Effect of stress on acid dissolution of enamel

Objectives: This study was designed to measure the dissolution of buccal enamel of extracted teeth exposed to acid with or without simultaneous cyclic occlusal loading. Methods: Twenty mandibular premolars were mounted in pairs in a servohydraulic testing machine, and immersed in 1% lactic acid (pH 4.5) or water. One tooth of each pair was subjected to cyclic loading (100 N at 2 Hz for 200,000 cycles), with the load applied at 45° to the tooth axis on the buccal incline of the buccal cusp. The second tooth of each pair was immersed in acid but not subjected to load. Control teeth were immersed in water, with one tooth of each pair undergoing cyclic loading. Impressions of the teeth were taken before and after exposure to acid and occlusal loading, and a profiling system was used to measure the depth and volume loss of enamel on the buccal surface. Results: The depth of enamel dissolved ranged from approximately 50–200 μm. In certain locations teeth undergoing cyclic loading during acid exposure showed greater volumetric loss than teeth not subjected to load. Loaded teeth showed a complex pattern of enamel dissolution; volumetric loss in the cervical third was greater than in the middle third, and was much greater in the mesiobuccal segment (under tension) than in the distobuccal segment (under compression). Unloaded teeth showed greater volumetric loss in the cervical third than in the middle third, with a uniform pattern of enamel dissolution from mesiobuccal to distobuccal aspects. Significance: Enamel dissolution is increased significantly in sites subjected to cyclic tensile load.