Point Of Tooth Contact Research Articles

Stability of maxillary anterior teeth after 2 years of retention in adolescents: a randomized controlled trial comparing two bonded and a vacuum-formed retainer.

Retention of the maxillary anterior teeth is commonly recommended to maintain the teeth in their corrected positions. Both fixed and removable retention methods are used, but the certainty of evidence is low. To evaluate post-treatment changes in irregularity of the maxillary six anterior teeth and single tooth contact point discrepancy (CPD) of three different retention methods. Three-arm parallel group single-centre randomized controlled trial. Ninety patients, 54 girls and 36 boys, were recruited to the study. The inclusion criteria were adolescent patients treated with fixed appliances at least in the maxilla. After gaining informed consent from the patient and their custodians, the patients were randomized to one of three groups: bonded retainer 13-23, bonded retainer 12-22, and removable vacuum-formed retainer (VFR) covering the maxillary teeth including the second molars. The randomization, prepared by an independent person, used blocks of 30. The primary outcomes were changes in single CPD and Little's irregularity index (LII) measured on digitalized three-dimensional study casts before and after 2-year retention. The study casts were anonymized before assessment and the changes were blinded for the assessor. Data were evaluated on an intention-to-treat basis. Thus, all randomized patients were incorporated into the final analysis. The LII and CPDs increased slightly in all three groups without any statistically significant differences between the groups. The VFR group showed a small intercanine width increase and some more changes of canine rotations than in the other groups. No harm was observed in any subjects and none of the patients needed retreatment. The trial was a single-centre study and short-term changes were evaluated. All three retention methods showed equally effective retention capacity and all the changes found in the three groups were small and considered clinically insignificant. Thus, the null hypothesis was confirmed. All three methods can be recommended. NCT04616755.

An innovative semi-analytical determination approach to numerical loaded tooth contact analysis (NLTCA) for spiral bevel and hypoid gears

Loaded tooth contact analysis (LTCA) has always been a significant contact mechanical performance optimization technique for spiral bevel and hypoid gears. To distinguish with the conventional simulated loaded tooth contact analysis (SLTCA) based on economical software package, numerical loaded tooth contact analysis (NLTCA) and its innovative semi-analytical determination approach is developed. In full consideration of tooth flank flexural behavior characteristic, double-curved shell finite element modeling is performed and then improved tooth contact analysis (TCA) is applied for data-driven determination of loaded tooth contact points. Then, in additional to the global boundary condition, the accurate local boundary conditions is also investigated. In particular, local Rayleigh-Ritz method is used to get new semi-analytically tooth compliance determination by considering computational accuracy and efficiency. Furthermore, NLTCA model is established in considerations of the accurate contact point matching, compatibility and equilibrium conditions. Finally, the main NLTCA evaluations including load distribution, loaded contact pattern, loaded contact pressure and distribution, and loaded transmission error in consideration of time-varying meshing characteristics, respectively. The provided numerical instance can verify the proposed methodology.

Nonlinear analysis of a geared rotor system supported by fluid film journal bearings

This paper presents a novel approach for modeling and analyzing a geared rotor-bearing system including nonlinear forces in the gear set and the supporting fluid film journal bearings. The rotordynamics system model has five degrees of freedom that define the transverse displacements of the shaft-gear centerlines and the relative displacement of the gear tooth contact point. The journal bearing nonlinear forces are obtained via a solution of Reynolds equation for lubricant film pressure utilizing the finite element method. Co-existing, steady-state, autonomous and non-autonomous responses are obtained in an accurate and computationally efficient manner utilizing the multiple shooting and continuation algorithms. This yields the full manifolds of the multiple bifurcation system. Chaos is identified with maximum Lyapunov exponents, frequency spectra, Poincaré attractors, etc. The results reveal a dependence of the gear set contact conditions and system nonlinear response characteristics, i.e. jump, co-existing responses, subharmonic resonances and chaos on the choice of journal bearing parameters. The results also show that Hopf bifurcations, which occur along with oil whirl in a journal bearing system, can be attenuated by increasing the gear torque.

Influence of finite element model, load-sharing and load distribution on crack propagation path in spur gear drive

The tooth fracture is one of the main failure modes in spur gear drives which is due to the bending fatigue load acting on the spur gear tooth during power transmission. The fatigue load initiates the crack at the tooth root region and propagate along the least resistance path which leads to complete tooth/rim fracture. The crack propagation path is influenced by the magnitude of the stress intensity factor (SIF) and its location along the face width at the crack front. Generally, the prediction of crack propagation studies was carried out using a three-dimensional (3D) finite element (FE) model in literature with uniform / parabolic load distribution on the contact line along the face width. An attempt has been made to explore the finite element (FE) model and the load distribution on the SIF for the given crack size. Two different 3D models namely three teeth sector model (TTSM) and Single tooth sector model (STSM) are developed with the initial crack with the size of 1 mm at the location of maximum principal stress in the fillet region. The load is moved from lowest point of tooth contact (LPTC) to highest point of tooth contact (HPTC) in the case of STSM whereas in TTSM the loads are applied simultaneously to the leading and trailing teeth whenever there is a double pair contact established as per the gear kinematics. The results are compared with the published results and found that the STSM and TTSM predict a deeper crack propagation path. The results of the FE models are compared with the single tooth fatigue load test results and found that the simulation results with actual load distribution predicting almost similar crack path as that obtained from the experiment.

Automatic data-driven operation and optimization of uncertain misalignment by considering mechanical power transmission performances of spiral bevel and hypoid gears

The misalignment has always become an increasingly important factor affecting the mechanical power transmission performances for the spiral bevel and hypoid gears. Its uncertainty problem usually exists in the actual manufacturing and transmission. This paper presents an automatic data-driven operation and optimization to determine the uncertain misalignment. Firstly, an improved tooth contact analysis (TCA) model is given to identify the tooth contact point by using a novel kinematic arrangement. This improved TCA is used to establish the data-driven functional relationships of uncertain misalignment with respect to the mechanical power transmission performance evaluations, namely the transmission error, tooth stiffness and contact pressure distribution. Then, data-driven operation of the uncertainty problem of misalignment is transformed into a deterministic optimization by introducing P-model. Finally, the optimal interval of the uncertain misalignment is determined by using an automatic data-driven operation and optimization in consideration of the different uncertainty levels. Where, the nonlinear interval number optimization is employed to perform a multi-objective optimization of the performance evaluations. The given instance can assess the validity of the proposed methodology.

A survey on gear meshing quality based on tooth contact analysis

Gears are common mechanical elements in power transmission systems. In order to avoid failure of transmission systems, it is necessary to inspect the gear meshing condition with respect to kinematic and dynamic parameters. Tooth contact analysis (TCA) method represents a useful tool for designing and analysing gear performance. It represents an important method to examine gear tooth contact points, contact ratios and kinematic errors. The primary objective of TCA is to establish the contact trail on gear tooth surfaces, and also to determine the transmission error functions generated by gear misalignments. TCA has several branches such as the loaded tooth contact analysis, unloaded tooth contact analysis and tooth contact analysis with errors. The determination of the initial contact point is necessary in order to achieve an accurate solution. The present survey allows a new insight into the improvement of the gear meshing quality, based on tooth contact analysis and transmission error.

Investigation of the effect of load distribution along the face width and load sharing between the pairs in contact on the fracture parameters of the spur gear tooth with root crack

Abstract The magnitude and location of stress intensity factor (SIF) in mode I (KI), mode II (KII), mode III (KIII) relies mainly on the geometry and location of the crack tip, variation in magnitude of load due to multiple pair contact along the active profile and the distribution of the load along the face width of a spur gear drive. Mostly, in literature the calculation of SIF in gear were carried out either by using a two dimensional (2D) Finite element model (FEM) with point load for unit width or a three dimensional (3D) FEM with uniform / parabolic load distribution along the face width without considering load sharing effect between the multiple pairs in contact. In the present study, an attempt has been made to explore the significance of the load distribution along the face width and the load sharing between the pairs when the contact moves from the highest point of tooth contact (HPTC) to the lowest point of tooth contact (LPTC) on the SIF calculation. A comparative study has been made by using a validated 3D single tooth spur gear FEM with four different load cases such as case 1: Uniform load distribution along face width without considering load sharing between the pairs, case 2: Uniform load distribution along face width by including the effect of load sharing between the pairs, case 3: Actual load distribution along the face width without considering load sharing between the pairs, case 4: Actual load distribution along the face width by including the effect of load sharing between the pairs. The stiffness based approach was used to calculate the load distribution ratio (LDR) of a contact point along the contact line and the load sharing ratio (LSR) between the pairs in contact. The detailed analysis showed that case 1, case 2 and case 3 load cases overestimate the SIFs comparing to the case 4. The first three load cases overestimate the KI by 39%, 2.5%, and 45% and KII by 390%, 36%, and 129% and KIII by 282%, 47%, and 132% respectively when compared to load case 4. The results of this study provide valuable guidelines for the crack propagation as well as life prediction calculations for spur gear drives.

A new analytical identification approach to the tooth contact points considering misalignments for spiral bevel or hypoid gears

With the increasing demands of low noise and high strength from industry applications for spiral bevel and hypoid gears, it is significant to consider the tooth contact performances, which dependents on tooth contact analysis (TCA) technology. The initial contact point, especially its initial value problem, is always of a great influence on TCA results. Furthermore, misalignments condition in the actual manufacturing is an important factor affecting tooth contact performance. A new multi-step integrated analytical identification approach is proposed to identify the initial contact point considering misalignments. First, the initial contact points on gear and pinion are identified to solve for the accurate initial values of TCA by considering the misalignments. In the consideration of misalignments, the assembly distance and the instantaneous transmission ratio are set the two constraints on solution of TCA. Then, the geometric kinematic transformation relation in tooth contact process is investigated to identify the initial contact point. Finally, a conic self-adaptive trust region algorithm is employed to get the contact points. The numerical test is given to validate the proposed methodology.

Spur Gears Static and Dynamic Meshing Simulation and Tooth Stress Calculation

Gear meshing is a complicated process, and is subjected to the simulation process in the following paper. A flexible quasi-static and dynamic finite element analysis (FEA) models were built, to calculate contact principal and shear stresses. Full sized 3D spur gears are simulated under different boundary conditions. The first model, was a quasi-static analysis, where torque was used as input; and the second model, which was transient dynamic analysis, where rotational speed was used as input. The static analysis showed high stress concentration at the tooth contact point and under the contacting surface. The dynamic analysis provided the highest stress value at the different stages of gear engagement points along the line of action. Analytical and simulation result were in agreement in general, and the use of the new simulation model was discussed.

Worm Shaving Cutter Tooth Stress and Deformation Analysis

This paper discusses a new type of worm gear shaver shaving cutter tooth contact point during deformation force, and the establishment of the shaving force model, through the instantaneous cutting force to analyze the force deformation cutter shaving cutter tooth and precision of impact. And making use of a simplified model for variable cross-section cantilever, analyzing of tooth stiffness at any cross section, find the maximum amount of deformation of worm gear shaving cutters do theoretical foundation structure optimization.

Can the intra-examiner variability of Little's Irregularity Index be improved using 3D digital models of study casts?

ObjectivesTo compare contact point displacement measurements, used to determine the Little's Irregularity Index (LII) score on study casts and digital models of study casts by an independent examiner. MethodsThe contact point displacement measurements of the six maxillary anterior labial teeth were measured on ten study casts using digital callipers and their associated digital models using Creo Parametric software on five occasions following scanning using a LAVA Chairside Oral Scanner (LCOS) three-dimensional (3D) intra oral scanner. Means, standard deviations and coefficients of variation (CoV) were determined, data analyses (Pearson's correlation coefficients (PCCs) and Intraclass correlation coefficients (ICCs)) and statistical analyses (three and two-way analyses of variance (ANOVAs) and Independent Sample Student's t-tests) were carried out (p<0.05). ResultsSignificant positive correlations for the contact point displacement measurements were evident between all measurement time points for the study casts (r>0.978; p<0.0001 and ICC>0.910; p<0.0001) and the digital models (r>0.963; p<0.0001 and ICC>0.986; p<0.0001). The CoV results showed that the contact point displacement measurement data from the digital models was more reproducible than the study casts. Of the 50 Independent Sample Student's t-tests, 21 significant increases (p<0.042) were reported in contact point displacement measurements <2.9mm for the digital models compared with the study casts. ConclusionThe use of 3D digital models can improve the reliability of LII measurements by reducing the subjectivity associated with choosing the anatomic tooth contact points and the awkwardness of measuring the contact point displacements on study casts using a cumbersome calliper technique. Clinical significanceIntra-examiner variability in the measurement of LII is still evident with digital models suggesting that either improved software specifically aimed at the orthodontic community be identified or a new method for measuring anterior incisor crowding be sought.

Function-Oriented Design and Verification of Point-Contact Tooth Surfaces of Spiral Bevel and Hypoid Gears with the Generated Gear

Establishing a general technical platform for the function-oriented design of point-contact tooth surfaces of spiral bevel and hypoid gears is an important and fundamental work. Based on the three-axis CNC bevel gear machine, a general mathematical model for the generated gear tooth surfaces of spiral bevel and hypoid gears is established. According to the principle and the method for the function-oriented design of point-contact tooth surfaces, the locus of spatial tooth contact points on the tooth surface is described on the axial plane of the gear, and then the formulae for the design with the generated gear are derived from the mathematical model. The mathematical model and the formulae can be used in the function-oriented design of point-contact tooth surfaces with the gear generated in different types on both the three-axis CNC bevel gear machine and the conventional cradle one. A theoretical method for the verification of point-contact tooth surfaces is proposed and the formulae for the verification are presented. And lastly an example is given to demonstrate the function-oriented design of point-contact tooth surfaces of the hypoid gear drive with the generated gear.

Function-Oriented Designing and Generating Technology for the Point-Contact Tooth Surfaces of Spiral Bevel and Hypoid Gears

A function-oriented designing and generating technology for the point-contact tooth surfaces of spiral bevel and hypoid gears is introduced. The tooth surface parameters are determined directly with the designing variables of the instantaneous transmission function, the locus of tooth contact points and the tooth contact ellipse dimension to design the point-contact tooth surfaces with the expected performances. The formulae for designing are provided. The designed tooth surfaces are generated with the free-form bevel gear machine, and the basic equations and formulae for the four-axis generating of the tooth surfaces are presented. The generating motions are expressed as the functions of the work gear rotary angle, which is taken as a motion parameter. The methods to determine the motion functions and the other machine setting parameters are explained through an example.

The Effect of Craniovertebral Fusion on Occlusion

The purpose of this study was to compare the effect of head posture on occlusion in subjects with craniovertebral fusion to that in normal unfused subjects. The experimental group consisted of five subjects (age range 30-76) who have all undergone previous surgical fusion of the craniovertebral region. The control group consisted of five unfused subjects matched by age, race and gender. Each subject's tooth contacts were recorded with a computerized dental instrument known as the T-scan. The tooth contacts were measured several times for each subject with the head tilted backwards (45 degrees) and forwards (30 degrees). A modification of Wilcoxon's rank sum test was used to compare the location of the tooth contacts and compare any variations between the craniovertebral-fused subjects' occlusal contact patterns and those of the normal nonfused patients. The results indicated that four of the five fused subjects had occlusal contact patterns that differed from their matched counterparts, thus suggesting that fusion of the craniovertebral region interferes with a normal mechanism that permits changes in head posture to shift tooth contact points. These results suggest that those who manage problems related to occlusion (craniofacial pain syndromes) need to consider the influence of the craniovertebral region on both occlusion and jaw position.

Does the mandible alter its functional position during activator treatment?

The study aimed at revealing possible changes, in activator-free periods, in the positions and movements of the mandible induced by the wearing of an activator. Twenty-one children being treated with three different types of activator for the correction of Angle Class II, Division 1 malocclusion were studied. The movement capacity of the mandible, the rest position, and the position of tooth contact during chewing were recorded with a Sirognathograph before treatment and repeatedly during the first year of treatment. With the exception of a slight increase in the maximal protrusion, no changes in mandibular movement capacity were found. The anteroposterior position of the mandible in the rest position was constant during the period of treatment, but the freeway space increased. No changes in the position of the point of tooth contact during chewing were found. The study produced no evidence of a treatment-induced forward positioning of the mandible in activator-free periods.

Calculation of Spur Gear Tooth Flexibility by the Complex Potential Method

Complex potentials have already been used to calculate analytically spur gear stresses. However, their application to the calculation of tooth flexibility is not so straightforward since displacements of interest are at the tooth contact point, which is a singular point for the equations being used. A method has been devised to circumvent this difficulty and to obtain the value of the displacement at each point of the line of action, and thus, the flexibility of a given pair of spur gears.

The influence of bearing misalignment on the performance of helicopter gear boxes

The misalignments in the bearings of a gear box affect the life of the bearings and the deflection of the tooth contact points of the gears and consequently the performance of the gear box as a whole. Owing to the interaction of the deflections of all component parts of a gear box such as gears, shafts, bearings, spacers etc. it is necessary to consider these in combination rather than individually. A computer program was developed for analysing typical helicopter gear boxes with cantilevered housings in which the gear shafts are supported by taper roller bearings. In this program such factors as the misalignment of the bearings, the torque transmitted, the bearing preload, the rigidity of the casing and shaft complete with the bearing spacer, the spacing between the bearings, the location of the external load and the elements of elastic deformations in the bearings are considered. The particular assembly used in this paper is based on a Wessex tail rotor gear box, although the program developed is of a general nature. The influence of the misalignments between the bearing races that may be present before the application of an external load is investigated in this paper. The effect of crowning of the rollers or race tracks, to reduce the edge loading, on the deflection components of the gear tooth contact points is also included in the investigation.

新しい咬合力測定システムについて

The purpose of this study was to develop a new method for measuring the force added to the tooth contact points in occlusion. A new system, which has a computer inside, measuring for the occlusal force recorded on pressure detecting sheets was developed. The pressure detecting sheets were originally produced by Fuji Photo Film Co. and it is called by the trade name of “Prescale”. The Prescale consists of two polyethylene sheets and numerous microcapsules containing a red dye between the sheets.When the teeth are brought into occlusion, these microcapsules rupture and discharge the dye staining one of the sheets red. The density of this color is in proportion to the degree of pressure added. Original thickness of the Prescale was 200μ. But it was too thick and too hard to study the tooth contacts in occlusion. The new Prescale was improved to be 95μ thick and became available for occlusal diagnosis and treatment. The applicable pressure is from 200kg/cm2 to 700kg/cm2. The device consists of microscope, T. V. camera, microcomputer, light-source and printer. The density of the color recorded on the improved Prescale was divided into 8 degrees, and at the same time, the area of each grade was measured.The force was given by the area of each grade multiplied by its pressure. The force of one occlusal contact point was expressed by adding the force of each grade. Ten subjects whose oral conditions were healthy were selected. Using this system, their occlusal force at their molars were measured ten times each subjects.The maximum occlusal forces were 31.4kg (1st molar), 30.9kg (2nd molar). The mean value of the occlusal forces at 1st molar was 10.85kg, and at 2nd molar was 19.83kg.

Reserarch on the Force-Fitted Gear : 7th Report, On the Change of Stresses at the Circumference of the Force-Fitted Part in the Slipping Test

The present test has been carried out for the purpose of investigating the change of stresses at the circumference of force-fitted surface caused by a load acting on tooth under running conditions. Momentary change of the stresses when a slip at the force-fitted surface between gear rim and hug occurs and when this slip is repeated three to four times, has been examined. Conclusions are that by a load that acts on tooth contact point, a partial decrease of internal pressure caused by force-fitting at the circumference of the inside diameter of gear rim occurs in the part corresponding to the meshing tooth and that the limit torque for the slip in a driving test of the force-fitting gear becomes much smaller than that in a slipping test of the force-fitting gear becomes much smaller than that in a slipping test under static condition.

13. 齒牙接触点の生理的変化(第 14 回九州歯科学会総会)

13. 齒牙接触点の生理的変化(第 14 回九州歯科学会総会)