Stability of skeletal, alveolar, and dental components in microimplant-supported Midfacial Skeletal Expander (MSE) expansion

Maxillary transverse deficiency is one of the most common skeletal problems in the craniofacial region. Rapid palatal expansion (RPE) has been the preferred standard treatment when transverse deficit is present, especially in young patients. While the main goal of RPE is to split the midpalatal suture, the circum-maxillary sutures are also affected and alveolar bone bending, and dental tipping are common. The desire is to produce a greater skeletal effect than dentoalveolar side-effects; however, the latter are commonly expressed in substantive magnitude. In order to assess skeletal expansion, alveolar bone bending and dental tipping after maxillary expansion, linear and angular measurements has been performed utilizing different craniofacial references. Since the expansion with Midfacial Skeletal Expander (MSE) is archial in nature, the aim of this paper is to quantify the differential components of MSE expansion using an angular measurement system described in a previous study, and assessing the stability of each component after orthodontic treatment. Methods: A total of fourteen subjects with a mean age of 20.4 � 3.5 years were treated with MSE. Pre-expansion (T0), post-expansion (T1), and post-treatment (T2) CBCT records were superimposed and compared. Based on methods in a previous study, the rotational fulcrum of the zygomaticomaxillary complex were identified and angular measurements were generated to assess changes of the zygomaticomaxillary complex (skeletal expansion), dentoalveolar bone (alveolar bone bending), and maxillary first molars (dental tipping). The stability of all three components after orthodontic treatment were also assessed by comparing measurements between post-expansion and post-treatment. Results: Immediately following MSE expansion, angular measurements showed that skeletal expansion accounted for 87.50% and 88.56% of total expansion, alveolar bone bending for 7.09% and 5.23%, and dental tipping for 5.41% and 6.21% on the right and left sides, respectively. At the end of orthodontic treatment, data showed that skeletal expansion relapsed by 11.20% and 13.28% on the right and left sides, respectively. Changes in alveolar bone bending and dental tipping between post-expansion and post-treatment varied greatly due to orthodontic dental decompensation after expansion. Conclusions: Maxillary skeletal expansion using the microimplant-supported Midfacial Skeletal Expander (MSE) produces mainly skeletal changes with insignificant dentoalveolar changes immediately after expansion. In the long term, the majority of the skeletal expansion was maintained. Long-term dentoalveolar changes were in the magnitude of 300-1500% in the opposite direction, induced by orthodontic decompensation of the pre-existing dental compensation. However, net gains in the intermolar width were maintained despite these changes due to the long-term stability of skeletal expansion