The reliability of electric pulp test after concussion injury

Traumatic injuries to teeth present a difficult diagnostic problem with respect to determining the vitality of the affected teeth. Conventionally, a latency period of 4 to 6 weeks is proposed as the amount of time required for the return of a positive electric pulp test (EPT) response; however, this has been based on empirical data. The purpose of this study was to 1) determine a time frame during which a return of a reliable response to EPT may be measured, and 2) correlate this time frame with pulpal vascular changes that occur after traumatic injuries. Four canines from each of nine ferrets were used for this experiment (18 traumatized and 18 control teeth). A reproducible concussion injury was devised by releasing a known weight at a constant height above the facial surface of the experimental teeth. The EPT response was confirmed by the use of an EMG muscle recorder. Animals were killed at 24, 48 and 72 h and 6, 12 and 28 days after the injury and the teeth analyzed histologically. The histological sections showed an absence of inflammatory cells in both groups; however, according to the NIH image system, an increase in the number of vessels was detected in the experimental group when compared to the controls. In a majority of the cases, a positive response to the EPT returned within 12 days post concussion injury and as early as 10 days. In addition, a significant vascular change was accompanied with the loss of the EPT response. This study provided a reliable method by which concussion injuries may be studied using an animal model.