The tonic (resting) and peak (maximum) lip pressures of 100 subjects were measured. The purpose was to evaluate the validity of the assumption that high peak pressures are indicative of high tonic pressures and vice versa. This paper describes the equipment and techniques devised to test these pressures. The results showed no statistically significant relationship whatsoever between tonic and peak lip pressures. We, therefore, suggest that maximum lip pressures not be used as a diagnostic aid in orthodontics. [Reprinted from The Angle Orthodontist, Fall 1990, vol. 60, pages 215-220]


lip pressure, oral muscular pressure, pneumohydraulic capillary infusion system