Timing of transverse arch expansion with fixed appliances
Fleming PS, Lee RT, McDonald T, Pandis N, Johal A. The timing of significant arch dimensional changes with fixed orthodontic appliances: data from a multicenter randomised controlled trial. J Dent 2014;42:1-6
Historically, it was believed that transverse arch dimensions only increased significantly after placement of stainless steel archwires. The purpose of this article was to measure the changes in transverse dimensions while following the standard Damon archwire sequence, beginning with a round copper-nickel-titanium, ending with a rectangular stainless steel archwire, and using self-ligating bracket systems (Damon Q and In-Ovation C) and conventional twin brackets (Ovation). Data from a 3-arm, parallel-group randomized trial were collected from 3 centers in the United Kingdom and consisted of 71 subjects, ages 16 years and above, with maxillary arch crowding less than 6 mm, who were amenable to nonextraction treatment. The sample had a fairly equal sex distribution, a larger proportion of Class III malocclusion patients, and mild crowding (2.47 mm, SD 2.28). When only copper-nickel-titanium archwires were used, the overall transverse dimensions increased by 1.48 mm (intercanine), 4.1 mm (interfirst premolar), 3.84 mm (intersecond premolar), and 1.53 mm (intermolar) from T1 through T4. With each successive copper-nickel-titanium wire, the arch expansion increased linearly; however, after placement of the 0.019 × 0.025-in stainless steel archwire (T5), there was no difference in the intercanine dimensions, and no more than 0.19 mm of increase for the other 3 transverse dimensions. In addition, no significant differences were found among active or passive self-ligating brackets and conventional twin brackets with respect to transverse expansion. This study shows that nickel-titanium wires might play a more significant role in transverse expansion during the initial phases of treatment, especially of premolars, than previously thought. However, the authors cautioned that stainless steel wires are still necessary for proper torque expression.
Reviewed by Jonathan D. Albaugh and Giri Chelian
Pharyngeal airway volume changes after extractions and surgery
Kim MA, Park YH. Does upper premolar extraction affect the changes of pharyngeal airway volume after bimaxillary surgery in skeletal Class III patients? J Oral Maxillofac Surg 2014;72:165.e1-10
A great deal of importance has been given to airway volume in the orthodontic literature lately. There is conflicting evidence on the effects of extractions on pharyngeal airway volume, especially in orthodontic patients treated without surgery. The pharyngeal airway is divided into the nasopharyngeal, oropharyngeal, and hypopharyngeal airways superoinferiorly. The purpose of this study was to assess pharyngeal airway volume changes in nongrowing skeletal Class III patients who underwent orthodontic treatment and corrective bimaxillary surgery; they were further subgrouped as those with maxillary premolar extractions (EG) and those without extractions (NG). The total sample included 23 nongrowing mandibular prognathic patients (EG, n = 13; NG, n = 10) with mean ages of 24.33 (EG) and 23.65 (NG) years. All patients had a bilateral split ramus osteotomy and a LeFort I osteotomy. Cone-beam computed tomography scans were taken before surgery (T0), 2 months after surgery (T2), and 6 months after surgery (T3). InVivoDental 3D imaging software was used to measure the volumetric changes pertaining to these time points. Dental changes, such as inclination of the maxillary central incisors, were also measured. No significant dental changes were noted between the 2 groups. However, there was a significant reduction in all pharyngeal airways in the EG, with oropharyngeal and total pharyngeal airway volumes showing the most significant changes between T0 and T3 compared with the NG. Given these interesting results with lesser airway volume reductions in the NG and minimal esthetic changes with extractions, the authors suggest that it might be beneficial to treat such Class III patients without extractions. Through further research, the authors propose to determine how mandibular premolar extraction along with bilateral split ramus osteotomy setback surgery would affect the pharyngeal airway volume.
Reviewed by Giri Chittivelu