Small Number Of Teeth Research Articles

Experimental Investigation of Flow Drilling and Flow Tapping of Thin-Walled Square and Circular Hollow Sections

One of the most important problems of automotive engineering is joining metal sheets, thin-walled tubes or profiles simply, efficiently, and economically. After conventional drilling and tapping in thin-walled materials, the strength remains low due to the small number of teeth and the connection can be easily unfastened. For increasing the strength there are several solutions such as using welded nuts, tapped rivets and welding extra nuts. Since nut welding cannot be done on the inner surfaces, these solutions are inadequate for square and circular tubes. In this study, holes of various diameters were drilled on 1.5 mm thick AISI 304 stainless steel and EN AW-6060 square and circular profiles by flow drilling at various rotational speeds, and then flow tapping was applied to the holes. The same processes were repeated with conventional drilling method to compare bushing heights and clamping strengths of the parts as well as the hardness values and capillary crack formations around the holes. According to the results obtained, the strength in flow drilling and tapping increases by 50-55% compared to the classical drilling method. The reason for this is that as the hole diameter increases, the amount of material plastered and the number of threads required for screwing increases approximately 2.5-3 times. Capillary cracks, which are observed in holes drilled with the traditional method as the hole diameter increases, are not observed with this method and thus increasing the strength of the connection.

A Computed Tomographic Study of the Molar Teeth of Babyrousa spp.

A photographic and computed tomography (CT) scanning study was carried out on 295 molar teeth of 18 adult male Babyrousa babyrussa skulls and 8 skulls of Babyrousa celebensis including seven adult males and one adult female. The occlusal morphology of the permanent maxillary and mandibular molar teeth of B. babyrussa was very similar to that of B. celebensis. Most B. babyrussa maxillary molar teeth had six roots, with small numbers of teeth having four, five or seven roots. A similar pattern was suggested in B. celebensis. Mandibular molar teeth had between four and eight roots. Tooth roots of maxillary and mandibular first and second molar teeth were largely tapering, rod-like structures. The roots of the right and left maxillary third molar teeth had a more complex arrangement; some were inserted almost vertically into the maxilla; others were orientated in a more distal direction. The mesial and distal roots were splayed in appearance. The right and left mandibular third molar tooth roots retained elements of the open 'C' shape and were generally orientated distally. The pulp chambers were arched to fit under the main cusps in all molar teeth. Pulp canals were variable in number.

Effects of Profile Shifting of a Cosine Gear

Cosine gears are a special type of gear drive, in which the tooth profile of the theoretical generating rack is described by the cosine function. According to recent research results, the cosine gear drive has a lower slip coefficient and the contact and bending stresses supported by the teeth during the load are smaller than those occurring in involute gears. The main advantage of the cosine drive pair lies in the apparent higher rigidity of the gear tooth: this can reduce flank wear and increase gear life, especially in heavy load and highspeed applications. In contrast to involute profile gears, cosine gears do not show undercut root fillet, even with small teeth number. This paper deals with cosine gear tooth profile design and the meshing of the cylindrical cosine gear pair conceived without, or with the application of the profile shifting. The mathematical model of the meshing was implemented in a Mathcad environment, showing that there exists a significant difference compared to the well-known involute gears. The simulation of the motion during the rolling of the gear pairs was realized with the Autolisp programming interface. Solid models were created and tested in the Autodesk Inventor environment.

Implant-assisted removable partial denture restoration in small number of residual teeth in mandible: A case report

Implant-assisted removable partial denture restoration in small number of residual teeth in mandible: A case report

Association of a lesser number of teeth with more risk of developing depressive symptoms among middle-aged and older adults in Japan: A 20-year population-based cohort study

ObjectivesThis 20-year prospective cohort study aimed to longitudinally explore the relationship between the number of teeth and the incidence of depressive symptoms among community-dwelling middle-aged and older adults. MethodsData were collected from the National Institute for Longevity Sciences-Longitudinal Study of Aging (NILS-LSA) database from 2002 to 2022 (3rd–9th waves). Data of adults aged ≥40 years were analyzed and those who had depressive symptoms at baseline (3rd wave), had missing data, or did not participate in follow-up, were excluded. We collected data on the number of teeth at baseline. Depressive symptoms were defined as a score of ≥16 on the Center for Epidemiologic Studies Depression Scale. The generalized estimating equation (GEE) model was used to examine the longitudinal relationships between the number of teeth at baseline and the subsequent incidence of depressive symptoms. ResultsThe final analysis included 1668 participants, with a mean (standard deviation) age of 58.8 (11.1) years and a mean follow-up time of 12.9 years. After GEE analysis with adjustment for multiple covariates, compared to participants with ≥20 teeth, participants with 10–19 teeth and < 10 teeth at baseline were associated with a higher risk of depressive symptoms. The subgroup analysis showed that the effect was stronger in men than in women. ConclusionsAmong middle-aged and older community dwellers, particularly men, a small number of teeth after the age of 40 was associated with the future incidence of depressive symptoms.

Infraocclusion – an anomaly in primary dentition

Infraocclusion is a developmental abnormality that affects a tooth lying below the plane of occlusion. It is most common in children with mixed dentition, past the age of six. It is usually noticeable in the posterior part of the dental arch, involving one of the deciduous molars. The presence of infraocclusion can be identified by clinical examination or on radiographs. The aim of the study was to present a literature review on the incidence of infraocclusion in primary molars in children in various populations and on further clinical management. The review covered publications from the last 20 years. The following online databases were searched: PubMed, Google Scholar, and Scopus. Eight scientific papers were eligible for the review. The inclusion criteria were as follows: children, without systemic diseases or syndromes, with infraocclusion. The analysed studies show that the process usually affects a small number of teeth – most children present two infraoccluded molars. The condition shows no predilection for any sex. Across different populations, the percentage of children affected by infraocclusion ranges from 2.8% to 21.8%. With age, there is a decrease in the incidence of mild infraocclusion, and an increase in the incidence of the moderate (ages 8–10) and severe (ages 11–13) forms of the condition. Our review reveals that infraocclusion most often affects the teeth in the mandible, mainly the first primary molars and, in older children, the second molars. The treatment of patients should be planned individually, considering the age of the subjects and their clinical status. Tooth extraction is performed in extremely severe cases, which are uncommon.

Prediction for surface roughness of the large-pitch internal thread based on homologous isomerism data

It is difficult to measure the surface roughness of large-pitch internal threads; predictions are used instead of measurements, whereas the common predictions are not highly accurate and narrow in the scope of use. The homologous isomerism data of vibration signal were utilized to establish a predictive model, which predicted the surface roughness of large-pitch internal threads. The corresponding homologous isomerism data were acquired by turning the large-pitch internal thread, and the data were processed using the Relief-F algorithm to obtain the weights, which are the effects of different features on surface roughness. Additionally, influenced by the structural characteristics of the workpiece with a large pitch and a small number of teeth, support vector machine (SVM) and radial basis function neural networks (RBF-NNs) were used to establish the predictive model with the homologous isomerism data of vibration signal as the input parameters. Eventually, the SVM model with higher accuracy of prediction and better ability of generalization was more appropriate for the research of this paper through comparison and analysis. It was verified that the absolute error of the SVM model was less than 0.05 μm, and the relative error was less than 4% for turning both left and right threaded surfaces, demonstrating that the predictive model could take the place of measuring the surface roughness in the mass production of large-pitch internal threads. The method proposed in this paper can also be extended to other parts for the prediction of surface roughness, especially those whose surface roughness is difficult to measure due to structural characteristics.

Cone beam computed tomography analysis of maxillary vestibular bone thickness in the esthetic region

Background/Aim. Insufficient buccal bone thickness (thickness less than 2 mm) frequently leads to fenestration and dehiscence, and their consequences are additional bone resorption. That represents an additional problem during implant placement. Cone beam computed tomography (CBCT) is becoming a priority in the diagnosis of bone thickness needed for implant placement since it has proven to be an accurate and largely reliable diagnostic tool in the image of morphology and buccal wall thickness. The aim of this study was to measure the vestibular bone thickness of the anterior maxillary region in the Serbian population and compare the difference between men and women, as well as between the left and right sides of the jaw. Methods. CBCT images of 68 patients were examined from the existing database. The length from the cementoenamel junction to the beginning of the alveolar bone was measured, followed by the thickness of the vestibular bone at various clinically relevant locations. The data were statistically processed and analyzed. Results. A total of 373 teeth of the frontal region of the upper jaw, including 128 central incisors, 124 lateral incisors, and 121 canines, were analyzed. The thickness of the buccal bone in more than 88% of cases was less than 1.5 mm at all reference points, with mean values from 0.72 to 1.02 mm. Conclusion. A very small number of maxillary teeth have a vestibular bone thickness greater than 2 mm; therefore, the criterion to provide at least 2 mm of thickness needed for implant placement is difficult to meet. That increases the use of auxiliary methods of bone augmentation during immediate implant placement.

Correlation between Skeletal Maturation and Developmental Stages of Canines and Second Molars among Iranian Population.

Statement of the Problem: Growth assessment has become an important issue in many medical and dental fields. Determining the stages of dental development and skeletal maturation are essential methods in evaluation of growth phases.Purpose: This study aimed to assess the relationship between developmental stages of maxillary and mandibular canines and second molars by Nolla’s method and skeletal maturation stages by cervical vertebral maturation. In addition, diagnostic performances of dental developmental stages were evaluated to identify growth phases.Materials and Method: In this descriptive-analytical study, 201 digital panoramic and lateral cephalometry of children referred to the Orthodontic Department of Babol Dental School (8 to 15 years) were examined. The stages of dental development were determined by Nolla’s method, and the stages of skeletal development were determined by cervical vertebral maturation stages (CVMs). Positive likelihood ratio (LHR+) was used to determine the diagnostic performances to identify growth phases. The Kendall's Tau-b correlation coefficient was used to measure the association between the CVM stages and dental calcification stages. In this study, p ≤ 0.05 was considered significant.Results: The relationship between dental development and skeletal maturation in different teeth was significant (p ≤ 0.05). Kendall's Tau-b correlation coefficient between the stages of dental development and skeletal maturity in girls ranged from 0.578 - 0.634 and in boys ranged from 0.588 - 0.655. The right second molar in maxilla presented the highest correlation coefficient. The right and left second molars in maxilla and left second molar in mandible in stage 5 had the highest LHR+ to identify the pre-pubertal growth phase.Conclusion: Despite the high correlation coefficient between dental development and skeletal maturity, the LHR+ for determining growth stages in only a small number of teeth was more than 10.

Doprinos medicinske sestre u praćenju rasta i razvoja dece sa Daunovim sindromom

Introduction: Down syndrome is a chromosomal disorder, which occurs when a third copy of the whole or part of the 21st chromosome in human hereditary material is present. Objective: To consider the activities of the nurse in monitoring the growth and development of children with Down syndrome, as well as differences in progress compared to healthy peers. Method: The study group consisted of N 21 subjects, children and adolescents, with Down syndrome. The control group consisted of the same number of healthy children who met the basic criteria of matching with the study group according to gender and age. Descriptive method and indirect observation method - documentation analysis were used. Documentation sheet was constructed. Results with discussion: The children with Down syndrome lag behind healthy children, more or less, in each observed segment. They are born in term, with an Apgar score in the range of 5-10, but with smaller body weight, body length and head volume, in which they lag behind until the end of the school period. Dentition occurs later in relation to healthy children, and they also have a smaller number of teeth. They also lag behind in the development of basic mental functions. They achieve most of the milestones, but at a later age. Conclusion: Children with Down syndrome lag behind in complete psychophysical development in relation to healthy children of the same age. The nurse has a multiple role in monitoring the growth and development and this improves the quality of the provided health services.

The impact of a "successfully treated stable periodontitis patient status" on patient-related outcome parameters during long-term supportive periodontal care.

To assess the importance of achieving a successfully treated stable periodontitis patient status (PPS) during long-term supportive periodontal care (SPC). This retrospective cohort study included 100 periodontitis patients, who continued for ≥7.5 years after active periodontal treatment with SPC and were judged as overall adherent. The effect of various predictors on three patient-related outcome parameters was assessed: (1) number of diseased teeth at last SPC, (2) number of teeth lost due to periodontitis, and (3) number of teeth lost due to any reason. One-fifth of the patients were classified as stable after active periodontal treatment. After a mean follow-up of 10.77 years, 24 patients lost 38 teeth due to periodontitis. An unstable PPS and a higher number of diseased teeth per patient at first SPC, and inadequate oral hygiene levels over time, significantly increased the risk for a higher number of diseased teeth per patient at last SPC and for more lost teeth due to periodontitis. However, high adherence to SPC appeared to mitigate the negative effect of an unstable PPS, especially regarding tooth loss due to periodontitis. Further, tooth loss due to any reason was about 3 times higher than tooth loss due to periodontitis and was affected by a larger number of predictors. Successfully treated patients with a stable PPS maintained a small number of diseased teeth and barely lost any teeth during long-term SPC compared to patients who did not achieve a stable PPS after active periodontal therapy.

Time-varying meshing stiffness calculation of an internal gear pair with small tooth number difference by considering the multi-tooth contact problem

Time-varying meshing stiffness calculation of an internal gear pair with small tooth number difference by considering the multi-tooth contact problem

Computation of meshing imprint and loading capacity of S-shaped gear pair with small number (2–6) of pinion teeth

Computation of meshing imprint and loading capacity of S-shaped gear pair with small number (2–6) of pinion teeth

The conjugate profile of the circular teeth of a spur gear. Part I: Problem statement

The paper presents the manner of finding the conjugate profile of a circular tooth of a spur gear. A synthesis of the method of enveloping applied to the cam mechanisms is presented in order to relate it the profile of the spur gears. The main argument of employing cam mechanisms is the possibility of obtaining any follower law of motion using a minimum number of parts- the cam and the follower. In the case of the mechanisms with flat face follower, the cam is obtained as an envelope of successive positions of the follower. The gear mechanisms are a particular case of cam mechanisms. The major requirement imposed to this mechanism is to transmit the rotational motion between two shafts with a constant transmission ratio. From here it results that the profile a geared wheel can be completely identified when there are known the distance between the axes, the transmission ratio and the profile of one of the wheels. The most used curve as tooth flank is the involute of a circle, due to the fact that this curve has as conjugate curve an involute, too. Although the involute profiles are common in most of the technical appliances, there are cases when they cannot satisfy the functional constraints of certain devices. As example, in the mechanical watches technology, large transmission ratios are needed and the gears with small number of teeth are used as routine. But this necessity is better fulfilled by cycloidal profiles than the involute ones. The circular profiles for the spur gear are the oldest gears due to the simple profile. The exact conjugate profile of a circular tooth obtained by enveloping by means of dedicated software is presented.

Theoretical aspects on internal cylindrical gears with small tooth number difference

Despite of some drawbacks, internal-external gear pairs with small tooth number difference have some advantages, especially when they are used in planetary or differentially gear mechanisms, as high transmission ratio and high torque at small size. In order to study the limits of these gears, regarding the minimum number of teeth of internal gear, the minimum tooth difference of the gear pair, the center distance, the addendum modification coefficients, the influence of the different geometric parameters on interference phenomena, an algorithm was designed that allowed to do that. In this paper, some numerical results based on a study on the theoretical aspects on such internal-external gear pairs will be reported.

Geometry optimization of the rolling tool for gear roll-forming process

Gear roll forming process is an innovative near-net-shape gear manufacturing technology for efficient manufacturing, high material utilization rate, high products strength, and outstanding surface quality. The profile of the Tooth of the Rolling Tool (TRT) has a direct impact on its strength/stiffness which further affects its life duration and the accuracy of the formed products. Research has been carried out to design the involute curve of TRT, however, the transaction curve of TRT which also has a significant impact on tooth strength and service durability remains to be designed and optimized in order to further improve the rolling performance. In this paper, an elliptical gear tooth root transaction curve is proposed to replace the traditional fillet curve for the enhancement of tooth bending performance. The maximum root stress and stiffness of the gear tooth with elliptical transaction curve are calculated and compared to the standard profile with different parameters (modulus, pressure angle, and coefficient of bottom clearance). The results show that proposed elliptical tooth reduces the maximum root stress and increase the strength and stiffness of TRT especially significant for rolling tools with small number of teeth and coefficient of bottom clearance.

Retrospectively analysed tooth loss in periodontally compromised patients: Long-term results 10 years after active periodontal therapy-Patient-related outcomes.

Long-term tooth retention is the ultimate goal of periodontal therapy. Aim of this study was to evaluate tooth loss (TL) during 10years of supportive periodontal therapy (SPT) in periodontal compromised patients and to identify factors influencing TL on patient level. Patients were re-examined 120±12months after active periodontal therapy. TL and risk factors [smoking, initial diagnosis, SPT adherence, interleukin-1 polymorphism, cardiovascular diseases, age at baseline, bleeding on probing (BOP), change of practitioner, insurance status, number of SPT, marital and educational status] influencing TL on patient level were assessed. One-hundred patients (52 female, mean age 65.6±11years) lost 121 of 2428 teeth (1.21 teeth/patient; 0.12 teeth/patient/y) during 10years of SPT. Forty-two of these were lost for periodontal reasons (0.42 teeth/patient; 0.04 teeth/patient/y). Significantly more teeth were lost due to other reasons (P<.001). Smoking, baseline severity of periodontitis, non-adherent SPT, positive interleukin-1 polymorphism, marital and educational status, private insurance, older age at baseline and BOP, small number of SPT were identified as patient-related risk factors for TL (P<.05). During 120±12months of SPT, only a small number of teeth was lost in periodontally compromised patients showing the positive effect of a well-established periodontal treatment concept. The remaining risk for TL should be considered using risk-adopted SPT allocation.

1607-P: Real-World Evidence of the Impact of Obesity on Residual Teeth in the Japanese Population

Previous studies have shown that diabetes and obesity increase the severity of periodontal disease—a well-known risk factor for tooth loss. However, the effect of obesity on tooth loss has not yet been fully characterized. Thus, we investigated the association between obesity and residual teeth (number and sites) using a large database of the Japanese population. We used the MinaCare database, composed of data from Japanese health insurance claims and health check-ups in 2015 to select 233,517 subjects from 706,150 based on the availability of BMI, HbA1c, teeth, and smoking information. Obesity was defined as BMI ≥25.0. The number of residual teeth at every age group was correlated with 4 BMI subsets (&amp;lt;18.5, 18.5-24.9, 25.0-30.0, &amp;gt;30.0). The unadjusted and adjusted odds ratios (ORs) for fewer than 24 residual teeth were estimated using logistic regression models. The number of residual teeth decreased with age (p for trend&amp;lt;0.001). Groups with higher BMIs had fewer residual teeth at all ages over 40s (p for trend&amp;lt;0.001). The number of residual teeth in the lowest vs. highest BMI groups in the 50s and 60s were 26.0 ± 3.2 vs. 25.2 ± 3.9 and 24.0 ± 5.0 vs. 23.3± 5.1, respectively. The negative effects of obesity on residual teeth were dominant in the right mandibular first molar. Additionally, smoking enhanced the effect of obesity. The OR for fewer than 24 residual teeth in obese people was 1.47 (95% CI: 1.43-1.52). Although diabetes (defined as HbA1c ≥6.5%) is an independent factor, the OR for fewer than 24 residual teeth in obese people after adjustment with sex, age, smoking status, and diabetes was 1.35 (95% CI: 1.31-1.40). Thus, obesity is an independent risk factor for tooth loss in the Japanese population, suggesting the importance of weight management to maintain oral health in obese people. Further studies are necessary to confirm our findings, due to limitations in our study such as data-availability from only the subject’s dental visit and the exclusion of full dentures and a small number of residual teeth. Disclosure M. Hayashi: Employee; Self; Sunstar Group. K. Morino: None. K. Harada: Employee; Self; Sunstar Group. M. Ishikawa: None. I. Miyazawa: None. A. Ishikado: Employee; Self; Sunstar Group. Employee; Spouse/Partner; Sunstar Group. H. Maegawa: Speaker’s Bureau; Self; Astellas Pharma Inc., Boehringer Ingelheim Pharmaceuticals, Inc., Daiichi Sankyo, Merck Sharp &amp; Dohme Corp., Mitsubishi Tanabe Pharma Corporation, Sanofi K.K., Takeda Pharmaceutical Company Limited.

Modal analysis and experimental research on a planetary reducer with small tooth number difference

To comprehensively analyze the modal characteristics of the planetary reducer with small tooth number difference, based on shaft–bearing–gear–shell coupling, a finite element modal analysis model was established in ABAQUS. The teeth meshing sites were constrained by binding, bearings were simulated by spring elements, and then the natural frequencies and corresponding vibration modes of the reducer were obtained by applying the Lanczos method. Further, a hammering modal experiment on the reducer was carried out utilizing LMS Test.Lab. The modal data were analyzed using a modal identification method, and the modal frequencies and damping ratios were achieved, also the experimental modal parameters were validated according to the modal assurance criterion. The research results indicate that the lowest-order natural frequency of the reducer is 148.53 Hz, which is much higher than the rotation frequency of the eccentric shaft, double gear, and output gear. Also, the two-stage gear mesh frequencies are away from the natural frequencies, therefore the reducer under normal operating conditions will not cause coupling resonance. This research provides a theoretical basis and experimental reference for the dynamic structure optimization of the planetary reducer.

Geometric design, meshing simulation, and stress analysis of pure rolling cylindrical helical gear drives

The geometric design, meshing performance, and mechanical behavior of pure rolling helical gear drives are presented. Parametric equations for contact curves on the pinion and gear are determined by coordinate transformation of the active designed pure rolling meshing line for the whole cycle of meshing. Moreover, parametric equations for the tooth surfaces of helical gears with convex-to-convex meshing type are derived according to the motion of generatrices in the transverse section along the calculated contact curves. Then, the basic design parameters are analyzed and formulas for calculation of the geometric size are given. The meshing performance and mechanical behavior, including contact patterns, loaded function of transmission errors, and variation of stresses for two pitch angles of meshing are compared with those of a reference design of micro-geometry modified involute helical gears. Besides, the influence of basic design parameters on tooth contact analysis and stress analysis is studied. The analysis of the results shows that the proposed pure rolling helical gears have the advantage of reducing the relative sliding between tooth surfaces and the possibility of designing pure rolling helical gears with a small number of teeth, though the contact strength of the surfaces is impaired. However, if the appropriate design parameters and Hermite curve parameters for the fillets are properly evaluated as proposed here, the mechanical behavior of the proposed pure rolling helical gear drive, in terms of contact patterns and variation of bending stresses can be superior to that of the micro-geometry modified involute helical gear drives.