Changes in lip and cheek pressure due to simulated maxillary dental arch expansion

Changes in labial and buccal soft tissue pressure are considered to affect the post-treatment stability of dental arch expansion. The purpose of the present study was to investigate changes in lip and cheek pressure in simulated maxillary dental arch expansion using a hydraulic capillary infusion system. Thirteen subjects (8 males and 5 females, mean age 27.7 ± 2.7 years) with normal occlusion were examined. Manometric catheters connected to pressure transducers were mounted on intra-oral stents of 0.7 mm thickness. The areas measured were the right and left maxillary central incisors, canines, and first molars. Three types of stents were fabricated with 3.0 mm and 5.5 mm thickness for simulation of anterior expansion, lateral expansion, and combined anterior and lateral expansion. The results showed that in all areas, lip and cheek pressure significantly increased with an increase in the thickness of the stent. At all stent thicknesses, the canine area showed significantly higher pressure than the other areas. In expansions of both 0.7–3.0 mm and 0.7–5.5 mm, the combined expansion showed lower pressure than the anterior or lateral expansion alone in all areas of the dental arch. These results suggest that combined anterior and lateral expansion may be more advantageous for post-treatment stability than anterior expansion or lateral expansion alone performed to create space for tooth alignment.