Effect of rapid maxillary expansion on the morphology of spheno-occipital synchondrosis in rats : A micro-CT study

Spheno-occipital synchondrosis (SOS) plays a significant role in the anterior growth of the midface. Orthopaedic forces acting during rapid maxillary expansion (RME) are transferred to the skull base and thus could alter the morphology of SOS. The aim of this study was to assess the influence of experimental RME on the rats' SOS by means of micro-computed tomography (micro-CT).

In all, 40 male 8‑week-old Wistar rats were enrolled into the study, among which 30 underwent experimental RME for 7, 14 and 21 days by means of custom designed spring-coil expander. Specimens were scanned by micro-CT and median palatal suture area, maxillary skeletal base and SOS width were analysed.

Experimental RME resulted in a significant increase of the median palatal suture space and maxillary skeletal base which was particularly pronounced between day 14 and 21 of expansion. SOS width increased significantly during the first 7 days at the lowest point of the synchondrosis. However, the SOS width assessed at its highest point was temporarily even decreased between days 8 and 14 of therapy.

Early SOS widening could be identified in the lowest part before median palatal suture opening. Similarly, narrowing of the SOS at its top was observed before the most significant median palatal suture expansion. Thus it can be hypothesized that changes within the SOS complex result from the transmission of the orthopaedic forces rather than from a displacement of the maxillary halves.