An evaluation of pulp cavity/chamber volume and shape changes after maxillary expansion performed with tooth-borne versus bone-borne expander. A CBCT short term study using surfacebased superimposition and deviation analysis

Aim: The effect of rapid palatal expansion, and in general of orthodontic forces, on the dentin-pulp complex is as yet unclear. There is evidence that orthodontic forces induce neurogenic inflammation, mediated by neuropeptides, that causes alteration of the pulpal blood flow and hyperemia. Until today the pulp tissue has been analyzed through inspection of histological material and assessment of the pulpal respiration rate. Also, panoramic or periapical radiographs have been used to assess the pulp cavity/ chamber size with their intrinsic limitations related to two-dimensional (2D) images analyses of threedimensional (3D) morphological changes of the pulp cavity. The aim of the study was to compare volume and shape changes of pulp cavity/chamber of maxillary posterior teeth between tooth-borne and bone-borne maxillary expansion in adolescents. Methods: This retrospective study included 36 adolescents with bilateral maxillary crossbite who received tooth-borne rapid maxillary expansion (TB group, average age: 14.4 years) or bone-borne rapid maxillary expansion (BB group, average age: 14.7 years). Cone-beam computed tomography (CBCT) were taken before treatment (T1) and after a 6-month retention period (T2). Volumetric and shape changes of pulp cavity/chamber of maxillary first molars, first and second premolars were detected by referring to a specific 3D digital technology involving surface-based registration of CBCT scans at T1 and T2 and deviation analysis of CBCT-derived models of pulp cavity/ chamber. Unpaired Student’s t test was used to 1) compare T1 and T2 volumes of pulp cavities in TB and BB groups, 2) assess if there were differences between the two groups in the post-treatment volumetric changes and in the percentage of matching of 3D pulp models. Results: All investigated teeth showed a reduction of pulp volume, being this difference statistically significant for the upper first molars in the TB and BB groups and for the upper first and second premolars in the TB groups (p<0.05). This volumetric reduction was significantly greater in the TB group, also subjects in the TB group showed a lower percentage of matching between T1 and T2 pulp models compare to BB group (p<0.05). The area most affected by shape change was that of pulp horns. Conclusions: When tooth-borne expander is used, rapid maxillary expansion could induce a higher volumetric reduction of pulp cavity/chamber of posterior teeth compared to bone-borne expander, in the short-term.