Comportamiento Mecánico de un Premolar Humano Sano Sometido a Fuerzas Funcionales y Disfuncionales en un MEF / Mechanical Behavior of a Healthy Human Premolar Subjected to Functional and Dysfunctional Forces in a FEM

El propósito de este estudio fue analizar el comportamiento mecánico de la estructura dental sana de un primer premolar inferior humano sometido a fuerzas funcionales y disfuncionales en diferentes direcciones. Se buscó comprender, bajo las variables contempladas, las zonas de concentración de esfuerzos que conllevan al daño estructural de sus constituyentes y tejidos adyacentes. Se realizó el modelo 3D de la reconstrucción de un archivo TAC de un primer premolar inferior, que incluyó esmalte, dentina, ligamento periodontal y hueso alveolar considerando tres variables: dirección, magnitud y área de la fuerza aplicada. La dirección fue dirigida en tres vectores (vertical, tangencial y horizontal) bajo cuatro magnitudes, una funcional de 35 N y tres disfuncionales de 170, 310 y 445 N, aplicadas sobre un área de la cara oclusal y/o vestibular del premolar que involucró tres contactos estabilizadores (A, B y C) y dos paradores de cierre. Los resultados obtenidos explican el fenómeno de combinar tres vectores, cuatro magnitudes y un área de aplicación de la fuerza, donde los valores de esfuerzo efectivo equivalente Von Mises muestran valores máximos a partir de los 60 MPa. Los valores de tensión máximos se localizan, bajo la carga horizontal a 170 N y en el proceso masticatorio en la zona cervical, cuando la fuerza pasa del 60 %. Sobre la base de los hallazgos de este estudio, se puede concluir que la reacción de los tejidos a fuerzas funcionales y disfuncionales varía de acuerdo con la magnitud, dirección y área de aplicación de la fuerza. Los valores de tensión resultan ser más altos bajo la aplicación de fuerzas disfuncionales tanto en magnitud como en dirección, produciendo esfuerzos tensiles significativos para la estructura dental y periodontal cervical, mientras que, bajo las cargas funcionales aplicadas en cualquier dirección, no se generan esfuerzos lesivos. Esto supone el reconocimiento del poder de detrimento estructural del diente y periodonto frente al bruxismo céntrico y excéntrico.

SUMMARY: The purpose of this study was to analyze the mechanical behavior of the healthy dental structure of a human mandibular first premolar subjected to functional and dysfunctional forces in different directions. It was sought to understand, under the contemplated variables, the areas of stress concentration that lead to structural damage of its constituents and adjacent tissues. The 3D model of the reconstruction of a CT file of a lower first premolar was made, which included enamel, dentin, periodontal ligament and alveolar bone considering three variables: direction, magnitude and area of the applied force. The direction was directed in three vectors (vertical, tangential and horizontal) under four magnitudes, one functional of 35 N and three dysfunctional of 170, 310 and 445 N, applied to an area of the occlusal and/or buccal face of the premolar that involved three stabilizing contacts (A, B and C) and two closing stops. The results obtained explain the phenomenon of combining three vectors, four magnitudes and an area of force application, where the values of effective equivalent Von Mises stress show maximum values from 60 MPa. The maximum tension values are located under the horizontal load at 170 N and in the masticatory process in the cervical area, when the force exceeds 60%. Based on the findings of this study, it can be concluded that the reaction of tissues to functional and dysfunctional forces varies according to the magnitude, direction, and area of application of the force. The stress values turn out to be higher under the application of dysfunctional forces both in magnitude and in direction, producing significant tensile stresses for the dental and cervical periodontal structure, while under functional loads applied in any direction, no damaging stresses are generated. This supposes the recognition of the power of structural detriment of the tooth and periodontium against centric and eccentric bruxism.

Relationship between cervical vertebral maturation and dental development in a sample of yemeni children and adolescents / Relación entre la maduración vertebral cervical y el desarrollo dental en una muestra de niños y adolescentes yemeníes

Objective: This study was conducted to investigate the relationship between dental development and cervical vertebral maturation stages in a group of Yemeni children and adolescents. Materials an Methods: The study included digital panoramic radiographs and lateral skull cephalograms obtained from 207 Yemeni subjects­122 females and 85 males aged between 8 to 18 years. Dental maturity was evaluated according to the method of Demirijian et al., calcification stages of the left mandibular canines, first and second premolars and second molars were assessed. Skeletal maturity was assessed by the cervical vertebral maturation (CVM) stages according to the method of Baccetti et al. Correlation between CVM and dental maturation was evaluated by Spearman rank-order correlation coefficient (SROCC). Results: CVM and dental calcification stages were highly correlated (p<0.001) in both genders, ranging from 0.686 to 0.873 for females and 0.787 to 0.871 for males. Calcification stages of the second molars showed the strongest correlation with CVM. Conclusion: Calcification stages of the second molar may be used as a reliable maturation indicator. Dental maturation may be applied to determine the skeletal maturity status of Yemeni children and adolescents.

Objetivo: Este estudio se realizó para investigar la relación entre el desarrollo dental y las etapas de maduración vertebral cervical en un grupo de niños y adolescentes yemeníes. Material y Métodos: El estudio incluyó radiografías panorámicas digitales y cefalogramas laterales del cráneo obtenidos de 207 sujetos yemeníes: 122 mujeres y 85 hombres de entre 8 y 18 años. La madurez dental se evaluó de acuerdo con el método de Demirijian et al. Se evaluaron las etapas de calcificación de los caninos mandibulares izquierdos, primer y segundo premolares y segundos molares. La madurez esquelética se evaluó mediante las etapas de maduración vertebral cervical (CVM) de acuerdo con el método de Baccetti et al. La correlación entre la CVM y la maduración dental se evaluó mediante el coeficiente de correlación de orden de rango de Spearman (SROCC). Resultado: Las etapas de CVM y calcificación dental estuvieron altamente correlacionadas (p<0.001) en ambos sexos, con un rango de 0.686 a 0.873 para las mujeres y 0.787 a 0.871 para los hombres. Las etapas de calcificación de los segundos molares mostraron la correlación más fuerte con CVM. Conclusión: las etapas de calcificación del segundo molar pueden usarse como un indicador de maduración confiable. La maduración dental puede aplicarse para determinar el estado de madurez esquelética de los niños y adolescentes yemeníes.

Estudo sobre o comportamento biomecânico de implantes curtos com variação da espessura da cortical óssea por meio do método dos elementos finitos / Biomechanical behavior of short implants varying thickness of cortical bone by finite element method

Este estudo teve como objetivo analisar e comparar o comportamento biomecânico de um implante de comprimento curto com um implante de comprimento padrão, no que diz respeito às tensões ósseas ao redor do implante. Foi considerado como variável o aumento da espessura óssea cortical, em dois tipos: fino e espesso. Os modelos de elementos finitos em três dimensões (3D) foram criados a partir de uma secção de mandíbula de 20 mm, referente ao segundo pré-molar, com um implante endósseo único inserido dentro do osso esponjoso com cortical fina de 0,5 mm e cortical espessa de 2,0 mm. Uma carga oclusal vertical de 100 N e uma carga oblíqua de 40 N foram aplicadas. Os ossos cortical e esponjoso foram considerados isotrópicos e linearmente elásticos e o critério de avaliação foi o de tensões de von Mises. O implante curto utilizado foi de 4,1 mm de diâmetro por 6,0 mm de comprimento, e o implante padrão de 4,1 mm de diâmetro por 10,0 mm de comprimento (ambos da marca Straumann®). A prótese sobre o implante foi composta por um pilar sólido de 5,5 mm de altura e por uma coroa de segundo pré-molar. Conforme as simulações pelo MEF, pôde-se concluir que: 1) O aumento da espessura óssea favoreceu uma melhor distribuição das tensões, registrando valores mais baixos na região cervical cortical. 2) O modelo de implante curto na situação de cortical espessa apresentou melhores resultados biomecânicos comparado com o modelo de implante padrão na situação de cortical fina.

The aim of this monograph was to analyze and compare the biomechanical behavior of a short length implant against a standard length implant, regarding stress distribution on the bone around the implant. Bone cortical thickness of the ridge was considered as thin and thick. The 3D finite element models were created of a 20-mm second premolar section of the mandible with a single endosseous implant embedded in cancellous bone with thin cortical of 0.5 mm and with thick cortical of 2.0 mm. A vertical occlusal load of 100 N and an oblique load of 40 N were applied. The cortical and cancellous bone were considered to be isotropic and linearly elastic Von Mises stress criterion was used for analysis. The short implant used was of 4.1 mm of diameter and 6 mm in length, and the standard implant was of 4.1 mm of diameter and 10 mm in length (both Straumann ®). The prosthesis on the implant consisted of a solid abutment of 5.5 mm in height and a crown of second premolar. Conclusions: 1) Increasing bone thickness favored a better stress distribution, showing lower values in the cervical cortical bone. 2) Short implants with thin cortical situations showed better biomechanical results compared to standard implants with thick cortical situations.

Profile changes in premolar extraction / Alterações no perfil em extrações de pré-molares

PURPOSE: This retrospective study assessed patients treated with extraction of premolars by analysis of lateral cephalograms, comparing the effect of different tooth extraction protocols on the profile. METHODS: Eighty-seven patients were selected from the private practices of three orthodontists certified by the Brazilian Board of Orthodontics and Facial Orthopedics. These patients were treated with fixed edgewise appliances and divided into three groups according to the sequence in which premolars were extracted: "Group 40", maxillary first premolars (22 patients); "Group 44", both maxillary and mandibular first premolars (43 patients); and "Group 45", maxillary first and mandibular second premolars (22 patients). The Z angle and the Burstone line were used to quantify and compare the profiles before and after treatment. RESULTS: Student's t-test showed profile improvement in all groups, as the Z angle value was higher at treatment completion and the lip measurements were in agreement with the values recommended by Burstone. Analysis of treatment changes by the ANOVA did not reveal significant differences between groups. CONCLUSION: The protocols produced similar facial appearance at treatment completion.

OBJETIVO: Este estudo retrospectivo avaliou pacientes tratados com exodontias de pré-molares através da análise de telerradiografias, comparando o efeito de diferentes protocolos de exodontias no perfil. METODOLOGIA: 87 pacientes foram selecionados da clínica particular de três ortodontistas diplomados pelo Board Brasileiro de Ortodontia e Ortopedia Facial. Estes pacientes foram tratados com aparelho fixo Edgewise e foram divididos em três grupos, de acordo com a sequência de pré-molares extraídos: "Grupo 40", primeiros pré-molares superiores (22 pacientes); "Grupo 44", quatro primeiros pré-molares (43 pacientes); e "Grupo 45", primeiros pré-molares superiores e segundos inferiores (22 pacientes). O Ângulo Z e a Linha de Burstone foram utilizados para quantificar e comparar os perfis antes e após o tratamento. RESULTADOS: O teste t-student mostrou melhora no perfil em todos os grupos, visto que o valor do ângulo Z apresentou-se maior ao final do tratamento e as medidas dos lábios vieram ao encontro dos valores preconizados por Burstone. A análise das mudanças proporcionadas pelo tratamento pela ANOVA não revelou diferenças significativas entre os grupos CONCLUSÃO: Os protocolos produzem aparências faciais semelhantes ao final do tratamento.

Three-dimensional finite element analysis of the stress distribution pattern in the design modifications of U-shaped palatal major connector.

Background: The U-shaped maxillary major connector is considered to be the least-desirable design by many prosthodontists as it lacks rigidity, which is a primary requisite for a major connector. Aims and Objectives: Design modifications in the U-shaped palatal major connector are desired because it lacks rigidity. The study also aimed to determine the best design when a U-shaped palatal major connector is indicated for clinical use. Materials and Methods: The normal design and the design-modified models (modification 1, 2, 3, 4) were loaded at the functional cusps of the premolars and the molars with a magnitude of 200 N, 250 N and 300 N at angulations of 60 o and 90 o on both sides of the maxillary arch. Results for each loading were obtained as stress distribution colored images and numerical values were recorded. A three-dimensional finite element analysis study of the design-modified models was performed using two finite element softwares, namely PRO-E and IDEAS. Results: The least stress value of 7.86 Megapascals (MPa) at 200 N, 60 o was recorded for the double-thickness design, followed by design 1, which was 8.03 MPa. The least stress value for the palatal mucosa and ligament was provided by design modification 1 (0.5 mm-thick U-shaped connector, 9 mm anteroposteiorly, 14.6 mm laterally), which was 9.78 MPa and 2.98 MPa, respectively. Conclusion: The double-thickness group exhibited the least internal stress for the U-shaped major connector. However, it delivered the greatest stress to the palatal mucosa and the periodontal ligaments.

Transient thermal and stress analysis of maxillary second premolar tooth using an exact three-dimensional model.

Aim : In this paper, the temperature and stress distributions in an exact 3D-model of a restored maxillary second premolar tooth are obtained with finite element approach. Objective : The carious teeth need to restore with appropriate restorative materials. There are too many restorative materials which can be used instead of tooth structures; since tooth structures are being replaced, the restorative materials should be similar to original structure as could as possible . Materials and Methods : In the present study, a Mesial Occlusal Distal (MOD) type of restoration is chosen and applied to a sound tooth model. Four cases of restoration are investigated: two cases in which base are used under restorative materials and two cases in which base is deleted. The restorative materials are amalgam and composite and glass-inomer is used as a base material. Modeling is done in the solid works ambient by means of an exact measuring of a typical human tooth dimensions. Tooth behavior under thermal load due to consuming hot liquids is analyzed by means of a three dimensional finite element method using ANSYS software. The highest values of tensile and compressive stresses are compared with tensile and compressive strength of the tooth and restorative materials and the value of shear stress on the tooth and restoration junctions is compared with the bond strength. Also, sound tooth under the same thermal load is analyzed and the results are compared with those obtained for restored models. Results : Temperature and stress distributions in the tooth are calculated for each case, with a special consideration in the vicinity of pulp and restoration region. Numerical results show that in two cases with amalgam, using the base material (Glass-ionomer) under the restorative material causes to decrease the maximum temperature in the restorative teeth . In the stress analysis, it is seen that the principal stress has its maximum values in composite restorations. Conclusion : The maximum temperatures are found in the restoration case of amalgam without base. Besides, it is found that restoration has not any influence on the stress values at DEJ, such that for all cases, these values are close to sound tooth results.

Proporción de tenascina y fibronectina en el ligamento periodontal de dientes sometidos a fuerzas ortodónticas / Tenascin and fibronectin proportions in human periodontal ligament of teeth undergoing orthodontic forces

El presente estudio tuvo como objetivo comprobar los cambios en la proporción de tenascina (T) y fibronectina (F) en la zona de tensión del ligamento periodontal humano (LPH) de dientes sometidos a fuerzas ortodónticas. Se tomaron muestras de LPH en 20 pacientes entre 18 y 25 años. A los dientes del grupo experimental se les aplicó una fuerza con intervalos de 1, 21 y 40 días. Las muestras fueron congeladas en nitrógeno líquido y posteriormente sometidas a tinción inmunohistoquímica. Para el grupo de F, el primer día se observó que los dientes del grupo control presentaban una tinción leve. En el grupo experimental se observó que las siete muestras presentaban una tinción leve. En el día 21, cinco de las siete muestras presentaban una tinción moderada y las dos restantes, una tinción intensa. En el día 40, en todas se observó una tinción intensa. En el grupo control de T, las muestras presentaron una tinción leve. En el primer día se observó una tinción moderada. En el día 21, cuatro presentaron una tinción intensa y las tres restantes, una tinción moderada. En el día 40 fue leve. Los resultados sugieren la posible relación de la F y la T en los procesos de neoformación en la zona de tensión, contribuyendo a la mejor comprensión de los procesos moleculares involucrados al aplicar fuerzas ortodónticas en los dientes