The infrabony pocket and its relationship to trauma from occlusion and subgingival plaque.

The role of trauma from occlusion and subgingival plaque in the pathogenesis of the infrabony pocket as observed in the radiograph was studied in 48 teeth which had to be extracted because of advanced periodontal disease. Prior to extraction the teeth were examined with regard to the degree of mobility and the direction of the horizontal components of the masticatory forces. Following extraction, the teeth were stained and examined under the stereomicroscope. When the tooth is adequately stained, the subgingival plaque and the remaining attachment fibers can be distinguished easily from the area of the junctional epithelium. The observations which were made on the extracted teeth were then correlated with what could be seen in the radiograph. The following major observations were made: In the depth of the infrabony pocket there was a close congruence between the front of the subgingival plaque and the borderline of the remaining attachment fibers, the distance varying between 0.2 and 2.0 mm. There was also a close relationship between the front of the subgingival plaque and the alveolar crest adjacent to the tooth as well as between the surface of the subgingival plaque and the opposite vertical wall of the infrabony pocket, the distances ranging between 1 and 3 mm. The horizontal forces were mainly or exclusively oriented bucco-lingually, whereas the infrabony pockets were located mesially or distally, i.e. parallel to the direction of the force and not at a right angle to it as observed in experimental studies. The mobility of the teeth adjacent to which infrabony pockets developed was normal in 42% of the cases, slightly increased in 31%, and only in 11% of the cases was it excessively increased. In 19 cases the infrabony pocket was located on one of the roots of lower molars which were removed by hemisection. In eight of the 12 cases, which were observed for periods from 1 to 10 years, the remaining root functioned well without further development of angular bone defects or infrabony pockets. All of them became markedly firmer as a consequence of successful periodontal treatment. Three of the four remaining roots were extracted because of periapical problems. There was no evidence to indicate that trauma from occlusion had been involved in the pathogenesis of the infrabony pockets.