation, tooth direction deviation, accumulated pitch error, largest pitch difference and radial runout error) and the corresponding graphical dependencies have been constructed. A 7- 12 degree of accuracy of the machined tooth profiles has been ensured.

A double-layer iterative analytical model for mesh stiffness and load distribution of early-stage cracked gear based on the slicing method

To reveal the coupling relationship between the time-varying mesh stiffness (TVMS) and the load distribution along the tooth width direction (TWD) of gears with early-stage crack (ESC), a double-layer iterative analytical model for the TVMS and load distributions of gears is proposed considering the effects of the non-uniformly distributed load (NDL) along TWD caused by the ESC. In the proposed model, an analytical model of tooth torsional deformation and a parallel slice stiffness model of the tooth pair with ESC are separately developed based on the slicing method. On this basis, a double-layer iterative calculation method for the TVMS and load distributions is proposed, in which the coupling relationships between the slice stiffness and load distribution along TWD as well as the TVMS and load distribution between the meshing tooth pairs are respectively presented with the inner- and outer- layer iterations. Finite element (FE) models are established to verify the proposed double-layer iterative model. The effects of crack parameters and applied torque on the tooth torsional deformation, TVMS, and load distributions of the gear with ESC are finally investigated based on the proposed model. The results show that the proposed model can realize the accurate and fast decoupling calculation of the TVMS and load distributions of gears with ESC. This study can provide a basis for the establishment of the refined ESC fault diagnosis method and the rapid evaluation of the load distributions of gears with asymmetric errors or faults along TWD.

Approximate expression for the single tooth pair slice mesh stiffness

In many gear mesh stiffness models, the single tooth pair mesh stiffness is commonly approximated as having a parabolic-like symmetric shape along the path of contact with a fixed or contact ratio dependent amplitude. Even though this is a valid approximation under certain conditions, there is an asymmetry being disregarded and an amplitude being roughly approximated. In this work, a new straightforward analytical expression for the single tooth pair slice mesh stiffness is defined resorting to a parabolic approximation of the tooth pair structural stiffness that requires the definition of the asymmetry, relative amplitude and maximum value as a function of the gear parameters. In order to validate the developed work in terms of applicability and accuracy, a random sample of gears have their tooth pair structural stiffness approximation tested. The established asymmetry, relative amplitude and maximum value allow, in a fast and simple fashion, to obtain an accurate approximation. Different formulations of the single tooth pair slice mesh stiffness are compared, highlighting the importance of including the asymmetry and showing the improvements due to the new parameters.

A New Sinamiin Fish (Actinopterygii) from the Early Cretaceous of Thailand: Implications on the Evolutionary History of the Amiid Lineage

The Sinamiidae are a family of halecomorph fishes (Holostei) stratigraphically limited to the Lower Cretaceous and confined to East Asia. The first species of sinamiids were discovered in China, and then new occurrences were recorded in Thailand and Japan. The three recognized genera, Sinamia, Siamamia and Ikechaoamia, are notably characterized by an unpaired parietal. Here, we describe a new genus and species of sinamiid based on material from the Aptian Khok Kruat Formation of Ban Krok Duean Ha, Nakhon Ratchasima, Thailand. The new taxon known from preserved specimens in 3D is characterized by four pairs of extrascapular and tall cylindrical teeth with a conical enamel stalk topped by an arrowhead-shaped acrodine cap, among other characters. A phylogenetic analysis of the halecomorph fishes shows that the new taxon is the sister of the other Thai species, Siamamia naga, and that the two are grouped with two Chinese genera in a strongly supported clade, the Sinamiinae. This subfamily is here grouped with the Amiinae that contained the extant Amia. This new discovery is a clue that Southeast Asia may have been a center of diversification for this fish clade, and the phylogenetic analysis reveals that amiines may have originated somewhere in Asia during the Cretaceous before they spread throughout the northern hemisphere.

Lithocarpusdahuensis (Fagaceae), a new species from Fujian Province based on morphology and genomic data.

Lithocarpusdahuensis, a new Fagaceae species from Fujian Province, China, is described and illustrated. The new species is morphologically similar to L.konishii, but its oblanceolate leaf blade has more pairs of acute teeth on the margin, denser lateral veins, smaller cupules enclosing up to 1/4-1/3 of the nut, and its nut is only half as long as those of L.konishii. The plastome of L.dahuensis was 161,303 bp in length and displayed the typical quadripartite structure. Phylogenetic analyses distinguished L.dahuensis from L.konishii with strong support based on whole plastome and nrITS, respectively.