IADR Abstract Archives

Effects of Water Sorption on Stiffness of Unfilled Dental Resins

Objective: As dental resins become more hydrophilic, they absorb more water.  Absorbed water plasticizes the polymers and weakens their modulus of elasticity (E).  This may jeopardize the durability of resin-dentin bonds.  The purpose of this study was to correlate the hydrophilicity ranking of experimental resins (using Hoy's solubility parameter, δp) with water sorption and decreases in E over-time.  The null hypothesis was that resin stiffness is unaffected by water sorption.  Methods:  Five experimental resins of increasing hydrophilicity (Resin 1 = 70% ethoxyl/BisGMA/29% TEGDMA; 2 = 70% BisGMA/29% TEGDMA; 3 = 70% BisGMA/29% HEMA; 4 = 40% BisGMA/29% TEGMDA/30% TCDM; 5 = 40% BisGMA/30% HEMA/30% BisMEP) were cast into 6 mm diameter x 0.5 mm thick disks.  Twenty-four hrs after light-curing, the dry disks were subjected to biaxial flexure in an Instron to measure their initial E values.  Half of the disks were stored in hexadecane and the other half in water.  The E values were repeatedly measured for 3 days.  Results:  Intial E/Final E (GPa):

Storage media

Resin 1

Resin 2

Resin 3

Resin 4

Resin 5

Hexadecane E

2.34/2.34

4.18/4.21

3.98/4.16

3.54/3.74

3.23/3.18

Water E (GPa)

2.34/2.00

4.19/3.72

4.23/3.21

3.37/2.40

3.29/2.42

% change in EH2O

-14.0

-11.1

-24.2

-29.0

-68.8

δp (J/cm3)½

10.2

12.1

13.1

12.2

13.7

Water sorption (%)

0.8

4.5

6.5

5.5

10.5

Water sorption increased as resin δp increased.  This caused a significant (p<0.05) decrease in E.  Conclusions:  Resin storage in hexadecane caused no decrease in stiffness of resin disks.  The stiffness of resins stored in water fell in proportion to their water sorption which, in turn, was proportional to their Hoy's solubility parameter for polar forces.  The use of hydrophobic resins in resin-dentin bonds should provide stronger more durable bonds, but requires new bonding procedures.  Supported, in part, by USPHS R01 DE015306 from the NIDCR.


IADR/AADR/CADR General Session
2005 IADR/AADR/CADR General Session (Baltimore, Maryland)
Baltimore, Maryland
2005
43
Dental Materials: II - Adhesion-Other
  • Ito, Shuichi  ( University of Hokkaido, Hokkaido, N/A, Japan )
  • Wadgaonkar, Bakul  ( Medical College of Georgia, Augusta, GA, USA )
  • Svizero, Nadia  ( University of Sacred Heart, Sao Paulo, N/A, Brazil )
  • Tay, Franklin R.  ( University of Hong Kong, Hong Kong, N/A, China )
  • Rueggeberg, Frederick  ( Medical College of Georgia, Augusta, GA, USA )
  • Pashley, David  ( Medical College of Georgia, Augusta, GA, USA )
    • Oral Session
    Ceramics, Alloys, and Resins
    03/09/2005