Sliding velocity and resistance to sliding
Savoldi F, Visconti L, Dalessandri D, Bonetti S, Tsoi JK, Matinlinna JP, et al. In vitro evaluation of the influence of velocity on sliding resistance of stainless steel arch wires in a self-ligating orthodontic bracket. Orthod Craniofac Res 2017;20:119-25
Many variables have been studied with respect to resistance to sliding (RS) in orthodontics. Sliding velocity (SV) is 1 element that has not received much consideration, even though it has a definitive influence on RS. The purpose of this study was to investigate the effect of SV on RS in a self-ligating bracket using an in-vitro model. A stainless steel self-ligating bracket with a nickel-titanium clip (Empower; American Orthodontics) was fixed to a custom model. The bracket was bonded to ensure that second- and third-order resistance values were negligible and only RS was tested. Orthodontic wires of 4 sizes and 2 types (round 0.020 and 0.022 in, rectangular 0.016 × 0.022 and 0.017 × 0.025 in) were examined with a testing machine. The wires were pulled through the machine at 4 SV values: 1 × 10 −2 , 1 × 10 −3 , 1 x 10 −4 , and 1 × 10 −5 mm per second. Each combination was tested 10 times to ensure validity and minimize the effect of any potential outliers. The results showed that lower SV values produced smaller RS effects. Smaller wires and round wires also generated less RS than larger wires and rectangular wires, respectively. The authors found that the relationship between RS and SV is nonlinear and logarithmic, similar to other studies’ findings outside orthodontics. Most in-vitro studies do not consider the effects of SV when testing for RS; consequently, the true RS values of these studies are likely to be higher than those reported. Future in-vitro studies should implement and consider evaluating RS at realistic SV values to achieve the greatest clinical validity and generalizability.
Reviewed by Vincent Khang
Skeletal mandibular changes with the Herbst appliance
Souki BQ, Vilefort PL, Oliveira DD, Andrade I Jr, Ruellas AC, Yatabe MS, et al. Three-dimensional skeletal mandibular changes associated with Herbst appliance treatment. Orthod Craniofac Res 2017;20:111-8
The Herbst appliance has been used to treat Class II malocclusion and improve facial profile. However, its ability to stimulate greater mandibular growth has been debatable. Most studies to date have been performed using 2-dimensional imaging techniques. These techniques cannot explain the complex 3-dimensional morphologic changes that occur during Herbst treatment. The aim of this retrospective study was to compare mandibular skeletal changes in pubertal Class II patients treated with the Herbst appliance vs untreated Class II patients with 3-dimensional virtual modelling. Fifty Class II pubertal patients who had cone-beam computed tomography images acquired as a routine diagnostic measure at pretreatment and posttreatment were selected. Twenty-five patients who had received treatment with the Herbst appliance were included in the Herbst appliance group (HAG), and the remaining 25 subjects who received other nonorthopedic treatment were assigned to the comparison group (CG). Three-dimensional models were generated from the cone-beam computed tomography images. Volumetric registration on the cranial base was used to assess mandibular displacement analysis. Volumetric regional registration was performed to evaluate mandibular growth analysis. The HAG showed a significant anterior displacement of the mandible compared with the CG (mean difference, 1.7 mm). The HAG showed greater condylar growth in the superior and posterior surfaces (3.5 and 2.0 mm, respectively) compared with the CG, with the exception of vertical growth of the medial condylar pole. The HAG showed greater posterior growth of the ramus compared with the CG. The results support the idea that condylar and ramal growth are modified with Herbst treatment. The authors concluded that significantly more mandibular forward displacement, due to increased bone remodeling of condyles and rami, can be achieved with Herbst therapy.
Reviewed by Satya C Nayak
Skeletal mandibular changes with the Herbst appliance
Souki BQ, Vilefort PL, Oliveira DD, Andrade I Jr, Ruellas AC, Yatabe MS, et al. Three-dimensional skeletal mandibular changes associated with Herbst appliance treatment. Orthod Craniofac Res 2017;20:111-8
The Herbst appliance has been used to treat Class II malocclusion and improve facial profile. However, its ability to stimulate greater mandibular growth has been debatable. Most studies to date have been performed using 2-dimensional imaging techniques. These techniques cannot explain the complex 3-dimensional morphologic changes that occur during Herbst treatment. The aim of this retrospective study was to compare mandibular skeletal changes in pubertal Class II patients treated with the Herbst appliance vs untreated Class II patients with 3-dimensional virtual modelling. Fifty Class II pubertal patients who had cone-beam computed tomography images acquired as a routine diagnostic measure at pretreatment and posttreatment were selected. Twenty-five patients who had received treatment with the Herbst appliance were included in the Herbst appliance group (HAG), and the remaining 25 subjects who received other nonorthopedic treatment were assigned to the comparison group (CG). Three-dimensional models were generated from the cone-beam computed tomography images. Volumetric registration on the cranial base was used to assess mandibular displacement analysis. Volumetric regional registration was performed to evaluate mandibular growth analysis. The HAG showed a significant anterior displacement of the mandible compared with the CG (mean difference, 1.7 mm). The HAG showed greater condylar growth in the superior and posterior surfaces (3.5 and 2.0 mm, respectively) compared with the CG, with the exception of vertical growth of the medial condylar pole. The HAG showed greater posterior growth of the ramus compared with the CG. The results support the idea that condylar and ramal growth are modified with Herbst treatment. The authors concluded that significantly more mandibular forward displacement, due to increased bone remodeling of condyles and rami, can be achieved with Herbst therapy.
Reviewed by Satya C Nayak
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