in vivo fractures of ally treated posterior teeth restored with enamel-bonded resin

8/3/2019 In Vivo Fractures of ally Treated Posterior Teeth Restored With Enamel-bonded Resin

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I n w k ? f r a c t u r e s of e n d o d o n t i c a l l y t r e a t e d

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

In vivo fractures of endodontically

the M O D resin-restored teeth was equal to that of M O /D O

a macrofilled or hybrid resin. It was also found that a beveling

erm ed iat e layer of low-viscosity resin resulted in a sign ificant

E r ik K e i th H a n s e n , E r ik A s m u s s e n

Ins t i tu te of Dental Mater ia ls and Technology

Royal Dental Col lege, Copenhagen, Denmark

Key words: ac id etch-res in technique; res in

t i o n ; tooth t rac ture; cusp f rac ture.

Er i k Ke i t h Hansen , He is ingorsgade 7 , DK-3

H i l l e r o d , Denma r k

Accep ted fo r publ icat ion Apr i l 6, 1 9 9 0 .

her risk of fracture tha n does a vital one ( 1- 3) .

f end odo ntica lly treated teeth

t be decreased with an intra-co rona l am algam

amalga m-restored and non -etched resin-restored

An al ternat ive treatment option, enamel-bonded

teeth are restored with an etch-retained resin finstead of am alg am . This has been confirmed in vivo study on endodontically treated premrestored with either amalgam or enamel-bo

resin (16): the survival rate (retention of both c

ofthe resin-restored teeth was markedly better that of the teeth restored with am alg am . Instudy (16), however, the number of resin-resteeth was rath er sm all (n = 40) .

The purpose of this retrospective study was ta more comprehensive knowledge ofthe cumulsurvival rate and the fracture pattern of endotically treated posterior teeth restored with ena

bonded resin with or without the use of a debonding agent .

M a t e r i a l and m e t h o d s



F r a c t u r e o f r e s i n - r e s t e r e d e n d e d o n t ic a l ly t r e a t e d t e e

The criteria for including data were: i) an endo-

The dentists were asked to record the following

endod ontic the rapy, cavity type (M O, D O, orand the date of control or last contact.

In cases of fracture, the dentists were asked to

The survival time was defined as the time elapsed

no distinction was made between MO and DO

D filhngs, the teeth were recorded as w ithdraw n

In the previously mentioned study on endodon-

lower "MOD premolars" and upper and low"MOD molars"; and Group G consis ted of upp"MOD premolars". The same grouping was usein the present study. The cumulative survival rafor each gro up w as calculated with life table analys( 1 7 ) . Differences between the three groups weanalyzed with log-rank tests (17) at the 5% level

significance. Analyses of the fracture pattern adifferences as to type of restorative resin and trement of the cavo-surface margin were done wicontingency tables, Kruskal-Wallis one-way analsis of variance, Mann-Whitney's U test, and tFisher exact probability test (18). The significanlevel for the use of low-viscosity resin and for tfracture pattern was set to 1%; the reason for thwill be explained in Results.

Most of the analyses were carried out withcomputerized statistical program (MEDSTAT, v

s ion 2 .1 , Astra , Gopenhagen, De nm ark).

R e s u l t s

Data were obtained on 213 endodontically treatposterior teeth restored with resin, but 11 teewere rejected because the cavity type or the dateendodontic therapy was not recorded or becausecuspal ove rlays. A further 12 sets of dat a were parrejected because some ofthe dentists misunderstothe instructions and only recorded fractured tee

not fractured and non-fractured at random. Th12 teeth were excluded from the survival analysbut included in the analyses of the fracture patteTa ble 1 shows the 190 teeth in the survival analydistributed by cavity type and fracture mode.

In this article, no distinction is made betweteeth from the right side of the mouth and tefrom the left side. In the tables, only right side tonumbers will be used.

S u r v i v a l r a t e ( r e t e n t i o n of b o t h c u s p s )

Th e num ber of endodon tically treated teeth distruted by tooth number, cavity type, and fractmode are shown in Table 1.

T he re was no statistically significant differebetween the cumulative survival rates of GroupsB and G (P = 0.98), i.e., teeth with an MOD cavhad the same failure rate as teeth with an MO/cavity. The survival rates of the three groups depicted in Fig. 1, and the 95% confidence intervare shown in Table 2 for the 3-, 5-, and 10-y

surviv al rates. W ith no statistically significant difence between the three groups, the pooled cumu



H a n s e n & A s m u s s e n

Ta b l e 1 . N umbe r of endodon t i ca l l y t r e a t ed t ee t h in t h e su r v i v a l a n a l y s e s d i s t r i b u t e d on too th numbe r , cav i t y t ype , and f ra c t u re mode .

Tooth

n umbe r ^

Ca v i t y t y p e Fractu re mode^

MO/DO

6

3

4

14

5

4

1

7

1

1

1

4

3

01

MOD

21

13

5

00

5

1

3

44

28

6

0

4

84

1

Fac ia l L i n g u a l Tota l

MO/DO MOD MO /DO MOD MO/DO MOD

14

15

16

1744

45

16

47

14

15

16

17

44

45

46

47

2

1

-f-

2

1

1

5

4

2

1

' = No ve r t i ca l f r a c t u re s we re found .

- = V ioh l ' s t wo - d i g i t s y s t em .

' = Use of d e n t i n - bon d i n g a g e n t .

survival rate will be used in the Discussion where a

comparison ismade between the failure rate of acid-etch resin-restored teeth and amalgam-restoredteeth.

The cumulative survival rate of the resin-restored

teeth depended on several variables:Restorative resins - The endodontically treated

/o

100

L U

< 80

60

CO

U J

>

<

Z)

o

20

B

A

C

2 A 6 8 10 12

teeth had been restored with 20 different rAnalyses ofthe survival rates of 190 fillings wimany materials are not possible. The teeth therefore first divided into two groups: Teetstored with a chemically-activated and teet

stored with a light-activated resin.Teeth restored with a chemically-activated had a 5-year cumulative survival rate of 92

contrast to 59% for teeth restored with a

activated material (the 95% confidence limits 8 7 - 9 8 % and 29-89%, respectively). This diffewas highly significant (P< 0.001). Even the 10survival rate of teeth restored with a chemic

Tab le 2 . Cumu la t i ve su rv i va l r a t e s ofGroups A , B , and C w i t h 95% co

l im i t s in p a r e n t h e s i s .

Group

(n )

Toot h n um be r '

C a v i t y t y p e

MO/DO MOD

Cumu l a t i v e s u r v i v a l r a t e s (%)

3 y e a r s 5 y e a r s 10 y

A

(42)

B

( 4 1 )

C

14 ,

4 4 , 4 5

16 ,17

46 ,47

1 5 4 4 , 4 5

16 ,17

46 , 4 7

1 4 , 1 5

9 2 ( 8 1 - 1 0 0 ) 81 ( 6 ^ 9 9 ) 73 ( 4

8 9 ( 7 8 - 1 0 0 ) 8 5 ( 7 0 - 1 0 0 ) 7 8 ( 4 6

9 4 ( 8 9 - 9 9 ) 89 ( 8 1 - 9 6 ) 71 ( 5



u s s e n

o //o

1 0 0

8 0

60

O

2 0

J 1 I I I 1 I I

2 A 6 8 10

Y E A R S A F T E R T R E A T M E N T

12

3. Comparison of survival rates for resin-restored and amal-

= Amalgam, Group A. AB = Amalgam,

B, AC = Amalgam, Group C. R = Resin, Groups A, B

d C pooled.

of fractures in the beveled and in

our previous study on endodontically treated(5), three analyses of

be made: tooth surface,and effect of tooth position in the jaw.

the two first analyses were made in this studyup more than 65%

Tooth surface - Most of the fractures involved the

For the upper first premolar, 71% ofthe pooled

of facial cusp fracture for the other pos-

not statisti-No difference was found

a light-activated resina chemically-activated ma-

{P=0A6).

Fracture level - There were more subgingival and

for teeth restored with a light-for teeth restored with a chem-

(P= 0.048); this differenceas not considered as statistically significant be-

l ingual and facial failure was not statistically scant (P=0.12) . There also was a tendency for

lar fractures" to be more severe than "prefractures", but a detailed analysis was not

because of the smal l number of molar fra(Table 1). None of the 32 fractures was so vethat the tooth had to be extracted.

D i s c u s s i o n

In a retrospective study, a registration form wimany questions may result in a reduced respFurthermore, some of the answers may havebased upon memory, not upon actual knowlThus, several variables were not included i

registration form, first of all variables that may

been important for the assessment of th e low surate of the light-activated resins, e.g. matrix s(metal or clear strips), the use of light guwedges, the thickness of the increments, and

irradiation from the facial and lingual aspecttooth. Not only this lack of information, bu

the high proportion of unrecorded use of a

viscosity resin and unrecorded fracture levelsfor a cautious interpretation.

Nevertheless, the high failure rate of teetstored with a light-activated material is astoni(Fig. 2); the statistical analyses showed that restored with a light-activated resin had n

three times as many fractures as expected (theber of expected fractures is derived from the

rank tests). It should once again be noted thlight-activated resins were applied with a laytechnique.

There may be several causes for the low surate of teeth restored with a light-activated bu t the main one is presumably the initiatithe polymerization process: teeth restored wchemically-activated microfilled resin for anuse had a higher survival rate than teeth res

with the corresponding l ight-activated materianter ior use (e.g. the chemically-activated Sithe light-activated Silux); and the same was

for resins intended for posterior use (e.g. the cically-activated resion P-10 vs the two lightvated resins, P-30 and P-50). Even old-fashmacrofilled resins like Concise and Adaptic better survival rates than did modern l ight-actiresins provisionally or finally accepted for posuse by the American Dental Association: EPosterior, Fulfil, Heliomolar, Herculite, and Osin, all of which were used in the present study.problem, polymerization of light-activated res



ent in the cavity of an end odo ntically treated

When light-activated restoratives are used, most

There were 45 teeth which had been restored

these restorative resins gave the lowest survival

The fracture resistance of teeth restored with re-

in vitro studies, and the results are contradic-

F r a c t u r e o f r o s i n - r e s t o r e d e n d o i i o n t i c a i l y t r e a t e d

light-activated resin, and one cannot expect anproved survival rate if the restorative resin is popolymerized.

The use of an intermediate layer of low-viscoresin resulted in a pronounced improvement ofsurvival rate for teeth restored with a chemicactivated material, but not for teeth restored

a light-activated one. The cause for this differmay be the following:

In vitro studies have shown that an acid-etenamel surface is fragile (23, 24): even a very pressure may result in a significant reduction inbond strength between resin and etched enaBut if the enamel has been covered with a viscosity resin prior to application of the restoraresin, the risk of impairing the bond strength be significantly reduced. An additional explanacould be that both the amount and the siz

marginal voids is increased when no intermedresin layer is used (25). Marginal voids will rethe contact area between resin and enamel, fewer sites are therefore a vailable to hinde r the wto-wall shrinkage of the polymerizing restoraresin. The result may be the formation of a paor total gap between the restorative resin andcavity wall, and thereby a diminished capabilitthe resin restoration to increase the strength oftooth. The reason why the use of a low-viscoresin did not improve the survival rate of t

restored with a light-activated resin conceivablthat an increased contact area between the resttive resin and the etched enamel is of no valuthe restorative material is pooriy polymerized.

The fracture resistance of prepared teeth wibeveled cavo-surface margin has been tested in

( 8 , 11, 15). These studies all show no, or onsHght, improvement of the tooth strength, whicin agreement with the present investigation.

The survival rate of the acid-etch resin-rest

teeth in this study may be compared with thathe corresponding amalgam-restored teeth in previous investigation (5). This comparison ispicted in Fig. 3 where the pooled 12-year survrate of the resin-restored teeth is applied. As samalgam-restored MO/DO teeth had a sl igbetter 12-year survival rate than that found forpooled MO/DO and MOD res in-res tored teeth ,the difference was not statistically significant0.2). One may argue that a comparison betwthe survival rate of am algam -restored M O /

teeth and pooled MO/DO plus MOD resin-stoteeth is incorrect, but as reported in Results,



(5). Teeth with MOD amalgam res-

a pro-

for the

MOD cavities;one year, the difference between the

the two types of restora-is statistically significant at the level of

0.05 (Group B) and below 0.001

Group C). The difference between the 12-year sur-

of resin- and amalgam-restored MOD

washighly significant at a level of probabil i ty3). It should be noted that the

of the resin-restored MOD teethstudy w as obtained in spite of the poor results

the light-activated materials (Fig. 2).

The periodonal damage caused by the cusp frac-of the acid-etch resin-restored teeth was not

as found in our previous study wherewas used as the restorative material (5).

for this may be that the strength-of an etch-retained filhng will give a

in case of cusp failure. Thisrestorative resin is sufficiently

The fracture resistance of teeth re-

an insufficiently irradiated resin fillingto be equivalent to that of an unrestored

Our hypothesis, insufficient polymerizationof the light-activated restorations, was sup-

by the fact that teeth restored with these

had more subgingival and subcrestal frac-had teeth restored with chemically-acti-

In the latter group, all but one fracturethe fractures of

the periodontal damage in

of tooth failure was less severe than found for

in out previous study

. The acid-etch resin technique may be a betterfor temporary or

of endodontically treatedan MOD

. Light-activated resins must be polymerized prop-We suggest at least 60 s per increment .

. The increments in the proximal part of the cavitybe less than 2 mm thick.

. Microfilled resins intended for anterior use

not be used to restore posterior teeth.

. The acid-etched enamel should be covered withof low-viscosity resin.

Acknowledgements - The authors want to thadentists who collected the information on whicstudy is based. This investigation was supportethe Research Foundation of Dental Aktieselsaf 1934, the Insurance Association of Danishtists in Hafnia Insurance, and the Research Fdation of the Danish Dental Association.

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in vivo fractures of ally treated posterior teeth restored with enamel-bonded resin

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