Gisele Alexandre Goes Tadeu

How Wet Should Dentin Be?

Comparison of Methods to Remove

Excess Water During Moist

Bonding

Gi

se

l

e Da

mi

a

na d

a S

il

ve

ir

a Pe

r

e

i

ra

a/Luis Al

exa

nd

re

Maffei S

a

rtini P

a

ulillo

b/

Mario Fern

a

ndo De G

oes

c/Carl

os

Tad

e

u dos Santos Dias

d

Purpose: The aim of this study was to evaluate the shear bond strength of two adhesive systems when ap

-plied on dentin surfaces with different degree'sof wetnesS.

Materials and Methods: Two-hundredten dentin specimens wereused. After conditioning with 35% phos-phoric acidgeland washing, seven,.rnethods'ofClryirig«en,tHi were used: 30 s air spray (groups 1 and 2), 5

" -" !",·/r)"i', t oJt ,";, I

Sair spray (groups 3 and if),dry cotton pellets'(groups'7and 8), wet cotton pellets (groups 9 and 10), mi-crobrush (groups 11 and 12), absorbent paper (groups 13'and 14). The last group was not dried; the dentin surfaces were left overwet (grQUPS5and'6): P.rim~&Bond 2.1 adhesive was applied onthe odd-numbered groups and,Scotchbond Multi..purpQseon tH,eev~n-numbered groups. Z100 composite cylin-ders werebonded to tM ',;Idhesive ~l!ldtli~,spedmei:lsw~resubjected toa shear bond test.

;,: "~~,io". -. \oJ: ;-!~.>;,:i;"rl • -. __:~" _ "

Results: The Least-sqQa're~'Means testwasuseB't9 compare the following results, where different letters indicate;significantly diff,€rent mElar'va'lo~;'Group 9~(~~)~;':}23:2-

M

P

~

(a); G3

=

21.3 MPa(ab), G2

=

19.5 MPa (be),G10

=

18.6 MRa(-be),G14

=

16(:{NPa (Cd),:G8'''; ~6.1.'MPa(cd), G4=14.6 MPa (de), G13=14.0 MPa (de), G11

=

13.9 'MPa

~

de)

;

(;

.

<

7

'

=

'1

3

;

5

~p~

(de)

i

GI1~l,~~±2:fMPa(~), G1

=

8.2 MPa (f), G.5=2.7 MPa (g), G6=2.4 MPa (g).' .' ",

,"-Conclusion: The adhesidri values were affeciE;Gi,both by

t

h

e

degree of dentin wetness and by the adhesive

systems. .i

O

ne of the principal aims of restorative dentistry is to obtain dental materials capable of bonding

a Professor ofRestorative Dentistry, Gama FilhoUniversity, School of

Dentistry, Riode Janeiro, Brazil, and Postgraduate student, UNI -CAMp, Piracicaba School of Dentistry, Gampinas State University, Sao Paulo,Brazil.

b Professor of Restorative Dentistry at UNICAMp, Piracicaba School

ofDentistry, Campinas State University,Sao Paulo, Brazil. e Professor of Dental Materials at UNICAMP,Piracicaba School of

Dentistry, Campinas State University, sao Paulo, Brazil.

d Professor, Mathematics Department, Luiz deQueiroz Agronomy

School, Sao Paulo State University, USP,Piracicaba, Sao Paulo,

Brazil.

Reprint requests: Gise/e Damiana da Silveira Pereira, Moraes

Bar-ros,1336\101, BairroAlto, Piracicaba, Sao Paulo,Brazil, CEP-13416 -740. Tel: +55-19422-7902, Fax: +55-19430-5218, e-mail:

gise/edamiana@yahoo.com

effectively to dental tissues in order to minimize mi-croleakage and subsequent secondary caries,17

In

1955,

Buonocore2 proposed that acid etch-ants could be used to alter the enamel surface and make it more receptive to adhesion. Acid etching enamel creates a microporous layer ranging from 5 to

50

IJm deep. When a lOW-Viscosity resin is ap-plied, it flows into the microporosities and polymer-izes, forming a micromechanical bond with the

enamel. Adhesion of restorative materials to ena-mel has been very successful, and its reliability is verified by the absence of marginal leakage and by high adhesive bond strengths that make several conservative and esthetic restorative procedures possible,17

On the other hand, dentinal adhesion has proved to be more difficult and less predictable.10 Much of the difficulty in bonding to dentin results from its

structure, which is morphologically heterogeneous

and physiologically dynamic.10 Its composition by

weight is 20% water, 30% organic matrix, and 50%

inorganic hydroxyapatite,10.17 arranged in

intertubu-lar and peritubular matrices, which form the tubule

walls from which pulp fluids emerge and keep

dentin constantly moist.10 Dentinal adhesion is

fur-ther complicated by the formation of the smear

layer which appears on the dentinal surface when

the dentin is cut or ground.10

Adhesive systems have undergone a great evolu

-tion,10.11 with major improvements in dentinal

bonding occurring when hydrophilic monomers and

organic solvents were added to primers and

adhe-sives, enabling their use on a moist dentin sub

-strate.6,7 When these adhesive systems are applied

on conditioned dentin,7.16 a hybrid layer composed

of collagen fibrils and residual hydroxyapatite

crys-tallites encased in resin13 is formed. The hybrid

layer recovers much of the resistance and rigidity19

of the original mineralized dentin, and it is the main

bonding mechanism of most current dentin

adhe-sive systems.16,19

The bond strength of a dentin adhesive may rely

on its ability to completely replace the dissolved

hy-droxyapatite with polymerized resin.15.17If this does

not happen, an exposed layer of collagen fibrils not

impregnated by resin14.15.17and containing

nanometer-sized porosities19 within the hybrid layer

may be formed. These may serve as critically-sized

defects that promote fracture propagation and de

-crease the resistance and durability of the adhe

-sion.14.15

The maintenance of a moist dentin surface after

acid conditioning is of major importance for optimal

development of a uniform hybrid layer,6-8.14,15,18.22

asthe organic solvents contained in the primers act

as water chasers, displacing water and carrying the

resin monomers into the demineralized dentin,17 fa

-voring hybridization.6 On the other hand, if the

etched dentinal surface is desiccated, the

interac-tion of the above elements does not occur.7 The

primer is deposited on the dentinal surface without

diffusing into the underlying collagen network.7

The removal of hydroxyapatite crystals by dentin

conditioning exposes the collagen fibrils of the ma

-trix. The separation of the fibrils into a meshwork

only occurs when water is present.20-22 Dehydration

of the conditioned dentin surface with air jets can

collapse the collagen fibril meshwork,5,9 causing

the interfibrillar spaces to disappear and thereby

in-hibiting penetration of the primer. Thus, the

me-chanical retention is reduced.5.9.20-22 Nevertheless,

the integrity of the fibril network is partially recov

-ered by rewetting the substrate.5.9

However, the dentinal surface should not be

overwet, as excess water can dilute the primer and

render it less effective. Excess water can promote

phase separations in the primer and the formation

of resin globules, which prevent adequate adhesive

wetting, infiltration, and polymerization.15.20.22 As a

result, the quality of the adhesive interface is re

-duced.15.22

The importance of the composition of adhesive

systems and the drying method used inthe bonding

procedures are evident, as they favor the formation

of a homogeneous and uniform hybrid layer, en

-abling an effective bond between dentin and

restorative materials,12 The aim of this study was to

evaluate the influence of seven drying methods on

the shear bond strength of two adhesive systems to

acid-conditioned dentin.

One hundred-five caries-free third molars were se

-lected. The teeth were cleaned and stored in 0.9%

saline solution at 4°C and used within one month

of extraction.

An initial cut was made perpendicular to the

long axis of the molars, 1 mm below the cemento

-enamel junction, using diamond disks with double

sharp-edged facettes in a low-speed handpiece

under air-water spray to remove the roots. A second

cut was made in the mesiodistal direction, dividing

each crown into two halves, thereby creating 210

coronal fragments that were embedded in poly

-styrene resin. When the resin was fully polymerized,

the resulting cylindrical blocks were removed from

the molds. Subsequently, the buccal, palatinal, or

lingual enamel surfaces were ground off using 20

0-and 320-grit wet silicon carbide (SiC) abrasive

paper until a flat superficial dentin area was ex

-posed. Final polishing was carried out using 60

0-and 1000-grit wet SiC abrasive paper.

After being coded, the samples were randomly

assigned to 14 experimental groups of 15 speci

-mens each. Due the large number of specimens,

adhesive procedures were done in blocks, with

each block containing one sample of each exper

i-mental group (total = 15 blocks). Adhesive tape with

a 3-mm-diameter hole was used to demarcate the

Table 1 One-way ANOVA for shear bond strength means Source OF SO MO F PR>F Model 27 6100.94146 225.96070 13.04 0.0001 Error 160 2771.81846 17.32387 Total 187 8872.75992 CV 28.4%

DF:degrees of freedom; SQ:sum of squares; MQ:meansquare; F:Fvalue;CV:coefficient ofvariation.

to the application of the subsequent treatments. All

the specimens were conditioned with 35% phos -phoric acid gel (3M Dental Products Division, St

Paul, MN, USA)for 15 s and rinsed with distilled

water for 20 s. Oncethis was done, one of the dr

y-ing methods was applied according to the following

experimental groups. Groups 1 and 2: The dentin

was dried with an oil- and dust-free air blast for 30

s parallel to the surface at a distance of 1 cm.8 Groups 3 and 4: The dentin was dried with oil- and

dust-free air for 5 s parallel to the surface at a dis

-tance of 10 cm.8 Groups 5 and 6: The dentin sur -face remained overwet and no drying method was

applied. Groups 7 and 8: The dentin was dried with

a dry hydrophilic cotton pellet gently applied to the

surface for 10 s. Groups 9 and 10: The dentin was

dried with a moist hydrophilic cotton pellet gently

applied to the surface for 10 s. Groups 11 and 12:

The dentin was dried using a microbrush (Dentsplyj Caulk, Milford, DE, USA)gently applied to the sur -face for 10 s. Groups 13 and 14: The dentin sur -face was dried by using small pieces of absorbent

filter paper gently applied to the surface for 10 s.

Immediately after drying, the adhesive Prime

&

Bond 2.1 (DentsplyjCaulk) was applied in the odd

groups and the adhesive Scotchbond Multi Purpose

(3M Dental) was applied inthe even groups, accord

-ing to the respective manufacturer's instructions. A split teflon matrix having a3-mm-diameter cen

-tral perforation was positioned over the adhesive

area of the samples, and the composite resin Z100

(3M Dental, shade A-2)was applied in incremental

layers 2 mm thick. Each layer was photopolymer

-ized for 20 s. The teflon matrix was then carefully

separated and a final polymerization was carried

cylinder. All the specimens were created under sta

-ble temperature conditions (23°C) and 55% humid

-ity.After bonding, the specimens were immersed in

distilled water and stored for 7 days at

3

r

C

± 1°C

prior to the shear bond strength test.

The tests were performed on a universal testing

machine (Emic-DL 500, Ind Bras, Sao Paulo, Brazil),

at a crosshead speed of 0.5 mmjmin.3 The shear

load was applied by means of a chisel with a 0.5

-mm-wide blade, positioned near the base of the

composite cylinder, as close as possible to the ad

-hesive interface. The load (in MPa) necessary to

fracture each specimen was recorded.

The means of shear bond strengths were calcu

-lated for each group (group = dentin wetness and

adhesive system). The shear bond strengths for var

-ious dentin wetnesses for each bonding system

were compared using one-way ANOVA (Table 1 and

2) and the Least-Squares Means multiple compari

-son test (Table 3)at

a

=0.05.

A contrast analysis test was done to compare the

bond strengths results of the two adhesive systems

(Table 4) at

a

=0.05.

Statistical analysis of the data by one-way ANOVA

showed a statistically significant F value at p =

0.0001. ANOVA decomposition showed a statis

-tically significant difference for the group bond

strengths values, but no effect of blocks (p= 0.217,

Table 2). The Least-Squares Means test at

a

=0.05

was used to compare the statistical difference

Table 2 One-way ANOVA analysis decomposition to evaluate the block

and group effects

Source OF Type III SS MQ F Value PR>F

Block 14 313.48226 22.39159 1.29 0.2172

Group 13 5573.82919 428.75609 24.75 0.0001*

* Meanvalues were significantlydifferent(p< 0.0001).

DF:degreesof freedom;MQ:mean square.

Table 3 Least-Squares Means test for shear bond stregths (MPa) of the

groups

Group Mean Shear Bond (MPa) LS Means

G9 23.2 a* Prime &Bond 2.1, moist cotton pellet

G3 21.3 ab Prime & Bond 2.1, air dried 5 s

G2 19.5 bc SBMP,air dried 30 s

G10 18.6 bc SBMP, moist cotton pellet

G14 16.3 cd SBMP,absorbent paper

G8 16.1 cd SBMP, dry cotton pellet

G4 14.6 de SBMP,air dried 5 s

G13 14.0 de Prime & Bond 2.1, absorbent paper

G11 13.9 de Prime &Bond 2.1, microbrush

G7 13.5 de Prime &Bond 2.1, dry cotton pellet

G12 12.1 e SBMP, microbrush

G1 8.2 f Prime &Bond 2.1, air dried 30 s

G5 2.7 g Prime &Bond 2.1, overwet

G6 2.4 g SBMU, overwet

a=0.05

*Different lettersindicatesignificantly different mean values(p<0.05).

Table 4 Contrast analysis test for adhesive systems shear bond

strengths

OF Contrast MQ F Value PR>F

SBMP vs P&B 2.1 1 6.97487 6.97487 0.40 0.5266*

*Meanvalueswere not statisticallydifferent(p>0.05).

tistical difference between mean values of Prime &

Bond 2.1 and Scotchbond Multi Purpose.

The box-plot diagram (Fig 1) is aschematic

repre-sentation of the distribution of bond strength val

-ues. The vertical lines in the box mark the 25th,

50th, and 75th percentiles of the data. The 50th

percentile is called the median, which is repre

-sented in the box by a horizontal line, and the 25th and 75th are called quartiles. The '+' sign repre

-sents means, and asterisks represent outliers.1,25

ForPrime

&

Bond 2.1, the highest bond strengths were obtained when dentin was dried with moist cotton pellet (23.2 MPa). Interestingly, similar bond strengths were obtained when dentin was dried

Fig 1 Box-plot diagram for mean shear bond strengths (MPa) of the groups. G

=

groups, P&B

=

Prime & Bond 2.1, SBMP

=

Scotchbond Multi Purpose. 30 s

=

30-s air blast, 05 s

=

5-s air blast, MC

=

moist cotton, mB

=

microbrush, AP

=

absorbent paper, DC=drycotton, OW=overwet. Vertical lines in the box=25th, 50th and 75th percentiles. Horizontal line in box=median. Hori-lontallines outside of the box=quartiles. + =means,

*

=outliers.

with a 5-s air blast (21.3 MPa). For Scotchbond Multi-Purpose, the highest mean bond strength was obtained when dentin was dried with a 30-s air blast (19.5 MPa). For both adhesive systems, the lowest means were obtained when the dentin sur-faces remained overwet (G5: 2.7 MPa; and G6: 2.4 MPa).

In spite of the fact that resin adhesion to dentin is more difficult and less predictable due to its mor-phology and heterogeneous composition,10 signifi-cant progress has been achieved after increasing understanding of the properties the substrate. In order to obtain a strong and long-lasting adhesion of resin to dentin, it is important that a dense, ho

-mogeneous, and uniform hybrid layer be formed, re-gardless of its thickness.3,15 To accomplish this, it is necessary for the demineralized dentin to be completely infiltrated by the adhesive, encasing all

the exposed collagen and the hydroxyapatite.14,15,17 However, several factors can jeopardize monomer diffusion.14 The amount of surface moisture is ex

-tremely important for hybridization of dentin. Higher bond strength can be achieved under moist condi-tions than dry.5-7,21,23The results obtained in the present study support the findings of other studies, in which the drying methods that kept the dentin surface moist and the adhesive systems that rewet the dehydrated substrate were the ones that ob-tained the highest shear bond strength values.3,4,6

This is substantiated by the bond strength va

-lues obtained in Group 9 (23.2 MPa), in which acid-etched dentin was dried with moist cotton pellets prior to the application of Prime & Bond 2.1. This drying method left the dentin visibly moist. We speculate that the water occupying the interfibrillar spaces of intertubular dentin was responsible for maintaining the collagen network in an expanded state, thereby preserving the porosity necessary for resin infiltration into intertubular and tubular dentin. The acetone present in the primer interact

-ed with this water.3-5,7,22 This interaction

presum-ably promoted water evaporation and made the

primer and the adhesive spread, penetrate, and

adapt into the open interfibrillar spaces.16

Despite the fact that the results for this group

were the highest values obtained, they did not dif

-fer significantly from the values of group 3 (21.3 MPa). In group 3, the dentin was airdried for 5 s at

a distance of 10 em from the surface prior to the

application of Prime & Bond 2.1. The average bond

strength for this group was lower, probably due to

slight overdrying, which can cause a collapse of the

collagen fibril network,4,5,7 although the degree of

wetness in the two groups seemed to be similar to

the naked eye.

A satisfactory value for adhesive strength was

also obtained in group 2 (19.5 MPa), where the

conditioned dentin surface was dried by an air blast

for 30 s from a distance of 1 em. However, the

Scotch bond Multi Purpose system was applied in

this group; it contains sufficient water to rewet the

dentin, recovering the integrity of the collagen

net-work and its spaces.24 Once dried, collapsed

colla-gen needs water to lower the modulus of elasticity

enough to let it re-expand and enable the diffusion

of monomers into the collagen fibril network, form-ing the hybrid layer.5,9,20,21,23,24 The same result

was not observed when the Prime & Bond 2.1 was

applied to similarly treated dentin (Group 1). Appar -ently, the acetone present in this system was not

capable of expanding the collapsed matrix. Presum -ably, the monomers could not diffuse into the dried

sUbstrate,4,9,20,21,24 resulting in the lower values for

adhesion4.9,20,21,24 found in group 1 (8.2 MPa). These were statistically significantly lower than

those of the other groups (Table 3, Fig 1).

Scotch bond Multi Purpose produced satisfactory

results regardless of how dentin was dried7.24 (air

dried for 30 s, absorbent paper, or dry cotton pel

-lets, G2

=

19.4 MPa, G14

=

16.3 MPa, and G8

=

16.1 MPa, respectively). We believe that the water

content of the primer allowed the collagen fibril net

-work to re-expand to the same degree. These

val-ues were not significantly different from those

obtained in group 10 (18.6 MPa), where the same

adhesive system was applied to a substrate left vi

s-ibly moist3 after being dried with moist cotton

pel-lets. Apparently, the hydrophilic monomers in the

Scotch bond Multi Purpose system can tolerate wide

variations in surface moisture.3,6,24 Thus, reliable

adhesion can be obtained when this system is

em-ployed either in moist or dry conditions.6.9.24

When Prime & Bond 2.1 was applied, the bond

strengths obtained with moist substrates (G9 =

23.2 MPa and G3

=

21.3 MPa) were higher (p <

0.05) than with dry substrates (G1

=

8.2 MPa). The

application of Prime & Bond 2.1 to relatively dry

dentin, as in the groups where the absorbent paper

(G13 = 13.9 MPa) or dry cotton pellet was used (G7

=13.5 MPa), produced significantly (p<0.05) lower

bond strengths (Table 3). This was probably be

-cause the composition of this system does not in

-clude water, and the drying techniques decreased

the surface water concentration of the dentin to a

point which allowed the primer's organic solvent to

stiffen the collagen network faster than the water

could plasticize ip,9

When the microbrush was used as a drying me

-thod, a moister surface was observed compared to

the previously described conditions. Even though

this situation should have favored the Prime &

Bond 2.1 system,? it resulted in low values of adhe

-sion for both systems (G11

=

13.9, G12 = 12.1

MPa). This might have occurred because there was

excess water on the substrate. Acetone, the volatile

polar solvent found in Prime & Bond 2.1, has the

ability to displace water, although in this case, it

was not capable of evaporating all the excess

water. Consequently, much water remained on the

surface, which may have caused phase changes

and reduced polymerization,21,23 thus reducing the

bond strength values, as exemplified by group 11

(13.9 MPa). This group did not differ statistically

from the average obtained when this adhesive was

applied to the drier substrate of groups 13 (14.0

MPa, absorbent paper) and 7 (13.5 MPa, dry cot

-ton) even though it was visibly wetter. This situation

worsened when the water-containing Scotchbond

Multi Purpose system was applied to wet dentin

that was left "dried" by a microbrush in group 12

(12.1 MPa). The resulting bond strength was proba

-bly due to the large amount of residual water that

was not evaporated prior to polymerization.21,23,24

The worst results in this study were obtained

when no drying method was used and the dentin

was left with excess water on its surface (G5 = 2.7,

G6

=

2.4, Table 3). According to Tay and others,21-23

the presence of excessive water dilutes the primer

of some adhesive systems, and its components

separate into different phases. This leads to the for

-mation of water blisters and micelles of resin which

are located on the adhesive interface, preventing

the penetration of the resinous agent into the

-ized matrix difficult. The presence of water-filled

blisters may promote the degradation of the bond

by hydrolysis of the exposed collagen.21,22

Although both systems had different composi

-tions that resulted in affinity to substrates with dif

-ferent degrees of wetness, the results obtained in

the Contrast Analysis Test (Table 4) of these sys

-tems did not show significant statistical differ

-ences, no matter which drying method was used.

Adhesion is highly influenced by the operator,

who can commit errors during the different stages

of the adhesive procedure, including drying of the

dentin. Thus, adhesive systems that are less mois

-ture-sensitive should be employed, because they

are less technique sensitive.

The highest shear bond strength was achieved with

Prime

&

Bond 2.1 applied to wet dentin dried with a

moist cotton pellet. However, this value was not sig

-nificantly different from bond strengths obtained

when the same adhesive was applied to the dentin

dried by a 5-s air blast.

The lowest shear bond strengths were obtained

when either adhesive system was applied to over

-wet dentin, and there was no significant difference

between their bond strengths to overwet dentin (ca

2 to 3 MPa).

Prime

&

Bond 2.1 showed higher (p < 0.05)

shear bond strength values when applied to dentin

kept moist after the drying process than when it

was applied to the drier dentin.

Scotch bond Multi Purpose achieved satisfactory

bond strengths (ca 15 to 20 MPa) not only with

moist dentin but also with drier dentin surfaces,

showing no significant statistical difference

be-tween substrates.

There was no significant statistical difference be

-tween the averages of shear bond strength pro

-duced by Prime

&

Bond 2.1 and Scotch bond Multi

Purpose adhesive systems when they were com

-pared with each other, independent of the dentinal

drying methods.

This study was supported by the FAPESP Foundation, grant

97/04569.

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New Frontiers in

Adhesive Dentistry

HYBR

IDIZATION OF DENTAL HARD TISSUES

Nobuo Nakabayashi and David H. Pashley

T

he h

y

bridi

za

tion of d

e

ntin

-a

p

r

ocess

th

a

t

c

r

e-ates

a

molecular-level mixtur

e o

f

a

dh

esiv

e p

o

l

y-mer

s

and dental hard ti

ss

ue

s

-

g

i

ves

c

l

i

n

icians a

versatile ne

w

material

,

u

sef

ul in

a wi

d

e array of

advanced dental treatm

e

nt

s. As

th

e first in-

d

epth

ex

p

lorati

o

n of the

s

ubj

ec

t

,

thi

s

b

oo

k

cove

r

s the

d

ev

e

lopm

e

nt, pre

se

nt und

e

r

s

t

a

nd

i

n

g, a

nd futur

e

research areas of thi

s

multifu

n

cti

o

n

a

l d

e

nt

al ma

t

e-ria

l

.

A thorough re

v

i

ew o

f th

e c

urr

e

nt lit

e

r

a

tur

e

round

s

out the text.

Valuable for stud

e

nt

s, r

e

searc

h

e

r

s, an

d

c

l

ini-cian

s

seek

i

ng a greater und

ers

t

a

ndin

g

of resin

hybridization of tooth st

r

uctur

e

.

Evolution of Dentin-Resin Bonding

Properties of Dentin

Acid Conditioning and Hybridization of

Substrates

4 Characterization oftheHybrid Layer

5 The Quality of the Hybridized Dentin

6 Clinical Applications of Hybrid Layer

Formation

129pp; 80 iI/us (some incolor);

ISBN 0-87417-575-9 C3047; US $401£26

Call +44 (0)2089496087

or Fax +44 (0)2083361484

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