In a dental operatory system a master device coordinates the activity levels of multiple slave devices. The master device coordinates activity via a communication link with all slave devices. A communication protocol incorporates a closed system addresses scheme in which the master device learns all associated addresses of slave devices, and all slave devices learn all associated addresses of the master device. Each communication between master device and any slave device includes both the master device address and the slave device address. The master device scans all slave devices for an activity status and determines which slave device exhibits a threshold level of activity, and whether activity is increasing or decreasing. The master device passes a communication control token to the slave device to be controlled by operation of the master device.