Evaluación de la precisión de dos metodos de transferencia para cementación indirecta de brackets preajustados. Estudio in vitro

Abstract

Con el advenimiento de las técnicas de cementación indirecta, resulta importante determinar cual de ellas es la mas precisa respecto a la no modificación o alteración en la posición tridimensional de los brackets, tendientes a garantizar una expresión real de los valores de inclinación y de torque propuestos para una formulación en particular; sin que se ven afectados los objetivos del tratamiento por una inadecuada ubicación o por variables que afecten la estabilidad dimensional del medio de transferencia que se utilice para el montaje. Por lo anterior el objetivo del presente estudio es evaluar la precisión de dos técnicas de transferencia para la cementación indirecta de brackets preajustados. Para tal fin se compararon dos técnicas de cementación indirecta descritas a continuación; La primera técnica (grupo 1 – 6 modelos) consistió de 2 placas termo formables elaboradas al vacío: la primera es una lámina de caucho flexible de 0.4 mm de espesor que contacta íntimamente la placa; y la segunda es una placa mas rígida CLEAR ADVANTAGE series I, Ortho technology, de 0.4mm de espesor. La segunda técnica (grupo 2 – 6 modelos) requirió de la aplicación por la cara vestibular del modelo, incluyendo los Brackets, de una silicona PVS transparente Memosil ™ de Heraeus Kulzer, Alemania. Una vez polimerizada la silicona, se procedio a elaborar una placa al vacio rigida CLEAR ADVANTAGE series I, Ortho technology, de 0.4 de espesor para hacer la transferencia. Los dos métodos de transferencia evaluados tuvieron globalmente un comportamiento similar, sin diferencias de peso estadístico a favor de alguno de ellos. Sin embargo al hacer un análisis posicional detallado se observaron cambios notables en la ubicación final de los brackets en el grupo de la doble placa, contrastando con las mediciones encontradas para el grupo de silicona y placa, las cuales se comportaron de manera mas homogenea

Abstract. With the advent of techniques for indirect cementation in orthodontics, it is important to determine which one is the most accurate and reliable in the three-dimensional positioning of the brackets, in order to ensure genuine expression of the values of tip and proposed torque for a particular formulation; affected without treatment goals by improper location or variables affecting the dimensional stability of the transfer medium that is used for mounting; regarding this process the objectives of present study are: - Evaluate the accuracy and reliability of two techniques of cementing indirect preadjusted brackets. - Determine which of the two methods of transfer is more dimensionally stable to ensure proper position of the preadjusted brackets - Evaluate the operator's ability to place the brackets preadjusted in the same position at different times from the same patient. Materials and methods: A rubber mold ORT 1006 is used 28 (ideal Occlusion) house Nissin Dental Products INC (Kyoto, Japan) in order to make emptying in acrylic, 20 accurate models (10 upper and 10 lower ). Master Series preadjusted brackets System, Technical MBT slot 0.022 (American Orthodontics, USA) for upper and lower jaw (5 to 5) and direct cementation tubes for first upper and lower molars (American Orthodontics, USA) were positioned. The method of adhesion of the brackets to the model, will be held following the methodology described by White in 2002, using a water soluble adhesive (Aleenes's Tacky Glue, USA). Once positioned the brackets, proceed to capture digital images using 3D laser scanner processing laboratory models of American Orthodontics in Sheboygan, Wisconsin (USA), for Harmony Custom System. The procedure will be performed following the standard to minimize errors in radius and distance between centers and archives will be obtained in .stl format protocol. Subsequently transfer buckets customized for each of the two techniques to assess were manufactured: • The first technique consists of 2 plates thermos vacuum formable made: the first is a flexible rubber sheet 0.4 mm thick intimately contacting plate; and the second is a more rigid plate Essix C + 0.6 mm thick which is empty on the above, in order to give more rigidity to the transfer system. • The second technique requires the application by the vestibular face of the model, including the brackets, a transparent PVS Memosil Heraeus Kulzer ™ silicone, Germany. Once polymerized silicone, we will proceed to develop a rigid vacuum plate Essix C + 0.6 mm thick to make the transfer. Once obtained the transfer plates, trimmed and adapted the model that will serve for assembly (the same previously scanned with brackets in position). To prepare this model, it was washed with hot water and stiff brush; it dried and subsequently Sandblast the labial surface to improve adhesion of the resin. After washing and drying again the model is applied to the bracket and the vestibular acrylic surface model liquid resin Assure Plus (liquid resin multipurpose increase adhesion acrylic) following the manufacturer's instructions (Reliance Orthodontic Products, Inc., USA ). Subsequently nano-hybrid resin fluid Flow Grandio (VOCO, Germany) was applied to the base of the bracket and the bucket to settle in the model. For both types of plates transfer is perform photocuring using an LED light-curing. VALO (Ultradent, USA). Once polymerized resin, proceed to remove the transfer buckets of the first technique; and transfer tray and silicone to the second technique. Models with the brackets will again be scanned using the same 3D scanner Orthodontic processing laboratory models of American Orthodontics. The data obtained were evaluated by superimposing the images obtained so as to evaluate the precision in placing the brackets operator, and the accuracy of the transfer method of indirect mounting cubettes. To this end, the program Geomagic Qualify 12.1.2, used in engineering for CAD analysis and 3D metrology is used. This program allows you to completely choose the parameters they want to study when making the comparison. By achieving establish which of the two indirect cementation techniques is more accurate and reliable, it is possible to recommend a clinical protocol with the advantages of indirect mounting ensures ideal positioning of brackets preset in the three planes of space