Occlusal Displacement of Teeth Due to Flexure of the Mandible

Abstract

It has been proposed that jaw deformation during function may be a contributor to supraosseous tooth eruption. This could be through a transient pressure gradient in the flexed bone and/or tension in the PDL fibers produced by socket deformation. Thus, the purpose of this study was to determine if forces applied to a fresh frozen canine mandible can lead to occlusal displacement of a tooth. Seven hemisected canine mandibles (14 specimens) were used to test this hypothesis. A force cycle (10 N to 100 N to 300 N) was applied by a Bionix testing machine (MTS TM Systems Corp., Minneapolis, Minn.) to the mandible in three point bending. Digital radiographs were taken at each change in force level using computer digitized radiography (CDR, TM Schick Technologies, Inc., Long Island City, N.Y.). By measuring the relative movement of metal markers (1 mm steel balls) placed into the mandible and the crown of the 2nd premolar, the amount of tooth eruption was calculated. With cyanoacrylate cement (Archer® Instant Bonding Adhesive, Tandy Corp, Ft. Worth, Texas) injected into the PDL space of the same tooth, the test was repeated one week later. These "ankylosed" teeth served as controls. The eruption distances were compared between the experimental and the ankylosed teeth by means of repeated measures analysis of variance. The only significant occlusal displacement was noted as the force was initially raised to 100 N (21.7 ± 40.6 μm). Due to the possible breakdown of the cyanoacrylate cement, the ankylosed teeth also showed evidence of eruption with the continued application of force. Although significant eruption was noted, the displacements were very small. PDL degradation, viscoelastic behavior, measurement of small displacements, limited resolution radiography, and two dimensional analysis are contributing factors to the uncertainty of the results. Further investigation is required to determine if jaw deformation during function is a viable mechanism leading to the occlusal displacement of teeth.