Instability of palatal rugae following rapid maxillary expansion

Existing evidence on changes of the palatal rugae following rapid maxillary expansion (RME) is scarce and inconclusive, particularly immediate post-expansion changes in three-dimensional assessments.

Our aims were to assess the dimensional stability of the palatal rugae in the antero-posterior and transverse dimensions following RME treatment, as well as the three-dimensional changes in palatal volume and area.

The sample consisted of the dental casts of 30 adolescents (16 males; 14 females, age 11.46 ± 1.42 years) who underwent RME. The models, available at T1 (pretreatment) and T2 (immediately after expansion) were scanned using a laser scanning system. Various parameters were recorded including individual ruga transverse and antero-posterior linear and angular measurements; palatal dimensions (width, length, volume, surface area, vault depth/height); and dental characteristics (interincisor, intercanine, interpremolar, and intermolar distances). Statistical analyses included paired t-tests for group comparisons, and Pearson moment product for associations among variables.

Palatal rugae were altered by RME in all dimensions in both linear and angular measurements, almost equally on right and left sides, albeit the average linear changes were about 1 mm. Correlation coefficients among rugal and dental measures suggested an association between rugae changes and the underlying bony movements. Except for the first rugae that had higher correlations to the intercanine width, the correspondence of changes seems to be asymmetric, thus not precisely predictable.

The results suggest a variable trend in the rugae response to expansion, likely reflecting the constitutional asymmetric pattern or nature of pairs of rugae.