It is well documented in the literature that a contracted maxilla is commonly associated with nasal obstruction. Midpalatal splitting using the rapid maxillary expansion (RME) technique produces separation of the maxillary halves with consequent widening of the nasal cavity. Although clinicians agree about many of the indications for and outcomes of RME, some disagreements persist in relation to the biomechanical effects induced. The present research was based on the parametric analysis of a finite element model (FEM) of a dry human skull with the RME appliance cemented in place in order to evaluate these effects on the overall craniofacial complex with different suture ossification. The behaviour of the FEM was compared with the findings of a clinical study and to an in vitro experiment of the same dry skull. Comparisons refer to the opening pattern and associated displacements of four anatomical points located at the left and right maxilla (MI, UM, EM, CN). It was found that the maxillolacrymal, the frontomaxillary, the nasomaxillary, the transverse midpalatal sutures, and the suture between the maxilla and pterygoid process of the sphenoid bone did not influence the outcome of RME, while the zygomatico-maxillary suture influenced the response of the craniofacial complex to the expansion forces. Moreover, the sagittal suture at the level of the frontal part of the midpalatal suture plays an important role in the degree and manner of maxillary separation. Maximum displacements were observed in the area of maxilla below the hard palate, from the central incisors to second premolars, which dissipated at the frontal and parietal bone and nullified at the occipital bone.

This paper discusses several aspects related to the development of a reliable finite element model to simulate the craniofacial changes during rapid maxillary expansion treatment. The mechanical model concerns the entire human skull (bony structure and sutures) as well as the jackscrew device; the latter transforms the manual openings into orthodontic forces usually applied to the two maxillary halves through the first premolars and first permanent molars, which are the support points of the appliance. A sensitivity analysis of an approximate finite element model is performed in order to investigate the influence of the model size, the influence of the degree of sutural ossification by assigning different mechanical properties to the sutures and the influence of bone relaxation concerning the effects of dentofacial orthopaedics. Moreover, a more accurate model including the aforementioned teeth and their periodontal ligament as solid elastic structures was analysed in order to evaluate the orthodontic effects induced. Results refer to the opening pattern and associated stresses/displacements/strains on the cranium, the maxillae and the periodontal ligament.