Displacement and stress distribution by different bone-borne palatal expanders with facemask: A 3-dimensional finite element analysis.

INTRODUCTION

The purpose of this study was to analyze displacement and stress distribution in the maxilla during maxillary expansion followed by protraction using bone-borne and conventional tooth-borne palatal expanders and a facemask via 3-dimensional finite element analysis.

METHODS

A finite element model of an adolescent skull was created, and 4 different types of appliances were integrated into it: facemask (type A); facemask with paramedian bone-borne expander (type B), facemask with palatal-slope bone-borne expander (type C), and facemask with conventional expander (type D). Expansion of 0.25 mm followed by 500 g of force per side was applied.

RESULTS

Type A showed anterior displacement of the dentition combined with downward displacement of posterior teeth and upward displacement of anterior teeth. The combination of protraction and expansion in type D showed the greatest anterior displacement. In types B and C, the expansion forces resulted in posterior displacement decreasing the net displacement of the combination. Stresses concentrated around the miniscrews in types B and C. In types A and D, stresses concentrated at the first premolar and first molar. Type B had the highest stresses followed by type C and then D.

CONCLUSIONS

The conventional tooth-borne expander (type D) enhanced the effect of maxillary protraction. Facemask alone (type A) resulted in more anterior displacement of the maxilla than the combination of facemask and bone-borne expanders (types B and C). The clinician should be aware of the initial stresses and movements from different expanders with facemask found in this study and confirm the movements in future clinical Class III studies.