Ternary Solvent System for Dental Bonding Agents.

Objectives: This study aims to assess the impact on initial physico-mechanical properties of an adhesive formulated with a ternary solvent system.
Methods: Solvent study was defined by Design of Experiment (DoE) using Design Expert 11, varying amounts of water/ethanol/methylethyketone (MEK) within 13 formulations at fixed total %solvent. Duplications validated model accuracy.
Responses included initial shear bond strength (iSBS) (following ISO/FDIS-29022:2012(E)), pH, viscosity (distance travelled during 10sec on a glass slide at 66°), evaporation (%wt loss over 5min ambient air drying, 30sec interval weight recordings). Surface plots for the responses were generated and two sided Dunnett post-hoc test analysed iSBS data.
Results: Excluding immiscible solvent mixes (not tested), iSBS ranged 13.8-25.9MPa with only these highest/lowest values significantly different.

pH range was 2.81-3.24, excepted 100%MEK (1.72).
Increasing %water decreased pH and increasing %ethanol or %MEK increased pH although DoE indicated weak trends. Most likely, water increases ionisation of acidic adhesive monomers, not promoted with ethanol nor MEK. However, surface plot analysis showed a lack of fit results, indicating hindrance by outliers not explained by compositional factors.

Evaporation increased with ethanol or MEK. MEK presents a greater change than ethanol, possibly due to greater %water in the MEK/water azeotrope (11%) compared to the ethanol/water azeotrope (4.5%). DoE showed that decreasing %water greatly increased the extent of evaporation but decreased iSBS.

Viscosity varied matching solvent viscosities. DoE suggested decreasing viscosity (%water) results in iSBS drop. However, low viscosity should improve SBS by helping tubule penetration.
Conclusions: Within the limitations of this study and specific solvents used, data showed that evaporation and viscosity are not as important as etching ability. However, this may only be true for initial SBS. Residual water may weaken the bond in the long term. These experiments need to be repeated in a long-term study.