Abstract
This study evaluated different techniques for surgically assisted rapid maxillary expansion (SARME) according to the type of transverse maxillary deficiency using computed tomography (CT). Six adult patients with bilateral transverse maxillary deficiencies underwent SARME. The patients were equally divided into three groups: Group I, maxillary atresia in both the anterior and posterior regions; Group II, greater maxillary atresia in the anterior region; and Group III, increased maxillary atresia in the posterior region. In Group I, a subtotal Le Fort I osteotomy was used. In Group II, a subtotal Le Fort I osteotomy was used without pterygomaxillary suture disjunction. In Group III, a subtotal Le Fort I osteotomy was used with pterygomaxillary suture disjunction and fixation of the anterior nasal spine with steel wire. The midpalatal suture opening was evaluated preoperatively and immediately after the activation period using CT. For Group I, the opening occurred parallel to midpalatal suture; for Group II, the opening comprised a V-shape with a vertex on the posterior nasal spine; and for Group III, the opening comprised a V-shape with a vertex at the anterior nasal spine. The conclusion was that the SARME technique should be individualized according to the type of transverse maxillary deficiency.
For normal occlusion, the upper dental arch must maintain larger dimensions than the lower dental arch. When such proportionality is lacking and the dimensions are smaller in the transverse direction, a transverse maxillary deficiency occurs. Transverse maxillary deficiency is associated with functional and aesthetic impairments, such as a posterior bilateral or unilateral cross bite, dental crowding, nasal obstruction and apnoea.
The differential diagnosis of transverse maxillary deficiency should be established by clinical examination, radiographs and dental casts. Expansion can be predicted by clinical assessment of the study models. In most cases, the maxillary atresia involves both the anterior and posterior maxilla, but in some individuals, this condition may demonstrate a greater involvement in the anterior or the posterior region. A differential diagnosis is the determining factor when deciding which surgical technique should be used.
It is possible to obtain tomographic images with good resolution and accuracy in the absence of an overlap for the evaluation of maxillary expansion. Computed tomography (CT) provides greater reliability for these evaluations compared with other radiographic methods, such as periapical, occlusal and anteroposterior radiographs, which provide poor accuracy and reliability due to overlap.
Using CT, Loddi et al. observed that suture opening occurs in parallel from the anterior to the posterior region in patients who are undergoing surgically assisted rapid maxillary expansion (SARME) via a subtotal Le Fort I technique with pterygomaxillary disjunction.
In many instances, however, the transverse maxillary deficiency can demonstrate greater anterior or posterior involvement, and the parallel opening in the anteroposterior direction can lead to an unnecessary expansion in regions that are considered normal. Therefore, the treatment must be individualized according to the location of the transverse maxillary deficiency. Various combinations of osteotomies, such as in the pterygomaxillary, anterior maxillary wall, nasal septum, midpalatal suture (MPS) and the expander apparatus locations, can be used to correct each region of the maxilla.
The authors did not find any studies in the literature that used CT specifically to evaluate the different types of MPS openings according to the SARME technique. The aim of the present study was to evaluate SARME techniques according to the type of transverse maxillary deficiency using CT.
Materials and methods
The authors evaluated 12 CT scans of the maxilla from six adult patients aged 20–27 years (mean 23.5 years; two males and four females) who underwent SARME in the Craniomaxillofacial Unit of the Plastic Surgery Division at the Federal University of São Paulo (UNIFESP). All patients signed an inform consent form before surgery. The study included adult patients with bilateral transverse maxillary deficiencies. Patients who had undergone previous surgery or who presented with trauma of the maxilla as well as those with congenital craniofacial deformities were excluded.
The patients were separated into three groups: Group I, two patients with maxillary atresia in the anterior and posterior regions; Group II, two patients with greater maxillary atresia in the anterior region; and Group III, two patients with greater maxillary atresia in the posterior region A transverse maxillary deficiency was diagnosed based on clinical, radiological and plaster model evaluations.
1 week before surgery, the Hyrax appliances (Dentaurum, 602-802 Ispringen, Germany) were cemented in all patients by the same orthodontist. In Groups I and II, the expander was placed in the region of the maxillary first premolars and first molars; in Group III, the expander was located in the region of the maxillary first and second molars.
The surgical procedures were performed under general anaesthesia with orotracheal intubation by the same surgeon (MDP). In Group I, the subtotal Le Fort I technique was applied with pterygomaxillary disjunction. In Group II, the Le Fort I technique was performed without pterygomaxillary disjunction. In Group III, the subtotal Le Fort I technique was conducted with pterygomaxillary disjunction, and a 1/16 in. stainless steel wire was positioned in the anterior nasal spine (ANS) region to fix both sides of the maxilla ( Fig. 1 ).
On the fifth postoperative day, a professional health care provider initiated the activations, and the following activations were performed by the patient or by an accompanying individual: a standard 1/4 turn of the screw in the morning and in the evening, which corresponded to 0.4 mm/day. On completion of the expansion, the expansion screw was fixed with a stainless steel wire.
All patients underwent two helical CT scans (Tomoscan AV Philips, Eindhoven, Netherlands, 120 kV, 100 mA, exposure time of 1 s/cut). The first scan was performed preoperatively, and the second was performed immediately after completion of the activations. 1 mm thick axial sections were generated (a total of 36–40 sections) parallel to the palatal plane. The CT axial images were used to evaluate the different types of MPS openings according to the variations in the surgical techniques.
Two maxillary plaster models of each patient were made: one immediately (preoperatively) and the other after expansion. Linear measurements of the maxillary plaster models were obtained using a digital caliper. The distances between the cusp tips of the maxillary canines, the tips of the buccal cusps of the maxillary second premolars and the tips of the mesiobuccal cusps of the maxillary second molars were measured.
Results
The six preoperative and six postoperative CT scans were evaluated in axial tomographic sections that were parallel to the palatal plane, and different behaviours were observed in each group. In Group I, the opening was observed parallel to the ANS and to the posterior nasal spine (PNS) axis ( Fig. 2 ). In Group II, the opening comprised a V-form with a vertex in the PNS ( Fig. 3 ). In Group III, the opening consisted of a V-form with a vertex in the ANS ( Fig. 4 ).
Measurements obtained at the cusps of the maxillary canines, second premolars and second molars demonstrated a parallel expansion in Group I, a V-shaped expansion with a vertex in the PNS in Group II and a V-shaped expansion with a vertex in the ANS in Group III ( Table 1 ).
| Patient | Inter-dental distance | Canine | 2° PM | 2° M | Total screw activation |
|---|---|---|---|---|---|
| 1 (Group I) | Pre-operative | 29.6 | 42.8 | 55.2 | |
| Post-operative | 37.8 | 56.8 | 63.4 | 7.9 | |
| (Post-Pre) | 8.2 | 8.4 | 8.2 | ||
| 2 (Group I) | Pre-operative | 31.7 | 41.2 | 56.5 | |
| Post-operative | 39.7 | 49.6 | 64.6 | 8.1 | |
| (Post-Pre) | 8 | 8.6 | 8.1 | ||
| 3 (Group II) | Pre-operative | 17.9 | 46.8 | 63.2 | |
| Post-operative | 27.1 | 55.4 | 66.8 | 7.0 | |
| (Post-Pre) | 9.2 | 8.6 | 3.4 | ||
| 4 (Group II) | Pre-operative | 32.2 | 47.8 | 63.2 | |
| Post-operative | 42.6 | 56.8 | 66.8 | 7.3 | |
| (Post-Pre) | 10.4 | 9 | 3.6 | ||
| 5 (Group III) | Pre-operative | 32.4 | 49.2 | 52.4 | |
| Post-operative | 35.9 | 55.7 | 60.7 | 8.1 | |
| (Post-Pre) | 3.5 | 6.5 | 8.3 | ||
| 6 (Group III) | Pre-operative | 38.7 | 43.4 | 51 | |
| Post-operative | 42.7 | 49 | 59.4 | 7.8 | |
| (Post-Pre) | 4 | 5.6 | 8.4 |
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