Reflectometry: a new method for quantitative determinations of intraoral film formation

A simple optical method--reflectometry--is described to determine the thickness and mass of salivary films formed on solid surfaces at oral exposure. Reflectometry is based on the fact that p-polarized light is reflected with minimum intensity at an interface when the angle of incidence equals the so-called pseudo-Brewster angle. Hydrophilic and hydrophobized silica surfaces were used as substrates and the reflectometer was calibrated against a null ellipsometer. A linear relation was found between the square of the ellipsometrically measured thickness of silicon oxides on silicon substrates and the reflectometrically registered intensity of the reflected light at these surfaces. Thirty volunteers participated in the study of the thickness of films formed on the test substrates at oral exposure. The test silica surfaces were positioned in the vestibular sulcus of each test subject for periods of 1, 5, 15, 30, 60, and 120 min. The results show that films formed on hydrophobic surfaces leveled-off to a thickness value of 140 A after 60 min. Films formed on hydrophilic surfaces, however, reached a plateau value of approximately 100 A after only 300 min. Reflectometry seems to be an accurate and valid, yet inexpensive and quick method for quantitative investigations and thickness measurements of early salivary pellicles in large subject groups.