Which type of appliance demonstrated more transverse expansion at the molars?

The acrylic group demonstrates more transverse expansion at the molars because they are designed to actively engage the teeth in a more flexible manner than rigid appliances. Acrylic appliances often have components that allow for broader activation, which can be adjusted to achieve skin-tight transverse expansion. This is particularly effective at the molars, as the adaptability of the acrylic material provides the pressure necessary to expand the arch width.

In contrast, other appliance types, such as fixed braces or round stainless steel wires, tend to have limited capabilities in achieving significant width changes due to their structural rigidity and the nature of how they exert forces on the teeth. Fixed braces are primarily concerned with aligning teeth within their existing curvature, while removable appliances can offer some degree of expansion but generally do not match the effectiveness and control achieved with acrylic-based systems.

Thus, the unique properties and functionalities of acrylic appliances allow them to provide superior transverse expansion at the molars compared to other orthodontic options.