Root canal treatment


Root canal treatment is a treatment sequence for the infected pulp of a tooth that is intended to result in the elimination of infection and the protection of the decontaminated tooth from future microbial invasion. It is generally done when the cavity is too big for a normal filling. Root canals, and their associated pulp chamber, are the physical hollows within a tooth that are naturally inhabited by nerve tissue, blood vessels and other cellular entities.
Endodontic therapy involves the removal of these structures, disinfection and the subsequent shaping, cleaning, and decontamination of the hollows with small files and irrigating solutions, and the obturation of the decontaminated canals. Filling of the cleaned and decontaminated canals is done with an inert filling such as gutta-percha and typically a zinc oxide eugenol-based cement. Epoxy resin is employed to bind gutta-percha in some root canal procedures. In the past, in the discredited Sargenti method, an antiseptic filling material containing paraformaldehyde like N2 was used. Endodontics includes both primary and secondary endodontic treatments as well as periradicular surgery which is generally used for teeth that still have potential for salvage.

History

Treatment procedure

The procedure is often complicated and may involve multiple visits over a period of weeks.

Diagnosis and preparation

Before endodontic therapy is carried out, a correct diagnosis of the dental pulp and the surrounding periapical tissues is required. This allows the endodontist to choose the most appropriate treatment option, allowing preservation and longevity of the tooth and surrounding tissues. Treatment options for an irreversibly inflamed pulp include either extraction of the tooth or removal of the pulp. Partial pulp amputation is the treatment of choice to preserve the pulp in teeth with open apical foramen.
Removing the infected/inflamed pulpal tissue enables the endodontist to preserve the longevity and function of the tooth. The treatment option chosen involves taking into account the expected prognosis of the tooth, as well as the patient's wishes. A full history is required, along with a clinical examination, and the use of diagnostic tests.
There are several tests that can aid in the diagnosis of the dental pulp and the surrounding tissues:
If a tooth is so compromised that future infection is considered very likely or inevitable, a pulpectomy is advisable to prevent such infection. Usually, some inflammation and/or infection is already present within and/or below the tooth. To cure the infection and save the tooth, the dentist drills into the pulp chamber and removes the infected pulp. To eliminate bacteria from the pulp chamber and root canals, the use of efficient antiseptics and disinfectants is necessary. The soft tissues are either drilled out of the root canal with engine driven rotary files, or with long needle-shaped hand files.

Opening the crown

The endodontist makes an opening through the enamel and dentin tissues of the tooth, usually using a dental drill fitted with a dental burr.
Isolating the tooth
The use of a rubber dam for tooth isolation is mandatory in endodontic treatment for several reasons:
  1. It provides an aseptic operating field, isolating the tooth from oral and salivary contamination. Root canal contamination with saliva introduces new microorganisms to the root canal which compromise the prognosis.
  2. It facilitates the use of the strong medicaments necessary to clean the root canal system.
  3. It protects the patient from the inhalation or ingestion of endodontic instruments.

    Removal of pulp tissue

There have been a number of progressive iterations to the mechanical preparation of the root canal for endodontic therapy. The first, referred to as the standardized technique, was developed by Ingle in 1961, and had disadvantages such as the potential for loss of working length and inadvertent ledging, zipping or perforation. Subsequent refinements have been numerous, and are usually described as techniques. These include the step-back, circumferential filing, incremental, anticurvature filing, step-down, double flare, crown-down-pressureless, balanced force, canal master, apical box, progressive enlargement, modified double flare, passive stepback, alternated rotary motions, and apical patency techniques.
The step back technique, also known as telescopic or serial root canal preparation, is divided in two phases: in the first, the working length is established and then the apical part of the canal is delicately shaped since a size 25 K-file reaches the working length; in the second, the remaining canal is prepared with manual or rotating instrumentation. This procedure, however, has some disadvantages, such as the potential for inadvertent apical transportation. Incorrect instrumentation length can occur, which can be addressed by the modified step back. Obstructing debris can be dealt with by the passive step back technique. The crown down is a procedure in which the dentist prepares the canal beginning from the coronal part after exploring the patency of the whole canal with the master apical file.
There is a hybrid procedure combining step back and crown down: after the canal's patency check, the coronal third is prepared with hand or Gates Glidden drills, then the working length is determined and finally the apical portion is shaped using step back techniques. The double flare is a procedure introduced by Fava where the canal is explored using a small file. The canal is prepared in crown down manner using K-files then follows a "step back" preparation with 1 mm increments with increasing file sizes. With early coronal enlargement, also described as "three times technique", apical canals are prepared after a working length assessment using an apex locator; then progressively enlarged with Gates Glidden drills. For the eponymic third time the dentist "arrives at the apex" and, if necessary, prepares the foramen with a size 25 K-file; the last phase is divided in two refining passages: the first with a 1-mm staggered instrument, the second with 0.5-mm staggering. From the early nineties engine-driven instrumentation were gradually introduced including the ProFile system, the Greater Taper files, the ProTaper files, and other systems like Light Speed, Quantec, K-3 rotary, Real World Endo, and the Hero 642.
All of these procedures involve frequent irrigation and recapitulation with the master apical file, a small file that reaches the apical foramen. High frequency ultrasound based techniques have also been described. These can be useful in particular for cases with complex anatomy, or for retained foreign body retrieval from a failed prior endodontic procedure.
There are two slightly different anti-curvature techniques. In the balanced forces technique, the dentist inserts a file into the canal and rotates clockwise a quarter of a turn, engaging dentin, then rotates counter-clockwise half/ three-quarter of a revolution, applying pressure in an apical direction, shearing off tissue previously meshed. From the balanced forces stem two other techniques: the reverse balanced force and the gentler "feed and pull" where the instrument is rotated only a quarter of a revolution and moved coronally after an engagement, but not drawn out.

Use of anesthetics

Since 2000, lidocaine is the most commonly used local anesthetic for root canal therapy.

Irrigation

The root canal is flushed with an irrigant. Some common ones are listed below:
The primary aim of chemical irrigation is to kill microbes and dissolve pulpal tissue. Certain irrigants, such as sodium hypochlorite and chlorhexidine, have proved to be effective antimicrobials in vitro and are widely used during root canal therapy worldwide. According to a systematic review, however, there is a lack of good quality evidence to support the use of one irrigant over another in terms of both short and long term prognosis of therapy.
Root canal irrigation systems are divided into two categories: manual agitation techniques and machine-assisted agitation techniques. Manual irrigation includes positive-pressure irrigation, which is commonly performed with a syringe and a side vented needle. Machine-assisted irrigation techniques include sonics and ultrasonics, as well as newer systems which deliver apical negative-pressure irrigation.

Filling the root canal

The standard filling material is gutta-percha, a natural polymer prepared from latex from the percha tree. The standard endodontic technique involves inserting a gutta-percha cone into the cleaned-out root canal along with a sealing cement. Another technique uses melted or heat-softened gutta-percha which is then injected or pressed into the root canal passage. However, since gutta-percha shrinks as it cools, thermal techniques can be unreliable and sometimes a combination of techniques is used. Gutta-percha is radiopaque, allowing verification afterwards that the root canal passages have been completely filled and are without voids.
Pain control can be difficult to achieve at times because of anesthetic inactivation by the acidity of the abscess around the tooth apex. Sometimes the abscess can be drained, antibiotics prescribed, and the procedure reattempted when inflammation has been mitigated. The tooth can also be unroofed to allow drainage and help relieve pressure.
A root treated tooth may be eased from the occlusion as a measure to prevent tooth fracture prior to the cementation of a crown or similar restoration. Sometimes the dentist performs preliminary treatment of the tooth by removing all of the infected pulp of the tooth and applying a dressing and temporary filling to the tooth. This is called a pulpectomy. The dentist may also remove just the coronal portion of the dental pulp, which contains 90% of the nerve tissue, and leave intact the pulp in the canals. This procedure, called a "pulpotomy", tends to essentially eliminate all the pain. A pulpotomy may be a relatively definitive treatment for infected primary teeth. The pulpectomy and pulpotomy procedures aim to eliminate pain until the follow-up visit for finishing the root canal procedure. Further occurrences of pain could indicate the presence of continuing infection or retention of vital nerve tissue.
Some dentists may decide to temporarily fill the canal with calcium hydroxide paste in order to thoroughly sterilize the site. This strong base is left in place for a week or more to disinfect and reduce inflammation in surrounding tissue, requiring the patient to return for a second or third visit to complete the procedure. There appears to be no benefit from this multi-visit option, however, and single-visit procedures actually show better patient outcomes than multi-visit ones.