Leeway Space and the Resolution of Crowding in the Mixed Dentition.

7/26/2019 Leeway Space and the Resolution of Crowding in the Mixed Dentition.

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Leeway Space and the Resolution of

rowding 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 mainta ined by preserving arch length w ith a lingual arch as the p rimary

teeth begin to exfoliate unless conditions such as the pre mat ure 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.

Co p y r i g h t 1 99 5 b y W B Sa u n d e r s C om p a n y

o wd i n g , wh i c h c a n b e p r e s e n t i n al l c l as s es

o f m a l o c c l u s i o n s , i s p r o b a b l y t h e m o s t

c o m m o n p r o b l e m r e s o l ve d by o r t h o d o n t i c

t r e a t m e n t . T o a l i g n a c r o w d e d d e n t i t i o n , s p a c e

i s n e c e s s a ry . I n t h e m i x e d d e n t i t i o n , o n e m e c h -

a n i s m f b r g a i n i n g s p a c e f o r a l i g n m e n t is t o

p re s e rv e t h e l e e wa y s p a c e , wh i c h c a n b e a s

m u c h a s 4 .3 r a m . ~ T h i s g e n e r o u s s p a c e m a y b e

o n e r e a s o n w h y c r o w d i n g i n t h e m i x e d d e n t i -

t i o n b e c o m e s l e s s p r o n o u n c e d w i t h t h e d e v e l -

o p m e n t o f t he p e r m a n e n t d e n ti t io n . F o r e x a m -

p le , M o o r r e e s a n d C h a d a i n d i c a t e d t h a t 1 t o 2

m m o f c r o w d i n g is a c h a r a c te r i s ti c f e a t u r e i n

i n d i v id u a l s w h o d e m o n s t r a t e n o r m a l a li g n-

m e n t i n t h e p e r m a n e n t d e n t i t i o n .

T h i s o b s e r v a t i o n r a i s e s a s e r i e s o f i n t e r e s t -

i n g q u e s t i o n s , s u c h a s wh a t i s t h e i n c i d e n c e o f

c r o w d i n g i n th e m i x e d d e n t i t i o n , a n d h o w o f-

t e n c a n t h e l e e w a y s p a c e p r o v i d e a d e q u a t e

s p a c e t o r e s o l v e t h i s c ro wd i n g ? (S i n c e l o we r

a rc h c o n d i t i o n s d i c t a t e t h e s t r a t e g y fo r m a x i l -

l a r y a r c h t r e a t m e n t , o n l y t h e c h a n g e s i n t h e

l o we r a r c h w i l l b e d i s c u s s e d . )

T o a n s w e r t h e s e q u e s t i o n s , t h e m a n d i b u l a r

m o d e l s o f t 0 0 p a t i e n t s i n t h e m i x e d d e n t i t i o n

s t ag e o f d e v e l o p m e n t w e r e e v a l u a t e d , i n t h e

s a m p l e , c r o w d i n g , w h i c h a v e r a g e d 4 . 5 r a m ,

w a s p r e s e n t i n 8 5 o f t h e 1 0 0 i n d i v i d u a l s . ~

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~ , 100 E Newton St,

Boston, MA 02118.

Copyright 1995 by W.B. Saunders Company

1073-8746/95/0103-000655.00/0

C r o w d i n g w a s d e f i n e d a s a t o o t h -s i z e / a rc h - s i z e

d i s c re p a n c y a n d w a s d e t e r m i n e d b y c o m p a r i n g

t h e m e s io d i st a l d i a m e t e r s o f t h e p r i m a r y a n d

p e r m a n e n t t e e t h t o a r c h p e r i m e t e r . W h e n

t e e t h w e r e a b s e n t , t h e i r s i ze w as e s t i m a t e d

f r o m t h e i r a n ti m e r e , w h e n p r e s e nt , o r f r o m

d a t a p ro v i d e d b y M o y e r s e t a l . 3

W h e n t i l e l e e wa y s p a c e g a i n wa s i n c l u d e d i n

t h e a n a l ys i s , o n l y 2 3 o f t h e 1 0 0 i n d i v i d u a l s h a d

i n s u f f i c i e n t s p a c e fo r a l i g n m e n t . I n a c t u a l i t y ,

t h e l e e w ay s p a c e r e p r e s e n t s th e E s p a c e o r

t h e d i f f e r e n c e b e t w e e n t h e m e s i o - d is t a l ( m - d )

d i a m e t e r o f t he s e c o n d p r i m a r y m o l a r a n d t h e

s e c o n d p r e m o l a r b e c a u s e t h e c o m b i n e d m - d

d i a m e t e r o f t h e p r i m a r y c a n i n e a n d f i rs t m o l a r

( 1 3 .6 4 r a m ) i s a p p ro x i m a t e l y e q u a l t o t h e c o m -

b i n e d m - d d i a m e t e r ( 1 3. 8 5 r am ) o f t h e p e r m a -

n e n t c a n i n e a n d f i r s t p r e m o l a r . :~ T h i s s i m p l i-

f i e s t h e u s u a l l e e wa y s p a c e c a l c u l a t i o n .

T h u s , w i t h t h e i n c l u s i o n o f t h e E s p a c e , 7 7

o f t h e 1 0 0 p a t i e n t s h a d a d e q u a t e s p a c e i n t h e

a r c h t o a c c o m m o d a t e a n a l i g n e d d e n t i t i o n .

( T h e s iz e o f u n e r u p t e d p e r m a n e n t t e e t h w a s

d e r i v e d f r o m m - d d i a m e t e r r a ti os o f p r i m a r y

t o c o r r e s p o n d i n g p e r m a n e n t t e e t h as d e f i n e d

by M oy er s et al. :~)

I n s e v e n o f ti le r e m a i n i n g 2 3 p a t i e n t s w h o

wo u l d s ti ll e x h i b i t a s p a c e d e f i c i t e v e n a f t e r t h e

i n c l u s i o n o f t h e E s p a c e , t il e c ro wd i n g d i d n o t

e x c e e d 2 r a m , i n d i c a t i n g t h a t 8 4 o u t o f 1 0 0

s u b j e c t s w o u l d h a v e n o m o r e t h a n 2 m m o f

c r o w d i n g b y s im p l y m a i n t a i n i n g t h e E s p a c e.

D e v e l o p m e n t a l l y , t h e r e a r e t h r e e s i g n s t h a t

a r e u s u a l l y d e s c r i b e d t o i d e n t i fy t h e p o t e n t i a l

f o r c r o w d i n g i n t h e p e r m a n e n t d e n t it i o n. 4 T h e

f i r st is t h e l a c k o f i n t e r d e n t a l s p a c e s i n t h e p r i -

188 Semi nars in Orthodontics, Vol 1, No 3 (September), 1995 : pp 188 -19 4


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Leeway Space and Crowding in the M ed Dentition

189

mary dentition. This sign is not especially reli-

able since Baume showed that 9 of 16 individ-

uals with no interdental spaces in the primary

dentition did not exhibit crowding in the per-

man ent dentition. 5 The second sign is crowd-

ing of the permanent incisors in the mixed

dentition. The third sign is the premature loss

of a primary canine, presumably reflecting in-

adequate space for the eruption of the lateral

incisor. In crowded conditions, the erupting

lateral incisor promo tes the resorpti on of the

root of the primary canine which then exfoli-

ates.

In the group of 100 patients, the most se-

vere crowding was most often associated with

the early loss of a primary canine.

Mainte nance of the E Space

Two common appliances used to maintain the

E space are the lingual arch and the lip bum-

per.

Lingual Arch

Despite its widespread use, comparatively little

is known concerning the effect of lingual arch

placement on the dimensions of the lower

arch. In one of the few reported investigations

on this topic, Singer observed that both arch

length and arch width were increased slightly

by appro ximat ely 0.5 mm. 6 Alth oug h n ot a

clinically useful increase, this led him to state,

It can be seen that the appellation 'passive lin-

gual arch' is a misnomer. Certain basic dental

changes were noted with the use of this appli-

ance. A portion of the e ffect may be construe d

as active mo veme nt (distal reposition ing of the

molars) although the reason remains obscure.

The results of Singer's study indicated that the

lingual arch should readily maintain the E

space.

Timing of lingual

arch placement

The lingual

arch is used when a primary canine is lost pre-

maturely, disrupting the integrity of the dental

arch (Fig 1). The opposite primary canine is

then removed for purposes of symmetry and a

lingual arch is inserted. The function of the

lingual arch at this stage is to prevent the lin-

gual movement (uprighting) of the incisors

with consequent loss of arch length. For in

Figure 1. (A) Models illustrating early loss of right

primary canine, the removal of the lef t primary ca-

nine, and a lingual arch in place to maintain arch

length. (B) Lingual arch in place as permanent teeth

erupt. Space is available for all teeth.

stance, in a review article on space closure fol-

lowing the early loss of primary teeth, Owen

indicated that most investigators found that

space closure in the lower arch is primarily due

to lingual movement of the Iower incisor

teeth. 7

This raises a question: Why not consider a

serial extraction protocol in patients who lose a

primary canine early, because exfoliation of

the canine represents a space deficit and the

most severe crowding was often noted in pa-

tients who lost a primary canine early? This

would avoid the routine insertion of a lingual

arch in these patients. An answer to this ques-

tion is that the predic tion of imp end ing crowd-

ing in the permanent dentition is difficult.5'8

For example, Sampson and Richards 8 were

unable to predict incisor crowding from dental

arch parameters and pre-eruptive tooth posi-

tions because of unpredic table chan ges in den-

tal arch width and depth. They advised that,

Considering the great individual variation,

lack of reliable radiographic and dental arch


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190 Anthony A Gianelly

p a r a m e t e r s o f c r o w d i n g , a n d t h e u n e x p e c t e d

t e n d e n c y f o r m a n y i n i t i a l l y c r o w d e d c a s e s t o a t

l e a s t p a r t i a l l y r e s o l v e t h e i n c i s o r a n d / o r c a n i n e

c r o w d i n g , e x t r e m e c a u t i o n s h o u l d b e e x e r c i s e d

i n d e c i d i n g w h i c h p a t i e n t s w i l l t r u l y b e n e f i t

f r o m s e r i a l e x t r a c t i o n o r e a r l y s p a c e g a i n i n g

p r o c e d u r e s .

A n o t h e r r e a s o n f o r n o t ro u t i ne l y e n d o r s i n g

s e ri al e x tr a c t i o n p r o c e d u r e s w h e n c r o w d i n g

e x i st s i n t h e m i x e d d e n t i t i o n i s t h e o b s e r v a t i o n

b y R i n g e n b e r g t h a t t h e r e w a s n o d i f f e r e n c e i n

t r e a t m e n t r e s u lt s o b t a i n e d i n a g r o u p o f p a-

t i e n ts t r e a t e d b y m e a n s o f s er i a l e x t r a c t i o n

w h e n c o m p a r e d w i th p a t ie n ts w h o s e t r e a t m e n t

i n v o l v e d c o n v e n t i o n a l p r e m o l a r e x t r a c t io n s , l

A c t iv e t r e a t m e n t i n t h e s e ri a l e x t r a c t i o n g r o u p

w a s a p p r o x i m a t e l y 6 m o n t h s s h o r t e r . T h i s i n -

d i c a t e d t h a t t h e e x t r a c t i o n p r o c e d u r e c a n b e

d e l a y e d w i t h l i t t l e c o n s e q u e n c e .

A c c o r d i n g l y , a r e c o m r n e n d e d s t r a t e g y is t o

m a i n t a i n a r c h l e n g t h u n t i l t h e f i r s t p r e m o l a r s

e r u p t . A t t h a t t im e , a d e c i s i o n c o n c e r n i n g e x -

t r a c t i o n c a r l b e m a d e w i t h m o r e p r e c i s i o n b e -

c a u s e m o s t d e v e l o p m e n t a l c h a n g e s w i l l h a v e

o c c u r r e d , r e d u c i n g t h e c h a n c e f o r e r r o r .

T h e r e a r e e x c e p t i o n s t o t h i s p r o t o c o l . O n e i s

t h e p r e s e n c e o f a d e h i s c e n c e o n t h e l a b i a l a s -

p e c t o f a m a n d i b u l a r i n c i so r t o o th . L i n g u a l

m o v e m e n t o f t h e i n ci s o r m i g h t h e f a v o r a b l e

s i n ce l in g u a l m o v e m e n t is a s s o c i a t ed w i t h m o r e

p e r i o d o n t a l s u p p o r t ) ) A s e c o n d e x c e p t i o n is

w h e n e r u p t i n g t e e t h a r e f o r c e d t o e r u p t i n a n

a r e a o f n o n - k e r a t i n i z e d g i n g i v a. I n t h i s i n-

s t an c e , th e p e r i o d o n t a l s u p p o r t o f t h e t o o t h

m i g h t b e c o m p r o m i s e d d u e t o t h e l ac k o f k e-

ra t in i zed t i s sue .

A l i n g u a l a r c h is a l so c o m m o n l y u s e d w h e n

t h e l a t e r a l i n c i s o r s e r u p t l i n g u a l t o t i l e c e n t r a l

i n c i s o rs ( F ig 2 ). T h e f u n c t i o n o f t h e a p p l i a n c e

is t o p r e v e n t l os s o f a r c h l e n g t h t h a t c o u l d o c -

Figure 2. Pre- and pos t- l ingual arch placement .

c u r i f t h e l a t e r a l i n c i so r s m o v e d l i n g u a ll y , f o l -

l o w e d b y t h e c e n t r a l i n c i s o r t e e t h .

Lip umper

T h e l ip b u m p e r is a n e f f e c ti v e a p p l i a n c e f o r

m a i n t a i n i n g a n d / o r i n c r e a s i n g a r c h l e n g t h ( F i g

3 ) . A n y i n c r e a s e i n a r c h l e n g t h g e n e r a l l y r e -

f le c ts b o t h d i st a l m o v e m e n t o f t h e m o l a r s a n d

lab ia l m ov em en t o f t he inc i sors , l L. 12 Also , mo s t

o f t h e c h a n g e s i n d u c e d b y l ip b u m p e r t r e a t-

m e n t o c c u r w i t h i n t h e f i r st y e a r . t t A s a n e x -

a m p l e , B e r g e r s o n n o t e d t h a t a 1 m m i n c r e a s e

i n a r c h l e n g t h c a n r o u t i n e l y b e a c h i e v e d i n a s

l it tl e a s 3 m o n t h s o f f u l l - t i m e l i p b u m p e r u s e . 12

A r c h w i d t h a l s o i n c r e a s e s w i t h l i p b u m p e r

t r e a t m e n t . 1:~ C e t l i n a n d T e n H o e v e l t d e m o n -

s t r a t e d a 2 . 5 m m i n c r e a s e i n i n t e r c a n i n e w i d t h

a n d a 4 m m g a i n i n i n t e r p r e m o l a r w i d t h . T h e y

e m p h a s i z e d t h a t t h is a r c h w i d t h i n c r e a s e i s a n

i m p o r t a n t m e c h a n i s m f o r g a i n i n g s p a c e f o r i n -

c i so r a l i g n m e n t . O t h e r s h a v e o b s e r v e d s i m i la r

inc rease s in a rch wid th . 13

Ne van t e t a l l:~ ind ic a ted tha t t he type of l i p

b u m p e r a n d t h e a c t i v a t i o n s c h e d u l e c a n i n f l u -

e n c e t h e c h a n g e s i n t h e m a n d i b u l a r a r c h o b -

t a i n e d w it h l ip b u m p e r t h e r a p y . T h e y n o t e d a

l a r g e r i n c r e as e s in a r c h l e n g t h a n d w i d t h w h e n

a l ip b u m p e r w i t h a n a c r y l i c s h i e l d w a s a c ti -

v a t e d e v e r y 4 to 5 w e e k s w h e n c o m p a r e d w i th

t h e c h a n g e s o b s e r v e d w i t h t h e u s e o f a t h i n n e r

l i p b u m p e r w h i c h w a s a c t i v a t e d e v e r y 2 t o 3

m o n t h s . T h u s , m o r e f r e q u e n t a c t iv a t i o n o f a

l i p b u m p e r w i t h a r e l a t i v e l y t h i c k l a b i a l s h i e l d

c a n e n h a n c e t h e c h a n g e s i n t h e d e n t a l a r c h .

T h e a r c h l e n g t h a n d w i d t h c h a n g e s p r o d u c e d

b y th e l i p b u m p e r l e ad t o a n i n c r e a s e i n a r c h

c i r c u m f i ~ r e n c e w h i c h , i n o n e s t u d y , a v e r a g e d

4 .1 m m. II

B e c a u s e b o t h t h e l e n g t h a n d w i d t h o f th e

l o w e r d e n t a l a r c h c a n b e i n c r e a se d b y b u m p e r

u s e , w h a t a r e r e a s o n a b l e o b j e c t i v es o f li p

b u m p e r t r e a t m e n t ? T h i s i s a d i f f ic u l t q u e s t i o n

t o a n s w e r b e c a u s e o p i n i o n s d i f f e r c o n c e r n i n g

t h e s ta b il it y o f e x p a n d e d m a n d i b u l a r d e n t a l

a r c h e s . N a n c e t6 b e l i e v e d t h a t e x c e s s i v e l a b i al

m o v e m e n t o f a n t e r i o r t e e t h l e a d s t o e v e n t u a l

r e l a p s e a n d p o s s i b l e t i ss u e d a m a g e : t o l i n e u p

t h e t e e t h i n a n a r c h t o n o r m a l c o n t a c t p o i n t

r e l a t io n s h i p s . . . is d o w n r i g h t e a s y p r o v i d e d

o n e i g n o r e s t h e r e l a t i o n s h i p s o f t e e t h t o su p -


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Leeway Space and rowding in the Mixe d Dentition 191

Figure 3 . (A) Lip bumper in place. (B) Adequate space is present to al ign the teeth . Arch length was

increased by i mm.

p o r t i n g b o n e s . H i s v i e w r e i t e r a t e s t h e wel l-

k n o w n e x t r a c t i o n / n o n - e x t r a c t i o n c o n t r o v e r sy

b e t w e e n E d w a r d A n g l e a n d C a l v i n C a s e .

A n g l e , a s r e f e r e n c e d b y B e r n s t e i n , r e p r e -

s e n t e d t h e n e w s c h o o l o f d e n t i s t r y w h i c h

s t r e s s e d t h a t n o r m a l o c c l u s i o n c o u l d e x i s t o n l y

wh e n t h e re wa s a fu l l c o m p l e m e n t o f t e e t h . 17

A n g l e a l s o b e l i e v e d t h a t b a s a l b o n e g r o w t h

c o u l d b e i n d u c e d b y f u n c t i o n a l f o r c e s so t h a t

t e e t h t h a t w e r e m o v e d t o a n e w p o s i t io n w o u l d

b e s u r r o u n d e d b y n e w l y - f o r m e d b a sa l b on e .

T h u s , e x p a n s i o n w a s a c c e p t a b l e a n d e x t r a c -

t i on s n e v e r i n d i c a t e d . I n d i s a g r e e m e n t , C a s e,

w h o s u p p o r t e d t h e v i ew s o f t h e r a t i o n a l

s c h o o l, a r g u e d t h a t n e w b o n e c a n n o t b e i n-

d u c e d t o g r ow b e y o n d i ts i n h e r e n t s iz e a n d ,

t h e r e f o r e , t h e r e a r e i n d i c a t io n s f o r e x t r a c t io n s

in cer t a in types o f maloc c lus ion s . ~8

O n e o f t h e m o r e c o m p e l l i n g t a le s o f o r t h -

o d o n t i c f o l k l o r e i s t h e c o n v e r s i o n o f D r

C h a r l e s T w e e d f r o m a n o n - e x t r a c t i o n i s t t o

a n e x t r a c t i o n i s t . As h e r e c a l l e d , I p r a c t i c e d

t h e p h i l o s o p h y o f th e f u l l c o m p l e m e n t o f t e e t h

d i l i g e n t l y fo r s i x y e a r s . A t t h e e n d o f s ix a n d a

h a l f y e a rs o f o r t h o d o n t i c p r a c t ic e , I c a l le d 7 0 %

o f t h e p a t i e n t s I h a d t r e a t e d a n d c l a s s if i e d t h e

r e s u l t s i n t o s u c c e s s e s a n d f a i l u r e s . T o m y

a m a z e m e n t , m y s u c c e s s e s w e r e l e s s t h a n 2 0 %

a n d m y f a i l u r e s m o r e t h a n 8 0 % . ' 'm

T w e e d t h e n p e r f o r m e d a s e ri e s o f t ri a ls

t h a t , to t h is d a y , a r e u n i q u e . H e n o t e d , I n t h e

b e g i n n i n g , t wo p a t i e n t s w i t h s i m i l a r o c c l u s i o n s

w e r e s e l e c t e d , b o t h 1 3 y e a r s o l d . O n e w a s

t r e a t e d w i t h t h e r e t e n t i o n o f t e e t h a n d t h e

o t h e r h a d f o u r f i rs t p r e m o l a r s r e m o v e d b e f o r e

t r e a t m e n t . A f t e r t r e a t m e n t , t h e r e s u lt s w e r e

m o s t g r a t i f y i n g . N o t s o f o r t h e o t h e r , t h e c o n -

t r ol ca se . . . . T h e e x p e r i m e n t w a s r e p e a t e d ,

d o u b l i n g t h e n u m b e r s a n d t h e r e s u l t s w e r e

s i m i la r . ' '2 F in a l l y, a g r o u p o f p a t i e n t s p r e s e n t -

i n g a d i s c r e p a n c y b e t w e e n t h e s iz e o f t e e t h a n d

b a s a l b o n e w e r e s e l e c t e d . T h e y w e r e f i r s t

t r e a t e d b y r e t e n t i o n o f al l t e e t h . T h e s e s a m e

p a t i e n ts w e r e r e t r e a t e d a f t e r t h e r e m o v a l o f al l

f i rs t p r e m o l a r s . T h e m a n d i b u l a r i n c i s or s w e r e

p o s i t i o n e d o v e r b as a l b o n e . T h e c h a n g e s i n f a-

c ia l e s t he t i cs w e r e r e m a r k a b l e a n d t h e c a s es a r e

n o w o u t o f r e t e n t i o n a n d f r e e f r o m a n y s e ri o u s

rela pse . ' '19

T w e e d a l s o s t a t e d t h a t w h e n p a t i e n t s w i t h

b i m a x i l la r y p r o t r u s i o n s w e r e t r e a t e d b y n o n

e x t r a c t i o n p r o c e d u r e s , t h e c a se s w e r e f i n i sh e d

w i t h t h e m a n d i b u l a r i n c is o r s e i t h e r t i p p e d o r

b o d i l y d i s p l a c e d m e s i al f r o m t h e i r n o r m a l p o -

s i t i o n . F a c i a l a e s t h e t i c s we re b a d a n d t h e d i s -

h a r m o n y o f f a ci a l l in e s i n c r e a s e d i n d i r e c t r e -

l a t io n t o t h e e x t e n t o f m e s i a l d i s p l a c e m e n t o f

t h e m a n d i b u l a r i n c i s o r s f r o m t h e i r n o r m a l p o -

s i ti o n . Ye a r s o f r e t e n t i o n we re fu t i le , a n d , a s a

r u l e , c o ll a p se o f t h e m a n d i b u l a r a r c h i n t h e

i n ci s or r e g i o n o c c u r r e d . . . a n d i r r e p a r a b l e

d a m a g e t o h a r d a n d s o f t i n v e s t i ng t i ss u e s p a r -

t i c u l a r l y i n th e i n c i s al a n d p re m o l a r a r e a s , wa s

t h e u s u a l a f t e r m a t h o f s u c h t r e a t m e n t . ''19

T h i s b r i e f r e v i e w i n d i c a t e s t h a t , h i s t o r i c a l l y,

t h e e x p a n d e d l o w e r de n t a l a r c h w a s p e r c e iv e d

t o b e u n s t a b l e . S i n c e t h e re i s c o n fu s i o n , o n e

a p p r o a c h t o d e v e l o p a s o u n d s t r a t e g y m i g h t b e

t o e v a l u a t e c o m p a r a t i v e o u t c o m e s . F o r e x a m -

p l e , is t h e s t a bi l it y o f l o we r d e n t a l a r c h e s wh i c h

h a v e b e e n e x p a n d e d i n t h e m i x e d d e n t i t i o n

e q u a l t o o r g r e a t e r t h a n t h e s t a bi li ty o f d e n t a l


5/7

192

Anthony A Gianelly

a r c h e s w h ic h h a v e n o t b e e n e x p a n d e d ? T h i s

q u e s t i o n h a s b e e n a d d r e s s e d i n o n e s t u d y . L i t-

t l e e t a l c o m p a r e d t h e s t a b i l i t y o f m a n d i b u l a r

d e n t a l a r c h e s t h a t w e r e e x p a n d e d i n t h e m i x e d

d e n t i t i o n s t a g e o f d e v e l o p m e n t t o re s o lv e

c ro w d i n g w i t h t h e s t ab i l it y o f a r c h e s t h a t w e re

n o t e x p a n d e d . 21 T h e y f o u n d t h a t l o w e r a r c h e s

t h a t u n d e r w e n t a n i n c r e a se o f m o r e t h a n 1 m m

i n a r c h l e n g t h ( a s m e a s u r e d f r o m o n e m o l a r t o

t h e m i d p o i n t b e t we e n t h e c e n t r a l i n c i s o r s t o

t h e o t h e r m o l a r ) e x p e r i e n c e d m o r e r e c r o w d -

i n g w h e n c o m p a r e d w i th t h e r e c r o w d i n g n o t e d

w h e n a r c h e s w e r e n o t e x p a n d e d . T h i s ob s e r -

v a t io n l ed t h e a u t h o r s t o r e c o m m e n d a n o n e x -

p a n s i o n t r e a t m e n t p r o t o c o l .

I s t h e t r a n s v e r s e e x p a n s i o n n o t e d w i t h l i p

b u m p e r t r e a t m e n t s t a b le ? M o st e m p h a s i s h a s

b e e n p l a c e d o n t h e i n t e r c a n i n e d i m e n s i o n b e -

c a u s e a n i n c r e a s e i n i n t e r c u s p i d w i d t h p r o v i d e s

m o r e s p a c e t o c o r r e c t c r o w d i n g t h a n o t h e r

t r a n s v e r s e c h a n g e s . S p e c i f i c a l l y, o n e e s t i m a t e i s

t h a t 1 m m o f i n t e r c a n i n e e x p a n s i o n p r o d u c e s a

0 . 7 3 m m s p a c e t h a t ( :a n b e u s e d t o t a l i g n m e n t ,

w h e r e a s a 1 m m e x p a n s i o n a t t he l e ve l o f t h e

m o l a r s p r o d u c e s o n l y a 0 .2 5 m m i n c r e a s e in

space . 22

T h e v a s t m a j o r i t y o f i n v e s t i g a t o r s wh o a s-

s e s s e d th e l o n g - t e rm s t a bi l it y o f i n t e r c a n i n e e x -

p a n s i o n i n d i c a t e d t h a t e x p a n s i o n o f th i s z o n e i s

i n h e re n t l y u n s t a b l e . 9 ~-3 i n a r e l e v a n t s t u d y

t h a t e m p h a s i z e d s t ab i li ty o f n o n e x t r a c t i o n

t r e a t m e n t r e s ul t s, t h e i n t e r c a n i n e w i d t h w a s i n-

c r e a s e d s l i g h t l y i n t r e a t m e n t f r o m 2 5 . 4 m m t o

2 6 r a m . A f t e r r e t e n t i o n , t h e i n t e r c a n i n e w i d t h

c o n t r a c t e d t o 2 5 r a m . Arc h l e n g t h wa s n o t i n -

c r e a s e d i n t h i s s a m p l e . A t t h e s t a r t o f t r e a t -

m e n t , a r c h l e n g t h w a s 6 0 m m , w h e r e a s i m m e -

d i a t e l y a f t e r t r e a t m e n t , i t wa s 6 0 . 2 r a m . Af t e r

r e t e n t i o n , a r c h l e n g t h w a s 5 8 m m , r e f l e c t i n g a

loss o f 2 ra m . :~1

T h e i n ab i li ty t o e n l a r g e m a n d i l m l a r i n t e r ca -

n i n e w i d t h p e r m a n e n t l y i s p r o b a b l y o n e o f t h e

m o s t d o c u m e n t e d p o s t t r e a t m e n t c h a n g e s . Al -

t h o u g h m o s t o f t he i n f o r m a t i o n f o r th is c o n-

c l u si o n h a s b e e n d e r i v e d b y e v a l u a t in g r e c o r d s

o f p a t i e n t s w h o w e r e n o t t r e a t e d e a r l y i n t h e

m i x e d d e n t i t i o n s t ag e o f d e v e l o p m e n t , i t p l ac e s

t h e b u r d e n o f p r o o f t o v e r i f y t h e s t a bi li ty o f

e x p a n s i o n o f th e i n t e r c a n i n e w i d t h in th e

m i x e d d e n t i t i o n o n t h o s e w h o p r o p o s e t h i s

t r e a t m e n t p l an .

T h e f i n d i n g s o f th e a b o v e - m e n t i o n e d i n v es -

t i g a t i o n s i n d i c a t e s t h a t t h e o r i g i n a l a r c h d i -

m e n s i o n s a r e n o t e a si ly c h a n g e d . T h e r e f o r e , a

p r u d e n t g o al o f l ip b u m p e r t h e r a p y m a y b e to

g a i n n o m o r e t h a n 1 m m o f a r c h l e n g t h a n d

l i tt le a r c h w i d t h , p ro d u c i n g o n l y a 2 m m i n -

c r e a s e in a r c h p e r i m e t e r . I f t h is 2 m m i n c r e a se

i n a r c h p e r i m e t e r is a p p l i e d t o t h e 1 0 0 i n d i v i d -

u a ls p r e v i o u s l y d e s c r i b e d , s p a c e f o r a l i g n m e n t

wo u l d b e a v a i la b l e i n 8 4 o f t h e s e i n d i v i d u a l s o r

i n 8 4% o f t he s t u d y g r o u p .

Timing of lip bumper placement T h e a u t h o r ' s

p r e f e r e n c e i s t o i n s e r t a l i p b u m p e r a f t e r t h e

e r u p t i o n o f t h e f i r st p r e m o l a r s , p a r t i c u l a r l y

s in c e t h e p r i m a r y g o a l o f b u m p e r p l a c e m e n t is

t o m a i n t a i n t h e E s p a c e . I f a d e c i s i o n is m a d e t o

i n c re a s e a r c h l e n g t h 1 r a m , i t c a n b e r e a d i l y

a c h i e v e d a s t h e s e c o n d d e c i d u o u s m o l a r s e x f o -

l ia te a n d t h e s e c o n d p r e m o l a r s e r u p t .

As d i s c u ss e d p re v i o u s l y , o n e o f t h e i n d i c a -

t io n s f o r e a rl i e r i n t e r v e n t i o n is t h e p r e m a t u r e

l os s o f a p r i m a r y c a n i n e . T h e t r e a t m e n t e n t a i ls

t h e r e m o v a l o f th e c o n t r a l a t e r a l p r i m a r y c a -

n i n e a n d t h e p l a c e m e n t o f a l i n g u al a r c h .

W h e n t h e f i r s t p r e m o l a r t e e t h a r e e r u p t i n g , a

s p a c e a n a ly s i s is p e r fo rm e d . I f s p a c e is a d e -

q u a t e fo r a l i g n m e n t , t h e l i n g u a l a r c h i s l e f t i n

p l a c e u n t i l a l l p r e m o l a r s h a v e e r u p t e d . A n y

n e c e s s a r y a l i g n m e n t i s p e r f o r m e d a t t h i s t i m e .

I f t h e r e is a s p a c e d e f i c i t wh i c h d o e s n o t e x c e e d

2 r a m , t h e l i n g u a l a r c h i s r e m o v e d w h e n t h e

f i rs t p r e m o l a r s a r e e r u p t i n g a n d a l ip b u m p e r

i n s e r t e d . I f t h e s h o r t a g e o f s p a c e is g r e a t e r

t h a n 2 m m , e x t r a c t io n t r e a t m e n t m a y b e t h e

t r e a t m e n t o f c h o i ce u n l es s s k e l e t o - d e n t a l c o n -

d i t io n s c o n t r a i n d i c a t e t h e e x t r a c t i o n o f t e e t h .

In t h e s t u d y s a m p l e , o n l y 1 6 o f t h e 1 0 0 p a -

t i en t s e v a l u a t e d h a d c r o w d i n g i n e x c e s s o f 2

i n h i

S o m e m i g h t a r g u e t h a t e a r l i e r i n t e r v e n t i o n

c o u l d a l s o p r o v i d e t h e s p a c e n e c e s s a r y f o r

t h e s e t 6 p a t i e n t s . F o r e x a m p l e , o n e s t r a t e g y i s

t o e x p a n d t h e m a x i l l a (R P E ) t o g a i n s p a c e i n

t h e m a x i l l a r y a r c h , a n d a t t h e s a m e t i m e p r o -

v o k e s p o n t a n e o u s t r a n s v e r s e e x p a n s i o n o f th e

l o we r a r c h . :~9 A l t h o u g h t h e r e a r e t o o l i t t le d a t a

t o a s se s s t h e m e r i t s o f t h is a p p r o a c h a d e -

q u a t e l y , t h e r e s u l t s o f t wo s t u d i e s a r e n o t o p -

t i m i st i c . S a n d s t r o m e t a l 3~ e v a l u a t e d t h e

r e c o r d s o f 2 8 p a t i e nt s w h o s e m a x i l l a e w e r e e x -

p a n d e d o r t h o p e d i c a l l y a n d n o t e d a 2 m m i n-

c r e a s e i n i n t e r c a n i n e w i d t h w h i c h l a t e r c o n -

t r a c t e d t o o n l y 1 .1 r a m . Ad k i n s e t a1 34 o b s e rv e d


6/7

Leeway Space and rowding in the Mixed Dentition

193

that expansion o f the lower arch following rapid

palatal expansion did not exceed 0.8 mm.

If passive expansion of the lower arch

proves inadequate, there is the possibility of

actively exp and ing the transverse dimensi on of

the arch with an appliance such as a Schwartz

plate. 35 As Burs tone 36 indicated, the ability to

expand this apical base skeletally is limited

since there is no suture. Therefore any expan-

sion is principally dental in nature. The avail-

able data are sparse and equivocal concerning

the ability to expand the lower arch with active

appliances such as the Schwartz plate. Lutz and

Poulton 37 exp and ed the transverse d imens ion

of 13 patients in the prim ary den tition stage of

development and compared the changes to

those observed in 12 control subjects. Expan-

sion was accomplished with removable appli-

ances in 1 1 patients and with fixed appl iances

in the remaining two patients. After a three-

year retention period, the patients were fol-

lowed for another three years. At this time, (6

years posttreatment) the intercanine dimen-

sion of the treated sample was not different

from the control group, indicating total re-

lapse of the treatment gain. The findings of

this study are consistent with the many inves-

tigations, which concluded that expansion of

the intercanine dimension of the lower arch is

inh erentl y unstabl e. 23-3

McI nan ey et al 3s used Crozat appliances to

expand the transverse dimension of the lower

arch in 5-year-old and 6-year-old patients and

retained the changes until all the prima ry teeth

exfoliated. The intercanine dimension was ex-

panded approximately 5 ram. After retention

was discontinued, the arches remained stable.

In this study there were no control subjects

and data from other published sources were

used to represent the controls. As such, the

actual net expansion ( t reatment change/

growth change) was not reported. The net ex-

pansion would depend on the control sample

chosen for comparison. If the control sample

were comparable to the control group identi-

fied by Lutz and Poulton, in which the inter-

canine width increased 4 to 5 mm, s7 there

would be no net expansion. If, on the other

hand, the comparison involved the control

sample re porte d by Moorrees and Chada, 1 in

which the intercanine width increased only 2

or more mm as the permanent incisors

erupted, a net gain approximating 2 mm

would be apparent . This lack of correlation be-

tween control groups may indicate that arch

width changes that occur in conditions with a

space defici t may be different from the

changes noted when there is adequate space

for alignment.

Crowding can be easily resolved by nonex-

traction treatm ent procedures, if desired, in at

least 85% of all patients with modest treat-

ment, which can be started in the late mixed

dentition. (One exception previously noted is

the early loss of a primary canine, which re-

quires earlier intervention.) The fate of the

other 15% of the patients is debatable. Should

these be extraction type patients (assuming

there are no skeletal contraindications), or

should they be treat ed earlier, to pursue a non-

extraction approach more aggressively? One

view, shared by the author, is that extractions

are the preferable route. A reason for this is

that long-term consequences of early interven-

tion procedures, which are designed to avoid

extraction by producing active and/or passive

expansion of the anterior part of mandibular

dental arch (arch development), are not clear.

Often, the focus is lateral expansion of the in-

tercanine dimension, because this procedure,

as indicated, can readily provide space for

alignment. In this context, arch dev elop ment is

contra ry to the vast majority of available data,

which do cument the instability of mandibular

intercani ne expansion. 23-3 In addition, others

who have discussed and demonstrated post-

treatment stability have emphasized that the

mandibular intercanine dimension should not

be ex pan ded dur ing treatm ent. 39 4

Thus, for those who prefer not to expand

the mandibular dental arch more than 1 mm, a

fundamental difference between extraction

and non-extraction resolution of crowding is

the timing of treatment. Four to five millime-

ters of incisor crowding in the mix ed den tition

stage of develo pmen t can usually be treat ed by

nonextraction procedures whose goals include

maintaining the E space. Extraction treatmen t

is most often necessary to correct 4 to 5 mm of

crowding in the permanent dentition.

eferences

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Leeway Space and the Resolution of Crowding in the Mixed Dentition.

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