Chapter 13 Materials used in endodontics
Endodontology is the branch of dental science concerned with the form, function, health, trauma and disease of the dental pulp. Endodontics is the practice of endodontology. Many patients will report that they have had root treatment, which is a misleading term. The correct technical term is root canal therapy (RCT), which more accurately describes the process, i.e. of cleaning and filling all of the root canals in the tooth. The term root filling is often used synonymously with root canal therapy but this only refers to the material that is used to fill the root canal system.
It must be emphasized at the outset that the dental team’s primary objective should be to preserve the vitality of the tooth. Endodontic procedures should only become necessary if, despite best efforts, the pulp has become irreversibly compromised and requires partial or full removal.
The objective of successful root canal therapy is to access the entire root canal system, and thoroughly remove any necrotic (dead) tissue and microorganisms by canal preparation. This preparation involves cleaning and shaping the canals to facilitate the subsequent obturation (filling) of the dead space. It is critical that a coronal seal is then gained and maintained to prevent subsequent reinfection of the root canal system by oral microorganisms. Should this seal become compromised, the treatment is likely to fail, so underlining the importance of this final stage.
Reasons for use
The battle in endodontics is against the bacterial infection. To achieve a sterile root canal system the tooth should be isolated to prevent contamination with oral bacteria. The only predictable and effective method is the use of rubber dam, which is also referred to as dental dam (see Figures 13.1B, 13.2 and 13.4 below). The benefits of using rubber dam in relation to endodontics include:
As well as being used in endodontics, rubber dam also has many applications in general operative dentistry, particularly when the dentist is using hydrophobic materials, hence the many references to it in this text.
The rubber dam system
The rubber dam system consists of a sheet of an elastic material held taut over a frame. Some products have a frame incorporated in them, e.g. OptraDam (Ivoclar Vivadent). A hole or holes are punched into the sheet corresponding to the teeth that need to be isolated. The dam is retained by the use of a clamp or clamps or stabilizing cord such as Wedjets (Hygienic) (Figure 13.1).
Types and presentation of rubber dam
Rubber dam is available in latex and non-latex (elastic plastomer or polyolefin) presentations (Figure 13.2 and Table 13.1). It should be noted that the words ‘rubber’ and ‘dental’ in relation to dam are used synonymously although the elastic plastomers and polyolefins are polymers.
Rubber dam is either presented in precut squares of material (Figure 13.2) or in rolls where the dentist cuts off the desired amount. Different sheet thicknesses are available, the thicker sheets may be more difficult to place but they have a greater tear resistance and will retract the tissues more. Products are also available in different colours. Darker colours contrast with the operative site better so decreasing eye strain. Lighter shades, however, can naturally illuminate the area due to their greater translucency. Some products are supplied flavoured or scented in an attempt to improve the patient’s experience.
Rubber dam sealers
When rubber dam is placed for endodontics, it is advisable to create a seal around the dam using a caulk material. This prevents irrigants reaching the mouth and equally prevents saliva from leaking back into the operating field. The caulk material used is hectorite clay, which belongs to a group of materials called smectitec clays. In these materials platelets of a metal oxide are sandwiched between plates of silicon dioxide. This layered structure allows the clays to swell in contact with water. The metallic oxide in hectorite clay is magnesium (Figure 13.3). On taking up water the clay will expand to up to 35 times its original size effectively sealing any gaps adjacent to the dam.
(Photo courtesy of Elementist.)
The aim of root canal preparation is to remove as many of the microorganisms as possible and to shape the root canal to facilitate its subsequent obturation (filling) with an inert material. Effective cleaning of the complex root canal system requires using both mechanical and chemical means. Metal files are used to remove necrotic material from the lumen of the canals and also to remove hard tissue from the canal walls. It also removes the microorganisms that have penetrated the dentinal tubules in the canal walls. This process also facilitates the penetration of disinfecting agents so they can reach the bacteria in the root canal system.
Additionally files shape the root canals to provide a uniform-sized dead space, which may be filled using standard-sized cones of plastic material. This is not easy as the root canal system is complex (unlike a chimney!) and the internal anatomy is more akin to a three-dimensional spider’s web of major and minor canals within a network. It is therefore impossible to completely prepare the whole root canal system and the obturating material must be able to be adapted to the root canal walls to achieve a seal.
File preparation of root canals is done either by hand or using rotary files in a speed-reducing, torque-controlled handpiece (Figure 13.5). Rotary systems are much more efficient than those used by hand; however, hand files may be preferred to negotiate very curved root canals as rotary instruments may not be able to get round the curve due to lack of sufficient flexibility. The file may also break (separate) during use. The sharper the curve of the canal, the greater the incidence of fracture of the file due to cyclic fatigue.
Fracture may also occur due to flexural fatigue (i.e. overuse) or torsional fatigue, that is, forces placed on the instrument in rotation while the instrument is prevented from moving. The use of a torque controller is important so that the rotation of the file is stopped prior to receiving excessive torque, which may cause fracture. For further information on speed-reducing handpieces and torque, see Chapter 19. From this brief description, it can be seen that the selection of the material of which the file is made and its method of construction is critical in determining the performance of the instrument.
Anatomy of endodontic files
Hand and rotary files both have a cutting edge along the length of the file and at the other end is either a handle or an attachment that fits into the handpiece, respectively (Figure 13.6). The instrument cuts when its radial lands are in contact with the canal wall, the lead angle determining its cutting efficiency. Radial land areas are required for conventional helically fluted files because they prevent the file from over-engagement in the canal (Figure 13.7). Lack of radial land areas reduces friction. If a file becomes suddenly engaged or self-threaded, it may fracture. Radial lands are especially important for files that have positive rake angles. That is, the angle of action of the cutting blade is similar to a snow plough which is forced downward towards the surface of the road. Many files are designed so that the radial lands cannot screw themselves into the canal wall. Thus, the dentinal debris is directed towards the coronal part of the canal so that it is not compacted apically.
Fig. 13.6 The parts of (A) hand and (B) rotary files. The silicone stop is used as a measuring device: the required canal length is measured and the silicone stop is placed at this same distance measured from the tip of the file.
There are many different types of file available. For the clinician’s convenience and from a quality-control perspective, files are standardized according to their physical properties and dimensions (i.e. diameter and taper). To indicate the increase from one instrument size to the next, these are often numbered and colour coded. Files are available in a range of different shapes, tapers, lengths, cutting or non-cutting tips, safe edged (only cutting on one side). The material of which they are constructed is either stainless steel or nickel-titanium.
Stainless steel files
The traditional material used in the construction of endodontic files is stainless steel. This is an alloy of iron, carbon and chromium. Nickel may also be present. Originally steel was made by forming an alloy of carbon and iron. This was known as carbon steel. This alloy was prone to rusting in the presence of water, but the addition of a percentage of chromium was seen to prevent this rusting. Normally between 13% and 26% of a stainless steel alloy is chromium. The chromium forms a passivation layer of chromium oxide on the surface when exposed to air. This thin layer is not visible but preserves the steel from rust. If scratched, the oxide layer will rapidly re-form, preventing degradation.
Endodontic instruments are manufactured by machining stainless steel wire into a blank of the desired shape (for example either square or triangular in cross-section). This is then twisted into a spiral. During the twisting the material becomes work hardened. The greater the number of twists, the greater the work hardening. The other means of producing the instruments is by directly machining of the shape from a stainless steel rod into the final shape. This machining process also work hardens the material.
Work hardening: is the strengthening of a metal by plastic deformation. This strengthening occurs because the crystal structure of the material is dislocated by the movement. Any material with a fairly high melting point such as metals and alloys can be strengthened using this technique. Alloys such as low-carbon steel and stainless steel which are not amenable to heat treatment are often work hardened.
Particularly with larger sizes, stainless steel files do not bend easily and in order to maintain the canal shape which is invariably a curve, the clinician should bend or precurve the file prior to its introduction to the canal. It should be remembered that bending the instrument will further work harden the metal and make it more brittle. This can lead to fracture.
The mechanical properties of the file will depend on the composition of the material, the geometry of the file and the way in which it is loaded. Anticlockwise twisting of a file is inadvisable as this increasing the twisting of the file, which may result in brittle fracture. Files should therefore not be stressed in this way and definitely not when they are bound in the canal. Some irrigants such as sodium hypochlorite and ethylene diamine tetra-acetic acid (EDTA) can reduce the cutting ability of stainless steel files and so they should be rinsed immediately after use. The risk of this occurring has been substantially reduced as the current recommendation is that files should only be used once and discarded. However, if canal preparation is extended over a long period of time at one appointment, prolonged immersion of these instruments in these solutions in the canal will start the process of degradation.
All files should be regularly inspected for damage after their removal from a root canal. If any damage is seen then the file should be discarded and a new file used. Continued use of a stressed instrument (Figure 13.8) has a high risk of instrument separation with the fractured fragment being retained in the root canal system. If the file cannot be removed, or the canal negotiated beyond it, the success of the treatment will be compromised. Unfortunately, fracture of files can also occur without any visible signs of previous permanent deformation. In order to minimize file breakage, files should only be used in a wet canal and in accordance with the manufacturer’s instructions.
Debris retained on an endodontic file after use is called swarf. It may contain neural tissue with prions, which are theoretically associated with new-variant Creutzfeldt–Jakob disease (nvCJD). Prions are proteins that cannot be destroyed by the usual methods of surgical disinfection. Endodontic files should therefore be considered as single use (to be used only on the same patient) and then discarded. The other advantage of the single use policy is that instrument separation fracture is decreased as the file is used less. Furthermore, autoclaving can decrease the cutting ability of some files and may result in metal fatigue.
Types of stainless steel file
An alloy which has been more recently used to produce endodontic files is nickel-titanium (NiTi). This material is extremely flexible (Figure 13.10), some 500% more than stainless steel and has been termed super-elastic. This means that it is more likely to maintain the canal shape during preparation as it can memorize its original shape. It is also less likely to straighten curved canals as occurs with stainless steel. With nickel-titanium instruments, after a finite number of rotations cyclic fatigue leads to failure. However, they are three times stronger and have a superior resistance to torsional fracture compared with the equivalent stainless steel file. They are also corrosion resistant. It is the alloy of choice for rotary systems although hand files are also available (Figure 13.6).
When the alloy is stressed during use, its structure changes from an austenitic crystalline structure to a martensitic crystalline structure. This happens progressively and as a result the stress on the file reduces even though the strain may be increased. The modulus of elasticity is much higher for an austenitic structure than for the martensitic form, meaning that the latter state is more brittle than the former. When the stress on the alloy decreases, spring back occurs without permanent deformation and the alloy returns to the austenitic phase. This allows an 8% strain deformation with complete recovery compared with less than 1% with stainless steel.
The nature of this alloy dictates that to make a file, the desired shape must be machined out of the blank rather than just twisting a blank before grinding the cutting pattern into it. The production costs are thus increased as this process is more complicated than merely twisting the blank as with stainless steel instruments.
Commercially available products
There are so many files and file systems available to the endodontist these days that to list even a small selection would be prohibitive from a space perspective! Many systems have various nuances which may appeal to various operators. Practitioners are therefore advised to select the file system which they find most effective and are comfortable using. They should use the instruments within the principles of their recommended usage and should consult the manufacturer’s instructions prior to clinical use. Comprehensive lists of files and file systems are available from companies manufacturing or distributing them.
Root Canal Disinfection
Successful outcome of the treatment is dependent on the removal of microorganisms from the root canal system. Studies have shown that root canals free of infection at the time of obturation have a higher success rate, whereas residual bacteria retained in the canal at the time of obturation leads to a higher risk of failure. The dentist has a number of medicaments available to achieve this objective. Irrigants are used during root canal preparation. Other novel antibacterial systems that are now available include ozone and bacterial photo-dynamic therapy, which may also be used at this stage. Root canals may be dressed with antibacterial inter-visit intracanal medications if the procedure is to be carried out over more than one appointment.
• Contain any dentinal shavings in suspension, so facilitating their removal from the canals. This prevents impaction of debris in the apical portion of the canal which may prove difficult to renegotiate due to the blockage
• Disinfect the canal system: mechanical root canal preparation alone is ineffective at microbial removal. It is essential that solutions used during root canal preparation can disinfect the root canal system.
Biofilm and smear layer
Bacteria colonize not only on the necrotic material in the lumen of the root canal but also infect its walls. Microorganisms can penetrate into the dentinal tubules as well as forming complex, highly developed ecologies on the surface of the canal wall. This has been termed a biofilm. In order to kill these organisms the biofilm must be disrupted and penetrated. Furthermore, during instrumentation organic material is left behind on the dentinal surface, termed the smear layer, which must also be removed to allow the disinfectant to gain access to lateral canals (Figure 13.11). If this is achieved, then the disinfection process will be enhanced.
(From Pathways to the Pulp, 8th edition, Cohen and Burns, p. 306, Mosby.)
The removal of the smear layer (and so opening of the dentinal tubules) is achieved primarily by using chelating agents such as citric acid or EDTA. These also have some benefit in disrupting the biofilm but they are ineffective at killing bacteria. Disruption of the biofilm may be achieved, albeit slowly, by using sodium hypochlorite, which will break up proteinaceous material. The action of a chelating agent also provides a cleaner surface against which the final filling materials will adapt.
Irrigants for cleaning
Citric acid is a chelating agent that removes calcified tissue. It was first used in dentistry as a surface cleaner in conjunction with glass ionomer cements to prepare the tooth surface for bonding to these materials. It has been reported to successfully remove the proteinaceous material on the surface of dentine, allowing an interaction between the cement and the clean dentine surface. It is also effective as a decalcifying agent. It is used in solution at a concentration of 10–12.5%.
EDTA may also be used as a chelating agent as an alterative to citric acid, its action being more aggressive. It is used as either a synthetic amino acid or sodium salt of EDTA and is highly effective at removing the smear layer and emulsifying soft tissue. EDTA demineralizes and softens root canal wall dentine by 20–50 μm. Although it is neither bactericidal nor bacteriostatic, EDTA-containing compounds (Figure 13.12) will eventually kill bacteria by starving them of the metallic ions needed for growth as the chemical chelates the ions. It is non-toxic and non-corrosive to instruments.
EDTA is normally used in solution at a concentration of 15–17%. Products available include Endo-Solution EDTA (Cerkamed Dental-Medical Company). Alternatively, in the UK, a dentist can request a pharmacist to make up the required concentration by writing a prescription.
EDTA is used in liquid form for endodontic irrigation but is also available in gel form (Figure 13.13). These products are used to coat endodontic files. They act as lubricants as well as helping to remove smear when the file is used within the root canal, making canal preparation easier and faster. The increased viscosity of this presentation is better for holding debris in suspension.
Some products contain carbamide or urea peroxide, which effervesce during use, resulting in an ‘elevator action’ that helps to remove debris from the root canal system, so optimizing cleaning. Effervescence is caused by release of oxygen, which occurs when the product comes into contact with sodium hypochlorite solution. The release of oxygen may also kill anaerobic bacteria.
Commercially available products
• Chelating materials should be thoroughly washed from the root canal system as their retention for any length of time will continue to soften the dentine. This effect is eventually self-limiting as the chelator is used up. For best results, these irrigants should:
Irrigants for disinfection
Many disinfecting agents have been used for endodontic irrigation over the years. These include halogenated compounds such as sodium hypochlorite, iodine potassium iodide, chlorhexidine and a number of potent phenolic disinfecting agents. There is a significant problem with many disinfectants where the concentrations producing effective bactericidal activity are close to those concentrations where tissue toxicity has been reported.
Sodium hypochlorite solution
Of the disinfectants now commonly used, sodium hypochlorite (bleach) solution is preferred by the majority of endodontists. It is a potent organic tissue solvent that is proteolytic and dissolves necrotic organic material. It releases free chlorine, a powerful disinfecting agent which has a wide spectrum of bactericidal effects, so disinfecting the area of application. It is the chlorine that breaks down tissue and proteins into amino acids. These amino acids are then degraded by hydrolysis through the production of chloramine molecules. This is an oxidation reaction with the bleach. The bleach pH can be in excess of 11 and it has no effect on the calcium deposits in the smear layer.
Since the disinfecting component is consumed, i.e. it breaks down during use, the solution must be constantly replaced otherwise it will lose its efficacy. Some workers advocate constant washing of the root canal system for at least 30 minutes for the solution to be effective. This substantial dwell time is also desirable to ensure that the biofilm structure which the bacteria inhabit is disrupted allowing the disinfectant to effectively reach the bacteria. Current canal preparation techniques especially using rotary instrumentation are very efficient and canals may be prepared in no time at all. It is important that the clinician continues to flush the canal long after canal preparation has ceased for this disinfectant to be effective.
The therapeutic and toxic concentrations of sodium hypochlorite are undesirably close together. There is no difference in the antibacterial effect between 0.5% and 5% solutions but the efficiency of weak solutions decreases rapidly. A solution with concentration greater than 1% is required for pulpal tissue dissolution to occur. However, at higher concentrations, although the disinfecting process is faster, it is more likely that untoward tissue damage will occur as the chemical is more toxic at these concentrations. This is especially the case if the chemical is inadvertently extruded outwith the root canal system.
A further problem with sodium hypochlorite is that it has a higher surface tension than water. It does not wet the root canal walls as well as some other disinfecting solutions. This results in the canal walls being incompletely covered, and consequently the biofilm layer may not be disrupted effectively. This is more likely at higher concentrations as the solution is thicker.
The effects of the solution are increased if the solution is warmed prior to use as more chlorine is released as the temperature increases. Most dentists use a solution of 1% which presents a balance between effective disinfection and toxicity. The solution should be warmed just as it is about to be used.
Sodium hypochlorite is not totally effective at killing all the microorganisms found in the root canal system. Pathogens such as Enterococcus faecalis have been isolated from root canals which have been previously treated with this solution.
As its active ingredient is the chloride ion, sodium hypochlorite is a bleaching agent. It will damage clothes if it comes into contact with them so it is advisable that the patient’s clothes are adequately protected during treatment. It also has an unpleasant taste and is an irritant to the eyes, skin and oral mucosa. The patient and dental team’s eyes should be covered and rubber dam should be placed and sealed during treatment. This bleach effect is of course an advantage when the solution is used in the root canal system as it will lighten any stained tooth tissue. When a tooth loses its vitality, staining happens not infrequently due to the breakdown of blood products (iron from haemoglobin) and these molecules may penetrate into the dentinal tubules.
• Commercial sodium hypochlorite endodontic irrigant products include Parcan Solution (Septodont), which is a 3% solution, or Chlorax (which is available as a 2% or 5.25% sodium hypochlorite solution from Cerkamed Dental-Medical Company). It can also be obtained from a pharmacy. The advantage of using these products is that they do not have to be made up at the chairside and they are buffered. Buffering maintains the solution’s properties throughout its shelf-life and extends this time. There are also products containing other chemicals to enhance the effect of the solution. For example, Chlor-Xtra (Vista) is a combination of sodium hypochlorite and Triton-X. This latter chemical is a surfactant that lowers the viscosity of the irrigant so improving its penetration in the dentinal tubules and narrow canals.
• An alternative is household bleach bought from a supermarket. This is usually supplied as a 1% solution in which case should be used neat or it can be diluted with tap water if required. However, the clinician must be satisfied that any material being used on a patient is approved for contact with humans or has been certified with a CE mark for dental or medical applications. This may preclude the use of supermarket-bought household bleaching products.
Care should be taken with all materials used intraorally as the material safety data sheet (MSDS) has instructions on hazards, including those related to swallowing or inhalation. This means that the use in the oral cavity would be regarded as a hazard. In the UK, failure to carry out a risk assessment under COSHH regulations would be a potential problem if anything untoward occurred. This is a particular problem as proprietary solutions specifically for dental use are available.
Extracanal extrusion of endodontic irrigants
It is not uncommon for endodontic irrigating solutions to be extruded outwith the root canal system during use. Depending on the chemical involved the effects can range from insignificant to very serious. There are many documented cases in the literature where sodium hypochlorite solution has been inadvertently extruded outwith the root canal system. When sodium hypochlorite comes into contact with vital tissues it can cause severe inflammation and tissue necrosis. Severe complications such as neurological damage, facial atrophy, anaphylaxis and airway problems have also been reported.
Clinically, the problem manifests as immediate severe pain for the patient (even though local anaesthetic has been administered), rapid swelling and ecchymosis (bruising). Secondary infection and persistent pain may result subsequently. Management of this distressing problem for both patient and clinician involves:
To reduce the risk of extracanal extrusion of endodontic irrigants, the dentist is advised to use a side exiting endodontic irrigating needle. This should not bind tightly in the canal so that irrigating fluid may pass out in a coronal direction. The needle and syringe should be kept moving while performing slow, gentle irrigation.
Chlorhexidine digluconate (Figure 13.14) is used by many endodontists as it has a number of beneficial properties. This chemical is a cationic bis-biguanide that is bacteriostatic at low (0.2%) and bactericidal at higher (2%) concentrations. Its mode of action is to cause cell wall decomposition, leading to the loss of cellular components. It does not, however, dissolve any organic tissue. It is active against a wide spectrum of microorganisms, with its antibacterial properties similar or greater to that of sodium hypochlorite. It is known that the bacterial flora and ecology of endodontic cases which have failed is different. In these cases, chlorhexidine is thus preferred because it may have an effect on microorganisms resistant to sodium hypochlorite. Other clinicians use it in preference to sodium hypochlorite as it is a safer alterative (see below).
Fig. 13.14 Examples of products containing chlorhexidine that can be used for endodontic irrigation: (A) Corsodyl (GlaxoSmithKline) and (B) R4 (Septodont). The former product is also very effective against periodontal pathogens and is thus widely used in the treatment of periodontal disease (see Chapter 17).
Chlorhexidine binds to hydroxyapatite on the root canal walls and has a good substantivity, that is about 12 hours after application (with some products claiming much longer times than this). It should therefore be the last irrigant to be used in the canal.
If chlorhexidine is used in direct combination with sodium hypochlorite solution, an acid–base reaction between the two may occur with formation of an insoluble precipitate that can be difficult to remove. This potential problem may be circumvented by irrigation with sterile water or saline between these two chemicals.
Some chlorhexidine products have been specifically designed for endodontic irrigation. They commonly have a higher concentration of chlorhexidine (2%) and also contain a wetting agent to lower surface tension to improve its penetration into dentinal tubules and small canals. Examples include R4 (Septodont), which is 20% chlorhexidine digluconate in denatured alcohol and commonly used as a final soak, and Gluco-Chex 2.0% (Cerkamed Dental-Medical Company). Concentrations lower than this are likely to be ineffective.
Some products are supplied as a gel that can be coated onto endodontic files prior to their insertion in the root canal to lubricate their passage. Two examples are Hibiscrub (Regent Medical), which contains 4% chlorhexidine, and Gluco-Chex gel 2% (Cerkamed Dental-Medical Company) which is 2%.
Iodine potassium iodide
Iodine potassium iodide is an organic compound that releases iodine. Iodine is a potent antibacterial agent with a broad spectrum of action: it is bactericidal, fungicidal, tuberculocidal, virucidal and sporicidal. It is effective for a limited period of time, about 2 days. Its mode of action involves attacking proteins, nucleotides and fatty acids leading to cell death. It has a low toxicity but some patients are allergic to iodine so its use in these individuals is contraindicated. It is supplied as an irrigating solution containing 2% solution of iodine in 4% aqueous potassium iodide. In the UK, Videne (Adams), which is povidone iodine, can be sourced from the pharmacy.
Iodine is know to discolour teeth as it stains dentine but use of sodium hypochlorite solution early in the procedure will help negate this side effect. It can also stain clothing so care should be taken during its use to avoid contact with the patient’s or dental team’s clothing.
Hydrogen peroxide degrades to form water and oxygen, produces hydroxyl free radicals, which are effective against bacteria, yeasts and viruses as they attack proteins and DNA. Unfortunately it has not been shown to reduce bacterial load in root canals significantly. Furthermore due to effervescence of the chemical, oxygen may penetrate into the periradicular tissues causing surgical emphysema. In contemporary endodontics, it is considered to be a product of the past and should not be used. It is still available as Acqua ossigenata 12 V (Septodont), which is a 3.6% hydrogen-stabilized peroxide solution.
This has some support, as it is less toxic than sodium hypochlorite although its mode of action is similar. In solution, it dissociates into hypochlorite ions but the reduced level of dissociation compared with sodium hypochlorite means that any adverse effects are also reduced. Similarly, with solutions of the same concentration of hypochlorous acid and sodium hypochlorite, the efficiency of sodium hypochlorite is greater as there is more chlorine available.
Electronically activated water
This is a spin off from the medical industry in which a device electrochemically generates, through the process of electrolysis, a solution of hypochlorous acid from the raw materials water and common salt, sodium chloride. The solution is regarded to be safer than other disinfectants as is less irritant if extruded into the periradicular tissues but it is still strongly bactericidal. The acid produced has a pH of near neutral (5–7). It is marketed to the dental profession as Sterilox.
MTAD is a mixture of tetracycline isomer (doxycycline), an acid (citric acid) and a detergent (Tween 80). It is usually used in conjunction with sodium hypochlorite. The solution will disrupt pulp tissue and dentine to the same extent as EDTA. The doxycycline present in MTAD binds to the dentine and has also been reported to be effective against Enterococcus faecalis.
With every new product there is always concern about the cytotoxicity to the underlying tissue and the effect it may have on the strength of dentine. MTAD has been compared with commonly used irrigants and medications, and its level of cytotoxicity appears to be less than eugenol but greater than a 1% sodium hypochlorite solution.
Some dentists have advocated using sterile water or local anaesthetic solution to irrigant the root canal systems. While these solutions will lubricate the files and carry the swarf in solution, they do not have any disinfectant properties and are therefore not recommended to be used as the sole irrigant.
Combinations of irrigants
A number of techniques have been developed which use co-irrigants, to enhance the bactericidal effect, proteolytic disruption or removal of residual calcified debris on the root canal walls. The co-irrigants usually consist of an acid or chelating agent to dissolve the smear and assist in biofilm destruction, together with sodium hypochlorite, acting primarily as the disinfectant. They also may include alternative or additional disinfectants such as chlorhexidine.
Ozone is used in the food and environmental industries for large-scale sterilizing of water supplies. The gas is a very effective sterilizing agent but at levels close to which it has toxicological effects can damage normal tissue. Devices are now available whereby the gas can be produced and delivered down a handpiece to the operating site in the mouth (Figure 13.15). In one device the area is sealed from the surroundings. The residual gas is then drawn back to the generator and neutralized using a platinum filter. More recent devices deliver the ozone down a fine tip directly into the canal for very short exposure times. This system does not require a seal around the tooth.
Bacterial photo-dynamic therapy (bacterial PDT)
Despite major advances in instrumentation and techniques, it is still not possible to consistently disinfect the root canal system. Accessing parts of the complex internal root canal system anatomy where bacteria are harboured can be challenging with conventional instruments and irrigants. This possibly explains why the success rate of endodontics even under ideal conditions is no better than 87%. Another reason is that currently available disinfectants such as sodium hypochlorite, chlorhexidine and calcium hydroxide are ineffective against some organisms, such as E. faecalis and Streptococcus faecalis.
It has been known for a number of years that the combination of a photo-sensitizer and a specific wavelength of light is effective against all microorganisms found in the mouth. This system is called Bacterial photo-dynamic therapy (bacterial PDT). Some clinicians are using such a system to disinfect the root canal system during root canal therapy in an attempt to eradicate all microorganisms prior to obturation.
Depending on the system, there are a number of photo-sensitizers available with differing excitation wavelengths. The most commonly used photo-sensitizer is pharmaceutical grade tolonium chloride, a member of the phenothiazine family of compounds and a close relative of toluidine blue O, a vital stain. It is supplied as a solution at a concentration between 13–80 μg/ml.
Tolonium chloride has a lower surface tension and so it has better wetting properties than sodium hypochlorite solution, which means that it can penetrate into the dentinal tubules. It is also more biocompatible and does not pose a problem if it is inadvertently extruded outwith the root canal system.
The light source is generally a laser diode or LED, which produces a red light at 635 nm ± 2 nm. The light acts as a means of exciting the photo-sensitizer molecules and minimal heat is produced. The light is delivered through an endodontic tip whi/>