RESUMEN
BACKGROUND: In orthodontic treatment, the combination of an activator with a headgear is commonly used in treatment of the hyperdivergent Class II malocclusion. However, the distribution of stresses transmitted to the maxilla by these appliances has been little studied. This study aimed to compare the biomechanical effects of stresses transmitted to the maxilla and teeth by a Teuscher activator (TA) for different lines of action of extraoral force, using finite element analysis. MATERIAL AND METHODS: A tridimensional finite element model of the maxilla and teeth was created based on the true geometry of a human skull. The (TA) and the face bow were designed in 3D computer-aided design and fixed in the maxilla model. To study the effects of mechanical stress transmitted to the maxilla in the treatment of hyperdivergent Class II malocclusion with (TA) combined with extraoral forces, five different finite element models were used, considering the centers of resistance of the maxilla and dentition. RESULTS: The results showed that stresses increased progressively when the force line of action moved in posteroanterior direction. Von Mises equivalent stress was lower in Model 1 (0°) than in Model 5 (60°). In Models 1 (0°) and 2 (15°), molars suffered greater distal displacement and incisors showed extrusion. In Model 3 (30°), the force line of action promoted a distal displacement of molars and incisors. In Models 4 (45°) and 5 (60°), the whole maxillary anterior sector showed counterclockwise displacement. CONCLUSIONS: Different force lines of action influence the intensity and distribution of orthodontic and orthopedic forces in the maxilla. The extraoral force's line of action used in Model 3 (30°) is the most compatible with the objectives of the hyperdivergent Class II malocclusion treatment in growing patients. Key words:Class II, Headgear, Early treatment, FEA.
RESUMEN
Williams syndrome (WS) is a neurodevelopmental disorder of genetic origin that has been used as a model to understand visual cognition. We have investigated early deficits in the afferent magnocellular pathway and their relation to abnormal visual dorsal processing in WS. A spatiotemporal contrast sensitivity task that is known to selectively activate that pathway was used in six WS subjects. Additionally, we have compared visual performance in 2D and 3D motion integration tasks. A novel 3D motion coherence task (using spheres with unpredictable axis of rotation) was used in order to investigate possible impairment of occipitoparietal areas that are known to be involved in 3D structure from motion (SFM) perception. We have found a significant involvement of low-level magnocellular maps in WS as assessed by the contrast sensitivity task. On the contrary, no significant differences were observed between WS and the control groups in the 2D motion integration tasks. However, all WS subjects were significantly impaired in the 3D SFM task. Our findings suggest that magnocellular damage may occur in addition to dorsal stream deficits in these patients. They are also consistent with recently described genetic and neuroanatomic abnormalities in retinotopic visual areas. Finally, selective SFM coherence deficits support the proposal that there is a specific pathway in the dorsal stream that is involved in motion processing of 3D surfaces, which seems to be impaired in this disorder.