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El hidroxido de calcio, como paradigma clinico, es superado por el agregado de trioxido mineral (MTA)).

CALCIUM HYDROXIDE AS A CLINICAL PARADIGM IS SURPASSED BY MINERAL TRIOXIDE AGGREGATE (MTA)

INTRODUCCION

La investigacion cientifica situo al hidroxido de calcio (HC), desde hace varias decadas, como eleccion de uso con alta posibilidad predictiva en la terapia pulpar para preservar su vitalidad y lograr la accion de estimulo en la remineralizacion de los tejidos dentales, en condiciones clinicas tales como: recubrimientos pulpares, apexificacion, reabsorciones internas, entre otros. Sin embargo, en los ultimos anos se ha investigado el mineral trioxido agregado (MTA), en terapia pulpar, el cual, segun la investigacion cientifica, esta rompiendo el paradigma clinico del HC, para imponerse, dados los resultados obtenidos con su utilizacion.

El HC es un material que se obtiene por calcinacion del carbonato calcico: Ca[(OH).sub.2] + C[O.sub.2]_CaC[O.sub.3] + [H.sub.2]O. Ademas, este polvo granular, amorfo y fino posee marcadas propiedades basicas, como un pH alcalino aproximadamente de 12,4, lo cual le confiere un gran poder bactericida. (1, 2) Al ser aplicado sobre una pulpa vital, su accion caustica provoca una zona de necrosis esteril y superficial, con hemolisis y coagulacion de las albuminas, quedando atenuada por la formacion de una capa subyacente compacta, compuesta de carbonato de calcio debida al C[O.sub.2] de los tejidos y de proteinas, producto de la estimulacion dentinaria. (1, 2) Su densidad es de 2,1; puede disolverse ligeramente en agua y es insoluble en alcohol, con la particularidad de que al aumentar la temperatura disminuye su solubilidad. (1, 3)

El primer medicamento a base de HC fue introducido en odontologia por B. W. Hermann, en los anos 1920 y fue denominado Calxyl. (4) Desde entonces, el HC ha sido usado ampliamente en el tratamiento de las lesiones endodonticas.

En esta revision se encontraron investigaciones que analizan un material con las funciones del HC, como es el MTA, convirtiendose en el material de eleccion por haberse encontrado diferencias estadisticamente significativas respecto al HC.

El MTA fue desarrollado y reportado por primera vez en 1993 por Lee, Torabinejad y colaboradores; (5) se aprobo su uso en odontologia en 1998 por la FDA (Food and Drugs Administration) y fue lanzado comercialmente en 1999, con el nombre de ProRoot MTA (Dentsply), de color gris, hasta que en 2002 salio al mercado el MTA blanco, de igual composicion. (6)

Este material se presenta como un polvo hidrofilico que fragua en presencia de agua. (7) El MTA esta compuesto de silicato tricalcico, oxido tricalcico, oxido de silicio y otros oxidos minerales responsables de sus propiedades, como el oxido de bismuto, responsable de su radiopacidad. (8, 9) Posee elevada capacidad antimicrobiana, pues, el oxido de calcio, al mezclar el polvo de MTA con agua, reacciona con esta ultima, formando HC, que provoca aumento del pH por disociacion de iones calcio e hidroxilo, creando un ambiente inadecuado para el desarrollo bacteriano y fungico. (10)

El MTA es un material que ha sido usado internacionalmente, con aplicaciones clinicas tales como: apexificaciones, reparacion de perforaciones radiculares, en obturaciones retrogradas y en recubrimiento pulpar directo e indirecto. Ademas, puede ser el unico que consistentemente permite regeneracion del ligamento periodontal, aposicion de tejido parecido al cemento y formacion osea. (11)

El proposito de este trabajo fue actualizar la revision tematica que sobre el HC se habia hecho por Yepes. (12) debido a que aun se mantiene el interes por la investigacion del HC, como material tradicionalmente utilizado en la terapia pulpar. Asimismo, se hace revision del MTA, por ser el material que lo esta sustituyendo, dadas las cualidades que lo hacen preferible al HC, con lo cual se evidencia que esta ocurriendo segun la investigacion cientifica, la ruptura de un paradigma clinico, con el uso del MTA, remplazando al HC.

USOS CLINICOS DEL HIDROXIDO DE CALCIO

Recubrimiento pulpar directo y pulpotomia

El recubrimiento pulpar es un procedimiento que intenta preservar las funciones vitales de la pulpa, cuando no ha existido una historia de dolor persistente a los estimulos externos y cuando la pulpa ha sido expuesta al ambiente oral de manera accidental. (13, 14) El recubrimiento y el sellado marginal que se obtiene al aplicar sobre el tejido pulpar un material, puede ser el factor clave que determine el resultado final de dicho procedimiento. (15) Cox y colaboradores, (16) ratificaron que la pulpa podria formar una barrera de tejido duro si fuera proporcionado un selle biologico adecuado, de manera que los microorganismos no tengan acceso al tejido pulpar. El material ideal para el recubrimiento pulpar directo debe controlar la infeccion, adherirse a la dentina para evitar la microfiltracion, ser de manejo clinico simple y promover la formacion de un puente dentinario. (17) El material usado tradicionalmente en odontologia, que cumple en parte con estas cualidades, es el HC. (18) Sin embargo, los productos de autograbado han mostrado un buen desempeno en la prevencion de la microfiltracion (19) que, junto con su considerable efecto antibacteriano (20) (los productos que contengan glutaraldehido o que tienen una propiedad acida presentan algunos efectos antibacterianos), los hace agentes prometedores de recubrimiento pulpar directo. Estudios en animales han demostrado que estos materiales de restauracion no causan inflamacion pulpar o necrosis cuando se colocan directamente sobre la pulpa expuesta, si las bacterias han sido eliminadas de los margenes. (21) Algunas investigaciones reportan que el exito clinico del HC, va del 31 al 100%, en una pulpotomia. (22), 23 Otros investigadores no hablan de porcentajes, pero lo consideran muy exitoso para pulpotomia. (24-30) El pH alcalino inducido por el HC, no solo neutraliza el acido lactico de los osteoclastos, evitando asi la disolucion de los componentes minerales de la dentina, sino que tambien puede activar las fosfatasas alcalinas, que desempenan un papel importante en la formacion de tejido duro. (31)

Aunque la toxicidad sistemica y local esta ausente, se requiere el control de la hemorragia con el fin de permitir buen contacto entre el medicamento y el tejido pulpar. (32, 23) Cuando no se controla la hemorragia, no esta indicado el uso del HC.

Los principios de la odontologia basada en la evidencia, se utilizaron para comparar el MTA, con el formocresol (FC), sulfato ferrico (FS) y el HC como principales medicamentos en pulpotomia de molares. La evidencia disponible actualmente sugiere que el MTA en comparacion con ellos, dio lugar a exitos clinicos y radiograficos significativamente mayores en todos los periodos de tiempo comparados hasta la exfoliacion. (33)

Formacion del puente dentinario

El procedimiento de recubrimiento pulpar se basa principalmente en la capacidad del tejido pulpar para repararse. Varios factores afectan este proceso, incluyendo la edad, la condicion periodontal y el estadio de formacion radicular y durante el procedimiento influye el tamano de la exposicion, su naturaleza (traumatica, mecanica o bacteriana) y la contaminacion microbiana del sitio, los cuales se han considerado determinantes en el exito del recubrimiento pulpar. 34 El HC, con su pH basico (pH 12) lo convierte en un agente bactericida, pero ademas, permite la formacion de un puente dentinario cuando es colocado directamente sobre la pulpa. (25)

Estudios como el de Lu y colaboradores, (35) los cuales comparan los efectos de dos materiales colocados en forma directa sobre la pulpa, demuestran que el HC al inicio de la terapia produce inflamacion leve, la cual se convierte en necrosis superficial, permitiendo la formacion de un puente dentinario, mientras que con un agente adhesivo (Clearfill SE BOND), la formacion de esta barrera fue significativamente menor.

El control de la hemorragia es un procedimiento que determina el exito del recubrimiento pulpar directo. Segun Schroder, (36) la falta de una hemostasia antes de la colocacion del HC afecta el tratamiento, porque un coagulo puede formar una barrera que impida el contacto entre el material y la pulpa expuesta; ademas estos coagulos pueden actuar como un sustrato para los microorganismos, lo que conduce a la infeccion pulpar. (37)

El hecho de que el MTA se endurezca en presencia de humedad, puede permitir mejor sellado de la camara, y los resultados, en consecuencia, son mejores en comparacion con el HC, el MTA se puede utilizar en areas en las que es practicamente imposible lograr un ambiente totalmente seco. (38)

El recubrimiento pulpar con MTA produce cambios citologicos y funcionales de las celulas pulpares, resultando en la produccion de dentina reparativa sobre la superficie de una pulpa expuesta mecanicamente. El MTA ofrece un sustrato biologicamente activo para las celulas pulpares, necesario para regular los eventos dentinogenicos. El efecto inicial del MTA sobre la superficie de la pulpa expuesta mecanicamente es la formacion de una capa de estructuras cristalinas. Esta reaccion inmediata indica la estimulacion de la actividad biosintetica de las celulas pulpares por el recubrimiento, pero no puede ser caracterizada como una induccion directa de la formacion de dentina reparativa. Una nueva matriz de formas atubulares con inclusiones celulares se observan debajo del material a las dos semanas. Al evaluarlo bajo microscopio electronico de barrido se encontraron fibras colagenas, contacto directo con la capa cristalina superficial. La dentinogenesis reparativa se obtiene claramente a las tres semanas del recubrimiento, asociada con una matriz fibrodentinal. Por lo tanto el MTA es un material efectivo para el recubrimiento pulpar directo, al favorecer la formacion de un puente de tejido duro durante el proceso de reparacion, si el procedimiento es hecho bajo asepsia. (39)

Efectos del recubrimiento pulpar directo (RPD)

La terapia pulpar vital ha sido conocida como una de las opciones de tratamiento para conservar la pulpa despues de ser expuesta por trauma o caries.

El tejido pulpar en contacto inmediato con el HC es completamente desorganizado y destruido por el efecto caustico (una cauterizacion quimica), esta zona es llamada zona de obliteracion, la cual consiste en escombros, fragmentos de dentina, hemorragia, coagulo de sangre, pigmentos de sangre y particulas de HC, formandose la zona momificada que es de necrosis por coagulacion y trombosis capilar. Esta zona tiene un espesor entre 0,2 y 0,5 mm representado por un tejido desvitalizado sin perdida completa de su arquitectura estructural y poco infiltrado inflamatorio. La zona momificada estimula el tejido pulpar subyacente para responder con todo su potencial de cicatrizacion y producir un puente dentinario. (40) La secuencia en la cicatrizacion del tejido es basicamente la normal de una herida del tejido conjuntivo. El proceso de reparacion ocurre con la migracion y la proliferacion de celulas pulpares mesenquimatosas, endoteliales y formacion de colageno. (41) Cuando la pulpa esta protegida de irritacion se produce la diferenciacion de odontoblastos y la formacion de tejido dentinario, por lo que la funcion de la pulpa es normalizada. (42)

Se han empleado muchos materiales para el recubrimiento pulpar directo y tradicionalmente se acepto el HC como el material de eleccion, debido a su capacidad comprobada para obtener altos porcentajes de exito. Actualmente se esta evaluando la posibilidad de la utilizacion de los adhesivos dentinarios como recubridores pulpares. Pero existen controversias por resultados poco favorables; (43) otro material utilizado para el recubrimiento pulpar directo es el MTA, el cual ha demostrado que estimula la formacion de puentes de dentina adyacentes a la pulpa dental. Esta formacion de dentina puede ser debida a la capacidad de sellado, alcalinidad, biocompatibilidad y a otras propiedades remineralizantes del MTA. (44)

Eskandarizadeh y colaboradores (45) hicieron un estudio comparativo sobre la respuesta de la pulpa dental con HC y MTA como agentes de recubrimiento pulpar. Con base en el resultado de este estudio, se puede sugerir al MTA como material de eleccion para el recubrimiento pulpar directo.

Leye Benoist laboradores, (46) en un estudio controlado aleatorio en dientes humanos, compararon el HC con MTA: el espesor de la dentina recien formada se midio a intervalos de 3 y 6 meses; la formacion de la dentina se controlo con mediciones radiologicas en imagenes digitalizadas, utilizando Mesurim Pro[R] de software. Se observaron mejores resultados (estadisticamente significativos) en el grupo del MTA despues de 3 meses; pero luego de 6 meses no hubo diferencia en el espesor de la dentina, entre los dos grupos.

Controversias

Hay autores que dicen que el HC puede degradarse durante el proceso de grabado acido que se hace antes de una restauracion y piensan que otros materiales como el MTA, podrian remplazarlo; (47, 48) durante las ultimas tres decadas, aparecieron varias publicaciones en relacion con el recubrimiento pulpar en seres humanos, utilizando HC, agentes de union y otros materiales, incluyendo MTA. Este se ha evaluado en varias investigaciones, demostrandose su biocompatibilidad y buena capacidad de sellado. (49)

El tejido conocido como puente de dentina fue observado cuando el MTA fue investigado preliminarmente en modelos animales, antes de su aplicacion clinica en seres humanos; (50) los resultados indican que los compromisos pulpares por causas iatrogenicas, tratados con MTA, se presentan libres de inflamacion despues de 1 semana y se forma de manera compacta el puente de dentina, con una longitud y un espesor considerable en menos de 3 meses. (51) Con el HC se impide la contaminacion y se han observado pocos defectos visibles, lo cual indica la compactacion de la barrera de tejido duro formado para lograrse buena calidad del puente formado. (16)

La formacion del tejido duro subyacente a la barrera de MTA, es probablemente multifactorial, ya que implica factores determinantes como su capacidad de sellado; (5, 52, 53) su biocompatibilidad, (54, 55) y la produccion de un medio ambiente alcalino sobre la pulpa. (56-58) Los resultados del estudio hecho por Olsson y colaboradores (51) permiten concluir que el MTA es clinicamente facil de usar, ademas los resultados en la pulpa son de menos inflamacion y la formacion de una barrera de tejido duro es mas previsible que con el HC. Por lo tanto, el MTA, deberia ser el material de eleccion para el recubrimiento pulpar directo. (51)

Un estudio hecho por Moretti y colaboradores (59) que interviene en la controversia, evaluo y comparo clinica y radiograficamente los efectos del MTA, el HC y el formocresol (FC), como apositos despues de la amputacion de la pulpa coronal en molares deciduos cariados. En los grupos de FC y de MTA, el 100% de los dientes fueron evaluados clinica y radiologicamente con exito durante todas las citas de seguimiento. En el grupo de HC, se detecto radiograficamente reabsorcion interna, en cinco dientes (35,7%) en los 3 meses de seguimiento. Despues de 6 meses, seis dientes (42,9%), tenian evidencia radiografica de fracaso con reabsorcion, destruccion del hueso alveolar y furca con radiolucidez en el mismo grupo del HC, por otra parte hay controversia sobre su aplicacion en pulpotomias de dientes deciduos debido a la posibilidad de reabsorcion interna. (23)

Recubrimiento pulpar indirecto (RPI)

La tecnica de RPI sigue siendo estudiada por muchos autores, es asi como Fagundes y colaboradores (60) describen, a traves de un reporte de caso, utilizando HC, como se logra la conservacion exitosa de la vitalidad pulpar de un molar permanente con caries, en un paciente de 16 anos, al que se le hizo seguimiento de 4 anos; cabe agregar que existe una relacion directa entre el grado de citotoxicidad de determinado material y el exito de este tipo de procedimientos, por lo que Modena y colaboradores (61) demuestran, a traves de una revision, que el HC es el material de eleccion cuando se trata de mayor biocompatibilidad y menor grado de citotoxicidad, comparado con sistemas adhesivos, las resinas y los cementos de ionomero de vidrio. (62, 63) Estos autores no mencionan al MTA, que tiene comprobada su biocompatibilidad con los tejidos humanos.

Conforme son referidos en la literatura, tanto en estudios in vitro como in vivo, el MTA demostro ser el material indicado para recubrimientos pulpares directos e indirectos, por su capacidad excelente de sellado pulpar y biocompatibilidad para prevenir toxicidad e irritabilidad a los tejidos, asi como la induccion y proliferacion celular, regeneracion del cemento y formacion de puente dentinario. (64-66)

Fundamentos biologicos de la respuesta clinica del organo dentino pulpar

El HC ha sido ampliamente utilizado para inducir la regeneracion de la dentina mediante la formacion de puente dentinario en los lugares de exposicion de la pulpa despues de una lesion del tejido dental; sin embargo, los procesos biologicos que subyacen en estos eventos no eran claros; Graham y colaboradores, (67) en su estudio sobre el efecto del HC en la solubilizacion de los componentes bioactivos de la matriz de dentina implicados en la formacion del puente dentinario, proporcionan una explicacion racional para la accion del HC durante el recubrimiento pulpar, en el que las actividades celulares pueden ser mediadas a traves de la liberacion de factores de crecimiento como BMP TGF-beta1, colageno-1 alfa y la expresion de genes y otras moleculas bioactivas a partir de la dentina y del HC.

En la presencia de humedad, el MTA se disocia en un gel hidratado de silicato de calcio lo que puede explicar el exito clinico de este material en los procesos biologicos de reparacion pulpar. (56) Por otro lado, el proceso de reparacion dentinaria puede estar relacionado con una reaccion fisico-quimica que ocurre entre el MTA y el diente como ha sido descrito por Sarkar y colaboradores. (65) Segun los autores; el MTA es un material bioactivo que en contacto con la dentina forma en la interface del diente/material compuestos de hidroxiapatita.

Obturacion endodontica con hidroxido de calcio

Una gran variedad de selladores de conductos radiculares se han recomendado para este uso, en combinacion con materiales de relleno. Estos materiales deben tener propiedades fisico-quimicas satisfactorias, asi como la biocompatibilidad. Al estudiar los efectos citotoxicos y la biocompatibilidad a largo plazo de tres tipos de selladores (a base de resinas, de oxido de zinc y de HC), en ligamento periodontal humano, se encontro que el material sellador basado en el HC, ofrecio una respuesta mas favorable a los tejidos perirradiculares. (68) La genotoxicidad de estos materiales fue evaluada por Huang T-H y colaboradores (69) a traves de un estudio con electroforesis.

Los resultados se obtuvieron mediante un analisis de varianza para comparar los distintos materiales de obturacion. El mayor nivel de dano en el ADN fue inducido por los materiales a base de resina, el obturador basado en oxido de zinc, no siempre provoco aumento en la genotoxicidad, pero ese efecto no se evidencio con el material basado en HC (Sealapex).

Se ha descrito in vitro el efecto del HC como obturante de conductos radiculares; para relacionarlo con la resistencia a la fractura microtensil (MTF) de los dientes, se prepararon con instrumentos rotatorios un total de 40 incisivos superiores permanentes extraidos, libres de enfermedad y los obturaron con HC. Los dientes se almacenaron en un ambiente humedo por 7, 28 y 84 dias. Como grupo control, 10 dientes se obturaron solo con gutapercha. Como resultado se observo que la obturacion de conductos con HC facilita la MTF de los dientes en 13,9 Mpa luego de 77 dias. El debilitamiento de la dentina de 23 a 43,9% despues de la obturacion con HC proporciona evidencia convincente para revaluar el uso de este material en la terapia endodontica. (70) Quiere decir que la obturacion de conductos radiculares con HC produce debilitamiento de los dientes despues de un periodo de 70 dias. (71, 72)

Controversias

Segun los estudios de Rosenberg y colaboradores (70) el HC no es un buen material de obturacion de conductos radiculares; sin embargo, Huang y colaboradores, (68) en un estudio in vitro, determinaron la citotoxicidad en el ligamento periodontal humano de tres tipos diferentes de selladores de conductos radiculares uno a base de resina (AH26 y AHPlus), otro a base de oxido de zinc-eugenol (Canals, Endomethansone y N2) y uno basado en el HC (Sealapex), los resultados confirmaron que los obturadores de conductos constantemente se disuelven cuando son expuestos a un ambiente acuoso durante periodos prolongados de tiempo, lo que podria causar reacciones citotoxicas. El material basado en el HC ofrecio una respuesta mas favorable a los tejidos perirradiculares. Otros autores expresan que otros medicamentos pueden tener mayor potencial (73) que el HC como lo son el paramonoclorofenol-alcanforado, los corticoides, antibioticos y asociaciones antibiotico-corticoide.

Efecto bactericida

El HC sigue siendo utilizado como desinfectante local en endodoncia. La infeccion del conducto radicular es predominante en bacterias anaerobias que utilizan los restos de tejidos y proteinas del suero como nutrientes. Varios estudios han demostrado mayor tasa de exito en los casos en que el canal esta libre de bacterias cuando se obtura. (74)

El HC es el medicamento recomendado para el tratamiento de la infeccion del conducto radicular. Su mecanismo de accion antimicrobiano esta influido por la velocidad de disociacion en iones de calcio y de iones hidroxilo, en un ambiente de pH alto que inhibe la actividad enzimatica que es esencial para la vida microbiana; es decir, el metabolismo, el crecimiento y la division celular. (75, 76) Los efectos letales del HC en las celulas bacterianas se debe probablemente a la desnaturalizacion de las proteinas y los danos en el ADN y en las membranas citoplasmatica. (77)

Hoy en dia se ha demostrado que la preparacion mecanica sola no garantiza la completa recuperacion, por lo que se necesita aplicar un medicamento. (78) La eliminacion de los microorganismos no es uniforme debido a la diferente vulnerabilidad de las especies involucradas. (79) Las bacterias anaerobias Gram negativas pigmentadas, como Porphyromonas gingivalis, se han vinculado a los signos y sintomas de dientes infectados. Sin embargo, los microorganismos facultativos, tales como el Enterococus faecalis, Actinomyces spp, e incluso Candida albicans, son considerados por muchos las especies mas resistentes en la cavidad oral, y una posible causa del fracaso en el tratamiento endodontico. (80, 81) Los microorganismos y sus productos derivados pueden difundir la infeccion del conducto radicular a traves de varias vias, incluyendo el foramen apical, los canales laterales y accesorios con la promocion de una lesion periodontal adyacente. (82)

Para trabajar con un agente antimicrobiano efectivo, este debe actuar tanto en el conducto como hasta una cierta distancia, en los tubulos dentinarios y en una situacion ideal debe llegar a la superficie externa de la raiz. (83)

El HC es un excelente medicamento con efecto antimicrobiano; sin embargo, se ha sugerido el empleo de numerosos vehiculos para asociarlo, a fin de mejorar sus propiedades. Como se requiere un tiempo ideal de accion para la efectiva destruccion de las bacterias por contacto directo en la luz del conducto radicular y por contacto indirecto en los tubulos dentinarios, mas importante que el efecto antimicrobiano del vehiculo empleado, sera su capacidad de solubilidad, a fin de que actue de manera sinergica, lo ayude a difundir y a disociarse rapidamente, permitiendole llegar a aquellos conductos laterales, que son inaccesibles a la preparacion mecanica, mejorando en consecuencia la propiedad antimicrobiana que el HC tiene per se. Mientras mayor es la velocidad de disociacion y difusion de los iones hidroxilos de las pastas de HC, mayor sera el efecto antimicrobiano, lograndose esto con los vehiculos hidrosolubles. (76)

Entre las sustancias utilizadas como vehiculo para el HC, se incluyen el agua destilada, la solucion salina y la glicerina. Recientemente, la clorhexidina ha demostrado ser un medio quimico eficaz para la desinfeccion (84) por su accion antimicrobiana y su adsorcion a los tejidos duros dentales con una liberacion gradual y prolongada en niveles terapeuticos (85-89) la han sugerido como medicacion intraconducto.

Candida albicans y Enterococcus faecalis han demostrado ser resistentes a la accion antimicrobiana de HC, pero son sensibles al gluconato de clorhexidina. Ballal V y colaboradores (90) investigaron in vitro la eficacia antimicrobiana de la pasta de HC, gel de clorhexidina al 2% y su combinacion, frente a Candida albicans y Enterococcus faecalis, concluyendo que para evitar fracasos en los tratamientos de endodoncia, el gel de clorhexidina al 2%, puede ser un medicamento mas efectivo que la pasta de HC.

Al determinar la influencia de los vehiculos (91) en la accion antimicrobiana del HC, se concluyo que en las condiciones del estudio de Estrela y colaboradores, (92) los diversos vehiculos relacionados con las pastas de HC no influyeron en el tiempo requerido para la inactivacion microbiana.

Aunque estudios in vivo han indicado al HC como el medicamento intraconducto mas efectivo de uso multiple, (93) otros han demostrado que el yoduro de potasio (IKI) y la clorhexidina (CHX) son eficaces contra bacterias resistentes al HC, complementando la actividad antibacteriana del HC. (94-98) Las preparaciones de HC con IKI o CHX, por lo tanto, pueden ser una forma de mejorar la eficacia del tratamiento intraconducto.

Evans y colaboradores, (121) hicieron un estudio in vitro para medir el efecto antibacteriano de la combinacion de HC con IKI o con CHX contra E. faecalis. (73) Los resultados del estudio mostraron los beneficios mediante la combinacion de HC, ya sea con IKI o la CHX.

El uso generalizado del HC en gran medida, se basa en la larga duracion de la alcalinidad y el bloqueo a la difusion de nutrientes a las bacterias residuales. Estas propiedades no se vieron afectadas por la adicion de CHX o IKI, aumentando evidentemente el efecto antibacteriano de la medicacion. (98)

Actinomyces israelii ha sido repetidamente citado como una causa de fracaso del tratamiento endodontico. Barnard y colaboradores, (101) investigaron el efecto antimicrobiano de este importante patogeno, con medicamentos utilizados en la limpieza de conductos como el hipoclorito de sodio e HC. Se encontro que tanto la solucion de hipoclorito de sodio al 1% como la de HC son muy efectivas en la eliminacion del A. israelii como microorganismo planctonico.

El HC es un excelente antimicrobiano, como medicacion intraconducto, ya que controla la infeccion en el sistema de conductos radiculares de dientes necroticos y favorece el proceso de reparacion periapical. (102) Asimismo, existen microorganismos tales como E. faecalis, resistentes al HC, vulnerables a la accion del gluconato de clorhexidina cuando son estudiados en su estado planctonico. (103) La correcta eleccion de los agentes antimicrobianos para la medicacion entre citas, es tan importante como la instrumentacion y la irrigacion de los canales para eliminar los patogenos etiologicos. De los diferentes medicamentos el HC es quizas el mas utilizado (104-107) y su efecto antibacteriano se debe principalmente a la liberacion de radicales libres (hidroxilo) (105) y a que mantienen el pH basico. (108, 109) Algunos investigadores han encontrado bacterias viables dentro de los tubulos dentinarios, incluso despues de largos periodos de medicacion con HC. (95, 110) Curiosamente, Haapasalo y colaboradores, (111) encontraron que el efecto antimicrobiano del HC se podria neutralizar in vitro por el polvo de la dentina.

Tang y colaboradores (112) evaluaron los microorganismos residuales luego de un tratamiento convencional de endodoncia, utilizando medicamentos como Septomixine o HC; encontraron que ninguno de los dos puede inhibir efectivamente el crecimiento bacteriano residual en todos los conductos durante los intervalos entre las citas. Se necesitan mas investigaciones para determinar cual es el medicamento mas adecuado para las infecciones del conducto radicular. (113)

Soriano y colaboradores (114) indican el uso limitado del HC en la terapia convencional de endodoncia, ya que no elimina todo el espectro de microorganismos asociados con la necrosis pulpar. En estos casos las especies mas prevalentes son: F. nucleatum spp. Borriela vicentii, C. sputigena, C. ochracea, S. constellatus, V. parvula, P. gingivalis, P. melaninogenica y S. sanguis. La mayoria de los microorganismos se redujeron despues del tratamiento, especialmente: A. gerencseriae, A. israelii, A. naeslundii, C. gingivalis, C. ochracea, P. gingivalis, S. noxia, sanguis y S. oral. Por el contrario, A. actinomycetemcomitans, C. sputigena y E. corrodens, aumentaron en numero despues de la terapia con HC. El HC cuenta con amplia gama de actividad antimicrobiana frente a patogenos comunes en endodoncia, pero es menos eficaz frente a Enterococcus faecalis y Candida albicans. Ademas, su efecto sobre las biopeliculas microbianas tambien es objeto de controversia.

La creencia de que el tratamiento endodontico de dientes necroticos debe ser hecho en varias citas, debido a que ya ha ocurrido propagacion y proliferacion bacteriana en todo el sistema de conductos, (115-117) postulan que en una sola cita es imposible desinfectar completamente el sistema de conductos radiculares, por lo que proponen la utilizacion de medicaciones intraconducto con HC para eliminar las bacterias que no pudieron ser eliminadas durante la preparacion biomecanica. (102, 118)

Sin embargo, hay estudios que reportan que aun utilizando HC no se logra la desinfeccion completa del conducto radicular, e incluso a los 7 dias de colocado es posible que ocurra recolonizacion bacteriana a niveles similares a los que se encontraban previos a la instrumentacion del conducto. (93, 107, 119) Caviedes y colaboradores (120) presentan una revision sobre la evidencia disponible en la literatura cientifica acerca de la efectividad de la endodoncia en una sola cita, basada tanto en la incidencia de exacerbaciones, como en la reparacion periapical a largo plazo y concluyen que todos los dientes pueden tratarse adecuadamente en una cita, sin importar su estado pulpar y periapical; Aunque el numero de conductos, el tiempo disponible y la habilidad del operador son factores que pueden dificultar la conclusion del tratamiento en la misma cita.

Existen muchos estudios, (92, 104, 105) que reportan que el HC tiene efectos letales sobre las bacterias. Sin embargo, estos estudios fueron hechos in vitro y en contacto directo con las bacterias, lo cual en el sistema de conductos radiculares (por su anatomia compleja) generalmente no es posible. Otro aspecto que debe resaltarse, es la ineficacia del HC para eliminar las bacterias dentro de los tubulos dentinales. (121)

Se ha reportado que diferentes preparaciones de HC son incapaces de eliminar E. faecalis de los tubulos dentinales, aun cuando este se encuentra en la entrada de los tubulos. (122, 123)

Para que el HC pueda ser efectivo en eliminar las bacterias presentes en los tubulos dentinales, los iones hidroxilo deben difundirse dentro de la dentina en concentraciones elevadas. Se ha reportado que la alta tension superficial del HC no le permite entrar en los tubulos dentinales. Esto ha hecho, que se intente mezclar el HC con gran numero de vehiculos, por dos razones principalmente, la primera, modificar su tension superficial, y la segunda, prolongar la liberacion ionica. (124-127) Se ha reportado que la solucion anestesica es el vehiculo mas favorable para reducir la tension superficial del HC. (128)

Induccion de tejido duro

Por la capacidad del HC para formar puentes dentinarios se ha propuesto su aplicacion para inducir el cierre apical en dientes inmaduros y en la reparacion de perforaciones. En la actualidad se ha demostrado que el MTA tambien tiene esta capacidad.

Tratamiento en dientes fracturados y perforaciones

El HC ha sido incluido en formulaciones que se utilizan durante el tratamiento de perforaciones, fracturas y reabsorcion radicular, ademas tienen un papel en la traumatologia dental, despues de la avulsion y las luxaciones. (116) El problema encontrado con este metodo ha sido el efecto de debilitamiento de la dentina por el HC, lo que origina el riesgo de fracturas de la raiz a nivel cervical. (129-131) El HC ha demostrado su capacidad para inducir tejido duro en apexificacion, en las fracturas radiculares y su efecto en la reabsorcion externa relacionada con infecciones. (132-136) Un material ideal debe sellar las vias de comunicacion entre el sistema de conductos radiculares, la perforacion, la fractura y sus tejidos circundantes, no debe ser toxico, ni cancerigeno, debe ser biocompatible, insoluble en los liquidos tisulares, y dimensionalmente estable. El MTA se recomendo inicialmente indicando que tenia estas caracteristicas "ideales", ademas tambien ha sido recomendado para el recubrimiento pulpar; pulpotomia, formacion de la barrera apical en dientes con apices abiertos; la reparacion de perforaciones y la obturacion de conductos radiculares. (131)

En un estudio de laboratorio, Hakki y colaboradores, (132) analizaron la respuesta de los fibroblastos del ligamento periodontal (PDL) de perforaciones radiculares restauradas con diferentes materiales como amalgama, Dyract, IRM, Super Bond C y B y el MTA. La microscopia electronica revelo que el grupo de MTA tenia la mayor poblacion de celulas viables en las perforaciones restauradas en comparacion con los otros materiales.

Las fracturas radiculares son frecuentes. El manejo de las fracturas verticales y horizontales es diferente, asi como su forma de diagnostico y su pronostico. Dentro de las causas de las fracturas verticales estan la iatrogenia (excesivo trabajo en el conducto, excesiva compactacion durante la condensacion, colocacion de postes con espacios, o bien, la colocacion de estos sin una buena relacion corono-radicular), el traumatismo fisico, el bruxismo, entre otras. Las fracturas se manejan como las apexificaciones, pero requieren el diagnostico de la parte coronal. Cuando son verticales el pronostico es malo.

Apexificacion

El traumatismo dental en dientes con raices no formadas completamente puede causar necrosis de la pulpa, detencion de la formacion de las raices y el posterior desarrollo de lesiones periapicales.

En su tratamiento puede buscarse la induccion de un cierre apical, por medio de la aplicacion de biomateriales intraconducto para inducir la reparacion periapical, en un procedimiento llamado apexificacion. (133)

En la apexificacion, por medio de desbridamiento quimico-mecanico y el mantenimiento, renovando periodicamente, el HC, era alternativa de eleccion para el sellado biologico de una amplia apertura del foramen, aunque en algunas ocasiones no se lograba. (134, 137, 138) Ahora es el MTA y se hace en una sola cita.

Caliskan y Turkun (139) publicaron un caso clinico de un incisivo central superior con el apice ampliamente abierto y con una gran lesion periapical que se formo como resultado de la necrosis pulpar debido a un traumatismo sufrido hacia doce anos. Despues de un tratamiento con HC se observo exito total a los 15 meses. En otro estudio hecho por Vellore, (138) se enfatiza sobre las bondades que sigue teniendo el HC en dientes despulpados con apice abierto.

Mohammadi y Dummer (77) reportan los multiples beneficios que tiene el HC en tratamientos de apexificacion que tiene mayor exito a largo plazo, por sus propiedades antimicrobianas y su capacidad para estimular la formacion de nuevo hueso.

Tradicionalmente se han hecho procedimientos de apexificacion que pueden tardar un ano o mas. Se ha demostrado que estos dientes son propensos a la fractura y pueden perderse antes o despues de la finalizacion de un largo periodo de apexificacion con HC. (140) Chala y colaboradores (141) hicieron una revision sistematica cuantitativa, para comparar la eficacia del MTA y el HC como materiales utilizados en el tratamiento endodontico de los dientes permanentes inmaduros. Obtuvieron como resultado que ambos pueden ser utilizados.

Controversias

Se ha reportado que el HC ha sido exitoso en la induccion de cierre apical en un gran numero de formulaciones, relacionando la formacion de un cierre apical, con el efecto antibacterial a largo plazo, ya que se ha observado que la formacion de tejido calcificado ocurre en ausencia de microorganismos. (142)

Tambien se ha considerado que la alcalinidad del material, puede actuar como buffer para las reacciones acidas inflamatorias, favoreciendo el remodelado oseo, ya que se neutralizan los acidos producidos por los osteoclastos y los macrofagos. (143) A este respecto, es importante hacer notar que es poco probable que el calcio liberado por la disociacion del HC pueda ser utilizado para la formacion de una barrera apical, puesto que es un ion muy inestable, y para poder ser util en la formacion de este tejido calcificado se necesita de un aporte constante de calcio, el cual puede provenir por via hematogena. (143) Por ultimo, tambien se ha reportado que los remanentes de la vaina epitelial radicular de Hertwig que se mantengan intactos, pueden contribuir a que se produzca el cierre apical. (144)

Meligy y Avery, (145) hicieron un estudio donde compararon clinica y radiograficamente dos materiales utilizados para inducir el selle de raices de dientes permanentes con necrosis pulpar y apices inmaduros (apexificacion): el MTA y el HC. as evaluaciones de seguimiento revelaron el fracaso debido a la inflamacion perirradicular persistente y dolor a la percusion, detectado a los 6 y 12 meses de evaluacion posoperatoria en dos dientes tratados con HC. Los 13 dientes restantes tuvieron clinica y radiograficamente exito luego de 12 meses de la intervencion. Ninguno de los dientes tratados con MTA, mostro patologia clinica ni radiologica. Este estudio llego a la conclusion que el MTA es un sustituto adecuado para el HC en los procedimientos de apexificacion.

Los estudios de microscopia electronica sugieren que las propiedades fisicas del MTA son esenciales en el exito del tratamiento. (146) Nair y colaboradores (147) confirman que el MTA es de mas facil aplicacion clinica y tiene exito en los procedimientos de terapia pulpar vital, tanto en animales (148, 149) como en humanos. (150-154) El MTA es un material con capacidad de selle mejor que la amalgama y el oxido de zinc. (152, 155, 156) Ademas, se ha demostrado su capacidad para estimular la liberacion de citoquinas de las celulas del tejido oseo, lo que indica que promueve activamente la formacion de tejido duro. (152)

Torabinejad y Chivian (156) dicen que el HC se disocia en dos iones con efectos totalmente contrarios, ya que mientras el ion [Ca.sup.++] estimula la proliferacion celular, el ion OH- actua suprimiendo la actividad celular y provocando un arresto en los procesos vitales pulpares. Esto hace pensar que no es el HC como tal el que estimula la formacion del puente dentinario, sino mas bien es el potencial de reparacion del tejido pulpar que trata de defenderse ante la injuria quimica a la que es sometido. (157, 158)

Reabsorciones radiculares internas y externas

La reabsorcion radicular inflamatoria sigue siendo una de las complicaciones mas comunes del trauma dental. Recientemente, con el desarrollo de materiales que no solo son biocompatibles, sino tambien bioinductivos, se ha desplazado la idea de la simple conservacion, para hacer enfasis en la regeneracion del tejido pulpar remanente; siendo el MTA un material que ha demostrado un enorme potencial para la regeneracion. (9) Guzeler y colaboradores, (159) describieron los beneficios del MTA en el tratamiento de dientes inmaduros fracturados que presentan ademas lesion periapical, y observaron detencion de la reabsorcion y cicatrizacion completa de la zona periapical, con restablecimiento del espacio del ligamento periodontal, con seguimientos a los 12 y 24 meses. Cuando se trata de reabsorciones externas, resultado de avulsiones, es de eleccion el uso de MTA como el material de mayor eficacia en comparacion con HC; (160) sin embargo, otros autores continuan apoyando su uso como complemento para el manejo de las reabsorciones internas y externas. (161-163)

Controversias

Para que el HC logre los efectos antes mencionados, debe tener alto grado de difusion al periapice y a la dentina externa por penetracion a traves de los tubulos dentinales, lo cual, debido a la gran reactividad de los iones O[H.sup.-], al sistema buffer de la dentina y a su alta tension superficial es improbable. (125, 164-167)

Segun varios estudios, (163, 168-171) el HC es el material de eleccion para el manejo de la reabsorcion radicular al ser utilizado como medicacion intraconducto, dado que su alto pH tiene la capacidad de destruir las bacterias y ademas alterar el ambiente local de los sitios de reabsorcion en la superficie radicular a traves de los tubulos dentinales. Sin embargo, ya se discutio la dificultad de cambiar el pH con una medicacion intraconducto de HC, en particular en un proceso de reabsorcion externa, donde el pH en la superficie radicular se ha calculado que se encuentra en 4,5.

La apexificacion con HC sigue siendo una buena alternativa de tratamiento para algunos autores, pero el gran consenso en este momento es el uso del MTA. (141, 146)

El HC como agente desensibilizante

La sensibilidad dental es un cuadro clinico muy comun. Es definido como un dolor ocasionado por la exposicion dentinaria, en respuesta a estimulos termicos, quimicos, tactiles y osmoticos. En algunas personas se debe a una anomalia del desarrollo de los tejidos dentarios, cuando el cemento y el esmalte, que normalmente cubren la dentina, no lo hacen.

En general, la hipersensibilidad dentinaria es multifactorial. (172) Independientemente de la etiologia de la exposicion de la dentina, una caracteristica que parece ser comun, es la exposicion de los tubulos dentinarios, que sirven de vinculo directo entre el medio externo y la pulpa dentaria. Si los tubulos no estan expuestos, parece poco probable que la sensibilidad se de. De ahi que una vez la sensibilidad se ha establecido, la pulpa puede ser irreversiblemente sensible. El tratamiento es, por lo tanto, no solo dirigido a restaurar la impermeabilidad original de los tubulos, sino tambien del control de los elementos neurales dentro de la pulpa, para evitar los efectos estimulantes externos. (173, 174)

La hipersensibilidad dental se trata mas comunmente con la aplicacion de barnices, antiinflamatorios, procedimientos de obturacion tubular o el uso de resina de restauracion. (175) Diferentes sistemas no invasivos y reversibles, han sido recomendados para el tratamiento de esta condicion con base en su capacidad para ocluir los tubulos dentinarios. Dos metodos utilizados para el cierre de los tubulos dentinarios son la aplicacion de la suspension de HC (176, 177) y la aplicacion de un imprimador a base de glutaraldehido (PIB).

La hipersensibilidad dental despues del tallado para una corona completa se caracteriza por dolor, que surge como resultado de la transmision de estimulos a traves de la dentina expuesta, es decir, por el mecanismo hidrodinamico. (178) Ademas es frecuente la perdida de los provisionales (179) o desadaptacion de los mismos, la penetracion de microorganismos en los tubulos dentinarios pueda ocurrir y ocasionar dolor o incluso enfermedad pulpar. (180) En un estudio in vivo, Wolfart y colaboradores, (181) evaluaron el efecto de una suspension de HC para reducir la sensibilidad dental y llegaron a la conclusion que hay reduccion de esta. Es importante aclarar que al desensibilizar los dientes despues del tallado, el uso del HC no altera el ajuste de la restauracion final. (182, 183) Pashley y colaboradores (184) demostraron el efecto desensibilizante del HC para sellar la superficie de la dentina y reduce en 48% la permeabilidad tubular en comparacion con la dentina no tratada. Se recomienda el uso del HC para los dientes que quedan sensibles despues de la preparacion de una corona completa. (185, 186) Se ha demostrado que el HC en pasta tiene buen efecto desensibilizante en las superficies radiculares hipersensibles. (187-189)

En las revisiones de Bartold (189) y de McFall (190) se hace referencia a varios estudios que indican la eficacia de cubrir los tubulos dentinarios con HC en la eliminacion de la hipersensibilidad dentinal. Sin embargo, Scherman y Jacobsen (191) dicen que el HC puede irritar el tejido gingival. Resulta importante resaltar que la mayor parte de los estudios que reportan cambios de pH en la capa externa de la dentina y en la region periapical son estudios in vitro, hechos en dientes extraidos, donde posiblemente el sistema buffer de la dentina este alterado y los iones OH-posiblemente no tengan con que reaccionar, reduciendo asi los obstaculos para difundirse a traves del sistema de conductos radiculares. (191-193)

Controversias

Hay amplia variedad de productos para tratar la sensibilidad; algunos parecen ser mas eficaces que otros y varios pueden ser aplicados en el hogar, como: el fluoruro de estano, el fluoruro de sodio, el monofluorofosfato y cloruro de estroncio que han sido ampliamente estudiados y se ha demostrado que son eficaces. En este aspecto tiene desventaja el HC, porque su aplicacion debe ser hecha en el consultorio.

Caviedes y colaboradores (194) concluyen que el HC ha sido el mas utilizado en el mundo de la endodoncia actual; sin embargo, su mecanismo de accion no se encuentra bien sustentado. Su alta tension superficial y su deficiente habilidad para disolver tejidos, no lo hacen un buen candidato para la irrigacion durante la terapia endodontica convencional; debe anotarse ademas, que el MTA se proyecta como el material que esta rompiendo el paradigma del uso clinico predominante del HC en terapia pulpar.

CONCLUSIONES

El MTA, en las ultimas dos decadas, comenzo a tomar el lugar del HC en el tratamiento de una variedad de diagnosticos pulpares. Las principales razones para la sustitucion, ha sido el efecto retardado del HC para inducir tejidos duros; la calidad de los tejidos duros formados y, finalmente, el efecto de debilitamiento de la dentina, que en algunos casos llevan a fracturas en los dientes aun en formacion.

El HC, durante muchas decadas, ha sido el principal material utilizado en recubrimientos pulpares, pulpotomia, dientes con formacion radicular incompleta (apexogenesis), necrosis pulpar (apexificacion), en dientes con fracturas radiculares y necrosis de la pulpa ubicada en la parte coronal y en los dientes con infeccion relacionada con la reabsorcion radicular externa. (133) A pesar de su exito en muchas de las complicaciones mencionadas, se han observado una serie de deficiencias, demostrando, con la investigacion, mejores resultados del MTA, aunque aun sigue utilizandose el HC.

Los estudios revisados pueden llevar a considerar que ha llegado el momento de sustituir el HC por el MTA, en situaciones tales como recubrimiento pulpar, pulpotomia, apexogenesis, perforaciones y apexificacion. Antes de llegar a una conclusion en ese sentido, es necesario revisar nuevos estudios de diferentes metodos con resultados a largo plazo. Los estudios analizados al momento le dan al MTA un serio respaldo cientifico.

CORRESPONDENCIA

Fanny Lucia Yepes Delgado

Profesora titular Facultad de Odontologia Universidad de Antioquia Calle 64 No. 52-59 Medellin, Colombia

Correo electronico: faluyede@gmail.com

INTRODUCTION

For several decades, scientific research situated calcium hydroxide (CH) in a privileged position as a choice with high predictive abilities for pulp therapy since it allows preserving vitality and stimulating dental tissue remineralization in clinical conditions such as pulp capping, apexification, and internal resorption, to name just a few. However, recent studies on the role of mineral trioxide aggregate (MTA) in pulp therapy claim that this material is challenging the clinical paradigm of CH and is gradually becoming more prevalent due to the good results it offers.

CH is obtained by calcining calcium carbonate: Ca[(OH).sub.2] + C[O.sub.2]_CaC[O.sub.3] + [H.sub.2]O. Moreover, this granular, amorphous, thin powder has distinctive basic properties, such as an alkaline pH of about 12.4, which provides it with a great bactericide power. (1, 2) When applied on vital pulp, its caustic action produces an area of sterile surface necrosis coupled with hemolysis and albumin coagulation, being attenuated by the formation of a compact underlying layer consisting of calcium carbonate due to the C[O.sub.2] produced on tissues and proteins as a result of tooth stimulation. (1, 2) CH has a density of 2.1; it may be slightly dissolved in water and is insoluble in alcohol. As a distinctive feature, the higher the temperature the lower its solubility. (1, 3)

The first CH-based medicine was introduced in dentistry by B. W. Hermann in the 1920s and was known as Calxyl. (4) Since then, CH has been widely used for treating endodontic lesions.

Some of the studies explored during this review examine a material that exhibits CH functions such as MTA, which has become an alternative material as it shows statistically significant differences compared to CH.

MTA was first developed and reported in 1993 by Lee, Torabinejad et al; (5) its use in dentistry was approved in 1998 by the Food and Drugs Administration and it was commercially launched in 1999 as MTA ProRoot (Dentsply) in gray color until 2002, when its white form entered the market, with the same composition. (6)

This material is a hydrophilic powder that forges in water. (7) It is composed of tricalcium silicate, tricalcium oxide, silicon oxide, and other mineral oxides that provide it with its properties, such as bismuth oxide, responsible for its radiopacity. (8, 9) It has a high antimicrobial activity since calcium oxide, when mixed with water, reacts producing CH, which causes an increase in pH by dissociation of calcium ions and hydroxyl, creating an environment that prevents the development of bacteria and fungi. (10)

MTA has been internationally used in clinical applications such as apexification, root perforation repairs, retrograde fillings, and direct and indirect pulp capping. It may also be the only material that consistently allows regeneration of periodontal ligament--a cementum-like tissue--and bone formation. (11)

The goal of this study was to update the CH review previously made by Yepes, (12) since the interest on CH research is still current as this has been the material traditionally used in pulp therapy. MTA was also included in this review because it is gradually replacing CH due to qualities that make of it a better choice; this review reveals that scientific research is witnessing a rupture of a clinical paradigm due to the use of MTA instead of CH.

CLINICAL USES OF CALCIUM HYDROXIDE

Direct pulp capping and pulpotomy

Pulp capping is intended to preserve the vital functions of the pulp in the absence of persistent pain due to external stimuli and when the pulp has been accidently exposed to the oral environment. (13, 14) Pulp capping and the marginal seal obtained by applying a material on pulp tissue may be the key factor for the final outcome of this procedure. (15) Cox et al (16) showed that the pulp is able to develop a barrier of hard tissue if an adequate biological seal is provided and therefore microorganisms are prevented from reaching pulp tissue. The ideal material for direct pulp capping must be able to control infection, adhere to dentin to prevent microleakage, offer simple clinical management, and promote dentin bridge formation. (17) CH has traditionally been the material of choice as it complies in part with these qualities. (18) However, etching products have shown good performance in preventing microleakage, (19) and their considerable antibacterial effect (20) (products containing glutaraldehyde or an acidic property have some antibacterial effects) makes them promising agents for direct pulp capping. Studies on animals have shown that these restorative materials do not cause pulp inflammation or necrosis when directly applied on the exposed pulp if bacteria have been eliminated from the margins. (21) Some studies suggest that the clinical success of CH ranges from 31 to 100% in pulpotomy. (22, 23) Other researchers do not mention percentages but describe CH as very successful for pulpotomy. (24-30) The alkaline pH induced by CH not only neutralizes osteoclasts lactic acid, thus preventing dissolution of the dentin's mineral components, but it can also activate alkaline phosphatases, which play an important role in the formation of hard tissue. (31)

Even if local systemic toxicity is absent, bleeding must be controlled in order to allow good contact between drug and pulp tissue. (23, 32) When bleeding is not controlled, CH is not recommended.

The notions of evidence-based dentistry were used to compare MTA with formocresol (FC), ferric sulfate (FS), and CH as the drugs most commonly used for molar pulpotomy. Current evidence suggests that, in comparison, MTA offers successful clinical and radiographic outcomes significantly higher in all compared periods until exfoliation. (33)

Dentin bridge formation

The basic principle of pulp capping is the ability of pulp tissue to repair itself. Several factors affect this process, including age, periodontal status, and stage of root formation, and during the procedure, the main influences are size of the area exposed, its nature (traumatic, mechanical, or bacterial), and microbial contamination of the area, all of which have been considered crucial for pulp capping success. (34) The basic pH of CH (pH 12) makes it a good bactericidal agent, and it also allows the formation of a dentin bridge when directly placed on the pulp. (25)

Studies such as the one by Lu et al, (35) which compares the effects of two materials directly placed on the pulp, show that CH at the start of therapy produces mild inflammation which later turns into a superficial necrosis, allowing the formation of dentin bridge, while with the use of a bonding agent (Clearfill SE BOND), the formation of such barrier was significantly lower.

Bleeding control is a procedure that determines the success of direct pulp capping. According to Schroder, (36) lack of hemostasis before applying CH affects treatment because clots may form a barrier that prevents contact between the material and the exposed pulp; furthermore, clots may also act as a substrate for microorganisms, leading to pulp infection. (37)

The fact that MTA hardens in the presence of moisture may allow a better seal, and the results are therefore better in comparison to those obtained with CH; MTA may be used in areas where it is practically impossible to achieve a completely dry environment. (38)

Pulp capping with MTA produces functional and cytological changes in pulp cells, resulting in the production of reparative dentin on the surface of mechanically exposed pulps. MTA provides pulp cells with a biologically active substrate, which is necessary to control dentinogenic events. The initial effect of MTA on the surface of a mechanically exposed pulp is formation of a layer of crystalline structures. This immediate reaction indicates stimulation of the pulp cells biosynthetic activity by the coating, but it cannot be considered as a direct induction of reparative dentin formation. A new array of non-tubular structures with cell inclusions may be observed under the material within two weeks. Evaluation with scanning electron microscopy shows collagen fibers in direct contact with the surface crystalline layer. Reparative dentinogenesis is evident three weeks after capping, associated with a fibrodentinal matrix. Therefore, MTA is an effective material for direct pulp capping, as it favors the formation of hard tissue bridges during the repair process, if it is performed under aseptic conditions. (39)

Effects of direct pulp capping (DPC)

Vital pulp therapy is a treatment option intended to preserve the pulp when previously exposed by trauma or decay.

In direct contact with CH, pulp tissue is totally dislocated and destroyed by a caustic effect (a chemical cauterization). This area is known as "obliteration area" consisting of debris, dentin fragments, bleeding, blood clots, blood pigments, and CH particles which form a mummified zone of necrosis due to coagulation and capillary thrombosis. This area, of about 0.2-0.5 mm in thickness, consists of devitalized tissue that has not completely lost its structural architecture and presents little inflammation. The mummified area stimulates the underlying pulp tissue to respond to its full healing potential and to produce dentin bridge. (40) Basically, tissue healing follows the typical sequence of conjunctive tissue wounds. It implies migration and proliferation of mesenchymal and endothelial pulp cells, as well as collagen formation. (41) When the pulp is protected against irritation, it results in odontoblast differentiation and dentin tissue formation, so the pulp function is normalized. (42)

A number of materials have been used for direct pulp capping, CH being traditionally accepted as the material of choice because of its proven ability to achieve high success rates. The possibility of using dentin adhesives as pulp coatings is currently under evaluation--but there is some discussion concerning unfavorable results--. (43) Another material used for direct pulp capping is MTA, which has been shown to stimulate formation of dentin bridges adjacent to dental pulp. This effect of dentin formation may be connected to sealing strength, alkalinity, biocompatibility, and other remineralizing properties of MTA. (44)

Eskandarizadeh et al (45) conducted a comparative study on dental pulp response to CH and MTA as pulp capping agents. Based on the results of this study, MTA may be suggested as a material of choice for direct pulp capping.

In a randomized controlled study on human teeth, Leye Benoist et al (46) compared CH and MTA: the thickness of newly formed dentin was measured at intervals of 3 and 6 months; dentin formation was monitored with radiological measurements through digitized images, using Mesurim Pro[R] software. The best results (statistically significant) were observed in the MTA group after 3 months, but after 6 months there were no differences in dentine thickness between the two groups.

Controversies

Some authors claim that CH may degrade during the etching process performed before a restoration, and they think that other materials, such as MTA, may replace it. (47, 48) Over the past three decades, several studies have been published concerning pulp capping in humans, using CH, binders, and other materials including MTA, which has been evaluated in several studies that have demonstrated its good biocompatibility and sealing properties. (49)

The so-called dentin bridge was first observed when MTA was preliminarily tested in animal models before clinical application in humans; (50) the results suggest that iatrogenic-based pulp conditions treated with MTA are free of inflammation after 1 week and that a compact dentin bridge forms in less than 3 months, with considerable length and thickness. (51) CH prevents contamination, and few visible defects have been observed, indicating compaction of the hard tissue barrier formed to achieve "good quality" of the bridge. (16)

The hard tissue formed under the MTA barrier is probably multifactorial as it involves factors such as sealing ability, (5, 52, 53) biocompatibility, (54, 55) and the production of an alkaline environment on the pulp. (56-58) The results of the study by Olsson et al (51) allow to conclude that MTA is clinically easy to use; they also suggest that the pulp experiences less inflammation, and the formation of a hard tissue barrier is more predictable than with CH. Therefore, MTA should be the material of choice for direct pulp capping. (51)

As part of this debate, Moretti et al (59) performed a study in which they evaluated and compared the effects of MTA, CH, and formocresol (FC) as wound dressings after coronal pulp amputation in decayed deciduous molars. In this study, 100% of the teeth treated with FC and MTA were clinically and radiographically evaluated with successful results at all follow-up appointments. In the CH group, internal resorption was radiographically detected in five teeth (35.7 %) during the 3 follow-up months. After six months, six teeth (42.9 %) showed radiographic evidence of failure with resorption, destruction of alveolar bone, and furcation--they also presented radiolucency--; on the other hand, there is still some controversy on its application in deciduous teeth pulpotomy due to the possibility of internal resorption. (23)

Indirect pulp capping (IPC)

Indirect pulp capping (IPC) is a technique still studied by many authors. Fagundes et al, (60) for example, reported a case in which CH was successfully used to preserve pulp vitality of a decayed permanent molar in a 16-year-old patient who was monitored for four years. It should be added that there is a direct relation between the degree of cytotoxicity of a given material and the success of these procedures; for that reason, Modena et al (61) conducted a study to demonstrate that CH is the material of choice when seeking greater biocompatibility and less cytotoxicity, as it is better than adhesive systems, resins, and glass ionomer cements. (62,63) These authors do not mention MTA, which has been proven to have biocompatibility with human tissue.

As referenced in the literature, both in vitro and in vivo studies have demonstrated that MTA is the most suitable material for direct or indirect pulp capping due to its excellent pulp sealing ability and its biocompatibility (which prevents toxicity and tissue irritability), as well as cell induction, cell proliferation, cementum regeneration, and dentin bridge formation. (64-66)

Biological basis of the dentin-pulp complex clinical response

CH has been widely used to induce dentin regeneration by means of dentinal bridge formation in areas where the pulp is exposed due to dental tissue injury; however, the biological processes underlying such events are unclear. Graham et al, (67) in their study on the effect of CH in solubilization of the dentin matrix bioactive components involved in dentin bridge formation, provide a rational explanation for the action of CH during pulp capping, in which cellular activity may be mediated by release of growth factors such as BMP, TGF-beta1, collagen alpha-1, and the expression of genes and other bioactive molecules from dentin and CH.

In the presence of moisture, the MTA dissociates into a gel of calcium silicate hydrate which may explain the clinical success of this material in the biological processes of pulp repair. (56) Furthermore, the process of dentin repair may be related to a physical-chemical reaction occurring between MTA and the tooth as described by Sarkar et al. (65) According to these authors, MTA is a bioactive material which, when in contact with the dentin, produces hydroxyapatite composites at the tooth/ material interface.

Endodontic filling with calcium hydroxide

A variety of root canal sealers have been recommended for this purpose, in combination with fillers. These materials must have satisfactory physical-chemical properties as well as biocompatibility. Studies of the cytotoxic and long-term biocompatibility of three types of sealants (resin-based, eugenol-zinc oxide, and CH) in human periodontal ligament have shown that CH-based sealants offer a more favorable response to periradicular tissues. (68) The genotoxicity of these materials was evaluated by Huang et al (69) through an electrophoresis study.

The results were obtained by analysis of variance to compare the different filling materials. The highest level of DNA damage was induced by resin-based materials; the eugenol-zinc oxide filler did not always lead to an increase in genotoxicity, but this effect was not evidenced with the CH-based material (Sealapex).

The effect of CH as a root canal sealant has been described in vitro. In order to associate CH with teeth microtensile fracture toughness (MFT), a total of 40 extracted healthy permanent upper incisors were prepared with rotary instruments and filled with CH. The teeth were stored in a moist environment for 7, 28, and 84 days. As a control group, 10 teeth were filled with gutta-percha alone. As a result, the researchers noted that filling with CH facilitates teeth MFT in 13.9 Mpa after 77 days. Weakening of dentin from 23 to 43.9% after sealing with CH provides convincing evidence to reconsider the use of this material in endodontic therapy. (70) This means that root canal filling with CH weakens teeth after a period of 70 days. (71, 72)

Controversies

According to studies by Rosenberg et al, (70) CH is not a good material for root canal filling; however, in an in vitro study, Huang et al (68) demonstrated the cytotoxicity of three different root canal sealers in human periodontal ligament: a resin-base sealer (AH26 and AHPlus), an eugenol-zinc oxide sealer (Canals, Endomethansone and N2) and a CH-based sealer (Sealapex). Their results proved that root canal fillers constantly dissolve when exposed to an aqueous environment for extended periods of time, which may cause cytotoxic reactions. The CHbased material offered a more favorable response to periradicular tissues. Other authors (73) state that other drugs may have a greater potential than CH, such as camphor paramonochlorophenol, corticosteroids, antibiotics, and antibiotic-corticosteroid compounds.

Bactericidal effect

CH is still used as a disinfectant agent in endodontics. Root canal infection is rich in anaerobic bacteria, which use tissue debris and serum proteins as nutrients. Several studies have shown higher success rates when root canals are free of bacteria when sealed. (74)

CH is recommended as the drug of choice for treating root canal infection. Its antimicrobial mechanism of action is influenced by the rate of dissociation of calcium ions and hydroxyl ions in a high pH environment, which inhibits enzymatic activity--essential for microbial life, that is to say, for metabolism, cell growth, and cell division--. (75, 76) The lethal effects of CH in bacterial cells are probably due to protein denaturation, as well as to damage to DNA and cytoplasmic membranes. (77)

It has been recently shown that mechanical preparation alone does not guarantee full healing, so a drug is also needed. (78) Microorganism elimination is not always uniform due to different vulnerability levels of the species involved. (79) Pigmented gramnegative anaerobic bacteria such as Porphyromonas gingivalis have been linked to the signs and symptoms of infected teeth. However, facultative microorganisms such as Enterococcus faecalis, Actinomyces spp. and even Candida albicans are considered by many to be the most resistant species in the oral cavity, and a possible cause of endodontic treatment failure. (80, 81) Microorganisms and their products may spread the infection from the root canal through several routes, including the apical foramen as well as lateral and accessory canals, promoting adjacent periodontal lesions. (82)

For an antimicrobial agent to be effective, it must act not only in the root canal but also up to a certain distance, in the dentinal tubules, and ideally it should reach the root's outer surface. (83)

CH is an excellent antimicrobial drug; however, a number of associating vehicles have been suggested in order to improve its properties. As a certain period of time is required for effective destruction of bacteria by direct contact with the root canal and indirect contact with dentinal tubules, the vehicle's solubility is more important than its antimicrobial effect so that it works in a synergistic manner and rapidly spreads reaching those lateral canals that are inaccessible by mechanical preparation, thereby improving the natural antimicrobial property of CH. The greater the rate of dissociation and diffusion of hydroxyl ions from CH paste the greater its antimicrobial effect--and this is achieved with soluble vehicles. (76)

Among the substances used as CH vehicles are distilled water, saline solution, and glycerin. Recently, chlorhexidine has proven to be an effective chemical disinfectant; (84) due to its antimicrobial action and its adsorption to hard tissues with gradual and constant release at therapeutic levels, (85-89) it has been recommended as an intracanal medication.

Candida albicans and Enterococcus faecalis have proved resistant to the antimicrobial action of CH, but they are sensitive to chlorhexidine gluconate. In an in vitro study, Ballal et al (90) examined the antimicrobial effect of CH paste, 2% chlorhexidine gel, and their combination against Candida albicans and Enterococcus faecalis, concluding that in avoiding root canal treatment failures, 2% chlorhexidine gel may be more effective than CH paste.

In determining the vehicle's influence (91) on the antimicrobial action of CH, Estrela et al concluded that, under the conditions of their study, (92) the various vehicles related with CH pastes did not influence the time required for microbial inactivation.

Although in vivo studies have concluded that CH is the most effective intracanal medication, (93) other studies have shown that potassium iodide (KI) and chlorhexidine (CHN) are effective against CH-resistant bacteria, thus complementing the antibacterial activity of CH.94-98 CH preparations with KI or CHN may therefore be one way to improve the efficacy of intracanal treatment.

Evans et al (121) conducted an in vitro study to assess the antibacterial effect of CH-KI and CH-CHN combinations against E. faecalis. (13) Their findings showed the benefits of combining CH with either KI or CHN.

The widespread use of CH is largely due to its long lasting alkalinity and its ability to stop the provision of nutrients to residual bacteria. These properties were not affected by the addition of CHN or KI, which clearly increased the medication's antibacterial effect. (98)

Actinomyces israelii has been constantly cited as a cause of endodontic treatment failure. Barnard et al (101) studied the antimicrobial effect of this important pathogen, with medicines normally used in root canal cleaning such as sodium hypochlorite and CH. They found out that both 1% sodium hypochlorite and CH are very effective in the elimination of A. israelii as a planktonic microorganism.

Used as an intracanal medication, CH is an excellent antimicrobial because it controls infection in the root canal system of necrotic teeth and promotes periapical repair. (102) Similarly, CHresistant microorganisms such as E. faecalis are sensitive to the action of chlorhexidine gluconate in its planktonic state. (103) The correct selection of antimicrobial agents as medication between appointments is as important as root canal instrumentation and irrigation to remove etiologic pathogens. Among the different medications available, CH is perhaps the most widely used; (104-107) its antibacterial effect is mainly due to the release of free radicals (hydroxyl) (105) and to its permanent basic pH. (108, 109) Some researchers have found viable bacteria within the dentinal tubules, even after long periods of treatment with CH. (95, 110) Interestingly enough, Haapasalo et al (111) found out that the antimicrobial effect of CH could be neutralized in vitro by dentine powder.

Tang et al (112) evaluated residual microorganisms after conventional endodontic treatment, by using medicines such as Septomixine or CH and found out that neither could effectively inhibit residual bacterial growth in canals during appointment intervals. More research is needed to determine the most appropriate medication for root canal infections. (113)

Soriano et al (114) recommend a limited use of CH in conventional endodontic therapy, because it does not eliminate the entire spectrum of microorganisms associated with pulp necrosis. In these cases, the most common species are: F. nucleatum spp, Borriela vicentii, C. sputigena, C. ochracea, S. constellatus, V. parvula, P. gingivalis, P. melaninogenica and S. sanguis. Most microorganisms were reduced after treatment, especially A. gerencseriae, A. israelii, A. naeslundii, C. gingivalis, C. ochracea, P. gingivalis, S. noxia, sanguis and S. oral. On the contrary, A. actinomycetemcomitans, C. sputigena and E. corrodens, increased in number after CH therapy. CH has a wide range of antimicrobial activity against common endodontic pathogens, but it is less effective against Enterococcus faecalis and Candida albicans. In addition, its effect on microbial biofilms is also controversial.

The common belief that endodontic treatment of necrotic teeth should be done in several appointments because by then bacteria have grown and spread throughout the canal system (115-117) suggests that it is impossible to fully disinfect the root canal system in a single session and therefore it is necessary to use intracanal medications with CH in order to remove the bacteria that was not removed during biomechanical preparation. (102,118)

Nevertheless, some studies report that, even using CH, complete root canal disinfection is not achieved, and even 7 days after it has been placed, there is a possibility of bacterial recolonization at similar levels to those that existed before canal instrumentation. (93, 107, 119) Caviedes et al (120) published a review of the evidence available in the scientific literature about the effectiveness of endodontic therapy in a single appointment, based on both the incidence of exacerbations and long-term periapical repair; they concluded that all teeth may be adequately treated in one session regardless of pulp and periapical status. However, the number of canals, the time available and the operator skills are factors that may hinder the completion of treatment in one session.

Many studies (92, 103, 105) claim that CH has lethal effects on bacteria. However, these studies were performed in vitro and in direct contact with bacteria, a condition that is not generally possible within the root canal system due to its complex anatomy. Another aspect to be highlighted is failure of CH to kill bacteria inside the dentinal tubules. (121)

It has been reported that several CH preparations are unable to eliminate E. faecalis inside the dentinal tubules even if it is located at the tubules entrance. 122, 123

For CH to be effective in removing bacteria from the dentinal tubules, the hydroxyl ions must diffuse into the dentin in high concentrations. It has been reported that the high surface tension of CH prevents it from entering the dentinal tubules. For this reason, several attempts have been made to mix CH with a number of vehicles for two basic purposes: to modify surface tension and to prolong ionic release. (124-127) It has been reported that the anesthetic solution is the most favorable agent to reduce CH surface tension. (128)

Induction of hard tissue

Due to the ability of CH to form dentinal bridges, it has been used to induce apical closure in immature teeth and to repair perforations. Recent studies have shown that MTA also has this ability.

Treatment of fractured teeth and perforations

CH has been included in compounds used for treating perforations, fractures, and root resorption; these compounds also play an important role in dental trauma following avulsion and luxations (116) The problem with this method is dentin weakening caused by CH, resulting in possible fractures of the cervical third of the root. (129-131) CH has demonstrated an ability to induce hard tissue in apexification and root fractures, and it also has an effect on infection-related external resorption. (132-136) An ideal material should be able to seal the communication passages within the root canal system, the perforation, the fracture, and their surrounding tissues; it should not be toxic or carcinogenic and must be biocompatible, insoluble in tissue fluids, and dimensionally stable. MTA was initially recommended for having these "ideal" features; it has also been recommended for pulp capping, pulpotomy, apical barrier formation in teeth with open apexes, perforations repair, and root canal filling. (131)

In a laboratory study, Hakki et al (132) analyzed the response of periodontal ligament fibroblasts (PLF) of root perforations restored with materials as varied as amalgam, Dyract, IRM, Super Bond C and B, and MTA. Electron microscopy revealed that the group of perforations treated with MTA presented the largest population of viable cells compared to the other materials.

Root fractures are common. Vertical and horizontal fractures should be treated differently, as well as their diagnosis and prognosis. Among the causes of vertical fractures are iatrogenesis (canal overwork, excessive compaction during condensation, placing posts with spaces or without good crownroot ratio), physical trauma, and bruxism, to name just a few. Fractures are handled as apexifications, but they require crown diagnosis. Vertical fractures usually have a poor prognosis. In the case of horizontal fractures, the prognosis depends on the level at which the fracture happens.

Apexification

Dental trauma in teeth with incomplete root formation may cause pulp necrosis, interruption of root formation, and the subsequent development of periapical lesions.

Its treatment may include induction of apical closure through the application of intracanal biomaterials to induce periapical repair in a procedure called apexification. (133).

In apexification, through chemical-mechanical debridement and periodical maintenance, CH used to be the material of choice for biological sealing of wide foramen openings, although sometimes this was not achieved. (134, 137, 138) Now this can be done with MTA in a single appointment.

Caliskan et al (139) reported a case of a maxillary central incisor with a widely open apex and a large periapical lesion as a result of pulp necrosis due to trauma suffered 12 years before. After treatment with CH overall success was achieved in 15 months. In another study by Vellore, (138) the author emphasized the benefits still offered by CH in pulpless teeth with open apex.

Mohammadi et al (77) reported the many benefits of CH in apexification, with greater success in longterm treatments due to its antimicrobial properties and its ability to stimulate new bone formation.

Apexification treatments generally last for one year or more. It has been shown that these teeth are prone to fracture and may be lost before or after a long period of apexification with CH. (140) Chala et al (141) conducted a quantitative systematic review to compare the efficacy of MTA and CH during the endodontic treatment of immature permanent teeth. As a result, they found out that both materials can be used.

Controversies

It has been reported that CH is successful in inducing apical closure in a large number of formulations, linking apical closure with the long-term antibacterial effect of CH, since it has been observed that calcified tissue forms in the absence of microorganisms. (142)

It has also been noted that the material's alkalinity may act as acidic buffer to inflammatory reactions, favoring bone remodeling since they neutralize the acids produced by osteoclasts and macrophages. (143) In this regard, it is important to note that it is unlikely that calcium released by CH dissociation can be used in the formation of an apical barrier, since it is a very unstable ion, and in order to be useful in the formation of this calcified tissue it needs a constant supply of calcium, which may come through blood. (142) Finally, it is also been reported that the remnants of Hertwig's epithelial root sheath that remain intact may favor apical closure. (144)

Meligy et al (145) conducted a clinical and radiographic study to compare two materials used to induce root seal of permanent teeth with pulp necrosis and immature apices (apexification): MTA and CH. Follow-up evaluations revealed failure due to persistent periradicular inflammation and pain on percussion at 6 and 12 months postoperative evaluation in 2 teeth treated with CH. The remaining 13 teeth showed clinical and radiographic success after 12 months of intervention. None of the teeth treated with MTA showed clinical or radiographic pathology. This study concluded that MTA is a suitable replacement for the CH in apexification procedures.

Electron microscopy studies suggest that MTA's physical properties are essential to treatment success. (146) Nair et al (147) demonstrated that MTA offers easier clinical application and is successful in vital pulp therapy procedures in both animals (148), 149 and humans. (150-154) MTA has better seal abilities than amalgam and eugenol-zinc oxide. (152, 155, 156) Furthermore, its ability to stimulate cytokine release from bone tissue cells has been demonstrated, which suggests that it actively promotes hard tissue formation. (152)

Torabinejad et al (155) argue that CH dissociates into two ions with exactly the opposite effects, since while the [Ca.sup.++] ion stimulates cell proliferation the O[H.sup.-] ion suppresses cell activity and interrupts the pulp's vital processes. This suggests that it is not CH the one that actually stimulates dentin bridge formation, but rather that the pulp tissue potential to repair itself seeks protection against the chemical damage to which it is subjected. (157, 158)

Internal and external root resorption

Inflammatory root resorption remains one of the most common complications of dental trauma. With the recent emergence of materials that are not only biocompatible but also bio-inductive, the idea of simple conservation is shifting towards an emphasis on residual pulp tissue regeneration--MTA being a materialwith tremendouspotential forregeneration--. (9) Guzeler et al (159) described the benefits of MTA in the treatment of fractured immature teeth with periapical lesions, observing resorption interruption, complete healing of the periapical area, and restoration of periodontal ligament space in follow-up periods of 12 and 24 months. When dealing with external resorption resulting from avulsions, MTA is usually the material of choice as it offers greater efficiency compared to CH; (159) however, other authors still support its use as complement for handling internal and external resorptions. (161-163)

Controversies

For CH to achieve the aforementioned effects, it must have a high degree of diffusion to the periapex and the dentin's outer layer by penetrating through the dentinal tubules--something that is improbable due to the high reactivity of the OHions, the dentine buffer system, and its high surface tension. (125, 164-167)

According to several studies, (163, 168-171) CH is the material of choice for root resorption treatment when used as an intracanal medication, since its high pH has the ability to kill bacteria while at the same time altering the local environment of resorption sites on the root surface through the dentinal tubules. However, it has been discussed that changing the pH with a CH intracanal medication is hard to achieve, particularly in an external resorption process where root surface pH has been calculated to be 4.5.

For some authors, apexification with CH is still a good alternative treatment but the current general consensus recommends using MTA. (141, 146)

CH as a desensitizing agent

Tooth sensitivity is a common clinical condition. It is defined as pain caused by dentin exposure in response to thermal, chemical, tactile, or osmotic stimuli. In some people it is due to anomalies in dental tissue development, when cement and enamel are not covering the dentin as they normally should. In general, dentin hypersensitivity is multifactorial. (171) Regardless of the etiology of dentin exposure, a feature that seems to be common is the exposure of dentinal tubules--which serve as a direct connection between the external environment and dental pulp--. If the tubules are not exposed, it seems unlikely for sensitivity to occur, so once it is established, the pulp may be irreversibly sensitive. The treatment is therefore not only aimed at restoring the tubules' original impermeability but also to control neural elements inside the pulp to avoid external stimulant effects. (173, 174)

Dental hypersensitivity is commonly treated with coatings, anti-inflammatories, tubular sealing procedures, or restoration resins. (175) Several non-invasive, reversible systems have been recommended to treat this condition based on their ability to occlude dentinal tubules. Two methods used for closing the dentinal tubules are the application of either a CH suspension (176, 177) or a glutaraldehyde-based primer (GDP).

Dental hypersensitivity after grinding for a full crown is characterized by pain resulting from the transmission of stimuli through the exposed dentin, that is, by a hydrodynamic mechanism. (178) Moreover, loss or maladjustment of temporary restorations is common, (179) and microorganisms may penetrate the dentinal tubules causing pain or even pulp disease. (180) In an in vivo study, Wolfart et al (181) evaluated the effect of a CH suspension in reducing tooth sensitivity and concluded that it does occur. It is important to clarify that using CH to desensitize teeth after grinding does not alter the results of the final restoration. (182, 183) Pashley et al (184) demonstrated the desensitizing effect of CH to seal dentin surface and to reduce by 48% the tubular permeability in comparison with an untreated dentin. CH is recommended for teeth that remain sensitive after preparation of a full crown. (185, 186) It has been demonstrated that CH paste has a good desensitizing effect on hypersensitive root surfaces. (187-189)

In their topic reviews, Bartold (189) and McFall (190) mention several studies that refer to the effectiveness of covering dentinal tubules with CH to eliminate tooth sensitivity. However, Scherman and Jacobsen (191) point out that CH may irritate gingival tissue. It is important to note that most of the studies that report pH changes in the dentin outer layer and the periapical area are in vitro studies performed on extracted teeth, where the dentin buffer system may be altered and O[H.sup.-] ions may not be able to react, thereby reducing the barriers to spread through the root canal system. (191-193)

Controversies

There is a large variety of products for treating sensitivity; some appear to be more effective than others and some can even be applied at home, such as stannous fluoride, sodium fluoride, monofluorophosphate, and strontium chloride which have been extensively studied and have shown to be effective. In this sense CH is in disadvantage because it must be applied at the dentist's office.

Caviedes et al concluded (194) that CH has been the material most widely used in current endodontics; however, its mechanism of action is not well supported. Its high surface tension and its poor ability to dissolve tissue prevent it from being a good candidate for irrigation during conventional endodontic therapy. It should also be noted that MTA is gradually breaking the paradigm of the predominant clinical use of CH in pulp therapy.

CONCLUSIONS

During the last two decades, MTA began to take the place of CH in the treatment of a variety of pulp-related conditions. The main reasons for this replacement has been the delayed effect of CH to stimulate hard tissue formation, the quality of hard tissue formed, and the dentin weakening effect, which in some cases leads to fractures in immature teeth.

For many decades, CH has been the material of choice in pulp capping, pulpotomy, teeth with incomplete root formation (apexogenesis), and pulp necrosis (apexification). It has also played an important role in teeth with root fractures and pulp necrosis at the coronal area, as well as in teeth with infection related to external root resorption. (133) Despite its success in many of the aforementioned complications, a number of deficiencies have been observed, and several studies have demonstrated better results with MTA, although CH is still used.

The studies included in this topic review may lead to the conclusion that it is now the time to replace CH by MTA in situations such as pulp capping, pulpotomy, apexogenesis, perforations, and apexification. Before reaching a conclusion in that regard, it is necessary to review new studies of different methods with long-term results. The studies analyzed this time provide MTA with serious scientific support.

CORRESPONDING AUTHOR

Fanny Lucia Yepes Delgado

Professor Facultad de Odontologia Universidad de Antioquia Calle 64 No. 52-59 Medellin, Colombia

E-mail Address: faluyede@gmail.com

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FANNY LUCIA YEPES DELGADO [1], CESAR AUGUSTO CASTRILLON YEPES [2]

[1] Odontologa, especialista en Odontologia Integral del Adulto, magister en Educacion: Sociologia de la Educacion. Profesora titular e investigadora, Facultad de Odontologia Universidad de Antioquia. Correo electronico: faluyede@gmail.com

[2] Odontologo, especialista clinico en Odontologia Integral del Adulto con enfasis en Periodoncia. Investigador, Facultad de Odontologia Universidad de Antioquia. Correo electronico: cesarmadrid11@hotmail.com

[1] Dentist. Specialist in Comprehensive Dentistry of the Adult. MEd. Sociology of Education. Full Professor-Researcher, School of Dentistry, Universidad de Antioquia. E-mail Address: faluyede@gmail.com.

[2] Dentist. Candidate to the clinical specialization in Comprehensive Dentistry of the Adult with emphasis in Periodontics. Postgraduate Student and Researcher, School of Dentistry, Universidad de Antioquia. E-mail Address: cesarmadrid11@hotmail.com.

RECIBIDO: FEBRERO 14/2012-ACEPTADO: ENERO 22/2013

SUMBITTED: FEBRUARY 14/2012-ACCEPTED: JANUARY 22/2013
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Author:Yepes Delgado, Fanny Lucia; Castrillon Yepes, Cesar Augusto
Publication:Revista Facultad de Odontologia
Date:Jul 1, 2013
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