In 2017, based on our experience with slow maxillary expansion (11-13) using the Leaf Expander,(14,15*) we introduced the completely preactivated Self Expander.* With no need for further activation either in the office or at home, the Self Expander does not rely on patient cooperation. Because the device employs light and continuous forces, it causes no pain even in the early stages of expansion.
The design of the Self Expander is similar to that of a Leaf Expander,(16) except that it is equipped with three preactivated, nickel titanium double springs instead of a leaf spring and a reactivation screw (Fig. 1). These leaf springs, which are compressed during fabrication in the laboratory, recover their shape during deactivation, generating a constant 450g of force for as much as 9mm of calibrated expansion.
Fig. 1 A. Self Expander* with three double-leaf springs compressed by laboratory before delivery. B. Springs decompress during treatment and generate constant 450g of force.
Like the Leaf Expander, the Self Expander is typically anchored to the deciduous teeth,(17,18) with the upper first permanent molars left free to expand spontaneously (Fig. 2). The body of the 11mm × 12mm × 4mm screw can be adapted to fit a narrow palate or an arch with transverse deficiency. The arms connecting the screw and the lateral components must be kept about 2.5mm clear of the palatal mucosa to avoid ulceration. The screw is blocked with metal ligatures that are removed immediately after cementation to start the self-expansion.
The patient should be monitored monthly for expansion and oral hygiene. Active expansion takes about six months, after which the appliance should be maintained passively in place for three months of retention.
Fig. 2 A. Self Expander on prototype model created from stereolithographic (STL) file of intraoral scan. B. Expander in mouth, with metal ligature still blocking compressed expansion leaves. C. Ligature wire removed immediately after banding. D. Appliance during active expansion.
A 6-year-old male in the mixed dentition presented with a lack of space for his lateral incisors and a crossbite associated with a lateral mandibular shift to the right and a transverse discrepancy (Fig. 3, Table 1). The upper right central incisor had been extracted following an intrusive trauma at age 4; the space had been maintained with a transpalatal arch and composite pontic.
Fig. 3 Case 1. A. 6-year-old male patient with maxillary transverse deficiency, crossbite, mandibular deviation, and missing upper right central incisor (extracted at age 4) before treatment. (Panoramic radiograph taken seven months earlier.) B. Arch-width measurements on STL digital cast obtained from laboratory scan of polyvinyl siloxane impressions.
A Self Expander was placed with bands on the second deciduous molars and extensions to the canines and first deciduous molars (Fig. 4).
After six months
After six months of expansion, the crossbite was resolved, the midlines were coincident, the archform had improved, and the first permanent molars exhibited spontaneous expansion. The Self Expander was left in place for five months, until eruption of the lateral incisors. Because the screw was not blocked in any way, its flexibility could facilitate active functional adaptation of the occlusion with the lower arch (Fig. 5).
Fig. 4 Case 1. A. Self Expander in place at beginning of treatment.
B. After six months of expansion.
Fig. 5 Case 1. A. Self Expander removed after five months of passive retention. B. Arch-width measurements on STL digital cast. C. Superimposition of pre- and post-treatment scans on palatal rugae.
The results remained stable nine months after treatment (Fig. 6).
Fig. 6 Case 1. Patient nine months after treatment.
A 6-year-old female in the mixed dentition presented with a bilateral crossbite associated with a transverse deficiency (Fig. 7A and 7B, Table 2).
Fig. 7 Case 2. A. 6-year-old female patient with maxillary transverse deficiency and bilateral crossbite before treatment (continued in next image).
Fig. 7 (cont.) Case 2 B. Arch-width measurements on STL digital cast obtained from laboratory scan of polyvinyl siloxane impressions.
A Self Expander was bonded rather than banded to the upper first deciduous molars, with extensions to the canines (Fig. 8).
The patient was checked six times during seven months of active expansion, and the Self Expander was then left in place for three months of retention. The crossbite was corrected, the maxilla was expanded enough to allow eruption of the permanent lateral incisors, and the first permanent molars showed spontaneous expansion and derotation, guided by the occlusion (Fig. 9).
Fig. 8 Case 2 A. Self Expander in place at beginning of treatment. B. After seven months of expansion.
Fig. 9 Case 2 A. Self Expander removed after three months of passive retention. B. Arch-width measurements on STL digital cast. C. Superimposition of pre- and post-treatment scans on palatal rugae.