The recent surge in the number of dentin bonding agents
available for clinical use has created a quagmire for the dental professional.
Many practitioners are undecided about which bonding agent is best to utilize
in a particular clinical situation. Even more disconcerting is the fact that
the restorative procedure may fail if the application of an adhesive is
Dentin/enamel bonding agents are classified as either
etch-and-rinse (total-etch with phosphoric acid on enamel and dentin) or self-etch
(phosphoric acid not utilized) adhesives.1 Dental manufacturers
have developed simplified versions of each system, reducing steps by combining
of primers and bonding resins into one bottle.
However, recent in vitro studies indicate that a nanoleakage
phenomenon, described as a leakage pattern occurring within the nanometer-sized
spaces around the collagen fibrils within the hybrid layer, may develop more
frequently with simplified bonding systems. These bonding agents are more
hydrophilic in composition and may also attract water from underlying hydrated
dentin at the resin-dentin interface. Increased water sorption into the hybrid
and adhesive layers may weaken properties of the adhesive, and account for
reduced bond strength.2 The scientific evidence must,
therefore, be examined to determine how the limitations of these bonding agents
may be overcome to ensure a successfully executed clinical protocol. Several
methodologies have been introduced in the literature to improve the
effectiveness of current adhesive systems to dentin and enamel.
Some researchers recommend the placement of a viscous phosphoric
acid etch on enamel prior to self-etch bonding agent application, particularly
when a mild self-etch (pH2 or above) is utilized as a means to
increase the bonding effectiveness of self-etch adhesives to enamel.3 It
is mandated that the phosphoric acid etch not come in contact with the dentin
in this protocol, because it will reduce the bonding effectiveness of the
self-etch primer to dentin.
Other methods suggested in the literature to improve the
effectiveness of bonding agents are multiple applications and agitation of the
bonding agents.4,5 Consecutive applications of adhesive caused
a decrease in nanoleakage, possibly due to the removal of more water and the
uptake of additional resin into the collagen fibril meshwork. Agitation of the
bonding agents resulted in improved bond strength for the dentin structures
only. Most importantly, however, is that the correct time allocated for
material placement and drying must be strictly followed according to the
manufacturer’s directions for use.6
In vitro studies indicate that the application of a phosphoric
acid on enamel prior to the application of a self-etch bonding agent may
increase the bonding effectiveness of self-etch adhesives to enamel. Other
methods to improve the effectiveness of bonding agents to dentin are multiple
applications and agitation of the bonding agents. It is most important,
however, to strictly follow the manufacturer’s directions for use.
These recommendations are based on in vitro studies. It will be
necessary, however, to validate their results in long-term clinical studies to
better understand bonding mechanisms and their impact on the clinical outcomes.
Meerbeek B, De Munck J, Yoshida Y, et al. Buonocore memorial lecture. Adhesion
to enamel and dentin: Current status and future challenges. Oper Dent
AF, Giannini M, Pereira PR. Long-term TEM analysis of the nanoleakage patterns
in resin–dentin interfaces produced by different bonding strategies. Dent Mater 2007; 23(9):1164-1172
Landuyt KL, Kanumilli P, De Munck J, et al. Bond strength of a mild self-etch
adhesive with and without prior acid-etching. J Dent 2006;34(1):77-85
- Hashimoto M, De Munck J, Ito S, et al. In
vitro effect of nanoleakage expression on resin-dentin bond strengths analyzed
by microtensile bond test, SEM/EDX and TEM. Biomater 2004;25(25):5565-5574
- Velasquez LM, Sergent RS, Burgess JO, Mercante DE. Effect
of placement agitation and placement time on the shear bond strength of 3
self-etching adhesives. Oper Dent 2006;31(4):426-430
- Cavalheiro A, Vargas MA, Armstrong SR, et al.
Effect of incorrect primer application on dentin permeability. J Adhes Dent 2006;8(6):393-400.