Quality Resource Guide –

Dental Adhesives 4th Edition

www.metdental.com

Page 5

•

On enamel, 1-step self-etch adhesives result in

the formation of water blisters on the surface of

the adhesive, which compromises durability of

enamel bonding

•

One-step self-etch adhesives undergo phase

separation very rapidly

•

Water in their composition may become

entrapped if not properly evaporated, which

results in dentin leakage

Universal Adhesives

niversal adhesives are basically 1-step

self-etch adhesives that can be used in

different adhesion strategies. In the past,

dentists have used dentin adhesives following the

adhesion strategy recommended by the respective

manufacturer. With the advent of universal adhesives

(Table 1) dentists are now using the same dentin

adhesive for different adhesion strategies (i.e. self-

etch, etch-and-rinse, or selective enamel etch),

according to each specific clinical situation. This new

generation of 1-bottle dental adhesives has become

very popular in Dentistry.

The major difference between traditional 1-step

self-etch adhesives and universal adhesives is that

most universal adhesives contain 10-MDP monomer

(methacryloyloxydecyl

dihydrogen

phosphate),

which has been shown to bond chemically to calcium

in hydroxyapatite through a mechanism known as

nano-layering.

This molecule may be responsible

for the excellent long-term clinical success of the

2-step self-etch adhesive Clearfil SE Bond (Kuraray

America, Inc.).

Because chemical bonding provided

by 10-MDP depends on the concentration of this

molecule, the extent of chemical bonding in universal

adhesives is very weak compared to that observed

for the 2-step self-etch adhesive Clearfil SE Bond.

Enamel

etching

with

phosphoric

acid

needed for these new

universal adhesives

(Compare Figures 6A and 6B). Consequently, the

recommended adhesive strategy for most clinical

applications of universal adhesives is selective

enamel etching (no dentin etching). In Pediatric

Dentistry it is sometimes difficult to etch and

rinse enamel.

It has been shown that the active

application (rubbing) of universal adhesives on

enamel results in higher bond strengths to intact

enamel for some universal adhesives compared

to the bond strengths obtained with passive

application, except for Adhese Universal and

Scotchbond Universal. For these two adhesives

enamel bond strengths are identical when applied

passively or with rubbing action.

Clinical

and

laboratory

evaluations

have

demonstrated that some universal adhesives form

a hybrid layer (Figure 7A) and may perform at the

same level of existing materials.

36,37

However, In

case universal adhesives are used as etch-and-

rinse adhesives, it is not necessary to leave dentin

moist for two reasons:

(1) Universal adhesives contain 10-20% water.

Their bond strengths to dentin that has been

air-dried for 5 seconds is similar to their bond

strengths to moist dentin.

(2) Manufacturers recommend the evaporation

of the solvent with air for 5 seconds after

the application of the universal adhesive

(10 seconds for All-Bond Universal). However,

SEM image of the adhesive interface formed with

All-Bond Universal applied on human dentin as an

etch-and-rinse adhesive.

Cr= Composite resin

Ad = Adhesive

Rt = Resin tag

D= Dentin

The hybrid layer (H) was resistant to the

deproteinizing effect of sodium hypochlorite.

Original magnification = X5,000.

Figure 7A

SEM image of the adhesive interface formed with

Prime & Bond Elect applied on human dentin as

an etch-and-rinse adhesive.

Cr= Composite resin

Ad = Adhesive

Rt = Resin tag

D= Dentin

The asterisks (*) correspond to the areas in which

part of the hybrid layer is missing as a result of its

susceptibility to degradation by sodium

hypochlorite. Original magnification = X5,000.

Figure 7B

5 seconds is not enough to evaporate the water

added to the composition of the adhesive.

If dentists leave dentin moist prior to applying

universal adhesives, the amount of residual

water left into the dentin substrate may hamper

the formation of a hybrid layer for some

universal adhesives (Figure 7B), reduce bond

strengths, and substantially increase hydrolytic

degradation of the bonded interface.

38.39

Enamel etching pattern after etching with Scotch-

bond Universal etchant (34% phosphoric acid, 3M

ESPE). Original magnification = X2,500.

Figure 6B

Enamel etching pattern of Scotchbond Universal

Adhesive (3M ESPE) applied as a 1-step self-etch

adhesive. Original magnification = X2,500.

Figure 6A