Characteristics of dentoskeletal morphology and treatment changes in 2-maxillary premolar extraction: A comparison with 4-premolar extraction

Abstract

BackgroundThe present study aimed to clarify the characteristics of dentoskeletal morphology and treatment changes after 2-maxillary premolar extractions to treat Class II malocclusion, by comparing pre- and post-treatment lateral cephalograms and dental casts from cases with 4-premolar extractions. MethodsSubjects comprised patients who had undergone orthodontic treatment for Class II molar relationship using either maxillary first premolar extraction (U2 group, n = 27) or maxillary and mandibular first premolar extraction (UL4 group, n = 27). Pretreatment (T1) and post-treatment (T2) lateral cephalograms and dental casts were examined. Groups were compared for differences at T1 and T2, and in T2–T1 change using unpaired t tests. Among the analysis items showing significant differences at T1, those that could discriminate between groups U2 and UL4 at T1 were extracted by stepwise logistic regression analysis. ResultsDentoskeletal morphology in the U2 group exhibited a severe Class II molar relationship, little need for maxillary incisor retraction, and a morphology in which bite opening was severe. Treatment changes in the U2 group showed that extraction spaces were used for mesial movement of maxillary molars in many cases, that bite-opening resulted from mandibular clockwise rotation, and that contraction of the upper arch and expansion of the lower arch occurred in anteroposterior and lateral directions. Severity of Class II molar relationship, anteroposterior position of mandibular incisors, and lower arch depth were selected as criteria for distinguishing pretreatment between groups U2 and UL4. ConclusionCases with 2-maxillary premolar extraction showed a characteristic dentoskeletal morphology compared to cases with 4-premolar extraction.