arch perimeter changes on rapid palatal expansion

7/27/2019 Arch Perimeter Changes on Rapid Palatal Expansion

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A rch p erimeter changes on rapid palatal exp ansionMichae l D . Adk ins , DMD, MS, * Ram S . Nanda , DDS, M S, PhD, ** andG. Frans Curr ier , DDS, MSD, MEd***Oklahoma Ci ty , Okla .Relationships betw een chang es in arch perimeter and arch width resulting from r ap id palatalexpansion with the Hyrax appliance were analyzed with the use of dental study casts of 21adolescent patients. Photographs and measurements from the dental casts obtained beforetreatment and approximately 3 months after stabilization were used. Regression analysis indicatedthat changes in premolar width were highly predictive of changes in arch perimeter (r2 = 0.69) atapproximately 0.7 times the premolar expansion. Without any orthodontic appliances attached to themandibular teeth in 16 of the 21 patients, buccal uprighting of the posterior teeth was observedbecause of the redirection of occlusal forces. In addition, posterior movement of the maxillaryincisors and buccal tipping of the anchor teeth were quantified. The prediction of arch perimeterchange for a given amount of expansion is helpful in the treatment planning of rapid palatalexpans ion ca ses and may fac il itate nonextraction orthodontic treatm ent. (AM J ORTHOD DENTOFACORTHOP 199 0;97:194-9.)

T h e c u r r e n t t r en d s in th e p r a c t ic e o f o r t h o -don t i c s ha ve sh i f t e d tow a rd the p r inc ip l e s o f de n to fa c i a lo r thope d ic s a nd none x t ra c t ion t r e a tme n t mod a l i t i e s . I-aT h e u s e o f h e a d g e a r a n d f u n c t io n a l a p p li a n c es h a s d e m -ons t ra t e d o r tho pe d ic e f fe c t s mos t ly i n t he sa g i tt a l a ndv e r t ic a l d i m e n s i o n s . O n e o f t h e m o s t i m p r e s s i v e o r t h o -pe d ic p roc e du re s i s t he t r a nsve r se se pa ra t ion o f t hema x i l l a e t h rough ra p id pa l a t a l e xpa ns ion . Th i s p roc e -du re ha s l a t e ly be e n the sub je c t o f r e ne w e d in t e re s t i no r thodo n t i c tr e a tme n t m e c ha n ic s be c a u se o f i ts po t e n t i alfo r i nc re a s ing a rc h pe r ime te r t o a l l e v i a t e c row d ing inthe ma x i l l a ry a rc h w i thou t a dve r se ly a f fe c t ing f a c i a lp ro f i l e . In a dd i t i on , i t a ss is t s i n t he c o r re c t ion o f d i s -ha rm on ie s i n t he t r a nsve r se p l a ne be tw e e n the ma x i l l a ryand the mandibular a rches.~ '5-9

R a p id pa l a t a l e xpa ns ion (R PE) t r e a tme n t ha s be e na d v o c a t e d b y H a a s 8 a s a p r e f e r r e d m e t h o d f o r t h e c o r -re c t ion o f ma x i l l a ry a rc h c ons t r i c t i on . S inc e the a pp l i -a n c e p r o d u c e s o r t h o p e d i c m o v e m e n t s , t h e e x p a n s i o nw a s d e e m e d t o b e s k e l e t a l a nd t h e r e f o r e m o r e s t a b le .In t he f ron ta l p l a ne the R PE i s sa id t o se pa ra t e une qua l lythe tw o ha lve s o f t he ma x i l l a supe ro in fe r io r ly , t he fu l -c r u m o f r o t a ti o n b e i n g s o m e w h e r e c l o s e to t h e f r o n -toma x i l l a ry s u t u r e . 7 . l 't l

K re bs t s tud ie d the e f fe c t s o f R PE w i th t he u se o fme ta l l i c imp la n t s i n t he i n f ra z ygom a t i c r i dge a nd in t hea lve o la r p roc e ss l i ngua l to t he uppe r c a n ine s . H e foundF rom the C ol l ege o f D ent i s t ry , U nive rs i t y o f O klahoma .*Graduate s tudent , Department of Orthodont ics .**Professor and Chairm an, Dep artmen t of Orthodont ics.***A ssociate Professor, D epartm ent of Orthodont ics.811113549194

t he ga in i n the w id th o f the de n ta l a rc h w a s a bou t tw ic etha t o f t he ba sa l ma x i l l a ry se gme n t s .

H a a s 8 found in pa t i e n ts t r e a t e d w i th R P E the ma x i l l ai s d i sp l a c e d dow nw a rd a nd fo rw a rd . S imi l a r ly , W e r t z tn o t e d t h e m a x i l l a m o v e d d o w n w a r d I t o 2 m m o n ar e g u l a r b a s i s. T h e f o r w a r d m o v e m e n t w a s n o t c o n s is -t e n t, h o w e v e r , a n d w a s r a r e l y m o r e t h a n 1 .5 m m . H ea l s o c o m m e n t e d o n t h e c o n s i s t e n t u p r i g h t i n g o r p o s -t e r i o r m o v e m e n t o f t h e m a x i l l a r y i n c i so r s .

A re v i e w o f t he l i t e ra tu re suppor t s t he c on te n t iontha t t he R PE de v ic e , i n a dd i t ion to i t s o the r e f fe c t s , c a np rov id e a dd i t i ona l spa c e in t he a rc h to r e l i e ve c row d ing .Th e a pp l i a nc e , i f u se d w i th in c e r ta in a ge l im i ts w h e reind ic a t e d , i s a u se fu l a d junc t t o o r thodon t i c t r e a tme n t .T h e s e p a r a ti o n o f t h e m a x i l la e a n d t h e e f f e c t o n t h ea r c h p e r i m e t e r h a s n o t y e t b e e n q u a n t i fi e d . T h e p u r p o s eo f t h i s i nve s t iga t ion w a s to e s t im a te i nc re a se i n de n ta la r c h p e r i m e t e r f o l l o w i n g R P E o f t h e m a x i l l a e . I n a d -d i t i on , o the r c ha nge s i n t he ma x i l l a ry a nd ma nd ibu la rde n ta l a rc he s a ssoc i a t e d w i th t h i s t r e a tme n t p roc e du rew e re e va lua t e d .M A T E R I A L A N D M E T H O D SS a m p l e

T h e s a m p l e i n c l u d e d 2 1 c o n s e c u t i v e l y t r ea t e d o r th o -d o n t i c p at i e n ts w h o r e q u i r e d t h e u s e o f a R P E d e v i c eon the ba s i s o f t he i r ind iv idua l t r e a tme n t p l a ns . A l l t hepa t i e n t s w e re i n t he l a t e t r a ns i t iona l o r e a r ly pe rm a ne n tde n t i t i on s t a ge . N o ne o f t he pa t i e n t s ha d c ra n io fa c i a la noma l i e s suc h a s c l e f t l i p , c l e f t pa l a t e , o r bo th . N oo the r o r thodon t i c a pp l i a nc e s w e re u se d in t he ma x i l l a rya rc h du r ing the s tudy . In t he ma n d ibu la r a rc h , 5 o f the


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voh,me 97 Arch perimeter changes on RPE 1 9 5Number 3

Fig. 1A. Arch width measurement. A is the intercanine widthfrom p oints 5 to 9, B is the interpremolar width from points 3 to11, C is the intermo lar width f rom points 1 to 13 . All points arethe most l ingual points at the gingival margin.

21 pa t i en t s had fu l l - banded app l i ances ; t he r e fo re on l yt h e r e m a i n i n g 1 6 w e r e u s e d i n t h e a p p r a i s a l o f m a n -d i b u l a r a r c h c h a n g e s a c c o m p a n y i n g t h e u s e o f R P E .

T h e p a t i e n t s r a n g e d i n a g e f r o m 11 y e a r s 6 m o n t h st o 17 yea r s . T he re were 14 g i r l s and 7 boys . W i t h i nt he sampl e , e i gh t pa t i en t s had no pos t e r i o r c ros sb i t e .Of t he 13 pa t ien t s who ex h i b i t ed pos t e r i o r c ros sb i t e , 9ha d un i l a t e r a l c ros sb i t e w i t h a f unc t i ona l sh i f t and 4had b i l a t e r a l c ros sb i t e w i t hou t a f unc t i ona l sh i f t .Cl in ical procedures

E a c h p a t i e n t w a s t r e a t e d w i t h a H y r a x ( O S I ; W i l -m i n g t o n , D e l . ) e x p a n s i o n a p p l i a n c e . T h e a r m s o f th ee x p a n s i o n s c r e w w e r e s o l d e r e d t o t h e b a n d s t h a t w e r ef i t t ed on t he f i r s t p r emol a r and f i r s t pe rmanen t mol a r .T h e H y r a x d e v i c e w a s c e n t e r e d i n t h e m a x i l l a r y a r c hand wa s sag i t t a l ly p l aced pa ra l l e l t o t he mes i a l ha l f o ft h e p e r m a n e n t f ir st m o l a r a n d s e c o n d p r e m o l a r r e g i o n .T h e e x p a n s i o n s c r e w w a s v e r t i c a l ly p l a c e d a t t h e l ev e lo f t h e c e r v i c a l m a r g i n s o f t he p r e m o l a r s a n d f ir stm o l a r s .T h e a p p l i a n c e s w e r e a c t i v a t e d tw i c e a d a y w i t h o n e -qua r t e r t u rn i n t he morn i ng and i n t he even i ng un t i l t hed e s i re d e x p a n s i o n w a s a t t ai n e d . T h e a m o u n t o f e x p a n -s i o n an t i c ip a t e d w a s 0 . 5 m m p e r d a y . T h e a v e r a g e s t a -b i l i za t i on pe r i od was 14 .5 weeks wi t h a r ange o f 10 t o2 1 w e e k s . M a x i l l a r y a n d m a n d i b u l a r s t u d y c a s t s w e r eo b t a i n e d b e f o r e t r e a t m e n t a n d a g a i n a t t h e e n d o f th es t a b i l i z a t i o n p e r i o d w h e n t h e a p p l i a n c e w a s r e m o v e d .C a s t a n a l y s is

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

Fig. l B . A rch length measurement. D is arch length, which isthe perpendicular distance from point 7 to a line constructedbetween points 2 and 12 . Points 2 and 12 are contact points,mesial of the p erma nent fi rst molars. Point 7 is the most facia lpoint on the most pro minen t central incisor.

w e r e t o b e t a k e n w e r e m a r k e d w i t h a f i n e - l e a d p e n c i lt o f ac i li t a t e i den t i f i ca ti on . O nce m arke d , t he cas t s weret h e n p h o t o g r a p h e d f r o m a n o c c l u s a l v i e w w i t h a 3 5 m mc a m e r a . A c a m e r a s t a n d w a s e m p l o y e d t o s u p p o r t t h ecas t s and t o ho l d t he camera a t a f i xed foca l l eng t h o f3 0 c m f r o m t h e o c c l u s a l p l a n e o f th e c a s t s . T o p r o v i d ea sca l e o f d i s t ance , a mi l l i me t e r ru l e was f i xed a t t hehee l o f each cas t a t t he l eve l o f t he occ l usa l p l ane .S e v e r a l 5 7 i n c h p h o t o g r a p h s w e r e o b t a in e d o f e a c hcas t .M e a s u r e m e n t s

T h e p o i n ! s m a r k e d a n d d i g i t i z e d o n t h e m a x i l l a r yden t a l cas t s were t he mos t l i ngua l po i n t s a t t he g i ng i va lma rg i n o f the f i r s t mo l a r s , t he f i r s t p r em ol a r s , and t hec a n i n e s , a s s h o w n i n F i g . I A . T h e c o n t a c t p o i n t s o nt he mes i a l su r f ac e o f t he f ir s t mo l a r s , t he me s i a l su r f aceof t he f i r s t p r em ol a r , an d t he d i s t a l su r f ace o f t he cen t r a li nc i so r s , a s we l l a s t he mos t f ac i a l po i n t on t he mos tp r o m i n e n t c e n t r a l i n c i s o r , w e r e a l s o m a r k e d a n d d i g i -t i zed (F i gs . 1B and IC) . A l l po i n t s , whi ch w ere d i g -i t iz e d , a n d m e a s u r e m e n t s m a d e w e r e i d e n ti c a l f o r b o t ht h e m a x i l l a r y a n d t h e m a n d i b u l a r a r c h e s w i t h t h e e x -c e p t i o n o f m a n d i b u l a r m o l a r a r c h w id t h . T h e m a n d i b -u l a r m o l a r a r c h w i d t h w a s m e a s u r e d a t t h e c e n tr a lg roove i n t he d i s t a l cen t r a l f os sa because t he g i ng i va lm a r g i n o f t h e m a n d i b u l a r f ir st m o l a r s c o u l d n o t b e v i s -u a l i ze d f r o m a n o c c l u s a l v i e w . M e a s u r e m e n t o f w i d t ha t th e g i n g i v a l m a r g i n o f t h e t e e t h m i n i m i z e d t h e e r r o rt h a t c o u l d h a v e r e s u l te d f r o m b u c c a l c r o w n t i p p in g d u r -i n g t h e e x p a n s i o n p r o c e d u r e s .


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1 9 6 Adkhzs, Nanda, an d Cur ri er Am. J. Orthod. Dentofac. Orthop.March 1990BEFORE

-..-.._

Fig. l C . Arch per ime ter measurement. Arch per ime ter is thesum of the lengths of the segments connect ing points 2 , 4 , 6 ,8 , 10 , an d 12 . Points 2 a nd 1 2 are contact points, mesial to theperm anent f irst molars. Points 4 and 1 0 are contact points,me sial to the first premolars. Points 6 and 8 ar e contact points,distal to the central incisors.

PREMOLAR BEFORE

17g*

A r c h p e r i m e t e r m e a s u r e m e n t p o i n ts ( F i g . I C ) w e r ec h o s e n o n t h e m e s i a l a s p e c t o f t h e f ir s t p r e m o l a r s a n dt h e d i s ta l a s p e c t o f th e c e n t r a l i n c i s o r s b e c a u s e t h e m a x -i l l a r y c a n i n e s a n d l a t e r a l i n c i s o r s w e r e o f t e n b l o c k e do u t l a b i a l l y o r li n g u a l l y . A r c h p e r i m e t e r i s a c u r v e d e -s c r ib e d o n t h e d en t a l a r c h f o r m . T h e m e t h o d o f u si n gs e g m e n t s i n t h i s s t u d y w o u l d u n d e r e s t i m a t e t h e t r u ea r c h p e r i m e t e r . H o w e v e r , w i t h i n t h e c l i n ic a l l i m i t a t i o n s ,t h e e s t i m a t e d m e a s u r e m e n t s w e r e c o n s i d e r e d r e a s o n -a b l e i n e v a l u a t i n g t h e c h a n g e s i n a r c h p e r i m e t e r .

T o m e a s u r e t h e c h a n g e s i n t h e a n g u l a t io n o f a n c h o rt e e t h , e a c h m a x i l l a r y d e n t a l c a s t w a s s e c t i o n e d a t t h ef ir s t p r e m o l a r a n d a t t h e fi rs t m o l a r . B e f o r e s e c t i o n i n g ,t h e f i r s t p r e m o l a r s w e r e m a r k e d w i t h a f i n e - l e a d p e n c i la t t h e m e s i o d i s t a l m i d p o i n t o f t h e te e t h . S i m i l a r l y , t h ef i rs t m o l a r s w e r e m a r k e d a t a p o i n t o f i n t e r s e c ti o n o ft h e b u c c a l g r o o v e w i t h t h e b u c c a l a n d o c c l u s a l s u r f a ce so f t h e te e th . S e c t i o n s w e r e o b t a i n e d b y t r i m m i n g t h ec a s t s o n a m o d e l t r i m m e r , f i r s t w i t h a r o u g h w h e e l a n dt h e n w i t h a f i n e w h e e l , u n t i l t h e m a r k e d p o i n t s w e r er e a c h e d . A f t e r d r y i n g , t h e c a s t s w e r e t r a c e d . A t a n g e n tw a s c a r e f u l l y c o n s t r u c t e d t o t h e o c c l u s a l o u t l in e o f e a c ht o o t h a n d t h e r e s u l t i n g a n g l e s w e r e m e a s u r e d . F i g . 2i l lu s t r at e s t h e t y p i c a l t r a c i n g a n d m e a s u r e m e n t o f p r e e x -p e n s i o n a n d p o s t e x p a n s i o n d e n t a l c a s t s .E x p e r i m e n t a l e r r o r a n d s ta t i s t ic a l a n a l y s i s

E v a l u a t i n g t h e e r r o r i n l a n d m a r k i d e n t i f i c a ti o n , p h o -t o g r a p h i c m a g n i f i c a t i o n , a n d d i g i t i z a t i o n o f th e m e a -s u r e m e n t s , a l l o f t h e p r e e x p a n s i o n m a x i l l a r y c a s t s w e r ep h o t o g r a p h e d a n d d i g i ti z e d a t o n e t im e . T h e s a m e c a s t sw e r e p h o t o g r a p h e d a n d d i g i t i z e d a g a i n a f te r 1 w e e k .

AFTER

173"

Fig. 2. Typica l t racing and mea surem ent of sect ioned dupl icatecasts. Tangents we re constructed through the cusp t ips to pro-duce an gular measurements for sect ions of molar and premola rancho r teeth before and a f ter rapid palatal expansion.

M e a s u r e m e n t e r r o r w a s d e t e r m i n e d a s th e s t a n d ar d d e -v i a t i o n o f t h e d i f fe r e n c e s b e t w e e n t h e f i r s t a n d s e c o n dm e a s u r e m e n t s . T h e m e a s u r e m e n t e r ro r w a s ___0 . 1 9 m mf o r i n t e r c a n i n e w i d t h , - - - 0 .1 5 m m f o r i n t e r p r e m o l a rw i d t h , _ _ _ 0 .1 6 m m f o r i n t e r m o l a r w i d t h , + - 0 . 2 6 m mf o r a r c h l e n g t h , a n d + - 0 . 4 9 m m f o r a r c h p e r im e t e r .P o s s i bl e s o u r c e s o f e r r o r f o r a n g u la t i o n m e a s u r e m e n t si n c l u d e d i n c o n s i s t e n c i e s i n th e l o c a t i o n o f l a n d m a r k s ,t h e t r i m m i n g o f d e n t a l c a s ts , a n d t h e t r a c i n g a n d c o n -s t r u c t i o n o f ta n g e n t l i n e s . T h e e r r o r w a s a s s e s s e d b yr e p e a ti n g t h e m e a s u r e m e n t p r o c e d u r e s 2 w e e k s l a t e r o nd u p l i c at e d c a s t s. A g a i n t h e m e a s u r e m e n t o f e rr o r w a sd e t e r m i n e d a s t h e s t a n d a r d d e v i a t i o n o f t h e d i f f e r e n c e sb e t w e e n t h e f i rs t a n d s e c o n d m e a s u r e m e n t s . T h e e r r o rw a s f o u n d t o b e a s f o l l o w s :

M o l a r a n g u l a t i o n B e f o r e t r e a tm e n t _ 2 . 6 A f te r t re a tm ent ___ 2 .9

P r e m o l a r a n g u l a t i o n B e f o r e t r e a t m e n t .4_ 2 . 6 A f t e r t r e a t m e n t _+ 2 . 7


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Vohtme97 A r c h p e r i m e t e r c h a n g e s o n R P E 1 9 7Number 3

Table I . Me a n , s t a nda rd de v ia t ion , a nd ra nge o f pos t e xpa ns ion c ha nge s i n ma x i l l a ry me a su re me n t sI I S O I I

M o l a r w i d t h c h a n g e 6 . 5 1 . 2 4 . 8 8 . 9P r e m o l a r w i d t h c h a n g e 6 . l ! . 3 3 . 8 8 . 7C a n i n e w i d t h c h a n g e 2 . 9 1 . 4 0 . 6 6 . 4A r c h l e n g t h c h a n g e - 0 . 4 0 . 5 - 1 . 4 1 . 0A r c h p e r i m e t e r c h a n g e 4 . 7 1 .1 2 . 6 6 . 5

T h e e r r o r s f o r a l l o f t h e m e a s u r e m e n t s w e r e f o u n d t obe sma l l a nd w e re c ons ide re d no t c l i n i c a l ly s ign if i c a n t.

Fo r p re d ic t ion o f a rc h pe r ime te r c ha nge s , a s t e pw isemul t ip l e l i ne a r r e g re ss ion a na ly s i s w a s pe r fo rme d tode t e rmine the be s t se t o f i nde pe nde n t va r i a b l e s , w h ic hw e r e m o l a r , p r e m o l a r , a n d c a n i n e w i d t h c h a n g e s .RESULTS

M e a ns , s t a nda rd de v ia t ions , a nd ra nge fo r pos t e x -pa ns ion c ha nge s i n t he ma x i l l a ry me a su re me n t s a reg ive n in Ta b le I . Expa ns ion a ve ra ge d 6 .5 mm a t t hef ir st mo la r s , 6 .1 m m a t the f ir s t p re m o la r s , a nd 2 .9 mma t t he c a n ine s . A rc h l e ng th de mons t ra t e d a n a ve ra ged e c r e a s e o f 0 . 4 m m d u r i n g t h e p e ri o d o f s t u d y . T h ere su l t a n t a rc h pe r ime te r a f t e r c o r re c t ion fo r a n t e ropos-t e r io r m o v e m e n t o f t h e i n c i s o rs s h o w e d a m e a n i n c r ea s eo f 4 . 7 m m .

S te pw ise mu l t ip l e l i ne a r r e g re ss ion a na ly s i s o fthe t h re e i nde pe nde n t va r i a b l e s ( i . e . , mo la r , p re -mo la r , a nd c a n ine w id th inc re a se ) i nd i c a t e d tha t p re -mo la r w id th inc re a se w a s the be s t p re d ic to r o f t heinc re a se in a rc h pe r ime te r . Th i s r e l a t i onsh ip w a s foundto be l i ne a r a nd w a s r e p re se n te d by the fo l low inge qua t ion : y = 0 .68 x + 0 .56 w he re y is a rc h pe r im-e t e r c ha nge a n d x i s mo la r w id th c ha nge . P re d ic t -a b i l it y o f t h i s r e l a t ionsh ip w a s fo und to be s t rong( r2 = 0 .69 , p = 0 .0001 ) . The r 2 va lue s fo r c ha nge sin a rc h pe r ime te r a nd mo la r w id th w a s 0 .54 w i thp = 0 . 0 0 0 2 .

P o s t e x p a n s i o n c h a n g e s i n a n g u l a ti o n o f t h e m a x i l -l a r y a n c h o r t e e t h s h o w e d a m e a n m o l a r c h a n g eo f 7 .3 ___ 5 .8 a nd a me a n p re m ola r c ha ng e o f5 .2 _ 5 .1 . The va r i a b i l i t y w a s foun d to be h igh int h es e m e a s u r e m e n t s .

R e g re ss ion a na ly s i s w a s pe r f o rm e d to i nve s t iga t ea ny poss ib l e e f fe c t o f e x i s t ing c ro ssb i t e , i n i ti a l w id tho f th e a r c h , a m o u n t o f e x p a n s i o n o b t a i n e d , a n d a g e o nthe pos t e xpa ns ion buc c a l t i pp ing o f t he ma x i l l a ry a n -c ho r t e e th . Th e s t a t is t i c a l va lue s o f r 2 ob ta ine d ra nge df rom 0 .01 to 0 .07 fo r t he d i f f e re n t va r i a b l e s te s t e d .Th e y ind ic a t e d no s t a t i s t ic a l ly s ign i f i c a n t re l a t i onsh ips .

D e sc r ip t ive s t a t i s ti c s fo r ma nd ibu la r d ig i t i z e d me a -su re me n t s i nd i c a t e d the ove ra l l c ha nge s w e re sma l l ( l e ss

tha n 0 .8 mm) a nd the va r i a b l e w i th s t a nda rd de v ia t ionv a l u e s g r e a te r t h an t h e m e a n c h a n g e s f o u n d .

A l l pa t i e n t s w e re d iv ide d in to subg roups a c c o rd ingto p re se nc e o f b i l a t e ra l c ro ssb i t e s , un i l a t e ra l c ro ssb i t e ,o r n o c r o s s b i t e t o c o m p a r e t h e c h a n g e s f o r t h e m e a nm a n d i b u l a r m o l a r a n d f o r p r e m o l a r w i d t h . C h a n g e s i nm e a n w i d t h i n c r e a s e d , m o v i n g f r o m p a t i e n t s w i t h b i -l a te r a l c r o s s b it e ( 0 . 2 m m m o l a r , - 0 . 4 m m p r e m o l a r ) ,t o pa t i en t s w i th un i l a t e ra l e ro ssb i t e (0 .7 m m mola r , 0 .6m m p r e m o l a r ) , t o t h o s e p a t i e n ts w i t h n o c r o s s b i t e ( 1 .4m m m o l a r , 1 . 0 m m p r e m o l a r ) .DISCUSSION

R P E i s an a c c e p te d p roc e du re t o re l i e ve de f i c i e nc i e sin a rc h pe r ime te r . D ur ing the pa s t 20 ye a r s , w i th t heinc re a s ing e mpha s i s on none x t ra c t ion the ra py , t he p ro -c e d u r e h a s g a i n e d i n p o p u l a r i t y b e c a u s e o f th e r e l i e f o fc r o w d i n g i t p r o v i d e s . R P E c o m p e n s a t e s f o r a r c h p e r im -e t e r de f i c i e nc i e s t h rough t r a nsve r se e xpa ns ion o f t hea lve o la r a nd de n ta l a rc he s . R e c e n t l i t e ra tu re z -~ ha s doc -ume n te d the ske l e t a l a s w e l l a s t he de n ta l c ha nge s t ha to c c u r w i t h r a p i d e x p a n s i o n o f t h e m a x i l l a. H o w e v e r ,t h e m a g n i t u d e o f c h a n g e i n a r c h p e r i m e t e r w i t h t r an s -ve r se e xpa ns ion o f t he de n ta l a rc h ha s no t be e n e va l -u a t e d . D e t e r m i n a t io n o f a s i m p l e m e t h o d f o r p r o j ec t i n ginc re a se s i n a rc h pe r im e te r w ou ld be be ne f i c i a l i n p la n -n ing o r thodon t i c t r e a tme n t .

The p r inc ipa l goa l o f t h i s s tudy w a s to de t e rminet h e r e l a t i o n s h i p b e t w e e n t r a n s v e r s e m a x i l l a r y e x p a n -s ion a nd the r e su l t a n t ga in i n a rc h pe r ime te r . L ine a rr e g r e s s io n a n a l y s i s o f b o t h m o l a r w i d t h a n d p r e -mo la r w id th c ha nge s p roduc e d s t a t i s t i c a l ly s ign i f i c a n tl i ne a r r e l a t i onsh ips w i th t he a rc h pe r ime te r c ha nge( m o l a r r 2 = 0 . 5 4 , p = 0 . 0 0 0 2 ; p r e m o l a r ra = 0 . 6 9 ,p = 0 .000 1 ) . P re d ic t ion e qua t ions fo r mo la r a nd p re -m o l a r w i d t h c h a n g e s y i e l d e d s lo p e s o f 0 . 6 5 a n d 0 . 6 8 ,r e s p e c t iv e l y , a n d i n t e r c ep t s o f 0 .4 8 m m a n d 0 . 5 6 m m ,re spe c t ive ly . F rom a c l i n i c a l s t a ndpo in t , t he se a re ve rysma l l d i f f e re nc e s a nd the i n t e rc e p t i s c lo se e nough toz e ro tha t pe r ime te r ga in c ou ld be p ra c t i c a l ly p re d ic t e da s 0 . 7 t i m e s t h e a m o u n t o f p o s t e r i o r e x p a n s i o n . T h e s ef ind ings a re d i f f e re n t f rom those o f B e r loc he r e t a l . , ~w h o re po r t e d inc re a se s i n a rc h pe r ime te r to be e qua l t o


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198 Adk ins , Nan da, and Currie r Am. J. Orthod. Dentofiw. Orthop.March 1990

No . o fC a s e s10

987654321

M o l a rI I p r e m l a r

< _ ( - ) 5 ( - ) 4 t o ( + ) 2 3 t o 8 9 t o 1 4B u c c a l C r o w n T i p p i n g ( D e g r e e s )

>15

F i g . 3 . D i s t r ib u t i o n o f s a m p l e f o r d e g r e e o f t i p p i n g o f m a x i l l a r y m o l a r a n d p r e m o l a r a n c h o r t e e t h .

t h e g a i n in a r c h w i d th . T h e i r s a m p l e w a s f r o m a y o u n g e rage g roup (3 t o 7 yea r s ) , i nc l uded pa t i en t s w i t h c l e f tpa l a t e (10 o f t he 29) , and had a p r i mary den t i t i on s t ageo f d e n t a l d e v e l o p m e n t . T h e s e f a c t o rs , i n a d d i t io n t ov a r i a t io n s i n m e t h o d , c a n e a s i l y a c c o u n t f o r th e d i f f e r -ences i n t he f i nd i ngs .

T h e p a l a ta l m o v e m e n t o f m a x i l l a r y i n ci s o rs a s r e -f l ec t ed in t he r educ t i on o f a r ch l eng t h was no t ed i n t hes t udy . T h i s f i nd i ng was i n agreement w i t h t hose o fW e r t z . '5 T h e m a g n i t u d e o f t h is m o v e m e n t w a s s m a l land va r i ab l e (0 .4 m m ___ 0 .5 ) . How ever , i t was no t edi n 18 o f a t o t a l s amp l e o f 21 pa t i en t s .

B o t h m a x i l l a ry m o l a r a n d p r e m o l a r te e t h d e m o n -s t r a t e d b u c c a l c r o w n t i p p i n g w i t h e x p a n s i o n . T h e r e -su l t s , however , were h i gh l y va r i ab l e t o t he ex t en t t ha ts o m e p a t i e n t s ' t e e t h d e m o n s t r a t e d l i tt le o r n o t i p p i n g ,w h i l e o t h e r s d e m o n s t r a t e d t i p p i n g o f m o r e t h a n 1 5 F i g . 3 s h o w s t h e d i st r ib u t i o n o f t h e d e g r e e o f t i p p in gf o r t h e s a m p l e .

R e g r e s s i o n a n a l y s i s w a s p e r f o r m e d t o s t u d y t h e r e -l a t i onsh i p o f bucca l c row n t i pp i ng , i f any , t o age , i n it i alp a l a t al w i d t h , a m o u n t o f e x p a n s i o n , a n d c r o s s b i te . S t a -t i s t i ca l ana l yses showed no s i gn i f i can t r e l a t i onsh i ps .Bucca l t i pp i ng o f anchor t ee t h i s a f ac t o r t o be cons i d -e r e d a s a p a r t o f t h e R P E p r o c e d u r e .

T o d e t e r m i n e w h e t h e r t h e l a r g e v a r i a ti o n s i n b u c c a lt i p p in g o f a n c h o r t e e th w e r e d u e t o c r o s s b i te , t h e s a m p l ew a s d i v i d e d a m o n g g r o u p s w i t h b i l a t e r a l , u n i l a t e r a l ,a n d n o c r o s s b i t e . B e c a u s e o f th e s m a l l s a m p l e o f p a -t i en t s i n each ca t egory , i t was no t poss i b l e t o d r aw anyc o n c l u s i o n s . H o w e v e r , t h e r e w e r e i n d i c a ti o n s o f g r e a t e rc rown t i pp i ng i n pa t i en t s w i t h b i l a t e r a l c ros sb i t e , l e s s

wi t h un i l a t e r a l c ros sb i t e , and l eas t w i t h i n t he g roup w i t hno c ros sb i t e .

I t appea r s t ha t i n pa t i en t s w i t h b i l a t e r a l c ros sb i t e ,dur i ng RP E , t he r e i s a s t age when t he pa l a t a l i nc l i neso f t h e p a l a t a l c u s p s o f t h e m a x i l l a r y t e e t h o c c l u d e w i t ht he bucca l i nc l i nes o f t he li ngua l cusps o f t he mand i b-u l a r t ee t h , t hus p roduc i ng occ l usa l f o r ces t ha t may en-hance t he bu cca l t i pp i ng o f the ma xi l l a ry t ee th . I n pa -t i en ts w i t h no c ro s sb i t e , t he bu cca l i nc l i nes o f t he pa l a t a lc u s p s o f t h e m a x i l l a r y t e e t h m o v e d i r e c t l y i n c o n t a c twi t h t he l i ngua l i nc l i nes o f t he bucca l cusps o f them a n d i b u l a r t e e t h , w h i c h m a y t e n d t o m a k e t h e m a x i l -l a ry t ee t h more upr i gh t . I n t he man di bu l a r a r ch , t heses a m e o c c l u s a l f o r c e s m a y b e r e s p o n s i b l e f o r t h e s m a l lb u c c a l u p r i g h t i n g o f t h e m a n d i b u l a r p o s t e r i o r t e e th .CONCLUS I ONS

R a p i d p a l a t a l e x p a n s i o n w i t h t h e H y r a x a p p l i a n c ep r o d u c e s i n c r e a s e s i n m a x i l l a r y a r c h p e r i m e t e r a t t h er a te o f a p p r o x i m a t e l y 0 . 7 t i m e s t h e c h a n g e i n f ir st p r e -m o l a r w id t h . I n p l a n n i n g t r e a t m e n t , i t w o u l d b e h e l p f u lt o be ab l e t o p r ed i c t t h i s ga i n i n a r ch pe r i me t e r f o r ag i v e n a m o u n t o f t ra n s v e r s e e x p a n s i o n . T h e a b i l i ty t opred i c t t h i s r e l a t i onsh i p cou l d p romot e an i nc r eased useo f b o n y e x p a n s i o n f a c il it a ti n g n o n e x t r a c t io n o r t h o d o n -t i c t r ea t ment .

S l i g h t p a l a t a l m o v e m e n t o f t h e m a x i l l a r y i n c i s o r swas n o t ed i n 18 o f 21 pa t i en t s a f t e r s t ab i l iza t i on o f t heH y r a x a p p l i a n c e . T h i s m o v e m e n t w a s v a r i a b l e a t a p -p r o x i m a t e l y 0 . 5 _ 0 . 5 m m , w i t h a r a n g e f r o m - 1 .4m m p a la t al m o v e m e n t to 1 .0 m m l ab i al m o v e m e n t .

M i l d b u c c a l c r o w n t i p p in g o f t h e a n c h o r t e e t h o c -


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Volume97 Arch perimeter changes on RPE 1 9 9Number 3

c u r r e d w i t h t h e H y r a x a p p l i a n c e i n t h e s e a d o l e s c e n tpat ients , but the extent of t ipping w as variab le at ap-p r o x i m a t e l y 6 --- 6 . R e g r e s s i o n a n a l y s e s f o u n d n o s t a -t i s t ic a l l y s i g n i f ic a n t r e l a t i o n s h ip s b e t w e e n t i p p i n g o f t h eanchor teeth and age , in i t ia l palata l width, and thea m o u n t o f e x p a n s i o n .

S l i g h t c o m p e n s a t o r y b u c c a l u p r i g h t i n g o f t h e m a n -dibular poster ior teeth resul ted frorr i exp ansio n o f them a x i l la r y a r c h a n d t h e r e su l ta n t o c c l u s a l f o r c e s . D u r i n gthe s tabi l izat ion per iod, greater buccal upright ing of them a n d i b u l a r p o s t e r i o r t e e t h w a s a s s o c i a t e d m o r e w i t hp a t i e n t s w h o e x h i b i t e d n o p o s t e r i o r c r o s s b i t e .

R E F E R E N C E S1. Haas A J. Just the beginning of dentofacia l o rthodpedics . AM J

ORTHOD 1970;57:219-5 5.2. Ha rvold EP. The activator in interceptive orth odon tics. St. Louis:CV Mosby, 1974 .

3 . Pancherez H. Treatment of Class II malocclusions by jumpin gthe b i te w i th the Herbst appl iance: a eephalom etrie invest iga t ion .AM J ORTHOD 1979;76:423-41.

4. Sub telny JD. Oral respiration: facial ma ldevelopm ent and cor-rec t ive dentofacia l o rthopedics . A ngle O rthod 1980;50:147-64 .

5 . Ange l l EH. Treatm ent of i rregularit ies o f the permane nt o r adul tteeth. De nt Cosm os 1860;1:540-4.

6 . Bishara SE, Sta ley RN. Maxi l lary expansion: c lin ica l impl ica-tion s. AM J O R'nIOD DEN'rOFACORrr~OP 1987;91:3-14.

7 . Haas AJ . Rapid expansion of the maxi l lary denta l a rch and nasalcavity by opening the midpalatal suture. A ngle Orthod 1961;31:73-90.8 . Haas A J. The t rea tm ent of maxi l lary defic iency by opening themidpalatal su ture. An gle Orthod 1965;35:200-17.

9 . Haas AJ. Longterm post t rea tment evaluat ion of rap id pala ta lexpansion . Angle Orthod 1980;50:189-217 .

10. Kre bs A. Rap id expans ion of midpalatal suture by fixed appli-ance: an implan t s tudy over a 7 year period . Trans Eur OrthodSoc 1964:141-2.

11 . Wertz RA. Skele ta l and denta l changes accompanying rap id mid-palatal suture open ing. AM J ORTttOD 1970;58:41-66.

12 . Davis MW , Kron man JH. A natomical changes induced by sp li t-t ing of the midpalatal suture. Angle Orthod 1969;39:126-32.

13 . Gard ner GE, Kronm an JH. Cranioskele ta l d i sp lacements causedby rap id palatal expan sion in the rhesus m onkey. AM J ORTItOD1971 ;59:146-55.

14 . Timms DJ. A study of basa l movement wi th rap id maxi l laryexpan sion. AM J ORTtlOD 1980;50:500-7.

15 . Berlocher WC, M uel ler BH, Tinaoff N. The effec t o f maxi l larypala ta l expansion on the primary denta l a rch c i rcumference . Pe-diatr Dent 1980;2:27-30.

Reprint requests to:Dr. R a m S . Na n d aDe p a r t me n t o f Or t h o d o n ti c sCol lege of Dent i s t ryUn i v e rs it y o f Ok l a h o maP.O. Box 269011001 Staunton L. Young Blvd .Oklahoma Ci ty , OK 72190

arch perimeter changes on rapid palatal expansion

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