Summary.
This article focuses on an important topic in endodontics: whether or not to remove the smear layer during endodontic treatment. It describes the structure and composition of the smear layer, explores its potential impact on treatment outcomes depending on the clinical situation, and proposes a clinical decision-making algorithm along with recommendations regarding the sequence and duration of irrigant application.
This article focuses on an important topic in endodontics: whether or not to remove the smear layer during endodontic treatment. It describes the structure and composition of the smear layer, explores its potential impact on treatment outcomes depending on the clinical situation, and proposes a clinical decision-making algorithm along with recommendations regarding the sequence and duration of irrigant application.
Keywords: smear layer, root canal irrigation, EDTA, sodium hypochlorite.
During endodontic instrumentation, a layer forms on the canal walls due to the action of endodontic files. This layer consists of residual organic tissue, fragmented hydroxyapatite crystals (dentin debris), and—if the canal was infected—microbial remnants. This is known as the smear layer, also referred to in some languages as a “muddy” layer.
The smear layer has two components:
During endodontic instrumentation, a layer forms on the canal walls due to the action of endodontic files. This layer consists of residual organic tissue, fragmented hydroxyapatite crystals (dentin debris), and—if the canal was infected—microbial remnants. This is known as the smear layer, also referred to in some languages as a “muddy” layer.
The smear layer has two components:
A superficial layer, 1–2 microns thick, made of organic debris and dentin shavings.
An inner layer, extending into the dentinal tubules, called smear plugs, which can reach depths of up to 40 microns (Mader C.L. et al., 1984).
The influence of the smear layer on the success of endodontic treatment has long interested researchers and clinicians. Today, most advocate for its complete removal (White et al., 1975; Mader et al., 1984; White et al., 1987; Lloyd et al., 1995; Khayat & Jahanbin, 2005).
A key argument for removing it is that the smear layer impairs the penetration of sealer and thermoplasticized gutta-percha into dentinal tubules, lateral canals, and apical ramifications (White et al., 1975, 1987; Lloyd et al., 1995). There’s also concern that microbes may survive within the smear layer, protected from irrigants (Berutti et al., 1997).
Unfortunately, few clinicians have taken note of the study by Ørstavik and Haapasalo (1990), which showed that the smear layer delays the action of irrigants and intracanal medicaments on microbes within the dentinal tubules.
Most endodontists recommend removing the smear layer before obturation (filling), primarily to obtain a "clean" radiograph. However, a good two-dimensional X-ray image doesn't necessarily reflect high-quality treatment.
As always, there’s another side to the story. The smear layer greatly reduces dentin permeability (Pashley et al., 1981). Thus, two independent research teams concluded that the smear layer inhibits microbial penetration into dentinal tubules (Love et al., 1996; Peters et al., 2000).
So, clinicians face a dilemma: remove the smear layer or not?
Here’s the author’s personal view, dividing cases into two categories:
1. Vital cases:
When treating a vital tooth, there’s no risk of the smear layer harboring microbes or reducing the efficacy of irrigants.
On the contrary, if future contamination occurs (e.g., due to poor coronal sealing), the smear layer may reduce bacterial penetration into dentinal tubules.
Conclusion: In vital cases, do not remove the smear layer.
2. Necrotic/infected cases:
The smear layer may contain microbes and hinder the action of irrigants and medicaments.
In such cases, it should be removed. But when should it be done?
Removing it just before obturation makes little sense, as it may expose surviving microbes to the canal. Instead, it’s more logical to remove it after instrumentation, as part of the final irrigation phase (which may include passive ultrasonic irrigation or a solution like Helling’s cocktail). Also, if treatment is to be completed in two visits, the smear layer should be removed before placing calcium hydroxide.
How to effectively remove the smear layer?
Since it consists of two components—organic and inorganic—we need two agents:
Claims like “EDTA removes the smear layer” are imprecise. EDTA only acts on the inorganic part; it does not dissolve organic matter. Sodium hypochlorite is responsible for that.
An inner layer, extending into the dentinal tubules, called smear plugs, which can reach depths of up to 40 microns (Mader C.L. et al., 1984).
The influence of the smear layer on the success of endodontic treatment has long interested researchers and clinicians. Today, most advocate for its complete removal (White et al., 1975; Mader et al., 1984; White et al., 1987; Lloyd et al., 1995; Khayat & Jahanbin, 2005).
A key argument for removing it is that the smear layer impairs the penetration of sealer and thermoplasticized gutta-percha into dentinal tubules, lateral canals, and apical ramifications (White et al., 1975, 1987; Lloyd et al., 1995). There’s also concern that microbes may survive within the smear layer, protected from irrigants (Berutti et al., 1997).
Unfortunately, few clinicians have taken note of the study by Ørstavik and Haapasalo (1990), which showed that the smear layer delays the action of irrigants and intracanal medicaments on microbes within the dentinal tubules.
Most endodontists recommend removing the smear layer before obturation (filling), primarily to obtain a "clean" radiograph. However, a good two-dimensional X-ray image doesn't necessarily reflect high-quality treatment.
As always, there’s another side to the story. The smear layer greatly reduces dentin permeability (Pashley et al., 1981). Thus, two independent research teams concluded that the smear layer inhibits microbial penetration into dentinal tubules (Love et al., 1996; Peters et al., 2000).
So, clinicians face a dilemma: remove the smear layer or not?
Here’s the author’s personal view, dividing cases into two categories:
1. Vital cases:
When treating a vital tooth, there’s no risk of the smear layer harboring microbes or reducing the efficacy of irrigants.
On the contrary, if future contamination occurs (e.g., due to poor coronal sealing), the smear layer may reduce bacterial penetration into dentinal tubules.
Conclusion: In vital cases, do not remove the smear layer.
2. Necrotic/infected cases:
The smear layer may contain microbes and hinder the action of irrigants and medicaments.
In such cases, it should be removed. But when should it be done?
Removing it just before obturation makes little sense, as it may expose surviving microbes to the canal. Instead, it’s more logical to remove it after instrumentation, as part of the final irrigation phase (which may include passive ultrasonic irrigation or a solution like Helling’s cocktail). Also, if treatment is to be completed in two visits, the smear layer should be removed before placing calcium hydroxide.
How to effectively remove the smear layer?
Since it consists of two components—organic and inorganic—we need two agents:
- An agent to dissolve inorganic debris (hydroxyapatite crystals): EDTA or citric acid.
- An agent to dissolve organic matter (pulp remnants, microbes, collagen): sodium hypochlorite.
Claims like “EDTA removes the smear layer” are imprecise. EDTA only acts on the inorganic part; it does not dissolve organic matter. Sodium hypochlorite is responsible for that.
What is the best sequence?
Given the smear layer's structure—an outer mixed layer and a deeper inorganic-only layer—studies show that the sequence EDTA–NaOCl–EDTA is more effective than NaOCl–EDTA–NaOCl (Abbott et al., 1991).
Irrigation time?
Studies report irrigation times from 30 seconds to 10 minutes (Abbott et al., 1991; Lloyd et al., 1995; Garberoglio & Becce, 1994). A 2005 study compared 1, 3, and 5-minute irrigation in straight canals and found no significant difference (Teixeira et al., 2005).
→ Minimum effective time per solution: 1 minute.
Conclusion: Hopefully, this article has clarified some questions relevant to your daily clinical practice.Таким образом, мы будем использовать 2 вещества. Следующий вопрос, в какой последовательности?
Given the smear layer's structure—an outer mixed layer and a deeper inorganic-only layer—studies show that the sequence EDTA–NaOCl–EDTA is more effective than NaOCl–EDTA–NaOCl (Abbott et al., 1991).
Irrigation time?
Studies report irrigation times from 30 seconds to 10 minutes (Abbott et al., 1991; Lloyd et al., 1995; Garberoglio & Becce, 1994). A 2005 study compared 1, 3, and 5-minute irrigation in straight canals and found no significant difference (Teixeira et al., 2005).
→ Minimum effective time per solution: 1 minute.
Conclusion: Hopefully, this article has clarified some questions relevant to your daily clinical practice.Таким образом, мы будем использовать 2 вещества. Следующий вопрос, в какой последовательности?
