OBJECTIVETo establish a model of cephalometric variables for identification of indication of early treatment of class III malocclusion in mixed dentition.

METHODSCephalograms taken in the mixed dentition were available for twenty-eight patients (16 males, 12 females, mean age: 9.1 +/- 1.4 years) in early treatment group and twenty-one patients (12 males, 9 females, mean age: 10.0 +/- 2.0 years) in orthognathic surgery group. Patients in early treatment group received successful treatment to correct anterior crossbites in mixed dentition and later received non-extraction comprehensive treatment in permanent dentition. Patients in orthognathic surgery group received orthognathic surgery after growth ceased.

RESULTSThe mean value of AB-MP in early treatment and orthognathic surgery groups was 65.1 degrees and 61.2 degrees, respectively (P < 0.05). The mean value of the angle between upper incisor inclination and AB line was 23.1 degrees in early treatment group and 27.3 degrees in orthognathic surgery group (P < 0.05).

CONCLUSIONSThe resulting equation was: individual score (IS) = 0.164 x (AB-MP)-0.15 x (U1-AB)-6.675. When IS > 0, greater success in early treatment of class III malocclusion in mixed dentition was expected and when IS < 0, delayed treatment with orthognathic surgery is recommended.