Problem-Solving Challenges in the Tooth With a Necrotic Pulp and Immature Apical Development: Apexification

Historically, when a dental pulp had undergone demise before full root formation, an apexification procedure was indicated and still is the treatment of choice.^29,55 However, multiple directions in the management of this clinical challenge have emerged that differ from the traditional calcium hydroxide apexification procedure.²³ The details of the traditional technique will be discussed briefly, as it has withstood the test of time. This will be followed by alternatives that are currently being advocated^78,79 that include the use of mineral trioxide aggregate (ProRoot MTA [Dentsply Tulsa Dental Specialties, Tulsa, OK, USA])⁶² and a technique that is referred to by some as revascularization and by others as regeneration within the pulpal space.¹⁰

The traditional apexification procedure requires complete canal cleaning, shaping, removal of smear layer, and disinfection (see Chapters 10 and 11) before the placement of calcium hydroxide (Ca[OH]₂) to promote the formation of osteocementum or apical bridge formation. This technique is often referred to as the Frank technique.²³ The calcium hydroxide kills bacteria, dissolves tissue, and creates an environment conducive to hard-tissue formation.^69,75,80 The material is left in place or changed every 3 months, with intervals as long as 12 months in later stages to enhance the tissue response.²⁹ The mean time to barrier formation in incisor teeth has been shown to be 34.2 weeks (range 13 to 67 weeks),²² but data on posterior teeth is unavailable. Recently this technique of changing the Ca(OH)₂ has been shown to be counterproductive to the formation of hard tissue, although it did seem to lessen inflammatory response.²⁰ The hard tissue that ultimately forms is not dentin, because odontoblasts rarely if ever survive pulpal necrosis (Fig. 13-1). This important concept, while understood in the context of traditional apexification, has not necessarily been elucidated or addressed in the purported revascularization or regenerative techniques that will be discussed later. The tissue response in the traditional technique has been shown to be a gnarled osteocementum type of material³⁰ (Fig. 13-2). It is often porous, and its formation, thickness, and location are often irregular in nature. It is a valid procedure for both anterior and posterior teeth. Figs. 13-3 and 13-4 offer detailed descriptions of traditional apexification using Ca(OH)₂ technique in anterior and posterior teeth.

FIGURE 13-1 A, Developing root apex showing the Hertwig epithelial root sheath (arrows). B, Note how the sheath invaginates into the mesenchymal tissues (dental sac) on its way to root development. Once this sheath dies, the chance for normal root development ceases. C, View of tooth root that has not closed; perimeter of the opening represents the area of the root sheath.

FIGURE 13-2 Apical closure of a primate’s tooth during apexification with calcium hydroxide, showing a gnarled-type of hard tissue has formed over the root canal. There is no root lengthening or root wall strengthening.

FIGURE 13-3 A, Two traumatized maxillary central incisors with immature root formation and necrotic pulps. B, Calcium hydroxide was placed. The patient is symptom free, and the teeth are functional. C, Removal of the calcium hydroxide at 1 year and verification of apical bridge formation. D, Both canals filled with gutta-percha and sealer. Note the porosity of the apical bridging.

FIGURE 13-4 A, This 10-year-old male has significant decay and delayed root development on the mandibular first molar. Apical and furcation bone loss is evident, and the tooth is scheduled for extraction. B, The pulp chamber and canals are cleaned and shaped, and calcium hydroxide is placed. The open apices and slight extrusion of the material is noted. C, Six-month assessment shows great healing and the beginning formation of apical bridging. The roots are filled with gutta-percha and sealer. Slight porosity of the apical bridge is noted, but the healing response is excellent. A space maintainer is placed on the tooth.

From a contemporary standpoint, Ca(OH)₂ is still used for bacterial control,^69,76 but its presence over a long period may weaken the dentin.^2,3,15,48,58 A major problem inherent in the tooth with immature root formation is the structural weakness of root walls (root wall thickness) (Fig. 13-5).^1,12,68 If the impact of Ca(OH)₂ is added to this weakness, the chance for long-term retention of these teeth would be doubtful. Often over time, these teeth—even with apical closure—may be unable to withstand not only the occlusal and functional stresses but also the impact of the wide range of restorative procedures that have been used to maintain these teeth. Furthermore, the use of preformed, intraradicular metallic posts in the tooth are not indicated; even if used, they would not likely strengthen the root structure (see Chapter 20). A bonded, carbon fiber post may be a consideration, although little is known about its ability to enhance treatment outcome.¹ Therefore, exit Ca(OH)₂ and enter MTA^62,78,79 as the contemporary material of choice for apexification techniques, even to the point of citing this approach as being “regenerative” in nature.¹⁰ This material has been shown to be inductive for hard-tissue formation,^26,57 in particular in its use in apexification.* Moreover, its sealing properties in the root have been shown to be acceptable with or without the use of an accelerator that would enhance its physical properties for placement.³⁷

FIGURE 13-5 A, Maxillary central incisor that has undergone apexification and canal filling. B, Four months later, the patient had not had the tooth restored and complained of soreness in his gingival tissues. Radiograph shows a horizontal root fracture on the central incisor.

MTA, while effective in most cases in securing a positive tissue response and healing when used in a variety of applications,^47,57 has been difficult to manipulate in its present form. To meet these challenges, a number of techniques have been advocated for its placement and retention. For example, pellets of the material can be mixed to a workable consistency and then measured in length to determine the amount to be placed into the canal. The MTA can be placed in this form and compacted with measured pluggers or a custom fit gutta-percha cone.⁶⁷ This procedure seems to work well (Fig. 13-6). A second option would be to use an appropriately sized amalgam carrier or any one of a number of devices designed for this purpose (see Chapter 16 for further details). Presently, many studies have attempted to alter the physical properties of MTA to enhance its clinical management.^6,44

FIGURE 13-6 A, Maxillary lateral incisor with an open apex, thin root walls, and a large periapical lesion. The tooth was opened by her general dentist 2 months subsequent to a coronal fracture in which the pulp was exposed. B, The root canal was cleaned and a plugger (compactor) fitted into the canal for both length and width assessment. C, Mineral trioxide aggregate (MTA) is placed and compacted using the plugger. D, Canal is completely filled and a 6-month evaluation shows good bony response. Healing is not complete but is progressing.

The use of MTA in one-visit apexification treatment has received some significant attention,^42,65,79 with outcomes favoring this approach as opposed to the use of Ca(OH)₂ followed by MTA (Fig. 13-7, A-E).* However, what is defined as a one-visit treatment may be ambiguous⁴⁷ insofar as many clinicians access, enlarge, shape, and clean, then place Ca(OH)₂ for 7 to 14 days. Instead of waiting for a lengthy period, the canal is filled with MTA within 2 weeks or less (Fig. 13-8). If everything could be done in one visit, it would also negate the potential for leakage that has been identified when MTA has been placed following the use of Ca(OH)₂.⁶⁶ In some cases, it may be wise to use MTA in a one-visit placement surgically to manage an open apex in light of other complications (Fig. 13-9).⁴⁷

FIGURE 13-7 A, A 13-year-old male with a large periapical lesion on a mandibular second premolar. B, Calcium hydroxide was placed. C, Within 3 months, the apex appears to be closing. D, Entire canal filled with MTA. Note slight amount of material that is past the foramen, probably calcium hydroxide. E, Three months later, the tooth and periapical tissues are stable.

FIGURE 13-8 A, Mandibular molar with significant decay, periapical lesions, and open apices. B, Decay was excavated, and calcium hydroxide was placed. Four months later, the root apices appear to be closing. C, Mineral trioxide aggregate (MTA) was placed in the canal, and the tooth was restored.

FIGURE 13-9 A, Maxillary lateral incisor with a dens in dente, open, immature apex, periapical lesion, and no response to sensibility testing. The dens in dente was intact, and surgery was chosen. B, Apical fill with mineral trioxide aggregate (MTA). C, 19-Month reevaluation healing is excellent.

Following placement of MTA in the canal, some options are available to the clinician for restoring the tooth, depending on whether only apical plugs were placed or the entire canal was filled.⁵⁰ First, a glass ionomer can be placed on top of the MTA, followed by a bonded composite or bonded post.¹⁶ Second, bonded materials can be placed directly against the MTA after allowing the MTA to set for a minimum of 2 to 4 hours; some clinicians bring the patient back the following day for this procedure. Bonding the canal walls in these cases is a wise choice to prevent fracture.^36,43 As mentioned, the use of metallic posts is contraindicated, but the newer resin-bonded obturation materials may be a choice because the strength of the root may be enhanced.⁶⁸ Clinical evidence of this effect is unavailable, but what is known is that MTA itself may enhance the strength of the root structure by an interesting mechanism in which it induces the expression of tissue inhibitors of metalloproteinases (TIMPs), thereby preventing destruction of the collagen matrix.³⁴ In adhesive restorations, one major problem is hybrid layer degradation. At present, this deterioration is explained by the activation of endogenous matrix metalloproteinases (MMPs) present in dentin owing to the acidic property of adhesive systems. Even mild self-etching adhesives activate latent MMPs without denaturing these enzymes and may adversely affect the longevity of bonded root canal fillings and posts.⁷⁰ In this regard, the use of chlorhexidine (CHX) has been advocated to prevent the release of MMPs,³⁵ and it is possible that CHX should also be advocated in place of Ca(OH)₂ for bacterial control in teeth with immature root development and a necrotic pulp. The concept of inducing TIMPs and preventing the release of MMPs is essential in achieving bonding in the root canal system with products such as Epiphany/Resilon (Pentron Technologies Inc., Wallingford, CT, USA).

The most contemporary approach to the management of teeth with immature root formation and either irreversible pulpitis and periapical periodontitis^{5,10,11,39,40} or necrotic infected pulps^41,71 has been promulgated as revascularization,⁵⁶ or even regeneration.^10,32,73 In their infancy, these techniques claimed to be taking advantage of the pluripotential cells in the dental papilla and/or periodontal ligament, inducing them to form hard tissue into the root canal or to somehow continue the development of Hertwig’s epithelial root sheath (HERS; see Fig. 13-1 and Chapter 7).⁴⁰

Preliminary technique: The technique to achieve this goal consists of an access to the canal, drainage as necessary, rinsing the canal with sodium hypochlorite (NaOCl) and CHX, drying the canal, and placement of a mixture of ciprofloxacin, metronidazole, and minocycline with a lentulo spiral.^5,38,41,59 Placement to the working length or extent of the root apically does not appear to be important, and there is no compaction of the antibiotic paste. If successful, this is followed by the ingrowth of soft tissue (revascularization) and the presence of hard tissue building up along the internal walls of the root to varying degrees of thickness. In some cases this thickness is uniform, in others it may only occur in the apical portion of the root canal. In essence, what is being achieved is possibly a revitalization to some extent that encourages the apexogenesis process, as described in Chapter 7.

This initiative has even developed some of its own nomenclature in its claims, such as bioroot engineering, pulp revascularization, regenerative endodontic treatment or regenerative therapies, and stem cells from the apical papilla (SCAP).^39,40 While only supported by diverse case reports at this moment, there is a significant research initiative to pursue this model, calling it “the hidden treasure in apical papilla.”⁴⁰ The treasure refers to the uniqueness of the SCAP relative to cellular types and their potential for differentiation and expression of their genetic potential—that is, cells with the phenotypic capability of becoming new odontoblasts. In combination with the genetic capabilities of cells from the periodontal ligament (periodontal ligament stem cells [PDLSCs]), they offer the promise of truly regenerating lost or damaged tissues.

It is not the intent of this text to espouse these theories or clinical innovations, but rather to raise some challenging problem-solving questions relative to the thought and direction behind them. The concept of stem cell identification and their potential applications is laudable, exciting, and should be pursued. However, there are issues that need distillation and clarification before these concepts and potential techniques can become meaningful and sought after by the clinician:

Problem-Solving Challenges in the Tooth With Fine and Calcified Canals

The problem of calcification was introduced in Chapter 8 in reference to access preparation and location of the canal orifices. Calcification in the root canal system is also a frequently encountered problem in root canal treatment.^14,63 Radiographs often indicate an apparent complete obliteration of the pulp chamber and the canal spaces (Fig. 13-10). The process of calcification appears to be a linear phenomenon beginning in the crown and progressing apically in most cases. Therefore, the failure to locate a canal orifice during a non-surgical access procedure, even if it is extended quite deep, does not rule out the possibility that canal space exists more apical than can be reached.

FIGURE 13-10 A, Maxillary molar with significant calcification present. B Histologic variations that may be noted in these types of calcified canals (H&E stain ×40).

CLINICAL PROBLEM

Problem

A 71-year-old female sought dental consultation because the porcelain fused to metal crown on her left maxillary lateral incisor fractured off at the gingival margin. There were no symptoms and the tooth had no clinical or radiographic signs of pathosis. A root canal space is evident on the examination film (Fig. 13-11, A). Intraradicular root canal treatment was initiated with the object of providing space for a post. Following careful excavation with a No. 2 surgical length round bur deep into the root, no canal could be identified. A control radiograph was made with an endodontic explorer in the excavation to assess the direction of excavation (see Fig. 13-11, B). The direction of excavation appeared to be accurate in the mesial-distal orientation and clinically, the excavation appeared centered in the buccal-lingual orientation. Further excavation was no longer considered prudent due to the limited ability to assess the buccal-lingual orientation of the bur angulation. What is the best course of treatment at this point?

FIGURE 13-11 A, Complete crown fracture on a maxillary lateral incisor with extensive calcification. B, Unsuccessful attempt to negotiate canal. C, Two-year reevaluation following restoration with resin-fiber post retained crown. Apical pathosis is evident. Note: Conversion of access excavation into post space. D, Post operative radiograph. Apical surgery was indicated to clean and seal remaining canal space at the apex.

Solution

In the absence of symptoms or signs of pathosis, conversion of the excavation to a preparation for an intraradicular post is indicated. The tooth was subsequently restored with a resin-fiber type of post, followed by a new full crown. Two years later, the patient developed symptoms of periapical inflammation. A radiograph revealed an apical lesion(see Fig. 13-11, C). Periapical surgery was the appropriate remedial treatment. At surgery, an ultrasonically energized endodontic file was used for the root-end preparation (see chapter 16). The file followed the existing canal space to the point of calcified occlusion at which point the apical canal space was enlarged and filled with MTA (see Fig. 13-11, D).

In these types of cases, the eventual development of periapical pathosis has been observed by the authors to be uncommon. It is also fortunate that only a small percentage of cases that radiographically exhibit fine or unidentifiable canals prove to be unmanageable using nonsurgical root canal techniques (Fig. 13-12). However, when patent canal space is present, successful negotiation of this type of canal to its apical extent is extremely diffcult.⁶⁴ Of the numerous techniques available to locate and negotiate these canals, those procedures known to be most effective in clinical practice and used by the authors are considered here. Success in negotiating small or calcified canals is predicated on a proper access opening and identifying the canal orifice or orifices as discussed in Chapter 8. Typically, the canal is ready for penetration with an endodontic file when the endodontic explorer firmly “sticks” when forcibly inserted into the orifice. If available, it is often helpful to use the ultrasonic instrument with a probe type of tip (see Fig. 14-4) to both enlarge the orfice and circumferentially remove some of the calcified material.

FIGURE 13-12 A, Mandibular premolar with apparent complete calcification of the entire root canal system.

B, Successful negotiation of the canal with a .08 file in combination with a solution containing EDTA.

This discussion will assume that the orifices have been located. Each tooth group will be somewhat different, but the concept and technique of gaining access to these canals are the same.

A 21-mm No. 8 K-file can be used initially to negotiate the calcified canal (Fig. 13-13). This file is flexible enough to negotiate around curvatures and calcifications. If the flexibility is too great, then instruments such as the C+ file or ProFinder files (Dentsply Maillefer, Ballaigues, Switzerland) will serve. The C+ file is possibly better in some canals; the instrument shaft provides as much as a 300% increase in resistance to a buckling force during penetration. If chosen, a 21-mm No. 6 C+ file will work nicely for canal penetration, because even though it is smaller than the No. 8 file, it has a stiffer shaft. If the canal is longer than 21 mm, changing to a 25-mm instrument once 21 mm of penetration has been achieved is simple. A No. 10 K-file is usually too large and a No. 6 K-file is too weak to apply any firm apical pressure, particularly if precurved. Nickel-titanium (NiTi) files are contraindicated for this purpose because of their lack of torsional strength.

FIGURE 13-13 A, 38-year-old male presented with a history of tooth trauma to his mandibular anterior teeth. His chief complaint was periodic pain to pressure in the left lateral incisor. The tooth was nonresponsive to sensibility tests, with a slightly abnormal response to palpation and percussion. A radiograph showed significant pulp chamber and coronal canal calcification. B, Initial penetration of the pulpal space shows a mesial deviation of the file in the root and how the dental dam clamp can block direct vision of the file penetration. C, After failing to penetrate the canal, a temporary filling was placed and a radiograph was exposed without the dental dam in place to determine the angle of the access relative to the residual canal position. D, Reorientation and penetration with a small apically curved file. E, the canal was located, and penetration was achieved to the apex.

Before file insertion, a small curve is placed in its apical 1 mm. This can also be done with the C+ file. The precurved instrument must be directed along the pathway the canal is most likely to follow (see Fig. 13-13, D). Consequently, knowing the direction in which the curve in the instrument is pointed is vitally important. Observing the rubber stop on the instrument shaft of the directional type makes this determination easy. Penetrate slowly, using a slight 90-degree back-and-forth rotation to assess for patency. If patent, proceed apically until resistance is met, but do not try to just push the file apically in a linear fashion. The operative word is tease; teasing the file will allow it to find its way through the milieu of tissue debris and calcified matter.

During penetration, the chamber must be filled with NaOCl . A chelating agent can be used, but this will not dissolve loose debris, and it will negate the action of NaOCl. The calcified canal should never be negotiated without irrigant. This approach only serves to pack debris or calcifications into the canal and risks complete blockage. As the file is teased into the canal, try to establish a “sense of the patency” as this will provide a guideline for subsequent instrument use. Obtaining radiographs to verify the file position is exceedingly important⁶⁴ (Fig. 13-14). Once a few millimeters of penetration have been achieved, the file should be used in a circumferential manner, opening the orifice. This is followed by removing the file, irrigating, and replacing the file to the previous depth. The file should fit loosely; if not, the first step should be repeated with a No. 10 or possibly a No. 15 K-file, or C+ file. As the irrigant penetrates into this small opening, the instruments loosen debris and begin to create a coronal pathway to the middle portion of the canal.

FIGURE 13-14 A, 66-year-old male presents with per/>

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