Positional Changes of TMJ Disc and Condyle Using ARS Treatment

Objectives: To measure the positional changes of temporomandibular joint disc and condyle before and after anterior repositioning splint (ARS) treatment using MRI for further investigation of the splint therapy mechanisms. Methods: 20 patients who had finished the ARS treatment were scanned oblique-sagittally by MRI before treatment, after splint insertion, and after treatment finished. Results: 1) Disc-condyle angles: after splint insertion, the displaced disc moved backward significantly (P<0.01) to the normal position; the removal of the splint after 6 month treatment the reduced disc moved forward significantly (P<0.01), 62.07% of discs were displaced anteriorly again; 2) Disc positions: after splint insertion, the displaced disc moved backward significantly (P<0.01), and was located to the summit of the joint fossa; the removal of the splint after 6 month treatment, the reduced disc moved forward significantly (P<0.05); compared closed-mouth positions before and after the treatment, the displaced disc moved backward significantly (P<0.01); 3) Condyle positions: after splint insertion, the condyle moved forward significantly (P<0.01); the removal of the splint after 6 month treatment, the condyle moved backward significantly (P<0.01); compared closed-mouth positions before and after the treatment, the condyle positions had no significant difference (P>0.05). Conclusions: With ARS insertion, 96.5% displaced discs could be reduced to the normal disc-condyle relationship. However, 62.07% of those reduced discs would displace anteriorly again when the condyle moved backward gradually during the course of the treatment. Our results suggested that the anterior displaced disc could be reduced to normal position after ARS insertion, and the possible role of ARS was to protrude condyle forward and prevent the reduced disc from displacing forward again.