FAILURE MODE ANALYSIS OF CERAMIC BRACKETS BONDED TO ENAMEL

The purpose of this study was to evaluate in vitro the failure pattern of ceramic brackets bonded to enamel with a light-cured orthodontic adhesive. Five types of ceramic brackets and 125 incisors were used in the study. The brackets were bonded onto enamel with a light-cured orthodontic adhesive. After 1 week storage and thermal cycling, the samples were debonded by one operator according to the individual technique for each bracket group proposed by each manufacturer. The fracture surfaces were examined under a stereomicroscope to reveal the type of failures. The effect of the debonding procedure on enamel structure was significantly affected by the various bonding mechanisms of the bracket bases. Cohesive enamel fractures were detected from brackets that provided a bonding mechanism of micromechanical retention and chemical adhesion. The brackets that combined mechanical retention and chemical adhesion, presented both cohesive resin fractures and fractures located at the bracket resin or the resin enamel interface. The higher frequency of cohesive bracket fractures was obtained from a monocrystalline bracket

Comparative Evaluation of varying Photo-polymerization Time on Shear Bond Strength and Microleakage of Four Orthodontic Adhesives: An in vitro Study

Introduction High early bond strength, extended working time for optimal bracket placement, and easy cleanup of excess adhesive are few advantages of visible light-cure orthodontic adhesives. However, the shorter duration of polymerization may lead to polymer shrinkage and eventually microleakage. Objective To observe and evaluate shear bond strength (SBS) and microleakage of orthodontic brackets bonded to enamel with four commercially available orthodontic adhesives, cured only from incisal direction at various polymerization times. Materials and methods A total of 160 bovine incisors were randomly assigned to four groups according to adhesive used. Group I: bonded with Transbond XT (3M Unitek™, USA); group II: Enlight (Ormco, USA); group III: Light Bond (Reliance Ortho, USA); and group IV: Discover (Prime Dental, USA). Each group was further divided into four subgroups of A, B, C, and D according to the polymerization duration of 5, 10, 15, and 20 seconds respectively. The bonded teeth were immersed in dye solution. Brackets were then subjected to SBS test on a Universal testing machine. Surface microleakage was observed with the help of optical stereomicroscope. Results The SBS was obtained within the range of clinically accepted values, with curing time for Enlight at 5 seconds, Transbond XT and Discover at 15 seconds, and Light Bond at 20 seconds. However, Enlight was demonstrated to provide optimum SBS at least curing time: Minimum duration of 5 seconds achieved adequate SBS ~11 MPa SBS for each of Transbond XT and Enlight. The surface microleakage observed is statistically insignificant among the groups. Conclusion From a clinical perspective, a composite resin that needs minimum curing time without compromising on the bond strength is most advantageous. The results for SBS tests showed a better performance for Enlight as compared with the other adhesives: it reached its bond strength of optimum value at curing time of 5 seconds. How to cite this article Zanke PN, Patni V, Maskarenj M. Comparative Evaluation of varying Photo-polymerization Time on Shear Bond Strength and Microleakage of Four Orthodontic Adhesives: An in vitro Study. J Contemp Dent 2017;7(3):156-160

Simulação 3D de movimento ortodôntico 3D simulation of orthodontic tooth movement

OBJETIVO: desenvolver e validar, através do Método dos Elementos Finitos (MEF), um modelo numérico tridimensional (3D) de um incisivo central superior para simular o movimento dentário. MÉTODOS: esse modelo contempla a unidade dentária, o osso alveolar e o ligamento periodontal. Permite a simulação dos diferentes movimentos dentários e a determinação dos centros de rotação e de resistência. Limita o movimento ao espaço periodontal, registrando a direção, quantificando o deslocamento dentário e as tensões iniciais no ligamento periodontal. RESULTADOS: a análise dos deslocamentos dentários e das áreas que recebem tensões iniciais possibilita determinar os tipos de movimentos dentários. Com base nas forças ortodônticas, é possível quantificar a intensidade das tensões em cada região do dente, do ligamento periodontal ou do osso alveolar. Com base nas tensões axiais ao longo do ligamento periodontal e da tensão capilar, é possível predizer, teoricamente, as regiões em que deve ocorrer a remodelação óssea. CONCLUSÃO: o modelo foi validado pela determinação do módulo de elasticidade do ligamento periodontal de forma compatível com dados experimentais existentes na literatura. Os métodos utilizados na construção do modelo permitiram a criação de um modelo completo para uma arcada dentária, o qual possibilita realizar variadas simulações que envolvem a mecânica ortodôntica.<br>OBJECTIVE: To develop and validate a three-dimensional (3D) numerical model of a maxillary central incisor to simulate tooth movement using the Finite Element Method (FEM). METHODS: This model encompasses the tooth, alveolar bone and periodontal ligament. It allows the simulation of different tooth movements and the establishment of centers of rotation and resistance. It limits the movement into the periodontal space, recording the direction, quantifying tooth displacement and initial stress in the periodontal ligament. RESULTS: By assessing tooth displacements and the areas that receive initial stress it is possible to determine the different types of tooth movement. Orthodontic forces make it possible to quantify stress magnitude in each tooth area, in the periodontal ligament and in the alveolar bone. Based on the axial stress along the periodontal ligament and the stress in the capillary blood vessel (capillary blood stress) it is theoretically possible to predict the areas where bone remodeling is likely to occur. CONCLUSIONS: The model was validated by determining the modulus of elasticity of the periodontal ligament in a manner consistent with experimental data in the literature. The methods used in building the model enabled the creation of a complete model for a dental arch, which allows a number of simulations involving orthodontic mechanics

Assessment of changes in smile after rapid maxillary expansion

INTRODUCTION: This study evaluated changes in the smile characteristics of patients with maxillary constriction submitted to rapid maxillary expansion (RME). METHODS: The sample consisted of 81 extraoral photographs of maximum smile of 27 patients with mean age of 10 years, before expansion and 3 and 6 months after fixation of the expanding screw. The photographs were analyzed on the software Cef X 2001, with achievement of the following measurements: Transverse smile area, buccal corridors, exposure of maxillary incisors, gingival exposure of maxillary incisors, smile height, upper and lower lip thickness, smile symmetry and smile arch. Statistical analysis was performed by analysis of variance (ANOVA), at a significance level of 5%. RESULTS: RME promoted statistically significant increase in the transverse smile dimension and exposure of maxillary central and lateral incisors; maintenance of right and left side smile symmetry and of the lack of parallelism between the curvature of the maxillary incisal edges and lower lip border. CONCLUSIONS: RME was beneficial for the smile esthetics with the increase of the transverse smile dimension and exposure of maxillary central and lateral incisors.<br>INTRODUÇÃO: esse estudo avaliou as alterações das características do sorriso de pacientes com atresia maxilar submetidos à expansão rápida da maxila (ERM). MÉTODOS: a amostra consistiu de 81 fotografias extrabucais do sorriso máximo de 27 pacientes, com idade média de 10 anos, antes da expansão e aos três e seis meses após a fixação do parafuso expansor. As análises das fotografias foram realizadas por meio do programa Cef X 2001, e as seguintes medidas foram analisadas: dimensão transversal do sorriso, corredores bucais, quantidade de exposição dos incisivos superiores, exposição gengival dos incisivos superiores, altura do sorriso, espessuras dos lábios superior e inferior, simetria e arco do sorriso. As alterações no sorriso durante as diferentes fases foram avaliadas por meio da análise de variância (ANOVA), seguida pelo teste de comparações múltiplas de Bonferroni, com nível de significância de 5%. RESULTADOS: a ERM promoveu aumento estatisticamente significativo da dimensão transversal do sorriso e da quantidade de exposição dos incisivos centrais e laterais superiores; manutenção da simetria entre os lados direito e esquerdo e da falta de paralelismo entre a curvatura das bordas dos incisivos superiores e a do lábio inferior. CONCLUSÃO: a ERM beneficiou a estética do sorriso com o aumento da dimensão transversal do sorriso e da quantidade de exposição dos incisivos centrais e laterais superiores