Resina Silicona Dentina Interface

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Lopes

et al

ome recent dye penetration studies of packable

umatic extraction.

The aim of this study was to evaluate the effect of

METHOD ND M TERI LS

A box-type Class II cavity was prepared on each

In total, 12 cavities could be restored. The vital-

1:100 000 epinephrine was administered.

After the cavity preparation, a visual examination

One cavity in each tooth (n = 6) was restored with

ced distaUy. The bulk restorations were irradiated for

The other six cavities were restored with Filtek

Z250 (3M Dental), placed with an oblique Incremen-

tal technique in three layers. Each increment was irra-

diated with the XL 1500 curing unit for 40 seconds.

The finishing procedures were carried out with fine

diamond burs (Brasseler) and sandpaper strips (3M

Dental),

After 1 week, the teeth were carefully extracted

with minimal trauma to the restored area. The roots

were immediately removed by diamond bur sectioning

under water. The teeth were cross sectioned mesiodis-

tay through the center of the restoration with a dia-

mond-impregnated copper disk (South Bay Tech-

nology) in an oil-cooled low-speed cutting machine

(Isomet. Buehler),

A polyvinyl si loxan e impres sion (Pre siden t ,

Coltene/Whaledent) was taken of the resin-dentin in-

terface to control for artifacts created during the

preparation for SEM, The specimens were subse-

quently fixed in 2.5% glutaraldehyde in 0,1-M sodium

cacodylate huffer at pH 7,4 for at least 12 hours at

4''C,

After fixation, the teeth were rinsed ivith 20 mL

of 0,2-M soditim cacodylate buffer at pH 7,4 for 1

hour with three changes, followed by distilled water

for 1 min ute. They were deh ydrated in ascending

grades of ethanol (25;o for 20 minutes, 50". ) for 20

minutes, 75 for 20 minutes, 9O''/o for 30 minutes,

and lOO^b for 60 minutes). After the final ethanol

step,

the specimens were dried by immersion in hexa-

methyldisilazane for 10 minutes'^ and air dried at

room temperature.

The specimens were then embedded in self-curing

epoxy resin and stored for 12 hours. After setting, the

epoxy casts were pohshed with waterproof sificon car-

bide papers of decreasing abrasiveness (420, 600, and

1,000 grit) and polished to a high gloss with soft fissue

disks vvith increasingly fine diamond suspensions to a

particle size of 1 pm. The specimens were washed,

dried, demineralized in 6 N of hydrochloric acid for 30

seconds, and deproteinized in2 sodium hypochlorite

for 10 minutes. After drying, the specimens were sput-

ter coated with gold-palladium by means of a Polaron

E-5000 sputter coater (Polaron), and observed under a

Phihps XL 30 SEM (Philips Electric),

RESULTS

The enamel-resin interface did not show any gap for-

mation. The dentin-resin interface formed gaps above

the hybrid layer in three specimens prepared with the

bulk placement technique (Figs la and lb) and five

specimens prepared with the incremental placement

technique (Fig 2). Table 1 shows the percentage of gap


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Lopes et al

i l a Class II cavity restored with the bulK placement technique (Filtek and P60) A gap naa formed Sequence ot the resin-denti

face of a cavity restored w itii ttiebull* placement technique.

For the restorafions placed with the oblique

mental technique (Filtek and Z250), the mean ga

mation was 6,1 , For restorations placed wit

bulk technique (Filtek and P60), the mean gap f

tion was 18.7 . A

test revealed that the increm

placement technique resuUed in a significantly

percentage of gap formafion than did the hulk

densadon technique.

i 1b Gap formed at the resm-de ntii inle -ace of a

cavity restored w ith the Puik placement rechnique.

DISCUSSION

The initial polymerization shrinkage of resin co

ites,the different coefficients of therm al exp an

this material, and dental hard tissues and adh

problems of cervical areas are the essential facto

sponsible for marginal leakage at the proximal as

and gap formation at the resin-dentin interfa


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Lopes el al

2 Class II cavity restored with the incremental placement te clinique (Fiftek and Z250). There is no gap formation. Sequence of trie

tir interface ot a cavity restored by incrementat piacement techn ique.

can reach 2.6% to 7.1% on light-cured

ed by many au tho rs. ^ ^ Layering resin com posite

ty walls.^'

The reason for the lesser amount of gap formation

Class II resin composite restoration is in the range

.0 to 2.0 when the bulk technique is use d. The in-

prep aratio n. Increm ental restoration techniques

T BLE

Gap percentage by placement technique

and resin composite

Specimen

1

2

3

4

5

6

Mean

Incremental

Z250 ( )

0.0

6.7

0.0

0.0

7.4

2Z.4

6,1

Bulk

P (

0.0

17.3

23.8

35.4

18,9

26.9

18.7

The incremental technique can incorporate air bub-

bles. Alster et a P have shown that the stress relief in

thin resin increments is proportional to the amount of


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L o D e s

et l

contributes to stress reduction. - Tbe role of air incor-

poration in the stress relief of resin composite seems

to be important and should be investigated furtber.

Altbough tbe incremental layering tecbnique bas

been widely advocated for reduction of polymerization

sbrinkage, reports and recent finite element analyses

now dispute this tbeory. ' In one of tbese studies, it

was concluded that layering resin composites results

in bigher overall sbrinkage stress and deformation of

remaining bard tissue walls.- Tbe autbors pointed out,

bowever, tbat tbe incremental tecbnique still has some

advantages over bulk placement, sucb as improved

marginal adaptation and wetting,-' wbicb was, in part,

confirmed in tbe present study.

Tbe incremental placement technique is still re-

garded as tbe most practical for otber reasons as well.

This procedure provides enbanced control of over-

bangs in tbe lateral margins prior to curing^ and a

more effective and uniform cure. ^

The present results are in agreement witb recent re-

searcb conducted in vivo, in wbicb tbere was signif-

cantly more gap formation at tbe dentin-restoration

interface, and postoperative sensitivity, after bulk

placement tban after restorations were applied in lay-

ers.''

In botb studies, neither tecbnique resulted in a

perfectly sealed interface between tbe restoration and

tbe tootb structure. Tbe bigh modulus of elasticity of

tbe bybrid resin composites probably could not relieve

tbe stress produced during polymerization. Furtber in-

vestigations should be conducted in vivo with an in-

termediate layer of tlowable resin composite, because

the use of a low-modulus resin composite may in-

crease the flexibility of the bonded assembly and may

act as stress-relaxation buffers, absorbing tbe tension

stress induced by polymerization of tbe resin compos-

ite placed over tbe resin. ' ^

CONCLUSION

Within tbe limitations of tbis short-term study, it is

concluded that tbe placement tecbnique is an impor-

tant factor wben posterior teetb are restored witb

resin composites. Tbe incremental placement of poste-

rior composites stili provides better seal than does tbe

new bulk condensation technique.

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lFE D o rg

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