Orthodontic movement with continuous and interrupted electrical stimulation

Abstract

It has been reporteq th.at exoge.nous application of dir~ct currents can enhance the rate pf orthodontic tooth movement. In the present study externally applied constant direct current was ·delivered either continuously (24 hr/day) or discontinuously (8 hr/day) to, feline maxillary ( segments fitted with orthodontic app 1 i ances in order to ·compare the ·rates·· of in vivo orthodontic tooth movement that resulted from these two different modes_ of stimulation. The maxillary canines of 8 adult female· cats were tipped distally with bilateral coil springs attached between the canine and third premolar. · Curreni generators were incorporated into custom made appl ia·nces· that were· secured in the palate. These generators:_ delivered 15±1 ~A aGross the alveolus of the canines undergoing orthodontic movement~ Independent circuits established for the left. and right ~ani.nes in the s_ame cat allowed us· to compare the effects- of 24 h'r/day stimulation of one canine with the effects of 8 hr/day stimulation of the oppos.ite canine. These two periods of stimulation emulated full-time and overnight treatment periods,. respectively. ·oirect measurements of tooth movement were made using Vernier calipers in the following 3 areas: (1) canine to third incisor; (2) canine to second premolar; and (3) third incisor· to second premolar. Continuous (24 hr/day) application· of· electrical stimulation to orthodontically treated teeth enhanced the rate of tooth movement· when compared with orthodontically treated controls·. Nostatistically significant differenc.es ·(P<05) were found between continuous (24 hr/day) and interrupted (8 hr/day) electrical stimulation. Histological analyses of the treated tissues were employed in an attempt to correlate clinically measured tooth movement with ultrast~uctural events. Microscopic cell counts of··asteoclasts were made along the inner wall of canihe alveoli fa~ regions of orthodontic compressibn. Values· were determined for numbers of osteoc 1 asts per mil J imeter of 1 ami ria dura. · No significant differences (P<~OS) were found when comparisons were performed for teeth treated with continuous (24 hr/day), interrupted (8 hr/day) ~and control (.O hr/day) periods of electrical stimulation. · The immature bone area- analysis was then performed for· zones · of canine 1 am·; na dura corresponding to orthodontic tension. Polarized light photomicrographs allowed for mature and imm·ature bone to be distinguished and quantified using histomorphometric-. techniques. Significantly (.P<.OS). less immature· bone was found in _teeth· treated 8 hrs/day when compared with contrb 1 s. , .· Teeth treated with _interrupted applications of electricity (8 hrs/day) a.lso _showed significantly less immature bone when compared with-the continuously (24 hr/day) stj~ulat~d group~