The smear layer in endodontics – a review

Root canal instrumentation produces a layer of organic and inorganic material called the smear layer that may also contain bacteria and their by-products. It can prevent the penetration of intracanal medicaments into dentinal tubules and influence the adaptation of filling materials to canal walls. This article provides an overview of the smear layer, focusing on its relevance to endodontics. The PubMed database was used initially; the reference list for smear layer featured 1277 articles, and for both smear layer dentine and smear layer root canal revealed 1455 publications. Smear layer endodontics disclosed 408 papers. A forward search was undertaken on selected articles and using some author names. Potentially relevant material was also sought in contemporary endodontic texts, whilst older books revealed historic information and primary research not found electronically, such that this paper does not represent a 'classical' review. Data obtained suggests that smear layer removal should enhance canal disinfection. Current methods of smear removal include chemical, ultrasonic and laser techniques – none of which are totally effective throughout the length of all canals or are universally accepted. If smear is to be removed, the method of choice seems to be the alternate use of ethylenediaminetetraacetic acid and sodium hypochlorite solutions. Conflict remains regarding the removal of the smear layer before filling root canals, with investigations required to determine the role of the smear layer in the outcomes of root canal treatment.     

The use of glass ionomer cements in both conventional and surgical endodontics

The capacity to bond to dental tissues, especially to dentine, their long-term fluoride release and their biocompatibility make glass ionomer cements (GICs) advantageous for use in endodontics, as well as in restorative dentistry. This review provides information on the basic properties of GICs, such as adhesion, antimicrobial effects and biocompatibility, particularly as they relate to use in endodontics. Indications for the use of GICs in endodontics are orthograde root canal sealing, root-end filling, repair of perforations and root resorption defects, treatment of vertical fractures and maintenance of the coronal seal. The paper includes a review on each of these indications. It is concluded that in spite of the critical handling characteristics and the inconclusive findings regarding sealing ability and antimicrobial activity, there is substantial evidence to confirm their satisfactory clinical performance. Both soft tissue and bone compatibility make them suitable for use during endodontic surgery.     

一种新的根管冲洗剂——MTAD

与器械预备相伴的根管冲洗是根管预备过程的重要环节,冲洗液应当能够溶解坏死组织,有消毒杀菌作用,并且能够去除玷污层.本文将介绍一种新的根管冲洗剂--MTAD.MTAD是强力霉素、柠檬酸和清洁剂的混合物,它能有效去除玷污层,抗微生物作用强,细胞毒性小,临床使用安全.     

Ultrasonics in endodontics: a review of the literature

During the past few decades endodontic treatment has benefited from the development of new techniques and equipment, which have improved outcome and predictability. Important attributes such as the operating microscope and ultrasonics (US) have found indispensable applications in a number of dental procedures in periodontology, to a much lesser extent in restorative dentistry, while being very prominently used in endodontics. US in endodontics has enhanced the quality of treatment and represents an important adjunct in the treatment of difficult cases. Since its introduction, US has become increasingly more useful in applications such as gaining access to canal openings, cleaning and shaping, obturation of root canals, removal of intracanal materials and obstructions, and endodontic surgery. This comprehensive review of the literature aims at presenting the numerous uses of US in clinical endodontics and emphasizes the broad applications in a modern-day endodontic practice.     

The use of ultrasound for the removal of the smear layer. The effect of sodium hypochlorite concentration; SEM study

This study was carried out to determine the optimum concentration of sodium hypochlorite activated by ultrasound needed to remove the smear layer from an instrumented root canal wall. The results indicated that under the conditions of this experiment a 4 per cent solution of sodium hypochlorite removed all of the smear layer from all 5 specimens; a 2 per cent solution was almost as effective; 1 per cent or 1/2 per cent solutions were less effective, and water was the least effective. A 2 per cent solution of sodium hypochlorite activated by ultrasound would appear to be the optimum concentration for the production of a smear free root canal wall under clinical conditions.     

激光活化荡洗在根管治疗中的作用

根管清理和感染控制是根管治疗的两个重要步骤。在根管内细菌以生物膜的形式存在,其可隐藏在根管峡部、根尖分歧、根尖分叉、侧枝根管等复杂的解剖结构中;同时,在根管预备过程中可产生玷污层,玷污层能为细菌的生长繁殖提供基质,其也可附着于上述复杂的解剖结构中。由于根管系统的复杂性,难以通过常规的冲洗消毒方法彻底清除菌斑生物膜,近年来激光作为一种新型的辅助冲洗消毒的工具逐渐应用于临床,最为常用的是铒激光（Er∶YAG和Er,Cr∶YSGG激光）,研究报道激光辅助根管荡洗可有效去除玷污层并清除根管内的感染,从而获得更好的消毒效果。文章就激光活化荡洗在根管治疗中的作用做一概述。     

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??Root canal debridement and infection control are two of the main steps in root canal therapy. Bacteria will be present as biofilm colonies inside the root canal??and it will be well within fins??intercanal anastomoses??apical ramification??apical furcation or lateral accessory canal. Meanwhile??during the cleaning and shaping process??smear layer can be produced??which can be used for the viable bacteria inside the complex anatomical structure to sustain growth and activity. In addition??due to the complexity of the root canal system??the conventional irrigation and disinfection technology is superficial??then the smear layer and Enterococcus faecalis biofilms are difficult to remove. In recent years??lasers??as a novel adjuncting irrigation tool??are used clinically??such as Er??YAG laser and Er??Cr??YSGG laser. As is reported??laser-activated irrigations can effectively remove the smear layer and the infection and obtain better disinfection rates. So in this a review??we made a summary of the effect of laser-activated irrigations on endodontics.     

A survey of self-perceived educational needs of general dental practitioners in the Merseyside region.

AIM: The aim of this study was to evaluate the self-perceived educational needs of a randomly selected group of general dental practitioners (GDPs) in the Merseyside region (UK). MATERIALS AND METHODS: Eighty-seven GDPs were randomly selected from 850 in the region and asked to complete a self-evaluation questionnaire regarding their self-perceived educational needs. RESULTS: Seventy-five (86%) responded, of which 52 (69.3%) were male and 23 (30.7%) female. There was no significant difference in self-perceived knowledge in any of the dental disciplines when gender and period of time since qualification were used as predictor variables. The majority of the GDPs felt they had a good knowledge of restorative dentistry and dental radiography. Some of the GDPs felt they had poor knowledge in implant dentistry, oral medicine, orthodontics, dental sedation techniques, oral surgery, endodontics, periodontics and dental radiography. None of the respondents felt they had poor knowledge in restorative dentistry, prosthodontics and paediatric dentistry. Seventy-four (98.7%) of the responding GDPs were motivated to attend continuing professional development (CPD) courses because of an interest in a particular dental discipline and only one reported attending out of personal learning needs. Implant dentistry was indicated by 30 (40.0%) of the respondents as their training programme of choice. CONCLUSIONS: The respondents had high self-perceived knowledge of restorative dentistry, dental radiography, periodontics, endodontics, paediatric dentistry and prosthodontics. The respondents had low self-perceived knowledge of implant dentistry, orthodontics, oral medicine and dental sedation techniques. Of GDPs surveyed, 98.7% applied for courses they liked to attend, rather than needed to attend. Fifty-two per cent of male GDPs surveyed expressed a desire for training in implant dentistry.     

Microporous, demineralized collagen matrices in intact radicular dentin created by commonly used calcium-depleting endodontic irrigants

The use of calcium-depleting solutions in restorative dentistry results in demineralization of intact coronal dentin beneath smear layers. Likewise, application of calcium-depleting irrigants as final rinses might create demineralized collagen matrices in intact radicular dentin after removal of root canal wall smear layers created during canal shaping. These unsupported collagen matrices collapse on desiccation and might be difficult to detect in scanning electron microscopy dehydration techniques traditionally used in endodontic research. Demineralized collagen matrices were identified, by using a hexamethyldisilazane dehydration protocol, on the surface of smear layer-depleted radicular dentin when NaOCl was used as initial rinse, followed by the use of 17% ethylenediaminetetraacetic acid or BioPure MTAD as the final rinse. Compaction of conventional root filling materials over a demineralized collagen matrix in instrumented dentin is analogous to performing the same procedure against the predentin collagen network in the uninstrumented parts of root canals. The potential consequences of this process are, however, unknown.     

Irrigation: beyond the smear layer

Traditionally, much of the attention placed on irrigation in endodontics has focused on smear layer removal. While the smear layer continues to be a relevant topic, other areas related to irrigation and irrigants have emerged that also require a more in‐depth analysis and understanding. This review starts with the smear layer, partially from a new angle, and expands into other topics such as uninstrumented root canal areas, and effect of irrigation in lateral canals and dentin canals. Advanced microbiological models for irrigation research will be presented and discussed. The effect of sodium hypochlorite and decalcifying solutions on dentin structure and dentin strength has become an important topic, which is related to the possible harmful effects of irrigation such as dentin erosion and even vertical root fracture. The impact of irrigant sequence and time of exposure will also be discussed, and recommendations for irrigation protocols will be made.     

Sealing root canals with low-viscosity resins in vitro: a scanning electron microscopy study of canal cleansing and resin adaption

Low-viscosity resins of the fissure sealant type have been suggested in the literature as having potential for use as root canal filling materials. A low-viscosity resin may seal a root canal by flowing into clean dentinal tubules after smear layer removal. This investigation with scanning electron microscopy examines the efficacy of two methods of root canal preparation and the effectiveness of different chemicals on smear layer removal. Ultrasonic preparation with 0.25% sodium hypochlorite solution and final agitation with 50% citric acid solution were found to produce a very clean canal wall, free of smear layer in coronal and middle parts. However, low-viscosity resin used in conditions that aimed to simulate in vivo conditions failed to penetrate open dentinal tubules to a significant extent. On the basis of these observations made with scanning electron microscopy, low-viscosity resins would not seem suitable as root canal filling materials, because they are unlikely to form a satisfactory adaption to the canal wall. In addition, if treatment fails, these resins are impossible to remove from a root canal without much destruction of tooth substance.     

The use of ultrasound and an EDTA-urea peroxide compound in the cleansing of root canals. An SEM study

Abstract — Thirty-two human teeth with constricted root canals were prepared using an EDTA-urea peroxide compound as an aid to root canal instrumentation. A final irrigation of 3 per cent sodium hypochlorite with up to five minutes of indirect ultrasound was not sufficient to remove the debris and smear layer from the canal wall when viewed under the scanning electron microscope. It was suggested that the wax-like smear layer could have clinical benefits and required further investigation.     

Adhesive dentistry and endodontics. Part 2: bonding in the root canal system-the promise and the problems: a review

One of the recent trends in endodontics has been the development of bonded obturating materials, in an effort to provide a more effective seal coronally and apically. Materials utilizing dentin adhesive technology have been borrowed from restorative dentistry and adapted to obturating materials. This review discusses the obstacles to effective bonding in the root canal system, the progress that has been made, and possible strategies for improved materials in the future. Much of the literature reviewed and many of the principles discussed are taken from the restorative dentistry literature and applied to the unique environment of the root canal system.     

Photodynamic therapy: An adjunct to conventional root canal disinfection strategies

Although chemical‐based root canal disinfectants are important to reduce microbial loads and remove infected smear layer from root dentin, they have only a limited ability to eliminate biofilm bacteria, especially from root complexities. This paper explores the novel photodynamic therapy (PDT) for antimicrobial disinfection of root canals. The combination of an effective photosensitizer, the appropriate wavelength of light and ambient oxygen is the key factor in PDT. PDT uses a specific wavelength of light to activate a non‐toxic dye (photosensitizer), leading to the formation of reactive oxygen species. These reactive oxygen molecules can damage bacterial proteins, membrane lipids and nucleic acids, which promote bacterial cell death. In, addition PDT may enhance cross‐linking of collagen fibrils in the dentin matrix and thereby improving dentin stability. The concept of PDT is plausible and could foster new therapy concepts for endodontics. The available knowledge should enable and encourage steps forward into more clinical‐oriented research and development. This article discusses PDT as related to root canal disinfection, including its components, mechanism of action, reviews the current endodontic literature and also highlights the shortcomings and advancements in PDT techniques.     

Root canal irrigation--a historical perspective

The concept of the germ theory of disease combined with the development of dentistry during the latter half of the 19th century had a direct effect on the practice of endodontics. The significance of root canal irrigation to endodontics strengthened in the period between 1859 when Taft recommended frequent syringing of the root canal to remove "irritants" until the mid-1940s when endodontics became a special field within dentistry and the American Endodontic Society was established. This paper reviews the role of irrigants and irrigation in root canal treatment during this period. A variety of recommendations on the use of solutions to clean root canals appeared in the dental literature, often innovative and at times entrepreneurial, but invariably empirically based. While it was widely assumed that by wiping the root canal with disinfectants sterilization would be achieved, many of the principles associated with cleaning the root canal published during this period, in particular by Willoughby Dayton Miller in the 1890s and Louis Grossman in the 1940s, remain equally relevant in the 21st century.     

Current clinical applications of photo-activated disinfection in restorative dentistry

The traditional treatment of dental caries has been limited to bulk removal of the diseased tissue. Recently, disinfection rather than the removal of all the carious tissue has been advocated with the aim of more effective and conservative treatment. In endodontics, prognosis is dependent on the complete disinfection of the root canal system. Evidence exists that Photo-Activated Disinfection is more effective than traditional chemo-mechanical canal preparation. Photo-Activated Disinfection may also have a place in the treatment of other infective oral conditions, including periodontal disease. CLINICAL RELEVANCE: Removal or disruption of micro-organisms and their ecosystem is important in many branches of restorative dentistry. A novel disinfection system is now available which has the potential to improve treatment methods and prognoses.     

The controlled placement and delayed polymerization technique for the direct Class 2 posterior composite restoration

Adhesion dentistry and its application to the direct posterior composite restoration is the most controversial topic in dentistry today. The concepts behind this procedure are now the backbone of restorative dentistry. Adhesion dentistry influences basic fillings, crown buildups, post-and-core restorations, cementation, orthodontics, and endodontics. Yet, controversy remains about the correct way to place a direct Class 2 posterior composite restoration. This article will examine the scientific evidence to determine which materials and placement techniques will achieve the optimum direct Class 2 posterior composite restoration at or below the cementoenamel junction using the controlled placement and delayed polymerization technique.     

Review of ultrasonic irrigation in endodontics: increasing action of irrigating solutions

Introduction: Effective irrigant delivery and agitation are prerequisites for successful endodontic treatment. Ultrasonic irrigation can be performed with or without simultaneous ultrasonic instrumentation. Existing literature reveals that ultrasonic irrigation may have a very positive effect on chemical, biological and physical debridement of the root canal system as investigated in many in vitro studies. Objective: The purpose of this review article was to summarize and discuss the available information concerning ultrasonic irrigation in endodontics. Methods: This article presents an overview of ultrasonic irrigation methods and their debridement efficacy. In this paper the relevant literature on passive ultrasonic irrigation is reviewed. Information from original scientific papers or reviews listed in MEDLINE and Cochrane were included in the review. Results: The use of ultrasound in the irrigation procedure results in improved canal cleanliness, better irrigant transfer to the canal system, soft tissue debridement, and removal of smear layer and bacteria. There are many in vitro studies, but there is a need to standardize protocols, and correlate the clinical efficacy of ultrasonic devices with improved treatment outcomes. Understanding the basis of ultrasonic irrigation is fundamental for clinicians and researchers to improve the design and use of ultrasonic irrigation. Key words:Ultrasonic irrigation, ultrasound, smear layer, endodontics.     

Evaluation and clinical management of previous endodontic therapy

Endodontic recall studies and clinical experience have resulted in more universal criteria for acceptable and unacceptable endodontic treatment. Before the initiation of restorative treatment on teeth previously treated endodontically, the prosthodontist should evaluate the quality of endodontic treatment to assure that it will provide a risk-free, permanent, solid foundation for the future restorative work. Lack of symptoms alone does not indicate success of endodontic treatment. Radiographic evaluation is also not sufficient. The prosthodontist should use a thorough and combined evaluation of the endodontic history, radiographic evaluation, and tooth and tissue examination, as well as physically assess the treatment of all canals and their seals. As a rule, endodontics of questionable quality should be retreated by way of the canal. The removal of defective restorations is done to facilitate the retreatment effort and assure the soundness of tooth structure. Following retreatment, the tooth is restored and healing of the patient is followed up.Surgical endodontics is avoided unless retreatment is first attempted or the quality of previous root canal therapy is acceptable or the canal obstructed.     

超声冲洗在根管治疗术中应用

超声冲洗在根管治疗术中的应用越来越多。超声工作尖震动使冲洗剂产生空穴作用和声流作用,所产生的剪切力可清除根管壁上的牙本质碎屑及生物物质。镍钛工作尖能更好地顺应根管解剖形态。工作尖为光滑或K锉形态对牙本质碎屑和玷污层的清洁效果无明显区别。超声冲洗能更好地清除根管内的细菌、玷污层和牙本质碎屑等,并对根管内的复杂结构有更强的清洁效果。超声冲洗选用次氯酸钠为冲洗剂可取得良好效果。冲洗液的使用量较其浓度更为重要,间断冲洗比连续冲洗更有效。超声工作尖插入的方向和深度亦会对冲洗效果产生影响。现从超声冲洗的作用机制、仪器设备、冲洗效果和影响因素等方面做一总结,以指导临床实践。