Comparison of Artificial Saliva Substitutes

Human saliva consists of water, glycoproteins, enzymes, antimicrobial substances and electrolytes. From biophysical point of view, saliva is a viscoelastic fluid with distinct surface activity. Commercial artificial saliva used in salivary gland disorders should resemble normal saliva in biophysical properties. In this study we evaluated the biophysical properties of saliva and existing saliva substitutes. We compared three existing substitutes Saliveze, Xialine 1, and Xialine 2. Saliveze is based on carboxymethylcellulose and the others on xanthan gum. The choice of carbohydrate polymers is justifiable because of mucoadhesive nature. Both Saliveze, and xialine 1 are Newtonian fluids (viscosity of 5.71 cP and1.36 cP respectively) where as normal saliva is nonNewtonian (15.51 cP – 2.75 cP at shear rates 0.5 94.5 s-1). Similar to normal saliva Xialine 2 is shear-thinning fluid but has a lower viscosity (6.60 3.78 cP Vs 15.51 2.75 cP at shear rates 0.5 – 94.5 s-1). Shear thinning property is essential to ensure proper flow and cleansing action. The surface activity of both saliva and the substitutes has not been dealt with in the literature. Minimum surface tension of saliveze, xialine 1 and xialine 2 are 64.17, 66.15 and 64.89 mN/ m respectively where as that of natural saliva is 24.85 mN/m. Also, unlike natural saliva, none of the substitutes studied showed hysteresis in their surface tension area isotherms. The low minimum surface tension is essential for saliva film formation on the oral mucosa. The existing substitutes fall short of required biophysical criteria and modifications are required to improve them. We need surface active, shear thinning and mucoadhesive polymer as saliva substitute, possible additions could be surfaceactive phospholipids, known to be present in saliva and/or mucin, the predominant surface-active protein of natural saliva. Consideration of the biophysical criteria could lead to future development of improved substitutes.