State-of-the-art orthograde endodontic treatment

Richard Mounce and Brett Gilbert provide the clinical, foundational and sequential stages of an orthograde endodontic procedure.

Significant advances in technology, instrumentation, and scientific evidence have been made in recent decades. However, the clinical objectives of endodontic therapy remain unchanged. The classic goals of three-dimensional cleaning, shaping, obturation of the pulp space and placement of a coronal seal/restoration remain the foundation of quality endodontic treatment. 

This article aims to provide the GDP with a clinical roadmap to achieve these objectives in orthograde root canal treatment. It incorporates the latest literature with time-honoured principles.  

Clinically, an orthograde endodontic procedure has foundational and sequential stages. These stages include: preoperative diagnosis and treatment planning; anaesthesia; rubber dam placement; access; canal location; cleaning and shaping (chemo mechanical disinfection); obturation and coronal restoration. Below, we describe each critical step in succession:

Preoperative diagnosis and treatment planning

  • Figures 1a and 1b: Clinically challenging case: note the curvature, calcification and tooth position limiting access (Dr Brett Gilbert)

The state-of-the-art in all endodontic procedures relies on diagnosis, risk assessment and written informed consent. These are three of its vital cornerstones. To arrive at an accurate diagnosis, a thorough clinical and radiographic preoperative examination is essential. 

The key elements of a definitive diagnosis include the clinical history and examination. You need a proper diagnostic radiographic record. This will show the apices of each root and surrounding tissues of the tooth in question. Also, reproduction of the patient’s chief complaint by thermal and clinical testing. The clinical and legal importance of making and recording a definitive pulpal and periapical diagnosis from these findings to justify treatment cannot be overstated.

In addition, the tooth’s restorability, strategic value, and a risk assessment must be considered preoperatively. 

The above assessment includes determining the risk of iatrogenic events. For example; perforation, separated files, canal transportation. As well as strategies on how to best avoid these misadventures. 

It is incumbent on the clinician to determine if they have the skill, time, patience, and armamentarium to successfully manage the case at the highest level. If not, referral should be considered. 

Clinical opinions vary on one visit versus multiple visits. Although, you can generally complete treatment in one visit in the absence of swelling (indurated or fluctuant), apical drainage, severe percussion sensitivity, numbness, trismus, or a lack of time to complete treatment adequately (Figure 1). 

Local anaesthesia (LA)

Figure 2: The X-tip intraosseous anesthesia system (Dentsply Tulsa Dental)

Profound LA is critical to obtain visual and tactile control during endodontic treatment. You may require adequate solution volumes, accurate placement, allowing time for full onset and using various injection techniques (Akinosi, Gow-Gates, lingual infiltration, intrapulpal, PDL, among others), to treat patients successfully and comfortably.  

In addition, having the armamentarium and ability to immediately and confidently administer an intraosseous injection (X-Tip, Dentsply; Stabident, Fairfax Dental) to supplement the above techniques is a crucial skill to the endodontic clinician in select difficult cases. We highly recommend mastery of these techniques (Figure 2).   

Rubber dam placement

Practising endodontics without a rubber dam is below the clinical and legal standard of care. It is not possible to obtain visual, tactile or microbial control and/or protect the patient’s airway without a rubber dam.

If you cannot place a rubber dam due to patient anxiety, consider IV or oral conscious sedation. Otherwise, extract the tooth.

Endodontic access does not require a rubber dam be in place, however, prior to introducing files, irrigation, or anything into a canal orifice, a rubber dam must be in position. If  tooth structure is limited, where required, placement of the rubber dam clamp on gingival tissue is acceptable.

Coronal access 

Figure 3: Contracted access cavity. Note the colouration of the pulp chamber floor leading to the canal orifices

Access and all stages of endodontic treatment should be performed under a surgical operating microscope due to its optimal lighting, magnification, depth of field and visual acuity. Generally, GDPs favour loupes. However, the majority of endodontists use microscopes.

‘Minimally invasive’, ‘Ninja’, and contracted access cavities (CAC) have gained popularity in the past decade. Especially among specialists. These micro access preparations are generally much smaller than their traditional counterparts. They can create more limited room to utilise rotary files safely.  

When working through a CAC, the resulting canal shaping relies heavily on the controlled memory (CM) characteristics of nickel titanium files during shaping in the absence of straight-line access. 

These instruments can be pre-curved. This assists in the insertion of the file, often at a severe angle. CM files maintain their curvature when rotated around a curvature and can adapt relatively easily to CAC.  

Regardless of the philosophy of access (MI, Ninja, CAC), coronal access should provide unfettered visual and tactile control with preservation of tooth structure as a primary objective (Figure 3). 

Canal location

Figure 4: Tun Ultrasonic tips

Coronal access and canal location are inter-related, but ultimately different. Greater calcification obviously makes canal location more challenging, and accentuates the value of magnification, lighting and ultrasonic tips (Tun tips, Tun Ultrasonics; Helse tips, Helse) for selective dentine removal and avoidance of perforation.  

Knowing the probable anatomy of any given tooth is critical when looking for canals. Understanding the maximum number of canals possible in any given tooth is essential (for example, two canals in a lower anterior tooth are present approximately 45% of the time). A pre- or intraoperative CBCT can be invaluable in assessing canal anatomy preoperatively.  

In all teeth (with a slight exception in maxillary molars), canal anatomy is symmetrical. Canal symmetry aids in canal location. Canals are symmetrical to each other and the external circumference of the tooth.  

Dentine colour can help guide canal location. The walls of the chamber are always lighter than the floor of the chamber. Dark lines (the lines of imbrication) on the chamber floor indicate canal location. Highly calcified dentine is much darker than non-calcified dentine and provides a clue to canal location. 

Placing sodium hypochlorite in a calcified chamber and observing the origin of the resulting bubbles also provides valuable clues to canal location (Figure 4). 

Hand files: canal negotiation

  • Figure 5a: D Finder (Mani)

Canal shaping objectives include keeping the canal centred in its original position, keeping the minor constriction (MC) of the apical foramen at its original size and position, preparing a tapering funnel with narrowing cross sectional diameters, and creating a minimal taper than can be adequately disinfected and obturated in three dimensions. 

Hand files are critical to achieve these goals. In all cases, the clinician is advised not to insert hand files until all canals are located and the pulp chamber unroofed. Hand files are used to negotiate canal spaces, assure patency (the canal is open from the orifice to the MC) and create a minimal diameter before further canal shaping (ie, prepare a glide path).  

The quintessential hand file for canal scouting and negotiation is the standard K-File and/or carbon steel (C+ files, Dentsply; Mani K-Files and D-Finders). 

All hand files should be inserted into the canal both pre-curved and long enough to achieve patency. Scouting files should be advanced slowly, passively, and gently to the apex and never be forced to length. 

Once the canal has been enlarged to the equivalent of a #15 hand K-File, this serves as a glide path for the introduction of nickel titanium files. Glide paths can be prepared using subsequently larger hand files, #6, 8, 10, 12, 15 (Mani K-Files and D-Finders) or via the use of designated nickel titanium glide path preparation Instruments (Proglider, Dentsply) (Figure 5).

True working length

The MC of the apical foramen is the natural termination for all endodontic procedures, including instrumentation, irrigation, and obturation. Obtaining patency is essential. Patency aids in keeping the MC of the apical foramen open and clear of debris.  

Conversely, losing patency is the harbinger of iatrogenic events (fractured instruments, canal transportation, perforation etc). Recapitulation (assuring patency with a K-File) after every shaping file insertion is essential to avoid apical blockage.  

Irrespective of the instrumentation system employed, precisely locating the end point of irrigation, instrumentation and obturation, ie the true working length (TWL/MC), is a key determinant of avoiding iatrogenic misadventure and simultaneously optimising clinical success. 

An accurate TWL sets the stage for thorough debridement of the root canal space while protecting the periapical tissues from over-instrumentation, transportation of apical architecture, and possible irrigant extrusion. 

The clinician should use multiple means of TWL determination, including preoperative two-dimensional periapical radiographs, possibly CBCT, apex locators (Zoot ZX, Morita; Iroot, Metabiomed), resistance to hand file passage through the MC (felt digitally as a ‘pop’), the ‘bleeding point’ as measured with paper points taken to the MC, and the time honoured radiographic TWL images. These multiple means should confirm one another. No one single method should be utilised exclusively. 

Universal canal shaping steps  

Canal shaping algorithms vary based on the system being used and the anatomy encountered. From a mechanical viewpoint, this variability in protocols is due to the functionality, safety and efficiency inherent in various file designs.

Regardless of the file system, extensive practice using extracted teeth and/or plastic canal models is highly recommended prior to taking any new file system into the mouth and/or to gain proficiency. 

The above notwithstanding, all canal shaping systems employ the following universal steps:

Smaller Instruments

Smaller instruments prepare the canal for larger subsequent instruments. Taking larger instruments into complex canal systems, without a glide path or minimal preparatory shaping, puts the clinician at high risk of file separation, canal transportation and blockage. One of the authors (RM), after preparing the glide path to approximately a #15 K-File equivalent, will use a .03/15 nickel titanium instrument followed by a .04/25 and .01/30 and larger files as required to prepare the master apical diameter (Logic-Bassiendo)  

Smaller canal shapes

The endodontic literature would argue persuasively that larger apical diameters create cleaner canals. Currently, more systems abide by smaller tip and taper sizes to preserve dentine. With smaller canal shapes, emphasis on the quality and volumetric quantity of irrigation and activation is necessary to make up for the lack of mechanical debridement in these canals. This stated, there is no proven scientific literature-based protocol stating an optimal taper and tip size and a corresponding irrigation and activation method

Irrigation

All canal scouting, glide path creation and shaping should be accomplished in the presence of copious irrigation and lubrication. This is generally sodium hypochlorite and/or a liquid or viscous EDTA solution (Prolube, Dentsply; Glyde, Dentsply; MD-Chelcream, Meta). Especially if the canal has a great deal of pulp tissue present

File systems

Figure 6a: Clinical case done with rotational endodontics using the Gentlewave irrigation system and Edge Endo files (Dr David McCarty)

There is no literature-based superiority of rotational (Endosequence, Brasseler; Edge Endo, Protaper, Dentsply) versus reciprocating nickel titanium instruments (Procodile, Komet; Waveone Gold, Dentsply; Reciproc, Dentsply). Choosing a rotational (360-degree continuous rotation) versus reciprocating file system (a clockwise or counterclockwise cutting motion followed by a reverse movement to relieve the torsion on the instrument), or a hybrid of these (TF Adaptive, Kerr) is a matter of preference. Current file systems vary greatly in their heat treatments, cross-sectional design, cutting angle, flute width, flute depth, taper, cutting efficiencies, fracture resistance, manufacturing method/physical characteristics/metal composition, among a wide array of other variables. The above notwithstanding, the authors recommend using controlled memory (CM) nickel titanium. This is regardless of the rotary, reciprocating, or hybrid motion (Figure 6)

Figure 6B: Clinical case done with reciprocated endodontic files (Waveone Gold Dentsply)
(Dr Julian Webber)

Torque limits

Reliance upon the technology of nickel titanium and the torque control and speed settings among other limiting features in standard endodontic motors to avoid file separation is not advised. Insertion of all nickel titanium files, whether via rotational or reciprocated motions should be advanced passively and never forced. This said, observing manufacturer recommended torque limits and speeds has obvious value.  

Irrigation and irrigant activation

The canal preparation detailed above is complete when the clinician can adequately irrigate and obturate the prepared canal. Using standard methods of irrigation activation (ultrasonic, sonic, apical negative pressure, laser, mechanical), based on the literature, a .04/30 preparation can be adequately activated and disinfected. 

Some clinicians using laser (Biolase, Fotona) or multisonic neutral to negative pressure activation systems (Gentlewave, Sonendo) are preparing their canals to smaller diameters than .04/30. There is belief and some evidence that chemical debridement with minimal canal preparation is adequate using these technologies or at least comparable to the other methods. 

Sodium hypochlorite is the primary bactericidal irrigant used to remove organic canal contents. Sodium hypochlorite remains the gold standard in endodontic irrigation. It is the only solution (despite its toxicity when extruded) that dissolves pulpal tissue effectively, is inexpensive, widely available, and highly bactericidal, among other properties. The authors use full strength sodium hypochlorite. 

An alternative to sodium hypochlorite is 2% chlorhexidine (CHX). CHX does not dissolve pulp tissue. It retains its antimicrobial effects for many hours after you dry the canal through a phenomenon known as substantivity.  

Endodontic literature

Irrigant combinations are also available commercially (Chlor-Xtra, Vista Dental) that offer chemical consistency, stability and transparency regarding solution expiration. EDTA 17% solution is used to remove the inorganic contents (the smear layer).

The endodontic literature guides irrigation protocols. It is accepted that larger volumes of irrigation are more effective than smaller. Activation of irrigation solutions with energy is more efficacious than passively soaking canals.

 Warmed irrigation solution is preferred to cold. Although, warming can create chemical instability if not used quickly. 

Deeper penetration of irrigants into the apical third is desirable but you must accomplish this safely. 

Consistent and frequent refreshment of irrigant is critical. The alternation of inorganic solvents (liquid EDTA) and organic solvents (sodium hypochlorite) is desirable. 

Application of irrigant solutions should be passive and as deep as possible without extrusion. To avoid extrusion, an irrigation needle tip with a safety design to limit solution acceleration to the apical foramen is critical. Safety designs include side vents of varying designs and proper gauge sizes (minimally 27 gauge, optimally 30 gauge).

Activation

Figure 7a: Easy Clean (Bassi Endo)

Activation methods involve varying levels of sophistication, expense and corresponding clinical efficacy. The list of available activation methods ranges from ‘low tech’ activation that is economical and simple to apply, to much more ‘high tech’. Basic activation methods include mechanical activation (Easy Clean, Bassi Endo; Finishing Files, Tun; XP Shaper, Brasseler).  

Figure 7b: Irrisonic (Helse)

Sonic activation demonstrates the next level (acoustic streaming) (Endoactivator, Dentsply) and ultrasonic activation (cavitation bubbles) (Irrisonic E1 Tip, Helse; Irrisafe, Acteon). 

Apical negative pressure irrigation pulls solution down through the canal from the pulp chamber to the apex via high-speed suction cannulas. It then carries the solution out coronally through the cannula and into the high-speed evacuation line (Endovac, Kerr). 

The most technologically complex options currently are laser activation (cavitation bubbles) (Fotona, Biolase) and multisonic negative/neutral pressure/degassed solutions (Gentlewave, Sonendo). 

Figure 7c: Waterlase (Biolase)

There is no literature-based superiority of one irrigation technique over another, as no technique is able to deliver a reproducibly sterile canal (Figure 7). 

Obturation

Figure 8a: Well obturated clinical upper second bicuspid highlighting the complex anatomy cleared by adequate irrigation (Dr Brett Gilbert)

Once you disinfect the canal and dry with paper points, it is ready for obturation. 

Gutta percha is the gold standard material for canal obturation. This is due to its biocompatibility, thermo-softened ability and ability to compact into the narrowing cross-sectional diameters of the canal preparation. Another favourable characteristic is its re-treatability in the event of post-treatment disease. 

Methods of obturation vary widely, from carrier-based obturation, single cone obturation with and without warm vertical compaction and the traditional cold lateral condensation technique.  

Many hybrid methods, including some aspect of the above methods, have also been developed.  There is no literature-based superiority of one obturation method over another. Heat sources and gutta percha extrusion devices to facilitate warm obturation are reliable and affordable (Evofill, Diadent; EQV, Metabiomed).

Figure 8b: Diaroot Bio sealer (Diadent)

Regardless of the chosen obturation method, the biologic objectives of obturation do not change. They include using a biocompatible sealer and gutta percha to seal off the canal space from the apical tissues. This eliminates possible coronal microbial contamination. The clinician should feel comfortable with a number of different techniques to match the obturated anatomy. Obturation technique is not ‘one size fits all’.

Sealers are non-toxic and biocompatible after setting. Therefore, it is desirable to minimise the amount of sealer extruded apically. It will prevent inflammation and possible toxicity to vital structures (mental and inferior alveolar nerve). Hydrophilic bioceramic sealers in the form of tricalcium silicate derivatives have become widely utilised by specialists over the past decade relative to the resin, ZOE and calcium hydroxide alternatives (Bioceramic sealer, Brasseler; Bioroot RCS, Septodont; Dia-Root Bio Sealer, Diadent) (Figure 8). 

Post-endodontic coronal seal

The optimal time to place the post endodontic coronal seal and final tooth restoration is immediately after obturation. Under a rubber dam and surgical microscope. An excellent post-endodontic coronal seal/restoration correlates with clinical success. 

Posts are indicated only if adequate coronal tooth structure is not present and/or possibly if a ferrule is missing. Metal posts correlate with vertical root fracture. Especially when placed too short, long, large, or threaded etc.  

Fibre posts have a modulus of elasticity similar to dentine and can be more fortifying than metal posts. Preservation of tooth structure, microbial control, surgical microscopic visualisation and tactile control, and patient convenience are all benefits of placing the coronal restoration immediately after obturation. 

Summary

Figure 9: Excellent immediate post endodontic coronal seal placed under the microscope and rubber dam. Clinical case done with rotational endodontic files (Dr Richard Mounce)

This article has discussed the current state-of-the-art in endodontics for first time or initial orthograde root canal treatment. Endodontists place emphasis on achieving a reproducible pulpal and periapical diagnosis, preoperative risk assessment, minimally invasive access and canal shaping, the vital importance of activating irrigants, the use of warm obturation techniques and early coronal seal (Figure 9).  

This article first appeared in Clinical Dentistry magazine. You can read the latest issue here.

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