Jiggling Force Aggravates Orthodontic Root Resorption Via TNF-α during Rat Experimental Tooth Movement

Orthodontic root resorption(ORR)is an unavoidable pathological consequence of orthodontic tooth movement. Swinging of the root due to the reciprocating movement of the tooth(jiggling)mayexacerbate ORR.However, little is known about the mechanism how jiggling induces ORR. We herein investigated the tumor necrosis factor(TNF)-α expression in odontoclasts in resorbed roots by jiggling force <i>in vivo</i>.<br>　Twenty-four eight-week old of male Wistar rats were divided into four groups, a heavy force group(HF:50g), optimal force group(OP: 10g), jiggling force group(JF: compression and tension, repetition; 10g)and a control group(no appliances: 0g). The expression levels of the TNF-α protein in odontoclasts in the dental root were determined using an immunohistochemical analysis.<br>　The immunoreactivity for TNF-α in resorbed roots exposed to the jiggling force was stronger than that in the other groups on day 21. The number of TNF-α-positive odontoclasts was significantly increased in the JF group on day 21 compared with the other groups.<br>　These results suggest that a jiggling force may aggravate ORR via TNF-α expression during orthodontic tooth movement.