Original article
Keys to Class II correction: A comparison of 2 extraction protocols

https://doi.org/10.1016/j.ajodo.2020.01.018Get rights and content

Highlights

  • Extraction of mandibular second premolars enhances Class II molar correction.

  • Mandibular second premolar extraction produces less distal incisor movement.

  • Both 4/4 and 4/5 extractions do not affect MPA or vertical dimension.

Introduction

The purpose of this study was to evaluate the effects of 2 extraction patterns on incisor and molar movements in patients with growing Class II Division 1.

Methods

The sample included 54 patients 10-17 years of age treated by 2 private practice orthodontists using Tweed directional force mechanics, 4 premolar extractions, J-hook headgears, and Class II elastics or Saif springs. The sample was divided on the basis of having maxillary and mandibular first premolars (4/4) or maxillary first and 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. Pretreatment (T1) and posttreatment lateral cephalograms and dental casts were evaluated. Cranial base, mandibular, and maxillary superimpositions were performed to quantify tooth movements and displacements.

Results

There were no statistically significant T1 between-group differences in crowding or in the SNA, SNB, ANB, and MPA angles. Analyses of covariance, controlling for statistically significant (P <0.05) differences in T1 mandibular incisor position, showed that mandibular first premolars extractions produced greater (1.6 mm) mandibular incisor retraction than second premolar extractions. The mandibular first molars were protracted significantly more (0.7 mm) after the second premolar than the first premolar extractions. Within-group changes of the MPA, 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 2 extraction patterns.

Conclusions

Extraction of mandibular second premolars enhances Class II molar correction, with greater mesial first molar movement and less distal incisor movement. Neither extraction pattern has an effect on the MPA or the vertical dimension (ie, there was no “wedge effect”).

Section snippets

Material and methods

The sample includes 54 growing extraction patients treated by 2 private practice orthodontists. The treatment mechanics used included Tweed directional force mechanics, headgears, and Class II elastics or Saif springs. Archwires and sometimes headgears were used to derotate the maxillary first molars. Sliding and frictionless (closing loops) mechanics were used for space closure on a 19 × 25-in stainless steel archwire. High-pull J-hook headgears were used to retract maxillary anterior teeth.

Results

There were no statistically significant T1 between-group differences for SNA, SNB, ANB, MPA, maxillary TSALD, and mandibular TSALD (Table II). Both treatment groups exhibited Class II maxillomandibular relationships (ANB, 5.52°) and normodivergent (MPA, 34.5°) skeletal patterns. There were statistically significant (P <0.05) differences in IMPA, L1:NB, and L1:Apg at T1.

The SNA, SNB, ANB, and MPA angles showed no statistically significant between-group treatment differences in the treatment

Discussion

Historically, the teeth most commonly extracted for orthodontic treatment have been the 4 first premolars. Maxillary and mandibular first premolars extractions are recommended in patients with Class II Division 1 malocclusion with protrusive lips.13 Nance14 was among the first to suggest extracting second premolars to limit incisor and lip retraction. Second premolar extractions provide an alternative in patients with mild crowding, acceptable incisor position, and relatively acceptable

Conclusions

This study evaluated horizontal and vertical incisor and molar movements in normodivergent patients with Class II Division I malocclusion with 4/4 or 4/5 extraction patterns. The following conclusions can be drawn:

  • 1.

    The mandibular incisors are retracted significantly more after mandibular first than mandibular second premolar extractions.

  • 2.

    The mandibular first molars migrate mesially significantly more after mandibular second than mandibular first premolar extractions.

Neither extraction pattern

Acknowlegments

The authors thank Drs Jimmy Boley and James L. Vaden for providing the patients.

References (45)

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All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported.

This research was partially funded by the Robert E. Gaylord Endowed Chair in Orthodontics.

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