Root Canal Therapy

Dr. Karina Roth
Authored by:
Dr. Karina Roth

Please note: For clarity of illustration, certain graphical representations within the videos you will view do not show the rubber dam. However, be aware that a rubber dam is a critical part of standard treatment and MUST be used throughout this procedure without exception.

Introduction

Injury to the dental pulp can lead to pulp infection and/or necrosis.

The most frequent etiological factors which ultimately lead to pulp injury are:

  1. Extensive decay.
  2. Microleakage under restorations.
  3. Restorations.
  4. Traumatic injuries leading to pulp exposure.
  5. Dentin cracks.
  6. Advanced periodontal disease.

Root Canal Therapy must be instituted in order to avoid the spread of infection to the surrounding apical tissues and avoid its extraction. Restoring an endodontic treated tooth is far less expensive than replacing an extracted one by means of prosthetic devices or implants.

The procedural steps necessary to carry out Root Canal Therapy involve:

  1. Establishing an aseptic field.
  2. Removing pulp, microorganisms and toxic products from the pulp chamber and the root canal.
  3. Enlarging and shaping the canal space  to receive a root canal filling.
  4. Sealing the root canal space with a biocompatible filling material to provide a barrier between oral cavity and periapical tissues.
  5. Returning dental tissue to follow proper resolution (temporary or permanent) at the completion of treatment.

“The general objective of endodontic initial treatment is to retain the treated tooth in a healthy state to act as support for a suitable restoration that will allow the tooth to return to normal function, and the specific goal is to prevent or heal apical periodontitis.”1 In Phase 4 of the Toronto Study,2 137 teeth were examined to establish the outcome of endodontic treatment after a follow-up period of 4-6 years. Without preoperative radiolucency, 93% of the teeth remained free of disease, and 94% were functional and asymptomatic. Among teeth with preoperative radiolucency, 82% healed and 96% were functional.

As in the treatment of all infectious diseases, early treatment ie. treatment of the pulp infarction prior to the extension of the inflammation to the periapical tissues, will afford the patient a better chance for a favorable treatment outcome.

Contraindications to Root Canal Therapy include:

  • Unmanageable variations in root canal anatomy.
  • The ability to adequately isolate the tooth with a rubber dam (standard of care).
  • Non-restorable teeth.
  • Inadequate periodontal support which cannot be corrected.
  • Vertical root fractures.
  • Canal instrumentation.
  • Surgery or implantation.

Procedure

Diagnosis and Pre-Operative Considerations

A new good quality pre-operative radiograph must be taken, especially if the previous radiographs are old (3 months or older) or if the patient was treated due to an emergency by a different operator. The tooth should be centered and seen in its entirety (from crown to apex).

When no previous radiograph is available, a second off-angle radiograph is helpful in disclosing variations in most anatomy.

In addition, a series of tests must be performed in order to replicate the symptoms from which the patient is complaining (more so if several teeth are affected); this way we can find the offending tooth and establish an accurate diagnosis. Petersson et al3 evaluated the ability of thermal and electric tests to register pulp vitality.

Their results were as follows:

Sensitivity = ability of a test to identify fully developed teeth that are diseased. Necrotic teeth were correctly identified:

  • 83% with cold tests.
  • 86% with heat tests.
  • 72% with EPT (electric pulp tester).

Specificity = ability of a test to identify fully developed teeth without disease. Teeth with healthy pulps were correctly identified:

  • 93% by both the cold and EPT (electric pulp tester).
  • 41% by the heat test.

Before testing the teeth, the patient should be informed about the procedure and what is the expected response (tingling/warming sensation, response to cold, etc) in order to decrease anxiety levels and thus alter the patient’s real response (if the patient is in pain, he/she may answer even before the stimulus elicits a response to avoid it).

Tests should be first performed on a “normal” tooth (for example: if the chief complaint is on tooth 11, first test tooth 21). Make sure that when testing adjacent teeth they are not endodontically treated (see full mouth set of radiographs; if the patient does not have a full set, test teeth adjacent to the tooth in question and analyze the pre-operative radiograph from that area).

A series of different stimuli can be applied, after which the patient will feel a sharp, brief painful sensation.

  • if this response on the “diseased tooth” is more intense and lingers, it can be an indication of inflammatory changes within the pulp.
  • if no response is obtained, it may be an indication of a necrotic pulp.

False-negative responses

  • In teeth that have been traumatically injured, follow-up testing should be scheduled for several months as they may not respond to tests but still be vital.
  • Teeth exhibiting narrowed pulp chambers or canals.
  • Partially developed teeth.

Before performing any tests, all teeth should be isolated from the soft tissues with cotton rolls, and from adjacent teeth with small pieces of rubber dam (in order to avoid false responses arising in other teeth than the one being tested).

Tests include:

Cold Test

Accuracy = 86%.

EndoIce® (Coltene-Whaledent): (1,1,1,2-tetrafluoroethane)
- 26.20ºC.

This cold gas is sprayed onto a #2 cotton pellet4 which is then applied over the incisal third and midfacial area of the tooth to be tested. Effective for testing teeth covered with crowns.

EPT, electric pulp tester

Accuracy = 81%.

There has been some controversy over the safe use of these devices in patients with pacemakers. In an In Vivo study on several apex locator and electric pulp testing devices, Wilson concluded that when an increased pacing frequency was observed, this was related to a slower intrinsic heart rate and not to  electrical interference with the cardiac devices.5

A small amount of a conductivity gel such as toothpaste is applied over the incisal third on the buccal surface of the tooth.6 The tip of the testing device is placed on the enamel and the patient must hold it in order to complete the circuit. The operator should gradually increase the current level until the patient feels a tingling sensation.

Heat Test:

Accuracy = 71%.

Transmission of heat to the tooth by:

  • Application of the melted tip of a gutta-percha stick onto the midfacial area of the tooth;
  • Running a dry prophy cup (no refrigeration) over the tooth, thus creating frictional heat;
  • Isolating teeth from the most posterior to the most anterior one and irrigating with hot water.

Delayed responses may occur. If so, wait at least 10 seconds between tests.

Percussion

Pain to percussion indicates the presence of periradicular inflammation (this may not always be of pulpal origin) so the results from this test should be used in conjunction with those from other tests.

Hyperocclussion can lead to a more positive response. If a recent restoration has been placed, check contact points in all excursions.

Try first with light pressure applied digitally with a gloved finger. Next, gently tap vertically with the blunt end of the handle of a mirror on an incisal edge or occlusal surface, or by tapping horizontally over the buccal surface of a tooth.

Palpation

Apply firm digital pressure in the area where the offending tooth’s apex is located. The results should indicate if inflammation has extended into the periapical area. A change in contour and sensation will be noticed.

Tooth Sleuth

This device is placed on one cusp at a time while the patient grinds with opposing teeth. Sharp pain on pressure or release may indicate a cusp fracture or cracked tooth.

Anaesthesia

The first step in starting root canal therapy is to achieve complete anaesthesia.

Select the appropriate technique according to tooth type/location:

  1. Blocks are generally used to achieve anaesthesia when treating mandibular teeth.
  2. Infiltration is generally used when treating maxillary teeth.

In the absence of pulpal or periapical pathosis, the success of an Inferior Alveolar Nerve block is between 85 and 90%. It has been well documented7,8,9 that in some cases (for example, patients presenting irreversible pulpitis) the success rate drops as low as 20%. In these cases supplemental techniques should be used to achieve complete anaesthesia and then be able to treat the patient.

Supplemental techniques

  • Intraosseous injection.
  • Periodontal ligament injection.
  • Intrapulpal injection.

The onset of the anesthesia usually occurs in 3-5 minutes. Before applying the rubber dam and starting the procedure, verify if complete pulpal anesthesia has been achieved by carefully testing the tooth with cold water or EndoIce®. Lip numbness after an inferior alveolar block has been given is NOT an indicator of complete pulpal anesthesia.

Rubber Dam Isolation

It is of paramount importance to isolate the tooth with rubber dam:

  • to work in a sterile environment;
  • to avoid leakage of saliva into the tooth;
  • to prevent aspiration/inhalation of instruments10,11,12/chemicals13,14 by the patient.

Both the tooth and the rubber dam should be disinfected before starting the procedure (ex. Chlorhexidine) in order to reduce the bacterial count in the area and work in a sterile environment.

Access

Access is prepared into the core of the tooth where the pulp is located. This is one of the most important phases of the treatment, since the success and ease of subsequent steps hinge on it.

Objective: to attain straight line access from the coronal portion of the tooth into the most apical area of the tooth: this way, intracanal complications (bending/fracture of instruments, changes in working length, modifications in the apical anatomy, etc) will be avoided.

Select the appropriate size of bur according to the tooth’s anatomy. In anterior teeth, start your access by directing the bur at a 45º angle. Once dentin is encountered, the bur should be directed parallel to the long axis of the tooth and continue cutting apically until the bur penetrates into the pulp chamber. Confirm the location with an endodontic explorer (DG-16). If accessing posterior teeth, start the access cavity following the long axis of the tooth and directing the bur to the center of the pulp chamber.

Remove dentin triangles with round burs in a slow speed handpiece or using an Endo-Z bur in a high speed handpiece (this bur has a non-cutting tip making its use safer for this purpose).

Coronal preflaring

Objective: to eliminate dentinal triangles which occlude the orifices or prevent straight line access into the canal. Gates-Glidden burs are used sequentially from the largest to the smallest (example: GG #4, #3, #2). To decide which is the first instrument to be used, verify that only one head of the instrument is below the orifice entrance. Use these instruments brushing in an out-stroke and always against the danger areas (example: furcation walls).

Working Length

  1. Measure against radiograph between an occlusal or incisal reference point and another located aproximately 0.5 to 1 mm from the radiographic apex of the tooth. (estimated working length]).
  2. Measure this distance with ruler and transfer to a K-file (#10 or #15).
  3. Insert file into the canal with light pressure to avoid extruding the instrument past the constriction, thus altering this area and/or damaging the periapical tissues.
  4. Place the largest file that binds at WL into tooth and use an apex locator to confirm length (a loose file will not contact all the walls in the canal and will not give an accurate reading and it may go beyond the apex). Apex locators are very reliable instruments. Many different units have been tested both In Vitro and In Vivo, and it has been concluded that they are 96.2% reliable.15 There has been some controversy about the safety in the utilization of apex locators in patients with pacemakers. Garofalo16 conducted an In Vitro study in which he tested different devices. He concluded that even these results cannot be directly extrapolated into a clinical scenario. It seems that their use should be safe in these patients.
  5. Adjust the rubber stop to a reference point (RP) (choose a stable RP, NEVER use one on a temporary restoration or unsupported tooth structure as they may be lost during the procedure).
  6.  Once a reliable and reproducible reading has been obtained take a radiograph with file inserted in the canal.

Cleaning and Shaping

This stage is accomplished by a combination of the action both by instruments and irrigating solutions. It’s final objective as defined by Schilder17 is “to develop a continuously shaped conical form from apical to coronal. The apical preparation should be as small as practical and in its original position spatially”. This will facilitate the progressive access of irrigating solutions into areas within the root canal system which are difficult to get into with instruments due to its irregularities (“irregular canal cross-sections, accessory canals and apical deltas are mostly inaccessible to mechanical preparations”18,19), although it has been proved many years ago that irrigants do not have an extensive and intimate contact with all areas of tissue.20

The complete cleaning and shaping of the canal can be accomplished by using either hand files and/or rotary instruments.

Initial Apical Enlargement

Objective: initial negotiation of the root canal space with hand files #06, 08, 10...

A minimal apical enlargement is started in order to direct irrigating solutions at that level. Each tooth and its unique anatomy should be individually considered, but as a general guide, it should not be prepared over a file #20 - #25.

Body Shaping

Step back / rotary instruments.

Objective: to obtain a continuously tapered/flared preparation that will smoothly blend with the coronal and apical ones, maintaining the original anatomy. This step can be successfully completed either by using hand or rotary instruments.

Hand instrumentation: Step-back technique

This is accomplished by using sequentially larger files, each shorter by 1 mm from the previously used in order to create a coronal taper. The SB is started with the last file that reached WL in the IAE, and 4 to 6 files should be used. Irrigation and patency should be checked between each instrument to avoid packing debris in the apical portion of the canal.

Protaper Sequence

In several studies it has been demonstrated that ProTaper instruments can prepare canals without any obvious procedural errors to a smooth tapered shape of appropriate sizes. Although it should be remembered that due to the irregular anatomy of most canals, these instruments leave 43-49% of the walls “untouched.”21

The motor should be set at 300 rpm and the torque level at 3. Verify the reduction of your handpiece and select the same one in the motor (example: 1/8).

Always adjust the rubber stopper to the appropriate WL and check throughout the procedure. Clean periodically the instruments with wet gauze with alcohol or NaOCl. If the instrument is packed with dentinal debris, the flutes will not cut efficiently. Never force the instruments.

Use copious irrigation and check patency between instruments.

S1 and S2 are shaping instruments. They should be inserted passively through the center of the canal, and should cut in the out stroke with a brushing motion against all walls. Only after the instrument has flared the walls, it should go to WL only once or twice to avoid canal transportation.

The use of the SX instrument is optional, and should only be used after flaring the canal with S1 and S2.

The finisher files (F1, F2, F3, F4 and F5) DO NOT brush against the walls. They should only go to WL once or twice.

Final Apical Enlargement

Objective: to create an apical stop. The original anatomy of the canal should be maintained, as well as the position, size and location of the apical foramen.

Select the appropriate MAF according to tooth anatomy (refer to chart enclosed in clinical manual describing suggested parameters). The ideal size of the preparation can only be determined if the file that is taken apically has no contact against the walls of the canal in the middle or coronal thirds and is able to flow into the apical curvature engaging only at its tip: that is why straight line access is of paramount importance.22 If canals are prepared to sufficiently large apical sizes, the irrigating solutions will be better able to disinfect areas of irregular anatomy23 and to facilitate the elimination of debris mechanically.24

The apical enlargement is continued from the last instrument that had reached total WL before initiating the step-back technique or the equivalent to the last Protaper that has been used (example: F3 = #30), and is continued until the desired file is selected (according to canal size / curvature, etc). These files should work with a ¼ clockwise turning motion with apical pressure.

Although a maximum size cannot be given due to the wide anatomical variety of canals, most should be prepared at least to a size #30.

Throughout the procedure, constant and copious irrigation with sodium hypochlorite should be done after the use of each instrument, using side vented irrigation needles to avoid the extrusion of the solution into periapical area. “A suggested concentration of sodium hypochlorite is common household bleach (5.25%) diluted with equal parts of water for a 2.6% solution. This is just as effective as full strength and is safer and more pleasant both for the patient and the operator.”25 Also verify that the needle does not engage tightly against the walls of the canal. If so, withdraw a couple of mm and inject the solution with light pressure with corono-apically movements.

The most important factors to remember when irrigating within the canal are the depth of penetration of the needle and the volume being used. The irrigation will occur only coronally to the apical extent of the needle, so the more flared the preparation, the deeper the needle can access and thus the deeper that the irrigating solution will reach.26,27 This coupled with copious and frequent rinses, will allow better flushing of the floating debris within the canal. it is very important to ensure that the needle is NOT binding in the canal in order to avoid any NaOCl accidents (ex. extrusion of the solution into the soft tissues). Once the preparation has been completed, a master apical file radiograph should be taken. The tooth is now ready to be filled.

Endodontic Filling

According to Walton and Torabinejad, the objective of the obturation is to create a complete seal along the length of the root canal system from the coronal opening to the apical termination. According to the AAE, “root canal sealers are used in conjunction with a biologically acceptable semi-solid or solid obturating material to establish an adequate seal of the root canal system”. These materials should be as inert as possible but also prevent any reinfection or any proliferation of microorganisms that might have been left within the canal.28

Several techniques can be used to fill the canals, cold lateral condensation, warm vertical condensation, obturations with carriers, etc.

Cold lateral condensation

Lateral compaction is a widely taught and used technique29 mostly due to the operator’s ability to have control over the length during condensation. It is also popular because it can be used in most clinical cases. In many studies it is used as the golden standard against which many other techniques are compared.

The obturation of the canal contains a core (gutta-percha) and a sealer. Sealers can contain resins, zinc-oxide and eugenol, glass ionomer, calcium hydroxide, resins, etc. Sealers should always be mixed according to manufacturer’s instructions.

A master gutta-percha cone is selected according to the MAF and fitted. The cone should only bind at the tip, which should fit snuggly into the apical preparation created during C&S. The sides of the cone should not bind against the walls of the preparation. Position the cotton pliers at the reference point and try to remove the master cone from the canal. Tug-back is the resistance of the cone to removal, so perfect tug-back should be achieved. If there is no TB, a different cone should be fitted.

Master cone radiograph

A radiograph with the master cone is taken to verify its correct fit that should coincide with the length and position of the MAF.

In Clinic 1, we use the Roth 801 formula, which is based on ZOE. Powder and liquid should be mixed on a glass slab incorporating (in increments) as much powder as possible (respecting the ratio) to avoid having excess of eugenol which is irritating for the patient and can lead to a painful post-op.

Mix in a circular motion pressing the granules to dissolve them into the liquid. Mix for about 2-3 minutes until a string can be lifted 1 inch / 2-3 cm, and maintained for about 5 seconds.

Next, the canal (s) is/are dried with sterile paper points selected according to the size of the canal.

The sealer can be placed using either:

  • Lentulo spirals
  • Paper points
  • Master cone
  • Master apical file

Once the sealer and the master cone are inserted into the canal, a finger spreader is selected.

Finger spreaders are manufactured both in stainless steel and nickel-titanium alloys. The latter have been proven to be superior to the former, as they have increased flexibility,30 they reduce stress during condensation31 and provide deeper penetration and better access into curved canals.32,33

It should match the taper of the canal and be able to reach an area within 2 mm of the working length. 34 This length should be recorded on the spreader by adjusting the rubber stop against the reference point. Remove the finger spreader from the canal and measure. Re-insert in the canal. Allow enough time for the spreader to plasticize the gutta-percha against the wall of the canal which is furthest from the operator. In this way, visibility is enhanced. Make sure to condense always against the same wall to avoid creating voids.

Select the corresponding accessory GP points matching the spreader that is being used, and transfer this new length to it to make sure that the cone will fill the space created by the finger spreader. Remember that the correlation between the spreader size and the conventional cones many time is highly variable.35,36 Butter the accessory cone with sealer. Remove the spreader from the canal by rotating it back and forth while it is being withdrawn and immediately insert the accessory GP point to fill the space created. Repeat this step 2-3 times.

A mid-obturation radiograph is taken, to confirm that the filling procedure is being completed with no voids in the apical third. If there is suspicion of an incomplete fill, remove all the gutta-percha and recommence.

Once the canal is completely filled, the excess of cones is seared with heat (for example, with a Touch’n Heat unit) and the gutta-percha is then condensed with a hand plugger. This warm vertical compaction at this level enhances the seal at the orifice level.37

Gutta-percha should be removed to the CEJ (cemento-enamel-junction) or 1 mm apical to it to avoid tooth discoloration.

Temporization

Once the root canal treatment has been completed, a restoration with adequate coronal seal should be placed. Even if the canals have been well obturated, if there is coronal leakage, there will be bacterial recontamination and the treatment might be a failure.38 Coronal leakage has been proven to be one of the main etiological factors leading to an adverse outcome of an endodontic treatment.39,40

A sponge pellet41,42 is placed at the orifice level to avoid any material blocking the entrance into the canal, and a tight double seal should be placed to avoid leakage (Cavit + IRM or GI).

The temporary material should be chosen according to:

  • Required duration (time).
  • Occlusal load and wear.
  • Complexity of access.
  • Loss of tooth structure.

Post-Operative Considerations

A post-operative radiograph is taken. The radiographic criteria for evaluating obturation include: length, taper, density, gutta-percha and sealer removal up to the CEJ in anterior teeth and to the canal orifice in posterior teeth, and an adequate provisional restoration with adequate margins should be in place.43

The patient is given the final indications: if medications need to be prescribed, the patient should be instructed on how to take them (dose, frequency,etc); care in the area (foods to eat, not biting until anesthesia has worn off completely); next appointment, payment, etc.

An appointment for placement of a permanent restoration MUST be booked, and the patient MUST be aware that only a TEMPORARY restoration has been placed.

Intracanal Medication

Root canal therapy can be completed after several appointments. The root canal space should not be left open between visits because bacterial contamination of the cleansed canal may occur.44

Additionally, teeth left open to the environment are often involved in exacerbations during treatment.45

Several chemical substances have been used as interim dressings, but the most widely used is Calcium Hydroxide (in powder that should be mixed with distilled water or anesthetic solution, or in preloaded syringes). This is intended to act as a second front to prevent invasion of oral microorganisms into the root canal in the event of leakage or breakdown of the temporary filling.46

 

References: 

Ørstavik D, Pitt Ford TR. Apical periodontitis: microbial infection and host responses. In: Ørstavik D, Pitt Ford TR, eds. Essential endodontology: prevention and treatment of apical periodontitis. Oxford: Blackwell Science, 1998; 1-8.

De Chevigny C, Dao T, Basrani B, Marquis V, Farzaneh M, Abitbol S and Friedman S. J Endod 2008, article in press.

Petersson K, Söderström C, Kiani-Anaraki M, Lẻvy G. Evaluation of the ability of thermal and electrical tests to register pulp vitality. Endod Dent Traumat 1999; 15 (3): 127.

Jones DM. Effect of the type carrier used on the results of dichlorodifluoromethane application to teeth. JEndod 1999; 25: 692.

Wilson BL, Broberg C, Baumgartner JC, Harris C, Kron J. Safety of electronic apex locators and pulp testers in patients with implanted cardiac pacemakers or carioverter defibrillators. J Endod 2006; 32: 847-852.

Bender IB et al. The optimum placement-site of the electrode in electric pulp testing of the 12 anterior teeth. JADA 1989; 118: 305.

Malamed SF. Handbook of local anesthesia. Elseviver Mosby, 5th edition, 2004; p.269.

Potočnik I, Bajrović F. Failure of inferior alveolar nerve block in endodontics. Dent Traumatol 1999; 15 (6): 247-251.

Hargreaves K, Keiser K. Local anesthetic failure in endodontics: Mechanisms and Management. Endod Topics 2002; 1 (1): 26-39.

Israel HA, Leban SG. Aspiration of an endodontic instrument. J Endod 1984; 10 (9); 452-454.

Susini G, Pommel L, Camps J. Accidental ingestion and aspiration of root canal instruments and other dental foreign bodies in a French population. Int Endod J 2007; 40 (8); 585-589

Lambrianidis T, Beltes P. Accidental swallowing of endodontic instruments. Dent Traumatol 1996; 12 (6): 301-304.

Whitworth JM, Seccombe GV, Shoker K & Steele JG. Use of rubber dam and irrigant selection in UK general dental practice. Int Endod J 2000; 33 (5), 435–441.

Hühlsmann M, Hahn W. complications during root canal irrigation – literature review and case reports. Int Endod J 2000; 33: 186.

Shabahang S, Goon WWY, Gluskin A. An in vivo evaluation of Root ZX electronic apex locator. J Endod 1996; 22 (11): 616-618.

Garofalo R et al. Effect of electronic apex locators on cardiac pacemaker function. J Endod 2002; 28: 831.

Schilder H. Cleaning and shaping the root canal. Dent Clin North Am 1974; 18: 269.

Ida RD, Gutmann JL. Importance of anatomic variables in endodontic treatmet outcomes: case report. Endod Dent Traumatol 1995; 11: 199–203.

Siqueira JF, Araujo MCP. Histological evaluation of the effectiveness of five instrumentation techniques for cleaning the apical third of root canals J Endod 1997; 23: 499-502.

Senia ES, Marshall FJ, Rosen S. the solvent action of sodium hypochlorite on pulp tissue of extracted teeth. Oral Surg Oral Med Oral Pathol 1971; 31: 96.

Peters OA, Peters CI, Schönenberger K, Barbakow F. ProTaper rotary root canal preparation: effects of canal anatomy on final shape analysed by micro CT. Int Endod J 2003; 36: 86-92.

Leeb J. canal orifice enlargement as related to biomechanical preparation. J Endod 1983; 9: 463.

Ruddle C. cleaning and shaping the root canal system in Cohen S, Burns RC. Pathways of the pulp. 8th edition, 2002. Mosby p. 231-292.

Dalton BC, Ørstavik D, Philips C, Pettiette M, Trope M. bacterial reduction with nickel-titanium rotary instrumentation. J End

Walton RE, Torabinejad M. principles and Practice of Endodontics. 3rd edition. Saunders 2002; p. 219.

Abou-Rass M, Piccinino M. the effectiveness of four clinical irrigation methods on the removal of tooth canal debris. Oral Surg Oral Med Oral Pathol 1982; 54: 323.

Ram A. Effectiveness of root canal irrigation. Oral Surg Oral Med Oral Pathol 1977; 44: 306.

Beer R, Baumann M, Kielbassa A. Pocket atlas of endodontics. Thieme 2004, p.176.

Cailleteau JG, Mullaney TP. Prevalence of teaching apical patency and various instrumentation and obturation techniques in United States dental schools. J Endod 1997; 23: 394.

Berry KA< Loushine RJ, Primack PD, Runyan DA. Nickel-titanium versus stainless-steel finger spreaders in curved canals. J Endod 1998; 24: 752.

Dawn JJ, Glickman GN. 2-D photoelastic stress analysis of Ni-Ti and stainless-steel finger spreaders during lateral condensation. J Endod 1995; 21: 221.

Joyce AP, Loushine RJ, West LA, Runyan DA, Cameron SM. Photoelastic comparison of stress induced by using stainless-steel versus nickel-titanium spreaders in vitro. J Endod 1998; 24: 714.

Schmidt KJ, Walker TL, Johnson JD, Nicoll BK. Comparison of nickel-titanium and stainless-steel spreader penetration and accessory cone fit in curved canals. J Endod 2000. 26: 42.

Allison DA, Michelich RJ, Walton RE. The influence of the master cone adaptation on the quality of the apical seal. J Endod 1981; 7: 61.

Briseno BA, Marroquin B, Wolter D, Willershausen-Zonnchen B. Dimensional variability of nonstandarized greater taper finger spreaders with matching gutta-percha points. Int Endod J 2001; 34: 23.

Zmener O, Hilu R, Scavo R. Compatibility between standardized endodontic finger spreaders and accessory gutta-percha cones. Endod Dent TRaumatol 1996; 12: 237.

Yared GM, Dagher FB, Machtou P. influence of the removal of coronal gutta-percha on the seal of root canal obturations. J Endod 1997; 23: 146.

Magura ME, Kafrawy AH, Brown CE Jr, Newton CW. Human saliva coronal microleakage in obturated root canals: an in vitro study. J Endod 1991; 17: 324.

Saunders WP, Saunders EM. Coronal leakage as a cause of failure in root-canal therapy: a review. Endod Dent Traumatol 1994; 10: 105.

Ray H, Trope M. periapical status of endodontically treated teeth in relation to the technical quality of the root filling and the coronal restoration. Int Endod J 1995; 28: 12.

Vail M, Steffel C. Preference of temporary restorations and spacers: a survey of Diplomates of the American Board of Endodontists. J Endod 2006; 32 (6): 513-515.

Newcomb B, Clark S, Eleazer P. Degradation of the sealing properties of a Zinc Oxide-Calcium Sulfate-based temporary filling material by entrapped cotton fibers. J Endod 2001; 27 (12): 789-790.

Cohen S, Hargreaves K. Pathways of the pulp. 9th edition. Mosby Elsevier 2006 p. 367.

August DS. Managing the abscessed open tooth: instrument and close – part 2. J Endod 1982; 8 (8); 364-366.

Seltzer S, Naidorf IJ. Flare-ups in endodontics: I. Etiological factors. J Endod 1985; 11(11); 472- 478.

Chong BS, Pitt Ford TR. The role of intracanal medication in root canal treatment. Int Endod J 1992; 25 (2): 97-106.