Modern endodontic planning part 2: access and strategy

To locate the pulp (Figure 1)

The use of radiographs is essential to correlate canal position and the extent of access. The approach to the pulp should follow the long axis of the tooth and preserve as much coronal tissue as possible. Using these ‘laws’ demands good spatial awareness and access should optimally be achieved before the rubber dam is placed. It is often sensible to ‘eyeball’ the distance from cusp tip to CEJ with the selected bur before entering the tooth. If the bur is not going to depth, the access is too shallow. Conversely, if the bur is well beyond the CEJ and the pulp not located, stop instrumentation, reassess and take a radiograph.

The floor of the tooth is darker than the walls or the roof of the pulp chamber and, by definition, is located at or below the CEJ. Non-end-cutting burs (such as the Endo Z bur, Dentsply, Weybridge, UK) can be used to expand the coronal access safely and remove the chamber roof remnants whilst protecting the pulpal floor. The DG16 probe remains invaluable in fine exploration of the pulp chamber and canal system. It is essential to remove the entire roof of the pulp chamber.

Once in the pulp chamber, canals must be identified. To locate the canals, further laws have been proposed1 (Figure 2). It is important to note that these ‘laws’ should only be used as a guide to access and do not apply to upper first and second molars:

Diamond-coated ultrasonic tips can be useful in removing dentine to facilitate canal access (Figure 3). It is also good practice to have smaller stainless steel K-files available, including finer ISO 06 and ISO 08 sizes. With these instruments, blockages and sclerosed regions may be successfully instrumented. Unfortunately, the rules of symmetry do not apply to maxillary molars, which are asymmetrical in shape, but the other rules may be applied. For maxillary molars, do not access distal to the oblique ridge, and expect to find the canals central to the cusp tips (Figures 4 and 5). Maxillary second molars tend to have a more ovoid pulp chamber extending from mesio-buccal to palatal rather than the more triangular appearance on the floor of the maxillary first molar.

Additional roots (Radix entomolaris/radix paramolaris) (Figure 10)

These include additional disto-lingual and disto-buccal roots (respectively) on lower molars. An accessory cusp may be an early warning sign for an additional root. These can be conical, curved or double curved and may present in up to 14.4% of the population with a predisposition to certain ethnic groups (those with Mongoloid genetics).5 Often, these are only revealed with parallax radiography or CBCT. If present, coronal access must be widened to follow the root form and standard endodontic treatment can follow. The clinician should be aware that these canals may be severely curved.

Pulp stones

These are discrete calcifications free within the pulp or attached to dentine. A true pulp stone is an odontoblastlined ball of dentine. A false pulp stone is simply calcification of fibrous tissue and a denticle is a dentine ball that is cavitated with epithelial remnants. Multiple pulp stones may be present within teeth and are most commonly found in molars and restored teeth:6 practically all may present as blockages to canal patency but can be readily removed. Care must be taken when these are present that they are not inadvertently pushed down canals where they can cause an iatrogenic blockage! Copious irrigation with hypochlorite and EDTA and the use of ultrasonics should dislodge these.

Pulpal obliteration (calcific metamorphosis/pulpal sclerosis/dystrophic calcification)

Ageing results in the deposition of tertiary dentine. An inflammatory stimulus may result in generalized dystrophic calcification of the pulp system. This usually affects anterior teeth following trauma. Teeth are often yellow and may elicit unreliable responses to sensitivity testing due to an increase in the density of the dentine. Sclerosed anterior teeth may only become periapically involved in 8.5% of cases, therefore obliteration alone is not necessarily an indication for endodontic intervention.7 If there is evidence of sclerosis and periodical change, intervention may become necessary. These are invariably patent despite the radiographic appearance to the contrary.8 Treatment involves using small files with a watch-winding motion and an irrigant that dissolves mineralized tissue (EDTA). Magnification, illumination and ultrasonics will help.9

Dens in dente (dens invaginalis)

This is a distortion of the enamel organ during development that can range in presentation from a small pit on the cingulum of incisors to a deep penetrating canal that opens apically. This canal may or may not connect with the pulp space.10 The extent is often only quantified following CBCT examination. When present, root canal treatment of the invagination alone may suffice but, with deep extensions and endodontic involvement, treatment must include the canal and the tooth may require endodontic surgery.

Taurodontism

This is a deformation of the pulp chamber morphology resulting in an alteration of the ratio of pulp chamber height to root length.11 Practically, the canal orifices are located more apically and this may complicate access. Good illumination and magnification are essential.

Once accessed, the focus of treatment moves towards working length determination and shaping. These will be covered in the next paper. This paper will now address the single vs multiple visit debate and give some consideration to the ‘art of temporization’.

Two-visit strategy

The root canal system is complex.2 Accessory and lateral canals are common in all teeth.2^,13 Canals may have isthmuses, fins and ramifications. Apically there may be multiple branches forming the apical delta. As a result, complete mechanical cleaning of the root canal system is impossible. Furthermore, studies have demonstrated persistent bacterial presence in root canals after cleaning and shaping.12^,14 The use of inter-appointment dressings, such as calcium hydroxide, may help eradication of residual bacteria and has been proposed as an important step in the chemo-mechanical disinfection of the canal system.15 Thus, a two-visit approach has significant theoretical and practical benefits.

Should a two-visit strategy be chosen, the practitioner should aim for complete mechanical preparation on visit one followed by the placement of an intracanal medicament and final chemical lavage and obturation at visit two around 5–7 days later.16

Single-visit strategy

A negative bacterial culture before obturation is not always predictive of success and complete bacterial eradication is not possible. One could go to great lengths with a multi-visit approach and not improve the outcome.12^,14^,17 Intracanal medicaments are only beneficial when in contact with bacteria, and this may not occur if they are not introduced throughout the canal system. Thus calcium hydroxide may not sterilize the canal and bacterial colonies may persist.15^,18 Multiple visits necessitate more appointments which demands greater time from the patient, greater cost and more dental exposure than many patients would want. Furthermore, the placement of a temporary restoration may act as a portal of entry for bacteria between visits, thus negating any benefit. It has been suggested that immediate obturation entombs any remaining bacteria and ensures that a good coronal seal is established immediately, preventing recolonization and improving success.19

The evidence, however, suggests that there is no difference in success between single and multiple visit strategies (Table 2).^20,21,22,23 Clinical scenarios do remain when it is logical to follow a defined strategy. In previously vital or non-infected teeth, single visit treatment should be practised wherever possible: bacterial eradication is not necessary and multiple visits may increase the likelihood of bacterial contamination. If there is pre-existing infection and frank periapical change, the clinician must be aware that a more robust disinfection is required. Thus it is up to the operator to decide, in conjunction with the patient, what strategy is better considering time, cost, personal experience, disease type and presentation. Complex re-treatments and teeth with complex anatomy may necessitate more time than a single visit would allow and, in these instances, a multiple-visit approach may be essential.

Intracanal medicaments

Intracanal medicaments help:

Benefits of intra-appointment dressing.24

Steroid-containing pastes (Ledermix) are often used in irreversibly inflamed teeth that are ‘hot’ but best practice should always involve supplementary local anaesthetic and extirpation of the pulp. Calcium hydroxide remains the gold standard for dressing root canals. There is a synergistic effect with calcium hydroxide and sodium hypochlorite thus there is no need to dry canals fully after irrigation and before dressing.25 Calcium hydroxide with iodine potassium iodide may have additional antibacterial action and is available in a variety of forms.26 Such medicaments can be introduced on flexible ‘navi-tips’ safely to the apex. All dressings are cytotoxic (at least for 48 hours) and if extruded patients must be informed, there may be some post-operative tenderness. Care should be taken to avoid extrusion adjacent to critical structures, most notably around the inferior dental canal when dressing lower 7s and 8s. Some dressings are radio-opaque and this can be of benefit diagnosing cracks and internal resorption (Figure 11). It is wise to take a post-dressing radiograph after placement. Not only does this indicate the shape and length of preparation, but it confirms that any extruded material is from the dressing, not the definitive obturation. Those pastes in silicone-based carriers (Vitapex, NeoDental International, USA) may be very troublesome to remove. A fine interdental brush may help remove dressings. When using iodine-containing medicaments it is prudent to check that the patient is not allergic to iodine.

The long-term use of calcium hydroxide within the canal system has been shown to reduce the fracture resistance of dentine.27 As such its use should be limited to short duration, ideally for no more than 4–6 weeks.

Temporary restorations

Without adequate temporization it is not possible to achieve a bacteria tight seal between visits and, as such, the whole rationale for endodontic therapy of chemo-mechanical disinfection may be compromised. A lack of satisfactory temporary restoration has been ranked the second most common reason for inter-appointment pain.28

Cavity design is important; if there are no supportive features, the wedging effect of occlusal loading can displace the temporary into the pulp chamber, thus allowing contamination of the canal system. It is important to design a cavity that is wider coronally than apically. Barriers may then be placed before the temporary material. The use of cotton wool is commonplace but is losing favour as a sound technique because:

PTFE tape may also be used to the same effect and may not have the same weakness to leakage. Some clinicians do not use a barrier at all but one must be confident that any temporary cement will not block the canal space. Ultrasonic tips are very effective at removing temporary restorative materials.

The clinician may choose a conventional restorative material (composite or glass ionomer) or a material developed specifically for temporization (Cavit, Fermit, IRM etc). The former bond to the remaining tooth structure but can be difficult to remove in isolation, especially if tooth-coloured materials are used: without vigilance precious natural tooth structure can be easily removed in the process. The latter are often more easy to use, inexpensive, often a different colour and can, where necessary, provide both good coronal seal and aesthetics.

It is not clear that one material has any greater benefits over another; whatever material is used, thickness is essential (3–4 mm minimum)29 (Figure 12). Temporary materials may deteriorate over time; if a long delay is foreseen between stages of root canal therapy or completion of obturation and definitive restoration, consideration must be given to the use of a definitive restorative material. There is evidence that temporary post crowns leak and are not recommended.30 It is better practice to seal the root and provide an overdenture or place a post and core immediately following obturation.