Using the Response Surface Methodology for Periodontitis Diagnosis / Uso da Metodologia de Superfície de Resposta para Diagnóstico de Periodontite

Response surface methodology (RSM) consists of mathematical and statistical techniques to develop models which help to understand the influence of various factors on a dependent variable of interest. The feasibility of RSM use to detect cases of periodontitis and its correlated factors has not yet been evaluated. This study developed mathematical models for periodontitis diagnosis independent of periodontal probing using the RSM. Demographic, socioeconomic, behavioral, systemic, local factors, and periodontitis were assessed in 176 volunteers. Periodontitis case was defined according to three different definitions: 1) ≥3 sites with clinical attachment level (CAL) ≥4 mm; 2) at least one site with CAL ≥4 mm and bleeding on probing; 3) ≥2 proximal sites with CAL ≥3 mm and ≥2 proximal sites with probing depth (PD) ≥4 mm (not on the same tooth) OR 1 site with PD ≥5 mm. 4th-degree polynomial equations showed high coefficients of determination (R²= 1) and were used to represent the mathematical models of periodontitis cases. According to definition 1, the diagnosis of periodontitis was accurate by including in the model: age, sex, education level, plaque index (PI), number of missing teeth, previous hygiene instructions, and body mass index (BMI). According to definition 2, the diagnosis of periodontitis was accurate by including in the model: age, sex, education level, income, PI, previous oral hygiene instructions, frequency of brushing and type of toothbrush, and use of mouthwash in the model. For an accurate diagnosis of periodontitis according to definition 3, the model included: age, education level, IP, number of missing teeth, previous oral hygiene instruction, BMI, and diabetes. The multifactorial mathematical models were able to diagnosis periodontitis according to different periodontitis case definitions using only variables of easy evaluation and non-invasive. (AU)

A metodologia de superfície de resposta (MSR) consiste em técnicas matemáticas e estatísticas para desenvolver modelos que ajudam a entender a influência de vários fatores em uma variável dependente de interesse. A viabilidade do uso da MSR para detectar casos de periodontite e seus fatores correlacionados ainda não foi avaliada. Este estudo desenvolveu modelos matemáticos para diagnóstico de periodontite independente da sondagem periodontal usando a MSR. Fatores demográficos, socioeconômicos, comportamentais, sistêmicos, locais e periodontite foram avaliados em 176 voluntários. O caso de periodontite foi definido de acordo com três definições diferentes: 1) ≥3 locais com nível de inserção clínica (NIC) ≥4 mm; 2) Um local com NIC ≥4 mm e sangramento à sondagem; 3) ≥2 locais proximais com NIC ≥3 mm e ≥2 locais proximais com profundidade de sondagem (PS) ≥4 mm (não no mesmo dente) OU 1 local com PS ≥5 mm. Equações polinomiais de 4º grau apresentaram altos coeficientes de determinação (R²= 1) e foram utilizadas para representar os modelos matemáticos dos casos de periodontite. De acordo com a definição 1, o diagnóstico de periodontite foi preciso ao incluir no modelo: idade, sexo, escolaridade, índice de placa (IP), número de dentes perdidos, instruções de higiene anteriores e índice de massa corporal (IMC). De acordo com a definição 2, o diagnóstico de periodontite foi preciso ao incluir no modelo: idade, sexo, escolaridade, renda, IP, instruções prévias de higiene bucal, frequência de escovação e tipo de escova dental e uso de enxaguatório bucal no modelo. Para um diagnóstico preciso de periodontite de acordo com a definição 3, o modelo incluiu: idade, escolaridade, IP, número de dentes perdidos, instrução prévia de higiene oral, IMC e diabetes. Os modelos matemáticos multifatoriais foram capazes de diagnosticar a periodontite de acordo com diferentes definições de casos de periodontite usando apenas variáveis de fácil avaliação e não invasivas. (AU)

Characterization of residual stresses in veneering ceramics for prostheses with zirconia framework

Abstract The aim of this study was to evaluate the influence of the coefficient of thermal expansion (CTE or α) and glass transition temperature (Tg) of three veneering ceramics used with zirconia frameworks of full-arch fixed prostheses. The generation of residual stresses and linear contraction after the simulation of the cooling process and mechanical loading were measured. The analysis was based on the finite element method in three-dimensional model of a maxillary full-arch fixed prosthesis with zirconia framework (e.max ZirCAD) and veneer by felsdpathic ceramics (GEC - IPS e.max Ceram, GVM - Vita VM9 and GLC - Lava Ceram). The linear contraction simulation was performed by cooling the structures from the Tg of each veneer ceramic at room temperature (25°C). A loading of 100 N on the occlusal region of the first molar was performed. The magnitude of the maximum principal stress (smax) and linear contraction were evaluated. The levels of CTE mismatch between veneering ceramics and framework showed no relevant influence on smax and linear contraction. The Tg values of the veneer ceramic showed to be directly proportional to amount of smax and linear contraction. The GEC presented the highest values of smax and linear contraction. The GVM and GLC did not present significant differences between them. In conclusion, GVM was similar to GLC, while GEC presented differences in relation to other veneer ceramics in terms of residual stress and linear contraction.

Resumo O objetivo neste estudo foi avaliar a influência do coeficiente de expansão térmica (CET) e da temperatura de transição vítrea (Tg) de três cerâmicas feldspáticas utilizadas para o recobrimento da infraestrutura de zircônia em prótese total fixa. A tensão residual e contração linear após a simulação do processo de esfriamento e carga oclusal foram mensuradas. A análise foi efetuada pelo método por elementos finitos num modelo tridimensional de uma prótese total maxilar com infraestrutura em zircônia (e.max ZirCAD) recoberta por três cerâmicas felsdpáticas (GEC - IPS e.max Ceram, GVM - Vita VM9 ou GLC - Lava Ceram). A simulação da contração linear foi realizada pelo esfriamento da estrutura a partir da Tg de cada cerâmica de cobertura até a temperatura ambiente (25 °C). Em seguida, um carregamento de 100 N foi realizado na região oclusal de primeiro molar. A magnitude da tensão máxima principal (smax) e contração linear foram avaliadas. Os níveis de diferença de CTE entre cerâmica de cobertura e infraestrutura não apresentaram influência significante na smax e na contração linear. Os valores da Tg da cerâmica de cobertura foram diretamente proporcionais à quantidade de smax e contração linear. O grupo GEC apresentou os maiores valores de smax e contração linear, enquanto os grupos GVM e GLC com menores valores não apresentaram diferenças significantes entre si. Em conclusão, o grupo GVM foi similar ao GLC, enquanto o grupo GEC apresentou diferenças em relação a outras cerâmicas de cobertura quanto à tensão residual e contração linear.

Three-dimensional geometric model of the middle segment of the thoracic spine based on graphical images for finite element analysis

Abstract Introduction: Biomedical studies involve complex anatomical structures, which require specific methodology to generate their geometric models. The middle segment of the thoracic spine (T5-T10) is the site of the highest incidence of vertebral deformity in adolescents. Traditionally, its geometries are derived from computed tomography or magnetic resonance imaging data. However, this approach may restrict certain studies. The study aimed to generate two 3D geometric model of the T5-T10 thoracic spine segment, obtained from graphical images, and to create mesh for finite element studies. Methods A 3D geometric model of T5-T10 was generated using two anatomical images of T6 vertebra (side and top). The geometric model was created in Autodesk® Maya® 3D 2013, and the mesh process in HiperMesh and MeshMixer (v11.0.544 Autodesk). Results The T5-T10 thoracic segment model is presented with its passive components, bones, intervertebral discs and flavum, intertransverse and supraspinous ligaments, in different views, as well as the volumetric mesh. Conclusion The 3D geometric model generated from graphical images is suitable for application in non-patient-specific finite element model studies or, with restrictions, in the use of computed tomography or magnetic resonance imaging. This model may be useful for biomechanical studies related to the middle thoracic spine, the most vulnerable site for vertebral deformations.

Total deformation of multiple implant-supported prostheses through three-dimensional finite element analysis / Deformación total de prótesis múltiple implanto-soportadas a través de un análisis tridimensional por elementos finitos

The purpose of this study was to evaluate through finite element analysis (FEA) the total deformation or displacement as a whole system of multiple implant-supported prostheses in the maxillary anterior region with different implant's length, connection, location and restoration material. An edentulous anterior region of a hemi-maxilla model was used in finite element analysis. The simulations were divided in two groups according to treatment plan: 1) two implants were placed in the upper central incisors, simulating an implant-supported fixed prosthesis (acrylic resin and metal-ceramic) of four elements with cantilever of both upper lateral incisors; 2) two implants placed in the upper lateral incisors, simulating a conventional fixed prosthesis of four elements with both upper central incisors as pontic. Models with cantilever prosthesis in acrylic resin showed the highest values of total deformation, which were 17 times higher than those of metal-ceramic in the distal face of the lateral incisors, regardless of the type of implant connection. In conventional prostheses in acrylic resin, external hexagon connections had lower total deformation values compared with morse taper connection. Also, the implant length was found to have no effect on the values of total deformation. In conclusion, total deformation was substantially greater in all models with acrylic resin restorations.

El propósito de este estudio fue evaluar mediante análisis de elementos finitos (FEA) la deformación total o desplazamiento como un sistema completo de prótesis múltiples implanto-soportadas en la región anterior de la maxila con diferentes longitudes, conexiones y posiciones del implantes y variando el material de restauración. Se utlizó un modelo hemi-maxilar de una región anterior desdentada de un modelo para ser analizado por medio de elementos finitos. Las simulaciones fueron divididas en dos grupos de acuerdo con el plan de tratamiento: 1) dos implantes se colocaron en los incisivos centrales superiores, simulando una prótesis fija implanto-soportada (resina acrílica y metal-cerámica) de cuatro elementos con cantilever de ambos incisivos laterales superiores; 2) dos implantes colocados en los incisivos laterales superiores, simulando una prótesis fija convencional de cuatro elementos con los dos incisivos centrales superiores como póntico. Los modelos con prótesis en cantilever en resina acrílica mostraron los mayores valores de deformación total, siendo 17 veces mayor a los de metal-cerámica en la cara distal de los incisivos laterales, independientemente del tipo de conexión del implante. En las prótesis convencionales en resina acrílica, las conexiones hexagonales externas tenían valores deformación total más bajos en comparación con la conexión cono morse. También, se encontró que la longitud del implante no mostró ninguna influencia en los valores de la deformación total. En conclusión, la deformación total fue sustancialmente mayor en todos los modelos con restauraciones de resina acrílica.

Finite element analysis and fracture resistance testing of a new intraradicular post

OBJECTIVES: The objective of the present study was to evaluate a prefabricated intraradicular threaded pure titanium post, designed and developed at the São José dos Campos School of Dentistry - UNESP, Brazil. This new post was designed to minimize stresses observed with prefabricated post systems and to improve cost-benefits. MATERIAL AND METHODS: Fracture resistance testing of the post/core/root complex, fracture analysis by microscopy and stress analysis by the finite element method were used for post evaluation. The following four prefabricated metal post systems were analyzed: group 1, experimental post; group 2, modification of the experimental post; group 3, Flexi Post, and group 4, Para Post. For the analysis of fracture resistance, 40 bovine teeth were randomly assigned to the four groups (n=10) and used for the fabrication of test specimens simulating the situation in the mouth. The test specimens were subjected to compressive strength testing until fracture in an EMIC universal testing machine. After fracture of the test specimens, their roots were sectioned and analyzed by microscopy. For the finite element method, specimens of the fracture resistance test were simulated by computer modeling to determine the stress distribution pattern in the post systems studied. RESULTS: The fracture test presented the following averages and standard deviation: G1 (45.63±8.77), G2 (49.98±7.08), G3 (43.84±5.52), G4 (47.61±7.23). Stress was homogenously distributed along the body of the intraradicular post in group 1, whereas high stress concentrations in certain regions were observed in the other groups. These stress concentrations in the body of the post induced the same stress concentration in root dentin. CONCLUSIONS: The experimental post (original and modified versions) presented similar fracture resistance and better results in the stress analysis when compared with the commercial post systems tested (08/2008-PA/CEP).