RESUMEN
Objective:To evaluate the therapeutic effects of orthodontic therapy with mandibular first molar extraction.Methods:77 cases of malocclusion were divided into 3 groups:Bilateral mandibular first premolar extraction group(A,30 cases),unilateral man-dibular first molar extraction group(B,27cases)and bilateral mandibular first molar extraction group(C,20 cases).The OGS indexes were measured before and after orthodontic treatment and statistically analysed.Results:Remarkable occlusal improvement was seen in all three groups after treatment(P0.05).OGS indexes among the three groups after treatment were significantly different(P<0.05).The improvement in group A was more significant than that in group C(P<0.01)and the improvement in group C was more significant than that in group B(P<0.01). Conclusion:Orthodontic therapy with bilateral mandibular first molar extraction is effective in orthodontic treatment of malocclusion, but is not as effective as that with bilateral mandibular first premolar extraction.