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Monomer-Solvent Phase-Separation in Contemporary One-step Self-etch Adhesives

One-step self-etch adhesives (1-SEA) have been associated with lower bonding effectiveness to tooth tissue than their multi-step versions. Objectives: To investigate that this lower bonding effectiveness must be attributed in part to phase-separation between adhesive ingredients. Methods: The micro-tensile bond strength (µTBS) of two experimental 1-SEAs, containing a carboxylate- and phosphate-based functional monomer dissolved in ethanol/water (exp-Eth) or in acetone/water (exp-Ac), of one commercial 1-SEA, iBond (Heræus-Kulzer), and of two commercial 2-SEAs, Unifil Bond (GC) and Clearfil SE (Kuraray) was determined to enamel/dentin. One additional exp. 2-SEA tested consisted of the application of exp-Eth followed by the application/curing of a non-solvent containing adhesive resin (Unifil Bond Bonding Agent, UFB). All adhesive solutions were examined for homogeneity by light-microscopy, and their interaction with enamel/dentin was imaged using Feg-SEM and TEM. Results:

µTBS exp-Eth exp -Ac exp-Eth+UFB iBond Unifil Bond Clearfil SE
Enamel 16.1±6.3a,b*

n=33

 15.4±8.6a,b#

n=14

 29.5±6.7b

n=13

 19.3±10.3a,b*

n=12

 14.5±6.0a*

n=14

 30.4±12.9a,b

n=14
Dentin 20.2±6.2c

n=29

 20.7±4.9c

n=14

 27.6±11.5c,d

n=11

 11.1±8.6e§

n=14

 30.4±12.9c,d

n=14

 39.6±5.4d

n=12

*1 pre-testing failure (ptf); #2 ptf; §4 ptf; Different superscript letters indicate significant difference; Kruskal-Wallis test, p<0.05.

The lower bond strength of the 1-SEAs was associated with light-microscopic observation of multiple droplets that disappeared relatively slowly with time. Interfacial analysis confirmed the entrapment of droplets within the adhesive layer, especially adjacent to the hybrid layer. Conclusion: The prompt disappearance of droplets upon application of a HEMA-containing bonding agent (exp-Eth+UFB), and upon adding a little drop of pure HEMA, as well as the absence of HEMA in the 1-SEA formulations and the absence of droplets at the interface of all HEMA-containing 2-SEAs, strongly suggest that upon evaporation of ethanol/acetone the adhesive monomers within the 1-SEAs separated from water. Water droplets were formed and got entrapped within the adhesive resin upon polymerization.

Supported by FWO Flanders.


Division: Continental European, Israeli, Scandinavian Divisions Meeting
Meeting: 2004 Continental European, Israeli, Scandinavian Divisions Meeting (Istanbul, Turkey)
Location: Istanbul, Turkey
Year: 2004
Final Presentation ID: 553
Abstract Category|Abstract Category(s): Scientific Program
Authors
  • Van Landuyt, Kirsten  ( Catholic University of Leuven, Leuven, N/A, Belgium )
  • De Munck, Jan  ( Catholic University of Leuven, Leuven, N/A, Belgium )
  • Snauwaert, Johan  ( Catholic University of Leuven, Leuven, N/A, Belgium )
  • Coutinho, Eduardo  ( Catholic University of Leuven, Leuven, N/A, Belgium )
  • Poitevin, André  ( Catholic University of Leuven, Leuven, N/A, Belgium )
  • Lambrechts, Paul  ( Catholic University of Leuven, Leuven, N/A, Belgium )
  • Van Meerbeek, Bart  ( Catholic University of Leuven, Leuven, N/A, Belgium )
    • SESSION INFORMATION
    Oral Session
    Dental Materials: Adhesion, Composite - Bonding
    08/28/2004