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CERECDOCTORS.COM
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QUARTER 2
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2015
M AT E R I A L S
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B Y D E N N I S J . FA S B I N D E R , D . D . S . , A . B . G . D .
doctors and their team members invest significant time and effort
to understanding and applying the imaging,
design and milling processes required to fabricate well-fitting, esthetic CEREC restorations.
A cornerstone to the successful longevity of these restorations is the adhesive bonding process. Well-fitting, esthetic restora-
tions are dependent on meticulous adhesive technique to ensure comfort and function for the long term.
Universal Adhesives
A Cornerstone for Longevity
Many in vitro studies have been published in an effort to ident-
ify the optimum adhesive bonding techniques and materials. The
introduction of the 4th generation bonding agents set the adhesive
bond strength bar for maximum bond strength. However, these
systems had a bottle for each step, and lengthy clinical application
techniques that were at risk of post-operative sensitivity. Since
their introduction, both manufacturers and dentists have been
searching for efficient, easy and dependable bonding systems for
adhesive delivery of CEREC restorations.
The release of Scotchbond Universal Adhesive by 3M ESPE
introduced a new category of universal adhesives that offer
substantial bond strength, versatility and ease of use (Table 1).
There is no consensus definition of universal adhesives, but theymay
be considered as a single-bottle adhesive that may be applied in self-
etch, selective-etch and total-etchmodes. And they generally bond to
multiple substrates besides enamel and dentin to include ceramics,
zirconia and metal alloys. An excellent review of universal adhesive
agents has recently been published, and readers looking for a more
in-depth discussion of their chemistry can review the article.
1
Self-etching adhesive agents are preferred for their perceived
lack of post-operative sensitivity. However, this benefit comes at
the cost of a weaker bond to the enamel. This is due to the weak
acid that is combined with the adhesive agent. Maximum bond
strengths to enamel are achieved with the use of 37% phosphoric
acid for 15-20 seconds, followed by thorough rinsing with water.
Universal adhesives tend to have a pH in the range of two to
four, making them somewhat mild etchants on enamel compared
to phosphoric acid at a pH of 0.3. A number of in vitro studies have
reported that good dentin bond strength values can be achieved
with the self-etch mode. However, more predictable enamel
bonding, especially on uncut enamel, would be achieved by using
37% phosphoric acid. For clinical situations requiring strong
bonds, it is recommended to use universal adhesives in either the
selective-etch or total etch modes.
Single bottle self-etching adhesive agents contain water that
enables the weak acid to ionize and minimally etch the surface
of the tooth. Unfortunately, this also results in increased dentin
permeability that may adversely affect the long-term durability
of the adhesive bond.
2
Almost all universal adhesives also contain
water to dissociate the weak acids they contain. (Prime & Bond
Elect is an exception that contains acetone.) Water improves
dentin wetting and engulfing the exposed collagen fibrils.
Application of the universal adhesive should be an “active”
process. This means that the universal adhesive should be lightly
scrubbed into the surface of the tooth for the time of application
rather than just painted on and left to react. Over-drying the tooth
surface tends tohavemore of a deleterious effect onbond strengths
than over-wetting the tooth surface; so, of the two, a little excess
water is preferred. The recommended clinical appearance is to
dry the surface of the adhesive carefully until no movement of the
liquid is visible. This does not mean blowing the adhesive off the
surface of the toothwith a strong streamof air. The treated surface
should be visibly shiny, rather than having a dull or matte surface.
If the surface is not shiny, a second application of the universal
adhesive may be applied.
Universal adhesives have improved on self-etching adhesives
by also including monomers capable of producing chemical adhe-
sion to the surface of the tooth.
3
It is suggested that these chem-
ical adhesives may also act to increase the durability of the bonds
compared to self-etching adhesives.
All universal adhesives include some sort of functional
monomer to facilitate an adhesive bond to the tooth surface. This
is not a simple combination, as the functional monomer is opti-
mally hydrophilic to wet and adhere well to the surface of the
tooth. However, once cured, it is optimally hydrophobic to prevent
water degradation of the adhesive bond over time.
Phosphate esters are the primary functional monomer in
universal adhesives. They provide the ability to bond to metal
alloys, zirconia and tooth structure. The most common one
used in universal adhesives in 10-MDP (methacryloxloxydecyl-
dihydrogen-phosphate), initially developed by Kuraray in the
1980s. 10-MDP has a documented effectiveness in adhesive
