An Artificial Oral Environment for Testing Dental Materials

Two servo-hydraulic actuators were combined to produce the force movement cycle of human mastication. A closed-loop method of control was used which functions in a manner similar to the human neuromuscular system. The horizontal closed-loop uses a linearly variable differential amplifier (LVDT) to monitor the position. The vertical closed-loop uses both an LVDT to monitor position and a load cell to monitor force with a “mode switch” being made between the two mechanisms of control. A function generator is used to produce a sine wave which is modified to produce the movement and force programs for the two servo-hydraulic actuators. An acrylic chamber was constructed which contains the test samples and maintains an environment similar to that which occurs in the mouth. Natural or artificial saliva maintained at 37°C is continuously circulated through the chamber. The time to complete a single chewing cycle was decreased by eliminating that part of the cycle where no force is produced. This enables the chewing rate to be increased to four cycles per second. The wear produced in the artificial mouth was found to have a high correlation with clinical wear if 250 000 cycles in the artificial mouth are assumed to be equivalent to one year in the human mouth.