Smear Layer Removal and Microhardness Alteration Potential of a Naturally Occurring Antioxidant – An In Vitro Study

Abstract

Introduction: It is well-known in the field of endodontics that the presence of a smear layer in the root canals can harbor bacteria and limit the penetration of irrigating solutions and intracanal medications into the dentinal tubules which, in turn, causes the failure of endodontic treatment. Removing the entire smear layer throughout the root canal is essential for the success of endodontic treatment and these chemical agents that facilitate the removal of the smear layer are called chelating agents. Ethylenediaminetetraacetic acid (EDTA), being the most widely used chelating agent, brings about increased reduction in the microhardness of the root dentin, thereby making it friable.N-acetyl cysteine (NAC) is naturally occurring antioxidant that has various beneficial properties for the human being. Several studies have been done in determining the antimicrobial efficacy of NAC against various endodontic pathogens and concluded NAC to be advantageous. The chelating property of NAC has been utilized in heavy metal detoxification, where it binds to the metal ion and removes them from the human system. However, this chelating property has not been explored in the field of endodontics.Aim: This study was aimed to compare the ability of N-acetyl cysteine with the conventional chelating agent in the removal of the smear layer and in altering the microhardness of root dentin.Materials and Methodology: A total of 84 single-rooted human mandibular premolars with relatively similar dimension and morphology, freshly extracted with closed apices, were collected from adult patients. The crowns of all specimens were cut transversally at the cementoenamel junction (CEJ) with the double-faced diamond disc at low speed, with water coolant, to obtain a 12 mm root length. The root canals were randomly divided into three equal groups according to the final irrigation solutions: Group I: 17% EDTA, Group II: 20% NAC, and Group III: distilled water (control). They were then randomly divided into two parts: scanning electron microscope (SEM) analysis for the extent of smear layer removal and microhardness evaluation using the Vicker’s hardness test.Results: The smear layer removal ability of EDTA and NAC were more effective in the coronal and middle thirds of the root canal. However, both groups showed less smear layer removal in the apical region. Specimens treated with distilled water showed the least reduction in the smear layer throughout the length of the root canals. Regarding the evaluation of microhardness, both EDTA and NAC had a significant reduction in root dentin microhardness. However, the percentage of dentin microhardness reduction was significantly more in the EDTA group (p < 0.05) than N-acetyl cysteine in the coronal, middle, and apical third of the root canals.Conclusion: The chelating property of NAC is equally effective to that of EDTA in the smear layer from the root canal, and it induced a significantly lesser reduction in microhardness of root dentin than EDTA.

Influência De Substâncias Irrigadoras Endodônticas Na Microdureza Da Dentina Radicular - Revisão Integrativa

“…O EDTA é capaz de amolecer a dentina do canal radicular, dissolver a camada de esfregaço e aumentar a permeabilidade da dentina. Além disso, o EDTA tem o potencial de causar erosão dentinária excessiva e um grau moderado de irritação 6,7,10 .…”

“…Entretanto, apesar dos efeitos benéficos, o EDTA tem um forte efeito desmineralizante, causa aumento dos túbulos dentinários, amolecimento da dentina, desnaturação das fibras colágenas, facilita a quelação da porção inorgânica da dentina e, consequentemente, a torna mais desmineralizada. Em todos os estudos analisados, o EDTA em concentrações de 5%, 15% e 17%, isoladamente ou em combinação com outros agentes irrigantes, diminuiu significativamente a microdureza da dentina radicular 7,8,10,11 .…”

“…O efeito das soluções de digluconato de clorexidina (CHX) a 2% e hipoclorito de sódio (NaOCl) a 6% testada nas propriedades mecânicas da dentina ainda é controverso na literatura e novos estudos são necessários para determinar as recomendações clínicas 9, 15. Levando em consideração grande parte dos trabalhos, o hipoclorito de sódio (NaOCl), digluconato de clorexidina (CHX) e o Ácido etileno diamino tetracético (EDTA) analisados causam redução na microdureza da dentina, descantando a hipótese de que os tratamentos de superfície com essas substâncias não afetam esse tecido 4,6,7,8,10,11,12,13,14,16,17,18 .…”

“…É utilizado para remover a camada de esfregaço e preparar as paredes dentinárias para melhor aderência dos materiais de preenchimento. No entanto, o EDTA também tem o potencial de causar erosão dentinária excessiva e pode causar um grau moderado de irritação 6,7 .…”

Efficacy of Various Final Irrigant Activation Procedures on Smear Layer Removal - A SEM Study

“…Smear layer is created on the root canals surfaces during cleaning and shaping, this shapeless irregular film is made of organic pulpal residues and inorganic dentinal fragments accumulation which stick onto the radicular wall of canal 1 . It has been stated that the smear layer obstruct the dentinal tubules and impede the penetration of irrigants solutions, disinfectant materials and endodontic sealers into the dentinal tubules 2 ,which may deteriorate the canal seal and encourage the microleakage, it was also established that existence of this contaminated layer full with bacteria in the dentinal tubules , lessen the success ratio of the root canal therapy. Smear layer is produced during instrumentation either with hand or rotary instruments 3,4 .…”