How do disc displacement without reduction (DDwoR) and disc displacement with reduction (DDwR) differ in terms of mouth opening and derangement signs?

How do disc displacement without reduction (DDwoR) and disc displacement with reduction (DDwR) differ in terms of mouth opening and derangement signs?

• A. DDwoR presents with limited mouth opening (<40 mm) and deflection toward the affected side on opening; DDwR has normal or near normal opening but with a joint click.
• B. DDwoR has normal opening and no derangement; DDwR has limited opening.
• C. DDwoR causes joint crepitus; DDwR causes muscle pain.
• D. DDwoR and DDwR have identical opening.

Answer: (A)

The main idea is that the position of the disc during opening determines the clinical signs. When the disc is displaced without reduction, it stays out of place as the jaw opens, so translation on the affected side is blocked. This leads to a noticeably limited mouth opening (often under about 40 mm) and a deflection of the mandible toward the side with the derangement because that side restricts movement first. Conversely, with disc displacement with reduction, the disc recaptures its normal position as the mouth opens, allowing the jaw to translate more normally. Patients typically have normal or near-normal opening, but they hear a joint click (the disc returning to its position) during opening or closing. So, the limited opening with deflection in DDwoR contrasts with the normal opening plus a joint click in DDwR.

The main idea is that the position of the disc during opening determines the clinical signs. When the disc is displaced without reduction, it stays out of place as the jaw opens, so translation on the affected side is blocked. This leads to a noticeably limited mouth opening (often under about 40 mm) and a deflection of the mandible toward the side with the derangement because that side restricts movement first. Conversely, with disc displacement with reduction, the disc recaptures its normal position as the mouth opens, allowing the jaw to translate more normally. Patients typically have normal or near-normal opening, but they hear a joint click (the disc returning to its position) during opening or closing. So, the limited opening with deflection in DDwoR contrasts with the normal opening plus a joint click in DDwR.