A Study of the Treatment Effects of Different Types of Orthodontic Devices on the Growth and Development of the Palate

In modern orthodontics treatment, mix dentition patients who have narrow maxillary dental arch width are treated by lateral expansion treatment of dental arch. Maxillary lateral expansion treatment can increase the width diameter of the dental arch and palatal width diameter. However, changes in the morphology of the palatal basal region due to expansion treatment have not been evaluated. First, we carried out an investigation of long-term growth changes in palatal morphology in the general Japanese population. Additionally, in the patients who were treated by expansion, we compared the effects of expansion with different types of expansion devices. Longitudinal records（34 study casts, 6 to 12 years of age）were classified according to growth stage（T1: early mixed dentition, T2: middle mixed dentition, and T3: late mixed dentition or permanent dentition）. A line drawn perpendicularly from the reference plane to the palatal basal region was divided into 10 sections, and the palatal width was measured in each region. Palatal widths were set at deep area（DA）, middle area（MA）, and shallow area（SA）. Comparison of the palatal width（three regions）between Rapid maxillary expansion （RME N=15）and Slow maxillary expansion（SME N=15）were evaluated same methods as above. DA and the Palatal depth were significantly smaller at T1 than T2 and at T2 than T3, respectively（both p <0.05）. The SA changed significantly less from T2 to T3 than did the DA（p <0.01）. Although, in DA, expansion amount was significant difference between RME and SME, there were not significant difference in SA. The growth amount of palatal width was different between the DA and the SA. RME was expanded greater in DA than SME.