1. Computational model for analysing the tooth deflection of polymer gearsAljaž Ignatijev, Srečko Glodež, Janez Kramberger, 2024, original scientific article Abstract: A computational model for analysing the tooth deflection of polymer gears is presented in this paper. Because polymer gears have less stiffness compared to metal gears, the proposed approach considers a comprehensive analysis to determine the most suitable numerical model, i.e., the number of teeth that should be modelled for a given gear’s geometry and material. The developed computational model has been evaluated using a spur gear pair, where the pinion made of POM was meshed with a support gear made of steel. Material properties were assigned with linear elastic characteristics for the gear, while the pinion was characterised by hyperelastic properties using POM material. Furthermore, a nonlubricated frictional contact between the gear and pinion was considered in the numerical computations. The computational results that were obtained were compared to the empirical results according to VDI 2736 guidelines. Here, the computational approach showed more accurate results due to the hyperelastic material characteristics of POM and the simulation of multiple teeth meshing. However, VDI 2736 calculation showed comparability with the computational results, with a slightly larger deviation at higher loads. In this respect, the proposed computational approach is more suitable for analysing the tooth deflection of polymer gears under higher loads.
Keywords: polymer gears, tooth deflection, computational modelling
Published in DKUM: 19.03.2024; Views: 266; Downloads: 22
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2. Opis redkega primera: Nadštevilen zob med koreninami prvega zgornjega stalnega kočnikaLucija Strmšek, Iztok Štamfelj, 2021, other scientific articles Abstract: Purpose: To present the case of a patient with an interradicular super - numerary tooth. Case report: A 45–year–old male patient presented with sepsis of odontogenic origin. Oral clinical investigation and panoramic radiography revealed the presence of four avital teeth with inadequate root canal fillings, including both maxillary first molars. The right one had periapical radiolucencies, indicating periapical periodontitis. The left one had an unusual radiopaque structure between the roots. Condensing osteitis, odontoma, and benign cementoblastoma were included in differential diagnosis; however, conebeam computed tomography (CBCT) showed a miniature supernumerary tooth located between the buccal roots of this tooth. Surgical removal of the interradicular tooth was not indicated, because there were no associated pathological changes. Subsequently, the right first molar was extracted as the most likely source of systemic infection. The remaining three avital teeth were endodontically retreated. Conclusion: An inter–radicular supernumerary tooth is a rare occurrence; however, it is important to take into account when evaluating a radiopacity associated with a permanent maxillary molar. Its image on conventional radiographs may be unclear due to overlap with the neighbouring roots. CBCT plays a leading role in radiologic diagnosis and the establishment of anatomical relationships.
Keywords: tooth abnormalities, hyperodontia, dental radiography
Published in DKUM: 22.01.2023; Views: 504; Downloads: 58
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4. Hypodontia prevalence and pattern in women with epithelial ovarian cancerAnita Fekonja, Andrej Čretnik, Iztok Takač, 2014, original scientific article Abstract: Objective: To analyze the possible association between hypodontia and epithelial ovarian cancer (EOC), with the special interest in hypodontia pattern.
Materials and Methods: One hundred twenty women with EOC treated at the Department of Gynecologic and Breast Oncology at the University Clinical Centre and 120 gynecologically healthy women of the same average age were reviewed for the presence and pattern of hypodontia. Collected data were analyzed for frequency, tooth type, location per jaw and side, number of missing teeth per person, and family history of hypodontia.
Results: The results of the study showed prevalence of hypodontia in 19.2% of women with EOC and in 6.7% of women in the control group (P = .004). The most frequently missing teeth for women with EOC and women in the control group were maxillary second premolars and maxillary lateral incisors, respectively. Unilateral occurrence of hypodontia was more common than bilateral occurrence in women with EOC (P = .034). Of women with EOC and hypodontia, 21.7% reported a positive family history of hypodontia compared with no report in the control group of women with hypodontia (P = .150).
Conclusions: The results statistically support possible association between EOC and hypodontia. Because hypdontia can be recognized early in life, this finding could possibly help in earlier detection of EOC, resulting in better prognosis and treatment in earlier stages of the disease. Earlier EOC diagnosis and treatment could save many lives.
Keywords: hypodontia, tooth agenesis, ovarian cancer, neoplasms
Published in DKUM: 07.08.2017; Views: 1558; Downloads: 370
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5. Methods for detecting fatigue cracks in gearsAleš Belšak, Jože Flašker, 2009, published scientific conference contribution Abstract: A crack in the tooth root is the least desirable damage caused to gear units and it often causes failure of gear unit operation. For fault analyses presented in this article, gear units with real damages or faults produced on the basis of numerical simulations of real operating conditions are used; tests were carried out in a laboratory test plant. Damages in gear units can be identified by monitoring vibrations. The influences of a crack in a single-stage gear unit on produced vibrations are presented. Significant changes in tooth stiffness are caused by a fatigue crack in the tooth root whereas, in relation to other faults, changes of other dynamic parameters are more expressed. Non-stationary signals are analysed, using the family of Time Frequency Analysis tools, which include Wavelets and Joint Time Frequency Analyses.
Keywords: gear unit, vibrations, tooth root, time frequency analysis tool
Published in DKUM: 30.06.2017; Views: 1268; Downloads: 408
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6. The influence of surface coatings on the tooth tip deflection of polymer gearsBoštjan Trobentar, Srečko Glodež, Jože Flašker, Boštjan Zafošnik, 2016, original scientific article Abstract: When designing gear drives made of polymer, the tooth tip deflection is a crucial parameter in respect to the proper gear drive operation. Excessive tooth tip deflection can lead to serious disturbances of gear meshing and consequently to increased noise and wear of the teeth flanks. In such cases the tooth tip deflection can be reduced through the use of stiff surface coatings on the tooth flanks. In this paper the influence of different coating materials and thicknesses on the tooth tip deflection of polymer gears is analysed using comprehensive finite element computational analysis. The numerical results obtained are then used to define an approximate equation for the calculation of gear tooth tip deflection for the coating material used and the thickness of the surface coating layer. The results show that the tooth tip deflection decreases with large values of the coating material Young’s modulus and with the coating layer thickness.
Keywords: polymer gears, surface coatings, tooth deflection, numerical analysis
Published in DKUM: 27.03.2017; Views: 1816; Downloads: 408
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7. Artificial tooth and polymer-base bond in removable dentures: the influence of pre-treatment on technological parameters to the bond`s strengthMartin Pavlin, Rebeka Rudolf, Vjekoslav Jerolimov, 2008, original scientific article Abstract: The aim of this study was to evaluate the artificial tooth and polymerbase bond, and to measure any formatted gaps between tooth and base. Acrylic models were classified into four groups depending on the type of surface pre-treatment. A pre-treatment surface combining mechanical and chemical led to the highest bond strength between acrylic tooth and denture-base. The fore-mentioned pre-treatment had an influenced on gap formation with an average value of 68.250 micro m, which is 70 % of the gap for the untreated samples. Furthermore, the measured compressive strength was above 6000 N/mm2, yet only 3200 N/mm2 on the untreated samples.
Keywords: artificial tooth, acrylic tooth, polymer base bond, dentistry
Published in DKUM: 21.12.2015; Views: 1083; Downloads: 39
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9. Automated landmark points detection by using a mixture of approaches : the vole-teeth caseBožidar Potočnik, 2015, original scientific article Abstract: This paper deals with the automated detection of a closed curvećs dominant points. We treat a curve as a 1-D function of the arc length. The problem of detecting dominant points is translated into seeking the extrema of the corresponding 1-D function. Three approaches for automated dominant points detection are presented: (1) an approach based on fitting polynomial, (2) an approach using 1-D computer registration and (3) an innovative approach based on a multi-resolution scheme, zero-crossing and hierarchical clustering. Afterwards, two methods are introduced based on the linearly and non-linearly mixing the results from the three approaches. We then mix the results in a mean-square error sense by using the linear and non-linear fittings, respectively. We experimentally demonstrate the problem of detecting 21 landmarks on 38 vole-teeth that by mixing, the detection accuracy is improved by up to 41.47 % with respect to the results for individual approaches, as applied within the mixture.
Keywords: closed curve, dominant point, landmark, automated detection, mixing model fitting, vole-tooth
Published in DKUM: 10.07.2015; Views: 1519; Downloads: 27
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10. Determination of stresses and forces on the orthodontic system by using numerical simulation of the finite elements methodJanko Ferčec, Branislav Glišić, I. Šćepan, Evgenija Marković, Dragoslav Stamenković, Ivan Anžel, Jože Flašker, Rebeka Rudolf, 2012, original scientific article Abstract: This study was addressed to use knowledge about the orthodontic system with numerical simulation of the nite elements method. For the rst time we simulated the stresses on the orthodontic system and, in this manner, calculated the orthodontic force on the tooth. A 3D orthodontic model or orthodontic system was designed resembling moderate crowding in the dental arch with all supporting structures. CATIA V5 computer software was used to set up a model for the orthodontic system and ABAQUS was used for simulation of the stresses on the orthodontic system. Our attention was focused on the stresses on the tooth lateral incisor and its periodontal ligament. The results of the numerical simulation showed complex stresses on the tooth lateral incisor and its periodontal ligament. In this paper is presented a calculation of the orthodontic force acting on the tooth lateral incisor due to the orthodontic wire. This orthodontic force was calculated from the stresses on the bracket. The calculated orthodontic force was in the area which is considered as the optimal orthodontic force for movement of the tooth.
Keywords: okluzija, ortodontski sistem, metoda končnih elementov, ortodonske sile, zobje, malocclusion, orthodontic system, finite elements method, orthodontic force, tooth
Published in DKUM: 10.07.2015; Views: 1361; Downloads: 106
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