Effects of residual ethanol on the rate and degree of conversion of five experimental resins.
OBJECTIVE
This study examined the extent of ethanol retention in five comonomer blends of experimental methacrylate-based dental adhesives, containing (10, 20, or 30 wt.%) ethanol, after solvent evaporation, as well as observing the effect of residual ethanol and exposure duration on degree of conversion (DC). The null hypothesis that was tested was that residual, unevaporated ethanol has no effect on the rate or extent of DC of polymerized adhesive resins.


METHODS
A known mass of each mixture was placed in glass wells and evaporated for 60s. The mass of the mixtures before and after evaporation was measured, allowing calculation of the gravimetric ethanol loss/retention.


RESULTS
The concentration of retained ethanol increased significantly with ethanol concentration (p<0.01): 1.1-1.9 mole/L for 10% ethanol/90% comonomers, 2.2-3.5 mole/L for 20% ethanol, and 2.6-3.7 mole/L for 30% ethanol/70% comonomers. As ethanol is evaporated from solvated comonomer mixtures, the molar concentration of comonomers increases, reducing the vapor pressure of the remaining ethanol. Thus, the fractional loss of ethanol solvent decreases as the comonomer concentration increases. The DC of 10, 20, and 30 wt.% ethanol blends increased with ethanol concentration in four of the five experimental resins (p<0.05), increasing by 30-45% when 10 or 20 wt.% ethanol was added to neat resins, regardless of exposure duration. Depending on the resin system, inclusion of 30% ethanol lowered DC at 20s but increased DC after 40-60s of light exposure.


CONCLUSIONS
Since 10 and 20 wt.% ethanol-resin blends increased the DC of solvated resins by 30-45% over neat resins, the test null hypothesis is rejected. Even with prolonged evaporation, 4-9% residual ethanol concentration can remain in 90/10 (wt./wt.) comonomer-ethanol mixtures. This is thought to be because comonomers lower the vapor pressure of ethanol. This amount of residual ethanol facilitates DC but lowers the rate of polymerization.
Cadenaro
Milena
M
Department of Biomedicine, Unit of Dental Sciences and Biomaterials, University of Trieste, Italy.
Breschi
Lorenzo
L
Rueggeberg
Frederick A
FA
Suchko
Michael
M
Grodin
Evan
E
Agee
Kelli
K
Di Lenarda
Roberto
R
Tay
Franklin R
FR
Pashley
David H
DH
D010129:4-Aminobenzoic Acid; D000180:Acrylic Resins / Q000737:chemistry; D000431:Ethanol / Q000032:analysis / Q000737:chemistry; D006244:Hardness; D055115:Light-Curing of Dental Adhesives; D044367:Phase Transition; D019279:Resin Cements / Q000737:chemistry*; D012997:Solvents / Q000032:analysis / Q000737:chemistry; D013729:Terpenes; D014835:Volatilization; D017155:Wettability
D000180:Acrylic Resins; D019279:Resin Cements; D012997:Solvents; D013729:Terpenes; D000431:Ethanol; C048339:camphoroquinone; D010129:4-Aminobenzoic Acid