Effects of resin hydrophilicity on water sorption and changes in modulus of elasticity.
As acidic monomers of self-etching adhesives are incorporated into dental adhesives at high concentrations, the adhesive becomes more hydrophilic. Water sorption by polymers causes plasticization and lowers mechanical properties. The purpose of this study was to compare the water sorption and modulus of elasticity (E) of five experimental neat resins (EX) of increasing hydrophilicity, as ranked by their Hoy's solubility parameters and five commercial resins.


METHODS
After measuring the initial modulus of all resin disks by biaxial flexure, half the specimens were stored in hexadecane and the rest were stored in water. Repeated measurements of stiffness were made for 3 days. Water sorption and solubility measurements were made in a parallel experiment.


RESULTS
None of the specimens stored in oil showed any significant decrease in modulus. All resins stored in water exhibited a time-dependent decrease in modulus that was proportional to their degree of water sorption. Water sorption of EX was proportional to Hoy's solubility parameter for polar forces (delta(p)) with increasing polarity resulting in higher sorption. The least hydrophilic resin absorbed 0.55 wt% water and showed a 15% decrease in modulus after 3 days. The most hydrophilic experimental resin absorbed 12.8 wt% water and showed a 73% modulus decrease during the same period. The commercial resins absorbed between 5% and 12% water that was associated with a 19-42% reduction in modulus over 3 days.
Ito
Shuichi
S
Department of Operative Dentistry and Endodontology, School of Dentistry, Health Sciences University of Hokkaido, Sapporo, Japan.
Hashimoto
Masanori
M
Wadgaonkar
Bakul
B
Svizero
Nadia
N
Carvalho
Ricardo M
RM
Yiu
Cynthia
C
Rueggeberg
Frederick A
FA
Foulger
Stephen
S
Saito
Takashi
T
Nishitani
Yoshihiro
Y
Yoshiyama
Masahiro
M
Tay
Franklin R
FR
Pashley
David H
DH
D000042:Absorption; D000473:Alkanes / Q000737:chemistry; D000704:Analysis of Variance; D001559:Benzhydryl Compounds; D001672:Biocompatible Materials; D003188:Composite Resins; D003738:Dental Cements / Q000737:chemistry*; D004548:Elasticity; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D009821:Oils; D010636:Phenols / Q000737:chemistry*; D019279:Resin Cements; D012117:Resins, Synthetic / Q000737:chemistry*; D012995:Solubility; D013718:Tensile Strength; D013997:Time Factors; D000267:Tissue Adhesions; D014867:Water / Q000737:chemistry*; D000098826:Bisphenol A Compounds
D000473:Alkanes; D001559:Benzhydryl Compounds; D001672:Biocompatible Materials; D003188:Composite Resins; D003738:Dental Cements; D008689:Methacrylates; D009821:Oils; D010636:Phenols; D019279:Resin Cements; D012117:Resins, Synthetic; D014867:Water; C005044:hydroxyethyl methacrylate; C007932:n-hexadecane; C006780:bisphenol A; D000098826:Bisphenol A Compounds