Removal of gutta-percha and root canal sealer: a literature review and an audit comparing current practice in dental schools

Literature review

The aim of endodontic treatment, or retreatment, is to reduce the microbial load within the root canal system sufficiently to enable the host response to favour periapical healing.1 According to Peters et al,2 50% of canal walls remain untouched by endodontic instruments following canal preparation.

A study undertaken in 1994 in Washington reported a 95% success rate of root treated teeth.3 Despite the recent improvements in endodontic instruments and techniques, Friedman and Mor showed a relatively similar incidence of endodontic failure between 2% and 14%.4 Ng et al, in a systematic review, found success of primary treatments to range from 68–85%.5 On the other hand, success rates for retreatment cases range from 40–100% in the literature.6

Different assessment criteria for success and failure have been reported. These are generally based on the interpretation of radiographs alongside patient signs and symptoms. According to Kvist and Reit, if a radiographic apical radiolucency shows no signs of resolution four years post-op, the case has failed.7 Cohen and Hargreaves suggest the following as aetiology of failure: poor access; missed canals; insufficient obturation; inadequate intra-operative asepsis; undiagnosed perio-endo lesions; or an inadequate coronal seal.8 Other possibilities are extra-radicular infection, foreign body reaction or a true cyst.

Treatment options available for failed cases include monitoring, non-surgical retreatment, surgical endodontics or extraction. The appraisal of the specific tooth and patient factors may conclude that an extraction is indicated. Monitoring is feasible if a tooth remains symptom-free and a periapical radiolucency has not increased in size.9 Non-surgical retreatment requires accessing the root canal system (RCS) coronally and removal of the failed root-filling and disinfection of the RCS. Surgical retreatment involves the removal of the apical 3 mm of a root followed by root end preparation and filling. Current literature supports microsurgical techniques for the latter.

Non-surgical and surgical approaches each have indications and contra-indications associated with them, but it is also important to compare their outcomes. Torabinejad et al undertook a systematic review on this topic and concluded that surgical endodontics resulted in better results after a 2–4 year period, but non-surgical retreatment gave more favourable results after a 4–6 year period of review.10 Del Fabbro and Taschieri undertook a systematic review and found that, after four years follow-up period, there was no significant difference between the outcomes of the two methods.11 The authors concluded that the choice between the two procedures should involve the clinical findings, operator experience and skill, complication risks, technical feasibility, cost and patient preference. Kvist and Reit studied the difference in post-operative discomfort associated with surgical and non-surgical endodontic retreatment.12 They concluded that surgical retreatment resulted in more discomfort and tended to bring about greater indirect costs than non-surgical retreatment. It is for these reasons that the non-surgical approach is considered the ideal treatment for endodontic failures.

Materials for obturation include gutta-percha (GP), Resilon^TM (Pentron Clinical Technologies, LLC, Wallingford, CT, USA) and, previously, silver points. GP is the most commonly used obturating material owing to its high level of biocompatibility,13 dimensional stability, low cost and ease of removal, and it is therefore the most likely to be encountered in retreatment cases. There are also many types of sealer on the market, such as zinc oxide eugenol (eg TubliSeal, Kerr Corporation, Orange, CA, USA); calcium hydroxide (eg Apexit, Ivoclar Vivadent Inc, Schaan, Liechtenstein); epoxy resin (eg AH Plus, Dentsply Ltd, Addlestone, Surrey, UK); glass ionomer (eg Ketac^TM Endo Aplicap^TM, 3M ESPE, St Paul, MN, USA); silicone-based sealer (eg RoekoSeal, Roeko, Langenau, Germany)14 and, more recently, tricalcium silicates (eg MTA Fillapex, Angelus®, Londrina, PR, Brazil).

There are a number of methods to remove gutta-percha during non-surgical root canal retreatment. These include thermal and/or mechanical methods and those that use a chemical adjunct. Thermal and/or mechanical methods include the use of hand files, rotary files (eg ProTaper® Rotary System, Dentsply Maillefer, Ballaigues, Switzerland), rotary files specifically designed for retreatments (eg ProTaper® Universal Rotary System, Dentsply Maillefer), GPX burs (Brasseler, Savannah, GA, USA), reciprocating files (eg Canal Finder System, Endo Technique Co, Tustin, CA), ultrasonic tips and files,15 heat pluggers16 and Nd:YAG lasers. These instruments remove gutta-percha and sealer by mechanical debridement and by frictional heat, which thermoplasticizes the root-filling mass. There is concern with the use of lasers regarding a reported increase in temperature of the root surface.17

Gutta-percha is made of a vegetable resin which can be softened by chemical solvents18 or heat (eg ultrasonics). Solvents, such as chloroform or xylol, can therefore be used as adjuncts to thermal and/or mechanical methods to help reduce the amount of dentine removal and risk of strip perforation. These can be applied on to the coronal portion of the RCS using an irrigating syringe and the GP penetrated with files, increasing the surface area for dissolution. Once the working length is reached, progressively larger diameter files, with or without a solvent, can be used to remove the bulk of the GP. Finally, more solvent can be placed into the coronal third of the canal, avoiding the apex, and any further dissolved GP can be removed using paper points in a ‘wicking’ technique.10

A number of studies have shown rotary endodontic files to be more efficient at removing GP than hand files.^19–23 Other studies reported no significant difference between the ProTaper® rotary system (Dentsply Maillefer) and a number of other instruments, including conventional hand files.^24–26 This discrepancy could be attributed to differences in obturation techniques and retreatment methods. According to Schirrmeister et al23 the use of ProTaper® finishing files (Dentsply Maillefer) for retreatment purposes yielded a high file separation incidence of 22.7%. However, the recent introduction of the ProTaper® Universal Rotary System (Dentsply Maillefer) includes instruments specifically for retreatment. These have a convex cross-section and are used at a higher rpm (500–700).27 Reciprocating files operate inside root canals by a longitudinal backward and forward motion. Barletta et al28 compared GP removal using reciprocating and rotary systems and concluded that neither system was able to remove the root-filling completely and no significant differences were observed between the two mechanical methods. Ultrasonic tips and files can also be used to remove GP from canals with and without the use of a solvent.^15,29 In a recent study,30 a conventional retreatment method was compared with the same technique plus ultrasonic instruments and microscope use. A significant difference in remaining GP and sealer was found, with this option giving the better result. Visualization with magnification therefore seems to enhance the ability to remove the failed root-filling, thereby improving the subsequent RCS disinfection.

Generally, GP is well condensed and can be resistant to penetration by endodontic files, so the use of an organic solvent can help by softening it. The ideal solvent should be efficient; non-toxic to the clinical staff, patient and environment; non-carcinogenic; viable for an adequate time; and cost-effective. Available solvents include chloroform, methyl chloroform, halothane, rectified oil of turpentine, orange oil, xylol, eucalyptol, d-limonene and ethyl acetate, but none of these fulfils all of the criteria above. Table 1 gives the properties of commonly used gutta-percha solvents.

Indirectly heating rectified oil of turpentine18 and eucalyptol increases their dissolution effect on GP.49 Different solvents have different effects on different types of sealers. Whitworth and Boursin found that a 10 min application of chloroform dissolved 62.5% of Tubliseal (Kerr Corporation) zinc oxide eugenol sealer, 96% AH Plus (Dentsply Ltd) epoxy resin sealer, and 11.6% Apexit (Ivoclar Vivadent) calcium hydroxide sealer,32 whereas Halothane dissolved 5.19% of Tubliseal (Kerr Corporation), 68% AH Plus (Dentsply Ltd), and 14.19% Apexit (Ivoclar Vivadent). Martos et al found orange oil and xylol to have significant solvent properties with zinc oxide eugenol, calcium hydroxide and silicone sealers.41

Solvents can also demonstrate antimicrobial properties.1 Retreatment cases tend to involve specific isolates such as Enterococcus faecalis, which has been identified in 22–77% of these cases.^50,51Enterococcus faecalis can survive harsh environments such as a high pH52 and lack of nutrition.9 Edgar et al demonstrated in an in vitro study that chloroform, when used at concentrations for dissolution of GP, can also significantly reduce levels of E. faecalis.33

The toxicity of some of these solvents, such as chloroform, could be of concern34 if inhaled or extruded beyond the apical constriction, however, McDonald and Vire reported that, during endodontic treatment, air vapour levels of chloroform were not substantial enough to induce negative health effects to either the dentist or patient.53 Chutich et al also demonstrated that using minimal amounts of chloroform negated any risk of toxicity.37 Despite this, it is important to note that chloroform is highly volatile and can completely evaporate within one minute of being in contact with air. An effective, safer alternative may be the essential orange oil.^18,40–42

Sae-Lim et al investigated endodontic retreatment using the ProFile.04 Taper Rotary System (Dentsply Maillefer, Ballaigues, Switzerland) with and without chloroform and demonstrated that canals prepared with chloroform were significantly quicker, but more residual GP remained where the solvent was placed.21 The author postulated that perhaps the softening effect of chloroform on GP resulted in inadvertent distribution of GP on the canal wall surface in the form of a film. This result is consistent with other studies.^27,54

An audit comparing current practice in Belfast with UK and Republic of Ireland dental schools

The literature review demonstrated that there are various methods of GP removal during non-surgical root canal retreatment which can be grouped into thermal and/or mechanical methods and those that involve the use of a chemical adjunct. At present, there are no guidelines on the removal of GP and root canal sealer from the British Endodontic Society (BES), the European Endodontic Society (EES) or the American Endodontic Society (AES). Owing to the range of techniques and solvents available and the lack of guidance, it was decided to undertake an audit to compare current practice in Belfast with the other dental schools across the UK and Ireland where dental students and endodontic specialists are trained. Current practice in the Restorative Department, School of Dentistry, Belfast was to use combinations of Gates-Glidden drills (Dentsply Maillefer), Hedström hand files, barbed broaches and the solvent eucalyptol.

Results

The response rate was 100%, with 16 dental schools participating (including Belfast). Figure 1 shows the percentage of schools using chloroform, eucalyptus oil or other solvent. The other solvents mentioned include oil of turpentine, orange solvent and cajeput oil. Figure 2 shows the percentage of schools using Gates-Glidden drills (Dentsply Maillefer), barbed broaches, hand files, rotary files or other techniques.

The following techniques were mentioned to avoid apical extrusion of solvents:

Solvent placement within coronal 1/3 –½ only;

Syringe measured 3 mm short of working length;

‘Wicking’ with paper points to within 1–2mm of working length;

Use of a small syringe and side-venting needle.

It was noted that rotary NiTi files were used at higher speeds, eg ProFile.04 Rotary System (Dentsply Maillefer, Ballaigues, Switzerland) at 500–600 rpm (normal use 150–350 rpm) and the ‘other’ mechanical techniques included the use of System B Heat Source (SybronEndo Corporation, Orange, CA, USA) or a heated spreader. Only 5 of the 16 schools allowed students to use chloroform. Further information provided included the use of a microscope for retreatment cases and that solvents can help locate Thermafil® carriers (Dentsply Maillefer, Ballaigues, Switzerland), aiding their removal.