# Maximally Deficiency: Treatments and Applications for Adolescents
## 2 Orthopedic Approaches
### Children in Primary and Early Mixed Dentition
#### 2.1.1.  
Lingual Arch and Leaf Expander  
Over time, the design and functionality of the spring expanders have evolved significantly, progressing from the Coffin spring appliance to the W-Arch, and ultimately to the quadhelix appliance [23; 53]. The Coffin spring, an omega-shaped heavy spring with ends embedded in acrylic, holds to the palatal contours to apply balanced forces on both tissue and teeth [54]. Originating from the Coffin appliance, the W-Arch is a fixed appliance constructed from W-shaped wire attached to molar bands. Activation of both appliances is achieved by using pliers to widen the spring's shape, expanding it 3-4 mm beyond its passive state before installation, thus allowing for maxillary expansion. The expansion rate is maintained at 2 mm per month until slight overcorrection of the crossbite is achieved. Compared to the removable appliance, the W-Arch can be adjusted to selectively expand either the anterior or posterior regions and derotate molars [53; 55].  
The quadhelix is an advanced modification of the W-Arch, designed to enhance flexibility and deliver a gentle, continuous force. It features four helices in the anterior and posterior segments of the palatal arch. Constructed from either 0.9 to 1.0 mm stainless steel or 0.95 mm cobalt chromium wire, the quadhelix spans from bands around the first molars across the palate. It is activated to expand roughly the width of one molar tooth, generating a force of about 400 g, primarily causing dental expansion by up to 4 mm and potentially inducing skeletal changes in preadolescent children [23; 24; 56]. Fixed expansion devices like W-arch or quadhelix appliances require a cast of the maxillary arch and are fabricated in dental laboratories. These appliances are effective in young patients with early mixed dentition, approximately yielding one-third skeletal and two-thirds dental changes [57]. Some evidence suggests that fixed appliances not only surpass removable plate in success rate but also offer enhanced comfort for the patient and shortened treatment time [26; 27].  
The Leaf Expander (LE) features a double leaf nickel-titanium spring core and adjustable screw. Anchored on deciduous teeth and the first permanent molars, it delivers a consistent 450 g force, achieving up to 6 mm of expansion. The device is preactivated by leaf spring for an initial 3-4.5 mm expansion. Monthly adjustments involve 10-15 quarter turns of the screw, each corresponding to 0.1 mm, to compress the spring further. Typically, active expansion requires five to six months, followed by three months of passive retention to stabilize the results [8; 25]. In patients with early mixed dentition, the LE and RME produce comparable skeletal and dentoalveolar effects. No significant changes have been observed at the periodontal level. The LE only shows a significantly less increase in the posterior nasal and maxillary mid-alveolar width compared to the RME, but the differences are minimal [8; 58; 59; 60]. In addition, the LE reduces the frequency of activations required by the orthodontist compared to the other fixed appliance for the SME, such as the W-Arch or quadhelix appliances. It is also well suited for patients with poor compliance, avoiding the issues of incorrect or insufficient activation of screws [61].