Inside Dentistry
March 2009
Volume 5, Issue 3

Relapse of Anterior Crowding in Patients Treated with Extraction and Nonextraction of Premolars

Howard E. Strassler, DMD

Erdinc AE, Nanda RS, Isiksal E. Am J Orthod Dentofacial Orthop. 2006;129(6):775-784.


Introduction: The purpose of this study was to evaluate long-term stability of incisor crowding in orthodontic patients treated with and without premolar extractions.

Methods: Dental casts and cephalometric records of 98 patients were evaluated before treatment (T1), at posttreatment (T2), and at postretention (T3). Half of the patients had been treated with extractions, and half were treated nonextraction.

Results: Irregularity, as measured by the irregularity index, decreased 5.51 mm in the extraction group and 2.38 mm in the nonextraction group. Mandibular incisor irregularity increased 0.97 mm in the extraction group and 0.99 mm in the nonextraction group, respectively, in the postretention period. Maxillary incisor irregularity relapse was smaller than mandibular incisor relapse for both groups. Intercanine width expanded during treatment. At T3, mandibular intercanine width decreased in both groups, but the differences were not statistically significant. At T3, intermolar width was stable, arch depth decreased, overbite and overjet slightly increased, SN mandibular plane angle decreased, and incisor positions in both groups tended to return to T1 values. Clinically acceptable stability was obtained.

Conclusions: With the exception of the interincisal angle, no statistically significant differences were recorded between the extraction and nonextraction groups from T2 to T3. No statistically significant correlations were found between any variables studied and mandibular incisor irregularity at T1, T2, and T3.


In general dental practices, and in the orthodontic practices of many of my colleagues, there has been an increasing number of adult patients seeking orthodontic treatment to esthetically correct crowding of the anterior teeth using clear plastic aligners. Many of these adult patients have a dental history of conventional orthodontic treatment. As adolescents, they had retainers, but when they stopped wearing the retainer, the teeth moved and were “crooked” again. They had not sought conventional orthodontic re-treatment because they were avoiding the appearance of brackets and bands on the teeth. This problem of relapse is something that we, as clinicians, see over and over again. Almost 10 years ago, I read a 40-year retrospective study by Little, who reviewed more than 800 sets of patient records to assess stability and relapse of orthodontic treatment.1 All of these patients had completed treatment 10 or more years before the last set of data. The results stated that arch length decreased after orthodontic treatment, arch width across the mandibular canines typically reduced posttreatment, and mandibular anterior crowding during the posttreatment (retention) phase lasted well into the 20–40 years of age range. Additionally, third molar absence or presence seemed to have little effect on the occurrence or degree of relapse and, most importantly, the degree of postretention anterior crowding was both unpredictable and variable. No pretreatment variables seemed to be useful predictors of outcome.

In 2004, Freitas and coworkers reported that when relapse of mandibular anterior crowding was assessed, and associations between this relapse and other clinical factors were also investigated, no clinical factor studied was predictive of crowding relapse in the long term.2

The two more-recent studies presented here provide important insight to the clinician referring a patient for orthodontic treatment to correct mandibular crowding or other malocclusions. The fact that neither extraction nor nonextraction of premolars is a predictor of relapse of mandi-bular crowding makes the decision more difficult. Will there be spacing left after treatment is completed, and will the spacing make postretention more of a challenge? The systematic review by Bonde-mark and coworkers provided an extensive investigation of over 1,000 abstracts or full-text articles with rigorous inclusion criteria. Of these, only 38 met the inclusion criteria. However, in the comment on the review, O’Neill concluded that the scientific evidence was insufficient to draw conclusions about the treatment of cross-bite, angle-class III, open-bite, and various other malocclusions, or about long-term patient satisfaction.3 More importantly, the evidence points to the fact that despite a large number of studies on long-term stability after orthodontic treatment, this systematic review shows that evidence-based conclusions are few. This is mostly because of inherent problems with retrospective reviews and inferior study design. There is a great need for well-designed, prospective studies with untreated control groups, sufficient sample sizes, and sample selection according to type of malocclusion, age, and growth pattern. Also, in recent years, knowing the prevalence of postretention changes in mandibular crowding, the use of fixed orthodontic retention using adhesives and a variety of bonded wires, retainers, and fiber ribbons has become a standard of care to prevent relapse of crowded mandibular arches.


1. Little RM. Stability and relapse of mandibular anterior alignment: University of Washington Studes. Semin Orthod. 1999;5(3):191-204.

2. Freitas KM, de Freitas MR, Henriques JF, et al. Postretention relapse of mandibular anterior crowding in patients treated without mandibular premolar extraction. Am J Orthod Dentofacial Orthop. 2004;125(4):480-487.

3. O’Neill J. Long-term stability after orthodontic treatment remains inconclusive. Evidence Based Dent. 2007;8(3): 81-82.

About the Author

Howard E. Strassler, DMD
Professor and Director of Operative Dentistry
Department of Endodontics, Prosthodontics, and Operative Dentistry
University of Maryland Dental School
Baltimore, Maryland

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