Effects of Different Implant Design Parameters on Mandibular Tooth Implantation / 医用生物力学

Objective To establish the implant-mandible model with different design parameters, observe stress distributions on the implant and surrounding bone, and analyze the influence of different design parameters on dental implant of the mandible. Methods Eight implant models were designed based on structural characteristic parameters (implant diameter, thread depth, height of abutment through gingiva, thread shape), and assembly of the mandibular model was performed respectively. The models were applied with static 150 N vertical and oblique 45° loads, so as to analyze peak von Mises stress of the implant and bone tissues and explore the structural parameter variables of implant most sensitive to peak von Mises stress. Results The peak stress of the mandible was larger under inclined load than that under vertical load. Implant diameter was the key factor affecting the peak von Mises stress of cortical bone, while thread depth was the key factor affecting the peak von Mises stress of cancellous bone. The peak von Mises stress was also affected by the height of abutment through gingiva, but the effect was not as significant as thread depth and implant diameter. Thread shape had little effect on the peak von Mises stress of the mandible. Conclusions Different implant design parameters can affect the peak stress of different tissues of the mandible, so it is necessary to carefully consider the selection of implant parameters for personalized implants. This study can provide theoretical guidance for structural parameter design of oral implants and provide references for accurate prediction of oral implants.

Evaluation of stability of three different mini-implants, based on thread shape factor and numerical analysis of stress around mini-implants with different insertion angle, with relation to en-masse retraction force

ABSTRACT Objectives: Assess the stability of three different mini-implants, based on thread shape factor (TSF), and evaluate stresses at the mini-implant site and surrounding cortical bone on application of retraction force, at two different insertion angles. Methods: Mini-implants of three different diameters (M1 - Orthoimplant, 1.8mm), (M2 - Tomas, 1.6mm) and (M3 - Vector TAS, 1.4mm) and length of 8mm were used. Using scanning electronic microscopy, the mean thread depth, pitch and relationship between the two (TSF) were calculated. The mini-implants were loaded into a synthetic bone block and the pull-out strength was tested. One way ANOVA and Tukey post-hoc tests were used to compare the pull-out strength of mini-implants. P values < 0.05 were considered statistically significant. Finite element models (FEM) were constructed with insertion angulation at 90° and 60°, with retraction force of 150 g. The results were analyzed using ANSYS software. Results: Statistically significant difference was found among all the three mini-implants for thread depth and pitch (< 0.001). Statistically significant higher pull-out force value was seen for Orthoimplant. The stress distribution level in mini-implant and surrounding bone was observed to be smaller for Orthoimplant. Conclusion: Orthoimplant mini-implants have more favorable geometric characteristics among the three types, and less stress with 90°angulation.

RESUMO Objetivos: Avaliar a estabilidade de três diferentes tipos de mini-implantes, com base no fator formato da rosca (thread shape factor, TSF), e avaliar a tensão no local de inserção e no osso cortical ao redor dos mini-implantes inseridos com dois ângulos diferentes, durante a aplicação de força para retração. Métodos: Foram usados três diferentes diâmetros de mini-implantes, sendo eles 1,8 mm (M1, ORTHO Implant), 1,6 mm (M2, Tomas) e 1,4 mm (M3, Vector TAS), todos com comprimento de 8 mm. Por meio da microscopia eletrônica de varredura, foram calculados a profundidade da rosca, o passo da rosca (distância entre os filetes da rosca) e a relação entre os dois (TSF). Para realização do teste de tração (pull-out), os mini-implantes foram inseridos em um bloco de osso sintético. Os testes ANOVA de uma via e post-hoc de Tukey foram usados para comparar as forças de resistência à tração dos mini-implantes, considerando-se estatisticamente significativos valores de p< 0,05. Modelos de elementos finitos (MEF) foram gerados com ângulos de inserção dos mini-implantes a 90° e 60°, com força de retração em 150g. Os resultados foram analisados usando-se o software ANSYS. Resultados: Diferenças estatisticamente significativas foram encontradas entre os três mini-implantes quanto à profundidade da rosca e o passo da rosca (p< 0,001). O ORTHO Implant apresentou a maior força de resistência à tração, com significância estatística. O nível de distribuição das tensões no mini-implante e no osso circundante também foi menor para o ORTHO Implant. Resultados: Entre os diferentes tipos de mini-implantes analisados, o ORTHO Implant apresentou as características geométricas mais favoráveis e a menor tensão com o ângulo de inserção de 90°.

Biomechanical Properties of Implants with Different Thread Shapes and Depths in Dental Immediate Implantation / 医用生物力学

Objective To analyze stress distributions of alveolar bone around implants with different types of implant thread shapes and thread depths during dental immediate implantation, so as to provide references for the design and selection of implants. Methods The simplified model of mandible bone block, implants and mandibular molar were established by Geomagic Studio, SolidWorks and ANSYS Workbench, and vertical and oblique loads were applied on this model, respectively. Stress distributions on implants with different thread shape and thread depth as well as alveolar bone around implants were calculated. Results Under vertical loading, the peak stresses of implants, cortical bone and cancellous bone were in the range of 120.51-129.63 MPa, 9.94-13.25 MPa and 3.92-8.01 MPa, respectively. And the stress of cortical bone around V-shaped, rectangular, buttress or reverse buttress implant remained stable in the range of 0.40-0.45 mm thread depth. Under oblique loading, the peak stresses of implants, cortical bone and cancellous bone were in the range of 220.23-286.51 MPa, 33.39-45.08 MPa, 4.96-12.5 MPa, respectively. Among the models, V-shaped, buttress, reverse buttress implant with 0.45 mm thread depth showed the minimum stress. Conclusions The V-shaped, buttress or reverse buttress implant with a thread depth of 0.45 mm, or the rectangular implant with a thread depth of 0.40 mm had better biomechanical properties.