The role of HEMA in one-step self-etch adhesives.
In spite of its high allergenic potential, 2-hydroxyethyl methacrylate (HEMA), a low-molecular-weight monomer, is frequently used in adhesives for its positive influence on the bond strength. In addition, the presence of HEMA in one-component one-step adhesives can prevent phase separation.


OBJECTIVE
In search of improved bonding effectiveness, the 24-h bond strength of four experimental one-step self-etch adhesives with different concentrations of HEMA to bur-cut enamel and dentin was determined using a micro-tensile bond strength protocol.


METHODS
The tested experimental adhesives (Exp-0, Exp-10, Exp-19 and Exp-36) only differed in their concentration of HEMA, which was 0, 10, 19 and 36%, respectively. With an increasing concentration of HEMA, the concentration of acetone was decreased. Besides bond strength, the adhesives were also examined by light-microscopy for phase separation. The interface was investigated by SEM and TEM.


RESULTS
Regarding bond strength, Exp-10 performed best. Even though Exp-36 was the only adhesive formulation that did not exhibit phase separation on a glass plate, it yielded the lowest bond strength. Accordingly, droplets could be observed by SEM and TEM in the adhesive layers of all adhesives, except for Exp-36 on enamel.


CONCLUSIONS
A small amount of HEMA (10%) improved the bond strength of a one-step self-etch adhesive. When added in higher concentrations, this beneficial effect of HEMA on the bond strength is lost due to increased osmosis, which resulted in many droplets; due to reduced polymerization conversion; and sub-optimal physico-mechanical properties of the resultant poly-HEMA containing adhesive interface.
Van Landuyt
K L
KL
Leuven BIOMAT Research Cluster, Department of Conservative Dentistry, School of Dentistry, Oral Pathology and Maxillo-Facial Surgery, Catholic University of Leuven, Kapucijnenvoer 7, B-3000 Leuven, Belgium.
Snauwaert
J
J
Peumans
M
M
De Munck
J
J
Lambrechts
P
P
Van Meerbeek
B
B
D000096:Acetone / Q000737:chemistry; D001840:Dental Bonding; D003743:Dental Enamel / Q000648:ultrastructure; D003804:Dentin / Q000648:ultrastructure; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D006801:Humans; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010755:Organophosphates / Q000737:chemistry; D044367:Phase Transition; D011108:Polymers / Q000737:chemistry; D019279:Resin Cements / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D013718:Tensile Strength; D013997:Time Factors; D014233:Tricarboxylic Acids / Q000737:chemistry; D014867:Water / Q000737:chemistry
D017220:Dentin-Bonding Agents; D008689:Methacrylates; D010755:Organophosphates; D011108:Polymers; D019279:Resin Cements; D012997:Solvents; D014233:Tricarboxylic Acids; D014867:Water; D000096:Acetone; C098756:4-methacryloxyethyltrimellitic acid; C005044:hydroxyethyl methacrylate