Leeway Space and the Resolution of
Crowding in the Mixed Dentmon
Anthony A. Gianelly
The leeway space provides adequate space to resolve crowding that is
present in the mixed dentition in the majority of individuals. This space can
be maintained by preserving arch length with a lingual arch as the primary
teeth begin to exfoliate, unless conditions such as the premature loss of a
primary canine require earlier intervention. A lip bumper can also be in-
serted after the eruption of the first premolars to preserve arch length.
Copyright © 1995 by W.B. Saunders Company
common problem resolved by orthodontic
treatment. To align a crowded dentition, space
is necessary. In the mixed dentition, one mech-
anism fbr gaining space for alignment is to
preserve the leeway space, which can be as
much as 4.3 ram. ~ This generous space may be
one reason why crowding in the mixed denti-
tion becomes less pronounced with the devel-
opment of the permanent dentition. For exam-
ple, Moorrees and Chada indicated that 1 to 2
mm of crowding is a characteristic feature in
individuals who demonstrate normal align-
ment in the permanent dentition.
This observation raises a series of interest-
ing questions, such as what is the incidence of
crowding in the mixed dentition, and how of-
ten can the leeway space provide adequate
space to resolve this crowding? (Since lower
arch conditions dictate the strategy for maxil-
lary arch treatment, only the changes in the
lower arch will be discussed.)
To answer these questions, the mandibular
models of t 00 patients in the mixed dentition
stage of development were evaluated, in the
sample, crowding, which averaged 4.5 ram,
was present in 85 of the 100 individuals. ~
rowding, which can be present in all classes
of malocclusions, is probably the most
From the Department of Orthodontics, Boston University
School of Graduate Dentist~, Boston, MA.
Address correspondence to Anthony A. Gianelly, DMD, PhD,
MD, Professor and Chairman, Department of Orthodontics, Bos-
ton University School of Graduate Dentist~ 7, 100 E Newton St,
Boston, MA 02118.
Copyright © 1995 by' W.B. Saunders Company
Crowding was defined as a tooth-size/arch-size
discrepancy and was determined by comparing
the mesiodistal diameters of the primary and
permanent teeth to arch perimeter. When
teeth were absent, their size was estimated
from their antimere, when present, or from
data provided by Moyers et al. 3
When tile leeway space gain was included in
the analysis, only 23 of the 100 individuals had
insufficient space for alignment. In actuality,
the leeway space represents the "E" space or
the difference between the mesio-distal (m-d)
diameter of the second primary molar and the
second premolar because the combined m-d
diameter of the primary canine and first molar
( 13.64 ram) is approximately equal to the com-
bined m-d diameter (13.85 ram) of the perma-
nent canine and first premolar. :~ This simpli-
fies the usual leeway space calculation.
Thus, with the inclusion of the E space, 77
of the 100 patients had adequate space in the
arch to accommodate an aligned dentition.
(The size of unerupted permanent teeth was
derived from m-d diameter ratios of primary
to corresponding permanent teeth as defined
by Moyers et al. :~)
In seven of tile remaining 23 patients who
would still exhibit a space deficit even after the
inclusion of the E space, tile crowding did not
exceed 2 ram, indicating that 84 out of 100
subjects would have no more than 2 mm of
crowding by simply maintaining the E space.
Developmentally, there are three signs that
are usually described to identify the potential
for crowding in the permanent dentition. 4 The
first is the lack of interdental spaces in the pri-
Seminars in Orthodontics, Vol 1, No 3 (September), 1995: pp 188-194
Anthony ,4. Gia~'~elly
2. Arnold S: Analysis of leeway space in the mixed den-
tition. Thesis for certification. Boston, Boston Univer-
3. Movers RE, van der Linden FPGM, Riolo ML, et al.
Standards of Human OcclusaI Development. Mono-
graph #5 Craniofacial Growth Series. Ann Harbor,
MI: Center of Human Development, The University
of Michigan, 1976.
4. Gianellv AA. Diagnosis of incipient malocclusions. J
Am Dent Assoc 1969;79:658-661.
5. Baume L. Physiological tooth migration and its signif-
icance for the development of occlusion. Part III. The
biogenesis of the successional dentition. J Dent Res
6. Singer J. The effect of the passive lingual arch on the
lower denture. Angle Orthod 1974;44:146-155.
7. Owen DG. The incidence and nature of space closure
following the premature extraction of deciduous
teeth: A literature survey. Am J Orthod Dentofacial
Orthop 1971 ;59:37-49.
8. Sampson WS, Richards LC. Prediction of mandibular
incisor and canine crowding changes in the mixed
dentition. Am J Orthod Dentofacial Orthop 1985;88:
9. Dorfman HS. Mucogingivat changes resulting from
mandibular incisor tooth movement. Am J Orthod
Dentofaciat Orthop 1978;74:286-297.
I0. Rigenberg AM. Influence of serial extraction on
growth and development of the maxilla and mandi-
ble. Am J Orthod Dentofacial Orthop 1967;53:47-58.
11. Osborn WS, Nanda RS, Currier GF. Mandibular arch
perimeter changes with lip bumper treatment Am J
Orthod DentofaciaI Orthop 1991 ;99:527-532.
12. Bergerson EO. A cephalometric study of the clinical
use of the mandibular labial bumper. Am J Orthod
Dentofacial Orthop 1972 ;61:578-602.
13. Nevant CT, Buschang PH, Alexander RG, et al. Lip
bumper therapy for gaining arch length. Am J
Orthod Dentofaciat Orthop 1991; I00:330-336.
14. Cetlin, NM, Ten Hoeve ?a. Non extraction treatment.
J Clin Orthod 1983;I7:396-413.
15. Moin K. Buccal shield for mandibular arch expansion.
J Clin Orthod 1988;22:588-590.
I6. Nance H. The limitations of orthodontic treatment.
Am J Orthod Oral Surg I947;33:253-301.
I7. Bernstein, L. Edward H. Angle versus Calvin S. Case.
Extraction versus non-extraction. Historical revision-
ism. Part 1. Am J Orthod DentofaciaI Orthop 1992;
18. Case CS. The question of extraction in Orthodontics.
Am J Orthod Dentofacial Orthop 1964;50:660-691.
19. Tweed CH. Clinical Orthodontics. VoI 1. St Louis,
MO: CV Mosby, 1966.
20. Tweed CH. Indications for extraction of teeth in orth-
odontic procedures. AmJ Orthod Oral Surg I944;30:
2I. Little RM, Reidel RA, Stein A. Mandibular arch length
increase during the mixed dentition: Post retention
evaluation of stability and relapse. Am J Orthod Den-
tofacial Orthop 1990:97:393-404.
22. Germane N, Lindauer SJ, Rubenstein LK, et al. In-
crease in arch perimeter due to orthodontic expan-
sion. Am J Orthod Dentofacial Orthop 1991 ; 100:421-
23. Peak JD. Cuspid stability. Am J Orthod Dentofacial
24. Bishara SE, Chada JM, Potter RB. Stability of interca-
nine width, overbite and overjet correction. Am J
Orthod Dentofacial Orthop 1973;63:588-595.
25. Shapiro PA. Mandibular dental arch and dimension.
Am J Orthod Dentofacial Orthop 1974;66:58-70.
26. Kuftinec MM. Effect of edgewise treatment and reten-
tion of mandibular incisors. Am J Orthod Dentofacial
27. EI-Mangoury NH. Orthodontic relapse in subjects
with varying degrees of anteroposterior and vertical
dysplasia. Am J Orthod Dentofacial Orthop 1979;75:
28. Sondhi A, Cleall JF, BeGole EA. Dimensional changes
in the arches of orthodontically treated cases. Am J
Orthod Dentofacial Orthop I980;77:60-74.
29. Little RM, Wallen TR, ReideI RA. Stability and relapse
of mandibular anterior alignment-first premolar ex-
traction cases treated by conventional edgewise orth-
odontics. Am J Orthod Dentofacial Orthop 1981;80:
30. Uhde MD, Sadowsky C, BeGole EA. Long term stabil-
ity of" dental relationships after orthodontic treatment.
Angle Orthod 1983;53:240-252.
31. Glenn G, Sinclair PM, Alexander RG. Nonextraction
orthodontic therapy: Post treatment dental and skel-
etal stability. Am J Ortho Dentofacial Orthop 1987;
32. Haas A. Long term post treatment evaluation of rapid
palatal expansion. Angle Orthod 1980;50: 189-217.
33. Sandstrom RA, Klapper L, Papaconstantinou S. Ex-
pansion of the lower arch concurrent with rapid max-
illary expansion. Am j Orthod Dentofacial Orthop
34. Adkins MA, Nanda RS, Currier GF. Arch perimeter
changes on rapid palatal expansion. Am J Orthod
Dentofacial Orthop 1990;97:194-199.
35. McNamara JA Jr, Brudon WL. Orthodontic and or-
thopedic treatment in the mixed dentition. Ann Ar-
bor, MI: Needham Press, 1993:78-80.
36. Burstone CJ. Perspective on orthodontic stability. In:
Nanda R, Burstone CJ, editors. Retention and Stabil-
ity in Orthodontics. Philadelphia: Saunders, 1993:45-
37. Lutz HD, Pouhon DR. Stability of dental arch expan-
sion in the deciduous dentition. Angle Orthod 1985;
38. McInanev JB, Adams RM, Freeman MM. A non-
extraction approach to crowded dentitions in young
children: Early recognition and treatment. J Am Dent
39. Gorman JC. The effects of premolar extraction on the
long term stability of the mandibular incisors. In:
Nanda R, Burstone C J, editors. Retention and Stabil-
ity in Orthodontics. Philadelphia: Saunders, 1993:81-
40. Alexander RG. Treatment and retention for long
term stabilitv. In: Nanda R, Burstone CJ, editors. Re-
tention and Stability in Orthodontics. Philadelphia: