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Objective@#To explore the effect of different miniscrew placement heights on the distribution of biological forces produced by clear aligner combined with intramaxillary traction for mandibular molar distalization, to identify the miniscrew location that is conducive to the protection of lower anterior tooth anchorage and to provide a reference that can be used when designing clinical treatments.@*Methods@#Mimics, GeomagicStudio 2017, SolidWorks 2016, and Ansys workbench were used to establish finite element analysis models and perform mechanical analysis under the following six working conditions: working condition 1 was the control group without miniscrews; working conditions 2 to 5 had miniscrew in the buccal bone cortex between the first and second molars of the lower jaw 10 mm, 7 mm, 4 mm, and 1 mm from the top of the alveolar crest, respectively; working condition 6 had the miniscrew in the center of the buccal tongue at the anterior edge of the ascending branch of the lower jaw 5 mm above the occlusal plane.@*Results@#On the sagittal axis, miniscrew anchorage caused distal displacement of all teeth. Compared to the control group, in the miniscrew group, the displacement of the anterior molars exceeded that of the second molars. On the vertical axis, the result in the control group was similar to backward bending; the results in the miniscrew groups resembled the effect of a lever, lowering the lateral incisors and canines and raising the central incisors and first premolars. On the coronal axis, the second premolars and the first molars showed lingual displacement in the control group, and only the premolars and first molars showed lingual displacementin the miniscrew groups. The canines were the teeth that were most strongly affected by the change in miniscrew placement height.@*Conclusion@#The higher the miniscrew position is, the stronger the protective effect on the anterior anchorage. According to the miniscrew placement height, the mandibular arch should be properly narrowed, the central incisors and first premolars should be lowered, and the lateral incisors and canines should be raised when designing clinical treatments.
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Objective: This study aims to compare the strain induced in the supporting structures of unilateral mandibular removable partial denture frameworks retained by extra-coronal attachments fabricated with three different materials. Material and Methods: Three mandibular class II digitally designed and printed acrylic models with detachable abutments were used to fabricate three removable partial denture framework with extra coronal attachments from three different materials. A total of 33 models were prepared for strain testing (n=11). Models were divided into three groups according to framework's material: porcelain fused to cobalt chromium (PFM), polyetherketoneketone (PEKK) and polyetheretherketone (PEEK) group. Unilateral load of 60 N was applied in the three groups and strains were measured around the main abutment and saddle area using strain gauge. Results: Statistical analysis was performed using Shapiro-Wilk's test and by checking data distribution. Data were found to be non-parametric and were analysed using Kruskal-Wallis test followed by Dunn's post hoc test with Bonferroni correction. PFM group showed significantly the highest strain values around abutment, slot 1 (1mm distal to the socket of the last abutment) and slot 2 (1 cm away from slot 1) respectively (843.00±23.08, 91.00±6.52 and 1274.00±65.71) than the other tested groups (p<0.05) at same tested sites respectively followed by PEKK group (384.00±37.48, 81.00±2.24 and 135.00±0.00) and PEEK group (29.00±4.18, 63.00±4.47 and 52.00±5.70). Conclusions: PEEK and PEKK for partial denture framework with extra coronal attachments are adequate alternative to PFM due to their good mechanical response applying less strain on supportive structures in free-end cases. PEEK induces lower strain magnitude on the supporting structures when compared to PEKK. (AU)
Objetivo: Este estudo tem como objetivo comparar a tensão induzida nas estruturas de suporte de estruturas de próteses parciais removíveis mandibulares unilateraisretidas por encaixes extracoronários fabricados com três materiais diferentes. Material e Métodos: Três modelos mandibulares de classe II digitalmente projetados e impressos em acrílico com pilares destacáveis foram usados para fabricar três estruturas de próteses parciais removíveis com encaixes extracoronários de três materiais diferentes. Um total de 33 modelos foram preparados para testes de deformação (n=11). Os modelos foram divididos em três grupos de acordo com o material da estrutura: porcelana fundida com cobalto-cromo (PFM), poliétercetonacetona (PEKK) e polieteretercetona (PEEK). Carga unilateral de 60 N foi aplicada nos três grupos e as deformações foram medidas em torno do pilar principal e área de sela usando medido de tensão. Resultados: A análise estatística foi realizada por meio do teste de Shapiro-Wilk e com a verificação da distribuição dos dados. Os dados mostraram-se não paramétricos e foram analisados pelo teste de Kruskal-Wallis seguido pelo de Dunn com correção de Bonferroni. O grupo PFM mostrou significativamente os maiores valores de tensão ao redor do pilar, slot 1 (1mm distal do último pilar) e slot 2 (1 cm de distância do slot 1) respectivamente (843,00±23,08, 91,00±6,52 e 1274,00±65,71) do que os outros grupos testados (p<0,05) nos mesmos locais testados, respectivamente, seguido pelo grupo PEKK (384,00±37,48, 81,00±2,24 e 135,00±0,00) e grupo PEEK (29,00±4,18, 63,00±4,47 e 52,00±5,70). Conclusão: PEEK e PEKK para estrutura de prótese parcial com encaixes extracoronários são alternativas adequadas ao PFM devido à sua boa resposta mecânica aplicando menos tensão nas estruturas de suporte em casos de extremidade livre. O PEEK induz menor magnitude de deformação nas estruturas de suporte quando comparado ao PEKK (AU)
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Denture, Partial , Denture, Partial, Removable , Denture Precision AttachmentABSTRACT
@#The aim of this review was to provide an update on the current status of digital occlusal force measurement devices, as well as clinical and research applications in complete arch maximum occlusal force measurement. SCOPUS, ScienceDirect, and PubMed databases were used to conduct a literature search from January 2001 to January 2021. Identification and screening of literature were done independently according to published guidelines and selection criteria. The electronic searches turned up 394 articles, 16 of which met the inclusion and exclusion criteria and were selected for study analysis. All of these studies used T-scan and Dental Prescale digital occlusal analysis system with pressure-sensitive foils as occlusal force measurement devices. The devices showed a promising potential for identifying and comprehending maximum occlusal forces objectively. According to the current review, maximum occlusal force measured with digital occlusal force devices can be used as a prosthodontic adjunct to address issues that arise during the treatment of occlusal disorders, temporomandibular disorders, and complete dentures. It is also useful in predicting cognitive and functional decline in the elderly.
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Fundamento: Los trastornos temporomandibulares tienen origen multifactorial y el factor psicológico ocupa un papel importante en su desencadenamiento. Objetivo: Determinar la vulnerabilidad al estrés en adolescentes de instituciones deportivas. Metodología: Se realizó un estudio observacional descriptivo de corte transversal, en la EIDE provincial de Sancti Spíritus "Lino Salabarría Pupo" entre octubre de 2020 y marzo de 2021. Se seleccionaron 70 escolares de décimo, onceno y duodécimo grados mediante muestreo aleatorio simple. Se midió la variable: rango de vulnerabilidad al estrés. Se utilizaron métodos del nivel teórico, empírico y estadístico. Resultados: El 51.4 %.de los estudiantes fueron clasificados con vulnerabilidad al estrés, el 40 % no vulnerables, el 8.6 % seriamente vulnerables y ninguno extremadamente vulnerables. Conclusiones: Existe un predominio de adolescentes de instituciones deportivas con vulnerabilidad al estrés.
Background: Temporomandibular disorders have a multifactorial origin and the psychological factor plays an important role in their triggering. Objective: To determine the vulnerability to stress in teenagers from sports institutions. Methodology: A cross-sectional descriptive observational study was conducted at the Sancti Spíritus provincial EIDE "Lino Salabarría Pupo" between October 2020 and March 2021. Seventy schoolchildren from tenth, eleventh and twelfth grades were selected by simple random sampling. The variable range of vulnerability to stress was measured. Theoretical, empirical and statistical methods were used. Results: 51.4 % of the students were classified with vulnerability to stress, 40 % not vulnerable, 8.6 % seriously vulnerable and none extremely vulnerable. Conclusions: There is a predominance of teenagers from sports institutions with vulnerability to stress.
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Adolescent , Risk Factors , Adolescent Health Services , Adolescent Health , Dental Stress Analysis/psychology , Health of Institutionalized Adolescents , Health Vulnerability , Athletes/psychologyABSTRACT
Introduction: The objective of this systematic review was to answer the question: Does the intraradicular post transfixed in the dental crown increases the fracture resistance of weakened and directly restored teeth? Methods: Electronic databases (MEDLINE/PubMed, LILACS, SCOPUS, EMBASE, Scientific Electronic Library Online - SCIELO, and Central Register of Controlled Trials - CENTRAL) were searched until March 2021, without language or year restriction. Grey literature was also searched through Google scholar and OpenGrey repository. Only in vitro stud-ies were included that evaluated the influence of the use of intraradicular post trans-fixed in the crown in the buccopalatal/lingual direction in the fracture resistance of the dental crown. Relevant results were summarized and evaluated. The risk of bias was also assessed in the studies. Results: Initial screening of databases resulted in 249 studies, of which 109 were excluded for being duplicates. Of 140 eligible pa-pers, fourteen studies met the inclusion criteria and were selected for full-text read-ing. Of these, two studies were excluded for not having access to the full article. All selected articles were classified as low risk of bias. Conclusion: Based on the studies, it is possible to conclude that the use of a transfixed post in the crown increases the fracture resistance of weakened and directly restored teeth.
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Humans , Dentistry, Operative , Systematic Review , Tooth Crown , Dental Stress AnalysisABSTRACT
@#Conservative endodontic access cavity (CEC) is the first step of minimally invasive endodontics. After that operation, teeth retain the dental hard tissue, such as crest and peri-cervical dentin, to a large extent. It is of great significance to reduce the tissue excision and achieve a favorable prognosis. There are a variety of approaches and corresponding cavities in CEC. The methods to determine the medullary approach include X-ray localization, micro CT/cone beam CT localization and digital guide plate localization. Among them, X-ray film and micro CT/cone beam CT are simple and commonly used in the clinic. For more complex root canal systems, the use of a digital guide plate can establish a more accurate pulp opening pathway and reduce the unnecessary loss of tooth hard tissue. However, the positioning price of a digital guide plate is high, and it has not been widely used in the clinic. The hole types of CEC include minimally invasive medullary hole type, super conservative minimally invasive medullary hole type, "Truss" hole type and cutting end hole type. The stress analysis of CEC and traditional endodontic access (TEC) cavity are mainly based on the loading of teeth by a universal mechanical testing machine in vitro, finite element analysis and clinical observation. Most scholars’ studies have shown that minimally invasive endodontics can improve the fracture resistance of teeth, but the differential capacities of CEC and TEC remain controversial. How does on balance the purpose of pulp treatment and the maximum retention of tooth tissue? Further exploration is still needed.
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Resumen Introducción: el uso de implantes personalizados es un tratamiento utilizado con mayor frecuencia, valorando y comparando su comportamiento frente a implantes convencionales. Este estudio tuvo como objetivo analizar si las zonas de esfuerzo del implante personalizado son diferentes a las que presenta el implante prefabricado convencional mediante fotoelasticidad. Métodos: muestra n=10 dientes premolares superiores, n=10 implantes personalizados sinterizados y n=10 implantes prefabricados convencionales, sometidos a 3 presiones fijas y controladas, observados a través de un polariscopio para analizar la distribución del esfuerzo generados. Resultados: zonas de esfuerzo presentes en las diferentes muestras analizadas aplicando 3 presiones. La cantidad de esfuerzo en la presión 1 (test de Chi-cuadrado, p=0,596) es diferente entre los dos tipos de implantes al igual que con la presión 2 (test de Chi-cuadrado, p=0,407), al aplicar la presión 3 (test de Levene, p=0,899) no hay diferencia en la distribución de fuerzas entre los dos tipos de implantes. Conclusiones: se determinó que el implante prefabricado convencional distribuye y concentra mejor el esfuerzo generado bajo diferentes presiones en comparación con el implante personalizado sinterizado.
Abstract Introduction: the use of custom implants is a very common treatment; we assess and compare their behavior against that of conventional implants. This study aimed to make sure that the stress zones of the custom implant are different from those presented by the conventional prefabricated implant by photoelasticity. Methods: we subjected samples of n=10 bicuspid teeth, n=10 sintered custom implants, and n=10 conventional prefabricated implants to 3 fixed and controlled forces and observed the samples through a polariscope to analyze the distributions of effort generated. The effort zones present in the different samples were analyzed under 3 different forces. Results: the amounts of effort in the two types of implants under force 1 (chi-square test, p=0.596) are different, as is also the case under force 2 (chi-square test, p=0.407). Under force 3 (Levene test, p=0.899), there is no difference in the distributions of effort between the two types of implants. Conclusions: it was determined that the conventional prefabricated implant distributes and concentrates the effort generated under different forces better than the sintered custom implant.
Subject(s)
Dental Implants , Bicuspid , Dental Prosthesis , Dental Stress AnalysisABSTRACT
Non-carious cervical lesions cause destructive dental disorders that actively contribute to the progressive loss of dental structure and the immediate need for dental treatment, due to their multiple symptoms and factors that produce them. Aim: The purpose of the study was to determine the relationship between extrinsic factors and non-carious cervical lesions in patients of the National Hospital Hipólito Unánue. Methods: The research was of a descriptive correlative type. The sample consisted of male and female patients between 18 and 65 years old, who attended the carielogy service of this hospital. For data collection, 2 questionnaires were used to estimate the values of the extrinsic factors that allowed us to obtain the necessary information on the variables to be studied. Spearman's Rho was applied to determine the relationship between the variable's study. Results: According to Spearman's Rho of 0.622, compared to p-0.000 <0.01. Between the variables studied; extrinsic factors and noncarious cervical lesions there is a moderate and significant positive correlation. Conclusion: Through this section it was possible to demonstrate the existing relationship between extrinsic variable factors and non-carious cervical lesions, therefore it was concluded that there is a moderate and significant positive correlation in the sample comprised by the patients of the Hospital in mention
Subject(s)
Humans , Male , Female , Tooth Abrasion , Tooth Erosion , Dental Stress Analysis , Dentin , Tooth WearABSTRACT
Objective: In this study, thermoelastic stress analysis was conducted to clarify the surface stress distribution of a femur in which a BiCONTACT E stem was inserted. The contact sites between the stem and femur were examined to investigate the association with the range of stress distribution.Materials and Methods: BiCONTACT E was set up using two synthetic femurs that mimic the morphology and mechanical properties of living bone. Preoperative planning was performed using three-dimensional imaging software. The synthetic bone was placed in a sample holder. After the stem was implanted into the synthetic bone, computed tomography imaging was performed. The contact sites between the stem and the cortical part of the synthetic bone were examined using the imaging software. Subsequently, thermoelastic stress measurements were performed on the sample.Results: The results of thermoelastic stress analysis indicated a minimum change in the sum of principal stresses [Δ (σ1+σ2)] on the medial side and a maximum change in the sum of principal stresses on the lateral side. Thus, no minimum change was observed in the sum of the principal stresses at the maximum proximal part. It is reasonable to assume that the use of a cementless stem can inevitably lead to bone atrophy in the proximal part of the femur. The contact sites between the stem and femur were also investigated, and the results of the study clearly and quantitatively demonstrated the correlation of the contact sites with a range of stress distributions.Conclusion: The surface stress distribution of a femur, in which a BiCONTACT E stem was inserted, was clarified. The contact sites between the stem and femur were also investigated. Furthermore, the correlation between these results and clinical bone response was investigated in this study.
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BACKGROUND: Pedicle screw fixation is the preferred surgical treatment for clinical treatment of lumbar degenerative disease currently. The stability of pedicle screw fixation system can be evaluated from the perspective of biomechanics and finite element method is more and more popular in analyzing stress of pedicle screw fixation of vertebral body for researchers. OBJECTIVE: To analyze the stress and displacement changes of human lumbar spine in bending movement from the biomechanical point of view when unilateral and bilateral pedicle screws are fixed, providing theoretical reference for practical clinical application. METHODS: Three-dimensional models were established based on CT data of the volunteers. The volunteers signed the informed consent. This study was approved by the Hospital Ethics Committee. Abaqus software was used to simulate the actual stress conditions. Finite element analysis of lumbar spine flexion was performed during unilateral and bilateral pedicle screw fixation. The stress and displacement of lumbar vertebra, disc and pedicle screw were observed under two fixation methods. RESULTS AND CONCLUSION: (1) Under bilateral fixation, the stress on the left screw was 22.2 MPa, and the stress on the right screw was 21.14 MPa, which was far less than the stress of the screw under unilateral fixation (79.19 MPa). The stress of intervertebral disc in unilateral fixation was 87% larger than that in bilateral fixation; the stress of vertebral body in bilateral fixation was 72% smaller than that in unilateral fixation. (2) From the perspective of displacement, the displacement of screw, lumbar disc and centrum under bilateral fixation were 53%, 55% and 62% smaller than that under unilateral fixation, respectively. (3) Therefore, from the mechanical point of view, bilateral pedicle screw fixation has less stress level, which is friendlier to the human body than unilateral fixation and thus more conducive to the recovery of patients.
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BACKGROUND: Posterior decompression and pedicle screw fixation combined with interbody fusion is a method for the treatment of cervical vertebral degenerative lesions. There are few reports on the measurement of strain electricity in simulating C5/6 intervertebral disc fusion after pedicle screw removal. OBJECTIVE: To analyze stress and strain immediately after C5/6 discectomy, pedicle screw fixation combined with interbody fusion. METHODS: Eighteen fresh pig cervical specimens were randomly divided into three groups: Bone cage fusion group, PEEK fusion group, and titanium mesh fusion group (n=6). Each group simulated C5/6 discectomy and pedicle screw fixation, and then different fusion cages were used for interbody fusion. Before and after fusion, the resistance strain gauges were attached under the vertebral body at the position of pedicle screw fixation, at the edge of vertebral body at the fusion position of fusion cage, at the edge of adjacent vertebral body. The strain values of each sample were measured under the compression state by static resistance strain gauge. The stress values at each measurement point before and after fusion in posterior fixation with pedicle screws for cervical vertebrae in each group were calculated by material mechanics formula. RESULTS AND CONCLUSION: (1) Under the same load, the strain and stress of each measurement point in the titanium mesh fusion group were smaller than those in the bone cage fusion group and the PEEK fusion group, and the difference was significant (P < 0.05). (2) Under the same load, the strain and stress of each test point in the bone cage fusion group were larger than those in the PEEK fusion group, and the difference was significant (P < 0.05). (3) These results confirm that simulated C5 discectomy in vitro, posterior pedicle screw fixation and implantation of different fusion cages have different changes of stress and strain. The selection of appropriate interbody fusion cage can reduce the effect of stress concentration on adjacent segments.
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Abstract Glaze application on monolithic zirconia (Y-TZP) can be a practical approach to improve the mechanical properties of this material. Objective Our study evaluated the effect of glazing side and mechanical cycling on the biaxial flexure strength (BFS) of a Y-TZP. Methodology Eighty sintered Y-TZP discs (Ø:12 mm; thickness: 1.2 mm - ISO 6872) were produced and randomly assigned into eight groups (n=10), according to the factors "glazing side" (control - no glazing; GT - glaze on tensile side; GC - glaze on compression side; GTC - glaze on both sides) and "mechanical aging" (non-aged and aged, A - mechanical cycling: 1.2×106, 84 N, 3 Hz, under water at 37°C). Specimens were subjected to BFS test (1 mm/min; 1,000 Kgf load cell) and fractured surfaces were analyzed by stereomicroscopy and SEM. Hsueh's rigorous solutions were used to estimate the stress at failure of glazed specimens. Two-way ANOVA, Tukey's test (5%), and Weibull analysis were performed. Results The "glazing side", "mechanical aging" and the interaction of the factors were significant (p<0.05). Groups GC (1157.9±146.9 MPa), GT (1156.1±195.3 MPa), GTC (986.0±187.4 MPa) and GTC-A (1131.9±128.9 MPa) presented higher BFS than control groups (Tukey, 5%). Hsueh's rigorous solutions showed that the maximum tensile stress was presented in the bottom of zirconia layer, at the zirconia/glaze interface. Weibull characteristic strength (σo) of the GC was higher than all groups (p<0.05), except to GT, GTC-A and GTC, which were similar among them. The fractography showed initiation of failures from zirconia the tensile side regardless of the side of glaze application and fatigue. Conclusion Glazing zirconia applied on both tensile and compression sides improves the flexural strength of Y-TZP, regardless the mechanical aging.
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Zirconium , Dental Porcelain , Flexural Strength , Stress, Mechanical , Surface Properties , Yttrium , Materials Testing , CeramicsABSTRACT
Aim: This study aimed the description of a protocol to acquire a 3D finite element (FE) model of a human maxillary central incisor tooth restored with ceramic crowns with enhanced geometric detail through an easy-to-use and low-cost concept and validate it through finite element analysis (FEA). Methods: A human maxillary central incisor was digitalized using a Cone Beam Computer Tomography (CBCT) scanner. The resulted tooth CBCT DICOM files were imported into a free medical imaging software (Invesalius) for 3D surface/geometric reconstruction in stereolithographic file format (STL). The STL file was exported to a computer-aided-design (CAD) software (SolidWorks), converted into a 3D solid model and edited to simulate different materials for full crown restorations. The obtained model was exported into a FEA software to evaluate the influence of different core materials (zirconia - Zr, lithium disilicate - Ds or palladium/silver - Ps) on the mechanical behavior of the restorations under a 100 N applied to the palatal surface at 135 degrees to the long axis of the tooth, followed by a load of 25.5 N perpendicular to the incisal edge of the crown. The quantitative and qualitative analysis of maximum principal stress (ceramic veneer) and maximum principal strain (core) were obtained. Results: The Zr model presented lower stress and strain concentration in the ceramic veneer and core than Ds and Ps models. For all models, the stresses were concentrated in the external surface of the veneering ceramic and strains in the internal surface of core, both near to the loading area. Conclusion: The described procedure is a quick, inexpensive and feasible protocol to obtain a highly detailed 3D FE model, and thus could be considered for future 3D FE analysis. The results of numerical simulation confirm that stiffer core materials result in a reduced stress concentration in ceramic veneer
Subject(s)
Ceramics , Finite Element Analysis , Imaging, Three-Dimensional , Dental Stress AnalysisABSTRACT
Aim: In dental implant treatment, there is a demand for mechanically stronger implants. Despite the existence of several studies showing the clinical success of narrow diameter implants, most of them are based on pure titanium (cpTi) alloys. There is a few clinical evidences of the success rate of titanium-zirconium (TiZr) narrow diameter implants. The aim of this study was to evaluate the stress distribution in the peri-implant area of narrow diameter cpTi and TiZr implants under axial and oblique loads. Methods: Photoelastic models were produced using epoxy resin (PL2, Vishay Precision Group) from a master model. The implants (cpTi and TiZr; Straumann AG) had 3.3 mm in diameter and 12 mm in height. Loads of 100 N and 200 N were applied to the abutment at angles of 0° (axial), 10°, 20°, and 30° (oblique). A circular polariscope (Eikonal) was used under dark field white-light configuration. The isochromatic fringes were analyzed in the peri-implant region in 5 areas, using ASTM table with isochromatic fringes; cervical-mesial, cervical-distal, mid-mesial, mid-distal and apical. Results: In general, under axial and oblique loads, the stress in the TiZr implant was lower than in the cpTi implant. The load of 200 N produced the highest stress values in cpTi and TiZr implants. In both implants and loads, the fringes were located more in apical area at all angles evaluated. Conclusion: It can be concluded that for small implants, the load inclination and intensity change the pattern of stress distribution and the cpTi implant exhibited the highest peri-implant stress
Subject(s)
Stress, Mechanical , Titanium , Dental Implants , Dental Stress AnalysisABSTRACT
Objective@#To investigate effect of the contact surface between the bridge and the adjacent teeth on the stress distribution of the implant and bone tissue and the displacement of the prosthesis in the cantilever fixed implant bridge restoring missing mandibular central incisors.@*Methods@#Two-dimensional images of the mandible and dentition in healthy adults were obtained using CT data. A three-dimensional finite element model of cantilever fixed bridge supported by implants with mandibular central incisor was established by computer reconstruction technique.The contact surface between the bridge and the adjacent natural tooth was designed as "oval" and "trapezoid". The "trapezoid" has a slightly smaller median diameter on the labial side and a slightly larger medial diameter on the lingual side. Loading of 120 N was applied on the tangential margin of the middle line of the long axis of the bridge 41. The direction was set at 0°, which was parallel to the long axis of the tooth and downward. The buccal to lingual and downward angles were 30°, 45° and 60°, respectively, perpendicular to the long axis of the tooth and 90° to the lingual side.The stress distribution of the implant and surrounding bone tissue and the displacement of the prosthesis were compared between the two models.@*Results@#Under axial and buccolingual loading, the maximum equivalent stress peak in the implant and surrounding bone tissue in the cantilever with trapezoidal contact surface design and the maximum displacement of the prosthesis were lower. Moreover, the distribution of stress was more balanced and the concentration range of stress was smaller. With the loading angle increasing, this trend was more obvious. When loading angle increased to 90°, the maximum equivalent stress and the maximum displacement of the elliptic contact surface model implant and surrounding bone tissue were 196 and 101 MPa and 0.196 mm, respectively, while the trapezoidal contact surface model were 157 and 72 MPa and 0.164 mm, respectively.@*Conclusions@#The trapezoidal contact surface of the bridge and the adjacent teeth in the cantilever fixed bridge supported by implants with mandibular central incisor is beneficial to reduce the impact of the leverage on the implant and surrounding bone tissue.
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Objective @#To analyze the initial displacement of the upper central incisor and stress distribution of periodontal ligament under different torque values of upper incisors under the action of a four-curved auxiliary arch to provide a reliable basis for the safety of clinical application of four-curved auxiliary arches.@*Methods @# A three-dimensional finite element model for torque control of upper anterior teeth with a homemade quadrilateral auxiliary arch was established. Four different states were analyzed: molar ligation without extraction space (group A), microimplant ligation without extraction space (group B), molar recovery with extraction space closure (group C) (the adductive traction force was set at 115 g) and microimplant recovery with extraction space closure (group D) (the adductive traction force was set at 115 g). When four types of torque (0.5 N, 1.0 N, 1.5 N, and 2.0 N) were applied. The initial displacement of upper central incisors and the stress distribution of periodontal ligament in 16 groups (A1-A4, B1-B4, C1-C4, D1-D4) were observed.@*Results @#Under different conditions, as the strength of the four-curve auxiliary arch increases, the maxillary anterior teeth has crown labial inclination and a root lingual inclination. The displacement of the incisor tip increases with the increase in the loading force of the torque auxiliary arch, and the displacement of the incisor root apex increases as the force increases. The difference in incisor-apex displacement distance in A1-A4, B1-B4, C1-C4, D2 and D4 groups increased as the torque force increases, while the difference between the D3 group and D1 and D2 groups decreased slightly. The stress of the cervical periodontal ligament of the upper central incisor did not exceed the stress of the periodontal ligament in the following groups: A1, A2, B1, B2, B3, C1, C2, D1, and D2. The stress of the lip side of the upper central incisor did exceed the stress of the periodontal ligament in the following groups: A3, A4, B4, C3, C4, D3, and D4. In other words, when using the four-curved auxiliary arch as an implant anchorage, the force applied in the absence of extraction space should not exceed 1.5 N, and the force applied in the adduction of extraction space should not exceed 1.0 N. When using the nonimplant anchorage, the force applied in the absence of extraction space and the adduction of extraction space should not exceed 1.0 N. In addition, the range of force should not exceed the maximum stress of the periodontal ligament in the cervical region such that the effective and safe torque movement can be achieved. Under other stress conditions, the stress of the labial and cervical periodontal ligament of the upper central incisor exceeded the stress value (2.6 × 10-2MPa). The stress value of periodontal ligament was 2.6 × 10-2MPa in all groups.@*Conclusion@#A four-curved auxiliary arch has a significant effect on the upper anterior teeth, and the use of microimplants can better control root movement such that the crown of upper central incisors cannot be excessively lip inclined.
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Objective@#To observe the stress distribution according to a model of the bucco-occluso-lingual (BOL) inlay of mandibular first molar after restoration to provide a basis for the clinical treatment of cracked tooth with BOL inlay.@*Methods@#A three-dimensional finite element model of mandibular first molar was established by combining micro-CT scanning technology with Mimics, UG, Ansys and Midas-FEA software. Based on this model, a BOL inlay restoration model was established. The material parameter of inlay IPS e.max CAD was given, and a Von-mises stress distribution nephogram under the same loading condition was obtained. The results of the stress distribution in each model were compared.@*Results @#The stress of intact teeth is mainly concentrated in the central fissure of the occlusal surface at the crown. The stress of the cavity after BOL inlay restoration is mainly concentrated in the mesial and distal walls of the cavity, the axial-pulpal line angle and the gingival wall. The stress of the inlay is mainly distributed at the bottom of the inlay, axial wall and the gingival wall.@*Conclusion@#BOL inlay restoration change the stress distribution in the complete dental model, which relieves the stress concentration in the fossa and groove of the occlusal surface and can play an active role in the treatment of cracked tooth.
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Objective@#To study the stress distribution in noncarious cervical lesions (NCCLs) of maxillary first premolars under the conditions of different defect shapes, restorative materials and loading directions and to analyze the effect of different conditions on the treatment of NCCLs.@*Methods @#Three-dimensional finite element models of cervical defects of the maxillary first premolar were established by oral CBCT in a healthy adult. According to the shape of the cavity bottom, the cavity was divided into two groups: acute angle and obtuse angle. In addition to healthy dental controls, defects in each group were simulated and virtually treated with three kinds of restorative materials (glass ionomer cement, Z350 resin and bulk resin) as research objects. Four kinds of loads (normal occlusal vertical load, normal occlusal lateral load, traumatic occlusal vertical and lateral load) were applied. The lateral load of occlusion was 100 N, and the stress distribution in the prosthesis was analyzed.@*Results @#Under the condition with different cavity types that the NCCL near the pulp line was sharp, the stress in the wedge-shaped defect repair material was concentrated and significantly higher than that in the other obtuse groups. Under the condition with different repair materials, in the bottom of the acute cavity, the glass ionomer cement showed less stress than the two kinds of resin. The maximum stress in the prosthetic material in the traumatic occlusion state was significantly higher than that in the normal occlusion state, and the lateral load was more concentrated than the vertical load on the neck defect.@*Conclusion @#The stress in maxillary first premolar NCCLs is affected by the shape of the cavity and the loading direction. A simulated acute cavity morphology and traumatic force mode produced concentrated stress in the material used to repair the NCCL. Before restoration, the bottom of an acute cavity should be adjusted to an obtuse angle. After treatment, the bite of the affected tooth adjusts over time to reduce traumatic occlusion, which is beneficial for improving the service life of the filling material.
ABSTRACT
Objective: The present study assessed the fracture strength of teeth subjected to endodontic access cavity preparation on buccal surfaces, or with the aid of operating microscopy when compared to the conventional technique. Material and methods: Sixty mandibular incisors were split into four groups (n=15): conventional access cavity preparation (CCP); conservative (C); buccal surface (BS); and control. The canals were prepared and filled and the cavities were restored. A static compressive strength test was conducted until crown fracture. The force data were compiled and assessed statistically. Kolmogorov-Smirnov and ShapiroWilk tests were performed to assess normality, Levene's test to assess variance homogeneity, the one-way ANOVA to compare fracture strength in the assessed groups. Tukey's HSD test was used to determine whether the differences in the means were significant between the groups. Results: The experimental groups did not show any statistically significant differences in mean fracture strength (CCP = 585.65 N±107.64 N)(BS = 530.52 N±129.35 N) (C = 517.83 N±114.68 N). Conclusion: Therefore, the selection of surface or size of access cavity proposed did not influence the fracture strength of mandibular incisors when compared to conventional cavity preparation (AU)
Objetivo: O presente estudo avaliou a resistência à fratura compressiva de dentes submetidos as cavidades de acesso endodôntico nas faces vestibulares, ou com o auxílio de microscópio operatório quando comparados à técnica convencional. Material e métodos: Sessenta incisivos inferiores foram divididos em quarto grupos (n=15): cavidade de acesso convencional (CAC); conservadora (C); na face vestibular (FV); e controle. Os canais foram preparados e obturados, e as cavidades restauradas. O teste estático de resistência compressiva foi procedido até a fratura coronária. Os dados de força foram compilados e analisados estatisticamente. Os testes de KolmogorovSmirnov e Shapiro-Wilk foram realizados com o intuito de avaliar a normalidade. O teste de Levene para verificar a homogeneidade de variâncias. O teste de análise de variância a um critério (ANOVA) para comparar a resistência à fratura entre os grupos. O teste de Tukey HSD foi realizado para determinar se as diferenças entre as médias dos grupos apresentava significância. Resultados: Os grupos experimentais não apresentaram diferenças estatisticamente significantes com relação a média de resistência à fratura. (CAC = 585.65 N±107.64 N)(FV = 530.52 N±129.35 N) (C = 517.83 N±114.68 N). Conclusão: Portanto, a variação da face ou do tamanho da cavidade de acesso endodôntico não exerceram influência na resistência à fratura de incisivos inferiores quando comparados a tradicional cavidade de acesso endodôntico. (AU)
Subject(s)
Tooth Fractures , Dental Pulp Cavity , EndodonticsABSTRACT
Introduction: Adults with sequelae of periodontal disease tend to have bone loss, with consequent flaring of the maxillary incisors. Objective: The influence of bone loss and the inclination of the maxillary incisor in the distribution of stresses due to simulated bite forces was studied. Material and method: Models in epoxy resin were made in three conditions (without bone loss and with bone loss of 5mm and 8mm). Increases in the labial inclination of the maxillary incisor of 10° and 20° were obtained with a beveled metallic block. Loads of 100N were applied five times in each condition using a universal test machine. The models were observed and filmed with a circular polariscope. Orders of isochromatic fringes (stresses) on the labial, lingual, and apex surfaces were recorded. The agreement of the data was evaluated using the weighted kappa test, and the results were 0.89 and 0.82 for intra- and inter-examiners, respectively. Result: The results of the Kruskal-Wallis and SNK tests indicated higher stresses (2.0) with increased labial inclination in the labial surface; higher stresses (2.67) with increased bone loss; higher greater stresses with the association of bone loss and labial-inclination (3.6); and the highest stresses tended to concentrate on the labial surfaces, except in cases of normal inclination and without bone loss (0.45). Conclusion: It was concluded that increases in both the labial inclination of the maxillary incisors and bone loss increase periradicular stresses, and the combination of these factors further increases the stresses due to bite forces, with the highest concentration on the labial side.
Introdução: Adultos com sequelas de doenças periodontais tendem a apresentar perda óssea, com consequente vestibularização dos incisivos superiores. Objetivo: A influência da perda óssea e da inclinação do incisivo superior na distribuição de tensões devido a forças mastigatórias simuladas foram avaliadas nesse estudo. Material e método: Modelos em resina epóxi foram confeccionados em três condições (sem perda óssea e com perda óssea de 5mm e 8mm). Aumentos na inclinação vestibular do incisivo superior de 10° e 20° foram obtidos com um bloco metálico chanfrado. Cargas de 100N foram aplicadas cinco vezes em cada condição usando uma máquina de ensaio universal. Os modelos foram observados e filmados com um polariscópio circular. Ordens de franjas isocromáticas (tensões) nas faces vestibular, lingual e apical foram registradas. A concordância dos dados foi avaliada pelo teste kappa ponderado e os resultados foram 0,89 e 0,82 para intra e interexaminadores, respectivamente. Resultado: Os resultados dos testes de Kruskal-Wallis e SNK indicaram maiores tensões (2,0) com aumento da inclinação vestibular na face vestibular; maiores tensões (2,67) com aumento da perda óssea; maior tensão com a associação de perda óssea e inclinação vestibular (3,6); e as maiores tensões tenderam a concentrar-se na face vestibular, exceto em casos de inclinação normal e sem perda óssea (0,45). Conclusão: Concluiu-se que aumentos tanto da inclinação vestibular dos incisivos superiores quanto da perda óssea aumentam as tensões perirradiculares, e a combinação desses fatores aumenta ainda mais as tensões devido às forças mastigatórias, com a maior concentração na face vestibular.