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Stability and relapse: early treatment of arch length deficiency.

Nearly 5 decades ago, the faculty of the Department of Orthodontics at the University of Washington began collecting postretention records for patients treated in their private practices and at the University's orthodontic clinic. This collection has grown to over 850 sets of records, the study of which has molded our diagnostic, treatment-planning, and retention strategies. Others have done parallel research, efforts we applaud, and from which we continue to learn. Our clinically based hypotheses have been tested, sometimes altered or even abandoned because of these data.

We have been encouraged and sometimes discouraged by our own findings for cases treated in the full permanent dentition. (1) Advocates of earlier intervention have been as enthusiastic as its opponents. However, it is incumbent on all to test their opinions with data--long-term postretention data.


What is the treatment of choice for a preadolescent patient with arch length deficiency? What if nothing is done? What if the arches are enlarged to accommodate the permanent teeth? What if premolars are extracted early (serial extraction) followed by full treatment plus retention? What if arch length is preserved in the mixed dentition to accommodate the future permanent successors?


Coenraad Moorrees, (2) in his classic 1959 textbook, reported serial changes in dental arch dimensions of untreated subjects with malocclusion. He showed that arch length typically decreases with time from the mixed dentition through the transitional dentition and into early adulthood. He shocked readers by demonstrating that arch length at age 5 is greater than at age 18! With canine eruption, arch width typically reaches a maximum in the preteen years, followed by a slow, persistent reduction over at least the next decade. Parents (and often dental practitioners) might have a problem with these concepts because the child obviously grows throughout these years, and one would logically assume that the arch would enlarge as well. Unfortunately, the arches tend to constrict in anteroposterior and transverse dimensions, leading to further crowding of an already inadequate dental arch. In our studies, we found that this same trend is evident in untreated normal subjects as well as those with spacing pretreatment. (3, 4)

Conclusion: Without treatment, a short arch length will only get worse.


The father of dental arch enlargement had to be Edward Angle. His adage that only a complete dental arch can yield an acceptable occlusion influenced many orthodontists of that day and later. But some were skeptical then (Case and others) and later (Tweed and others). Tweed grew up professionally under the Angle cloak. Noting significant relapse after his own nonextraction enlargement therapy, he went so far as to retreat his patients with premolar extraction after the significant relapse of his Angle-style nonextraction treatment. But what if the arches are enlarged earlier?

To test the value and the efficacy of mixed dentition arch enlargement (arch development), we gathered a sample of long-term postretention records at the University of Washington. (5) As noted in the preface of that article, advocates of enlargement suggest various strategies:

1. Actively move anterior teeth labially with fixed or removable appliances.

2. Passively move anterior teeth labially by removal of lip forces.

3. Actively push molars distally by extraoral or intraoral means.

4. Widen the arch with fixed or removable devices.

5. Widen the mandibular arch by reciprocal response to maxillary arch enlargement.

6. Enlarge the dental arch with a combination of devices and means.

Twenty-six cases with records at least 6 years postretention (range, 6-23 years) were evaluated. The degree of relapse was significant and alarming. Although the cases looked clinically acceptable at the end of active treatment, the degree and severity of relapse after retention was much worse than with other strategies. In fact, these cases showed the poorest long-term results of any strategies that we have studied.

Can the arches be enlarged? Absolutely! The practitioner may even look upon this treatment as "conservative" (no permanent teeth removed). Is anterior alignment stable after removing the retainers? Unfortunately, no.

Conclusion: Without lifetime retention, the strategy of arch development will yield unacceptable results.


Our studies have shown that premolar extraction in the full permanent dentition yields variable degrees of quality, with only about 1 in 3 considered a success at 10 years postretention and even fewer at 20 years. (6,7) No pretreatment variable, such as initial crowding, gave clues as to what to expect postretention.

Serial extraction, the sequential removal of certain deciduous teeth followed by premolar extraction, logically should yield improved results. After all, the commonly noted self-improvement of anterior crowding through physiologic drift should set the stage for improved long-term stability.

A study of 30 first premolar serial extraction cases that had subsequent orthodontic treatment and retention showed results nearly identical to those treated with first premolar extraction in the full permanent dentition. (8,9) The early extraction cases became simpler during the observation stage before active treatment, but to no avail. The same ratio of one-third acceptable versus two-thirds unacceptable seemed to prevail. Second premolar serial extraction fared no better. (10)

We cannot predict which premolar extraction cases will succeed and which will fail. Whether extracted early or late, the net result is the same.

Conclusion: Serial extraction of deciduous teeth to temper a developing arch length problem followed by premolar extraction and routine treatment yields no long-term improvement over premolar extraction in the full dentition and routine treatment. Long-term retention must be part of a premolar extraction strategy whether the teeth are extracted in the mixed dentition or in the full permanent dentition.


In 1947, Hays Nance (11) taught us that there is a difference between the space occupied by the deciduous canines and molars in both arches and that needed by the succedaneous permanent canines and premolars. From G. V. Black's material from 1902, Nance learned that the mandibular arch average excess amount was 3.4 mm. He labeled this beneficial size differential "leeway space." The maximum leeway space that he measured from cases in his practice was 8 mm and the least was 0 mm. Enlarging the arch beyond this leeway he considered futile. (12) The issue is whether we can use leeway space to offset crowded anterior teeth. Misinterpreting Nance, many thought that 3.4 mm of "leeway space" had to be lost, but that was not what Nance was recommending. He encouraged exact measuring of the available and required arch lengths to determine the leeway for each patient. He recommended a passive lingual arch when the leeway space was equal to or greater than the degree of anterior crowding. Review of his own postretention records was promising with this strategy, but are cases treated in this way stable in the long term?

We had to wait 48 more years to learn the answer. Thanks to Steve Dugoni et al, (13) looking at Art Dugoni's records, we learned that leeway space could be successfully held to offset anterior crowding with excellent long-term results. They reviewed the records of 25 patients treated with a mandibular lingual arch designed to maintain but not advance all 4 mandibular incisors a minimum of 5 years postretention. All had maxillary arch 2 x 4 appliances, some combined with headgear, as needed. The mandibular deciduous molars were extracted, as needed, to facilitate eruption of the premolars. About half had circumferential supracrestal fibrotomies, and a similar number had interproximal enamel reduction.

These cases fared much better in the long term than did our premolar extraction and arch development cases. Steve Dugoni prodded us to search for records from our collection, and we found a few, all with equally great results.

Apparently, Nance had been correct; we can use the full leeway space to our advantage.

Conclusion: For mixed dentition cases in which leeway space is favorable compared with anterior crowding, use a passive lingual arch. The results appear to be quite stable.


Dick Riedel, former orthodontic chairman at the University of Washington, enjoyed describing a chance meeting at an orthodontic conference many years ago. An elderly gentleman leaned over and whispered a question to Riedel as the speaker was going on and on about Nance and his many insights. "What do you think of this Nance material?" Riedel leaned over and replied, "Nance is my hero. He had it dead right!" The old gentleman quietly said, "That's a relief. Let me introduce myself. I'm Hays Nance."

I think I'll go back and read Hays Nance once more.


1. Little R. Stability and relapse of mandibular anterior alignment. University of Washington studies. Sem Orthod. 1999;5:191-204

2. Moorrees C. The dentition of the growing child. A longitudinal study of dental development between 3 and 18 years of age. Cambridge: : Harvard University Press 1959

3. Sinclair P, Little R. Maturation of untreated normal occlusions. Am J Orthod. 1983;83:114-123 Abstract | Abstract + References | PDF (897 KB) | MEDLINE | CrossRef

4. Little R, Riedel R. Postretention evaluation of stability and relapse: mandibular arches with generalized spacing. Am J Orthod Dentofacial Orthop. 1989;95:37-41 Abstract | Full Text | PDF (248 KB) | MEDLINE | CrossRef

5. Little R, Riedel R, Stein A. Mandibular arch length increase during the mixed dentition: postretention evaluation of stability and relapse. Am J Orthod Dentofacial Orthop. 1990;97:393-404 Abstract | Full Text | PDF (1448 KB) | MEDLINE

6. Little R, Wallen T, Riedel R. Stability and relapse of mandibular anterior alignment: first premolar extraction cases treated by traditional edgewise orthodontics. Am J Orthod. 1981;80:349-365 Abstract | Abstract + References | PDF (897 KB) | MEDLINE | CrossRef

7. Little R, Riedel R, Artun J. An evaluation of changes in mandibular anterior alignment from 10 to 20 years postretention. Am J Orthod Dentofacial Orthop. 1988;93:423-428 Abstract | Full Text | PDF (99 KB) | MEDLINE | CrossRef

8. Little R, Riedel R, Engst E. Serial extraction of first premolars--postretention evaluation of stability and relapse. Angle Orthod. 1990;60:255-262 Abstract | Full Text | PDF (657 KB) | MEDLINE

9. Little R. The effects of eruption guidance and serial extraction on the developing dentition. Ped Dent. 1987;9:65-70

10. McReynolds D, Little R. Mandibular second premolar extraction--postretention evaluation of stability and relapse. Angle Orthod. 1991;61:133-144 Abstract | Full Text | PDF (657 KB) | MEDLINE

11. Nance H. The limitations of orthodontic treatment. I. Mixed dentition diagnosis and treatment. Am J Orthod Oral Surg. 1947;33:177-223

12. Nance H. The limitations of orthodontic treatment. II. Diagnosis and treatment in the permanent dentition. Am J Orthod Oral Surg. 1947;33:253-301

13. Dugoni S, Lee J, Varela J, Dugoni A. Early mixed dentition treatment: postretention evaluation of stability and relapse. Angle Orthod. 1995;65:311-320

Rresented at the International Symposium on Early Orthodonitic Treatment, February 8-10, 2002; Phoenix, Ariz.

Robert M. Little

Reprinted from: Am J Orthod Dentofacial Orthop 2002;121:578-81
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Author:Little, Robert M.
Publication:American Academy of Gnathologic Orthopedics Journal
Date:Dec 1, 2006
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