http://www.guident.net/articles/orthodontics/SLOW-PALATAL-EXPANSION--A-NOVEL-METHOD-OF-ARCH-EXPANSION.html

(see site for picture):

NITI PALATAL EXPANDER

The appliance was introduced by Wendell. V, Arndt in the year 1993. It is a tandem-loop, nickel titanium palatal expander which is activated by temperature that produces light, continuous pressure on the midpalatal suture which simultaneously helps in uprighting, rotating, and distalizing the maxillary first molars. The adjustable stainless steel extensions which are inserted into standard horizontal lingual sheaths are spot- welded to the molar bands. A locking indent on the lingual attachment holds the expander to the molar band for patient safety. The nickel titanium expander has a transition temperature of 94°F. When chilled before insertion, it becomes flexible and can easily be bent to facilitate placement. As the mouth begins to warm the appliance, the metal stiffens, the shape memory is restored, and the expander begins to exert a light, continuous force on the teeth and the midpalatal suture. Nickel titanium expanders are available in eight different intermolar widths, ranging from 26mm to 47mm, and generates forces of upto 180-300g. The 26-32mm sizes have softer wires that produce lower force levels for younger patients. Marzban et al in 1999 stated that it delivers a uniform, slow, continuous force for maxillary expansion, molar rotation and distalization, and arch development. This appliance expands at a rate that maintains tissue integrity during repositioning and remodeling of the teeth and bone

Looks good imo

@mr_man thank you for that information that very helpful.