Tissue changes in the rat molar periodontium following application of intrusive forces

Abstract

The effect of intrusive forces on periodontal structures has been studied in maxillary molars of 55 young male rats. The tissues in the interradicular and apical regions had the typical characteristics of pressure zones: periodontal ligament compression, cellfree and semi-cellfree zones and initial undermining bone resorption in the earlier phases of the force application, a widening of the periodontal space, a decrease in the incidence of cellfree and semi-cellfree zones, bone and root resorption in the later phases. In the marginal and middle third region of the periodontium the characteristics of pressure zones and tension zones were found in the same areas: cellfree and semi-cellfree zones, bone and root resorption, stretched fibres and deposition of osteoid tissue. Bone resorption was also observed on the alveolar crest, bone deposition on the external maxillary surface adjacent to the root apices. The reaction to forces of different magnitude, varying between 0.29 and 0.98 N was essentially the same. However, the incidence of cellfree zones and root resorption lacunae seemed to increase as the force increased.