The surface free energy of dental gold-based materials

Objective: A gold composite material (Captek™) has been developed which is claimed to resist plaque deposition. This study's aim was to compare the surface free energy (SFE) of this composite material with that of a type III casting gold. Methods: Contact angle measurements, using the Wilhelmy technique, were made on four bar-shaped samples of each material, using five test liquids (diiodomethane, ethylene glycol, formamide, glycerol and water) and four measurements per sample per liquid. For each material, the dispersive, Lewis acid and Lewis base components of SFE (γ_S^D, γ_S⁺, γ_S^-, respectively) were estimated by least squares analysis and also by a Bayesian method. Results: The gold composite material and the type III casting gold did not differ significantly in their γ_S^D values (95% confidence interval for gold composite minus type III gold, -5.0 to +2.7). Both materials had low γ_S⁺ values in common with most solids. The gold composite had a significantly lower Lewis base component of SFE than the type III gold-8.4mN/m for the former material compared to 19.1mN/m for the latter (95% confidence interval for gold composite minus type III gold, -16.4 to -4.9). The difference between materials could be related to the lack of non-precious metals and the structure of the gold composite material. Conclusions: It is hypothesized that difference in γ_S ^- components of SFE may be an important parameter in predicting bacterial adhesion and plaque resistance. Methods that only determine SFE as a single parameter may be unable to differentiate adequately between dental restorative materials.