Correlation Between Microimplant-Assisted Rapid Palatal Expansion Effectiveness And Mid-Facial Geometric Morphology

Objectives:Microimplant-assisted rapid palatal expansion(MARPE)is an effective technology to correct the maxillary transverse deficiency(MTD)in patients with advanced bone maturation.Studies have shown that the MARPE effectiveness may be related to differences in craniofacial structures.This project intended to preliminarily investigate the correlation between the midfacial morphology and the MARPE effectiveness by geometric morphometrics(GM).And to improve the accuracy of diagnosis,assist in judging the effect of MARPE,and provide guidance for the selection of treatment objectives.Materials:CBCT scans of 44 subjects(22.7±5.8 years)treated with MARPE at the Department of Orthodontics,Stomatology Hospital of Shandong University were obtained before and after treatment.The maxillary expansion ratio(MER)was defined as the ratio of maxillary expansion width to the MARPE jackscrew expansion width and it was used to evaluate the MARPE effectiveness.The subjects were divided into two groups by the MARPE effectiveness:the high maxillary expansion ratio(HMER)group and the low maxillary expansion ratio(LMER)group.Landmarks and semi-landmarks were digitized on mid-face by four aspects of the morphology:zygomatic process,zygomatic bone,nasal and alveolar dataset.Generalized Procrustes analysis and principal component analysis were performed to remove information other than shape and reveal the main patterns of shape variation.The shape and size differences between the two groups were analyzed by Procrustes analysis of variance,respectively.The influences of size differences on shape analysis were evaluated finally.Results:1.The success rate of the MARPE treatment in this study was 90.9%.The maxillary expansion ratio did not conform to a normal distribution.The mean value of the maxillary expansion ratio was 39.77%±20.99%(range:2.88%-94.33%,median:35.86%).2.There were no statistical size differences between the HMER and LMER group in each dataset(P>0.05).3.A statistical difference was found in the shape of zygomatic process between the two groups(P<0.05).The principal component 1(PC1)explained 39.37%of the total variance and showed variability was mainly manifested in the length of the zygomatic process,which described the most crucial variance statistical difference in the shape of the zygomatic process.The principal component 2(PC2)explained 15.03%of the total variance and showed variability was mainly manifested in the diameter and the curvature of the zygomatic process.Subjects in the HMER group presented slender and straight zygomatic processes.4.The shape of the zygomatic bone and nasal region was correlated with the size(P<0.01;P<0.001).The shape variation of the zygomatic process was independent of size,thus,the shape differences between groups were not due to differences in size(P>0.05).Conclusions:1.Mid-facial morphology,especially the shape of the zygomatic process may influence the MARPE effectiveness in patients with advanced bone maturation.Patients with long,slender and straight zygomatic processes may be prone to have a better effect of MARPE.2.The shape of the zygomatic bone and the maxilla were not correlated with the MARPE effectiveness.3.The size of the zygomatic process,zygomatic bone and maxilla were not correlated with the MARPE effectiveness.