Immediate postexpansion changes following the use of the transpalatal distractor

This study analyzed the immediate postexpansion positional changes of the maxillary halves resulting from the use of the transpalatal distractor (Surgi-Tec NV, Bruges, Belgium).

Corticotomies were performed in the same way as surgically assisted rapid palatal expansion, all from a buccal sulcus approach. Titanium abutment plates with box extension were placed horizontally in the vertical wall of the palatal vault overlying the second premolar root through a mucoperiosteal incision and fixed with titanium screws 5 mm in length. An appropriate telescopic distraction module was fitted in the slots of the boxes. Expansion started 1 week after surgery, at a rate of 0.33 mm/d. Digital measurements on digital photographs of the models were obtained from 20 postadolescent patients before and immediately after transpalatal distraction. The distractor was placed at the level of the second premolar. Pterygomaxillary separation was not performed. Changes in the intercanine, interpremolar and intermolar width, in the dental arch perimeter, and in the premolar and molar angulations in the frontal plane were analyzed and correlated.

Width expansions of 35.7%, 31.7%, and 22.7% were noted in the canine, premolar, and molar regions, respectively. There was a mean increase of the arch perimeter of 10.5%, which correlated well (P <.001) with the expansion at the canine and premolar level. The mean angulation changes in the frontal plane of the premolar and molar segments were minimal, -8.3 degrees +/- 9.6 degrees and 0.9 degrees +/- 9.9 degrees, respectively. The change in angulation at the molar level correlated (P <.005) with the amount of expansion in that region. Premolar angulation did not correlate with the expansion, and segment angulation did not correlate with age.

The expansion at the canine level was 1.5 times greater than at the molar level (corrected value relative to the original intermolar width). The change in arch perimeter can be predicted from the expansion at the canine and premolar level. Expansion in the frontal plane occurs with little tipping of the segments.