Keys to Class II Correction: A Comparison of Two Extraction Protocols
MetadataShow full item record
Purpose: To evaluate the effects of two different extraction patterns on incisor and molar movements in growing Class II Division 1 patients. Materials and Methods: The treated sample included 54 patients 10 to 17 years of age treated by two private practice orthodontists using Tweed mechanics, headgears, class II elastics or safe springs. The sample was divided based on having either the mandibular first premolars (4/4) or mandibular second premolars (4/5) extracted. Each group included 27 patients. Treatment lasted 2.8 ± 0.60 years and 2.6 ± 0.54 years for the 4/4 and 4/5 groups, respectively. Pre- and post-treatment lateral cephalograms and models were evaluated. Cranial base, mandibular and maxillary superimpositions were performed to quantify vertical and horizontal tooth movements and displacements. Results: There were no statistically significant pre-treatment between-group differences in SNA, SNB, ANB, MPA, or crowding. There was statistically significant (p<.05) differences in pre-treatment IMPA, L1:NB, and L1:APvo. Extraction of mandibular first premolars produced greater (1.6 mm) lower incisor retraction than extraction of second mandibular premolars. The mandibular first molar protracted significantly more (0.74 mm) when second premolars were extracted than when first premolars were extracted. The within-group changes in MPA, the between-group differences in the changes in MPA, and the amount of vertical eruption of the maxillary and mandibular molars were not significantly different between the two extraction patterns. Conclusions: Extraction of lower second premolars enhances Class II correction. Compared to the first premolar extractions, mandibular second premolar extractions produce greater mesial movement of the mandibular first molar and less distal movement of the mandibular incisors. Neither first or second premolar extractions have an effect on the mandibular plane angle or the vertical dimension.
George, Sarah Marie (2018). Keys to Class II Correction: A Comparison of Two Extraction Protocols. Master's thesis, Texas A&M University. Available electronically from