John F. Nelson’s research while affiliated with The University of Texas Health Science Center at San Antonio and other places

Twenty-four Wistar rats were anesthetized and 200 degrees C heat was applied for 4 minutes to each mandibular left first molar. Eight of these rats were then killed at 2, 8, and 14 weeks. The subject and control teeth were radiographed and compared. They were then prepared for histologic evaluation and scored for levels of inflammation in both the pulpal and periradicular tissues. Furcal, interproximal, and apical radiographic changes were found at all three time intervals. These changes involved progressively larger percentages of teeth at 8 and 14 weeks. Histologically, complete necrosis and/or abscess formation were found in the coronal portions of all experimental pulps. With time, inflammatory changes increased in intensity and progressed through the radicular pulps, resulting in necrosis or calcific changes and, finally, inflammatory changes in the periradicular areas. The pathosis created by the application of heat was devoid of microorganisms as evaluated by the Brown and Brenn stain.