Patient-specific pre-operative simulation of the surgically assisted rapid maxillary expansion using finite element method and Latin hypercube sampling: workflow and first clinical results.

Asymmetric distraction with different expansions of left and right maxillary parts is a serious complication of surgically assisted rapid maxillary expansion. An individual, highly standardized surgical intervention based on three-dimensional finite element analysis (FEA) is a new method to improve the quality of therapy. We describe a fundamental simulation-based workflow for preoperative evaluation of the osteotomies in a pilot study to achieve symmetry. A CT scan of the skull was used for analysis. Many feasible osteotomy configurations were generated and optimized using Latin hypercube sampling method and FEA choosing an individual osteotomy and maxillary movement. We successfully applied this workflow to 14 patients with symmetrical distraction.

Experimental study on the influence of model variations on the airway occlusion of an obstructive sleep apnea patient.

This study deals with the analysis of model parameters to mimic the airway collapse of an obstructive sleep apnea patient during nasal breathing. Different material properties and geometry variations of a patient-specific airway model are analyzed in detail. The patient-specific airway geometry is obtained from MRI data. A completely rigid model is compared to two partly elastic variations with different elasticities. Furthermore, the influence of the nasal cavities and the treatment effect of a mandibular protrusion are studied. Rigid model parts are 3D-printed and elastic parts cast from silicone. The models are analyzed under the impact of a transient airflow which is realized through a computer controlled piston pump. The results suggest, that, for moderate deformations, the elasticity of the soft tissue replicate influences rather the level of the pressure drop inside the airway than the shape of the pressure curve. The same suggestion can be made for the influence of the nasal cavities. Often, the spatial location of the minimum pressure is taken as the collapse site of the airway geometry. This study demonstrates, that the spatial locations of the minimum pressure and the maximum deformation do not match. This reveals the importance of a coupled approach of soft tissue and airflow analysis in the search of the collapse site and therefore the best treatment option. A treatment effect of the mandibular protrusion can be anticipated with an accurate patient-specific airway model.

Evaluation of symmetry behavior of surgically assisted rapid maxillary expansion with simulation-driven targeted bone weakening.

OBJECTIVES: Surgically assisted rapid maxillary expansion (SARME) is a treatment modality to overcome maxillary constrictions. During the procedure of transverse expansion, unwanted asymmetries can occur. This retrospective study investigates the transverse expansion behavior of the maxilla utilizing a simulation-driven SARME with targeted bone weakening. MATERIALS AND METHODS: Cone beam computer tomographies of 21 patients before (T1) and 4 months after treatment (T2) with simulation-driven SARME combined with a transpalatal distractor (TPD) and targeted bone weakening were superimposed. The movements of the left, right, and frontal segments were evaluated at the modified WALA ridge, mid root level, and at the root tip of all upper teeth. Linear and angular measurements were performed to detect dentoalveolar changes. RESULTS: Dentoalveolar changes were unavoidable, and buccal tipping of the premolars (6.1° ± 5.0°) was significant (p < 0.05). Transverse expansion in premolar region was higher (6.13 ± 4.63mm) than that in the molar region (4.20 ± 4.64mm). Expansion of left and right segments did not differ significantly (p > 0.05). CONCLUSION: Simulation-driven SARME with targeted bone weakening is effective to achieve symmetrical expansion in the transverse plane. CLINICAL RELEVANCE: Simulation-driven targeted bone weakening is a novel method for SARME to achieve symmetric expansion. Dental side effects cannot be prohibited.