Comparison of splinted and non-splinted superstructures of three implants placed in a mandibular distal extension model with missing teeth using modal analysis

Development and validation of a digital twin of the human lower jaw under impact loading by using non-linear finite element analyses

Mandibular fractures are one of the most frequently observed injuries within craniofacial region mostly due to tumor-related problems and traumatic events, often related to non-linear effects like impact loading. Therefore, a validated digital twin of the mandible is required to develop the best possible patient-specific treatment. However, there is a need to obtain a fully compatible numerical model that can reflect the patients' characteristics, be available and accessible quickly, require an acceptable level of modeling efforts and knowledge to provide accurate, robust and fast results at the same time under highly non-linear effects. In this study, a validated simulation methodology is suggested to develop a digital twin of mandible, capable of predicting the non-linear response of the biomechanical system under impact loading, which then can be utilized to design treatment strategies even for multiple fractures of the mandibular system. Using Computed Tomography data containing cranial (skull) images of a patient, a 3-dimensional mandibular model, which consists cortical and cancellous bones, disks and fossa is obtained with high accuracy that is compatible with anatomical boundaries. A Finite Element Model (FEM) of the biomechanical system is then developed for a three-level validation procedure including (A) modal analysis, (B) dynamic loading and (C) impact loading. For the modal analysis stage: Free-free vibration modes and frequencies of the system are validated against cadaver test results. For the dynamic loading stage: Two different regions of the mandible are loaded, and maximum stress levels of the system are validated against finite element analyses (FEA) results, where the first loading condition (i) transfers a 2000 N force acting on the symphysis region and, the second loading condition (ii) transfers a 2000 N force acting on the left body region. In both cases, equivalent muscle forces dependent on time are applied. For the impact loading stage: Thirteen different human mandibular models with various tooth deficiencies are used under the effects of traumatic impact forces that are generated by using an impact hammer with different initial velocities to transfer the impulse and momentum, where contact forces and fracture patterns are validated against cadaver tests. Five different anatomical regions are selected as the impact site. The results of the analyzes (modal, dynamic and impact) performed to validate the digital twin model are compared with the similar FEA and cadaver test results published in the literature and the results are found to be compatible. It has been evaluated that the digital twin model and numerical models are quite realistic and perform well in terms of predicting the biomechanical behavior of the mandible. The three-level validation methodology that is suggested in this research by utilizing non-linear FEA has provided a reliable road map to develop a digital twin of a biomechanical system with enough confidence that it can be utilized for similar structures to offer patient-specific treatments and can help develop custom or tailor-made implants or prosthesis for best compliance with the patient even considering the most catastrophic effects of impact related trauma.

A modal analysis of implant-supported overdentures installed on differently positioned sets of dental implants

This study evaluated the three vibration characteristics, namely, natural frequency, damping ratio, and natural mode, together with maximum displacement of a two-implant-supported overdenture (IOD) at different locator attachment positions using experimental modal analysis (EMA). Edentulous mandibular models with a gingival thickness of 1 mm or 3 mm were prepared, into which dental implants were placed using a fully guided surgical template designed with simulation software, the locator abutments were fastened, and the IODs were then fabricated. The implant positions were bilaterally marked at the lateral incisor, first premolar, and first molar regions. EMA was performed by hammering the test structures to measure the impulse response and obtain the vibration characteristics (n = 5). The Kruskal-Wallis test was performed for natural frequency and maximum displacement, and the Games-Howell test for damping ratio. The significance level was set at α = 0.05. The study indicated that the gingival thickness had a significant effect on the vibration characteristics. Moreover, the natural frequency and damping ratio results showed that the vibration subsided faster when the attachment was placed on the molar implants in the thick gingival model. Furthermore, according to the effect of lateral force on IODs, the difference in maximum displacement between the anterior and posterior regions of the IOD was smaller when the attachments were designed on the pair of lateral incisors. Thus, within the limits of this experiment, our results suggested that two anterior implant-supported IODs are preferable treatment designs in terms of vibration engineering, especially when the gingiva is thick; the molar attachment design could be considered for thin gingival conditions. The differences in gingival thickness and abutment position affected the vibration characteristics of the IOD. Further in vivo studies would be necessary to validate the implant positions and their IOD designs for the mandibular edentulous shapes and the occlusal relationship.