Despite of the complexity of the surgical scenario, the available technologies must ultimately serve as a vehicle for the surgeon to plan the surgical plan in a seamless manner. It is thus crucial to develop technologies that leverage the work of the surgeon, allowing him to test different options and interact with the bone and soft tissue components of the surgical plan.

Recently, a shift paradigm was presented whereby the necessary planning is computed from the desired post-operative outcome [75]. This paradigm shift, coined “Inverse Planning”, enables the surgeon to look at the surgical plan from a different perspective, allowing him to directly define the desired outcome, without the need of the commonly used trial-and-error scheme available in current solutions.

The proposed approach employs a fast biomechanical model to derive from the desired facial outlook the necessary surgical plan. Based on the desired facial outlook the deformation of internal soft tissues is calculated, followed by constrained surface registration between bone segments and internal soft tissues. The proposed registration component considers collision and occlusion constraints, and its formulation allows us to derive in a straightforward manner different levels of interplay between quality of occlusion and compliance to the desired outlook (i.e. constraints relaxation). Furthermore, and in regards to a biomechanical simulation that would model the entire ensemble of bone and soft tissues, the proposed approach avoids known issues of layer detachment and convergence related to the high elasticity transition present at the interface of bone and soft tissue materials. We remark that this approach differs from the classical inverse modeling proposed in computational mechanics and used in implant shape design in [28], as our method deals with the ill-posedness of the problem by considering occlusion and geometrical constraints through a registration component that effectively penalizes the set of numerical solutions.

By combining the direct (i.e. soft tissue simulation from bone displacements) and the inverse soft tissue modeling (i.e. specification of bone displacement to yield a desired outcome) it is possible to yield an effective system that, in a transparent way, enables the surgeon to work on the surgical plan.

Due to airways and tongue volume constraints in complex CMF cases, large rotational and translational planning are rarely operated in one single step and surgeons typically divide it into a series of surgeries, which in turns translates into small deformations in engineering mechanics. Nonetheless, to cover these rare cases for large deformation problems, we will consider modifying the classical FEM inverse approach [77] in which the inverse modelling is transferred to a direct problem by super-imposing boundary conditions and transferring the unknown set of displacements to the other side of the continuity equation [78].

Preliminary results, shown on Fig. 5.3, on a set of clinical cases showed in five out of six CT cases a high level of agreement to the actual surgical plan. In one case the proposed approach was confirmed to improve the actual executed plan. As an additional evaluation, simulated soft-tissue outcomes were compared using the predicted and real clinical plan, resulting in a close agreement between the facial simulation results using the predicted and actual planed approach (Fig. 5.4.).

The human face is a fundamental part of our identity. It centralizes the senses of vision, hearing, taste and smelling, and provides us with channels to participate and integrate in society. The complexity of the clinical scenario is complex, as it requires high understanding of the balance amongst aesthetic, functional, psychological and sociological implications of the surgical outcome. Furthermore, the degree of unpredictability on the surgical outcome makes the decision-making process, on a patient-basis, highly complex. This has called for the development of computational means to assist the surgeon on the task of planning the surgical approach. We believe, however, that more research efforts are essential and needed in order to bring these tools to a level where they can effectively and jointly consider aesthetic and functional aspects for the planning of CMF surgeries.

Based on the observations from the state of the art it can be concluded that functional aspects are of importance and need to be considered in CMF planning. However, there is need to foster the interdisciplinary research with the development of novel approaches that concurrently make use of functional and aesthetic information, and are developed in light of the clinical requirements and workflow. In this regard, it is necessary to enhance these enabling-technologies by developing advanced segmentation algorithms for CBCT imaging as well as algorithms allowing the surgeon to seamlessly interact with the surgical plan or the desired soft tissue outcome, all while jointly considering the functional and aesthetics aspects mentioned above.