Year : 2015 | Volume
: 5 | Issue : 1 | Page : 13--19
Root canals-from concretion to patency
Chandrakar Chaman, Paridhi Garg, Shashi Prabha Tyagi, Udai Pratap Singh
Department of Conservative Dentistry and Endodontics, Kothiwal Dental College and Research Centre, Moradabad, Uttar Pradesh, India
Kothiwal Dental College and Research Centre, Moradabad - 244 001, Uttar Pradesh
Teeth with calcification provide an endodontic treatment challenge; traumatized teeth usually develop partial or total pulpal obliteration which is characterized by apparent loss of the pulp space radiographically and a yellow discoloration of the clinical crown. Since only 7-27% of such teeth develop pulp necrosis with radiographic signs of apical periodontitis, it is difficult to decide whether to treat these teeth immediately upon detection of the pulpal obliteration or to wait until signs and symptoms of pulp and/or apical periodontitis occur. This article reviews the etiology, prevalence, classification, mechanism, diagnosis as well as treatment options for teeth with pulp obliteration and the various management approaches and treatment strategies for overcoming potential complications. A search of articles from «DQ»PubMed«DQ» and «DQ»Medline«DQ» from 1965 to present was done with the keywords dental trauma, discoloration, pathfinding instruments, pulp canal obliteration, and root canal treatment was conducted. A total of 94 abstracts were collected, of which 70 relevant articles were read and 31 most relevant articles were included in this article.
|How to cite this article:|
Chaman C, Garg P, Tyagi SP, Singh UP. Root canals-from concretion to patency.Saudi Endod J 2015;5:13-19
|How to cite this URL:|
Chaman C, Garg P, Tyagi SP, Singh UP. Root canals-from concretion to patency. Saudi Endod J [serial online] 2015 [cited 2020 Apr 9 ];5:13-19
Available from: http://www.saudiendodj.com/text.asp?2015/5/1/13/149081
Pulp canal obliteration is defined as a pulpal response to trauma that is characterized by deposition of hard tissue within the root canal space.  It has also been referred to as calcific metamorphosis, dystrophic calcification, diffuse calcification, and calcific degeneration. It is seen commonly after traumatic tooth injuries and is recognized clinically as early as 3 months after injury, but in most instances, it is not detected for about 1 year. 
Eitology and Prevalence
Their prevalence varies widely from 8% to 95% of the studied population.  The etiological factors are not well understood, apart from trauma, age, gender, various systemic diseases, and long-term irritation such as deep caries and restorations have been proposed as possible implicated factors. 
Age-related changes, such as reduction in size of pulp due to secondary dentin deposition, occur throughout life resulting in reduction in root canal length and width. There is increased deposition of intratubular dentin leading to dentinal sclerosis; as a consequence, there is tendency toward pulp chamber obliteration. In addition, the blood supply decreases with age. Soames and Southam  related this generalized pulp obliteration to certain genetic diseases like Marfan syndrome. An association with systemic diseases like renal osteodystrophy and atherosclerosis has also been seen though it has not been established scientifically. Andreasen  reported an increased incidence of pulp obliteration after orthodontic band fixation of traumatized teeth, and they assumed that band application might have caused displacement of root with compression of the apical vessels. Orthodontic intrusive movements are considered to have the greatest impact on the apical region and pulpal blood supply. Pulp canal obliteration was found in all luxation categories, and 69% of the teeth demonstrated yellow crown discoloration.  It was observed that calcific metamorphosis developed more in teeth with concussion and subluxation injuries. The frequency of pulp obliteration is dependent on the extent of the luxation injuries and the stage of root formation.  It has been seen that in teeth with closed apices, there is constriction of blood vessels leading to pulpal necrosis, whereas if the apices are open, the tooth will react with increased deposition of sclerotic dentin. Restorative materials can also have an effect on the underlying pulp resulting in odontoblastic injury. Resolution maybe accompanied by fibrosis and premature "ageing" of the pulp. This effect ceases within 30 days. 
According to Kronfeld and Boyle,  there are two distinct types of calcification that occur in the pulp: Those more frequent in the radicular pulp are generally termed diffuse or linear calcifications, whereas those more commonly found in the coronal region are known as pulp stones (denticles). Denticles can be classified according to their structure into true or false. True denticles have dentinal tubules like dentin, odontoblastic processes, and few odontoblasts, whereas false denticles are concentric layers of calcified tissue with a central cellular area, which might be necrotic and acts as nidus of denticle formation. The difference between the two is morphological not chemical. According to their location, they can be classified into embedded, interstitial, adherent, and free denticles. The degree of pulp obliteration can further be classified as total obliteration, in which the pulp chamber and root canal are hardly or completely not discernible, and partial obliteration, in which the pulp chamber is not discernible and root canal is markedly narrowed but clearly visible.  However, total pulp obliteration is rare and usually a thin fine residual filament of pulp tissue or tract of organic material is present. It has been found that partial obliteration has no detrimental effect on the pulp. This may be explained by the fact that partial obliteration involves primarily the pulp chamber and has a more limited effect in the root canal and apical region. This might allow the circulatory system of these teeth to react adequately to maintain sufficient blood perfusion.  There is yet another classification of pulp obliteration-localized and generalized.  In the localized form, the etiologic agent most often is trauma and this condition has been described relatively frequently after crown and root fractures, tooth luxation, jaw fractures, tooth replantation, and endodontic procedures The prevalence of pulp canal obliteration subsequent to traumatic injuries varies widely from 3.8% to 24%. , The generalized form is probably part of the aging process and is usually seen in older individuals. The pulp chamber may be completely obliterated or hairline thin in most teeth and it is often accompanied by attrition.
The mechanism of hard tissue formation during calcific metamorphosis is not yet clear. Several hypotheses have been proposed to explain this phenomenon. Torneck hypothesized that the deposition of hard tissue is either a result of stimulation of the pre-existing odontoblasts or a result of the loss of their regulatory mechanism containing a maze of small irregular spaces and cul-de-sacs, which extend from the pulp chamber to the apical foramen.  On the other hand, Andreasen and Andreasen  described calcific metamorphosis as a response to severe injury to the neurovascular supply to the pulp, which after healing leads to accelerated dentin deposition, and is closely related to the loss and re-establishment of the pulpal neural supply.  Neither mechanism has been proven nor studied, and further investigation is required to provide an evidence-based understanding of this occurrence.
Calcification is characterized by an osteoid tissue that is produced by the odontoblasts at the periphery of the pulp space or can be produced by undifferentiated pulpal cells that undergo differentiation as a result of traumatic injury. This results in simultaneous deposition of a dentin-like tissue along the periphery of the pulp space and within the pulp space proper. These tissues can eventually fuse with one another, producing a rapidly and completely obliterated pulp chamber and canal. 
Ten Cate  identified this process as deposition of tertiary or reparative dentin in response to irritation or trauma. The cells constituting this hard tissue originate from cell divisions in deeper layers of the pulp; the type of cells that divide has not been established. They might be undifferentiated perivascular cells, pulpal fibroblasts, or cells formed from the odontoblast lineage but not exposed to the final epithelial influence. Evidence indicated that reparative dentin is produced by odontoblast-like cells and incorporates type I and III collagen in its matrix, which exhibits diminished phosphophoryn content. 
It has also been hypothesized that these newly differentiated cells first express a mixture of collagen (including types I, II, III, and IV), which forms a matrix surface. The deposition of fibronectin on predentin provides the mechanism for positioning the cells that then produce a matrix of type I and II collagen that accepts mineral in the absence of phosphophoryn. 
Calcified canals may pose diagnostic challenge. The attempt to locate calcified canals may result in significantly increased chair time for both the patient and the practitioner. Despite improved magnification technologies, it may be difficult to locate and negotiate them. In the process, excessive tooth structure may be removed and the tooth or a root may be at risk of untoward sequelae of perforation. The new imaging technologies such as Cone Beam Computed Tomography (CBCT) show great promise to ascertain if the root canal lumen is present in a tooth that appears calcified on periapical radiograph, and if the tooth is amenable to conventional endodontic treatment. 
The clinical picture of calcific metamorphosis has been described by Patterson and Mitchell  as a tooth that is darker in hue than the adjacent teeth and exhibits a dark yellow color because of a decrease in translucency due to a greater thickness of dentin under the enamel. Some teeth also have a grey discoloration. Studies have shown that the change in tooth color was not a reliable indication of pulp or periapical pathosis.  Most authors have concluded that tooth discoloration had no diagnostic value. It should be remembered that not all teeth with radiographic signs of pulpal obliteration undergo a color change.  It has also been found that more than two-thirds of teeth with pulpal obliteration are asymptomatic. These teeth are often an incidental finding following clinical or radiographic investigations.
As the pulp calcification is pronounced, there is a progressive decrease in the response to thermal and electrical pulp testing. In addition, it has been reported that there is a significant difference to electric pulp testing between partially obliterated teeth compared to those that were totally obliterated. Partially obliterated teeth can give positive results. In the presence of pulp obliteration, it is generally accepted that sensibility tests are unreliable. 
Studies have reported that root canal lumina were detected in an average of 98% of the roots using (CBCT) and 64% of roots using periapical radiographs.  Therefore, conventional projection radiography is not accurate diagnostic tool for determining with certainty if the canal lumen is present. The radiographic appearance of calcific metamorphosis is partial or total obliteration of the pulp canal space with a normal periodontal membrane space and intact lamina dura. A thickening of the periodontal ligament space or perirapical radiolucency may be observed with or without subjective symptoms. Complete radiographic obliteration of the root canal space, however, does not necessarily mean the absence of the pulp or canal space; in the majority of these cases, there is a pulp canal space with pulpal tissue. Usually, a single canal will lie in the center of the root. 
Histopathologic studies designed to assess the pulpal status of teeth with calcific metamorphosis have failed to show any inflammatory component indicative of a pathologic process. The histopathologic appearance of pulp canal obliteration in traumatized teeth shows three types of calcific tissue occluding the pulp lumen: Dentin-like, bone-like, and fibrotic. 
There is considerable disagreement in the literature regarding the optimum treatment of teeth showing signs of pulpal obliteration. However, most authors believe that endodontic treatment should only be initiated following the development of periapical disease radiographically. Literature suggests that pulpal necrosis and periapical disease are not a common complication of pulp obliteration. The incidence is variable ranging from 7% to 27%, which is considered low.  Teeth demonstrating pulpal obliteration but no periapical disease should be managed conservatively through clinical observation and periodic radiographic examination. Teeth with pulpal obliteration requiring root canal treatment fall into the high difficulty category of the American Association of Endodontists Case Assessment criteria.  It has been recommended that root canal treatment should be initiated in teeth that are tender to percussion and do not respond to sensibility tests. Periapical Index (PAI) scores can also be used to assess the tooth. PAI scores more than or equal to 3 should be indicated for root canal treatment.  Moreover, it may also be reasonable to consider an elective or intentional root canal treatment where there are aesthetic concerns and the tooth is unresponsive to vital bleaching techniques.
The canal may be very tiny or difficult to find or negotiate but it is present. Unfortunately, these spaces have adequate room to allow passage of millions of microorganisms. Canals become less calcified as they approach the root apex. Despite severe coronal calcifications, the clinician must assume that all canals exist and must be shaped, cleaned, and obturated to the canal terminus. However, treating calcified canals can lead to certain technical complications such as excessive tooth structure removal, root perforation, or irretrievable instrument breakage if caution is not exercised. If these complications are excluded, the outcome for root canal treated teeth with reduced canal lumens is the same as for "normal" teeth with necrotic pulp. 
The clinician must use a rubber dam for isolation for ideal visualization, which would give a visual command over the canal. In a tooth with a calcified pulp chamber, the distance from the occlusal surface to the projected pulp chamber floor is measured from the preoperative radiograph. The two dimensional radiographic image should be correlated with the three-dimensional morphology of the tooth. An access cavity of normal size and shape is created in the crown to a depth equal to that of the pulp chamber floor in a non-calcified tooth. It is essential to remember that the pulp chamber is always located in the centre of the tooth at the level of the cementoenamel junction (CEJ), which is the most consistent repeatable landmark for locating the pulp chamber.  If aesthetics are not a concern, then in case of anterior teeth, the ideal location of the access preparation would be through the incisal edge. Otherwise an ideal access opening at angle of 45° to the long axis, bur penetration of 3-4 mm will intersect with the pulp chamber and then the direction of the bur should be made parallel. However, the operating microscope has proven to be indispensable for the localization of calcified canals.  The microscope brings the practitioner right into the pulp chamber floor, with high-intensity light revealing in intimate detail an area that was once under-illuminated and required guesswork and greater caution. Recently introduced, Pulpout bur (Essential Dental Systems NJ, USA) is designed to aid in initial endodontic access-opening procedures of calcified teeth. The bur is a friction-grip #4 round carbide bur with a plastic stop fixed at 7 mm. This length has been determined as the "critical depth" from the cusp tip to the pulp chamber that allows access to the pulp chamber without perforation of the furcation. Subtle and minute differences in color and calcification patterns become immediately obvious, serving as a road map in removing the obstructions. Dyes such as methylene blue may assist in locating the canal system under the microscope. Sodium hypochlorite may also be used to assist with the identification of a calcified canal being enhanced using the "bubble" or "champagne" test. Placing 5% sodium hypochlorite into the pulp chamber over a calcified canal containing remnants of pulp tissue will result in a stream of bubbles emerging from the oxygenation of the tissue. This can be seen under the microscope and be used to identify the canal orifice.  In very deep access preparations, it is wise to take radiographic images at multiple angles to maintain alignment and direction. In certain situations, it may be beneficial to remove the rubber dam as this often lies over the area of interest at the level of the CEJ. Small files are required for initial pathfinding; however, these files lack the rigidity required to transverse restricted spaces and can often buckle or fracture when used with vertical watch-winding forces. One approach is to alternate between size 8 and 10 K files with a gentle watch-winding motion with minimal vertical pressure with regular replacement of the instruments before fatigue occurs. 
Negotiation and Penetration
A variety of "pathfinding" instruments have been introduced.  DG-16 explorer is a very useful instrument in the location of canal orifice. Instruments with reduced flute can also be used, such as a Canal Pathfinder (JS Dental, Ridgefield. Conn) or instruments with greater shaft strength such as the Pathfinder CS (Kerr Manufacturing Co.), which are more likely to penetrate highly calcified canals. C+ Files (Denstply, Tulsa, OK, USA) are also ideal for initial instrumentation of calcified root canals. They have a cutting tip that engages the dentin. The long neck (LN-bur) round bur (Caulk/Denstply, Tulsa, OK, USA), extended-shank round burs, such as the Mueller bur (Brasseler, Savannah, GA, USA), can also be used for locating the orifices of calcified canals. Apart from these, there is also the Munce Discovery bur (CJM Engineering, Santa Barbara, CA), which is similar to the Mueller but has a stiffer shaft and is available in smaller head sizes. The extra-long shank of these burs moves the head of the handpiece away from the tooth, improving the clinician's visibility during this delicate procedure. Recently introduced, EndoGuide® Burs (SS white, NJ, USA) increase visibility and control during endodontic exploration while locating hidden canals and navigating deeply calcified canals. A technique using K files with modified tips has also been developed for the penetration of constricted canals. The tip of a #10 K file was sliced diagonally to make it thinner. Because this modified K file has an especially fine tip and an appropriate stiffness, it followed constricted or sharply curved canals well and had a high penetration potential.  Use of nickel titanium files is contraindicated because of lack of torsional strength. 
When negotiating with #6 or #8 K files, they should be precurved with Endo Bender pliers (SybronEndo, Orange, Calif.). Precurving them will allow the file to more easily follow natural canal curvatures that may be present, as opposed to trying to passively place a straight instrument into a curved canal space. The rubber stop should be directed in the direction of the curve. If the orifice still cannot be negotiated with a fine instrument, drill 1-2 mm into the center of the orifice with a no. 2 round bur on slow speed and use the DG-16 explorer to re-establish the canal orifice. When counter-sinking or troughing in an area where an orifice is located, be sure the pulp chamber is dry. The bur rotating at a slow speed will remove whitish chips that then accumulate in the orifice. After a light stream of air is blown into the chamber, these chips appear as white spots on the dark floor of the chamber and serve as markers for exploration or further countersinking.
Ultrasonic endodontic instruments can also help to open up a calcified root canal. When the tip vibrates at a very high rate, it creates miniature sound waves that break up the calcification. Recently, a combination of access refinement ultrasonic tips and magnification has revolutionized the basic concept of access cavity preparation. The uncovering of the floor of the pulp chamber can be accomplished with the help of the CPR 2D or BUC 1 tips (SybronEndo, Orange, California, USA). The pulp stones sometimes can be vibrated or teased out by the CPR 2D or BUC 1 tips; at other times, they can be planed with the help of a BUC 2 tip-a process similar to planing the root surface. Grind the floor until the dark colored dentin becomes visible. It is of critical importance because it dictates and guides the extension of access cavity. Dentsply has launched Start-X (Dentsply India Pvt. Ltd.), a set of 5 ultrasonic tips, in which tip #3 is a canal opening scouter and helps in removing any obstruction in the pulp chamber and tip #5 reveals the original pulp chamber floor anatomy. Canal orifice location is made easier by the removal of calcifications and filling materials that hide the original pulp chamber floor anatomy. The drawback of ultrasonic tips is that its use is restricted to the straight portion of the canal to remove the calcified barrier. Locating canals and initial penetration under the microscope is also aided by fine instruments like the Micro-Orifice Opener. 
Given the above strategies for approaching a calcified tooth, it is vital that the clinician not rush down the canal and that files be inserted passively. A difficult canal can be made impossible if an impassable blockage of debris is created and/or a ledge develops. Both these situations are in the control of the clinician.
Calcification occurs in a coronoapical direction; therefore, once the initial canal has been captured, an instrument tends to progress more easily as it advances towards the canal terminus. Incremental instrumentation can be done by creating new increments between the established widths by cutting off a portion of the file tip, thus making it slightly wider in diameter. For example, if a 1-mm segment is clipped from a size-10 file, the instrument becomes a size 12. By trimming file sizes #15, #20, and #25, instruments of sizes #17, #22, and #27, respectively, can be created. In extremely sclerotic canals, only 0.5-mm segments are trimmed, increasing the instrument width by 0.01 mm and making a #10 file into a #11 file. Since cutting the shaft imparts a flat tip, a metal nail file is used to smooth the end and reestablish a bevel after the removal of any segment.  The working length can be achieved if the canal is negotiated in this way.
Chelator preparations have been advocated frequently as adjuncts for root canal preparation, especially in narrow and calcified root canals. Apical dentin is more frequently sclerosed and is more mineralized.  Ethylenediaminetetraacetic acid (EDTA) acts on calcified tissue by substituting the calcium ions of sclerosed dentin by sodium ions, giving soluble salts. At a normal concentration, EDTA removes 10.6 g of calcium from 100 g of calcium.  Liquid EDTA solution should be introduced into the pulp chamber through a pipette or a cotton pellet to identify the entrance to calcified canals. Though the actual degree to which chelators facilitate negotiation and preparation of calcified and narrow root canals is still unknown, their use can help in negotiation and lubrication of canal.
After creating clean, tapered canals, clinicians need to adequately obturate the root canal system, provide an impermeable fluid tight seal within the entire root canal system, and prevent coronal and apical microleakage. The canals can be obturated using the lateral compaction, vertical compaction, continuous wave, warm lateral, and injection- and carrier-based techniques. In the absence of symptoms or evidence of apical periodontitis, it is acceptable to instrument and fill the canal to the level negotiated but the tooth should be evaluated periodically. 
Root-end resection and filling should be considered when a canal cannot be located. Clearly, such endodontic microsurgery is an option in the treatment of calcified canals as it offers a direct approach to the root apex.  Canal identification can be problematic in the calcified canal after root resection. The guiding influence of a canal space will be non-existent in the calcified and previously unprepared canal system. It is likely that this will be a further complicating factor in carrying out surgery on a calcified canal system where there has been no attempt at orthograde root filling. Thus, it seems reasonable to conclude that the surgical treatment approach should be considered only in cases where nonsurgical treatment or retreatment has resulted in a persistence of periapical disease and/or symptoms. 
If there are aesthetic concerns, there are potentially four treatment options for bringing the discolored, pulpally obliterated teeth to an acceptable color. External or vital bleaching should be considered first as it is the most conservative option. Greenwall described a single vital tooth whitening technique using 20% carbamide peroxide gel in a conventional vital bleaching tray.  A full arch tray is made first, after which a window is cut on either side of the tooth to be bleached to prevent the adjacent tooth from lightening which would result in uneven bleaching. The upper anterior teeth should be bleached for two weeks using 10% carbamide peroxide to evaluate the speed and progress of the bleaching of the whole arch. Thereafter, 20% carbamide peroxide gel should be placed in the tray adjacent to the single tooth for a period of four to six weeks or until the single tooth matches all the upper teeth and they are all the same shade. However, progress can be slow because of the nature of the discoloration which had been packed very densely from the secondary and tertiary dentin depositions. There is generally little or no sensitivity experienced during the whitening treatment. Second treatment option can be intentional root canal treatment followed by intracoronal bleaching. A fully extended access cavity identical to that in a tooth with normal chamber size can be made. In this way, a large amount of tertiary dentin can be removed, thereby contributing to the restoration of translucency in the crown. Third treatment modality can be internal and external bleaching without root canal treatment. Pedorella et al. described preparing an access cavity and removing the coronal sclerotic dentin and placing an appropriate base on the floor of the access cavity without considering root canal treatment and then carrying out internal and external bleaching.  While this technique is a possible treatment option, it does not have widespread support, since opening into the pulp chamber of these teeth without considering root canal treatment opens up this pulp tissue to infection. West suggested that the most expedient option to restore aesthetically, a discolored tooth with a full coverage restoration.  Given that most of these teeth are intact, such a destructive measure should really only be considered when the more conservative approaches have not been successful.
Though negotiating and managing calcified canals can be challenging, they can be managed if a proper protocol is followed. Operator's skill, patience, and a proper armamentarium are the requisites to overcome the difficulties posed by these unforgiving canals for their successful treatment.
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