Which of the following diseases limits mouth opening?

Scleroderma is the correct choice as it is a systemic autoimmune disease that leads to the hardening and tightening of the skin and connective tissues. One of the significant effects of scleroderma is the involvement of facial structures, which can restrict mouth opening. This occurs due to fibrosis and tightening of the skin around the mouth and affecting the muscles that control jaw movement. As a result, individuals with scleroderma often experience difficulties with oral function, including limited mouth opening.

In contrast, the other conditions listed do not primarily cause limitations in the ability to open the mouth. Lown-Ganong-Levine syndrome is primarily associated with cardiac conduction disturbances. Sturge-Weber syndrome relates to neurological and dermatological symptoms due to vascular malformations and does not typically affect mouth opening. Paget's disease involves the abnormal growth of bones but does not directly impact the muscles or structures surrounding the mouth in a way that would limit its opening.