Which of the following is the best indication of the appliance given in the color plate?

In children with finger/thumb sucking habit and posterior crossbite, quad helix is one of the most useful appliances to intercept the habit and correct the posterior crossbite. Quad helix is made of two anterior and two posterior helices; the anterior helices are adapted close to the maxillary palatal mucosa and in this way, it reduces the space in the oral cavity. When child tries to place the thumb or finger into the oral cavity, it will touch the helices and it will cause an unpleasant sensation and reaction in the child. This acts as a reminder for the child. At the same time, this appliance tips the posterior teeth in labial direction and corrects the posterior crossbite, which is caused by the altered buccinator mechanism.