Ceramic vs. Steel Brackets

7/21/2019 Ceramic vs. Steel Brackets

1/5

T he sh ea r bond st r en g t h s o f st a i n l e ss st eel an d

cer am i c b r a c ket s u sed w i t h chem i c a l l y an d

l i g h t ac t i v a t ed com posi t e r e si n s

V . P . J o s e p h , B D S , M S c D e n t . ) ,* a n d E . R o s s o u w , B S c , B C h D , B C h D H o n s . ) , M C h D * *

Tygerberg, Republic of South Africa

Sin c e t h e i n t r o d u c t i o n o f c e r a m ic b r a c k e t s t o o r t h o d o n t i c t h e r a p y , a n e e d h a s a r i s e n t o t e s t t h e

m a n u f a c t u r e r 's c l a im s r e g a r d in g t h e s e b r a c k e t s . F o r t y - e ig h t n o n c a r i o u s h u m a n c a n i n e t e e th w e r e

d i v id e d e q u a l l y i n to g r o u p s A t o D . B r a c k e t s w e r e b o n d e d t o t h e s e t e e t h w i t h t h e u s e o f t h e

a c id - e t c h t e c h n iq u e a n d a c o m p o s i t e r e s i n a c c o r d i n g t o t h e m a n u f a c t u r e r ' s i n s t r u c t i o n s . T h e

c o m b i n a t i o n w i t h i n e a c h g r o u p w a s a s f o l lo w s : A = s t a in l e s s s t e e l b r a c k e ts a n d c h e m i c a l ly c u r e d

r e s i n ; B = c e r a m ic b r a c k e t s a n d c h e m ic a l l y c u r e d r e s i n ; C = c e r a m ic b r a c k e t s a n d l i g h t - c u r e d r e s i n ;

D = s t a i n l e s s s t e e l b r a c k e t s a n d l i g h t - c u r e d r e s i n ( v i a t r a n s i ll u m in a t i o n ) . A f t e r c u r in g , t h e t e e t h we r e

s t o r e d f o r 1 w e e k i n d i s ti ll e d w a t e r a t 3 7 C . T h e I n s tr o n m a c h i n e w a s u s e d t o t e s t t h e s h e a r b o n d

s t r e n g t h s o f t h e b r a c k e t s t o t h e t e e t h . T h e b r a c k e t s we r e i n d i v i d u a l l y t e s t e d t o f a i l u r e o f t h e b o n d ,

wh i c h wa s r e c o r d e d a l o n g w i t h t h e s i t e o f f r a c t u r e . T h e c o n c lu s i o n s a r e a s f o l l o ws : ( 1 ) a l l

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

c l i n i c a l l y a c c e p t a b le , ( 2 ) t h e c e r a m ic g r o u p s e x h ib i t e d a s i g n i f i c a n t l y h i g h e r b o n d s t r e n g t h t h a n t h a t

o f t h e s ta i n le s s s t e e l g r o u p , a n d (3 ) e n a m e l f ra c t u r e s o c c u r r e d a m o n g t h e B g r o u p i n 4 0 o f t h e

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

t h e r a p y o r a t d e b o n d in g o f t h e c e r a m ic b r a c k e t s , e s p e c ia l l y i f t h e t o o t h i s n o n v i t a l. ( AM J O RT HO D

DENTOFAC ORTHOP 1990 ;97 :12 1-5 . )

B u o n o c o r e t d e m o n st r at e d th a t th e b o n d

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

inc re a se d s ign i f i c a n t ly by e t c h ing the e na me l su r fa c e

w i t h 8 5 % o r t h o p h o s p h o r i c a c id . A n e p o x y r es i n s y s t e m

tha t p rove d to be o f su f f i c i e n t s t r e ng th to w i th s t a nd

o r thodon t i c fo rc e s ha s be e n de sc r ibe d . 2 D ia c ry l a t e r e s -

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

Bowen s reshz

or b i s -

g lyc e ra l me tha c ry l a t e (b i sphe no l A g lyc idy l d ime th -

a c r y l a te ) , w e r e d e s i g n e d t o i m p r o v e b o n d s t r en g t h a n d

inc re a se d ime n s iona l s t a b i l it y by c ro ss l i nk ing , s S t a in -

l e ss s t e e l o r thodon t i c b ra c ke t s c a n be se c u re d to t e e th

w i th t h i s r e s in . The p re domina n t ly w e a k l i nk in t h i s

b o n d i n g c h a i n i s a t t h e r e s i n / b r a c k e t b a s e i n t e r f a c e :

I t w a s no t un t i l 1977 tha t t he f i r s t de t a i l e d pos t -

t r e a tme n t e va lua t ion o f d i r e c t bond ing in o r thodon t i c s

du r ing a fu l l t r e a tme n t t ime (me a n o f 17 mon ths ) i n a

l a rg e s a m p l e o f p a ti e n ts w a s p u b l i s h e d : T h i s s t u d y

c onc lude d tha t a c id e t c h ing a nd bond ing w i th f i l l e d

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

o r thodon t i c w or ld .

Department of Conservative Dentistry, Oral and Dental Teaching Hospital,

University of the W estem Cape.

Departm ent of Orthodontics, O ral and Dental Teaching Hospital, University

of Stellenbosch.

8 /1 /10370

In a su rve y in t he U n i t e d S ta t e s , i t w a s found tha t

9 3 % o f o r t h o d o n t i st s u s e d c h e m i c a l l y cu r e d r e s i n b o n d -

i n g f o r b r a c k e t p l a c e m e n t : A m a j o r d r a w b a c k o f t h is

sys t e m i s t he i na b i l i t y o f t he p ra c t i t i one r to ma n ipu la t e

the se t t i ng t ime o f t he c ompos i t e r e s in . The c l i n i c i a n

mus t pos i t i on the b ra c ke t s c o r re c t ly on the t e e th t o

a ssu re a func t iona l e nd re su l t . 7 Th i s , how e ve r , mus t be

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

b e c a u s e p o l y m e r i z a t io n s t a rt s i m m e d i a t e ly o n m i x i n g .

I f l e f t a round the b ra c ke t , t he e xc e ss c ompos i t e r e s in

w i l l l e a d to p l a que a c c umula t ion a nd re su l t a n t e na me l

de c a l c i f i c a t ion : ~ H ow e ve r , t he c l i n i c i a n mus t w a i t un -

t i l f i na l se t t i ng o f t he c ompos i t e r e s in t o r e move a ny

e x c e s s f r o m a ro u n d t h e b r a c k e t . T h e i n c o r p o r a t io n o f

a i r in mix ing the c om pos i t e r e s in c ou ld l e a d to a w e a k -

e n ing o f t he bon d s t r e ng th o f t he r es in s a nd to i nc re a se d

su r fa c e po ros i ty . The fa c t t ha t l i gh t -c u re d c ompos i t e

re s in s e xh ib i t ma rke d ly l e ss po ros i ty t ha n c he mic a l ly

c u r e d r e s i ns h a s b e e n r e p o r t e d b y n u m e r o u s a u t h o r s ) 2

T h e p o l y m e r i z a t i o n o f l i g h t- a c ti v a te d r e s i n s u n d e r

me ta l b ra c ke t s by t r a ns i l l umina t ion ha s be e n show n to

be suc c e ss fu l , be c a use the t oo th c onduc t s v i s ib l e l i gh t

w e l l . a 3 C la ims ha ve be e n ma de tha t l i gh t po lyme r i -

z a t i o n ( c o m m a n d c u r i n g ) i m p r o v e s t h e a c c u r a c y o f

b ra c ke t pos i t i on ing a nd thus min imiz e s t he ne e d fo r

121


2/5

22 oseph att d Ro sso tt w Am. J. Orthod. Dente~w. Orthol,.

February

1990

Table

I

Recorded mean shear bond s t rengths ,

s tandard deviat ions , and Duncan's mul t iple

range tes t groupings

Group J Mean SBS

A 17.34

B 28.27

C 24.25

D 17.80

SD I Duncan s MRT

2.93 ~ ~

7.91

7.88

3.54

SBS. Shear bond s trength m meganewtons per square meter ; SD.

standard deviation; Duncan s MRTo Duncan s multiple range test.

Fig 1 Photograph of apparatus ready for testing shear bond

strengths of brackets

realignin g of teeth after debonding.~4 Exce ss comp osite

materia l can a lso be removed before l ight polymeri-

zat ion because any accidental movement of the bracket

wil l not affect the bonding capaci ty of the res in. Onc e

the bracket pos i t ion has been correct ly determined, the

res in can be command cured.

The advent of ceramic brackets in the orthodont ic

f ield has led to a t rend of more cosm et ic orthodont ics .

The manufacturer* c la ims that these brackets bond to

comp osi te res ins by chemical bond s and exhibi t a higher

bond s t rength than s ta inless s teel brackets . A m inimu m

value of 60 to 80 kg/cm '- (6 to 8 MN /M 2) would appear

to be necessary for successful clinical bonding.~5 There

was obvious ly a need to tes t the manufacturer ' s c la ims

in regard to the higher bond s t rength of these ceramic

brackets , wi th the mesh-b acked s ta inless s teel brackets

used as a control . Two different types of or thodont ic

composi te res ins were a lso tes ted.

The purpose of this s tudy was to es tabl ish the di f-

ference, i f any, between the shear bond s t rengths of

s ta inless s teel and ceramic brackets used with chemi-

cal ly and l ight-activated res ins .

*Unitek Corporation. Monrovia, Calif.

M TERI LS ND METHODS

Forty-eight noncarious extracted human canine

teeth were col lected over a period of months . After

extract ion, the teeth were c leaned on a dental la the wi th

pumice and s tored in 70% ethyl a lcohol as has been

reported in the li terature. ,6 Th ey w ere divid ed into two

groups of 24 teeth each. One group was used in the

tes t ing of the chemical ly cured res in Concise ,* whi le

the other was used in the testing of the light-cured resin

He l ios i t . i

The chemical ly cured group was further subdivided

in two groups of 12 teeth each. Group A had s ta inless

s teel brackets~ bonded to the teeth, and group B had

ceramic brackets ~ bonded to the teeth.

The l ight-cured group of 24 teeth was s imilar ly sub-

divided in two groups of 12 teeth each. Group C had

ceramic brackets ~ bonded to the teeth wi th a l ight-cured

microfi lled res in, t which was handled acco rding to the

manu facturer ' s ins t ruct ions. Group D had s ta inless s teel

brackets~ bonded to the teeth wi th t rans i lluminat ion of

vis ible l ight . Thes e teeth were l ight-cured a t the brack-

et 's gingival and incisal margins for 10 seconds initially

and then exposed to a further 2 minutes of t rans i l lu-

minat ion of v is ible l ight through the pala ta l s ide of the

tooth.

The bonding of these brackets was according to

accepted techniqu es. 17 All teeth were polished with

pumice before a 60-second etch of 37% orthophos-

phoric acid. T hey were w ashed for 20 seconds under

running tap water to remove the orthophosphoric acid

and blown dry with c lean uncontaminated a i r . During

al l stages of bonding of the brackets , a l l materia ls were

*Chemically activated concise orthodontic bonding system (large-particle

macrofilled esin). Manufacturedby 3M Dental Products, St. Paul, Minn. Batch

No. 1960,

i Light-activated teliosit Ortho (microfilled resin). Manufactured by Vivadent

AG. Schaan, Liechtenstein. Batch No. 392 401 .

:~Standard stainless steel springwing brackets with mesh backing for direct

bonding. Manufactured by Unitek Corporation, Monrovia, Calif.

Transcend ceramic brackets. M anufactured by Un itek Corporation.


3/5

Vo l um e

97

hear bond strengths of various orthodontic brackets 123

Num b e r

14

12

1

8

6

4

2

Samp les

A

G r o u p s

R/E ~ R/B ~ In E

C D

Fig 2 Graph of fracture sites after debond ing RIB Betwee n resin and brac ket; R/E between resin

and enam el; in E in enamel

h a n d l e d i n a c c o r d a n c e w i t h m a n u f a c t u r e r ' s i n s t r u c -

t i ons .

T h e t e e th w e r e t h e n p r e p a r e d f o r m o u n t i n g i n b r a s s

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

cha mb er s a s de sc r i bed i n t he l i t e r a t u r e ) 8 A l l t he t ee t h

p r o t r u d e d a b o v e th e l i p o f t he c u p b y 1 m m a n d w e r e

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

fo r t y - e i gh t t ee t h w ere s t o r ed a t 37 C i n an i n cuba t o r

i n d i s t i l l ed wa t e r f o r 1 week .

T h e s p e c i m e n s w e r e s e c u r e d i n a c l a m p d e v i c e a n d

a 0 . 2 0 - i n c h g a u g e w i r e w a s p l a c e d u n d e r t h e w i n g s o f

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

c e n t e r i n g d e v i c e ( F i g . 1 ) . T h e s p e c i m e n s w e r e t h e n

s t r e s sed i n a g i ng i vo- i nc i sa l d i r ec t i on t o f a i l u r e w i t h

a shea r bond t e s t on t he Ins t ron un i ve r sa l t e s t i ng

machi ne .' [ T he p roc edu re was s i mi l a r t o one t ha t

was desc r i bed i n t he p r ev i ous l i t e ra t u r e . + A l l t he

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

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

p e r u n i t a r e a ( m e g a n e w t o n s p e r s q u a r e m e t e r ) b y d i -

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

b r a c k e t . T h e b o n d i n g s u r f a c e a r e a o f th e b r a c k e t s w a s

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

p u t e r p r o g r a m .

T h e s a m p l e s e q u e n c e w a s d e t e r m in e d b y m e a n s o f

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

f r ac t u r es o f a l l t he t ee t h were exami ned wi t h a l i gh t

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

Fastcure. Manufactured by Kerr F, dnufacturing Co., Romulus, Mich. Batch

No. 64248.

tlnstron testing machine. Manufactured by lnstron Corp., Canton, Mass.

b r a c k e t s w e r e a l s o e x a m i n e d f o r d a m a g e a f t e r d e -

b o n d i n g .

R E S U L T S

S h e a r b o n d s t r e n g th s

A di f f e r enc e i n t he shea r bond s t r eng t hs was r e -

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

f r o m g r o u p t o g r o u p ( T a b l e I ) . W h e n t h e m e a n w a s

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

g r o u p s t h a t i n c l u d e d t h e c e r a m i c b r a c k e t s e x h i b i te d t h e

h i ghes t va l ues (T ab l e I ) .

F r ac t u r e s i t es

T h e s i te s o f f r a c t u r e a r e r e p r e s e n te d i n t h e g r a p h i n

F i g . 2 . T h e s e f r a c t u r e s it e s w e r e d i v i d e d a m o n g t h o s e

t h a t w e r e b e t w e e n r e s i n a n d b r a c k e t , b e t w e e n r e s i n a n d

e n a m e l , a n d t o t a l ly i n e n a m e l . M o r e t h a n t w o t h ir d s o f

t he f r ac t u r e had t o be ev i den t i n any one o f t hese s i t e s

t o c l a s s i f y it a s a p a r t i c u l a r t y p e o f f r a c t u r e . T h e . o n l y

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

w a s g r o u p B ( c h e m i c a l l y c u r e d r e s i n a n d c e r a m i c

bracke t s ) .

r a c k e t f r a c t u re

A f r a c tu r e i n t h e b o d y o f th e c e r a m i c b r a c k e t t y p e

w a s o b s e r v e d i n 6 . 6 6 % o f t he c e r a m i c s a m p l e s fr o m

g r o u p B . N o n e o f t h e s t a in l e ss s t e e l b r a c k e ts w a s o b -

s e r v e d t o f r a c t u r e . O n e s p e c i m e n i n g r o u p C a n d D

fa i l ed when a f r ac t u r e o f t he r e t a i n i ng r e s i n i n the b r as s

cup a l l owed t he whol e t oo t h t o d i s l odge . T h i s i s r e -

f lected in the resul t s .


4/5

124 Joseph and Ro ss ou w Am J Orthod Dentofac Orthop

February

199

Fig 3 Photograph of fracture of enam el and ceramic bracket

tatistical analysis

The m ean and s t anda rd deviat ion of each group was

calculated (Table I) . An analys is of variance was used

to test the hypothesis that there was no significant dif-

ference between the resul ts of the four groups . The

analys is of variance show ed a s ignif icant di fference be-

tween the grou ps at the p = 0.0001 level of signifi-

cance.

The grouping of these di fferences by Dun can's m ul-

t iple range tes t showed that groups A and D were not

s ignif icant ly di fferent and were grouped together as

were groups B and C. However, groups A and D were

significantly different from groups B and C (Table 1).

DIS USSION

Stainless steel bracket groups

The resul ts obtained from both the l ight-cured and

chemical ly cured groups were in accordance with the

bond strengths quoted in the li terature when stainless

steel brackets w ere tested. ~9 Wh en the mea n of the bo nd

strengths of the two groups A and D of s ta inless s teel

brackets were compared, they were found to be very

s imi la r (17 .34 M N/ M 2 and 17 .80 M N/M z) even though

the res ins used were di fferent (chemical ly act ivated

macrofi l led and l ight-cured microfi l led res ins) . Chem-

ical ly cured macrofi l led res ins are reported to have

higher bond strengths (more elastic) than light-cui 'ed

microfilled resins (more britt le). '8

I t can therefore be assumed that some extra inf lu-

ence was ex erted on the res ins before they reached their

cohes ive fracture s t rength to create a debonding of the

bracket . This inf luence was l ikely to be the deformat ion

of the metal of the bracket when the shearing forc es

were appl ied. This deformat ion could create a fracture

plane, which would p ropagate through the union. Thus

the propert ies of the bonding comp osi te res ins (bri tt le

or e las t ic) were masked by this deformat ion in the

brackets when the brackets were placed under s t ress .

No enam el or bracket fractures were noted in groups

A and D.

eramic bracket groups

The shear bond s t rengths of both ceramic bracket

groups B (28 .27 MN /M z) and C (24 .25 M N/ M ~) were

s ignifca nt ly higher than those of s ta inless s teel bracket

groups A (17 .34 MN /M 2) and D (17 .80 MN/M 2) ,

whether the chem ical ly cured or l ight-cured resins were

used (Table I) . This di fference may be explained as

follows:

I t can be assum ed that because the ceramic b rackets

are so r igid, no deformat ion occurred when shearing

forces were appl ied to the brackets . Thus chemical ly

cured composi te res in (macrofi l led and more e las t ic)

fractured a t higher bond s t rengths than the l ight-cured

compo si te res in samples (m icrofi lled and m ore bri t t le) .

These grou ps exhibi ted the di fferences between the two

types o f resins as repo rted in the li terature. ~8 Ho we ver

the increased bond s t rength resul ted in enamel fractures

in four of the samples (Fig. 3) . This dis turbing feature

must be emphasized, inasmuch as the use of ceramic

brackets on nonvi ta l teeth could cause a higher inci -

dence of enam el fractures during therapy and at de-

bonding. Tes t ing for vi ta l i ty before bonding and de-

bonding would seem to be a necess i ty. Special de-

bonding procedures are described by the manufacturer

of the ceramic brackets .

Because of the high bond s t rength obtained with

the r igid ceramic brackets , the safety margin of the

s t resses that could be wi ths tood b y the cohes ive s t rength

of enamel is reduced. This in turn could lead to an

increase in enamel fractures .

The incidence of fractures of the ceramic brackets

themselves (6.66 ) i s of concern. Pieces of bracket

could be inges ted or inhaled inadvertent ly i f the fracture

occurred in the mouth during funct ion.

I t appears imperat ive that informed consent be ob-

ta ined before ceramic bracket therapy is begun, a long

with tes t ing of the vi ta l i ty of teeth before both bonding

and debonding.

Fracture sites

When the fracture s i tes were examined by means

of a s tereoscopic microscop e, the s i tes could be divided

into res in/bracket , res in/enamel , and in enamel (Fig.


5/5

Voh me 97 S h e a r b o n d s t r e n g t h s o f v a r i o u s o r t h o d o n t i c b r a c k e t s 125

Number 2

2). Group B had the highest mean shear bond strengths

(Table I), but 40 of samples exhibited ename l frac-

tures (Fig. 2).

Many of the ceramic brackets after debonding ex-

hibited a smooth and shining debonde d surface. This

suggests that the union to these brackets is chemical

and not mechanical.

O N L U S I O N S

1. The most im portant feature of this study was the

observation of the fracture sites. Enamel fractures oc-

curred in 40 of the chemic ally cured resin and ceramic

bracket group (group B) and this must be noted when

teeth that are nonvital or have been endodont icall y

treated are to be bonded with a ceramic bracket. De-

bonding, either intentionally or unintentionally, may

lead to fractures of enamel.

2. The need for vitality testing before bondin g and

before debon ding appears to be essential in the light of

this information.

3. The brackets of groups A and B (bonded with

the heavily macrofilled resin, Concise) and the brackets

of groups C and D (bonded with the lighter microfilled

resin, Heliosit) produced a shear bond strength that is

greater than that considered cl inicall y acceptable.

4. Groups A and D (stainless steel brackets) ex-

hibited no significant difference in bond strengths, be-

cause the metal deforms and produces a fracture plane

before the cohesive fracture strength of the composite

is reached.

5. Groups B and C (ceramic brackets) both had

significantly higher bond strengths than groups A a nd

D (stainless steel), but were not significantly different

from each other (Table I). This could be the influence

of the different types of resins used.

6. The inciden ce of fracture of the ceramic brackets

was 6.66 .

7. It is advised that informed consent regarding the

complications listed above be obtained.

We acknowledge Miss Gina Joubert of Medical Research

Council for her help with the statistics and Dr. C. Jooste for

research advice.

R E F E R E N E S

1. BuonocoreMG. A simple method of increasing he adhesion of

acrylic filling material to enamel surfaces. J Dent Res 1955;

34:849-53.

2. Retief DH, Dreyer CJ. Epoxy resins for bonding orthodontic

attachments to teeth. J Dent Assoc South Afr 1967;22:338-46.

3. GraberTM, Swain BF. Orthodontics:currentprinciplesand tech-

niques. St. Louis: CV Mosby, 1985.

4. Knoll M, Gwinnett AJ, Wolff MS. Shear strength of brackets

bonded to anterior and posterior teeth. AM J ORTtlOD 1986;

89:476-9.

5. ZachrissonBU. A postoperative evaluationof direct bonding n

orthodontics. AM J ORTHOD 1977;73:173-89.

6. Gorelick L. Bonding: the state of the ar t- -a national survey.

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7. Andrews LF. Six keys to normal occlusion. AM J ORTHOD

1972;62:296-309.

8. StratemanMW, ShannonIL. Controlof decalcification n ortho-

dontic patients by daily self-administeredapplicationof a water

free 0.4 stannous fluoride gel. AM J ORTHOD 1974;66:273-9.

9. ZachrissonBU. Fluoride applicationprocedures in orthodontic

practice, current concepts. Angle Orthod 1975;45:72-81.

I0. Gwinnett JA, Ceen RF. An ultraviolet photographic technique

for monitoringplaque during direct bonding procedures. AM J

OR'nIOD 1978;73:178-86.

11. KingL, Smith RT, Wendt SL, Behrents RG. Bond strengths of

lingual orthodontic brackets bonded with light-curedcomposite

resins cured by transillumination. AM J ORTHOD DENTOFAC

ORTHOP 1987;91:312-5.

12. Joseph VP, Cohen J. Porosities of chemically cured and light

cured composite resins. Delivered at the annual meeting of the

InternationalAssociationfor Dental Research in Johannesburg,

1986. InternationalAssociation or Dental Research Abstract No.

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13. TavasMA, Watts DC. Bondingof orthodontic brackets by trans-

illuminationof a light activated composite: an in vitro study. Br

J Orthod 1979;6:207-8.

14. Read MJF. The bonding of orthodontic attachments using a vis-

ible light cured adhesive. Br J Orthod 1984;11:16-20.

15. Reynolds R. A reviewof direct orthodonticbonding.BrJ Orthod

1975;2:171-8.

16. Bryant S, Retief DH, Russell CM, Denys FR. Tensile bond

strengths of orthodonticbonding esins and attachments o etched

enamel. AM J ORTHODDENTOFACORTtIOP 1987;92:225-31.

17. Daft KS, Lugassy AA. A preliminary tudy of orthodontic reat-

ment with the use of directly bonded brackets. AM J ORTItOD

1974;65:407-18.

18. Joseph VP. A laboratory evaluationof conventionalchemlcally

activated and microfilled light activated composite restorative

resins [Thesis]. Cape Town, Republicof South Africa: Univer-

sity of the Western Cape; 1987.

19. Lopez JJ. Retentive shear strengths of various bonding attach-

ment bases. AM J ORTtIOD 1980;77:669-78.

Reprin t requests to :

Dr. E. Rossouw

Department of Orthodontics

Oral and Dental Teaching Hospital

Universityof Stellenbosch

Private Bag XI

Tygerberg, 7505, Republic of South Africa

Ceramic vs. Steel Brackets

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