Circumaxillary Suture Stain during Midpalatal Suture Opening and Maxillary Protraction

Objective: Midpalatal suture expansion has been proposed as useful to assist maxillary protraction in preadolescent patients with maxillary deficiency despite a lack of direct mechanical data. This study measured mechanical strain (deformation) in several circumaxillary sutures caused by maxillary protraction before and after midpalatal suture opening (MSO).

Method: Six fresh skulls of 1-month old piglets (equivalent to human preadolescent age) were used. Strain gages were implanted at the surface of 5 circumaxillary (MZ: maxillary-zygomatic; MP: maxillary-premaxillary; ML: maxillary-lacrimal; ZT: zygomatic-temporal; IN, internasal) sutures. Through arms anchored on maxillary molars, maxillary protraction was performed by using varied force levels (100, 250 and 500g) generated by latex elastics. Midpalatal suture opening was achieved by inserting metal shims with standardized thickness (1-5mm) into this suture. Circumaxillary suture strains were recorded during maxillary protraction and MSO. Strain changes with protraction force level and MSO amount were compared by repeated measures ANOVA.

Result: When isolated effect was considered, maxillary protraction produced compressive and tensile strains at the MP and MZ sutures, respectively, both of which increased significantly (p<0.05) with protraction force level but decreased significantly (p<0.05) with the amount of pre-protraction MSO  (p<0.05). MSO alone caused tensile and compressive strains at the MP and MZ sutures, respectively, both of which increased  significantly with the amount of MSO (p<0.05). When strain changes relative to initial baselines (pre-MSO and pre-protraction) were considered, strains at the MP and MZ sutures were dominated by MSO-generated strains (tensile and compressive, respectively) with lessening effects from maxillary protraction. Generally, strains in the other three sutures tested were smaller than the MP and MZ sutures.

Conclusion: Compared to maxillary protraction, opening of the midpalatal suture generates stronger but opposite strains at anterior and posterior circumaxillary sutures, suggesting that the immediate mechanical effect caused by midpalatal suture opening may counteract maxillary protraction mechanics.