A Study For The Extraction Decision Classâ…¡, Division 1 Malocclusion

Objective: This retrospective study was designed to observe correlativefactors which has influenced on extraction decision in Classâ…¡,Division 1malocclusion with the investigating of the outcome of orthodontic treatment,provided a help in clinical treatment planning. Methods: The sample consisted143 children which were in early permanent dentition of Classâ…¡,Division 1malocclusion .Pre-and post-treatment study models were assessed using PeerAssessment Rating (PAR) index. According to the outcome of treatment, thesecases were classified into three types as "worse, no different", "improved"and"greatly improved". The cephalometric analysis and Model Analysis werepreformed with pretreatment lateral cephalograms and study models for"improved"and "greatly improved"cases. "T"–test was assessed to find out thesignificant difference between the extraction and nonextraction, and the resultsincluding age factor were analyzed by stepwise discriminant analysis.Results: Among of these 143 patients, 120 were improved or greatly improvedby PAR. And the significant different items between extraction and nonextractionin morphology were found in (1) hard-tissue: SNB, ANB, NA-PA, Npg-FH,Go-Pog, Ptm-S, FMIA, U1-L1 and U1-Apgmm. (2) soft-tissue: upper lipthickness, the length of the lower lip and chin-lip groove thickness. (3) models:the tooth crowd degree, the depth of Spee curve, overjet, the width of maxillaryand mandibular middle and posterior arch and the length of maxillary middlearch. A discriminate function, Z=0.952X₁(lower tooth crowd degree) +0.591X₂(U1-Apgmm) –0.430X₃(upper lip thickness) was produced by multiplefactorial discrminate analysis. Z≥0 is an indication of extraction ,and Z<0 is anindication of nonextraction on the other side. Conclusion: After any kind oforthodontic treatment for the malocclusion, the relationship of denti-occlusionand craniofacial skeleton should be harmonious, the amount of tooth and the sizeof the jaw should be matched, and the arch and oral muscle should be equilibriumin the same. The results showed that the lower tooth crowd degree, protrusion ofthe maxillary incisor and upper lip thickness were keys to decide weatherextraction or not getting rid of the influence of subjective factors.