Magnitude Effect of Dynamic Occlusal Guidance Force on Root Resorption in Dog

Abstract

Its goals are to treat abnormalities of dentition and occlusion that develop during the growth period and to predict and thus prevent abnormalities in the permanent teeth of the adult phase by imparting dynamic occlusal guidance force in an early stage to establish healthy permanent occlusion. For this study, the authors sought to obtain a detailed picture of tooth movement when a superelastic Nickel-Titanium coil spring was applied. To achieve this, we conducted mechanical tests on Nickel-Titanium coil springs and Cobalt-Chromium coil springs with different coil wire diameters and coil outer diameters. Four kinds of coil spring were attached the space which formed by extraction of maxillary first premolar in dog. Root resorption accompanying molar tooth movement was compared Nickel-Titanium coil and Cobalt- Chromium coil based on micro-CT finding and histopathological findings in beagle dogs. In Nickel-Titanium spring, no permanent deformation was observed when compression was sufficient to bring the coils into contact. In contrast, with the Cobalt-Chromium spring,permanent deformation was recognized when compression was sufficient to bring the coils into contact. In the animal experiments at 80-g load, which is considered the optimum orthodontic force,bone resorption was seen on the pressure side and findings of new bone like tissue observed on the tension side. At occlusal guidance force of 240-g load, remarkable bone resorption and root resorption were seen in all of springs. Nickel-Titanium spring exhibited significantly greater root resorption than the Cobalt-Chromium spring. As these results show, when a Cobalt-Chromium spring is applied to 80-g load, the load decreased as the tooth moves, in the contrast no load decreased in Nickel-Titanium spring. Slight root resortion was seen in the case of 80-g load in Nickel-Titanium spring and CobaltChromium spring. In clinical practice, a great care is needed in the case of using Nickel-Titanium spring for dynamic occlusal guidance.