Effect of miniscrew placement height on the distribution of biological forces produced by clear aligner for mandibular molar distalization / 口腔疾病防治

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.

Evaluation of polymerization shrinkage stress and cuspal strain in natural and typodont teeth

Abstract To evaluate the polymerization shrinkage stress and cuspal strain (CS) generated in an artificial (typodont) and in a natural tooth using different resin composites. Twenty artificial and 20 extracted natural molars were selected. Each tooth was prepared with a 4x4 mm MOD cavity. The natural and typodont teeth were divided into four experimental groups (n=10), according to the resin composite used: Filtek Z100 (3M Oral Care) and Beautifil II LS (Shofu Dental). The cavities were filled using two horizontal increments and the CS (µS) was measured by the strain gauge method. Samples were sectioned into stick-shaped specimens and the bond strength (BS) (MPa) was evaluated using a microtensile BS test. Shrinkage stress and CS were analyzed using 3D finite element analysis. No difference was found between the type of teeth for the CS as shown by the pooled averages: Natural tooth: 541.2 A; Typodont model: 591.4 A. Filtek Z100 CS values were higher than those obtained for Beautifil II LS, regardless of the type of teeth. No statistical difference was found for the BS data. Adhesive failures were more prevalent (79.9%). High shrinkage stress values were observed for Filtek Z100 resin, regardless of tooth type. The CS of typodont teeth showed a shrinkage stress effect, generated during restoration, equivalent to that of natural teeth.

Measurement of Maximum Occlusal Force Using Digital Occlusal Force Measurement Device: A Scoping Review

@#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.

Three-dimensional finite element stress analysis of surface-mounted inlays in repairing pulp-penetrating non-carious cervical lesion of maxillary first premolar / 华西口腔医学杂志

OBJECTIVES@#This study aimed to explore the stress distribution of surface-mounted inlays with two ceramic materials and different strategies for fiber post-restoration on pulp-penetrating non-carious cervical lesion in a maxillary first premolar to provide minimally invasive and reasonable restorative methods.@*METHODS@#The cone beam computed tomography data of the standard right upper first premolar were selected. Healthy control (HC) and defective control (DC) finite element models were established. Then, eight experimental models were established according to two different ceramic materials (IPS e.max CAD [LD] and Lava Ultimate [LU]) and different locations of fiber post (without fiber post [NP], fiber post in buccal root canal [B], fiber post in palatal root canal [P], fiber post in both root canals [BP]), namely, LDNP, LDB, LDP, LDBP, LUNP, LUB, LUP, and LUBP. Axial load F1 and lateral load F2 were applied. Maximum principal stress and displacement of the buccal tip were investigated using finite element analysis software. Then, the percentage change of the following indicators in each experimental group was analyzed: stress of defective tip with group DC, stress of enamel and dentine, and displacement of buccal tips with group HC. It was considered similar when the percentage change was less than 5%.@*RESULTS@#LD and LU groups could effectively reduce the stress of the defective tip, but the decreasing amplitude in the former was greater than that of the latter. For the stress of surface-mounted inlays and resin adhesive layer, LD groups were higher than LU groups, and no significant difference in stress peak was found among different experimental groups in the same material. In addition, fiber posts in double root canals could significantly reduce buccal tip displacement.@*CONCLUSIONS@#For pulp-penetrating non-carious cervical lesions, the restorative strategy of surface-mounted inlays could be applied. Compared with Lava Ultimate, IPS e.max CAD could better protect the defective tip tooth. Furthermore, fiber posts in double root canals could decrease overall deformation and increase the retention of surface-mounted inlays.

The effect of different framework's material on strain induced in distal abutment in mandibular Kennedy's class II: an in-vitro study / O efeito de diferentes materiais de estrutura na deformação induzida na distal do pilar da classe II de Kennedy mandibular: um estudo in vitro

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)

Vulnerabilidad al estrés en adolescentes de instituciones deportivas / Vulnerability to stress in teenagers in sports institutions

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.

The post transfixed in the coronal cavity increases the fracture resistance of weakened and directly restored teeth? A systematic review

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.

Research progress on conservative endodontic access cavities and its stress analysis of teeth / 口腔疾病防治

@#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.

Evaluación de zonas de esfuerzo entre implante personalizado sinterizado e implante prefabricado mediante fotoelasticidad / Evaluation of effort zones between custom implant sinterized and the prefabricated implant though photoelasticity

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.

Relationship between extrinsic factors and non-carious cervical lesions in patients of the National Hospital "Hipólito Unánue"

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

Digital flow and mechanical devices innovating photoelastic methodology: technique description / Fluxo digital e dispositivos mecânicos inovando a metodologia fotoelástica: descrição de técnica

The technique describes the development and production of photoelastic models used in dentistry, which simulate structures subject to the action of forces. It proposes to standardize, with more accuracy, the assessment of stresses generated by the stomatognathic system when dental arches are rehabilitated using implants and prosthetic devices. The technique details the insertion of digital flow and new mechanical devices, such as vacuum mixers and bubble-eliminating pan, in addition to describing the necessary precautions to avoid frequent problems in its creation, obtaining more reliable results when using the photoelastic method

técnica descreve o desenvolvimento e a produção de modelos fotoelásticos empregados em odontologia, que simulam estruturas sujeitas à ação de forças. Propõe padronizar, com mais acertividade, a avaliação das tensões geradas pelo sistema estomatognático quando os arcos dentários são reabilitados utilizando implantes e dispositivos protéticos. A técnica detalha a inserção do fluxo digital e novos dispositivos mecânicos, como misturadores a vácuo e panela eliminadora de bolha, além de descrever os cuidados necessários para evitar problemas frequentes na sua criação, obtendo resultados mais confiáveis na utilização do método fotoelástico

Stress distribution of cementless stems with unique flanges in a rectangular cross-section: thermoelastic stress imaging study / Journal of Rural Medicine

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.

Immediate stress and strain analysis of posterior pedicle screw fixation combined with different fusion cages in C5/6discectomy of simulated pig cervical vertebrae / 中国组织工程研究

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.

Comparison of biomechanical characteristics of lumbar spine after unilateral and bilateral internal fixation / 中国组织工程研究

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.

3D finite element model based on CT images of tooth: a simplified method of modeling

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

Effect of glazing application side and mechanical cycling on the biaxial flexural strength and Weibull characteristics of a Y-TZP ceramic

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.

Influence of the shape, materials and occlusal mode of the maxillary first premolars on stress in noncarious cervical lesions / 口腔疾病防治

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.

Establishment and stress analysis of buccal-occlusal-lingual inlay finite element model of mandibular first molar / 口腔疾病防治

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.

Finite element analysis of torque control efficiency of a homemade four-curved auxiliary arch for anterior teeth / 口腔疾病防治

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.

Three-dimensional finite element analysis of cantilever fixed bridge supported by implants with mandibular central incisor / 中华口腔医学杂志

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.