Objectives. 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 thatwas testedwas 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 60 s.
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 20 s but increased DC after 40–60 s of light exposure.
Significance. 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.
