Endodontic materials

L. Han, T. Okiji, Uptake of calcium and silicon released from calcium silicate-based endodontic materials into root canal dentine, Int. Endod. J. 44 (2011) 1081-1087. 

Key words dental biomaterials, resin composites, flowahle composites, endodontic materials, calcium phosphate cements. 

Chlorhexidine initially was used as a general disinfectant because of its broad antibacterial action (9). It was later shown to inhibit dental caries and reduce the formation of dental plaque (10). In vitro inhibition studies have shown chlorhexidine to be effective against species found in infected root canals such as Enterococcus faecalis (11) and Streptococcus mutans (12), and because of this, it was introduced as an endodontic irrigant in the early 1960 s (10). Chlorhexidine is increasingly being incorporated into endodontic materials due to its ability to increase antimicrobial properties and improve prognosis. 

Bottino, M.C., Yassen, G.H., Platt, J.A., Labban, N., Windsor, L.J., Spolnik, K.J., Bressiani, A.H., 2013. A novel three-dimensional scaffold for regenerative endodontics materials and biological characterizations. Journal of Tissue Engineering and Regenerative Medicine, http //dx.doi.org/10.1002/term.1712. 

Leirskar, J. Helgeland, K. (1987). Mechanism of an in vitro toxicity of restorative materials pH, fluoride and zinc. International Endodontic Journal, 20, 246-7. 

Leirskar J, Heigeland K. 1981. Mechanism of toxicity of dental materials. International Endodontic Journal 14 42-48. 

In the last generation endodontic and restorative materials molecules such as 2-hydroxyethylmethacrylate (HEMA), triethyleneglycol dimethacrylate (TEGDMA) and 2,2-bis[4-(2-hydroxy-3-methacryloxy)-phenyl]propane (Bis-GMA) are present. In the clinical use these compounds are chemically or photochemically polymerised and the degree of polymerization - which is never complete - determines the release of some quantity of uncured monomers in the pulpar cavity. Thus, the pulpal tissues can be exposed - through the dentinal diffusion - to these compounds that may cause inflammatory reactions and cellular damage, as confirmed by several reports. ... 

Ma PX, Zhang R, Xiao G, Franceschi R (2001) Engineering new bone tissue in vitro on highly porous poly (alpha-hydroxyl acids)/hydroxylapatite composite scaffolds. J Biomed Mater Res 54 284-293 Macdonald A, Moore BK, Newton CW, Brown CE (1994) Evalrration of an apatite cement as a root end filling material. J Endodontics 20 598-604... 

The structural transformation between austenite and martensite occurs when the mechanical stress attains a certain level, or with an appropriate temperature change, A reversible twinning process takes place at the atomic level, which can result in superelastic behaviour and shape memory [8], The properties of the nickel-titanium endodontic instruments and orthodontic wires depend critically upon the nature and proportions of the NiTi phases in their microstructures, as discussed in the following sections. While X-ray diffraction has been used to study the phases in nickel-titanium endodontic instruments [15,16] and orthodontic wires [7,17,18], this analytical technique is limited to a near-surface region less than 50 pm in depth for metallic materials [19], and study of the phase transformations with temperature is not generally convenient. In contrast, DSC can provide information about the phases present in bulk nickel-titanium endodontic instruments and orthodontic wires with facility, and the effect of temperature changes on the NiTi phase transformations is easily studied. 

Endodontics is concerned with the removal of damaged, diseased or necrotic pulp tissue from root canals of teeth, followed by placement of filling and seeing materials. In current practice, rotary drills in the dental handpiece are commonly used to rapidly enlarge root canals to facilitate subsequent removal of pulp tissue. 

On the other hand, the new material known commercially as Biodentine is much more promising [61,69]. It is a hydraulic cement manufactnred by the French company Septodont and consisting mainly of tricalcinm silicate [70]. In this it resembles the endodontic sealer Mineral Trioxide Aggregate, MTA, thongh it has a different... 

The main material used for obmration of the cleaned and disinfected root canal in contemporary endodontics is gutta percha. This is used because it is plastic and will take up the shape of the root canal when pressed into place [74]. A sealant is used in association with these gutta percha points, and its function is to fill any gaps between the points and the canal walls. This has the effect of improving the quality of the overall seal at the tooth root [73]. 

P. Carotte, Endodontics Part 5. Basic instruments and materials for root canal treatment, Br. Dent. J. 197 (2004) 455 64. 

Alternatively the pulp may be saved by the process of pulp capping. This involves placing some sort of material over the pulp to protect it and maintain its viability so that more extreme treatment (extraction or endodontic therapy) can be avoided [1]. Two possible approaches are available, namely direct pulp capping, in which a bioactive material is placed directly over the exposed pulp, and indirect pulp capping, in which a cavity liner or sealant material is placed over a residual thin layer of dentine, which may be sound or carious. In the latter approach, the pulp has not been exposed, but it is at risk of becoming so either by the progress of the residual caries or by the process of tooth preparation. 

Biodentine is a specific proprietary brand of calcium silicate cement that has been available to the profession since 2009 [20], It is manufactured by Septodont, St Maur des Faussds, France. The material is formulated to set more rapidly than MTA or similar calcium silicate cements, and is produced as a dentine replacement material. It is recommended for pulp capping, and also for various aspects of endodontic repair, including root perforations, apexification and retrograde filling [20],... 

Literature provided by the manufacturers suggests that Biodentine can be used for various applications, not only for pulp capping but also for other endodontic applications, such as repair of pulp chamber floor perforations and of lateral root perforations [95]. It can also be used for indirect pulp capping and to line deep carious lesions. However, to date systanatic smdies are lacking, and there is only limited evidence of clinical success of Biodentine in these applications. Early published results are promising, but more work is necessary before a definitive opinion on this material is possible [95]. 

Materials employed as points are usually fabricated from gutta percha, though other materials have been considered (see Sections 10.2 and 10.3). Materials for sealers may be cements, including acid-base cements, or methacrylate monomer-based materials of the type used in composite resins. However, more commonly in modem endodontics, cements based on tricalcium silicate systems that set by hydration processes are used. This chapter discusses the wide variety of possible materials that can be used for this purpose, with some indication of the clinical effectiveness. 

Gutta percha is the most widely used material for endodontic points, for the reasons already described. However, other materials have been used, of which until recently, silver was the most important [13], and silver points had the advantage of being inherently bactericidal. 

Endodontic points based on synthetic polymers are also available. One relatively new material is supplied as Resilon, manufactured by the Penton Clinical company, USA [15], and comprises a blend of polycaprolactone polymer with small amounts... 

It should be noted in passing that the possibility of using only one of the materials (eg, gutta percha points or sealer paste) has been considered for endodontic therapy [17]. The concept has been called monoblock . However, though it would be advantages in the clinic if it were feasible, it has not proved possible to develop the approach for practical use. Either gutta percha or sealer alone cannot produce a seal of sufficient soundness or durability to give acceptable clinical results. 

The essential features of some of them have already been described in other chapters, and these details are not repeated. Rather, what follows emphasizes the application of these materials as endodontic sealers. 

Zinc oxide-eugenol is a somewhat old-fashioned material, but it is widely used as an endodontic sealer [18]. It has relatively poor mechanical properties, but is easy to use in the dental clinic [19] and outcomes are good, which explains its continuing popularity. When set, it is biocompatible towards dental hard tissues, though it is cytotoxic towards soft tissues [20]. Zinc oxide-eugenol is susceptible to hydrolysis, which causes the material to decompose and release eugenol. It is this latter substance which is responsible for the cement s adverse effects on soft tissues, but which also makes the material bactericidal. 

Overall, despite not having completely ideal properties as sealing materials, zinc oxide-eugenol is an effective material. Its many years of satisfactory clinical service demonstrate this, and outcomes with it are generally good. There is little current research on zinc oxide-eugenol endodontic sealers, bnt this is a reflection on the fact that it is a mature material with a proven track record. It ranains one of the most widely used materials for endodontic sealing [18], and is likely to remain so for the foreseeable future. 

Leakage around calcium hydroxide sealers has been studied experimentally, and findings have generally been satisfactory [34-36]. However, there have been some adverse reports [37], and these variations have been attributed to crucial differences in experimental methods [38]. Leakage appears to be related to both the solubility of the material and the questionable adhesion to both the dentine walls and the gutta percha points. The calcium hydroxide sealer Apexit, for example, was found to have a high solubility when set compared with other types of endodontic sealer [39] and, in some studies, sealer particles have been found to occur with the tissues at a considerable distance from the sample [40,41],... 

The physical properties of calcium hydroxide materials are acceptable for their use as endodontic sealers. They flow well in their unset state, so they can reach and seal the apical foramen of the affected tooth, and also adapt to the shape of any irregularities of the dentinal wall. 

Overall, calcium hydroxide materials appear satisfactory as endodontic sealers in clinical service [47,48], though they are not outstanding in this application [30]. Established brands continue to be made available for practitioners, and clearly find favour with certain members of the profession. They must be... 

Silicone-based endodontic sealers have to be mixed immediately prior to use [62,63], and this is done using a mechanical delivery system that ensures complete mixing of both pastes without the incorporation of air. Also present in one of the pastes is a trace of platinum to act as catalyst for the setting reaction. Setting involves pendant unsaturated groups on one of the polymer chains reacting with a hydrogen atom attached directly to a silicon atom (Fig. 10.4). The reaction results in cross-links between the polysiloxane chains, and these cause the material to set to a resilient rubbery solid [13]. 

Silicone endodontic sealers in their set state are insoluble materials with good dimensional stability [62,63]. They undergo a slight expansion on setting, which... 

Epoxy resin-based materials are available for use as endodontic sealers [64], They set by a ring-opening polymerization reaction between hexamethylene tetratramine (Fig. 10.5), which is part of the powder component, and iiw-phenol resin monomer, which comprises the liquid component [13]. In addition to the reactive molecule, the powder contains bismuth oxide (50%) to impart radiopacity and titanium dioxide (5%) as a pigment. The powder also contains silver particles (10%) to make the set material anti-bacterial. 

Over the years, a number of brands of this type of endodontic sealer have become available [75]. In recent years, there has been considerable interest in two brands, which have been widely studied. These are EndoREZ (Ultradent Products, Utah) and Epiphany (Penton Clinical, Connecticut), though other materials of this type are also discussed in recent publications [76]. The brand Epiphany has been designed specifically to be used in conjunction with the polycaprolactone endodontic points marketed under the brand name Resilon. The good adhesion obtained between the resin and these points has led to the suggestion that this system may be capable of behaving effectively as a monoblock [75], though experimental results do not really support this concept. 

These biological findings suggest that these resin-based endodontic sealers are acceptable for clinical use, a result that has been confirmed by clinical evaluations [86-88]. In one 5-year smdy involving 129 patients, results showed that root canals were adequately filled in 76.66% of cases (92) and were short in 10.83% (13) of cases. In 15 cases (12.50%), there was evidence of slight resorption of the sealer at the apex within the lumen of the root canal. These clinical results show that resin-based sealers compare well with sealers based on other types of material, and that they are satisfactory for use in endodontics [48,89],... 

MTA has a wide variety of clinical uses within endodontics. The main one is a root-end filling material [116-120], but it is also used for pulp capping, pulpotomy and to repair lateral root perforations [121-125]. It can be used for apical barrier formation in teeth with open apexes [126], Its relatively long setting time may be a disadvantage, but this has been addressed in related products such as Biodentine by the inclusion of calcium chloride as an accelerator. 

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