ABSTRACT
Objective To analyze the mechanical effect of invisible appliances with different material hardness and provide theoretical basis for selecting the suitable material for invisible appliance and its clinical application. Methods Three different three-dimensional (3D) finite element models of invisible appliance were established, of which the elastic modulus was chosen as 415.6, 816.308 and 2 400 MPa, respectively. In these models, the upper central incisors were all designed to move 0.3 mm mesially. Then 3D nonlinear finite element method was used to analyze the stress-distribution in invisible appliance, teeth and periodontal ligament and the instant displacement of every tooth. The comparative study was made among three invisible appliances with different hardness． Results Under experimental condition, the most instant stress and displacement of teeth was the upper central incisor, with initial displacement greater in crown section than that in apical section and the greatest displacement was 0.17 mm. The tendency of central incisor movement was tipping in all situations. The movement of lateral incisor had the second greatest distance (the greatest displacement was 0.10 mm) and the tendency of its movement was in the opposite directions of aimed teeth. When elastic modulus of material decreased, the stress on the invisible appliance increased. The stress in periodontal ligament and the displacement of aimed teeth were also increased. Conclusions If the hardness of invisible appliance increases, the displacement of the designed tooth and treatment efficacy increases, but the appliance with more hardness couldn’t provide better ability in controlling of orthodontic tooth movement. The study suggested clinicians should use attachments or cooperate with fixed appliance to help move teeth bodily.
ABSTRACT
The main type of four root canals in maxillary second molar is two-mesiobuccal. Incidence rate of maxillary second molar with two palatal root canals is especially rare. A case of maxillary second molar with two palatal root canals was reported in this article.
Subject(s)
Humans , Dental Pulp Cavity , Maxilla , Molar , Tooth RootABSTRACT
<p><b>OBJECTIVE</b>To explore a new method and estimate its outcome to repair deep heel tissue injuries with local tissue flap.</p><p><b>METHODS</b>At lower cnemis, a fat fascial flap combined with perineal tendofascial flap were designed and elevated between the lateral malleolars blank, the largest area is 6 cm x 13 cm, which were transplanted to cover naked calcaneal tendon and calcaneal bone, full-thickness free skin graft or middle-thickness free skin graft were grafted on flap.</p><p><b>RESULTS</b>6 patients suffered from heel tissue defects had been treated from January 2004 to November 2005. The smallest area was 3.5 cm x 4.0 cm and the largest was 4 cm x 6 cm. All fascial flaps and free skin grafts were successfully survived after operations. All patients were followed up 3-23 months, the operation areas were healed, the functions and configurations were satisfied.</p><p><b>CONCLUSIONS</b>Perineal tendofascial flap conjoined with adipofasical flap and free skin graft are used to repair heel deep tissue defects, which is a handy, dependable way for repairing of the small tissue defects of the lower third of leg and heel.</p>