<b>Jiggling Force Induces Orthodontic Root Resorption during Tooth Movement in Rats </b>

Orthodontic root resorption (ORR) is an unavoidable pathological consequence of orthodontic tooth movement. It is thought that swinging of the root due to the reciprocating movement of the tooth(jiggling)mayexacerbate ORR. However, little is known about the relationship between ORR and jiggling. We herein investigated the tartrate-resistant acid phosphatase(TRAP)expression in odontoclasts in resorbed roots during experimental tooth movement(jiggling)<i>in vivo</i>.<br>　Twenty-four eight-week-old male Wistar rats were divided into four groups; a heavy force group(50 g), an optimal force group(10 g), a jiggling force group(compression and tension, repetition; 10 g)and a control group. The expression levels of TRAP protein in odontoclasts in the dental root were determined by immunohistochemical analysis.<br>　Immunoreactivity for TRAP in resorbed roots exposed to the jiggling force was stronger than that in the other groups on day 21. The number of TRAP-positive odontoclasts wassignificantly elevated in the JF group on day 21 when compared with the other groups.<br>　These results suggest that "jiggling force" may induce ORR during orthodontic tooth movement, and may be a risk factor for ORR.