Assessment of Degree of Conversion and Knoop Microhardness of Different Resin Cementing Agents

There are still controversies in the literature as to which is the best resinous cementing agent. Due to this fact and the immense availability of types and brands of cementing agents, further studies are needed to evaluate the properties of these important dental materials.

To assess the degree of monomer conversion (DC) and Knoop microhardness (KHN) of four resin cements: two conventional dual-cured resin cements (EnForce and RelyXARC); one self-etching cement (RelyXU100); and one chemically-activated cement (Cement-Post).

20 Pieces were made to assess KHN, and 20 to assess DC (n = 5). The DC was analyzed using a Fourier-transform infrared spectrometer, and KHN of the base and the top of the pieces were assessed using the Future-Tech microhardness tester. The data of KHN were statistically analyzed by two-factor ANOVA, and data related to DC were analyzed by the Kruskal-Wallis non-parametric test. The analysis of the correlation between KHN and DC of the cementing agents was performed by linear regression.

Dual-cured cements exhibited lower average KHN values at the base than at the top of the pieces (p <0.05). The self-etching cement had a significantly higher average KHN value than the other assessed cements (p <0.05). The DC of the dual-cured cement did not differ (p >0.05). The chemically-activated cement exhibited the lowest averages of KHN and DC values (p <0.05). Linear regression analysis indicated a strong correlation between DC and KNH (p = 0.043; R² = 0.96); however, a specific hardness value could not be correlated to a specific DC value.

Preferably, dual-cured resin cements (conventional or self-etching) should be used. Chemically-activated resin cements should be avoided due to their lower averages of DC and KHN values.