brazjoralsci 2007 vol6 issue23 p1462 6

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Braz J Oral Sci. October-December 2007 - Vol. 6 - Number 23

Bond strength evaluation of self-etchand total-etch adhesive systems onintact and ground human enamel

Marina Di Francescantonio1

Marcelo Tavares de Oliveira2

Mirela Sanae Shinohara3

Gláucia Maria Bovi Ambrosano4

Marcelo Giannini5

1 DDS, Graduate student (Master degree),

Department of Restorative Dentistry2 DDS, MSc, Graduate student (Doctor degree),

Department of Restorative Dentistry3 DDS, MSc, PhD, Assistant Professor, School of

Dentistry, State University of Amazonas, Manaus,

AM, Brazil4 DDS, MSc, PhD, Professor, Department of

Social Dentistry5 DDS, MSc, PhD, Associate Professor,

Department of Restorative Dentistry

Piracicaba Dental School, State University of

Campinas, Piracicaba, SP, Brazil

Received for publication: October 10, 2007

Accepted: December 20, 2007

Correspondence to:Marcelo Giannini

Department of Restorative Dentistry –

Operative Dentistry Division

Piracicaba Dental School – State University of

Campinas

Av. Limeira, 901 – Piracicaba/SP – Brazil CP 52

CEP: 13414-903

Telephone: +55 19 21065338

Fax: +55 19 21065218

E-mail: [email protected]

Abstract

The aim of this study was to evaluate the bond strength of adhesive

systems to intact and ground enamel. Enamel blocks from buccal and

lingual surfaces of third molars were used for bonding procedures.

Intact or ground (600-grit SiC paper) enamel surfaces were bonded

using two “etch&rinse” adhesives (Prime&Bond 2.1 and Single Bond),

three self-etching primer systems (Optibond Solo Plus SE; Tyrian

SPE/One-Step Plus and UniFil Bond) or two self-etching adhesives

(One-Up Bond F and Xeno III). A 6-mm composite crown was built

on the bonded surfaces and samples were stored for 24 hs at 37oC.

Samples were sectioned into 0.9-mm-thick slabs, each slab trimmed

to a cross-sectional area of 0.8 mm2 and specimens loaded to failure at

a crosshead speed of 0.5 mm/min, using a universal testing machine.

Microtensile bond strength data (n=6) were analyzed using Kruskal-

Wallis and Dunn tests. Differences in bond strength between intact

and ground surfaces were not significant for both “etch&rinse”

adhesives, Tyrian SPE/One-Step Plus, UniFil Bond and Xeno III

systems. The enamel surface preparation resulted in higher bond

strength for Optibond Solo Plus SE and One-Up Bond F systems.

Enamel preparation using 600-grit SiC paper is unlikely to affect

resin-enamel bond strengths.

Keywords:

dental enamel, dentin-bonding agents, tensile strength.



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Introduction

Although phosphoric acid has been intensely used to etch

the dental substrates (enamel and dentin) for bonding, self-

etching adhesives are consider alternative methods to prepare

the tooth for restorative procedures. Self-etching adhesive

systems were developed in attempt to simplify the clinical useof dental adhesives, because they do not require separated

phosphoric acid etching, water-rinsing or superficial moist

controlling steps. The self-etching primers and adhesives are

composed of aqueous solutions of acidic functional monomers

and methacrylate components, with a pH relatively higher than

that of phosphoric acid etchants1.

While the adhesion to dentin produced by self-etching

adhesives has been considered effective2, studies are in

disagreement regarding the efficacy of conditioning and

monomer infiltrations on enamel3-6. Morphological analyses

of enamel surface treated with self-etching primers have

showed not very demineralized surfaces and other areas that

were predominantly unetched, which could impair the monomer

infiltrations and hybridization process7-10.

To improve the bonding of self-etching systems to enamel, it

has been recommended, surface pre-treatments, increase in

acidic monomer concentration, increase of etching time as

well as different application methods 3,8,11-12. Moreover, the

removal of superficial, aprismatic layer could facilitate the

etching and the infiltration of adhesive monomers7,13-14, forming

a strong and durable bonding. The purpose of this in vitro

study was to evaluate the bond strength of self-etching

adhesive systems and conventional systems (“etch & rinse”

adhesives) to intact and ground enamel. The null hypothesis

was that bond strength is not influenced by the characteristics

of the enamel surface (intact and ground) regardless of the

type of adhesive system used.

Materials and Methods

Forty-two extracted, caries-free erupted human third molars

were used in this study according to protocols approved bythe institutional review board of the Piracicaba School of

Dentistry – University of Campinas (069/2003). Teeth were

obtained by patients from 19 to 25 years old and stored in

physiological saline solution with 0.1% thymol for no longer

than 3 months.

Tooth roots were severed and the crowns were longitudinally

sectioned (mesio-distally direction) into two-halves, using a

diamond blade (Isomet, Buehler Ltd., Lake Bluff, IL, USA)

under water cooling. Eighty-four dental fragments were

obtained (6 mm in length X 5 mm in width X 1.0 mm in thickness).

A buccal or a lingual flat enamel surface of each fragment was

chosen and selected for conditioning treatments and bonding

procedures. All specimens were randomly assigned to fourteen

groups (n = 6), according to surface treatment of enamel

(grounded and intact) and type of adhesive system (self-

etching and “etch & rinse” systems). The dental fragments

from the grounded surface groups had their enamel surface

abraded with a #600-grit SiC paper on a polishing machine

(APL-4, Arotec S.A. Ind. Com., Cotia, SP, Brazil) under water

cooling for 15 seconds.

Seven adhesive systems: two 2-step “etch & rinse” single

bottle adhesives (Single Bond and Prime&Bond 2.1), three 2-

step self-etching primer systems (OptiBond Solo Plus SE;

Tyrian SPE/One-Step Plus and Unifil Bond) and two one-step

self-etching systems (One-Up Bond F and Xeno III) were

Table 1 - Compositions of adhesive systems used in this study.

Bi s-GMA = bi spheno l-glyc idyl -met hacryl ate; HEMA = 2-hydro xyethy lmethacr yl ate; PAA = po lyalkeno ic ac id copo lymer; MAC-10 =

methacryloxyundecane dicarboxylic acid; TEGDMA = triethylene glycol dimethacrylate; 4-MET = 4-methacryloxyethyl trimellitate anhydride;

UDMA = urethane dimethacrylate; PENTA: dipentaerythritol penta-acrylate monophosphate.

Braz J Oral Sci. 6(23):1462-1466 Bond strength evaluation of self -etch and total-etch adhesive systems on intact and ground human enamel

Adh esi ve Syst ems Comp osi tio n pH Manufac tur er

One-Up Bond F(self-etching

adhesive)

Bonding A: Water, methyl methacrylate, HEMA, coumarin dye, metacryloyloxyalkyl acid phosphate, MAC-10.Bonding B: multifuntional methacrylic monomer, fluoraluminosilicate glass, photoinitiator (arylboratecatalyst)

2.6 okuyama Dental Corp,Taitou-ku, Tokyo,

Japan

OptiBond Solo PlusSE

(self-primer)

Primer: Ethyl alcohol, water, alkyl dimethacrylate resins, stabilizers, activators. Adhesive resin: uncured methacrylate ester monomers, photo-initiators, stabilizers.

1.5 Kerr,Orange, CA,

USA

Prime&Bond 2.1

(etch & rinse)

Etchant: 34%phosphoric acid.

Adhesive: PENTA dimethacrylate resins UDMA cetylamine hydrofluoride acetone

2. 4 Dentspl y DeTrey,

Konstanz Germany

Single Bond(etch & rinse)

Etchant: 35%phosphoric acid. Adhesive: Bis-GMA, HEMA, ethanol, water, UDMA, bisphenol A glycerolate, polyalkenoic acid copolymer,dimethacrylate canphorquinone

4.33M ESPE,

St. Paul, MN,USA

Tyrian SPE/One-StepPlus

(self -primer)

Primer: 2-acrylamido-2-methyl propanesulfonic acid, bis (2-(methacryloyloxy) ethyl) phosphate, ethanol. Adhesive: Biphenyl dimethacrylate, hydroxyethyl m ethacrylate, acetone, glass frit.

0.5 sco Inc., Schuamburg, IL,USA

UniFil Bond(self-primer)

Primer: HEMA, 4-MET, ethanol, water. Adhesive resin : UDMA,HEMA, TEGDMA, silanated colloidal silica.

2.2 GC Corp.,Itabashi-ku, Tokyo,

Japan

Xeno III(self-etching

adhesive)

Liquid A: HEMA, purified water, ethanol, butylated hydroxy toluene, highly dispersed silicon dioxide.Liquid B: phosphoric acid functionalised polymethacrylate resins, di- and polyfunctionalised methacrylateresins, butylated hidroxy toluene, camphorquinone, 4-dimethylamino-ethyl-benzoate.

1. 4 Dentspl y DeTrey,Konstanz,Germany



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Table 2 - Median values (range) of bond strength for experimental groups.

Medians followed by different letters (lower case – column, upper case – row) differ among them by Kruskal-Wallis and Dunn tests.

evaluated (Table 1). Adhesive systems were applied according

to the manufacturer’s instructions. Resin composite build-ups

were constructed incrementally on the adhesive-bonded

surfaces of enamel in 3, 2-mm thick layers using a hybrid resin

composite (Clearfil APX; Kuraray Medical Inc, Kurashiki,

Japan). Each layer was light-cured for 40 s (670 mW/cm2) using

a light-curing unit (XL 3000; 3M ESPE, St. Paul, MN, USA).

After 24 hours of water storage, restored fragments were

sectioned into 0.9 mm thick slabs with a diamond blade (Isomet

1000; Buehler Ltd, Lake Bluff, IL, USA). For each fragment

sectioned, 2 slabs were selected and prepared for micro-tensile

bond strength testing. Each slab was ground at the bonded

interface and along both sides with a fine diamond rotary

cutting instrument (#8835KR.314.012; Brasseler, Lemgo,

Germany) under water irrigation to produce an “hour-glass”

shaped specimen. This reduced the cross-sectional area of

the specimen “necks” (0.7 × 0.7 mm) to approximately 0.8 mm2

for micro-tensile strength testing. Each specimen was fixed to

the grips of a micro-tensile testing device with cyanoacrylate

adhesive (Zapit; DVA, Corona, CA, USA) and tested in tension

in a testing machine (4411, Instron Corp., Canton, MA, USA)

at 0.5 mm/minute until failure. After testing, specimens were

carefully removed from the device with a scalpel blade (BD,

Franklin Lakes, NJ, USA). The cross-sectional area at the site

of fracture was measured to the nearest 0.01 mm with a digital

caliper (Starret 727-6/150; Starret, Itu, SP, Brazil) and used to

calculate test results in units of stress (MPa). Means of thetwo specimens (“hour-glass” shaped) were calculated for each

restored tooth fragment. Microtensile bond strength data were

analyzed statistically by Kruskal-Wallis and Dunn tests.

Results

Table 2 shows the median values of tensile bond strength for

the adhesive systems applied to intact and ground enamel.

For Optibond Solo Plus SE and One-Up Bond F systems, the

grounding of enamel surface before adhesive application

improved the bond strength. When applied them on intact

enamel surfaces, low bond strengths were found for One-Up

Bond F and pre-testing debonding occurred for specimens

restored with Optibond Solo Plus SE.

For most adhesive systems (Prime&Bond 2.1, Single Bond,

Tyrian SPE/One-Step Plus, UniFil Bond and Xeno III), the

enamel surface preparation did not increase the bond strength.

In the cases of bonding to grounded enamel, the adhesive

systems produced similar bond strengths; however OptiBond

Solo Plus SE had lower bond strength than Prime&Bond 2.1.

Discussion

Although some studies suggested to abraded the enamel

surface before application of moderate or mild two-step self-

etching primers or single-step, “all-in-one” adhesives7,10,13, the

results of this study indicated that only two of them had theirs

bond strengths increased by surface preparation with #600-

grit SiC paper. Thus, the null hypothesis was only partially

confirmed because two self-etching adhesive systems tested

were influenced by the characteristics of the enamel surface.

The two etch & rinse, one-bottle adhesives (Prime&Bond 2.1

and Single Bond), which are used after conditioning with

phosphoric acid, were not affect by abrading or not the enamel

surface. The grounded or the unprepared enamel surfaces

treated with phosphoric acids result in an etching pattern,

which consist of the formation of a porous surface with

exposed enamel crystallites and dissolution of both inter and

intraprismatic areas. The aggressive etching effect of

phosphoric acid on enamel surface overcomes the difficulty

of conditioning of intact or unprepared surfaces. The formationof a deep etching pattern6,10,15 lead to similar bond strength

when the adhesives are applied in both enamel surfaces.

Self-etching systems contain acidic monomers based on esters

from phosphoric acid, carboxylic acid or derivatives6-7,12-13. Their

etching efficacy and bonding formation depends on type of

acidic monomer, pH of adhesive solution, etching time and

application method6,8,16. Acidic monomers are responsible for

etching the dental substrates, whereas methacrylate

components, such as HEMA, are available for monomer

infiltration and polymerization of the bonding agent3-4,12. Self-

etching systems can be classified as strong, moderate and

mild, depending on their etching aggressiveness or acid

Braz J Oral Sci. 6(23):1462-1466 Bond strength evaluation of self-etch and total-etch adhesive systems on intac t and ground human enamel

Enamel Adh esiv e Sy stem

Unground Ground

One-Up Bond F 5.8 (5.6 - 9.2) B b 16.4 (10.2 – 20.1) A ab

OptiBond Solo Plus SE 0.0 (0.0 - 0.0) B c 12.8 (5.0 – 13,0) A b

Prime&Bond 2.1 23.7 (16.7 - 23.4) A a 24.3 (13.4 – 28.6) A a

Single Bond 19.8 (11.2 - 23.6) A ab 18.3 (12.9 – 22.5) A ab

Tyrian SPE/One-Step Plus 21.1 (17.2 - 28.2) A a 20.8 (12.8 – 23.9) A ab

UniFil Bond 16.0 (8.7 – 17.3) A ab 17.2 (9.6 – 18.9) A ab

Xeno III 25.0 (11.1 – 30.6) A a 21.5 (10.9 – 28.4) A ab



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dissociation constants (pKa values)2,6. In this study, it was

selected a strong system (Tyrian SPE primer), two moderates

(OptiBond Solo Plus SE and Xeno III) and two milds (Unifil

Bond and One-Up Bond F).

Studies have shown that most of the self-etching adhesives

did not etch enamel as deeply as the phosphoric acid etchantsdid and the shallow etching pattern could compromise the

bonding to enamel3,13,17. Pashley and Tay6 reported that the

efficacy of self-etching primers in intact enamel does not

depend solely upon their etching aggressiveness, but on

monomeric composition of each material. It is also possible

that the low enamel bond strengths might be caused by the

high amount of unpolymerized acidic monomers remaining

after curing4. Thus, no correlation among degree of primer

aggressiveness, enamel etching pattern and bond strength to

intact enamel has been established for self-etching adhesives18.

The pH values of all self-etching systems tested were higher

than phosphoric acid. In general, the demineralization effects

of these systems are proportional to the acidity of the acidic-

primers or self-etching adhesive solutions. The self-etching

primers are less aggressive than phosphoric acid etchants, do

not form a proper and defined acid etching pattern3,7,13-14 and

the conditioning effects are also reduced in intact enamel

surfaces, except for Tyrian SPE self-etching primer10.

The Tyrian SPE primer is considered a strong self-etching

adhesive with a very low pH (0.5). The etching pattern formed

on both ground and intact enamel surfaces is similar to that

promoted by phosphoric acid10. Moderate self-etch systems

include Optibond Solo Plus SE and Xeno III adhesives with

pH 1.4 and 1.5, respectively, while Unifil Bond (pH 2.2) and

One-Up Bond F (pH 2.6) systems are considered mild. The

bonding mechanism of these self-etching systems to enamel

is based on nanoretentive interlocking between crystallites

and adhesive resin18-19. These morphological features of the

resin-enamel bonds are different from that formed with the

etch&rinse adhesive systems18-20. This thin hybridized complex

of resin formed in enamel and produced by self-etchings

without the usual micrometer-size resin tags can be responsible

for lower bond strengths presented by some self-etching

systems and the questionable effectiveness of this type of

dental adhesives on enamel surfaces9,21-22.

Optibond Solo Plus SE and One-Up Bond F systems performed

better on prepared enamel than on unprepared enamel.

Although Optibond Solo Plus SE primer presents low pH (1.5),

it did not bond to unprepared enamel, leading to pre-testing

debonding in all specimens. Moreover, Shinohara et al.10 did

not observed proper conditioning effects promoted by the

acidic primer on intact enamel surfaces , which could

compromise the adhesion to enamel, as observed in this study.

However, Xeno III and Unifil Bond present similar and higher

pH than Optibond Solo Plus SE, respectively, and were not

affected by the mode of enamel surface preparation. Thus,

other factors, such as, monomer infiltration, polymeric network

formation and degree of conversion could also influence on

the results of bond strength.

For One-Up Bond F, SEM analysis of treated enamel surfaces

with adhesive solution revealed an extremely mild etching

pattern, regardless of the surface preparation10,13,15. This

probably occurred due to the very mild pH (2.6) of the system,which would not provide adequate demineralization for

infiltration of monomers. This pattern helps to explain the bond

strength results, which were lower when compared to the

ground surface. The higher bond strengths to the SiC-prepared

surface can be attributed to the roughness of the surface that

facilitates the activity of the self-etching adhesive to form a

defined etching pattern for infiltration of adhesive resin.

The removal of superficial, aprismatic layer by wet-grinding

with 600-grit SiC paper improves the etching effects7,10,13. As

the morphological structure and composition of the intact

peripheral surface of the enamel is different from that of the

middle enamel layer23, these differences can be favorable for

etching effects in sub-enamel surface. Since in clinical

situations the enamel is usually prepared with dental drills

prior to application of the adhesive system, the concerns about

effectiveness of self-etching adhesives can be reduced.

In conclusion, most of the self-etching systems and the two

“etch & rinse” adhesives showed the similar bond strength

values for grounded or intact enamel surfaces. For Optibond

Solo Plus SE and One-Up Bond F systems, the enamel surface

preparation resulted in higher bond strength Enamel

preparation using 600-grit SiC paper is unlikely to affect resin-

enamel bond strengths.

Acknowledgement

This study was supported by grants 01/13034-3 from FAPESP

and by grants from Capes, Brazil.

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Braz J Oral Sci. 6(23):1462-1466 Bond strength evaluation of self-etch and total-etch adhesive systems on intac t and ground human enamel

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