Dental Engineering

D ENTA L ENGINEERING Shall We Adjust an Articulator to Conform to Anatomical and Technical Require­ ments or May We Expect Our Patients to Fit an Average Articulator? By R U D O L P H L. H A N A U , M.E., Buffalo, New York

(R ead before the N ational Society of D enture Prosthetists, M ilwaukee, Wisconsin, August 1-13, 1921)

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I S t h e p u r p o s e o f t h i s p a p e r to b r i n g b e f o r e y o u a n i n v e s t ig a t io n o f m a n d i b u l a r m o v e m e n ts a n d t h e i r r e ­ p r o d u c t i o n i n t h e a r t i c u l a t o r m e c h a n is m f r o m t h e v i e w p o i n t o f d e n t a l e n g in e e r ­ in g . G r it m a n a n d S n o w a re a m o n g th e p io n e e r s i n t h e f i e l d o f r e s e a r c h w h i c h is t h e s u b je c t o f t h i s p a p e r . These p io n e e r s h a v e le v e le d t h e g r o u n d u p o n w h i c h G y s i b u i l t h is w o n d e r f u l s tr u c ­ t u r e , m a s t i c a t o r y m o v e m e n ts . T h e s e a rc h f o r th e r o t a t io n a l ax e s a n d p o in t s , t o w h i c h G y s i c o r r e c t ly r e ­ fe r s w h e n e l u c i d a t i n g h is t h e o r y , h a s s t a r t e d a h u n t f o r t h e r o t a t i o n p o in t s a n d axes. T h e a x e s o f r o t a t i o n to w h i c h G y s i r e f e r s a r e to b e u n d e r s t o o d a s m o m e n ­ t a r y a x e s o f r o t a t i o n a n d t h e lo c a tio n s h e s h o w s a re m o s t n e a r ly a n d m o s t f r e q u e n t l y to b e e x p e c te d f o r p a r t i c u l a r m o v e m e n ts . T h e H a ll and M onson t h e o r ie s , s o f r e q u e n t l y m e n t io n e d , a r e a m i s i n t e r p r e t a t i o n o f m a s t ic a t o r y m o v e ­ m e n ts as a p p lie d to th e a r tic u la to r m e c h a n is m . T h e lo c a t io n s o f t h e a x e s b y H a l l a n d b y M o n s o n , a n d th e ir p re ­ c u r s o r s , a r e s o u n f o r t u n a t e l y s e le c te d th a t th e y ca u s e m a n d ib u la r m o v e m e n t i n t h e a r t i c u l a t o r , w h i c h p r e s e n t d is ­ t o r t i o n o f a n a t o m i c a l c o n d it io n s a b o u t t h e c o n d y le s . T h e m o v e m e n ts d o n o t c o in c id e w i t h t h e i r r e s p e c tiv e th e o r ie s ,

Jour. N .D . A., Ju ly ,1922

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T h e s t u d y o f m a n d i b u l a r m o v e m e n ts is s o i n t i m a t e l y c o n n e c te d w i t h th e e v o l u t i o n o f a r t i c u l a t o r d e s ig n s t h a t I c a n n o t b u t m e n t io n th e s e t w o ite m s a lo n g s id e o f e a c h o th e r . V a r io u s a r t ic ­ u l a t o r d e s ig n s w h i c h w e h a v e t o d e a l w i t h a r e t h e v e r y e x p r e s s io n o f t h e c o n ­ c e p t io n o f m a s t i c a t o r y m o v e m e n ts b y t h e i r r e s p e c tiv e a u th o r s . T h e c a p i t a l q u e s tio n i n v o l v e d a lw a y s was: I s i t p e r m is s ib le t o u s e a n o n - a d j u s t a b l e m e c h a n is m b a s e d o n a v e r a g e s o r s h o u ld w e h a v e a n -a d ju s t a b le a p ­ p a r a t u s t o c o m p ly w i t h t h e a n a t o m ic a l c o n d it io n s a n d w i t h t h e t e c h n ic a l s e le c ­ t io n s ? U n d e r th e l a t t e r I u n d e r s t a n d th e to o t h f o r m a n d a r c h f o r m s e le c te d . I h a v e c o m e to th e f i n a l c o n c lu s io n t h a t i t is a b s o lu t e ly n e c e s s a r y t o a d j u s t a n a r t i c u l a t o r t o c o m p ly w i t h g i v e n i n d i ­ v i d u a l r e q u ir e m e n t s . S o m e o f t h e e r r o r s in t r o d u c e d b y r e l y i n g u p o n a v e r a g e s m a y b e m o re r e a d ily d e m o n s tra te d b y th e tw o -d im e n s io n a l d e m o n s tra to r ( F ig . 1 ). T e c h n ic s to m a k e and a p p ly m e a s u r e m e n ts h a v e b e e n g i v e n t o t h e p r o f e s s io n b y v a r io u s a u t h o r s , a n d to th e s e I h a v e a d d e d b y i n t r o d u c i n g n e w fe a tu re s . I a g a i n c a l l s p e c ia l a t t e n t i o n to t h e e m p lo y m e n t o f th e S n o w f a c e b o w . W e r e l y u p o n t h i s i n s t r u m e n t to e s ta b lis h

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is t h e f in e s t , s im p le s t a n d m o s t e le g a n t c o n t r i b u t i o n t o d e n t a l m e t r o lo g y . I t s u s e ­ f u ln e s s m a y j u s t l y b e c o m p a r e d w i t h t h e o p h th a lm o m e te r in v e n te d b y H e lm h o lt z . I d e f in e t h e f a c e b o w a s a n i n s t r u ­ m e n t f o r d e t e r m i n i n g t h e p o s i t io n a l r e l a ­ t i o n o f t h e d e n t u r e to t h e c o n d y le l i n e i n t h e p a t i e n t , a n d t o r e - e s t a b lis h s a id r e l a t i o n i n t h e a r t i c u l a t o r m e c h a n is m . F i g u r e 2 s h o w s a f a c e b o w d e s ig n e d b y m e a fte r S now . I m a in t a in t h a t a flo a tin g o f th e c o n ­ d y l e h e a d s s h o u ld o c c u r w i t h i n t h e n a t u r a l lim its o f fre e d o m o f m o v e m e n t o f t h e c o n d y le h e a d s i n t h e g le n o id fo s s a o n l y , a n d t h a t t h e r e is n o e x c u s e fo r g r in d in g -in a d e n tu re w h ic h w i l l fo r c e c o n d y le h e a d s t o m o v e b e y o n d t h e n a tu r a l sp ace o f th e ir fre e d o m o f m o v e ­ m e n t. I t is t h e r e f o r e o f u t m o s t i m ­ p o r t a n c e t o t h e p r o s t h e t is t t o k n o w t h e

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m o v e m e n ts e x e c u te d b y t h e l o w e r j a w m e m b e r i n r e l a t i o n to t h e u p p e r , a s is o u r e v e ry d a y in te r p r e t a t io n o f m a s tic a ­ t o r y m o v e m e n ts . T h e s y m b o ls g i v e n i n

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a n d h a s t h e r e v e r s e e f fe c t u p o n p o in t s lo c a t e d p o s t e r i o r ly . T h e a n te r io r a n d p o s t e r i o r l o c a t i o n is r e f e r r e d t o a p l a n e p a r a l l e l to a m o m e n t a r y m o v e m e n t a n d t h r u t h e c o n d y le l i n e . b T h e c lo s in g c o m p o n e n t \ / is a r o t a t i o n r e v e r s e d t o t h e o p e n in g c o m ­ p o n e n t. 2. T h e p r o t r u s iv e a n d r e t r u s iv e c o m ­ p o n e n ts ^ a r e r e c ip r o c a tin g m o v e ­ m e n ts o f t h e c o n d y le h e a d s a l o n g th e c o n d y le p a t h s . T h e s e c o m p o n e n ts s u f­ f e r a d i s t u r b a n c e w h e r e v e r t h e a n t e r io ­ p o s t e r io r i n c l i n a t i o n o f t h e c o n d y le p a t h s is n o t a l i k e o n b o t h s id e s . a The p r o t r u s iv e com ponent ^ i n f e r s a s i m u lt a n e o u s e x c u r s io n o f t h e c o n d y le h e a d s a l o n g t h e c o n d y le p a t h s a n t e r i o r l y , i r r e s p e c t iv e o f o t h e r m o v e ­ m e n ts o f t h e m a n d i b l e w h i c h m a y a c ­ c o m p a n y it. b The r e t r u s iv e com ponent ^ is r e v e r s e d t o t h e p r o t r u s iv e c o m p o n e n t . 3. L a t e r a l c o m p o n e n ts T T a r e o s c illa ­ tio n s , a n d l i k e a l l o t h e r c o m p o n e n ts a r e c o n s id e r e d ir r e s p e c t iv e o f t h e a c c o m ­ p a n y i n g m o v e m e n ts . a T h e r i g h t la t e r a l c o m p o n e n t T T is a r o t a t i o n a l m o v e m e n t o f t h e m a n ­ d i b l e , c a u s in g t h e r i g h t c o n d y le h e a d to a p p r o a c h it s s o c k e t w i t h a g r e a t e r v e lo c ­ it y th a n th e le ft. S u c h a d e fin itio tn . c o v e rs a l l p o s s ib le r i g h t l a t e r a l m o v e ­ m e n ts . W h e n t h e l e f t c o n d y le h e a d le a v e s it s s o c k e t, it s m o v e m e n t , i n r e l a ­ t i o n t o t h e s o c k e t, b e c o m e s n e g a t iv e , w h ic h o f c o u r s e is le s s t h a n n o m o v e ­ m e n t , t h e l a t t e r b e in g t h e c o n d i t io n o f t h e r i g h t c o n d y le h e a d w h e n i t o c c u p ie s i t s s o c k e t. D u r i n g m a s t i c a t i o n i t a ls o h a p p e n s t h a t t h e l e f t c o n d y le h e a d r e ­

The Journal of the National Dental Association

598

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c o n d y le p a t h . T h e d is t a n c e b e tw e e n t h is t h e o r e t i c a l s u r f a c e a n d t h e c o n d y le p a t h is t h e a c c e p te d r a d i u s o f t h e c o n d y le head. T h e i n t r u s i v e a b e r r a t i o n is d u e to t h e c h a n g e o f t h e r a d i u s o f t h e c o n ­ d y l e h e a d s a n d to t h e r e s i li e n c y a n d u n e v e n n e s s o f th e fib r o -c a r tila g e .

b T h e e x tr u s iv e a b e r r a t io n « is t h e d e v i a t i o n r e v e r s e d to t h e in t r u s i v e . A m a x im u m m ay be fo u n d a b o u t th e m i d d l e o f t h e c o n d y le p a t h , w h e n t h e c o n d y le r a d i u s in c r e a s e s a n d w h e n t h e m a n d ib le p e r fo r m s a p r o tr u s iv e e x c u r ­ s io n . I w o u l d e x p e c t a n in c r e a s e o f t h e e x t r u s iv e a b e r r a t i o n w i t h t h e in c r e a s e o f th e h o r iz o n ta l in c lin a t io n o f th e c o n d y le p a t h . The m ost im p o r ta n t m a s tic a to r y m o v e m e n ts , a s t h e y a r e g e n e r a l l y s p o k e n o f, a re e n u m e ra te d i n F ig u r e 4 u n d e r h e a d in g “ M o v e m e n ts .” U nder “ Com ­ p o n e n ts ” w e f in d th e c o m p o n e n ts o f th e d is s o lv e d m o v e m e n ts . The s y m b o ls v iv id ly illu s tr a t e th e c o m p le x ity of s o m e m o v e m e n ts w h ic h w e c o m m o n ly r e f e r t o b y o n e d e s ig n a t io n . I f w e a c c e p t t w o m o r e s y m b o ls O m e a s u r in g th is p o in t o f th e m a n d ib le n o t a ffe c t e d b y t h e m o v e m e n t , a n d • a p p e r ta in in g to m o v e m e n t o f th is p o in t o f th e m a n d ib le o n ly , th e n w e w i l l b e a b le to m a k e v e r y fin e d iffe r e n tia tio n s i n e l u c i d a t i n g m a s t i c a t o r y m o v e m e n ts , e. g . X T (u n n a tu r a l)1

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c o m p o n e n t to t h e r i g h t a n d th e r i g h t c o n d y le h e a d i n r e s t p o s it io n is u n ­ n a tu r a l, a n d T T w h e n ^ m eans a la t­ e r a l o s c i l l a t i o n a f f e c t i n g b o t h c o n d y le h e a d s , p o s s ib le o n ly w h e n b o t h j a w s a r e s e p a r a te d . '* 9 ( n a t u r a l n e a r ) ^ b u t r* y (u n ­ n a tu r a l) in d ic a t e s o p e n in g a n d c lo s ­ i n g m o v e m e n t n o t a f f e c t i n g th e p o s it io n o f t h e c o n d y le h e a d is n a t u r a l n e a r a p o s i t i o n o f c lo s e d ja w s ( c e n t r a l o c c lu ­ s io n ), b u t u n n a tu r a l w h e n th e ja w s a re s e p a r a te d . T h e r e a re n o lim its fo r u s e ­ f u l a p p l i c a t i o n o f th e s e s y m b o ls i n c la s s ­ r o o m s b y te a c h e r s .

‘I t is associated w ith partial ankylosis.

W ith

th e

e ig h t

c o m p o n e n ts ,

it

is

p o s s ib le to m a k e 2 5 5 d i f f e r e n t c o m b i n a ­ tio n s

w ith o u t

r e p e t i t io n .

C o n s id e r in g

a ls o t h e p e r p e n d i c u l a r a b e r r a t io n s d i f f e r e n t c o m b in a t io n s a r e p o s s ib le . in s t a n c e w i t h

1023 For

th r e e c o m p o n e n t s a , b , c,

w e h a v e s e v e n d i f f e r e n t c o m b in a t io n s w i t h o u t r e p e t i t io n , b u t i f w e p e r m i t r e p e t i t io n o f t h e c o m p o n e n t s i n d i f f e r e n t o r d e r w e h a v e fift e e n v a r ia tio n s . For e ig h t c o m p o n e n ts th e r e a re 4 4 1 6 2 4 9 6 0 v a ria tio n s , w h ile fo r te n c o m p o ­ n e n ts , 2 8 1 0 4 0 8 1 9 8 4 0 0 a r e p o s s ib le . T h e f o llo w in g fo r m u la e a re u s e d fo r c a lc u la tio n s : = 2 n — 1, a n d S 2 = n [2 ( n — 1 )! + ( n — 2 )\ + . . . . + (n — n +

1 )!]

F

reedo m

or M

o vem en ts

ular

P

of

M

a n d ib ­

o in t s

A l l p o in t s o f t h e m a n d i b l e h a v e f r e e ­ d o m o f m o v e m e n t in a l l th r e e d im e n ­ s io n s . T h e s e m a y b e in v e s t i g a t e d b y r e f e r r i n g t h e m to a n y c o - o r d in a t e s y s te m . G y s i, w h o h a s c h o s e n th e r e c t a n g u la r c o - o r d in a t e s , h a s g i v e n u s t h e m o s t s u c c in c t a n d c o rre c t d a ta . I have c h o s e n G y s i ’s w o r k a s a b a s is . G y s i h a s d e m o n s tra te d t h a t th e i n ­ c is a l c o n ta c t p o i n t h a s a f r e e d o m o f m o v e m e n t w i t h i n a f ig u r e k n o w n a s t h e G o t h ic a r c h . T h i s f i g u r e is in t e n d e d to i l l u s t r a t e t h e m o v e m e n t o f th e c o n ­ t a c t p o i n t o f t h e c e n t r a ls i n r e l a t i o n t o -a p l a n e , w h i c h a p p r o x i m a t e s t h e s o c a ll e d o c c lu s a l p l a n e , t h e l a t t e r b e in g a r b i t r a r i l y r e la t e d to t h e m a x i l l a o r p o in t s t h e r e o f . F i g u r e 5 r e la t e s t h e f a m i l i a r a r b i t r a r y t r i a n g l e r e p r e s e n t in g th e m a x illa r y tr ia n g le , a n d a n a r b it r a r y e llip s e r e p r e s e n t in g t h e lo iw e r d e n t a l a r c h t o th e m a n d i b l e . T h e b a s e lin e B C o f t h e a r b i t r a r y t r i a n g l e i s th e c o n ­ n e c t in g l i n e o f t h e c e n te r s o f t h e c o n ­ d y l e h e a d s , a n d t h e a p e x A is a c c e p te d a t t h e c o n ta c t p o i n t o f t h e l o w e r c e n t r a l in c is o r s . B o n w i l l a c c e p te d t h e m a n d i b ­ u l a r t r i a n g l e i n r e l a t i o n to t h e c o n ta c t p o in t s o f t h e u p p e r c e n t r a l in c is o r s . T h e a r c h e llip s e D A E is a s s u m e d t h r u

Hanau—Dental Engineering t h e c o n ta c t p o i n t s o f t h e te e th .

A

s u r­

fa c e l a i d t h r u t h i s e l l i p s e a p p r o x i m a t e l y c o in c id e s

w ith

p la n e .

An

because

it

s e m b lin g

th e

e llip s e is

th e

c o n v e n ie n t a n d

a

s o - c a lle d has

g e o m e t r ic a l

a rc h

fo rm

fle x ib le

o c c lu s a l

been

s e le c te d

fig u r e

and, in

is

re ­ v e ry

F i g u r e 6 is a n e x t e n s io n o f th e G y s i s p a tia l fig u r e m a y b e k n o w n

m uch

d is t o r t e d ,

and

th e

in d i­

v i d u a l s u r fa c e s le s s d is t in c t . F i g u r e 7 i l l u s t r a t e s s e v e r a l b ic u s p o id s , th e

m e d i a n . b ic u s p o id

p o in t s

in

and

o th e r s

fo r

s p a c e , n o t n e c e s s a r ily o f t h e

m a n d ib le . T h e c o n d y le b ic u s p o id ( F i g . 8 ) f o r a l l

d e s ig n .

G o t h i c a r c h i n t o th r e e d im e n s io n s .

becom e

601

The

(fo r w an t

o f a b e t t e r n a m e ) a s th e m e d i u m - b ic u s -

p r a c t i c a l p u r p o s e s m a y b e s u b s t it u t e d b y t w o e x t r e m e s u r fa c e s , a lm o s t e q u i d i s t a n t to t h e c o n d y le s u r fa c e s .

B e t w e e n th e s e

s u r fa c e s , w h i c h in te r s e c t i n t h e r e t r u s iv e

Fig. 6

p o id .1 A n y p o in t o n a n d w it h in th e s u r­ fa c e s o f t h i s b i c u s p o id is a p o s s ib le p o s i t i o n f o r t h e c o n ta c t p o i n t o f t h e l o w e r c e n t r a ls d u r i n g m a n d i b u l a r m o v e ­ m e n ts . A l l o t h e r p o in t s o f t h e m a n d i ­ b le h a v e a ls o f r e e d o m o f m ovem ent w i t h i n b ic u s p o id s , w h i c h a r e g e o m e t r i­ c a l l y r e l a t e d to t h e o n e h e r e s h o w n . B ic u s p o id s h a v e f i v e s u r fa c e s m o r e o r le s s c u r v e d : t w o s u p e r i o r s u r fa c e s , t w o p o s t e r i o - l a t e r a l s u r fa c e s a n d o n e a n te r io r s u rfa c e . T h e p o s te r io -la te r a l s u r fa c e s u n i t e i n a r id g e a n d t h e t w o s u p e r io r s u r fa c e s a l o n g a fo s s a , e tc . T o w a r d t h e c o n d y le s , th e s e b ic u s p o id s

‘“Bicuspoid” is derived , from “ bicuspid”, the form ation being bicuspid-like; “bicuspidoid” may be more correct.

p o s it io n s

of

th e

c e n te r o f

th e

c o n d y le

s o c k e ts , w e f i n d a l l p o s s ib le p o s it io n s o f th e

c o n d y le

c e n te r s

fo r

m a s t ic a t o r y

m o v e m e n ts . T h e s p a c e , j u s t d e s c r ib e d , is t h a t o c c u p ie d b y th e c o n d y le b ic u s p o id , a n d t h e c o n d y le m o v e m e n t w h i c h G y s i r e c o r d s is a l a t e r a l p r o j e c t i o n o f t h i s b ic u s p o id . I t is a n a v e r a g e r e p r e s e n t a ­ t i v e o f t h e l a t e r a l p r o je c t io n p f c o n d y le m o v e m e n ts . T h e u p p e r s u r f a c e o f th e c o n d y le b i c u s p o id is o f p r i m a r y in t e r e s t to t h e p r o s t h e t i s t i n g r i n d i n g m a s t ic a t o r y s u r fa c e s . T h e h e ig h t a n d th e tra n s v e rs e d im e n ­ s io n s o f t h e b ic u s p o id s d e c re a s e f o r p o in t s a p p r o a c h in g t h e c o n d y le h e a d . T h e s e th e m s e lv e s a r e a b le t o m o v e o n p a t h s u r fa c e s , a lm o s t e q u i d i s t a n t t o t h e

The Journal of the National Dental Association

602

c o n d y le p a t h i t s e l f . T h e e q u id is t a n c e is s o m e w h a t d is t u r b e d b y th e p e r p e n d i c ­ u la r a b e r r a tio n a n d b y th e s h a p e o f t h e c o n d y le h e a d , w h i c h is n o t a r o t a r y f o r m a t i o n . T h e d im e n s io n o f t h e b ic u s ­ p i d s r e m a i n c o n s ta n t i n t h e d i r e c t i o n o f t h e i n c i s i v e c o m p o n e n ts . I t m u s t b e k e p t in m in d th a t a n y p o i n t w i t h o u t t h e m a n d i b l e i n d e f in i t e g e o m e t r ic a l r e l a t i o n t o t h e m a n d i b l e h a s its c o r r e s p o n d in g b ic u s p o id . W ith in t h is b ic u s p o id i t c a n m o v e i n r e l a t i o n to th e m a x i l l a . T h e p in a n d in c is iv e g u i d e o f m a n y a n a r t i c u l a t o r d e s ig n a r e

W e u n d e r s t a n d t h a t t h e p ro c e s s is s u b je c t to a b s o r p t io n , a n d r e g e n e r a t io n n o t a b l y d u r i n g th e p e r io d o f n a t u r a l d e v e lo p m e n t o f t h e d e n t a l a p p a r a t u s , a n d n o t c o n f in e d to t h i s p e r io d . How­ e v e r , w e a s s u m e t h a t t h e r e is a l i m i t w i t h i n w h i c h n a t u r e a c c o m m o d a te s w i t h ­ o u t c a u s in g p h y s i c a l d e fe c ts o r p a t h o ­ l o g i c a l c o n d it io n s a n d c o n s e q u e n t i n c o n ­ v e n ie n c e . T h is lim it has n o t been d e ­ t e r m i n e d a n d c a n n o t b e d e t e r m in e d w i t h m a th e m a tic a l a c c u ra c y . W e k n o w f r o m o b s e r v a t io n t h a t i n ­ c o n v e n ie n c e is c a u s e d to th e p a t ie n t s b y

Û

Fig. 7

Fig. 8

illu s tr a tio n s of th e im p o r ta n t th a t s h o u ld b e g i v e n to p o in t s r e l a t e d to th e m a s t i c a t o r y a p p a r a t u s , n o t n e c e s s a r ily w i t h i n its o w n s p a t i a l e x te n t. I f w e c o n fin e o u r a t t e n t i o n t o th e m o v e m e n ts o f a n y th r e e p o in t s d e f i n i t e l y r e la t e d to t h e m a n d i b l e a n d r e l a t e th e m o v e m e n ts t o t h e m a x i l l a , a n d p r o d u c e a n a p p a r a t u s w h ic h w i l l p e r m i t e q u i v ­ a l e n t m a n d i b u l a r m o v e m e n ts , t h e n w e h a v e a n a rtic u la to r. T

he

F

l o a t in g

' Û

C o n dyle

T h e c o n d y le p a t h is a f r a g m e n t o f th e m a x i l l a r y m a s t ic a t o r y s u r f a c e ; u p o n i t o p e r a te s t h e c o n d y le h e a d , t h e l a t t e r b e in g a f r a g m e n t o f th e m a n d i b u l a r m a s t i c a t o r y s u r f a c e ; b e tw e e n t h e t w o w e f i n d t h e f i b r o - c a r t i l a g e , a c t in g a s c u s h io n a n d l u b r i c a n t .

ill- f it t in g to

d e n tu r e s ,

d is lo c a t e

space w ith in

th e

w h ic h

c o n d y le

w h ic h

heads

space, w ith in

in

te n d

fro m

a

n a t u r a l m a s t ic a t io n

r e q u ir e s a f r e e d o m c o n d y le

u n d u ly heads

o f m o v e m e n t o f th e th e ir

w h ic h

c a v it ie s .

fr e e d o m

T h is

o f m ove­

m e n t o f a n a c c e p te d c e n te r o f th e c o n ­ d y l e h e a d ta k e s p la c e , w a s d e s c r ib e d as th e c o n d y l e b ic u s p o id . I d o n o t fo r a m o m e n t d e n y t h e e x is te n c e o f b o n e a b ­ s o r p t io n a n d b o n e r e g e n e r a t io n , w h ic h n a tu r e s o c h a r it a b ly h a s in s titu te d , b u t m a in ta in t h a t t h e p r o s t h e t is t s h o u ld k n o w “ w h e n a n d w h e re ” h e w a n ts to s t i m u l a t e a c h a n g e o f t h e p ro c e s s a n d “ h o w ” h e m a y d o it. I a m a b s o lu t e ly opposed to t h e h i t - a n d - m i s s m e th o d w h i c h d o e s n o t d ia g n o s e , a n a l y z e n o r a p p l y t h e b e s t, b e c a u s e i t is a n a c k n o w l ­

603

Hanau— Dental Engineering edged

f a c t t h a t p h y s i c a l d e fe c ts o f t h e

d e n ta l a p p a ra tu s

a n d p a th o lo g ic a l c o n ­

cause

d e fo r m a tio n .

d itio n s h a v e b e e n c a u s e d b y a n d tr a c e d

d y le h e a d a n d

to i l l - f i t t i n g

d y l e fo s s a .

The

p la te s .

in flu e n c e

upon

fo rtu n a te m any

and

w ays

u n fo rtu n a te

th a t

th e

c o n d it io n s

o f t h e w a l l o f th e c o n ­

T o o g re a t a p re s s u re causes

and

b o n e a b s o r p t io n a n d t o o l i t t l e o r a n e g a ­

I t is b o th

t i v e p r e s s u r e r e s u lt s i n b o n e r e g e n e r a t io n

d e n tu re

c o n d y le s u r f a c e is r e c ip r o c a l.

S im ila r

a p p l y to t h e b o n e s t r u c t u r e o f t h e c o n ­

fo r

a rtific ia l

us

in

d e n tu re

o r d in a r ily . e r a t io n

B o t h a b s o r p t io n a n d r e g e n ­

occur

v e ry

g r a d u a lly

and

in -

to

th e

is m a d e t o r e s t o n tis s u e w h i c h i t s e l f is r e s ilie n t

and

s u b je c t t o

a b s o r p t io n .

I

k n o w t h a t t h i s s ta te o f a f f a i r s m a k e s i t d iffic u lt w h ic h

to

I

m e a s u re

am

“ v e ry ”

a c c u r a t e ly ,

a c c u s e d o f r e c o m m e n d in g

Y e t I m a i n t a i n t h a t e x i s t in g a n a t o m i c a l c o n d it io n s

s h o u ld

o r in d ir e c tly

be m e a s u re d

w ith

is p o s s ib le a n d

d ir e c tly

th a t

a c c u ra c y w h ic h

w ith in

p r a c t ic a l re a c h .

I n d i r e c t r e l a t i v e m e a s u r e m e n ts a r e v e r y p r a c tic a l

and

if

c a r e fu lly

m ade

m ost

r e lia b le . To have (F ig .

illu s tr a t e th o u g h t 9 ).

o f c la y

th e

f l o a t in g

o u t th e

It

c o n d y le ,

fo llo w in g

I

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c o n s is ts o f a b a s e m a d e

o r p u tty

r e p r e s e n t in g

w a l l o f t h e g l e n o i d c a v it y .

th e b o n y

T h e g re a s e d

r u b b e r s h e e t ta k e s t h e p la c e o f t h e f i b r o c a r t il a g e , a n d th e b a l l a t t h e e n d o f th e r o d , t h a t o f t h e c o n d y le h e a d . end

has

s u rfa c e

fre e d o m

T h e b a ll

of m ovem ent on

th e

o f t h e r u b b e r s h e e t, e q u i v a l e n t

t o t h e c o n d y le h e a d m o v e m e n t u p o n th e fib r o -c a r tila g e . T h e s o - c a lle d f l o a t i n g o f t h e b a l l e n d (c o n d y le

head)

ta k e s

p e r p e n d ic u la rly

to

(fib r o -c a r tila g e ).

p la c e

th e A

a lo n g

ru b b e r fre e

sheet

m ovem ent

a l o n g t h e s u r f a c e o c c u rs w h e n n o p r e s ­ s u r e is e x e r t e d . u l a r to

th e

A m o v e m e n t p e r p e n d ic ­

s u r f a c e s e ts i n

Fig. 9

and

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as

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p a tie n t.

Is

in c o n v e n ie n c e

th a t

th e

I t is q u i t e e a s y to d e t e r m in e w i t h t h e a id

o f check

b ite s ,

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e n d is e i t h e r l i f t e d

o ff th e ru b b e r sheet

fa u lty

o r p re s s e d in to it.

A n y p re ss u re w ith in

t io n s o f a r t i c u l a t i o n .

and

lim its w ith in

of

e la s t ic it y

th e

lim its

of of

th e

ru b b e r

w h ic h

t h e p r o s t h e t is t d e s ire s ?

a p e r p e n d i c u l a r fo r c e a c ts a n d t h e b a l l

th e

“ flo a tin g ”

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o c c lu s io n

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d is tr ib u tio n

m u s t b e e x p e c te d in

th e

d iffe r e n t

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fro m p o s i­

I f w e a s s u m e t h e s a m e m u s c le a c t i o n

r e s i li e n c y

of

f o r d e f e c t iv e o c c lu s io n t h e n t h e f o l l o w ­

t h e c l a y b e lo w h a s n o l a s t i n g e ffe c t.

A

in g

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

change

o c c u rs :

in

d is tr ib u tio n

of

fo r c e s

604

T h e Jo u rn a l of the National D ental Association

Bite

Intended Occlusion

Pressure D istribution in Fossa

Open posteriorly O pen posteriorly O pen anteriorly O pen anteriorly

Central Protrusion Central Protrusion

Increased Increased Decreased Decreased

Faulty distribution or pressure by de­ fective occlusion or unsatisfactory plates invariably stimulates bone and tissue changes. The check bites indirectly serve as a means to find out whether the condyle movements were correctly adjusted in the articulator mechanism. It is evident that a denture correctly articulating in the articulator, will of necessity correctly articulate in the mouth only if the articulator has been correctly adjusted. If a denture correctly articulates in the adjusted articulator but shows de­ fective occlusions in the mouth, then the articulator should be readjusted to compensate for these defects. Their exists a reciprocal relation be­ tween the tissue changes in the mouth and the bone changes in the glenoid fossa. Unless the relation of the respec­ tive changes are thoroly studied and un­ derstood, the period of accommodation of the artificial denture to the patient’s existing masticatory function is unduly prolonged. The reciprocal relation may very readily be studied and demon­ strated by statics by accepting the jaws as moving levers upon which the forces of mastication are exerted by the muscles and distributed by the plates and the condyle heads. Tho we are not able to establish rigid formulas which apply to individual cases, it may be stated that it presents no particular difficulty to follow up the conditions which pertain to a hypothetical case. The advance of surgery has accom­ plished the feat of amputating the con­ dyles to eliminate the handicap of ankylosis. The operation re-establishes the possibility of performing mandib­ ular movements after a fashion.

posteriorly anteriorly posteriorly anteriorly

Pressure D istribution in M outh Increased Increased Increased Increased

anteriorly anteriorly posteriorly posteriorly

The resulting masticatory function is abnormal in every respect. An entirely different co-ordination of the magnitude and direction of muscular forces is the result. It is but an example of nature’s wonderful adaptability to master a most intricate instability. N atural

D en tu r es V ersu s c ia l D e n t u r e s

Ar t if i­

In earlier readings I have shown that natural mastication is not identical with artificial mastication. The only part of the edentulous mandible which moves or attempts to move in exact compliance with natural dictates is the condyle head in the glenoid fossa, anterioposteriorly, laterally, as well as in opening and closing. The magnitudes of these movements suffer a change unless incidentally a duplicate of the natural denture has been made and provided no bone and tissue changes have taken place about the condyles during the past, toothless period. Usually artificial dentures are made for patients, who have not been under the constant care of the dentist and whose records are not available. Thus we are confronted with fragmen­ tary, often mutilated, remnants, which may evidence that the original mastica­ tory surfaces were different. It is right here that the prosthetist will analyze and diagnose his case to deter­ mine the course he must pursue. No so-called anatomic, automatic or adjust­ able articulator will fill the gap which has to be bridged by concentrated analytic and constructive thinking. I will endeavor to give in short the most prominent characteristic of natural and artificial mastication and sum up

605

Hanau— Dental Engineering A r t ic u l a t o r s

t h e r e q u i r e m e n t s f o r in c r e a s e d e ffic ie n c y o f a r t if ic ia l m a s tic a tio n . The

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g u m s u p o n w h i c h t h e p la t e s a r e s e a te d we s h o u ld d e c re a s e th e m a s t ic a t o r y c o m p o n e n ts i n t h e d ir e c t io n s w h ic h o f f e r a m in im u m o f a n c h o ra g e a n d i f neces­ s a r y o r a d v i s a b l e in c r e a s e i n t h e d ir e c ­ t io n o f m a x i m u m a n c h o r a g e . I n o th e r w o r d s w e m u s t b u i l d a c o m p r o m is e d e n t u r e a n d e ffe c t c o m p r o m is e a r t i c u l a ­ tio n . T o a c c o m p lis h t h is w e m u s t b e a c q u a i n t e d w i t h t h e r e l a t i o n b e tw e e n c o n d y le g u i d a n c e t o o t h p o s i t i o n a n d a n d to o th fo r m . These a re p u r e ly s t a t i c a l a n d g e o m e t r ic a l c o n s id e r a t io n s , w h i c h m u s t b e h a r m o n i z e d t o c o m p ly w i t h t h e c o m p lic a t e d k i n e m a t i c a l r e ­ q u ir e m e n t s o f m a s t i c a t io n . T h e to o t h fo r m a n d a rc h f o r m i n c o n ju n c tio n w it h t h e c o n d y le p a t h m u s t c o n s titu t e a h a r ­ m o n io u s s t r u c t u r e w h i c h p e r m i t s a r t i c u l a ­ t io n . T h e c o n d y le g u id a n c e is g iv e n b y th e p a tie n t; i t m a y r e q u ir e m o d ific a ­ tio n in o n e d ir e c tio n o r a n o th e r. T h is is a q u e s t io n to b e d e c id e d b y t h e p r o s ­ th e tis t a n d n o t b y a n y th u m b r u le , o r a n a r t i c u l a t o r m e c h a n is m . N e x t i n o r d e r is t h e s e le c tio n o f to o t h f o r m . T h e v a r io u s f o r m s a v a i l ­ a b le i n t h e m a r k e t o f f e r a s p le n d id v a r i a t i o n f r o m w h i c h to s e le c t f o r m o s t r e q u ir e m e n t s . T h e a r c h f o r m , I v e n t u r e to s a y , s h o u ld b e a r e s u l t a n t o f t h e d e ­ t e r m i n e d o r a c c e p te d c o n d y le p a t h s , o f t h e s e le c te d to o t h t y p e , o f t h e r id g e s , w h e re th e y a re p la c e d a n d f in a lly o f th e k i n e m a t i c a l r e q u ir e m e n t s . T o com ­ p ly w it h th e la t t e r w e n e e d th e a r t ic ­ u l a t o r m e c h a n is m , t h e p a t i e n t ’s d u m m y .

d e n t a l a r t i c u l a t o r is

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g r i n d i n g i n a r t i f i c i a l te e th . W e d i s t in g u s h t h e p l a i n l i n e a r t i c ­ u la to r , a r b itr a r y m o v e m e n t a rtic u la to r , a v e ra g e m o v e m e n t a r t ic u la t o r , s e m i-a d ­ ju s ta b le a r tic u la to r , a d ju s ta b le a r tic ­ u la to r . P l a i n li n e a r t ic u la t o r s a r e f r e q u e n t l y e m p lo y e d in p a r t ia l d e n tu r e re c o n s tru c ­ t i o n to e s t a b lis h o c c lu s io n . T h e y , e x e c u te a n a r b i t r a r y o p e n in g c o m p o n e n t m o v e ­ m e n t a n d c o n s is t o f t w o v ic e j a w s h i n g e d i n th e b a c k . A d j u s m e n t o f t h e p o s it i o n o f o n e j a w o r b o th j a w s i n r e l a t i o n to t h e h i n g e a x is b y m e a n s o f lo c k s c re w s is u s u a l l y p r o v i d e d f o r . A r b i t r a r y m o v e m e n t a r t ic u la t o r s p e r ­ m i t t h e e x e c u tio n o f tw o o r m o re m a n d i b u l a r c o m p o n e n t m o v e m e n ts in a r b i t r a r i l y a c c e p te d d ir e c t io n s . A v e r a g e m o v e m e n t a r t ic u la t o r s e x e ­ c u te m o v e m e n ts d e t e r m in e d o r a c c e p te d b y t h e i r o r i g in a t o r s a s a v e r a g e s . S e m i- a d ju s t a b le a r t ic u la t o r s p e r m it a d ju s t m e n t o f d ir e c t io n o f a t le a s t o n e a r t i c u l a t o r m o v e m e n t to c o n f o r m w i t h m a n d i b u l a r c o m p o n e n t m o v e m e n ts of th e p a tie n t. A d j u s t a b le a r t ic u la t o r s p e r m i t a d j u s t ­ m e n t s o f a l l a r t i c u l a t o r m o v e m e n ts to c o n fo rm w i t h m a n d i b u l a r m o v e m e n ts o f th e p a tie n t. A d ju s tm e n t m u s t b e p o s s ib le w i t h i n m e a s u r a b l e l i m i t s . The m e a s u r e m e n ts m a y b e d i r e c t l y o r i n ­ d ir e c t ly m a d e . I t is o f t e n v e r y d i f f i c u l t to d is t i n g u is h b e tw e e n a r b i t r a r y m o v e m e n t a n d a v e r ­ a g e m o v e m e n t a rtic u la to rs . A s a r u le i t w i l l b e f o u n d t h a t b o t h ty p e s a r e e q u a lly u n tru s tw o rth y . T h e i r u n iv e r s a l a p p l i c a t i o n is b a s e d u p o n f a ls e e c o n o m y a n d m i s u n d e r s t a n d in g o f th e a r t i c u l a t o r m e c h a n is m a n d o f m a s tic a to r y r e q u ir e ­ m e n ts . A r tic u la to r s e m p lo y i n g gauges fo r p l a c i n g t h e d e n tu r e s i n t h e a r t i c u l a t o r a re r a n k e d w ith a r b itr a r y m o v e m e n t a r t ic u la t o r s , f o r t h e o m is s io n o f c o r ­

The Journal of the National Dental Association

606

r e c t l y p l a c i n g a d e n t u r e is e q u i v a l e n t to

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A s e x a m p le o f i n d i r e c t m e a s u r e ­

a ll k n o w

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th e

t a b l e is g iv e n t h e l i m i t s o f a c c u r a c y w e m a y e x p e c t, w h e n m a k i n g m a n d i b u l a r m e a s u r e m e n ts . E rro rs w ith in th e s e l i m i t s a r e n e g l i g i b l e o r m a y b e c o r r e c te d in d ir e c tly .

M easurem ents L im its Position of condyle socket center..... 2 mm. A ngular deviation of m axillary con­ dyle line ....................................................3° A ngular deviation of occlusal plane....3° D istance of incisal contact point from condyle line ..........................................2 mm. H orizontal inclination of condyle movement anterio-posteriorly .............. 5° Horizontal inclination of condyle movement laterally ................................10° Inclination of lateral excursion of condyle head from socket anterioposteriorly .............................................. 10° D iam eters of teeth ...................................0.05 mm. Contact of teeth during articulation in articulator .........................................0.10 mm. Angles of tooth cusps .............................. 15° Angles of worn tooth cusps................ 5° T issue compression w ith new plates in m outh ............................................... 0.50 mm. L ateral excursion of condyle heads....0.50 mm. T o o th relation in one jaw (horizontal ...........................................0.10 mm. (vertical ................................................. 0.20 mm. T o o th relation in two 'jaw s (horizontal ............................................. 0.30 mm. (vertical ............................................ -..0.10 mm. Inclination of tooth axis...................... arbitrary By d i r e c t m e a s u r e m e n ts we m ean th o s e m a d e b y m e a n s o f c a l i b r a t e d i n ­ s t r u m e n t s ; t h e y a r e a b s o lu t e a n d ex­ p re s s e d i n le n g th , a re a , s p a c e , d e g re e , e tc . I n d i r e c t m e a s u r e m e n ts a r e m a d e b y

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1 0 ).

T o a d ju s t th e h o r iz o n ta l a n d la t e r a l in c lin a tio n s in th e a r t ic u la t o r w e u se w a x b ite s . T h e s e w e re ta k e n in r ig h t a n d l e f t l a t e r a l o c c lu s io n a n d f o r c h e c k ­ in g p u r p o s e s a ls o i n p r o t r u s iv e o c c lu ­ s io n . T h e b ite s s h o u ld n o t b e t a k e n i n e x t r e m e o c c lu s a l p o s itio n s . W e u se th e r ig h t la t e r a l b ite to a d ­ j u s t t h e h o r i z o n t a l i n c l i n a t i o n o f th e le f t fo r w a r d , a n d o f th e r ig h t la t e r a l c o n ­ d y le m o v e m e n t , b e c a u s e i n t h i s o c c lu s a l p o s it io n th e r i g h t c o n d y le h e a d m o v e s o n o r n e a r t h e m a x i l l a r y c o n d y le l i n e o n ly , w h i l e th e l e f t c o n d y le h e a d h a s m a d e a n e x c u r s io n a n t e r i o r l y f r o m it s s o c k e t. E q u a l l y w e d e t e r m in e w i t h th e l e f t la t e r a l b ite th e in c lin a t io n o f th e r ig h t f o r w a r d a n d th e le f t la t e r a l c o n ­ d y le m o v e m e n t . W e m a n i p u l a t e th e le v e r s A 1 a n d A 2 u n t i l t h e o c c lu s a l r i m s s e a t th e m s e lv e s s e c u r e ly i n t o th e w a x b it e . T o a d ju s t t h e r i g h t h o r iz o n t a l i n ­

c lin a t i o n ,

we

use

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la t e r a l

b ite

a n d m a n i p u l a t e t h e le v e r A 1 o n t h e r i g h t s id e u n t i l t h e o c c lu s a l r i m s s e a t t h e m s e lv e s i n t o t h e w a x b i t e a n d e s ta b ­ l i s h c o r r e c t l e f t l a t e r a l o c c lu s io n i n th e a r tic u la to r . F o r d e t e r m in in g t h e l e f t

h o r iz o n t a l in c l in a t io n , w e u s e th e r i g h t la t e r a l b ite a n d a d j u s t t h e l e f t le v e r A 2 u n t i l w e e s ta b lis h r i g h t l a t e r a l o c ­ c lu s io n . B o t h le v e r s a r e s e c u r e ly lo c k e d b y lo c k n u t s C j a n d C 2 a n d B t a n d B 2. I t is s u g g e s te d t h a t d u r i n g th e s e a d ­ ju s t m e n t s th e l o c k n u t E o f t h e b a c k

Hanau— Dental Engineering

center socket is loosened to eliminate lateral interference. An adjustment of the center socket E changes the magnitude and direction of the lateral movements in relation to those of the incisal contact point. A backward adjustment of E increases the magnitude of lateral movements and decreases the forward-backward inclina­ tion of lateral movements of mandibular points posterior to the central incisal contact point and vise versa.

607

of these components. It will be noted in Figure 11 that the change in posi­ tion of socket caries the rotational point in the direction of the adjustment. The inclination of the condyle plate F 1 (Fig. 10) is also adjustable by rotating the latter. The rotational point so-called is to be found on a perpendicular to the inter­ section of the surface of F t with the drawing-plane. The intersection of the perpendicular lines to the directions of

Fig. 10.— Ai and A2, right and left condyle levers. Bi and B2 right and left bores for face bow. Ci and C 2 right and left locknuts for condyle levers. D! and D 2 cast plates. E, center socket. F i and F 2 right and left condyle socket wall plates. G, incisal guide. H , incisal pin. J, locknut for incisal guide. K i and K 2 and left condyle socket supports. L t and L 2, locknuts for cast plates.

It is erroneous to consider this center socket as a common central rotation point. E being movable anterioposteriorly in conjunction with the articulator condyle centers becomes a rotational point of a moving system only. The mandibular member of the articulator is guided directly in the condyle sur­ face plate F t or F 2 and the incisal guide G and is indirectly guided by the center socket E. The common rotational point of the components of movements in a plane is given by the intersection of the perpendicular lines to the directions

the movements is the common rotational point for the components under consid­ eration. By adjusting the inclination of the surface of F x (Fig. 10) we are at liberty to change the position of the rotational point laterally. Plates F 1 and F 2, having an inclination of 15°, as are at present provided in the artic­ ulator, enable us to adjust the location of the rotational point in the drawingplane within the shaded area shown in Figure 11. We may use the protrusive bite to check the adjustments of the horizontal

608

T he Jo u rn a l o f the National D ental Association

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O p e n i n g a n d c lo s ­

i n g o f t h e b i t e i s a c c o m p lis h e d b y a d ju s tin g th e g u id e u p o r d o w n , r e ­ s p e c t iv e ly . N o u n d u e fo r c e s o r r e s is ta n c e s i n t e r ­ f e r e w i t h s e n s itiv e o p e r a t io n o f t h is a rtic u la to r , d u e to th e fa c t th a t c o n ­ s t r a in e d m o v e m e n ts a r e e m p lo y e d to

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C o n c l u s io n s 1.

P o in ts o f th e m a n d ib le g a v e fr e e ­

d o m o f m o v e m e n t w i t h i n b ic u s p o id s . 2.

A r tic u la tio n

o c c u rs

upon

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s u p e r io r s u r fa c e s o f th e s e b ic u s p o id s . 3.

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Hanau— Dental Engineering c a to ry s u r fa c e s , a r tic u la tio n .

in

any

p o s i t io n

of

4. A v e r y c o m p le x r e l a t i o n e x is t s b e tw e e n m a s t i c a t o r y s u r fa c e s a n d a r c h fo r m a tio n . 5. M a n d i b u l a r m o v e m e n ts a r e d i s ­ s o lv e d i n t o t h e i r c o m p o n e n t s to e n a b le e x a c t a n a ly s is . 6. Ten m o v e m e n ts

c o m p o n e n ts o f a r e c o n s id e r e d .

m a n d ib u la r

7. I t is o b s o le te , t o e x p e c t a r t i c u l a ­ tio n o f tw o a r b it r a r ily c h o sen a n d o c­ c lu d e d a r c h e s , w i t h o u t d u e c o n s id e r a ­ tio n o f th e r e la tio n o f th e a r c h fo r m a n d t h e o c c lu d in g s u r fa c e s t o t h e c o n d y le f o r ­ m a tio n . 8. M a n d i b u l a r m o v e m e n ts d o n o t o c c u r a b o u t a p o i n t o r a n a x is p e r m a n ­ e n t l y r e l a t e d to t h e m a x i l l a . 9. M a n d i b u l a r m o v e m e n ts o f n a t ­ u r a l d e n tu r e s a n d a r t i f i c i a l d e n t u r e s a r e n o t id e n t i c a l . 10. A r tic u la to r and a n a to m ic a l m o v e m e n ts n e e d n o t b e i d e n t i c a l , b u t m u s t b e e q u iv a le n t, in o r d e r to p r o c u r e c o rre c t g r in d in g i n th e a r tic u la to r . 11. A r t i c u l a t o r s e m p l o y in g a r b i t r a r y o r a v e r a g e m o v e m e n ts a r e in a d e q u a t e , b e c a u s e t h e y d o n o t g r i n d - i n te e t h to c o m p ly w i t h i n d i v i d u a l r e q u ir e m e n t s . 12. A r t i c u l a t o r s e m p lo y i n g a r b i t r a r y g a u g e s o r jig s in d e fin ite r e la tio n to a j a w m e m b e r s h o u ld n o t b e u s e d , b e c a u s e a g a u g e d o e s n o t e s t a b li s h c o r r e c t p o s i­ t io n a l r e la tio n . 13. A te c h n ic e m p l o y i n g t h e fa c e b o w a n d t h e w a x b i t e m e t h o d is r e c o m ­ m ended. 14. A r t ic u la t o r a r tic u la tio n m u s t b e d ir e c t e d b y th r e e g u i d i n g s u r fa c e s to p r o d u c e m o v e m e n ts e q u iv a le n t t o a n a t o m ­ ic a l a r tic u la tio n . 15.

An

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tw o

609

c o n s t r a in e d a n d a d j u s t a b le c o n d y le p a t h g u i d i n g s u r f a c e s a n d o n e a d j u s t a b le , in te r c h a n g e a b le in c i s i v e g u i d i n g s u r­ fa c e , is a d v o c a t e d . 16. A n a r t ic u la t o r m u s t b e a d ju s t­ a b le t o c o m p ly w i t h a n a t o m i c a l a n d t e c h n i c a l r e q u ir e m e n t s . 17. T h e d ir e c t i o n a n d m a g n i t u d e o f t h e c o n d y le m o v e m e n t m u s t b e a d j u s t ­ a b le to c o m p l y w i t h a n a t o m i c a l r e q u i r e ­ m e n ts . 18. T h e d ir e c t io n a n d m a g n i t u d e o f t h e in c i s a l g u id a n c e m u s t b e a d ju s t a b le or i n t e r c h a n g e a b le to c o n fo rm w ith t e c h n ic a l r e q u ir e m e n t s . 19. T e c h n i c a l r e q u ir e m e n t s a r e th o s e g iv e n b y th e fo r m a t io n o f th e a r t if ic ia l m a s t ic a t o r y s u r fa c e s . I n c lo s in g p e r m i t m e t o e x p r e s s m y th a n k s to D rs . M a r t in D e w e y o f N e w Y o r k , H . E . R e y n o ld s , E . J . F a n n e r o f B u ffa lo a n d to M r . J . L . S te m , m y as­ s o c ia te , f o r t h e g e n e r o u s a s s is ta n c e e x ­ te n d e d t o m e i n t h e p r e p a r a t i o n o f t h i s p a p e r. B

ib l io g r a p h y

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